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Solution and Solid-State Behavior of Amphiphilic ABA Triblock Copolymers of Poly(acrylic acid-stat-styrene)-block-poly(butyl acrylate)-block-poly(acrylic acid-stat-styrene)
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Solution and Solid-State Behavior of Amphiphilic ABA Triblock Copolymers of Poly(acrylic acid-stat-styrene)-block-poly(butyl acrylate)-block-poly(acrylic acid-stat-styrene)
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Cite this: Macromolecules 2022, 55, 21, 9726–9739
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https://doi.org/10.1021/acs.macromol.2c01299
Published October 28, 2022

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Abstract

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A combination of statistical and triblock copolymer properties is explored to produce stable aqueous polymer dispersions suitable for the film formation. In order to perform an extensive structural characterization of the products in the dissolved, dispersed, and solid states, a wide range of symmetrical poly(acrylic acid-stat-styrene)x-block-poly(butyl acrylate)y-block-poly(acrylic acid-stat-styrene)x, poly(AA-st-St)x-b-PBAy-b-poly(AA-st-St)x, (x = 56, 108 and 140, y = 100–750; the AA:St molar ratio is 42:58) triblock copolymers were synthesized by reversible addition–fragmentation chain transfer (RAFT) solution polymerization using a bifunctional symmetrical RAFT agent. It is demonstrated that the amphiphilic statistical outer blocks can provide sufficient stabilization to largely hydrophobic particles in aqueous dispersions. Such a molecular design provides an advantage over copolymers composed only of homoblocks, as a simple variation of the statistical block component ratio provides an efficient way to control the hydrophilicity of the stabilizer block, which ultimately affects the copolymer morphology in solutions and solid films. It was found by small-angle X-ray scattering (SAXS) that the copolymers behaved as dissolved chains in methylethylketone (MEK) but self-assembled in water into stable and well-defined spherical particles that increased in size with the length of the hydrophobic PBA block. These particles possessed an additional particulate surface structure formed by the statistical copolymer stabilizer block, which self-folded through the hydrophobic interactions between the styrene units. SAXS and atomic force microscopy showed that the copolymer films cast from the MEK solutions formed structures predicted by self-consistent field theory for symmetrical triblock copolymers, while the aqueous dispersions formed structural morphologies similar to a close-packed spheres, as would be expected for copolymer particles trapped kinetically due to the restricted movement of the blocks in the initial aqueous dispersion. A strong correlation between the structural morphology and mechanical properties of the films was observed. It was found that the properties of the solvent cast films were highly dependent on the ratios of the hard [poly(AA-st-St)] and soft (PBA) blocks, while the aqueous cast films did not show such a dependence. The continuous phase of hard blocks, always formed in the case of the aqueous cast films, produced films with a higher elastic modulus and a lower extension-to-break in a comparison with the solvent-cast films.

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Introduction

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The self-assembly of block copolymers in both solution and in the bulk has been widely researched over many decades. (1−8) In solution, these systems are known to form various morphologies, such as spheres, (9−17) worms, (18,19) and vesicles, (20,21) and can be used for a variety of applications such as for drug delivery (22) or as thickening agents. (23) In the solid state, block copolymers self-assemble to form gyroid, hexagonally packed cylindrical, body-centered cubic (BCC), and lamellae structures that are often used in industry (e.g., as thermoplastic elastomers). (8,24) It is widely known that the self-assembly of block copolymers is dictated by the length and chemical properties of each block. (25) Using a combination of blocks with a high glass transition temperature (Tg) and blocks with a low Tg, one can create materials that are both tough and flexible. (26−28) The family of synthetic rubbers known as Kratons is an example of such systems. Kratons are ABA triblock copolymers, where the A block has a high Tg (hard block) such as polystyrene and the B block has a low Tg (soft block) such as polybutadiene. In the solid state, these triblocks self-assemble into hard spherical domains of polystyrene that are covalently linked by a matrix of rubbery polybutadiene. Due to the physically cross-linked structure of the copolymer, the resulting film has very favorable mechanical properties (i.e., strong and flexible).
Although copolymers such as Kraton provide a useful “gold-standard” for block copolymer materials in the bulk, they are not suitable for use as coatings, as they would need to be cast from solutions in harmful organic solvents. For this reason, a large amount of block copolymer research is focused on water-dispersed systems. (29−31) In these systems, a purely hydrophilic stabilizer block is often used, as it provides good colloidal stability within the dispersion through either steric (32) or electrostatic (30) stabilization. However, in the solid phase this leads to large regions of hydrophilic groups, which may be disadvantageous for some applications, such as water-resistant coatings, e.g. gloss paints. For example, it was recently reported (27) that poly(acrylic acid)-b-poly(butyl acrylate) (PAA-b-PBA) diblock copolymer particles synthesized by reversible addition–fragmentation chain transfer (RAFT) aqueous emulsion polymerization-induced self-assembly could be used to form tough and transparent films. As the latex dries, the core–shell structure of the particle is maintained because the hard acrylic acid shell prevents the interdiffusion of the soft butyl acrylate cores. This results in a honeycomb-like network of cores separated by a a percolating network of poly(acrylic acid) . However, despite some benefits of a percolating network of acrylic acid in regards to the film toughness, this continuous network of hydrophilic units offers a potential path for the transport of water through the copolymer coating. Furthermore, the more thermodynamically stable conformation (spherical regions of poly(acrylic acid) in a continuous matrix of poly(butyl acrylate)) is only achieved once the polymer is annealed above the Tg of poly(acrylic acid). (27) Rieger and co-workers developed this work further by integrating high-Tg polystyrene-core nanofibers into a dispersion of PAA-b-PBA spherical nanoparticles. (26) The anisotropic high-Tg nanofibers act as reinforcing fillers once the acrylic aqueous dispersion dries onto a film and are responsible for both the increased stiffness of the material and maintaining high extensibility. (26)
Similar studies have been performed on more complex multiblock copolymers. Qiao et al. reported the synthesis of symmetrical ABCBA pentablock copolymers via solvent-free aqueous RAFT emulsion polymerization using a symmetrical RAFT agent, where the copolymers self-assembled into a three-layer core–shell spherical structure during the polymerization. (33) Here, the particles were also stabilized by a block of poly(acrylic acid); thus, when the copolymer dispersion was dried, a similar structure was observed in the copolymer film compared to that previously observed by Chenal et al., i.e., a percolating network of poly(acrylic acid). (33)
Compared to block copolymers, the self-assembly of statistical copolymers is relatively understudied. However, there has been a recent resurgence in interest in these systems, as they are know to self-assemble into useful nano-objects such as spheres, (34−36) rods or worms, (37−39) vesicles, (36,40) and “bowl-like” morphologies (41) and can also be tuned to form single-chain nanoparticles (SCNPs). (42−50) Furthermore, the self-assembly behavior of statistical copolymers is very predictable on the basis of the copolymer composition and the solvophobic nature of the copolymer units. (42,51) It was recently demonstrated that charge-stabilized amphiphilic statistical copolymers undergo spontaneous self-assembly driven by hydrophobic interactions to form well-defined spherical particles, where the relationship between particle size and the copolymer composition can be described using a particle surface charge (PSC) model. (42,51)
Statistical copolymers can form a range of different morphologies. It was recently reported that amphiphilic statistical copolymers formed “multicompartment” nanostructures in solution by orthogonal folding. (49) The copolymers studied therein were composed of two distinct statistical blocks of statistical copolymers [i.e., P(A-st-C)-b-P(B-st-C) ,where A and B are different hydrophobic monomers and C is a hydrophilic monomer]. It was reported that the two distinct blocks will “self-sort” or phase-separate. This phase separation, in addition to the hydrophobic interactions that drive the self-assembly into micelle-like structures in which the hydrophilic component remains at the water interface and the hydrophobic components aggregate to form a particle core, leads to these complex multicompartmented structures. (49) In addition, it was also examined how amphiphilic crystalline statistical copolymer dispersions assemble in the bulk once the dispersion is dried. (52) It was found that statistical copolymers with a low hydrophobe content (<50 mol %) self-assembled into spherical micelles, whereas copolymers with higher hydrophobe content (>50 mol %) self-assembled into vesicles. Furthermore, after the removal of the solvent, the bulk structures observed for both the spherical micelle and the vesicle dispersions were vastly different, forming a BCC structure and a lamellar structure, respectively. (52)
In this study, to challenge whether a purely hydrophilic stabilizer is required to stabilize a hydrophobic particle, properties of both statistical and block copolymers are explored in combination by synthesizing block copolymers that can be dispersed in water using an amphiphilic statistical stabilizer block. Furthermore, it is demonstrated that an amphiphilic statistical copolymer block can provide sufficient stabilization to a largely hydrophobic particle.
It is found herein that the proposed copolymer systems undergo a twofold self-assembly process when dispersed in water: (i) self-assembly of the hydrophobic core and (ii) self-assembly within the amphiphilic stabilizer block. Specifically, it is demonstrated that the poly(acrylic acid-stat-styrene)-b-poly(butyl acrylate)-b-poly(acrylic acid-stat-styrene) [P(AA-st-St)x-b-PBAy-b-P(AA-st-St)x or ABA] triblock copolymer composition allows a wide range of copolymer properties to be varied. The solution structures of these copolymers were assessed in both solvent and water using small-angle X-ray scattering (SAXS) to observe how they affected the bulk copolymer structure when cast as films. The resultant mechanical properties of both the solvent-cast films and the water-cast films were also assessed and linked to structural morphologies.

Experimental Section

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Materials

Butyl acrylate (BA, 99%), acrylic acid (AA, 99%), styrene (St, 99%), isopropanol (IPA, 99.9%), methyl ethyl ketone (MEK, 99.9%), ammonia (NH3, 25%), glacial acetic acid (99.85%), high-performance liquid chromatography-grade tetrahydrofuran (THF), and deuterated dimethyl sulfoxide (d6-DMSO) were purchased from Sigma-Aldrich (Gillingham, UK). S,S-Dibenzyl trithiocarbonate (DBzTTC) was purchased from Boron Molecular (Raleigh, NC). All materials were used as received unless otherwise stated. Deionized water was obtained from an ELGA Elgastat Option 3A water purifier (High Wycombe, UK). All materials were used as received unless stated otherwise in the text.

Synthesis of P(AA-st-St) Macro-CTA via RAFT Solution Polymerization

Three P(AA-st-St)x-DBzTTC-P(AA-st-St)x (Ax-DBzTTC-Ax or, for the sake of simplicity, AxAx, which should not be confused with the AA abbreviation used for acrylic acid) macro-CTAs with a targeted AA/St molar ratio of 50:50 but different degrees of polymerization (DP) (x = DP/2 = 56, 108, and 140) were synthesized (Figure 1a and Table 1). The protocol describes the quantities used to synthesize A56-DBzTTC-A56 (A56A56); a full table of quantities can be found in the Supporting Information (Table S1). AA (33.9 g, 0.471 mol), St (49.1 g, 0.471 mol), AIBN (0.186 g, 0.00114 mol), and DBzTTC (1.65 g, 0.00568 mol) were dissolved in MEK (105 mL). The solution was degassed with bubbling N2 for 60 min and then heated to 80 °C to initiate polymerization. This polymerization was quenched in air after 7 h at a monomer conversion of 68%. The initial P(AA-st-St) macro-CTA was purified by multiple precipitations from hexane, and the product was collected as a solid yellow powder.

Figure 1

Figure 1. RAFT polymerization protocol used to produce the sets of different P(AA-st-St)x-b-PBAy/2-DBzTTC-PBAy/2-b-P(AA-st-St)x (AxByAx) triblock copolymers, namely (a) the P(AA-st-St)x-DBzTTC-P(AA-st-St)x (Ax-DBzTTC-Ax) macro-CTA synthesis used to prepare A56-DBzTTC-A56 (A56A56), A108A108, and A140A140 (Table 1) and (b) the high-throughput synthesis of the triblock copolymers A56B100-750A56, A112B100-750A112, and A140B100-750A140 (Table 2) using a Chemspeed high-throughput robot.

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Table 1. Compositions and Molar Masses of Macro-CTAs Used for the P(AA-st-St)-b-PBA-b-P(AA-st-St) (ABA) Triblock Copolymer Synthesis
 NMRSECc
copolymerconversion (%)DP of copolymeramole fraction of AAbMn (kDa)Mw (kDa)Mw/Mn
A56A5668112 (56 + 56)0.429.111.41.26
A108A10858216 (108 + 108)0.4215.919.81.24
A140A14056280 (140 + 140)0.4219.224.51.28
a

The total DP of both A blocks used to synthesize the ABA triblock, where the A blocks will be half the DP of the respective macro-CTA. The DPs were calculated using the ratio of the integrals from the RAFT chain end and the copolymer backbone.

b

The copolymer composition was calculated by examining the respective integrals in the 1H NMR spectrum in DMSO.

c

SEC measurements were performed using a THF eluent containing 1% v/v acetic acid against PSt standards.

Parallel Syntheses of Triblock Copolymers via RAFT Solution Polymerization

Specific quantities (Table S1) of the purified P(AA-st-St) macro-CTA were added to eight reaction vessels of the Chemspeed Autoplant A100 high-throughput robot (Chemspeed Technologies, Switzerland). The macro-CTA was then dissolved in MEK at 50 °C. Once the macro-CTAs were fully dissolved, the solution was cooled to ambient temperature, and BA (5.00 g, 35.2 mmol) was added. Quantities of an AIBN solution (14 mg mL–1) in MEK were added to the eight reaction vessels and then a stream of nitrogen was blown through all the reaction vessels for 30 min in order to expel any oxygen. The mixtures were then heated to 80 °C and stirred with an overhead anchor stirrer for 8 h. The reaction mixtures were left to cool to ambient temperature overnight and decanted into 100 mL sample pots (Figure 1b). These copolymers were either precipitated into hexane, dried, and redispersed in water or dried as films straight from the reaction solution. Since butyl acrylate is a volatile organic compound, it is assumed that once the butyl acrylate dries there is no monomer present in the final copolymer film.

1H Nuclear Magnetic Resonance (NMR) Spectroscopy

1H NMR spectra were recorded on a Bruker AV1-400 or AV3HD-400 MHz spectrometer in d6-DMSO. These spectra were analyzed using Bruker Topspin software (version 3.5pl7), and chemical shifts are reported relative to a residual solvent peak.

Size Exclusion Chromatography/Advanced Polymer Chromatography (SEC/APC)

Molar mass distributions of the triblock copolymers were determined by SEC using THF with 1% v/v acetic acid as the eluent. Measurements were performed on a Waters ACQUITY APC system equipped with a refractive index detector. Separations were carried out using a set of 150 mm XT columns (45, 125, and 450 Å) at a flow rate of 1.0 mL min–1. All the samples were filtered through 0.2 μm PTFE membrane filters prior to analysis and measured relative to low-dispersity polystyrene (PSt) standards with peak molar masses ranging from 580 to 8 000 000 Da.

Small-Angle X-ray Scattering (SAXS) Measurements

SAXS samples were prepared by diluting the investigated polymer solution or dispersions with the appropriate solvent (MEK or water) to the desired concentration (e.g., 1%, 5% or 20% w/w). SAXS patterns were collected using laboratory SAXS instruments, either a Bruker AXS Nanostar instrument equipped with a two-dimensional (2D) Hi-STAR multiwire gas detector and modified with Xenocs GeniX 3D X-ray source (Cu Kα radiation, X-ray wavelength λ = 1.54 Å) and motorized collimating scatterless slits or a Xenocs Xeuss 2.0 laboratory beamline equipped with a 2D Dectris Pilatus 1 M detector and an Excillum liquid gallium MetalJet X-ray source (λ = 1.34 Å). The scattering patterns of the liquids were collected in a 2 mm glass capillary either positioned in a capillary holder or integrated in a flow-through cell to allow scattering patterns to be collected under vacuum. The patterns were collected over a scattering vector length range of 0.008 Å–1 < q < 0.16 Å–1, where q=4πλsin⁡θ and θ is a half the scattering angle. One-dimensional (1D) scattering curves were obtained by azimuthal binning and averaging the corresponding two-dimensional scattering patterns using software packages supplied with the SAXS instruments. Calibration, background subtraction, and further analysis of the 1D SAXS data were performed using Irena SAS macros for Igor Pro. (53)

Grazing-Incident Small-Angle X-ray Scattering (GISAXS) Measurements

The grazing-incident SAXS samples were prepared by drop-casting approximately 100 μL of the 20% w/w aqueous dispersion onto a clear ruby-grade mica disc 25 μm thick with a 15 mm diameter (Attwater group, UK). The dispersion was left to dry for 1 week. GISAXS measurements were performed using the Xenocs Xeuss 2.0 laboratory beamline. Time-resolved GISAXS was performed on block copolymer films during annealing in air at elevated temperatures (150 °C). To perform the measurements, the films were cast on to a mica substrate that was then mounted on a modified Linkam heating stage attached to a goniometer head. The measurements were performed at a critical angle, which was established prior to data acquisition. 1D scattering curves were obtained by azimuthal binning, taking into account the incident angle, and averaging the corresponding 2D scattering patterns using the software package supplied with the laboratory SAXS beamline.

Atomic Force Microscopy (AFM)

The investigated triblock copolymers were either drop-cast directly onto small metal AFM plates or drop-cast onto a silicone-coated dry-release film with a 300 μm thickness (Avery Dennison) and then attached to an AFM plate using double-sided tape. AFM height (topographic) images were collected using the ScanAsyst PeakForce tapping mode on a Bruker MultiMode atomic force microscope. A 2 nm silicon ScanAsyst-Air cantilever was used to perform the measurements. The WsXM 4.0 software was used for the image analysis, including measurements of the copolymer phase-separation length scale. (54)

Mechanical Testing

Triblock copolymer films were cast in plastic molds and left to dry under ambient conditions for one week. The films were then removed from the molds and cut into strips with a width of 7 mm and a length greater than 13 mm (the set gap). The individual thicknesses were measured using a micrometer, and both the extension-to-break and the Young’s modulus were measured at ambient conditions using an Instron 5500R instrument. All the triblock copolymer films cast from MEK were very uniform and showed no signs of either dewetting from the substrate or forming bubbles within the film. However, the copolymer films cast from water showed large amounts of dewetting from the plastic mold, and the formation of bubbles was observed during the drying process; in some cases, these two factors made it difficult to prepare uniform films. The observed dewetting is likely to be due to incompatibilities between the water and the substrate, (55,56) whereas the formation and stabilization of bubbles within the aqueous dispersions is a result of the amphiphilic nature of the copolymers and their ability to behave like surfactants. (56)

Results and Discussion

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Synthesis and Characterization of Copolymers

A set of P(AA-st-St)x-b-PBAy/2-DBzTTC-PBAy/2-b-P(AA-st-St)x (AxByAx) triblock copolymers was synthesized using RAFT copolymerization. A symmetrical bifunctional RAFT agent (DBzTTC) was used in order to achieve symmetrical triblock copolymers in two steps: (i) synthesis of a poly(acrylic acid-stat-styrene) macro-CTA with a midchain trithiocarbonate (Figure 1a) and (ii) chain extension “from the middle” with butyl acrylate to yield the desired AxByAx triblock copolymer (Figure 1b). First, a series of statistical copolymer macro-CTAs that would form the “A” blocks of the triblock copolymers were synthesized via RAFT copolymerization of styrene and acrylic acid at 50% w/w in MEK (Figure 1a). The resulting copolymers were isolated by precipitation from hexane.
Since both PSt and PAA are reported to have high glass transition temperatures (Tg ∼ 100 °C), (57,58) they will be denoted as the “hard” blocks within the triblock copolymers. Once the macro-CTAs were synthesized and purified, their compositions were determined by 1H NMR spectroscopy and their molar masses were determined using size-exclusion chromatography (SEC, Table 1). It was found that the composition of all three of macro-CTAs was 42:58 (AA:St, Figure S1), which deviates slightly from the initial monomer feed ratio (50:50). The observed deviation is consistent with the reactivity ratios for this monomer pair (e.g., rSt = 0.15 and rAA = 0.25, bulk polymerization), (59) which should result in a slight enrichment in styrene content at lower total monomer conversions. From the reactivity ratios, it could be expected that at a targeted 50:50 (AA:St) composition a block with a close to alternating component sequence should form. However, since there is a lower mole fraction of AA in the final synthesized copolymer composition, styrene-rich regions are less likely. The DPs of the three macro-CTAs were determined by NMR spectroscopy to be 112, 216, and 280 (Table 1). However, these macro-CTAs were synthesized with a symmetrical bifunctional RAFT agent (Figure 1a), meaning that the trithiocarbonate functional group of the RAFT agent was located approximately in the middle of the macro-CTA (Figure 1a). (60) Therefore, the copolymer will grow from the middle when chain extended to create an AxByAx triblock structure, where the A blocks will be half the length of the respective macro-CTA (i.e., x = DP/2 = 56, 108, and 140). SEC analysis showed that the molar masses of the macro-CTAs increased with the DP, and all the copolymers had relatively low dispersity (Mw/Mn < 1.3, Table 1).
The macro-CTAs were chain-extended using an automated synthesizer that targeted six different DPs for the central poly(butyl acrylate) “B” block for each macro-CTA (Figure 1b, 18 triblock copolymer compositions in total). Since the Tg of PBA is about −50 °C, (61) the BA blocks will be denoted as the “soft” blocks within the triblock copolymers. The BA block lengths were chosen such that the DPs of both the hard (A) and soft (B) blocks were varied as well as the total DP of the triblock copolymer (Figure S2). All the copolymerizations were performed at 40% w/w in MEK and reached moderate to high monomer conversions (70–95%) within 8 h (Table 2; specific reaction quantities can be found in Table S1). However, the conversions were lower when the longest macro-CTA (A140) was used, with these triblocks having an average conversion of 74%. SEC analysis of the triblock copolymers confirmed that a high blocking efficiency was achieved with BA and that Mn increased as the targeted DP of the soft block increased. In all cases, the triblock copolymers had dispersities less than or equal to 1.43 (Table 2 and Figure S3).
Table 2. Conversion and Molar Mass of the P(AA-st-St)-b-PBA-b-P(AA-st-St) Triblock Copolymers
  NMRSECa
macro-CTAtriblocktargeted DP (BA)conversion (%)synthesized DP (BA)Mn (kDa)Mw (kDa)Mw/Mn
A56A56A56B100A56100898911400154001.34
A56B150A561509314013400181001.35
A56B200A562009218414500197001.25
A56B300A563009227618500250001.35
A56B500A565009246024800331001.34
A56B750A567508866032200415001.29
A108A108A108B100A108100787817300216001.25
A108B150A1081508212318000230001.28
A108B200A1082008617221300262001.23
A108B300A1083008525519897263001.32
A108B500A1085008844025300350001.38
A108B750A1087508664529300420001.43
A140A140A140B100A140100747420500258001.26
A140B150A1401507210822500279001.24
A140B200A1402007114222900291001.27
A140B300A1403007622824900323001.30
A140B500A1405007236025300322001.28
A140B750A1407507556334600472001.37
a

SEC measurements were performed using a THF eluent containing 1% v/v acetic acid against PSt standards on an APC instrument.

Structure of the Macro-CTAs and Triblock Copolymers in MEK and Water Solutions

The structural behavior of the synthesized copolymers was investigated in MEK, which is a reasonable solvent for polystyrene and poly(butyl acrylate), and water, where polystyrene and poly(butyl acrylate) are insoluble. Copolymers were first dissolved in MEK to form 1% w/w solutions and then analyzed using SAXS. SAXS patterns of the macro-CTAs (Figure 2a) show a clear plateau in scattering intensity in the low q-region (q < 0.04 Å–1) and a slope with a gradient close to −2. This scattering is indicative of a Gaussian coil. Consequently, these scattering patterns were all modeled using the Debye function (eq S8). Using this model, the radius of gyration (Rg) of the copolymer chains was calculated; as expected, Rg increased monotonically as the length of the copolymer chain increased (Rg = 27, 37, and 42 Å for A56A56, A108A108, and A140A140, respectively).

Figure 2

Figure 2. SAXS patterns of (a) 1% w/w macro-CTA solutions in MEK (symbols) fitted using the Debye function (eq S8) (black line) and (b) 1% w/w triblock copolymer solutions in MEK (symbols). Some patterns have been shifted upward (the multiplication factors are indicated on the plots) to avoid overlap. Scattering patterns were collected using a Bruker AXS Nanostar instrument.

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The SAXS patterns collected for the triblock copolymers in the MEK solution (Figures 2b and S4) are characteristic of adjacent coils of copolymer blocks. Scattering intensity slopes close to −2 were observed at high q-values for the SAXS patterns, with no evidence of phase separation. This indicates that MEK is a reasonable solvent for the synthesized triblock copolymers. The SAXS analysis is also consistent with the visual observation of the triblock copolymer MEK solutions, which appear as clear transparent liquids. Nevertheless, it must be noted that a nonzero gradient at low q-values, which changes slightly with the copolymer composition, suggests that some of the chains interact with each other and possibly form larger objects. As a result, the radius of gyration of the copolymer blocks could not be obtained. However, it must be stressed that these interactions are weak and that the triblocks are in an unconstrained structure.
The macro-CTAs (A56A56, A108A108, and A140A140) were formulated in water using a solvent-switch method in which the copolymers were initially dissolved at 75% w/w in IPA, then the mixtures were diluted with ammonia and water to produce stable dispersions. The macro-CTA dispersions were further diluted with water to 1% w/w for the SAXS analysis (Figure 3).

Figure 3

Figure 3. SAXS patterns of macro-CTA (A56A56, A108A108, and A140A140) aqueous dispersions (symbols) at a 1% w/w concentration. Patterns were fitted with the sphere model (eqs S9–S12) (solid line). Some patterns have been shifted upward (the multiplication factors are indicated on the plot) to avoid overlap. Scattering patterns were collected using a Bruker AXS Nanostar instrument.

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The SAXS patterns of the macro-CTA dispersions (Figure 3) show that these copolymers self-assemble into particulate structures, and the patterns can be fitted with a simple-sphere structural model (eqs S9–S12). However, a simple hard-sphere structure factor was also incorporated based on the Percus–Yevick approximation (eq S7) to account for the long-range charge interactions of the particles (Figure 5), as has been seen in similar systems. (51,62) All macro-CTAs formed spherical particles of a similar size (R = 17 Å) independent of their molar masses. This is consistent with previous reports for statistical copolymers, where it was found the copolymer composition, rather than degree of polymerization, controlled the particle size. (42,51) As the particle size remains constant while the molar mass of the copolymer increases, the aggregation number of the particle must decrease. Therefore, A56A56 particles will have a larger aggregation number than either A108A108 or A140A140 particles.
Aqueous dispersions of the triblock copolymers were formulated using the same solvent-switch method used for the macro-CTAs and then diluted to 1% w/w in water for the SAXS analysis. It is clear from the SAXS patterns collected for the 1% w/w triblock copolymer dispersions (Figures 4a and S5) that these copolymers self-assemble to form particles, presumably through the hydrophobic interactions within the BA block, which induce copolymer aggregation to reduce any unfavorable interactions between BA and water. The positions of the form factor intensity minima move to lower q-values as the length of the BA block increases, suggesting that the particle size increases with BA DP (Figure 4a). Again, a broad peak in the scattering pattern, caused by the electrostatic particle–particle interactions, was observed in the Guinier region (low q-region) for most of the collected patterns. This peak feature can be fitted by incorporating the structure factor for hard spheres (eq S7) into the SAXS model, similar to the macro-CTA dispersions.

Figure 4

Figure 4. SAXS patterns of (a) 1% w/w A108B100–750A108 triblock copolymer aqueous dispersions (symbols) fitted with the two-population model (eqs S13–S15) (solid line); (b) A108B100–750A108 triblock copolymer aqueous dispersions at 20% w/w concentration; and (c) A108B100A108 triblock copolymer aqueous dispersion at 1, 5, and 20% w/w concentrations. The arrow is used to highlight the presence of the structural peak referred to in the text. Some patterns have been shifted upward (the multiplication factors are indicated on the plots) to avoid overlap. Scattering patterns were collected using a Bruker AXS Nanostar instrument.

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Typically, dispersions of spherical block copolymer particles produce scattering patterns with a −2 gradient of scattering intensity in the high q-region, as the soluble stabilizer block behaves like a Gaussian chain. However, gradients shallower than −2 were observed in the high q-regions (q > 0.08 Å–1) of the scattering patterns for the majority of triblock copolymer aqueous dispersions (Figure 4a). This suggests that there is an additional structural feature that produces scattering within the high q-region and that the source of the scattering has a relatively short length scale in comparison to the size of the primary copolymer particle. Additionally, this high-q feature is more prominent in the copolymers with greater weight fractions of the P(AA-st-St) stabilizer blocks (e.g., A140B100A140) (Figure 4b) and is clearly evident when the concentration of the dispersion is higher (indicated by the arrows in Figures 4b and c). This suggests that the high-q feature is related to an additional structural organization within the stabilizer block.
The P(AA-st-St) block is expected to be located at or near the particle surface. Consequently, two potential explanations were considered: (1) there are SLD fluctuations within the corona block of the particle caused by the statistical distribution of styrene and acrylic acid and (2) the hydrophobic nature of styrene causes the statistical hard block to phase-separate within the particle surface through hydrophobic interactions in a manner similar to that observed for aqueous dispersions of amphiphilic statistical copolymers (42,51) and in the SAXS analysis of the aqueous dispersions of the macro-CTAs. (47) Both cases appear to be valid explanations for this phenomenon; however, the observation that the macro-CTAs will undergo spontaneous self-assembly to form spherical particles (Figure 3) indicates that the amphiphilic nature of the stabilizer block is enough to initiate the self-folding of the chain (Figure 5). The presence of this additional surface structure is caused by the hydrophobicity of the polystyrene units along the stabilizer backbone. This surface structure is not found in block copolymer dispersions with a fully hydrophilic stabilizer block [e.g., poly(acrylic acid)]. (63−65)
Since the stabilizer block of the copolymer particle provides an additional structural morphology that is assumed to be spherical based on the behavior of the macro-CTAs in water (Figure 3) and thus does not behave as a Gaussian chain, the standard copolymer micelle structural model (66) cannot be fitted to the SAXS patterns of the triblock copolymer dispersions. Instead, a two-population structural model that accounts for the spherical structures on the surface of the copolymer particle (Figure S6), as described in the Supporting Information (eqs S13–S15), was used to fit the SAXS data (Figure 4a). This model was developed to analyze polymer–silica colloidal particles, (67) where the silica forms a particulate shell around a spherical polymer core.
For simplicity, the radius of the surface P(AA-st-St) spheres (r2) was fixed while fitting the SAXS patterns. It was assumed that these surface spheres were unimolecular (i.e., the statistical block formed a self-folded chain or a single-chain nanoparticle); therefore, the radius is given by r2=3VAA−St4π3, where VAA-St is the volume of the statistical copolymer block and is directly related to the DP of the respective macro-CTA. The VAA-St values for A56A56, A108A108, and A140A140 were calculated to be 6988, 13477, and 17470 Å3, respectively. Therefore, r2 values for the A56B100–750A56, A108B100–750A108, and A140B100–750A140 particles were fixed at 12, 15, and 16 Å, respectively. The core radius of the main particle, Rcore, was fitted during the SAXS model analysis (Tables 3 and S2).
Table 3. Structural Analysis Results for P(AA-st-St) and P(AA-st-St)-b-PBA-b-(AA-st-St) Copolymer 1% w/w Aqueous Dispersionsa
copolymerRcore (Å)σcore (Å)r2 (Å)
A56A5616b5 
A108A10816b7 
A140A14017b7 
A56B100A56531412
A56B150A56901312
A56B200A561191812
A56B300A561562012
A56B500A562472812
A56B750A562815212
A108B100A10818915
A108B150A108553415
A108B200A108992415
A108B300A1081202215
A108B500A1081913915
A108B750A1082195215
A140B100A14015516
A140B150A140261016
A140B200A140322316
A140B300A1401014116
A140B500A1401504116
A140B750A1402195016
a

Rcore is the mean particle core radius, σcore is the standard deviation of the mean particle core radius, and r2 is the radius of the self-folded P(AA-st-St) chain on the surface of the particle (this value based upon the volume of the hard block is fixed throughout the fitting).

b

Note: Rcore refers to the total particle radius for the A56A56, A108A108, and A140A140 macro-CTAs.

The modeling results show a clear trend in particle size, where the core radius increases as the length of the hydrophobic core-forming B block increases. Additionally, the core radius increases as the stabilizer block length decreases. These two influencing factors are commonly seen for block copolymer nanoparticle assembles. (8) Furthermore, when the triblock copolymers possess very large stabilizer blocks (e.g., the A140B100–750A140 copolymers), their aggregation into larger particles appears to be significantly hindered until the B block DP reaches 300, with the core radii for A140B100A140, A140B150A140, and A140B200A140 remaining between 10 and 40 Å (Table 3). This behavior is seen at the beginning of the A108B100–750A108 series as well. The observed effect likely originates from a geometrical confinement caused by the copolymer aggregation number and the packing density of the A block spheres on the triblock copolymer particle surface (Figure 5). The relatively large spheres formed by the A blocks are comparable with the Rcore of the triblock copolymer particle core formed by the relatively short B block, restricting the formation of larger particles. When the B block becomes significantly larger than the A block, this effect is negligible.

Figure 5

Figure 5. A diagram describing the predicted structure of a particle formed by P(AA-st-St)-b-PBA-b-P(AA-st-St) triblock copolymers in water, where the P(AA-st-St) stabilizer block was confined by the copolymer particle surface and “self-folded” through hydrophobic interactions.

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These results demonstrate that copolymer particles can be successfully stabilized as a dispersion in water using an amphiphilic statistical stabilizer block rather than a wholly hydrophilic block. Additionally, particles display an interesting surface structure due to the hydrophobic units within the stabilizer block. The hydrophobic units cause the chains to collapse into single-chain assemblies on the particle surface. These hydrophobic surface domains are similar to the structures observed for the orthogonal folding of random block copolymers. (49) Finally, these results demonstrate that the particle size can be easily tuned by varying the DP of either the core block or the amphiphilic stabilizer block, as seen in other triblock copolymer systems.

Structural Characterization of Triblock Copolymer Films Cast from an Organic Solvent

The analysis of the triblock copolymers in both MEK and aqueous media demonstrate that the copolymers form very different morphologies depending on their interactions with the solvents. In MEK, a reasonably good solvent for all the copolymer components, the copolymers were found to be dissolved chains with some weak association into loose aggregates, whereas in water the copolymers assembled into well-defined spherical particles with a particulate shell. Such a different solution behaviors of the synthesized copolymers could be reflected in the bulk morphologies of films cast from the triblock copolymer solutions or dispersions. Therefore, triblock copolymer films were prepared from both the organic solutions and the aqueous dispersions. The presence and type of structural phase separation within these films were assessed by SAXS and atomic force microscopy (AFM) (see the Supporting Information).
The volume fraction of the A (hard) blocks (fA) in the composition of the synthesized triblock copolymers changes for the A56, A108 and A140 series from 0.13 to 0.45, 0.18 to 0.65, and 0.24 to 0.71, respectively. It has to be pointed out that the A108B100A108, A140B100A140, and A140B150A140 films, which are associated with largest volume fraction of hard A block (fA) in their copolymer series, show no structural peaks indicating phase separation (Figure S6). On the basis of a phase diagram predicted by self-consistent field theory (SCFT) for symmetrical triblock copolymers, (68) this observation suggests that the A108B100A108, A140B100A140, and A140B150A140 copolymers form disordered structural morphologies (Figure 6). In contrast, the A56B100A56 film, with the largest fA value of A56 series, shows a structural peak indicating an ordered structure (Figure S6a). Thus, the A56B100A56 copolymer with fA close to 0.5, which is usually associated with the critical point of copolymer phase diagrams, is likely to be in the ordered structural morphology region of the phase diagram (Figure 6).

Figure 6

Figure 6. Predicted phase diagram of the bulk triblock copolymer morphologies based on SCFT theory, AFM images, and SAXS, where fA is the volume fraction of the A block, χ is the Flory–Huggins segment interaction parameter, and rv is the overall length of the copolymer molecule in segments, taking into account the difference in the volume occupied by the A and B block. rv was calculated using the equation rv = x + y(vB/vA) where vA and vB are the averaged volumes occupied by the A and B monomer units, respectively. (69) The A56ByA56, A108ByA108, and A140ByA140 series are represented by hexagon, diamond, and triangle symbols, respectively. BCC, Hex and G indicate zones of existance of body-centered cubic, hexagonally-packed cylinder and gyroid copolymer phases, respectively.

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According to a theoretical symmetrical triblock copolymer phase diagram predicted by SCFT, the triblock copolymer morphologies in the bulk change as a factor of the block volume fraction f. (68) In particular, SCFT suggests that as fA decreases (i.e., 0.45 > 0.36 > 0.25 > 0.18) the morphology will transition from lamellae, to a gyroid, then to hexagonally packed cylinders, and finally to a body-centered cubic structure. (70) The sequence of phases observed by AFM in this work for triblock copolymers with statistical side blocks (Figures S8 and S9) agrees reasonably well with the symmetrical triblock copolymer phase diagram. For example, the A108 series shows transitions from a bicontinuous structure (likely to be gyroid) to cylinders to spheres as the BA block increases in size (i.e., as fA decreases). Furthermore, a phase diagram of the bulk triblock copolymer morphologies predicted with respect to χrv (the product of the Flory–Huggins interaction parameter, χ, and the overall copolymer length in the segments, rv (69)) and fA was constructed using SCFT theory, AFM images and SAXS data (Figure 6). It was assumed that the A56B100A56 copolymer composition with a fA value about 0.5 was close to the composition corresponding to the critical point of the copolymer phase diagrams, with χrv = 10.5. Since the A56B100A56 copolymer shows phase separation and should belong to the ordered region of the phase diagram, its χrv value was taken to be 11.0, which was slightly above the order–disorder boundary (Figure 6). The combined analysis of AFM images (Figure S8) and SAXS results (Figure S6), summarized in Table S3, enabled approximate boundaries between ordered phases to be established for the soft (B) block-rich compositions (Figure 6, left side of the diagram). Some of the observed morphologies appear to have some mixed phases (e.g., the A108B750A108 image shows small cylinders and spheres, Figure S8). The lack of order could be caused by both nonequilibrium conditions of the film preparations and relatively large dispersity in the chain lengths (Table 2). (71) While the order–disorder transition for the hard-block-rich compositions was evident from the SAXS measurements (Figure S6), it was not possible to identify the ordered phase structures (Figure 6, left side of the diagram). It could be expected that the statistical nature of the hard blocks would affect the ordered phase symmetry, resulting in distorted (ill-defined) structures. Thus, contrasting behavior between block copolymers and statistical copolymers may cause the triblock copolymer phase diagram to be asymmetrical, with the homogeneous (B) block-dominating side represented by well-ordered phases expected for block copolymers and the statistical (A) block-dominating side represented by ill-defined structures (Figure 6). The obtained results demonstrate that varying the DP of the either the hard block or the soft block has a direct effect on both object size and interobject distances and that the copolymer composition determines the phase-separated morphology formed by self-assembled P(AA-st-St)-b-PBA-b-P(AA-st-St) macromolecules in the film when cast from MEK.

Structural Characterization of Triblock Copolymer Films Cast from Aqueous Dispersions

To assess how the solvent environment affected the phase-separated structure in the film, films were also cast from aqueous dispersions of the copolymers and analyzed by SAXS and AFM as before (see the Supporting Information). A primary scattering intensity peak observed in the SAXS patterns of this triblock films demonstrates (Figure S13) that phase separation is present in all the films. This was not the case for the films cast from MEK, where A108B100A108, A140B100A140, and A140B150A140 triblock copolymers had little or no phase separation (Figure S6). This comparison suggests that film-casting from an aqueous environment facilitates phase separation, presumably because the initial aqueous dispersions are already phase-separated into particles to minimize the strongly unfavorable interactions between the PBA block and water. Therefore, when an aqueous film is cast, the copolymers are largely preassembled with aggregated regions of hard and soft blocks, making it easy for large-scale phase separation to occur within the film (Figure 7). Conversely, in MEK, the triblock copolymers are molecularly dissolved and therefore not phase-separated in the solution, making it more difficult to induce phase separation within the film. This can be thought of in terms of Flory–Huggins interaction parameters. Since the copolymers are the same in each case, χ will be the same between the blocks. However, the polymer–solvent interaction parameter will be different based on whether the copolymer is in water or MEK. In the case of the PBA (soft) block, χ will be high for water but lower for MEK, since PBA is insoluble in water but soluble in MEK. The fact that the A108B100A108 films show little phase separation when cast from MEK suggests that a higher DP is required for the given χ of the blocks to induce phase separation. However, the high χ between the PBA block and water drives the self-assembly in water, which remains within the water-cast films.

Figure 7

Figure 7. Schematics of the formation of the kinetically trapped structure within the water-cast films that occurs during the drying process. (a) The formation of the packed soft sphere structure within a matrix of the hard phase, where the BA-reach domains reduce during the drying process. (b) The formation of a structure of distorted packed spheres that is formed by copolymers with a large soft block.

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Previous studies investigating the structures of similar diblock copolymer spherical micelle films suggest that while the spherical cores keep their shape as the film dries, the corona blocks coalesce to form a continuous matrix (Figure 7). (27) This phenomenon will produce different scattering patterns depending on how the particles stack upon drying. A well-ordered cubic structure, such as body-centered cubic and face-centered cubic structures, would produce sharp diffraction peaks related to the crystallographic planes of the crystal structure. However, the water-cast films of P(AA-st-St)-b-PBA-b-P(AA-st-St) show relatively broad peaks (Figure S13) similar to the scattering patterns observed for randomly packed spherical particles. (72−74) Indeed, the SAXS patterns of the majority of the water-cast triblock copolymer films (A56B100–300A56, A108B100–300A108, and A140B100–300A140) were fit using a spherical form factor (eqs S9–S12) combined with a structure factor of interacting hard spheres (eq S7) (Figure S15). This result supports the observations made in other studies on similar systems. (26,27,33,75,76) However, the additional features at high q-values, which are associated with the packing of particles formed by the hard (A) block and the packing of the BA chains (for further discussion, see the Supporting Information), are not accounted for within this structural model and are not fitted by the model. The results from this modeling indicate that the spherical domain size increases as the length of the hydrophobic BA block increases; this observation is similar to the observation for the triblock copolymer dispersions (Table S4).
The triblock films that do not fit to the spherical particle model are the copolymers that have large volume fractions of the PBA component, i.e., A56B500A56, A56B750A56, A108B500A108, A108B750A108, A140B500A140, and A140B750A140. This suggests that the particles within these copolymer films arrange in a different structure compared to the previously examined films. Assuming that the particle PBA cores form a close-packed structure of spheres upon drying and that the residual volume is filled by the hard P(AA-st-St) matrix, a maximum volume fraction of about 0.74 can be filled by the undistorted spherical PBA cores. However, all the copolymer films produced SAXS patterns that did not follow the spherical form factor model (eqs S7 and S9–S12) and had soft PBA block volume fractions greater than 0.74. This means that the spherical cores will distort during the drying process in order to reduce the residual volume (Figure 7b); therefore, this structure cannot be analyzed by the sphere model. (77,78)
AFM images of the water-cast films (Figure S16), unlike the AFM images of the solvent-cast films (Figure S8), show that there is little surface phase separation, and there is no long-range structural order visible in the images of the water-cast films. This is consistent with the SAXS results that suggest a randomly packed (amorphous) structure formed by spheres. The absence of well-defined phase separation is likely due to the lack of mobility that would allow the blocks to rearrange upon drying, with the majority of the soft hydrophobic blocks potentially buried within a continuous surface of the hard P(AA-st-St) matrix (Figure 7). Some films show surface structure that is thought to be caused by drying defects resulting in an uneven film (e.g., A56B500A56). However, images of the A108B200A108 and A108B300A108 films show a better-defined structural morphology, where the dark and light regions could correspond to spherical soft regions in a matrix of the hard phase (Figure S16).

Structural Characterization of Annealed Triblock Copolymer Films Cast from Aqueous Dispersion

The results gathered through SAXS and AFM demonstrate that the solvent environment from which the copolymer film is cast plays a major role in the resultant structure within the film. The film structure is linked to the initial state of copolymer within the solution phase. If the copolymer is dissolved within the solvent phase (the MEK solvent case), then it will have the freedom to arrange into a more favorable and lower energy structure. However, if the copolymers are preassembled in solution through solvophobic interactions (the aqueous case), then their mobility is restricted and they are unable to rearrange into a favorable conformation upon drying.
The aqueous-cast films were thought to be in a kinetically trapped state due to the high Tg of the stabilizer block preventing the coalescence of the soft particle cores. Therefore, if the temperature is raised above the Tg of the hard block (∼120 °C), then the copolymer mobility should increase, allowing the structure to rearrange into a more thermodynamically stable conformation. To test this hypothesis, in situ grazing incident SAXS was performed on an aqueous-cast A108B500A108 film while the film was annealed (Figure 8). In this experiment, an initial scattering pattern was acquired at ambient temperature (22 °C). Afterward, the triblock film was heated to 150 °C, above the Tg of the hard block (120 °C), then frames were collected every 60 s to monitor any change in structure during the annealing process. The SAXS analysis shows that the structure present in the water-cast film at 22 °C begins to rearrange when heated to 150 °C. An equilibrated structure was eventually reached after 30 min, and the film was cooled to ambient temperature.

Figure 8

Figure 8. Time-resolved GISAXS patterns collected for the A108B500A108 water-cast film during the annealing process at 150 °C. The temperature protocol is shown at the right side of the plot. Scattering patterns were collected using a Xenocs Xeuss laboratory beamline.

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The final SAXS pattern of the water-cast film taken after the annealing process is almost identical to the SAXS pattern collected for the solvent-cast film of the same triblock copolymer (Figures S13 and S14). Since a change was observed in the structure of the water-cast film once the temperature was raised above the Tg of both blocks, it is evident that the original structure was in a kinetically trapped state and a more thermodynamically stable structure could only be achieved by annealing. This rearrangement of the bulk structure, where the kinetically trapped hard matrix undergoes inversion when the film is annealed to form a structure wherein the hard domains are surrounded by a continuous matrix of the soft component, was reported previously. (27) AFM images were taken of the film before (Figure 9a and b) and after (Figure 9c and d) annealing and compared with the images taken of the films cast from solvent in ambient conditions (Figure 9e and f). These images show a clear change in the phase-separated structure once the water-cast film is annealed. The AFM images also demonstrate that the structure of the annealed film is similar to that of the film cast from solvent in ambient conditions (Figure S8).

Figure 9

Figure 9. AFM height (tomographic) images of triblock copolymer films recorded using the ScanAsyst PeakForce tapping mode. (a and b) Images of A108B500A108 cast from a 20% w/w aqueous solution; images were recorded for 1 μm × 1 and 5 μm × 5 μm areas, respectively. (c and d) Images of A108B500A108 cast from a 20% w/w aqueous solution and annealed for 30 min at 150 °C; images were recorded for 1 μm × 1 and 5 μm × 5 μm areas, respectively. (e and f) Images of A108B500A108 cast from a 40% w/w solution in MEK; images were recorded for 1 μm × 1 and 5 μm × 5 μm areas, respectively.

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The SAXS and AFM data are in good agreement with each other. They demonstrate the structural differences in the films cast from different solvent environments and how the copolymer properties affect the phase separation within the films. When the triblock copolymer is fully dissolved in the solution phase, the triblock copolymer has a large amount of mobility that is not restricted by unfavorable interactions with the solvent. This mobility allows the copolymer to arrange into a lower-energy structure as the solvent evaporates and a film forms. However, when the selected solvent is not compatible with one of the copolymer blocks, then the triblock copolymers aggregate together to form particles to avoid any unfavorable solvent interactions. As a result, the copolymers have a restricted mobility and cannot rearrange into a thermodynamically stable structure, as the solvent evaporates and so remain kinetically trapped. Annealing the aqueous film above the Tg of the hard block provides mobility to the copolymer chains, allowing them to rearrange into a lower-energy structure. However, annealing the film does not provide as much mobility to the copolymer chains as their solvation by MEK, which is why the annealed film appears less well-defined in AFM images (Figure 9) and may require a longer annealing time to complete the morphology transformation.

Mechanical Characterization of the Triblock Copolymer Films

The structural morphology is likely to have a significant impact on the mechanical properties of films. In order to establish structure–property relationships, the mechanical properties of water-cast films and solvent-cast films were investigated.
Since the lengths of the soft and hard blocks varied across all 18 triblock copolymers (Figure S2), a range of structural morphologies were achieved. However, some films were either too brittle or too soft to undergo mechanical testing. For the solvent-cast films, the mechanical tests show that increasing the length of the soft block systematically increases the flexibility of the film (higher extension-to-break and lower modulus, Table S5 and Figure 10a), while increasing the length of the hard block increases the film strength (higher modulus, lower extension-to-break, Table S5). This behavior is predictable, since it is well-known that, at a fixed temperature, polymers become more pliable by lowering their Tgs. (79) Therefore, by introducing a larger soft component to the copolymer, the triblock copolymer film has a larger volume of low-Tg phase. Furthermore, the hard segments within the triblock copolymer film will aggregate together (as indicated by SAXS and AFM) to form glassy regions that act as cross-linking points across the film. Therefore, increasing the length of the hard block increases the size of the glassy regions and consequently increases the strength of the cross-linking and the toughness of the triblock film.

Figure 10

Figure 10. Tensile extension traces of triblock copolymer films. (a) Trace demonstrating the effect of increasing the length of the soft block when cast from MEK. (b) Trace demonstrating the effect of changing the solvent environment from which the A56B200A56 copolymer film is cast.

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Although the film properties are largely dictated by the copolymer composition and design, the solvent environment also has a significant effect on the film behavior. The mechanical tests indicate that a triblock copolymer film cast from water produces a harder film (higher modulus) than the same copolymer cast from MEK (Table S5 and Figure 10b). This is likely a result of the phase-separated structure within the film and the respective location of the hard and soft blocks. Casting the copolymer from water produces a kinetically trapped phase-separated structure in which the hard P(AA-st-St) block forms a continuous matrix. However, when conditions allow the copolymers to reach thermodynamic phase-separation the continuous phase is often formed by the soft block, as it is the larger component by volume. The variations of the initial copolymer state (either in a solution or in a dispersion) result in the different mechanical properties of dried films, which clearly demonstrates the importance of the solvent environment.

Conclusions

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In this study, a combination of statistical and triblock copolymer properties was explored with regard to their ability to stabilize hydrophobic particles and the properties of the polymers once cast into films. It is demonstrated that amphiphilic statistical A blocks of ABA triblock copolymers can provide sufficient stabilization to largely hydrophobic particles formed upon the self-assembly of the copolymers. This may allow the hydrophobicity of the stabilizer block to be tuned by varying the block composition, which may ultimately affect the copolymer morphology in solutions and solid films.
A bifunctional symmetrical RAFT agent was used for the RAFT synthesis of symmetrical ABA triblock copolymers with statistical copolymer A blocks. S,S-Dibenzyl trithiocarbonate was used in order to achieve symmetrical poly(acrylic acid-stat-styrene)-block-poly(butyl acrylate)-block-poly(acrylic acid-stat-styrene) triblock copolymers in two steps: (i) the synthesis of a poly(acrylic acid-stat-styrene) macro-CTA with a midchain trithiocarbonate and (ii) chain extension from the chain center with butyl acrylate to yield the desired triblock copolymer. Molar mass analysis demonstrated that the macro-CTAs were extended with high blocking efficiency and all had a relatively low dispersities (Mw/Mn < 1.5).
SAXS analysis showed that the solubility of the triblock copolymer in MEK varied with the copolymer composition. However, none of the copolymers dissolved in MEK assembled into particles. In water, the triblock copolymers self-assembled into spherical particles. As expected, the particle size increased with the length of the hydrophobic soft block. It was found that the copolymer systems underwent a twofold self-assembly process when dispersed in water: (i) self-assembly of the hydrophobic core and (ii) self-assembly within the amphiphilic P(AA-st-St) stabilizer blocks, which form small, folded structures on the particle surface to reduce any unfavorable interactions with water.
SAXS and AFM analyses of organic solvent (MEK) cast films demonstrated that the length scale of the phase separation increased as the length of the soft [poly(butyl acrylate)] block increased. Additionally, the length scale of the phase separation increased as both the hard block length and the overall triblock length increased. The observed morphological transitions agreed well with the well-established phase separation of the diblock and symmetrical triblock copolymers, where the structural morphology changed from a gyroid, to cylinders, to spheres as the volume fraction of the soft block increases. It is also found that the packing of poly(butyl acrylate) blocks in the phase-separated copolymer structure is controlled by their relatively long pendent groups, which keep the copolymer backbones at a fixed distance from each other. AFM showed that the surface structure of the solvent cast films was highly dependent on the ratio of the hard and soft components. When there were significantly higher amounts of the soft block in the copolymer, the soft component would form the continuous phase and vice versa.
It is found that, analogous to the solvent-cast films, the copolymer phase-separation length scale of the aqueous-cast films increases with the lengths of the individual blocks. However, the phase-separation structure within copolymer films dried from aqueous dispersions is dominated by a close-packed sphere-like structure. This structure is formed by copolymer particles kinetically trapped due to the restricted movement of the blocks in the initial aqueous dispersion.
The mechanical properties of the solvent-cast copolymer films were consistent with the copolymer composition; the higher the hard block content in the films, the higher the elastic modulus and the lower the extension-to-break. In contrast, when the amount of the soft block increases, the elastic modulus decreases and the extension-to-break increases. However, the films cast from water did not show such an obvious trend, and the triblock copolymer films of different compositions show similar behavior. These similarities in the mechanical properties of the films are likely due to the similar structural morphologies formed from water by the triblock copolymers upon drying. The aqueous-cast copolymer films are characterized by a higher elastic modulus and a lower extension-to-break than their solvent-cast counterparts. This behavior is associated with the differences in the structural morphologies formed in these two systems, where the continuous phase of hard blocks, always formed in the case of the aqueous-cast films, produces a harder film. These results have demonstrated that the solution behavior of block copolymers has a direct effect on the film structure and the resulting mechanical properties.

Supporting Information

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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.macromol.2c01299.

  • Further characterization of triblock copolymer solutions, dispersions films, and SAXS models (PDF)

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Author Information

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  • Corresponding Authors
  • Authors
    • Thomas J. Neal - Department of Chemistry, The University of Sheffield, Dainton Building, Sheffield, South YourkshireS3 7HF, U.K.
    • Robert D. Bradley - AkzoNobel Decorative Paints, Wexham Road, Slough, BerkshireSL2 5DS, U.K.
    • Martin W. Murray - AkzoNobel Decorative Paints, Wexham Road, Slough, BerkshireSL2 5DS, U.K.
    • Neal S. J. Williams - AkzoNobel Decorative Paints, Wexham Road, Slough, BerkshireSL2 5DS, U.K.
    • Simon N. Emmett - AkzoNobel Decorative Paints, Wexham Road, Slough, BerkshireSL2 5DS, U.K.
    • Anthony J. Ryan - Department of Chemistry, The University of Sheffield, Dainton Building, Sheffield, South YourkshireS3 7HF, U.K.;  Orcidhttps://orcid.org/0000-0001-7737-0526
  • Author Contributions

    The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript.

  • Notes
    The authors declare no competing financial interest.

Acknowledgments

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AkzoNobel (Slough, UK) and EPSRC (EP/L016281/1) are thanked for funding a CDT Ph.D. CASE studentship of T.J.N. O.O.M. thanks EPSRC for the capital equipment grants to purchase (EP/M028437/1) and upgrade (EP/V034804/1) the laboratory-based Xenocs/Excillum SAXS instrument used to characterize the studied copolymer dispersions.

References

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This article references 79 other publications.

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    A review with 18 refs. discusses the structure, morphol., phase behavior, and self-assembly properties of block copolymers.
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    Amphiphilic Block Copolymers: Self-Assembly and Applications; Alexandridis, P.; Lindman, B., Eds.; Elsevier: Amsterdam, The Netherlands, 2000.
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    Zhang, L.; Yu, K.; Eisenberg, A. Ion-Induced Morphological Changes in “Crew-Cut” Aggregates of Amphiphilic Block Copolymers. Science 1996, 272, 1777– 1779,  DOI: 10.1126/science.272.5269.1777
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    Ion-induced morphological changes in "crew-cut" aggregates of amphiphilic block copolymers
    Zhang, Lifeng; Yu, Kui; Eisenberg, Adi
    Science (Washington, D. C.) (1996), 272 (5269), 1777-1779CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
    The addn. of ions in micromolar (CaCl2 or HCl) or millimolar (NaCl) concns. can change the morphol. of "crew-cut" aggregates of amphiphilic block copolymers in dil. solns. In addn. to spherical, rodlike, and univesicular or lamellar aggregates, an unusual large compd. vesicle morphol. can be obtained from a single block copolymer. Some features of the spontaneously formed large compd. vesicles may make them esp. useful as vehicles for delivering drugs and as models of biol. cells. Gelation of a dil. spherical micelle soln. can also be induced by ions as the result of the formation of a cross-linked "pearl necklace" morphol.
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  5. 5
    Zhang, L.; Eisenberg, A. Multiple Morphologies of “Crew-Cut” Aggregates of Polystyrene-b-Poly(Acrylic Acid) Block Copolymers. Science 1995, 268, 1728– 1731,  DOI: 10.1126/science.268.5218.1728
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    Multiple morphologies of "crew-cut" aggregates of polystyrene-b-poly(acrylic acid) block copolymers
    Zhang, Lifeng; Eisenberg, Adi
    Science (Washington, D. C.) (1995), 268 (5218), 1728-31CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
    The observation by transmission electron microscopy of six different stable aggregate morphologies is reported for the same family of highly asym. styrene-acrylic acid diblock copolymers prepd. in a low-mol.-wt. solvent system. Four of the morphologies consist of spheres, rods, lamellae, and vesicles in aq. soln., whereas the fifth consists of simple reverse micelle-like aggregates. The sixth consists of up to micrometer-size spheres in aq. soln. that have hydrophilic surfaces and are filled with the reverse micelle-like aggregates. In addn., a needle-like solid, which is highly birefringent, is obtained on drying of aq. solns. of the spherical micelles. This range of morphologies is believed to be unprecedented for a block copolymer system.
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    van Hest, J. C. M.; Delnoye, D. A. P.; Baars, M. W. P. L.; van Genderen, M. H. P.; Meijer, E. W. Polystyrene-Dendrimer Amphiphilic Block Copolymers with a Generation-Dependent Aggregation. Science 1995, 268 (268), 1592– 1595,  DOI: 10.1126/science.268.5217.1592
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    Polystyrene-dendrimer amphiphilic block copolymers with a generation-dependent aggregation
    van Hest, J. C. M.; Delnoye, D. A. P.; Baars, M. W. P. L.; van Genderen, M. H. P.; Meijer, E. W.
    Science (Washington, D. C.) (1995), 268 (5217), 1592-5CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
    A class of amphiphilic macromols. has been synthesized by combining well-defined polystyrene (PS) with poly(propylene imine) dendrimers. Five different generations, from PS-dendr-NH2 up to Ps-dendr-(NH2)32, were prepd. in yields of 70 to 90 percent. Dynamic light scattering, cond. measurements, and transmission electron microscopy show that in aq. phases, PS-dendr-(NH2)32 forms spherical micelles, PS-dendr-(NH2)16 forms micellar rods, and PS-dendr-(NH2)8 forms vesicular structures. The lower generations of this class of macromols. show inverted micellar behavior. The obsd. effect of amphiphile geometry on aggregation behavior is in qual. agreement with the theory of J. N. Israelachvili, et al. (1976). The amphiphiles presented here are similar in shape but different in size as compared with traditional surfactants, whereas they are similar in size but different in shape as compared with traditional block copolymers.
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    Bates, F. S. Polymer-Polymer Phase Behaviour. Science 1991, 251 (251), 898– 905,  DOI: 10.1126/science.251.4996.898
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    7
    Polymer-polymer phase behavior
    Bates, Frank S.
    Science (Washington, DC, United States) (1991), 251 (4996), 898-905CODEN: SCIEAS; ISSN:0036-8075.
    A review with 57 refs. on basic factors governing polymer-polymer phase behavior with emphasis on linear homopolymer blends and diblock copolymers as representative model mol. architectures. Equil. thermodn. and phase sepn. dynamics are reviewed and discussed.
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    Mai, Y.; Eisenberg, A. Self-Assembly of Block Copolymers. Chem. Soc. Rev. 2012, 41 (18), 5969– 5985,  DOI: 10.1039/c2cs35115c
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    Self-assembly of block copolymers
    Mai, Yiyong; Eisenberg, Adi
    Chemical Society Reviews (2012), 41 (18), 5969-5985CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
    A review. Block copolymer (BCP) self-assembly has attracted considerable attention for many decades. The present tutorial review introduces the primary principles of BCP self-assembly in bulk and in soln., by describing expts., theories, accessible morphologies, etc.
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  9. 9
    Xu, R.; Winnik, M. A.; Hallett, F. R.; Riess, G.; Croucher, M. D. Light-Scattering Study of the Association Behavior of Styrene-Ethylene Oxide Block Copolymers in Aqueous Solution. Macromolecules 1991, 24 (1), 87– 93,  DOI: 10.1021/ma00001a014
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    9
    Light-scattering study of the association behavior of styrene-ethylene oxide block copolymers in aqueous solution
    Xu, Renliang; Winnik, Mitchell A.; Hallett, F. R.; Riess, Gerard; Croucher, Melvin D.
    Macromolecules (1991), 24 (1), 87-93CODEN: MAMOBX; ISSN:0024-9297.
    The micellization behavior of styrene (I)-ethylene oxide (II) diblock and triblock copolymers in aq. solns. is studied via static and dynamic light scattering. There are 2 narrowly distributed populations of particles in the soln. The sizes of both sets of particles are unchanged in concn. range of 2 × 10 -5 - 2 × 10-3 g/mL. The wt. fraction of the larger particles decreases with increasing polymer concn. The small particles are regular micelles with an assocn. no. of several hundred; the large particles are loose micellar clusters of tens of micelles. The micelle structure is core-shell with a core of I and a shell of II.
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  10. 10
    Wilhelm, M.; Zhao, C. Le; Wang, Y.; Xu, R.; Winnik, M. A.; Mura, J. L.; Riess, G.; Croucher, M. D. Poly(Styrene-Ethylene Oxide) Block Copolymer Micelle Formation in Water: A Fluorescence Probe Study. Macromolecules 1991, 24 (5), 1033– 1040,  DOI: 10.1021/ma00005a010
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    10
    Poly(styrene-ethylene oxide) block copolymer micelle formation in water: a fluorescence probe study
    Wilhelm, Manfred; Zhao, Cheng Le; Wang, Yongcai; Xu, Renliang; Winnik, Mitchell A.; Mura, Jean Luc; Riess, Gerard; Croucher, Melvin D.
    Macromolecules (1991), 24 (5), 1033-40CODEN: MAMOBX; ISSN:0024-9297.
    Block copolymer micelle formation was studied by a combination of fluorescent and quasielastic light scattering (QELS) techniques. Ethylene oxide-styrene diblock and triblock copolymers, with mol. wts. 8500-29,000, formed spherical micelles in H2O over the entire concn. range over which QELS signals could be detected. Pyrene (I) in H2O (6 × 10-7 M) partitions between the aq. and micellar phases, accompanied by 3 changes in I spectroscopy. A red shift in the excitation spectrum, a change in the vibrational fine structure of I fluorescence, and an increase in the fluorescence decay time (from 200 to ∼350 ns) accompanied the transfer of I from an aq. to a hydrophobic micellar environment. From these data, crit. micelle concns. (1-5 mg/L) and partition coeffs. (3 × 105) were calcd.
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  11. 11
    Prochazka, K.; Kiserow, D.; Ramireddy, C.; Tuzar, Z.; Munk, P.; Webber, S. E. Time-Resolved Fluorescence Studies of the Chain Dynamics of Naphthalene-Labeled Polystyrene-Block-Poly(Methacrylic Acid) Micelles in Aqueous Media. Macromolecules 1992, 25 (1), 454– 460,  DOI: 10.1021/ma00027a071
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    11
    Time-resolved fluorescence studies of the chain dynamics of naphthalene-labeled polystyrene-block-poly(methacrylic acid) micelles in aqueous media
    Prochazka, K.; Kiserow, D.; Ramireddy, C.; Tuzar, Z.; Munk, P.; Webber, S. E.
    Macromolecules (1992), 25 (1), 454-60CODEN: MAMOBX; ISSN:0024-9297.
    A-B block copolymers of polystyrene and poly(methacrylic acid) and polystyrene and poly(tert-Bu methacrylate), both with short-chain oligovinyl-2-naphthalene moieties attached to the end of the polystyrene block, were prepd. by anionic polymn. and micelles were formed by hydrolysis. Intramol. excimer formation (which is controlled by the mobility of the pendant fluorescent groups and the polymer chain dynamics) was sterically hindered in the micellar cores as they become more compact. Both steady-state and time-resolved excimer fluorescence were significantly influenced by the gradual collapse of the micellar cores and the increase in segment d. within the cores with an increasing content of water. Changes in lifetimes and preexponential factors for naphthalene fluorescence (monomer as well as excimer) were sensitive indicators of micelle formation.
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  12. 12
    Astafieva, I.; Zhong, X. F.; Eisenberg, A. Critical Micellization Phenomena in Block Polyelectrolyte Solutions. Macromolecules 1993, 26 (26), 7339– 7352,  DOI: 10.1021/ma00078a034
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    12
    Critical micellization phenomena in block polyelectrolyte solutions
    Astafieva, Irina; Zhong, Xing Fu; Eisenberg, Adi
    Macromolecules (1993), 26 (26), 7339-52CODEN: MAMOBX; ISSN:0024-9297.
    Crit. micelle concn. (CMC) was measured for a range of block copolyelectrolytes based on styrene (the insol. block) and Na acrylate. The length of the styrene blocks was 6-110, while that of the polyelectrolyte was ∼300-1400. The fluorescent probe technique was used with pyrene as a probe mol., and the data were treated by 5 different methods. CMC results were interpolated for a const. polyelectrolyte block length of 1000 units. Changing the insol. block length from 6 to 110 lowed the CMC from 1.6 × 10-5 to 5 × 10-8 M. By contrast, changing the sol. block length from 300 to 1400 typically changed the CMC values by a factor of <2. For very short polystyrene block lengths, the CMC decreased very rapidly with increasing length of the insol. block. By contrast, for higher block lengths (>12) the drop in the CMC was much more gradual. The results are compared with those of previous studies of block copolymer micelles and theories of block copolymer micellization.
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  13. 13
    Qin, A.; Tian, M.; Ramireddy, C.; Webber, S. E.; Munk, P.; Tuzar, Z. Polystyrene-Poly(Methacrylic Acid) Block Copolymer Micelles. Macromolecules 1994, 27 (1), 120– 126,  DOI: 10.1021/ma00079a018
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    13
    Polystyrene-poly(methacrylic acid) block copolymer micelles
    Qin, Anwei; Tian, Minmin; Ramireddy, C.; Webber, Stephen E.; Munk, Petr; Tuzar, Zdenek
    Macromolecules (1994), 27 (1), 120-6CODEN: MAMOBX; ISSN:0024-9297.
    Block copolymer micelles formed by diblock and triblock copolymers of styrene (I) and methacrylic acid (II) were characterized in soln. in a mixed solvent with 80 vol % of dioxane and 20 vol % of water. Methods of static light scattering, quasielastic light scattering, differential refractometry, viscometry, sedimentation velocity, and densitometry were used. No unattached unimer mols. were obsd. Three independent methods were employed for obtaining micellar wts. and agreed well with each other. No anomalous behavior was obsd. by any method. The micellar solns. contained almost exclusively single micelles; only a few samples (those producing the largest micelles) contained micellar clusters. The micelles behaved hydrodynamically and thermodynamically as impermeable spheres. The structure of the micellar shell was characterized in some detail. Relations between the aggregation no. and the hydrodynamic radius of the micelles on the one hand and the sizes of the I and II blocks on the other were presented as scaling-type phenomenol. equations.
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  14. 14
    Guo, M.; Pitet, L. M.; Wyss, H. M.; Vos, M.; Dankers, P. Y. W.; Meijer, E. W. Tough Stimuli-Responsive Supramolecular Hydrogels with Hydrogen-Bonding Network Junctions. J. Am. Chem. Soc. 2014, 136 (19), 6969– 6977,  DOI: 10.1021/ja500205v
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    14
    Tough Stimuli-Responsive Supramolecular Hydrogels with Hydrogen-Bonding Network Junctions
    Guo, Mingyu; Pitet, Louis M.; Wyss, Hans M.; Vos, Matthijn; Dankers, Patricia Y. W.; Meijer, E. W.
    Journal of the American Chemical Society (2014), 136 (19), 6969-6977CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    Hydrogels were prepd. with phys. crosslinks comprising 2-ureido-4[1H]-pyrimidinone (UPy) hydrogen-bonding units within the backbone of segmented amphiphilic macromols. contg. hydrophilic poly(ethylene glycol) (PEG). The bulk materials adopt nanoscopic phys. crosslinks composed of UPy-UPy dimers embedded in segregated hydrophobic domains dispersed within the PEG matrix as confirmed by cryo-electron microscopy. The amphiphilic network was swollen with high wt. fractions of water (wH2O ≈ 0.8) owing to the high PEG wt. fraction within the pristine polymers (wPEG ≈ 0.9). Two different PEG chain lengths were investigated and illustrate the corresponding consequences of crosslink d. on mech. properties. The resulting hydrogels exhibited high strength and resilience upon deformation, consistent with a microphase sepd. network, in which the UPy-UPy interactions were adequately shielded within hydrophobic nanoscale pockets that maintain the network despite extensive water content. The cumulative result is a series of tough hydrogels with tunable mech. properties and tractable synthetic prepn. and processing. Furthermore, the melting transition of PEG in the dry polymer was shown to be an effective stimulus for shape memory behavior.
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  15. 15
    Huo, M.; Yuan, J.; Tao, L.; Wei, Y. Redox-Responsive Polymers for Drug Delivery: From Molecular Design to Applications. Polym. Chem. 2014, 5 (5), 1519– 1528,  DOI: 10.1039/C3PY01192E
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    15
    Redox-responsive polymers for drug delivery: from molecular design to applications
    Huo, Meng; Yuan, Jinying; Tao, Lei; Wei, Yen
    Polymer Chemistry (2014), 5 (5), 1519-1528CODEN: PCOHC2; ISSN:1759-9962. (Royal Society of Chemistry)
    A review. Glutathione has been regarded as a significant signal for distinguishing between tumor and normal tissue. Recently, reactive oxygen species have attracted much attention for their close connection with many diseases. Taking advantage of the physiol. signals, redox-responsive polymeric drug carriers constitute a significant research area in the various stimuli-responsive polymers for biomedical applications. During the rapid development of redox-responsive polymers, mol. design and related synthetic methodol. plays a crucial role. In this review, we discuss the redn.- and oxidn.-responsive polymeric drug carriers from the view of functional groups, as well as their applications in controlled release.
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  16. 16
    Schattling, P.; Jochum, F. D.; Theato, P. Multi-Stimuli Responsive Polymers - the All-in-One Talents. Polym. Chem. 2014, 5 (1), 25– 36,  DOI: 10.1039/C3PY00880K
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    16
    Multi-stimuli responsive polymers - the all-in-one talents
    Schattling, Philipp; Jochum, Florian D.; Theato, Patrick
    Polymer Chemistry (2014), 5 (1), 25-36CODEN: PCOHC2; ISSN:1759-9962. (Royal Society of Chemistry)
    Stimuli-responsive polymers have gained increasing attention, which is attributed to the manifold applications they can be used for. Several years' intensive research was invested in stimuli-responsive polymers. Their stimuli-responsiveness led not only to novel responsive groups, which enabled the translation of an external phys. impact into a change of a material property, but also to polymers that are equipped with more than one responsive group. The integration of several responsive moieties within one polymer yields smart polymers exhibiting complex responsive behavior of the polymers. This review summarises recent developments in the area of multi-stimuli responsive polymers, laying the focus on the improved, multifaceted response of polymer materials depending on the impact of several external stimuli.
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  17. 17
    Sun, Y.; Wang, Z.; Li, Y.; Zhang, Z.; Zhang, W.; Pan, X.; Zhou, N.; Zhu, X. Photoresponsive Amphiphilic Macrocycles Containing Main-Chain Azobenzene Polymers. Macromol. Rapid Commun. 2015, 36, 1341– 1347,  DOI: 10.1002/marc.201500136
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    17
    Photoresponsive Amphiphilic Macrocycles Containing Main-Chain Azobenzene Polymers
    Sun, Yadong; Wang, Zhao; Li, Yiwen; Zhang, Zhengbiao; Zhang, Wei; Pan, Xiangqiang; Zhou, Nianchen; Zhu, Xiulin
    Macromolecular Rapid Communications (2015), 36 (14), 1341-1347CODEN: MRCOE3; ISSN:1022-1336. (Wiley-VCH Verlag GmbH & Co. KGaA)
    Herein, the first example of photosensitive cyclic amphiphilic homopolymers consisting of multiple biphenyl azobenzene chromophores in the cyclic main chain tethered with hydrophilic tetraethylene glycol monomethyl ether units is presented. The synthetic approach involves sequentially performed thermal catalyzed "click" step-growth polymn. in bulk, and Cu(I)-catalyzed azide-alkyne cycloaddn. (CuAAC) intramol. cyclization from α-alkyne/ω-azide linear precursors. It is obsd. that such amphiphilic macrocycles exhibit increased glass transition temps. (Tg), slightly faster trans-cis-trans photoisomerization, and enhanced fluorescence emission intensity compared with the corresponding linear polymers. In addn., the cyclic amphiphilic homopolymers self-assemble into spherical nanoparticles with smaller sizes which possess slower photoresponsive behaviors in a tetrahydrofuran/water mixt. compared with those of the linear ones. All these interesting observations suggest that the cyclic topol. has a great influence on the phys. properties and self-assembly behavior of these photoresponsive amphiphilic macrocycles in general.
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  18. 18
    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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    18
    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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  19. 19
    Lovett, J. R.; Ratcliffe, L. P. D.; Warren, N. J.; Armes, S. P.; Smallridge, M. J.; Cracknell, R. B.; Saunders, B. R. A Robust Cross-Linking Strategy for Block Copolymer Worms Prepared via Polymerization-Induced Self-Assembly. Macromolecules 2016, 49 (8), 2928– 2941,  DOI: 10.1021/acs.macromol.6b00422
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    19
    A Robust Cross-Linking Strategy for Block Copolymer Worms Prepared via Polymerization-Induced Self-Assembly
    Lovett, J. R.; Ratcliffe, L. P. D.; Warren, N. J.; Armes, S. P.; Smallridge, M. J.; Cracknell, R. B.; Saunders, B. R.
    Macromolecules (Washington, DC, United States) (2016), 49 (8), 2928-2941CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    A poly(glycerol monomethacrylate) (PGMA) chain transfer agent is chain-extended by reversible addn.-fragmentation chain transfer (RAFT) statistical copolymn. of 2-hydroxypropyl methacrylate (HPMA) with glycidyl methacrylate (GlyMA) in concd. aq. soln. via polymn.-induced self-assembly (PISA). A series of five free-standing worm gels is prepd. by fixing the overall d.p. of the core-forming block at 144 while varying its GlyMA content from 0 to 20 mol %. 1H NMR kinetics indicated that GlyMA is consumed much faster than HPMA, producing a GlyMA-rich sequence close to the PGMA stabilizer block. Temp.-dependent oscillatory rheol. studies indicate that increasing the GlyMA content leads to progressively less thermoresponsive worm gels, with no degelation on cooling being obsd. for worms contg. 20 mol % GlyMA. The epoxy groups in the GlyMA residues can be ring-opened using 3-aminopropyltriethoxysilane (APTES) in order to prep. core crosslinked worms via hydrolysis-condensation with the siloxane groups and/or hydroxyl groups on the HPMA residues. Perhaps surprisingly, 1H NMR anal. indicates that the epoxy-amine reaction and the intermol. crosslinking occur on similar time scales. Crosslinking leads to stiffer worm gels that do not undergo degelation upon cooling. Dynamic light scattering studies and TEM analyses conducted on linear worms exposed to either methanol (a good solvent for both blocks) or anionic surfactant result in immediate worm dissocn. In contrast, crosslinked worms remain intact under such conditions, provided that the worm cores comprise at least 10 mol % GlyMA.
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    Blanazs, A.; Ryan, A. J.; Armes, S. P. Predictive Phase Diagrams for RAFT Aqueous Dispersion Polymerization: Effect of Block Copolymer Composition, Molecular Weight, and Copolymer Concentration. Macromolecules 2012, 45 (12), 5099– 5107,  DOI: 10.1021/ma301059r
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    20
    Predictive Phase Diagrams for RAFT Aqueous Dispersion Polymerization: Effect of Block Copolymer Composition, Molecular Weight, and Copolymer Concentration
    Blanazs, A.; Ryan, A. J.; Armes, S. P.
    Macromolecules (Washington, DC, United States) (2012), 45 (12), 5099-5107CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    Polymn.-induced self-assembly (PISA) of poly(glycerol monomethacrylate)-poly(2-hydroxypropyl methacrylate) (PGMA-PHPMA) diblocks is conducted using a RAFT aq. dispersion polymn. formulation at 70 °C. Several PGMA macromol. chain transfer agents (macro-CTAs) are chain-extended using a water-miscible monomer (HPMA): the growing PHPMA block becomes increasingly hydrophobic and hence drives in situ self-assembly. The final copolymer morphol. in such PISA syntheses depends on just three parameters: the mean d.p. (DP) of the PGMA stabilizer block, the mean DP of the PHPMA core-forming block, and the total solids concn. TEM is used to construct detailed diblock copolymer phase diagrams for PGMA DPs of 47, 78, and 112. For the shortest stabilizer block, there is essentially no concn. dependence: spheres, worms, or vesicles can be obtained even at 10% wt./wt. solids simply by selecting the DP of the PHPMA block that gives the appropriate mol. curvature. For a PGMA DP of 78, the phase diagram is rich: and the copolymer morphol. depends strongly on the total solids concn. There is also a narrow region where spheres, worms, and vesicles coexist, which may be due to the effect of polydispersity. For a PGMA112 macro-CTA, the phase diagram is dominated by spherical morphologies. This is probably because the longer core-forming block DPs required to reduce the mol. curvature are significantly more dehydrated and hence less mobile, which prevents the in situ evolution of morphol. from spheres to higher order morphologies. This hypothesis is supported by the observation that addn. of ethanol to aq. PISA syntheses conducted using the longer macro-CTAs allows access to diblock copolymer worms or vesicles, since this cosolvent solvates the core-forming PHPMA chains and hence increases their mobility at 70 °C. Elucidation of such phase diagrams is vital to ensure reproducible targeting of pure phases, rather than mixed phases.
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  21. 21
    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 (51), 16098– 16108,  DOI: 10.1021/jacs.5b10415
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    21
    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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    Rösler, A.; Vandermeulen, G. W. M.; Klok, H. A. Advanced Drug Delivery Devices via Self-Assembly of Amphiphilic Block Copolymers. Adv. Drug Delivery Rev. 2012, 64, 270– 279,  DOI: 10.1016/j.addr.2012.09.026
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    Derry, M. J.; Mykhaylyk, O. O.; Armes, S. P. A Vesicle-to-Worm Transition Provides a New High-Temperature Oil Thickening Mechanism. Angew. Chemie - Int. Ed. 2017, 56 (7), 1746– 1750,  DOI: 10.1002/anie.201609365
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    A Vesicle-to-Worm Transition Provides a New High-Temperature Oil Thickening Mechanism
    Derry, Matthew J.; Mykhaylyk, Oleksandr O.; Armes, Steven P.
    Angewandte Chemie, International Edition (2017), 56 (7), 1746-1750CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
    Diblock copolymer vesicles are prepd. via RAFT dispersion polymn. directly in mineral oil. Such vesicles undergo a vesicle-to-worm transition on heating to 150 °C, as judged by TEM and SAXS. Variable-temp. 1H NMR spectroscopy indicates that this transition is the result of surface plasticization of the membrane-forming block by hot solvent, effectively increasing the vol. fraction of the stabilizer block and so reducing the packing parameter for the copolymer chains. The rheol. behavior of a 10 % wt./wt. copolymer dispersion in mineral oil is strongly temp.-dependent: the storage modulus increases by five orders of magnitude on heating above the crit. gelation temp. of 135 °C, as the non-interacting vesicles are converted into weakly interacting worms. SAXS studies indicate that, on av., three worms are formed per vesicle. Such vesicle-to-worm transitions offer an interesting new mechanism for the high-temp. thickening of oils.
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    Bates, F. S. Polymer-Polymer Phase Behavior. Science (80-.). 1991, 251 (4996), 898– 905,  DOI: 10.1126/science.251.4996.898
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    Polymer-polymer phase behavior
    Bates, Frank S.
    Science (Washington, DC, United States) (1991), 251 (4996), 898-905CODEN: SCIEAS; ISSN:0036-8075.
    A review with 57 refs. on basic factors governing polymer-polymer phase behavior with emphasis on linear homopolymer blends and diblock copolymers as representative model mol. architectures. Equil. thermodn. and phase sepn. dynamics are reviewed and discussed.
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    Blanazs, A.; Armes, S. P.; Ryan, A. J. Self-Assembled Block Copolymer Aggregates: From Micelles to Vesicles and Their Biological Applications. Macromol. Rapid Commun. 2009, 30 (4), 267– 277,  DOI: 10.1002/marc.200800713
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    Self-assembled block copolymer aggregates: from micelles to vesicles and their biological applications
    Blanazs, Adam; Armes, Steven P.; Ryan, Anthony J.
    Macromolecular Rapid Communications (2009), 30 (4-5), 267-277CODEN: MRCOE3; ISSN:1022-1336. (Wiley-VCH Verlag GmbH & Co. KGaA)
    A review. The ability of amphiphilic block copolymers to self-assemble in selective solvents has been widely studied in academia and utilized for various com. products. The self-assembled polymer vesicle is at the forefront of this nanotechnol. revolution with seemingly endless possible uses, ranging from biomedical to nanometer-scale enzymic reactors. This review is focused on the inherent advantages in using polymer vesicles over their small mol. lipid counterparts and the potential applications in biol. for both drug delivery and synthetic cellular reactors.
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    Albigès, R.; Klein, P.; Roi, S.; Stoffelbach, F.; Creton, C.; Bouteiller, L.; Rieger, J. Water-Based Acrylic Coatings Reinforced by PISA-Derived Fibers. Polym. Chem. 2017, 8 (34), 4992– 4995,  DOI: 10.1039/C7PY00302A
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    Water-based acrylic coatings reinforced by PISA-derived fibers
    Albiges, Richard; Klein, Pauline; Roi, Stephanie; Stoffelbach, Francois; Creton, Costantino; Bouteiller, Laurent; Rieger, Jutta
    Polymer Chemistry (2017), 8 (34), 4992-4995CODEN: PCOHC2; ISSN:1759-9962. (Royal Society of Chemistry)
    Polymn.-induced self-assembly (PISA) is an efficient approach to synthesize self-assembled core-shell nanofibers in water, made of amphiphilic block copolymers. We demonstrate here for the first time that such anisotropic and high Tg nanofibers can be used as reinforcing fillers for water-based acrylic materials. This strategy opens the way for strong all-org. aq. coatings.
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    Chenal, M.; Rieger, J.; Vechambre, C.; Chenal, J.-M.; Chazeau, L.; Creton, C.; Bouteiller, L. Soft Nanostructured Films with an Ultra-Low Volume Fraction of Percolating Hard Phase. Macromol. Rapid Commun. 2013, 34 (34), 1524– 1529,  DOI: 10.1002/marc.201300410
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    Soft Nanostructured Films with an Ultra-Low Volume Fraction of Percolating Hard Phase
    Chenal, Marion; Rieger, Jutta; Vechambre, Cyril; Chenal, Jean-Marc; Chazeau, Laurent; Creton, Costantino; Bouteiller, Laurent
    Macromolecular Rapid Communications (2013), 34 (19), 1524-1529CODEN: MRCOE3; ISSN:1022-1336. (Wiley-VCH Verlag GmbH & Co. KGaA)
    In this study, aq. emulsion polymn. of Bu acrylate is performed in batch conditions without surfactants using a poly(acrylic acid)-trithiocarbonate macro-RAFT agent to control the polymn. and to stabilize the emulsion. According to the polymn.-induced self-assembly (PISA) approach, well-defined amphiphilic PAA-b-PBA diblock copolymers form and self-assemble during synthesis to yield highly stable core-shell particles with an extremely thin hard PAA shell. For the first time, we report here the specific properties of films obtained from these particular latexes. After drying the aq. dispersion, tough and transparent films are obtained. Although the films are not chem. crosslinked, they do not dissolve in good solvents for PBA. Moreover, they remain transparent even after immersion in water. Rheol. shows that the films are both stiff and ductile, thanks to the nanostructured but very low vol. fraction (less than 3 wt%) of PAA forming a percolating network in the soft PBA. Compared with conventional core-shell-based films, this approach affords for the first time a route to a thin percolating honeycomb nanostructure with a sharp and strong interface between the two phases. The versatility of the synthetic procedure opens perspectives for a large range of functional materials.
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    Rieger, J.; Osterwinter, G.; Bui, C.; Stoffelbach, F.; Charleux, B. Surfactant-Free Controlled/Living Radical Emulsion (Co)Polymerization of n-Butyl Acrylate and Methyl Methacrylate via RAFT Using Amphiphilic Polyethylene Oxide-Based Trithiocarbonate Chain Transfer Agents. Macromolecules 2009, 42 (15), 5518– 5525,  DOI: 10.1021/ma9008803
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    Surfactant-Free Controlled/Living Radical Emulsion (Co)polymerization of n-Butyl Acrylate and Methyl Methacrylate via RAFT Using Amphiphilic Poly(ethylene oxide)-Based Trithiocarbonate Chain Transfer Agents
    Rieger, Jutta; Osterwinter, Gregor; Bui, Chuong; Stoffelbach, Francois; Charleux, Bernadette
    Macromolecules (Washington, DC, United States) (2009), 42 (15), 5518-5525CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    The RAFT-mediated, surfactant-free, ab initio, batch emulsion polymn. of Bu acrylate (nBA) and its copolymn. with Me methacrylate (MMA) were studied. The control agent was a surface-active trithiocarbonate macromol. RAFT agent composed of a hydrophilic poly(ethylene oxide) (PEO) block and a hydrophobic dodecyl chain. The homopolymns. of nBA were fast with high final conversions, and the polymer chains were well-controlled with narrow molar mass distribution. The length of the PEO chain was shown to affect the particle size and the polymn. kinetics directly. We found the conditions to tune the particle size independently from the poly(Bu acrylate) chain length by playing with a mixt. of macro-RAFT agents with long and short PEO segment or by adding a PEO-based nonionic surfactant. The copolymns. of nBA and MMA exhibited features very similar to those of the nBA homopolymns. provided that the molar percentage of MMA did not exceed approx. 75%. In all cases, stable, submicrometric particles composed of amphiphilic diblock copolymer chains were formed.
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    Cockram, A. A.; Bradley, R. D.; Lynch, S. A.; Fleming, P. C. D.; Williams, N. S. J.; Murray, M. W.; Emmett, S. N.; Armes, S. P. Optimization of the High-Throughput Synthesis of Multiblock Copolymer Nanoparticles in Aqueous Media: Via Polymerization-Induced Self-Assembly. React. Chem. Eng. 2018, 3 (5), 645– 657,  DOI: 10.1039/C8RE00066B
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    Optimization of the high-throughput synthesis of multiblock copolymer nanoparticles in aqueous media via polymerization-induced self-assembly
    Cockram, Amy A.; Bradley, Robert D.; Lynch, Sylvie A.; Fleming, Patricia C. D.; Williams, Neal S. J.; Murray, Martin W.; Emmett, Simon N.; Armes, Steven P.
    Reaction Chemistry & Engineering (2018), 3 (5), 645-657CODEN: RCEEBW; ISSN:2058-9883. (Royal Society of Chemistry)
    In the present study, we report that PISA formulations are sufficiently robust to enable high-throughput expts. using a com. synthesis robot (Chemspeed Autoplant A100). More specifically, we use reversible addn.-fragmentation chain transfer (RAFT) aq. emulsion polymn. of either Bu methacrylate and/or benzyl methacrylate to prep. various examples of methacrylic multiblock copolymer nanoparticles using a poly(methacrylic acid) stabilizer block. Adequate stirring is essential to generate sufficiently small monomer droplets for such heterogeneous polymns. to proceed efficiently. Good reproducibility can be achieved under such conditions, with well-defined spherical morphologies being obtained at up to 45% wt./wt. solids. GPC studies indicate high blocking efficiencies but relatively broad mol. wt. distributions (Mw/Mn = 1.36-1.85), suggesting well-defined (albeit rather polydisperse) block copolymer chains. These preliminary studies provide a sound basis for high-throughput screening of RAFT-mediated PISA formulations, which is likely to be required for commercialization of this technol. Our results indicate that methacrylic PISA formulations enable the synthesis of diblock and triblock copolymer nanoparticles in high overall yield (94-99%) within 1-3 h at 70 °C. However, tetrablocks suffer from incomplete conversions (87-96% within 5 h) and hence most likely represent the upper limit for this approach.
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  30. 30
    Cockram, A. A.; Neal, T. J.; Derry, M. J.; Mykhaylyk, O. O.; Williams, N. S. J.; Murray, M. W.; Emmett, S. N.; Armes, S. P. Effect of Monomer Solubility on the Evolution of Copolymer Morphology during Polymerization-Induced Self-Assembly in Aqueous Solution. Macromolecules 2017, 50 (3), 796– 802,  DOI: 10.1021/acs.macromol.6b02309
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    Effect of Monomer Solubility on the Evolution of Copolymer Morphology during Polymerization-Induced Self-Assembly in Aqueous Solution
    Cockram, Amy A.; Neal, Thomas J.; Derry, Matthew J.; Mykhaylyk, Oleksandr O.; Williams, Neal S. J.; Murray, Martin W.; Emmett, Simon N.; Armes, Steven P.
    Macromolecules (Washington, DC, United States) (2017), 50 (3), 796-802CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    Polymn.-induced self-assembly (PISA) has become a widely used technique for the design of diblock copolymer nano-objects in concd. aq. soln. Depending on the specific PISA formulation, reversible addn.-fragmentation chain transfer (RAFT) aq. dispersion polymn. typically provides straightforward access to either spheres, worms or vesicles. In contrast, RAFT aq. emulsion polymn. formulations often lead to just kinetically trapped spheres. This limitation is currently not understood and only a few empirical exceptions were reported in the literature. In the present work, the effect of monomer soly. on copolymer morphol. is explored for an aq. polymn.-induced self-assembly (PISA) formulation. Using 2-hydroxybutyl methacrylate (aq. soly. =20 g dm-3 at 70 °C) instead of benzyl methacrylate (0.40 g dm-3 at 70 °C) for the core-forming block allows access to an unusual "monkey nut" copolymer morphol. over a relatively narrow range of target ds.p. when using a poly(methacrylic acid) RAFT agent at pH 5. These new nanoparticles have been characterized by transmission electron microscopy, dynamic light scattering, aq. electrophoresis, shear-induced polarized light imaging (SIPLI) and small-angle X-ray scattering.
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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 (16), 1458– 1471,  DOI: 10.1002/marc.201500028
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    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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    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 (4), 1653– 1662,  DOI: 10.1021/acs.macromol.8b02491
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    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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    Qiao, Z.; Qiu, T.; Liu, W.; Zhang, L.; Tu, J.; Guo, L.; Li, X. A “Green” Method for Preparing ABCBA Penta-Block Elastomers by Using RAFT Emulsion Polymerization. Polym. Chem. 2017, 8 (19), 3013– 3021,  DOI: 10.1039/C7PY00464H
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    A "green" method for preparing ABCBA penta-block elastomers by using RAFT emulsion polymerization
    Qiao, Zhi; Qiu, Teng; Liu, Weiwei; Zhang, Liangdong; Tu, Jinqiang; Guo, Longhai; Li, Xiaoyu
    Polymer Chemistry (2017), 8 (19), 3013-3021CODEN: PCOHC2; ISSN:1759-9962. (Royal Society of Chemistry)
    A clean method for prepg. ABCBA penta-block terpolymers was developed in a surfactant and org. solvent free emulsion system via one-pot RAFT polymn. The prepd. ABCBA penta-block terpolymers show large fracture tensile strain, low permanent set and potential application as elastomer materials. During the prepn. process, polyacrylic acid (PAA) was firstly synthesized as the A block via RAFT polymn. in water in the presence of a dual-functional RAFT agent. Subsequently, a partially water-sol. monomer 2,2,2-trifluoroethyl acrylate (TFEA) was used to synthesize the B block, and ABA tri-block copolymers could be obtained via org. solvent free RAFT emulsion polymn. Using the ABA tri-block copolymers as a surfactant, the ABCBA penta-block terpolymers were further synthesized using 2,2,3,4,4,4-hexafluorobutyl acrylate (HFBA) as the third monomer in an org. solvent free system. It has been found that the emulsification efficiency of the ABA tri-block copolymers is higher than that of the corresponding AB di-block copolymers. The assembly mechanism of penta-block terpolymers to form a tri-layer core-shell latex particle was proposed and confirmed by TEM images. Finally, a transparent and hydrophobic elastomeric film was obtained by directly casting the synthesized penta-block terpolymer latexes and subsequent heat treatment. The films have excellent mech. properties and water resistance.
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    Wu, X.; Qiao, Y.; Yang, H.; Wang, J. Self-Assembly of a Series of Random Copolymers Bearing Amphiphilic Side Chains. J. Colloid Interface Sci. 2010, 349 (2), 560– 564,  DOI: 10.1016/j.jcis.2010.05.093
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    Self-assembly of a series of random copolymers bearing amphiphilic side chains
    Wu, Xu; Qiao, Yingjie; Yang, Hui; Wang, Jinben
    Journal of Colloid and Interface Science (2010), 349 (2), 560-564CODEN: JCISA5; ISSN:0021-9797. (Elsevier B.V.)
    A novel series of comb-like random copolymers were prepd. by polymn. of amphiphilic macromonomers, 2-(acrylamido)-octane sulfonic acid (AMC8S), 2-(acrylamido)-dodecane sulfonic acid (AMC12S), and 2-(acrylamido)-hexadecane sulfonic acid (AMC16S), with 2-(acrylamido)-2-methylpropanesulfonic acid (AMPS) resp. The synthesis of the polymers with the same contents of amphiphilic units as side chains, but different chain length, enabled us to study the chain length dependence of their assocn. in salt soln. Steady-state fluorescence measurements with pyrene as a polarity probe, quasielastic light scattering techniques (QELS) and transmission electron micrograph (TEM) were employed to investigate the associative properties of the system. The above investigations showed that all kinds of side chains begin to assemble at certain polymer concns. and the crit. aggregation concn. (CAC) decrease dramatically with the increase in the length and content of alkyl. An interesting phenomenon is that the assembly tends more favorably to occur among different mols. rather than within single mol. when the no. of carbon atoms in the alkyl groups or the polymer concn. increases, leading to the formation of larger multimol. micelle-like aggregate. The aim of the present work is to establish the fundamental preconditions of intramol. and intermol. assocn. fashions for the polymers, which is useful for the exploitation of functional groups and contributes to the development of amphiphilic random polymers.
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    Kawata, T.; Hashidzume, A.; Sato, T. Micellar Structure of Amphiphilic Statistical Copolymers Bearing Dodecyl Hydrophobes in Aqueous Media. Macromolecules 2007, 40 (4), 1174– 1180,  DOI: 10.1021/ma062299x
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    Micellar Structure of Amphiphilic Statistical Copolymers Bearing Dodecyl Hydrophobes in Aqueous Media
    Kawata, Takefumi; Hashidzume, Akihito; Sato, Takahiro
    Macromolecules (2007), 40 (4), 1174-1180CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    The structure of micellar aggregates formed from ionic statistical copolymers of N-acryloyl-amino acids and N-dodecylmethacrylamide in 0.05 M aq. NaCl was studied by light scattering and fluorescence. The exptl. results indicated that the tendency of the interchain aggregation increased with the hydrophobic monomer content for each series of the copolymers but decreased with hydrophobicity of the amino acid residue in the copolymers. On the other hand, while the micellar structure of the statistical copolymers strongly depended on the kind of the hydrophobe, it is little dependent on the kind of the electrolyte monomer unit at low ionic strength. Using these data, a theor. anal. taking into account the chain stiffness effect revealed that uni-core micelles formed from the ionic statistical copolymers were of flower type with a min. loop size.
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    Zhu, X.; Liu, M. Self-Assembly and Morphology Control of New l -Glutamic Acid-Based Amphiphilic Random Copolymers: Giant Vesicles, Vesicles, Spheres, and Honeycomb Film. Langmuir 2011, 27 (21), 12844– 12850,  DOI: 10.1021/la202680j
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    Self-Assembly and Morphology Control of New L-Glutamic Acid-Based Amphiphilic Random Copolymers: Giant Vesicles, Vesicles, Spheres, and Honeycomb Film
    Zhu, Xuewang; Liu, Minghua
    Langmuir (2011), 27 (21), 12844-12850CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
    New amphiphilic random copolymers contg. hydrophobic dodecyl (C12) chain and hydrophilic L-glutamic acid were synthesized, and their self-assembly in soln. as well as on the solid surfaces was investigated. The self-assembly behavior of these polymers are largely dependent on their hydrophilic and hydrophobic balances. The copolymer with a more hydrophobic alkyl chain (∼90%) self-assembled into giant vesicles with a diam. of several micrometers in a mixed solvent of ethanol and water. When the hydrophobic ratio decreased to ca. 76%, the polymer self-assembled into conventional vesicles with several hundred nanometers. The giant vesicles could be fused in certain conditions, while the conventional vesicles were stable. When the content of the hydrophilic part was further increased, no organized structures were formed. On the other hand, when the copolymer solns. were directly cast on solid substrates such as silicon plates, films with organized nanostructures could also be obtained, the morphol. of which depended on solvent selection. When ethanol or methanol was used, spheres were obtained. When dichloromethane was used as the solvent, honeycomb-like morphologies were obtained. These results showed that through appropriate mol. design, random copolymer could self-assemble into various organized structures, which could be regulated through the hydrophobic/hydrophilic balance and the solvents.
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    Tian, F.; Yu, Y.; Wang, C.; Yang, S. Consecutive Morphological Transitions in Nanoaggregates Assembled from Amphiphilic Random Copolymer via Water Driven Micellization and Light-Triggered Dissociation. Macromolecules 2008, 41 (10), 3385– 3388,  DOI: 10.1021/ma800142j
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    Consecutive Morphological Transitions in Nanoaggregates Assembled from Amphiphilic Random Copolymer via Water-Driven Micellization and Light-Triggered Dissociation
    Tian, Feng; Yu, Yuanyuan; Wang, Changchun; Yang, Shu
    Macromolecules (Washington, DC, United States) (2008), 41 (10), 3385-3388CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    We report a study of continuous morphol. transitions from spherical micelles, through hollow tubes and wormlike rods, to large vesicles in nanoaggregates self-assembled from photoresponsive amphiphilic random copolymer. Through esterification of the side chain hydroxyl groups, the hydrophilic poly(hydroxyethyl methacrylate) (PHEMA) backbone is partially and randomly modified by the hydrophobic, light-responsive 2-diazo-1,2-naphthoquinone (DNQ) mols. The micellization and transition are then triggered simply by adding water into the copolymer/DMF soln. Upon irradn. to UV light at 405 nm, large vesicles become increasingly hydrophilic with time and gradually dissoc. into globular hydrogel particles in the aq. soln. (Scheme 1), releasing the encapsulated dye mols.
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    Sun, G.; Zhang, M.; He, J.; Ni, P. Synthesis of Amphiphilic Cationic Copolymers Poly[2-(Methacryloyloxy)Ethyl Trimethylammonium Chloride-co-stearyl Methacrylate] and Their Self-Assembly Behavior in Water and Water-Ethanol Mixtures. J. Polym. Sci. Part A Polym. Chem. 2009, 47, 4670– 4684,  DOI: 10.1002/pola.23517
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    Synthesis of amphiphilic cationic copolymers poly[2-(methacryloyloxy)ethyl trimethylammonium chloride-co-stearyl methacrylate] and their self-assembly behavior in water and water-ethanol mixtures
    Sun, Guixiang; Zhang, Mingzu; He, Jinlin; Ni, Peihong
    Journal of Polymer Science, Part A: Polymer Chemistry (2009), 47 (18), 4670-4684CODEN: JPACEC; ISSN:0887-624X. (John Wiley & Sons, Inc.)
    A series of amphiphilic cationic random copolymers, namely poly[2-(methacryloyloxy)ethyl trimethylammonium chloride-co-stearyl methacrylate] or poly(MADQUAT-co-SMA), were synthesized via conventional free-radical copolymn. using 2,2'-azobisisobutyronitrile (AIBN) as initiator and n-dodecanethiol as chain transfer agent. The resultant products were then characterized by FT-IR, 1H NMR, MALDI-TOF MS measurements. From the no.-av. mol. wts. of the copolymers, we can conclude that these copolymers have oligomeric structure with a limited no. of hydrophilic and hydrophobic moieties in a short polymer chain. The reactivity ratios (rMADQUAT = 0.83, rSMA = 0.25) between the hydrophilic MADQUAT monomer and the hydrophobic SMA monomer were calcd. by the Finemann and Ross method, which was based on the results of 1H NMR anal. The surface activity of the random copolymers was studied by the combination of surface tension and contact angle measurement, and these copolymers possess relatively high surface activity. The crit. aggregation concns. (cac) of the copolymers in aq. soln. were detd. by fluorescence probe method and surface tension measurement. The different nanoparticles of poly(MADQUAT-co-SMA) copolymers formed in pure water or ethanol-water mixt. were proved by the particle size and size distribution in the measurement of dynamic light scattering (DLS). Furthermore, using TEM, we could observe various self-assembly morphologies of these random copolymer. All the amphiphilic cationic random copolymers have a good self-assembly behavior, even if they are ill-defined copolymers.
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    Stephan, T.; Muth, S.; Schmidt, M. Shape Changes of Statistical Copolymacromonomers: From Wormlike Cylinders to Horseshoe- and Meanderlike Structures. Macromolecules 2002, 35 (27), 9857– 9860,  DOI: 10.1021/ma025711r
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    Shape Changes of Statistical Copolymacromonomers: From Wormlike Cylinders to Horseshoe- and Meander-like Structures
    Stephan, Tim; Muth, Sandra; Schmidt, Manfred
    Macromolecules (2002), 35 (27), 9857-9860CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    Depending on the solvent, statistical copolymer cylindrical brushes adopt different shapes from worm-like to horseshoe or meander-like structures when spin-cast onto mica. To the best of our knowledge, this is the first time that shape persistent synthetic macromols. could be chem. manipulated to change their conformation from a wormlike to regularly curved structures. It should be mentioned, though, that for cylindrical brushes with Bu acrylate side chains a collapse of the wormlike conformation to spherical structures could be induced under pressure on a Langmuir-Blodgett trough. Also, poly(p-phenylene)s with amphipolar dendritic side chains were reported to have the potential to intramol. segregate lengthwise, particularly when spread on a LB trough as well. Our next step will address the question of whether the collapse of the minority component could be detected by scattering expts. in soln., which, however, was not successful so far.
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    Ilhan, F.; Galow, T. H.; Gray, M.; Clavier, G.; Rotello, V. M. Giant Vesicle Formation through Self-Assembly of Complementary Random Copolymers. J. Am. Chem. Soc. 2000, 122 (24), 5895– 5896,  DOI: 10.1021/ja0011966
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    Giant Vesicle Formation through Self-Assembly of Complementary Random Copolymers
    Ilhan, Faysal; Galow, Trent H.; Gray, Mark; Clavier, Gilles; Rotello, Vincent M.
    Journal of the American Chemical Society (2000), 122 (24), 5895-5896CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    Differential interference contrast optical microscopy and confocal laser scanning microscopy showed that vesicular H-bond complexes formed between chains of 4-(chloromethyl)styrene-styrene copolymer (I)-2,6-bis(propionamido)pyrid-4-one adducts and I-thymine-1-acetic acid adducts in CHCl3 solns.
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    Liu, X.; Kim, J.-S.; Wu, J.; Eisenberg, A. Bowl-Shaped Aggregates from the Self-Assembly of an Amphiphilic Random Copolymer of Poly(Styrene- Co -Methacrylic Acid). Macromolecules 2005, 38 (16), 6749– 6751,  DOI: 10.1021/ma050665r
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    Bowl-Shaped Aggregates from the Self-Assembly of an Amphiphilic Random Copolymer of Poly(styrene-co-methacrylic acid)
    Liu, Xiaoya; Kim, Joon-Seop; Wu, Jun; Eisenberg, Adi
    Macromolecules (2005), 38 (16), 6749-6751CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    A bowl-shaped structure of random poly(styrene-co-methacrylic acid) was prepd. by self-assembly in dil. soln. We emphasize that the copolymer was a random copolymer in contrast to the block copolymers or functionally terminated homopolymers used before. The added viscosity control is probably provided by H bond interactions among OH groups along the backbone as in encountered in carboxylic acids in bulk or in org. solvents.
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    Neal, T. J.; Parnell, A. J.; King, S. M.; Beattie, D. L.; Murray, M. W.; Williams, N. S. J.; Emmett, S. N.; Armes, S. P.; Spain, S. G.; Mykhaylyk, O. O. Control of Particle Size in the Self-Assembly of Amphiphilic Statistical Copolymers. Macromolecules 2021, 54 (3), 1425– 1440,  DOI: 10.1021/acs.macromol.0c02341
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    Control of Particle Size in the Self-Assembly of Amphiphilic Statistical Copolymers
    Neal, Thomas J.; Parnell, Andrew J.; King, Stephen M.; Beattie, Deborah L.; Murray, Martin W.; Williams, Neal S. J.; Emmett, Simon N.; Armes, Steven P.; Spain, Sebastian G.; Mykhaylyk, Oleksandr O.
    Macromolecules (Washington, DC, United States) (2021), 54 (3), 1425-1440CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    A range of amphiphilic statistical copolymers is synthesized where the hydrophilic component is either methacrylic acid (MAA) or 2-(dimethylamino)ethyl methacrylate (DMAEMA) and the hydrophobic component comprises Me, Et, Bu, hexyl, or 2-ethylhexyl methacrylate, which provide a broad range of partition coeffs. (log P). Small-angle x-ray scattering studies confirm that these amphiphilic copolymers self-assemble to form well-defined spherical nanoparticles in an aq. soln., with more hydrophobic copolymers forming larger nanoparticles. Varying the nature of the alkyl substituent also influenced self-assembly with more hydrophobic comonomers producing larger nanoparticles at a given copolymer compn. A model based on particle surface charge d. (PSC model) is used to describe the relation between copolymer compn. and nanoparticle size. This model assumes that the hydrophilic monomer is preferentially located at the particle surface and provides a good fit to all of the exptl. data. More specifically, a linear relation is obsd. between the surface area fraction covered by the hydrophilic comonomer required to achieve stabilization and the log P value for the hydrophobic comonomer. Contrast variation small-angle neutron scattering is used to study the internal structure of these nanoparticles. This technique indicates partial phase sepn. within the nanoparticles, with about half of the available hydrophilic comonomer repeat units being located at the surface and hydrophobic comonomer-rich cores. This information enables a refined PSC model to be developed, which indicates the same relation between the surface area fraction of the hydrophilic comonomer and the log P of the hydrophobic comonomer repeat units for the anionic (MAA) and cationic (DMAEMA) comonomer systems. This study demonstrates how nanoparticle size can be readily controlled and predicted using relatively ill-defined statistical copolymers, making such systems a viable attractive alternative to diblock copolymer nanoparticles for a range of industrial applications.
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    Azuma, Y.; Terashima, T.; Sawamoto, M. Self-Folding Polymer Iron Catalysts for Living Radical Polymerization. ACS Macro Lett. 2017, 6 (8), 830– 835,  DOI: 10.1021/acsmacrolett.7b00498
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    Self-Folding Polymer Iron Catalysts for Living Radical Polymerization
    Azuma, Yusuke; Terashima, Takaya; Sawamoto, Mitsuo
    ACS Macro Letters (2017), 6 (8), 830-835CODEN: AMLCCD; ISSN:2161-1653. (American Chemical Society)
    Iron-bearing self-folding polymers were created with amphiphilic random copolymers as active, versatile, and recyclable polymer-supported catalysts for living radical polymn. (LRP). The key is to build bis(imino)pyridine ligand cavities for iron complexes as linking units within self-folding polymers. Self-folding polymer ligands are synthesized by the intramol. imine crosslinking of self-folded amphiphilic random copolymers bearing hydrophilic poly(ethylene glycol) (PEG), hydrophobic dodecyl, and urea/aniline pendants with 2,6-pyridinedicarboxaldehyde in water. The folding polymers efficiently formed iron complex catalysts in the cores to induce LRP and random or block copolymn. of various methacrylates. The self-folding polymer catalysts not only showed high activity and tolerance to functional groups such as acid, hydroxyl groups, and oxygen but also afforded easy product recovery and catalyst recycle thanks to hydrophilic PEG chains.
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    Lyon, C. K.; Prasher, A.; Hanlon, A. M.; Tuten, B. T.; Tooley, C. A.; Frank, P. G.; Berda, E. B. A Brief User’s Guide to Single-Chain Nanoparticles. Polym. Chem. 2015, 6 (2), 181– 197,  DOI: 10.1039/C4PY01217H
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    A brief user's guide to single-chain nanoparticles
    Lyon, Christopher K.; Prasher, Alka; Hanlon, Ashley M.; Tuten, Bryan T.; Tooley, Christian A.; Frank, Peter G.; Berda, Erik B.
    Polymer Chemistry (2015), 6 (2), 181-197CODEN: PCOHC2; ISSN:1759-9962. (Royal Society of Chemistry)
    In this review we outline the various methods that have been explored to synthesize architecturally defined nanoparticles from discrete polymer chains, summarize the methods of characterization that are required to prove their formation and probe their morphol., and introduce a no. of potential applications that are being explored currently. Given the small size of the nanostructures produced by these methods and the relative ease with which they can be tailored to specific end use applications it is likely such efforts will intensify in the coming years. So far, simple chem. has been utilized and high-level characterization and modeling studies have been applied to understand the process by which these particles form and how they behave, both in the bulk and in soln. Although impossible to predict where this work will lead, we hope this "user's guide" will prove useful to the community as research on single-chain nanoparticles continues to evolve.
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    Romulus, J.; Weck, M. Single-Chain Polymer Self-Assembly Using Complementary Hydrogen Bonding Units. Macromol. Rapid Commun. 2013, 34 (19), 1518– 1523,  DOI: 10.1002/marc.201300501
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    Single-Chain Polymer Self-Assembly Using Complementary Hydrogen Bonding Units
    Romulus, Joy; Weck, Marcus
    Macromolecular Rapid Communications (2013), 34 (19), 1518-1523CODEN: MRCOE3; ISSN:1022-1336. (Wiley-VCH Verlag GmbH & Co. KGaA)
    A triblock copolymer contg. the complementary hydrogen bonding recognition pair ureidoguanosine-diaminonaphthyridine (UG-DAN) as pendant functional groups is synthesized using ring-opening metathesis polymn. (ROMP). The norbornene-based DAN monomer is shown to allow for a controlled polymn. when polymd. in the presence of a modified-UG mol. that serves as a protecting group, subsequently allowing for the fabrication of functionalized triblock copolymers. The self-assembly of the copolymers was characterized using dynamic light scattering and 1H NMR spectroscopy. It is demonstrated that the polymers self-assemble via complementary hydrogen bonding motifs even at low dilns., indicating intramol. interactions.
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    Gillissen, M. A. J.; Voets, I. K.; Meijer, E. W.; Palmans, A. R. A. Single Chain Polymeric Nanoparticles as Compartmentalised Sensors for Metal Ions. Polym. Chem. 2012, 3 (11), 3166– 3174,  DOI: 10.1039/c2py20350b
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    Single chain polymeric nanoparticles as compartmentalised sensors for metal ions
    Gillissen, Martijn A. J.; Voets, Ilja K.; Meijer, E. W.; Palmans, Anja. R. A.
    Polymer Chemistry (2012), 3 (11), 3166-3174CODEN: PCOHC2; ISSN:1759-9962. (Royal Society of Chemistry)
    3,3'-Bis(acylamino)-2,2'-bipyridine substituted benzene-1,3,5-tricarboxamide (BiPy-BTA) grafted polynorbornene polymers were prepd. via ring-opening metathesis polymn. using a third generation Grubbs catalyst. The polymers fold intramolecularly via π-π interactions into fluorescent, compartmentalized particles of nanometer-size in mixts. of THF and methylcyclohexane. Spectroscopic and light scattering techniques show that the compact conformation of the folded polymer is affected by increasing the BiPy-BTA functionalization degree and by changing the solvent polarity. Changes in the conformation are accompanied by changes in the fluorescence intensity. Due to the affinity of the 2,2'-bipyridine units for metal ions such as Cu, the particles obtained are effective sensors for these metals. The compartmentalization of the binding motifs in SCPNs proves to be advantageous in sensor applications of these particles.
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    Terashima, T.; Sugita, T.; Fukae, K.; Sawamoto, M. Synthesis and Single-Chain Folding of Amphiphilic Random Copolymers in Water. Macromolecules 2014, 47 (2), 589– 600,  DOI: 10.1021/ma402355v
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    Synthesis and Single-Chain Folding of Amphiphilic Random Copolymers in Water
    Terashima, Takaya; Sugita, Takanori; Fukae, Kaoru; Sawamoto, Mitsuo
    Macromolecules (Washington, DC, United States) (2014), 47 (2), 589-600CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    Amphiphilic random methacrylate copolymers, consisting of poly(ethylene glycol) (PEG) and alkyl pendent groups, undergo reversible single-chain self-folding in water via intramol. hydrophobic interaction, to generate a dynamic unimol. hydrophobic nanospace, similar in shape but structurally different relative to micelles and microgel star polymers. These copolymers were prepd. by the ruthenium-catalyzed living radical copolymn. of a PEG methacrylate (PEGMA) and an alkyl methacrylate (RMA; R, -CnH2n+1, n = 1-18), where copolymer compn., d.p., and hydrophobic R moiety were varied. Detailed structural and chain-folding characterization has revealed: single-chain folding is favored with the RMA content 20-40 mol % per chain; the hydrophobic inner compartment (or the self-folded structure) is stable even at a high polymer concn. (up to ∼6 wt. %); and folded-unfolded transition occurs on addn. of methanol or by elevating soln. temp., finally to phase-sepn. above a lower crit. soln. temp.
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    Terashima, T.; Mes, T.; De Greef, T. F. A.; Gillissen, M. A. J.; Besenius, P.; Palmans, A. R. A.; Meijer, E. W. Single-Chain Folding of Polymers for Catalytic Systems in Water. J. Am. Chem. Soc. 2011, 133 (13), 4742– 4745,  DOI: 10.1021/ja2004494
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    Single-Chain Folding of Polymers for Catalytic Systems in Water
    Terashima, Takaya; Mes, Tristan; De Greef, Tom F. A.; Gillissen, Martijn A. J.; Besenius, Pol; Palmans, Anja R. A.; Meijer, E. W.
    Journal of the American Chemical Society (2011), 133 (13), 4742-4745CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    Enzymes are a source of inspiration for chemists attempting to create versatile synthetic catalysts. In order to arrive at a polymeric chain carrying catalytic units sepd. spatially, it is a prerequisite to fold these polymers in water into well-defined compartmentalized architectures thus creating a catalytic core. Herein, we report the synthesis, phys. properties, and catalytic activity of a water-sol. segmented terpolymer in which a helical structure in the apolar core is created around a ruthenium-based catalyst. The supramol. chirality of this catalytic system is the result of the self-assembly of benzene-1,3,5-tricarboxamide side chains, while the catalyst arises from the sequential ruthenium-catalyzed living radical polymn. of the different monomers followed by ligand exchange. The polymers exhibit a two-state folding process and show transfer hydrogenation in water.
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    Matsumoto, M.; Sawamoto, M.; Terashima, T. Orthogonal Folding of Amphiphilic/Fluorous Random Block Copolymers for Double and Multicompartment Micelles in Water. ACS Macro Lett. 2019, 8 (3), 320– 325,  DOI: 10.1021/acsmacrolett.9b00078
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    Orthogonal Folding of Amphiphilic/Fluorous Random Block Copolymers for Double and Multicompartment Micelles in Water
    Matsumoto, Mayuko; Sawamoto, Mitsuo; Terashima, Takaya
    ACS Macro Letters (2019), 8 (3), 320-325CODEN: AMLCCD; ISSN:2161-1653. (American Chemical Society)
    Here, we report orthogonal folding and self-assembly systems of amphiphilic/fluorous random block copolymers for double core and multicompartment micelles in water. For this, we developed the precision folding techniques of polymer chains via the selective self-assembly of the pendant groups. Typically, A/C-B/C random block copolymers were designed: Hydrophobic dodecyl groups (A) and fluorous fluorinated octyl groups (B) were introduced into the resp. blocks, while hydrophilic poly(ethylene glycol) chains (C) were randomly incorporated into all the segments. By controlling the chain length and compn. of the resp. blocks, the copolymers induce orthogonal single-chain folding in water to form double-compartment micelles comprising hydrophobic and fluorous cores. The copolymers were site-selectively folded in a fluoroalc. to result in tadpole unimer micelles comprising a hydrophobic A/C unimer micelle and an unfolded fluorous B/C chain. Addnl., asym. A/C-B/C random block copolymers with short and highly hydrophobic or fluorous segments were effective for multicompartment micelles in water.
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    Matsumoto, M.; Terashima, T.; Matsumoto, K.; Takenaka, M.; Sawamoto, M. Compartmentalization Technologies via Self-Assembly and Cross-Linking of Amphiphilic Random Block Copolymers in Water. J. Am. Chem. Soc. 2017, 139 (21), 7164– 7167,  DOI: 10.1021/jacs.7b03152
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    Compartmentalization Technologies via Self-Assembly and Cross-Linking of Amphiphilic Random Block Copolymers in Water
    Matsumoto, Mayuko; Terashima, Takaya; Matsumoto, Kazuma; Takenaka, Mikihito; Sawamoto, Mitsuo
    Journal of the American Chemical Society (2017), 139 (21), 7164-7167CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    Orthogonal self-assembly and intramol. crosslinking of amphiphilic random block copolymers in water afforded an approach to tailor-make well-defined compartments and domains in single polymer chains and nanoaggregates. For a double compartment single-chain polymer, an amphiphilic random block copolymer bearing hydrophilic poly(ethylene glycol) (PEG) and hydrophobic dodecyl, benzyl, and olefin pendants was synthesized by living radical polymn. (LRP) and postfunctionalization; the dodecyl and benzyl units were incorporated into the different block segments, whereas PEG pendants were statistically attached along a chain. The copolymer self-folded via the orthogonal self-assembly of hydrophobic dodecyl and benzyl pendants in water, followed by intramol. crosslinking, to form a single-chain polymer carrying double yet distinct hydrophobic nanocompartments. A single-chain crosslinked polymer with a chlorine terminal served as a globular macroinitiator for LRP to provide an amphiphilic tadpole macromol. comprising a hydrophilic nanoparticle and a hydrophobic polymer tail; the tadpole thus self-assembled into multicompartment aggregates in water.
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    Neal, T. J.; Beattie, D. L.; Byard, S. J.; Smith, G. N.; Murray, M. W.; Williams, N. S. J.; Emmett, S. N.; Armes, S. P.; Spain, S. G.; Mykhaylyk, O. O. Self-Assembly of Amphiphilic Statistical Copolymers and Their Aqueous Rheological Properties. Macromolecules 2018, 51 (4), 1474– 1487,  DOI: 10.1021/acs.macromol.7b02134
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    Self-Assembly of Amphiphilic Statistical Copolymers and Their Aqueous Rheological Properties
    Neal, Thomas J.; Beattie, Deborah L.; Byard, Sarah J.; Smith, Gregory N.; Murray, Martin W.; Williams, Neal S. J.; Emmett, Simon N.; Armes, Steven P.; Spain, Sebastian G.; Mykhaylyk, Oleksandr O.
    Macromolecules (Washington, DC, United States) (2018), 51 (4), 1474-1487CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    A range of poly(Bu methacrylate-stat-methacrylic acid) [P(BMA-stat-MAA)] statistical copolymers of various compns. and mol. wts. ranging from 5 to 30 kDa were prepd. using either reversible addn.-fragmentation chain transfer (RAFT) soln. copolymn. or conventional free radical polymn. in isopropanol (IPA). On diln. with water, these amphiphilic copolymers self-assembled to form spherical nano-objects as confirmed by small-angle X-ray scattering (SAXS) and transmission electron microscopy. Various structural models were examd. to ext. information regarding the mean nano-object size and morphol. It is found that nano-object radii are independent of copolymer mol. wt. but depend on the copolymer compn.: the smaller the amt. of MAA units in the copolymer chains, the larger the nano-objects that are formed. Combined SAXS and aq. electrophoretic measurements indicated that most of the MAA units are located at the nano-object surface. Furthermore, SAXS and rheol. measurements were used to monitor the effect of solvent compn. on the copolymer morphol. both at a fixed copolymer concn. (either 1 or 25 wt. %) and also for a gradual variation in copolymer concns. (from 1 to 40 wt. %) when adding water to the initial copolymer soln. in IPA. These studies revealed that the copolymers are present in soln. as molecularly dissolved Gaussian chains when the solvent compn. is IPA-rich. However, the copolymer chains self-assemble into spherical nano-objects when the solvent compn. is water-rich. At intermediate solvent compns., SAXS anal. confirmed the formation of an interconnected nano-object network, which accounts for the apparently anomalous increase in soln. viscosity on diln. indicated by rheol. measurements.
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    Hattori, G.; Takenaka, M.; Sawamoto, M.; Terashima, T. Nanostructured Materials via the Pendant Self-Assembly of Amphiphilic Crystalline Random Copolymers. J. Am. Chem. Soc. 2018, 140 (27), 8376– 8379,  DOI: 10.1021/jacs.8b03838
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    Nanostructured Materials via the Pendant Self-Assembly of Amphiphilic Crystalline Random Copolymers
    Hattori, Goki; Takenaka, Mikihito; Sawamoto, Mitsuo; Terashima, Takaya
    Journal of the American Chemical Society (2018), 140 (27), 8376-8379CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    Versatile self-assembly systems to nanostructured materials in both solid and soln. were developed with common amphiphilic random copolymers bearing hydrophilic poly(ethylene glycol) (PEG) and hydrophobic cryst. octadecyl pendants. The copolymers efficiently induced precision self-assembly of the pendants to provide not only core-cryst., thermoresponsive micelles and vesicles in water and reverse micelles in hexane but also sub-10 nm lamellar or spherical microphase sepn. structure in solid. Typically, the solid random copolymers with 50-80 mol % octadecyl units formed lamellar structure of a hydrophilic PEG layer and a hydrophobic, cryst. octadecyl layer. Importantly, the domain spacing is about 5 nm, much smaller than that generally obtained with conventional block copolymers. The domain structure is controlled by compn., independent of chain length. The copolymers further gave various thermoresponsive, compartmentalized materials in aq. and org. media, where the 3D structure can be also controlled by the compn. and sample prepn. protocols.
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    Ilavsky, J.; Jemian, P. R. Irena : Tool Suite for Modeling and Analysis of Small-Angle Scattering. J. Appl. Crystallogr. 2009, 42 (2), 347– 353,  DOI: 10.1107/S0021889809002222
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    Irena: tool suite for modeling and analysis of small-angle scattering
    Ilavsky, Jan; Jemian, Peter R.
    Journal of Applied Crystallography (2009), 42 (2), 347-353CODEN: JACGAR; ISSN:0021-8898. (International Union of Crystallography)
    Irena, a tool suite for anal. of both x-ray and neutron small-angle scattering (SAS) data within the com. Igor Pro application, brings together a comprehensive suite of tools useful for studies in materials science, physics, chem., polymer science and other fields. In addn. to Guinier and Porod fits, the suite combines a variety of advanced SAS data evaluation tools for the modeling of size distribution in the dil. limit using max. entropy and other methods, dil. limit small-angle scattering from multiple noninteracting populations of scatterers, the pair-distance distribution function, a unified fit, the Debye-Bueche model, the reflectivity (x-ray and neutron) using Parratt's formalism, and small-angle diffraction. There are also a no. of support tools, such as a data import/export tool supporting a broad sampling of common data formats, a data modification tool, a presentation-quality graphics tool optimized for small-angle scattering data, and a neutron and x-ray scattering contrast calculator. These tools are brought together into one suite with consistent interfaces and functionality. The suite allows robust automated note recording and saving of parameters during export.
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    Horcas, I.; Fernández, R.; Gómez-Rodríguez, J. M.; Colchero, J.; Gómez-Herrero, J.; Baro, A. M. WSXM: A Software for Scanning Probe Microscopy and a Tool for Nanotechnology. Rev. Sci. Instrum. 2007, 78, 013705,  DOI: 10.1063/1.2432410
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    WSXM: a software for scanning probe microscopy and a tool for nanotechnology
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    Review of Scientific Instruments (2007), 78 (1), 013705/1-013705/8CODEN: RSINAK; ISSN:0034-6748. (American Institute of Physics)
    In this work we briefly describe the most relevant features of WSXM, a freeware scanning probe microscopy software based on MS-Windows. The article is structured in three different sections: The introduction is a perspective on the importance of software on scanning probe microscopy. The second section is devoted to describe the general structure of the application; in this section the capabilities of WSXM to read third party files are stressed. Finally, a detailed discussion of some relevant procedures of the software is carried out.
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    Kheshgi, S.; Scriven, L. E. Dewetting: Nucleation and Growth of Dry Regions. Chem. Eng. Sci. 1991, 46 (2), 519– 526,  DOI: 10.1016/0009-2509(91)80012-N
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    Dewetting: nucleation and growth of dry regions
    Kheshgi, Haroon S.; Scriven, L. E.
    Chemical Engineering Science (1991), 46 (2), 519-26CODEN: CESCAC; ISSN:0009-2509.
    Dewetting of a solid surface covered by a film of nonwetting liq. proceeds from a preexisting dry patch or edge or initiates from some film-thinning disturbance that grows until the film ruptures. Local thinning can be caused by evapn.; by drainage due to gravity or capillarity-driven flow, esp. from sharp surfaces; or by surface tension gradients, such as are caused by surfactants delivered by particles falling on the film. Once a nonwetting film is sufficiently thinned, conjoining (neg. disjoining) pressure can accelerate thinning until rupture. This catastrophic rupture is modeled by solving the Navier-Stokes system approximated for thickness variations over distances that are long compared with the mean film thickness, and augmented with conjoining pressure. Rupture leads to film retraction and formation of a dry patch. These phenomena are visualized via moire topog. Of special interest are local spreading disturbances, where airborne particles fall on the film surface; craters or dry patches often nucleate. Implications for coating operations are discussed.
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    Xue, L.; Han, Y. Inhibition of Dewetting of Thin Polymer Films. Prog. Mater. Sci. 2012, 57 (6), 947– 979,  DOI: 10.1016/j.pmatsci.2012.01.003
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    Inhibition of dewetting of thin polymer films
    Xue, Longjian; Han, Yanchun
    Progress in Materials Science (2012), 57 (6), 947-979CODEN: PRMSAQ; ISSN:0079-6425. (Elsevier Ltd.)
    A review. Strategies for the inhibition of dewetting of thin polymer films are reviewed. First, a brief introduction to the theory and the dynamics of dewetting of thin polymer films is given. Methods for the inhibition of dewetting of thin polymer films, including the modification of the substrate and the polymer, the crosslinking of the polymer and the addn. of an additive as well as their mechanisms for inhibition are discussed. The chem. modification of the substrate or the polymer itself and the phase sepn. increase the thermodn. stability of the system, while the crosslinking of the polymers reduces the mobility of the polymer chains, kinetically arresting the dewetting. The addn. of an additive appears to thermodynamically and kinetically inhibit the dewetting. Finally, the future outlook in this research field is highlighted.
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    Barsbay, M.; Güven, O.; Stenzel, M. H.; Davis, T. P.; Barner-Kowollik, C.; Barner, L. Verification of Controlled Grafting of Styrene from Cellulose via Radiation-Induced RAFT Polymerization. Macromolecules 2007, 40 (20), 7140– 7147,  DOI: 10.1021/ma070825u
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    Verification of Controlled Grafting of Styrene from Cellulose via Radiation-Induced RAFT Polymerization
    Barsbay, Murat; Gueven, Olgun; Stenzel, Martina H.; Davis, Thomas P.; Barner-Kowollik, Christopher; Barner, Leonie
    Macromolecules (Washington, DC, United States) (2007), 40 (20), 7140-7147CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    Reversible addn.-fragmentation chain transfer (RAFT) polymn. was applied to radiation-induced graft polymn. of styrene from cellulose. The grafting of styrene from cellulose substrates using the chain transfer agent cumyl phenyldithioacetate was confirmed by Raman and XPS, differential scanning calorimetery, thermogravimetric anal., SEM, and contact angle anal. Grafted polystyrene chains were cleaved from the cellulose surface by acidic hydrolysis of the cellulose. The no.-av. mol. wt. and polydispersity index of the grafted and the free (nongrafted) polystyrenes obtained under identical conditions were detd. by size exclusion chromatog. Grafted and nongrafted polystyrenes have almost the same (near theor.) mol. wt. and narrow polydispersity, thus proving for the first time the control of the grafting process mediated via RAFT without any prior functionalization of the surface.
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    Eisenberg, A.; Yokoyama, T.; Sambalido, E. Dehydration Kinetics and Glass Transition of Poly(Acrylic Acid). J. Polym. Sci. Part A-1 Polym. Chem. 1969, 7 (7), 1717– 1728,  DOI: 10.1002/pol.1969.150070714
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    Dehydration kinetics and glass transition of poly(acrylic acid)
    Eisenberg, Adi; Yokoyama, Tetsuo; Sambalido, Emma
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    The kinetics of dehydration and decarboxylation as well as the glass transition temp. as a function of anhydride content were measured for poly(acrylic acid) (I). The glass transition of I is of the order of 103° and increases with increasing anhydride content, reaching an extrapolated value of 140° for the pure linear anhydride. Anhydride formation is a first-order reaction, as is also decarboxylation, the latter being much slower than the former. The rate consts. are: for dehydration, ka = 2.5 × 109 exp (-26,000/RT); for decarboxylation, kd = 2.9 × 108 exp (-27,000/RT). Anhydride formation occurs primarily by an intramol. process.
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    Chapin, E. C.; Ham, G. E.; Mills, C. L. Copolymerization. VII. Relative Rates of Addition of Various Monomers in Copolymerization. J. Polym. Sci. 1949, 4, 597– 604,  DOI: 10.1002/pol.1949.120040505
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    Copolymerization. VII. Relative rates of addition of various monomers in copolymerization
    Chapin, Earl C.; Ham, George E.; Mills, Charles L.
    Journal of Polymer Science (1949), 4 (), 597-604CODEN: JPSCAU; ISSN:0022-3832.
    cf. C.A. 43, 8736g; 42, 4151i. Data are presented on monomer reactivity in copolymerization for these 13 systems: styrene (I)-methacrylic acid (II), I-acrylic acid (III), vinylidene chloride (IV)-crotonic acid (V), vinyl acetate (VI)-V, acrylonitrile (VII)-vinyl 2-ethylhexoate (VIII), VII-vinyl formate (IX), VII-vinyl benzoate (X), VII-α-acetoxystyrene (XI), VII-allyl chloride (XII), IV-X, IV-methyl isopropenyl ketone (XIII), vinyl chloride (XIV)-vinyl isobutyl ether (XV), and I-citraconic anydride (XVI). The reactivity ratios, γ1 and γ2, for these copolymerizations were obtained by choosing values which gave the best curve fit on substitution in the differential copolymer equation. The azeotrope of the system I-II occurs at 74% II while that of I-III occurs at 48% III. By using the Price and Alfrey relationship for the consts. Q and e these values are interpreted as evidence of higher resonance stability of the radical adduct formed from II than from III and lower polarity of II than III. Azeotropes also occur in the systems VI-V, VII-XI, and I-XVI. The copolymerization of I and XVI yielded a copolymerization curve similar to that of I-maleic anhydride reported by Alfrey and Lavin (C.A. 40, 1149.2); evidently XVI is less reactive toward a I-free radical than maleic anhydride.
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    Mayadunne, R. T. A.; Rizzardo, E.; Chiefari, J.; Krstina, J.; Moad, G.; Postma, A.; Thang, S. H. Radical Polymerization in Two Steps. Macromolecules 2000, 33, 243– 245,  DOI: 10.1021/ma991451a
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    Living polymers by the use of trithiocarbonates as reversible addition-fragmentation chain transfer (RAFT) agents. ABA triblock copolymers by radical polymerization in two steps
    Mayadunne, Roshan T. A.; Rizzardo, Ezio; Chiefari, John; Krstina, Julia; Moad, Graeme; Postma, Almar; Thang, San H.
    Macromolecules (2000), 33 (2), 243-245CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    Trithiocarbonates RS-CS-SR', where R and R' are homolytic leaving groups, were used as effective reversible addn.-fragmentation chain transfer agents. Styrene, Me acrylate, Bu acrylate and Me methacrylate were polymd. in the presence of various trithiocarbonate compds. (R/R': Me/C(Me)2CN, Me/CH(Ph)COOH, benzyl/benzyl, and α-methylbenzyl/α-methylbenzyl) and mol. wt. and conversion data were detd. Homopolymers and block copolymers of controlled mol. wt. and narrow polydispersity were prepd. Important ABA triblock copolymers of predetd. mol. wt. are accessible in 2 steps.
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    Buzin, A. I.; Pyda, M.; Costanzo, P.; Matyjaszewski, K.; Wunderlich, B. Calorimetric Study of Block-Copolymers of Poly(n-Butyl Acrylate) and Gradient Poly(n-Butyl Acrylate-Co-Methyl Methacrylate). Polymer (Guildf). 2002, 43 (20), 5563– 5569,  DOI: 10.1016/S0032-3861(02)00358-0
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    Sanchez-Fernandez, A.; Edler, K. J.; Arnold, T.; Heenan, R. K.; Porcar, L.; Terrill, N. J.; Terry, A. E.; Jackson, A. J. Micelle Structure in a Deep Eutectic Solvent: A Small-Angle Scattering Study. Phys. Chem. Chem. Phys. 2016, 18 (20), 14063– 14073,  DOI: 10.1039/C6CP01757F
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    Micelle structure in a deep eutectic solvent: a small-angle scattering study
    Sanchez-Fernandez, A.; Edler, K. J.; Arnold, T.; Heenan, R. K.; Porcar, L.; Terrill, N. J.; Terry, A. E.; Jackson, A. J.
    Physical Chemistry Chemical Physics (2016), 18 (20), 14063-14073CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
    In recent years many studies into green solvents have been undertaken and deep eutectic solvents (DES) have emerged as sustainable and green alternatives to conventional solvents since they may be formed from cheap non-toxic org. precursors. In this study we examine amphiphile behavior in these novel media to test our understanding of amphiphile self-assembly within environments that have an intermediate polarity between polar and non-polar extremes. We have built on our recently published results to present a more detailed structural characterization of micelles of sodium dodecylsulfate (SDS) within the eutectic mixt. of choline chloride and urea. Here we show that SDS adopts an unusual cylindrical aggregate morphol., unlike that seen in water and other polar solvents. A new morphol. transition to shorter aggregates was found with increasing concn. The self-assembly of SDS was also investigated in the presence of water; which promotes the formation of shorter aggregates.
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    Gaillard, N.; Guyot, A.; Claverie, J. Block Copolymers of Acrylic Acid and Butyl Acrylate Prepared by Reversible Addition-Fragmentation Chain Transfer Polymerization: Synthesis, Characterization, and Use in Emulsion Polymerization. J. Polym. Sci. Part A Polym. Chem. 2003, 41 (5), 684– 698,  DOI: 10.1002/pola.10606
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    Block copolymers of acrylic acid and butyl acrylate prepared by reversible addition-fragmentation chain transfer polymerization: synthesis, characterization, and use in emulsion polymerization
    Gaillard, Nicolas; Guyot, Alain; Claverie, Jerome
    Journal of Polymer Science, Part A: Polymer Chemistry (2003), 41 (5), 684-698CODEN: JPACEC; ISSN:0887-624X. (John Wiley & Sons, Inc.)
    Amphiphilic block copolymers of poly(acrylic acid-b-Bu acrylate) (I) were prepd. by reversible addn.-fragmentation chain transfer polymn. in a one-pot reaction. I were characterized by NMR, static and dynamic light scattering, tensiometry, and size exclusion chromatog. The aggregation characteristics of I corresponded to those theor. predicted for a star micelle. In a Bu acrylate-Me methacrylate emulsion copolymn., low amts. of I could stabilize the latexes with solid contents up to 50%.
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    Chernikova, E. V.; Lysenko, E. A.; Serkhacheva, N. S.; Prokopov, N. I. Self-Assembly of Amphiphilic Block Copolymers during Reversible Addition-Fragmentation Chain Transfer Heterophase Polymerization: Problems, Achievements, and Outlook. Polym. Sci. - Ser. C 2018, 60 (2), 192– 218,  DOI: 10.1134/S1811238218020042
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    Self-Assembly of Amphiphilic Block Copolymers during Reversible Addition-Fragmentation Chain Transfer Heterophase Polymerization: Problems, Achievements, and Outlook
    Chernikova, E. V.; Lysenko, E. A.; Serkhacheva, N. S.; Prokopov, N. I.
    Polymer Science, Series C: Selected Topics (2018), 60 (S1), 192-218CODEN: PSSCCH; ISSN:1555-614X. (Pleiades Publishing, Ltd.)
    The formation of dispersions of amphiphilic block copolymer particles with the controlled morphol. via heterophase polymn. mediated by reversible addn.-fragmentation agents is considered. Variants of dispersion, emulsion, and seeded polymns. are analyzed, and the mechanism of this process is discussed. Special attention is focused on issues related to control over the morphol. of the formed particles immediately during synthesis and methods of its transformation in the resulting dispersions.
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    Chenal, M.; Rieger, J.; Vechambre, C.; Chenal, J.-M.; Chazeau, L.; Creton, C.; Bouteiller, L. Soft Nanostructured Films with an Ultra-Low Volume Fraction of Percolating Hard Phase. Macromol. Rapid Commun. 2013, 34, 1524– 1529,  DOI: 10.1002/marc.201300410
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    Soft Nanostructured Films with an Ultra-Low Volume Fraction of Percolating Hard Phase
    Chenal, Marion; Rieger, Jutta; Vechambre, Cyril; Chenal, Jean-Marc; Chazeau, Laurent; Creton, Costantino; Bouteiller, Laurent
    Macromolecular Rapid Communications (2013), 34 (19), 1524-1529CODEN: MRCOE3; ISSN:1022-1336. (Wiley-VCH Verlag GmbH & Co. KGaA)
    In this study, aq. emulsion polymn. of Bu acrylate is performed in batch conditions without surfactants using a poly(acrylic acid)-trithiocarbonate macro-RAFT agent to control the polymn. and to stabilize the emulsion. According to the polymn.-induced self-assembly (PISA) approach, well-defined amphiphilic PAA-b-PBA diblock copolymers form and self-assemble during synthesis to yield highly stable core-shell particles with an extremely thin hard PAA shell. For the first time, we report here the specific properties of films obtained from these particular latexes. After drying the aq. dispersion, tough and transparent films are obtained. Although the films are not chem. crosslinked, they do not dissolve in good solvents for PBA. Moreover, they remain transparent even after immersion in water. Rheol. shows that the films are both stiff and ductile, thanks to the nanostructured but very low vol. fraction (less than 3 wt%) of PAA forming a percolating network in the soft PBA. Compared with conventional core-shell-based films, this approach affords for the first time a route to a thin percolating honeycomb nanostructure with a sharp and strong interface between the two phases. The versatility of the synthetic procedure opens perspectives for a large range of functional materials.
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    Pedersen, J. S.; Gerstenberg, M. C. Scattering Form Factor of Block Copolymer Micelles. Macromolecules 1996, 29 (4), 1363– 1365,  DOI: 10.1021/ma9512115
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    Scattering Form Factor of Block Copolymer Micelles
    Pedersen, Jan Skov; Gerstenberg, Michael C.
    Macromolecules (1996), 29 (4), 1363-5CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    The form factor of a micelle model with a spherical core and Gaussian polymer chains attached to the surface was calcd. anal. and the results were compared to Monte Carlo simulations. Excluded vol. interactions between the core and the polymers were introduced in the simulations. The expansion of the coils due to this effect can be mimicked in the anal. calcns. by moving the center of mass of the chains away from the surface of the core. The anal. expression for the form factor has been used for analyzing small-angle scattering data.
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    Balmer, J. A.; Mykhaylyk, O. O.; Schmid, A.; Armes, S. P.; Fairclough, J. P. A.; Ryan, A. J. Characterization of Polymer-Silica Nanocomposite Particles with Core-Shell Morphologies Using Monte Carlo Simulations and Small Angle X-Ray Scattering. Langmuir 2011, 27 (13), 8075– 8089,  DOI: 10.1021/la201319h
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    Characterization of Polymer-Silica Nanocomposite Particles with Core-Shell Morphologies using Monte Carlo Simulations and Small Angle X-ray Scattering
    Balmer, Jennifer A.; Mykhaylyk, Oleksandr O.; Schmid, Andreas; Armes, Steven P.; Fairclough, J. Patrick A.; Ryan, Anthony J.
    Langmuir (2011), 27 (13), 8075-8089CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
    A two-population model based on std. small-angle x-ray scattering (SAXS) equations is verified for the anal. of core-shell structures comprising spherical colloidal particles with particulate shells. First, Monte Carlo simulations of core-shell structures are performed to demonstrate the applicability of the model. Three possible shell packings are considered: ordered silica shells due to either charge-dependent repulsive or size-dependent Lennard-Jones interactions or randomly arranged silica particles. In most cases, the two-population model produces an excellent fit to calcd. SAXS patterns for the simulated core-shell structures, together with a good correlation between the fitting parameters and structural parameters used for the simulation. The limits of application are discussed, and then, this two-population model is applied to the anal. of well-defined core-shell vinyl polymer/silica nanocomposite particles, where the shell comprises a monolayer of spherical silica nanoparticles. Comprehensive SAXS anal. of poly(styrene-co-Bu acrylate)/silica colloidal nanocomposite particles (prepd. by the in situ emulsion copolymn. of styrene and Bu acrylate in the presence of a glycerol-functionalized silica sol) allows the overall core-shell particle diam., the copolymer latex core diam. and polydispersity, the mean silica shell thickness, the mean silica diam. and polydispersity, the vol. fractions of the two components, the silica packing d., and the silica shell structure to be obtained. These exptl. SAXS results are consistent with electron microscopy, dynamic light scattering, TG, helium pycnometry, and BET surface area studies. The high electron d. contrast between the (co)polymer and the silica components, together with the relatively low polydispersity of these core-shell nanocomposite particles, makes SAXS ideally suited for the characterization of this system. Also, these results can be generalized for other types of core-shell colloidal particles.
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    A major drawback of conventional emulsion polymers arises from the presence of migrating low molar mass surfactants that contribute to poor water barrier properties and low adhesion to substrates. In this paper, we demonstrate how living polymer chains obtained by reversible addn.-fragmentation chain transfer (RAFT) can be used as an efficient stabilizer in emulsion polymn., leading to the prodn. of surfactant-free latexes, which then form crosslinked films with beneficial properties. Hydrophilic poly(methacrylic acid) (PMAA) chains obtained by RAFT performed in water are used to mediate emulsion polymn. and produce film-forming latex particles from mixts. of Me methacrylate, Bu acrylate, and styrene. Stable dispersions of particles with sizes between 100 and 200 nm are obtained, with very low amts. of coagulum (<0.5 wt. %). The particles are stabilized by the PMAA segment of amphiphilic block copolymers formed during the polymn. Remarkably, low amts. of PMAA chains (from 1.5 down to 0.75 wt. %) are enough to ensure particle stabilization. Only traces of residual PMAA macroRAFT agents are detected in the final latexes, showing that most of them are successfully chain extended and anchored on the particle surface. The glass transition temp. of the final material is adjusted by the compn. of the hydrophobic monomer mixt. so that film formation occurs at room temp. Conventional crosslinking strategies using addnl. hydrophobic comonomers, such as 1,3-butanediol diacrylate (BuDA), diacetone acrylamide (DAAm), and (2-acetoacetoxy)ethyl methacrylate (AAEM), are successfully applied to these formulations as attested by gel fractions of 100%. When particles are internally crosslinked with BuDA, chain interdiffusion between particles is restricted, and a weak and brittle film is formed. In contrast, when DAAm-contg. chains undergoes crosslinking during film formation, full coalescence is achieved along with the creation of a crosslinked network. The resulting film has a higher Young's modulus and tensile strength as a result of crosslinking. This synthetic strategy advantageously yields a surfactant-free latex that can be formed into a film at room temp. with mech. properties that can be tuned via the crosslinking d.
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  • Abstract

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    Figure 1

    Figure 1. RAFT polymerization protocol used to produce the sets of different P(AA-st-St)x-b-PBAy/2-DBzTTC-PBAy/2-b-P(AA-st-St)x (AxByAx) triblock copolymers, namely (a) the P(AA-st-St)x-DBzTTC-P(AA-st-St)x (Ax-DBzTTC-Ax) macro-CTA synthesis used to prepare A56-DBzTTC-A56 (A56A56), A108A108, and A140A140 (Table 1) and (b) the high-throughput synthesis of the triblock copolymers A56B100-750A56, A112B100-750A112, and A140B100-750A140 (Table 2) using a Chemspeed high-throughput robot.

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    Figure 2

    Figure 2. SAXS patterns of (a) 1% w/w macro-CTA solutions in MEK (symbols) fitted using the Debye function (eq S8) (black line) and (b) 1% w/w triblock copolymer solutions in MEK (symbols). Some patterns have been shifted upward (the multiplication factors are indicated on the plots) to avoid overlap. Scattering patterns were collected using a Bruker AXS Nanostar instrument.

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    Figure 3

    Figure 3. SAXS patterns of macro-CTA (A56A56, A108A108, and A140A140) aqueous dispersions (symbols) at a 1% w/w concentration. Patterns were fitted with the sphere model (eqs S9–S12) (solid line). Some patterns have been shifted upward (the multiplication factors are indicated on the plot) to avoid overlap. Scattering patterns were collected using a Bruker AXS Nanostar instrument.

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    Figure 4

    Figure 4. SAXS patterns of (a) 1% w/w A108B100–750A108 triblock copolymer aqueous dispersions (symbols) fitted with the two-population model (eqs S13–S15) (solid line); (b) A108B100–750A108 triblock copolymer aqueous dispersions at 20% w/w concentration; and (c) A108B100A108 triblock copolymer aqueous dispersion at 1, 5, and 20% w/w concentrations. The arrow is used to highlight the presence of the structural peak referred to in the text. Some patterns have been shifted upward (the multiplication factors are indicated on the plots) to avoid overlap. Scattering patterns were collected using a Bruker AXS Nanostar instrument.

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    Figure 5

    Figure 5. A diagram describing the predicted structure of a particle formed by P(AA-st-St)-b-PBA-b-P(AA-st-St) triblock copolymers in water, where the P(AA-st-St) stabilizer block was confined by the copolymer particle surface and “self-folded” through hydrophobic interactions.

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    Figure 6

    Figure 6. Predicted phase diagram of the bulk triblock copolymer morphologies based on SCFT theory, AFM images, and SAXS, where fA is the volume fraction of the A block, χ is the Flory–Huggins segment interaction parameter, and rv is the overall length of the copolymer molecule in segments, taking into account the difference in the volume occupied by the A and B block. rv was calculated using the equation rv = x + y(vB/vA) where vA and vB are the averaged volumes occupied by the A and B monomer units, respectively. (69) The A56ByA56, A108ByA108, and A140ByA140 series are represented by hexagon, diamond, and triangle symbols, respectively. BCC, Hex and G indicate zones of existance of body-centered cubic, hexagonally-packed cylinder and gyroid copolymer phases, respectively.

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    Figure 7

    Figure 7. Schematics of the formation of the kinetically trapped structure within the water-cast films that occurs during the drying process. (a) The formation of the packed soft sphere structure within a matrix of the hard phase, where the BA-reach domains reduce during the drying process. (b) The formation of a structure of distorted packed spheres that is formed by copolymers with a large soft block.

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    Figure 8

    Figure 8. Time-resolved GISAXS patterns collected for the A108B500A108 water-cast film during the annealing process at 150 °C. The temperature protocol is shown at the right side of the plot. Scattering patterns were collected using a Xenocs Xeuss laboratory beamline.

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    Figure 9

    Figure 9. AFM height (tomographic) images of triblock copolymer films recorded using the ScanAsyst PeakForce tapping mode. (a and b) Images of A108B500A108 cast from a 20% w/w aqueous solution; images were recorded for 1 μm × 1 and 5 μm × 5 μm areas, respectively. (c and d) Images of A108B500A108 cast from a 20% w/w aqueous solution and annealed for 30 min at 150 °C; images were recorded for 1 μm × 1 and 5 μm × 5 μm areas, respectively. (e and f) Images of A108B500A108 cast from a 40% w/w solution in MEK; images were recorded for 1 μm × 1 and 5 μm × 5 μm areas, respectively.

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    Figure 10

    Figure 10. Tensile extension traces of triblock copolymer films. (a) Trace demonstrating the effect of increasing the length of the soft block when cast from MEK. (b) Trace demonstrating the effect of changing the solvent environment from which the A56B200A56 copolymer film is cast.

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  • References

    This article references 79 other publications.

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      Bradford, E. B.; McKeever, L. D. Block Copolymers. Prog. Polym. Sci. 1971, 3, 109– 143,  DOI: 10.1016/0079-6700(71)90003-7
      1
      Block copolymers
      Bradford, E. B.; McKeever, L. D.
      Progress in Polymer Science (1971), 3 (), 109-43CODEN: PRPSB8; ISSN:0079-6700.
      A review with 234 refs. discusses the synthesis, characterization, properties, and uses of block copolymers.
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      Bates, F. S.; Fredrickson, G. H. Block Copolymers-Designer Soft Materials. Phys. Today 1999, 52 (2), 32– 38,  DOI: 10.1063/1.882522
      2
      Block copolymers-designer soft materials
      Bates, Frank S.; Fredrickson, Glenn H.
      Physics Today (1999), 52 (2), 32-38CODEN: PHTOAD; ISSN:0031-9228. (American Institute of Physics)
      A review with 18 refs. discusses the structure, morphol., phase behavior, and self-assembly properties of block copolymers.
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      Amphiphilic Block Copolymers: Self-Assembly and Applications; Alexandridis, P.; Lindman, B., Eds.; Elsevier: Amsterdam, The Netherlands, 2000.
      There is no corresponding record for this reference.
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      Zhang, L.; Yu, K.; Eisenberg, A. Ion-Induced Morphological Changes in “Crew-Cut” Aggregates of Amphiphilic Block Copolymers. Science 1996, 272, 1777– 1779,  DOI: 10.1126/science.272.5269.1777
      4
      Ion-induced morphological changes in "crew-cut" aggregates of amphiphilic block copolymers
      Zhang, Lifeng; Yu, Kui; Eisenberg, Adi
      Science (Washington, D. C.) (1996), 272 (5269), 1777-1779CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
      The addn. of ions in micromolar (CaCl2 or HCl) or millimolar (NaCl) concns. can change the morphol. of "crew-cut" aggregates of amphiphilic block copolymers in dil. solns. In addn. to spherical, rodlike, and univesicular or lamellar aggregates, an unusual large compd. vesicle morphol. can be obtained from a single block copolymer. Some features of the spontaneously formed large compd. vesicles may make them esp. useful as vehicles for delivering drugs and as models of biol. cells. Gelation of a dil. spherical micelle soln. can also be induced by ions as the result of the formation of a cross-linked "pearl necklace" morphol.
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    5. 5
      Zhang, L.; Eisenberg, A. Multiple Morphologies of “Crew-Cut” Aggregates of Polystyrene-b-Poly(Acrylic Acid) Block Copolymers. Science 1995, 268, 1728– 1731,  DOI: 10.1126/science.268.5218.1728
      5
      Multiple morphologies of "crew-cut" aggregates of polystyrene-b-poly(acrylic acid) block copolymers
      Zhang, Lifeng; Eisenberg, Adi
      Science (Washington, D. C.) (1995), 268 (5218), 1728-31CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
      The observation by transmission electron microscopy of six different stable aggregate morphologies is reported for the same family of highly asym. styrene-acrylic acid diblock copolymers prepd. in a low-mol.-wt. solvent system. Four of the morphologies consist of spheres, rods, lamellae, and vesicles in aq. soln., whereas the fifth consists of simple reverse micelle-like aggregates. The sixth consists of up to micrometer-size spheres in aq. soln. that have hydrophilic surfaces and are filled with the reverse micelle-like aggregates. In addn., a needle-like solid, which is highly birefringent, is obtained on drying of aq. solns. of the spherical micelles. This range of morphologies is believed to be unprecedented for a block copolymer system.
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    6. 6
      van Hest, J. C. M.; Delnoye, D. A. P.; Baars, M. W. P. L.; van Genderen, M. H. P.; Meijer, E. W. Polystyrene-Dendrimer Amphiphilic Block Copolymers with a Generation-Dependent Aggregation. Science 1995, 268 (268), 1592– 1595,  DOI: 10.1126/science.268.5217.1592
      6
      Polystyrene-dendrimer amphiphilic block copolymers with a generation-dependent aggregation
      van Hest, J. C. M.; Delnoye, D. A. P.; Baars, M. W. P. L.; van Genderen, M. H. P.; Meijer, E. W.
      Science (Washington, D. C.) (1995), 268 (5217), 1592-5CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
      A class of amphiphilic macromols. has been synthesized by combining well-defined polystyrene (PS) with poly(propylene imine) dendrimers. Five different generations, from PS-dendr-NH2 up to Ps-dendr-(NH2)32, were prepd. in yields of 70 to 90 percent. Dynamic light scattering, cond. measurements, and transmission electron microscopy show that in aq. phases, PS-dendr-(NH2)32 forms spherical micelles, PS-dendr-(NH2)16 forms micellar rods, and PS-dendr-(NH2)8 forms vesicular structures. The lower generations of this class of macromols. show inverted micellar behavior. The obsd. effect of amphiphile geometry on aggregation behavior is in qual. agreement with the theory of J. N. Israelachvili, et al. (1976). The amphiphiles presented here are similar in shape but different in size as compared with traditional surfactants, whereas they are similar in size but different in shape as compared with traditional block copolymers.
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    7. 7
      Bates, F. S. Polymer-Polymer Phase Behaviour. Science 1991, 251 (251), 898– 905,  DOI: 10.1126/science.251.4996.898
      7
      Polymer-polymer phase behavior
      Bates, Frank S.
      Science (Washington, DC, United States) (1991), 251 (4996), 898-905CODEN: SCIEAS; ISSN:0036-8075.
      A review with 57 refs. on basic factors governing polymer-polymer phase behavior with emphasis on linear homopolymer blends and diblock copolymers as representative model mol. architectures. Equil. thermodn. and phase sepn. dynamics are reviewed and discussed.
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    8. 8
      Mai, Y.; Eisenberg, A. Self-Assembly of Block Copolymers. Chem. Soc. Rev. 2012, 41 (18), 5969– 5985,  DOI: 10.1039/c2cs35115c
      8
      Self-assembly of block copolymers
      Mai, Yiyong; Eisenberg, Adi
      Chemical Society Reviews (2012), 41 (18), 5969-5985CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
      A review. Block copolymer (BCP) self-assembly has attracted considerable attention for many decades. The present tutorial review introduces the primary principles of BCP self-assembly in bulk and in soln., by describing expts., theories, accessible morphologies, etc.
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    9. 9
      Xu, R.; Winnik, M. A.; Hallett, F. R.; Riess, G.; Croucher, M. D. Light-Scattering Study of the Association Behavior of Styrene-Ethylene Oxide Block Copolymers in Aqueous Solution. Macromolecules 1991, 24 (1), 87– 93,  DOI: 10.1021/ma00001a014
      9
      Light-scattering study of the association behavior of styrene-ethylene oxide block copolymers in aqueous solution
      Xu, Renliang; Winnik, Mitchell A.; Hallett, F. R.; Riess, Gerard; Croucher, Melvin D.
      Macromolecules (1991), 24 (1), 87-93CODEN: MAMOBX; ISSN:0024-9297.
      The micellization behavior of styrene (I)-ethylene oxide (II) diblock and triblock copolymers in aq. solns. is studied via static and dynamic light scattering. There are 2 narrowly distributed populations of particles in the soln. The sizes of both sets of particles are unchanged in concn. range of 2 × 10 -5 - 2 × 10-3 g/mL. The wt. fraction of the larger particles decreases with increasing polymer concn. The small particles are regular micelles with an assocn. no. of several hundred; the large particles are loose micellar clusters of tens of micelles. The micelle structure is core-shell with a core of I and a shell of II.
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    10. 10
      Wilhelm, M.; Zhao, C. Le; Wang, Y.; Xu, R.; Winnik, M. A.; Mura, J. L.; Riess, G.; Croucher, M. D. Poly(Styrene-Ethylene Oxide) Block Copolymer Micelle Formation in Water: A Fluorescence Probe Study. Macromolecules 1991, 24 (5), 1033– 1040,  DOI: 10.1021/ma00005a010
      10
      Poly(styrene-ethylene oxide) block copolymer micelle formation in water: a fluorescence probe study
      Wilhelm, Manfred; Zhao, Cheng Le; Wang, Yongcai; Xu, Renliang; Winnik, Mitchell A.; Mura, Jean Luc; Riess, Gerard; Croucher, Melvin D.
      Macromolecules (1991), 24 (5), 1033-40CODEN: MAMOBX; ISSN:0024-9297.
      Block copolymer micelle formation was studied by a combination of fluorescent and quasielastic light scattering (QELS) techniques. Ethylene oxide-styrene diblock and triblock copolymers, with mol. wts. 8500-29,000, formed spherical micelles in H2O over the entire concn. range over which QELS signals could be detected. Pyrene (I) in H2O (6 × 10-7 M) partitions between the aq. and micellar phases, accompanied by 3 changes in I spectroscopy. A red shift in the excitation spectrum, a change in the vibrational fine structure of I fluorescence, and an increase in the fluorescence decay time (from 200 to ∼350 ns) accompanied the transfer of I from an aq. to a hydrophobic micellar environment. From these data, crit. micelle concns. (1-5 mg/L) and partition coeffs. (3 × 105) were calcd.
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    11. 11
      Prochazka, K.; Kiserow, D.; Ramireddy, C.; Tuzar, Z.; Munk, P.; Webber, S. E. Time-Resolved Fluorescence Studies of the Chain Dynamics of Naphthalene-Labeled Polystyrene-Block-Poly(Methacrylic Acid) Micelles in Aqueous Media. Macromolecules 1992, 25 (1), 454– 460,  DOI: 10.1021/ma00027a071
      11
      Time-resolved fluorescence studies of the chain dynamics of naphthalene-labeled polystyrene-block-poly(methacrylic acid) micelles in aqueous media
      Prochazka, K.; Kiserow, D.; Ramireddy, C.; Tuzar, Z.; Munk, P.; Webber, S. E.
      Macromolecules (1992), 25 (1), 454-60CODEN: MAMOBX; ISSN:0024-9297.
      A-B block copolymers of polystyrene and poly(methacrylic acid) and polystyrene and poly(tert-Bu methacrylate), both with short-chain oligovinyl-2-naphthalene moieties attached to the end of the polystyrene block, were prepd. by anionic polymn. and micelles were formed by hydrolysis. Intramol. excimer formation (which is controlled by the mobility of the pendant fluorescent groups and the polymer chain dynamics) was sterically hindered in the micellar cores as they become more compact. Both steady-state and time-resolved excimer fluorescence were significantly influenced by the gradual collapse of the micellar cores and the increase in segment d. within the cores with an increasing content of water. Changes in lifetimes and preexponential factors for naphthalene fluorescence (monomer as well as excimer) were sensitive indicators of micelle formation.
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    12. 12
      Astafieva, I.; Zhong, X. F.; Eisenberg, A. Critical Micellization Phenomena in Block Polyelectrolyte Solutions. Macromolecules 1993, 26 (26), 7339– 7352,  DOI: 10.1021/ma00078a034
      12
      Critical micellization phenomena in block polyelectrolyte solutions
      Astafieva, Irina; Zhong, Xing Fu; Eisenberg, Adi
      Macromolecules (1993), 26 (26), 7339-52CODEN: MAMOBX; ISSN:0024-9297.
      Crit. micelle concn. (CMC) was measured for a range of block copolyelectrolytes based on styrene (the insol. block) and Na acrylate. The length of the styrene blocks was 6-110, while that of the polyelectrolyte was ∼300-1400. The fluorescent probe technique was used with pyrene as a probe mol., and the data were treated by 5 different methods. CMC results were interpolated for a const. polyelectrolyte block length of 1000 units. Changing the insol. block length from 6 to 110 lowed the CMC from 1.6 × 10-5 to 5 × 10-8 M. By contrast, changing the sol. block length from 300 to 1400 typically changed the CMC values by a factor of <2. For very short polystyrene block lengths, the CMC decreased very rapidly with increasing length of the insol. block. By contrast, for higher block lengths (>12) the drop in the CMC was much more gradual. The results are compared with those of previous studies of block copolymer micelles and theories of block copolymer micellization.
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    13. 13
      Qin, A.; Tian, M.; Ramireddy, C.; Webber, S. E.; Munk, P.; Tuzar, Z. Polystyrene-Poly(Methacrylic Acid) Block Copolymer Micelles. Macromolecules 1994, 27 (1), 120– 126,  DOI: 10.1021/ma00079a018
      13
      Polystyrene-poly(methacrylic acid) block copolymer micelles
      Qin, Anwei; Tian, Minmin; Ramireddy, C.; Webber, Stephen E.; Munk, Petr; Tuzar, Zdenek
      Macromolecules (1994), 27 (1), 120-6CODEN: MAMOBX; ISSN:0024-9297.
      Block copolymer micelles formed by diblock and triblock copolymers of styrene (I) and methacrylic acid (II) were characterized in soln. in a mixed solvent with 80 vol % of dioxane and 20 vol % of water. Methods of static light scattering, quasielastic light scattering, differential refractometry, viscometry, sedimentation velocity, and densitometry were used. No unattached unimer mols. were obsd. Three independent methods were employed for obtaining micellar wts. and agreed well with each other. No anomalous behavior was obsd. by any method. The micellar solns. contained almost exclusively single micelles; only a few samples (those producing the largest micelles) contained micellar clusters. The micelles behaved hydrodynamically and thermodynamically as impermeable spheres. The structure of the micellar shell was characterized in some detail. Relations between the aggregation no. and the hydrodynamic radius of the micelles on the one hand and the sizes of the I and II blocks on the other were presented as scaling-type phenomenol. equations.
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    14. 14
      Guo, M.; Pitet, L. M.; Wyss, H. M.; Vos, M.; Dankers, P. Y. W.; Meijer, E. W. Tough Stimuli-Responsive Supramolecular Hydrogels with Hydrogen-Bonding Network Junctions. J. Am. Chem. Soc. 2014, 136 (19), 6969– 6977,  DOI: 10.1021/ja500205v
      14
      Tough Stimuli-Responsive Supramolecular Hydrogels with Hydrogen-Bonding Network Junctions
      Guo, Mingyu; Pitet, Louis M.; Wyss, Hans M.; Vos, Matthijn; Dankers, Patricia Y. W.; Meijer, E. W.
      Journal of the American Chemical Society (2014), 136 (19), 6969-6977CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Hydrogels were prepd. with phys. crosslinks comprising 2-ureido-4[1H]-pyrimidinone (UPy) hydrogen-bonding units within the backbone of segmented amphiphilic macromols. contg. hydrophilic poly(ethylene glycol) (PEG). The bulk materials adopt nanoscopic phys. crosslinks composed of UPy-UPy dimers embedded in segregated hydrophobic domains dispersed within the PEG matrix as confirmed by cryo-electron microscopy. The amphiphilic network was swollen with high wt. fractions of water (wH2O ≈ 0.8) owing to the high PEG wt. fraction within the pristine polymers (wPEG ≈ 0.9). Two different PEG chain lengths were investigated and illustrate the corresponding consequences of crosslink d. on mech. properties. The resulting hydrogels exhibited high strength and resilience upon deformation, consistent with a microphase sepd. network, in which the UPy-UPy interactions were adequately shielded within hydrophobic nanoscale pockets that maintain the network despite extensive water content. The cumulative result is a series of tough hydrogels with tunable mech. properties and tractable synthetic prepn. and processing. Furthermore, the melting transition of PEG in the dry polymer was shown to be an effective stimulus for shape memory behavior.
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    15. 15
      Huo, M.; Yuan, J.; Tao, L.; Wei, Y. Redox-Responsive Polymers for Drug Delivery: From Molecular Design to Applications. Polym. Chem. 2014, 5 (5), 1519– 1528,  DOI: 10.1039/C3PY01192E
      15
      Redox-responsive polymers for drug delivery: from molecular design to applications
      Huo, Meng; Yuan, Jinying; Tao, Lei; Wei, Yen
      Polymer Chemistry (2014), 5 (5), 1519-1528CODEN: PCOHC2; ISSN:1759-9962. (Royal Society of Chemistry)
      A review. Glutathione has been regarded as a significant signal for distinguishing between tumor and normal tissue. Recently, reactive oxygen species have attracted much attention for their close connection with many diseases. Taking advantage of the physiol. signals, redox-responsive polymeric drug carriers constitute a significant research area in the various stimuli-responsive polymers for biomedical applications. During the rapid development of redox-responsive polymers, mol. design and related synthetic methodol. plays a crucial role. In this review, we discuss the redn.- and oxidn.-responsive polymeric drug carriers from the view of functional groups, as well as their applications in controlled release.
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    16. 16
      Schattling, P.; Jochum, F. D.; Theato, P. Multi-Stimuli Responsive Polymers - the All-in-One Talents. Polym. Chem. 2014, 5 (1), 25– 36,  DOI: 10.1039/C3PY00880K
      16
      Multi-stimuli responsive polymers - the all-in-one talents
      Schattling, Philipp; Jochum, Florian D.; Theato, Patrick
      Polymer Chemistry (2014), 5 (1), 25-36CODEN: PCOHC2; ISSN:1759-9962. (Royal Society of Chemistry)
      Stimuli-responsive polymers have gained increasing attention, which is attributed to the manifold applications they can be used for. Several years' intensive research was invested in stimuli-responsive polymers. Their stimuli-responsiveness led not only to novel responsive groups, which enabled the translation of an external phys. impact into a change of a material property, but also to polymers that are equipped with more than one responsive group. The integration of several responsive moieties within one polymer yields smart polymers exhibiting complex responsive behavior of the polymers. This review summarises recent developments in the area of multi-stimuli responsive polymers, laying the focus on the improved, multifaceted response of polymer materials depending on the impact of several external stimuli.
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    17. 17
      Sun, Y.; Wang, Z.; Li, Y.; Zhang, Z.; Zhang, W.; Pan, X.; Zhou, N.; Zhu, X. Photoresponsive Amphiphilic Macrocycles Containing Main-Chain Azobenzene Polymers. Macromol. Rapid Commun. 2015, 36, 1341– 1347,  DOI: 10.1002/marc.201500136
      17
      Photoresponsive Amphiphilic Macrocycles Containing Main-Chain Azobenzene Polymers
      Sun, Yadong; Wang, Zhao; Li, Yiwen; Zhang, Zhengbiao; Zhang, Wei; Pan, Xiangqiang; Zhou, Nianchen; Zhu, Xiulin
      Macromolecular Rapid Communications (2015), 36 (14), 1341-1347CODEN: MRCOE3; ISSN:1022-1336. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Herein, the first example of photosensitive cyclic amphiphilic homopolymers consisting of multiple biphenyl azobenzene chromophores in the cyclic main chain tethered with hydrophilic tetraethylene glycol monomethyl ether units is presented. The synthetic approach involves sequentially performed thermal catalyzed "click" step-growth polymn. in bulk, and Cu(I)-catalyzed azide-alkyne cycloaddn. (CuAAC) intramol. cyclization from α-alkyne/ω-azide linear precursors. It is obsd. that such amphiphilic macrocycles exhibit increased glass transition temps. (Tg), slightly faster trans-cis-trans photoisomerization, and enhanced fluorescence emission intensity compared with the corresponding linear polymers. In addn., the cyclic amphiphilic homopolymers self-assemble into spherical nanoparticles with smaller sizes which possess slower photoresponsive behaviors in a tetrahydrofuran/water mixt. compared with those of the linear ones. All these interesting observations suggest that the cyclic topol. has a great influence on the phys. properties and self-assembly behavior of these photoresponsive amphiphilic macrocycles in general.
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    18. 18
      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
      18
      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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    19. 19
      Lovett, J. R.; Ratcliffe, L. P. D.; Warren, N. J.; Armes, S. P.; Smallridge, M. J.; Cracknell, R. B.; Saunders, B. R. A Robust Cross-Linking Strategy for Block Copolymer Worms Prepared via Polymerization-Induced Self-Assembly. Macromolecules 2016, 49 (8), 2928– 2941,  DOI: 10.1021/acs.macromol.6b00422
      19
      A Robust Cross-Linking Strategy for Block Copolymer Worms Prepared via Polymerization-Induced Self-Assembly
      Lovett, J. R.; Ratcliffe, L. P. D.; Warren, N. J.; Armes, S. P.; Smallridge, M. J.; Cracknell, R. B.; Saunders, B. R.
      Macromolecules (Washington, DC, United States) (2016), 49 (8), 2928-2941CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      A poly(glycerol monomethacrylate) (PGMA) chain transfer agent is chain-extended by reversible addn.-fragmentation chain transfer (RAFT) statistical copolymn. of 2-hydroxypropyl methacrylate (HPMA) with glycidyl methacrylate (GlyMA) in concd. aq. soln. via polymn.-induced self-assembly (PISA). A series of five free-standing worm gels is prepd. by fixing the overall d.p. of the core-forming block at 144 while varying its GlyMA content from 0 to 20 mol %. 1H NMR kinetics indicated that GlyMA is consumed much faster than HPMA, producing a GlyMA-rich sequence close to the PGMA stabilizer block. Temp.-dependent oscillatory rheol. studies indicate that increasing the GlyMA content leads to progressively less thermoresponsive worm gels, with no degelation on cooling being obsd. for worms contg. 20 mol % GlyMA. The epoxy groups in the GlyMA residues can be ring-opened using 3-aminopropyltriethoxysilane (APTES) in order to prep. core crosslinked worms via hydrolysis-condensation with the siloxane groups and/or hydroxyl groups on the HPMA residues. Perhaps surprisingly, 1H NMR anal. indicates that the epoxy-amine reaction and the intermol. crosslinking occur on similar time scales. Crosslinking leads to stiffer worm gels that do not undergo degelation upon cooling. Dynamic light scattering studies and TEM analyses conducted on linear worms exposed to either methanol (a good solvent for both blocks) or anionic surfactant result in immediate worm dissocn. In contrast, crosslinked worms remain intact under such conditions, provided that the worm cores comprise at least 10 mol % GlyMA.
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    20. 20
      Blanazs, A.; Ryan, A. J.; Armes, S. P. Predictive Phase Diagrams for RAFT Aqueous Dispersion Polymerization: Effect of Block Copolymer Composition, Molecular Weight, and Copolymer Concentration. Macromolecules 2012, 45 (12), 5099– 5107,  DOI: 10.1021/ma301059r
      20
      Predictive Phase Diagrams for RAFT Aqueous Dispersion Polymerization: Effect of Block Copolymer Composition, Molecular Weight, and Copolymer Concentration
      Blanazs, A.; Ryan, A. J.; Armes, S. P.
      Macromolecules (Washington, DC, United States) (2012), 45 (12), 5099-5107CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      Polymn.-induced self-assembly (PISA) of poly(glycerol monomethacrylate)-poly(2-hydroxypropyl methacrylate) (PGMA-PHPMA) diblocks is conducted using a RAFT aq. dispersion polymn. formulation at 70 °C. Several PGMA macromol. chain transfer agents (macro-CTAs) are chain-extended using a water-miscible monomer (HPMA): the growing PHPMA block becomes increasingly hydrophobic and hence drives in situ self-assembly. The final copolymer morphol. in such PISA syntheses depends on just three parameters: the mean d.p. (DP) of the PGMA stabilizer block, the mean DP of the PHPMA core-forming block, and the total solids concn. TEM is used to construct detailed diblock copolymer phase diagrams for PGMA DPs of 47, 78, and 112. For the shortest stabilizer block, there is essentially no concn. dependence: spheres, worms, or vesicles can be obtained even at 10% wt./wt. solids simply by selecting the DP of the PHPMA block that gives the appropriate mol. curvature. For a PGMA DP of 78, the phase diagram is rich: and the copolymer morphol. depends strongly on the total solids concn. There is also a narrow region where spheres, worms, and vesicles coexist, which may be due to the effect of polydispersity. For a PGMA112 macro-CTA, the phase diagram is dominated by spherical morphologies. This is probably because the longer core-forming block DPs required to reduce the mol. curvature are significantly more dehydrated and hence less mobile, which prevents the in situ evolution of morphol. from spheres to higher order morphologies. This hypothesis is supported by the observation that addn. of ethanol to aq. PISA syntheses conducted using the longer macro-CTAs allows access to diblock copolymer worms or vesicles, since this cosolvent solvates the core-forming PHPMA chains and hence increases their mobility at 70 °C. Elucidation of such phase diagrams is vital to ensure reproducible targeting of pure phases, rather than mixed phases.
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    21. 21
      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 (51), 16098– 16108,  DOI: 10.1021/jacs.5b10415
      21
      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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    22. 22
      Rösler, A.; Vandermeulen, G. W. M.; Klok, H. A. Advanced Drug Delivery Devices via Self-Assembly of Amphiphilic Block Copolymers. Adv. Drug Delivery Rev. 2012, 64, 270– 279,  DOI: 10.1016/j.addr.2012.09.026
      There is no corresponding record for this reference.
    23. 23
      Derry, M. J.; Mykhaylyk, O. O.; Armes, S. P. A Vesicle-to-Worm Transition Provides a New High-Temperature Oil Thickening Mechanism. Angew. Chemie - Int. Ed. 2017, 56 (7), 1746– 1750,  DOI: 10.1002/anie.201609365
      23
      A Vesicle-to-Worm Transition Provides a New High-Temperature Oil Thickening Mechanism
      Derry, Matthew J.; Mykhaylyk, Oleksandr O.; Armes, Steven P.
      Angewandte Chemie, International Edition (2017), 56 (7), 1746-1750CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Diblock copolymer vesicles are prepd. via RAFT dispersion polymn. directly in mineral oil. Such vesicles undergo a vesicle-to-worm transition on heating to 150 °C, as judged by TEM and SAXS. Variable-temp. 1H NMR spectroscopy indicates that this transition is the result of surface plasticization of the membrane-forming block by hot solvent, effectively increasing the vol. fraction of the stabilizer block and so reducing the packing parameter for the copolymer chains. The rheol. behavior of a 10 % wt./wt. copolymer dispersion in mineral oil is strongly temp.-dependent: the storage modulus increases by five orders of magnitude on heating above the crit. gelation temp. of 135 °C, as the non-interacting vesicles are converted into weakly interacting worms. SAXS studies indicate that, on av., three worms are formed per vesicle. Such vesicle-to-worm transitions offer an interesting new mechanism for the high-temp. thickening of oils.
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    24. 24
      Bates, F. S. Polymer-Polymer Phase Behavior. Science (80-.). 1991, 251 (4996), 898– 905,  DOI: 10.1126/science.251.4996.898
      24
      Polymer-polymer phase behavior
      Bates, Frank S.
      Science (Washington, DC, United States) (1991), 251 (4996), 898-905CODEN: SCIEAS; ISSN:0036-8075.
      A review with 57 refs. on basic factors governing polymer-polymer phase behavior with emphasis on linear homopolymer blends and diblock copolymers as representative model mol. architectures. Equil. thermodn. and phase sepn. dynamics are reviewed and discussed.
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    25. 25
      Blanazs, A.; Armes, S. P.; Ryan, A. J. Self-Assembled Block Copolymer Aggregates: From Micelles to Vesicles and Their Biological Applications. Macromol. Rapid Commun. 2009, 30 (4), 267– 277,  DOI: 10.1002/marc.200800713
      25
      Self-assembled block copolymer aggregates: from micelles to vesicles and their biological applications
      Blanazs, Adam; Armes, Steven P.; Ryan, Anthony J.
      Macromolecular Rapid Communications (2009), 30 (4-5), 267-277CODEN: MRCOE3; ISSN:1022-1336. (Wiley-VCH Verlag GmbH & Co. KGaA)
      A review. The ability of amphiphilic block copolymers to self-assemble in selective solvents has been widely studied in academia and utilized for various com. products. The self-assembled polymer vesicle is at the forefront of this nanotechnol. revolution with seemingly endless possible uses, ranging from biomedical to nanometer-scale enzymic reactors. This review is focused on the inherent advantages in using polymer vesicles over their small mol. lipid counterparts and the potential applications in biol. for both drug delivery and synthetic cellular reactors.
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    26. 26
      Albigès, R.; Klein, P.; Roi, S.; Stoffelbach, F.; Creton, C.; Bouteiller, L.; Rieger, J. Water-Based Acrylic Coatings Reinforced by PISA-Derived Fibers. Polym. Chem. 2017, 8 (34), 4992– 4995,  DOI: 10.1039/C7PY00302A
      26
      Water-based acrylic coatings reinforced by PISA-derived fibers
      Albiges, Richard; Klein, Pauline; Roi, Stephanie; Stoffelbach, Francois; Creton, Costantino; Bouteiller, Laurent; Rieger, Jutta
      Polymer Chemistry (2017), 8 (34), 4992-4995CODEN: PCOHC2; ISSN:1759-9962. (Royal Society of Chemistry)
      Polymn.-induced self-assembly (PISA) is an efficient approach to synthesize self-assembled core-shell nanofibers in water, made of amphiphilic block copolymers. We demonstrate here for the first time that such anisotropic and high Tg nanofibers can be used as reinforcing fillers for water-based acrylic materials. This strategy opens the way for strong all-org. aq. coatings.
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    27. 27
      Chenal, M.; Rieger, J.; Vechambre, C.; Chenal, J.-M.; Chazeau, L.; Creton, C.; Bouteiller, L. Soft Nanostructured Films with an Ultra-Low Volume Fraction of Percolating Hard Phase. Macromol. Rapid Commun. 2013, 34 (34), 1524– 1529,  DOI: 10.1002/marc.201300410
      27
      Soft Nanostructured Films with an Ultra-Low Volume Fraction of Percolating Hard Phase
      Chenal, Marion; Rieger, Jutta; Vechambre, Cyril; Chenal, Jean-Marc; Chazeau, Laurent; Creton, Costantino; Bouteiller, Laurent
      Macromolecular Rapid Communications (2013), 34 (19), 1524-1529CODEN: MRCOE3; ISSN:1022-1336. (Wiley-VCH Verlag GmbH & Co. KGaA)
      In this study, aq. emulsion polymn. of Bu acrylate is performed in batch conditions without surfactants using a poly(acrylic acid)-trithiocarbonate macro-RAFT agent to control the polymn. and to stabilize the emulsion. According to the polymn.-induced self-assembly (PISA) approach, well-defined amphiphilic PAA-b-PBA diblock copolymers form and self-assemble during synthesis to yield highly stable core-shell particles with an extremely thin hard PAA shell. For the first time, we report here the specific properties of films obtained from these particular latexes. After drying the aq. dispersion, tough and transparent films are obtained. Although the films are not chem. crosslinked, they do not dissolve in good solvents for PBA. Moreover, they remain transparent even after immersion in water. Rheol. shows that the films are both stiff and ductile, thanks to the nanostructured but very low vol. fraction (less than 3 wt%) of PAA forming a percolating network in the soft PBA. Compared with conventional core-shell-based films, this approach affords for the first time a route to a thin percolating honeycomb nanostructure with a sharp and strong interface between the two phases. The versatility of the synthetic procedure opens perspectives for a large range of functional materials.
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    28. 28
      Rieger, J.; Osterwinter, G.; Bui, C.; Stoffelbach, F.; Charleux, B. Surfactant-Free Controlled/Living Radical Emulsion (Co)Polymerization of n-Butyl Acrylate and Methyl Methacrylate via RAFT Using Amphiphilic Polyethylene Oxide-Based Trithiocarbonate Chain Transfer Agents. Macromolecules 2009, 42 (15), 5518– 5525,  DOI: 10.1021/ma9008803
      28
      Surfactant-Free Controlled/Living Radical Emulsion (Co)polymerization of n-Butyl Acrylate and Methyl Methacrylate via RAFT Using Amphiphilic Poly(ethylene oxide)-Based Trithiocarbonate Chain Transfer Agents
      Rieger, Jutta; Osterwinter, Gregor; Bui, Chuong; Stoffelbach, Francois; Charleux, Bernadette
      Macromolecules (Washington, DC, United States) (2009), 42 (15), 5518-5525CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      The RAFT-mediated, surfactant-free, ab initio, batch emulsion polymn. of Bu acrylate (nBA) and its copolymn. with Me methacrylate (MMA) were studied. The control agent was a surface-active trithiocarbonate macromol. RAFT agent composed of a hydrophilic poly(ethylene oxide) (PEO) block and a hydrophobic dodecyl chain. The homopolymns. of nBA were fast with high final conversions, and the polymer chains were well-controlled with narrow molar mass distribution. The length of the PEO chain was shown to affect the particle size and the polymn. kinetics directly. We found the conditions to tune the particle size independently from the poly(Bu acrylate) chain length by playing with a mixt. of macro-RAFT agents with long and short PEO segment or by adding a PEO-based nonionic surfactant. The copolymns. of nBA and MMA exhibited features very similar to those of the nBA homopolymns. provided that the molar percentage of MMA did not exceed approx. 75%. In all cases, stable, submicrometric particles composed of amphiphilic diblock copolymer chains were formed.
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    29. 29
      Cockram, A. A.; Bradley, R. D.; Lynch, S. A.; Fleming, P. C. D.; Williams, N. S. J.; Murray, M. W.; Emmett, S. N.; Armes, S. P. Optimization of the High-Throughput Synthesis of Multiblock Copolymer Nanoparticles in Aqueous Media: Via Polymerization-Induced Self-Assembly. React. Chem. Eng. 2018, 3 (5), 645– 657,  DOI: 10.1039/C8RE00066B
      29
      Optimization of the high-throughput synthesis of multiblock copolymer nanoparticles in aqueous media via polymerization-induced self-assembly
      Cockram, Amy A.; Bradley, Robert D.; Lynch, Sylvie A.; Fleming, Patricia C. D.; Williams, Neal S. J.; Murray, Martin W.; Emmett, Simon N.; Armes, Steven P.
      Reaction Chemistry & Engineering (2018), 3 (5), 645-657CODEN: RCEEBW; ISSN:2058-9883. (Royal Society of Chemistry)
      In the present study, we report that PISA formulations are sufficiently robust to enable high-throughput expts. using a com. synthesis robot (Chemspeed Autoplant A100). More specifically, we use reversible addn.-fragmentation chain transfer (RAFT) aq. emulsion polymn. of either Bu methacrylate and/or benzyl methacrylate to prep. various examples of methacrylic multiblock copolymer nanoparticles using a poly(methacrylic acid) stabilizer block. Adequate stirring is essential to generate sufficiently small monomer droplets for such heterogeneous polymns. to proceed efficiently. Good reproducibility can be achieved under such conditions, with well-defined spherical morphologies being obtained at up to 45% wt./wt. solids. GPC studies indicate high blocking efficiencies but relatively broad mol. wt. distributions (Mw/Mn = 1.36-1.85), suggesting well-defined (albeit rather polydisperse) block copolymer chains. These preliminary studies provide a sound basis for high-throughput screening of RAFT-mediated PISA formulations, which is likely to be required for commercialization of this technol. Our results indicate that methacrylic PISA formulations enable the synthesis of diblock and triblock copolymer nanoparticles in high overall yield (94-99%) within 1-3 h at 70 °C. However, tetrablocks suffer from incomplete conversions (87-96% within 5 h) and hence most likely represent the upper limit for this approach.
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    30. 30
      Cockram, A. A.; Neal, T. J.; Derry, M. J.; Mykhaylyk, O. O.; Williams, N. S. J.; Murray, M. W.; Emmett, S. N.; Armes, S. P. Effect of Monomer Solubility on the Evolution of Copolymer Morphology during Polymerization-Induced Self-Assembly in Aqueous Solution. Macromolecules 2017, 50 (3), 796– 802,  DOI: 10.1021/acs.macromol.6b02309
      30
      Effect of Monomer Solubility on the Evolution of Copolymer Morphology during Polymerization-Induced Self-Assembly in Aqueous Solution
      Cockram, Amy A.; Neal, Thomas J.; Derry, Matthew J.; Mykhaylyk, Oleksandr O.; Williams, Neal S. J.; Murray, Martin W.; Emmett, Simon N.; Armes, Steven P.
      Macromolecules (Washington, DC, United States) (2017), 50 (3), 796-802CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      Polymn.-induced self-assembly (PISA) has become a widely used technique for the design of diblock copolymer nano-objects in concd. aq. soln. Depending on the specific PISA formulation, reversible addn.-fragmentation chain transfer (RAFT) aq. dispersion polymn. typically provides straightforward access to either spheres, worms or vesicles. In contrast, RAFT aq. emulsion polymn. formulations often lead to just kinetically trapped spheres. This limitation is currently not understood and only a few empirical exceptions were reported in the literature. In the present work, the effect of monomer soly. on copolymer morphol. is explored for an aq. polymn.-induced self-assembly (PISA) formulation. Using 2-hydroxybutyl methacrylate (aq. soly. =20 g dm-3 at 70 °C) instead of benzyl methacrylate (0.40 g dm-3 at 70 °C) for the core-forming block allows access to an unusual "monkey nut" copolymer morphol. over a relatively narrow range of target ds.p. when using a poly(methacrylic acid) RAFT agent at pH 5. These new nanoparticles have been characterized by transmission electron microscopy, dynamic light scattering, aq. electrophoresis, shear-induced polarized light imaging (SIPLI) and small-angle X-ray scattering.
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    31. 31
      Rieger, J. Guidelines for the Synthesis of Block Copolymer Particles of Various Morphologies by RAFT Dispersion Polymerization. Macromol. Rapid Commun. 2015, 36 (16), 1458– 1471,  DOI: 10.1002/marc.201500028
      31
      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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    32. 32
      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 (4), 1653– 1662,  DOI: 10.1021/acs.macromol.8b02491
      32
      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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    33. 33
      Qiao, Z.; Qiu, T.; Liu, W.; Zhang, L.; Tu, J.; Guo, L.; Li, X. A “Green” Method for Preparing ABCBA Penta-Block Elastomers by Using RAFT Emulsion Polymerization. Polym. Chem. 2017, 8 (19), 3013– 3021,  DOI: 10.1039/C7PY00464H
      33
      A "green" method for preparing ABCBA penta-block elastomers by using RAFT emulsion polymerization
      Qiao, Zhi; Qiu, Teng; Liu, Weiwei; Zhang, Liangdong; Tu, Jinqiang; Guo, Longhai; Li, Xiaoyu
      Polymer Chemistry (2017), 8 (19), 3013-3021CODEN: PCOHC2; ISSN:1759-9962. (Royal Society of Chemistry)
      A clean method for prepg. ABCBA penta-block terpolymers was developed in a surfactant and org. solvent free emulsion system via one-pot RAFT polymn. The prepd. ABCBA penta-block terpolymers show large fracture tensile strain, low permanent set and potential application as elastomer materials. During the prepn. process, polyacrylic acid (PAA) was firstly synthesized as the A block via RAFT polymn. in water in the presence of a dual-functional RAFT agent. Subsequently, a partially water-sol. monomer 2,2,2-trifluoroethyl acrylate (TFEA) was used to synthesize the B block, and ABA tri-block copolymers could be obtained via org. solvent free RAFT emulsion polymn. Using the ABA tri-block copolymers as a surfactant, the ABCBA penta-block terpolymers were further synthesized using 2,2,3,4,4,4-hexafluorobutyl acrylate (HFBA) as the third monomer in an org. solvent free system. It has been found that the emulsification efficiency of the ABA tri-block copolymers is higher than that of the corresponding AB di-block copolymers. The assembly mechanism of penta-block terpolymers to form a tri-layer core-shell latex particle was proposed and confirmed by TEM images. Finally, a transparent and hydrophobic elastomeric film was obtained by directly casting the synthesized penta-block terpolymer latexes and subsequent heat treatment. The films have excellent mech. properties and water resistance.
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    34. 34
      Wu, X.; Qiao, Y.; Yang, H.; Wang, J. Self-Assembly of a Series of Random Copolymers Bearing Amphiphilic Side Chains. J. Colloid Interface Sci. 2010, 349 (2), 560– 564,  DOI: 10.1016/j.jcis.2010.05.093
      34
      Self-assembly of a series of random copolymers bearing amphiphilic side chains
      Wu, Xu; Qiao, Yingjie; Yang, Hui; Wang, Jinben
      Journal of Colloid and Interface Science (2010), 349 (2), 560-564CODEN: JCISA5; ISSN:0021-9797. (Elsevier B.V.)
      A novel series of comb-like random copolymers were prepd. by polymn. of amphiphilic macromonomers, 2-(acrylamido)-octane sulfonic acid (AMC8S), 2-(acrylamido)-dodecane sulfonic acid (AMC12S), and 2-(acrylamido)-hexadecane sulfonic acid (AMC16S), with 2-(acrylamido)-2-methylpropanesulfonic acid (AMPS) resp. The synthesis of the polymers with the same contents of amphiphilic units as side chains, but different chain length, enabled us to study the chain length dependence of their assocn. in salt soln. Steady-state fluorescence measurements with pyrene as a polarity probe, quasielastic light scattering techniques (QELS) and transmission electron micrograph (TEM) were employed to investigate the associative properties of the system. The above investigations showed that all kinds of side chains begin to assemble at certain polymer concns. and the crit. aggregation concn. (CAC) decrease dramatically with the increase in the length and content of alkyl. An interesting phenomenon is that the assembly tends more favorably to occur among different mols. rather than within single mol. when the no. of carbon atoms in the alkyl groups or the polymer concn. increases, leading to the formation of larger multimol. micelle-like aggregate. The aim of the present work is to establish the fundamental preconditions of intramol. and intermol. assocn. fashions for the polymers, which is useful for the exploitation of functional groups and contributes to the development of amphiphilic random polymers.
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    35. 35
      Kawata, T.; Hashidzume, A.; Sato, T. Micellar Structure of Amphiphilic Statistical Copolymers Bearing Dodecyl Hydrophobes in Aqueous Media. Macromolecules 2007, 40 (4), 1174– 1180,  DOI: 10.1021/ma062299x
      35
      Micellar Structure of Amphiphilic Statistical Copolymers Bearing Dodecyl Hydrophobes in Aqueous Media
      Kawata, Takefumi; Hashidzume, Akihito; Sato, Takahiro
      Macromolecules (2007), 40 (4), 1174-1180CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      The structure of micellar aggregates formed from ionic statistical copolymers of N-acryloyl-amino acids and N-dodecylmethacrylamide in 0.05 M aq. NaCl was studied by light scattering and fluorescence. The exptl. results indicated that the tendency of the interchain aggregation increased with the hydrophobic monomer content for each series of the copolymers but decreased with hydrophobicity of the amino acid residue in the copolymers. On the other hand, while the micellar structure of the statistical copolymers strongly depended on the kind of the hydrophobe, it is little dependent on the kind of the electrolyte monomer unit at low ionic strength. Using these data, a theor. anal. taking into account the chain stiffness effect revealed that uni-core micelles formed from the ionic statistical copolymers were of flower type with a min. loop size.
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    36. 36
      Zhu, X.; Liu, M. Self-Assembly and Morphology Control of New l -Glutamic Acid-Based Amphiphilic Random Copolymers: Giant Vesicles, Vesicles, Spheres, and Honeycomb Film. Langmuir 2011, 27 (21), 12844– 12850,  DOI: 10.1021/la202680j
      36
      Self-Assembly and Morphology Control of New L-Glutamic Acid-Based Amphiphilic Random Copolymers: Giant Vesicles, Vesicles, Spheres, and Honeycomb Film
      Zhu, Xuewang; Liu, Minghua
      Langmuir (2011), 27 (21), 12844-12850CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
      New amphiphilic random copolymers contg. hydrophobic dodecyl (C12) chain and hydrophilic L-glutamic acid were synthesized, and their self-assembly in soln. as well as on the solid surfaces was investigated. The self-assembly behavior of these polymers are largely dependent on their hydrophilic and hydrophobic balances. The copolymer with a more hydrophobic alkyl chain (∼90%) self-assembled into giant vesicles with a diam. of several micrometers in a mixed solvent of ethanol and water. When the hydrophobic ratio decreased to ca. 76%, the polymer self-assembled into conventional vesicles with several hundred nanometers. The giant vesicles could be fused in certain conditions, while the conventional vesicles were stable. When the content of the hydrophilic part was further increased, no organized structures were formed. On the other hand, when the copolymer solns. were directly cast on solid substrates such as silicon plates, films with organized nanostructures could also be obtained, the morphol. of which depended on solvent selection. When ethanol or methanol was used, spheres were obtained. When dichloromethane was used as the solvent, honeycomb-like morphologies were obtained. These results showed that through appropriate mol. design, random copolymer could self-assemble into various organized structures, which could be regulated through the hydrophobic/hydrophilic balance and the solvents.
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    37. 37
      Tian, F.; Yu, Y.; Wang, C.; Yang, S. Consecutive Morphological Transitions in Nanoaggregates Assembled from Amphiphilic Random Copolymer via Water Driven Micellization and Light-Triggered Dissociation. Macromolecules 2008, 41 (10), 3385– 3388,  DOI: 10.1021/ma800142j
      37
      Consecutive Morphological Transitions in Nanoaggregates Assembled from Amphiphilic Random Copolymer via Water-Driven Micellization and Light-Triggered Dissociation
      Tian, Feng; Yu, Yuanyuan; Wang, Changchun; Yang, Shu
      Macromolecules (Washington, DC, United States) (2008), 41 (10), 3385-3388CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      We report a study of continuous morphol. transitions from spherical micelles, through hollow tubes and wormlike rods, to large vesicles in nanoaggregates self-assembled from photoresponsive amphiphilic random copolymer. Through esterification of the side chain hydroxyl groups, the hydrophilic poly(hydroxyethyl methacrylate) (PHEMA) backbone is partially and randomly modified by the hydrophobic, light-responsive 2-diazo-1,2-naphthoquinone (DNQ) mols. The micellization and transition are then triggered simply by adding water into the copolymer/DMF soln. Upon irradn. to UV light at 405 nm, large vesicles become increasingly hydrophilic with time and gradually dissoc. into globular hydrogel particles in the aq. soln. (Scheme 1), releasing the encapsulated dye mols.
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    38. 38
      Sun, G.; Zhang, M.; He, J.; Ni, P. Synthesis of Amphiphilic Cationic Copolymers Poly[2-(Methacryloyloxy)Ethyl Trimethylammonium Chloride-co-stearyl Methacrylate] and Their Self-Assembly Behavior in Water and Water-Ethanol Mixtures. J. Polym. Sci. Part A Polym. Chem. 2009, 47, 4670– 4684,  DOI: 10.1002/pola.23517
      38
      Synthesis of amphiphilic cationic copolymers poly[2-(methacryloyloxy)ethyl trimethylammonium chloride-co-stearyl methacrylate] and their self-assembly behavior in water and water-ethanol mixtures
      Sun, Guixiang; Zhang, Mingzu; He, Jinlin; Ni, Peihong
      Journal of Polymer Science, Part A: Polymer Chemistry (2009), 47 (18), 4670-4684CODEN: JPACEC; ISSN:0887-624X. (John Wiley & Sons, Inc.)
      A series of amphiphilic cationic random copolymers, namely poly[2-(methacryloyloxy)ethyl trimethylammonium chloride-co-stearyl methacrylate] or poly(MADQUAT-co-SMA), were synthesized via conventional free-radical copolymn. using 2,2'-azobisisobutyronitrile (AIBN) as initiator and n-dodecanethiol as chain transfer agent. The resultant products were then characterized by FT-IR, 1H NMR, MALDI-TOF MS measurements. From the no.-av. mol. wts. of the copolymers, we can conclude that these copolymers have oligomeric structure with a limited no. of hydrophilic and hydrophobic moieties in a short polymer chain. The reactivity ratios (rMADQUAT = 0.83, rSMA = 0.25) between the hydrophilic MADQUAT monomer and the hydrophobic SMA monomer were calcd. by the Finemann and Ross method, which was based on the results of 1H NMR anal. The surface activity of the random copolymers was studied by the combination of surface tension and contact angle measurement, and these copolymers possess relatively high surface activity. The crit. aggregation concns. (cac) of the copolymers in aq. soln. were detd. by fluorescence probe method and surface tension measurement. The different nanoparticles of poly(MADQUAT-co-SMA) copolymers formed in pure water or ethanol-water mixt. were proved by the particle size and size distribution in the measurement of dynamic light scattering (DLS). Furthermore, using TEM, we could observe various self-assembly morphologies of these random copolymer. All the amphiphilic cationic random copolymers have a good self-assembly behavior, even if they are ill-defined copolymers.
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    39. 39
      Stephan, T.; Muth, S.; Schmidt, M. Shape Changes of Statistical Copolymacromonomers: From Wormlike Cylinders to Horseshoe- and Meanderlike Structures. Macromolecules 2002, 35 (27), 9857– 9860,  DOI: 10.1021/ma025711r
      39
      Shape Changes of Statistical Copolymacromonomers: From Wormlike Cylinders to Horseshoe- and Meander-like Structures
      Stephan, Tim; Muth, Sandra; Schmidt, Manfred
      Macromolecules (2002), 35 (27), 9857-9860CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      Depending on the solvent, statistical copolymer cylindrical brushes adopt different shapes from worm-like to horseshoe or meander-like structures when spin-cast onto mica. To the best of our knowledge, this is the first time that shape persistent synthetic macromols. could be chem. manipulated to change their conformation from a wormlike to regularly curved structures. It should be mentioned, though, that for cylindrical brushes with Bu acrylate side chains a collapse of the wormlike conformation to spherical structures could be induced under pressure on a Langmuir-Blodgett trough. Also, poly(p-phenylene)s with amphipolar dendritic side chains were reported to have the potential to intramol. segregate lengthwise, particularly when spread on a LB trough as well. Our next step will address the question of whether the collapse of the minority component could be detected by scattering expts. in soln., which, however, was not successful so far.
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    40. 40
      Ilhan, F.; Galow, T. H.; Gray, M.; Clavier, G.; Rotello, V. M. Giant Vesicle Formation through Self-Assembly of Complementary Random Copolymers. J. Am. Chem. Soc. 2000, 122 (24), 5895– 5896,  DOI: 10.1021/ja0011966
      40
      Giant Vesicle Formation through Self-Assembly of Complementary Random Copolymers
      Ilhan, Faysal; Galow, Trent H.; Gray, Mark; Clavier, Gilles; Rotello, Vincent M.
      Journal of the American Chemical Society (2000), 122 (24), 5895-5896CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Differential interference contrast optical microscopy and confocal laser scanning microscopy showed that vesicular H-bond complexes formed between chains of 4-(chloromethyl)styrene-styrene copolymer (I)-2,6-bis(propionamido)pyrid-4-one adducts and I-thymine-1-acetic acid adducts in CHCl3 solns.
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    41. 41
      Liu, X.; Kim, J.-S.; Wu, J.; Eisenberg, A. Bowl-Shaped Aggregates from the Self-Assembly of an Amphiphilic Random Copolymer of Poly(Styrene- Co -Methacrylic Acid). Macromolecules 2005, 38 (16), 6749– 6751,  DOI: 10.1021/ma050665r
      41
      Bowl-Shaped Aggregates from the Self-Assembly of an Amphiphilic Random Copolymer of Poly(styrene-co-methacrylic acid)
      Liu, Xiaoya; Kim, Joon-Seop; Wu, Jun; Eisenberg, Adi
      Macromolecules (2005), 38 (16), 6749-6751CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      A bowl-shaped structure of random poly(styrene-co-methacrylic acid) was prepd. by self-assembly in dil. soln. We emphasize that the copolymer was a random copolymer in contrast to the block copolymers or functionally terminated homopolymers used before. The added viscosity control is probably provided by H bond interactions among OH groups along the backbone as in encountered in carboxylic acids in bulk or in org. solvents.
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    42. 42
      Neal, T. J.; Parnell, A. J.; King, S. M.; Beattie, D. L.; Murray, M. W.; Williams, N. S. J.; Emmett, S. N.; Armes, S. P.; Spain, S. G.; Mykhaylyk, O. O. Control of Particle Size in the Self-Assembly of Amphiphilic Statistical Copolymers. Macromolecules 2021, 54 (3), 1425– 1440,  DOI: 10.1021/acs.macromol.0c02341
      42
      Control of Particle Size in the Self-Assembly of Amphiphilic Statistical Copolymers
      Neal, Thomas J.; Parnell, Andrew J.; King, Stephen M.; Beattie, Deborah L.; Murray, Martin W.; Williams, Neal S. J.; Emmett, Simon N.; Armes, Steven P.; Spain, Sebastian G.; Mykhaylyk, Oleksandr O.
      Macromolecules (Washington, DC, United States) (2021), 54 (3), 1425-1440CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      A range of amphiphilic statistical copolymers is synthesized where the hydrophilic component is either methacrylic acid (MAA) or 2-(dimethylamino)ethyl methacrylate (DMAEMA) and the hydrophobic component comprises Me, Et, Bu, hexyl, or 2-ethylhexyl methacrylate, which provide a broad range of partition coeffs. (log P). Small-angle x-ray scattering studies confirm that these amphiphilic copolymers self-assemble to form well-defined spherical nanoparticles in an aq. soln., with more hydrophobic copolymers forming larger nanoparticles. Varying the nature of the alkyl substituent also influenced self-assembly with more hydrophobic comonomers producing larger nanoparticles at a given copolymer compn. A model based on particle surface charge d. (PSC model) is used to describe the relation between copolymer compn. and nanoparticle size. This model assumes that the hydrophilic monomer is preferentially located at the particle surface and provides a good fit to all of the exptl. data. More specifically, a linear relation is obsd. between the surface area fraction covered by the hydrophilic comonomer required to achieve stabilization and the log P value for the hydrophobic comonomer. Contrast variation small-angle neutron scattering is used to study the internal structure of these nanoparticles. This technique indicates partial phase sepn. within the nanoparticles, with about half of the available hydrophilic comonomer repeat units being located at the surface and hydrophobic comonomer-rich cores. This information enables a refined PSC model to be developed, which indicates the same relation between the surface area fraction of the hydrophilic comonomer and the log P of the hydrophobic comonomer repeat units for the anionic (MAA) and cationic (DMAEMA) comonomer systems. This study demonstrates how nanoparticle size can be readily controlled and predicted using relatively ill-defined statistical copolymers, making such systems a viable attractive alternative to diblock copolymer nanoparticles for a range of industrial applications.
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    43. 43
      Azuma, Y.; Terashima, T.; Sawamoto, M. Self-Folding Polymer Iron Catalysts for Living Radical Polymerization. ACS Macro Lett. 2017, 6 (8), 830– 835,  DOI: 10.1021/acsmacrolett.7b00498
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      Self-Folding Polymer Iron Catalysts for Living Radical Polymerization
      Azuma, Yusuke; Terashima, Takaya; Sawamoto, Mitsuo
      ACS Macro Letters (2017), 6 (8), 830-835CODEN: AMLCCD; ISSN:2161-1653. (American Chemical Society)
      Iron-bearing self-folding polymers were created with amphiphilic random copolymers as active, versatile, and recyclable polymer-supported catalysts for living radical polymn. (LRP). The key is to build bis(imino)pyridine ligand cavities for iron complexes as linking units within self-folding polymers. Self-folding polymer ligands are synthesized by the intramol. imine crosslinking of self-folded amphiphilic random copolymers bearing hydrophilic poly(ethylene glycol) (PEG), hydrophobic dodecyl, and urea/aniline pendants with 2,6-pyridinedicarboxaldehyde in water. The folding polymers efficiently formed iron complex catalysts in the cores to induce LRP and random or block copolymn. of various methacrylates. The self-folding polymer catalysts not only showed high activity and tolerance to functional groups such as acid, hydroxyl groups, and oxygen but also afforded easy product recovery and catalyst recycle thanks to hydrophilic PEG chains.
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    44. 44
      Lyon, C. K.; Prasher, A.; Hanlon, A. M.; Tuten, B. T.; Tooley, C. A.; Frank, P. G.; Berda, E. B. A Brief User’s Guide to Single-Chain Nanoparticles. Polym. Chem. 2015, 6 (2), 181– 197,  DOI: 10.1039/C4PY01217H
      44
      A brief user's guide to single-chain nanoparticles
      Lyon, Christopher K.; Prasher, Alka; Hanlon, Ashley M.; Tuten, Bryan T.; Tooley, Christian A.; Frank, Peter G.; Berda, Erik B.
      Polymer Chemistry (2015), 6 (2), 181-197CODEN: PCOHC2; ISSN:1759-9962. (Royal Society of Chemistry)
      In this review we outline the various methods that have been explored to synthesize architecturally defined nanoparticles from discrete polymer chains, summarize the methods of characterization that are required to prove their formation and probe their morphol., and introduce a no. of potential applications that are being explored currently. Given the small size of the nanostructures produced by these methods and the relative ease with which they can be tailored to specific end use applications it is likely such efforts will intensify in the coming years. So far, simple chem. has been utilized and high-level characterization and modeling studies have been applied to understand the process by which these particles form and how they behave, both in the bulk and in soln. Although impossible to predict where this work will lead, we hope this "user's guide" will prove useful to the community as research on single-chain nanoparticles continues to evolve.
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    45. 45
      Romulus, J.; Weck, M. Single-Chain Polymer Self-Assembly Using Complementary Hydrogen Bonding Units. Macromol. Rapid Commun. 2013, 34 (19), 1518– 1523,  DOI: 10.1002/marc.201300501
      45
      Single-Chain Polymer Self-Assembly Using Complementary Hydrogen Bonding Units
      Romulus, Joy; Weck, Marcus
      Macromolecular Rapid Communications (2013), 34 (19), 1518-1523CODEN: MRCOE3; ISSN:1022-1336. (Wiley-VCH Verlag GmbH & Co. KGaA)
      A triblock copolymer contg. the complementary hydrogen bonding recognition pair ureidoguanosine-diaminonaphthyridine (UG-DAN) as pendant functional groups is synthesized using ring-opening metathesis polymn. (ROMP). The norbornene-based DAN monomer is shown to allow for a controlled polymn. when polymd. in the presence of a modified-UG mol. that serves as a protecting group, subsequently allowing for the fabrication of functionalized triblock copolymers. The self-assembly of the copolymers was characterized using dynamic light scattering and 1H NMR spectroscopy. It is demonstrated that the polymers self-assemble via complementary hydrogen bonding motifs even at low dilns., indicating intramol. interactions.
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    46. 46
      Gillissen, M. A. J.; Voets, I. K.; Meijer, E. W.; Palmans, A. R. A. Single Chain Polymeric Nanoparticles as Compartmentalised Sensors for Metal Ions. Polym. Chem. 2012, 3 (11), 3166– 3174,  DOI: 10.1039/c2py20350b
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      Single chain polymeric nanoparticles as compartmentalised sensors for metal ions
      Gillissen, Martijn A. J.; Voets, Ilja K.; Meijer, E. W.; Palmans, Anja. R. A.
      Polymer Chemistry (2012), 3 (11), 3166-3174CODEN: PCOHC2; ISSN:1759-9962. (Royal Society of Chemistry)
      3,3'-Bis(acylamino)-2,2'-bipyridine substituted benzene-1,3,5-tricarboxamide (BiPy-BTA) grafted polynorbornene polymers were prepd. via ring-opening metathesis polymn. using a third generation Grubbs catalyst. The polymers fold intramolecularly via π-π interactions into fluorescent, compartmentalized particles of nanometer-size in mixts. of THF and methylcyclohexane. Spectroscopic and light scattering techniques show that the compact conformation of the folded polymer is affected by increasing the BiPy-BTA functionalization degree and by changing the solvent polarity. Changes in the conformation are accompanied by changes in the fluorescence intensity. Due to the affinity of the 2,2'-bipyridine units for metal ions such as Cu, the particles obtained are effective sensors for these metals. The compartmentalization of the binding motifs in SCPNs proves to be advantageous in sensor applications of these particles.
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    47. 47
      Terashima, T.; Sugita, T.; Fukae, K.; Sawamoto, M. Synthesis and Single-Chain Folding of Amphiphilic Random Copolymers in Water. Macromolecules 2014, 47 (2), 589– 600,  DOI: 10.1021/ma402355v
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      Synthesis and Single-Chain Folding of Amphiphilic Random Copolymers in Water
      Terashima, Takaya; Sugita, Takanori; Fukae, Kaoru; Sawamoto, Mitsuo
      Macromolecules (Washington, DC, United States) (2014), 47 (2), 589-600CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      Amphiphilic random methacrylate copolymers, consisting of poly(ethylene glycol) (PEG) and alkyl pendent groups, undergo reversible single-chain self-folding in water via intramol. hydrophobic interaction, to generate a dynamic unimol. hydrophobic nanospace, similar in shape but structurally different relative to micelles and microgel star polymers. These copolymers were prepd. by the ruthenium-catalyzed living radical copolymn. of a PEG methacrylate (PEGMA) and an alkyl methacrylate (RMA; R, -CnH2n+1, n = 1-18), where copolymer compn., d.p., and hydrophobic R moiety were varied. Detailed structural and chain-folding characterization has revealed: single-chain folding is favored with the RMA content 20-40 mol % per chain; the hydrophobic inner compartment (or the self-folded structure) is stable even at a high polymer concn. (up to ∼6 wt. %); and folded-unfolded transition occurs on addn. of methanol or by elevating soln. temp., finally to phase-sepn. above a lower crit. soln. temp.
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    48. 48
      Terashima, T.; Mes, T.; De Greef, T. F. A.; Gillissen, M. A. J.; Besenius, P.; Palmans, A. R. A.; Meijer, E. W. Single-Chain Folding of Polymers for Catalytic Systems in Water. J. Am. Chem. Soc. 2011, 133 (13), 4742– 4745,  DOI: 10.1021/ja2004494
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      Single-Chain Folding of Polymers for Catalytic Systems in Water
      Terashima, Takaya; Mes, Tristan; De Greef, Tom F. A.; Gillissen, Martijn A. J.; Besenius, Pol; Palmans, Anja R. A.; Meijer, E. W.
      Journal of the American Chemical Society (2011), 133 (13), 4742-4745CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Enzymes are a source of inspiration for chemists attempting to create versatile synthetic catalysts. In order to arrive at a polymeric chain carrying catalytic units sepd. spatially, it is a prerequisite to fold these polymers in water into well-defined compartmentalized architectures thus creating a catalytic core. Herein, we report the synthesis, phys. properties, and catalytic activity of a water-sol. segmented terpolymer in which a helical structure in the apolar core is created around a ruthenium-based catalyst. The supramol. chirality of this catalytic system is the result of the self-assembly of benzene-1,3,5-tricarboxamide side chains, while the catalyst arises from the sequential ruthenium-catalyzed living radical polymn. of the different monomers followed by ligand exchange. The polymers exhibit a two-state folding process and show transfer hydrogenation in water.
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    49. 49
      Matsumoto, M.; Sawamoto, M.; Terashima, T. Orthogonal Folding of Amphiphilic/Fluorous Random Block Copolymers for Double and Multicompartment Micelles in Water. ACS Macro Lett. 2019, 8 (3), 320– 325,  DOI: 10.1021/acsmacrolett.9b00078
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      Orthogonal Folding of Amphiphilic/Fluorous Random Block Copolymers for Double and Multicompartment Micelles in Water
      Matsumoto, Mayuko; Sawamoto, Mitsuo; Terashima, Takaya
      ACS Macro Letters (2019), 8 (3), 320-325CODEN: AMLCCD; ISSN:2161-1653. (American Chemical Society)
      Here, we report orthogonal folding and self-assembly systems of amphiphilic/fluorous random block copolymers for double core and multicompartment micelles in water. For this, we developed the precision folding techniques of polymer chains via the selective self-assembly of the pendant groups. Typically, A/C-B/C random block copolymers were designed: Hydrophobic dodecyl groups (A) and fluorous fluorinated octyl groups (B) were introduced into the resp. blocks, while hydrophilic poly(ethylene glycol) chains (C) were randomly incorporated into all the segments. By controlling the chain length and compn. of the resp. blocks, the copolymers induce orthogonal single-chain folding in water to form double-compartment micelles comprising hydrophobic and fluorous cores. The copolymers were site-selectively folded in a fluoroalc. to result in tadpole unimer micelles comprising a hydrophobic A/C unimer micelle and an unfolded fluorous B/C chain. Addnl., asym. A/C-B/C random block copolymers with short and highly hydrophobic or fluorous segments were effective for multicompartment micelles in water.
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    50. 50
      Matsumoto, M.; Terashima, T.; Matsumoto, K.; Takenaka, M.; Sawamoto, M. Compartmentalization Technologies via Self-Assembly and Cross-Linking of Amphiphilic Random Block Copolymers in Water. J. Am. Chem. Soc. 2017, 139 (21), 7164– 7167,  DOI: 10.1021/jacs.7b03152
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      Compartmentalization Technologies via Self-Assembly and Cross-Linking of Amphiphilic Random Block Copolymers in Water
      Matsumoto, Mayuko; Terashima, Takaya; Matsumoto, Kazuma; Takenaka, Mikihito; Sawamoto, Mitsuo
      Journal of the American Chemical Society (2017), 139 (21), 7164-7167CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Orthogonal self-assembly and intramol. crosslinking of amphiphilic random block copolymers in water afforded an approach to tailor-make well-defined compartments and domains in single polymer chains and nanoaggregates. For a double compartment single-chain polymer, an amphiphilic random block copolymer bearing hydrophilic poly(ethylene glycol) (PEG) and hydrophobic dodecyl, benzyl, and olefin pendants was synthesized by living radical polymn. (LRP) and postfunctionalization; the dodecyl and benzyl units were incorporated into the different block segments, whereas PEG pendants were statistically attached along a chain. The copolymer self-folded via the orthogonal self-assembly of hydrophobic dodecyl and benzyl pendants in water, followed by intramol. crosslinking, to form a single-chain polymer carrying double yet distinct hydrophobic nanocompartments. A single-chain crosslinked polymer with a chlorine terminal served as a globular macroinitiator for LRP to provide an amphiphilic tadpole macromol. comprising a hydrophilic nanoparticle and a hydrophobic polymer tail; the tadpole thus self-assembled into multicompartment aggregates in water.
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    51. 51
      Neal, T. J.; Beattie, D. L.; Byard, S. J.; Smith, G. N.; Murray, M. W.; Williams, N. S. J.; Emmett, S. N.; Armes, S. P.; Spain, S. G.; Mykhaylyk, O. O. Self-Assembly of Amphiphilic Statistical Copolymers and Their Aqueous Rheological Properties. Macromolecules 2018, 51 (4), 1474– 1487,  DOI: 10.1021/acs.macromol.7b02134
      51
      Self-Assembly of Amphiphilic Statistical Copolymers and Their Aqueous Rheological Properties
      Neal, Thomas J.; Beattie, Deborah L.; Byard, Sarah J.; Smith, Gregory N.; Murray, Martin W.; Williams, Neal S. J.; Emmett, Simon N.; Armes, Steven P.; Spain, Sebastian G.; Mykhaylyk, Oleksandr O.
      Macromolecules (Washington, DC, United States) (2018), 51 (4), 1474-1487CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      A range of poly(Bu methacrylate-stat-methacrylic acid) [P(BMA-stat-MAA)] statistical copolymers of various compns. and mol. wts. ranging from 5 to 30 kDa were prepd. using either reversible addn.-fragmentation chain transfer (RAFT) soln. copolymn. or conventional free radical polymn. in isopropanol (IPA). On diln. with water, these amphiphilic copolymers self-assembled to form spherical nano-objects as confirmed by small-angle X-ray scattering (SAXS) and transmission electron microscopy. Various structural models were examd. to ext. information regarding the mean nano-object size and morphol. It is found that nano-object radii are independent of copolymer mol. wt. but depend on the copolymer compn.: the smaller the amt. of MAA units in the copolymer chains, the larger the nano-objects that are formed. Combined SAXS and aq. electrophoretic measurements indicated that most of the MAA units are located at the nano-object surface. Furthermore, SAXS and rheol. measurements were used to monitor the effect of solvent compn. on the copolymer morphol. both at a fixed copolymer concn. (either 1 or 25 wt. %) and also for a gradual variation in copolymer concns. (from 1 to 40 wt. %) when adding water to the initial copolymer soln. in IPA. These studies revealed that the copolymers are present in soln. as molecularly dissolved Gaussian chains when the solvent compn. is IPA-rich. However, the copolymer chains self-assemble into spherical nano-objects when the solvent compn. is water-rich. At intermediate solvent compns., SAXS anal. confirmed the formation of an interconnected nano-object network, which accounts for the apparently anomalous increase in soln. viscosity on diln. indicated by rheol. measurements.
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    52. 52
      Hattori, G.; Takenaka, M.; Sawamoto, M.; Terashima, T. Nanostructured Materials via the Pendant Self-Assembly of Amphiphilic Crystalline Random Copolymers. J. Am. Chem. Soc. 2018, 140 (27), 8376– 8379,  DOI: 10.1021/jacs.8b03838
      52
      Nanostructured Materials via the Pendant Self-Assembly of Amphiphilic Crystalline Random Copolymers
      Hattori, Goki; Takenaka, Mikihito; Sawamoto, Mitsuo; Terashima, Takaya
      Journal of the American Chemical Society (2018), 140 (27), 8376-8379CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Versatile self-assembly systems to nanostructured materials in both solid and soln. were developed with common amphiphilic random copolymers bearing hydrophilic poly(ethylene glycol) (PEG) and hydrophobic cryst. octadecyl pendants. The copolymers efficiently induced precision self-assembly of the pendants to provide not only core-cryst., thermoresponsive micelles and vesicles in water and reverse micelles in hexane but also sub-10 nm lamellar or spherical microphase sepn. structure in solid. Typically, the solid random copolymers with 50-80 mol % octadecyl units formed lamellar structure of a hydrophilic PEG layer and a hydrophobic, cryst. octadecyl layer. Importantly, the domain spacing is about 5 nm, much smaller than that generally obtained with conventional block copolymers. The domain structure is controlled by compn., independent of chain length. The copolymers further gave various thermoresponsive, compartmentalized materials in aq. and org. media, where the 3D structure can be also controlled by the compn. and sample prepn. protocols.
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    53. 53
      Ilavsky, J.; Jemian, P. R. Irena : Tool Suite for Modeling and Analysis of Small-Angle Scattering. J. Appl. Crystallogr. 2009, 42 (2), 347– 353,  DOI: 10.1107/S0021889809002222
      53
      Irena: tool suite for modeling and analysis of small-angle scattering
      Ilavsky, Jan; Jemian, Peter R.
      Journal of Applied Crystallography (2009), 42 (2), 347-353CODEN: JACGAR; ISSN:0021-8898. (International Union of Crystallography)
      Irena, a tool suite for anal. of both x-ray and neutron small-angle scattering (SAS) data within the com. Igor Pro application, brings together a comprehensive suite of tools useful for studies in materials science, physics, chem., polymer science and other fields. In addn. to Guinier and Porod fits, the suite combines a variety of advanced SAS data evaluation tools for the modeling of size distribution in the dil. limit using max. entropy and other methods, dil. limit small-angle scattering from multiple noninteracting populations of scatterers, the pair-distance distribution function, a unified fit, the Debye-Bueche model, the reflectivity (x-ray and neutron) using Parratt's formalism, and small-angle diffraction. There are also a no. of support tools, such as a data import/export tool supporting a broad sampling of common data formats, a data modification tool, a presentation-quality graphics tool optimized for small-angle scattering data, and a neutron and x-ray scattering contrast calculator. These tools are brought together into one suite with consistent interfaces and functionality. The suite allows robust automated note recording and saving of parameters during export.
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    54. 54
      Horcas, I.; Fernández, R.; Gómez-Rodríguez, J. M.; Colchero, J.; Gómez-Herrero, J.; Baro, A. M. WSXM: A Software for Scanning Probe Microscopy and a Tool for Nanotechnology. Rev. Sci. Instrum. 2007, 78, 013705,  DOI: 10.1063/1.2432410
      54
      WSXM: a software for scanning probe microscopy and a tool for nanotechnology
      Horcas, I.; Fernandez, R.; Gomez-Rodriguez, J. M.; Colchero, J.; Gomez-Herrero, J.; Baro, A. M.
      Review of Scientific Instruments (2007), 78 (1), 013705/1-013705/8CODEN: RSINAK; ISSN:0034-6748. (American Institute of Physics)
      In this work we briefly describe the most relevant features of WSXM, a freeware scanning probe microscopy software based on MS-Windows. The article is structured in three different sections: The introduction is a perspective on the importance of software on scanning probe microscopy. The second section is devoted to describe the general structure of the application; in this section the capabilities of WSXM to read third party files are stressed. Finally, a detailed discussion of some relevant procedures of the software is carried out.
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    55. 55
      Kheshgi, S.; Scriven, L. E. Dewetting: Nucleation and Growth of Dry Regions. Chem. Eng. Sci. 1991, 46 (2), 519– 526,  DOI: 10.1016/0009-2509(91)80012-N
      55
      Dewetting: nucleation and growth of dry regions
      Kheshgi, Haroon S.; Scriven, L. E.
      Chemical Engineering Science (1991), 46 (2), 519-26CODEN: CESCAC; ISSN:0009-2509.
      Dewetting of a solid surface covered by a film of nonwetting liq. proceeds from a preexisting dry patch or edge or initiates from some film-thinning disturbance that grows until the film ruptures. Local thinning can be caused by evapn.; by drainage due to gravity or capillarity-driven flow, esp. from sharp surfaces; or by surface tension gradients, such as are caused by surfactants delivered by particles falling on the film. Once a nonwetting film is sufficiently thinned, conjoining (neg. disjoining) pressure can accelerate thinning until rupture. This catastrophic rupture is modeled by solving the Navier-Stokes system approximated for thickness variations over distances that are long compared with the mean film thickness, and augmented with conjoining pressure. Rupture leads to film retraction and formation of a dry patch. These phenomena are visualized via moire topog. Of special interest are local spreading disturbances, where airborne particles fall on the film surface; craters or dry patches often nucleate. Implications for coating operations are discussed.
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    56. 56
      Xue, L.; Han, Y. Inhibition of Dewetting of Thin Polymer Films. Prog. Mater. Sci. 2012, 57 (6), 947– 979,  DOI: 10.1016/j.pmatsci.2012.01.003
      56
      Inhibition of dewetting of thin polymer films
      Xue, Longjian; Han, Yanchun
      Progress in Materials Science (2012), 57 (6), 947-979CODEN: PRMSAQ; ISSN:0079-6425. (Elsevier Ltd.)
      A review. Strategies for the inhibition of dewetting of thin polymer films are reviewed. First, a brief introduction to the theory and the dynamics of dewetting of thin polymer films is given. Methods for the inhibition of dewetting of thin polymer films, including the modification of the substrate and the polymer, the crosslinking of the polymer and the addn. of an additive as well as their mechanisms for inhibition are discussed. The chem. modification of the substrate or the polymer itself and the phase sepn. increase the thermodn. stability of the system, while the crosslinking of the polymers reduces the mobility of the polymer chains, kinetically arresting the dewetting. The addn. of an additive appears to thermodynamically and kinetically inhibit the dewetting. Finally, the future outlook in this research field is highlighted.
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    57. 57
      Barsbay, M.; Güven, O.; Stenzel, M. H.; Davis, T. P.; Barner-Kowollik, C.; Barner, L. Verification of Controlled Grafting of Styrene from Cellulose via Radiation-Induced RAFT Polymerization. Macromolecules 2007, 40 (20), 7140– 7147,  DOI: 10.1021/ma070825u
      57
      Verification of Controlled Grafting of Styrene from Cellulose via Radiation-Induced RAFT Polymerization
      Barsbay, Murat; Gueven, Olgun; Stenzel, Martina H.; Davis, Thomas P.; Barner-Kowollik, Christopher; Barner, Leonie
      Macromolecules (Washington, DC, United States) (2007), 40 (20), 7140-7147CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      Reversible addn.-fragmentation chain transfer (RAFT) polymn. was applied to radiation-induced graft polymn. of styrene from cellulose. The grafting of styrene from cellulose substrates using the chain transfer agent cumyl phenyldithioacetate was confirmed by Raman and XPS, differential scanning calorimetery, thermogravimetric anal., SEM, and contact angle anal. Grafted polystyrene chains were cleaved from the cellulose surface by acidic hydrolysis of the cellulose. The no.-av. mol. wt. and polydispersity index of the grafted and the free (nongrafted) polystyrenes obtained under identical conditions were detd. by size exclusion chromatog. Grafted and nongrafted polystyrenes have almost the same (near theor.) mol. wt. and narrow polydispersity, thus proving for the first time the control of the grafting process mediated via RAFT without any prior functionalization of the surface.
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    58. 58
      Eisenberg, A.; Yokoyama, T.; Sambalido, E. Dehydration Kinetics and Glass Transition of Poly(Acrylic Acid). J. Polym. Sci. Part A-1 Polym. Chem. 1969, 7 (7), 1717– 1728,  DOI: 10.1002/pol.1969.150070714
      58
      Dehydration kinetics and glass transition of poly(acrylic acid)
      Eisenberg, Adi; Yokoyama, Tetsuo; Sambalido, Emma
      Journal of Polymer Science, Part A-1: Polymer Chemistry (1969), 7 (7), 1717-28CODEN: JPSPC3; ISSN:0449-296X.
      The kinetics of dehydration and decarboxylation as well as the glass transition temp. as a function of anhydride content were measured for poly(acrylic acid) (I). The glass transition of I is of the order of 103° and increases with increasing anhydride content, reaching an extrapolated value of 140° for the pure linear anhydride. Anhydride formation is a first-order reaction, as is also decarboxylation, the latter being much slower than the former. The rate consts. are: for dehydration, ka = 2.5 × 109 exp (-26,000/RT); for decarboxylation, kd = 2.9 × 108 exp (-27,000/RT). Anhydride formation occurs primarily by an intramol. process.
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    59. 59
      Chapin, E. C.; Ham, G. E.; Mills, C. L. Copolymerization. VII. Relative Rates of Addition of Various Monomers in Copolymerization. J. Polym. Sci. 1949, 4, 597– 604,  DOI: 10.1002/pol.1949.120040505
      59
      Copolymerization. VII. Relative rates of addition of various monomers in copolymerization
      Chapin, Earl C.; Ham, George E.; Mills, Charles L.
      Journal of Polymer Science (1949), 4 (), 597-604CODEN: JPSCAU; ISSN:0022-3832.
      cf. C.A. 43, 8736g; 42, 4151i. Data are presented on monomer reactivity in copolymerization for these 13 systems: styrene (I)-methacrylic acid (II), I-acrylic acid (III), vinylidene chloride (IV)-crotonic acid (V), vinyl acetate (VI)-V, acrylonitrile (VII)-vinyl 2-ethylhexoate (VIII), VII-vinyl formate (IX), VII-vinyl benzoate (X), VII-α-acetoxystyrene (XI), VII-allyl chloride (XII), IV-X, IV-methyl isopropenyl ketone (XIII), vinyl chloride (XIV)-vinyl isobutyl ether (XV), and I-citraconic anydride (XVI). The reactivity ratios, γ1 and γ2, for these copolymerizations were obtained by choosing values which gave the best curve fit on substitution in the differential copolymer equation. The azeotrope of the system I-II occurs at 74% II while that of I-III occurs at 48% III. By using the Price and Alfrey relationship for the consts. Q and e these values are interpreted as evidence of higher resonance stability of the radical adduct formed from II than from III and lower polarity of II than III. Azeotropes also occur in the systems VI-V, VII-XI, and I-XVI. The copolymerization of I and XVI yielded a copolymerization curve similar to that of I-maleic anhydride reported by Alfrey and Lavin (C.A. 40, 1149.2); evidently XVI is less reactive toward a I-free radical than maleic anhydride.
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    60. 60
      Mayadunne, R. T. A.; Rizzardo, E.; Chiefari, J.; Krstina, J.; Moad, G.; Postma, A.; Thang, S. H. Radical Polymerization in Two Steps. Macromolecules 2000, 33, 243– 245,  DOI: 10.1021/ma991451a
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      Living polymers by the use of trithiocarbonates as reversible addition-fragmentation chain transfer (RAFT) agents. ABA triblock copolymers by radical polymerization in two steps
      Mayadunne, Roshan T. A.; Rizzardo, Ezio; Chiefari, John; Krstina, Julia; Moad, Graeme; Postma, Almar; Thang, San H.
      Macromolecules (2000), 33 (2), 243-245CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      Trithiocarbonates RS-CS-SR', where R and R' are homolytic leaving groups, were used as effective reversible addn.-fragmentation chain transfer agents. Styrene, Me acrylate, Bu acrylate and Me methacrylate were polymd. in the presence of various trithiocarbonate compds. (R/R': Me/C(Me)2CN, Me/CH(Ph)COOH, benzyl/benzyl, and α-methylbenzyl/α-methylbenzyl) and mol. wt. and conversion data were detd. Homopolymers and block copolymers of controlled mol. wt. and narrow polydispersity were prepd. Important ABA triblock copolymers of predetd. mol. wt. are accessible in 2 steps.
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    61. 61
      Buzin, A. I.; Pyda, M.; Costanzo, P.; Matyjaszewski, K.; Wunderlich, B. Calorimetric Study of Block-Copolymers of Poly(n-Butyl Acrylate) and Gradient Poly(n-Butyl Acrylate-Co-Methyl Methacrylate). Polymer (Guildf). 2002, 43 (20), 5563– 5569,  DOI: 10.1016/S0032-3861(02)00358-0
      There is no corresponding record for this reference.
    62. 62
      Sanchez-Fernandez, A.; Edler, K. J.; Arnold, T.; Heenan, R. K.; Porcar, L.; Terrill, N. J.; Terry, A. E.; Jackson, A. J. Micelle Structure in a Deep Eutectic Solvent: A Small-Angle Scattering Study. Phys. Chem. Chem. Phys. 2016, 18 (20), 14063– 14073,  DOI: 10.1039/C6CP01757F
      62
      Micelle structure in a deep eutectic solvent: a small-angle scattering study
      Sanchez-Fernandez, A.; Edler, K. J.; Arnold, T.; Heenan, R. K.; Porcar, L.; Terrill, N. J.; Terry, A. E.; Jackson, A. J.
      Physical Chemistry Chemical Physics (2016), 18 (20), 14063-14073CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
      In recent years many studies into green solvents have been undertaken and deep eutectic solvents (DES) have emerged as sustainable and green alternatives to conventional solvents since they may be formed from cheap non-toxic org. precursors. In this study we examine amphiphile behavior in these novel media to test our understanding of amphiphile self-assembly within environments that have an intermediate polarity between polar and non-polar extremes. We have built on our recently published results to present a more detailed structural characterization of micelles of sodium dodecylsulfate (SDS) within the eutectic mixt. of choline chloride and urea. Here we show that SDS adopts an unusual cylindrical aggregate morphol., unlike that seen in water and other polar solvents. A new morphol. transition to shorter aggregates was found with increasing concn. The self-assembly of SDS was also investigated in the presence of water; which promotes the formation of shorter aggregates.
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    63. 63
      Gaillard, N.; Guyot, A.; Claverie, J. Block Copolymers of Acrylic Acid and Butyl Acrylate Prepared by Reversible Addition-Fragmentation Chain Transfer Polymerization: Synthesis, Characterization, and Use in Emulsion Polymerization. J. Polym. Sci. Part A Polym. Chem. 2003, 41 (5), 684– 698,  DOI: 10.1002/pola.10606
      63
      Block copolymers of acrylic acid and butyl acrylate prepared by reversible addition-fragmentation chain transfer polymerization: synthesis, characterization, and use in emulsion polymerization
      Gaillard, Nicolas; Guyot, Alain; Claverie, Jerome
      Journal of Polymer Science, Part A: Polymer Chemistry (2003), 41 (5), 684-698CODEN: JPACEC; ISSN:0887-624X. (John Wiley & Sons, Inc.)
      Amphiphilic block copolymers of poly(acrylic acid-b-Bu acrylate) (I) were prepd. by reversible addn.-fragmentation chain transfer polymn. in a one-pot reaction. I were characterized by NMR, static and dynamic light scattering, tensiometry, and size exclusion chromatog. The aggregation characteristics of I corresponded to those theor. predicted for a star micelle. In a Bu acrylate-Me methacrylate emulsion copolymn., low amts. of I could stabilize the latexes with solid contents up to 50%.
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    64. 64
      Chernikova, E. V.; Lysenko, E. A.; Serkhacheva, N. S.; Prokopov, N. I. Self-Assembly of Amphiphilic Block Copolymers during Reversible Addition-Fragmentation Chain Transfer Heterophase Polymerization: Problems, Achievements, and Outlook. Polym. Sci. - Ser. C 2018, 60 (2), 192– 218,  DOI: 10.1134/S1811238218020042
      64
      Self-Assembly of Amphiphilic Block Copolymers during Reversible Addition-Fragmentation Chain Transfer Heterophase Polymerization: Problems, Achievements, and Outlook
      Chernikova, E. V.; Lysenko, E. A.; Serkhacheva, N. S.; Prokopov, N. I.
      Polymer Science, Series C: Selected Topics (2018), 60 (S1), 192-218CODEN: PSSCCH; ISSN:1555-614X. (Pleiades Publishing, Ltd.)
      The formation of dispersions of amphiphilic block copolymer particles with the controlled morphol. via heterophase polymn. mediated by reversible addn.-fragmentation agents is considered. Variants of dispersion, emulsion, and seeded polymns. are analyzed, and the mechanism of this process is discussed. Special attention is focused on issues related to control over the morphol. of the formed particles immediately during synthesis and methods of its transformation in the resulting dispersions.
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    65. 65
      Chenal, M.; Rieger, J.; Vechambre, C.; Chenal, J.-M.; Chazeau, L.; Creton, C.; Bouteiller, L. Soft Nanostructured Films with an Ultra-Low Volume Fraction of Percolating Hard Phase. Macromol. Rapid Commun. 2013, 34, 1524– 1529,  DOI: 10.1002/marc.201300410
      65
      Soft Nanostructured Films with an Ultra-Low Volume Fraction of Percolating Hard Phase
      Chenal, Marion; Rieger, Jutta; Vechambre, Cyril; Chenal, Jean-Marc; Chazeau, Laurent; Creton, Costantino; Bouteiller, Laurent
      Macromolecular Rapid Communications (2013), 34 (19), 1524-1529CODEN: MRCOE3; ISSN:1022-1336. (Wiley-VCH Verlag GmbH & Co. KGaA)
      In this study, aq. emulsion polymn. of Bu acrylate is performed in batch conditions without surfactants using a poly(acrylic acid)-trithiocarbonate macro-RAFT agent to control the polymn. and to stabilize the emulsion. According to the polymn.-induced self-assembly (PISA) approach, well-defined amphiphilic PAA-b-PBA diblock copolymers form and self-assemble during synthesis to yield highly stable core-shell particles with an extremely thin hard PAA shell. For the first time, we report here the specific properties of films obtained from these particular latexes. After drying the aq. dispersion, tough and transparent films are obtained. Although the films are not chem. crosslinked, they do not dissolve in good solvents for PBA. Moreover, they remain transparent even after immersion in water. Rheol. shows that the films are both stiff and ductile, thanks to the nanostructured but very low vol. fraction (less than 3 wt%) of PAA forming a percolating network in the soft PBA. Compared with conventional core-shell-based films, this approach affords for the first time a route to a thin percolating honeycomb nanostructure with a sharp and strong interface between the two phases. The versatility of the synthetic procedure opens perspectives for a large range of functional materials.
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    66. 66
      Pedersen, J. S.; Gerstenberg, M. C. Scattering Form Factor of Block Copolymer Micelles. Macromolecules 1996, 29 (4), 1363– 1365,  DOI: 10.1021/ma9512115
      66
      Scattering Form Factor of Block Copolymer Micelles
      Pedersen, Jan Skov; Gerstenberg, Michael C.
      Macromolecules (1996), 29 (4), 1363-5CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      The form factor of a micelle model with a spherical core and Gaussian polymer chains attached to the surface was calcd. anal. and the results were compared to Monte Carlo simulations. Excluded vol. interactions between the core and the polymers were introduced in the simulations. The expansion of the coils due to this effect can be mimicked in the anal. calcns. by moving the center of mass of the chains away from the surface of the core. The anal. expression for the form factor has been used for analyzing small-angle scattering data.
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    67. 67
      Balmer, J. A.; Mykhaylyk, O. O.; Schmid, A.; Armes, S. P.; Fairclough, J. P. A.; Ryan, A. J. Characterization of Polymer-Silica Nanocomposite Particles with Core-Shell Morphologies Using Monte Carlo Simulations and Small Angle X-Ray Scattering. Langmuir 2011, 27 (13), 8075– 8089,  DOI: 10.1021/la201319h
      67
      Characterization of Polymer-Silica Nanocomposite Particles with Core-Shell Morphologies using Monte Carlo Simulations and Small Angle X-ray Scattering
      Balmer, Jennifer A.; Mykhaylyk, Oleksandr O.; Schmid, Andreas; Armes, Steven P.; Fairclough, J. Patrick A.; Ryan, Anthony J.
      Langmuir (2011), 27 (13), 8075-8089CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
      A two-population model based on std. small-angle x-ray scattering (SAXS) equations is verified for the anal. of core-shell structures comprising spherical colloidal particles with particulate shells. First, Monte Carlo simulations of core-shell structures are performed to demonstrate the applicability of the model. Three possible shell packings are considered: ordered silica shells due to either charge-dependent repulsive or size-dependent Lennard-Jones interactions or randomly arranged silica particles. In most cases, the two-population model produces an excellent fit to calcd. SAXS patterns for the simulated core-shell structures, together with a good correlation between the fitting parameters and structural parameters used for the simulation. The limits of application are discussed, and then, this two-population model is applied to the anal. of well-defined core-shell vinyl polymer/silica nanocomposite particles, where the shell comprises a monolayer of spherical silica nanoparticles. Comprehensive SAXS anal. of poly(styrene-co-Bu acrylate)/silica colloidal nanocomposite particles (prepd. by the in situ emulsion copolymn. of styrene and Bu acrylate in the presence of a glycerol-functionalized silica sol) allows the overall core-shell particle diam., the copolymer latex core diam. and polydispersity, the mean silica shell thickness, the mean silica diam. and polydispersity, the vol. fractions of the two components, the silica packing d., and the silica shell structure to be obtained. These exptl. SAXS results are consistent with electron microscopy, dynamic light scattering, TG, helium pycnometry, and BET surface area studies. The high electron d. contrast between the (co)polymer and the silica components, together with the relatively low polydispersity of these core-shell nanocomposite particles, makes SAXS ideally suited for the characterization of this system. Also, these results can be generalized for other types of core-shell colloidal particles.
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    68. 68
      Matsen, M. W.; Thompson, R. B. Equilibrium Behavior of Asymmetric ABA Triblock Copolymer Melts. J. Chem. Phys. 1999, 111, 7139,  DOI: 10.1063/1.480006
      68
      Equilibrium behavior of symmetric ABA triblock copolymer melts
      Matsen, M. W.; Thompson, R. B.
      Journal of Chemical Physics (1999), 111 (15), 7139-7146CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
      Melts of ABA triblock copolymer mols. with identical end blocks are examd. using SCF theory. Phase diagrams are calcd. and compared with those of homologous AB diblock copolymers formed by snipping the triblocks in half. This creates addnl. end segments which decreases the degree of segregation. Consequently, triblock melts remain ordered to higher temps. than their diblock counterparts. We also find that middle-block domains are easier to stretch than end-block domains. As a result, domain spacings are slightly larger, the complex phase regions are shifted towards smaller A-segment compns., and the perforated-lamellar phase becomes more metastable in triblock melts as compared to diblock melts. Although triblock and diblock melts exhibit very similar phase behavior, their mech. properties can differ substantially due to triblock copolymers that bridge between otherwise disconnected A domains. We evaluate the bridging fraction for lamellar, cylindrical, and spherical morphologies to be about 40%-45%, 60%-65%, and 75%-80%, resp. These fractions only depend weakly on the degree of segregation and the copolymer compn.
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    69. 69
      Ryan, A. J.; Mai, S. M.; Fairclough, J. P. A.; Hamley, I. W.; Booth, C. Ordered Melts of Block Copolymers of Ethylene Oxide and 1,2-Butylene Oxide. Phys. Chem. Chem. Phys. 2001, 3 (15), 2961– 2971,  DOI: 10.1039/b102784k
      69
      Ordered melts of block copolymers of ethylene oxide and 1,2-butylene oxide
      Ryan, Anthony J.; Mai, Shao-Min; Fairclough, J. Patrick A.; Hamley, Ian W.; Booth, Colin
      Physical Chemistry Chemical Physics (2001), 3 (15), 2961-2971CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
      An account is presented of recent work on specially synthesized diblock, triblock and cyclic block copolymers of ethylene oxide and 1,2-butylene oxide. Simultaneous small-angle X-ray scattering and differential scanning calorimetry have been used to investigate the effects of block architecture on the stabilities and structures of microphase-sepd. melts. Stable lamellar, hexagonal, body-centered cubic and gyroid phases were detected. Phase diagrams are compared, one with another and with those predicted by the exact self-consistent mean-field theory, and center-block stretching in lamellar phases is confirmed.
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    70. 70
      Mai, Y.; Eisenberg, A. Self-Assembly of Block Copolymers. Chem. Soc. Rev. 2012, 41 (18), 5969,  DOI: 10.1039/c2cs35115c
      70
      Self-assembly of block copolymers
      Mai, Yiyong; Eisenberg, Adi
      Chemical Society Reviews (2012), 41 (18), 5969-5985CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
      A review. Block copolymer (BCP) self-assembly has attracted considerable attention for many decades. The present tutorial review introduces the primary principles of BCP self-assembly in bulk and in soln., by describing expts., theories, accessible morphologies, etc.
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    71. 71
      Lynd, N. A.; Meuler, A. J.; Hillmyer, M. A. Polydispersity and Block Copolymer Self-Assembly. Prog. Polym. Sci. 2008, 33 (9), 875– 893,  DOI: 10.1016/j.progpolymsci.2008.07.003
      71
      Polydispersity and block copolymer self-assembly
      Lynd, Nathaniel A.; Meuler, Adam J.; Hillmyer, Marc A.
      Progress in Polymer Science (2008), 33 (9), 875-893CODEN: PRPSB8; ISSN:0079-6700. (Elsevier Ltd.)
      A review. Block copolymers consist of two or more chem. distinct polymers that are covalently bound. These materials self-assemble into fascinating mesostructures with features on the nanometer length scale and have been the subject of intense research interest for about four decades. These efforts have generally focused on model block copolymer systems where the mol. wt. distributions of all blocks are very narrow. Traditionally, many block copolymer systems have been prepd. by living anionic polymn. and thus usually exhibit narrow mol. wt. distributions in all blocks. Therefore, the assumption of monodisperse blocks that greatly simplifies theor. work is on solid exptl. ground. Prepn. of block copolymers with relatively broad mol. wt. distributions in one or more block has become increasingly common, however, as use of synthetic techniques such as controlled radical polymn. has proliferated. A review. Advances in these techniques have increased the no. of monomers readily incorporated into block copolymers and potentially will drive com. costs down. These polymn. strategies often, however, result in broader mol. wt. distributions than are typically obtained using living anionic, cationic, or metal-catalyzed techniques; understanding polydispersity effects should aid deployment of these block copolymers in advanced materials applications. This review describes both theor. and exptl. investigations of the effects of polydispersity on the melt-phase morphol. behavior of block copolymers. The summary includes research efforts focused on both continuous mol. wt. distributions and multicomponent blends. The review concludes with a summary and outlook on the potential utility of polydispersity as a tool to tune the morphol. behavior of block copolymers.
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    72. 72
      Stieger, M.; Pedersen, J. S.; Lindner, P.; Richtering, W. Are Thermoresponsive Microgels Model Systems for Concentrated Colloidal Suspensions? A Rheology and Small-Angle Neutron Scattering Study. Langmuir 2004, 20 (17), 7283– 7292,  DOI: 10.1021/la049518x
      72
      Are Thermoresponsive Microgels Model Systems for Concentrated Colloidal Suspensions? A Rheology and Small-Angle Neutron Scattering Study
      Stieger, Markus; Pedersen, Jan Skov; Lindner, Peter; Richtering, Walter
      Langmuir (2004), 20 (17), 7283-7292CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
      The structure of concd. temp.-sensitive poly(N-isopropylacrylamide) (PNiPAM) microgel suspensions has been investigated employing rheol. and small-angle neutron scattering (SANS). A previously described model expression for the particle form factor Pinho(q) is extended by a model hard sphere structure factor S(q), and the av. radial d. profiles φ(r) are calcd. from the amplitude of the form factor A(q) and the structure factor S(q). By this procedure, a direct real space description of the spatial ordering in the neighborhood of a single particle is obtained. The overall particle size and the correlation length ξ of the concn. fluctuations of the internal polymer network decrease with concn., revealing the increasing compression of the spheres. Thus, the particle form factor Pinho(q) of the swollen PNiPAM microgels depends on concn. The particle-particle interaction potential does not change significantly between 25 and 32 °C. Even approx. 1 K below the lower crit. soln. temp. (LCST), the exptl. scattering intensity distributions I(q)/c are described very well by the hard sphere structure factor when an equiv. hard sphere particle size RHS and vol. fraction ηHS are used. Microgels with different degrees of crosslinking and particle size resemble true hard sphere behavior up to effective vol. fractions of φeff < 0.35. At higher effective vol. fractions φeff > 0.35 strong deviations from true hard spheres are obsd. Interpenetration of the outer, less crosslinked regions of the soft spheres as well as particle compression occurred at higher concns. In agreement with this, the equil. colloidal phase behavior and rheol. also has some features of soft sphere systems. At temps. well above the LCST, the interaction potential becomes strongly attractive and the collapsed microgel spheres form aggregates consisting of flocculated particles without significant long-range order. Hence, an attractive interaction potential in concd. suspensions of PNiPAM microgels leads to distinctively different structures as compared to attractive hard sphere colloids. When the peculiar structural properties of the PNiPAM microgels are considered, they can be used as model systems in colloidal science.
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    73. 73
      De Kruif, C. G.; Briels, W. J.; May, R. P.; Vrij, A. Hard-Sphere Colloidal Silica Dispersions. the Structure Factor Determined with SANS. Langmuir 1988, 4 (3), 668– 676,  DOI: 10.1021/la00081a029
      73
      Hard-sphere colloidal silica dispersions. The structure factor determined with SANS
      De Kruif, C. G.; Briels, W. J.; May, R. P.; Vrij, A.
      Langmuir (1988), 4 (3), 668-76CODEN: LANGD5; ISSN:0743-7463.
      Small-angle neutron-scattering expts. were performed on the D11 instrument at Grenoble. The colloidal dispersions in cyclohexane studied contained silica particles sterically stabilized by octadecyl chains terminally grafted to the surface. From dil. dispersions the mean particle radius and the radius distribution were obtained. With these single-particle parameters the scattering behavior can be modeled with a hard-sphere interaction potential at all vol. fractions up to .vphi. = 0.4-0.5. Polydispersity effects on the representation of the structure factor were explicitly taken into account. These results confirm and amplify previous results on the modeling of a silica dispersion as a hard-sphere supramol. fluid.
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    74. 74
      Pedersen, J. S.; Gerstenberg, M. C. Scattering Form Factor of Block Copolymer Micelles. Macromolecules 1996, 29 (4), 1363– 1365,  DOI: 10.1021/ma9512115
      74
      Scattering Form Factor of Block Copolymer Micelles
      Pedersen, Jan Skov; Gerstenberg, Michael C.
      Macromolecules (1996), 29 (4), 1363-5CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      The form factor of a micelle model with a spherical core and Gaussian polymer chains attached to the surface was calcd. anal. and the results were compared to Monte Carlo simulations. Excluded vol. interactions between the core and the polymers were introduced in the simulations. The expansion of the coils due to this effect can be mimicked in the anal. calcns. by moving the center of mass of the chains away from the surface of the core. The anal. expression for the form factor has been used for analyzing small-angle scattering data.
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    75. 75
      Lesage De La Haye, J.; Martin-Fabiani, I.; Schulz, M.; Keddie, J. L.; D’Agosto, F.; Lansalot, M. Hydrophilic MacroRAFT-Mediated Emulsion Polymerization: Synthesis of Latexes for Cross-Linked and Surfactant-Free Films. Macromolecules 2017, 50 (23), 9315– 9328,  DOI: 10.1021/acs.macromol.7b01885
      75
      Hydrophilic MacroRAFT-Mediated Emulsion Polymerization: Synthesis of Latexes for Cross-Linked and Surfactant-Free Films
      Lesage de la Haye, Jennifer; Martin-Fabiani, Ignacio; Schulz, Malin; Keddie, Joseph L.; D'Agosto, Franck; Lansalot, Muriel
      Macromolecules (Washington, DC, United States) (2017), 50 (23), 9315-9328CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      A major drawback of conventional emulsion polymers arises from the presence of migrating low molar mass surfactants that contribute to poor water barrier properties and low adhesion to substrates. In this paper, we demonstrate how living polymer chains obtained by reversible addn.-fragmentation chain transfer (RAFT) can be used as an efficient stabilizer in emulsion polymn., leading to the prodn. of surfactant-free latexes, which then form crosslinked films with beneficial properties. Hydrophilic poly(methacrylic acid) (PMAA) chains obtained by RAFT performed in water are used to mediate emulsion polymn. and produce film-forming latex particles from mixts. of Me methacrylate, Bu acrylate, and styrene. Stable dispersions of particles with sizes between 100 and 200 nm are obtained, with very low amts. of coagulum (<0.5 wt. %). The particles are stabilized by the PMAA segment of amphiphilic block copolymers formed during the polymn. Remarkably, low amts. of PMAA chains (from 1.5 down to 0.75 wt. %) are enough to ensure particle stabilization. Only traces of residual PMAA macroRAFT agents are detected in the final latexes, showing that most of them are successfully chain extended and anchored on the particle surface. The glass transition temp. of the final material is adjusted by the compn. of the hydrophobic monomer mixt. so that film formation occurs at room temp. Conventional crosslinking strategies using addnl. hydrophobic comonomers, such as 1,3-butanediol diacrylate (BuDA), diacetone acrylamide (DAAm), and (2-acetoacetoxy)ethyl methacrylate (AAEM), are successfully applied to these formulations as attested by gel fractions of 100%. When particles are internally crosslinked with BuDA, chain interdiffusion between particles is restricted, and a weak and brittle film is formed. In contrast, when DAAm-contg. chains undergoes crosslinking during film formation, full coalescence is achieved along with the creation of a crosslinked network. The resulting film has a higher Young's modulus and tensile strength as a result of crosslinking. This synthetic strategy advantageously yields a surfactant-free latex that can be formed into a film at room temp. with mech. properties that can be tuned via the crosslinking d.
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    76. 76
      Martín-Fabiani, I.; Lesage De La Haye, J.; Schulz, M.; Liu, Y.; Lee, M.; Duffy, B.; D’Agosto, F.; Lansalot, M.; Keddie, J. L. Enhanced Water Barrier Properties of Surfactant-Free Polymer Films Obtained by MacroRAFT-Mediated Emulsion Polymerization. ACS Appl. Mater. Interfaces 2018, 10 (13), 11221– 11232,  DOI: 10.1021/acsami.8b01040
      76
      Enhanced Water Barrier Properties of Surfactant-Free Polymer Films Obtained by MacroRAFT-Mediated Emulsion Polymerization
      Martin-Fabiani, Ignacio; Lesage de la Haye, Jennifer; Schulz, Malin; Liu, Yang; Lee, Michelle; Duffy, Brendan; D'Agosto, Franck; Lansalot, Muriel; Keddie, Joseph L.
      ACS Applied Materials & Interfaces (2018), 10 (13), 11221-11232CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
      The presence of low-molar-mass surfactants in latex films results in detrimental effects on their water permeability, gloss, and adhesion. For applications such as coatings, there is a need to develop formulations that do not contain surfactants and have better water barrier properties. Having previously reported the synthesis of surfactant-free latex particles in water using low amts. (<2 wt %) of chains synthesized by controlled radical polymn., here we study the water barrier properties of films made from these particles and their application in anticorrosion coatings. When films cast from aq. dispersions of acrylate copolymer particles stabilized with poly(sodium 4-styrenesulfonate) (PSSNa) were immersed in water for 3 days, they sorbed only 4 wt % water. This uptake is only slightly higher than the value predicted for the pure copolymer, indicating that the neg. effects of any particle boundaries and hydrophilic-stabilizing mols. are minimal. This sorption of liq. water is 5 times lower than what is found in films cast from particles stabilized with the same proportion of poly(methacrylic acid) (PMAA), which is more hydrophilic than PSSNa. In water vapor with 90% relative humidity, the PSSNa-based film had an equil. sorption of only 4 wt %. A small increase in the PMAA content has a strong and neg. impact on the barrier properties. NMR relaxometry on polymer films after immersion in water shows that water clusters have the smallest size in the films contg. PSSNa. Furthermore, these films retain their optical clarity during immersion in liq. water for up to 90 min, whereas all other compns. quickly develop opacity ("water whitening") as a result of light scattering from sorbed water. This implies a remarkably complete coalescence and a very small d. of defects, which yields properties matching those of some solvent-borne films. The latex stabilized with PSSNa is implemented as the binder in a paint formulation for application as an anticorrosive barrier coating on steel substrates and evaluated in accelerated weathering and corrosion tests. Our results demonstrate the potential of self-stabilized latex particles for the development of different applications, such as waterborne protective coatings and pressure-sensitive adhesives.
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    77. 77
      Singh, K. B.; Tirumkudulu, M. S. Cracking in Drying Colloidal Films. Phys. Rev. Lett. 2007, 98 (21), 218302,  DOI: 10.1103/PhysRevLett.98.218302
      77
      Cracking in Drying Colloidal Films
      Singh, Karnail B.; Tirumkudulu, Mahesh S.
      Physical Review Letters (2007), 98 (21), 218302/1-218302/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)
      It has long been known that thick films of colloidal dispersions such as wet clays, paints, and coatings crack under drying. Although capillary stresses generated during drying have been recently identified as the cause for cracking, the existence of a max. crack-free film thickness that depends on particle size, rigidity, and packing has not been understood. Here, we identify two distinct regimes for crack-free films based on the magnitude of compressive strain at the max. attainable capillary pressure and show remarkable agreement of measurements with our theory. We anticipate our results to not only form the basis for design of coating formulations for the paints, coatings, and ceramics industry but also assist in the prodn. of crack-free photonic band gap crystals.
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    78. 78
      Roberts, C. C.; Francis, L. F. Drying and Cracking of Soft Latex Coatings. J. Coatings Technol. Res. 2013, 10 (4), 441– 451,  DOI: 10.1007/s11998-012-9425-7
      78
      Drying and cracking of soft latex coatings
      Roberts, Christine C.; Francis, Lorraine F.
      Journal of Coatings Technology and Research (2013), 10 (4), 441-451CODEN: JCTRCP; ISSN:1935-3804. (Springer)
      The min. film formation temp. (MFFT) is the min. drying temp. needed for a latex coating to coalesce into an optically clear, dense crack-free film. To better understand the interplay of forces near this crit. temp., cryogenic SEM (cryoSEM) was used to track the latex particle deformation and water migration in coatings dried at temps. just above and below the MFFT. Although the latex particles completely coalesced at both temps. by the end of the drying process, it was discovered that particle deformation during the early drying stages was drastically different. Below the MFFT, cracks initiated just as menisci began to recede into the packing of consolidated particles, whereas above the MFFT, partial particle deformation occurred before menisci entered the coating and cracks were not obsd. The spacing between cracks measured in coatings dried at varying temps. decreased with decreasing drying temp. near the MFFT, whereas it was independent of temp. below a crit. temp. Finally, the addn. of small amts. of silica aggregates was found to lessen the cracking of latex coatings near the MFFT without adversely affecting their optical clarity.
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    79. 79
      Cowie, J. M. G.; Arrighi, V. Polymers: Chemistry and Physics of Modern Materials, 3rd ed.; CRC Press: Boca Raton, 2007.
      There is no corresponding record for this reference.

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