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Synthesis and Aqueous Solution Properties of Shape-Shifting Stimulus-Responsive Diblock Copolymer Nano-Objects

  • Oliver J. Deane
    Oliver J. Deane
    Dainton Building, Department of Chemistry, University of Sheffield, Sheffield S3 7HF, U.K.
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  • James Jennings
    James Jennings
    Dainton Building, Department of Chemistry, University of Sheffield, Sheffield S3 7HF, U.K.
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  • , 
  • Thomas J. Neal
    Thomas J. Neal
    Dainton Building, Department of Chemistry, University of Sheffield, Sheffield S3 7HF, U.K.
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  • Osama M. Musa
    Osama M. Musa
    Ashland Specialty Ingredients, 1005 US 202/206, Bridgewater, New Jersey 08807, United States
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  • Alan Fernyhough
    Alan Fernyhough
    Ashland Specialty Ingredients, Listers Mills, Heaton Road, Bradford BD9 4SH, U.K.
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  • Steven P. Armes*
    Steven P. Armes
    Dainton Building, Department of Chemistry, University of Sheffield, Sheffield S3 7HF, U.K.
    *Email: [email protected]
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    Orcidhttps://orcid.org/0000-0002-8289-6351
Cite this: Chem. Mater. 2021, 33, 19, 7767–7779
Publication Date (Web):September 28, 2021
https://doi.org/10.1021/acs.chemmater.1c02096

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Abstract

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We report the synthesis of poly(N-(2-acryloyloxyethyl)pyrrolidone)-poly(4-hydroxybutyl acrylate) (PNAEP85-PHBAx) diblock copolymer nano-objects via reversible addition–fragmentation chain transfer (RAFT) aqueous dispersion polymerization of 4-hydroxybutyl acrylate (HBA) at 30 °C using an efficient two-step one-pot protocol. Given the relatively low glass transition temperature of the PHBA block, these nano-objects required covalent stabilization prior to transmission electron microscopy (TEM) studies. This was achieved by core crosslinking using glutaraldehyde. TEM analysis of the glutaraldehyde-fixed nano-objects combined with small-angle X-ray scattering (SAXS) studies of linear nano-objects confirmed that pure spheres, worms or vesicles could be obtained at 20 °C in an acidic aqueous solution by simply varying the mean degree of polymerization (x) of the PHBA block. Aqueous electrophoresis, dynamic light scattering and TEM studies indicated that raising the dispersion pH above the pKa of the terminal carboxylic acid group located on each PNAEP chain induced a vesicle-to-sphere transition. 1H NMR studies of linear PNAEP85-PHBAx nano-objects indicated a concomitant increase in the degree of partial hydration of PHBA chains on switching from pH 2-3 to pH 7-8, which is interpreted in terms of a surface plasticization mechanism. Rheological and SAXS studies confirmed that the critical temperature corresponding to the maximum worm gel viscosity could be tuned from 2 to 50 °C by adjusting the PHBA DP. Such tunability is expected to be useful for potential biomedical applications of these worm gels.

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Introduction

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It is well known that AB diblock copolymers can self-assemble in solution to form a range of sterically stabilized nanoparticles. (1−4) Depending on the relative volume fractions of the two blocks, (1) the copolymer morphology can be spheres, (1) worms (4,5) or vesicles. (6) However, traditional postpolymerization processing routes to such nano-objects usually require co-solvents and are invariably conducted in dilute solution. (1,5,7,8) These are important constraints that have severely limited potential commercial applications. In contrast, polymerization-induced self-assembly (PISA) enables the efficient synthesis of block copolymer nano-objects of controllable size, morphology, and surface composition directly in the form of concentrated dispersions in a wide range of polar (4,9−11) or non-polar (12,13) solvents. PISA involves chain extension of a soluble homopolymer precursor using a suitable second monomer in an appropriate solvent, with the latter being chosen so that the growing second block becomes insoluble at some critical chain length, thus leading to the formation of diblock copolymer nano-objects. (14−19) In principle, such nanoparticles offer a wide range of potential applications, including new biocompatible hydrogels for cell culture and long-term storage, (10,20,21) microencapsulation of proteins and enzymes within vesicles, (22−27) bespoke Pickering emulsifiers, (28) novel flocculants, (29) dispersants for agrochemical actives such as azoxystrobin, (30) and new lubricants for the formulation of ultralow-viscosity automotive engine oils. (31) The majority of the PISA literature involves reversible addition–fragmentation chain transfer (RAFT) polymerization. (32−40) This chemistry is based on the principle of rapid reversible chain transfer: an organosulfur-based CTA is used to produce well-defined block copolymers with low dispersities and predictable mean DPs. (41−43)
Recently, we reported the RAFT aqueous solution polymerization of N-(2-acryloyloxyethyl) pyrrolidone (NAEP) to produce various homopolymers and block copolymers. (44) Subsequently, a trithiocarbonate-capped poly(N-(2-acryloyloxyethyl)pyrrolidone) precursor was employed for the RAFT aqueous emulsion polymerization of styrene, n-butyl acrylate (nBA), and mixtures thereof. (45) The mean particle diameter and glass-transition temperature could be varied over a wide range by adjusting the target DP and comonomer composition of the structure-directing block. However, only kinetically trapped spheres could be obtained and the highly hydrophobic nature of their core-forming chains ensured that such nanoparticles did not exhibit any thermoresponsive behavior.
According to the PISA literature, RAFT aqueous dispersion polymerization often leads to thermoresponsive block copolymer nano-objects. (46−54) This is not particularly surprising because water-miscible monomers lead to more weakly hydrophobic structure-directing blocks than water-immiscible monomers. (10,55) In this context, we recently reported two examples of thermoresponsive diblock copolymers of fixed composition that can form spheres, worms or vesicles in an aqueous solution simply by adjusting the solution temperature. (18,56) In both cases, spheres are formed at subambient temperature, worms are produced at around ambient temperature, and vesicles are observed on heating above ambient temperature. Variable temperature 1H NMR spectroscopy studies indicate that this remarkable behavior is the result of subtle changes in the degree of hydration of the weakly hydrophobic structure-directing block, (18,56) which was chosen to be poly(2-hydroxypropyl methacrylate) (PHPMA) in the first study and a statistical copolymer comprising 80 mol % 4-hydroxybutyl acrylate (HBA) and 20 mol % diacetone acrylamide (DAAM) in the second study. In the latter case, significantly greater chain mobility exhibited by the HBA-rich block led to thermoreversible sphere/worm and worm/vesicle transitions, whereas the corresponding transitions observed for PHPMA-based nano-objects exhibited strong hysteresis. Unfortunately, the HBA-rich block has a relatively low Tg, which prevented transmission electron microscopy (TEM) studies of the copolymer morphologies. In principle, this technical issue can be addressed using cryo-TEM. (57−59) However, the weakly hydrophobic nature of HBA-rich chains leads to a relatively high degree of hydration, which minimizes electron contrast with the frozen aqueous phase and leads to poor-quality images. Byard and co-workers addressed this problem by reacting the pendent methyl ketone groups on DAAM repeat units with a water-soluble crosslinker (adipic acid dihydrazide). (18) Such covalent stabilization enables TEM studies, but introducing the DAAM comonomer reduces the thermoresponsive behavior exhibited by the HBA-rich structure-directing block. In principle, the maximum thermoresponsive character should be obtained by omitting the DAAM comonomer from the PISA formulation to produce purely PHBA-based nano-objects. However, this approach requires the identification of a suitable alternative crosslinking protocol to enable the assignment of copolymer morphologies by conventional TEM. This is one of the main objectives of the present study.
Herein, we report the two-step one-pot synthesis of a series of new thermoresponsive pyrrolidone-functional diblock copolymer nano-objects via RAFT aqueous dispersion homopolymerization of HBA using PNAEP as a nonionic hydrophilic steric stabilizer (see Scheme 1). (44,45) For this highly efficient new PISA formulation, we explore the following four questions. Can a single diblock copolymer composition be identified that can form spheres, worms, or vesicles simply by varying the solution temperature? If so, can the local maximum in dispersion viscosity corresponding to the presence of linear worms be tuned over a wide range of temperature by systematic variation of the diblock copolymer composition? Given that each steric stabilizer chain contains a terminal carboxylic acid, do these nano-objects exhibit pH-responsive behavior via end-group ionization? Finally, can a robust new crosslinking strategy be developed to enable conventional TEM studies of such nano-objects?

Scheme 1

Scheme 1. Two-Step One-Pot Synthesis of PNAEP85-PHBAx Diblock Copolymer Nano-Objects via RAFT Aqueous Dispersion Polymerization of HBA at 30 °C Using a [PNAEP85]/[KPS] Molar Ratio of 5.0 and a [KPS]/[AsAc] Molar Ratio of 1.0 [N.B. “KPS” Denotes K2S2O8 and “AsAc” Denotes Ascorbic Acid]
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Results and Discussion

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A series of PNAEP precursors were prepared via RAFT aqueous solution polymerization of NAEP using DDMAT as a RAFT agent at 30 °C (see Scheme 1). To minimize the well-known problem of chain transfer to polymer during acrylic polymerization, (60) a low-temperature redox initiator based on KPS and AsAc (61−63) at pH 3 or KPS and N,N,N′,N′-tetramethylethylenediamine (TMEDA) at pH 7 was employed at a [DDMAT]/[KPS] molar ratio of 5.0. 1H NMR studies confirmed good reproducibility when conducting this first step at pH 3: the PNAEP precursor had a mean DP of 85 ± 1 and 96 ± 1% NAEP conversion was achieved within just 10 min at 30 °C; these data are averaged over the 30 PNAEP precursors that were used to construct the pseudo-phase diagram (see later). Dimethyl formamide gel permeation chromatography (DMF GPC) analysis of the aliquots extracted from the reaction solution for 1H NMR analysis confirmed good reproducibility for the target Mn of the 30 PNAEP85 precursors prepared via RAFT aqueous solution polymerization (19.1 ± 0.4 kg mol–1; Figure S1). Moreover, each precursor had a relatively narrow molecular weight distribution (Mw/Mn < 1.20; Figure S1). [N.B. The KPS/TMEDA redox initiator was also employed to prepare the PNAEP85 precursor at pH 7, with 1H NMR and DMF GPC analysis (see Figure S2b), indicating that essentially the same precursor was obtained compared to that synthesized at pH 3.]
The kinetics for the subsequent RAFT aqueous dispersion polymerization of HBA at 30 °C were examined when targeting a PNAEP85-PHBA435 diblock copolymer at either pH 3 or pH 7 (see Figure S2). 1H NMR studies were used to monitor the disappearance of vinyl signals at 5.8 and 6.4 ppm relative to the integrated two oxymethylene protons at 4.2–4.3 ppm assigned to the growing PHBA block (see Figure S3). These studies indicated that more than 95% conversion was achieved within 60 min for the synthesis at pH 3 and within 120 min at pH 7 when targeting 20% w/w solids at 30 °C. DMF GPC analysis indicated good RAFT control in both cases, with slightly lower blocking efficiencies being achieved at pH 7 (see Figure S4). GPC analysis using either a refractive index detector or a UV detector indicated the presence of a high molecular weight shoulder in each case (see Figure S5). This is consistent with chain transfer to polymer during the RAFT aqueous dispersion polymerization of HBA, even though such syntheses were conducted at 30 °C. Indeed, literature precedent suggests that this side reaction occurs even under such mild conditions. (60,64,65)
It is perhaps worth noting that the similarity between the RI and UV GPC traces indicates that essentially all of the copolymer chains retain their living character. This was expected owing to the greater hydrolytic stability afforded by trithicarbonate-based CTAs (such as the DDMAT employed in this study) compared to that of dithioesters. (66−68) Moreover, performing these syntheses under mild conditions (e.g., 30 °C, pH 3–7) should ensure minimal loss of RAFT chain ends.
Depending on the solution pH chosen for the RAFT aqueous dispersion polymerization of HBA, dynamic light scattering (DLS) analysis indicated significant differences for the evolution in particle size (Figure S6). At pH 3, four distinct morphology regions were identified that correspond to dissolved chains, spheres, worms, and vesicles (Figure S6a). This sequence of copolymer morphologies is well established for RAFT aqueous dispersion polymerization formulations reported in the literature. (69) In striking contrast, DLS analysis of a series of aliquots periodically extracted during the RAFT dispersion polymerization of HBA conducted at pH 7 suggested that this formulation produced only spheres (Figure S6b). After nucleation (which occurs at 40% HBA conversion), the z-average diameter for these spheres increased monotonically from 26 to 43 nm throughout the rest of the polymerization. ζ-Potential studies suggested that this was the result of deprotonation of the carboxylic acid end group on each PNAEP stabilizer at pH 7, which introduces significant anionic character. (70) This is sufficient to prevent one-dimensional (1D) sphere–sphere fusion and hence leads to the formation of kinetically trapped spheres (Figure S6b).
TEM characterization of such PHBA-based nano-objects is extremely challenging. This is because the PHBA block has a relatively low Tg, as indicated by its soft, gum-like appearance at ambient temperature and confirmed by DSC analysis of a PHBA300 homopolymer (see Figure S7). Five dried linear PNAEP85-PHBAx diblock copolymers prepared via RAFT aqueous dispersion polymerization were also analyzed by DSC. The Tg observed for the PHBA block was reduced from −14.3 to −40.5 °C on increasing its DP (x) from 125 to 525 (Figure S8), which is contrary to the trend predicted by the Fox equation. (71) However, this relationship assumes that there are no specific interactions between the comonomer repeat units, whereas strong hydrogen bonding between the pyrrolidone rings within the PNAEP block and the hydroxyl groups on the HBA repeat units almost certainly occurs in the solid state (see Figure S9 for Fourier transform infrared (FT-IR) spectra and corresponding text). (72) The low Tg values recorded for the PHBA block (Figures S7 and S8) invariably led to film formation on the TEM grid (Figure S10a), which makes the original linear copolymer morphology impossible to assess.
Glutaraldehyde (GA) is a water-soluble reagent that is widely used as a crosslinker for various biomedical applications, (73,74) including the covalent stabilization of proteins to facilitate their characterization by electron microscopy. (75−77) GA has also been used to crosslink various water-soluble polymers. (78−83) However, as far as we are aware, this reagent has not been previously used to crosslink thermoresponsive diblock copolymer nanoparticles. GA can undergo a remarkable range of reactions in aqueous solution, producing a complex mixture of monomeric GA, unsaturated polymeric GA and cyclic GA species. (73,75−77,84−88) The major species depends on both the initial GA concentration and the solution pH. (74) The crosslinking of proteins using GA is not fully understood but is believed to involve multiple mechanisms, including Schiff base chemistry to form imine bonds (84,88) and Michael addition of protein-based amine groups to α,β-unsaturated aldehydes formed by aldol condensation of GA. (85,86) Intramolecular crosslinks are favored over intermolecular crosslinks when GA reacts with proteins. (76,87) However, the relative proportion of these two types of linkages depends on the concentration of both GA and the protein. (76,87) GA has also been widely investigated as a crosslinker for the acid-catalyzed synthesis of water-insoluble poly(vinyl alcohol) (PVA) membranes. (78−83) In this case, FT-IR spectroscopy studies indicated that the major product contained an acetal ring, which is produced when two pairs of neighboring secondary hydroxyl groups on PVA chains react with two aldehyde groups on GA (see Scheme 2). (89) However, monofunctional addition of GA has also been reported. (79,89) Given this extensive literature precedent, we postulated that GA should act as an effective crosslinker for PHBA-based nanoparticles in an aqueous solution by forming acetal linkages between the pendent hydroxyl groups on the weakly hydrophobic PHBA chains (Scheme 2). (74)

Scheme 2

Scheme 2. Intermolecular Crosslinking of PHBA Chains within PNAEP85-PHBAx Diblock Copolymer Nano-Objects (In This Case, Spheres) via Acid-Catalyzed Nucleophilic Attack of Pendent Hydroxyl Groups by Glutaraldehyde (GA)a
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aThis enabled a range of PNAEP85-PHBAx nano-objects to be covalently stabilized under various conditions (e.g., pH 3–7, 11–41 °C).

In principle, one GA molecule can react with four PHBA hydroxy groups to form two acetal linkages. This suggests that a GA/HBA molar ratio of 0.25 should be sufficient to afford covalently stabilized nanoparticles that do not undergo film formation during TEM grid preparation. However, it was found empirically that a GA/HBA molar ratio of 0.66 was required to ensure that good-quality TEM images were obtained (see Figure S10). FT-IR spectroscopy studies of freeze-dried GA-crosslinked PNAEP85-PHBA500 nano-objects indicated the formation of acetal linkages (see Figure S11). (73,75−77,84−88) Unfortunately, the addition of GA to 20% w/w aqueous dispersions of PNAEP85-PHBAx spheres, worms or vesicles led to macroscopic gelation within 5 min when using a GA/HBA molar ratio of 0.66. To avoid this gelation problem, all crosslinking reactions were conducted at 5% w/w for 16 h (Scheme 2).
Accordingly, various copolymer morphologies were targeted at pH 3 by systematically varying the DP of the core-forming PHBA block between 100 and 550 while adjusting the copolymer concentration between 5% w/w and 40% w/w (see Table S1). GA crosslinking of the PNAEP85-PHBAx nano-objects formed at 22 °C enabled conventional TEM analysis, see Figure 1a–c. Moreover, DSC analysis indicated that the Tg of the PHBA block (observed at around −14.3 to −40.5 °C for the original linear nano-objects) was no longer detected for GA-crosslinked nano-objects, while the Tg for the PNAEP block remained discernible (Figure S7). Furthermore, DLS studies confirmed that GA crosslinking eliminated the stimulus-responsive behavior exhibited by such nano-objects, hence preserving the copolymer morphology that is formed at any given temperature or pH (Figure S12). These TEM-assigned copolymer morphologies were used to construct a pseudophase diagram (Figures 1d and S13). SAXS patterns recorded for 1.0% w/w aqueous dispersions of linear PNAEP85-PHBA110, PNAEP85-PHBA350 and PNAEP85-PHBA450 nano-objects at pH 3 are shown in Figure 1e.

Figure 1

Figure 1. Representative TEM images recorded for: (a) GA-crosslinked PNAEP85-PHBA170 spheres prepared at 10% w/w; (b) GA-crosslinked PNAEP85-PHBA340 worms prepared at 20% w/w; and (c) GA-crosslinked PNAEP85-PHBA530 vesicles prepared at 5% w/w. (d) Pseudo-phase diagram constructed for PNAEP85-PHBAx diblock copolymer nano-objects. S = pure spheres; S + W = a mixed phase comprising spheres and worms; W = pure worms; W + V = a mixed phase comprising worms and vesicles; and V = pure vesicles. Each copolymer morphology was assigned on the basis of TEM analysis of covalently stabilized nano-objects prepared using glutaraldehyde as a crosslinker at pH 3 and 22 °C (GA/HBA molar ratio = 0.66). (e) SAXS patterns (black, blue, and red symbols) and corresponding data fits (solid white lines) obtained for 1.0% w/w aqueous copolymer dispersions of linear PNAEP85-PHBA110 spheres, PNAEP85-PHBA350 worms, and PNAEP85-PHBA450 vesicles (each of these nano-objects was synthesized at 20% w/w solids).

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Unlike TEM, the SAXS data are averaged over many millions of nanoparticles, so the latter technique is expected to provide much more statistically robust information. Moreover, SAXS studies are conducted on aqueous dispersions, so GA crosslinking is not required to stabilize the copolymer morphology. The low q gradient in the SAXS pattern recorded for PNAEP85-PHBA110 nano-objects is close to zero, which indicates the presence of spheres. (90)
In contrast, the low q gradient in the SAXS pattern obtained for PNAEP85-PHBA350 nano-objects is close to −1, suggesting highly anisotropic worms. (18,48) Finally, a low q gradient of −2 was observed in the SAXS pattern for PNAEP85-PHBA350 nano-objects, which is characteristic of vesicles (or bilayers). (18,48) In each case, these findings are consistent with the corresponding TEM images (Figure 1a–c). Moreover, these three SAXS patterns could be satisfactorily fitted using well-known scattering models developed for spheres, worms and vesicles, respectively (see Table S2 for a summary of nano-object dimensions obtained when using such models). (91,92) Overall, these TEM and SAXS data demonstrate that GA crosslinking does not perturb the original copolymer morphology.
Lovett and co-workers reported that ionization of a single carboxylic acid end-group increased the volume fraction of the stabilizer block of PGMA56-PHPMA155 worms sufficiently to induce a worm-to-sphere transition. (70) This pH-induced change in the packing parameter, P, proved to be reversible and could be prevented by the addition of salt. Furthermore, the gradual addition of NaOH to PGMA43-PHPMA200 vesicles led to the irreversible formation of a free-standing worm gel. To examine whether ionization of carboxylic acid end-groups also induced a change in copolymer morphology for PNAEP85-PHBA545 nano-objects, GA crosslinking was conducted at pH 3, pH 5 and pH 7 prior to TEM analysis (Figure 2a).

Figure 2

Figure 2. (a) TEM images recorded for PNAEP85-PHBA545 diblock copolymer nano-objects crosslinked using glutaraldehyde at 22 °C for 24 h at pH 7, pH 5 or pH 3. (b) Z-average diameter (blue squares) and ζ-potential (red squares) as a function of dispersion pH recorded for the same PNAEP85-PHBA545 nano-objects, where the anionic character observed above pH 4 is attributed to ionization of the carboxylic acid group located at the end of each PNAEP stabilizer chain.

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The carboxylic acid end-groups are protonated at pH 3 and rather polydisperse vesicles are obtained under such conditions (z-average diameter = 1020 nm; TEM diameter = 690 ± 260 nm; see Figure 2). The dispersion pH was adjusted to pH 5 using NaOH and TEM studies indicated the formation of a mixed phase comprising vesicles and worms. According to DLS analysis, a concomitant reduction in z-average diameter occurred during this partial phase transition from vesicles to mixed vesicles/worms (Figure 2). Further addition of NaOH produced somewhat ill-defined, pseudo-spherical nano-objects at pH 7 (z-average diameter = 38 nm; TEM diameter = 87 ± 18 nm; Figure 2). The relatively large apparent number-average diameter indicated by TEM suggests that only partial GA crosslinking was achieved in this latter case, which allows some degree of nanoparticle deformation (spreading) to occur during TEM grid preparation. These observations suggest that ionization of the carboxylic acid end-group present at the end of each PNAEP stabilizer chain is sufficient to drive a vesicle-to-sphere transition. This interpretation is supported by aqueous electrophoresis data and DLS studies (see Figure 2b). Furthermore, this pH-induced transition proved to be both rapid and reversible and could not be prevented by addition of up to 1.0 M KCl (see Figure S14).
Linear PNAEP85-PHBAx nano-objects were studied by 1H NMR spectroscopy to determine the apparent degree of hydration of the structure-directing PHBA block as a function of pH (Figure 3). This involved comparing the −CH2OH signals assigned to the partially hydrated PHBA chains to the methylene signals assigned to pendent pyrrolidone rings on PNAEP chains. At low pH, there is a significant difference in the apparent degree of hydration of PHBA chains depending on its DP (spheres > worms > vesicles). For PNAEP85-PHBA545 vesicles, switching from pH 3 to pH 7 leads to a significant increase in the apparent degree of hydration of the PHBA block from 31% to 65% (Figure 3; see Figure S15 for partial 1H NMR spectra), which accounts for the associated vesicle-to-sphere transition indicated by TEM studies (Figure 2a). When the PHBA block becomes more hydrated via ionization of the carboxylic acid end-group on each stabilizer chain, this induces surface plasticization of nano-objects such that HBA repeat units located near the block junction become solvated. This results in an effective increase in the volume fraction of the stabilizer block relative to that of the core block and hence a concomitant reduction in the packing parameter, which accounts for the vesicle-to-sphere transition that occurs when switching from pH 3 to pH 7. 1H NMR studies of PNAEP85-PHBA340 worms prepared at pH 3 also indicated an increase in the apparent degree of hydration of PHBA chains on switching to pH 7, which induces a worm-to-sphere transition (Figures 3 and S15). Perhaps surprisingly, 1H NMR studies of PNAEP85-PHBA140 spheres indicated only minimal change in the degree of hydration of the PHBA block (from 65 to 70%) when switching from pH 2 to pH 8 (Figures 3 and S15). In this case, no change in copolymer morphology was observed (nor did molecular dissolution occur). This suggests that introducing a single anionic charge at the end of each PNAEP85 stabilizer chain leads to an upper limit degree of hydration of approximately 70% for the PHBA block (see Figure 3), regardless of the PHBA DP.

Figure 3

Figure 3. Apparent degree of hydration of the weakly hydrophobic PHBA block as a function of pH for linear PNAEP85-PHBAx nano-objects at 20 °C as determined by 1H NMR spectroscopy studies. [N.B. 100% hydration corresponds to the actual DP of the PHBA block, as calculated by studies of molecularly dissolved copolymer chains in CD3OD (see Figure S16)].

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Variable temperature DLS experiments were conducted on dilute aqueous dispersions of PNAEP85-PHBA295 nano-objects, while rheology studies were performed on 20% w/w aqueous dispersions of the same nano-objects as a function of temperature (Figure 4a). DLS studies indicated that relatively small spheres were formed between 5 and 13 °C. TEM analysis of GA-crosslinked PNAEP85-PHBA295 nanoparticles prepared at 11 °C (see image (i) in Figure 4b) indicates the presence of mainly spheres with a minor population of dimers and short worms. Heating from 13 to 23 °C leads to a larger z-average diameter and a higher complex viscosity (|η*|); a maximum |η*| is observed at 22 °C, which corresponds to the formation of a soft, transparent free-standing gel. This is consistent with the formation of highly anisotropic worms, with a three-dimensional (3D) gel network being formed via multiple inter-worm contacts. (77) We have recently reported that the maximum |η*| corresponds to the presence of highly linear worms. (4) Indeed, TEM studies of GA-crosslinked nano-objects prepared at 23 °C indicate a pure worm phase with minimal branching (see image (ii) in Figure 4). Further heating led to a significant reduction in |η*| owing to vesicle formation (see image (iii) in Figure 4b). Heating the turbid, free-flowing vesicular dispersion above 36 °C led to another increase in |η*|, with TEM analysis suggesting the formation of lamellae (see image (iv) in Figure 4b). The relatively soft nature of these PNAEP85-PHBAx worm gels (G′ = 24–28 Pa) is likely to be related to the highly hydrated PHBA block, which leads to flexible worm cores. Moreover, variable temperature SAXS studies conducted on a 1.0% w/w aqueous dispersion of PNAEP85-PHBA295 nano-objects enabled patterns to be recorded at 5, 23, 34 and 41 °C (Figure 4c). Such patterns could be satisfactorily fitted using well-known scattering models developed for spheres, worms, or vesicles, respectively. (91,92) In each case, nano-object dimensions calculated from SAXS fits were consistent with those determined by DLS and estimated by TEM (Table S3). The SAXS pattern obtained for lamellae could not be satisfactorily fitted but a mean lamellae spacing of 43 nm was calculated from the diffraction peak using q = 2π/d.

Figure 4

Figure 4. (a) Variation in z-average diameter (blue circles) and complex viscosity (red squares) with temperature for an aqueous dispersion of linear PNAEP85-PHBA295 nano-objects. DLS studies were conducted on 0.1% w/w aqueous dispersions, while rheological measurements were performed on a 10% w/w aqueous dispersion at an applied strain of 1.0% and an angular frequency of 1.0 rad s–1 during a run starting at 1 °C (15 min was allowed for thermal equilibration at this initial temperature prior to heating). (b) Prior to TEM analysis, 5% w/w aqueous dispersions of PNAEP85-PHBA295 nanoparticles were crosslinked with glutaraldehyde for 24 h at (i) 11 °C, (ii) 23 °C, (iii) 34 °C or (iv) 41 °C. (c) Small-angle X-ray scattering patterns recorded for a 1.0% w/w aqueous dispersion of linear thermoresponsive PNAEP85-PHBA295 nano-objects at 5 °C (black data), 23 °C (blue data), 34 °C (purple data) and 41 °C (red data; red triangle indicates the diffraction peak used to calculate D). The white lines indicate data fits obtained using appropriate scattering models (see the Supporting Information for further details).

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Rheological studies performed on the same 20% w/w aqueous dispersion of PNAEP85-PHBA295 nano-objects indicated excellent thermoreversibility for the sphere-to-worm and worm-to-vesicle transitions (see Figure S17). In contrast, significant hysteresis was observed for the lamellae-to-vesicle transition when cooling PNAEP85-PHBA295 lamellae from 45 °C. More specifically, vesicles were only formed at 27 °C, despite being present at up to 34 °C during the heating run (see Figure S17). Moreover, the lamellae-to-vesicle transition observed on cooling occurs at the same temperature at which the worm-to-vesicle transition is complete on heating (27 °C in Figure S17). However, further cooling indicates little or no hysteresis during the vesicle-to-worm transition, with the maximum |η*| being achieved at comparable temperatures (27.4 Pa·s at 22 °C on heating and 27.8 Pa·s at 21 °C on cooling). Similarly, no evidence for hysteresis was observed for the worm-to-sphere transition when cooling from 21 to 0 °C, with almost identical |η*| data sets being recorded for the heating and cooling cycles. This indicates that sphere-to-worm and worm-to-vesicle transitions (and also the corresponding vesicle-to-worm and worm-to-sphere transitions) both occur within the experimental timescale of 55 min allowed for the heating (and cooling) run. One might expect the associative pathway to be slower than the dissociative pathway because the former requires highly co-operative events (e.g., the stochastic 1D fusion of multiple spheres during the sphere-to-worm transition (93)). However, in both cases, the highly mobile nature of the partially hydrated PHBA chains enables each of these four morphology transitions to occur within 5–10 min.
In principle, systematic variation of the PHBA DP should enable the critical temperature, Tc, for such morphology transitions to be tuned. (94) This important point is illustrated in Figure 5, which shows the rheological behavior observed for five different PNAEP85-PHBAx nano-objects (where x = 110, 200, 295, 380 or 475). In particular, a large increase in |η*| occurs when these thermoresponsive nano-objects undergo a sphere-to-worm transition (see Figure 5a–d). (18,95) For a PHBA DP of 110, the Tc for this transition is around 50 °C (see Figure 5a). However, longer PHBA blocks exhibit lower Tc values (see Figure 5b–d). It is also noteworthy that heating PNAEP85-PHBA110 nano-objects up to 60 °C resulted in no further morphological transitions being observed. In striking contrast, the rheology data obtained for PNAEP85-PHBA200 suggests the formation of spheres between 10 and 20 °C, worms at around 37 °C, vesicles at approximately 40 °C and lamellae at 50 °C. Interestingly, these worms exhibit a maximum |η*| at around physiological temperature. In principle, this may be useful for potential biomedical applications, e.g., long-term cell culture within a wholly synthetic 3D matrix (96) or stasis induction studies. (97,98) However, these rheological experiments were conducted at pH 3. Nevertheless, it should be feasible to similarly tune the critical temperature required for maximum |η*| (i.e., for the formation of highly linear worms) at physiological pH in the presence of a suitable cell culture medium (e.g., PBS or Nutristem). Clearly, such optimization would require using an alternative RAFT agent that did not contain a carboxylic acid group. (99)

Figure 5

Figure 5. Variable temperature complex viscosity measurements for 20% w/w aqueous dispersions of PNAEP85-PHBAx nano-objects at pH 3 using an applied strain of 1.0% and an angular frequency of 1.0 rad s–1: (a) x = 110, (b) x = 200, (c) x = 295, (d) x = 380 and (e) x = 475. Dashed lines indicate the inferred copolymer morphology at specific temperatures (S = spheres, W = worms, V = vesicles and L = lamellae). These assignments are based on the data shown in Figure 4 and are consistent with a recent study by Byard et al. (18) (f) Relationship between the critical temperature (Tc) corresponding to the maximum |η*| and the PHBA DP for the same five aqueous dispersions of PNAEP85-PHBAx nano-objects.

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Returning to Figure 5, increasing the PHBA DP changes the preferred copolymer morphology at 20 °C from spheres (x = 110 or 200) to worms (x = 295 or 380) to vesicles (x = 475). In the latter case, the copolymer dispersion had to be cooled to 2 °C to partially dehydrate the PHBA block and hence induce a vesicle-to-worm transition. It is perhaps worth emphasizing here that PHPMA-based nano-objects with DPs greater than 220 exhibit no discernible thermoresponsive behavior owing to the significantly greater hydrophobic character of this block. (48,94,100) Finally, an inverse linear correlation is observed between Tc and the PHBA DP over a wide temperature range (2–50 °C), see Figure 5f. In principle, this relationship can be used to predict Tc for other diblock copolymer compositions by interpolating between x values.

Conclusions

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A series of PNAEP85-PHBAx nano-objects have been prepared via redox-initiated RAFT aqueous dispersion polymerization of HBA at 30 °C using a highly efficient and reproducible one-pot protocol. High HBA conversions could be achieved within 60 min at pH 3 and within 120 min at pH 7. In both cases, DMF GPC analysis indicated a linear evolution in copolymer molecular weight with conversion, as expected for a well-controlled RAFT polymerization. However, relatively broad molecular weight distributions (Mw/Mn ∼ 1.2–2.1) are obtained, particularly when targeting higher PHBA DPs. This is attributed to chain transfer to polymer, which is well documented for acrylic monomers even at relatively low reaction temperatures. (60,64,101)
To enable assignment of copolymer morphologies, PNAEP85-PHBAx nano-objects were crosslinked using glutaraldehyde, which forms acetal linkages between pendent hydroxyl groups on PHBA chains. Careful optimization of the copolymer concentration and glutaraldehyde/HBA molar ratio enabled such covalent stabilization to be conducted at pH 3–7 over a wide temperature range. For example, the TEM studies of the resulting crosslinked nano-objects confirmed that pure spheres, worms and vesicles could be obtained at 20 °C and pH 3 by adjusting the target diblock copolymer composition. Systematic variation of the PHBA DP between 100 and 550 while targeting copolymer concentrations of 5–40% w/w enabled the construction of a pseudo-phase diagram.
TEM studies of crosslinked PNAEP85-PHBA545 nano-objects prepared while varying the dispersion pH at 20 °C indicated that the copolymer morphology was pure vesicles at pH 3, a mixed phase comprising spheres, worms and vesicles at pH 5 and pure spheres at pH 7. 1H NMR studies of linear PNAEP85-PHBAx nano-objects suggest that this pH-driven shift in copolymer morphology is driven by surface plasticization of PHBA cores, which occurs on raising the dispersion pH above the pKa of carboxylic acid end-groups located on each PNAEP85 stabilizer chain. This introduces sufficient anionic charge to drive a vesicle-to-sphere transition via an overall reduction in the fractional packing parameter despite the higher degree of (partial) hydration of the PHBA block. On the other hand, uniform plasticization of PHBA chains occurs on heating at pH 3, which increases the fractional packing parameter and hence drives sphere-to-worm, worm-to-vesicle and vesicle-to-lamellae transitions. Clearly, this new PISA formulation exhibits rich self-assembly behavior despite the relatively broad molecular weight distributions obtained for diblock copolymer chains.
Rheology, DLS and TEM studies were conducted on aqueous dispersions of five examples of PNAEP85-PHBAx nano-objects as a function of temperature. This series of experiments indicates that the critical temperature corresponding to the maximum complex viscosity (|η*|), which indicates the formation of highly linear worms, can be tuned by systematically varying the PHBA DP. Furthermore, |η*| could be adjusted from 1 to 297 Pa·s and there is an inverse linear relationship between this critical temperature and the PHBA DP over a relatively wide temperature range (2–50 °C).
Given their anticipated biocompatibility, we envisage that next-generation PNAEPx-PHBAy worm gels comprising neutral (e.g., ester- or amide-capped) chain ends are likely to offer new opportunities as wholly synthetic 3D matrices for long-term cell culture studies (96) or possibly for inducing stasis in embryonic human stem cells. (97,98) However, for this potential application to be realized, such PISA formulations need to be optimized to produce free-standing thermoresponsive worm gels at pH 7, rather than at pH 3.

Experimental Section

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Materials

2-(N-Acryloyloxy)ethyl pyrrolidone (NAEP; 95%) was provided by Ashland Specialty Ingredients (Cherry Hill, NJ) and purified by dilution with chloroform followed by sequential washes with 5% Na2CO3 solution, saturated NaCl solution, and finally deionized water. This aqueous solution was then dried over anhydrous MgSO4 and concentrated prior to use. HBA was kindly donated by BASF (Ludwigshafen, Germany) and was purified via extraction using n-hexane (20 times) to remove diacrylate impurities. All chemicals used for NAEP and HBA purification were purchased from Sigma-Aldrich (Dorset, U.K.) and were used as received. N,N,N′,N′-Tetramethylethylenediamine (TMEDA), ascorbic acid (AsAc), potassium persulfate (KPS), 3-(trimethylsilyl)-1-propanesulfonic acid sodium salt (DSS), glutaraldehyde (GA; supplied as a 50% w/w aqueous solution), and 2-(dodecylthiocarbonothioylthio)-2-methylpropionic acid (DDMAT; 98%) were purchased from Sigma-Aldrich (Dorset, U.K.). CD3OD and D2O were purchased from Goss Scientific Instruments Ltd. (Cheshire, U.K.). All other solvents were purchased from Fisher Scientific (Loughborough, U.K.) and were used as received. Deionized water was used for all experiments.

One-Pot Synthesis of PNAEP85-PHBAx Diblock Copolymer Nano-Objects via RAFT Aqueous Dispersion Polymerization

A typical protocol used for the one-pot synthesis of PNAEP85-PHBA435 diblock copolymer nano-objects at 20% w/w solids was as follows: DDMAT RAFT agent (5.30 mg, 14.6 μmol) was added to NAEP (0.200 g, 1.09 mmol; target PNAEP DP = 75) and KPS (0.80 mg, 2.9 μmol; [DDMAT]/[KPS] molar ratio = 5.0) was weighed into a 28 mL glass vial charged with a magnetic flea. This vial was then placed in an ice bath and nitrogen was passed over the top of the solution for 30 min. After 30 min, the vial was immersed in an oil bath set at 30 °C. AsAc (0.50 mg, 2.9 μmol; [DDMAT]/[AsAc] molar ratio = 5.0; [KPS]/[AsAc] molar ratio = 1.0) and acidified deionized water (57.0 mg; pH 3; final solids concentration = 78% w/w) were combined and degassed before being added via a degassed syringe/needle to the vial under a nitrogen atmosphere. The NAEP polymerization was allowed to proceed for 10 min prior to dilution of the viscous aqueous reaction solution via the addition of degassed acidified water (5.85 g; pH 3; final target solids concentration = 20% w/w). The resulting reaction solution was stirred magnetically for 2 min to ensure that the PNAEP homopolymer became fully solubilized. A degassed syringe/needle was used to extract an aliquot for 1H NMR spectroscopy analysis. The disappearance of vinyl signals at 5.9 and 6.4 ppm relative to the integrated four ethyl protons at 3.4–3.8 ppm assigned to PNAEP indicated a final monomer conversion of 98%. The mean PNAEP DP was calculated to be 86 (DDMAT RAFT efficiency = 87%) as judged by 1H NMR studies in CD3OD [the integrated signal at 3.4–3.8 ppm (m, 4H) was compared with that assigned to the methyl RAFT chain-end at 0.86–0.96 ppm (t, 3H)]. DMF GPC analysis indicated an Mn of 19.2 kg mol–1 and an Mw/Mn of 1.16 compared to a series of 10 near-monodisperse poly(methyl methacrylate) calibration standards. To perform the second-stage polymerization, degassed HBA (1.19 g, 8.29 mmol; PHBA target DP = 435) was added to the reaction solution. KPS (1.03 mg, 3.80 μmol; [PNAEP]/[KPS] molar ratio = 5.0) and AsAc (0.67 mg, 3.80 μmol; [PNAEP]/[AsAc] molar ratio = 5.0; [KPS]/[AsAc] molar ratio = 1.0) were added to the reaction mixture as dilute aqueous solutions (0.13 and 0.08 mM, respectively) using degassed syringe/needles. The HBA polymerization was allowed to proceed for 1 h at 30 °C (N.B. polymerizations targeting 5% w/w solids were allowed to run for 2 h at 30 °C) before being quenched by exposing the reaction mixture to air and immersing the glass vial into an ice bath. The extent of polymerization was determined by 1H NMR spectroscopy: comparison of the integrated vinyl proton signals at 5.8 and 6.5 ppm assigned to the residual HBA monomer to the two oxymethylene protons at 4.2–4.3 ppm assigned to PHBA indicated a final HBA conversion of 98%. The mean DP of the PHBA block was calculated to be 435 as judged by 1H NMR spectroscopy analysis in CD3OD (the integrated signal at 3.6–3.8 ppm (t, 2H) was compared with that assigned to two oxymethylene protons assigned to PNAEP85 at 2.1–2.2 ppm (m, 170H)). DMF GPC analysis indicated an Mn of 64.5 kg mol–1 and an Mw/Mn of 1.31. For analogous PISA syntheses, the volume of water was adjusted to afford the desired final solids concentrations. Other target diblock copolymer compositions were obtained by adjusting the [HBA]/[PNAEP85] molar ratio.

Covalent Stabilization of the PNAEP85-PHBAx Diblock Copolymer Nano-Objects via Crosslinking with Glutaraldehyde

A typical protocol used for crosslinking PNAEP85-PHBA255 spheres is as follows. A 5.0% w/w acidic aqueous dispersion of PNAEP85-PHBA255 spheres (0.50 g; PHBA = 121 μmol, pH 3) and glutaraldehyde (GA; 8.0 mg, 80 μmol, GA/PHBA molar ratio = 0.66) were added to a 7 mL vial. This reaction mixture was stirred at 25 °C for 16 h. Then an aliquot (10.0 mg) was extracted and diluted with water (4.99 g; final target solids’ concentration = 0.05% w/w) and stirred for 24 h prior to preparation of the corresponding TEM grid (see below for further details). Crosslinking of PNAEP85-PHBA340-375 worms and PNAEP85-PHBA435-565 vesicles was also performed at 5.0% w/w; in the former case, this copolymer concentration was sufficiently low to avoid chemical gelation during crosslinking. To crosslink PNAEP85-PHBAx diblock copolymer nano-objects at a given temperature or pH, 5.0% w/w dispersions were either equilibrated at the desired reaction temperature for 1 h or after an appropriate amount of 1 M NaOH or HCl had been added prior to GA addition. Then GA crosslinking was allowed to proceed for 16 h prior to dilution with water (final target solids concentration = 0.05% w/w) that had been pre-equilibrated at the appropriate temperature or solution pH.

Copolymer Characterization

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1H NMR Spectroscopy

Spectra were recorded in either CD3OD or D2O using a 400 MHz Bruker Avance-400 spectrometer with 64 scans being averaged per spectrum.

Gel Permeation Chromatography

Copolymer molecular weights and dispersities were determined using an Agilent 1260 Infinity GPC system equipped with both refractive index and UV–visible detectors. Two Agilent PLgel 5 μm Mixed-C columns and a guard column were connected in series and maintained at 60 °C. High-performance liquid chromatography (HPLC)-grade DMF containing 10 mM LiBr was used as the eluent and the flow rate was set at 1.0 mL min–1. Refractive index detection was used for the calculation of molecular weights and dispersities by calibration against a series of 10 near-monodisperse PMMA standards (with Mn values ranging from 370 to 2 520 000 g mol–1).

Transmission Electron Microscopy

Unless stated otherwise, as-prepared copolymer dispersions were diluted at 20 °C using acidified deionized water (pH 3) to generate 0.05% w/w aqueous dispersions. Copper/palladium TEM grids (Agar Scientific, U.K.) were coated in-house to produce thin films of amorphous carbon. These grids were then treated with a plasma glow discharge for 30 s to create a hydrophilic surface. One droplet of an aqueous copolymer dispersion (20 μL; 0.05% w/w) was placed on a freshly treated grid for 1 min and then blotted with a filter paper to remove excess solution. To stain deposited nanoparticles, one 10 μL droplet of a 0.75% w/w aqueous solution of uranyl formate was placed on the sample-loaded grid using a micropipet for 45 s and then carefully blotted to remove excess stain. Each grid was then dried using a vacuum hose. Imaging was performed using a Philips CM100 instrument operating at 100 kV and equipped with a Gatan 1k CCD camera.

Dynamic Light Scattering

Unless stated otherwise, measurements were conducted at 25 °C using a Malvern Instruments Zetasizer Nano ZS instrument equipped with a 4 mW He–Ne laser (λ = 633 nm) and an avalanche photodiode detector. Scattered light was detected at 173°. Copolymer dispersions were diluted to 0.10% w/w prior to analysis. Intensity-average hydrodynamic diameters were averaged over three runs and calculated using the Stokes–Einstein equation. Variable temperature studies were performed at 2 °C intervals during a 5 to 41 °C to 5 °C thermal cycle. Between each measurement, 5 min was allowed for thermal equilibration.

Aqueous Electrophoresis

ζ-Potential measurements were performed on 0.1% w/w aqueous copolymer dispersions at 20 °C in the presence of 1 mM KCl using the same Malvern Zetasizer Nano ZS instrument. The initial copolymer dispersion pH was pH 2.5 and was adjusted by the addition of small amounts of aqueous 0.1 M NaOH, with 10 min being allowed for equilibrium at each pH. ζ-Potentials were calculated from the Henry equation using the Smoluchowski approximation. Hydrodynamic DLS diameters were also recorded during these pH sweep experiments. All data were averaged over three consecutive runs.

Rheology

An AR-G2 rheometer equipped with a variable temperature Peltier plate and a 40 mL 2° aluminum cone was used for all experiments. The dispersion viscosity, loss modulus and storage modulus were measured as a function of applied strain, angular frequency and temperature to assess the gel strength, gel viscosity and critical gelation temperature. Percentage strain sweeps were conducted at 25 °C using a constant angular frequency of 1.0 rad s–1. Angular frequency sweeps were conducted at the critical gelation temperature corresponding to the maximum complex viscosity using an applied strain of 1.0%. Temperature sweeps were conducted using 20% w/w copolymer dispersions at an applied strain of 1.0% and an angular frequency of 1.0 rad s–1. In these latter experiments, the copolymer dispersion was subjected to a single thermal cycle (heating up to 60 °C, followed by cooling to 1 °C) and then equilibrated at 1 °C for 15 min prior to measurements. The temperature was adjusted at 2 °C intervals, allowing 60 s for thermal equilibration between each measurement.

Small-Angle X-ray Scattering Studies

SAXS patterns of 1.0% w/w aqueous diblock copolymer dispersions were recorded at a synchrotron source (Diamond Light Source, station I22, Didcot, U.K.) using monochromatic X-ray radiation (wavelength, λ = 0.124 nm, sample-to-detector distance = 9 m, such that q ranged from 0.015 to 1.3 nm–1, where q = 4π sin θ/λ is the length of the scattering vector and θ is one-half of the scattering angle) and a 2D Pilatus 2M pixel detector (Dectris, Switzerland). Alternatively, some SAXS experiments were conducted using a Xeuss 2.0 SAXS instrument (Xenocs) equipped with a FOX 3D multilayered X-ray mirror, two sets of scatterless slits for collimation, a hybrid pixel area detector (Pilatus 1M, Dectris), and a liquid gallium MetalJet X-ray source (Excillum, λ = 1.34 Å). In this case, SAXS patterns were recorded at a sample-to-detector distance of approximately 1.20 m (calibrated using a silver behenate standard). Glass capillaries of 2.0 mm diameter were used as a sample holder. SAXS data were reduced (integration, normalization, and absolute intensity calibration using SAXS patterns obtained for deionized water, assuming a differential scattering cross-section for water of 0.0162 cm–1) using either Dawn software supplied by Diamond Light Source or Irena SAS macros for Igor Pro. (102) The temperature was adjusted using a HFSX350-CAP temperature-controlled stage (Linkam Scientific, Tadworth, U.K.) and 10 min was allowed between each measurement to ensure thermal equilibration.

Supporting Information

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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.chemmater.1c02096.

  • Mn and Mw/Mn data for PNAEP85 precursors; kinetic data recorded during the RAFT aqueous dispersion polymerization of HBA; 1H NMR spectra recorded during the RAFT aqueous dispersion polymerization of HBA; GPC traces recorded for the RAFT aqueous dispersion polymerization of HBA conducted at pH 3 and pH 7; GPC curves recorded using either a RI detector or a UV detector; z-average diameter vs monomer conversion; DSC curves for a PNAEP85 homopolymer, PHBA300 homopolymer, a GA-crosslinked PNAEP85-PHBA350, and a series of PNAEP85-PHBAx diblock copolymers; FT-IR spectra recorded for freeze-dried powders of the PHBA200 homopolymer, PNAEP85-PHBA200 diblock copolymer, and PNAEP85 homopolymer; TEM images recorded for linear and GA-crosslinked PNAEP85-PHBA265; FT-IR spectra recorded for freeze-dried powders of the linear and crosslinked PNAEP85-PHBA265; summary table of diblock compositions, HBA conversions, molecular weight data, DLS particle diameters, DLS polydispersities, and TEM assignments; DLS studies of linear and crosslinked PNAEP85-PHBAx nano-objects as a function of temperature and pH; TEM images for all GA-crosslinked PNAEP85-PHBAx nano-objects; summary table of DLS, SAXS, and TEM data obtained for PNAEP85-PHBAx nano-objects at pH 3 and 20 °C; digital photographs of the reversible vesicle-to-sphere transition; partially assigned 1H NMR spectra recorded at various solution pH; 1H NMR spectra for molecularly dissolved diblock copolymers; summary of DLS, SAXS, and TEM data obtained at 5, 23, 34, and 41 °C; and complex viscosity vs temperature measurements (PDF)

Terms & Conditions

Most electronic Supporting Information files are available without a subscription to ACS Web Editions. Such files may be downloaded by article for research use (if there is a public use license linked to the relevant article, that license may permit other uses). Permission may be obtained from ACS for other uses through requests via the RightsLink permission system: http://pubs.acs.org/page/copyright/permissions.html.

Author Information

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  • Corresponding Author
  • Authors
    • Oliver J. Deane - Dainton Building, Department of Chemistry, University of Sheffield, Sheffield S3 7HF, U.K.
    • James Jennings - Dainton Building, Department of Chemistry, University of Sheffield, Sheffield S3 7HF, U.K.
    • Thomas J. Neal - Dainton Building, Department of Chemistry, University of Sheffield, Sheffield S3 7HF, U.K.
    • Osama M. Musa - Ashland Specialty Ingredients, 1005 US 202/206, Bridgewater, New Jersey 08807, United States
    • Alan Fernyhough - Ashland Specialty Ingredients, Listers Mills, Heaton Road, Bradford BD9 4SH, U.K.
  • Notes
    The authors declare no competing financial interest.

Acknowledgments

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EPSRC is thanked for funding a CDT Ph.D. studentship for the first author (EP/L016281). Ashland Specialty Ingredients (Bridgewater, New Jersey) is thanked for financial support of this Ph.D. project, for supplying the NAEP monomer, and for permission to publish this work. S.P.A. also thanks the EPSRC for an Established Career Particle Technology Fellowship (EP/R003009).

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    Soft Matter (2012), 8 (38), 9915-9922CODEN: SMOABF; ISSN:1744-683X. (Royal Society of Chemistry)
    A series of diblock copolymer worms are prepd. via aq. dispersion polymn. using reversible addn.-fragmentation chain transfer (RAFT) polymn. chem. More specifically, a poly(glycerol monomethacrylate) (PGMA) RAFT chain transfer agent is used to polymerize a water-miscible monomer, 2-hydroxypropyl methacrylate, at 70 °C. The poly(2-hydroxypropyl methacrylate) (PHPMA) chains become increasingly hydrophobic as they grow, which leads to nanoparticle formation. Careful control of the diblock compn. is achieved by fixing the mean d.p. (DP) of the PGMA stabilizer block at 54 and systematically varying the DP of the core-forming PHPMA block. This strategy enables the worm phase space to be targeted reproducibly. These worms form soft free-standing gels in aq. soln. due to inter-worm entanglements. Rheol. studies enable the influence of the diblock copolymer compn. on the gel strength, crit. gelation concn. (CGC) and crit. gelation temp. (CGT) to be assessed. A max. in gel strength is obsd. as the DP of the PHPMA block is increased from 130 to 170. The initial increase is due to longer worms, while the subsequent decrease is assocd. with worm clustering, which leads to more brittle gels. The gel strength is reduced from approx. 100 Pa to 10 Pa as the copolymer concn. is lowered from 10 to 5 wt./wt.%, with a CGC being obsd. at around 3 to 4 wt./wt.%. The CGT is relatively concn.-independent, but sensitive to the diblock copolymer compn.: longer (more PHPMA-rich) chains lead to the CGT being reduced from 20 °C to 7 °C. This is because longer PHPMA blocks require a greater degree of hydration to induce the worm-to-sphere transition, which can only achieved at progressively lower temps. Reversible de-gelation also occurs on cooling, since there can be no entanglements between isotropic particles. This RAFT formulation also provides a rare example of thermo-responsive diblock copolymer worms.
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    Won, Y.-Y.; Davis, H. T.; Bates, F. S. Giant Wormlike Rubber Micelles. Science 1999, 283, 960– 963,  DOI: 10.1126/science.283.5404.960
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    Giant wormlike rubber micelles
    Won, You-Yeon; Davis, H. Ted; Bates, Frank S.
    Science (Washington, D. C.) (1999), 283 (5404), 960-963CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
    A low-mol.-wt. poly(ethylene oxide)-poly(butadiene) (PEO-PB) diblock copolymer contg. 50 wt. percent PEO forms gigantic wormlike micelles at low concns. (<5 percent by wt.) in water. Subsequent generation of free radicals with a conventional water-based redox reaction leads to chem. crosslinking of the PB cores without disruption of the cylindrical morphol., as evidenced by cryotransmission electron microscopy and small-angle neutron-scattering expts. These wormlike rubber micelles exhibit unusual viscoelastic properties in water.
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  6. 6
    Discher, B. M.; Won, Y.-Y.; Ege, D. S.; Lee, J. C.-M.; Bates, F. S.; Discher, D. E.; Hammer, D. A. Polymersomes: Tough Vesicles Made from Diblock Copolymers. Science 1999, 284, 1143– 1146,  DOI: 10.1126/science.284.5417.1143
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    Polymersomes: Tough vesicles made from diblock copolymers
    Discher, Bohdana M.; Won, You-Yeon; Ege, David S.; Lee, James C.-M.; Bates, Frank S.; Discher, Dennis E.; Hammer, Daniel A.
    Science (Washington, D. C.) (1999), 284 (5417), 1143-1146CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
    Vesicles were made from amphiphilic diblock copolymers and characterized by micromanipulation. The av. mol. wt. of the specific polymer studied, polyethylene oxide-polyethylethylene (EO40-EE37), is several times greater than that of typical phospholipids in natural membranes. Both the membrane bending and area expansion moduli of electroformed polymersomes (polymer-based liposomes) fell within the range of lipid membrane measurements, but the giant polymersomes proved to be almost an order of magnitude tougher and sustained far greater areal strain before rupture. The polymersome membrane was also at least 10 times less permeable to water than common phospholipid bilayers. The results suggest a new class of synthetic thin-shelled capsules based on block copolymer chem.
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    Wang, X.; Guerin, G.; Wang, H.; Wang, Y.; Manners, I.; Winnik, M. A. Cylindrical Block Copolymer Micelles and Co-Micelles of Controlled Length and Architecture. Science 2007, 317, 644– 647,  DOI: 10.1126/science.1141382
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    Cylindrical block copolymer micelles and co-micelles of controlled length and architecture
    Wang, Xiaosong; Guerin, Gerald; Wang, Hai; Wang, Yishan; Manners, Ian; Winnik, Mitchell A.
    Science (Washington, DC, United States) (2007), 317 (5838), 644-647CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
    Block copolymers consist of two or more chem. different polymers connected by covalent linkages. In soln., repulsion between the blocks leads to a variety of morphologies, which are thermodynamically driven. Polyferrocenyidimethylsilane block copolymers show an unusual propensity to forming cylindrical micelles in soln. We found that the micelle structure grows epitaxially through the addn. of more polymer, producing micelles with a narrow size dispersity, in a process analogous to the growth of living polymer. By adding a different block copolymer, we could form co-micelles. We were also able to selectively functionalize different parts of the micelle. Potential applications for these materials include their use in lithog. etch resists, in redox-active templates, and as catalytically active metal nanoparticle precursors.
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    Gilroy, J. B.; Gädt, T.; Whittell, G. R.; Chabanne, L.; Mitchels, J. M.; Richardson, R. M.; Winnik, M. A.; Manners, I. Monodisperse Cylindrical Micelles by Crystallization-Driven Living Self-Assembly. Nat. Chem. 2010, 2, 566– 570,  DOI: 10.1038/nchem.664
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    Monodisperse cylindrical micelles by crystallization-driven living self-assembly
    Gilroy, Joe B.; Gaedt, Torben; Whittell, George R.; Chabanne, Laurent; Mitchels, John M.; Richardson, Robert M.; Winnik, Mitchell A.; Manners, Ian
    Nature Chemistry (2010), 2 (7), 566-570CODEN: NCAHBB; ISSN:1755-4330. (Nature Publishing Group)
    Non-spherical nanostructures derived from soft matter and with uniform size-i.e., monodisperse materials-are of particular utility and interest, but are very rare outside the biol. domain. We report the controlled formation of highly monodisperse cylindrical block copolymer micelles (length dispersity ≤ 1.03; length range, ∼200 nm to 2 μm) by the use of very small (∼20 nm) uniform crystallite seeds that serve as initiators for the crystn.-driven living self-assembly of added block-copolymer unimers with a crystallizable, core-forming metalloblock. This process is analogous to the use of small initiator mols. in classical living polymn. reactions. The length of the nanocylinders could be precisely controlled by variation of the unimer-to-crystallite seed ratio. Samples of the highly monodisperse nanocylinders of different lengths that are accessible using this approach have been shown to exhibit distinct liq.-cryst. alignment behavior.
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    Charleux, B.; Delaittre, G.; Rieger, J.; D’Agosto, F. Polymerization-Induced Self-Assembly: From Soluble Macromolecules to Block Copolymer Nano-Objects in One Step. Macromolecules 2012, 45, 6753– 6765,  DOI: 10.1021/ma300713f
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    9
    Polymerization-Induced Self-Assembly: From Soluble Macromolecules to Block Copolymer Nano-Objects in One Step
    Charleux, Bernadette; Delaittre, Guillaume; Rieger, Jutta; D'Agosto, Franck
    Macromolecules (Washington, DC, United States) (2012), 45 (17), 6753-6765CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    A review. This Perspective describes the recent developments of polymn.-induced self-assembly of amphiphilic block copolymers based on controlled/living free-radical polymn. (CRP) in water. This method relies on the use of a hydrophilic living polymer precursor prepd. via CRP that is extended with a hydrophobic second block in an aq. environment. The process thus leads to amphiphilic block copolymers that self-assemble in situ into self-stabilized nano-objects in the frame of an emulsion or dispersion polymn. process. Depending on the nature and the structure of the so-formed copolymer, not only spherical particles can be achieved but also all morphologies that can be found in the phase diagram of an amphiphilic block copolymer in a selective solvent. This paper focuses mainly on aq. emulsion or dispersion polymn. and gives an overview of the CRP techniques used, the general conditions, and the morphologies obtained.
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    Warren, N. J.; Armes, S. P. Polymerization-Induced Self-Assembly of Block Copolymer Nano-Objects via RAFT Aqueous Dispersion Polymerization. J. Am. Chem. Soc. 2014, 136, 10174– 10185,  DOI: 10.1021/ja502843f
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    10
    Polymerization-Induced Self-Assembly of Block Copolymer Nano-objects via RAFT Aqueous Dispersion Polymerization
    Warren, Nicholas J.; Armes, Steven P.
    Journal of the American Chemical Society (2014), 136 (29), 10174-10185CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    A review. In this Perspective, we discuss the recent development of polymn.-induced self-assembly mediated by reversible addn.-fragmentation chain transfer (RAFT) aq. dispersion polymn. This approach has quickly become a powerful and versatile technique for the synthesis of a wide range of bespoke org. diblock copolymer nano-objects of controllable size, morphol., and surface functionality. Given its potential scalability, such environmentally-friendly formulations are expected to offer many potential applications, such as novel Pickering emulsifiers, efficient microencapsulation vehicles, and sterilizable thermo-responsive hydrogels for the cost-effective long-term storage of mammalian cells.
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    Rieger, J. Guidelines for the Synthesis of Block Copolymer Particles of Various Morphologies by RAFT Dispersion Polymerization. Macromol. Rapid Commun. 2015, 36, 1458– 1471,  DOI: 10.1002/marc.201500028
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    11
    Guidelines for the Synthesis of Block Copolymer Particles of Various Morphologies by RAFT Dispersion Polymerization
    Rieger, Jutta
    Macromolecular Rapid Communications (2015), 36 (16), 1458-1471CODEN: MRCOE3; ISSN:1022-1336. (Wiley-VCH Verlag GmbH & Co. KGaA)
    A review. This article presents the recent developments of radical dispersion polymerizaton controlled by reversible addn. fragmentation chain transfer (RAFT) for the prodn. of block copoly-mer particles of various morphologies, such as core-shell spheres, worms, or vesicles. It is not meant to be an exhaustive review but it rather provides guidelines for non-specialists. The article is subdivided into eight sections. After a general introduction, the mechanism of polymn.-induced self-assembly (PISA) through RAFT-mediated dispersion polymn. is presented and the different parameters that control the morphol. produced are discussed. The next two sections are devoted to the choice of the monomer/solvent pair and the macroRAFT agent. Afterwards, post-polymn. morphol. order-to-order transitions (i.e. morphol. transitions triggered by extrinsic stimuli) or order-to-disorder transitions (i.e. disassembly of chains) are discussed. Assemblies based on more complex polymer architectures, such as triblock copolymers, are presented next, and finally the possibility to stabilize these structures by crosslinking is reported. The manuscript ends with a short conclusion and an outlook.
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    Derry, M. J.; Fielding, L. A.; Armes, S. P. Polymerization-Induced Self-Assembly of Block Copolymer Nanoparticles via RAFT Non-Aqueous Dispersion Polymerization. Prog. Polym. Sci. 2016, 52, 1– 18,  DOI: 10.1016/j.progpolymsci.2015.10.002
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    12
    Polymerization-induced self-assembly of block copolymer nanoparticles via RAFT non-aqueous dispersion polymerization
    Derry, Matthew J.; Fielding, Lee A.; Armes, Steven P.
    Progress in Polymer Science (2016), 52 (), 1-18CODEN: PRPSB8; ISSN:0079-6700. (Elsevier Ltd.)
    There is considerable current interest in polymn.-induced self-assembly (PISA) via reversible addn.-fragmentation chain transfer (RAFT) polymn. as a versatile and efficient route to various types of block copolymer nano-objects. Many successful PISA syntheses have been conducted in water using either RAFT aq. dispersion polymn. or RAFT aq. emulsion polymn. In contrast, this review article is focused on the growing no. of RAFT PISA formulations developed for non-aq. media. A wide range of monomers have been utilized for both the stabilizer and core-forming blocks to produce diblock copolymer nanoparticles in either polar or non-polar media (including supercrit. CO2 and ionic liqs.) via RAFT dispersion polymn. Such nanoparticles possess spherical, worm-like or vesicular morphologies, often with controllable size and functionality. Detailed characterization of such sterically stabilized diblock copolymer dispersions provides important insights into the various morphol. transformations that can occur both during the PISA synthesis and also on subsequent exposure to a suitable external stimulus (e.g. temp.).
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    Boott, C. E.; Gwyther, J.; Harniman, R. L.; Hayward, D. W.; Manners, I. Scalable and Uniform 1D Nanoparticles by Synchronous Polymerization, Crystallization and Self-Assembly. Nat. Chem. 2017, 9, 785– 792,  DOI: 10.1038/nchem.2721
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    13
    Scalable and uniform 1D nanoparticles by synchronous polymerization, crystallization and self-assembly
    Boott, Charlotte E.; Gwyther, Jessica; Harniman, Robert L.; Hayward, Dominic W.; Manners, Ian
    Nature Chemistry (2017), 9 (8), 785-792CODEN: NCAHBB; ISSN:1755-4330. (Nature Publishing Group)
    The prepn. of well-defined nanoparticles based on soft matter, using soln.-processing techniques on a com. viable scale, is a major challenge of widespread importance. Self-assembly of block copolymers in solvents that selectively solvate one of the segments provides a promising route to core-corona nanoparticles (micelles) with a wide range of potential uses. Nevertheless, significant limitations to this approach also exist. For example, the soln. processing of block copolymers generally follows a sep. synthesis step and is normally performed at high diln. Moreover, non-spherical micelles-which are promising for many applications-are generally difficult to access, samples are polydisperse and precise dimensional control is not possible. Here we demonstrate the formation of platelet and cylindrical micelles at concns. up to 25% solids via a one-pot approach-starting from monomers-that combines polymn.-induced and crystn.-driven self-assembly. We also show that performing the procedure in the presence of small seed micelles allows the scalable formation of low dispersity samples of cylindrical micelles of controlled length up to three micrometres.
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    Chaduc, I.; Zhang, W.; Rieger, J.; Lansalot, M.; D’Agosto, F.; Charleux, B. Amphiphilic Block Copolymers from a Direct and One-Pot RAFT Synthesis in Water. Macromol. Rapid Commun. 2011, 32, 1270– 1276,  DOI: 10.1002/marc.201100240
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    14
    Amphiphilic Block Copolymers from a Direct and One-pot RAFT Synthesis in Water
    Chaduc, Isabelle; Zhang, Wenjing; Rieger, Jutta; Lansalot, Muriel; D'Agosto, Franck; Charleux, Bernadette
    Macromolecular Rapid Communications (2011), 32 (16), 1270-1276CODEN: MRCOE3; ISSN:1022-1336. (Wiley-VCH Verlag GmbH & Co. KGaA)
    The syntheses of amphiphilic block copolymers are successfully performed in water by chain extension of hydrophilic macromols. with styrene at 80 °C. The employed strategy is a one-pot procedure in which poly(acrylic acid), poly(methacrylic acid) or poly(methacrylic acid-co-poly(ethylene oxide) Me ether methacrylate) macroRAFTs are first formed in water using 4-cyano-4-thiothiopropylsulfanyl pentanoic acid (CTPPA) as a chain transfer agent. The resulting macroRAFTs are then directly used without further purifn. for the RAFT polymn. of styrene in water in the same reactor. This simple and straightforward strategy leads to a very good control of the resulting amphiphilic block copolymers.
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    Gody, G.; Maschmeyer, T.; Zetterlund, P. B.; Perrier, S. Pushing the Limit of the RAFT Process: Multiblock Copolymers by One-Pot Rapid Multiple Chain Extensions at Full Monomer Conversion. Macromolecules 2014, 47, 3451– 3460,  DOI: 10.1021/ma402435n
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    15
    Pushing the Limit of the RAFT Process: Multiblock Copolymers by One-Pot Rapid Multiple Chain Extensions at Full Monomer Conversion
    Gody, Guillaume; Maschmeyer, Thomas; Zetterlund, Per B.; Perrier, Sebastien
    Macromolecules (Washington, DC, United States) (2014), 47 (10), 3451-3460CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    We describe an optimized method to prep. multiblock copolymers. The approach is based on our previously reported use of reversible addn.-fragmentation chain transfer (RAFT) polymn., which here has been optimized into a fast, versatile, efficient, and scalable process. The one-pot, multistep sequential polymn. proceeds in water, to quant. yields (>99%) for each monomer addn., thus circumventing requirements for intermediate purifn., in 2 h of polymn. per block. The optimization of the process is initially demonstrated via the synthesis of a model decablock homopolymer (10 blocks) of 4-acryloylmorpholine with an av. d.p. of 10 for each block (D = 1.15 and livingness >93% for the final polymer). Both the potential and the limitations of this approach are illustrated by the synthesis of more complex high-order multiblock copolymers: a dodecablock copolymer (12 blocks with 4 different acrylamide monomers) with an av. d.p. of 10 for each block and two higher mol. wt. pentablock copolymers (5 blocks with 3 different acrylamide monomers) with an av. d.p. of 100 per block.
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    Lesage de la Haye, J.; Zhang, X.; Chaduc, I.; Brunel, F.; Lansalot, M.; D’Agosto, F. The Effect of Hydrophile Topology in RAFT-Mediated Polymerization-Induced Self-Assembly. Angew. Chem., Int. Ed. 2016, 55, 3739– 3743,  DOI: 10.1002/anie.201511159
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    16
    The Effect of Hydrophile Topology in RAFT-Mediated Polymerization-Induced Self-Assembly
    Lesage de la Haye, Jennifer; Zhang, Xuewei; Chaduc, Isabelle; Brunel, Fabrice; Lansalot, Muriel; D'Agosto, Franck
    Angewandte Chemie, International Edition (2016), 55 (11), 3739-3743CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
    Polymn.-induced self-assembly (PISA) was employed to compare the self-assembly of different amphiphilic block copolymers. They were obtained by emulsion polymn. of styrene in water using hydrophilic poly(N-acryloylmorpholine) (PNAM)-based macromol. RAFT agents with different structures. An av. of three poly(ethylene glycol acrylate) (PEGA) units were introduced either at the beginning, statistically, or at the end of a PNAM backbone, resulting in formation of nanometric vesicles and spheres from the two former macroRAFT architectures, and large vesicles from the latter. Compared to the spheres obtained with a pure PNAM macroRAFT agent, composite macroRAFT architectures promoted a dramatic morphol. change. The change was induced by the presence of PEGA hydrophilic side-chains close to the hydrophobic polystyrene segment.
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    Penfold, N. J. W.; Yeow, J.; Boyer, C.; Armes, S. P. Emerging Trends in Polymerization-Induced Self-Assembly.. ACS Macro Lett. 2019, 8, 1029– 1054,  DOI: 10.1021/acsmacrolett.9b00464
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    17
    Emerging Trends in Polymerization-Induced Self-Assembly
    Penfold, Nicholas J. W.; Yeow, Jonathan; Boyer, Cyrille; Armes, Steven P.
    ACS Macro Letters (2019), 8 (8), 1029-1054CODEN: AMLCCD; ISSN:2161-1653. (American Chemical Society)
    A review. In this Perspective, we summarize recent progress in polymn.-induced self-assembly (PISA) for the rational synthesis of block copolymer nanoparticles with various morphologies. Much of the PISA literature has been based on thermally initiated reversible addn.-fragmentation chain transfer (RAFT) polymn. Herein, we pay particular attention to alternative PISA protocols, which allow the prepn. of nanoparticles with improved control over copolymer morphol. and functionality. For example, initiation based on visible light, redox chem., or enzymes enables the incorporation of sensitive monomers and fragile biomols. into block copolymer nanoparticles. Furthermore, PISA syntheses and postfunctionalization of the resulting nanoparticles (e.g., crosslinking) can be conducted sequentially without intermediate purifn. by using various external stimuli. Finally, PISA formulations have been optimized via high-throughput polymn. and recently evaluated within flow reactors for facile scale-up syntheses.
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    Byard, S. J.; O’Brien, C. T.; Derry, M. J.; Williams, M.; Mykhaylyk, O. O.; Blanazs, A.; Armes, S. P. Unique Aqueous Self-Assembly Behavior of a Thermoresponsive Diblock Copolymer. Chem. Sci. 2020, 11, 396– 402,  DOI: 10.1039/C9SC04197D
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    18
    Unique aqueous self-assembly behavior of a thermoresponsive diblock copolymer
    Byard, Sarah J.; O'Brien, Cate T.; Derry, Matthew J.; Williams, Mark; Mykhaylyk, Oleksandr O.; Blanazs, Adam; Armes, Steven P.
    Chemical Science (2020), 11 (2), 396-402CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
    It is well-recognized that block copolymer self-assembly in soln. typically produces spheres, worms or vesicles, with the relative vol. fraction of each block dictating the copolymer morphol. Stimulus-responsive diblock copolymers that can undergo either sphere/worm or vesicle/worm transitions are also well-documented. Herein we report a new amphiphilic diblock copolymer that can form spheres, worms, vesicles or lamellae in aq. soln. Such self-assembly behavior is unprecedented for a single diblock copolymer of fixed compn. yet is achieved simply by raising the soln. temp. from 1°C (spheres) to 25°C (worms) to 50°C (vesicles) to 70°C (lamellae). Heating increases the degree of hydration (and hence the effective vol. fraction) of the core-forming block, with this parameter being solely responsible for driving the sphere-to-worm, worm-to-vesicle and vesicle-to-lamellae transitions. The first two transitions exhibit excellent reversibility but the vesicle-to-lamellae transition exhibits hysteresis on cooling. This new thermoresponsive diblock copolymer provides a useful model for studying such morphol. transitions and is likely to be of significant interest for theor. studies.
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    D’Agosto, F.; Rieger, J.; Lansalot, M. RAFT-Mediated Polymerization-Induced Self-Assembly. Angew. Chem., Int. Ed. 2020, 59, 8368– 8392,  DOI: 10.1002/anie.201911758
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    19
    RAFT-Mediated Polymerization-Induced Self-Assembly
    D'Agosto, Franck; Rieger, Jutta; Lansalot, Muriel
    Angewandte Chemie, International Edition (2020), 59 (22), 8368-8392CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
    A review. After a brief history that positions polymn.-induced self-assembly (PISA) in the field of polymer chem., this Review will cover the fundamentals of the PISA mechanism. Furthermore, this Review will also give an overview of some of the features and limitations of RAFT-mediated PISA in terms of the choice of the components involved, the nature of the nanoobjects that can be obtained and how the syntheses can be controlled, as well as some potential applications.
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    Griffith, L. G.; Swartz, M. A. Capturing Complex 3D Tissue Physiology in Vitro. Nat. Rev. Mol. Cell Biol. 2006, 7, 211– 224,  DOI: 10.1038/nrm1858
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    Capturing complex 3D tissue physiology in vitro
    Griffith, Linda G.; Swartz, Melody A.
    Nature Reviews Molecular Cell Biology (2006), 7 (3), 211-224CODEN: NRMCBP; ISSN:1471-0072. (Nature Publishing Group)
    A review. The emergence of tissue engineering raises new possibilities for the study of complex physiol. and pathophysiol. processes in vitro. Many tools are now available to create 3D tissue models in vitro, but the blueprints for what to make have been slower to arrive. The authors discuss here some of the 'design principles' for recreating the interwoven set of biochem. and mech. cues in the cellular microenvironment, and the methods for implementing them. The authors emphasize applications that involve epithelial tissues for which 3D models could explain mechanisms of disease or aid in drug development.
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  21. 21
    Blanazs, A.; Verber, R.; Mykhaylyk, O. O.; Ryan, A. J.; Heath, J. Z.; Douglas, C. W. I.; Armes, S. P. Sterilizable Gels from Thermoresponsive Block Copolymer Worms. J. Am. Chem. Soc. 2012, 134, 9741– 9748,  DOI: 10.1021/ja3024059
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    21
    Sterilizable Gels from Thermoresponsive Block Copolymer Worms
    Blanazs, Adam; Verber, Robert; Mykhaylyk, Oleksandr O.; Ryan, Anthony J.; Heath, Jason Z.; Douglas, C. W. Ian; Armes, Steven P.
    Journal of the American Chemical Society (2012), 134 (23), 9741-9748CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    Biocompatible hydrogels have many applications, ranging from contact lenses to tissue engineering scaffolds. In most cases, rigorous sterilization is essential. Herein we show that a biocompatible diblock copolymer forms wormlike micelles via polymn.-induced self-assembly in aq. soln. At a copolymer concn. of 10.0 wt./wt. %, interworm entanglements lead to the formation of a free-standing phys. hydrogel at 21 °C. Gel dissoln. occurs on cooling to 4 °C due to an unusual worm-to-sphere order-order transition, as confirmed by rheol., electron microscopy, variable temp. 1H NMR spectroscopy, and scattering studies. Moreover, this thermo-reversible behavior allows the facile prepn. of sterile gels, since ultrafiltration of the diblock copolymer nanoparticles in their low-viscosity spherical form at 4 °C efficiently removes micrometer-sized bacteria; regelation occurs at 21 °C as the copolymer chains regain their wormlike morphol. Biocompatibility tests indicate good cell viabilities for these worm gels, which suggest potential biomedical applications.
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  22. 22
    Kataoka, K.; Harada, A.; Nagasaki, Y. Block Copolymer Micelles for Drug Delivery: Design, Characterization and Biological Significance. Adv. Drug Delivery Rev. 2001, 47, 113– 131,  DOI: 10.1016/S0169-409X(00)00124-1
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    Block copolymer micelles for drug delivery: design, characterization and biological significance
    Kataoka, K.; Harada, A.; Nagasaki, Y.
    Advanced Drug Delivery Reviews (2001), 47 (1), 113-131CODEN: ADDREP; ISSN:0169-409X. (Elsevier Science Ireland Ltd.)
    A review with 94 refs. Recently, colloidal carrier systems have been receiving much attention in the field of drug targeting because of their high loading capacity for drugs as well as their unique disposition characteristics in the body. This paper highlights the utility of polymeric micelles formed through the multimol. assembly of block copolymers as novel core-shell typed colloidal carriers for drug and gene targeting. The process of micellization in aq. milieu is described in detail based on differences in the driving force of core segregation, including hydrophobic interaction, electrostatic interaction, metal complexation, and hydrogen bonding of constituent block copolymers. The segregated core embedded in the hydrophilic palisade is shown to function as a reservoir for genes, enzymes, and a variety of drugs with diverse characteristics. Functionalization of the outer surface of the polymeric micelle to modify its physicochem. and biol. properties is reviewed from the standpoint of designing micellar carrier systems for receptor-mediated drug delivery. Further, the distribution of polymeric micelles is described to demonstrate their long-circulating characteristics and significant tumor accumulation, emphasizing their promising utility in tumor-targeting therapy. As an important perspective on carrier systems based on polymeric micelles, their feasibility as non-viral gene vectors is also summarized in this review article.
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    Kabanov, A. V.; Batrakova, E. V.; Alakhov, V. Y. Pluronic Block Copolymers as Novel Polymer Therapeutics for Drug and Gene Delivery. J. Controlled Release 2002, 82, 189– 212,  DOI: 10.1016/S0168-3659(02)00009-3
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    23
    Pluronic block copolymers as novel polymer therapeutics for drug and gene delivery
    Kabanov, Alexander V.; Batrakova, Elena V.; Alakhov, Valery Yu.
    Journal of Controlled Release (2002), 82 (2-3), 189-212CODEN: JCREEC; ISSN:0168-3659. (Elsevier Science Ltd.)
    A review. Pluronic block copolymers are found to be an efficient drug delivery system with multiple effects. The incorporation of drugs into the core of the micelles formed by Pluronic results in increased soly., metabolic stability and circulation time for the drug. The interactions of the Pluronic unimers with multidrug-resistant cancer cells result in sensitization of these cells with respect to various anticancer agents. Furthermore, the single mol. chains of copolymer, unimers, inhibit drug efflux transporters in both the blood-brain barrier and in the small intestine, which provides for the enhanced transport of select drugs to the brain and increases oral bioavailability. These and other applications of Pluronic block copolymers in various drug delivery and gene delivery systems are considered.
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    Rodriguez-Hernandez, J.; Checot, F.; Gnanou, Y.; Lecommandoux, S. Toward ‘Smart’ Nano-Objects by Self-Assembly of Block Copolymers in Solution.. Prog. Polym. Sci. 2005, 30, 691– 724,  DOI: 10.1016/j.progpolymsci.2005.04.002
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    Toward 'smart' nano-objects by self-assembly of block copolymers in solution
    Rodriguez-Hernandez, J.; Checot, F.; Gnanou, Y.; Lecommandoux, S.
    Progress in Polymer Science (2005), 30 (7), 691-724CODEN: PRPSB8; ISSN:0079-6700. (Elsevier B.V.)
    A review describes the most significant developments in the prepn. and characterization of nano-objects. In recent years, the synthesis and anal. of novel copolymer-based nanomaterials in soln. have been extensively pursued. The interest in such structures lies in the fact that their dimensions, in the mesoscopic range (<100 nm), and factors such as compn. or structure lead to materials with singular properties and applications. First, the basic principles of self-assembly and micellization of block copolymers in dil. soln. will be discussed. A review of the methods for stabilization of the macromol. aggregates will be then given, including selected recent examples. Finally, we will conc. on stabilized nanoparticles, so-called 'smart materials' that show responses to environmental changes (pH, temp., ionic-strength, among others), focusing on their applications principally in the biomedical field.
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    Roy, D.; Cambre, J. N.; Sumerlin, B. S. Future Perspectives and Recent Advances in Stimuli-Responsive Materials.. Prog. Polym. Sci. 2010, 35, 278– 301,  DOI: 10.1016/j.progpolymsci.2009.10.008
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    25
    Future perspectives and recent advances in stimuli-responsive materials
    Roy, Debashish; Cambre, Jennifer N.; Sumerlin, Brent S.
    Progress in Polymer Science (2010), 35 (1-2), 278-301CODEN: PRPSB8; ISSN:0079-6700. (Elsevier Ltd.)
    A review. Interest in stimuli-responsive polymers has persisted over many decades, and a great deal of work has been dedicated to developing environmentally sensitive macromols. that can be crafted into new smart materials. However, the overwhelming majority of reports in the literature describe stimuli-responsive polymers that are sensitive to only a few common triggers, including changes in pH, temp., and electrolyte concn. Herein, we aim to highlight recent results and future trends that exploit stimuli that have not yet been as heavily considered, despite their unique potential. Many of the topics represent clear opportunities for making advances in biomedical fields due to their specificity and the ability to respond to stimuli that are inherently present in living systems. Recent results in the area of polymers that respond to specific antigen-antibody interactions, enzymes, and glucose are specifically discussed. Also considered are polymeric systems that respond to light, elec., magnetic, and sonic fields, all of which have potential in the area of controlled release as a result of their ability to be applied in a non-invasive and easily controlled manner. Thiol-responsive and redox-responsive polymers are also highlighted, with particular attention being devoted to their reversible dynamic covalent chem. It is our goal to emphasize these underutilized adaptive behaviors so that novel applications and new generations of smart materials can be realized.
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    Brinkhuis, R. P.; Rutjes, F. P. J. T.; van Hest, J. C. M. Polymeric Vesicles in Biomedical Applications. Polym. Chem. 2011, 2, 1449– 1462,  DOI: 10.1039/c1py00061f
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    Polymeric vesicles in biomedical applications
    Brinkhuis, Rene P.; Rutjes, Floris P. J. T.; van Hest, Jan C. M.
    Polymer Chemistry (2011), 2 (7), 1449-1462CODEN: PCOHC2; ISSN:1759-9962. (Royal Society of Chemistry)
    A review. Polymeric vesicles, or polymersomes, are nano- to micrometer sized polymeric capsules with a bilayered membrane. Applications of these vesicles are foreseen in nanomedicine, in vivo imaging and drug delivery. These applications put many restrictions on the choice of polymer, the size and the surface of the vesicle. In this respect much can be learned and translated to polymersome science from lines of research with a longer history of practical knowledge such as liposomal formulation and polymer drug conjugation. The dimensions of a vesicle, such as size and shape can be controlled for polymersomes and will influence the in vivo circulation time. The surface can be adjusted to induce stealth character, or chem. modified to introduce targeting moieties. And last but not least the choice of block copolymers-the building blocks of a polymersome-can introduce features like biocompatibility, inherent or induced permeability and triggered release. In this review the authors will discuss the recent advances in polymersome science with regard to biomedical applications and will specifically address the abovementioned features which affect their biol. behavior.
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    Blackman, L. D.; Varlas, S.; Arno, M. C.; Fayter, A.; Gibson, M. I.; O’Reilly, R. K. Permeable Protein-Loaded Polymersome Cascade Nanoreactors by Polymerization-Induced Self-Assembly.. ACS Macro Lett 2017, 6, 1263– 1267,  DOI: 10.1021/acsmacrolett.7b00725
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    27
    Permeable Protein-Loaded Polymersome Cascade Nanoreactors by Polymerization-Induced Self-Assembly
    Blackman, Lewis D.; Varlas, Spyridon; Arno, Maria C.; Fayter, Alice; Gibson, Matthew I.; OReilly, Rachel K.
    ACS Macro Letters (2017), 6 (11), 1263-1267CODEN: AMLCCD; ISSN:2161-1653. (American Chemical Society)
    Enzyme loading of polymersomes requires permeability to enable them to interact with the external environment, typically requiring addn. of complex functionality to enable porosity. Herein, we describe a synthetic route toward intrinsically permeable polymersomes loaded with functional proteins using initiator-free visible light-mediated polymn.-induced self-assembly (photo-PISA) under mild, aq. conditions using a com. monomer. Compartmentalization and retention of protein functionality was demonstrated using green fluorescent protein as a macromol. chromophore. Catalytic enzyme-loaded vesicles using horseradish peroxidase and glucose oxidase were also prepd. and the permeability of the membrane toward their small mol. substrates was revealed for the first time. Finally, the interaction of the compartmentalized enzymes between sep. vesicles was validated by means of an enzymic cascade reaction. These findings have a broad scope as the methodol. could be applied for the encapsulation of a large range of macromols. for advancements in the fields of nanotechnol., biomimicry and nanomedicine.
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  28. 28
    Growney, D. J.; Mykhaylyk, O. O.; Armes, S. P. Micellization and Adsorption Behavior of a Near-Monodisperse Polystyrene-Based Diblock Copolymer in Nonpolar Media. Langmuir 2014, 30, 6047– 6056,  DOI: 10.1021/la501084a
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    28
    Micellization and Adsorption Behavior of a Near-Monodisperse Polystyrene-Based Diblock Copolymer in Nonpolar Media
    Growney, David J.; Mykhaylyk, Oleksandr O.; Armes, Steven P.
    Langmuir (2014), 30 (21), 6047-6056CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
    The micellar self-assembly behavior of a near-monodisperse polystyrene-hydrogenated polyisoprene (PS-PEP) diblock copolymer is examd. in non-polar media (either n-heptane or n-dodecane). Direct dissoln. of this diblock copolymer leads to the formation of relatively large polydisperse colloidal aggregates that are kinetically frozen artifacts of the solid-state copolymer morphol. Dynamic light scattering (DLS) and transmission electron microscopy studies indicate that heating such copolymer dispersions up to 90-110 °C leads to a structural rearrangement, with the generation of relatively small, well-defined spherical micelles that persist on cooling to 20 °C. Variable temp. 1H NMR studies using deuterated n-alkanes confirm that partial solvation (plasticization) of the polystyrene micelle cores occurs on heating. This increased mobility of the core-forming polystyrene chains is consistent with the evolution from a kinetically-trapped to a thermodynamically-favored copolymer morphol. via exchange of individual copolymer chains, which are obsd. by DLS. These micellar self-assembly observations are also consistent with small-angle X-ray scattering (SAXS) studies, which indicate the formation of star-like micelles in n-heptane, with a mean polystyrene core diam. of about 20 nm and an overall diam. (core plus corona) of about 80 nm. Micelle dissocn. occurs on addn. of chloroform, which is a good solvent for both blocks. Finally, phys. adsorption of this PS-PEP diblock copolymer onto a model colloidal substrate (carbon black) has been confirmed using XPS. A Langmuir-type adsorption isotherm has been constructed using a supernatant depletion assay based on UV spectroscopy anal. of the arom. chromophore in the polystyrene block. Comparable results were obtained using thermogravimetric anal. to directly det. the amt. of adsorbed copolymer. Based on the max. adsorbed amts. obsd. at 20 °C, these studies strongly suggest that individual PS-PEP copolymer chains adsorb onto carbon black from chloroform, whereas micellar adsorption occurs from n-alkanes.
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  29. 29
    Penfold, N. J. W.; Ning, Y.; Verstraete, P.; Smets, J.; Armes, S. P. Cross-Linked Cationic Diblock Copolymer Worms Are Superflocculants for Micrometer-Sized Silica Particles. Chem. Sci. 2016, 7, 6894– 6904,  DOI: 10.1039/C6SC03732A
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    29
    Crosslinked cationic diblock copolymer worms are superflocculants for micrometer-sized silica particles
    Penfold, Nicholas J. W.; Ning, Yin; Verstraete, Pierre; Smets, Johan; Armes, Steven P.
    Chemical Science (2016), 7 (12), 6894-6904CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
    A series of linear cationic diblock copolymer nanoparticles are prepd. by polymn.-induced self-assembly (PISA) via reversible addn.-fragmentation chain transfer (RAFT) aq. dispersion polymn. of 2-hydroxypropyl methacrylate (HPMA) using a binary mixt. of non-ionic and cationic macromol. RAFT agents, namely poly(ethylene oxide) (PEO113, Mn = 4400 g mol-1; Mw/Mn = 1.08) and poly([2-(methacryloyloxy)ethyl]trimethylammonium chloride) (PQDMA125, Mn = 31 800 g mol-1, Mw/Mn = 1.19). A detailed phase diagram was constructed to det. the max. amt. of PQDMA125 stabilizer block that could be incorporated while still allowing access to a pure worm copolymer morphol. Aq. electrophoresis studies indicated that zeta potentials of +35 mV could be achieved for such cationic worms over a wide pH range. Core crosslinked worms were prepd. via statistical copolymn. of glycidyl methacrylate (GlyMA) with HPMA using a slightly modified PISA formulation, followed by reacting the epoxy groups of the GlyMA residues located within the worm cores with 3-aminopropyl triethoxysilane (APTES), and concomitant hydrolysis/condensation of the pendent silanol groups with the secondary alc. on the HPMA residues. TEM and DLS studies confirmed that such core crosslinked cationic worms remained colloidally stable when challenged with either excess methanol or a cationic surfactant. These crosslinked cationic worms are shown to be much more effective bridging flocculants for 1.0μm silica particles at pH 9 than the corresponding linear cationic worms (and also various com. high mol. wt. water-sol. polymers.). Laser diffraction studies indicated silica aggregates of around 25-28μm diam. when using the former worms but only 3-5μm diam. when employing the latter worms. Moreover, SEM studies confirmed that the crosslinked worms remained intact after their adsorption onto the silica particles, whereas the much more delicate linear worms underwent fragmentation under the same conditions. Similar results were obtained with 4μm silica particles.
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  30. 30
    Chan, D. H. H.; Kynaston, E. L.; Lindsay, C.; Taylor, P.; Armes, S. P. Block Copolymer Nanoparticles Are Effective Dispersant for Micrometer-Sized Organic Crystalline Particles. ACS Appl. Mater. Interfaces 2021, 13, 30235– 30243,  DOI: 10.1021/acsami.1c08261
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    30
    Block Copolymer Nanoparticles are Effective Dispersants for Micrometer-Sized Organic Crystalline Particles
    Chan, Derek H. H.; Kynaston, Emily L.; Lindsay, Christopher; Taylor, Philip; Armes, Steven P.
    ACS Applied Materials & Interfaces (2021), 13 (25), 30235-30243CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
    Well-defined sterically stabilized diblock copolymer nanoparticles of 29 nm diam. are prepd. by RAFT aq. emulsion polymn. of Me methacrylate using a dithiobenzoate-capped poly(glycerol monomethacrylate) precursor. These nanoparticles are evaluated as a dispersant for the prepn. of org. cryst. microparticles via ball milling. This is exemplified for azoxystrobin, which is a broad-spectrum fungicide that is widely used to protect various food crops. Laser diffraction and optical microscopy studies indicate the formation of azoxystrobin microparticles of approx. 2μm diam. after ball milling for 10 min at 400 rpm. Nanoparticle adsorption at the surface of these azoxystrobin microparticles is confirmed by electron microscopy studies. The extent of nanoparticle adsorption on the azoxystrobin microparticles can be quantified using a supernatant assay based on soln. densitometry. This technique indicates an adsorbed amt. of approx. 5.5 mg m-2, which is sufficient to significantly reduce the neg. zeta potential exhibited by azoxystrobin. Moreover, this adsorbed amt. appears to be essentially independent of the nature of the core-forming block, with similar data being obtained for both poly(Me methacrylate)- and poly(2,2,2-trifluoroethyl methacrylate)-based nanoparticles. Finally, XPS studies confirm attenuation of the underlying N1s signal arising from the azoxystrobin microparticles by the former adsorbed nanoparticles, suggesting a fractional surface coverage of approx. 0.24. This value is consistent with a theor. surface coverage of 0.25 calcd. from the adsorption isotherm data. Overall, this study suggests that sterically stabilized diblock copolymer nanoparticles may offer a useful alternative approach to traditional sol. copolymer dispersants for the prepn. of suspension concs. affecting the context of agrochem. applications.
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  31. 31
    Derry, M. J.; Fielding, L. A.; Armes, S. P. Industrially-Relevant Polymerization-Induced Self-Assembly Formulations in Non-Polar Solvents: RAFT Dispersion Polymerization of Benzyl Methacrylate. Polym. Chem. 2015, 6, 3054– 3062,  DOI: 10.1039/C5PY00157A
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    31
    Industrially-relevant polymerization-induced self-assembly formulations in non-polar solvents: RAFT dispersion polymerization of benzyl methacrylate
    Derry, Matthew J.; Fielding, Lee A.; Armes, Steven P.
    Polymer Chemistry (2015), 6 (16), 3054-3062CODEN: PCOHC2; ISSN:1759-9962. (Royal Society of Chemistry)
    Industrially-sourced mineral oil and a poly(α-olefin) were used as solvents for the reversible addn.-fragmentation chain transfer (RAFT) dispersion polymn. of benzyl methacrylate (BzMA) using a poly(lauryl methacrylate) macromol. chain transfer agent (PLMA macro-CTA) at 90 °C. The insoly. of the growing PBzMA chains under such conditions leads to polymn.-induced self-assembly (PISA), whereby poly(lauryl methacrylate)-poly(benzyl methacrylate) (PLMA-PBzMA) diblock copolymer spheres, worms or vesicles were produced directly as concd. dispersions. The particular diblock copolymer compn. required to access each individual morphol. depends on the nature of the oil. Moreover, the solvent type also affects important properties of the phys. free-standing gels that are formed by the PLMA-PBzMA worm dispersions, including the storage modulus (G'), crit. gelation temp. (CGT) and crit. gelation concn. (CGC). Spherical PLMA-PBzMA diblock copolymer nanoparticles can be prepd. at up to 50% wt./wt. solids and an efficient 'one-pot' protocol involving soln. polymn. of LMA followed immediately by dispersion polymn. of BzMA was developed. The latter formulation enables high BzMA conversions to be achieved, with spherical nanoparticles being produced at 30% wt./wt. solids.
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    Perrier, S.; Takolpuckdee, P. Macromolecular Design via Reversible Addition-Fragmentation Chain Transfer (RAFT)/Xanthates (MADIX) Polymerization.. J. Polym. Sci., Part A: Polym. Chem. 2005, 43, 5347– 5393,  DOI: 10.1002/pola.20986
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    Macromolecular design via reversible addition-fragmentation chain transfer (RAFT)/xanthates (MADIX) polymerization
    Perrier, Sebastien; Takolpuckdee, Pittaya
    Journal of Polymer Science, Part A: Polymer Chemistry (2005), 43 (22), 5347-5393CODEN: JPACEC; ISSN:0887-624X. (John Wiley & Sons, Inc.)
    A review highlighting the progress made in RAFT/MADIX polymn. since the first report in 1998. Among the living radical polymn. techniques, reversible addn.-fragmentation chain transfer (RAFT) and macromol. design via the interchange of xanthates (MADIX) polymns. appear to be the most versatile processes in terms of the reaction conditions, the variety of monomers for which polymn. can be controlled, tolerance to functionalities, and the range of polymeric architectures that can be produced. It addresses, in turn, the mechanism and kinetics of the process, examines the various components of the system, including the synthesis paths of the thiocarbonyl-thio compds. used as chain-transfer agents, and the conditions of polymn., and gives an account of the wide range of monomers that were successfully polymd. to date, and the various polymeric architectures that were produced. In the last section, this review describes the future challenges that the process will face and shows its opening to a wider scientific community as a synthetic tool for the prodn. of functional macromols. and materials.
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    Sugihara, S.; Blanazs, A.; Armes, S. P.; Ryan, A. J.; Lewis, A. L. Aqueous Dispersion Polymerization: A New Paradigm for in Situ Block Copolymer Self-Assembly in Concentrated Solution. J. Am. Chem. Soc. 2011, 133, 15707– 15713,  DOI: 10.1021/ja205887v
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    Aqueous Dispersion Polymerization: A New Paradigm for in Situ Block Copolymer Self-Assembly in Concentrated Solution
    Sugihara, Shinji; Blanazs, Adam; Armes, Steven P.; Ryan, Anthony J.; Lewis, Andrew L.
    Journal of the American Chemical Society (2011), 133 (39), 15707-15713CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    Reversible addn.-fragmentation chain transfer polymn. has been utilized to polymerize 2-hydroxypropyl methacrylate (HPMA) using a water-sol. macromol. chain transfer agent based on poly(2-(methacryloyloxy)ethylphosphorylcholine) (PMPC). A detailed phase diagram has been elucidated for this aq. dispersion polymn. formulation that reliably predicts the precise block compns. assocd. with well-defined particle morphologies (i.e., pure phases). Unlike the ad hoc approaches described in the literature, this strategy enables the facile, efficient, and reproducible prepn. of diblock copolymer spheres, worms, or vesicles directly in concd. aq. soln. Chain extension of the highly hydrated zwitterionic PMPC block with HPMA in water at 70° produces a hydrophobic poly(2-hydroxypropyl methacrylate) (PHPMA) block, which drives in situ self-assembly to form well-defined diblock copolymer spheres, worms, or vesicles. The final particle morphol. obtained at full monomer conversion is dictated by (i) the target d.p. of the PHPMA block and (ii) the total solids concn. at which the HPMA polymn. is conducted. Moreover, if the targeted diblock copolymer compn. corresponds to vesicle phase space at full monomer conversion, the in situ particle morphol. evolves from spheres to worms to vesicles during the in situ polymn. of HPMA. In the case of PMPC25-PHPMA400 particles, this systematic approach allows the direct, reproducible, and highly efficient prepn. of either block copolymer vesicles at up to 25% solids or well-defined worms at 16-25% solids in aq. soln.
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    Zhang, X.; Boissé, S.; Zhang, W.; Beaunier, P.; D’Agosto, F.; Rieger, J.; Charleux, B. Well-Defined Amphiphilic Block Copolymers and Nano-Objects Formed in Situ via RAFT-Mediated Aqueous Emulsion Polymerization. Macromolecules 2011, 44, 4149– 415,  DOI: 10.1021/ma2005926
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    34
    Well-Defined Amphiphilic Block Copolymers and Nano-objects Formed in Situ via RAFT-Mediated Aqueous Emulsion Polymerization
    Zhang, Xuewei; Boisse, Stephanie; Zhang, Wenjing; Beaunier, Patricia; D'Agosto, Franck; Rieger, Jutta; Charleux, Bernadette
    Macromolecules (Washington, DC, United States) (2011), 44 (11), 4149-4158CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    A hydrophilic poly(methacrylic acid-co-poly(ethylene oxide) Me ether methacrylate) copolymer with a trithiocarbonate reactive group was used in the free-radical, batch emulsion polymn. of styrene. It allowed fast polymns. and high final conversions to be achieved, and the parameters for a good control over the formation of well-defined amphiphilic diblock copolymers were identified. These diblock copolymers self-assembled in situ into nano-objects of various morphologies upon chain extension. Achieving a good control over the formed diblock copolymers was an important step toward a better understanding of the parameters that affect the shape and size of the self-assembled objects, the ultimate goal being the ability to predict and fine-tune them on purpose.
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    Karagoz, B.; Esser, L.; Duong, H. T.; Basuki, J. S.; Boyer, C.; Davis, T. P. Polymerization-Induced Self-Assembly (PISA)—Control over the Morphology of Nanoparticles for Drug Delivery Applications. Polym. Chem. 2014, 5, 350– 355,  DOI: 10.1039/C3PY01306E
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    Polymerization-Induced Self-Assembly (PISA) - control over the morphology of nanoparticles for drug delivery applications
    Karagoz, Bunyamin; Esser, Lars; Duong, Hien T.; Basuki, Johan S.; Boyer, Cyrille; Davis, Thomas P.
    Polymer Chemistry (2014), 5 (2), 350-355CODEN: PCOHC2; ISSN:1759-9962. (Royal Society of Chemistry)
    In this paper, we describe the synthesis of asym. functional POEGMA-b-P(ST-co-VBA) copolymers in methanol, yielding in one-pot polymn. a range of nanoparticle morphologies, including spherical micelles, worm-like, rod-like micelles and vesicles. The presence of the aldehyde group was then exploited to form crosslinks or to conjugate chemotherapy compds., such as doxorubicin, via pH-breakable bonds (Schiff base or imine) directly to the preformed nanoparticles. The influence of the nanoparticle morphologies on the MCF-7 breast cancer cell line uptake was investigated using flow cytometry and confocal microscopy. Finally, the IC50 of DOX, following nanoparticle delivery, was studied showing significant influence of the nanoparticle carrier morphol. on therapeutic efficacy for breast cancer.
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    Tan, J.; Sun, H.; Yu, M.; Sumerlin, B. S.; Zhang, L. Photo-PISA: Shedding Light on Polymerization-Induced Self-Assembly. ACS Macro Lett. 2015, 4, 1249– 1253,  DOI: 10.1021/acsmacrolett.5b00748
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    Photo-PISA: Shedding Light on Polymerization-Induced Self-Assembly
    Tan, Jianbo; Sun, Hao; Yu, Mingguang; Sumerlin, Brent S.; Zhang, Li
    ACS Macro Letters (2015), 4 (11), 1249-1253CODEN: AMLCCD; ISSN:2161-1653. (American Chemical Society)
    Herein we report an aq. photoinitiated polymn.-induced self-assembly (photo-PISA) for the prepn. of a remarkably diverse set of complex polymer nanoparticle morphologies (e.g., spheres, worms, and vesicles) at room temp. Ultrafast polymn. rates were achieved, with near quant. monomer conversion within 15 min of visible light irradn. An important feature of the photo-PISA is that diblock copolymer vesicles can be prepd. under mild conditions (room temp., aq. medium, visible light), which will be important for the prepn. of functional vesicles loaded with biorelated species (e.g., proteins). As a proof of concept, silica nanoparticles and bovine serum albumin (BSA) were encapsulated in situ within vesicles via the photo-PISA process.
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    Jiang, Y.; Xu, N.; Han, J.; Yu, Q.; Guo, L.; Gao, P.; Lu, X.; Cai, Y. The Direct Synthesis of Interface-Decorated Reactive Block Copolymer Nanoparticles via Polymerisation-Induced Self-Assembly. Polym. Chem. 2015, 6, 4955– 4965,  DOI: 10.1039/C5PY00656B
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    The direct synthesis of interface-decorated reactive block copolymer nanoparticles via polymerisation-induced self-assembly
    Jiang, Yanyan; Xu, Na; Han, Jie; Yu, Qiuping; Guo, Lei; Gao, Pan; Lu, Xinhua; Cai, Yuanli
    Polymer Chemistry (2015), 6 (27), 4955-4965CODEN: PCOHC2; ISSN:1759-9962. (Royal Society of Chemistry)
    Self-assembly of amphiphilic block copolymers in water suffers from the undesired encapsulation of hydrophobic reactive motifs in a core-forming block, which deteriorates their performance as aq. catalysts. This problem can be circumvented by polymn.-induced self-assembly (PISA). Herein, we report a new strategy for one-pot synthesis of reactive block copolymer nanoparticles whose hydrophobic reactive motifs decorate the surrounding core-shell interfaces. We demonstrate fast RAFT aq. dispersion polymn. of a com. available specialty monomer, diacetone acrylamide (DAAM), under visible light irradn. at 25°C. PISA is induced by polymn. via sequential dehydration, phase sepn. and reaction acceleration, thus achieving complete conversion in 30 min. The replacement of minimal DAAM by an NH3+-monomer induces slight hydration of the core-forming block, and thus a low polydispersity of the resulting statistic-block copolymer. Moreover, simultaneous in situ self-assembly and chain growth favor the adjustment of newly-added NH3+-units outward to core-shell interfaces while the major DAAM units collapse into hydrophobic PISA-cores. Both lead to timely and selective self-assembly into the new reactive nanoparticles whose NH3+-motifs decorate the surrounding core-shell interfaces. These nanoparticles are well-suited for fabrication of advanced nanoreactors whose hydrophobic dative metal centers decorate the surrounding interfaces via simultaneous imine conversion and Zn(II)-coordination. Such PISA-nanostructures endow hydrophobic metal centers with a huge and accessible sp. surface area and are stabilized by water-sol. shells. Therefore, this strategy holds fascinating potential for the fabrication of metalloenzyme-inspired aq. catalysts.
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    Zhou, D.; Dong, S.; Kuchel, R. P.; Perrier, S.; Zetterlund, P. B. Polymerization Induced Self-Assembly: Tuning of Morphology Using Ionic Strength and PH. Polym. Chem. 2017, 8, 3082– 3089,  DOI: 10.1039/C7PY00552K
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    Polymerization induced self-assembly: tuning of morphology using ionic strength and pH
    Zhou, Dewen; Dong, Siming; Kuchel, Rhiannon P.; Perrier, Sebastien; Zetterlund, Per B.
    Polymer Chemistry (2017), 8 (20), 3082-3089CODEN: PCOHC2; ISSN:1759-9962. (Royal Society of Chemistry)
    Investigations of RAFT dispersion polymn.-induced self-assembly (PISA) of 2-hydroxypropyl methacrylate (HPMA) in water/methanol at 60 °C using a cationically charged macroRAFT agent as the stabilizer block, namely P(N,N-diethylaminoethyl methacrylate)-stat-poly((ethylene glycol) Me ether methacrylate) (PDEAEMA-stat-PEGMA), have been conducted with a view to tune particle morphologies by manipulation of the pH and the ionic strength. Above the LCST (45 °C) of (PDEAEMA-stat-PEGMA), the system can only be conducted as a dispersion polymn. at sufficiently low pH such that the stabilizer block is sufficiently protonated to ensure soly. in the continuous phase. It is demonstrated (reported in the form of an extensive morphol. diagram) that a range of morphologies including spherical particles, rods and vesicles can be accessed by adjustment of the pH (via addn. of HCl) and the ionic strength (via the concn. of NaCl). A decrease in the charge d. of the coronal stabilizer layer via an increase in the pH (less protonation) shifts the system towards higher order morphologies. At a given pH, an increase in ionic strength leads to more extensive charge screening, thus allowing formation of higher order morphologies.
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    Perrier, S. 50th Anniversary Perspective: RAFT Polymerization—A User Guide. Macromolecules 2017, 50, 7433– 7447,  DOI: 10.1021/acs.macromol.7b00767
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    50th Anniversary Perspective: RAFT Polymerization-A User Guide
    Perrier, Sebastien
    Macromolecules (Washington, DC, United States) (2017), 50 (19), 7433-7447CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    A review. This Perspective summarizes the features and limitations of reversible addn.-fragmentation chain transfer (RAFT) polymn., highlighting its strengths and weaknesses, as our understanding of the process, from both a mechanistic and an application point of view, has matured over the past 20 years. It is aimed at both experts in the field and newcomers, including undergraduate and postgraduate students, as well as nonexperts in polymn. who are interested in developing their own polymeric structures by exploiting the simple setup of a RAFT polymn.
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    Khor, S. Y.; Quinn, J. F.; Whittaker, M. R.; Truong, N. P.; Davis, T. P. Controlling Nanomaterial Size and Shape for Biomedical Applications via Polymerization-Induced Self-Assembly. Macromol. Rapid Commun. 2019, 40, 1800438  DOI: 10.1002/marc.201800438
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    Moad, G.; Rizzardo, E.; Thang, S. H. Living Radical Polymerization by the RAFT Process—A First Update. Aust. J. Chem. 2006, 59, 669– 692,  DOI: 10.1071/CH06250
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    Living radical polymerization by the RAFT process-A first update
    Moad, Graeme; Rizzardo, Ezio; Thang, San H.
    Australian Journal of Chemistry (2006), 59 (10), 669-692CODEN: AJCHAS; ISSN:0004-9425. (CSIRO Publishing)
    A review. This paper provides a first update to the review of living radical polymn. achieved with thiocarbonylthio compds. (ZC(=S)SR) by a mechanism of reversible addn.-fragmentation chain transfer (RAFT) published in June 2005. The time since that publication has witnessed an increased rate of publication on the topic with the appearance of well over 200 papers covering various aspects of RAFT polymn. ranging over reagent synthesis and properties, kinetics, and mechanism of polymn., novel polymer syntheses, and diverse applications.
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    Moad, G.; Rizzardo, E.; Thang, S. H. Living Radical Polymerization by the RAFT Process A Second Update. Aust. J. Chem. 2009, 62, 1402– 1472,  DOI: 10.1071/CH09311
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    Living Radical Polymerization by the RAFT Process - A Second Update
    Moad, Graeme; Rizzardo, Ezio; Thang, San H.
    Australian Journal of Chemistry (2009), 62 (11), 1402-1472CODEN: AJCHAS; ISSN:0004-9425. (CSIRO Publishing)
    A review. This paper provides a second update to the review of reversible deactivation radical polymn. achieved with thiocarbonylthio compds. (ZC(=S)SR) by a mechanism of reversible addn.-fragmentation chain transfer (RAFT) that was published in June 2005 (Aust. J. Chem. 2005, 58, 379-410). The first update was published in Nov. 2006 (Aust. J. Chem. 2006, 59, 669-692). This review cites over 500 papers that appeared during the period mid-2006 to mid-2009 covering various aspects of RAFT polymn. ranging from reagent synthesis and properties, kinetics and mechanism of polymn., novel polymer syntheses and a diverse range of applications. Significant developments have occurred, particularly in the areas of novel RAFT agents, techniques for end-group removal and transformation, the prodn. of micro/nanoparticles and modified surfaces, and biopolymer conjugates both for therapeutic and diagnostic applications.
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    Moad, G.; Rizzardo, E.; Thang, S. H. Living Radical Polymerization by the RAFT Process—A Third Update. Aust. J. Chem. 2012, 65, 985– 1076,  DOI: 10.1071/CH12295
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    Living Radical Polymerization by the RAFT Process - A Third Update
    Moad, Graeme; Rizzardo, Ezio; Thang, San H.
    Australian Journal of Chemistry (2012), 65 (8), 985-1076CODEN: AJCHAS; ISSN:0004-9425. (CSIRO Publishing)
    A review. This paper provides a third update to the review of reversible deactivation radical polymn. (RDRP) achieved with thiocarbonylthio compds. (ZC(=S)SR) by a mechanism of reversible addn.-fragmentation chain transfer (RAFT) that was published in June 2005 (Aust. J. Chem. 2005, 58, 379). The first update was published in Nov. 2006 (Aust. J. Chem. 2006, 59, 669) and the second in Dec. 2009 (Aust. J. Chem. 2009, 62, 1402). This review cites over 700 publications that appeared during the period mid 2009 to early 2012 covering various aspects of RAFT polymn. which include reagent synthesis and properties, kinetics and mechanism of polymn., novel polymer syntheses, and a diverse range of applications. This period has witnessed further significant developments, particularly in the areas of novel RAFT agents, techniques for end-group transformation, the prodn. of micro/nanoparticles and modified surfaces, and biopolymer conjugates both for therapeutic and diagnostic applications.
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    Deane, O. J.; Lovett, J. R.; Musa, O. M.; Fernyhough, A.; Armes, S. P. Synthesis of Well-Defined Pyrrolidone-Based Homopolymers and Stimulus-Responsive Diblock Copolymers via RAFT Aqueous Solution Polymerization of 2-(N-Acryloyloxy)Ethylpyrrolidone. Macromolecules 2018, 51, 7756– 7766,  DOI: 10.1021/acs.macromol.8b01627
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    44
    Synthesis of Well-Defined Pyrrolidone-Based Homopolymers and Stimulus-Responsive Diblock Copolymers via RAFT Aqueous Solution Polymerization of 2-(N-Acryloyloxy)ethylpyrrolidone
    Deane, O. J.; Lovett, J. R.; Musa, O. M.; Fernyhough, A.; Armes, S. P.
    Macromolecules (Washington, DC, United States) (2018), 51 (19), 7756-7766CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    Poly(N-vinylpyrrolidone) (PNVP) is a well-known, highly polar, nonionic water-sol. polymer. However, N-vinylpyrrolidone (NVP) usually exhibits strongly non-ideal behavior when copolymd. with methacrylic or styrenic monomers. Moreover, NVP is not particularly well-controlled under living radical polymn. conditions. For these reasons, alternative pyrrolidone-based monomers have been investigated. For example, the reversible addn.-fragmentation chain transfer (RAFT) polymn. of 2-(N-methacryloyloxy)ethylpyrrolidone (NMEP) has been recently investigated using various polymn. formulations. However, PNMEP homopolymers are significantly less hydrophilic than PNVP and exhibit inverse temp. soly. in aq. soln. In the present work, we studied the RAFT aq. soln. polymn. of 2-(N-acryloyloxy)ethylpyrrolidone (NAEP) using either AIBN at 70 °C or a low-temp. redox initiator at 30 °C. PNAEP homopolymers are obtained in high yield (>99%) with good control (Mw/Mn < 1.20) for target ds.p. (DP) of up to 400 using the latter initiator, which produced relatively fast rates of polymn. However, targeting DPs above 400 led to lower NAEP conversions and broader mol. wt. distributions. 2-Hydroxyethyl acrylate (HEA) and oligo(ethylene glycol) Me ether acrylate (OEGA) were chain-extended using a PNAEPx macro-CTA via RAFT aq. soln. polymn., yielding double-hydrophilic acrylic diblock copolymers with high conversions (>99%) and good control (Mw/Mn < 1.31). In addn., a PNAEP95 macro-CTA was chain-extended via RAFT aq. soln. polymn. of N-isopropylacrylamide (NIPAM) at 22 °C. Dynamic light scattering (DLS) anal. indicated that heating above the lower crit. soln. temp. of PNIPAM led to so-called "anomalous micellization" at 35 °C and the formation of near-monodisperse spherical micelles at 40 °C. Finally, 2-(diethylamino)ethyl methacrylate (DEA) was polymd. using an N-morpholine-functionalized trithiocarbonate-based RAFT chain transfer agent and subsequently chain-extended using NAEP to form a novel pH-responsive diblock copolymer. Above the pKa of PDEA (∼7.3), DLS and 1H NMR studies indicated the formation of well-defined PDEA-core spherical micelles.
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  45. 45
    Deane, O. J.; Musa, O. M.; Fernyhough, A.; Armes, S. P. Synthesis and Characterization of Waterborne Pyrrolidone-Functional Diblock Copolymer Nanoparticles Prepared via Surfactant-Free RAFT Emulsion Polymerization. Macromolecules 2020, 53, 1422– 1434,  DOI: 10.1021/acs.macromol.9b02394
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    45
    Synthesis and Characterization of Waterborne Pyrrolidone-Functional Diblock Copolymer Nanoparticles Prepared via Surfactant-free RAFT Emulsion Polymerization
    Deane, Oliver J.; Musa, Osama M.; Fernyhough, Alan; Armes, Steven P.
    Macromolecules (Washington, DC, United States) (2020), 53 (4), 1422-1434CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    Polymn.-induced self-assembly enables the facile synthesis of a wide range of block copolymer nano-objects in the form of concd. dispersions. In this context, many surfactant-free reversible addn.-fragmentation chain transfer (RAFT) aq. emulsion polymn. formulations have been reported using various nonionic and polyelectrolytic water-sol. precursors for the steric stabilizer block. In the present study, we examine poly(2-(N-acryloyloxy)ethyl pyrrolidone) (PNAEP) as a new nonionic stabilizer block. A trithiocarbonate-based PNAEP precursor with a mean d.p. of 67 was employed as the steric stabilizer for the RAFT emulsion polymn. of styrene, Bu acrylate (nBA), or statistical mixts. thereof. The RAFT emulsion polymn. of styrene using a VA-044 azo initiator at 80°C and pH 7 led to essentially full conversion within 40 min, with induction times as short as 10 min, whereas gel permeation chromatog. anal. confirmed efficient chain extension and relatively low dispersities (Mw/Mn < 1.30). Dynamic light scattering (DLS) studies indicated that systematically increasing the target d.p. (DP) from 100 to 700 enabled the z-av. diam. of the resulting kinetically trapped spherical nanoparticles to be varied from 55 to 156 nm. The same PNAEP67 precursor was then employed for the RAFT emulsion polymn. of nBA at 30°C using a low-temp. redox initiator at pH 3. More than 99% conversion was achieved within 25 min, and efficient chain extension was obsd. up to a target DP of 700. However, relatively broad mol. wt. distributions (Mw/Mn = 1.38-1.64) were obtained, presumably owing to side reactions such as chain transfer to polymer. DLS studies indicated that a series of kinetically-trapped PNAEP67-PnBAx spheres (where x = 100-700) exhibited z-av. diams. ranging from 45 to 141 nm. Attempts to use this low-temp. initiator protocol for the homopolymn. of styrene led to essentially no conversion after 48 h at 30°C. However, the statistical copolymn. of 45% styrene with 55% nBA could be achieved using this low-temp. redox initiator at 30°C using the same PNAEP67 precursor. In this case, 1H NMR studies indicated a significantly longer induction period (95 min) compared to either homopolymn. Nevertheless, once the statistical copolymn. commenced, essentially full conversion of both comonomers could be achieved within 45 min. Differential scanning calorimetry anal. indicated that these statistical copolymers exhibited intermediate glass transition temps. compared to the two resp. homopolymers. The film formation behavior of selected diblock copolymer nanoparticles was briefly explored.
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  46. 46
    An, Z.; Shi, Q.; Tang, W.; Tsung, C.-K.; Hawker, C. J.; Stucky, G. D. Facile RAFT Precipitation Polymerization for the Microwave-Assisted Synthesis of Well-Defined, Double Hydrophilic Block Copolymers and Nanostructured Hydrogels. J. Am. Chem. Soc. 2007, 129, 14493– 14499,  DOI: 10.1021/ja0756974
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    46
    Facile RAFT Precipitation Polymerization for the Microwave-Assisted Synthesis of Well-Defined, Double Hydrophilic Block Copolymers and Nanostructured Hydrogels
    An, Zesheng; Shi, Qihui; Tang, Wei; Tsung, Chia-Kuang; Hawker, Craig J.; Stucky, Galen D.
    Journal of the American Chemical Society (2007), 129 (46), 14493-14499CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    Water-sol. macromol. chain transfer agents (Macro-CTAs) were developed for the microwave-assisted pptn. polymn. of N-isopropylacrylamide. Two types of Macro-CTAs, amphiphilic (Macro-CTA1) and hydrophilic (Macro-CTA2), were studied regarding their activity for the facile formation of nanoparticles and double hydrophilic block copolymers by RAFT processes. While both Macro-CTAs functioned as steric stabilization agents, the variation in their surface activity afforded different levels of control over the resulting nanoparticles in the presence of crosslinkers. The crosslinked nanoparticles produced using the amphiphilic Macro-CTA1 were less uniform than those produced using the fully hydrophilic Macro-CTA2. The nanoparticles spontaneously formed core-shell structures with surface functionalities derived from those of the Macro-CTAs. In the absence of crosslinkers, both types of Macro-CTAs showed excellent control over the RAFT pptn. polymn. process with well-defined, double hydrophilic block copolymers being obtained. The power of combining microwave irradn. with RAFT procedures was evident in the high efficiency and high solids content of the polymn. systems. In addn., the "living" nature of the nanoparticles allowed for further copolymn. leading to multiresponsive nanostructured hydrogels contg. surface functional groups, which were used for surface bioconjugation.
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  47. 47
    Grazon, C.; Rieger, J.; Sanson, N.; Charleux, B. Study of Poly(N,N-Diethylacrylamide) Nanogel Formation by Aqueous Dispersion Polymerization of N,N-Diethylacrylamide in the Presence of Poly(Ethylene Oxide)-b-Poly(N,N-Dimethylacrylamide) Amphiphilic Macromolecular RAFT Agents. Soft Matter 2011, 7, 3482– 3490,  DOI: 10.1039/c0sm01181a
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    47
    Study of poly(N,N-diethylacrylamide) nanogel formation by aqueous dispersion polymerization of N,N-diethylacrylamide in the presence of poly(ethylene oxide)-b-poly(N,N-dimethylacrylamide) amphiphilic macromolecular RAFT agents
    Grazon, Chloe; Rieger, Jutta; Sanson, Nicolas; Charleux, Bernadette
    Soft Matter (2011), 7 (7), 3482-3490CODEN: SMOABF; ISSN:1744-683X. (Royal Society of Chemistry)
    The formation of thermoresponsive poly(N,N-diethylacrylamide) (PDEAAm) nanogels via an aq. dispersion polymn. process in the presence of poly(ethylene oxide)-b-poly(N,N-dimethylacrylamide) macromol. reversible addn.-fragmentation chain transfer agents (macro RAFT agents) was studied. The latter exhibit a hydrophobic trithiocarbonate reactive group with a dodecyl substituent, and had previously proved to act simultaneously as control agents and stabilizers in such a synthesis process (Rieger et al., J. Polym. Sci. Part A: Polym. Chem., 2009, 47, 2373). The nanogel size and stability were found to depend strongly on the chain length of the macro RAFT agents, but also on the crosslinker (N,N'-methylene bisacrylamide) and monomer concns. The aim of the present work was to better understand the mechanisms that govern the nanogel formation in such heterogeneous polymn. conditions performed under RAFT control, with special emphasis on the role of the macro RAFT agents. In the first part, the aq. soln. properties of the macro RAFT agents in the conditions of the dispersion polymns. were studied by light scattering and fluorescence spectroscopy and they self-assemble to form star micelles. In the second part, the nanogel formation at different DEAAm and crosslinker concns. was monitored by dynamic and static light scattering, and by size exclusion chromatog. It appeared that at low monomer conversion the calcd. no. of chains per nanogel particle was close to the aggregation no., Nagg, of the macro RAFT agent micelles. With increasing conversions, however, the no. of chains clearly increased and exceeded the initial Nagg. Higher monomer concns. hardly influenced the formation process and thus the gel particle size, whereas enhanced crosslinker concn. had a strong impact on the latter. These results strongly suggest that precursor particles are formed rapidly at the polymn. onset and then aggregate with each other to form complex inter-crosslinked particles.
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  48. 48
    Warren, N. J.; Mykhaylyk, O. O.; Mahmood, D.; Ryan, A. J.; Armes, S. P. RAFT Aqueous Dispersion Polymerization Yields Poly(Ethylene Glycol)-Based Diblock Copolymer Nano-Objects with Predictable Single Phase Morphologies. J. Am. Chem. Soc. 2014, 136, 1023– 1033,  DOI: 10.1021/ja410593n
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    48
    RAFT Aqueous Dispersion Polymerization Yields Poly(ethylene glycol)-Based Diblock Copolymer Nano-Objects with Predictable Single Phase Morphologies
    Warren, Nicholas J.; Mykhaylyk, Oleksandr O.; Mahmood, Daniel; Ryan, Anthony J.; Armes, Steven P.
    Journal of the American Chemical Society (2014), 136 (3), 1023-1033CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    A poly(ethylene glycol) (PEG) macromol. chain transfer agent (macro-CTA) is prepd. in high yield (>95%) with 97% dithiobenzoate chain-end functionality in a three-step synthesis starting from a monohydroxy PEG113 precursor. This PEG113-dithiobenzoate is then used for the reversible addn.-fragmentation chain transfer (RAFT) aq. dispersion polymn. of 2-hydroxypropyl methacrylate (HPMA). Polymns. conducted under optimized conditions at 50 °C led to high conversions as judged by 1H NMR spectroscopy and relatively low diblock copolymer polydispersities (Mw/Mn < 1.25) as judged by GPC. The latter technique also indicated good blocking efficiencies, since there was minimal PEG113 macro-CTA contamination. Systematic variation of the mean d.p. of the core-forming PHPMA block allowed PEG113-PHPMAx diblock copolymer spheres, worms, or vesicles to be prepd. at up to 17.5% wt./wt. solids, as judged by dynamic light scattering and transmission electron microscopy studies. Small-angle X-ray scattering (SAXS) anal. revealed that more exotic oligolamellar vesicles were obsd. at 20% wt./wt. solids when targeting highly asym. diblock compns. Detailed anal. of SAXS curves indicated that the mean no. of membranes per oligolamellar vesicle is approx. three. A PEG113-PHPMAx phase diagram was constructed to enable the reproducible targeting of pure phases, as opposed to mixed morphologies (e.g., spheres plus worms or worms plus vesicles). This new RAFT PISA formulation is expected to be important for the rational and efficient synthesis of a wide range of biocompatible, thermo-responsive PEGylated diblock copolymer nano-objects for various biomedical applications.
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  49. 49
    Xu, Y.; Li, Y.; Cao, X.; Chen, Q.; An, Z. Versatile RAFT Dispersion Polymerization in Cononsolvents for the Synthesis of Thermoresponsive Nanogels with Controlled Composition, Functionality and Architecture. Polym. Chem. 2014, 5, 6244– 6255,  DOI: 10.1039/C4PY00867G
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    49
    Versatile RAFT dispersion polymerization in cononsolvents for the synthesis of thermoresponsive nanogels with controlled composition, functionality and architecture
    Xu, Yuanyuan; Li, Youcheng; Cao, Xueteng; Chen, Qijing; An, Zesheng
    Polymer Chemistry (2014), 5 (21), 6244-6255CODEN: PCOHC2; ISSN:1759-9962. (Royal Society of Chemistry)
    Reversible addn.-fragmentation chain transfer (RAFT) dispersion polymn. in cononsolvents of poly(N-isopropylacrylamide) (PNIPAM) was developed as a versatile strategy for the synthesis of thermoresponsive nanogels with controlled compn., functionality and architecture. Cononsolvents composed of mixts. of methanol, ethanol and isopropanol with water were first screened for their suitability as the media for dispersion polymn. of NIPAM, and water-ethanol (75 : 25, v : v) soln. was selected due to good RAFT control, efficient formation of nanogels and low toxicity. RAFT dispersion polymn. of NIPAM in the cononsolvent using poly(N,N-dimethylacrylamide) (PDMA) as the macromol. chain transfer agent (Macro-CTA) showed good control over the mol. wt., polydispersity and pseudo linear polymn. kinetics, as characterized by gel permeation chromatog. (GPC) and 1H NMR. The effect of the mol. wt. of Macro-CTA, the d.p. of PNIPAM, the molar ratio of [crosslinker] : [Macro-CTA] and the solid content on the formation and size of nanogels was investigated. The thermal profiles of nanogels were characterized by dynamic light scattering (DLS) both in cononsolvents and water. This cononsolvency strategy for dispersion polymn. was shown to be compatible with the incorporation of hydrophilic comonomers of N-(2-hydroxyethyl)acrylamide (HEAM) and diacetone acrylamide (DAAM). The nanogel contg. DAAM was demonstrated for postpolymn. modification using ketone-alkoxyamine chem. More importantly, dispersion polymn. in cononsolvents allowed various hydrophobic components, e.g. Bu acrylate (BA), fluorescein O-acrylate (FLA), and 1,6-hexanediol diacrylate (HDDA), to be reliably copolymd. with NIPAM, showing well controlled polymn., compn., nanogel size and colloidal stability. Finally, an amphiphilic block copolymer PDMA-b-PBA was used as a Macro-CTA to produce the PDMA-b-PBA-b-PNIPAM triblock copolymer and triple-layered nanogel, taking advantage of the soly. of PDMA-b-PBA and the insoly. of PNIPAM in the water-ethanol soln. at the polymn. temp.
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    Figg, C. A.; Simula, A.; Gebre, K. A.; Tucker, B. S.; Haddleton, D. M.; Sumerlin, B. S. Polymerization-Induced Thermal Self-Assembly (PITSA). Chem. Sci. 2015, 6, 1230– 1236,  DOI: 10.1039/C4SC03334E
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    Polymerization-induced thermal self-assembly (PITSA)
    Figg, C. Adrian; Simula, Alexandre; Gebre, Kalkidan A.; Tucker, Bryan S.; Haddleton, David M.; Sumerlin, Brent S.
    Chemical Science (2015), 6 (2), 1230-1236CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
    Polymn.-induced self-assembly (PISA) is a versatile technique to achieve a wide range of polymeric nanoparticle morphologies. Most previous examples of self-assembled soft nanoparticle synthesis by PISA rely on a growing solvophobic polymer block that leads to changes in nanoparticle architecture during polymn. in a selective solvent. However, synthesis of block copolymers with a growing stimuli-responsive block to form various nanoparticle shapes has yet to be reported. This new concept using thermo-responsive polymers is termed polymn.-induced thermal self-assembly (PITSA). A reversible addn.-fragmentation chain transfer (RAFT) polymn. of N-isopropylacrylamide from a hydrophilic chain transfer agent composed of N,N-dimethylacrylamide and acrylic acid was carried out in water above the known lower crit. soln. temp. (LCST) of poly(N-isopropylacrylamide) (PNIPAm). After reaching a certain chain length, the growing PNIPAm self-assembled, as induced by the LCST, into block copolymer aggregates within which dispersion polymn. continued. To characterize the nanoparticles at ambient temps. without their dissoln., the particles were crosslinked immediately following polymn. at elevated temps. via the reaction of the acid groups with a diamine in the presence of a carbodiimide. Size exclusion chromatog. was used to evaluate the unimer mol. wt. distributions and reaction kinetics. Dynamic light scattering and transmission electron microscopy provided insight into the size and morphologies of the nanoparticles. The resulting block copolymers formed polymeric nanoparticles with a range of morphologies (e.g., micelles, worms, and vesicles), which were a function of the PNIPAm block length.
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    Blackman, L. D.; Doncom, K. E. B.; Gibson, M. I.; O’Reilly, R. K. Comparison of Photo- and Thermally Initiated Polymerization-Induced Self-Assembly: A Lack of End Group Fidelity Drives the Formation of Higher Order Morphologies. Polym. Chem. 2017, 8, 2860– 2871,  DOI: 10.1039/C7PY00407A
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    51
    Comparison of photo- and thermally initiated polymerization-induced self-assembly: a lack of end group fidelity drives the formation of higher order morphologies
    Blackman, Lewis D.; Doncom, Kay E. B.; Gibson, Matthew I.; O'Reilly, Rachel K.
    Polymer Chemistry (2017), 8 (18), 2860-2871CODEN: PCOHC2; ISSN:1759-9962. (Royal Society of Chemistry)
    Polymn.-induced self-assembly (PISA) is an emerging industrially relevant technol., which allows the prepn. of defined and predictable polymer self-assemblies with a wide range of morphologies. In recent years, interest has turned to photoinitiated PISA processes, which show markedly accelerated reaction kinetics and milder conditions, thereby making it an attractive alternative to thermally initiated PISA. Herein, we attempt to elucidate the differences between these two initiation methods using isothermally derived phase diagrams of a well-documented poly(ethylene glycol)-b-(2-hydroxypropyl methacrylate) (PEG-b-HPMA) PISA system. By studying the influence of the intensity of the light source used, as well as an investigation into the thermodynamically favorable morphologies, the factors dictating differences in the obtained morphologies when comparing photo- and thermally initiated PISA were explored. Our findings indicate that differences in a combination of both reaction kinetics and end group fidelity led to the obsd. discrepancies between the two techniques. We find that the loss of the end group in photoinitiated PISA drives the formation of higher order structures and that a morphol. transition from worms to unilamellar vesicles could be induced by extended periods of light and heat irradn. Our findings demonstrate that PISA of identical block copolymers by the two different initiation methods can lead to structures that are both chem. and morphol. distinct.
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    Sun, W.; An, Z.; Wu, P. Hydrogen Bonding Reinforcement as a Strategy to Improve Upper Critical Solution Temperature of Poly(N-Acryloylglycinamide-Co-Methacrylic Acid). Polym. Chem. 2018, 9, 3667– 3673,  DOI: 10.1039/C8PY00733K
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    Hydrogen bonding reinforcement as a strategy to improve upper critical solution temperature of poly(N-acryloylglycinamide-co-methacrylic acid)
    Sun, Wenhui; An, Zesheng; Wu, Peiyi
    Polymer Chemistry (2018), 9 (26), 3667-3673CODEN: PCOHC2; ISSN:1759-9962. (Royal Society of Chemistry)
    Hydrogen bonding reinforcement via copolymn. of N-acryloylglycinamide (NAGA) with methacrylic acid (MAA) is employed as a strategy to improve the upper crit. soln. temp. (UCST) to a biol. relevant range. P(NAGA-co-MAA) copolymers with MAA molar fraction in the range of 1-81 mol% are synthesized via reversible addn.-fragmentation chain transfer (RAFT) polymn. The UCST (3.5-37.5°C) of the copolymers scales with MAA molar fraction in the range of 10-60 mol% when measured at pH 4 and 1 wt.% concn. Using a copolymer with a suitably high UCST as a macromol. chain transfer agent, doubly thermoresponsive nanogels consisting of P(NAGA-co-MAA) copolymer as the shell and crosslinked poly(N-isopropylacrylamide) (PNIPAM) as the core are synthesized via RAFT aq. dispersion polymn. The nanogels show distinct thermal transitions with both upper and lower crit. soln. temps. (UCST and LCST).
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    Liu, D.; Cai, W.; Zhang, L.; Boyer, C.; Tan, J. Efficient Photoinitiated Polymerization-Induced Self-Assembly with Oxygen Tolerance through Dual-Wavelength Type I Photoinitiation and Photoinduced Deoxygenation. Macromolecules 2020, 53, 1212– 1223,  DOI: 10.1021/acs.macromol.9b02710
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    53
    Efficient Photoinitiated Polymerization-Induced Self-Assembly with Oxygen Tolerance through Dual-Wavelength Type I Photoinitiation and Photoinduced Deoxygenation
    Liu, Dongdong; Cai, Weibin; Zhang, Li; Boyer, Cyrille; Tan, Jianbo
    Macromolecules (Washington, DC, United States) (2020), 53 (4), 1212-1223CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    Recently, reversible addn.-fragmentation chain transfer (RAFT)-mediated polymn.-induced self-assembly (PISA) has emerged as a powerful method for the prepn. of a variety of block copolymer nano-objects. Although numerous RAFT-mediated PISA formulations have been successfully explored, inert atmospheres (e.g., nitrogen) are often needed to overcome the oxygen inhibition problem, making this process challenging when polymg. at low vols. Moreover, this restriction also reduces the versatility of RAFT-mediated PISA for non-experts. Herein, we report an efficient photoinitiated polymn.-induced self-assembly (photo-PISA) with excellent oxygen tolerance through dual-wavelength type I photoinitiation and photoinduced deoxygenation. The dual-wavelength photo-PISA was explored in water and alc./water using 2-hydroxypropyl methacrylate (HPMA), benzyl methacrylate (BzMA), and isobornyl acrylate (IBOA) as core-forming monomers. Polymn. kinetics indicated that dual-wavelength photo-PISA was performed in a batch reactor, flow reactor, and microliter plate with excellent oxygen tolerance. Block copolymer nano-objects with different morphologies (spheres, worms, and vesicles) were successfully prepd. by these dual-wavelength photo-PISA techniques. This is a fast RAFT-mediated PISA under air, which is a clear improvement from previous systems. We believe that this method can greatly increase the accessibility of RAFT-mediated PISA for the prepn. of block copolymer nano-objects either at low vols. or at a large scale.
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    Xu, S.; Corrigan, N.; Boyer, C. Forced Gradient Copolymerisation: A Simplified Approach for Polymerisation-Induced Self-Assembly. Polym. Chem. 2021, 12, 57– 68,  DOI: 10.1039/D0PY00889C
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    Forced gradient copolymerisation: a simplified approach for polymerisation-induced self-assembly
    Xu, Sihao; Corrigan, Nathaniel; Boyer, Cyrille
    Polymer Chemistry (2021), 12 (1), 57-68CODEN: PCOHC2; ISSN:1759-9962. (Royal Society of Chemistry)
    In this work, a novel and versatile gradient copolymn. approach to simplify polymeric nanoparticle synthesis through polymn.-induced self-assembly (PISA) is reported. In contrast with the commonly performed two-step PISA process, which involves chain-extension of a pre-synthesized stabilizer (or solvophilic block), this work demonstrates a one pot PISA approach via the formation of gradient copolymers through a gradual injection of the core-forming monomer in the presence of a solvophilic monomer. To demonstrate this concept, two model PISA systems were tested using a methacrylate monomer pair and an acrylamide pair. PISA using dimethylacrylamide (DMA) and diacetone acrylamide (DAAm) was first established to form a range of nanoparticle morphologies (spheres and worms), and importantly, a pure worm phase was obsd. without the addn. of a co-solvent or a second solvophilic monomer during the polymn. of the core-forming monomer. To demonstrate the gradient approach can be applied to other PISA monomer pairs, this methodol. was applied to a system using oligo(ethylene glycol)methyl ether methacrylate (OEGMA300) and 2-hydroxypropyl methacrylate (HPMA) as monomers. PISA of this monomer pair resulted in the formation of nanoparticles with various morphologies, including spheres, worms and vesicles. More interestingly, the nanoparticles formed using these gradient copolymers presented thermoresponsive behavior, exhibiting a sphere-to-worm transition with an increase in temp. from 25°C to 40°C. Thus, this facile gradient copolymn. approach was shown to simplify the PISA process into a single step approach with easily tuneable solvophilic block length and copolymer compn., and addnl. provide nanoparticle structures that afford unique properties.
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    Liu, G.; Qiu, Q.; An, Z. Development of Thermosensitive Copolymers of Poly(2-Methoxyethyl Acrylate-Co-Poly(Ethylene Glycol) Methyl Ether Acrylate) and Their Nanogels Synthesized by RAFT Dispersion Polymerization in Water. Polym. Chem. 2012, 3, 504– 513,  DOI: 10.1039/C2PY00533F
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    Development of thermosensitive copolymers of poly(2-methoxyethyl acrylate-co-poly(ethylene glycol) methyl ether acrylate) and their nanogels synthesized by RAFT dispersion polymerization in water
    Liu, Guangyao; Qiu, Qian; An, Zesheng
    Polymer Chemistry (2012), 3 (2), 504-513CODEN: PCOHC2; ISSN:1759-9962. (Royal Society of Chemistry)
    The prepn. of thermosensitive oligo(ethylene glycol) methacrylate-based microgels/nanogels via aq. dispersion polymn. is limited due to low monomer loading and thus low solid content of the final colloids. Moreover, the prepn. of nanogels by reversible addn.-fragmentation chain transfer (RAFT) mediated dispersion polymn. has been hampered by the poor RAFT control of the polymn. process. In this work, thermosensitive copolymers based on 2-methoxyethyl acrylate (MEA) and poly(ethylene glycol) Me ether acrylate (PEGA) were developed and used for nanogel synthesis by RAFT dispersion polymn. in water. The thermosensitive copolymers exhibited sharp thermal transitions upon temp. increase above their lower crit. soln. temp. The use of MEA as the major comonomer and poly(N,N'-dimethylacrylamide) as the RAFT agent and stabilizer for the nanogel synthesis allowed monomer loadings of up to 20%, which significantly improved the solid content of the dispersion polymn. system. Moreover, the dispersion copolymn. of MEA with PEGA was under excellent RAFT control up to complete monomer conversion. The nanogels showed a linear relationship between nanogel size and temp., suggesting expanded applications of these materials.
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    Ratcliffe, L. P. D.; Derry, M. J.; Ianiro, A.; Tuinier, R.; Armes, S. P. A Single Thermoresponsive Diblock Copolymer Can Form Spheres, Worms or Vesicles in Aqueous Solution. Angew. Chem., Int. Ed. 2019, 58, 18964– 18970,  DOI: 10.1002/anie.201909124
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    A Single Thermoresponsive Diblock Copolymer Can Form Spheres, Worms or Vesicles in Aqueous Solution
    Ratcliffe, Liam P. D.; Derry, Matthew J.; Ianiro, Alessandro; Tuinier, Remco; Armes, Steven P.
    Angewandte Chemie, International Edition (2019), 58 (52), 18964-18970CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
    It is well-known that the self-assembly of AB diblock copolymers in soln. can produce various morphologies depending on the relative vol. fraction of each block. Recently, polymn.-induced self-assembly (PISA) has become widely recognized as a powerful platform technol. for the rational design and efficient synthesis of a wide range of block copolymer nano-objects. In this study, PISA is used to prep. a new thermoresponsive poly(N-(2-hydroxypropyl) methacrylamide)-poly(2-hydroxypropyl methacrylate) [PHPMAC-PHPMA] diblock copolymer. Remarkably, TEM, rheol. and SAXS studies indicate that a single copolymer compn. can form well-defined spheres (4 °), worms (22 °) or vesicles (50 °) in aq. soln. Given that the two monomer repeat units have almost identical chem. structures, this system is particularly well-suited to theor. anal. Self-consistent mean field theory suggests this rich self-assembly behavior is the result of the greater degree of hydration of the PHPMA block at lower temp., which is in agreement with variable temp. 1H NMR studies.
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    Petzetakis, N.; Dove, A. P.; O’Reilly, R. K. Cylindrical Micelles from the Living Crystallization-Driven Self-Assembly of Poly(Lactide)-Containing Block Copolymers. Chem. Sci. 2011, 2, 955– 960,  DOI: 10.1039/C0SC00596G
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    Cylindrical micelles from the living crystallization-driven self-assembly of poly(lactide)-containing block copolymers
    Petzetakis, Nikos; Dove, Andrew P.; O'Reilly, Rachel K.
    Chemical Science (2011), 2 (5), 955-960CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
    The synthesis and self-assembly of poly(lactide)-b-poly(acrylic acid) and poly(lactide)-b-poly(dimethylaminoethyl acrylate) block copolymers by a combination of ring-opening polymn. and reverse-addn. fragmentation chain transfer (RAFT) polymn. is reported. The self-assembly of block copolymers contg. enantiopure homochiral poly(lactide), PLA, by a simple direct dissoln. methodol. results in core-crystn. to afford micelles with cylindrical morphol. Amorphous atactic PLA cores and conditions that did not promote crystn. resulted in spherical micelles. The cylindrical micelles were characterized by transmission electron microscopy (TEM) with cryo-TEM, small angle neutron scattering (SANS) and angular dependent dynamic light scattering (DLS) proving that the cylindrical morphol. was persistent in soln. Manipulation of the assembly conditions enabled the length and dispersity of the resultant cylindrical micelles to be controlled.
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    Zhao, W.; Gody, G.; Dong, S.; Zetterlund, P. B.; Perrier, S. Optimization of the RAFT Polymerization Conditions for the in Situ Formation of Nano-Objects via Dispersion Polymerization in Alcoholic Medium. Polym. Chem. 2014, 5, 6990– 7003,  DOI: 10.1039/C4PY00855C
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    Optimization of the RAFT polymerization conditions for the in situ formation of nano-objects via dispersion polymerization in alcoholic medium
    Zhao, Wei; Gody, Guillaume; Dong, Siming; Zetterlund, Per B.; Perrier, Sebastien
    Polymer Chemistry (2014), 5 (24), 6990-7003CODEN: PCOHC2; ISSN:1759-9962. (Royal Society of Chemistry)
    Hydrophilic polymer brushes based on poly(ethylene glycol) Me ether acrylate (P(PEGA454)) or poly(ethylene glycol) Me ether methacrylate (P(PEGMA475)), both having a trithiocarbonate end group, were prepd. in water-dioxane (9 : 1) at 44 °C via RAFT polymn. and subsequently used in RAFT dispersion polymn. of styrene in isopropanol at 90 °C. RAFT reaction conditions were first optimized to prep. P(PEGA454) and P(PEGMA475) macro-RAFT agents at high monomer conversions (>90%) and very low fraction of dead chains (<1%). Both polymer brushes allowed the prepn. of well-defined amphiphilic diblock copolymers (P(PEGA454)-b-PS and P(PEGMA475)-b-PS) which self-assemble in situ into nano-objects with various morphologies. Using relatively long chain P(PEGA454) or P(PEGMA475) macro-RAFT agents (DP ~ 75) leads to the formation of near uniform spherical nanoparticles with diams. ranging from 30 to 140 nm, depending on the targeted DP of the PS block. In contrast, TEM and DLS studies demonstrated that using a shorter P(PEGA454) or P(PEGMA475) macro-RAFT agent (DP ~ 20) enables the formation of worm-like micelles, vesicles and large compd. vesicle morphologies in addn. to spheres. Cryo-TEM was used to confirm polymn. induced morphol. transition, rather than morphologies obtained via self-assembly driven by selective solvent or solvent evapn. during the prepn. of samples for characterization.
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    Mable, C. J.; Gibson, R. R.; Prevost, S.; McKenzie, B. E.; Mykhaylyk, O. O.; Armes, S. P. Loading of Silica Nanoparticles in Block Copolymer Vesicles during Polymerization-Induced Self-Assembly: Encapsulation Efficiency and Thermally Triggered Release. J. Am. Chem. Soc. 2015, 137, 16098– 16108,  DOI: 10.1021/jacs.5b10415
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    Loading of Silica Nanoparticles in Block Copolymer Vesicles during Polymerization-Induced Self-Assembly: Encapsulation Efficiency and Thermally Triggered Release
    Mable, Charlotte J.; Gibson, Rebecca R.; Prevost, Sylvain; McKenzie, Beulah E.; Mykhaylyk, Oleksandr O.; Armes, Steven P.
    Journal of the American Chemical Society (2015), 137 (51), 16098-16108CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    Poly(glycerol monomethacrylate)-poly(2-hydroxypropyl methacrylate) diblock copolymer vesicles can be prepd. in the form of concd. aq. dispersions via polymn.-induced self-assembly (PISA). In the present study, these syntheses are conducted in the presence of varying amts. of silica nanoparticles of approx. 18 nm diam. This approach leads to encapsulation of up to hundreds of silica nanoparticles per vesicle. Silica has high electron contrast compared to the copolymer which facilitates TEM anal., and its thermal stability enables quantification of the loading efficiency via thermogravimetric anal. Encapsulation efficiencies can be calcd. using disk centrifuge photosedimentometry, since the vesicle d. increases at higher silica loadings while the mean vesicle diam. remains essentially unchanged. Small angle X-ray scattering (SAXS) is used to confirm silica encapsulation, since a structure factor is obsd. at q ≈ 0.25 nm-1. A new two-population model provides satisfactory data fits to the SAXS patterns and allows the mean silica vol. fraction within the vesicles to be detd. Finally, the thermoresponsive nature of the diblock copolymer vesicles enables thermally triggered release of the encapsulated silica nanoparticles simply by cooling to 0-10 °C, which induces a morphol. transition. These silica-loaded vesicles constitute a useful model system for understanding the encapsulation of globular proteins, enzymes, or antibodies for potential biomedical applications. They may also serve as an active payload for self-healing hydrogels or repair of biol. tissue. Finally, we also encapsulate a model globular protein, bovine serum albumin, and calc. its loading efficiency using fluorescence spectroscopy.
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    Ahmad, N. M.; Charleux, B.; Farcet, C.; Ferguson, C. J.; Gaynor, S. G.; Hawkett, B. S.; Heatley, F.; Klumperman, B.; Konkolewicz, D.; Lovell, P. A.; Matyjaszewski, K.; Venkatesh, R. Chain Transfer to Polymer and Branching in Controlled Radical Polymerizations of N-Butyl Acrylate. Macromol. Rapid Commun. 2009, 30, 2002– 2021,  DOI: 10.1002/marc.200900450
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    Chain Transfer to Polymer and Branching in Controlled Radical Polymerizations of n-Butyl Acrylate
    Ahmad, Nasir M.; Charleux, Bernadette; Farcet, Celine; Ferguson, Christopher J.; Gaynor, Scott G.; Hawkett, Brian S.; Heatley, Frank; Klumperman, Bert; Konkolewicz, Dominik; Lovell, Peter A.; Matyjaszewski, Krzysztof; Venkatesh, Rajan
    Macromolecular Rapid Communications (2009), 30 (23), 2002-2021CODEN: MRCOE3; ISSN:1022-1336. (Wiley-VCH Verlag GmbH & Co. KGaA)
    Chain transfer to polymer (CTP) in conventional free-radical polymns. (FRPs) and controlled radical polymns. (ATRP, RAFT and NMP) of Bu acrylate (BA) has been investigated using 13C NMR measurements of branching in the poly(Bu acrylate) produced. The mol-% branches are reduced significantly in the controlled radical polymns. as compared to conventional FRPs. Several possible explanations for this observation are discussed critically and all except one refuted. The observations are explained in terms of differences in the concn. of highly reactive short-chain radicals which can be expected to undergo both intra- and inter-mol. CTP at much higher rates than long-chain radicals. In conventional FRP, the distribution of radical concns. is broad and there always is present a significant proportion of short-chain radicals, whereas in controlled radical polymns., the distribution is narrow with only a small proportion of short-chain radicals which diminishes as the living chains grow. Hence, irresp. of the type of control, controlled radical polymns. give rise to lower levels of branching, when performed under otherwise similar conditions to conventional FRP. Similar observations are expected for other acrylates and monomers that undergo chain transfer to polymer during radical polymn.
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    Misra, G. S.; Gupta, C. V. Aqueous Polymerization of Methacrylamide Initiated by the Redox System K2S2O8/Ascorbic Acid. Die Makromol. Chem. 1973, 165, 205– 216,  DOI: 10.1002/macp.1973.021650119
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    Narain, H.; Jagadale, S. M.; Ghatge, N. D. Studies of Redox Polymerization. I. Aqueous Polymerization of Acrylamide by an Ascorbic Acid–Peroxydisulfate System. J. Polym. Sci., Polym. Chem. Ed. 1981, 19, 1225– 1238,  DOI: 10.1002/pol.1981.170190518
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    Studies of redox polymerization. I. Aqueous polymerization of acrylamide by an ascorbic acid-peroxydisulfate system
    Narain, H.; Jagadale, S. M.; Ghatge, N. D.
    Journal of Polymer Science, Polymer Chemistry Edition (1981), 19 (5), 1225-38CODEN: JPLCAT; ISSN:0360-6376.
    The polymn. of acrylamide [79-06-1] initiated by an ascorbic acid (I) [50-81-7]-peroxydisulfate redox system was studied in aq. soln. at 35 ± 0.2° in the presence of air. The concns. studied were [monomer] = (2.0-15.0) × 10-2; [peroxydisulfate] = (1.5-10.0) × 10-3; and [I] = (2.84-28.4) × 10-4 M; temps. were 25-50°. Within these ranges the initial rate showed a half-order dependence on peroxydisulfate, a first-order dependence on initial monomer concn., and a first-order dependence on low concns. of I [(2.84-8.54) × 10-4 M]. At higher concns. of I the rate remained const. in the concn. range (8.54-22.72) × 10-4 M, then varied as an inverse half-power at still higher concns. of [(22.72-28.4) × 10-4 M]. The initial rate increased with an increase in polymn. temp. The overall energy of activation was 12.203 kcal/mol at 25-50°. Water-miscible org. solvents depressed the initial rate and the limiting conversion. The viscometric av. mol. wt. increased with an increase in temp. and initial monomer concn. but decreased with increasing concn. of peroxydisulfate and an additive, DMF.
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    Cabelli, D. E.; Bielski, B. H. J. Kinetics and Mechanism for the Oxidation of Ascorbic Acid/Ascorbate by HO2/O2- (Hydroperoxyl/Superoxide) Radicals. A Pulse Radiolysis and Stopped-Flow Photolysis Study. J. Phys. Chem. A 1983, 87, 1809– 1812,  DOI: 10.1021/j100233a031
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    Ahmad, N. M.; Heatley, F.; Lovell, P. A. Chain Transfer to Polymer in Free-Radical Solution Polymerization of n-Butyl Acrylate Studied by NMR Spectroscopy. Macromolecules 1998, 31, 2822– 2827,  DOI: 10.1021/ma971283r
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    Chain transfer to polymer in free-radical solution polymerization of n-butyl acrylate studied by NMR spectroscopy
    Ahmad, Nasir M.; Heatley, Frank; Lovell, Peter A.
    Macromolecules (1998), 31 (9), 2822-2827CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    The effects of the initial monomer concn., [M]o, and percent conversion on the extent of chain transfer to polymer in free-radical soln. polymn. of Bu acrylate has been studied. The polymns. were carried out in cyclohexane at 70° using 0.1% (wt./wt.) 2,2'-azobis(2-cyanopropane) as initiator and the mole percent branched repeat units (mole percent branches) in the poly(Bu acrylate) was detd. from unique resonances of branch-point carbons in the 13C NMR spectra. At [M]o > 10% (wt./wt.) the mole percent branches is independent of [M]o and increases from 0.8 to ∼2.2% as conversion increases from 35 to ∼95%. However, for more dil. solns., with [M]o ≤ 10% (wt./wt.), the mole percent branches increases as [M]o decreases and is higher than at equiv. conversions for the more concd. soln. polymns.; e.g., at ∼25% conversion the mole percent branches increases from 2.7% for [M]o = 10% (wt./wt.) to 5.9% for [M]o = 3% (wt./wt.). These observations are explained in terms of the ratio of the concns. of polymer repeat units and monomer in the vicinity of the propagating chain end. In more concd. solns., intermol. chain transfer to polymer dominates because, at all except the lowest percent conversions, the overall polymer repeat unit concn. is sufficient for overlap of individual polymer coils. However, in the dil. solns. the overall polymer repeat unit concn. is too low for overlap of individual polymer coils and intramol. chain transfer to polymer dominates. Under these conditions, the local polymer repeat unit concn. within the isolated propagating chains is defined by the chain statistics and so is approx. const., whereas the monomer is distributed uniformly throughout the soln. Thus, for dil. solns., as [M]o decreases, the probability of chain transfer to polymer (and hence the mole percent branches) increases.
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  65. 65
    Agirre, A.; Santos, J. I.; Etxeberria, A.; Sauerland, V.; Leiza, J. R. Polymerization of N-Butyl Acrylate with High Concentration of a Chain Transfer Agent (CBr4): Detailed Characterization and Impact on Branching. Polym. Chem. 2013, 4, 2062– 2079,  DOI: 10.1039/c2py21123h
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    Polymerization of n-butyl acrylate with high concentration of a chain transfer agent (CBr4): detailed characterization and impact on branching
    Agirre, A.; Santos, J. I.; Etxeberria, A.; Sauerland, V.; Leiza, J. R.
    Polymer Chemistry (2013), 4 (6), 2062-2079CODEN: PCOHC2; ISSN:1759-9962. (Royal Society of Chemistry)
    Poly(Bu acrylate) (polyn-BA) polymers synthesized by radical bulk polymn. in the presence and absence of a high concn. (0.4 mol L-1) of carbon tetrabromide (CBr4) as a chain transfer agent at nominal temps. of 60, 100 and 140 °C were fully characterized by 1D and 2D NMR, SEC/MALS and MALDI-TOF mass spectrometry. The structures generated by chain transfer to CBr4 in secondary chain-end radicals and reinitiation of polymer chains by CBr3 radicals formed by chain transfer to CBr4 reactions were identified by MALDI-TOF and NMR anal. The potential structures that might have been created by chain-transfer to tertiary radicals (quaternary carbons with a Br unit) formed by backbiting or intermol. chain transfer to polymer could not be detected and hence their abundance was not important. The branching d. (BD) of the polymers synthesized in the presence and absence of CBr4 was also detd. The BD increases with temp. in both cases, and for each temp. the branching d. considerably reduced when CBr4 was employed in the polymn. as found for other transfer agents and controlled radical mediated polymns. However, the explanation that patching on the tertiary radicals was the cause of redn. of the branching in the polyn-BA was discarded in this case because the resulting structures could not be identified.
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    Baussard, J.-F.; Habib-Jiwan, J.-L.; Laschewsky, A.; Mertoglu, M.; Storsberg, J. New Chain Transfer Agents for Reversible Addition-Fragmentation Chain Transfer (RAFT) Polymerisation in Aqueous Solution. Polymer 2004, 45, 3615– 3626,  DOI: 10.1016/j.polymer.2004.03.081
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    New chain transfer agents for reversible addition-fragmentation chain transfer (RAFT) polymerisation in aqueous solution
    Baussard, Jean-Francois; Habib-Jiwan, Jean-Louis; Laschewsky, Andre; Mertoglu, Murat; Storsberg, Joachim
    Polymer (2004), 45 (11), 3615-3626CODEN: POLMAG; ISSN:0032-3861. (Elsevier Science Ltd.)
    New chain transfer agents for free radical polymn. via reversible addn.-fragmentation chain transfer (RAFT) were synthesized that are particularly suited for aq. soln. polymn. The new compds. bear dithioester and trithiocarbonate moieties as well as permanently ionic groups to confer soly. in water. Their stability against hydrolysis was studied, and compared with a frequently used water-sol. RAFT agent, i.e., 4-(thiobenzoylthio)-4-cyanopentanoic acid (I), using UV-visible spectroscopy and 1H NMR measurements. An improved resistance to hydrolysis was found for the new RAFT agents compared to I, providing good stabilities in the pH range between 1 and 8, and up to temps. of 70°.
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    Thomas, D. B.; Convertine, A. J.; Hester, R. D.; Lowe, A. B.; McCormick, C. L. Hydrolytic Susceptibility of Dithioester Chain Transfer Agents and Implications in Aqueous RAFT Polymerizations. Macromolecules 2004, 37, 1735– 1741,  DOI: 10.1021/ma035572t
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    Hydrolytic Susceptibility of Dithioester Chain Transfer Agents and Implications in Aqueous RAFT Polymerizations
    Thomas, David B.; Convertine, Anthony J.; Hester, Roger D.; Lowe, Andrew B.; McCormick, Charles L.
    Macromolecules (2004), 37 (5), 1735-1741CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    The controlled radical polymn. (CRP) technique reversible addn.-fragmentation chain transfer (RAFT) has potential for prepg. functional (co)polymers directly in an aq. environment. Hydrolysis and aminolysis can eliminate the active end groups necessary for maintaining "livingness" in water. These reactions have not previously been evaluated with respect to their effect on aq. RAFT polymns. Herein we det. rate consts. of hydrolysis and aminolysis for representative water-sol. chain transfer agents (CTAs) cyanopentanoic acid dithiobenzoate (CTP) and the macro-chain-transfer agents (macro-CTAs) of poly(sodium 2-acrylamido-2-methylpropanesulfonate) (AMPSX) and poly(acrylamide) (AMX) at selected pH values. Rates of hydrolysis and aminolysis both increase with increasing pH and decrease with increasing mol. wt. of the dithioester. On the basis of these rate consts., math. relationships have been developed to predict the no. of living chain ends and the mol. wt. with competitive hydrolysis. Utilizing this approach, predictions of mol. wt. at specific conversions are in agreement with exptl. values detd. by SEC/MALLS.
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    Fuchs, A. V.; Thurecht, K. J. Stability of Trithiocarbonate RAFT Agents Containing Both a Cyano and a Carboxylic Acid Functional Group. ACS Macro Lett 2017, 6, 287– 291,  DOI: 10.1021/acsmacrolett.7b00100
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    Stability of Trithiocarbonate RAFT Agents Containing Both a Cyano and a Carboxylic Acid Functional Group
    Fuchs, Adrian V.; Thurecht, Kristofer J.
    ACS Macro Letters (2017), 6 (3), 287-291CODEN: AMLCCD; ISSN:2161-1653. (American Chemical Society)
    The hydrolytic degrdn. of widely used cyano-contg., acid-bearing trithiocarbonate reversible addn.-fragmentation chain-transfer (RAFT) agents has been identified and shown to effect the RAFT polymn. and end-group fidelity of PMMA polymers. The hydrolysis occurred when the RAFT agents were stored under the recommended conditions. Degrdn. was identified in both com. available and popular synthetic RAFT agents. 1H and 13C NMR as well as mass spectroscopy show that the cyano functionality hydrolyzes to the amide adduct. Doping of this amide degrdn. product into RAFT polymns. of MMA results in increased dispersities and changes in expected end-group fidelities. The ability to identify this degrdn. product and remove it from the RAFT agent before use will allow better control over polymer properties and postmodification processes commonly used in complex polymer systems, nanomedicines, and bioconjugates.
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    Blanazs, A.; Madsen, J.; Battaglia, G.; Ryan, A. J.; Armes, S. P. Mechanistic Insights for Block Copolymer Morphologies: How Do Worms Form Vesicles?. J. Am. Chem. Soc. 2011, 133, 16581– 16587,  DOI: 10.1021/ja206301a
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    Mechanistic Insights for Block Copolymer Morphologies: How Do Worms Form Vesicles?
    Blanazs, Adam; Madsen, Jeppe; Battaglia, Giuseppe; Ryan, Anthony J.; Armes, Steven P.
    Journal of the American Chemical Society (2011), 133 (41), 16581-16587CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    Amphiphilic diblock copolymers composed of two covalently linked, chem. distinct chains can be considered to be biol. mimics of cell membrane-forming lipid mols., but with typically more than an order of magnitude increase in mol. wt. These macromol. amphiphiles are known to form a wide range of nanostructures (spheres, worms, vesicles, etc.) in solvents that are selective for one of the blocks. However, such self-assembly is usually limited to dil. copolymer solns. (<1%), which is a significant disadvantage for potential com. applications such as drug delivery and coatings. In principle, this problem can be circumvented by polymn.-induced block copolymer self-assembly. Here the authors detail the synthesis and subsequent in situ self-assembly of amphiphilic AB diblock copolymers in a one pot concd. aq. dispersion polymn. formulation. The authors show that spherical micelles, wormlike micelles, and vesicles can be predictably and efficiently obtained (within 2 h of polymn., >99% monomer conversion) at relatively high solids in purely aq. soln. Furthermore, careful monitoring of the in situ polymn. by transmission electron microscopy reveals various novel intermediate structures (including branched worms, partially coalesced worms, nascent bilayers, "octopi", "jellyfish", and finally pure vesicles) that provide important mechanistic insights regarding the evolution of the particle morphol. during the sphere-to-worm and worm-to-vesicle transitions. This environmentally benign approach (which involves no toxic solvents, is conducted at relatively high solids, and requires no addnl. processing) is readily amenable to industrial scale-up, since it is based on com. available starting materials.
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    Lovett, J. R.; Warren, N. J.; Ratcliffe, L. P. D.; Kocik, M. K.; Armes, S. P. PH-Responsive Non-Ionic Diblock Copolymers: Ionization of Carboxylic Acid End-Groups Induces an Order-Order Morphological Transition. Angew. Chem., Int. Ed. 2015, 54, 1279– 1283,  DOI: 10.1002/anie.201409799
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    pH-Responsive Non-Ionic Diblock Copolymers: Ionization of Carboxylic Acid End-Groups Induces an Order-Order Morphological Transition
    Lovett, Joseph R.; Warren, Nicholas J.; Ratcliffe, Liam P. D.; Kocik, Marzena K.; Armes, Steven P.
    Angewandte Chemie, International Edition (2015), 54 (4), 1279-1283CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
    A carboxylic acid based reversible addn. fragmentation transfer (RAFT) agent is used to prep. gels composed of worm-like diblock copolymers using two non-ionic monomers, glycerol monomethacrylate (GMA) and 2-hydroxypropyl methacrylate (HPMA). Ionization of the carboxylic acid end-group on the PGMA stabilizer block induces a worm-to-sphere transition, which in turn causes immediate degelation. This morphol. transition is fully reversible as detd. by TEM and rheol. studies and occurs because of a subtle change in the packing parameter for the copolymer chains. A control expt. where the Me ester deriv. of the RAFT agent is used to prep. the same diblock copolymer confirms that no pH-responsive behavior occurs in this case. This end-group ionization approach is important for the design of new pH-responsive copolymer nano-objects as, unlike polyacids or polybases, only a minimal amt. of added base (or acid) is required to drive the morphol. transition.
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    Fox, T. G. Influence of Diluent and of Copolymer Composition on the Glass Temperature of a Polymer System. Bull. Am. Phys. Soc. 1956, 1, 123
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    Influence of diluent and of copolymer composition on the glass temperature of a polymer system
    Fox, T. G.
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    The above are titles of papers presented before the Am. Phys. Soc. and published in abstr. form.
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    Meng, F.; Jeon, Y.-S.; Chung, D.-J.; Kim, J.-H. Miscible Blend and Semi-IPN Gel of Poly(Hydroxyethyl Aspartamide) with Poly(N-Vinyl Pyrrolidone). Polym. Korea 2012, 36, 617– 621,  DOI: 10.7317/pk.2012.36.5.617
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    Miscible blend and semi-IPN gel of poly(hydroxyethyl aspartamide) with poly(N-vinyl pyrrolidone)
    Meng, Fan; Jeon, Young Sil; Chung, Dong June; Kim, Ji-Heung
    Polymer (Korea) (2012), 36 (5), 617-621CODEN: POLLDG; ISSN:0379-153X. (Polymer Society of Korea)
    PHEAs [α,β-poly(2-hydroxyethyl-DL-aspartamides)], a class of poly(amino acid), have been widely studied as biodegradable and biocompatible polymers for potential biomedical and pharmaceutical applications. In this study, we investigated a homogeneous blend of PHEA with poly(N-vinyl pyrrolidone) (PNVP) and its semi-IPN (semi-interpenetrating polymer network) gels. Blend films were prepd. by a soln. casting method. The resulting blends were totally transparent over the whole compn. ranges and the single Tg, changing monotonously with compn., was obsd. by DSC to confirm the miscibility between these two polymers. FTIR was used to discuss the possible hydrogen-bonding interaction between polymers. In addn., semi-IPN type gels were prepd. by chem. crosslinking of PHEA/PNVP blend soln. using hexamethylene diisocyanate (HMDI) as a crosslinking reagent. The prepd. gel was characterized by their swelling property and morphol.
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    Sabatini, D. D.; Bensch, K.; Barrnett, R. J. Cytochemistry and Electron Microscopy. J. Cell Biol. 1963, 17, 19– 58,  DOI: 10.1083/jcb.17.1.19
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    Cytochemistry and electron microscopy; the preservation of cellular ultrastructure and enzymic activity by aldehyde fixation
    Sabatini, David D.; Bensch, Klaus; Barrnett, Russell J.
    Journal of Cell Biology (1963), 17 (No. 1), 19-58CODEN: JCLBA3; ISSN:0021-9525.
    Tissue prepns. suitable for both electron microscopy and cytochem. studies were obtained by fixation in 4-6.5% glutaraldehyde, 4% glyoxal, 12.5% hydroxyadipaldehyde, 10% crotonaldehyde, 5% pyruvic aldehyde, 10% acetaldehyde, or 5% methacrolein. The aldehydes were prepd. as cacodylate- or phosphate-buffered solns., 0.l-0.2M, pH 6.5-7.6, that, except for glutaraldehyde, contained 0.22-0.55M sucrose. The blocks were fixed for 0.5-24 hrs. and stored at 4° in 0.1M buffer contg. 0.22M sucrose. Aliesterase, acetylcholinesterase, alk. and acid phosphatases, 5-nucleotidase, adenosinetriphosphatase, and di- and triphosphopyridine nucleotide diaphorase activities were histochemically demonstrable after most of the fixatives. Following hydroxyaldipaldehyde or glyoxal fixation, cytochrome oxidase, succinic dehydrogenase, and glucose-6-phosphatase were also detectable. Membranous differentiation in the cells was not visible by electron microscopy of the aldehyde-fixed tissues. However, a 2nd fixation with OsO4, even after prolonged storage, rendered an image comparable to that of tissues prepd. with OsO4 alone under standard conditions. Glutaraldehyde-fixed tissues were esp. well visualized by electron microscopy after the postfixation. 60 references.
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    Migneault, I.; Dartiguenave, C.; Bertrand, M. J.; Waldron, K. C. Glutaraldehyde: Behavior in Aqueous Solution, Reaction with Proteins, and Application to Enzyme Crosslinking. Biotechniques 2004, 37, 790– 802,  DOI: 10.2144/04375RV01
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    Glutaraldehyde: Behavior in aqueous solution, reaction with proteins, and application to enzyme crosslinking
    Migneault, Isabelle; Dartiguenave, Catherine; Bertrand, Michel J.; Waldron, Karen C.
    BioTechniques (2004), 37 (5), 790-796,798-802CODEN: BTNQDO; ISSN:0736-6205. (Life Sciences Publishing)
    A review. Glutaraldehyde possesses unique characteristics that render it one of the most effective protein crosslinking reagents. It can be present in at least 13 different forms depending on soln. conditions such as pH, concn., temp., etc. Substantial literature is found concerning the use of glutaraldehyde for protein immobilization, yet there is no agreement about the main reactive species that participates in the crosslinking process because monomeric and polymeric forms are in equil. Glutaraldehyde may react with proteins by several means such as aldol condensation or Michael-type addn., and we show here 8 different reactions for various aq. forms of this reagent. As a result of these discrepancies and the unique characteristics of each enzyme, crosslinking procedures using glutaraldehyde are largely developed through empirical observation. The choice of the enzyme-glutaraldehyde ratio, as well as their final concn., is crit. because insolubilization of the enzyme must result in minimal distortion of its structure in order to retain catalytic activity. The purpose of this paper is to give an overview of glutaraldehyde as a crosslinking reagent by describing its structure and chem. properties in aq. soln. in an attempt to explain its high reactivity toward proteins, particularly as applied to the prodn. of insol. enzymes.
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    Hayat, M. A. Glutaraldehyde: Role in Electron Microscopy. Micron Microsc. Acta 1986, 17, 115– 135,  DOI: 10.1016/0739-6260(86)90042-0
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    Hayat, M. A.
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    A review with ∼175 refs. on the history, properties, reactions with proteins and lipids, effect on OsO4, and fixation by glutaraldehyde in relation to its use in various electron microscopy and immunocytochem. methods.
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    Kiernan, J. A. Formaldehyde, Formalin, Paraformaldehyde And Glutaraldehyde: What They Are And What They Do. Microsc. Today 2000, 8, 8– 13,  DOI: 10.1017/S1551929500057060
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    Kim, K.-J.; Lee, S.-B.; Han, N. W. Effects of the Degree of Crosslinking on Properties of Poly(Vinyl Alcohol) Membranes. Polym. J. 1993, 25, 1295– 1302,  DOI: 10.1295/polymj.25.1295
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    Effects of the degree of crosslinking on properties of poly(vinyl alcohol) membranes
    Kim, Kwang Je; Lee, Soo Bok; Han, Neung Won
    Polymer Journal (Tokyo, Japan) (1993), 25 (12), 1295-302CODEN: POLJB8; ISSN:0032-3896.
    Asym. poly(vinyl alc.) (PVA) membranes were prepd. by the phase inversion technique, and crosslinked with glutaraldehyde. The degree of crosslinking of the membrane was controlled by varying the crosslinking conditions. The effects of the degree of crosslinking on the swelling characteristics, contact angles, crit. surface tensions, and pervaporation characteristics were examd. A method for the evaluation of the degree of crosslinking, which needs only the glutaraldehyde concn. of the crosslinking soln. to be measured after the crosslinking reaction, is proposed, and was found useful. The degree of swelling of PVA membrane for water decreases abruptly as the degree of crosslinking increases. However, the degree of swelling for ethanol is nearly independent of the degree of crosslinking. The crit. surface tension of the membrane increases more or less within the range of 37.0-40.0 dyn cm-1 with increasing degree of crosslinking below 30%. But, it is nearly const. at 40.5 dyn cm-1 above 30%. The wetting behavior of the membrane may not be greatly affected by the degree of crosslinking. The selectivity factor and permeate flux of the membrane in the pervaporation of the ethanol-water mixt. of 95 wt% ethanol concn. decrease similarly with increasing degree of crosslinking. The pervaporation characteristics seem to be closely related to the swelling behavior. The degree of crosslinking is an important variable for swelling behavior and pervaporation characteristics.
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    Yeom, C.-K.; Lee, K.-H. Pervaporation Separation of Water-Acetic Acid Mixtures through Poly(Vinyl Alcohol) Membranes Crosslinked with Glutaraldehyde. J. Membr. Sci. 1996, 109, 257– 265,  DOI: 10.1016/0376-7388(95)00196-4
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    Pervaporation separation of water-acetic acid mixtures through poly(vinyl alcohol) membranes crosslinked with glutaraldehyde
    Yeom, Choong-Kyun; Lee, Kew-Ho
    Journal of Membrane Science (1996), 109 (2), 257-65CODEN: JMESDO; ISSN:0376-7388. (Elsevier)
    Poly(vinyl alc.) (PVA) membranes crosslinked with glutaraldehyde (GA) were prepd. by a soln. method for the pervaporation sepn. of acetic acid-water mixts. In the soln. method, dry PVA films were crosslinked by immersion for 2 days at 40° in reaction solns. which contained different contents of GA, acetone and a catalyst, HCl. In order to fabricate the crosslinked PVA membranes which were stable in aq. solns., acetone was used as reaction medium instead of aq. inorg. salt solns. which have been commonly used in reaction soln. for PVA crosslinking reaction. The crosslinking reaction between the hydroxyl group of PVA and the aldehyde group of GA was characterized by IR spectroscopy. Swelling measurements were carried out in both water and acetic acid to investigate the swelling behavior of the membranes. The swelling behavior of a membrane fabricated at different GA content in a reaction soln. depended on crosslinking d. and chem. functional groups created as a result of the reaction between PVA and GA, such as the acetal group, ether linkage and unreacted pendent aldehydes in PVA. The pervaporation sepn. of acetic acid-water mixts. was performed over a range of 70-90 wt% acetic acid in the feed at 35-50° to examine the sepn. performances of the PVA membranes. Permeation behavior through the membranes was analyzed by using pervaporation activation energies which had been calcd. from the Arrhenius plots of permeation rates.
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    Kurihara, S.; Sakamaki, S.; Mogi, S.; Ogata, T.; Nonaka, T. Crosslinking of Poly(Vinyl Alcohol)-Graft-N-Isopropylacrylamide Copolymer Membranes with Glutaraldehyde and Permeation of Solutes through the Membranes. Polymer. 1996, 37, 1123– 1128,  DOI: 10.1016/0032-3861(96)80838-X
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    Crosslinking of poly(vinyl alcohol)-graft-N-isopropylacrylamide copolymer membranes with glutaraldehyde and permeation of solutes through the membranes
    Kurihara, Seiji; Sakamaki, Shinichi; Mogi, Satosi; Ogata, Tomonari; Nonaka, Takamasa
    Polymer (1996), 37 (7), 1123-8CODEN: POLMAG; ISSN:0032-3861. (Elsevier)
    The phase transition behavior of poly(vinyl alc.)-graft-N-isopropylacrylamide copolymer membranes was studied by measuring their steady-state fluorescence spectra and swelling ratios. Crosslinking with glutaraldehyde increased the tensile strength of copolymer membrane and also resulted in a considerable decrease in the swelling ratio of the membrane. Well defined thermo-control of permeation through the membrane was achieved by crosslinking of the copolymer membrane with glutaraldehyde.
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    Rao, P. S.; Sridhar, S.; Wey, M. Y.; Krishnaiah, A. Pervaporation Performance and Transport Phenomenon of PVA Blend Membranes for the Separation of THF/Water Azeotropic Mixtures. Polym. Bull. 2007, 59, 289– 298,  DOI: 10.1007/s00289-007-0769-6
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    Pervaporation performance and transport phenomenon of PVA blend membranes for the separation of THF/water azeotropic mixtures
    Rao, P. Srinivasa; Sridhar, S.; Wey, Ming Yen; Krishnaiah, A.
    Polymer Bulletin (Heidelberg, Germany) (2007), 59 (2), 289-298CODEN: POBUDR; ISSN:0170-0839. (Springer)
    Dense polymer membranes were made by mixing aq. solns. of hydrophilic polymers poly(vinyl alc.) (PVA) and polyethyleneimine (PEI) in different ratios for investigating the sepn. of THF/water azeotropic mixts. by pervaporation (PV). In order to gain a more detailed picture of the mol. transport phenomenon, we have performed sorption gravimetric expts. at 30° to compute diffusion, swelling, sorption and permeability coeffs. of PVA/PEI membranes in the presence of THF and water. The membranes were found to have good potential for breaking the azeotrope of THF at 6% concn. of water. An increase in PVA content in the blend caused a redn. in the flux and an increase in selectivity. Among the blends tested in the study, the 5:1 PVA/PEI blend membrane showed the highest sepn. factor of 181.5, exhibited a flux of 1.28 kg/m2h for THF, resp. at azeotropic feed compn.
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    Bolto, B.; Tran, T.; Hoang, M.; Xie, Z. Crosslinked Poly(Vinyl Alcohol) Membranes. Prog. Polym. Sci. 2009, 34, 969– 981,  DOI: 10.1016/j.progpolymsci.2009.05.003
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    Crosslinked poly(vinyl alcohol) membranes
    Bolto, Brian; Tran, Thuy; Hoang, Manh; Xie, Zongli
    Progress in Polymer Science (2009), 34 (9), 969-981CODEN: PRPSB8; ISSN:0079-6700. (Elsevier Ltd.)
    A review. The inherent hydrophilicity of poly(vinyl alc.) (PVA) makes it an attractive polymer for water treatment applications based on membranes. Thermal and chem. resistance and a high anti-fouling potential are accompanied by high water permeability. The large swelling capacity requires that the PVA be adequately crosslinked to ensure that the contaminants in water can be retained, and that compaction under pressure can be minimized. There is a challenge to achieve this and still obtain economical permeate fluxes. The literature on crosslinking of PVA is reviewed. Many reagents have been explored. Glutaraldehyde is a more effective crosslinking agent than formaldehyde or glycidyl acrylate, which in turn gives a less swollen product than that obtained by increasing the crystallinity by heating. Toluene diisocyanate and acrolien give similar results in the prepn. of reverse osmosis membranes, but at an extremely high applied pressure. Crosslinking with maleic anhydride/vinyl Me ether copolymers gives as good a result, but at even higher pressure. Thus the high swelling of PVA can be overcome by crosslinking reactions, but with the consumption of some of the OH groups responsible for the hydrophilicity. What is really needed is network formation that provides a tight restraining without serious loss of hydrophilic behavior. Similar membranes are used for the sepn. of org. compds. from one another or from water by pervaporation, where the vapor of one component is selectively transferred through the membrane on the basis of polarity differences. Here PVA membranes would be esp. suited to dehydration procedures. The high swelling behavior can be countered also by forming the active PVA component inside the pores of a microporous membrane. Crosslinked PVA inside such membranes has its swelling suppressed, and can function as salt removal membranes. By only coating the pore walls, leaving some porosity, microfiltration or ultrafiltration membranes can be prepd. In both situations a degree of grafting to the host membrane would be beneficial.
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    Fan, J.-B.; Song, Y.; Wang, S.; Meng, J.; Yang, G.; Guo, X.; Feng, L.; Jiang, L. Directly Coating Hydrogel on Filter Paper for Effective Oil-Water Separation in Highly Acidic, Alkaline, and Salty Environment. Adv. Funct. Mater. 2015, 25, 5368– 5375,  DOI: 10.1002/adfm.201501066
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    Directly Coating Hydrogel on Filter Paper for Effective Oil-Water Separation in Highly Acidic, Alkaline, and Salty Environment
    Fan, Jun-Bing; Song, Yongyang; Wang, Shutao; Meng, Jingxin; Yang, Gao; Guo, Xinglin; Feng, Lin; Jiang, Lei
    Advanced Functional Materials (2015), 25 (33), 5368-5375CODEN: AFMDC6; ISSN:1616-301X. (Wiley-VCH Verlag GmbH & Co. KGaA)
    The sepn. of oil-water mixts. in highly acidic, alk., and salty environment remains a great challenge. Simple, low-cost, efficient, eco-friendly, and easily scale-up processes for the fabrication of novel materials to effective oil-water sepn. in highly acidic, alk., and salty environment, are urgently desired. Here, a facile approach is reported for the fabrication of stable hydrogel-coated filter paper which not only can sep. oil-water mixt. in highly acidic, alk., and salty environment, but also sep. surfactant-stabilized emulsion. The hydrogel-coated filter paper is fabricated by smartly crosslinking filter paper with hydrophilic polyvinyl alc. through a simple aldol condensation reaction with glutaraldehyde as a crosslinker. The resultant multiple crosslinked networks enable the hydrogel-coated filter paper to tolerate high acid, alkali, and salt up to 8 M H2SO4, 10 M NaOH, and satd. NaCl. It is shown that the hydrogel-coated filter paper can sep. oil-water mixts. in highly acidic, alk., and salty environment and oil-in-water emulsion environment, with high sepn. efficiency (>99%).
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    Habeeb, A. F. S. A.; Hiramoto, R. Reaction of Proteins with Glutaraldehyde. Arch. Biochem. Biophys. 1968, 126, 16– 26,  DOI: 10.1016/0003-9861(68)90554-7
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    Reaction of proteins with glutaraldehyde
    Habeeb, A. F. S. A.; Hiramoto, R.
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    Glutaraldehyde was found to react with the α-amino groups of amino acids, the N-terminal amino groups of some peptides and the SH group of cysteine. The phenolic and the imidazole rings of tyrosine and histidine derivs. were partially reactive. With proteins such as bovine serum albumin, ovalbumin, and human γ-globulin, glutaraldehyde reacted predominantly with the ε-amino groups of lysine to form mainly intermol. cross-linkages. Some reaction, however, did occur with tyrosine, histidine, and SH residues. The sol. aggregated proteins were capable of reacting with antibodies against their resp. native proteins. Glutaraldehyde was also capable of conjugating ovalbumin to bovine serum albumin and the product contained only minor contaminants of aggregated ovalbumin and bovine serum albumin. 21 references.
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    Richards, F. M.; Knowles, J. R. Glutaraldehyde as a Protein Cross-Linking Reagent. J. Mol. Biol. 1968, 37, 231– 233,  DOI: 10.1016/0022-2836(68)90086-7
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    N.M.R. and other data excluded the possibility that glutaraldehyde forms protein cross-links through Schiff base formation. Instead, a mechanism is proposed which involves aldol condensation of glutaraldehyde and then the formation of Michael-type adducts.
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    Chemical cross-linking: reagents and problems in studies of membrane structure
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    A review with 92 refs.
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    Cheung, D. T.; Perelman, N.; Ko, E. C.; Nimni, M. E. Mechanism of Crosslinking of Proteins by Glutaraldehyde III. Reaction with Collagen in Tissues. Connect. Tissue Res. 1985, 13, 109– 115,  DOI: 10.3109/03008208509152389
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    Mechanism of crosslinking of proteins by glutaraldehyde. III. Reaction with collagen in tissues
    Cheung, David T.; Perelman, Natasha; Ko, Ellen C.; Nimni, Marcel E.
    Connective Tissue Research (1985), 13 (2), 109-15CODEN: CVTRBC; ISSN:0300-8207.
    Bovine pericardium, a dense collagenous connective tissue that is frequently used as a xenograft, was crosslinked with glutaraldehyde by using different modalities of fixation. The degree of crosslinking was evaluated as a function of the ability of CNBr and Pronase to solubilize collagen. Apparently, glutaraldehyde fixes primarily the surface of the fibers and creates a polymeric network which hinders the further crosslinking of the interstitium of the fiber. When a low concn. of glutaraldehyde was used, a slow time-dependent crosslinking process was obsd. This slow process is maintained over a long period of time, greatly beyond that required for the actual penetration of glutaraldehyde to occur.
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    Okuda, K.; Urabe, I.; Yamada, Y.; Okada, H. Reaction of Glutaraldehyde with Amino and Thiol Compounds. J. Ferment. Bioeng. 1991, 71, 100– 105,  DOI: 10.1016/0922-338X(91)90231-5
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    Reaction of glutaraldehyde with amino and thiol compounds
    Okuda, Keiko; Urabe, Itaru; Yamada, Yasuhiro; Okada, Hirosuke
    Journal of Fermentation and Bioengineering (1991), 71 (2), 100-5CODEN: JFBIEX; ISSN:0922-338X.
    Stoichiometry, pH dependence, and reversibility of the reaction of glutaraldehyde with various amino and thiol compds. were investigated to elucidate the chem. nature of glutaraldehyde. For glutaraldehyde, three com. samples were examd. They have different spectral characteristics probably due to the difference in the content of α, β-unsatd. aldehyde polymers formed by aldol condensations of glutaraldehyde, but the amt. of such unsatd. structures is very small, and the chem. reactivity of these samples are almost the same. Therefore, the chem. reactivity characteristic of glutaraldehyde is not due to the α, β-unsatd. aldehydes. Glutaraldehyde reacts with the amino group in a wide pH range (≥ pH 3). The reactions at pH 7 and 9 are almost irreversible, though a little reversibility is obsd. The reaction rate becomes very slow after the initial rapid phase. The av. molar ratio of the amino and aldehyde groups consumed during the reaction of glutaraldehyde with the amino group is in a range of 0.3-0.2. Glutaraldehyde reacts with cysteine with a stoichiometric relationship of one mol of the thiol and amino groups of cysteine per mol of glutaraldehyde. Glutaraldehyde does not react with the thiol group without the presence of the primary amino group; the av. stoichiometric relationship is 0.5-0.6 mol of the thiol group, about 0.4 mol of the amino group, and 1 mol of glutaraldehyde, under the conditions of excess in the thiol and amino groups. These results indicate the complex nature of the glutaraldehyde reaction.
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    Mansur, H. S.; Sadahira, C. M.; Souza, A. N.; Mansur, A. A. P. FTIR Spectroscopy Characterization of Poly (Vinyl Alcohol) Hydrogel with Different Hydrolysis Degree and Chemically Crosslinked with Glutaraldehyde. Mater. Sci. Eng., C 2008, 28, 539– 548,  DOI: 10.1016/j.msec.2007.10.088
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    FTIR spectroscopy characterization of poly(vinyl alcohol) hydrogel with different hydrolysis degree and chemically crosslinked with glutaraldehyde
    Mansur, Herman S.; Sadahira, Carolina M.; Souza, Adriana N.; Mansur, Alexandra A. P.
    Materials Science & Engineering, C: Biomimetic and Supramolecular Systems (2008), 28 (4), 539-548CODEN: MSCEEE; ISSN:0928-4931. (Elsevier B.V.)
    In this work, poly (vinyl alc.) (PVA) hydrogels with different degree of hydrolysis (DH) were prepd. by chem. crosslinking with glutaraldehyde (GA). The nanostructure of the resulting hydrogels was investigated by Fourier Transform IR Spectroscopy (FTIR) and Synchrotron small-angle X-ray scattering characterization (SAXS). In vitro tests were performed by swelling ratio assays in different pH solns. The IR spectra of the crosslinked PVA showed absorption bands of the acetal bridges resulted from the reaction of the GA with the OH groups from PVA. Also the FTIR spectroscopy was used to det. the crystallinity of the PVA film based on the relative intensity of the vibration band at 1141 cm-1. The results have showed an increase of hydrogel crystallinity with higher DH of PVA. SAXS patterns have clearly indicated important modifications on the PVA semicryst. structure when it was crosslinked by GA. The swelling ratio was significantly reduced by chem. crosslinking the PVA network. PVA-derived hydrogel with chem. modified network was found to be pH-sensitive, indicating a high potential to be used in drug delivery polymer system.
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    Pedersen, J. S. Form Factors of Block Copolymer Micelles with Spherical, Ellipsoidal and Cylindrical Cores. J. Appl. Crystallogr. 2000, 33, 637– 640,  DOI: 10.1107/S0021889899012248
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    Form factors of block copolymer micelles with spherical, ellipsoidal and cylindrical cores
    Pedersen, Jan Skov
    Journal of Applied Crystallography (2000), 33 (3, Pt. 1), 637-640CODEN: JACGAR; ISSN:0021-8898. (Munksgaard International Publishers Ltd.)
    The form factor of a micelle model with a spherical core and Gaussian polymer chains attached to the surface has previously been calcd. anal. by Pedersen and Gerstenberg. Non-penetration of the chains into the core region was mimicked in the anal. calcns. by moving the center of mass of the chains Rg away from the surface of the core, where Rg is the radius of gyration of the chains. In the present work, the calcns. have been extended to micelles with ellipsoidal and cylindrical cores. Non-penetration was also for these taken into account by moving the center of mass of the chains Rg away from the core surface. In addn. results for worm-like micelles, disk-shape micelles and micelles with a vesicle shape are given.
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    Bang, J.; Jain, S.; Li, Z.; Lodge, T. P.; Pedersen, J. S.; Kesselman, E.; Talmon, Y. Sphere, Cylinder, and Vesicle Nanoaggregates in Poly(Styrene-b-Isoprene) Diblock Copolymer Solutions. Macromolecules 2006, 39, 1199– 1208,  DOI: 10.1021/ma052023+
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    Sphere, Cylinder, and Vesicle Nanoaggregates in Poly(styrene-b-isoprene) Diblock Copolymer Solutions
    Bang, Joona; Jain, Sumeet; Li, Zhibo; Lodge, Timothy P.; Pedersen, Jan Skov; Kesselman, Ellina; Talmon, Yeshayahu
    Macromolecules (2006), 39 (3), 1199-1208CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    An asym. poly(styrene-b-isoprene) diblock copolymer with block mol. wts. of 13,000 and 71,000 g/mol, resp., was dissolved at 1 vol% in a series of solvents with varying selectivity for styrene: di-Bu phthalate (DBP), di-Et phthalate (DEP), and di-Me phthalate (DMP). The degree of solvent selectivity was adjusted by mixing DBP/DEP and DEP/DMP in various proportions. With increasing solvent selectivity, the predominant micellar shape changes from spheres to cylinders to vesicles, reflecting the changing interfacial curvature. The detailed micellar morphologies were characterized by small-angle X-ray scattering (SAXS) and cryogenic transmission electron microscopy (cryo-TEM). Recently developed form factors were used to characterize the micellar structures in detail, and a vesicle form factor was derived for this system. From the core dimensions, the packing properties, such as the interfacial area per chain and the core chain stretching, were detd. The cryo-TEM results demonstrate the suitability of the technique for these glass-forming solvents and gave micellar core dimensions in quant. agreement with those from SAXS. The universality of the shape sequence sphere/cylinder/vesicle, well-established for aq. solns. of surfactants and block copolymers, is thus confirmed for org. systems.
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    Czajka, A.; Armes, S. P. In Situ SAXS Studies of a Prototypical RAFT Aqueous Dispersion Polymerization Formulation: Monitoring the Evolution in Copolymer Morphology during Polymerization-Induced Self-Assembly. Chem. Sci. 2020, 11, 11443– 11454,  DOI: 10.1039/D0SC03411H
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    In situ SAXS studies of a prototypical RAFT aqueous dispersion polymerization formulation: monitoring the evolution in copolymer morphology during polymerization-induced self-assembly
    Czajka, Adam; Armes, Steven P.
    Chemical Science (2020), 11 (42), 11443-11454CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
    Small-angle X-ray scattering (SAXS) is used to characterize the in situ formation of diblock copolymer spheres, worms and vesicles during reversible addn.-fragmentation chain transfer (RAFT) aq. dispersion polymn. of 2-hydroxypropyl methacrylate at 70°C using a poly(glycerol monomethacrylate) steric stabilizer. The 1H NMR spectroscopy indicates more than 99% HPMA conversion within 80 min, while transmission electron microscopy and dynamic light scattering studies are consistent with the final morphol. being pure vesicles. Anal. of time-resolved SAXS patterns for this prototypical polymn.-induced self-assembly (PISA) formulation enables the evolution in copolymer morphol., particle diam., mean aggregation no., solvent vol. fraction, surface d. of copolymer chains and their mean inter-chain sepn. distance at the nanoparticle surface to be monitored. Furthermore, the change in vesicle diam. and membrane thickness during the final stages of polymn. supports an 'inward growth' mechanism.
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    Warren, N. J.; Derry, M. J.; Mykhaylyk, O. O.; Lovett, J. R.; Ratcliffe, L. P. D. D.; Ladmiral, V.; Blanazs, A.; Fielding, L. A.; Armes, S. P. Critical Dependence of Molecular Weight on Thermoresponsive Behavior of Diblock Copolymer Worm Gels in Aqueous Solution. Macromolecules 2018, 51, 8357– 8371,  DOI: 10.1021/acs.macromol.8b01617
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    Critical Dependence of Molecular Weight on Thermoresponsive Behavior of Diblock Copolymer Worm Gels in Aqueous Solution
    Warren, Nicholas J.; Derry, Matthew J.; Mykhaylyk, Oleksandr O.; Lovett, Joseph R.; Ratcliffe, Liam P. D.; Ladmiral, Vincent; Blanazs, Adam; Fielding, Lee A.; Armes, Steven P.
    Macromolecules (Washington, DC, United States) (2018), 51 (21), 8357-8371CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    Reversible addn.-fragmentation chain transfer (RAFT) aq. dispersion polymn. of 2-hydroxypropyl methacrylate was used to prep. three poly(glycerol monomethacrylate)x-poly(2-hydroxypropyl methacrylate)y (denoted Gx-Hy or PGMA-PHPMA) diblock copolymers, namely G37-H80, G54-H140, and G71-H200. A master phase diagram was used to select each copolymer compn. to ensure that a pure worm phase was obtained in each case, as confirmed by transmission electron microscopy (TEM) and small-angle x-ray scattering (SAXS) studies. The latter technique indicated a mean worm cross-sectional diam. (or worm width) ranging from 11 to 20 nm as the mean d.p. (DP) of the hydrophobic PHPMA block was increased from 80 to 200. These copolymer worms form soft hydrogels at 20 °C that undergo degelation on cooling. This thermoresponsive behavior was examd. using variable temp. DLS, oscillatory rheol., and SAXS. A 10% wt./wt. G37-H80 worm dispersion dissocd. to afford an aq. soln. of molecularly dissolved copolymer chains at 2 °C; on returning to ambient temp., these chains aggregated to form first spheres and then worms, with the original gel strength being recovered. In contrast, the G54-H140 and G71-H200 worms each only formed spheres on cooling to 2 °C, with thermoreversible (de)gelation being obsd. in the former case. The sphere-to-worm transition for G54-H140 was monitored by variable temp. SAXS: these expts. indicated the gradual formation of longer worms at higher temp., with a concomitant redn. in the no. of spheres, suggesting worm growth via multiple 1D sphere-sphere fusion events. DLS studies indicated that a 0.1% wt./wt. aq. dispersion of G71-H200 worms underwent an irreversible worm-to-sphere transition on cooling to 2 °C. Furthermore, irreversible degelation over the time scale of the expt. was also obsd. during rheol. studies of a 10% wt./wt. G71-H200 worm dispersion. Shear-induced polarized light imaging (SIPLI) studies revealed qual. different thermoreversible behavior for these three copolymer worm dispersions, although worm alignment was obsd. at a shear rate of 10 s-1 in each case. Subsequently conducting this technique at a lower shear rate of 1 s-1 combined with ultra small-angle x-ray scattering (USAXS) also indicated that worm branching occurred at a certain crit. temp. since an upturn in viscosity, distortion in the birefringence, and a characteristic feature in the USAXS pattern were obsd. Finally, SIPLI studies indicated that the characteristic relaxation times required for loss of worm alignment after cessation of shear depended markedly on the copolymer mol. wt.
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    Bannister, I.; Billingham, N. C.; Armes, S. P.; Rannard, S. P.; Findlay, P. Development of Branching in Living Radical Copolymerization of Vinyl and Divinyl Monomers. Macromolecules 2006, 39, 7483– 7492,  DOI: 10.1021/ma061811b
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    95
    Development of Branching in Living Radical Copolymerization of Vinyl and Divinyl Monomers
    Bannister, Iveta; Billingham, Norman C.; Armes, Steven P.; Rannard, Steven P.; Findlay, Paul
    Macromolecules (2006), 39 (22), 7483-7492CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    The branching copolymn. of 2-hydroxypropyl methacrylate (HPMA) with either ethylene glycol dimethacrylate (EGDMA) or bisphenol A dimethacrylate (BPDMA) as the branching agent has been carried out using atom transfer radical polymn. (ATRP) in methanol at 20 °C. With EGDMA, sol. branched copolymers were obtained provided that less than one branching agent was incorporated per primary chain: higher levels of EGDMA led to gelation, as expected. Anal. of the changes in the mol. wt. and polydispersity of the polymers shows that the formation of highly branched chains occurs only at high (>90%) conversions. Chain coupling is close to the ideal behavior predicted by the Flory-Stockmayer theory, suggesting that all double bonds are equally reactive and that there is no significant cyclization, in contrast to conventional free radical polymn. This anal. is confirmed by comparison of the consumption of the EGDMA branching agent with predictions from both theory and simulation. With BPDMA as the branching agent, similar results are obtained although branching is slightly less efficient.
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    Simon, K. A.; Warren, N. J.; Mosadegh, B.; Mohammady, M. R.; Whitesides, G. M.; Armes, S. P. Disulfide-Based Diblock Copolymer Worm Gels: A Wholly-Synthetic Thermoreversible 3D Matrix for Sheet-Based Cultures. Biomacromolecules 2015, 16, 3952– 3958,  DOI: 10.1021/acs.biomac.5b01266
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    Disulfide-based diblock copolymer worm gels: A wholly-synthetic thermoreversible 3D matrix for sheet-based cultures
    Simon, Karen A.; Warren, Nicholas J.; Mosadegh, Bobak; Mohammady, Marym R.; Whitesides, George M.; Armes, Steven P.
    Biomacromolecules (2015), 16 (12), 3952-3958CODEN: BOMAF6; ISSN:1525-7797. (American Chemical Society)
    It is well-known that 3D in vitro cell cultures provide a much better model than 2D cell cultures for understanding the in vivo microenvironment of cells. However, significant tech. challenges in handling and analyzing 3D cell cultures remain, which currently limits their widespread application. Herein, we demonstrate the application of wholly synthetic thermoresponsive block copolymer worms in sheet-based 3D cell culture. These worms form a soft, free-standing gel reversibly at 20-37 °C, which can be rapidly converted into a free-flowing dispersion of spheres on cooling to 5 °C. Functionalization of the worms with disulfide groups was found to be essential for ensuring sufficient mech. stability of these hydrogels to enable long-term cell culture. These disulfide groups are conveniently introduced via statistical copolymn. of a disulfide-based dimethacrylate under conditions that favor intramol. cyclization and subsequent thiol/disulfide exchange leads to the formation of reversible covalent bonds between adjacent worms within the gel. This new approach enables cells to be embedded within micrometer-thick slabs of gel with good viability, permits cell culture for at least 12 days, and facilitates recovery of viable cells from the gel simply by incubating the culture in buffer at 4 °C (thus, avoiding the enzymic degrdn. required for cell harvesting when using com. protein-based gels, such as Matrigel).
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    Canton, I.; Warren, N. J.; Chahal, A.; Amps, K.; Wood, A.; Weightman, R.; Wang, E.; Moore, H.; Armes, S. P. Mucin-Inspired Thermoresponsive Synthetic Hydrogels Induce Stasis in Human Pluripotent Stem Cells and Human Embryos. ACS Cent. Sci. 2016, 2, 65– 74,  DOI: 10.1021/acscentsci.5b00370
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    Mucin-Inspired Thermoresponsive Synthetic Hydrogels Induce Stasis in Human Pluripotent Stem Cells and Human Embryos
    Canton, Irene; Warren, Nicholas J.; Chahal, Aman; Amps, Katherine; Wood, Andrew; Weightman, Richard; Wang, Eugenia; Moore, Harry; Armes, Steven P.
    ACS Central Science (2016), 2 (2), 65-74CODEN: ACSCII; ISSN:2374-7951. (American Chemical Society)
    Human pluripotent stem cells (hPSCs; both embryonic and induced pluripotent) rapidly proliferate in adherent culture to maintain their undifferentiated state. However, for mammals exhibiting delayed gestation (diapause), mucin-coated embryos can remain dormant for days or months in utero, with their constituent PSCs remaining pluripotent under these conditions. Here we report cellular stasis for both hPSC colonies and preimplantation embryos immersed in a wholly synthetic thermoresponsive gel comprising poly(glycerol monomethacrylate)-poly(2-hydroxypropyl methacrylate) [PGMA55-PHPMA135] diblock copolymer worms. This hydroxyl-rich mucin-mimicking nonadherent 3D gel maintained PSC viability and pluripotency in the quiescent G0 state without passaging for at least 14 days. Similarly, gel-coated human embryos remain in a state of suspended animation (diapause) for up to 8 days. The discovery of a cryptic cell arrest mechanism for both hPSCs and embryos suggests an important connection between the cellular mechanisms that evoke embryonic diapause and pluripotency. Moreover, such synthetic worm gels offer considerable utility for the short-term (weeks) storage of either pluripotent stem cells or human embryos without cryopreservation.
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    Sponchioni, M.; O’Brien, C. T.; Borchers, C.; Wang, E.; Rivolta, M. N.; Penfold, N. J. W.; Canton, I.; Armes, S. P. Probing the Mechanism for Hydrogel-Based Stasis Induction in Human Pluripotent Stem Cells: Is the Chemical Functionality of the Hydrogel Important?. Chem. Sci. 2020, 11, 232– 240,  DOI: 10.1039/C9SC04734D
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    Probing the mechanism for hydrogel-based stasis induction in human pluripotent stem cells: is the chemical functionality of the hydrogel important
    Sponchioni, M.; O'Brien, C. T.; Borchers, C.; Wang, E.; Rivolta, M. N.; Penfold, N. J. W.; Canton, I.; Armes, S. P.
    Chemical Science (2020), 11 (1), 232-240CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
    It is well-known that pluripotent human embryonic stem cells (hPSC) can differentiate into any cell type. Recently, we reported that hPSC colonies enter stasis when immersed in an extremely soft hydrogel comprising hydroxyl-functional block copolymer worms (I. Canton, N. J. Warren, A. Chahal, K. Amps, A. Wood, R. Weightman, E. Wang, H. Moore and S. P. Armes, ACS Centr. Sci., 2016, 2, 65-74). The gel modulus and chem. structure of this synthetic hydrogel are similar to that of natural mucins, which are implicated in the mechanism of diapause for mammalian embryos. Does stasis induction occur merely because of the very soft nature of such hydrogels or does chem. functionality also play a role Herein, we address this key question by designing a new hydrogel of comparable softness in which the PGMA stabilizer chains are replaced with non-hydroxylated poly(ethylene glycol) [PEG]. Immunolabeling studies confirm that hPSC colonies immersed in such PEG-based hydrogels do not enter stasis but instead proliferate (and differentiate if no adhesion substrate is present). However, pluripotency is retained if an appropriate adhesion substrate is provided. Thus, the chem. functionality of the hydrogel clearly plays a decisive role in the stasis induction mechanism.
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  99. 99
    Gibson, R. R.; Armes, S. P.; Musa, O. M.; Fernyhough, A. End-Group Ionisation Enables the Use of Poly(N -(2-Methacryloyloxy)Ethyl Pyrrolidone) as an Electrosteric Stabiliser Block for Polymerisation-Induced Self-Assembly in Aqueous Media. Polym. Chem. 2019, 10, 1312– 1323,  DOI: 10.1039/C8PY01619D
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    End-group ionisation enables the use of poly(N-(2-methacryloyloxy)ethyl pyrrolidone) as an electrosteric stabiliser block for polymerisation-induced self-assembly in aqueous media
    Gibson, R. R.; Armes, S. P.; Musa, O. M.; Fernyhough, A.
    Polymer Chemistry (2019), 10 (11), 1312-1323CODEN: PCOHC2; ISSN:1759-9962. (Royal Society of Chemistry)
    A series of near-monodisperse poly(N-2-(methacryloyloxy)ethyl pyrrolidone) (PNMEP) homopolymers was prepd. via reversible addn.-fragmentation chain transfer (RAFT) soln. polymn. of NMEP in ethanol at 70°C using a carboxylic acid-functional RAFT agent. The mean degree of polymn. (DP) was varied from 19 to 89 and acid titrn. indicated end-group pKa values of 5.07-5.44. Turbidimetry studies indicated that homopolymer cloud points were significantly higher at pH 7 (anionic carboxylate) than at pH 3 (neutral carboxylic acid). Moreover, this enhanced hydrophilic character enabled PNMEP to be used as a steric stabilizer for aq. polymn.-induced self-assembly (PISA) syntheses. Thus, a PNMEP42 precursor was chain-extended via RAFT aq. dispersion polymn. of 2-hydroxypropyl methacrylate (HPMA) at 44°C. A series of PNMEP42-PHPMAx diblock copolymers were synthesized using this protocol, with target PHPMA DPs of 150 to 400. High conversions were achieved and a linear evolution in Mn with increasing PHPMA DP was obsd. Dynamic light scattering (DLS) and transmission electron microscopy (TEM) studies confirmed a spherical morphol. in all cases. The nanoparticles flocculated either below pH 4.5 (owing to protonation) or on addn. of 60 mM KCl (as a result of charge screening). Thus the anionic end-groups on the PNMEP stabilizer chains make an important contribution to the overall colloidal stability. Similarly, a PNMEP53 macro-CTA was chain-extended via RAFT aq. emulsion polymn. of 2-ethoxyethyl methacrylate (EEMA) at 44°C. Again, a neutral soln. pH was crit. for the synthesis of colloidally stable nanoparticles. High conversions were achieved as the target PEEMA DP was varied between 100 and 600 and a linear evolution in mol. wt. with PEEMA DP was confirmed by chloroform GPC studies. DLS expts. indicated a monotonic increase in nanoparticle diam. with PEEMA DP and TEM studies confirmed a spherical morphol. in each case. In summary, PNMEP can be used as a water-sol. steric stabilizer for aq. PISA syntheses provided that it contains an anionic carboxylate end-group to enhance its hydrophilic character.
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    Penfold, N. J. W.; Whatley, J. R.; Armes, S. P. Thermoreversible Block Copolymer Worm Gels Using Binary Mixtures of PEG Stabilizer Blocks. Macromolecules 2019, 52, 1653– 1662,  DOI: 10.1021/acs.macromol.8b02491
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    100
    Thermoreversible Block Copolymer Worm Gels Using Binary Mixtures of PEG Stabilizer Blocks
    Penfold, Nicholas J. W.; Whatley, Jessica R.; Armes, Steven P.
    Macromolecules (Washington, DC, United States) (2019), 52 (4), 1653-1662CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    Two trithiocarbonate-based poly(ethylene glycol) (PEG) macromol. chain transfer agents (macro-CTAs) with mean ds.p. of 45 and 113 were prepd. with ≥94% chain-end functionality. Binary mixts. of these PEG-trithiocarbonate macro-CTAs were then chain-extended via reversible addn.-fragmentation chain transfer (RAFT) aq. dispersion polymn. of 2-hydroxypropyl methacrylate (HPMA). Systematic variation of the relative proportions of PEG45 and PEG113 macro-CTAs and the d.p. of the PHPMA core-forming block resulted in the formation of [x PEG45 + z PEG113] - PHPMAn block copolymer spheres, worms, or vesicles, where x and z represent the mole fractions of PEG45 and PEG113, resp. A phase diagram was constructed to establish the relationship between block copolymer compn. and nanoparticle morphol. The thermoresponsive behavior of block copolymer worms was assessed by visual inspection, dynamic light scattering (DLS), transmission electron microscopy (TEM) and temp.-dependent oscillatory rheol. Increasing the proportion of PEG45 (x = 0.00-0.40) in the stabilizer block resulted in a moderate increase in worm gel strength, but cooling resulted in irreversible degelation owing to a worm-to-sphere morphol. transition. However, the phase diagram enabled identification of a single diblock copolymer compn. that exhibited reversible degelation behavior in pure water. This formulation was then further optimized to exhibit the same rheol. behavior in a com. cell culture medium (Nutristem) by fixing the PEG mole fraction at x = 0.70 while lowering the PHPMA DP from 115 to 75. Importantly, the gel strength at physiol. temp. can be readily tuned simply by variation of the copolymer concn. In principle, this study has important implications for the preservation of human stem cells, which can enter stasis when immersed in certain worm gels [see: Canton et al. ACS Cent. Sci.2016, 2, 65-74].
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    Canning, S. L.; Cunningham, V. J.; Ratcliffe, L. P. D.; Armes, S. P. Phenyl Acrylate Is a Versatile Monomer for the Synthesis of Acrylic Diblock Copolymer Nano-Objects via Polymerization-Induced Self-Assembly. Polym. Chem. 2017, 8, 4811– 4821,  DOI: 10.1039/C7PY01161J
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    Phenyl acrylate is a versatile monomer for the synthesis of acrylic diblock copolymer nano-objects via polymerization-induced self-assembly
    Canning, S. L.; Cunningham, V. J.; Ratcliffe, L. P. D.; Armes, S. P.
    Polymer Chemistry (2017), 8 (33), 4811-4821CODEN: PCOHC2; ISSN:1759-9962. (Royal Society of Chemistry)
    Over the last decade or so, polymn.-induced self-assembly (PISA) has become widely recognized as a versatile technique for the rational synthesis of diblock copolymer nano-objects in the form of concd. dispersions. However, there are relatively few examples of acrylic-based PISA formulations in the literature, partly because such copolymers typically possess relatively low glass transition temps. (Tg) that preclude morphol. characterization by transmission electron microscopy. To address this problem, authors have selected Ph acrylate (PhA) as a model monomer to generate the solvophobic block in three PISA formulations using reversible addn.-fragmentation chain transfer (RAFT) polymn. Thus, a poly(di-Me acrylamide)-based chain transfer agent (CTA) is chain-extended using PhA via RAFT aq. emulsion polymn. to produce a series of well-defined sterically-stabilized spheres whose mean diam. can be readily adjusted from 38 nm to 188 nm by varying the target d.p. (DP). In contrast, RAFT alc. dispersion polymn. of PhA using a poly(acrylic acid) CTA leads to an evolution of copolymer morphol. from spheres to worms to lamellae and finally vesicles as the target DP of the structure-directing PPhA block is increased. Similarly, RAFT dispersion polymn. of PhA in n-heptane also produces spheres, worms or vesicles depending on the target DP of the PPhA block. 1H NMR studies indicate that >98% PhA conversion is achieved in all cases, while GPC anal. indicates high blocking efficiencies. However, relatively broad mol. wt. distributions are obsd. (Mw/Mn = 1.37 to 2.48), which suggests extensive chain transfer to polymer in such PISA syntheses, particularly in the case of the RAFT aq. emulsion polymn. formulation. Nevertheless, the relatively high Tg of PPhA (50 °C) enables characterization of the various copolymer morphologies using conventional TEM.
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    Basham, M.; Filik, J.; Wharmby, M. T.; Chang, P. C. Y.; El Kassaby, B.; Gerring, M.; Aishima, J.; Levik, K.; Pulford, B. C. A.; Sikharulidze, I.; Sneddon, D.; Webber, M.; Dhesi, S. S.; Maccherozzi, F.; Svensson, O.; Brockhauser, S.; Náray, G.; Ashton, A. W. Data Analysis WorkbeNch (DAWN). J. Synchrotron Radiat. 2015, 22, 853– 858,  DOI: 10.1107/S1600577515002283
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    Data Analysis WorkbeNch (DAWN)
    Basham Mark; Filik Jacob; Wharmby Michael T; Chang Peter C Y; El Kassaby Baha; Gerring Matthew; Aishima Jun; Levik Karl; Pulford Bill C A; Sikharulidze Irakli; Sneddon Duncan; Webber Matthew; Dhesi Sarnjeet S; Maccherozzi Francesco; Ashton Alun W; Svensson Olof; Brockhauser Sandor; Naray Gabor
    Journal of synchrotron radiation (2015), 22 (3), 853-8 ISSN:.
    Synchrotron light source facilities worldwide generate terabytes of data in numerous incompatible data formats from a wide range of experiment types. The Data Analysis WorkbeNch (DAWN) was developed to address the challenge of providing a single visualization and analysis platform for data from any synchrotron experiment (including single-crystal and powder diffraction, tomography and spectroscopy), whilst also being sufficiently extensible for new specific use case analysis environments to be incorporated (e.g. ARPES, PEEM). In this work, the history and current state of DAWN are presented, with two case studies to demonstrate specific functionality. The first is an example of a data processing and reduction problem using the generic tools, whilst the second shows how these tools can be targeted to a specific scientific area.
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This article is cited by 13 publications.

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  2. Nicola Migliore, Aleksander Guzik, Marc C. A. Stuart, Marc Palà, Adrian Moreno, Gerard Lligadas, Patrizio Raffa. Lactic Acid-Derived Copolymeric Surfactants with Monomer Distribution Profile-Dependent Solution and Thermoresponsive Properties. ACS Sustainable Chemistry & Engineering 2022, 10 (45) , 14806-14816. https://doi.org/10.1021/acssuschemeng.2c04354
  3. Linlin Fan, Zhong Zeng, Ruixue Zhu, Aiping Liu, Hailong Che, Meng Huo. Polymerization-Induced Self-Assembly Toward Micelle-Crosslinked Tough and Ultrastretchable Hydrogels. Chemistry of Materials 2022, 34 (14) , 6408-6419. https://doi.org/10.1021/acs.chemmater.2c01001
  4. Saul J. Hunter, Nicholas J. W. Penfold, Elizabeth R. Jones, Thomas Zinn, Oleksandr O. Mykhaylyk, Steven P. Armes. Synthesis of Thermoresponsive Diblock Copolymer Nano-Objects via RAFT Aqueous Emulsion Polymerization of Hydroxybutyl Methacrylate. Macromolecules 2022, 55 (8) , 3051-3062. https://doi.org/10.1021/acs.macromol.2c00379
  5. Juliana M. Cumming, Oliver J. Deane, Steven P. Armes. Reversible Addition-Fragmentation Chain Transfer Aqueous Dispersion Polymerization of 4-Hydroxybutyl Acrylate Produces Highly Thermoresponsive Diblock Copolymer Nano-Objects. Macromolecules 2022, 55 (3) , 788-798. https://doi.org/10.1021/acs.macromol.1c02431
  6. Djallal Ikkene, Jean-Luc Six, Khalid Ferji. Progress in aqueous dispersion RAFT PISA. European Polymer Journal 2023, 188 , 111848. https://doi.org/10.1016/j.eurpolymj.2023.111848
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  • Abstract

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    Scheme 1

    Scheme 1. Two-Step One-Pot Synthesis of PNAEP85-PHBAx Diblock Copolymer Nano-Objects via RAFT Aqueous Dispersion Polymerization of HBA at 30 °C Using a [PNAEP85]/[KPS] Molar Ratio of 5.0 and a [KPS]/[AsAc] Molar Ratio of 1.0 [N.B. “KPS” Denotes K2S2O8 and “AsAc” Denotes Ascorbic Acid]
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    Scheme 2

    Scheme 2. Intermolecular Crosslinking of PHBA Chains within PNAEP85-PHBAx Diblock Copolymer Nano-Objects (In This Case, Spheres) via Acid-Catalyzed Nucleophilic Attack of Pendent Hydroxyl Groups by Glutaraldehyde (GA)a
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    aThis enabled a range of PNAEP85-PHBAx nano-objects to be covalently stabilized under various conditions (e.g., pH 3–7, 11–41 °C).

    Figure 1

    Figure 1. Representative TEM images recorded for: (a) GA-crosslinked PNAEP85-PHBA170 spheres prepared at 10% w/w; (b) GA-crosslinked PNAEP85-PHBA340 worms prepared at 20% w/w; and (c) GA-crosslinked PNAEP85-PHBA530 vesicles prepared at 5% w/w. (d) Pseudo-phase diagram constructed for PNAEP85-PHBAx diblock copolymer nano-objects. S = pure spheres; S + W = a mixed phase comprising spheres and worms; W = pure worms; W + V = a mixed phase comprising worms and vesicles; and V = pure vesicles. Each copolymer morphology was assigned on the basis of TEM analysis of covalently stabilized nano-objects prepared using glutaraldehyde as a crosslinker at pH 3 and 22 °C (GA/HBA molar ratio = 0.66). (e) SAXS patterns (black, blue, and red symbols) and corresponding data fits (solid white lines) obtained for 1.0% w/w aqueous copolymer dispersions of linear PNAEP85-PHBA110 spheres, PNAEP85-PHBA350 worms, and PNAEP85-PHBA450 vesicles (each of these nano-objects was synthesized at 20% w/w solids).

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    Figure 2

    Figure 2. (a) TEM images recorded for PNAEP85-PHBA545 diblock copolymer nano-objects crosslinked using glutaraldehyde at 22 °C for 24 h at pH 7, pH 5 or pH 3. (b) Z-average diameter (blue squares) and ζ-potential (red squares) as a function of dispersion pH recorded for the same PNAEP85-PHBA545 nano-objects, where the anionic character observed above pH 4 is attributed to ionization of the carboxylic acid group located at the end of each PNAEP stabilizer chain.

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    Figure 3

    Figure 3. Apparent degree of hydration of the weakly hydrophobic PHBA block as a function of pH for linear PNAEP85-PHBAx nano-objects at 20 °C as determined by 1H NMR spectroscopy studies. [N.B. 100% hydration corresponds to the actual DP of the PHBA block, as calculated by studies of molecularly dissolved copolymer chains in CD3OD (see Figure S16)].

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    Figure 4

    Figure 4. (a) Variation in z-average diameter (blue circles) and complex viscosity (red squares) with temperature for an aqueous dispersion of linear PNAEP85-PHBA295 nano-objects. DLS studies were conducted on 0.1% w/w aqueous dispersions, while rheological measurements were performed on a 10% w/w aqueous dispersion at an applied strain of 1.0% and an angular frequency of 1.0 rad s–1 during a run starting at 1 °C (15 min was allowed for thermal equilibration at this initial temperature prior to heating). (b) Prior to TEM analysis, 5% w/w aqueous dispersions of PNAEP85-PHBA295 nanoparticles were crosslinked with glutaraldehyde for 24 h at (i) 11 °C, (ii) 23 °C, (iii) 34 °C or (iv) 41 °C. (c) Small-angle X-ray scattering patterns recorded for a 1.0% w/w aqueous dispersion of linear thermoresponsive PNAEP85-PHBA295 nano-objects at 5 °C (black data), 23 °C (blue data), 34 °C (purple data) and 41 °C (red data; red triangle indicates the diffraction peak used to calculate D). The white lines indicate data fits obtained using appropriate scattering models (see the Supporting Information for further details).

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    Figure 5

    Figure 5. Variable temperature complex viscosity measurements for 20% w/w aqueous dispersions of PNAEP85-PHBAx nano-objects at pH 3 using an applied strain of 1.0% and an angular frequency of 1.0 rad s–1: (a) x = 110, (b) x = 200, (c) x = 295, (d) x = 380 and (e) x = 475. Dashed lines indicate the inferred copolymer morphology at specific temperatures (S = spheres, W = worms, V = vesicles and L = lamellae). These assignments are based on the data shown in Figure 4 and are consistent with a recent study by Byard et al. (18) (f) Relationship between the critical temperature (Tc) corresponding to the maximum |η*| and the PHBA DP for the same five aqueous dispersions of PNAEP85-PHBAx nano-objects.

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      There is considerable current interest in polymn.-induced self-assembly (PISA) via reversible addn.-fragmentation chain transfer (RAFT) polymn. as a versatile and efficient route to various types of block copolymer nano-objects. Many successful PISA syntheses have been conducted in water using either RAFT aq. dispersion polymn. or RAFT aq. emulsion polymn. In contrast, this review article is focused on the growing no. of RAFT PISA formulations developed for non-aq. media. A wide range of monomers have been utilized for both the stabilizer and core-forming blocks to produce diblock copolymer nanoparticles in either polar or non-polar media (including supercrit. CO2 and ionic liqs.) via RAFT dispersion polymn. Such nanoparticles possess spherical, worm-like or vesicular morphologies, often with controllable size and functionality. Detailed characterization of such sterically stabilized diblock copolymer dispersions provides important insights into the various morphol. transformations that can occur both during the PISA synthesis and also on subsequent exposure to a suitable external stimulus (e.g. temp.).
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      Boott, C. E.; Gwyther, J.; Harniman, R. L.; Hayward, D. W.; Manners, I. Scalable and Uniform 1D Nanoparticles by Synchronous Polymerization, Crystallization and Self-Assembly. Nat. Chem. 2017, 9, 785– 792,  DOI: 10.1038/nchem.2721
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      Scalable and uniform 1D nanoparticles by synchronous polymerization, crystallization and self-assembly
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      Nature Chemistry (2017), 9 (8), 785-792CODEN: NCAHBB; ISSN:1755-4330. (Nature Publishing Group)
      The prepn. of well-defined nanoparticles based on soft matter, using soln.-processing techniques on a com. viable scale, is a major challenge of widespread importance. Self-assembly of block copolymers in solvents that selectively solvate one of the segments provides a promising route to core-corona nanoparticles (micelles) with a wide range of potential uses. Nevertheless, significant limitations to this approach also exist. For example, the soln. processing of block copolymers generally follows a sep. synthesis step and is normally performed at high diln. Moreover, non-spherical micelles-which are promising for many applications-are generally difficult to access, samples are polydisperse and precise dimensional control is not possible. Here we demonstrate the formation of platelet and cylindrical micelles at concns. up to 25% solids via a one-pot approach-starting from monomers-that combines polymn.-induced and crystn.-driven self-assembly. We also show that performing the procedure in the presence of small seed micelles allows the scalable formation of low dispersity samples of cylindrical micelles of controlled length up to three micrometres.
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      Pushing the Limit of the RAFT Process: Multiblock Copolymers by One-Pot Rapid Multiple Chain Extensions at Full Monomer Conversion
      Gody, Guillaume; Maschmeyer, Thomas; Zetterlund, Per B.; Perrier, Sebastien
      Macromolecules (Washington, DC, United States) (2014), 47 (10), 3451-3460CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      We describe an optimized method to prep. multiblock copolymers. The approach is based on our previously reported use of reversible addn.-fragmentation chain transfer (RAFT) polymn., which here has been optimized into a fast, versatile, efficient, and scalable process. The one-pot, multistep sequential polymn. proceeds in water, to quant. yields (>99%) for each monomer addn., thus circumventing requirements for intermediate purifn., in 2 h of polymn. per block. The optimization of the process is initially demonstrated via the synthesis of a model decablock homopolymer (10 blocks) of 4-acryloylmorpholine with an av. d.p. of 10 for each block (D = 1.15 and livingness >93% for the final polymer). Both the potential and the limitations of this approach are illustrated by the synthesis of more complex high-order multiblock copolymers: a dodecablock copolymer (12 blocks with 4 different acrylamide monomers) with an av. d.p. of 10 for each block and two higher mol. wt. pentablock copolymers (5 blocks with 3 different acrylamide monomers) with an av. d.p. of 100 per block.
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    16. 16
      Lesage de la Haye, J.; Zhang, X.; Chaduc, I.; Brunel, F.; Lansalot, M.; D’Agosto, F. The Effect of Hydrophile Topology in RAFT-Mediated Polymerization-Induced Self-Assembly. Angew. Chem., Int. Ed. 2016, 55, 3739– 3743,  DOI: 10.1002/anie.201511159
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      16
      The Effect of Hydrophile Topology in RAFT-Mediated Polymerization-Induced Self-Assembly
      Lesage de la Haye, Jennifer; Zhang, Xuewei; Chaduc, Isabelle; Brunel, Fabrice; Lansalot, Muriel; D'Agosto, Franck
      Angewandte Chemie, International Edition (2016), 55 (11), 3739-3743CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Polymn.-induced self-assembly (PISA) was employed to compare the self-assembly of different amphiphilic block copolymers. They were obtained by emulsion polymn. of styrene in water using hydrophilic poly(N-acryloylmorpholine) (PNAM)-based macromol. RAFT agents with different structures. An av. of three poly(ethylene glycol acrylate) (PEGA) units were introduced either at the beginning, statistically, or at the end of a PNAM backbone, resulting in formation of nanometric vesicles and spheres from the two former macroRAFT architectures, and large vesicles from the latter. Compared to the spheres obtained with a pure PNAM macroRAFT agent, composite macroRAFT architectures promoted a dramatic morphol. change. The change was induced by the presence of PEGA hydrophilic side-chains close to the hydrophobic polystyrene segment.
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    17. 17
      Penfold, N. J. W.; Yeow, J.; Boyer, C.; Armes, S. P. Emerging Trends in Polymerization-Induced Self-Assembly.. ACS Macro Lett. 2019, 8, 1029– 1054,  DOI: 10.1021/acsmacrolett.9b00464
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      17
      Emerging Trends in Polymerization-Induced Self-Assembly
      Penfold, Nicholas J. W.; Yeow, Jonathan; Boyer, Cyrille; Armes, Steven P.
      ACS Macro Letters (2019), 8 (8), 1029-1054CODEN: AMLCCD; ISSN:2161-1653. (American Chemical Society)
      A review. In this Perspective, we summarize recent progress in polymn.-induced self-assembly (PISA) for the rational synthesis of block copolymer nanoparticles with various morphologies. Much of the PISA literature has been based on thermally initiated reversible addn.-fragmentation chain transfer (RAFT) polymn. Herein, we pay particular attention to alternative PISA protocols, which allow the prepn. of nanoparticles with improved control over copolymer morphol. and functionality. For example, initiation based on visible light, redox chem., or enzymes enables the incorporation of sensitive monomers and fragile biomols. into block copolymer nanoparticles. Furthermore, PISA syntheses and postfunctionalization of the resulting nanoparticles (e.g., crosslinking) can be conducted sequentially without intermediate purifn. by using various external stimuli. Finally, PISA formulations have been optimized via high-throughput polymn. and recently evaluated within flow reactors for facile scale-up syntheses.
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    18. 18
      Byard, S. J.; O’Brien, C. T.; Derry, M. J.; Williams, M.; Mykhaylyk, O. O.; Blanazs, A.; Armes, S. P. Unique Aqueous Self-Assembly Behavior of a Thermoresponsive Diblock Copolymer. Chem. Sci. 2020, 11, 396– 402,  DOI: 10.1039/C9SC04197D
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      18
      Unique aqueous self-assembly behavior of a thermoresponsive diblock copolymer
      Byard, Sarah J.; O'Brien, Cate T.; Derry, Matthew J.; Williams, Mark; Mykhaylyk, Oleksandr O.; Blanazs, Adam; Armes, Steven P.
      Chemical Science (2020), 11 (2), 396-402CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
      It is well-recognized that block copolymer self-assembly in soln. typically produces spheres, worms or vesicles, with the relative vol. fraction of each block dictating the copolymer morphol. Stimulus-responsive diblock copolymers that can undergo either sphere/worm or vesicle/worm transitions are also well-documented. Herein we report a new amphiphilic diblock copolymer that can form spheres, worms, vesicles or lamellae in aq. soln. Such self-assembly behavior is unprecedented for a single diblock copolymer of fixed compn. yet is achieved simply by raising the soln. temp. from 1°C (spheres) to 25°C (worms) to 50°C (vesicles) to 70°C (lamellae). Heating increases the degree of hydration (and hence the effective vol. fraction) of the core-forming block, with this parameter being solely responsible for driving the sphere-to-worm, worm-to-vesicle and vesicle-to-lamellae transitions. The first two transitions exhibit excellent reversibility but the vesicle-to-lamellae transition exhibits hysteresis on cooling. This new thermoresponsive diblock copolymer provides a useful model for studying such morphol. transitions and is likely to be of significant interest for theor. studies.
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    19. 19
      D’Agosto, F.; Rieger, J.; Lansalot, M. RAFT-Mediated Polymerization-Induced Self-Assembly. Angew. Chem., Int. Ed. 2020, 59, 8368– 8392,  DOI: 10.1002/anie.201911758
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      19
      RAFT-Mediated Polymerization-Induced Self-Assembly
      D'Agosto, Franck; Rieger, Jutta; Lansalot, Muriel
      Angewandte Chemie, International Edition (2020), 59 (22), 8368-8392CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
      A review. After a brief history that positions polymn.-induced self-assembly (PISA) in the field of polymer chem., this Review will cover the fundamentals of the PISA mechanism. Furthermore, this Review will also give an overview of some of the features and limitations of RAFT-mediated PISA in terms of the choice of the components involved, the nature of the nanoobjects that can be obtained and how the syntheses can be controlled, as well as some potential applications.
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    20. 20
      Griffith, L. G.; Swartz, M. A. Capturing Complex 3D Tissue Physiology in Vitro. Nat. Rev. Mol. Cell Biol. 2006, 7, 211– 224,  DOI: 10.1038/nrm1858
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      Capturing complex 3D tissue physiology in vitro
      Griffith, Linda G.; Swartz, Melody A.
      Nature Reviews Molecular Cell Biology (2006), 7 (3), 211-224CODEN: NRMCBP; ISSN:1471-0072. (Nature Publishing Group)
      A review. The emergence of tissue engineering raises new possibilities for the study of complex physiol. and pathophysiol. processes in vitro. Many tools are now available to create 3D tissue models in vitro, but the blueprints for what to make have been slower to arrive. The authors discuss here some of the 'design principles' for recreating the interwoven set of biochem. and mech. cues in the cellular microenvironment, and the methods for implementing them. The authors emphasize applications that involve epithelial tissues for which 3D models could explain mechanisms of disease or aid in drug development.
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      Blanazs, A.; Verber, R.; Mykhaylyk, O. O.; Ryan, A. J.; Heath, J. Z.; Douglas, C. W. I.; Armes, S. P. Sterilizable Gels from Thermoresponsive Block Copolymer Worms. J. Am. Chem. Soc. 2012, 134, 9741– 9748,  DOI: 10.1021/ja3024059
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      21
      Sterilizable Gels from Thermoresponsive Block Copolymer Worms
      Blanazs, Adam; Verber, Robert; Mykhaylyk, Oleksandr O.; Ryan, Anthony J.; Heath, Jason Z.; Douglas, C. W. Ian; Armes, Steven P.
      Journal of the American Chemical Society (2012), 134 (23), 9741-9748CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Biocompatible hydrogels have many applications, ranging from contact lenses to tissue engineering scaffolds. In most cases, rigorous sterilization is essential. Herein we show that a biocompatible diblock copolymer forms wormlike micelles via polymn.-induced self-assembly in aq. soln. At a copolymer concn. of 10.0 wt./wt. %, interworm entanglements lead to the formation of a free-standing phys. hydrogel at 21 °C. Gel dissoln. occurs on cooling to 4 °C due to an unusual worm-to-sphere order-order transition, as confirmed by rheol., electron microscopy, variable temp. 1H NMR spectroscopy, and scattering studies. Moreover, this thermo-reversible behavior allows the facile prepn. of sterile gels, since ultrafiltration of the diblock copolymer nanoparticles in their low-viscosity spherical form at 4 °C efficiently removes micrometer-sized bacteria; regelation occurs at 21 °C as the copolymer chains regain their wormlike morphol. Biocompatibility tests indicate good cell viabilities for these worm gels, which suggest potential biomedical applications.
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      Kataoka, K.; Harada, A.; Nagasaki, Y. Block Copolymer Micelles for Drug Delivery: Design, Characterization and Biological Significance. Adv. Drug Delivery Rev. 2001, 47, 113– 131,  DOI: 10.1016/S0169-409X(00)00124-1
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      Block copolymer micelles for drug delivery: design, characterization and biological significance
      Kataoka, K.; Harada, A.; Nagasaki, Y.
      Advanced Drug Delivery Reviews (2001), 47 (1), 113-131CODEN: ADDREP; ISSN:0169-409X. (Elsevier Science Ireland Ltd.)
      A review with 94 refs. Recently, colloidal carrier systems have been receiving much attention in the field of drug targeting because of their high loading capacity for drugs as well as their unique disposition characteristics in the body. This paper highlights the utility of polymeric micelles formed through the multimol. assembly of block copolymers as novel core-shell typed colloidal carriers for drug and gene targeting. The process of micellization in aq. milieu is described in detail based on differences in the driving force of core segregation, including hydrophobic interaction, electrostatic interaction, metal complexation, and hydrogen bonding of constituent block copolymers. The segregated core embedded in the hydrophilic palisade is shown to function as a reservoir for genes, enzymes, and a variety of drugs with diverse characteristics. Functionalization of the outer surface of the polymeric micelle to modify its physicochem. and biol. properties is reviewed from the standpoint of designing micellar carrier systems for receptor-mediated drug delivery. Further, the distribution of polymeric micelles is described to demonstrate their long-circulating characteristics and significant tumor accumulation, emphasizing their promising utility in tumor-targeting therapy. As an important perspective on carrier systems based on polymeric micelles, their feasibility as non-viral gene vectors is also summarized in this review article.
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      Kabanov, A. V.; Batrakova, E. V.; Alakhov, V. Y. Pluronic Block Copolymers as Novel Polymer Therapeutics for Drug and Gene Delivery. J. Controlled Release 2002, 82, 189– 212,  DOI: 10.1016/S0168-3659(02)00009-3
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      Pluronic block copolymers as novel polymer therapeutics for drug and gene delivery
      Kabanov, Alexander V.; Batrakova, Elena V.; Alakhov, Valery Yu.
      Journal of Controlled Release (2002), 82 (2-3), 189-212CODEN: JCREEC; ISSN:0168-3659. (Elsevier Science Ltd.)
      A review. Pluronic block copolymers are found to be an efficient drug delivery system with multiple effects. The incorporation of drugs into the core of the micelles formed by Pluronic results in increased soly., metabolic stability and circulation time for the drug. The interactions of the Pluronic unimers with multidrug-resistant cancer cells result in sensitization of these cells with respect to various anticancer agents. Furthermore, the single mol. chains of copolymer, unimers, inhibit drug efflux transporters in both the blood-brain barrier and in the small intestine, which provides for the enhanced transport of select drugs to the brain and increases oral bioavailability. These and other applications of Pluronic block copolymers in various drug delivery and gene delivery systems are considered.
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      Rodriguez-Hernandez, J.; Checot, F.; Gnanou, Y.; Lecommandoux, S. Toward ‘Smart’ Nano-Objects by Self-Assembly of Block Copolymers in Solution.. Prog. Polym. Sci. 2005, 30, 691– 724,  DOI: 10.1016/j.progpolymsci.2005.04.002
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      Toward 'smart' nano-objects by self-assembly of block copolymers in solution
      Rodriguez-Hernandez, J.; Checot, F.; Gnanou, Y.; Lecommandoux, S.
      Progress in Polymer Science (2005), 30 (7), 691-724CODEN: PRPSB8; ISSN:0079-6700. (Elsevier B.V.)
      A review describes the most significant developments in the prepn. and characterization of nano-objects. In recent years, the synthesis and anal. of novel copolymer-based nanomaterials in soln. have been extensively pursued. The interest in such structures lies in the fact that their dimensions, in the mesoscopic range (<100 nm), and factors such as compn. or structure lead to materials with singular properties and applications. First, the basic principles of self-assembly and micellization of block copolymers in dil. soln. will be discussed. A review of the methods for stabilization of the macromol. aggregates will be then given, including selected recent examples. Finally, we will conc. on stabilized nanoparticles, so-called 'smart materials' that show responses to environmental changes (pH, temp., ionic-strength, among others), focusing on their applications principally in the biomedical field.
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      Roy, D.; Cambre, J. N.; Sumerlin, B. S. Future Perspectives and Recent Advances in Stimuli-Responsive Materials.. Prog. Polym. Sci. 2010, 35, 278– 301,  DOI: 10.1016/j.progpolymsci.2009.10.008
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      Future perspectives and recent advances in stimuli-responsive materials
      Roy, Debashish; Cambre, Jennifer N.; Sumerlin, Brent S.
      Progress in Polymer Science (2010), 35 (1-2), 278-301CODEN: PRPSB8; ISSN:0079-6700. (Elsevier Ltd.)
      A review. Interest in stimuli-responsive polymers has persisted over many decades, and a great deal of work has been dedicated to developing environmentally sensitive macromols. that can be crafted into new smart materials. However, the overwhelming majority of reports in the literature describe stimuli-responsive polymers that are sensitive to only a few common triggers, including changes in pH, temp., and electrolyte concn. Herein, we aim to highlight recent results and future trends that exploit stimuli that have not yet been as heavily considered, despite their unique potential. Many of the topics represent clear opportunities for making advances in biomedical fields due to their specificity and the ability to respond to stimuli that are inherently present in living systems. Recent results in the area of polymers that respond to specific antigen-antibody interactions, enzymes, and glucose are specifically discussed. Also considered are polymeric systems that respond to light, elec., magnetic, and sonic fields, all of which have potential in the area of controlled release as a result of their ability to be applied in a non-invasive and easily controlled manner. Thiol-responsive and redox-responsive polymers are also highlighted, with particular attention being devoted to their reversible dynamic covalent chem. It is our goal to emphasize these underutilized adaptive behaviors so that novel applications and new generations of smart materials can be realized.
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      Brinkhuis, R. P.; Rutjes, F. P. J. T.; van Hest, J. C. M. Polymeric Vesicles in Biomedical Applications. Polym. Chem. 2011, 2, 1449– 1462,  DOI: 10.1039/c1py00061f
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      Polymeric vesicles in biomedical applications
      Brinkhuis, Rene P.; Rutjes, Floris P. J. T.; van Hest, Jan C. M.
      Polymer Chemistry (2011), 2 (7), 1449-1462CODEN: PCOHC2; ISSN:1759-9962. (Royal Society of Chemistry)
      A review. Polymeric vesicles, or polymersomes, are nano- to micrometer sized polymeric capsules with a bilayered membrane. Applications of these vesicles are foreseen in nanomedicine, in vivo imaging and drug delivery. These applications put many restrictions on the choice of polymer, the size and the surface of the vesicle. In this respect much can be learned and translated to polymersome science from lines of research with a longer history of practical knowledge such as liposomal formulation and polymer drug conjugation. The dimensions of a vesicle, such as size and shape can be controlled for polymersomes and will influence the in vivo circulation time. The surface can be adjusted to induce stealth character, or chem. modified to introduce targeting moieties. And last but not least the choice of block copolymers-the building blocks of a polymersome-can introduce features like biocompatibility, inherent or induced permeability and triggered release. In this review the authors will discuss the recent advances in polymersome science with regard to biomedical applications and will specifically address the abovementioned features which affect their biol. behavior.
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      Blackman, L. D.; Varlas, S.; Arno, M. C.; Fayter, A.; Gibson, M. I.; O’Reilly, R. K. Permeable Protein-Loaded Polymersome Cascade Nanoreactors by Polymerization-Induced Self-Assembly.. ACS Macro Lett 2017, 6, 1263– 1267,  DOI: 10.1021/acsmacrolett.7b00725
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      27
      Permeable Protein-Loaded Polymersome Cascade Nanoreactors by Polymerization-Induced Self-Assembly
      Blackman, Lewis D.; Varlas, Spyridon; Arno, Maria C.; Fayter, Alice; Gibson, Matthew I.; OReilly, Rachel K.
      ACS Macro Letters (2017), 6 (11), 1263-1267CODEN: AMLCCD; ISSN:2161-1653. (American Chemical Society)
      Enzyme loading of polymersomes requires permeability to enable them to interact with the external environment, typically requiring addn. of complex functionality to enable porosity. Herein, we describe a synthetic route toward intrinsically permeable polymersomes loaded with functional proteins using initiator-free visible light-mediated polymn.-induced self-assembly (photo-PISA) under mild, aq. conditions using a com. monomer. Compartmentalization and retention of protein functionality was demonstrated using green fluorescent protein as a macromol. chromophore. Catalytic enzyme-loaded vesicles using horseradish peroxidase and glucose oxidase were also prepd. and the permeability of the membrane toward their small mol. substrates was revealed for the first time. Finally, the interaction of the compartmentalized enzymes between sep. vesicles was validated by means of an enzymic cascade reaction. These findings have a broad scope as the methodol. could be applied for the encapsulation of a large range of macromols. for advancements in the fields of nanotechnol., biomimicry and nanomedicine.
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    28. 28
      Growney, D. J.; Mykhaylyk, O. O.; Armes, S. P. Micellization and Adsorption Behavior of a Near-Monodisperse Polystyrene-Based Diblock Copolymer in Nonpolar Media. Langmuir 2014, 30, 6047– 6056,  DOI: 10.1021/la501084a
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      28
      Micellization and Adsorption Behavior of a Near-Monodisperse Polystyrene-Based Diblock Copolymer in Nonpolar Media
      Growney, David J.; Mykhaylyk, Oleksandr O.; Armes, Steven P.
      Langmuir (2014), 30 (21), 6047-6056CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
      The micellar self-assembly behavior of a near-monodisperse polystyrene-hydrogenated polyisoprene (PS-PEP) diblock copolymer is examd. in non-polar media (either n-heptane or n-dodecane). Direct dissoln. of this diblock copolymer leads to the formation of relatively large polydisperse colloidal aggregates that are kinetically frozen artifacts of the solid-state copolymer morphol. Dynamic light scattering (DLS) and transmission electron microscopy studies indicate that heating such copolymer dispersions up to 90-110 °C leads to a structural rearrangement, with the generation of relatively small, well-defined spherical micelles that persist on cooling to 20 °C. Variable temp. 1H NMR studies using deuterated n-alkanes confirm that partial solvation (plasticization) of the polystyrene micelle cores occurs on heating. This increased mobility of the core-forming polystyrene chains is consistent with the evolution from a kinetically-trapped to a thermodynamically-favored copolymer morphol. via exchange of individual copolymer chains, which are obsd. by DLS. These micellar self-assembly observations are also consistent with small-angle X-ray scattering (SAXS) studies, which indicate the formation of star-like micelles in n-heptane, with a mean polystyrene core diam. of about 20 nm and an overall diam. (core plus corona) of about 80 nm. Micelle dissocn. occurs on addn. of chloroform, which is a good solvent for both blocks. Finally, phys. adsorption of this PS-PEP diblock copolymer onto a model colloidal substrate (carbon black) has been confirmed using XPS. A Langmuir-type adsorption isotherm has been constructed using a supernatant depletion assay based on UV spectroscopy anal. of the arom. chromophore in the polystyrene block. Comparable results were obtained using thermogravimetric anal. to directly det. the amt. of adsorbed copolymer. Based on the max. adsorbed amts. obsd. at 20 °C, these studies strongly suggest that individual PS-PEP copolymer chains adsorb onto carbon black from chloroform, whereas micellar adsorption occurs from n-alkanes.
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    29. 29
      Penfold, N. J. W.; Ning, Y.; Verstraete, P.; Smets, J.; Armes, S. P. Cross-Linked Cationic Diblock Copolymer Worms Are Superflocculants for Micrometer-Sized Silica Particles. Chem. Sci. 2016, 7, 6894– 6904,  DOI: 10.1039/C6SC03732A
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      29
      Crosslinked cationic diblock copolymer worms are superflocculants for micrometer-sized silica particles
      Penfold, Nicholas J. W.; Ning, Yin; Verstraete, Pierre; Smets, Johan; Armes, Steven P.
      Chemical Science (2016), 7 (12), 6894-6904CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
      A series of linear cationic diblock copolymer nanoparticles are prepd. by polymn.-induced self-assembly (PISA) via reversible addn.-fragmentation chain transfer (RAFT) aq. dispersion polymn. of 2-hydroxypropyl methacrylate (HPMA) using a binary mixt. of non-ionic and cationic macromol. RAFT agents, namely poly(ethylene oxide) (PEO113, Mn = 4400 g mol-1; Mw/Mn = 1.08) and poly([2-(methacryloyloxy)ethyl]trimethylammonium chloride) (PQDMA125, Mn = 31 800 g mol-1, Mw/Mn = 1.19). A detailed phase diagram was constructed to det. the max. amt. of PQDMA125 stabilizer block that could be incorporated while still allowing access to a pure worm copolymer morphol. Aq. electrophoresis studies indicated that zeta potentials of +35 mV could be achieved for such cationic worms over a wide pH range. Core crosslinked worms were prepd. via statistical copolymn. of glycidyl methacrylate (GlyMA) with HPMA using a slightly modified PISA formulation, followed by reacting the epoxy groups of the GlyMA residues located within the worm cores with 3-aminopropyl triethoxysilane (APTES), and concomitant hydrolysis/condensation of the pendent silanol groups with the secondary alc. on the HPMA residues. TEM and DLS studies confirmed that such core crosslinked cationic worms remained colloidally stable when challenged with either excess methanol or a cationic surfactant. These crosslinked cationic worms are shown to be much more effective bridging flocculants for 1.0μm silica particles at pH 9 than the corresponding linear cationic worms (and also various com. high mol. wt. water-sol. polymers.). Laser diffraction studies indicated silica aggregates of around 25-28μm diam. when using the former worms but only 3-5μm diam. when employing the latter worms. Moreover, SEM studies confirmed that the crosslinked worms remained intact after their adsorption onto the silica particles, whereas the much more delicate linear worms underwent fragmentation under the same conditions. Similar results were obtained with 4μm silica particles.
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    30. 30
      Chan, D. H. H.; Kynaston, E. L.; Lindsay, C.; Taylor, P.; Armes, S. P. Block Copolymer Nanoparticles Are Effective Dispersant for Micrometer-Sized Organic Crystalline Particles. ACS Appl. Mater. Interfaces 2021, 13, 30235– 30243,  DOI: 10.1021/acsami.1c08261
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      30
      Block Copolymer Nanoparticles are Effective Dispersants for Micrometer-Sized Organic Crystalline Particles
      Chan, Derek H. H.; Kynaston, Emily L.; Lindsay, Christopher; Taylor, Philip; Armes, Steven P.
      ACS Applied Materials & Interfaces (2021), 13 (25), 30235-30243CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
      Well-defined sterically stabilized diblock copolymer nanoparticles of 29 nm diam. are prepd. by RAFT aq. emulsion polymn. of Me methacrylate using a dithiobenzoate-capped poly(glycerol monomethacrylate) precursor. These nanoparticles are evaluated as a dispersant for the prepn. of org. cryst. microparticles via ball milling. This is exemplified for azoxystrobin, which is a broad-spectrum fungicide that is widely used to protect various food crops. Laser diffraction and optical microscopy studies indicate the formation of azoxystrobin microparticles of approx. 2μm diam. after ball milling for 10 min at 400 rpm. Nanoparticle adsorption at the surface of these azoxystrobin microparticles is confirmed by electron microscopy studies. The extent of nanoparticle adsorption on the azoxystrobin microparticles can be quantified using a supernatant assay based on soln. densitometry. This technique indicates an adsorbed amt. of approx. 5.5 mg m-2, which is sufficient to significantly reduce the neg. zeta potential exhibited by azoxystrobin. Moreover, this adsorbed amt. appears to be essentially independent of the nature of the core-forming block, with similar data being obtained for both poly(Me methacrylate)- and poly(2,2,2-trifluoroethyl methacrylate)-based nanoparticles. Finally, XPS studies confirm attenuation of the underlying N1s signal arising from the azoxystrobin microparticles by the former adsorbed nanoparticles, suggesting a fractional surface coverage of approx. 0.24. This value is consistent with a theor. surface coverage of 0.25 calcd. from the adsorption isotherm data. Overall, this study suggests that sterically stabilized diblock copolymer nanoparticles may offer a useful alternative approach to traditional sol. copolymer dispersants for the prepn. of suspension concs. affecting the context of agrochem. applications.
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    31. 31
      Derry, M. J.; Fielding, L. A.; Armes, S. P. Industrially-Relevant Polymerization-Induced Self-Assembly Formulations in Non-Polar Solvents: RAFT Dispersion Polymerization of Benzyl Methacrylate. Polym. Chem. 2015, 6, 3054– 3062,  DOI: 10.1039/C5PY00157A
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      Industrially-relevant polymerization-induced self-assembly formulations in non-polar solvents: RAFT dispersion polymerization of benzyl methacrylate
      Derry, Matthew J.; Fielding, Lee A.; Armes, Steven P.
      Polymer Chemistry (2015), 6 (16), 3054-3062CODEN: PCOHC2; ISSN:1759-9962. (Royal Society of Chemistry)
      Industrially-sourced mineral oil and a poly(α-olefin) were used as solvents for the reversible addn.-fragmentation chain transfer (RAFT) dispersion polymn. of benzyl methacrylate (BzMA) using a poly(lauryl methacrylate) macromol. chain transfer agent (PLMA macro-CTA) at 90 °C. The insoly. of the growing PBzMA chains under such conditions leads to polymn.-induced self-assembly (PISA), whereby poly(lauryl methacrylate)-poly(benzyl methacrylate) (PLMA-PBzMA) diblock copolymer spheres, worms or vesicles were produced directly as concd. dispersions. The particular diblock copolymer compn. required to access each individual morphol. depends on the nature of the oil. Moreover, the solvent type also affects important properties of the phys. free-standing gels that are formed by the PLMA-PBzMA worm dispersions, including the storage modulus (G'), crit. gelation temp. (CGT) and crit. gelation concn. (CGC). Spherical PLMA-PBzMA diblock copolymer nanoparticles can be prepd. at up to 50% wt./wt. solids and an efficient 'one-pot' protocol involving soln. polymn. of LMA followed immediately by dispersion polymn. of BzMA was developed. The latter formulation enables high BzMA conversions to be achieved, with spherical nanoparticles being produced at 30% wt./wt. solids.
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    32. 32
      Perrier, S.; Takolpuckdee, P. Macromolecular Design via Reversible Addition-Fragmentation Chain Transfer (RAFT)/Xanthates (MADIX) Polymerization.. J. Polym. Sci., Part A: Polym. Chem. 2005, 43, 5347– 5393,  DOI: 10.1002/pola.20986
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      Macromolecular design via reversible addition-fragmentation chain transfer (RAFT)/xanthates (MADIX) polymerization
      Perrier, Sebastien; Takolpuckdee, Pittaya
      Journal of Polymer Science, Part A: Polymer Chemistry (2005), 43 (22), 5347-5393CODEN: JPACEC; ISSN:0887-624X. (John Wiley & Sons, Inc.)
      A review highlighting the progress made in RAFT/MADIX polymn. since the first report in 1998. Among the living radical polymn. techniques, reversible addn.-fragmentation chain transfer (RAFT) and macromol. design via the interchange of xanthates (MADIX) polymns. appear to be the most versatile processes in terms of the reaction conditions, the variety of monomers for which polymn. can be controlled, tolerance to functionalities, and the range of polymeric architectures that can be produced. It addresses, in turn, the mechanism and kinetics of the process, examines the various components of the system, including the synthesis paths of the thiocarbonyl-thio compds. used as chain-transfer agents, and the conditions of polymn., and gives an account of the wide range of monomers that were successfully polymd. to date, and the various polymeric architectures that were produced. In the last section, this review describes the future challenges that the process will face and shows its opening to a wider scientific community as a synthetic tool for the prodn. of functional macromols. and materials.
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      Sugihara, S.; Blanazs, A.; Armes, S. P.; Ryan, A. J.; Lewis, A. L. Aqueous Dispersion Polymerization: A New Paradigm for in Situ Block Copolymer Self-Assembly in Concentrated Solution. J. Am. Chem. Soc. 2011, 133, 15707– 15713,  DOI: 10.1021/ja205887v
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      Aqueous Dispersion Polymerization: A New Paradigm for in Situ Block Copolymer Self-Assembly in Concentrated Solution
      Sugihara, Shinji; Blanazs, Adam; Armes, Steven P.; Ryan, Anthony J.; Lewis, Andrew L.
      Journal of the American Chemical Society (2011), 133 (39), 15707-15713CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Reversible addn.-fragmentation chain transfer polymn. has been utilized to polymerize 2-hydroxypropyl methacrylate (HPMA) using a water-sol. macromol. chain transfer agent based on poly(2-(methacryloyloxy)ethylphosphorylcholine) (PMPC). A detailed phase diagram has been elucidated for this aq. dispersion polymn. formulation that reliably predicts the precise block compns. assocd. with well-defined particle morphologies (i.e., pure phases). Unlike the ad hoc approaches described in the literature, this strategy enables the facile, efficient, and reproducible prepn. of diblock copolymer spheres, worms, or vesicles directly in concd. aq. soln. Chain extension of the highly hydrated zwitterionic PMPC block with HPMA in water at 70° produces a hydrophobic poly(2-hydroxypropyl methacrylate) (PHPMA) block, which drives in situ self-assembly to form well-defined diblock copolymer spheres, worms, or vesicles. The final particle morphol. obtained at full monomer conversion is dictated by (i) the target d.p. of the PHPMA block and (ii) the total solids concn. at which the HPMA polymn. is conducted. Moreover, if the targeted diblock copolymer compn. corresponds to vesicle phase space at full monomer conversion, the in situ particle morphol. evolves from spheres to worms to vesicles during the in situ polymn. of HPMA. In the case of PMPC25-PHPMA400 particles, this systematic approach allows the direct, reproducible, and highly efficient prepn. of either block copolymer vesicles at up to 25% solids or well-defined worms at 16-25% solids in aq. soln.
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      Zhang, X.; Boissé, S.; Zhang, W.; Beaunier, P.; D’Agosto, F.; Rieger, J.; Charleux, B. Well-Defined Amphiphilic Block Copolymers and Nano-Objects Formed in Situ via RAFT-Mediated Aqueous Emulsion Polymerization. Macromolecules 2011, 44, 4149– 415,  DOI: 10.1021/ma2005926
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      Well-Defined Amphiphilic Block Copolymers and Nano-objects Formed in Situ via RAFT-Mediated Aqueous Emulsion Polymerization
      Zhang, Xuewei; Boisse, Stephanie; Zhang, Wenjing; Beaunier, Patricia; D'Agosto, Franck; Rieger, Jutta; Charleux, Bernadette
      Macromolecules (Washington, DC, United States) (2011), 44 (11), 4149-4158CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      A hydrophilic poly(methacrylic acid-co-poly(ethylene oxide) Me ether methacrylate) copolymer with a trithiocarbonate reactive group was used in the free-radical, batch emulsion polymn. of styrene. It allowed fast polymns. and high final conversions to be achieved, and the parameters for a good control over the formation of well-defined amphiphilic diblock copolymers were identified. These diblock copolymers self-assembled in situ into nano-objects of various morphologies upon chain extension. Achieving a good control over the formed diblock copolymers was an important step toward a better understanding of the parameters that affect the shape and size of the self-assembled objects, the ultimate goal being the ability to predict and fine-tune them on purpose.
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      Karagoz, B.; Esser, L.; Duong, H. T.; Basuki, J. S.; Boyer, C.; Davis, T. P. Polymerization-Induced Self-Assembly (PISA)—Control over the Morphology of Nanoparticles for Drug Delivery Applications. Polym. Chem. 2014, 5, 350– 355,  DOI: 10.1039/C3PY01306E
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      Polymerization-Induced Self-Assembly (PISA) - control over the morphology of nanoparticles for drug delivery applications
      Karagoz, Bunyamin; Esser, Lars; Duong, Hien T.; Basuki, Johan S.; Boyer, Cyrille; Davis, Thomas P.
      Polymer Chemistry (2014), 5 (2), 350-355CODEN: PCOHC2; ISSN:1759-9962. (Royal Society of Chemistry)
      In this paper, we describe the synthesis of asym. functional POEGMA-b-P(ST-co-VBA) copolymers in methanol, yielding in one-pot polymn. a range of nanoparticle morphologies, including spherical micelles, worm-like, rod-like micelles and vesicles. The presence of the aldehyde group was then exploited to form crosslinks or to conjugate chemotherapy compds., such as doxorubicin, via pH-breakable bonds (Schiff base or imine) directly to the preformed nanoparticles. The influence of the nanoparticle morphologies on the MCF-7 breast cancer cell line uptake was investigated using flow cytometry and confocal microscopy. Finally, the IC50 of DOX, following nanoparticle delivery, was studied showing significant influence of the nanoparticle carrier morphol. on therapeutic efficacy for breast cancer.
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      Tan, J.; Sun, H.; Yu, M.; Sumerlin, B. S.; Zhang, L. Photo-PISA: Shedding Light on Polymerization-Induced Self-Assembly. ACS Macro Lett. 2015, 4, 1249– 1253,  DOI: 10.1021/acsmacrolett.5b00748
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      Photo-PISA: Shedding Light on Polymerization-Induced Self-Assembly
      Tan, Jianbo; Sun, Hao; Yu, Mingguang; Sumerlin, Brent S.; Zhang, Li
      ACS Macro Letters (2015), 4 (11), 1249-1253CODEN: AMLCCD; ISSN:2161-1653. (American Chemical Society)
      Herein we report an aq. photoinitiated polymn.-induced self-assembly (photo-PISA) for the prepn. of a remarkably diverse set of complex polymer nanoparticle morphologies (e.g., spheres, worms, and vesicles) at room temp. Ultrafast polymn. rates were achieved, with near quant. monomer conversion within 15 min of visible light irradn. An important feature of the photo-PISA is that diblock copolymer vesicles can be prepd. under mild conditions (room temp., aq. medium, visible light), which will be important for the prepn. of functional vesicles loaded with biorelated species (e.g., proteins). As a proof of concept, silica nanoparticles and bovine serum albumin (BSA) were encapsulated in situ within vesicles via the photo-PISA process.
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      Jiang, Y.; Xu, N.; Han, J.; Yu, Q.; Guo, L.; Gao, P.; Lu, X.; Cai, Y. The Direct Synthesis of Interface-Decorated Reactive Block Copolymer Nanoparticles via Polymerisation-Induced Self-Assembly. Polym. Chem. 2015, 6, 4955– 4965,  DOI: 10.1039/C5PY00656B
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      The direct synthesis of interface-decorated reactive block copolymer nanoparticles via polymerisation-induced self-assembly
      Jiang, Yanyan; Xu, Na; Han, Jie; Yu, Qiuping; Guo, Lei; Gao, Pan; Lu, Xinhua; Cai, Yuanli
      Polymer Chemistry (2015), 6 (27), 4955-4965CODEN: PCOHC2; ISSN:1759-9962. (Royal Society of Chemistry)
      Self-assembly of amphiphilic block copolymers in water suffers from the undesired encapsulation of hydrophobic reactive motifs in a core-forming block, which deteriorates their performance as aq. catalysts. This problem can be circumvented by polymn.-induced self-assembly (PISA). Herein, we report a new strategy for one-pot synthesis of reactive block copolymer nanoparticles whose hydrophobic reactive motifs decorate the surrounding core-shell interfaces. We demonstrate fast RAFT aq. dispersion polymn. of a com. available specialty monomer, diacetone acrylamide (DAAM), under visible light irradn. at 25°C. PISA is induced by polymn. via sequential dehydration, phase sepn. and reaction acceleration, thus achieving complete conversion in 30 min. The replacement of minimal DAAM by an NH3+-monomer induces slight hydration of the core-forming block, and thus a low polydispersity of the resulting statistic-block copolymer. Moreover, simultaneous in situ self-assembly and chain growth favor the adjustment of newly-added NH3+-units outward to core-shell interfaces while the major DAAM units collapse into hydrophobic PISA-cores. Both lead to timely and selective self-assembly into the new reactive nanoparticles whose NH3+-motifs decorate the surrounding core-shell interfaces. These nanoparticles are well-suited for fabrication of advanced nanoreactors whose hydrophobic dative metal centers decorate the surrounding interfaces via simultaneous imine conversion and Zn(II)-coordination. Such PISA-nanostructures endow hydrophobic metal centers with a huge and accessible sp. surface area and are stabilized by water-sol. shells. Therefore, this strategy holds fascinating potential for the fabrication of metalloenzyme-inspired aq. catalysts.
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      Zhou, D.; Dong, S.; Kuchel, R. P.; Perrier, S.; Zetterlund, P. B. Polymerization Induced Self-Assembly: Tuning of Morphology Using Ionic Strength and PH. Polym. Chem. 2017, 8, 3082– 3089,  DOI: 10.1039/C7PY00552K
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      Polymerization induced self-assembly: tuning of morphology using ionic strength and pH
      Zhou, Dewen; Dong, Siming; Kuchel, Rhiannon P.; Perrier, Sebastien; Zetterlund, Per B.
      Polymer Chemistry (2017), 8 (20), 3082-3089CODEN: PCOHC2; ISSN:1759-9962. (Royal Society of Chemistry)
      Investigations of RAFT dispersion polymn.-induced self-assembly (PISA) of 2-hydroxypropyl methacrylate (HPMA) in water/methanol at 60 °C using a cationically charged macroRAFT agent as the stabilizer block, namely P(N,N-diethylaminoethyl methacrylate)-stat-poly((ethylene glycol) Me ether methacrylate) (PDEAEMA-stat-PEGMA), have been conducted with a view to tune particle morphologies by manipulation of the pH and the ionic strength. Above the LCST (45 °C) of (PDEAEMA-stat-PEGMA), the system can only be conducted as a dispersion polymn. at sufficiently low pH such that the stabilizer block is sufficiently protonated to ensure soly. in the continuous phase. It is demonstrated (reported in the form of an extensive morphol. diagram) that a range of morphologies including spherical particles, rods and vesicles can be accessed by adjustment of the pH (via addn. of HCl) and the ionic strength (via the concn. of NaCl). A decrease in the charge d. of the coronal stabilizer layer via an increase in the pH (less protonation) shifts the system towards higher order morphologies. At a given pH, an increase in ionic strength leads to more extensive charge screening, thus allowing formation of higher order morphologies.
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      Perrier, S. 50th Anniversary Perspective: RAFT Polymerization—A User Guide. Macromolecules 2017, 50, 7433– 7447,  DOI: 10.1021/acs.macromol.7b00767
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      50th Anniversary Perspective: RAFT Polymerization-A User Guide
      Perrier, Sebastien
      Macromolecules (Washington, DC, United States) (2017), 50 (19), 7433-7447CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      A review. This Perspective summarizes the features and limitations of reversible addn.-fragmentation chain transfer (RAFT) polymn., highlighting its strengths and weaknesses, as our understanding of the process, from both a mechanistic and an application point of view, has matured over the past 20 years. It is aimed at both experts in the field and newcomers, including undergraduate and postgraduate students, as well as nonexperts in polymn. who are interested in developing their own polymeric structures by exploiting the simple setup of a RAFT polymn.
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      Khor, S. Y.; Quinn, J. F.; Whittaker, M. R.; Truong, N. P.; Davis, T. P. Controlling Nanomaterial Size and Shape for Biomedical Applications via Polymerization-Induced Self-Assembly. Macromol. Rapid Commun. 2019, 40, 1800438  DOI: 10.1002/marc.201800438
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      Moad, G.; Rizzardo, E.; Thang, S. H. Living Radical Polymerization by the RAFT Process—A First Update. Aust. J. Chem. 2006, 59, 669– 692,  DOI: 10.1071/CH06250
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      Living radical polymerization by the RAFT process-A first update
      Moad, Graeme; Rizzardo, Ezio; Thang, San H.
      Australian Journal of Chemistry (2006), 59 (10), 669-692CODEN: AJCHAS; ISSN:0004-9425. (CSIRO Publishing)
      A review. This paper provides a first update to the review of living radical polymn. achieved with thiocarbonylthio compds. (ZC(=S)SR) by a mechanism of reversible addn.-fragmentation chain transfer (RAFT) published in June 2005. The time since that publication has witnessed an increased rate of publication on the topic with the appearance of well over 200 papers covering various aspects of RAFT polymn. ranging over reagent synthesis and properties, kinetics, and mechanism of polymn., novel polymer syntheses, and diverse applications.
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      Moad, G.; Rizzardo, E.; Thang, S. H. Living Radical Polymerization by the RAFT Process A Second Update. Aust. J. Chem. 2009, 62, 1402– 1472,  DOI: 10.1071/CH09311
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      Living Radical Polymerization by the RAFT Process - A Second Update
      Moad, Graeme; Rizzardo, Ezio; Thang, San H.
      Australian Journal of Chemistry (2009), 62 (11), 1402-1472CODEN: AJCHAS; ISSN:0004-9425. (CSIRO Publishing)
      A review. This paper provides a second update to the review of reversible deactivation radical polymn. achieved with thiocarbonylthio compds. (ZC(=S)SR) by a mechanism of reversible addn.-fragmentation chain transfer (RAFT) that was published in June 2005 (Aust. J. Chem. 2005, 58, 379-410). The first update was published in Nov. 2006 (Aust. J. Chem. 2006, 59, 669-692). This review cites over 500 papers that appeared during the period mid-2006 to mid-2009 covering various aspects of RAFT polymn. ranging from reagent synthesis and properties, kinetics and mechanism of polymn., novel polymer syntheses and a diverse range of applications. Significant developments have occurred, particularly in the areas of novel RAFT agents, techniques for end-group removal and transformation, the prodn. of micro/nanoparticles and modified surfaces, and biopolymer conjugates both for therapeutic and diagnostic applications.
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      Moad, G.; Rizzardo, E.; Thang, S. H. Living Radical Polymerization by the RAFT Process—A Third Update. Aust. J. Chem. 2012, 65, 985– 1076,  DOI: 10.1071/CH12295
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      Living Radical Polymerization by the RAFT Process - A Third Update
      Moad, Graeme; Rizzardo, Ezio; Thang, San H.
      Australian Journal of Chemistry (2012), 65 (8), 985-1076CODEN: AJCHAS; ISSN:0004-9425. (CSIRO Publishing)
      A review. This paper provides a third update to the review of reversible deactivation radical polymn. (RDRP) achieved with thiocarbonylthio compds. (ZC(=S)SR) by a mechanism of reversible addn.-fragmentation chain transfer (RAFT) that was published in June 2005 (Aust. J. Chem. 2005, 58, 379). The first update was published in Nov. 2006 (Aust. J. Chem. 2006, 59, 669) and the second in Dec. 2009 (Aust. J. Chem. 2009, 62, 1402). This review cites over 700 publications that appeared during the period mid 2009 to early 2012 covering various aspects of RAFT polymn. which include reagent synthesis and properties, kinetics and mechanism of polymn., novel polymer syntheses, and a diverse range of applications. This period has witnessed further significant developments, particularly in the areas of novel RAFT agents, techniques for end-group transformation, the prodn. of micro/nanoparticles and modified surfaces, and biopolymer conjugates both for therapeutic and diagnostic applications.
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      Deane, O. J.; Lovett, J. R.; Musa, O. M.; Fernyhough, A.; Armes, S. P. Synthesis of Well-Defined Pyrrolidone-Based Homopolymers and Stimulus-Responsive Diblock Copolymers via RAFT Aqueous Solution Polymerization of 2-(N-Acryloyloxy)Ethylpyrrolidone. Macromolecules 2018, 51, 7756– 7766,  DOI: 10.1021/acs.macromol.8b01627
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      44
      Synthesis of Well-Defined Pyrrolidone-Based Homopolymers and Stimulus-Responsive Diblock Copolymers via RAFT Aqueous Solution Polymerization of 2-(N-Acryloyloxy)ethylpyrrolidone
      Deane, O. J.; Lovett, J. R.; Musa, O. M.; Fernyhough, A.; Armes, S. P.
      Macromolecules (Washington, DC, United States) (2018), 51 (19), 7756-7766CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      Poly(N-vinylpyrrolidone) (PNVP) is a well-known, highly polar, nonionic water-sol. polymer. However, N-vinylpyrrolidone (NVP) usually exhibits strongly non-ideal behavior when copolymd. with methacrylic or styrenic monomers. Moreover, NVP is not particularly well-controlled under living radical polymn. conditions. For these reasons, alternative pyrrolidone-based monomers have been investigated. For example, the reversible addn.-fragmentation chain transfer (RAFT) polymn. of 2-(N-methacryloyloxy)ethylpyrrolidone (NMEP) has been recently investigated using various polymn. formulations. However, PNMEP homopolymers are significantly less hydrophilic than PNVP and exhibit inverse temp. soly. in aq. soln. In the present work, we studied the RAFT aq. soln. polymn. of 2-(N-acryloyloxy)ethylpyrrolidone (NAEP) using either AIBN at 70 °C or a low-temp. redox initiator at 30 °C. PNAEP homopolymers are obtained in high yield (>99%) with good control (Mw/Mn < 1.20) for target ds.p. (DP) of up to 400 using the latter initiator, which produced relatively fast rates of polymn. However, targeting DPs above 400 led to lower NAEP conversions and broader mol. wt. distributions. 2-Hydroxyethyl acrylate (HEA) and oligo(ethylene glycol) Me ether acrylate (OEGA) were chain-extended using a PNAEPx macro-CTA via RAFT aq. soln. polymn., yielding double-hydrophilic acrylic diblock copolymers with high conversions (>99%) and good control (Mw/Mn < 1.31). In addn., a PNAEP95 macro-CTA was chain-extended via RAFT aq. soln. polymn. of N-isopropylacrylamide (NIPAM) at 22 °C. Dynamic light scattering (DLS) anal. indicated that heating above the lower crit. soln. temp. of PNIPAM led to so-called "anomalous micellization" at 35 °C and the formation of near-monodisperse spherical micelles at 40 °C. Finally, 2-(diethylamino)ethyl methacrylate (DEA) was polymd. using an N-morpholine-functionalized trithiocarbonate-based RAFT chain transfer agent and subsequently chain-extended using NAEP to form a novel pH-responsive diblock copolymer. Above the pKa of PDEA (∼7.3), DLS and 1H NMR studies indicated the formation of well-defined PDEA-core spherical micelles.
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      Deane, O. J.; Musa, O. M.; Fernyhough, A.; Armes, S. P. Synthesis and Characterization of Waterborne Pyrrolidone-Functional Diblock Copolymer Nanoparticles Prepared via Surfactant-Free RAFT Emulsion Polymerization. Macromolecules 2020, 53, 1422– 1434,  DOI: 10.1021/acs.macromol.9b02394
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      45
      Synthesis and Characterization of Waterborne Pyrrolidone-Functional Diblock Copolymer Nanoparticles Prepared via Surfactant-free RAFT Emulsion Polymerization
      Deane, Oliver J.; Musa, Osama M.; Fernyhough, Alan; Armes, Steven P.
      Macromolecules (Washington, DC, United States) (2020), 53 (4), 1422-1434CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      Polymn.-induced self-assembly enables the facile synthesis of a wide range of block copolymer nano-objects in the form of concd. dispersions. In this context, many surfactant-free reversible addn.-fragmentation chain transfer (RAFT) aq. emulsion polymn. formulations have been reported using various nonionic and polyelectrolytic water-sol. precursors for the steric stabilizer block. In the present study, we examine poly(2-(N-acryloyloxy)ethyl pyrrolidone) (PNAEP) as a new nonionic stabilizer block. A trithiocarbonate-based PNAEP precursor with a mean d.p. of 67 was employed as the steric stabilizer for the RAFT emulsion polymn. of styrene, Bu acrylate (nBA), or statistical mixts. thereof. The RAFT emulsion polymn. of styrene using a VA-044 azo initiator at 80°C and pH 7 led to essentially full conversion within 40 min, with induction times as short as 10 min, whereas gel permeation chromatog. anal. confirmed efficient chain extension and relatively low dispersities (Mw/Mn < 1.30). Dynamic light scattering (DLS) studies indicated that systematically increasing the target d.p. (DP) from 100 to 700 enabled the z-av. diam. of the resulting kinetically trapped spherical nanoparticles to be varied from 55 to 156 nm. The same PNAEP67 precursor was then employed for the RAFT emulsion polymn. of nBA at 30°C using a low-temp. redox initiator at pH 3. More than 99% conversion was achieved within 25 min, and efficient chain extension was obsd. up to a target DP of 700. However, relatively broad mol. wt. distributions (Mw/Mn = 1.38-1.64) were obtained, presumably owing to side reactions such as chain transfer to polymer. DLS studies indicated that a series of kinetically-trapped PNAEP67-PnBAx spheres (where x = 100-700) exhibited z-av. diams. ranging from 45 to 141 nm. Attempts to use this low-temp. initiator protocol for the homopolymn. of styrene led to essentially no conversion after 48 h at 30°C. However, the statistical copolymn. of 45% styrene with 55% nBA could be achieved using this low-temp. redox initiator at 30°C using the same PNAEP67 precursor. In this case, 1H NMR studies indicated a significantly longer induction period (95 min) compared to either homopolymn. Nevertheless, once the statistical copolymn. commenced, essentially full conversion of both comonomers could be achieved within 45 min. Differential scanning calorimetry anal. indicated that these statistical copolymers exhibited intermediate glass transition temps. compared to the two resp. homopolymers. The film formation behavior of selected diblock copolymer nanoparticles was briefly explored.
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    46. 46
      An, Z.; Shi, Q.; Tang, W.; Tsung, C.-K.; Hawker, C. J.; Stucky, G. D. Facile RAFT Precipitation Polymerization for the Microwave-Assisted Synthesis of Well-Defined, Double Hydrophilic Block Copolymers and Nanostructured Hydrogels. J. Am. Chem. Soc. 2007, 129, 14493– 14499,  DOI: 10.1021/ja0756974
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      46
      Facile RAFT Precipitation Polymerization for the Microwave-Assisted Synthesis of Well-Defined, Double Hydrophilic Block Copolymers and Nanostructured Hydrogels
      An, Zesheng; Shi, Qihui; Tang, Wei; Tsung, Chia-Kuang; Hawker, Craig J.; Stucky, Galen D.
      Journal of the American Chemical Society (2007), 129 (46), 14493-14499CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Water-sol. macromol. chain transfer agents (Macro-CTAs) were developed for the microwave-assisted pptn. polymn. of N-isopropylacrylamide. Two types of Macro-CTAs, amphiphilic (Macro-CTA1) and hydrophilic (Macro-CTA2), were studied regarding their activity for the facile formation of nanoparticles and double hydrophilic block copolymers by RAFT processes. While both Macro-CTAs functioned as steric stabilization agents, the variation in their surface activity afforded different levels of control over the resulting nanoparticles in the presence of crosslinkers. The crosslinked nanoparticles produced using the amphiphilic Macro-CTA1 were less uniform than those produced using the fully hydrophilic Macro-CTA2. The nanoparticles spontaneously formed core-shell structures with surface functionalities derived from those of the Macro-CTAs. In the absence of crosslinkers, both types of Macro-CTAs showed excellent control over the RAFT pptn. polymn. process with well-defined, double hydrophilic block copolymers being obtained. The power of combining microwave irradn. with RAFT procedures was evident in the high efficiency and high solids content of the polymn. systems. In addn., the "living" nature of the nanoparticles allowed for further copolymn. leading to multiresponsive nanostructured hydrogels contg. surface functional groups, which were used for surface bioconjugation.
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    47. 47
      Grazon, C.; Rieger, J.; Sanson, N.; Charleux, B. Study of Poly(N,N-Diethylacrylamide) Nanogel Formation by Aqueous Dispersion Polymerization of N,N-Diethylacrylamide in the Presence of Poly(Ethylene Oxide)-b-Poly(N,N-Dimethylacrylamide) Amphiphilic Macromolecular RAFT Agents. Soft Matter 2011, 7, 3482– 3490,  DOI: 10.1039/c0sm01181a
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      Study of poly(N,N-diethylacrylamide) nanogel formation by aqueous dispersion polymerization of N,N-diethylacrylamide in the presence of poly(ethylene oxide)-b-poly(N,N-dimethylacrylamide) amphiphilic macromolecular RAFT agents
      Grazon, Chloe; Rieger, Jutta; Sanson, Nicolas; Charleux, Bernadette
      Soft Matter (2011), 7 (7), 3482-3490CODEN: SMOABF; ISSN:1744-683X. (Royal Society of Chemistry)
      The formation of thermoresponsive poly(N,N-diethylacrylamide) (PDEAAm) nanogels via an aq. dispersion polymn. process in the presence of poly(ethylene oxide)-b-poly(N,N-dimethylacrylamide) macromol. reversible addn.-fragmentation chain transfer agents (macro RAFT agents) was studied. The latter exhibit a hydrophobic trithiocarbonate reactive group with a dodecyl substituent, and had previously proved to act simultaneously as control agents and stabilizers in such a synthesis process (Rieger et al., J. Polym. Sci. Part A: Polym. Chem., 2009, 47, 2373). The nanogel size and stability were found to depend strongly on the chain length of the macro RAFT agents, but also on the crosslinker (N,N'-methylene bisacrylamide) and monomer concns. The aim of the present work was to better understand the mechanisms that govern the nanogel formation in such heterogeneous polymn. conditions performed under RAFT control, with special emphasis on the role of the macro RAFT agents. In the first part, the aq. soln. properties of the macro RAFT agents in the conditions of the dispersion polymns. were studied by light scattering and fluorescence spectroscopy and they self-assemble to form star micelles. In the second part, the nanogel formation at different DEAAm and crosslinker concns. was monitored by dynamic and static light scattering, and by size exclusion chromatog. It appeared that at low monomer conversion the calcd. no. of chains per nanogel particle was close to the aggregation no., Nagg, of the macro RAFT agent micelles. With increasing conversions, however, the no. of chains clearly increased and exceeded the initial Nagg. Higher monomer concns. hardly influenced the formation process and thus the gel particle size, whereas enhanced crosslinker concn. had a strong impact on the latter. These results strongly suggest that precursor particles are formed rapidly at the polymn. onset and then aggregate with each other to form complex inter-crosslinked particles.
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    48. 48
      Warren, N. J.; Mykhaylyk, O. O.; Mahmood, D.; Ryan, A. J.; Armes, S. P. RAFT Aqueous Dispersion Polymerization Yields Poly(Ethylene Glycol)-Based Diblock Copolymer Nano-Objects with Predictable Single Phase Morphologies. J. Am. Chem. Soc. 2014, 136, 1023– 1033,  DOI: 10.1021/ja410593n
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      48
      RAFT Aqueous Dispersion Polymerization Yields Poly(ethylene glycol)-Based Diblock Copolymer Nano-Objects with Predictable Single Phase Morphologies
      Warren, Nicholas J.; Mykhaylyk, Oleksandr O.; Mahmood, Daniel; Ryan, Anthony J.; Armes, Steven P.
      Journal of the American Chemical Society (2014), 136 (3), 1023-1033CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      A poly(ethylene glycol) (PEG) macromol. chain transfer agent (macro-CTA) is prepd. in high yield (>95%) with 97% dithiobenzoate chain-end functionality in a three-step synthesis starting from a monohydroxy PEG113 precursor. This PEG113-dithiobenzoate is then used for the reversible addn.-fragmentation chain transfer (RAFT) aq. dispersion polymn. of 2-hydroxypropyl methacrylate (HPMA). Polymns. conducted under optimized conditions at 50 °C led to high conversions as judged by 1H NMR spectroscopy and relatively low diblock copolymer polydispersities (Mw/Mn < 1.25) as judged by GPC. The latter technique also indicated good blocking efficiencies, since there was minimal PEG113 macro-CTA contamination. Systematic variation of the mean d.p. of the core-forming PHPMA block allowed PEG113-PHPMAx diblock copolymer spheres, worms, or vesicles to be prepd. at up to 17.5% wt./wt. solids, as judged by dynamic light scattering and transmission electron microscopy studies. Small-angle X-ray scattering (SAXS) anal. revealed that more exotic oligolamellar vesicles were obsd. at 20% wt./wt. solids when targeting highly asym. diblock compns. Detailed anal. of SAXS curves indicated that the mean no. of membranes per oligolamellar vesicle is approx. three. A PEG113-PHPMAx phase diagram was constructed to enable the reproducible targeting of pure phases, as opposed to mixed morphologies (e.g., spheres plus worms or worms plus vesicles). This new RAFT PISA formulation is expected to be important for the rational and efficient synthesis of a wide range of biocompatible, thermo-responsive PEGylated diblock copolymer nano-objects for various biomedical applications.
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    49. 49
      Xu, Y.; Li, Y.; Cao, X.; Chen, Q.; An, Z. Versatile RAFT Dispersion Polymerization in Cononsolvents for the Synthesis of Thermoresponsive Nanogels with Controlled Composition, Functionality and Architecture. Polym. Chem. 2014, 5, 6244– 6255,  DOI: 10.1039/C4PY00867G
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      49
      Versatile RAFT dispersion polymerization in cononsolvents for the synthesis of thermoresponsive nanogels with controlled composition, functionality and architecture
      Xu, Yuanyuan; Li, Youcheng; Cao, Xueteng; Chen, Qijing; An, Zesheng
      Polymer Chemistry (2014), 5 (21), 6244-6255CODEN: PCOHC2; ISSN:1759-9962. (Royal Society of Chemistry)
      Reversible addn.-fragmentation chain transfer (RAFT) dispersion polymn. in cononsolvents of poly(N-isopropylacrylamide) (PNIPAM) was developed as a versatile strategy for the synthesis of thermoresponsive nanogels with controlled compn., functionality and architecture. Cononsolvents composed of mixts. of methanol, ethanol and isopropanol with water were first screened for their suitability as the media for dispersion polymn. of NIPAM, and water-ethanol (75 : 25, v : v) soln. was selected due to good RAFT control, efficient formation of nanogels and low toxicity. RAFT dispersion polymn. of NIPAM in the cononsolvent using poly(N,N-dimethylacrylamide) (PDMA) as the macromol. chain transfer agent (Macro-CTA) showed good control over the mol. wt., polydispersity and pseudo linear polymn. kinetics, as characterized by gel permeation chromatog. (GPC) and 1H NMR. The effect of the mol. wt. of Macro-CTA, the d.p. of PNIPAM, the molar ratio of [crosslinker] : [Macro-CTA] and the solid content on the formation and size of nanogels was investigated. The thermal profiles of nanogels were characterized by dynamic light scattering (DLS) both in cononsolvents and water. This cononsolvency strategy for dispersion polymn. was shown to be compatible with the incorporation of hydrophilic comonomers of N-(2-hydroxyethyl)acrylamide (HEAM) and diacetone acrylamide (DAAM). The nanogel contg. DAAM was demonstrated for postpolymn. modification using ketone-alkoxyamine chem. More importantly, dispersion polymn. in cononsolvents allowed various hydrophobic components, e.g. Bu acrylate (BA), fluorescein O-acrylate (FLA), and 1,6-hexanediol diacrylate (HDDA), to be reliably copolymd. with NIPAM, showing well controlled polymn., compn., nanogel size and colloidal stability. Finally, an amphiphilic block copolymer PDMA-b-PBA was used as a Macro-CTA to produce the PDMA-b-PBA-b-PNIPAM triblock copolymer and triple-layered nanogel, taking advantage of the soly. of PDMA-b-PBA and the insoly. of PNIPAM in the water-ethanol soln. at the polymn. temp.
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    50. 50
      Figg, C. A.; Simula, A.; Gebre, K. A.; Tucker, B. S.; Haddleton, D. M.; Sumerlin, B. S. Polymerization-Induced Thermal Self-Assembly (PITSA). Chem. Sci. 2015, 6, 1230– 1236,  DOI: 10.1039/C4SC03334E
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      Polymerization-induced thermal self-assembly (PITSA)
      Figg, C. Adrian; Simula, Alexandre; Gebre, Kalkidan A.; Tucker, Bryan S.; Haddleton, David M.; Sumerlin, Brent S.
      Chemical Science (2015), 6 (2), 1230-1236CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
      Polymn.-induced self-assembly (PISA) is a versatile technique to achieve a wide range of polymeric nanoparticle morphologies. Most previous examples of self-assembled soft nanoparticle synthesis by PISA rely on a growing solvophobic polymer block that leads to changes in nanoparticle architecture during polymn. in a selective solvent. However, synthesis of block copolymers with a growing stimuli-responsive block to form various nanoparticle shapes has yet to be reported. This new concept using thermo-responsive polymers is termed polymn.-induced thermal self-assembly (PITSA). A reversible addn.-fragmentation chain transfer (RAFT) polymn. of N-isopropylacrylamide from a hydrophilic chain transfer agent composed of N,N-dimethylacrylamide and acrylic acid was carried out in water above the known lower crit. soln. temp. (LCST) of poly(N-isopropylacrylamide) (PNIPAm). After reaching a certain chain length, the growing PNIPAm self-assembled, as induced by the LCST, into block copolymer aggregates within which dispersion polymn. continued. To characterize the nanoparticles at ambient temps. without their dissoln., the particles were crosslinked immediately following polymn. at elevated temps. via the reaction of the acid groups with a diamine in the presence of a carbodiimide. Size exclusion chromatog. was used to evaluate the unimer mol. wt. distributions and reaction kinetics. Dynamic light scattering and transmission electron microscopy provided insight into the size and morphologies of the nanoparticles. The resulting block copolymers formed polymeric nanoparticles with a range of morphologies (e.g., micelles, worms, and vesicles), which were a function of the PNIPAm block length.
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    51. 51
      Blackman, L. D.; Doncom, K. E. B.; Gibson, M. I.; O’Reilly, R. K. Comparison of Photo- and Thermally Initiated Polymerization-Induced Self-Assembly: A Lack of End Group Fidelity Drives the Formation of Higher Order Morphologies. Polym. Chem. 2017, 8, 2860– 2871,  DOI: 10.1039/C7PY00407A
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      51
      Comparison of photo- and thermally initiated polymerization-induced self-assembly: a lack of end group fidelity drives the formation of higher order morphologies
      Blackman, Lewis D.; Doncom, Kay E. B.; Gibson, Matthew I.; O'Reilly, Rachel K.
      Polymer Chemistry (2017), 8 (18), 2860-2871CODEN: PCOHC2; ISSN:1759-9962. (Royal Society of Chemistry)
      Polymn.-induced self-assembly (PISA) is an emerging industrially relevant technol., which allows the prepn. of defined and predictable polymer self-assemblies with a wide range of morphologies. In recent years, interest has turned to photoinitiated PISA processes, which show markedly accelerated reaction kinetics and milder conditions, thereby making it an attractive alternative to thermally initiated PISA. Herein, we attempt to elucidate the differences between these two initiation methods using isothermally derived phase diagrams of a well-documented poly(ethylene glycol)-b-(2-hydroxypropyl methacrylate) (PEG-b-HPMA) PISA system. By studying the influence of the intensity of the light source used, as well as an investigation into the thermodynamically favorable morphologies, the factors dictating differences in the obtained morphologies when comparing photo- and thermally initiated PISA were explored. Our findings indicate that differences in a combination of both reaction kinetics and end group fidelity led to the obsd. discrepancies between the two techniques. We find that the loss of the end group in photoinitiated PISA drives the formation of higher order structures and that a morphol. transition from worms to unilamellar vesicles could be induced by extended periods of light and heat irradn. Our findings demonstrate that PISA of identical block copolymers by the two different initiation methods can lead to structures that are both chem. and morphol. distinct.
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    52. 52
      Sun, W.; An, Z.; Wu, P. Hydrogen Bonding Reinforcement as a Strategy to Improve Upper Critical Solution Temperature of Poly(N-Acryloylglycinamide-Co-Methacrylic Acid). Polym. Chem. 2018, 9, 3667– 3673,  DOI: 10.1039/C8PY00733K
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      Hydrogen bonding reinforcement as a strategy to improve upper critical solution temperature of poly(N-acryloylglycinamide-co-methacrylic acid)
      Sun, Wenhui; An, Zesheng; Wu, Peiyi
      Polymer Chemistry (2018), 9 (26), 3667-3673CODEN: PCOHC2; ISSN:1759-9962. (Royal Society of Chemistry)
      Hydrogen bonding reinforcement via copolymn. of N-acryloylglycinamide (NAGA) with methacrylic acid (MAA) is employed as a strategy to improve the upper crit. soln. temp. (UCST) to a biol. relevant range. P(NAGA-co-MAA) copolymers with MAA molar fraction in the range of 1-81 mol% are synthesized via reversible addn.-fragmentation chain transfer (RAFT) polymn. The UCST (3.5-37.5°C) of the copolymers scales with MAA molar fraction in the range of 10-60 mol% when measured at pH 4 and 1 wt.% concn. Using a copolymer with a suitably high UCST as a macromol. chain transfer agent, doubly thermoresponsive nanogels consisting of P(NAGA-co-MAA) copolymer as the shell and crosslinked poly(N-isopropylacrylamide) (PNIPAM) as the core are synthesized via RAFT aq. dispersion polymn. The nanogels show distinct thermal transitions with both upper and lower crit. soln. temps. (UCST and LCST).
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    53. 53
      Liu, D.; Cai, W.; Zhang, L.; Boyer, C.; Tan, J. Efficient Photoinitiated Polymerization-Induced Self-Assembly with Oxygen Tolerance through Dual-Wavelength Type I Photoinitiation and Photoinduced Deoxygenation. Macromolecules 2020, 53, 1212– 1223,  DOI: 10.1021/acs.macromol.9b02710
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      53
      Efficient Photoinitiated Polymerization-Induced Self-Assembly with Oxygen Tolerance through Dual-Wavelength Type I Photoinitiation and Photoinduced Deoxygenation
      Liu, Dongdong; Cai, Weibin; Zhang, Li; Boyer, Cyrille; Tan, Jianbo
      Macromolecules (Washington, DC, United States) (2020), 53 (4), 1212-1223CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      Recently, reversible addn.-fragmentation chain transfer (RAFT)-mediated polymn.-induced self-assembly (PISA) has emerged as a powerful method for the prepn. of a variety of block copolymer nano-objects. Although numerous RAFT-mediated PISA formulations have been successfully explored, inert atmospheres (e.g., nitrogen) are often needed to overcome the oxygen inhibition problem, making this process challenging when polymg. at low vols. Moreover, this restriction also reduces the versatility of RAFT-mediated PISA for non-experts. Herein, we report an efficient photoinitiated polymn.-induced self-assembly (photo-PISA) with excellent oxygen tolerance through dual-wavelength type I photoinitiation and photoinduced deoxygenation. The dual-wavelength photo-PISA was explored in water and alc./water using 2-hydroxypropyl methacrylate (HPMA), benzyl methacrylate (BzMA), and isobornyl acrylate (IBOA) as core-forming monomers. Polymn. kinetics indicated that dual-wavelength photo-PISA was performed in a batch reactor, flow reactor, and microliter plate with excellent oxygen tolerance. Block copolymer nano-objects with different morphologies (spheres, worms, and vesicles) were successfully prepd. by these dual-wavelength photo-PISA techniques. This is a fast RAFT-mediated PISA under air, which is a clear improvement from previous systems. We believe that this method can greatly increase the accessibility of RAFT-mediated PISA for the prepn. of block copolymer nano-objects either at low vols. or at a large scale.
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    54. 54
      Xu, S.; Corrigan, N.; Boyer, C. Forced Gradient Copolymerisation: A Simplified Approach for Polymerisation-Induced Self-Assembly. Polym. Chem. 2021, 12, 57– 68,  DOI: 10.1039/D0PY00889C
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      54
      Forced gradient copolymerisation: a simplified approach for polymerisation-induced self-assembly
      Xu, Sihao; Corrigan, Nathaniel; Boyer, Cyrille
      Polymer Chemistry (2021), 12 (1), 57-68CODEN: PCOHC2; ISSN:1759-9962. (Royal Society of Chemistry)
      In this work, a novel and versatile gradient copolymn. approach to simplify polymeric nanoparticle synthesis through polymn.-induced self-assembly (PISA) is reported. In contrast with the commonly performed two-step PISA process, which involves chain-extension of a pre-synthesized stabilizer (or solvophilic block), this work demonstrates a one pot PISA approach via the formation of gradient copolymers through a gradual injection of the core-forming monomer in the presence of a solvophilic monomer. To demonstrate this concept, two model PISA systems were tested using a methacrylate monomer pair and an acrylamide pair. PISA using dimethylacrylamide (DMA) and diacetone acrylamide (DAAm) was first established to form a range of nanoparticle morphologies (spheres and worms), and importantly, a pure worm phase was obsd. without the addn. of a co-solvent or a second solvophilic monomer during the polymn. of the core-forming monomer. To demonstrate the gradient approach can be applied to other PISA monomer pairs, this methodol. was applied to a system using oligo(ethylene glycol)methyl ether methacrylate (OEGMA300) and 2-hydroxypropyl methacrylate (HPMA) as monomers. PISA of this monomer pair resulted in the formation of nanoparticles with various morphologies, including spheres, worms and vesicles. More interestingly, the nanoparticles formed using these gradient copolymers presented thermoresponsive behavior, exhibiting a sphere-to-worm transition with an increase in temp. from 25°C to 40°C. Thus, this facile gradient copolymn. approach was shown to simplify the PISA process into a single step approach with easily tuneable solvophilic block length and copolymer compn., and addnl. provide nanoparticle structures that afford unique properties.
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      Liu, G.; Qiu, Q.; An, Z. Development of Thermosensitive Copolymers of Poly(2-Methoxyethyl Acrylate-Co-Poly(Ethylene Glycol) Methyl Ether Acrylate) and Their Nanogels Synthesized by RAFT Dispersion Polymerization in Water. Polym. Chem. 2012, 3, 504– 513,  DOI: 10.1039/C2PY00533F
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      Development of thermosensitive copolymers of poly(2-methoxyethyl acrylate-co-poly(ethylene glycol) methyl ether acrylate) and their nanogels synthesized by RAFT dispersion polymerization in water
      Liu, Guangyao; Qiu, Qian; An, Zesheng
      Polymer Chemistry (2012), 3 (2), 504-513CODEN: PCOHC2; ISSN:1759-9962. (Royal Society of Chemistry)
      The prepn. of thermosensitive oligo(ethylene glycol) methacrylate-based microgels/nanogels via aq. dispersion polymn. is limited due to low monomer loading and thus low solid content of the final colloids. Moreover, the prepn. of nanogels by reversible addn.-fragmentation chain transfer (RAFT) mediated dispersion polymn. has been hampered by the poor RAFT control of the polymn. process. In this work, thermosensitive copolymers based on 2-methoxyethyl acrylate (MEA) and poly(ethylene glycol) Me ether acrylate (PEGA) were developed and used for nanogel synthesis by RAFT dispersion polymn. in water. The thermosensitive copolymers exhibited sharp thermal transitions upon temp. increase above their lower crit. soln. temp. The use of MEA as the major comonomer and poly(N,N'-dimethylacrylamide) as the RAFT agent and stabilizer for the nanogel synthesis allowed monomer loadings of up to 20%, which significantly improved the solid content of the dispersion polymn. system. Moreover, the dispersion copolymn. of MEA with PEGA was under excellent RAFT control up to complete monomer conversion. The nanogels showed a linear relationship between nanogel size and temp., suggesting expanded applications of these materials.
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      Ratcliffe, L. P. D.; Derry, M. J.; Ianiro, A.; Tuinier, R.; Armes, S. P. A Single Thermoresponsive Diblock Copolymer Can Form Spheres, Worms or Vesicles in Aqueous Solution. Angew. Chem., Int. Ed. 2019, 58, 18964– 18970,  DOI: 10.1002/anie.201909124
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      A Single Thermoresponsive Diblock Copolymer Can Form Spheres, Worms or Vesicles in Aqueous Solution
      Ratcliffe, Liam P. D.; Derry, Matthew J.; Ianiro, Alessandro; Tuinier, Remco; Armes, Steven P.
      Angewandte Chemie, International Edition (2019), 58 (52), 18964-18970CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
      It is well-known that the self-assembly of AB diblock copolymers in soln. can produce various morphologies depending on the relative vol. fraction of each block. Recently, polymn.-induced self-assembly (PISA) has become widely recognized as a powerful platform technol. for the rational design and efficient synthesis of a wide range of block copolymer nano-objects. In this study, PISA is used to prep. a new thermoresponsive poly(N-(2-hydroxypropyl) methacrylamide)-poly(2-hydroxypropyl methacrylate) [PHPMAC-PHPMA] diblock copolymer. Remarkably, TEM, rheol. and SAXS studies indicate that a single copolymer compn. can form well-defined spheres (4 °), worms (22 °) or vesicles (50 °) in aq. soln. Given that the two monomer repeat units have almost identical chem. structures, this system is particularly well-suited to theor. anal. Self-consistent mean field theory suggests this rich self-assembly behavior is the result of the greater degree of hydration of the PHPMA block at lower temp., which is in agreement with variable temp. 1H NMR studies.
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    57. 57
      Petzetakis, N.; Dove, A. P.; O’Reilly, R. K. Cylindrical Micelles from the Living Crystallization-Driven Self-Assembly of Poly(Lactide)-Containing Block Copolymers. Chem. Sci. 2011, 2, 955– 960,  DOI: 10.1039/C0SC00596G
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      Cylindrical micelles from the living crystallization-driven self-assembly of poly(lactide)-containing block copolymers
      Petzetakis, Nikos; Dove, Andrew P.; O'Reilly, Rachel K.
      Chemical Science (2011), 2 (5), 955-960CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
      The synthesis and self-assembly of poly(lactide)-b-poly(acrylic acid) and poly(lactide)-b-poly(dimethylaminoethyl acrylate) block copolymers by a combination of ring-opening polymn. and reverse-addn. fragmentation chain transfer (RAFT) polymn. is reported. The self-assembly of block copolymers contg. enantiopure homochiral poly(lactide), PLA, by a simple direct dissoln. methodol. results in core-crystn. to afford micelles with cylindrical morphol. Amorphous atactic PLA cores and conditions that did not promote crystn. resulted in spherical micelles. The cylindrical micelles were characterized by transmission electron microscopy (TEM) with cryo-TEM, small angle neutron scattering (SANS) and angular dependent dynamic light scattering (DLS) proving that the cylindrical morphol. was persistent in soln. Manipulation of the assembly conditions enabled the length and dispersity of the resultant cylindrical micelles to be controlled.
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      Zhao, W.; Gody, G.; Dong, S.; Zetterlund, P. B.; Perrier, S. Optimization of the RAFT Polymerization Conditions for the in Situ Formation of Nano-Objects via Dispersion Polymerization in Alcoholic Medium. Polym. Chem. 2014, 5, 6990– 7003,  DOI: 10.1039/C4PY00855C
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      Optimization of the RAFT polymerization conditions for the in situ formation of nano-objects via dispersion polymerization in alcoholic medium
      Zhao, Wei; Gody, Guillaume; Dong, Siming; Zetterlund, Per B.; Perrier, Sebastien
      Polymer Chemistry (2014), 5 (24), 6990-7003CODEN: PCOHC2; ISSN:1759-9962. (Royal Society of Chemistry)
      Hydrophilic polymer brushes based on poly(ethylene glycol) Me ether acrylate (P(PEGA454)) or poly(ethylene glycol) Me ether methacrylate (P(PEGMA475)), both having a trithiocarbonate end group, were prepd. in water-dioxane (9 : 1) at 44 °C via RAFT polymn. and subsequently used in RAFT dispersion polymn. of styrene in isopropanol at 90 °C. RAFT reaction conditions were first optimized to prep. P(PEGA454) and P(PEGMA475) macro-RAFT agents at high monomer conversions (>90%) and very low fraction of dead chains (<1%). Both polymer brushes allowed the prepn. of well-defined amphiphilic diblock copolymers (P(PEGA454)-b-PS and P(PEGMA475)-b-PS) which self-assemble in situ into nano-objects with various morphologies. Using relatively long chain P(PEGA454) or P(PEGMA475) macro-RAFT agents (DP ~ 75) leads to the formation of near uniform spherical nanoparticles with diams. ranging from 30 to 140 nm, depending on the targeted DP of the PS block. In contrast, TEM and DLS studies demonstrated that using a shorter P(PEGA454) or P(PEGMA475) macro-RAFT agent (DP ~ 20) enables the formation of worm-like micelles, vesicles and large compd. vesicle morphologies in addn. to spheres. Cryo-TEM was used to confirm polymn. induced morphol. transition, rather than morphologies obtained via self-assembly driven by selective solvent or solvent evapn. during the prepn. of samples for characterization.
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      Mable, C. J.; Gibson, R. R.; Prevost, S.; McKenzie, B. E.; Mykhaylyk, O. O.; Armes, S. P. Loading of Silica Nanoparticles in Block Copolymer Vesicles during Polymerization-Induced Self-Assembly: Encapsulation Efficiency and Thermally Triggered Release. J. Am. Chem. Soc. 2015, 137, 16098– 16108,  DOI: 10.1021/jacs.5b10415
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      Loading of Silica Nanoparticles in Block Copolymer Vesicles during Polymerization-Induced Self-Assembly: Encapsulation Efficiency and Thermally Triggered Release
      Mable, Charlotte J.; Gibson, Rebecca R.; Prevost, Sylvain; McKenzie, Beulah E.; Mykhaylyk, Oleksandr O.; Armes, Steven P.
      Journal of the American Chemical Society (2015), 137 (51), 16098-16108CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Poly(glycerol monomethacrylate)-poly(2-hydroxypropyl methacrylate) diblock copolymer vesicles can be prepd. in the form of concd. aq. dispersions via polymn.-induced self-assembly (PISA). In the present study, these syntheses are conducted in the presence of varying amts. of silica nanoparticles of approx. 18 nm diam. This approach leads to encapsulation of up to hundreds of silica nanoparticles per vesicle. Silica has high electron contrast compared to the copolymer which facilitates TEM anal., and its thermal stability enables quantification of the loading efficiency via thermogravimetric anal. Encapsulation efficiencies can be calcd. using disk centrifuge photosedimentometry, since the vesicle d. increases at higher silica loadings while the mean vesicle diam. remains essentially unchanged. Small angle X-ray scattering (SAXS) is used to confirm silica encapsulation, since a structure factor is obsd. at q ≈ 0.25 nm-1. A new two-population model provides satisfactory data fits to the SAXS patterns and allows the mean silica vol. fraction within the vesicles to be detd. Finally, the thermoresponsive nature of the diblock copolymer vesicles enables thermally triggered release of the encapsulated silica nanoparticles simply by cooling to 0-10 °C, which induces a morphol. transition. These silica-loaded vesicles constitute a useful model system for understanding the encapsulation of globular proteins, enzymes, or antibodies for potential biomedical applications. They may also serve as an active payload for self-healing hydrogels or repair of biol. tissue. Finally, we also encapsulate a model globular protein, bovine serum albumin, and calc. its loading efficiency using fluorescence spectroscopy.
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    60. 60
      Ahmad, N. M.; Charleux, B.; Farcet, C.; Ferguson, C. J.; Gaynor, S. G.; Hawkett, B. S.; Heatley, F.; Klumperman, B.; Konkolewicz, D.; Lovell, P. A.; Matyjaszewski, K.; Venkatesh, R. Chain Transfer to Polymer and Branching in Controlled Radical Polymerizations of N-Butyl Acrylate. Macromol. Rapid Commun. 2009, 30, 2002– 2021,  DOI: 10.1002/marc.200900450
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      Chain Transfer to Polymer and Branching in Controlled Radical Polymerizations of n-Butyl Acrylate
      Ahmad, Nasir M.; Charleux, Bernadette; Farcet, Celine; Ferguson, Christopher J.; Gaynor, Scott G.; Hawkett, Brian S.; Heatley, Frank; Klumperman, Bert; Konkolewicz, Dominik; Lovell, Peter A.; Matyjaszewski, Krzysztof; Venkatesh, Rajan
      Macromolecular Rapid Communications (2009), 30 (23), 2002-2021CODEN: MRCOE3; ISSN:1022-1336. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Chain transfer to polymer (CTP) in conventional free-radical polymns. (FRPs) and controlled radical polymns. (ATRP, RAFT and NMP) of Bu acrylate (BA) has been investigated using 13C NMR measurements of branching in the poly(Bu acrylate) produced. The mol-% branches are reduced significantly in the controlled radical polymns. as compared to conventional FRPs. Several possible explanations for this observation are discussed critically and all except one refuted. The observations are explained in terms of differences in the concn. of highly reactive short-chain radicals which can be expected to undergo both intra- and inter-mol. CTP at much higher rates than long-chain radicals. In conventional FRP, the distribution of radical concns. is broad and there always is present a significant proportion of short-chain radicals, whereas in controlled radical polymns., the distribution is narrow with only a small proportion of short-chain radicals which diminishes as the living chains grow. Hence, irresp. of the type of control, controlled radical polymns. give rise to lower levels of branching, when performed under otherwise similar conditions to conventional FRP. Similar observations are expected for other acrylates and monomers that undergo chain transfer to polymer during radical polymn.
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      Misra, G. S.; Gupta, C. V. Aqueous Polymerization of Methacrylamide Initiated by the Redox System K2S2O8/Ascorbic Acid. Die Makromol. Chem. 1973, 165, 205– 216,  DOI: 10.1002/macp.1973.021650119
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      Narain, H.; Jagadale, S. M.; Ghatge, N. D. Studies of Redox Polymerization. I. Aqueous Polymerization of Acrylamide by an Ascorbic Acid–Peroxydisulfate System. J. Polym. Sci., Polym. Chem. Ed. 1981, 19, 1225– 1238,  DOI: 10.1002/pol.1981.170190518
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      Studies of redox polymerization. I. Aqueous polymerization of acrylamide by an ascorbic acid-peroxydisulfate system
      Narain, H.; Jagadale, S. M.; Ghatge, N. D.
      Journal of Polymer Science, Polymer Chemistry Edition (1981), 19 (5), 1225-38CODEN: JPLCAT; ISSN:0360-6376.
      The polymn. of acrylamide [79-06-1] initiated by an ascorbic acid (I) [50-81-7]-peroxydisulfate redox system was studied in aq. soln. at 35 ± 0.2° in the presence of air. The concns. studied were [monomer] = (2.0-15.0) × 10-2; [peroxydisulfate] = (1.5-10.0) × 10-3; and [I] = (2.84-28.4) × 10-4 M; temps. were 25-50°. Within these ranges the initial rate showed a half-order dependence on peroxydisulfate, a first-order dependence on initial monomer concn., and a first-order dependence on low concns. of I [(2.84-8.54) × 10-4 M]. At higher concns. of I the rate remained const. in the concn. range (8.54-22.72) × 10-4 M, then varied as an inverse half-power at still higher concns. of [(22.72-28.4) × 10-4 M]. The initial rate increased with an increase in polymn. temp. The overall energy of activation was 12.203 kcal/mol at 25-50°. Water-miscible org. solvents depressed the initial rate and the limiting conversion. The viscometric av. mol. wt. increased with an increase in temp. and initial monomer concn. but decreased with increasing concn. of peroxydisulfate and an additive, DMF.
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      Cabelli, D. E.; Bielski, B. H. J. Kinetics and Mechanism for the Oxidation of Ascorbic Acid/Ascorbate by HO2/O2- (Hydroperoxyl/Superoxide) Radicals. A Pulse Radiolysis and Stopped-Flow Photolysis Study. J. Phys. Chem. A 1983, 87, 1809– 1812,  DOI: 10.1021/j100233a031
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      Ahmad, N. M.; Heatley, F.; Lovell, P. A. Chain Transfer to Polymer in Free-Radical Solution Polymerization of n-Butyl Acrylate Studied by NMR Spectroscopy. Macromolecules 1998, 31, 2822– 2827,  DOI: 10.1021/ma971283r
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      Chain transfer to polymer in free-radical solution polymerization of n-butyl acrylate studied by NMR spectroscopy
      Ahmad, Nasir M.; Heatley, Frank; Lovell, Peter A.
      Macromolecules (1998), 31 (9), 2822-2827CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      The effects of the initial monomer concn., [M]o, and percent conversion on the extent of chain transfer to polymer in free-radical soln. polymn. of Bu acrylate has been studied. The polymns. were carried out in cyclohexane at 70° using 0.1% (wt./wt.) 2,2'-azobis(2-cyanopropane) as initiator and the mole percent branched repeat units (mole percent branches) in the poly(Bu acrylate) was detd. from unique resonances of branch-point carbons in the 13C NMR spectra. At [M]o > 10% (wt./wt.) the mole percent branches is independent of [M]o and increases from 0.8 to ∼2.2% as conversion increases from 35 to ∼95%. However, for more dil. solns., with [M]o ≤ 10% (wt./wt.), the mole percent branches increases as [M]o decreases and is higher than at equiv. conversions for the more concd. soln. polymns.; e.g., at ∼25% conversion the mole percent branches increases from 2.7% for [M]o = 10% (wt./wt.) to 5.9% for [M]o = 3% (wt./wt.). These observations are explained in terms of the ratio of the concns. of polymer repeat units and monomer in the vicinity of the propagating chain end. In more concd. solns., intermol. chain transfer to polymer dominates because, at all except the lowest percent conversions, the overall polymer repeat unit concn. is sufficient for overlap of individual polymer coils. However, in the dil. solns. the overall polymer repeat unit concn. is too low for overlap of individual polymer coils and intramol. chain transfer to polymer dominates. Under these conditions, the local polymer repeat unit concn. within the isolated propagating chains is defined by the chain statistics and so is approx. const., whereas the monomer is distributed uniformly throughout the soln. Thus, for dil. solns., as [M]o decreases, the probability of chain transfer to polymer (and hence the mole percent branches) increases.
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    65. 65
      Agirre, A.; Santos, J. I.; Etxeberria, A.; Sauerland, V.; Leiza, J. R. Polymerization of N-Butyl Acrylate with High Concentration of a Chain Transfer Agent (CBr4): Detailed Characterization and Impact on Branching. Polym. Chem. 2013, 4, 2062– 2079,  DOI: 10.1039/c2py21123h
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      Polymerization of n-butyl acrylate with high concentration of a chain transfer agent (CBr4): detailed characterization and impact on branching
      Agirre, A.; Santos, J. I.; Etxeberria, A.; Sauerland, V.; Leiza, J. R.
      Polymer Chemistry (2013), 4 (6), 2062-2079CODEN: PCOHC2; ISSN:1759-9962. (Royal Society of Chemistry)
      Poly(Bu acrylate) (polyn-BA) polymers synthesized by radical bulk polymn. in the presence and absence of a high concn. (0.4 mol L-1) of carbon tetrabromide (CBr4) as a chain transfer agent at nominal temps. of 60, 100 and 140 °C were fully characterized by 1D and 2D NMR, SEC/MALS and MALDI-TOF mass spectrometry. The structures generated by chain transfer to CBr4 in secondary chain-end radicals and reinitiation of polymer chains by CBr3 radicals formed by chain transfer to CBr4 reactions were identified by MALDI-TOF and NMR anal. The potential structures that might have been created by chain-transfer to tertiary radicals (quaternary carbons with a Br unit) formed by backbiting or intermol. chain transfer to polymer could not be detected and hence their abundance was not important. The branching d. (BD) of the polymers synthesized in the presence and absence of CBr4 was also detd. The BD increases with temp. in both cases, and for each temp. the branching d. considerably reduced when CBr4 was employed in the polymn. as found for other transfer agents and controlled radical mediated polymns. However, the explanation that patching on the tertiary radicals was the cause of redn. of the branching in the polyn-BA was discarded in this case because the resulting structures could not be identified.
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      Baussard, J.-F.; Habib-Jiwan, J.-L.; Laschewsky, A.; Mertoglu, M.; Storsberg, J. New Chain Transfer Agents for Reversible Addition-Fragmentation Chain Transfer (RAFT) Polymerisation in Aqueous Solution. Polymer 2004, 45, 3615– 3626,  DOI: 10.1016/j.polymer.2004.03.081
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      New chain transfer agents for reversible addition-fragmentation chain transfer (RAFT) polymerisation in aqueous solution
      Baussard, Jean-Francois; Habib-Jiwan, Jean-Louis; Laschewsky, Andre; Mertoglu, Murat; Storsberg, Joachim
      Polymer (2004), 45 (11), 3615-3626CODEN: POLMAG; ISSN:0032-3861. (Elsevier Science Ltd.)
      New chain transfer agents for free radical polymn. via reversible addn.-fragmentation chain transfer (RAFT) were synthesized that are particularly suited for aq. soln. polymn. The new compds. bear dithioester and trithiocarbonate moieties as well as permanently ionic groups to confer soly. in water. Their stability against hydrolysis was studied, and compared with a frequently used water-sol. RAFT agent, i.e., 4-(thiobenzoylthio)-4-cyanopentanoic acid (I), using UV-visible spectroscopy and 1H NMR measurements. An improved resistance to hydrolysis was found for the new RAFT agents compared to I, providing good stabilities in the pH range between 1 and 8, and up to temps. of 70°.
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      Thomas, D. B.; Convertine, A. J.; Hester, R. D.; Lowe, A. B.; McCormick, C. L. Hydrolytic Susceptibility of Dithioester Chain Transfer Agents and Implications in Aqueous RAFT Polymerizations. Macromolecules 2004, 37, 1735– 1741,  DOI: 10.1021/ma035572t
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      Hydrolytic Susceptibility of Dithioester Chain Transfer Agents and Implications in Aqueous RAFT Polymerizations
      Thomas, David B.; Convertine, Anthony J.; Hester, Roger D.; Lowe, Andrew B.; McCormick, Charles L.
      Macromolecules (2004), 37 (5), 1735-1741CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      The controlled radical polymn. (CRP) technique reversible addn.-fragmentation chain transfer (RAFT) has potential for prepg. functional (co)polymers directly in an aq. environment. Hydrolysis and aminolysis can eliminate the active end groups necessary for maintaining "livingness" in water. These reactions have not previously been evaluated with respect to their effect on aq. RAFT polymns. Herein we det. rate consts. of hydrolysis and aminolysis for representative water-sol. chain transfer agents (CTAs) cyanopentanoic acid dithiobenzoate (CTP) and the macro-chain-transfer agents (macro-CTAs) of poly(sodium 2-acrylamido-2-methylpropanesulfonate) (AMPSX) and poly(acrylamide) (AMX) at selected pH values. Rates of hydrolysis and aminolysis both increase with increasing pH and decrease with increasing mol. wt. of the dithioester. On the basis of these rate consts., math. relationships have been developed to predict the no. of living chain ends and the mol. wt. with competitive hydrolysis. Utilizing this approach, predictions of mol. wt. at specific conversions are in agreement with exptl. values detd. by SEC/MALLS.
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      Fuchs, A. V.; Thurecht, K. J. Stability of Trithiocarbonate RAFT Agents Containing Both a Cyano and a Carboxylic Acid Functional Group. ACS Macro Lett 2017, 6, 287– 291,  DOI: 10.1021/acsmacrolett.7b00100
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      Stability of Trithiocarbonate RAFT Agents Containing Both a Cyano and a Carboxylic Acid Functional Group
      Fuchs, Adrian V.; Thurecht, Kristofer J.
      ACS Macro Letters (2017), 6 (3), 287-291CODEN: AMLCCD; ISSN:2161-1653. (American Chemical Society)
      The hydrolytic degrdn. of widely used cyano-contg., acid-bearing trithiocarbonate reversible addn.-fragmentation chain-transfer (RAFT) agents has been identified and shown to effect the RAFT polymn. and end-group fidelity of PMMA polymers. The hydrolysis occurred when the RAFT agents were stored under the recommended conditions. Degrdn. was identified in both com. available and popular synthetic RAFT agents. 1H and 13C NMR as well as mass spectroscopy show that the cyano functionality hydrolyzes to the amide adduct. Doping of this amide degrdn. product into RAFT polymns. of MMA results in increased dispersities and changes in expected end-group fidelities. The ability to identify this degrdn. product and remove it from the RAFT agent before use will allow better control over polymer properties and postmodification processes commonly used in complex polymer systems, nanomedicines, and bioconjugates.
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      Blanazs, A.; Madsen, J.; Battaglia, G.; Ryan, A. J.; Armes, S. P. Mechanistic Insights for Block Copolymer Morphologies: How Do Worms Form Vesicles?. J. Am. Chem. Soc. 2011, 133, 16581– 16587,  DOI: 10.1021/ja206301a
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      Mechanistic Insights for Block Copolymer Morphologies: How Do Worms Form Vesicles?
      Blanazs, Adam; Madsen, Jeppe; Battaglia, Giuseppe; Ryan, Anthony J.; Armes, Steven P.
      Journal of the American Chemical Society (2011), 133 (41), 16581-16587CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Amphiphilic diblock copolymers composed of two covalently linked, chem. distinct chains can be considered to be biol. mimics of cell membrane-forming lipid mols., but with typically more than an order of magnitude increase in mol. wt. These macromol. amphiphiles are known to form a wide range of nanostructures (spheres, worms, vesicles, etc.) in solvents that are selective for one of the blocks. However, such self-assembly is usually limited to dil. copolymer solns. (<1%), which is a significant disadvantage for potential com. applications such as drug delivery and coatings. In principle, this problem can be circumvented by polymn.-induced block copolymer self-assembly. Here the authors detail the synthesis and subsequent in situ self-assembly of amphiphilic AB diblock copolymers in a one pot concd. aq. dispersion polymn. formulation. The authors show that spherical micelles, wormlike micelles, and vesicles can be predictably and efficiently obtained (within 2 h of polymn., >99% monomer conversion) at relatively high solids in purely aq. soln. Furthermore, careful monitoring of the in situ polymn. by transmission electron microscopy reveals various novel intermediate structures (including branched worms, partially coalesced worms, nascent bilayers, "octopi", "jellyfish", and finally pure vesicles) that provide important mechanistic insights regarding the evolution of the particle morphol. during the sphere-to-worm and worm-to-vesicle transitions. This environmentally benign approach (which involves no toxic solvents, is conducted at relatively high solids, and requires no addnl. processing) is readily amenable to industrial scale-up, since it is based on com. available starting materials.
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      Lovett, J. R.; Warren, N. J.; Ratcliffe, L. P. D.; Kocik, M. K.; Armes, S. P. PH-Responsive Non-Ionic Diblock Copolymers: Ionization of Carboxylic Acid End-Groups Induces an Order-Order Morphological Transition. Angew. Chem., Int. Ed. 2015, 54, 1279– 1283,  DOI: 10.1002/anie.201409799
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      pH-Responsive Non-Ionic Diblock Copolymers: Ionization of Carboxylic Acid End-Groups Induces an Order-Order Morphological Transition
      Lovett, Joseph R.; Warren, Nicholas J.; Ratcliffe, Liam P. D.; Kocik, Marzena K.; Armes, Steven P.
      Angewandte Chemie, International Edition (2015), 54 (4), 1279-1283CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
      A carboxylic acid based reversible addn. fragmentation transfer (RAFT) agent is used to prep. gels composed of worm-like diblock copolymers using two non-ionic monomers, glycerol monomethacrylate (GMA) and 2-hydroxypropyl methacrylate (HPMA). Ionization of the carboxylic acid end-group on the PGMA stabilizer block induces a worm-to-sphere transition, which in turn causes immediate degelation. This morphol. transition is fully reversible as detd. by TEM and rheol. studies and occurs because of a subtle change in the packing parameter for the copolymer chains. A control expt. where the Me ester deriv. of the RAFT agent is used to prep. the same diblock copolymer confirms that no pH-responsive behavior occurs in this case. This end-group ionization approach is important for the design of new pH-responsive copolymer nano-objects as, unlike polyacids or polybases, only a minimal amt. of added base (or acid) is required to drive the morphol. transition.
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      Fox, T. G. Influence of Diluent and of Copolymer Composition on the Glass Temperature of a Polymer System. Bull. Am. Phys. Soc. 1956, 1, 123
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      Influence of diluent and of copolymer composition on the glass temperature of a polymer system
      Fox, T. G.
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      The above are titles of papers presented before the Am. Phys. Soc. and published in abstr. form.
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      Meng, F.; Jeon, Y.-S.; Chung, D.-J.; Kim, J.-H. Miscible Blend and Semi-IPN Gel of Poly(Hydroxyethyl Aspartamide) with Poly(N-Vinyl Pyrrolidone). Polym. Korea 2012, 36, 617– 621,  DOI: 10.7317/pk.2012.36.5.617
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      Miscible blend and semi-IPN gel of poly(hydroxyethyl aspartamide) with poly(N-vinyl pyrrolidone)
      Meng, Fan; Jeon, Young Sil; Chung, Dong June; Kim, Ji-Heung
      Polymer (Korea) (2012), 36 (5), 617-621CODEN: POLLDG; ISSN:0379-153X. (Polymer Society of Korea)
      PHEAs [α,β-poly(2-hydroxyethyl-DL-aspartamides)], a class of poly(amino acid), have been widely studied as biodegradable and biocompatible polymers for potential biomedical and pharmaceutical applications. In this study, we investigated a homogeneous blend of PHEA with poly(N-vinyl pyrrolidone) (PNVP) and its semi-IPN (semi-interpenetrating polymer network) gels. Blend films were prepd. by a soln. casting method. The resulting blends were totally transparent over the whole compn. ranges and the single Tg, changing monotonously with compn., was obsd. by DSC to confirm the miscibility between these two polymers. FTIR was used to discuss the possible hydrogen-bonding interaction between polymers. In addn., semi-IPN type gels were prepd. by chem. crosslinking of PHEA/PNVP blend soln. using hexamethylene diisocyanate (HMDI) as a crosslinking reagent. The prepd. gel was characterized by their swelling property and morphol.
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    73. 73
      Sabatini, D. D.; Bensch, K.; Barrnett, R. J. Cytochemistry and Electron Microscopy. J. Cell Biol. 1963, 17, 19– 58,  DOI: 10.1083/jcb.17.1.19
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      Cytochemistry and electron microscopy; the preservation of cellular ultrastructure and enzymic activity by aldehyde fixation
      Sabatini, David D.; Bensch, Klaus; Barrnett, Russell J.
      Journal of Cell Biology (1963), 17 (No. 1), 19-58CODEN: JCLBA3; ISSN:0021-9525.
      Tissue prepns. suitable for both electron microscopy and cytochem. studies were obtained by fixation in 4-6.5% glutaraldehyde, 4% glyoxal, 12.5% hydroxyadipaldehyde, 10% crotonaldehyde, 5% pyruvic aldehyde, 10% acetaldehyde, or 5% methacrolein. The aldehydes were prepd. as cacodylate- or phosphate-buffered solns., 0.l-0.2M, pH 6.5-7.6, that, except for glutaraldehyde, contained 0.22-0.55M sucrose. The blocks were fixed for 0.5-24 hrs. and stored at 4° in 0.1M buffer contg. 0.22M sucrose. Aliesterase, acetylcholinesterase, alk. and acid phosphatases, 5-nucleotidase, adenosinetriphosphatase, and di- and triphosphopyridine nucleotide diaphorase activities were histochemically demonstrable after most of the fixatives. Following hydroxyaldipaldehyde or glyoxal fixation, cytochrome oxidase, succinic dehydrogenase, and glucose-6-phosphatase were also detectable. Membranous differentiation in the cells was not visible by electron microscopy of the aldehyde-fixed tissues. However, a 2nd fixation with OsO4, even after prolonged storage, rendered an image comparable to that of tissues prepd. with OsO4 alone under standard conditions. Glutaraldehyde-fixed tissues were esp. well visualized by electron microscopy after the postfixation. 60 references.
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    74. 74
      Migneault, I.; Dartiguenave, C.; Bertrand, M. J.; Waldron, K. C. Glutaraldehyde: Behavior in Aqueous Solution, Reaction with Proteins, and Application to Enzyme Crosslinking. Biotechniques 2004, 37, 790– 802,  DOI: 10.2144/04375RV01
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      Glutaraldehyde: Behavior in aqueous solution, reaction with proteins, and application to enzyme crosslinking
      Migneault, Isabelle; Dartiguenave, Catherine; Bertrand, Michel J.; Waldron, Karen C.
      BioTechniques (2004), 37 (5), 790-796,798-802CODEN: BTNQDO; ISSN:0736-6205. (Life Sciences Publishing)
      A review. Glutaraldehyde possesses unique characteristics that render it one of the most effective protein crosslinking reagents. It can be present in at least 13 different forms depending on soln. conditions such as pH, concn., temp., etc. Substantial literature is found concerning the use of glutaraldehyde for protein immobilization, yet there is no agreement about the main reactive species that participates in the crosslinking process because monomeric and polymeric forms are in equil. Glutaraldehyde may react with proteins by several means such as aldol condensation or Michael-type addn., and we show here 8 different reactions for various aq. forms of this reagent. As a result of these discrepancies and the unique characteristics of each enzyme, crosslinking procedures using glutaraldehyde are largely developed through empirical observation. The choice of the enzyme-glutaraldehyde ratio, as well as their final concn., is crit. because insolubilization of the enzyme must result in minimal distortion of its structure in order to retain catalytic activity. The purpose of this paper is to give an overview of glutaraldehyde as a crosslinking reagent by describing its structure and chem. properties in aq. soln. in an attempt to explain its high reactivity toward proteins, particularly as applied to the prodn. of insol. enzymes.
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      Hayat, M. A. Glutaraldehyde: Role in Electron Microscopy. Micron Microsc. Acta 1986, 17, 115– 135,  DOI: 10.1016/0739-6260(86)90042-0
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      Glutaraldehyde: role in electron microscopy
      Hayat, M. A.
      Micron and Microscopica Acta (1986), 17 (2), 115-35CODEN: MMACDN; ISSN:0739-6260.
      A review with ∼175 refs. on the history, properties, reactions with proteins and lipids, effect on OsO4, and fixation by glutaraldehyde in relation to its use in various electron microscopy and immunocytochem. methods.
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      Kiernan, J. A. Formaldehyde, Formalin, Paraformaldehyde And Glutaraldehyde: What They Are And What They Do. Microsc. Today 2000, 8, 8– 13,  DOI: 10.1017/S1551929500057060
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      Kim, K.-J.; Lee, S.-B.; Han, N. W. Effects of the Degree of Crosslinking on Properties of Poly(Vinyl Alcohol) Membranes. Polym. J. 1993, 25, 1295– 1302,  DOI: 10.1295/polymj.25.1295
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      Effects of the degree of crosslinking on properties of poly(vinyl alcohol) membranes
      Kim, Kwang Je; Lee, Soo Bok; Han, Neung Won
      Polymer Journal (Tokyo, Japan) (1993), 25 (12), 1295-302CODEN: POLJB8; ISSN:0032-3896.
      Asym. poly(vinyl alc.) (PVA) membranes were prepd. by the phase inversion technique, and crosslinked with glutaraldehyde. The degree of crosslinking of the membrane was controlled by varying the crosslinking conditions. The effects of the degree of crosslinking on the swelling characteristics, contact angles, crit. surface tensions, and pervaporation characteristics were examd. A method for the evaluation of the degree of crosslinking, which needs only the glutaraldehyde concn. of the crosslinking soln. to be measured after the crosslinking reaction, is proposed, and was found useful. The degree of swelling of PVA membrane for water decreases abruptly as the degree of crosslinking increases. However, the degree of swelling for ethanol is nearly independent of the degree of crosslinking. The crit. surface tension of the membrane increases more or less within the range of 37.0-40.0 dyn cm-1 with increasing degree of crosslinking below 30%. But, it is nearly const. at 40.5 dyn cm-1 above 30%. The wetting behavior of the membrane may not be greatly affected by the degree of crosslinking. The selectivity factor and permeate flux of the membrane in the pervaporation of the ethanol-water mixt. of 95 wt% ethanol concn. decrease similarly with increasing degree of crosslinking. The pervaporation characteristics seem to be closely related to the swelling behavior. The degree of crosslinking is an important variable for swelling behavior and pervaporation characteristics.
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      Yeom, C.-K.; Lee, K.-H. Pervaporation Separation of Water-Acetic Acid Mixtures through Poly(Vinyl Alcohol) Membranes Crosslinked with Glutaraldehyde. J. Membr. Sci. 1996, 109, 257– 265,  DOI: 10.1016/0376-7388(95)00196-4
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      Pervaporation separation of water-acetic acid mixtures through poly(vinyl alcohol) membranes crosslinked with glutaraldehyde
      Yeom, Choong-Kyun; Lee, Kew-Ho
      Journal of Membrane Science (1996), 109 (2), 257-65CODEN: JMESDO; ISSN:0376-7388. (Elsevier)
      Poly(vinyl alc.) (PVA) membranes crosslinked with glutaraldehyde (GA) were prepd. by a soln. method for the pervaporation sepn. of acetic acid-water mixts. In the soln. method, dry PVA films were crosslinked by immersion for 2 days at 40° in reaction solns. which contained different contents of GA, acetone and a catalyst, HCl. In order to fabricate the crosslinked PVA membranes which were stable in aq. solns., acetone was used as reaction medium instead of aq. inorg. salt solns. which have been commonly used in reaction soln. for PVA crosslinking reaction. The crosslinking reaction between the hydroxyl group of PVA and the aldehyde group of GA was characterized by IR spectroscopy. Swelling measurements were carried out in both water and acetic acid to investigate the swelling behavior of the membranes. The swelling behavior of a membrane fabricated at different GA content in a reaction soln. depended on crosslinking d. and chem. functional groups created as a result of the reaction between PVA and GA, such as the acetal group, ether linkage and unreacted pendent aldehydes in PVA. The pervaporation sepn. of acetic acid-water mixts. was performed over a range of 70-90 wt% acetic acid in the feed at 35-50° to examine the sepn. performances of the PVA membranes. Permeation behavior through the membranes was analyzed by using pervaporation activation energies which had been calcd. from the Arrhenius plots of permeation rates.
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    80. 80
      Kurihara, S.; Sakamaki, S.; Mogi, S.; Ogata, T.; Nonaka, T. Crosslinking of Poly(Vinyl Alcohol)-Graft-N-Isopropylacrylamide Copolymer Membranes with Glutaraldehyde and Permeation of Solutes through the Membranes. Polymer. 1996, 37, 1123– 1128,  DOI: 10.1016/0032-3861(96)80838-X
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      Crosslinking of poly(vinyl alcohol)-graft-N-isopropylacrylamide copolymer membranes with glutaraldehyde and permeation of solutes through the membranes
      Kurihara, Seiji; Sakamaki, Shinichi; Mogi, Satosi; Ogata, Tomonari; Nonaka, Takamasa
      Polymer (1996), 37 (7), 1123-8CODEN: POLMAG; ISSN:0032-3861. (Elsevier)
      The phase transition behavior of poly(vinyl alc.)-graft-N-isopropylacrylamide copolymer membranes was studied by measuring their steady-state fluorescence spectra and swelling ratios. Crosslinking with glutaraldehyde increased the tensile strength of copolymer membrane and also resulted in a considerable decrease in the swelling ratio of the membrane. Well defined thermo-control of permeation through the membrane was achieved by crosslinking of the copolymer membrane with glutaraldehyde.
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    81. 81
      Rao, P. S.; Sridhar, S.; Wey, M. Y.; Krishnaiah, A. Pervaporation Performance and Transport Phenomenon of PVA Blend Membranes for the Separation of THF/Water Azeotropic Mixtures. Polym. Bull. 2007, 59, 289– 298,  DOI: 10.1007/s00289-007-0769-6
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      Pervaporation performance and transport phenomenon of PVA blend membranes for the separation of THF/water azeotropic mixtures
      Rao, P. Srinivasa; Sridhar, S.; Wey, Ming Yen; Krishnaiah, A.
      Polymer Bulletin (Heidelberg, Germany) (2007), 59 (2), 289-298CODEN: POBUDR; ISSN:0170-0839. (Springer)
      Dense polymer membranes were made by mixing aq. solns. of hydrophilic polymers poly(vinyl alc.) (PVA) and polyethyleneimine (PEI) in different ratios for investigating the sepn. of THF/water azeotropic mixts. by pervaporation (PV). In order to gain a more detailed picture of the mol. transport phenomenon, we have performed sorption gravimetric expts. at 30° to compute diffusion, swelling, sorption and permeability coeffs. of PVA/PEI membranes in the presence of THF and water. The membranes were found to have good potential for breaking the azeotrope of THF at 6% concn. of water. An increase in PVA content in the blend caused a redn. in the flux and an increase in selectivity. Among the blends tested in the study, the 5:1 PVA/PEI blend membrane showed the highest sepn. factor of 181.5, exhibited a flux of 1.28 kg/m2h for THF, resp. at azeotropic feed compn.
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    82. 82
      Bolto, B.; Tran, T.; Hoang, M.; Xie, Z. Crosslinked Poly(Vinyl Alcohol) Membranes. Prog. Polym. Sci. 2009, 34, 969– 981,  DOI: 10.1016/j.progpolymsci.2009.05.003
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      82
      Crosslinked poly(vinyl alcohol) membranes
      Bolto, Brian; Tran, Thuy; Hoang, Manh; Xie, Zongli
      Progress in Polymer Science (2009), 34 (9), 969-981CODEN: PRPSB8; ISSN:0079-6700. (Elsevier Ltd.)
      A review. The inherent hydrophilicity of poly(vinyl alc.) (PVA) makes it an attractive polymer for water treatment applications based on membranes. Thermal and chem. resistance and a high anti-fouling potential are accompanied by high water permeability. The large swelling capacity requires that the PVA be adequately crosslinked to ensure that the contaminants in water can be retained, and that compaction under pressure can be minimized. There is a challenge to achieve this and still obtain economical permeate fluxes. The literature on crosslinking of PVA is reviewed. Many reagents have been explored. Glutaraldehyde is a more effective crosslinking agent than formaldehyde or glycidyl acrylate, which in turn gives a less swollen product than that obtained by increasing the crystallinity by heating. Toluene diisocyanate and acrolien give similar results in the prepn. of reverse osmosis membranes, but at an extremely high applied pressure. Crosslinking with maleic anhydride/vinyl Me ether copolymers gives as good a result, but at even higher pressure. Thus the high swelling of PVA can be overcome by crosslinking reactions, but with the consumption of some of the OH groups responsible for the hydrophilicity. What is really needed is network formation that provides a tight restraining without serious loss of hydrophilic behavior. Similar membranes are used for the sepn. of org. compds. from one another or from water by pervaporation, where the vapor of one component is selectively transferred through the membrane on the basis of polarity differences. Here PVA membranes would be esp. suited to dehydration procedures. The high swelling behavior can be countered also by forming the active PVA component inside the pores of a microporous membrane. Crosslinked PVA inside such membranes has its swelling suppressed, and can function as salt removal membranes. By only coating the pore walls, leaving some porosity, microfiltration or ultrafiltration membranes can be prepd. In both situations a degree of grafting to the host membrane would be beneficial.
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    83. 83
      Fan, J.-B.; Song, Y.; Wang, S.; Meng, J.; Yang, G.; Guo, X.; Feng, L.; Jiang, L. Directly Coating Hydrogel on Filter Paper for Effective Oil-Water Separation in Highly Acidic, Alkaline, and Salty Environment. Adv. Funct. Mater. 2015, 25, 5368– 5375,  DOI: 10.1002/adfm.201501066
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      Directly Coating Hydrogel on Filter Paper for Effective Oil-Water Separation in Highly Acidic, Alkaline, and Salty Environment
      Fan, Jun-Bing; Song, Yongyang; Wang, Shutao; Meng, Jingxin; Yang, Gao; Guo, Xinglin; Feng, Lin; Jiang, Lei
      Advanced Functional Materials (2015), 25 (33), 5368-5375CODEN: AFMDC6; ISSN:1616-301X. (Wiley-VCH Verlag GmbH & Co. KGaA)
      The sepn. of oil-water mixts. in highly acidic, alk., and salty environment remains a great challenge. Simple, low-cost, efficient, eco-friendly, and easily scale-up processes for the fabrication of novel materials to effective oil-water sepn. in highly acidic, alk., and salty environment, are urgently desired. Here, a facile approach is reported for the fabrication of stable hydrogel-coated filter paper which not only can sep. oil-water mixt. in highly acidic, alk., and salty environment, but also sep. surfactant-stabilized emulsion. The hydrogel-coated filter paper is fabricated by smartly crosslinking filter paper with hydrophilic polyvinyl alc. through a simple aldol condensation reaction with glutaraldehyde as a crosslinker. The resultant multiple crosslinked networks enable the hydrogel-coated filter paper to tolerate high acid, alkali, and salt up to 8 M H2SO4, 10 M NaOH, and satd. NaCl. It is shown that the hydrogel-coated filter paper can sep. oil-water mixts. in highly acidic, alk., and salty environment and oil-in-water emulsion environment, with high sepn. efficiency (>99%).
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      Habeeb, A. F. S. A.; Hiramoto, R. Reaction of Proteins with Glutaraldehyde. Arch. Biochem. Biophys. 1968, 126, 16– 26,  DOI: 10.1016/0003-9861(68)90554-7
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      Reaction of proteins with glutaraldehyde
      Habeeb, A. F. S. A.; Hiramoto, R.
      Archives of Biochemistry and Biophysics (1968), 126 (1), 16-26CODEN: ABBIA4; ISSN:0003-9861.
      Glutaraldehyde was found to react with the α-amino groups of amino acids, the N-terminal amino groups of some peptides and the SH group of cysteine. The phenolic and the imidazole rings of tyrosine and histidine derivs. were partially reactive. With proteins such as bovine serum albumin, ovalbumin, and human γ-globulin, glutaraldehyde reacted predominantly with the ε-amino groups of lysine to form mainly intermol. cross-linkages. Some reaction, however, did occur with tyrosine, histidine, and SH residues. The sol. aggregated proteins were capable of reacting with antibodies against their resp. native proteins. Glutaraldehyde was also capable of conjugating ovalbumin to bovine serum albumin and the product contained only minor contaminants of aggregated ovalbumin and bovine serum albumin. 21 references.
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      Richards, F. M.; Knowles, J. R. Glutaraldehyde as a Protein Cross-Linking Reagent. J. Mol. Biol. 1968, 37, 231– 233,  DOI: 10.1016/0022-2836(68)90086-7
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      Glutaraldehyde as a protein cross-linking reagent
      Richards, Frederic; Knowles, J. R.
      Journal of Molecular Biology (1968), 37 (), 231-3CODEN: JMOBAK; ISSN:0022-2836.
      N.M.R. and other data excluded the possibility that glutaraldehyde forms protein cross-links through Schiff base formation. Instead, a mechanism is proposed which involves aldol condensation of glutaraldehyde and then the formation of Michael-type adducts.
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      Peters, K.; Richards, F. M. Chemical Cross-Linking: Reagents and Problems in Studies of Membrane Structure. Annu. Rev. Biochem. 1977, 46, 523– 551,  DOI: 10.1146/annurev.bi.46.070177.002515
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      Chemical cross-linking: reagents and problems in studies of membrane structure
      Peters, Kevin; Richards, Frederic M.
      Annual Review of Biochemistry (1977), 46 (), 523-51CODEN: ARBOAW; ISSN:0066-4154.
      A review with 92 refs.
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      Cheung, D. T.; Perelman, N.; Ko, E. C.; Nimni, M. E. Mechanism of Crosslinking of Proteins by Glutaraldehyde III. Reaction with Collagen in Tissues. Connect. Tissue Res. 1985, 13, 109– 115,  DOI: 10.3109/03008208509152389
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      Mechanism of crosslinking of proteins by glutaraldehyde. III. Reaction with collagen in tissues
      Cheung, David T.; Perelman, Natasha; Ko, Ellen C.; Nimni, Marcel E.
      Connective Tissue Research (1985), 13 (2), 109-15CODEN: CVTRBC; ISSN:0300-8207.
      Bovine pericardium, a dense collagenous connective tissue that is frequently used as a xenograft, was crosslinked with glutaraldehyde by using different modalities of fixation. The degree of crosslinking was evaluated as a function of the ability of CNBr and Pronase to solubilize collagen. Apparently, glutaraldehyde fixes primarily the surface of the fibers and creates a polymeric network which hinders the further crosslinking of the interstitium of the fiber. When a low concn. of glutaraldehyde was used, a slow time-dependent crosslinking process was obsd. This slow process is maintained over a long period of time, greatly beyond that required for the actual penetration of glutaraldehyde to occur.
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      Okuda, K.; Urabe, I.; Yamada, Y.; Okada, H. Reaction of Glutaraldehyde with Amino and Thiol Compounds. J. Ferment. Bioeng. 1991, 71, 100– 105,  DOI: 10.1016/0922-338X(91)90231-5
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      Reaction of glutaraldehyde with amino and thiol compounds
      Okuda, Keiko; Urabe, Itaru; Yamada, Yasuhiro; Okada, Hirosuke
      Journal of Fermentation and Bioengineering (1991), 71 (2), 100-5CODEN: JFBIEX; ISSN:0922-338X.
      Stoichiometry, pH dependence, and reversibility of the reaction of glutaraldehyde with various amino and thiol compds. were investigated to elucidate the chem. nature of glutaraldehyde. For glutaraldehyde, three com. samples were examd. They have different spectral characteristics probably due to the difference in the content of α, β-unsatd. aldehyde polymers formed by aldol condensations of glutaraldehyde, but the amt. of such unsatd. structures is very small, and the chem. reactivity of these samples are almost the same. Therefore, the chem. reactivity characteristic of glutaraldehyde is not due to the α, β-unsatd. aldehydes. Glutaraldehyde reacts with the amino group in a wide pH range (≥ pH 3). The reactions at pH 7 and 9 are almost irreversible, though a little reversibility is obsd. The reaction rate becomes very slow after the initial rapid phase. The av. molar ratio of the amino and aldehyde groups consumed during the reaction of glutaraldehyde with the amino group is in a range of 0.3-0.2. Glutaraldehyde reacts with cysteine with a stoichiometric relationship of one mol of the thiol and amino groups of cysteine per mol of glutaraldehyde. Glutaraldehyde does not react with the thiol group without the presence of the primary amino group; the av. stoichiometric relationship is 0.5-0.6 mol of the thiol group, about 0.4 mol of the amino group, and 1 mol of glutaraldehyde, under the conditions of excess in the thiol and amino groups. These results indicate the complex nature of the glutaraldehyde reaction.
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      Mansur, H. S.; Sadahira, C. M.; Souza, A. N.; Mansur, A. A. P. FTIR Spectroscopy Characterization of Poly (Vinyl Alcohol) Hydrogel with Different Hydrolysis Degree and Chemically Crosslinked with Glutaraldehyde. Mater. Sci. Eng., C 2008, 28, 539– 548,  DOI: 10.1016/j.msec.2007.10.088
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      FTIR spectroscopy characterization of poly(vinyl alcohol) hydrogel with different hydrolysis degree and chemically crosslinked with glutaraldehyde
      Mansur, Herman S.; Sadahira, Carolina M.; Souza, Adriana N.; Mansur, Alexandra A. P.
      Materials Science & Engineering, C: Biomimetic and Supramolecular Systems (2008), 28 (4), 539-548CODEN: MSCEEE; ISSN:0928-4931. (Elsevier B.V.)
      In this work, poly (vinyl alc.) (PVA) hydrogels with different degree of hydrolysis (DH) were prepd. by chem. crosslinking with glutaraldehyde (GA). The nanostructure of the resulting hydrogels was investigated by Fourier Transform IR Spectroscopy (FTIR) and Synchrotron small-angle X-ray scattering characterization (SAXS). In vitro tests were performed by swelling ratio assays in different pH solns. The IR spectra of the crosslinked PVA showed absorption bands of the acetal bridges resulted from the reaction of the GA with the OH groups from PVA. Also the FTIR spectroscopy was used to det. the crystallinity of the PVA film based on the relative intensity of the vibration band at 1141 cm-1. The results have showed an increase of hydrogel crystallinity with higher DH of PVA. SAXS patterns have clearly indicated important modifications on the PVA semicryst. structure when it was crosslinked by GA. The swelling ratio was significantly reduced by chem. crosslinking the PVA network. PVA-derived hydrogel with chem. modified network was found to be pH-sensitive, indicating a high potential to be used in drug delivery polymer system.
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      Glatter, O.; Kratky, O. Small Angle X-Ray Scattering; Acedemic Press: London, 1982.
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      Pedersen, J. S. Form Factors of Block Copolymer Micelles with Spherical, Ellipsoidal and Cylindrical Cores. J. Appl. Crystallogr. 2000, 33, 637– 640,  DOI: 10.1107/S0021889899012248
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      Form factors of block copolymer micelles with spherical, ellipsoidal and cylindrical cores
      Pedersen, Jan Skov
      Journal of Applied Crystallography (2000), 33 (3, Pt. 1), 637-640CODEN: JACGAR; ISSN:0021-8898. (Munksgaard International Publishers Ltd.)
      The form factor of a micelle model with a spherical core and Gaussian polymer chains attached to the surface has previously been calcd. anal. by Pedersen and Gerstenberg. Non-penetration of the chains into the core region was mimicked in the anal. calcns. by moving the center of mass of the chains Rg away from the surface of the core, where Rg is the radius of gyration of the chains. In the present work, the calcns. have been extended to micelles with ellipsoidal and cylindrical cores. Non-penetration was also for these taken into account by moving the center of mass of the chains Rg away from the core surface. In addn. results for worm-like micelles, disk-shape micelles and micelles with a vesicle shape are given.
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    92. 92
      Bang, J.; Jain, S.; Li, Z.; Lodge, T. P.; Pedersen, J. S.; Kesselman, E.; Talmon, Y. Sphere, Cylinder, and Vesicle Nanoaggregates in Poly(Styrene-b-Isoprene) Diblock Copolymer Solutions. Macromolecules 2006, 39, 1199– 1208,  DOI: 10.1021/ma052023+
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      92
      Sphere, Cylinder, and Vesicle Nanoaggregates in Poly(styrene-b-isoprene) Diblock Copolymer Solutions
      Bang, Joona; Jain, Sumeet; Li, Zhibo; Lodge, Timothy P.; Pedersen, Jan Skov; Kesselman, Ellina; Talmon, Yeshayahu
      Macromolecules (2006), 39 (3), 1199-1208CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      An asym. poly(styrene-b-isoprene) diblock copolymer with block mol. wts. of 13,000 and 71,000 g/mol, resp., was dissolved at 1 vol% in a series of solvents with varying selectivity for styrene: di-Bu phthalate (DBP), di-Et phthalate (DEP), and di-Me phthalate (DMP). The degree of solvent selectivity was adjusted by mixing DBP/DEP and DEP/DMP in various proportions. With increasing solvent selectivity, the predominant micellar shape changes from spheres to cylinders to vesicles, reflecting the changing interfacial curvature. The detailed micellar morphologies were characterized by small-angle X-ray scattering (SAXS) and cryogenic transmission electron microscopy (cryo-TEM). Recently developed form factors were used to characterize the micellar structures in detail, and a vesicle form factor was derived for this system. From the core dimensions, the packing properties, such as the interfacial area per chain and the core chain stretching, were detd. The cryo-TEM results demonstrate the suitability of the technique for these glass-forming solvents and gave micellar core dimensions in quant. agreement with those from SAXS. The universality of the shape sequence sphere/cylinder/vesicle, well-established for aq. solns. of surfactants and block copolymers, is thus confirmed for org. systems.
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    93. 93
      Czajka, A.; Armes, S. P. In Situ SAXS Studies of a Prototypical RAFT Aqueous Dispersion Polymerization Formulation: Monitoring the Evolution in Copolymer Morphology during Polymerization-Induced Self-Assembly. Chem. Sci. 2020, 11, 11443– 11454,  DOI: 10.1039/D0SC03411H
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      93
      In situ SAXS studies of a prototypical RAFT aqueous dispersion polymerization formulation: monitoring the evolution in copolymer morphology during polymerization-induced self-assembly
      Czajka, Adam; Armes, Steven P.
      Chemical Science (2020), 11 (42), 11443-11454CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
      Small-angle X-ray scattering (SAXS) is used to characterize the in situ formation of diblock copolymer spheres, worms and vesicles during reversible addn.-fragmentation chain transfer (RAFT) aq. dispersion polymn. of 2-hydroxypropyl methacrylate at 70°C using a poly(glycerol monomethacrylate) steric stabilizer. The 1H NMR spectroscopy indicates more than 99% HPMA conversion within 80 min, while transmission electron microscopy and dynamic light scattering studies are consistent with the final morphol. being pure vesicles. Anal. of time-resolved SAXS patterns for this prototypical polymn.-induced self-assembly (PISA) formulation enables the evolution in copolymer morphol., particle diam., mean aggregation no., solvent vol. fraction, surface d. of copolymer chains and their mean inter-chain sepn. distance at the nanoparticle surface to be monitored. Furthermore, the change in vesicle diam. and membrane thickness during the final stages of polymn. supports an 'inward growth' mechanism.
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    94. 94
      Warren, N. J.; Derry, M. J.; Mykhaylyk, O. O.; Lovett, J. R.; Ratcliffe, L. P. D. D.; Ladmiral, V.; Blanazs, A.; Fielding, L. A.; Armes, S. P. Critical Dependence of Molecular Weight on Thermoresponsive Behavior of Diblock Copolymer Worm Gels in Aqueous Solution. Macromolecules 2018, 51, 8357– 8371,  DOI: 10.1021/acs.macromol.8b01617
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      94
      Critical Dependence of Molecular Weight on Thermoresponsive Behavior of Diblock Copolymer Worm Gels in Aqueous Solution
      Warren, Nicholas J.; Derry, Matthew J.; Mykhaylyk, Oleksandr O.; Lovett, Joseph R.; Ratcliffe, Liam P. D.; Ladmiral, Vincent; Blanazs, Adam; Fielding, Lee A.; Armes, Steven P.
      Macromolecules (Washington, DC, United States) (2018), 51 (21), 8357-8371CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      Reversible addn.-fragmentation chain transfer (RAFT) aq. dispersion polymn. of 2-hydroxypropyl methacrylate was used to prep. three poly(glycerol monomethacrylate)x-poly(2-hydroxypropyl methacrylate)y (denoted Gx-Hy or PGMA-PHPMA) diblock copolymers, namely G37-H80, G54-H140, and G71-H200. A master phase diagram was used to select each copolymer compn. to ensure that a pure worm phase was obtained in each case, as confirmed by transmission electron microscopy (TEM) and small-angle x-ray scattering (SAXS) studies. The latter technique indicated a mean worm cross-sectional diam. (or worm width) ranging from 11 to 20 nm as the mean d.p. (DP) of the hydrophobic PHPMA block was increased from 80 to 200. These copolymer worms form soft hydrogels at 20 °C that undergo degelation on cooling. This thermoresponsive behavior was examd. using variable temp. DLS, oscillatory rheol., and SAXS. A 10% wt./wt. G37-H80 worm dispersion dissocd. to afford an aq. soln. of molecularly dissolved copolymer chains at 2 °C; on returning to ambient temp., these chains aggregated to form first spheres and then worms, with the original gel strength being recovered. In contrast, the G54-H140 and G71-H200 worms each only formed spheres on cooling to 2 °C, with thermoreversible (de)gelation being obsd. in the former case. The sphere-to-worm transition for G54-H140 was monitored by variable temp. SAXS: these expts. indicated the gradual formation of longer worms at higher temp., with a concomitant redn. in the no. of spheres, suggesting worm growth via multiple 1D sphere-sphere fusion events. DLS studies indicated that a 0.1% wt./wt. aq. dispersion of G71-H200 worms underwent an irreversible worm-to-sphere transition on cooling to 2 °C. Furthermore, irreversible degelation over the time scale of the expt. was also obsd. during rheol. studies of a 10% wt./wt. G71-H200 worm dispersion. Shear-induced polarized light imaging (SIPLI) studies revealed qual. different thermoreversible behavior for these three copolymer worm dispersions, although worm alignment was obsd. at a shear rate of 10 s-1 in each case. Subsequently conducting this technique at a lower shear rate of 1 s-1 combined with ultra small-angle x-ray scattering (USAXS) also indicated that worm branching occurred at a certain crit. temp. since an upturn in viscosity, distortion in the birefringence, and a characteristic feature in the USAXS pattern were obsd. Finally, SIPLI studies indicated that the characteristic relaxation times required for loss of worm alignment after cessation of shear depended markedly on the copolymer mol. wt.
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    95. 95
      Bannister, I.; Billingham, N. C.; Armes, S. P.; Rannard, S. P.; Findlay, P. Development of Branching in Living Radical Copolymerization of Vinyl and Divinyl Monomers. Macromolecules 2006, 39, 7483– 7492,  DOI: 10.1021/ma061811b
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      95
      Development of Branching in Living Radical Copolymerization of Vinyl and Divinyl Monomers
      Bannister, Iveta; Billingham, Norman C.; Armes, Steven P.; Rannard, Steven P.; Findlay, Paul
      Macromolecules (2006), 39 (22), 7483-7492CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      The branching copolymn. of 2-hydroxypropyl methacrylate (HPMA) with either ethylene glycol dimethacrylate (EGDMA) or bisphenol A dimethacrylate (BPDMA) as the branching agent has been carried out using atom transfer radical polymn. (ATRP) in methanol at 20 °C. With EGDMA, sol. branched copolymers were obtained provided that less than one branching agent was incorporated per primary chain: higher levels of EGDMA led to gelation, as expected. Anal. of the changes in the mol. wt. and polydispersity of the polymers shows that the formation of highly branched chains occurs only at high (>90%) conversions. Chain coupling is close to the ideal behavior predicted by the Flory-Stockmayer theory, suggesting that all double bonds are equally reactive and that there is no significant cyclization, in contrast to conventional free radical polymn. This anal. is confirmed by comparison of the consumption of the EGDMA branching agent with predictions from both theory and simulation. With BPDMA as the branching agent, similar results are obtained although branching is slightly less efficient.
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    96. 96
      Simon, K. A.; Warren, N. J.; Mosadegh, B.; Mohammady, M. R.; Whitesides, G. M.; Armes, S. P. Disulfide-Based Diblock Copolymer Worm Gels: A Wholly-Synthetic Thermoreversible 3D Matrix for Sheet-Based Cultures. Biomacromolecules 2015, 16, 3952– 3958,  DOI: 10.1021/acs.biomac.5b01266
      [ACS Full Text ACS Full Text], [