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Synthesis of High Molecular Weight Water-Soluble Polymers as Low-Viscosity Latex Particles by RAFT Aqueous Dispersion Polymerization in Highly Salty Media

Cite this: Macromolecules 2022, 55, 17, 7380–7391
Publication Date (Web):August 28, 2022
https://doi.org/10.1021/acs.macromol.2c01071

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Abstract

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We report the synthesis of sterically-stabilized diblock copolymer particles at 20% w/w solids via reversible addition–fragmentation chain transfer (RAFT) aqueous dispersion polymerization of N,N′-dimethylacrylamide (DMAC) in highly salty media (2.0 M (NH4)2SO4). This is achieved by selecting a well-known zwitterionic water-soluble polymer, poly(2-(methacryloyloxy)ethyl phosphorylcholine) (PMPC), to act as the salt-tolerant soluble precursor block. A relatively high degree of polymerization (DP) can be targeted for the salt-insoluble PDMAC block, which leads to the formation of a turbid free-flowing dispersion of PDMAC-core particles by a steric stabilization mechanism. 1H NMR spectroscopy studies indicate that relatively high DMAC conversions (>99%) can be achieved within a few hours at 30 °C. Aqueous GPC analysis indicates high blocking efficiencies and unimodal molecular weight distributions, although dispersities increase monotonically as higher degrees of polymerization (DPs) are targeted for the PDMAC block. Particle characterization techniques include dynamic light scattering (DLS) and electrophoretic light scattering (ELS) using a state-of-the-art instrument that enables accurate ζ potential measurements in a concentrated salt solution. 1H NMR spectroscopy studies confirm that dilution of the as-synthesized dispersions using deionized water lowers the background salt concentration and hence causes in situ molecular dissolution of the salt-intolerant PDMAC chains, which leads to a substantial thickening effect and the formation of transparent gels. Thus, this new polymerization-induced self-assembly (PISA) formulation enables high molecular weight water-soluble polymers to be prepared in a highly convenient, low-viscosity form. In principle, such aqueous PISA formulations are highly attractive: there are various commercial applications for high molecular weight water-soluble polymers, while the well-known negative aspects of using a RAFT agent (i.e., its cost, color, and malodor) are minimized when targeting such high DPs.

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Introduction

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It is well-known that reversible addition-fragmentation chain transfer (RAFT) polymerization enables the synthesis of a wide range of functional vinyl polymers with good control over the molecular weight distribution. (1−4) There are many literature examples of RAFT solution homopolymerization and, in some cases, mean degrees of polymerization (DP) up to (and even beyond) 10,000 have been targeted. (5−7) This latter aspect is interesting for two reasons. First, in the case of water-soluble polymers (e.g., polyacrylamide), such high molecular weights are useful for commercial applications such as flocculants, binders, or thickeners. (8−10) Second, the main disadvantage of RAFT chemistry is that the chain transfer agent is an organosulfur compound, which is relatively expensive and confers both malodor and color. (11) Since the mean DP is inversely proportional to the concentration of this RAFT agent, (12) targeting very high DPs minimizes the problems associated with its use, which could make a decisive difference to the feasibility of industrial scale-up. (13)
However, the synthesis of high molecular weight water-soluble polymers via RAFT aqueous solution polymerization leads to extremely viscous reaction mixtures. For example, gel formation was reported by Destarac and co-workers when preparing polyacrylamide with a mean DP of around 10,000. (6) Such gels can be difficult to remove from the reaction vessel after the polymerization, and heat dissipation during polymerization can become inefficient. In principle, this problem could be addressed by conducting such polymerizations in highly salty media. Under such conditions, the water-soluble polymer chains become insoluble, which leads to the formation of low-viscosity, free-flowing particulate dispersions rather than highly viscous or gel-like aqueous solutions. (14) Indeed, this approach is used to prepare high molecular weight polyacrylamide in the form of particles via conventional free radical polymerization conducted in aqueous solution in the presence of 2.0 M ammonium sulfate. (15−17)
Polymerization-induced self-assembly (PISA) involves the growth of an insoluble block from a soluble precursor block in a suitable solvent. In the case of an aqueous PISA formulation, the growing second block becomes water-insoluble while the first block remains water-soluble: the resulting amphiphilic diblock copolymer chains undergo micellar nucleation and ultimately sterically-stabilized diblock copolymer nanoparticles are produced. Depending on the aqueous solubility of the monomer used to generate the hydrophobic block, aqueous PISA formulations can involve either RAFT aqueous emulsion polymerization (18−20) or RAFT aqueous dispersion polymerization. (21−26) In both cases, the hydrophobic block normally remains insoluble at the end of the polymerization. However, there are several literature examples in which a temperature switch leads to in situ nanoparticle dissolution to yield molecularly dissolved diblock copolymer chains. (27−29) We hypothesized that a similar approach might involve the synthesis of a salt-intolerant water-soluble polymer in highly salty media to produce low-viscosity particles. Subsequent dilution using pure water would then lower the salt concentration in the aqueous continuous phase, which should lead to the molecular dissolution of the high molecular weight copolymer chains within the particle cores and hence a strong thickening effect (see Scheme 1).

Scheme 1

Scheme 1. Schematic Cartoon and Corresponding Digital Images to Illustrate the Sterically Stabilized Diblock Copolymer Particles in the Presence of 2.0 M Ammonium Sulfate Obtained after RAFT Aqueous Dispersion Polymerization of a Suitable Water-Soluble Monomer to Form the “Salted Out” Red Chainsa
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aA four-fold dilution with deionized water lowers the salt concentration of the initial aqueous dispersion and results in molecular dissolution of these particles, with the concomitant formation of a highly viscous transparent aqueous solution.

According to well-established principles in colloid science, steric stabilization is much more likely to be effective than charge stabilization for such aqueous PISA syntheses. (30−32) Clearly, such formulations would require a steric stabilizer that remains soluble in the presence of substantial amounts of salt to confer effective colloidal stabilization. According to the literature, suitable salt-tolerant water-soluble polymeric stabilizers are likely to be either certain types of polyelectrolytes (16,17,33,34) or polybetaines. (35−37)
Herein, we report the RAFT aqueous dispersion polymerization of N,N′-dimethylacrylamide (DMAC) in highly salty media using poly(2-(methacryloyloxy)ethyl phosphorylcholine) (PMPC) as a salt-tolerant steric stabilizer. According to the literature, PMPC remains soluble even in the presence of 5.0 M NaCl. (35) This approach is then extended to include polyelectrolytic steric stabilizers.

Experimental Section

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Materials

2-(Methacryloyloxy)ethyl phosphorylcholine (MPC) was kindly donated by Biocompatibles (U.K.), and ammonium sulfate was purchased from Alfa Aesar (U.K.) and Eisen-Golden Laboratories (CA). 2-Ethylhexanoyl tert-butyl peroxide (T21S) was obtained from AkzoNobel (Netherlands), potassium hydroxide was obtained from LabChem (PA), and 2,2′-azobis(2-imidazolinylpropane) dihydrochloride (VA-044) was obtained from Fluorochem (U.K.). N,N′-Dimethylacrylamide (DMAC), ascorbic acid (AsAc), potassium persulfate (KPS), 4,4′-azobis(4-cyanopentanoic acid) (ACVA), azobis(isobutyl)amidine dihydrochloride (AIBA), CH3COOH, NaH2PO4, NaNO3, KOH, a 50% solution of 2-acrylamido-2-methyl-1-propanesulfonic acid sodium salt (AMPS), phosphate buffer solution (PBS) tablets, and D2O were purchased from Sigma-Aldrich (U.K.). Each of these chemicals was used as received.
2-(Acryloyloxy)ethyl trimethylammonium chloride (ATAC) was donated by BASF (Germany) in the form of an 80% w/w aqueous solution. 4-Cyano-4-(2-phenylethanesulfanylthiocarbonyl)-sulfanylpentanoic acid (PETTC) was prepared and purified as reported elsewhere, (38) as was 2-(((butylthio)carbonothioyl)thio)-2-methylpropanoic acid (BDMAT). (39,40) All solvents were purchased from Fisher Scientific (U.K.) and were used as received.

Synthesis Protocols

Synthesis of the PMPC139 Precursor via RAFT Solution Polymerization of 2-(Methacryloyloxy)ethyl phosphorylcholine (MPC) in Methanol at 64 °C

PETTC (250 mg, 0.74 mmol), MPC (26.10 g, 88.4 mmol), ACVA (41 mg, 150 μmol), and methanol (49.0 g, corresponding to a 35% w/w solution) were weighed into a 250 mL round-bottom flask charged with a magnetic flea and this reaction solution was degassed using nitrogen gas for 45 min at 20 °C. The sealed flask was immersed into an oil bath set at 64 °C for 210 min, and the polymerization was subsequently quenched by exposing the reaction mixture to air while cooling to 20 °C. The final MPC conversion was 75%, as judged by 1H NMR spectroscopy (calculated by comparing the integrated vinyl signals assigned to the MPC monomer at 5.6–6.2 ppm to the integrated polymethacrylic backbone signals at 0.6–2.4 ppm). The reaction solution was precipitated into a ten-fold excess of acetone. The crude PMPC precursor was redissolved in methanol, and the precipitation was repeated. After dissolution using deionized water, the resulting aqueous polymer solution was freeze-dried overnight. The degree of polymerization was 135 ± 10, as judged by 1H NMR spectroscopy (calculated by comparing the integrated aromatic signals assigned to the RAFT end-group at 7.1–7.4 ppm to the integrated polymethacrylic backbone signals at 0.6–2.4 ppm). RAFT end-group analysis using UV spectroscopy indicated a mean degree of polymerization of 139 ± 1 (the Beer–Lambert plot for PETTC is provided in Figure S1). Aqueous GPC analysis indicated an Mn of 17 kg mol–1 and an Mw/Mn of 1.18 (see below for eluent and calibration details).

Preparation of 2.0 M Ammonium Sulfate Solution and Redox Initiator Solutions

Ammonium sulfate (26.43 g) was added to a 100 mL volumetric flask, which was subsequently filled with water to obtain a 2.0 M solution. The required molarity, refractive index, and dynamic viscosity for an aqueous solution of 2.0 M ammonium sulfate were calculated by interpolation of tabulated solution properties reported at 20 °C as recorded in Table S1. (41) The interpolated dynamic viscosity was estimated to 25 °C using the ratio of the dynamic viscosity for water at 20 and 25 °C. The following numerical values for a 2.0 M aqueous solution of ammonium sulfate were used in this study: molality = 2.32 mol kg–1; refractive index = 1.370, and dynamic viscosity = 1.367 × 10–3 kg m–1 s–1. The relative permittivity of a 2.0 M aqueous solution of ammonium sulfate was assumed to be that of pure water. According to the literature, the addition of salt leads to a lower relative permittivity compared to that of water. (42) However, this systematic error is not considered to be important relative to the likely error incurred when calculating the ζ potential for electrosterically-stabilized nanoparticles (43) (see Results and Discussion for further details).
KPS (30.0 mg) was dissolved in an aqueous solution of 2.0 M ammonium sulfate (30 g) to make up a 0.1% w/w KPS stock solution. Similarly, AsAc (30.0 mg) was dissolved in an aqueous solution of 2.0 M ammonium sulfate (30 g) to make up a 0.1% w/w AsAc stock solution. Each stock solution was stored in a refrigerator at 4 °C prior to use.

Synthesis of PMPC139–PDMACx Diblock Copolymer Particles via RAFT Aqueous Dispersion Polymerization of N,N′-Dimethylacrylamide (DMAC) in 2 M Ammonium Sulfate at 30 °C

A typical protocol for the synthesis of PMPC139–PDMAC5000 spheres at 20% w/w solids was conducted as follows. The PMPC139 precursor (140 mg, 4.0 μmol), DMAC (1.972 g, 19.9 mmol), the 0.1% aqueous solution of KPS (270 mg, 1.0 μmol), and an aqueous solution of 2.0 M ammonium sulfate (8.00 g) were weighed into a 25 mL round-bottom flask charged with a magnetic flea and this reaction solution was degassed using nitrogen gas for 30 min at 20 °C. The sealed flask was immersed into an oil bath set at 30 °C, and a 0.1% aqueous solution of AsAc (170 mg, 1.0 μmol) was added to initiate the DMAC polymerization. After 18 h, the polymerization was subsequently quenched by exposing the reaction mixture to air while cooling to 20 °C. The final DMAC conversion was more than 99%, as judged by 1H NMR spectroscopy (as calculated by comparing the integrated vinyl signals assigned to the DMAC monomer at 5.6–6.7 ppm to the integrated polyacrylamide backbone signals at 1.1–2.7 ppm). Aqueous GPC analysis indicated an Mn of 262 kg mol–1 and an Mw/Mn of 1.97 (see below for eluent and calibration details).

Synthesis of PATAC195–PDMAC1000 Diblock Copolymer Particles via RAFT Aqueous Dispersion Polymerization

PETTC (290 mg, 0.85 mmol), ATAC (80% w/w in water) (41.35 g, 170 mmol), AIBA (46 mg, 170 μmol), and methanol (50.1 g, corresponding to a 40% w/w solution) were weighed into a 250 mL round-bottom flask charged with a magnetic flea, and this reaction solution was degassed using nitrogen gas for 45 min at 20 °C. The sealed flask was immersed into an oil bath set at 56 °C for 120 min, and the polymerization was then quenched by exposing the reaction mixture to air while cooling to 20 °C. The final ATAC conversion was 97%, as judged by 1H NMR spectroscopy (calculated by comparing the integrated vinyl signals assigned to the ATAC monomer at 5.8–6.4 ppm to the integrated polyacrylic backbone signals at 1.3–2.7 ppm). Excess water was added, and the methanol was removed under reduced pressure. Afterward, the reaction solution was purified by dialysis over 3 days with regular water changes. The resulting aqueous polymer solution was freeze-dried overnight. The degree of polymerization was 195, as judged by 1H NMR spectroscopy (calculated by comparing the integrated aromatic signals assigned to the RAFT end-group at 7.1–7.4 ppm to the integrated polyacrylic backbone signals at 1.3–2.7 ppm). Aqueous GPC analysis indicated an Mn of 34 kg mol–1 and an Mw/Mn of 1.20 (see below for eluent and calibration details).
Subsequently, the PATAC195 precursor (120 mg, 3.2 μmol), DMAC (312 mg, 3.15 mmol), a 0.1% aqueous solution of VA-044 (339 mg, 1.0 μmol), and an aqueous solution of 2.0 M sulfate (3.55 g) were weighed into a 10 mL round-bottom flask charged with a magnetic stirrer, and this reaction solution was degassed using nitrogen gas for 30 min at 20 °C. The sealed flask was immersed into an oil bath set at 48 °C to initiate the DMAC polymerization. After 18 h, the polymerization was quenched by exposing the reaction mixture to air while cooling to 20 °C. The final DMAC conversion was more than 99%, as judged by 1H NMR spectroscopy (as calculated by comparing the integrated vinyl signals assigned to the DMAC monomer at 5.6–6.7 ppm to the integrated polyacrylamide backbone signals at 1.1–2.7 ppm). Aqueous GPC analysis indicated an Mn of 68 kg mol–1 and an Mw/Mn of 1.95 (see below for eluent and calibration details).

Synthesis of PAMPS250–PDMAC1000 Diblock Copolymer Particles via RAFT Aqueous Dispersion Polymerization

BDMAT (150 mg, 0.59 mmol), AMPS (55% w/w) (61.92 g, 149 mmol), T21S (25.7 mg, 119 μmol), and 1.0 M PBS (23.5 g, corresponding to a 40% w/w solution) were weighed into a 250 mL round-bottom flask charged with a magnetic flea, and this reaction solution was degassed using nitrogen gas for 45 min at 20 °C. The sealed flask was immersed into an oil bath set at 90 °C for 150 min and the polymerization was subsequently quenched by exposing the reaction mixture to air while cooling to 20 °C. The final AMPS conversion was 99% as judged by 1H NMR spectroscopy (calculated by comparing the integrated vinyl signals assigned to the AMPS monomer at 5.6–6.2 ppm to the integrated polyacrylic backbone signals at 1.2–2.3 ppm). The reaction solution was purified by dialysis against water for three days. The resulting aqueous polymer solution was freeze-dried overnight. The degree of polymerization was 250 as judged by 1H NMR spectroscopy (calculated by comparing the integrated methyl signals assigned to the RAFT end-group at 0.8–0.9 ppm to the integrated acrylic backbone signals at 1.2–2.3 ppm). Aqueous GPC analysis indicated an Mn of 28 kg mol–1 and an Mw/Mn of 1.35 (see below for eluent and calibration details).
Subsequently, the PAMPS250 precursor (220 mg, 3.8 μmol), DMAC (379 mg, 3.82 mmol), a 0.1% aqueous solution of VA-044 (344 mg, 1.3 μmol), and an aqueous solution of 2.0 M (NH4)2SO4 (2.05 g) were weighed into a 10 mL round-bottom flask charged with a magnetic stirrer, and this reaction solution was degassed using nitrogen gas for 30 min at 20 °C. The sealed flask was immersed into an oil bath set at 48 °C to initiate the DMAC polymerization. After 18 h, the polymerization was quenched by exposing the reaction mixture to air while cooling to 20 °C. The final DMAC conversion was more than 99% as judged by 1H NMR spectroscopy (calculated by comparing the integrated vinyl signals assigned to the DMAC monomer at 5.6–6.7 ppm to the integrated polyacrylamide backbone signals at 1.1–2.7 ppm). Aqueous GPC analysis indicated an Mn of 74 kg mol–1 and an Mw/Mn of 1.54 (see below for eluent and calibration details).

Preparation of Dilute Aqueous Dispersions for DLS and ζ Potential Studies

Aqueous dispersions of PMPC139–PDMAC1000, PATAC195–PDMAC1000, and PAMPS250–PDMAC1000 particles in 2.0 M ammonium sulfate were diluted to 0.1% w/w using 2.0 M ammonium sulfate, which had been adjusted to an apparent pH of 3.

Preparation of Titrant Solutions

A stock titrant solution was prepared gravimetrically comprising an aqueous solution of 1.0 M KOH (22.97 g), deionized water (99.98 g), and ammonium sulfate (30.40 g). Deionized water was filtered through a 0.2 μm polyethersulfone syringe filter prior to use.

Characterization Methods

1H NMR Spectroscopy

Spectra were recorded at 25 °C in D2O using a 400 MHz Bruker Avance-400 spectrometer with 64 scans being averaged per spectrum.

Gel Permeation Chromatography (GPC)

Molecular weights and dispersities were determined for the various homopolymers and diblock copolymers using an Agilent 1260 Infinity GPC instrument. The setup comprised a pump, a degasser, three columns in series (PL-Aquagel Mixed-H, OH-30, and OH-40), and a refractive index detector. The column and detector temperature was set at 30 °C, and the flow rate was 1.0 mL min–1. Calibration was achieved using nine near-monodisperse poly(ethylene oxide) standards (2.1–969 kDa), and data were analyzed using Agilent Technologies GPC/SEC software. For PMPCx and its copolymers, the eluent was an aqueous solution containing 0.20 M NaNO3 and 0.05 M Trizma buffer at pH 7.0. For PATACx and its copolymers, the eluent was an aqueous solution containing 0.50 M CH3COOH and 0.30 M NaH2PO4 at pH 2.0. For PAMPSx and its copolymers, the eluent was a 70% v/v aqueous solution containing 0.20 M NaNO3 and 0.01 M NaH2PO4 at pH 7.0, with 30% v/v methanol.

Potentiometric Titration

An acidified aqueous dispersion (25.0 mL) was placed in a 250 mL glass beaker and stirred with a magnetic flea. Titrant solution was passed through a 0.2 μm polyethersulfone syringe filter into a volumetric 50 mL burette and a standard glass pH electrode was immersed within the aqueous dispersion. A total titrant of 7.0 mL was added in aliquots of no more than 0.5 mL, with smaller aliquots being used where necessary to accurately determine the equivalence point. The apparent pH of the aqueous dispersion was recorded after adding each aliquot, with pH equilibration being achieved within 30 s of each addition. All measurements were performed at 22 ± 1 °C. Approximately 0.25 mL of the aqueous dispersion was removed at suitable intervals for electrophoretic light scattering (ELS) and dynamic light scattering (DLS) analyses. No attempt was made to remove dissolved CO2 or to prevent its dissolution into the samples. It was assumed that the samples were near to or at the saturation level of dissolved CO2.

Dynamic Light Scattering (DLS)

Hydrodynamic diameters were determined using a Zetasizer Nano ZS (Malvern Panalytical, Malvern, U.K.). Samples were analyzed without further dilution, and three measurements were made in each case at a scattering angle of 173°. The instrument was configured to automatically determine the experimental duration and optical attenuation. The experimental correlation functions were analyzed using the cumulants method to yield the z-average hydrodynamic diameter (Dz) and polydispersity index (PDI). The Stokes–Einstein equation was employed, which is valid for dilute, noninteracting, and monodisperse spheres. Method 1 involved using a quartz cuvette (10 mm path length; volume = 1.00 mL) and 0.05% w/w aqueous copolymer dispersions were analyzed at 20 °C. Method 2 involved using disposable polystyrene semi-micro cuvettes (4 mm path length; volume = 0.25 mL) and 0.1% w/w aqueous copolymer dispersions were analyzed at 25 °C.

Electrophoretic Light Scattering (ELS)

Electrophoretic mobilities were determined by electrophoretic light scattering (NG-ELS) using an instrument provided by Enlighten Scientific LLC (Hillsborough, NC). The functional design and operation of this instrument are similar to the original phase analysis light scattering (PALS) apparatus (44) that employed a crossed-beam optical configuration in contrast to the more common reference beam configuration used for other ELS instruments. The electrode assembly used for the NG-ELS equipment is similar to that described by Uzgiris. (45) Disposable polystyrene semi-micro cuvettes (4 mm path length; volume = 0.25 mL) were used as the sample holders. Two identical parallel plate platinized platinum (46) electrodes, placed 4 mm apart, were used to provide the driving voltage. The sample temperature was determined using a miniature NTC-type thermistor placed in direct contact with an ≈0.1% w/w aqueous copolymer dispersion. This temperature sensor was positioned at the mid-point between the electrodes and approximately 1 mm above the intersection point of the two laser beams. Temperature control was achieved by placing the sample cuvette in an aluminum block that ensured efficient heat transfer with the (cooler) water circulating through channels within the block. The water temperature depended on the amount of Joule heating of the sample and hence on both the sample conductivity and the voltage applied across the electrodes. Complex impedance analysis of the electrode waveform was used to quantify electrode polarization and Joule heating. Mobility measurements were made using sinusoidal electrode signal waveforms with a nominal amplitude of 4.5 V at frequencies of 64 and 128 Hz. Small adjustments (up to ± 0.3 V) to the amplitude were made prior to data collection to ensure that the cell temperature remained at 25 ± 1 °C during each measurement. The scattered light was analyzed using both the PALS and the laser Doppler electrophoresis (LDE) methods simultaneously. Data were collected for 1 min, and the same data set was used to calculate the electrophoretic mobility by each method. For each sample, five independent measurements were made at each electrode signal frequency, yielding a total of ten measurements per sample from which a mean value was calculated.

Small-Angle X-Ray Scattering (SAXS)

SAXS patterns were recorded for 1.0% w/w aqueous copolymer dispersions at Diamond Light Source (station I22, Didcot, U.K.) using a monochromatic X-ray beam (λ = 0.124 nm), a two-dimensional (2D) Pilatus 2M pixel detector (Dectris, Switzerland), and a q range of 0.02–2.00 nm–1, where q = (4π sin θ)/λ corresponds to the modulus of the scattering vector, and θ is half of the scattering angle. SAXS data were reduced (integrated, normalized, and background-subtracted) using Dawn software supplied by Diamond Light Source. The X-ray scattering intensity for water was used for absolute scale calibration of the scattering patterns with data manipulation via SAXS Utilities software. Irena SAS macros for Igor Pro were utilized for modeling.

Optical Microscopy (OM)

Images were recorded at ×400 magnification using a Cole-Parmer bifocal compound microscope equipped with a Moticam-BTW digital camera.

UV Absorption Spectroscopy

Spectra were recorded between 200 and 400 nm using a PC-controlled UV-1800 spectrophotometer at 25 °C using a 1 cm path length quartz cell. A Beer–Lambert curve was constructed using a series of five PETTC solutions in methanol. The absorption maximum at 306 nm assigned to the trithiocarbonate group was used for this calibration plot, and PETTC concentrations were selected such that the absorbance remained below 1.1. The molar extinction coefficient for PETTC was determined to be 10,900 ± 100 mol–1 dm3 cm–1; hence the mean DP for the PMPC homopolymer was calculated to be 139 ± 1.

Rheology

An MCR 502 rheometer (Anton Paar, Gratz, Austria) equipped with a Couette geometry was used for rotational rheology experiments. Measurements were performed at 20 °C and shear sweeps were conducted from 0.05 to 500 s–1 using approximately 10 mL of either 20% w/w aqueous copolymer dispersions or 10% w/w aqueous copolymer solutions.

Results and Discussion

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The RAFT solution polymerization of MPC was conducted in methanol at 64 °C using a trithiocarbonate-based RAFT agent (PETTC). The mean degree of polymerization (DP) of the PMPC homopolymer was determined via end-group analysis using UV spectroscopy to be 139 ± 1. Aqueous GPC analysis indicated a relatively narrow molecular weight distribution (Mw/Mn = 1.18) for the precursor. However, the poly(ethylene oxide) calibration standards used for GPC analysis meant that only relative Mn values could be obtained. The RAFT aqueous dispersion polymerization of DMAC was conducted in the presence of 2.0 M ammonium sulfate at 30 °C using the PMPC139 precursor as a salt-tolerant steric stabilizer block, as outlined in Scheme 2.

Scheme 2

Scheme 2. Reaction Scheme for the Synthesis of PMPC139–PDMACx (x = 500 to 7000) Diblock Copolymer Particles via RAFT Aqueous Dispersion Polymerization of DMAC at 30 °C in the Presence of 2.0 M Ammonium Sulfatea
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aConditions: targeting 20% w/w solids using a PMPC139–TTC/KPS molar ratio of 4.0 and a [KPS]/[AsAc] molar ratio of 1.0.

PMPC was chosen as the steric stabilizer block because its zwitterionic structure is known to confer aqueous solubility even at 5.0 M NaCl. (35) PDMAC was chosen as the core-forming block because it is a non-ionic water-soluble polymer that becomes water-insoluble in the presence of added salt. (47) Moreover, the resulting PMPC–PDMAC diblock copolymer chains were anticipated to be amenable to aqueous GPC analysis. (48) Inspecting the data presented in Table 1, using 2.0 M ammonium sulfate should be sufficient to produce an aqueous dispersion polymerization formulation since the PMPC precursor and the DMAC monomer are soluble in the aqueous continuous phase and the growing PDMAC chains should become insoluble. Accordingly, the series of aqueous PISA syntheses shown in Table 2 were conducted at 30 °C using a low-temperature persulfate/ascorbic acid (KPS/AsAc) redox initiator while targeting 20% w/w solids at pH 3.
Table 1. Aqueous Solubility of MPC Monomer, DMAC Monomer, PMPC139 Homopolymer, and PDMAC500 Homopolymer at 5.0% w/w Solids in the Presence of 0–4.0 M Ammonium Sulfate as Judged by Visual Inspection at pH 7 and 25 °C
 aqueous (NH4)2SO4 concentration/mol dm–3
 01.02.03.04.0
MPC monomersolublesolublesolublesolublesoluble
PMPC139solublesolublesolublesolublesoluble
DMAC monomersolublesolublesolublesolubleinsoluble
PDMAC500solublesolubleinsolubleinsolubleinsoluble
The PMPC139 precursor afforded colloidally stable dispersions of increasing turbidity when targeting PDMAC DPs ranging from 500 to 6000. However, precipitation was observed when targeting PDMAC DPs above 6000 or when the target copolymer concentration was increased to 25% w/w solids. The PDMAC core block DPs were determined relative to that of the stabilizer block by end-group analysis using 1H NMR spectroscopy. Reasonably good agreement (within experimental error) with the target PDMAC DPs was confirmed by comparing the integrated methine proton signal on the PDMAC backbone at 2.2–2.7 ppm and the PMPC139 azamethylene signal at 3.6 ppm. Comparing these NMR-derived Mn values to those determined by GPC analysis suggests a significant systematic error for the latter technique. This is understandable because poly(ethylene oxide) calibration standards are unlikely to be accurate for the analysis of PDMAC-rich diblock copolymers. Macroscopic precipitation was observed for the attempted synthesis conducted at 30% w/w solids. Essentially full DMAC conversion (>98%) was obtained for each of these syntheses as judged by 1H NMR spectroscopy studies. Targeting PDMAC DPs ≤1000 produced translucent gels, but lowering the solid concentration led to free-flowing dispersions. These gels are most likely caused by these relatively short PDMAC chains not being fully desolvated in the presence of 2.0 M ammonium sulfate.
There is a systematic increase in particle diameter when targeting higher PDMAC DPs. Similar observations have been reported for various other PISA formulations that produce kinetically-trapped spheres. (33,49,50) Moreover, there is also good evidence that targeting larger particles (i.e., higher PDMAC DPs) leads to a progressive broadening of the particle size distribution.
Aqueous GPC data obtained for the series of PMPC139–PDMACx diblock copolymers shown in Table 2 are summarized in Figure 1. Unimodal molecular weight distributions are obtained in each case, with a systematic shift to higher Mn observed when targeting higher PDMAC DPs, which can also be observed in the normalized GPC traces (see Figure S2). However, dispersities are above 1.50, which indicates imperfect RAFT control. We have reported similar dispersities when targeting relatively high DPs for the core-forming block in other PISA formulations. (51−54) Because Mn values are calculated relative to a series of near-monodisperse poly(ethylene oxide) calibration standards, a significant systematic error is expected in this case. Indeed, the theoretical Mn for PMPC139–PDMAC6000 is 636 kg mol–1, whereas the corresponding experimental GPC value is 338 kg mol–1.

Figure 1

Figure 1. Aqueous GPC curves recorded for the PMPC139 precursor and a series of PMPC139–PDMACx diblock copolymers prepared by chain extension via RAFT aqueous dispersion polymerization of DMAC at 30 °C in the presence of 2.0 M ammonium sulfate. Mn values are calculated relative to a series of near-monodisperse poly(ethylene oxide) calibration standards (see Figure S2 for the corresponding normalized GPC curves).

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Table 2. Summary of Conversion, GPC, and DLS Data Obtained for the RAFT Aqueous Dispersion Polymerization of DMAC at 30 °C Using a PMPC139 Precursor at 20–30% w/w Solids
   calculated for PDMAC block:     
solids/w/w%PDMAC DP (x)conversiona/%DPaMna/kg mol–1GPC Mnb/kg mol–1Mw/MnbDzc/nmPDIcphysical appearance
20500>9952052311.96700.09translucent gel
1000>99100099621.76980.12translucent gel
2000>9919801961311.652400.10free-flowing & turbid
3000>9930603031501.822530.17free-flowing & turbid
4000>9940203981681.973500.27free-flowing & turbid
5000>9949104872621.975600.31free-flowing & turbid
6000>9960906043382.106800.40free-flowing & turbid
7000>986630657unstable dispersion
255000>995110506unstable dispersion
305000macroscopic precipitation
a

Determined by 1H NMR spectroscopy (comparison between the integrated vinyl signals assigned to DMAC monomer at 5.6–6.7 ppm, the integrated PDMAC methine proton signal at 2.2–2.7 ppm, and the PMPC139 azamethylene signal at 3.6 ppm).

b

Determined by aqueous GPC using a series of near-monodisperse poly(ethylene oxide) calibration standards.

c

Dz denotes z-average diameter and PDI denotes polydispersity index as determined by DLS according to method 1 (see main text).

Small-angle X-ray scattering (SAXS) was used to characterize selected PMPC139–PDMACx particles (where x = 1000 or 3000), see Figure 2. A well-known spherical micelle model (55−57) was used to provide a satisfactory data fit to an I(q) vs q plot. This approach indicated a volume-average diameter (Dv) of 67 ± 8 nm for the PMPC139–PDMAC1000 particles and 213 ± 38 nm for the PMPC139–PDMAC3000 particles. As expected, these diameters are somewhat lower than the corresponding z-average diameters reported by DLS (see Table 2). (58)

Figure 2

Figure 2. SAXS patterns recorded for 1.0% w/w aqueous dispersions of PMPC139–PDMACx particles (where x = 1000 or 3000) at 25 °C. The black solid lines denote the data fit obtained using a well-known spherical micelle model. (55−57)Dv denotes the volume-average diameter. The red pattern has been scaled by a factor of ten relative to the blue pattern for the sake of clarity.

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1H NMR spectroscopy was used to study the kinetics of the DMAC polymerization at 30 °C when targeting PMPC139–PDMAC5000 particles at 20% w/w solids (see Figure 3a). Periodic sampling of the reaction mixture confirmed that a DMAC conversion of 98% was achieved within 2 h under such conditions, while the corresponding linear semilogarithmic plot indicated first-order kinetics with respect to monomer. Each aliquot taken from the reaction mixture was also subjected to analysis by aqueous GPC (see Figure 3b). Each GPC curve was unimodal, and there was a clear shift in the entire molecular weight distribution toward higher molecular weight, indicating a reasonably high blocking efficiency for the PMPC139 precursor and hence well-defined diblock copolymer chains. This is perhaps more apparent for the normalized GPC curves (see Figure S3). However, dispersities increased monotonically with monomer conversion and always remained above 1.50.

Figure 3

Figure 3. (a) Conversion vs time curve and corresponding semilogarithmic plot determined by 1H NMR spectroscopy for the RAFT aqueous dispersion polymerization of DMAC at 30 °C in 2.0 M ammonium sulfate when targeting a PDMAC DP of 5000 at 20% w/w solids. (b) Aqueous GPC curves obtained by periodic sampling of the reaction mixture to monitor the evolution in the molecular weight distribution (see Figure S3 for the corresponding normalized GPC curves).

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In principle, transmission electron microscopy (TEM) can be used to assign the morphology of diblock copolymer particles prepared via PISA. In practice, the particles prepared herein are unstable with respect to dilution with deionized water (see below). On the other hand, dilution using an aqueous solution of 2.0 M ammonium sulfate is also problematic because this leads to extensive salt crystal formation during TEM grid preparation. In view of these technical problems, we examined the PMPC139–PDMAC5000 particles by optical microscopy, see Figure 4. This technique indicates the presence of a population of micron-sized particles, but it is insensitive to the submicron-sized particle populations indicated by DLS and SAXS studies.

Figure 4

Figure 4. Optical microscopy image recorded for PMPC139–PDMAC5000 particles prepared at 20% w/w solids by RAFT aqueous dispersion polymerization of DMAC at 30 °C in the presence of 2.0 M ammonium sulfate.

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1H NMR spectroscopy was employed to investigate the extent of solvation of the core-forming PDMAC block before and after particle dissolution on dilution of a 20% w/w aqueous dispersion with deionized water. Accordingly, PMPC139–PDMAC5000 particles were prepared in D2O in the presence of 2.0 M ammonium sulfate using the same reaction conditions outlined in Scheme 2. 1H NMR spectra were recorded for the initial aqueous dispersion and the resulting aqueous solutions after up to a four-fold dilution using D2O (see Figure 5). The lower five spectra were normalized to the signal assigned to the two azamethylene protons (−CH2N(CH3)3) adjacent to the quaternary amine within the PMPC block, which remains fully solvated at all salt concentrations. The uppermost spectrum was recorded for a PDMAC500 homopolymer in D2O; the signals marked a and b correspond to the methylene and methine backbone protons, and c corresponds to the two equivalent pendent methyl groups.

Figure 5

Figure 5. 1H NMR spectra recorded for a PDMAC500 (red spectrum) and a PMPC139 (blue spectrum) homopolymers in the absence of salt, as well as a PMPC139–PDMAC5000 diblock copolymer prepared at 20% w/w in D2O in the presence of 2.0 M ammonium sulfate, see the lowest black spectrum. As the 20% w/w PMPC139–PDMAC5000 dispersion is diluted with further D2O, both the background salt concentration and the copolymer concentration are systematically reduced (see four other black spectra). Just a two-fold dilution of the turbid dispersion is sufficient to cause molecular dissolution of the particles as the PDMAC block becomes solvated in 1.0 M ammonium sulfate. A further two-fold dilution of this transparent solution with D2O results in PMPC139–PDMAC5000 chains dissolved in 0.5 M ammonium sulfate, for which the PDMAC signals are now indistinguishable from those of PDMAC500 homopolymer in water (compare the uppermost black spectrum with the red spectrum).

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Clearly, signal a is almost completely attenuated in the presence of 2.0 M ammonium sulfate. However, this signal becomes much more prominent as the ammonium sulfate concentration is lowered, indicating a much higher degree of hydration for the PDMAC block on dilution. Similar observations were made for signals b and c. However, the former signal overlaps with other signals, while the latter is only partially suppressed in the presence of 2.0 M ammonium sulfate. The spectra recorded using 0.5 M ammonium sulfate and the pure PDMAC homopolymer were almost identical, which suggests that this polymer is essentially fully solvated at this salt concentration. This indicates that lowering the ammonium sulfate concentration from 2.0 to 0.5 M via four-fold dilution of the as-synthesized 20% w/w aqueous dispersions of PMPC139–PDMAC5000 particles using deionized water should be sufficient to cause complete particle dissolution. (47,54)
Rotational rheology experiments were conducted on samples using shear sweeps from 0.05 to 500 s–1 at 20 °C. The viscosities of a range of 10% w/w aqueous solutions comprising molecularly-dissolved PMPC139–PDMACx chains in the presence of 1.0 M ammonium sulfate obtained after two-fold dilution of the as-synthesized dispersions using deionized water are shown in Figure 6a. A monotonic increase in solution viscosity is observed at all shear rates when increasing the PDMAC DP for the molecularly-dissolved chains. The viscosity of the aqueous solution remains relatively constant for shear rates ranging from 0.05 to 5.0 s–1, with shear-thinning behavior being observed at higher shear rates. Figure 6b compares the viscosities of as-synthesized 20% w/w aqueous dispersions of PMPC139–PDMACx particles (where x = 3000 or 5000) in 2.0 M ammonium sulfate with the corresponding two 10% w/w aqueous copolymer solutions in 1.0 M ammonium sulfate. Clearly, the viscosity of each dispersion is significantly lower than that of the more dilute solution at all shear rates. Moreover, the two dispersions are much more strongly shear-thinning at higher shear, leading to an order of magnitude reduction in viscosity at 5 s–1. Similar behavior has been reported in the literature when comparing colloidal particles with the corresponding solvated copolymer chains. (59,60)

Figure 6

Figure 6. (a) Viscosity vs shear rate data obtained by rotational rheology studies of 10% w/w aqueous solutions of molecularly-dissolved PMPC139–PDMACx chains in the presence of 1.0 M ammonium sulfate. (b) Viscosity vs shear rate data obtained by rotational rheology studies of 20% w/w aqueous dispersions of either PMPC139–PDMAC3000 or PMPC139–PDMAC5000 particles in 2.0 M ammonium sulfate compared to that for 10% w/w aqueous solutions of the same two copolymers in the presence of 1.0 M ammonium sulfate.

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Two alternative steric stabilizers were also evaluated for the RAFT aqueous dispersion polymerization of DMAC conducted in the presence of 2.0 M ammonium sulfate. To complement the zwitterionic nature of the salt-tolerant PMPC139 steric stabilizer, we evaluated a cationic polyelectrolyte (PATAC195) and an anionic polyelectrolyte (PAMPS250), see chemical structures shown in Scheme 3. Both these polyelectrolytes have been reported to exhibit salt-tolerant behavior. (34,61−63) A PDMAC DP of 1000 was targeted, and 1H NMR spectroscopy studies of the final reaction mixtures confirmed that more than 99% DMAC conversion was obtained in each case.

Scheme 3

Scheme 3. Chemical Structures of the Cationic PATAC195 and Anionic PAMPS250 Precursors Used to Stabilize PDMAC-Rich Diblock Copolymer Particles Prepared via RAFT Aqueous Dispersion Polymerization of DMAC in 2.0 M Ammonium Sulfate
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It is common practice to estimate the ζ potential of colloidal particles in aqueous solution as a function of pH. However, the correct interpretation of the experimental data for sterically-stabilized particles dispersed in highly salty aqueous media can be problematic for two reasons. First, the relatively high ionic strength reduces the hydrogen ion activity, which affects the accuracy of the glass Ag/AgCl reference electrode typically used to measure the pH. Moreover, additional errors may be incurred owing to a change in the junction potential of such electrodes when in contact with such salty media. Second, the steric stabilizer chains at the particle–liquid interface provide a permeable medium through which the solution phase can flow. If electrical charge arises from the ionic groups within such steric stabilizer chains, the electrokinetic models commonly used to calculate ζ potential from electrophoretic mobility become invalid. (64) To overcome these technical problems, we used a state-of-the-art instrument to determine apparent ζ potentials for the three types of PDMAC-rich particles prepared in high salt using the PMPC139, PATAC195, or PAMPS250 precursor in turn (see Supporting Information for further information).
In the present study, the electrophoretic mobility of the particles was measured as a function of the addition of varying amounts of KOH. The apparent pH was determined using a glass Ag/AgCl reference electrode without any compensation to offset the effect of the high ionic strength on the electrode response (although a temperature sensor within the electrode assembly did enable temperature compensation). Accordingly, ζ potentials calculated using the Smoluchowski model (65) are regarded as apparent zeta potentials. The hydrodynamic z-average diameter of the particles was also determined in the presence of 2.0 M ammonium sulfate as a function of pH during these measurements.
The apparent ζ potentials determined by electrophoretic light scattering for each of these three dispersions as a function of added KOH is shown in Figure 7. As expected, the electrophoretic footprint for each type of particle is dictated by the chemical nature of the steric stabilizer chains. Thus the cationic PATAC195–PDMAC1000 particles exhibit positive apparent ζ potentials of +15.8 ± 1.1 mV, whereas the anionic PAMPS250–PDMAC1000 particles exhibit negative apparent ζ potentials of −25.9 ± 1.5 mV. Finally, the zwitterionic PMPC250–PDMAC1000 particles exhibit apparent ζ potentials close to zero (+1.1 ± 1.2 mV). Similar observations have been reported for other PMPC-stabilized nano-objects at low salt. (66,67)

Figure 7

Figure 7. Apparent ζ potentials observed on addition of varying volumes of aqueous 0.2 M KOH solution in the presence of 2.0 M ammonium sulfate for 0.1% w/w aqueous dispersions of PATAC195–PDMAC1000 (red triangles), PMPC139–PDMAC1000 (green squares), or PAMPS250–PDMAC1000 (blue circles) particles.

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If these particles were hard spheres, the conventional interpretation for such electrophoretic observations is that the PAMPS250–PDMAC1000 particles possess a sufficiently high anionic ζ potential to prevent aggregation, the PATAC195–PDMAC1000 particles possess a moderate cationic ζ potential that is likely to retard but not prevent aggregation, while the PMPC250–PDMAC1000 particles are essentially uncharged and hence likely to be colloidally unstable. However, this is a naïve and incorrect interpretation, not least because the salt-tolerant PAMPS250, PATAC195, and PMPC139 chains confer additional steric stabilization. (68)

Conclusions

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We report the synthesis of a series of sterically-stabilized diblock copolymer particles via RAFT aqueous dispersion polymerization of DMAC in highly salty media. This is achieved by selecting a suitable salt-tolerant water-soluble polymer to act as an effective steric stabilizer. Such stabilizers can possess zwitterionic (e.g., PMPC), cationic (e.g., PATAC), or anionic (e.g., PAMPS) character, which leads to the corresponding diblock copolymer particles exhibiting essentially zero, negative, or positive apparent ζ potentials, respectively. It is non-trivial to make such aqueous electrophoresis measurements in highly salty media. Indeed, such experiments require state-of-the-art instrumentation. Relatively high DPs can be targeted for the salt-insoluble block to ensure that this component dominates the formulation. This approach enables high molecular weight water-soluble polymers to be prepared in a highly convenient low-viscosity form. Subsequent dilution using deionized water lowers the background salt concentration and causes in situ molecular dissolution of the particles, which leads to a substantial thickening effect and the formation of highly viscous transparent aqueous solutions. In principle, such aqueous PISA formulations are highly attractive: there are various potential commercial applications for high molecular weight water-soluble polymers while the well-known negative aspects of using RAFT agents (i.e., their cost, color, and malodor) are minimized. For example, the organosulfur content of the dry PMPC139–PDMAC6000 diblock copolymer targeted herein is only ≈0.03%, which corresponds to just ≈ 63 ppm for a 20% w/w aqueous copolymer dispersion.

Supporting Information

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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.macromol.2c01071.

  • UV absorption spectra and calibration plot; dynamic viscosities of various ammonium sulfate solutions; normalized GPC curves obtained for both final copolymers and during kinetic experiments; and further technical details regarding the determination of ζ potentials in highly salty media (PDF)

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

Author Information

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  • Corresponding Author
  • Authors
    • Rory J. McBride - Chemistry Department, University of Sheffield, Brook Hill, Sheffield, South Yorkshire S3 7HF, U.K.
    • John F. Miller - Enlighten Scientific LLC, Hillsborough, North Carolina 27278, United States;  Orcidhttps://orcid.org/0000-0001-6628-530X
    • Adam Blanazs - BASF SE, RAM/OB - B001, Carl-Bosch-Strasse 38, 67056 Ludwigshafen am Rhein, Germany
    • Hans-Joachim Hähnle - BASF SE, RAM/OB - B001, Carl-Bosch-Strasse 38, 67056 Ludwigshafen am Rhein, Germany
  • Notes
    The authors declare no competing financial interest.

Acknowledgments

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The authors thank EPSRC for a CASE PhD studentship for the first author. BASF is thanked for additional financial support for this project and for permission to publish these results. S.P.A. acknowledges an EPSRC Particle Technology Fellowship Grant (EP/R003009) and Dr. S. Ebbens for his contribution to this project. Dr. O. J. Deane and Dr. R. R. Gibson are thanked for their assistance in developing the aqueous GPC protocol, and Dr. A. Czajka is thanked for his help in modeling the SAXS data. Dr. A. L. Lewis (formerly of Biocompatibles U.K.) is acknowledged for the kind donation of the MPC monomer. Finally, we thank Dr. S. J. Byard for performing the preliminary experiments that led to the current study.

References

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    This article extends the preparative details of a series of nonionic copolymers of acrylamide with N,N-di-Me acrylamide, methacrylamide, and N-t-Bu acrylamide to the synthesis of cationic derivs. of these new copolymers. The described procedures gave products with cationicities of 14-26 mol %. We measured the mean squared radii of gyration and intrinsic viscosities of aq. solns. of these products at several different pH and NaCl concns. to compare these values with those detd. for the nonionic precursors and related com. cationic polymers. Because the mol. wts. of the examples measured varied widely, it was difficult to establish definite trends. However, the large values obtained for the mean squared radii of gyration and intrinsic viscosities, relative to the nonionic precursors of these polymers, demonstrated that the charged groups had a qual. greater effect on polymer extension than the nonpolar bulky groups.
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    Guyot, A.; Chu, F.; Schneider, M.; Graillat, C.; McKenna, T. F. High Solid Content Latexes. Prog. Polym. Sci. 2002, 27, 1573– 1615,  DOI: 10.1016/S0079-6700(02)00014-X
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    High solid content latexes
    Guyot, A.; Chu, F.; Schneider, M.; Graillat, C.; McKenna, T. F.
    Progress in Polymer Science (2002), 27 (8), 1573-1615CODEN: PRPSB8; ISSN:0079-6700. (Elsevier Science Ltd.)
    This article is a review of the rheol. of concd. latexes, followed by a discussion of the state of the art in the area of high solids latex prodn. High solids content latexes are of growing interest for many reasons; however, making this type of product entails many difficulties. Increasing the solids content (fraction of polymer relative to the continuous phase) in a reproducible manner entails the strict control of a complex particle size distribution (PSD). The PSD must be either quite broad, or multimodal in order to obtain solids contents much above 55 or 60 vol.%. In addn., the viscosity of a latex is highly sensitive to the PSD near the upper limit of solids content, but it is still not possible to predict a priori how a complex PSD will effect the viscosity. This article presents an overview of the rheol. of concd. latexes, followed by a discussion of the state of the art in the area of high solids latex prodn.
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    Perrier, S. 50th Anniversary Perspective: RAFT Polymerization - A User Guide. Macromolecules 2017, 50, 7433– 7447,  DOI: 10.1021/acs.macromol.7b00767
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    50th Anniversary Perspective: RAFT Polymerization-A User Guide
    Perrier, Sebastien
    Macromolecules (Washington, DC, United States) (2017), 50 (19), 7433-7447CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    A review. This Perspective summarizes the features and limitations of reversible addn.-fragmentation chain transfer (RAFT) polymn., highlighting its strengths and weaknesses, as our understanding of the process, from both a mechanistic and an application point of view, has matured over the past 20 years. It is aimed at both experts in the field and newcomers, including undergraduate and postgraduate students, as well as nonexperts in polymn. who are interested in developing their own polymeric structures by exploiting the simple setup of a RAFT polymn.
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    Chiefari, J.; Chong, Y. K.; Ercole, F.; Krstina, J.; Jeffery, J.; Le, T. P. T.; Mayadunne, R. T. A.; Meijs, G. F.; Moad, C. L.; Moad, G.; Rizzardo, E.; Thang, S. H. Living Free-Radical Polymerization by Reversible Addition - Fragmentation Chain Transfer: The RAFT Process. Macromolecules 1998, 31, 5559– 5562,  DOI: 10.1021/ma9804951
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    Living Free-Radical Polymerization by Reversible Addition-Fragmentation Chain Transfer: The RAFT Process
    Chiefari, John; Chong, Y. K.; Ercole, Frances; Krstina, Julia; Jeffery, Justine; Le, Tam P. T.; Mayadunne, Roshan T. A.; Meijs, Gordon F.; Moad, Catherine L.; Moad, Graeme; Rizzardo, Ezio; Thang, San H.
    Macromolecules (1998), 31 (16), 5559-5562CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    A new living free-radical polymn. that involves reversible addn.-fragmentation chain transfer and is designated RAFT polymn. can be used with a wide rage of monomers and reaction conditions and provides controlled mol. wt. polymers with very narrow polydispersities. The RAFT process involves free radical polymn. in the presence of dithio compds. Mol. wt/conversion data are presented for polymers formed by bulk, soln., emulsion and suspension polymn. of acrylic and styrene monomers using azo or peroxy initiators. Major advantages of the RAFT polymn. process over other processes for living/controlled free-radical polymn. are discussed.
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    Destarac, M. Industrial Development of Reversible-Deactivation Radical Polymerization: Is the Induction Period Over?. Polym. Chem. 2018, 9, 4947– 4967,  DOI: 10.1039/C8PY00970H
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    Industrial development of reversible-deactivation radical polymerization: is the induction period over?
    Destarac, Mathias
    Polymer Chemistry (2018), 9 (40), 4947-4967CODEN: PCOHC2; ISSN:1759-9962. (Royal Society of Chemistry)
    Reversible-deactivation radical polymn. (RDRP) techniques are essential in modern polymer chem. Over the years, they have become not only fantastic lab tools for the easy prepn. of structurally complex polymers but also an industrial reality. This article reviews industrial developments and com. success based on RDRP processes. The nature of RDRP control agents is discussed and numerous industrial polymers and their applications are exemplified. While RDRP is firmly established as a powerful means for the development of next generation high-valued polymer products, there is room for improvement in terms of the cost/performance ratio for a broader adoption by industry. Some directions are proposed for the future.
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    Destarac, M.; Wilson, D. J.; Silvia, S. Controlled Radical Polymerization in Water-in-Water Dispersion. US10160821B2, 2018.
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    Wu, Y. M.; Wang, Y. P.; Yu, Y. Q.; Xu, J.; Chen, Q. F. Dispersion Polymerization of Acrylamide with 2-Acrylamido-2-Methyl-1- Propane Sulfonate in Aqueous Solution. J. Appl. Polym. Sci. 2006, 102, 2379– 2385,  DOI: 10.1002/app.24494
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    Dispersion polymerization of acrylamide with 2-acrylamido-2-methyl-1-propane sulfonate in aqueous solution
    Wu, Y. M.; Wang, Y. P.; Yu, Y. Q.; Xu, J.; Chen, Q. F.
    Journal of Applied Polymer Science (2006), 102 (3), 2379-2385CODEN: JAPNAB; ISSN:0021-8995. (John Wiley & Sons, Inc.)
    The copolymer of acrylamide (AM) and 2-acrylamido-2-methyl-1-propane sulfonate (AMPS) was synthesized through the free radical dispersion polymn. in an aq. soln. of ammonium sulfate and in the presence of poly(2-acrylamido-2-methyl-1-propane sulfonate) as stabilizer. The av. particle size of the copolymer ranged from 1 to 4 μm, and the mol. wt. was from 2.0 × 106 to 7.0 × 106 g mol-1. By analyzing apparent viscosity and particle size, the swelling property of the dispersion copolymer was studied. When the dispersion was dild. with salt water in which the ammonium sulfate concn. kept equal with that of the original dispersion, particle size and particle size distribution of the dild. dispersion changed a little, compared with that of the original dispersion. While dild. with deionized water, particle size and particle size distribution could expand several times. The effects of varying concns. of the stabilizer, the monomer, the salt and the initiator on particle size, and mol. wt. of the copolymer were investigated, resp. The reaction conditions for prepg. stable dispersion were concns. of 20-28% of the salt, 6-14% of monomers, and 1.8-2.7% of the stabilizer.
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    Guo, A.; Geng, Y.; Zhao, L.; Li, J.; Liu, D.; Li, P. Preparation of Cationic Polyacrylamide Microsphere Emulsion and Its Performance for Permeability Reduction. Pet. Sci. 2014, 11, 408– 416,  DOI: 10.1007/s12182-014-0355-0
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    Preparation of cationic polyacrylamide microsphere emulsion and its performance for permeability reduction
    Guo, Aijun; Geng, Yiran; Zhao, Lili; Li, Jun; Liu, Dong; Li, Peng
    Petroleum Science (2014), 11 (3), 408-416CODEN: PSECCF; ISSN:1995-8226. (China University of Petroleum)
    In this paper, cationic polyacrylamide microspheres (CPAM) were synthesized using acrylamide (AM) and methacryloyloxyethyltri-methylammonium chloride (TMAEMC) as monomers, ammonium sulfate as dispersant, poly(acryloyloxyethyltri-Meammonium chloride) (PAETAC) as dispersion stabilizer, and ammonium persulfate as initiator. The synthetic method was dispersion polymn. The effects of monomer ratio (AM/TMAEMC), dispersant concn., and dispersion stabilizer dosage on dispersion polymn. were systematically studied to det. the optimal prepn. conditions. The structure and viscosity of the synthesized polymer were characterized by FTIR and capillary viscometry, resp., and the particle sizes and distribution of the polymer microspheres were characterized by microscopy and dynamic light scattering, resp. Finally, flow tests were conducted to measure the permeability redn. performance of the microspheres at various concns. in sand packs with different permeability. Results show that CPAM emulsion of a solids content of 1wt% has excellent performance in low-to-medium permeability formations (< 1,000 mD), and the efficiency may reach above 90%.
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    Cho, M. S.; Yoon, K. J.; Song, B. K. Dispersion Polymerization of Acrylamide in Aqueous Solution of Ammonium Sulfate: Synthesis and Characterization. J. Appl. Polym. Sci. 2002, 83, 1397– 1405,  DOI: 10.1002/app.2300
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    Dispersion polymerization of acrylamide in aqueous solution of ammonium sulfate: synthesis and characterization
    Cho, M. S.; Yoon, K. J.; Song, B. K.
    Journal of Applied Polymer Science (2002), 83 (7), 1397-1405CODEN: JAPNAB; ISSN:0021-8995. (John Wiley & Sons, Inc.)
    Dispersion polymn. of acrylamide has been successfully carried out in aq. ammonium sulfate media by using poly[2-(acryloyloxy)ethyltrimethylammonium chloride] (PAOTAC) as the polymeric stabilizer and 2,2'-azobis(2-methylpropionamidine) dihydrochloride (AIBA) as the initiator. The polymn. behaviors with varying concns. of acrylamide, PAOTAC, AIBA, and ammonium sulfate were investigated. The reaction conditions for stable dispersion were concns. of 5-10% for acrylamide, 0.6-1.8% for the stabilizer, 0.92-1.84 × 10-4 mol/L for the initiator, and 24-30% for the salt. The resulting conversion-time curves were S-shaped, as is typically obsd. in polymn. Polydisperse spherical particles were formed in the system. An image analyzer photographed the size of the dispersed particles and their distribution was measured. The mechanism and kinetics for the dispersion polymn. were discussed.
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    Ferguson, C. J.; Hughes, R. J.; Pham, B. T. T.; Hawkett, B. S.; Gilbert, R. G.; Serelis, A. K.; Such, C. H. Effective Ab Initio Emulsion Polymerization under RAFT Control. Macromolecules 2002, 35, 9243– 9245,  DOI: 10.1021/ma025626j
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    Effective ab Initio Emulsion Polymerization under RAFT Control
    Ferguson, Christopher J.; Hughes, Robert J.; Pham, Binh T. T.; Hawkett, Brian S.; Gilbert, Robert G.; Serelis, Algirdas K.; Such, Christopher H.
    Macromolecules (2002), 35 (25), 9243-9245CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    To avoid loss of colloidal stability and appearance of an intractable oily layer, a novel technique for ab initio reversible addn.-fragmentation chain transfer emulsion polymn. was developed. An amphipathic RAFT agent (i.e., 2-{[(butylsulfanyl)carbonothioyl]sulfanyl}-propanoic acid) was used, which can mediate polymn. in both aq. and org. phases. This was first polymd. with a water-sol. monomer (acrylic acid, AA) in the water phase to a low d.p. to form (AA)x-RAFT. A hydrophobic monomer (Bu acrylate, BA) was then added under controlled feed to give oligomers, (AA)x-(BA)y-RAFT, which formed rigid micelles. These RAFT-contg. micelles functioned as seeds for further polymn. At the completion of the polymn., the resulting latex showed no oily layer and no visible evidence of colloidal instability.
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    Ferguson, C. J.; Hughes, R. J.; Nguyen, D.; Pham, B. T. T.; Gilbert, R. G.; Serelis, A. K.; Such, C. H.; Hawkett, B. S. Ab Initio Emulsion Polymerization by RAFT-Controlled Self-Assembly. Macromolecules 2005, 38, 2191– 2204,  DOI: 10.1021/ma048787r
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    19
    Ab Initio Emulsion Polymerization by RAFT-Controlled Self-Assembly
    Ferguson, Christopher J.; Hughes, Robert J.; Nguyen, Duc; Pham, Binh T. T.; Gilbert, Robert G.; Serelis, Algirdas K.; Such, Christopher H.; Hawkett, Brian S.
    Macromolecules (2005), 38 (6), 2191-2204CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    A method is developed to enable emulsion polymn. to be performed under RAFT control to give living character without the problems that often affect such systems: formation of an oily layer, loss of colloidal stability, or loss of mol. wt. control. Trithiocarbonate RAFT agents are used to form short stabilizing blocks from a water-sol. monomer, from which diblocks can be created by the subsequent polymn. of a hydrophobic monomer. These diblocks are designed to self-assemble to form micelles. Polymn. is initially performed under conditions that avoid the presence of monomer droplets during the particle formation stage and until the hydrophobic ends of the diblocks have become sufficiently long to prevent them from desorbing from the newly formed particles. Polymn. is then continued at any desired feed rate and compn. of monomer. The polymer forming in the reaction remains under RAFT control throughout the polymn.; mol. wt. polydispersities are generally low. The no. of RAFT-ended chains within a particle is much larger than the aggregation no. at which the original micelles would have self-assembled, implying that in the early stages of the polymn., there is aggregation of the micelles and/or migration of the diblocks. The latexes resulting from this approach are stabilized by anchored blocks of the hydrophilic monomer, e.g., acrylic acid, with no labile surfactant present. Sequential polymn. of two hydrophobic monomers gives completely novel core-shell particles where most chains extend from the core of the particles through the shell layer to the surface.
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  20. 20
    Zhang, X.; Boissé, S.; Zhang, W.; Beaunier, P.; D’Agosto, F.; Rieger, J.; Charleux, B. Well-Defined Amphiphilic Block Copolymers and Nano-Objects Formed in Situ via RAFT-Mediated Aqueous Emulsion Polymerization. Macromolecules 2011, 44, 4149– 4158,  DOI: 10.1021/ma2005926
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    20
    Well-Defined Amphiphilic Block Copolymers and Nano-objects Formed in Situ via RAFT-Mediated Aqueous Emulsion Polymerization
    Zhang, Xuewei; Boisse, Stephanie; Zhang, Wenjing; Beaunier, Patricia; D'Agosto, Franck; Rieger, Jutta; Charleux, Bernadette
    Macromolecules (Washington, DC, United States) (2011), 44 (11), 4149-4158CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    A hydrophilic poly(methacrylic acid-co-poly(ethylene oxide) Me ether methacrylate) copolymer with a trithiocarbonate reactive group was used in the free-radical, batch emulsion polymn. of styrene. It allowed fast polymns. and high final conversions to be achieved, and the parameters for a good control over the formation of well-defined amphiphilic diblock copolymers were identified. These diblock copolymers self-assembled in situ into nano-objects of various morphologies upon chain extension. Achieving a good control over the formed diblock copolymers was an important step toward a better understanding of the parameters that affect the shape and size of the self-assembled objects, the ultimate goal being the ability to predict and fine-tune them on purpose.
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    Warren, N. J.; Armes, S. P. Polymerization-Induced Self-Assembly of Block Copolymer Nano-Objects via RAFT Aqueous Dispersion Polymerization. J. Am. Chem. Soc. 2014, 136, 10174– 10185,  DOI: 10.1021/ja502843f
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    Polymerization-Induced Self-Assembly of Block Copolymer Nano-objects via RAFT Aqueous Dispersion Polymerization
    Warren, Nicholas J.; Armes, Steven P.
    Journal of the American Chemical Society (2014), 136 (29), 10174-10185CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    A review. In this Perspective, we discuss the recent development of polymn.-induced self-assembly mediated by reversible addn.-fragmentation chain transfer (RAFT) aq. dispersion polymn. This approach has quickly become a powerful and versatile technique for the synthesis of a wide range of bespoke org. diblock copolymer nano-objects of controllable size, morphol., and surface functionality. Given its potential scalability, such environmentally-friendly formulations are expected to offer many potential applications, such as novel Pickering emulsifiers, efficient microencapsulation vehicles, and sterilizable thermo-responsive hydrogels for the cost-effective long-term storage of mammalian cells.
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    Charleux, B.; Delaittre, G.; Rieger, J.; D’Agosto, F. Polymerization-Induced Self-Assembly: From Soluble Macromolecules to Block Copolymer Nano-Objects in One Step. Macromolecules 2012, 45, 6753– 6765,  DOI: 10.1021/ma300713f
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    22
    Polymerization-Induced Self-Assembly: From Soluble Macromolecules to Block Copolymer Nano-Objects in One Step
    Charleux, Bernadette; Delaittre, Guillaume; Rieger, Jutta; D'Agosto, Franck
    Macromolecules (Washington, DC, United States) (2012), 45 (17), 6753-6765CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    A review. This Perspective describes the recent developments of polymn.-induced self-assembly of amphiphilic block copolymers based on controlled/living free-radical polymn. (CRP) in water. This method relies on the use of a hydrophilic living polymer precursor prepd. via CRP that is extended with a hydrophobic second block in an aq. environment. The process thus leads to amphiphilic block copolymers that self-assemble in situ into self-stabilized nano-objects in the frame of an emulsion or dispersion polymn. process. Depending on the nature and the structure of the so-formed copolymer, not only spherical particles can be achieved but also all morphologies that can be found in the phase diagram of an amphiphilic block copolymer in a selective solvent. This paper focuses mainly on aq. emulsion or dispersion polymn. and gives an overview of the CRP techniques used, the general conditions, and the morphologies obtained.
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    Boissé, S.; Rieger, J.; Belal, K.; Di-Cicco, A.; Beaunier, P.; Li, M. H.; Charleux, B. Amphiphilic Block Copolymer Nano-Fibers via RAFT-Mediated Polymerization in Aqueous Dispersed System. Chem. Commun. 2010, 46, 1950– 1952,  DOI: 10.1039/B923667H
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    Amphiphilic block copolymer nano-fibers via RAFT-mediated polymerization in aqueous dispersed system
    Boisse, Stephanie; Rieger, Jutta; Belal, Khaled; Di-Cicco, Aurelie; Beaunier, Patricia; Li, Min-Hui; Charleux, Bernadette
    Chemical Communications (Cambridge, United Kingdom) (2010), 46 (11), 1950-1952CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
    Self-assembled block copolymer nanofibers are attractive materials for multiple applications. We propose here a novel, very simple and straightforward method to prep. polymeric nanofibers at high solids contents directly in water. It is based on an aq. emulsion polymn. process performed under living radical polymn. conditions using the RAFT method. Polymn. of styrene in water in the presence of hydrophilic macromol. RAFT agent. The RAFT agent was dodecyl trithiocarbonate-end capped acrylic acid-poly(ethylene glycol) Me ether acrylate copolymer.
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    D’Agosto, F.; Rieger, J.; Lansalot, M. RAFT-Mediated Polymerization-Induced Self-Assembly. Angew. Chem., Int. Ed. 2019, 59, 8368– 8392,  DOI: 10.1002/anie.201911758
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    Liu, G.; Qiu, Q.; Shen, W.; An, Z. Aqueous Dispersion Polymerization of 2-Methoxyethyl Acrylate for the Synthesis of Biocompatible Nanoparticles Using a Hydrophilic RAFT Polymer and a Redox Initiator. Macromolecules 2011, 44, 5237– 5245,  DOI: 10.1021/ma200984h
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    Aqueous Dispersion Polymerization of 2-Methoxyethyl Acrylate for the Synthesis of Biocompatible Nanoparticles Using a Hydrophilic RAFT Polymer and a Redox Initiator
    Liu, Guangyao; Qiu, Qian; Shen, Wenqing; An, Zesheng
    Macromolecules (Washington, DC, United States) (2011), 44 (13), 5237-5245CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    Aq. dispersion polymn. systems mediated by reversible addn.-fragmentation chain transfer (RAFT) process have been less studied in comparison with other heterogeneous polymn. systems due to limited no. of monomer/polymer pairs that are suitable for such a condition. We report a novel dispersion polymn. system based on 2-methoxyethyl acrylate (MEA) which is highly water-sol., but its polymer is not. Using a hydrophilic polymer, poly(poly(ethylene glycol) Me ether methacrylate) (PPEGMA), as the macromol. chain transfer agent (Macro-CTA), both soln. and dispersion polymn. of MEA were studied. Chain extension by MEA from PPEGMA was successfully realized in DMF soln. polymn. In dispersion polymn. of MEA in water, PPEGMA was used as both a RAFT mediating species and a steric stabilizer for the formed nanoparticles. The dispersion polymn. of MEA in water was highly efficient using a redox initiator, potassium persulfate/sodium ascorbate, at low temps. Simultaneous control of both colloidal stability and RAFT process was realized. Block copolymers with small polydispersity indexes were efficiently produced up to complete monomer conversion at solids content up to 32% w/v, in the form of nanoparticles of 40-60 nm diam.
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    Sugihara, S.; Ma’Radzi, A. H.; Ida, S.; Irie, S.; Kikukawa, T.; Maeda, Y. In Situ Nano-Objects via RAFT Aqueous Dispersion Polymerization of 2-Methoxyethyl Acrylate Using Poly(Ethylene Oxide) Macromolecular Chain Transfer Agent as Steric Stabilizer. Polymer 2015, 76, 17– 24,  DOI: 10.1016/j.polymer.2015.08.051
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    In situ nano-objects via RAFT aqueous dispersion polymerization of 2-methoxyethyl acrylate using poly(ethylene oxide) macromolecular chain transfer agent as steric stabilizer
    Sugihara, Shinji; Ma'Radzi, Akmal Hadi; Ida, Shota; Irie, Satoshi; Kikukawa, Takamaru; Maeda, Yasushi
    Polymer (2015), 76 (), 17-24CODEN: POLMAG; ISSN:0032-3861. (Elsevier Ltd.)
    Poly(ethylene oxide)-poly(2-methoxyethyl acrylate) diblock copolymers (PEO-b-PMEA) are synthesized by RAFT aq. dispersion polymn. of MEA using poly(ethylene oxide) macromol. chain transfer agent as a reactive steric stabilizer. Both segments are well-known to be bio- and blood-compatible polymers. This formulation enables the prodn. of various particle morphologies such as spheres, worms, and vesicles from the same block copolymer in water. The synthesis starts when both the reactive steric stabilizer and MEA monomer are dissolved in water; however, the growing polymer is not water-sol. and begins to form nano-objects. In the case of the synthesis of PEO113-b-MEA300 diblock copolymers, the nano-objects change from spheres into larger aggregates of worms when the solids concn. in the polymn. increases from 5 to 15 wt% at full monomer conversion. The morphol. finally turns into vesicles as the solids concn. increases to 20 wt%. The final block copolymer morphol. at full monomer conversion is dictated by not only d.p. of MEA but also the solids concn. in the polymn. mixt.
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    An, Z.; Shi, Q.; Tang, W.; Tsung, C. K.; Hawker, C. J.; Stucky, G. D. Facile RAFT Precipitation Polymerization for the Microwave-Assisted Synthesis of Well-Defined, Double Hydrophilic Block Copolymers and Nanostructured Hydrogels. J. Am. Chem. Soc. 2007, 129, 14493– 14499,  DOI: 10.1021/ja0756974
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    27
    Facile RAFT Precipitation Polymerization for the Microwave-Assisted Synthesis of Well-Defined, Double Hydrophilic Block Copolymers and Nanostructured Hydrogels
    An, Zesheng; Shi, Qihui; Tang, Wei; Tsung, Chia-Kuang; Hawker, Craig J.; Stucky, Galen D.
    Journal of the American Chemical Society (2007), 129 (46), 14493-14499CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    Water-sol. macromol. chain transfer agents (Macro-CTAs) were developed for the microwave-assisted pptn. polymn. of N-isopropylacrylamide. Two types of Macro-CTAs, amphiphilic (Macro-CTA1) and hydrophilic (Macro-CTA2), were studied regarding their activity for the facile formation of nanoparticles and double hydrophilic block copolymers by RAFT processes. While both Macro-CTAs functioned as steric stabilization agents, the variation in their surface activity afforded different levels of control over the resulting nanoparticles in the presence of crosslinkers. The crosslinked nanoparticles produced using the amphiphilic Macro-CTA1 were less uniform than those produced using the fully hydrophilic Macro-CTA2. The nanoparticles spontaneously formed core-shell structures with surface functionalities derived from those of the Macro-CTAs. In the absence of crosslinkers, both types of Macro-CTAs showed excellent control over the RAFT pptn. polymn. process with well-defined, double hydrophilic block copolymers being obtained. The power of combining microwave irradn. with RAFT procedures was evident in the high efficiency and high solids content of the polymn. systems. In addn., the "living" nature of the nanoparticles allowed for further copolymn. leading to multiresponsive nanostructured hydrogels contg. surface functional groups, which were used for surface bioconjugation.
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    Figg, C. A.; Simula, A.; Gebre, K. A.; Tucker, B. S.; Haddleton, D. M.; Sumerlin, B. S. Polymerization-Induced Thermal Self-Assembly (PITSA). Chem. Sci. 2015, 6, 1230– 1236,  DOI: 10.1039/C4SC03334E
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    Polymerization-induced thermal self-assembly (PITSA)
    Figg, C. Adrian; Simula, Alexandre; Gebre, Kalkidan A.; Tucker, Bryan S.; Haddleton, David M.; Sumerlin, Brent S.
    Chemical Science (2015), 6 (2), 1230-1236CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
    Polymn.-induced self-assembly (PISA) is a versatile technique to achieve a wide range of polymeric nanoparticle morphologies. Most previous examples of self-assembled soft nanoparticle synthesis by PISA rely on a growing solvophobic polymer block that leads to changes in nanoparticle architecture during polymn. in a selective solvent. However, synthesis of block copolymers with a growing stimuli-responsive block to form various nanoparticle shapes has yet to be reported. This new concept using thermo-responsive polymers is termed polymn.-induced thermal self-assembly (PITSA). A reversible addn.-fragmentation chain transfer (RAFT) polymn. of N-isopropylacrylamide from a hydrophilic chain transfer agent composed of N,N-dimethylacrylamide and acrylic acid was carried out in water above the known lower crit. soln. temp. (LCST) of poly(N-isopropylacrylamide) (PNIPAm). After reaching a certain chain length, the growing PNIPAm self-assembled, as induced by the LCST, into block copolymer aggregates within which dispersion polymn. continued. To characterize the nanoparticles at ambient temps. without their dissoln., the particles were crosslinked immediately following polymn. at elevated temps. via the reaction of the acid groups with a diamine in the presence of a carbodiimide. Size exclusion chromatog. was used to evaluate the unimer mol. wt. distributions and reaction kinetics. Dynamic light scattering and transmission electron microscopy provided insight into the size and morphologies of the nanoparticles. The resulting block copolymers formed polymeric nanoparticles with a range of morphologies (e.g., micelles, worms, and vesicles), which were a function of the PNIPAm block length.
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    Cunningham, V. J.; Derry, M. J.; Fielding, L. A.; Musa, O. M.; Armes, S. P. RAFT Aqueous Dispersion Polymerization of N-(2-(Methacryloyloxy)Ethyl)Pyrrolidone: A Convenient Low Viscosity Route to High Molecular Weight Water-Soluble Copolymers. Macromolecules 2016, 49, 4520– 4533,  DOI: 10.1021/acs.macromol.6b00820
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    RAFT Aqueous Dispersion Polymerization of N-(2-(Methacryloyloxy)ethyl)pyrrolidone: A Convenient Low Viscosity Route to High Molecular Weight Water-Soluble Copolymers
    Cunningham, Victoria J.; Derry, Matthew J.; Fielding, Lee A.; Musa, Osama M.; Armes, Steven P.
    Macromolecules (Washington, DC, United States) (2016), 49 (12), 4520-4533CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    RAFT soln. polymn. of N-(2-(methacryoyloxy)ethyl)pyrrolidone (NMEP) in ethanol at 70 °C was conducted to produce a series of PNMEP homopolymers with mean ds.p. (DP) varying from 31 to 467. Turbidimetry was used to assess their inverse temp. soly. behavior in dil. aq. soln., with an LCST of approx. 55 °C being obsd. in the high mol. wt. limit. Then a poly(glycerol monomethacylate) (PGMA) macro-CTA with a mean DP of 63 was chain-extended with NMEP using a RAFT aq. dispersion polymn. formulation at 70 °C. The target PNMEP DP was systematically varied from 100 up to 6000 to generate a series of PGMA63-PNMEPx diblock copolymers. High conversions (≥92%) could be achieved when targeting up to x = 5000. GPC anal. confirmed high blocking efficiencies and a linear evolution in Mn with increasing PNMEP DP. A gradual increase in Mw/Mn was also obsd. when targeting higher DPs. However, this problem could be minimized (Mw/Mn < 1.50) by utilizing a higher purity grade of NMEP (98% vs 96%). This suggests that the broader mol. wt. distributions obsd. at higher DPs are simply the result of a dimethacrylate impurity causing light branching, rather than an intrinsic side reaction such as chain transfer to polymer. Kinetic studies confirmed that the RAFT aq. dispersion polymn. of NMEP was approx. four times faster than the RAFT soln. polymn. of NMEP in ethanol when targeting the same DP in each case. This is perhaps surprising because both 1H NMR and SAXS studies indicate that the core-forming PNMEP chains remain relatively solvated at 70 °C in the latter formulation. Moreover, dissoln. of the initial PGMA63-PNMEPx particles occurs on cooling from 70 to 20 °C as the PNMEP block passes through its LCST. Hence this RAFT aq. dispersion polymn. formulation offers an efficient route to a high mol. wt. water-sol. polymer in a rather convenient low-viscosity form. Finally, the relatively expensive PGMA macro-CTA was replaced with a poly(methacrylic acid) (PMAA) macro-CTA. High conversions were also achieved for PMAA85-PNMEPx diblock copolymers prepd. via RAFT aq. dispersion polymn. for x ≤ 4000. Again, better control was achieved when using the 98% purity NMEP monomer in such syntheses.
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    Einarson, M. B.; Berg, J. C. Electrosteric Stabilization of Colloidal Latex Dispersions. J. Colloid Interface Sci. 1993, 155, 165– 172,  DOI: 10.1006/jcis.1993.1022
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    Electrosteric stabilization of colloidal latex dispersions
    Einarson, Maryann B.; Berg, John C.
    Journal of Colloid and Interface Science (1993), 155 (1), 165-72CODEN: JCISA5; ISSN:0021-9797.
    Exptl. stability domains of monodisperse aq. polystyrene latexes, with and without steric stabilizers, are detd. in terms of early-stage kinetics of flocculation using photon correlation spectroscopy. Dispersion stability as a function of electrolyte concn. and counterion valence is investigated. A low-mol.-wt. ethylene oxide-propylene oxide block copolymer is used as the steric stabilizer. Aggregation is induced by the addn. of indifferent electrolyte. The rates of aggregate formation are expressed in terms of a stability ratio and interpreted in terms of the particle pair interaction potential function. For the system investigated both electrostatic and steric repulsions are important in maintaining dispersion stability. Consistent with earlier results, systems with adsorbed block copolymer increase the crit. coagulation concn. for fast aggregation by nearly an order of magnitude.
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    Romero-Cano, M. S.; Martín-Rodríguez, A.; De las Nieves, F. J. Electrosteric Stabilization of Polymer Colloids with Different Functionality. Langmuir 2001, 17, 3505– 3511,  DOI: 10.1021/la001659l
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    Electrosteric Stabilization of Polymer Colloids with Different Functionality
    Romero-Cano, M. S.; Martin-Rodriguez, A.; de Nieves, F. J.
    Langmuir (2001), 17 (11), 3505-3511CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
    The stability factor (W) of polymer colloids with different functionality before and after adsorption of Triton X-100 was studied. Exptl. log W vs. log [electrolyte] plots for bare particles were fitted using the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, and values of diffuse potential (ψd) and the Hamaker const. (A) were obtained. In the same way, log W vs. log [electrolyte] plots for some latex-surfactant complexes were fitted using the extended DLVO theory, which considers steric repulsive interactions. Kinetic information was used to reduce the no. of fitting parameters of the steric repulsive potentials. In this way, the thickness of the stabilizing layer (δ) was the fitting parameter. The extended DLVO theory explains directly the results of some of the latex-surfactant complexes. However, in other cases, addnl. mechanisms had to be considered to explain the results. All these discrepancies could indicate that electrostatic and steric repulsion energies are not completely independent.
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    Bremmell, K. E.; Jameson, G. J.; Biggs, S. Polyelectrolyte Adsorption at the Solid/Liquid Interface Interaction Forces and Stability. Colloids Surf., A 1998, 139, 199– 211,  DOI: 10.1016/S0927-7757(98)00281-7
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    The forces between neg. charged surfaces in the presence of an adsorbing cationic copolymer of acrylamide and 2-(methacryloyloxy)ethyltrimethylammonium chloride have been investigated using an at. force microscope. The results were compared with measurements from adsorption isotherm, electrophoretic mobility, stability, and light scattering expts. The adsorbed amt. of polyelectrolyte and adsorbed layer conformation at the solid/liq. interface were found to be strongly dependent on the polymer concn. from which initial adsorption takes place. At low polyelectrolyte concns. unstable silica suspensions were obsd. from stability tests; light scattering expts. indicate a large aggregate size under equiv. conditions. The adsorbed amt. was also seen to be low, well less than monolayer coverage, and force measurements indicated that the polymer was adsorbed in a flat conformation. At high polyelectrolyte concns., an increase in the adsorbed amt. was obsd. which resulted in a higher surface coverage, a higher mobility and a stable suspension. Direct force measurements indicated the presence of an electrosteric barrier.
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    Byard, S. J.; Blanazs, A.; Miller, J. F.; Armes, S. P. Cationic Sterically Stabilized Diblock Copolymer Nanoparticles Exhibit Exceptional Tolerance toward Added Salt. Langmuir 2019, 35, 14348– 14357,  DOI: 10.1021/acs.langmuir.9b02789
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    Cationic Sterically Stabilized Diblock Copolymer Nanoparticles Exhibit Exceptional Tolerance toward Added Salt
    Byard, Sarah J.; Blanazs, Adam; Miller, John F.; Armes, Steven P.
    Langmuir (2019), 35 (44), 14348-14357CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
    For certain com. applications such as enhanced oil recovery, sterically stabilized colloidal dispersions that exhibit high tolerance toward added salt are desirable. Herein, we report a series of new cationic diblock copolymer nanoparticles that display excellent colloidal stability in concd. aq. salt solns. More specifically, poly(2-(acryloyloxy)ethyltrimethylammonium chloride) (PATAC) has been chain-extended by reversible addn.-fragmentation chain transfer aq. dispersion polymn. of diacetone acrylamide (DAAM) at 70 °C to produce PATAC100-PDAAMx diblock copolymer spheres at 20% wt./wt. solids via polymn.-induced self-assembly. Transmission electron microscopy and dynamic light scattering (DLS) anal. confirm that the mean sphere diam. can be adjusted by systematic variation of the mean d.p. of the PDAAM block. Remarkably, DLS studies confirm that highly cationic PATAC100-PDAAM1500 spheres retain their colloidal stability in the presence of either 4.0 M KCl or 3.0 M ammonium sulfate for at least 115 days at 20 °C. The mole fraction of PATAC chains within the stabilizer shell was systematically varied by the chain extension of various binary mixts. of non-ionic poly(N,N-dimethylacrylamide) (PDMAC) and cationic PATAC with DAAM to produce ([n] PATAC100 + [1 - n] PDMAC67)-PDAAMz diblock copolymer spheres at 20% wt./wt. DLS studies confirmed that a relatively high mole fraction of cationic PATAC stabilizer chains (n ≥ 0.75) is required for the dispersions to remain colloidally stable in 4.0 M KCl. Cationic worms and vesicles could also be synthesized using a binary mixt. of PATAC and PDMAC precursors, where n = 0.10. However, the vesicles only remained colloidally stable up to 1.0 M KCl, whereas the worms proved to be stable up to 2.0 M KCl. Such block copolymer nanoparticles are expected to be useful model systems for understanding the behavior of aq. colloidal dispersions in extremely salty media. Finally, zeta potentials detd. using electrophoretic light scattering are presented for such nanoparticles dispersed in highly salty media.
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    Huang, B.; Jiang, J.; Kang, M.; Liu, P.; Sun, H.; Li, B. G.; Wang, W. J. Synthesis of Block Cationic Polyacrylamide Precursors Using an Aqueous RAFT Dispersion Polymerization. RSC Adv. 2019, 9, 12370– 12383,  DOI: 10.1039/C9RA02716E
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    Synthesis of block cationic polyacrylamide precursors using an aqueous RAFT dispersion polymerization
    Huang, Bo; Jiang, Jie; Kang, Mutian; Liu, Pingwei; Sun, Hailong; Li, Bo-Geng; Wang, Wen-Jun
    RSC Advances (2019), 9 (22), 12370-12383CODEN: RSCACL; ISSN:2046-2069. (Royal Society of Chemistry)
    Synthesis of cationic polyacrylamides (CPAMs) by introducing cationic polymer precursors followed by chain extension of acrylamide (AM) homopolymer blocks via RAFT polymn. is a promising approach for engineering high-performance CPAMs. Herein a novel approach is introduced that uses a random copolymer of AM and methacryloxyethyltrimethyl ammonium chloride (DMC) as a macro RAFT chain transfer agent (mCTA) and stabilizer for aq. RAFT dispersion polymn. of AM. The AM/DMC random copolymers synthesized by RAFT soln. polymn., having narrow dispersities (Ds) at different mol. wts. and cationic degrees (Cs), could serve as the mCTA, which was confirmed by mCTA chain extension in aq. soln. polymn. of AM under different Cs, solid contents, AM addn. contents, extended PAM block lengths, and mCTA chain lengths. The block CPAMs had a D value of less than 1.2.A model was developed using the method of moments with consideration of the diffusion control effect, for further understanding the chain extension kinetics. The AM/DMC random copolymers were further used for aq. RAFT dispersion polymn. of AM under different polymn. temps., Cs, and mCTA chain lengths. The products remained stable at room temp. storage for more than a month. The results indicate that aq. RAFT dispersion polymn. using random copolymers of AM and DMC at moderate cationic degrees as a stabilizer and mCTA is a suitable approach for synthesizing CPAM block precursors at an elevated solid content.
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    Kikuchi, M.; Terayama, Y.; Ishikawa, T.; Hoshino, T.; Kobayashi, M.; Ogawa, H.; Masunaga, H.; Koike, J. I.; Horigome, M.; Ishihara, K.; Takahara, A. Chain Dimension of Polyampholytes in Solution and Immobilized Brush States. Polym. J. 2012, 44, 121– 130,  DOI: 10.1038/pj.2011.116
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    Chain dimension of polyampholytes in solution and immobilized brush states
    Kikuchi, Moriya; Terayama, Yuki; Ishikawa, Tatsuya; Hoshino, Taiki; Kobayashi, Motoyasu; Ogawa, Hiroki; Masunaga, Hiroyasu; Koike, Jun-ichiro; Horigome, Misao; Ishihara, Kazuhiko; Takahara, Atsushi
    Polymer Journal (Tokyo, Japan) (2012), 44 (1), 121-130CODEN: POLJB8; ISSN:0032-3896. (NPG Nature Asia-Pacific)
    The dimensions and intermol. interactions of surface-grafted and unbound, free polyampholytes, poly[3-(N-2-methacryloyloxyethyl-N,N-dimethyl) ammonatopropanesulfonate] (PMAPS) and poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC), were estd. in an aq. NaCl soln. over a wide range of salt concns. (Cs). The free PMAPS and PMPC fractionated by a recycling preparative size-exclusion chromatog. system were characterized in aq. NaCl solns. for Cs over a range from 0 to 5.0 M by static light scattering and dynamic light scattering (DLS) measurements. The hydrodynamic radius (RH) and the concn. coeff. of the diffusion coeff. (kD) for PMPC were independent of Cs, whereas those for PMAPS were strongly dependent on Cs. Monodisperse silica nanoparticles immobilized with PMAPS (SiNP-PMAPS) and PMPC (SiNP-PMPC) by surface-initiated atom transfer radical polymn. were characterized in aq. NaCl solns. for Cs over a range from 0 to 5.0 M by DLS and synchrotron radiation small-angle X-ray scattering (SAXS) measurements. The SAXS profiles from SiNP-PMAPS and SiNP-PMPC solns. were well described by the core-shell model, taking into account interacting self-avoiding chains and assuming a Schulz-distributed core with two fitting parameters.
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    Jhan, Y. Y.; Tsay, R. Y. Salt Effects on the Hydration Behavior of Zwitterionic Poly(Sulfobetaine Methacrylate) Aqueous Solutions. J. Taiwan Inst. Chem. Eng. 2014, 45, 3139– 3145,  DOI: 10.1016/j.jtice.2014.08.022
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    Salt effects on the hydration behavior of zwitterionic poly(sulfobetaine methacrylate) aqueous solutions
    Jhan, Yong-Yu; Tsay, Ruey-Yug
    Journal of the Taiwan Institute of Chemical Engineers (2014), 45 (6), 3139-3145CODEN: JTICA8; ISSN:1876-1070. (Elsevier B.V.)
    Hydration behavior of a biomaterial is thought to be closely related to its bio/blood compatibility and subsequent biol. responses. Poly(sulfobetaine methacrylate) (pSBMA) is one of the biomimetic materials that exhibits excellent biocompatibility. It has been reported that the zwitterionic pSBMA exhibits "antipolyelectrolyte" behavior, which changes polymer conformations and antifouling properties, in solns. contg. salt ions. In this study, we identified water hydrated states of pSBMA by thermal anal. of DSC in various salt concns. With the addn. of miniscule salts, ions are attracted to the zwitterionic groups and the hydrated states are significantly changed. The attracted ions promote the incorporation of water mols. into polymer chains and enhance the soly. of pSBMA. Nevertheless, when large amts. of salts are added into the system, the excess ions tend to bind with free water mols., which may impose an osmotic pressure on the hydrated pSBMA mols. and causes the shrinkage of the mols. The present results demonstrated that salt has a significant effect on pSBMA-water interactions, which may affect the biocompatibility of the material.
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    Doncom, K. E. B.; Warren, N. J.; Armes, S. P. Polysulfobetaine-Based Diblock Copolymer Nano-Objects via Polymerization-Induced Self-Assembly. Polym. Chem. 2015, 6, 7264– 7273,  DOI: 10.1039/C5PY00396B
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    Polysulfobetaine-based diblock copolymer nano-objects via polymerization-induced self-assembly
    Doncom, Kay E. B.; Warren, Nicholas J.; Armes, Steven P.
    Polymer Chemistry (2015), 6 (41), 7264-7273CODEN: PCOHC2; ISSN:1759-9962. (Royal Society of Chemistry)
    A zwitterionic polysulfobetaine-based macromol. chain transfer agent (PSBMA38) was prepd. by reversible addn.-fragmentation chain transfer (RAFT) soln. polymn. of [2-(methacryloyloxy)ethyl] dimethyl(3-sulfopropyl) ammonium hydroxide (SBMA) in an aq. soln. contg. 0.5 M NaCl at 70 °C. This PSBMA38 macro-CTA was then utilized for the RAFT aq. dispersion polymn. of a water-miscible monomer, 2-hydroxypropyl methacrylate (HPMA). The growing PHPMA block became hydrophobic in situ, leading to polymn.-induced self-assembly. Systematic variation of the mean d.p. of the PHPMA block and the copolymer concn. enabled access to pure phases of spheres, worms or vesicles, as judged by transmission electron microscopy and dynamic light scattering studies. A detailed phase diagram was constructed and the thermo-responsive behavior of selected PSBMA38-PHPMAX nanoparticles was investigated. Finally, the salt tolerance of PSBMA38-PHPMA400 vesicles was compared to that of PGMA71-PHPMA400 vesicles; the former vesicles exhibit much better colloidal stability in the presence of 1 M MgSO4.
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    Jones, E. R.; Semsarilar, M.; Blanazs, A.; Armes, S. P. Efficient Synthesis of Amine-Functional Diblock Copolymer Nanoparticles via RAFT Dispersion Polymerization of Benzyl Methacrylate in Alcoholic Media. Macromolecules 2012, 45, 5091– 5098,  DOI: 10.1021/ma300898e
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    Efficient Synthesis of Amine-Functional Diblock Copolymer Nanoparticles via RAFT Dispersion Polymerization of Benzyl Methacrylate in Alcoholic Media
    Jones, Elizabeth R.; Semsarilar, Mona; Blanazs, Adam; Armes, Steven P.
    Macromolecules (Washington, DC, United States) (2012), 45 (12), 5091-5098CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    Benzyl methacrylate (BzMA) is polymd. via reversible addn.-fragmentation chain transfer (RAFT) chem. under alc. dispersion polymn. conditions in ethanol using a poly(2-(dimethylamino)ethyl methacrylate) (PDMA) chain transfer agent (CTA) at 70 °C. In principle, polymn.-induced self-assembly can lead to the formation of either spherical micelles, worm-like micelles, or vesicles, with the preferred morphol. being dictated by the hydrophilic-hydrophobic balance of the PDMA-PBzMA diblock copolymer chains. Very high monomer conversions (>99%) are routinely obtained within 24 h as judged by 1H NMR studies. Moreover, THF GPC analyses confirmed that relatively low polydispersities (Mw/Mn < 1.30) are achieved, indicating reasonably good pseudoliving character. A detailed phase diagram was constructed using a PDMA31 macro-CTA by systematically varying both the target d.p. of the PBzMA block and the total solids concn. of the reaction soln. This phase diagram can be used to reliably predict the synthesis conditions required to produce pure phases, rather than merely mixed phases (e.g., spheres plus worms or worms plus vesicles). Finally, these PDMA-PBzMA diblock copolymer nanoparticles remain colloidally stable when transferred from ethanol into water; aq. electrophoresis studies confirmed that the particles acquire appreciable cationic character below pH 7 due to protonation of the PDMA stabilizer chains.
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    Bray, C.; Peltier, R.; Kim, H.; Mastrangelo, A.; Perrier, S. Anionic Multiblock Core Cross-Linked Star Copolymers: Via RAFT Polymerization. Polym. Chem. 2017, 8, 5513– 5524,  DOI: 10.1039/C7PY01062A
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    Anionic multiblock core cross-linked star copolymers via RAFT polymerization
    Bray, Caroline; Peltier, Raoul; Kim, Hyungsoo; Mastrangelo, Antonio; Perrier, Sebastien
    Polymer Chemistry (2017), 8 (36), 5513-5524CODEN: PCOHC2; ISSN:1759-9962. (Royal Society of Chemistry)
    Reversible addn. fragmentation chain transfer (RAFT) polymn. was used to prep. a range of well-defined homopolymers and block copolymers of 2-acrylamido-2-methylpropane sulfonic acid (AMPS) and either N-hydroxyethyl acrylamide (HEAm) or 4-acryloylmorpholine (NAM) as a comonomer. The one-pot synthesis of multiblock core cross-linked star copolymers of AMPS and HEAm with low dispersities (<1.3) is also reported. The influence of several parameters such as the cross-linker type, cross-linker to chain transfer agent (CTA) ratio, arm length and compn. on the polymn. efficiency are investigated.
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    Functional Polymers from Novel Carboxyl-Terminated Trithiocarbonates as Highly Efficient RAFT Agents
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    Macromolecules (2002), 35 (18), 6754-6756CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    S,S'-bis-(isobutyric acid)-trithiocarbonate and derivs. can be used as a highly efficient chain transfer agent for polymns. of monomers such as free radical polymerizable monomers. Homopolymers, copolymers and the like and block copolymers can be made utilizing the trithiocarbonate compd. such as in a controlled free radical polymn., with narrow mol. distributions and to form telechelic and other functional polymers. These novel reversible addn.-fragmentation transfer (RAFT) agents are practically synthesized as pure solids with low sulfur odor. Process for making S,S'-bis-(isobutyric acid)-trithiocarbonate was successfully scaled up in a 100 gal reactor.
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    The complex permittivity of aq. solns. at 20 °C has been measured at concns. between 0.001 and 5 mol/L and over a frequency range 0.13-20 GHz. The results were combined with literature values to derive empirical equations to predict the dielec. behavior of sodium chloride solns. between 0 and 5 mol/L and 5°C-35°C. Bioelectromagnetics 28:264-274, 2007.
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    We theor. investigate electrostatic properties between two charged surfaces with a grafted polyelectrolyte layer in an aq. electrolyte soln. by using the Poisson-Boltzmann approach accounting for ion partitioning. In order to consider the ion partitioning effect, we focus on changes of electrostatic properties due to the difference in dielec. permittivity of the polyelectrolyte layer and the aq. electrolyte soln. We find that ion partitioning enhances electrostatic potential in the region between two charged soft surfaces and hence increases the electrostatic interaction between two charged soft surfaces. Ion partitioning effect on osmotic pressure is enhanced not only by an increase in the thickness of polyelectrolyte layer and Debye length but also by a decrease in ion radius.
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    Warren, N. J.; Muise, C.; Stephens, A.; Armes, S. P.; Lewis, A. L. Near-Monodisperse Poly(2-(Methacryloyloxy)Ethyl Phosphorylcholine)-Based Macromonomers Prepared by Atom Transfer Radical Polymerization and Thiol-Ene Click Chemistry: Novel Reactive Steric Stabilizers for Aqueous Emulsion Polymerization. Langmuir 2012, 28, 2928– 2936,  DOI: 10.1021/la204083z
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    Near-Monodisperse Poly(2-(methacryloyloxy)ethyl phosphorylcholine)-Based Macromonomers Prepared by Atom Transfer Radical Polymerization and Thiol-Ene Click Chemistry: Novel Reactive Steric Stabilizers for Aqueous Emulsion Polymerization
    Warren, Nicholas J.; Muise, Carl; Stephens, Alex; Armes, Steven P.; Lewis, Andrew L.
    Langmuir (2012), 28 (5), 2928-2936CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
    Poly(2-(methacryloyloxy)ethyl phosphorylcholine) (PMPC) macromonomers have been prepd. by the atom transfer radical polymn. (ATRP) of 2-(methacryloyloxy)ethyl phosphorylcholine (MPC) using a bifunctional disulfide-based initiator. To attach a terminal polymerizable methacrylate group, the central disulfide bond was cleaved and the resulting thiols were conjugated to 3-(acryloyloxy)-2-hydroxypropyl methacrylate using tris(2-carboxyethyl)phosphine (TCEP) in water. Here TCEP serves as both the disulfide cleavage agent and also the catalyst for the subsequent Michael addn., which is highly selective for the acrylate group. The resulting methacrylate-terminated macromonomers were used as a reactive steric stabilizer for the aq. emulsion polymn. of styrene, yielding near-monodisperse PMPC-stabilized polystyrene (PS) latexes of around 100-200 nm in diam. As a comparison, the disulfide-contg. PMPC homopolymer precursor and the intermediate thiol-functional PMPC homopolymer (PMPC-SH) were also evaluated as potential steric stabilizers. Interestingly, near-monodisperse latexes were also obtained in each case. These three sterically-stabilized latexes, prepd. using either PMPC macromonomer, disulfide-based PMPC homopolymer, or PMPC-SH homopolymer as a reactive steric stabilizer, remained colloidally stable after both freeze-thaw expts. and the addn. of an electrolyte, indicating that a coronal layer of PMPC chains prevented flocculation in each case. In contrast, both a charge-stabilized PS latex prepd. in the absence of any steric stabilizer and a PS latex prepd. in the presence of a nonfunctional PMPC homopolymer exhibited very poor colloidal stability when subjected to a freeze-thaw cycle or the addn. of an electrolyte, as expected.
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    Williams, M.; Penfold, N. J. W.; Armes, S. P. Cationic and Reactive Primary Amine-Stabilised Nanoparticles via RAFT Aqueous Dispersion Polymerisation. Polym. Chem. 2016, 7, 384– 393,  DOI: 10.1039/C5PY01577D
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    Cationic and reactive primary amine-stabilized nanoparticles via RAFT aqueous dispersion polymerisation
    Williams, M.; Penfold, N. J. W.; Armes, S. P.
    Polymer Chemistry (2016), 7 (2), 384-393CODEN: PCOHC2; ISSN:1759-9962. (Royal Society of Chemistry)
    The synthesis of primary amine-functionalized diblock copolymer nanoparticles via polymn.-induced self-assembly (PISA) using a RAFT aq. dispersion polymn. formulation is reported. The primary amine steric stabilizer is a macromol. chain transfer agent (macro-CTA) based on 2-aminoethyl methacrylate AMA, which can be readily polymd. in its hydrochloride salt form with good control (Mw/Mn < 1.30) using RAFT aq. soln. polymn. Subsequent chain extension of this macro-CTA with 2-hydroxypropyl methacrylate (HPMA) leads to the formation of relatively monodisperse spherical nanoparticles (68 to 288 nm) at pH 6. However, worms or vesicles could not be obtained, because strong lateral repulsion between the highly cationic PAMA stabilizer chains impedes the formation of these higher order copolymer morphologies. Deprotonation of the primary amine stabilizer chains at or above pH 9 results in flocculation of these spherical nanoparticles as the PAMA block becomes uncharged. Diblock copolymer spheres, worms or vesicles can be synthesized that remain stable at pH 9 by supplementing the PAMA macro-CTA with a poly(glycerol monomethacrylate) (PGMA) macro-CTA, since this non-ionic block confers effective steric stabilization in alk. media. A series of diblock copolymer nanoparticles with the general formula ([1 - n]PGMAx + nPAMAy)-PHPMAz can be synthesized by optimizing: (i) the mean degree of polymn. (DP, or x) of the PGMA block, (ii) the PHPMA core-forming DP (or z); (iii) the mol. fraction (n) of the PAMA stabilizer; and (iv) the copolymer concn. These spheres, worms and vesicles are both cationic at low pH and colloidally stable at high pH. Furthermore, deprotonation of the protonated primary amine groups on the PAMA stabilizer chains at high pH renders these particles susceptible to epoxy-amine conjugation. This is demonstrated by the reaction between the primary amine groups on (0.8PGMA101 + 0.2PAMA96)-PHPMA1000 diblock copolymer spheres, and epoxide-functionalised diblock copolymer nanoparticles in aq. soln. at pH 8.
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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, 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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    Derry, M. J.; Fielding, L. A.; Warren, N. J.; Mable, C. J.; Smith, A. J.; Mykhaylyk, O. O.; Armes, S. P. In Situ Small-Angle X-Ray Scattering Studies of Sterically-Stabilized Diblock Copolymer Nanoparticles Formed during Polymerization-Induced Self-Assembly in Non-Polar Media. Chem. Sci. 2016, 7, 5078– 5090,  DOI: 10.1039/C6SC01243D
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    In situ small-angle X-ray scattering studies of sterically-stabilized diblock copolymer nanoparticles formed during polymerization-induced self-assembly in non-polar media
    Derry, Matthew J.; Fielding, Lee A.; Warren, Nicholas J.; Mable, Charlotte J.; Smith, Andrew J.; Mykhaylyk, Oleksandr O.; Armes, Steven P.
    Chemical Science (2016), 7 (8), 5078-5090CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
    Reversible addn.-fragmentation chain transfer (RAFT) dispersion polymn. of benzyl methacrylate (BzMA) is utilized to prep. a series of poly(stearyl methacrylate)-poly(benzyl methacrylate) (PSMA-PBzMA) diblock copolymer nano-objects at 90°C directly in mineral oil. Polymn.-induced self-assembly (PISA) occurs under these conditions, with the resulting nanoparticles exhibiting spherical, worm-like or vesicular morphologies when using a relatively short PSMA13 macromol. chain transfer agent (macro-CTA), as confirmed by transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS) studies. Only kinetically-trapped spherical nanoparticles are obtained when using longer macro-CTAs (e.g. PSMA18 or PSMA31), with higher mean ds.p. (DPs) for the PBzMA core-forming block simply producing progressively larger spheres. SAXS is used for the first time to monitor the various morphol. transitions that occur in situ during the RAFT dispersion polymn. of BzMA when targeting either spheres or vesicles as the final copolymer morphol. This powerful characterization technique enables the evolution of particle diam., mean aggregation no., no. of copolymer chains per unit surface area (Sagg) and the distance between adjacent copolymer chains at the core-shell interface (ditt) to be monitored as a function of monomer conversion for kinetically-trapped spheres. Moreover, the gradual evolution of copolymer morphol. during PISA is confirmed unequivocally, with approx. 'lifetimes' assigned to the intermediate pure sphere and worm morphologies when targeting PSMA13-PBzMA150 vesicles. Within vesicle phase space, the membrane thickness (Tm) increases monotonically with PBzMA DP. Furthermore, a combination of dynamic light scattering (DLS), TEM and post mortem SAXS studies indicate that the lumen vol. is reduced while the overall vesicle dimensions remain essentially const. Thus the constrained vesicles grow inwards, as recently reported for an aq. PISA formulation. This suggests a universal vesicle growth mechanism for all PISA formulations.
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  52. 52
    Byard, S. J.; Williams, M.; McKenzie, B. E.; Blanazs, A.; Armes, S. P. Preparation and Cross-Linking of All-Acrylamide Diblock Copolymer Nano-Objects via Polymerization-Induced Self-Assembly in Aqueous Solution. Macromolecules 2017, 50, 1482– 1493,  DOI: 10.1021/acs.macromol.6b02643
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    Preparation and Cross-Linking of All-Acrylamide Diblock Copolymer Nano-Objects via Polymerization-Induced Self-Assembly in Aqueous Solution
    Byard, Sarah J.; Williams, Mark; McKenzie, Beulah E.; Blanazs, Adam; Armes, Steven P.
    Macromolecules (Washington, DC, United States) (2017), 50 (4), 1482-1493CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    Various carboxylic acid-functionalized poly(N,N-dimethylacrylamide) (PDMAC) macromol. chain transfer agents (macro-CTAs) were chain-extended with diacetone acrylamide (DAAM) by reversible addn.-fragmentation chain transfer (RAFT) aq. dispersion polymn. at 70 °C and 20% wt./wt. solids to produce a series of PDMAC-PDAAM diblock copolymer nano-objects via polymn.-induced self-assembly (PISA). TEM studies indicate that a PDMAC macro-CTA with a mean d.p. (DP) of 68 or higher results in the formation of well-defined spherical nanoparticles with mean diams. ranging from 40 to 150 nm. In contrast, either highly anisotropic worms or polydisperse vesicles are formed when relatively short macro-CTAs (DP = 40-58) are used. A phase diagram was constructed to enable accurate targeting of pure copolymer morphologies. Dynamic light scattering (DLS) and aq. electrophoresis studies indicated that in most cases these PDMAC-PDAAM nano-objects are surprisingly resistant to changes in either soln. pH or temp. However, PDMAC40-PDAAM99 worms do undergo partial dissocn. to form a mixt. of relatively short worms and spheres on adjusting the soln. pH from pH 2-3 to around pH 9 at 20 °C. Moreover, a change in copolymer morphol. from worms to a mixt. of short worms and vesicles was obsd. by DLS and TEM on heating this worm dispersion to 50 °C. Postpolymn. crosslinking of concd. aq. dispersions of PDMAC-PDAAM spheres, worms, or vesicles was performed at ambient temp. using adipic acid dihydrazide (ADH), which reacts with the hydrophobic ketone-functionalized PDAAM chains. The formation of hydrazone groups was monitored by FT-IR spectroscopy and afforded covalently stabilized nano-objects that remained intact on exposure to methanol, which is a good solvent for both blocks. Rheol. studies indicated that the cross-linked worms formed a stronger gel compared to linear precursor worms.
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  53. 53
    Parker, B. R.; Derry, M. J.; Ning, Y.; Armes, S. P. Exploring the Upper Size Limit for Sterically Stabilized Diblock Copolymer Nanoparticles Prepared by Polymerization-Induced Self-Assembly in Non-Polar Media. Langmuir 2020, 36, 3730– 3736,  DOI: 10.1021/acs.langmuir.0c00211
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    Exploring the Upper Size Limit for Sterically Stabilized Diblock Copolymer Nanoparticles Prepared by Polymerization-Induced Self-Assembly in Non-Polar Media
    Parker, Bryony R.; Derry, Matthew J.; Ning, Yin; Armes, Steven P.
    Langmuir (2020), 36 (14), 3730-3736CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
    Reversible addn.-fragmentation chain transfer (RAFT) dispersion polymn. of benzyl methacrylate is used to prep. a series of well-defined poly(stearyl methacrylate)-poly(benzyl methacrylate) (PSMA-PBzMA) diblock copolymer nanoparticles in mineral oil at 90°C. A relatively long PSMA54 precursor acts as a steric stabilizer block and also ensures that only kinetically trapped spheres are obtained, regardless of the target d.p. (DP) for the core-forming PBzMA block. This polymn.-induced self-assembly (PISA) formulation provides good control over the particle size distribution over a wide size range (24-459 nm diam.). 1H NMR spectroscopy studies confirm that high monomer conversions (≥96%) are obtained for all PISA syntheses while transmission electron microscopy and dynamic light scattering analyses show well-defined spheres with a power-law relationship between the target PBzMA DP and the mean particle diam. Gel permeation chromatog. studies indicate a gradual loss of control over the mol. wt. distribution as higher DPs are targeted, but well-defined morphologies and narrow particle size distributions can be obtained for PBzMA DPs up to 3500, which corresponds to an upper particle size limit of 459 nm. Thus, these are among the largest well-defined spheres with reasonably narrow size distributions (std. deviation ≤20%) produced by any PISA formulation. Such large spheres serve as model sterically stabilized particles for anal. centrifugation studies.
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    Cunningham, V. J.; Armes, S. P.; Musa, O. M. Synthesis, Characterisation and Pickering Emulsifier Performance of Poly(Stearyl Methacrylate)-Poly(N-2-(Methacryloyloxy)Ethyl Pyrrolidone) Diblock Copolymer Nano-Objects via RAFT Dispersion Polymerisation in n-Dodecane. Polym. Chem. 2016, 7, 1882– 1891,  DOI: 10.1039/C6PY00138F
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    Synthesis, characterisation and Pickering emulsifier performance of poly(stearyl methacrylate)-poly(N-2-(methacryloyloxy)ethyl pyrrolidone) diblock copolymer nano-objects via RAFT dispersion polymerization in n-dodecane
    Cunningham, V. J.; Armes, S. P.; Musa, O. M.
    Polymer Chemistry (2016), 7 (10), 1882-1891CODEN: PCOHC2; ISSN:1759-9962. (Royal Society of Chemistry)
    A near-monodisperse poly(stearyl methacrylate) macromol. chain transfer agent (PSMA macro-CTA) was prepd. via reversible addn.-fragmentation chain transfer (RAFT) soln. polymn. in toluene. This PSMA macro-CTA was then utilized as a stabilizer block for the RAFT dispersion polymn. of a highly polar monomer, N-2-(methacryloyloxy)ethyl pyrrolidone (NMEP), in n-dodecane at 90 °C. 1H NMR studies confirmed that the rate of NMEP polymn. was significantly faster than that of a non-polar monomer (benzyl methacrylate, BzMA) under the same conditions. For example, when targeting a PSMA14-PNMEP100 diblock copolymer, more than 99% NMEP conversion was achieved within 30 min, whereas only 19% BzMA conversion was obtained on the same time scale for the corresponding PSMA14-PBzMA100 synthesis. The resulting PSMA-PNMEP diblock copolymer chains underwent polymn.-induced self-assembly (PISA) during growth of the insol. PNMEP block to form either spherical micelles, highly anisotropic worms or polydisperse vesicles, depending on the target DP of the PNMEP chains. Systematic variation of this latter parameter, along with the solids content, allowed the construction of a phase diagram which enabled pure morphologies to be reproducibly targeted. Syntheses conducted at 10% wt./wt. solids led to the formation of kinetically-trapped spheres. A monotonic increase in particle diam. with PNMEP DP was obsd. for such PISA syntheses, with particle diams. of up to 462 nm being obtained for PSMA14-PNMEP960. Increasing the copolymer concn. to 15% wt./wt. solids led to worm-like micelles, while vesicles were obtained at 27.5% wt./wt. solids. High (≥95%) NMEP conversions were achieved in all cases and 3 : 1 chloroform/methanol GPC anal. indicated relatively high blocking efficiencies. However, relatively broad mol. wt. distributions (Mw/Mn > 1.50) were obsd. when targeting PNMEP DPs greater than 150. This indicates light branching caused by the presence of a low level of dimethacrylate impurity. Finally, PSMA14-PNMEP49 spheres were evaluated as Pickering emulsifiers. Unexpectedly, it was found that either water-in-oil or oil-in-water Pickering emulsions could be obtained depending on the shear rate employed for homogenization. Further investigation suggested that high shear rates lead to in situ inversion of the initial hydrophobic PSMA14-PNMEP49 spheres to form hydrophilic PNMEP49-PSMA14 spheres.
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  1. Emma E. Brotherton, Daniel Josland, Csilla György, Edwin C. Johnson, Derek H.H. Chan, Mark J. Smallridge, Steven P. Armes. Histidine‐Functionalized Diblock Copolymer Nanoparticles Exhibit Enhanced Adsorption onto Planar Stainless Steel. Macromolecular Rapid Communications 2023, 59 , 2200903. https://doi.org/10.1002/marc.202200903
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  • Abstract

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    Scheme 1

    Scheme 1. Schematic Cartoon and Corresponding Digital Images to Illustrate the Sterically Stabilized Diblock Copolymer Particles in the Presence of 2.0 M Ammonium Sulfate Obtained after RAFT Aqueous Dispersion Polymerization of a Suitable Water-Soluble Monomer to Form the “Salted Out” Red Chainsa
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    aA four-fold dilution with deionized water lowers the salt concentration of the initial aqueous dispersion and results in molecular dissolution of these particles, with the concomitant formation of a highly viscous transparent aqueous solution.

    Scheme 2

    Scheme 2. Reaction Scheme for the Synthesis of PMPC139–PDMACx (x = 500 to 7000) Diblock Copolymer Particles via RAFT Aqueous Dispersion Polymerization of DMAC at 30 °C in the Presence of 2.0 M Ammonium Sulfatea
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    aConditions: targeting 20% w/w solids using a PMPC139–TTC/KPS molar ratio of 4.0 and a [KPS]/[AsAc] molar ratio of 1.0.

    Figure 1

    Figure 1. Aqueous GPC curves recorded for the PMPC139 precursor and a series of PMPC139–PDMACx diblock copolymers prepared by chain extension via RAFT aqueous dispersion polymerization of DMAC at 30 °C in the presence of 2.0 M ammonium sulfate. Mn values are calculated relative to a series of near-monodisperse poly(ethylene oxide) calibration standards (see Figure S2 for the corresponding normalized GPC curves).

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    Figure 2

    Figure 2. SAXS patterns recorded for 1.0% w/w aqueous dispersions of PMPC139–PDMACx particles (where x = 1000 or 3000) at 25 °C. The black solid lines denote the data fit obtained using a well-known spherical micelle model. (55−57)Dv denotes the volume-average diameter. The red pattern has been scaled by a factor of ten relative to the blue pattern for the sake of clarity.

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    Figure 3

    Figure 3. (a) Conversion vs time curve and corresponding semilogarithmic plot determined by 1H NMR spectroscopy for the RAFT aqueous dispersion polymerization of DMAC at 30 °C in 2.0 M ammonium sulfate when targeting a PDMAC DP of 5000 at 20% w/w solids. (b) Aqueous GPC curves obtained by periodic sampling of the reaction mixture to monitor the evolution in the molecular weight distribution (see Figure S3 for the corresponding normalized GPC curves).

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    Figure 4

    Figure 4. Optical microscopy image recorded for PMPC139–PDMAC5000 particles prepared at 20% w/w solids by RAFT aqueous dispersion polymerization of DMAC at 30 °C in the presence of 2.0 M ammonium sulfate.

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    Figure 5

    Figure 5. 1H NMR spectra recorded for a PDMAC500 (red spectrum) and a PMPC139 (blue spectrum) homopolymers in the absence of salt, as well as a PMPC139–PDMAC5000 diblock copolymer prepared at 20% w/w in D2O in the presence of 2.0 M ammonium sulfate, see the lowest black spectrum. As the 20% w/w PMPC139–PDMAC5000 dispersion is diluted with further D2O, both the background salt concentration and the copolymer concentration are systematically reduced (see four other black spectra). Just a two-fold dilution of the turbid dispersion is sufficient to cause molecular dissolution of the particles as the PDMAC block becomes solvated in 1.0 M ammonium sulfate. A further two-fold dilution of this transparent solution with D2O results in PMPC139–PDMAC5000 chains dissolved in 0.5 M ammonium sulfate, for which the PDMAC signals are now indistinguishable from those of PDMAC500 homopolymer in water (compare the uppermost black spectrum with the red spectrum).

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    Figure 6

    Figure 6. (a) Viscosity vs shear rate data obtained by rotational rheology studies of 10% w/w aqueous solutions of molecularly-dissolved PMPC139–PDMACx chains in the presence of 1.0 M ammonium sulfate. (b) Viscosity vs shear rate data obtained by rotational rheology studies of 20% w/w aqueous dispersions of either PMPC139–PDMAC3000 or PMPC139–PDMAC5000 particles in 2.0 M ammonium sulfate compared to that for 10% w/w aqueous solutions of the same two copolymers in the presence of 1.0 M ammonium sulfate.

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    Scheme 3

    Scheme 3. Chemical Structures of the Cationic PATAC195 and Anionic PAMPS250 Precursors Used to Stabilize PDMAC-Rich Diblock Copolymer Particles Prepared via RAFT Aqueous Dispersion Polymerization of DMAC in 2.0 M Ammonium Sulfate
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    Figure 7

    Figure 7. Apparent ζ potentials observed on addition of varying volumes of aqueous 0.2 M KOH solution in the presence of 2.0 M ammonium sulfate for 0.1% w/w aqueous dispersions of PATAC195–PDMAC1000 (red triangles), PMPC139–PDMAC1000 (green squares), or PAMPS250–PDMAC1000 (blue circles) particles.

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  • References

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      Australian Journal of Chemistry (2006), 59 (10), 669-692CODEN: AJCHAS; ISSN:0004-9425. (CSIRO Publishing)
      A review. This paper provides a first update to the review of living radical polymn. achieved with thiocarbonylthio compds. (ZC(=S)SR) by a mechanism of reversible addn.-fragmentation chain transfer (RAFT) published in June 2005. The time since that publication has witnessed an increased rate of publication on the topic with the appearance of well over 200 papers covering various aspects of RAFT polymn. ranging over reagent synthesis and properties, kinetics, and mechanism of polymn., novel polymer syntheses, and diverse applications.
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    3. 3
      Moad, G.; Rizzardo, E.; Thang, S. H. Living Radical Polymerization by the RAFT Process - A Second Update. Aust. J. Chem. 2009, 62, 1402,  DOI: 10.1071/CH09311
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      Living Radical Polymerization by the RAFT Process - A Second Update
      Moad, Graeme; Rizzardo, Ezio; Thang, San H.
      Australian Journal of Chemistry (2009), 62 (11), 1402-1472CODEN: AJCHAS; ISSN:0004-9425. (CSIRO Publishing)
      A review. This paper provides a second update to the review of reversible deactivation radical polymn. achieved with thiocarbonylthio compds. (ZC(=S)SR) by a mechanism of reversible addn.-fragmentation chain transfer (RAFT) that was published in June 2005 (Aust. J. Chem. 2005, 58, 379-410). The first update was published in Nov. 2006 (Aust. J. Chem. 2006, 59, 669-692). This review cites over 500 papers that appeared during the period mid-2006 to mid-2009 covering various aspects of RAFT polymn. ranging from reagent synthesis and properties, kinetics and mechanism of polymn., novel polymer syntheses and a diverse range of applications. Significant developments have occurred, particularly in the areas of novel RAFT agents, techniques for end-group removal and transformation, the prodn. of micro/nanoparticles and modified surfaces, and biopolymer conjugates both for therapeutic and diagnostic applications.
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    4. 4
      Moad, G.; Rizzardo, E.; Thang, S. H. Living Radical Polymerization by the RAFT Process – A Third Update. Aust. J. Chem. 2012, 65, 985,  DOI: 10.1071/CH12295
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      Living Radical Polymerization by the RAFT Process - A Third Update
      Moad, Graeme; Rizzardo, Ezio; Thang, San H.
      Australian Journal of Chemistry (2012), 65 (8), 985-1076CODEN: AJCHAS; ISSN:0004-9425. (CSIRO Publishing)
      A review. This paper provides a third update to the review of reversible deactivation radical polymn. (RDRP) achieved with thiocarbonylthio compds. (ZC(=S)SR) by a mechanism of reversible addn.-fragmentation chain transfer (RAFT) that was published in June 2005 (Aust. J. Chem. 2005, 58, 379). The first update was published in Nov. 2006 (Aust. J. Chem. 2006, 59, 669) and the second in Dec. 2009 (Aust. J. Chem. 2009, 62, 1402). This review cites over 700 publications that appeared during the period mid 2009 to early 2012 covering various aspects of RAFT polymn. which include reagent synthesis and properties, kinetics and mechanism of polymn., novel polymer syntheses, and a diverse range of applications. This period has witnessed further significant developments, particularly in the areas of novel RAFT agents, techniques for end-group transformation, the prodn. of micro/nanoparticles and modified surfaces, and biopolymer conjugates both for therapeutic and diagnostic applications.
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    5. 5
      Carmean, R. N.; Becker, T. E.; Sims, M. B.; Sumerlin, B. S. Ultra-High Molecular Weights via Aqueous Reversible-Deactivation Radical Polymerization. Chem 2017, 2, 93– 101,  DOI: 10.1016/j.chempr.2016.12.007
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      Ultra-High Molecular Weights Via Aqueous Reversible-Deactivation Radical Polymerization
      Carmean, R. Nicholas; Becker, Troy E.; Sims, Michael B.; Sumerlin, Brent S.
      Chem (2017), 2 (1), 93-101CODEN: CHEMVE; ISSN:2451-9294. (Cell Press)
      Relying solely on mild UV irradn. of thiocarbonylthio compds. in the presence of vinyl monomers, a new avenue to well-defined ultra-high-mol.-wt. (UHMW) polymers has been developed. Through the use of aq. conditions, well-controlled UHMW polymers that are unprecedented for controlled radical polymns. have been achieved. This photomediated polymn. approach reaches no.-av. mol. wts. in excess of 8.00 x 106 g/mol with ds.p. above 85,000, making these, to our knowledge, the highest-mol.-wt. polymers ever achieved via reversible-deactivation radical polymn. In many cases, well-defined UHMW polymers can be obtained in minutes. The utility of the technique is further demonstrated through the synthesis of block copolymers, enabling access to a new field of well-defined UHMW materials.
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    6. 6
      Read, E.; Guinaudeau, A.; Wilson, D. J.; Cadix, A.; Violleau, F.; Destarac, M. Low Temperature RAFT/MADIX Gel Polymerisation: Access to Controlled Ultra-High Molar Mass Polyacrylamides. Polym. Chem. 2014, 5, 2202– 2207,  DOI: 10.1039/c3py01750h
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      Low temperature RAFT/MADIX gel polymerisation: access to controlled ultra-high molar mass polyacrylamides
      Read, Emmanuelle; Guinaudeau, Aymeric; James Wilson, D.; Cadix, Arnaud; Violleau, Frederic; Destarac, Mathias
      Polymer Chemistry (2014), 5 (7), 2202-2207CODEN: PCOHC2; ISSN:1759-9962. (Royal Society of Chemistry)
      We pushed back the limits of molar mass control in aq. RAFT/MADIX polymn. through a fast and quant. gel polymn. of a series of acrylamido monomers. Unprecedentedly high Mn up to 106 g mol-1 with low dispersities (D < 1.2) was achieved in homopolymn., statistical and block copolymn. of a selection of acrylamido monomers such as AM, DMA, AMPS and NIPAM. The reasons for access to an abnormally high kinetic chain length in the presence of a RAFT/MADIX agent were discussed.
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    7. 7
      Carmean, R. N.; Sims, M. B.; Figg, C. A.; Hurst, P. J.; Patterson, J. P.; Sumerlin, B. S. Ultrahigh Molecular Weight Hydrophobic Acrylic and Styrenic Polymers through Organic-Phase Photoiniferter-Mediated Polymerization. ACS Macro Lett. 2020, 9, 613– 618,  DOI: 10.1021/acsmacrolett.0c00203
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      7
      Ultrahigh Molecular Weight Hydrophobic Acrylic and Styrenic Polymers through Organic-Phase Photoiniferter-Mediated Polymerization
      Carmean, R. Nicholas; Sims, Michael B.; Figg, C. Adrian; Hurst, Paul J.; Patterson, Joseph P.; Sumerlin, Brent S.
      ACS Macro Letters (2020), 9 (4), 613-618CODEN: AMLCCD; ISSN:2161-1653. (American Chemical Society)
      As many phys. properties of polymers scale with mol. wt., the ability to achieve polymers of nearly inaccessibly high mol. wt. provides an opportunity to probe the upper size limit of macromol. phenomena. Yet many of the most stimulating macromol. designs remain out of reach of current ultrahigh mol. wt. (UHMW) polymer synthetic approaches. Herein, we show that UHMW polymers of diverse compn. can be achieved by irradn. of thiocarbonylthio photoiniferters with long-wave UV or visible light in concd. org. soln. This facile photopolymn. strategy is general to acrylic-, acrylamido-, methacrylic-, and styrenic-based monomers, enabling the synthesis of well-defined macromols. with mol. wts. in excess of 106 g/mol. The high chain-end fidelity afforded by photoiniferter polymn. conditions facilitated the design of UHMW amphiphilic block copolymers, which were found to self-assemble into micellar morphologies up to 200 nm in diam.
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    8. 8
      Pelton, R. H.; Allen, L. H. The Effects of Some Electrolytes on Flocculation with a Cationic Polyacrylamide. Colloid Polym. Sci. 1983, 261, 485– 492,  DOI: 10.1007/BF01419832
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      The effects of some electrolytes on flocculation with a cationic polyacrylamide
      Pelton, R. H.; Allen, L. H.
      Colloid and Polymer Science (1983), 261 (6), 485-92CODEN: CPMSB6; ISSN:0303-402X.
      NaCl and Na2SO4 in the concn. range from 1 × 10-5 to 1 × 10-2 M, in the presence of Betz 1260 (I) [74811-71-5], caused negligible changes in the electrophoretic mobility (Em) and 1st-pass retention of TiO2 in cellulose pulp. Al2(SO4)3 at concns. from 1 × 10-5 to 1 × 10-2 M increased the retention of TiO2 in the presence of I; higher Al2(SO4)3 concns. resulted in lower retention, and at pH 4.0 the Em of TiO2 was pos. over the range of Al2(SO4)3 concns. investigated, whereas at pH 4.5 the Em was neg. at 1 × 10-5M Al2(SO4)3, and charge reversal was obsd. at ∼4 × 10-5M Al2(SO4)3. The intrinsic viscosity of aq. I solns. was decreased by the addn. of Al2(SO4)3, NaCl,and Na2SO4.
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    9. 9
      Klimchuk, K. A.; Hocking, M. B.; Lowen, S. Water-Soluble Acrylamide Copolymers. IX. Preparation and Characterization of the Cationic Derivatives of Poly(Acrylamide-Co-N, N-Dimethylacrylamide), Poly(Acrylamide-Co-Methacrylamide), and Poly(Acrylamide-Co-N-t-Butylacrylamide). J. Polym. Sci., Part A: Polym. Chem. 2001, 39, 2525– 2535,  DOI: 10.1002/pola.1229
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      9
      Water-soluble acrylamide copolymers. IX. Preparation and characterization of the cationic derivatives of poly(acrylamide-co-N,N-dimethyl acrylamide), poly(acrylamide-co-methacrylamide), and poly(acrylamide-co-N-t-butyl acrylamide)
      Klimchuk, Keith A.; Hocking, Martin B.; Lowen, Stephen
      Journal of Polymer Science, Part A: Polymer Chemistry (2001), 39 (14), 2525-2535CODEN: JPACEC; ISSN:0887-624X. (John Wiley & Sons, Inc.)
      This article extends the preparative details of a series of nonionic copolymers of acrylamide with N,N-di-Me acrylamide, methacrylamide, and N-t-Bu acrylamide to the synthesis of cationic derivs. of these new copolymers. The described procedures gave products with cationicities of 14-26 mol %. We measured the mean squared radii of gyration and intrinsic viscosities of aq. solns. of these products at several different pH and NaCl concns. to compare these values with those detd. for the nonionic precursors and related com. cationic polymers. Because the mol. wts. of the examples measured varied widely, it was difficult to establish definite trends. However, the large values obtained for the mean squared radii of gyration and intrinsic viscosities, relative to the nonionic precursors of these polymers, demonstrated that the charged groups had a qual. greater effect on polymer extension than the nonpolar bulky groups.
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    10. 10
      Guyot, A.; Chu, F.; Schneider, M.; Graillat, C.; McKenna, T. F. High Solid Content Latexes. Prog. Polym. Sci. 2002, 27, 1573– 1615,  DOI: 10.1016/S0079-6700(02)00014-X
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      High solid content latexes
      Guyot, A.; Chu, F.; Schneider, M.; Graillat, C.; McKenna, T. F.
      Progress in Polymer Science (2002), 27 (8), 1573-1615CODEN: PRPSB8; ISSN:0079-6700. (Elsevier Science Ltd.)
      This article is a review of the rheol. of concd. latexes, followed by a discussion of the state of the art in the area of high solids latex prodn. High solids content latexes are of growing interest for many reasons; however, making this type of product entails many difficulties. Increasing the solids content (fraction of polymer relative to the continuous phase) in a reproducible manner entails the strict control of a complex particle size distribution (PSD). The PSD must be either quite broad, or multimodal in order to obtain solids contents much above 55 or 60 vol.%. In addn., the viscosity of a latex is highly sensitive to the PSD near the upper limit of solids content, but it is still not possible to predict a priori how a complex PSD will effect the viscosity. This article presents an overview of the rheol. of concd. latexes, followed by a discussion of the state of the art in the area of high solids latex prodn.
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    11. 11
      Perrier, S. 50th Anniversary Perspective: RAFT Polymerization - A User Guide. Macromolecules 2017, 50, 7433– 7447,  DOI: 10.1021/acs.macromol.7b00767
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      11
      50th Anniversary Perspective: RAFT Polymerization-A User Guide
      Perrier, Sebastien
      Macromolecules (Washington, DC, United States) (2017), 50 (19), 7433-7447CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      A review. This Perspective summarizes the features and limitations of reversible addn.-fragmentation chain transfer (RAFT) polymn., highlighting its strengths and weaknesses, as our understanding of the process, from both a mechanistic and an application point of view, has matured over the past 20 years. It is aimed at both experts in the field and newcomers, including undergraduate and postgraduate students, as well as nonexperts in polymn. who are interested in developing their own polymeric structures by exploiting the simple setup of a RAFT polymn.
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    12. 12
      Chiefari, J.; Chong, Y. K.; Ercole, F.; Krstina, J.; Jeffery, J.; Le, T. P. T.; Mayadunne, R. T. A.; Meijs, G. F.; Moad, C. L.; Moad, G.; Rizzardo, E.; Thang, S. H. Living Free-Radical Polymerization by Reversible Addition - Fragmentation Chain Transfer: The RAFT Process. Macromolecules 1998, 31, 5559– 5562,  DOI: 10.1021/ma9804951
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      12
      Living Free-Radical Polymerization by Reversible Addition-Fragmentation Chain Transfer: The RAFT Process
      Chiefari, John; Chong, Y. K.; Ercole, Frances; Krstina, Julia; Jeffery, Justine; Le, Tam P. T.; Mayadunne, Roshan T. A.; Meijs, Gordon F.; Moad, Catherine L.; Moad, Graeme; Rizzardo, Ezio; Thang, San H.
      Macromolecules (1998), 31 (16), 5559-5562CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      A new living free-radical polymn. that involves reversible addn.-fragmentation chain transfer and is designated RAFT polymn. can be used with a wide rage of monomers and reaction conditions and provides controlled mol. wt. polymers with very narrow polydispersities. The RAFT process involves free radical polymn. in the presence of dithio compds. Mol. wt/conversion data are presented for polymers formed by bulk, soln., emulsion and suspension polymn. of acrylic and styrene monomers using azo or peroxy initiators. Major advantages of the RAFT polymn. process over other processes for living/controlled free-radical polymn. are discussed.
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    13. 13
      Destarac, M. Industrial Development of Reversible-Deactivation Radical Polymerization: Is the Induction Period Over?. Polym. Chem. 2018, 9, 4947– 4967,  DOI: 10.1039/C8PY00970H
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      Industrial development of reversible-deactivation radical polymerization: is the induction period over?
      Destarac, Mathias
      Polymer Chemistry (2018), 9 (40), 4947-4967CODEN: PCOHC2; ISSN:1759-9962. (Royal Society of Chemistry)
      Reversible-deactivation radical polymn. (RDRP) techniques are essential in modern polymer chem. Over the years, they have become not only fantastic lab tools for the easy prepn. of structurally complex polymers but also an industrial reality. This article reviews industrial developments and com. success based on RDRP processes. The nature of RDRP control agents is discussed and numerous industrial polymers and their applications are exemplified. While RDRP is firmly established as a powerful means for the development of next generation high-valued polymer products, there is room for improvement in terms of the cost/performance ratio for a broader adoption by industry. Some directions are proposed for the future.
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      Destarac, M.; Wilson, D. J.; Silvia, S. Controlled Radical Polymerization in Water-in-Water Dispersion. US10160821B2, 2018.
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      Wu, Y. M.; Wang, Y. P.; Yu, Y. Q.; Xu, J.; Chen, Q. F. Dispersion Polymerization of Acrylamide with 2-Acrylamido-2-Methyl-1- Propane Sulfonate in Aqueous Solution. J. Appl. Polym. Sci. 2006, 102, 2379– 2385,  DOI: 10.1002/app.24494
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      Dispersion polymerization of acrylamide with 2-acrylamido-2-methyl-1-propane sulfonate in aqueous solution
      Wu, Y. M.; Wang, Y. P.; Yu, Y. Q.; Xu, J.; Chen, Q. F.
      Journal of Applied Polymer Science (2006), 102 (3), 2379-2385CODEN: JAPNAB; ISSN:0021-8995. (John Wiley & Sons, Inc.)
      The copolymer of acrylamide (AM) and 2-acrylamido-2-methyl-1-propane sulfonate (AMPS) was synthesized through the free radical dispersion polymn. in an aq. soln. of ammonium sulfate and in the presence of poly(2-acrylamido-2-methyl-1-propane sulfonate) as stabilizer. The av. particle size of the copolymer ranged from 1 to 4 μm, and the mol. wt. was from 2.0 × 106 to 7.0 × 106 g mol-1. By analyzing apparent viscosity and particle size, the swelling property of the dispersion copolymer was studied. When the dispersion was dild. with salt water in which the ammonium sulfate concn. kept equal with that of the original dispersion, particle size and particle size distribution of the dild. dispersion changed a little, compared with that of the original dispersion. While dild. with deionized water, particle size and particle size distribution could expand several times. The effects of varying concns. of the stabilizer, the monomer, the salt and the initiator on particle size, and mol. wt. of the copolymer were investigated, resp. The reaction conditions for prepg. stable dispersion were concns. of 20-28% of the salt, 6-14% of monomers, and 1.8-2.7% of the stabilizer.
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      Guo, A.; Geng, Y.; Zhao, L.; Li, J.; Liu, D.; Li, P. Preparation of Cationic Polyacrylamide Microsphere Emulsion and Its Performance for Permeability Reduction. Pet. Sci. 2014, 11, 408– 416,  DOI: 10.1007/s12182-014-0355-0
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      Preparation of cationic polyacrylamide microsphere emulsion and its performance for permeability reduction
      Guo, Aijun; Geng, Yiran; Zhao, Lili; Li, Jun; Liu, Dong; Li, Peng
      Petroleum Science (2014), 11 (3), 408-416CODEN: PSECCF; ISSN:1995-8226. (China University of Petroleum)
      In this paper, cationic polyacrylamide microspheres (CPAM) were synthesized using acrylamide (AM) and methacryloyloxyethyltri-methylammonium chloride (TMAEMC) as monomers, ammonium sulfate as dispersant, poly(acryloyloxyethyltri-Meammonium chloride) (PAETAC) as dispersion stabilizer, and ammonium persulfate as initiator. The synthetic method was dispersion polymn. The effects of monomer ratio (AM/TMAEMC), dispersant concn., and dispersion stabilizer dosage on dispersion polymn. were systematically studied to det. the optimal prepn. conditions. The structure and viscosity of the synthesized polymer were characterized by FTIR and capillary viscometry, resp., and the particle sizes and distribution of the polymer microspheres were characterized by microscopy and dynamic light scattering, resp. Finally, flow tests were conducted to measure the permeability redn. performance of the microspheres at various concns. in sand packs with different permeability. Results show that CPAM emulsion of a solids content of 1wt% has excellent performance in low-to-medium permeability formations (< 1,000 mD), and the efficiency may reach above 90%.
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    17. 17
      Cho, M. S.; Yoon, K. J.; Song, B. K. Dispersion Polymerization of Acrylamide in Aqueous Solution of Ammonium Sulfate: Synthesis and Characterization. J. Appl. Polym. Sci. 2002, 83, 1397– 1405,  DOI: 10.1002/app.2300
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      17
      Dispersion polymerization of acrylamide in aqueous solution of ammonium sulfate: synthesis and characterization
      Cho, M. S.; Yoon, K. J.; Song, B. K.
      Journal of Applied Polymer Science (2002), 83 (7), 1397-1405CODEN: JAPNAB; ISSN:0021-8995. (John Wiley & Sons, Inc.)
      Dispersion polymn. of acrylamide has been successfully carried out in aq. ammonium sulfate media by using poly[2-(acryloyloxy)ethyltrimethylammonium chloride] (PAOTAC) as the polymeric stabilizer and 2,2'-azobis(2-methylpropionamidine) dihydrochloride (AIBA) as the initiator. The polymn. behaviors with varying concns. of acrylamide, PAOTAC, AIBA, and ammonium sulfate were investigated. The reaction conditions for stable dispersion were concns. of 5-10% for acrylamide, 0.6-1.8% for the stabilizer, 0.92-1.84 × 10-4 mol/L for the initiator, and 24-30% for the salt. The resulting conversion-time curves were S-shaped, as is typically obsd. in polymn. Polydisperse spherical particles were formed in the system. An image analyzer photographed the size of the dispersed particles and their distribution was measured. The mechanism and kinetics for the dispersion polymn. were discussed.
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    18. 18
      Ferguson, C. J.; Hughes, R. J.; Pham, B. T. T.; Hawkett, B. S.; Gilbert, R. G.; Serelis, A. K.; Such, C. H. Effective Ab Initio Emulsion Polymerization under RAFT Control. Macromolecules 2002, 35, 9243– 9245,  DOI: 10.1021/ma025626j
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      18
      Effective ab Initio Emulsion Polymerization under RAFT Control
      Ferguson, Christopher J.; Hughes, Robert J.; Pham, Binh T. T.; Hawkett, Brian S.; Gilbert, Robert G.; Serelis, Algirdas K.; Such, Christopher H.
      Macromolecules (2002), 35 (25), 9243-9245CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      To avoid loss of colloidal stability and appearance of an intractable oily layer, a novel technique for ab initio reversible addn.-fragmentation chain transfer emulsion polymn. was developed. An amphipathic RAFT agent (i.e., 2-{[(butylsulfanyl)carbonothioyl]sulfanyl}-propanoic acid) was used, which can mediate polymn. in both aq. and org. phases. This was first polymd. with a water-sol. monomer (acrylic acid, AA) in the water phase to a low d.p. to form (AA)x-RAFT. A hydrophobic monomer (Bu acrylate, BA) was then added under controlled feed to give oligomers, (AA)x-(BA)y-RAFT, which formed rigid micelles. These RAFT-contg. micelles functioned as seeds for further polymn. At the completion of the polymn., the resulting latex showed no oily layer and no visible evidence of colloidal instability.
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    19. 19
      Ferguson, C. J.; Hughes, R. J.; Nguyen, D.; Pham, B. T. T.; Gilbert, R. G.; Serelis, A. K.; Such, C. H.; Hawkett, B. S. Ab Initio Emulsion Polymerization by RAFT-Controlled Self-Assembly. Macromolecules 2005, 38, 2191– 2204,  DOI: 10.1021/ma048787r
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      19
      Ab Initio Emulsion Polymerization by RAFT-Controlled Self-Assembly
      Ferguson, Christopher J.; Hughes, Robert J.; Nguyen, Duc; Pham, Binh T. T.; Gilbert, Robert G.; Serelis, Algirdas K.; Such, Christopher H.; Hawkett, Brian S.
      Macromolecules (2005), 38 (6), 2191-2204CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      A method is developed to enable emulsion polymn. to be performed under RAFT control to give living character without the problems that often affect such systems: formation of an oily layer, loss of colloidal stability, or loss of mol. wt. control. Trithiocarbonate RAFT agents are used to form short stabilizing blocks from a water-sol. monomer, from which diblocks can be created by the subsequent polymn. of a hydrophobic monomer. These diblocks are designed to self-assemble to form micelles. Polymn. is initially performed under conditions that avoid the presence of monomer droplets during the particle formation stage and until the hydrophobic ends of the diblocks have become sufficiently long to prevent them from desorbing from the newly formed particles. Polymn. is then continued at any desired feed rate and compn. of monomer. The polymer forming in the reaction remains under RAFT control throughout the polymn.; mol. wt. polydispersities are generally low. The no. of RAFT-ended chains within a particle is much larger than the aggregation no. at which the original micelles would have self-assembled, implying that in the early stages of the polymn., there is aggregation of the micelles and/or migration of the diblocks. The latexes resulting from this approach are stabilized by anchored blocks of the hydrophilic monomer, e.g., acrylic acid, with no labile surfactant present. Sequential polymn. of two hydrophobic monomers gives completely novel core-shell particles where most chains extend from the core of the particles through the shell layer to the surface.
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    20. 20
      Zhang, X.; Boissé, S.; Zhang, W.; Beaunier, P.; D’Agosto, F.; Rieger, J.; Charleux, B. Well-Defined Amphiphilic Block Copolymers and Nano-Objects Formed in Situ via RAFT-Mediated Aqueous Emulsion Polymerization. Macromolecules 2011, 44, 4149– 4158,  DOI: 10.1021/ma2005926
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      Well-Defined Amphiphilic Block Copolymers and Nano-objects Formed in Situ via RAFT-Mediated Aqueous Emulsion Polymerization
      Zhang, Xuewei; Boisse, Stephanie; Zhang, Wenjing; Beaunier, Patricia; D'Agosto, Franck; Rieger, Jutta; Charleux, Bernadette
      Macromolecules (Washington, DC, United States) (2011), 44 (11), 4149-4158CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      A hydrophilic poly(methacrylic acid-co-poly(ethylene oxide) Me ether methacrylate) copolymer with a trithiocarbonate reactive group was used in the free-radical, batch emulsion polymn. of styrene. It allowed fast polymns. and high final conversions to be achieved, and the parameters for a good control over the formation of well-defined amphiphilic diblock copolymers were identified. These diblock copolymers self-assembled in situ into nano-objects of various morphologies upon chain extension. Achieving a good control over the formed diblock copolymers was an important step toward a better understanding of the parameters that affect the shape and size of the self-assembled objects, the ultimate goal being the ability to predict and fine-tune them on purpose.
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      Warren, N. J.; Armes, S. P. Polymerization-Induced Self-Assembly of Block Copolymer Nano-Objects via RAFT Aqueous Dispersion Polymerization. J. Am. Chem. Soc. 2014, 136, 10174– 10185,  DOI: 10.1021/ja502843f
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      Polymerization-Induced Self-Assembly of Block Copolymer Nano-objects via RAFT Aqueous Dispersion Polymerization
      Warren, Nicholas J.; Armes, Steven P.
      Journal of the American Chemical Society (2014), 136 (29), 10174-10185CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      A review. In this Perspective, we discuss the recent development of polymn.-induced self-assembly mediated by reversible addn.-fragmentation chain transfer (RAFT) aq. dispersion polymn. This approach has quickly become a powerful and versatile technique for the synthesis of a wide range of bespoke org. diblock copolymer nano-objects of controllable size, morphol., and surface functionality. Given its potential scalability, such environmentally-friendly formulations are expected to offer many potential applications, such as novel Pickering emulsifiers, efficient microencapsulation vehicles, and sterilizable thermo-responsive hydrogels for the cost-effective long-term storage of mammalian cells.
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      Charleux, B.; Delaittre, G.; Rieger, J.; D’Agosto, F. Polymerization-Induced Self-Assembly: From Soluble Macromolecules to Block Copolymer Nano-Objects in One Step. Macromolecules 2012, 45, 6753– 6765,  DOI: 10.1021/ma300713f
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      22
      Polymerization-Induced Self-Assembly: From Soluble Macromolecules to Block Copolymer Nano-Objects in One Step
      Charleux, Bernadette; Delaittre, Guillaume; Rieger, Jutta; D'Agosto, Franck
      Macromolecules (Washington, DC, United States) (2012), 45 (17), 6753-6765CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      A review. This Perspective describes the recent developments of polymn.-induced self-assembly of amphiphilic block copolymers based on controlled/living free-radical polymn. (CRP) in water. This method relies on the use of a hydrophilic living polymer precursor prepd. via CRP that is extended with a hydrophobic second block in an aq. environment. The process thus leads to amphiphilic block copolymers that self-assemble in situ into self-stabilized nano-objects in the frame of an emulsion or dispersion polymn. process. Depending on the nature and the structure of the so-formed copolymer, not only spherical particles can be achieved but also all morphologies that can be found in the phase diagram of an amphiphilic block copolymer in a selective solvent. This paper focuses mainly on aq. emulsion or dispersion polymn. and gives an overview of the CRP techniques used, the general conditions, and the morphologies obtained.
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      Boissé, S.; Rieger, J.; Belal, K.; Di-Cicco, A.; Beaunier, P.; Li, M. H.; Charleux, B. Amphiphilic Block Copolymer Nano-Fibers via RAFT-Mediated Polymerization in Aqueous Dispersed System. Chem. Commun. 2010, 46, 1950– 1952,  DOI: 10.1039/B923667H
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      Amphiphilic block copolymer nano-fibers via RAFT-mediated polymerization in aqueous dispersed system
      Boisse, Stephanie; Rieger, Jutta; Belal, Khaled; Di-Cicco, Aurelie; Beaunier, Patricia; Li, Min-Hui; Charleux, Bernadette
      Chemical Communications (Cambridge, United Kingdom) (2010), 46 (11), 1950-1952CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
      Self-assembled block copolymer nanofibers are attractive materials for multiple applications. We propose here a novel, very simple and straightforward method to prep. polymeric nanofibers at high solids contents directly in water. It is based on an aq. emulsion polymn. process performed under living radical polymn. conditions using the RAFT method. Polymn. of styrene in water in the presence of hydrophilic macromol. RAFT agent. The RAFT agent was dodecyl trithiocarbonate-end capped acrylic acid-poly(ethylene glycol) Me ether acrylate copolymer.
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      D’Agosto, F.; Rieger, J.; Lansalot, M. RAFT-Mediated Polymerization-Induced Self-Assembly. Angew. Chem., Int. Ed. 2019, 59, 8368– 8392,  DOI: 10.1002/anie.201911758
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      Liu, G.; Qiu, Q.; Shen, W.; An, Z. Aqueous Dispersion Polymerization of 2-Methoxyethyl Acrylate for the Synthesis of Biocompatible Nanoparticles Using a Hydrophilic RAFT Polymer and a Redox Initiator. Macromolecules 2011, 44, 5237– 5245,  DOI: 10.1021/ma200984h
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      Aqueous Dispersion Polymerization of 2-Methoxyethyl Acrylate for the Synthesis of Biocompatible Nanoparticles Using a Hydrophilic RAFT Polymer and a Redox Initiator
      Liu, Guangyao; Qiu, Qian; Shen, Wenqing; An, Zesheng
      Macromolecules (Washington, DC, United States) (2011), 44 (13), 5237-5245CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      Aq. dispersion polymn. systems mediated by reversible addn.-fragmentation chain transfer (RAFT) process have been less studied in comparison with other heterogeneous polymn. systems due to limited no. of monomer/polymer pairs that are suitable for such a condition. We report a novel dispersion polymn. system based on 2-methoxyethyl acrylate (MEA) which is highly water-sol., but its polymer is not. Using a hydrophilic polymer, poly(poly(ethylene glycol) Me ether methacrylate) (PPEGMA), as the macromol. chain transfer agent (Macro-CTA), both soln. and dispersion polymn. of MEA were studied. Chain extension by MEA from PPEGMA was successfully realized in DMF soln. polymn. In dispersion polymn. of MEA in water, PPEGMA was used as both a RAFT mediating species and a steric stabilizer for the formed nanoparticles. The dispersion polymn. of MEA in water was highly efficient using a redox initiator, potassium persulfate/sodium ascorbate, at low temps. Simultaneous control of both colloidal stability and RAFT process was realized. Block copolymers with small polydispersity indexes were efficiently produced up to complete monomer conversion at solids content up to 32% w/v, in the form of nanoparticles of 40-60 nm diam.
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      Sugihara, S.; Ma’Radzi, A. H.; Ida, S.; Irie, S.; Kikukawa, T.; Maeda, Y. In Situ Nano-Objects via RAFT Aqueous Dispersion Polymerization of 2-Methoxyethyl Acrylate Using Poly(Ethylene Oxide) Macromolecular Chain Transfer Agent as Steric Stabilizer. Polymer 2015, 76, 17– 24,  DOI: 10.1016/j.polymer.2015.08.051
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      In situ nano-objects via RAFT aqueous dispersion polymerization of 2-methoxyethyl acrylate using poly(ethylene oxide) macromolecular chain transfer agent as steric stabilizer
      Sugihara, Shinji; Ma'Radzi, Akmal Hadi; Ida, Shota; Irie, Satoshi; Kikukawa, Takamaru; Maeda, Yasushi
      Polymer (2015), 76 (), 17-24CODEN: POLMAG; ISSN:0032-3861. (Elsevier Ltd.)
      Poly(ethylene oxide)-poly(2-methoxyethyl acrylate) diblock copolymers (PEO-b-PMEA) are synthesized by RAFT aq. dispersion polymn. of MEA using poly(ethylene oxide) macromol. chain transfer agent as a reactive steric stabilizer. Both segments are well-known to be bio- and blood-compatible polymers. This formulation enables the prodn. of various particle morphologies such as spheres, worms, and vesicles from the same block copolymer in water. The synthesis starts when both the reactive steric stabilizer and MEA monomer are dissolved in water; however, the growing polymer is not water-sol. and begins to form nano-objects. In the case of the synthesis of PEO113-b-MEA300 diblock copolymers, the nano-objects change from spheres into larger aggregates of worms when the solids concn. in the polymn. increases from 5 to 15 wt% at full monomer conversion. The morphol. finally turns into vesicles as the solids concn. increases to 20 wt%. The final block copolymer morphol. at full monomer conversion is dictated by not only d.p. of MEA but also the solids concn. in the polymn. mixt.
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      An, Z.; Shi, Q.; Tang, W.; Tsung, C. K.; Hawker, C. J.; Stucky, G. D. Facile RAFT Precipitation Polymerization for the Microwave-Assisted Synthesis of Well-Defined, Double Hydrophilic Block Copolymers and Nanostructured Hydrogels. J. Am. Chem. Soc. 2007, 129, 14493– 14499,  DOI: 10.1021/ja0756974
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      Facile RAFT Precipitation Polymerization for the Microwave-Assisted Synthesis of Well-Defined, Double Hydrophilic Block Copolymers and Nanostructured Hydrogels
      An, Zesheng; Shi, Qihui; Tang, Wei; Tsung, Chia-Kuang; Hawker, Craig J.; Stucky, Galen D.
      Journal of the American Chemical Society (2007), 129 (46), 14493-14499CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Water-sol. macromol. chain transfer agents (Macro-CTAs) were developed for the microwave-assisted pptn. polymn. of N-isopropylacrylamide. Two types of Macro-CTAs, amphiphilic (Macro-CTA1) and hydrophilic (Macro-CTA2), were studied regarding their activity for the facile formation of nanoparticles and double hydrophilic block copolymers by RAFT processes. While both Macro-CTAs functioned as steric stabilization agents, the variation in their surface activity afforded different levels of control over the resulting nanoparticles in the presence of crosslinkers. The crosslinked nanoparticles produced using the amphiphilic Macro-CTA1 were less uniform than those produced using the fully hydrophilic Macro-CTA2. The nanoparticles spontaneously formed core-shell structures with surface functionalities derived from those of the Macro-CTAs. In the absence of crosslinkers, both types of Macro-CTAs showed excellent control over the RAFT pptn. polymn. process with well-defined, double hydrophilic block copolymers being obtained. The power of combining microwave irradn. with RAFT procedures was evident in the high efficiency and high solids content of the polymn. systems. In addn., the "living" nature of the nanoparticles allowed for further copolymn. leading to multiresponsive nanostructured hydrogels contg. surface functional groups, which were used for surface bioconjugation.
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      Figg, C. A.; Simula, A.; Gebre, K. A.; Tucker, B. S.; Haddleton, D. M.; Sumerlin, B. S. Polymerization-Induced Thermal Self-Assembly (PITSA). Chem. Sci. 2015, 6, 1230– 1236,  DOI: 10.1039/C4SC03334E
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      Polymerization-induced thermal self-assembly (PITSA)
      Figg, C. Adrian; Simula, Alexandre; Gebre, Kalkidan A.; Tucker, Bryan S.; Haddleton, David M.; Sumerlin, Brent S.
      Chemical Science (2015), 6 (2), 1230-1236CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
      Polymn.-induced self-assembly (PISA) is a versatile technique to achieve a wide range of polymeric nanoparticle morphologies. Most previous examples of self-assembled soft nanoparticle synthesis by PISA rely on a growing solvophobic polymer block that leads to changes in nanoparticle architecture during polymn. in a selective solvent. However, synthesis of block copolymers with a growing stimuli-responsive block to form various nanoparticle shapes has yet to be reported. This new concept using thermo-responsive polymers is termed polymn.-induced thermal self-assembly (PITSA). A reversible addn.-fragmentation chain transfer (RAFT) polymn. of N-isopropylacrylamide from a hydrophilic chain transfer agent composed of N,N-dimethylacrylamide and acrylic acid was carried out in water above the known lower crit. soln. temp. (LCST) of poly(N-isopropylacrylamide) (PNIPAm). After reaching a certain chain length, the growing PNIPAm self-assembled, as induced by the LCST, into block copolymer aggregates within which dispersion polymn. continued. To characterize the nanoparticles at ambient temps. without their dissoln., the particles were crosslinked immediately following polymn. at elevated temps. via the reaction of the acid groups with a diamine in the presence of a carbodiimide. Size exclusion chromatog. was used to evaluate the unimer mol. wt. distributions and reaction kinetics. Dynamic light scattering and transmission electron microscopy provided insight into the size and morphologies of the nanoparticles. The resulting block copolymers formed polymeric nanoparticles with a range of morphologies (e.g., micelles, worms, and vesicles), which were a function of the PNIPAm block length.
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      Cunningham, V. J.; Derry, M. J.; Fielding, L. A.; Musa, O. M.; Armes, S. P. RAFT Aqueous Dispersion Polymerization of N-(2-(Methacryloyloxy)Ethyl)Pyrrolidone: A Convenient Low Viscosity Route to High Molecular Weight Water-Soluble Copolymers. Macromolecules 2016, 49, 4520– 4533,  DOI: 10.1021/acs.macromol.6b00820
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      29
      RAFT Aqueous Dispersion Polymerization of N-(2-(Methacryloyloxy)ethyl)pyrrolidone: A Convenient Low Viscosity Route to High Molecular Weight Water-Soluble Copolymers
      Cunningham, Victoria J.; Derry, Matthew J.; Fielding, Lee A.; Musa, Osama M.; Armes, Steven P.
      Macromolecules (Washington, DC, United States) (2016), 49 (12), 4520-4533CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      RAFT soln. polymn. of N-(2-(methacryoyloxy)ethyl)pyrrolidone (NMEP) in ethanol at 70 °C was conducted to produce a series of PNMEP homopolymers with mean ds.p. (DP) varying from 31 to 467. Turbidimetry was used to assess their inverse temp. soly. behavior in dil. aq. soln., with an LCST of approx. 55 °C being obsd. in the high mol. wt. limit. Then a poly(glycerol monomethacylate) (PGMA) macro-CTA with a mean DP of 63 was chain-extended with NMEP using a RAFT aq. dispersion polymn. formulation at 70 °C. The target PNMEP DP was systematically varied from 100 up to 6000 to generate a series of PGMA63-PNMEPx diblock copolymers. High conversions (≥92%) could be achieved when targeting up to x = 5000. GPC anal. confirmed high blocking efficiencies and a linear evolution in Mn with increasing PNMEP DP. A gradual increase in Mw/Mn was also obsd. when targeting higher DPs. However, this problem could be minimized (Mw/Mn < 1.50) by utilizing a higher purity grade of NMEP (98% vs 96%). This suggests that the broader mol. wt. distributions obsd. at higher DPs are simply the result of a dimethacrylate impurity causing light branching, rather than an intrinsic side reaction such as chain transfer to polymer. Kinetic studies confirmed that the RAFT aq. dispersion polymn. of NMEP was approx. four times faster than the RAFT soln. polymn. of NMEP in ethanol when targeting the same DP in each case. This is perhaps surprising because both 1H NMR and SAXS studies indicate that the core-forming PNMEP chains remain relatively solvated at 70 °C in the latter formulation. Moreover, dissoln. of the initial PGMA63-PNMEPx particles occurs on cooling from 70 to 20 °C as the PNMEP block passes through its LCST. Hence this RAFT aq. dispersion polymn. formulation offers an efficient route to a high mol. wt. water-sol. polymer in a rather convenient low-viscosity form. Finally, the relatively expensive PGMA macro-CTA was replaced with a poly(methacrylic acid) (PMAA) macro-CTA. High conversions were also achieved for PMAA85-PNMEPx diblock copolymers prepd. via RAFT aq. dispersion polymn. for x ≤ 4000. Again, better control was achieved when using the 98% purity NMEP monomer in such syntheses.
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      Einarson, M. B.; Berg, J. C. Electrosteric Stabilization of Colloidal Latex Dispersions. J. Colloid Interface Sci. 1993, 155, 165– 172,  DOI: 10.1006/jcis.1993.1022
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      Electrosteric stabilization of colloidal latex dispersions
      Einarson, Maryann B.; Berg, John C.
      Journal of Colloid and Interface Science (1993), 155 (1), 165-72CODEN: JCISA5; ISSN:0021-9797.
      Exptl. stability domains of monodisperse aq. polystyrene latexes, with and without steric stabilizers, are detd. in terms of early-stage kinetics of flocculation using photon correlation spectroscopy. Dispersion stability as a function of electrolyte concn. and counterion valence is investigated. A low-mol.-wt. ethylene oxide-propylene oxide block copolymer is used as the steric stabilizer. Aggregation is induced by the addn. of indifferent electrolyte. The rates of aggregate formation are expressed in terms of a stability ratio and interpreted in terms of the particle pair interaction potential function. For the system investigated both electrostatic and steric repulsions are important in maintaining dispersion stability. Consistent with earlier results, systems with adsorbed block copolymer increase the crit. coagulation concn. for fast aggregation by nearly an order of magnitude.
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      Romero-Cano, M. S.; Martín-Rodríguez, A.; De las Nieves, F. J. Electrosteric Stabilization of Polymer Colloids with Different Functionality. Langmuir 2001, 17, 3505– 3511,  DOI: 10.1021/la001659l
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      Electrosteric Stabilization of Polymer Colloids with Different Functionality
      Romero-Cano, M. S.; Martin-Rodriguez, A.; de Nieves, F. J.
      Langmuir (2001), 17 (11), 3505-3511CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
      The stability factor (W) of polymer colloids with different functionality before and after adsorption of Triton X-100 was studied. Exptl. log W vs. log [electrolyte] plots for bare particles were fitted using the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, and values of diffuse potential (ψd) and the Hamaker const. (A) were obtained. In the same way, log W vs. log [electrolyte] plots for some latex-surfactant complexes were fitted using the extended DLVO theory, which considers steric repulsive interactions. Kinetic information was used to reduce the no. of fitting parameters of the steric repulsive potentials. In this way, the thickness of the stabilizing layer (δ) was the fitting parameter. The extended DLVO theory explains directly the results of some of the latex-surfactant complexes. However, in other cases, addnl. mechanisms had to be considered to explain the results. All these discrepancies could indicate that electrostatic and steric repulsion energies are not completely independent.
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      Bremmell, K. E.; Jameson, G. J.; Biggs, S. Polyelectrolyte Adsorption at the Solid/Liquid Interface Interaction Forces and Stability. Colloids Surf., A 1998, 139, 199– 211,  DOI: 10.1016/S0927-7757(98)00281-7
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      Polyelectrolyte adsorption at the solid/liquid interface. Interaction forces and stability
      Bremmell, K. E.; Jameson, G. J.; Biggs, S.
      Colloids and Surfaces, A: Physicochemical and Engineering Aspects (1998), 139 (2), 199-211CODEN: CPEAEH; ISSN:0927-7757. (Elsevier Science B.V.)
      The forces between neg. charged surfaces in the presence of an adsorbing cationic copolymer of acrylamide and 2-(methacryloyloxy)ethyltrimethylammonium chloride have been investigated using an at. force microscope. The results were compared with measurements from adsorption isotherm, electrophoretic mobility, stability, and light scattering expts. The adsorbed amt. of polyelectrolyte and adsorbed layer conformation at the solid/liq. interface were found to be strongly dependent on the polymer concn. from which initial adsorption takes place. At low polyelectrolyte concns. unstable silica suspensions were obsd. from stability tests; light scattering expts. indicate a large aggregate size under equiv. conditions. The adsorbed amt. was also seen to be low, well less than monolayer coverage, and force measurements indicated that the polymer was adsorbed in a flat conformation. At high polyelectrolyte concns., an increase in the adsorbed amt. was obsd. which resulted in a higher surface coverage, a higher mobility and a stable suspension. Direct force measurements indicated the presence of an electrosteric barrier.
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      Byard, S. J.; Blanazs, A.; Miller, J. F.; Armes, S. P. Cationic Sterically Stabilized Diblock Copolymer Nanoparticles Exhibit Exceptional Tolerance toward Added Salt. Langmuir 2019, 35, 14348– 14357,  DOI: 10.1021/acs.langmuir.9b02789
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      Cationic Sterically Stabilized Diblock Copolymer Nanoparticles Exhibit Exceptional Tolerance toward Added Salt
      Byard, Sarah J.; Blanazs, Adam; Miller, John F.; Armes, Steven P.
      Langmuir (2019), 35 (44), 14348-14357CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
      For certain com. applications such as enhanced oil recovery, sterically stabilized colloidal dispersions that exhibit high tolerance toward added salt are desirable. Herein, we report a series of new cationic diblock copolymer nanoparticles that display excellent colloidal stability in concd. aq. salt solns. More specifically, poly(2-(acryloyloxy)ethyltrimethylammonium chloride) (PATAC) has been chain-extended by reversible addn.-fragmentation chain transfer aq. dispersion polymn. of diacetone acrylamide (DAAM) at 70 °C to produce PATAC100-PDAAMx diblock copolymer spheres at 20% wt./wt. solids via polymn.-induced self-assembly. Transmission electron microscopy and dynamic light scattering (DLS) anal. confirm that the mean sphere diam. can be adjusted by systematic variation of the mean d.p. of the PDAAM block. Remarkably, DLS studies confirm that highly cationic PATAC100-PDAAM1500 spheres retain their colloidal stability in the presence of either 4.0 M KCl or 3.0 M ammonium sulfate for at least 115 days at 20 °C. The mole fraction of PATAC chains within the stabilizer shell was systematically varied by the chain extension of various binary mixts. of non-ionic poly(N,N-dimethylacrylamide) (PDMAC) and cationic PATAC with DAAM to produce ([n] PATAC100 + [1 - n] PDMAC67)-PDAAMz diblock copolymer spheres at 20% wt./wt. DLS studies confirmed that a relatively high mole fraction of cationic PATAC stabilizer chains (n ≥ 0.75) is required for the dispersions to remain colloidally stable in 4.0 M KCl. Cationic worms and vesicles could also be synthesized using a binary mixt. of PATAC and PDMAC precursors, where n = 0.10. However, the vesicles only remained colloidally stable up to 1.0 M KCl, whereas the worms proved to be stable up to 2.0 M KCl. Such block copolymer nanoparticles are expected to be useful model systems for understanding the behavior of aq. colloidal dispersions in extremely salty media. Finally, zeta potentials detd. using electrophoretic light scattering are presented for such nanoparticles dispersed in highly salty media.
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      Huang, B.; Jiang, J.; Kang, M.; Liu, P.; Sun, H.; Li, B. G.; Wang, W. J. Synthesis of Block Cationic Polyacrylamide Precursors Using an Aqueous RAFT Dispersion Polymerization. RSC Adv. 2019, 9, 12370– 12383,  DOI: 10.1039/C9RA02716E
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      Synthesis of block cationic polyacrylamide precursors using an aqueous RAFT dispersion polymerization
      Huang, Bo; Jiang, Jie; Kang, Mutian; Liu, Pingwei; Sun, Hailong; Li, Bo-Geng; Wang, Wen-Jun
      RSC Advances (2019), 9 (22), 12370-12383CODEN: RSCACL; ISSN:2046-2069. (Royal Society of Chemistry)
      Synthesis of cationic polyacrylamides (CPAMs) by introducing cationic polymer precursors followed by chain extension of acrylamide (AM) homopolymer blocks via RAFT polymn. is a promising approach for engineering high-performance CPAMs. Herein a novel approach is introduced that uses a random copolymer of AM and methacryloxyethyltrimethyl ammonium chloride (DMC) as a macro RAFT chain transfer agent (mCTA) and stabilizer for aq. RAFT dispersion polymn. of AM. The AM/DMC random copolymers synthesized by RAFT soln. polymn., having narrow dispersities (Ds) at different mol. wts. and cationic degrees (Cs), could serve as the mCTA, which was confirmed by mCTA chain extension in aq. soln. polymn. of AM under different Cs, solid contents, AM addn. contents, extended PAM block lengths, and mCTA chain lengths. The block CPAMs had a D value of less than 1.2.A model was developed using the method of moments with consideration of the diffusion control effect, for further understanding the chain extension kinetics. The AM/DMC random copolymers were further used for aq. RAFT dispersion polymn. of AM under different polymn. temps., Cs, and mCTA chain lengths. The products remained stable at room temp. storage for more than a month. The results indicate that aq. RAFT dispersion polymn. using random copolymers of AM and DMC at moderate cationic degrees as a stabilizer and mCTA is a suitable approach for synthesizing CPAM block precursors at an elevated solid content.
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      Kikuchi, M.; Terayama, Y.; Ishikawa, T.; Hoshino, T.; Kobayashi, M.; Ogawa, H.; Masunaga, H.; Koike, J. I.; Horigome, M.; Ishihara, K.; Takahara, A. Chain Dimension of Polyampholytes in Solution and Immobilized Brush States. Polym. J. 2012, 44, 121– 130,  DOI: 10.1038/pj.2011.116
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      Chain dimension of polyampholytes in solution and immobilized brush states
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      Polymer Journal (Tokyo, Japan) (2012), 44 (1), 121-130CODEN: POLJB8; ISSN:0032-3896. (NPG Nature Asia-Pacific)
      The dimensions and intermol. interactions of surface-grafted and unbound, free polyampholytes, poly[3-(N-2-methacryloyloxyethyl-N,N-dimethyl) ammonatopropanesulfonate] (PMAPS) and poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC), were estd. in an aq. NaCl soln. over a wide range of salt concns. (Cs). The free PMAPS and PMPC fractionated by a recycling preparative size-exclusion chromatog. system were characterized in aq. NaCl solns. for Cs over a range from 0 to 5.0 M by static light scattering and dynamic light scattering (DLS) measurements. The hydrodynamic radius (RH) and the concn. coeff. of the diffusion coeff. (kD) for PMPC were independent of Cs, whereas those for PMAPS were strongly dependent on Cs. Monodisperse silica nanoparticles immobilized with PMAPS (SiNP-PMAPS) and PMPC (SiNP-PMPC) by surface-initiated atom transfer radical polymn. were characterized in aq. NaCl solns. for Cs over a range from 0 to 5.0 M by DLS and synchrotron radiation small-angle X-ray scattering (SAXS) measurements. The SAXS profiles from SiNP-PMAPS and SiNP-PMPC solns. were well described by the core-shell model, taking into account interacting self-avoiding chains and assuming a Schulz-distributed core with two fitting parameters.
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      Jhan, Y. Y.; Tsay, R. Y. Salt Effects on the Hydration Behavior of Zwitterionic Poly(Sulfobetaine Methacrylate) Aqueous Solutions. J. Taiwan Inst. Chem. Eng. 2014, 45, 3139– 3145,  DOI: 10.1016/j.jtice.2014.08.022
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      Salt effects on the hydration behavior of zwitterionic poly(sulfobetaine methacrylate) aqueous solutions
      Jhan, Yong-Yu; Tsay, Ruey-Yug
      Journal of the Taiwan Institute of Chemical Engineers (2014), 45 (6), 3139-3145CODEN: JTICA8; ISSN:1876-1070. (Elsevier B.V.)
      Hydration behavior of a biomaterial is thought to be closely related to its bio/blood compatibility and subsequent biol. responses. Poly(sulfobetaine methacrylate) (pSBMA) is one of the biomimetic materials that exhibits excellent biocompatibility. It has been reported that the zwitterionic pSBMA exhibits "antipolyelectrolyte" behavior, which changes polymer conformations and antifouling properties, in solns. contg. salt ions. In this study, we identified water hydrated states of pSBMA by thermal anal. of DSC in various salt concns. With the addn. of miniscule salts, ions are attracted to the zwitterionic groups and the hydrated states are significantly changed. The attracted ions promote the incorporation of water mols. into polymer chains and enhance the soly. of pSBMA. Nevertheless, when large amts. of salts are added into the system, the excess ions tend to bind with free water mols., which may impose an osmotic pressure on the hydrated pSBMA mols. and causes the shrinkage of the mols. The present results demonstrated that salt has a significant effect on pSBMA-water interactions, which may affect the biocompatibility of the material.
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      Doncom, K. E. B.; Warren, N. J.; Armes, S. P. Polysulfobetaine-Based Diblock Copolymer Nano-Objects via Polymerization-Induced Self-Assembly. Polym. Chem. 2015, 6, 7264– 7273,  DOI: 10.1039/C5PY00396B
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      Polysulfobetaine-based diblock copolymer nano-objects via polymerization-induced self-assembly
      Doncom, Kay E. B.; Warren, Nicholas J.; Armes, Steven P.
      Polymer Chemistry (2015), 6 (41), 7264-7273CODEN: PCOHC2; ISSN:1759-9962. (Royal Society of Chemistry)
      A zwitterionic polysulfobetaine-based macromol. chain transfer agent (PSBMA38) was prepd. by reversible addn.-fragmentation chain transfer (RAFT) soln. polymn. of [2-(methacryloyloxy)ethyl] dimethyl(3-sulfopropyl) ammonium hydroxide (SBMA) in an aq. soln. contg. 0.5 M NaCl at 70 °C. This PSBMA38 macro-CTA was then utilized for the RAFT aq. dispersion polymn. of a water-miscible monomer, 2-hydroxypropyl methacrylate (HPMA). The growing PHPMA block became hydrophobic in situ, leading to polymn.-induced self-assembly. Systematic variation of the mean d.p. of the PHPMA block and the copolymer concn. enabled access to pure phases of spheres, worms or vesicles, as judged by transmission electron microscopy and dynamic light scattering studies. A detailed phase diagram was constructed and the thermo-responsive behavior of selected PSBMA38-PHPMAX nanoparticles was investigated. Finally, the salt tolerance of PSBMA38-PHPMA400 vesicles was compared to that of PGMA71-PHPMA400 vesicles; the former vesicles exhibit much better colloidal stability in the presence of 1 M MgSO4.
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      Jones, E. R.; Semsarilar, M.; Blanazs, A.; Armes, S. P. Efficient Synthesis of Amine-Functional Diblock Copolymer Nanoparticles via RAFT Dispersion Polymerization of Benzyl Methacrylate in Alcoholic Media. Macromolecules 2012, 45, 5091– 5098,  DOI: 10.1021/ma300898e
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      Efficient Synthesis of Amine-Functional Diblock Copolymer Nanoparticles via RAFT Dispersion Polymerization of Benzyl Methacrylate in Alcoholic Media
      Jones, Elizabeth R.; Semsarilar, Mona; Blanazs, Adam; Armes, Steven P.
      Macromolecules (Washington, DC, United States) (2012), 45 (12), 5091-5098CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      Benzyl methacrylate (BzMA) is polymd. via reversible addn.-fragmentation chain transfer (RAFT) chem. under alc. dispersion polymn. conditions in ethanol using a poly(2-(dimethylamino)ethyl methacrylate) (PDMA) chain transfer agent (CTA) at 70 °C. In principle, polymn.-induced self-assembly can lead to the formation of either spherical micelles, worm-like micelles, or vesicles, with the preferred morphol. being dictated by the hydrophilic-hydrophobic balance of the PDMA-PBzMA diblock copolymer chains. Very high monomer conversions (>99%) are routinely obtained within 24 h as judged by 1H NMR studies. Moreover, THF GPC analyses confirmed that relatively low polydispersities (Mw/Mn < 1.30) are achieved, indicating reasonably good pseudoliving character. A detailed phase diagram was constructed using a PDMA31 macro-CTA by systematically varying both the target d.p. of the PBzMA block and the total solids concn. of the reaction soln. This phase diagram can be used to reliably predict the synthesis conditions required to produce pure phases, rather than merely mixed phases (e.g., spheres plus worms or worms plus vesicles). Finally, these PDMA-PBzMA diblock copolymer nanoparticles remain colloidally stable when transferred from ethanol into water; aq. electrophoresis studies confirmed that the particles acquire appreciable cationic character below pH 7 due to protonation of the PDMA stabilizer chains.
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      Bray, C.; Peltier, R.; Kim, H.; Mastrangelo, A.; Perrier, S. Anionic Multiblock Core Cross-Linked Star Copolymers: Via RAFT Polymerization. Polym. Chem. 2017, 8, 5513– 5524,  DOI: 10.1039/C7PY01062A
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      Anionic multiblock core cross-linked star copolymers via RAFT polymerization
      Bray, Caroline; Peltier, Raoul; Kim, Hyungsoo; Mastrangelo, Antonio; Perrier, Sebastien
      Polymer Chemistry (2017), 8 (36), 5513-5524CODEN: PCOHC2; ISSN:1759-9962. (Royal Society of Chemistry)
      Reversible addn. fragmentation chain transfer (RAFT) polymn. was used to prep. a range of well-defined homopolymers and block copolymers of 2-acrylamido-2-methylpropane sulfonic acid (AMPS) and either N-hydroxyethyl acrylamide (HEAm) or 4-acryloylmorpholine (NAM) as a comonomer. The one-pot synthesis of multiblock core cross-linked star copolymers of AMPS and HEAm with low dispersities (<1.3) is also reported. The influence of several parameters such as the cross-linker type, cross-linker to chain transfer agent (CTA) ratio, arm length and compn. on the polymn. efficiency are investigated.
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      Lai, J. T.; Filla, D.; Shea, R. Functional Polymers from Novel Carboxyl-Terminated Trithiocarbonates as Highly Efficient RAFT Agents. Macromolecules 2002, 35, 6754– 6756,  DOI: 10.1021/ma020362m
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      Functional Polymers from Novel Carboxyl-Terminated Trithiocarbonates as Highly Efficient RAFT Agents
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      Macromolecules (2002), 35 (18), 6754-6756CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      S,S'-bis-(isobutyric acid)-trithiocarbonate and derivs. can be used as a highly efficient chain transfer agent for polymns. of monomers such as free radical polymerizable monomers. Homopolymers, copolymers and the like and block copolymers can be made utilizing the trithiocarbonate compd. such as in a controlled free radical polymn., with narrow mol. distributions and to form telechelic and other functional polymers. These novel reversible addn.-fragmentation transfer (RAFT) agents are practically synthesized as pure solids with low sulfur odor. Process for making S,S'-bis-(isobutyric acid)-trithiocarbonate was successfully scaled up in a 100 gal reactor.
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      The complex permittivity of aq. solns. at 20 °C has been measured at concns. between 0.001 and 5 mol/L and over a frequency range 0.13-20 GHz. The results were combined with literature values to derive empirical equations to predict the dielec. behavior of sodium chloride solns. between 0 and 5 mol/L and 5°C-35°C. Bioelectromagnetics 28:264-274, 2007.
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      Colloids and Surfaces, A: Physicochemical and Engineering Aspects (2021), 628 (), 127296CODEN: CPEAEH; ISSN:0927-7757. (Elsevier B.V.)
      We theor. investigate electrostatic properties between two charged surfaces with a grafted polyelectrolyte layer in an aq. electrolyte soln. by using the Poisson-Boltzmann approach accounting for ion partitioning. In order to consider the ion partitioning effect, we focus on changes of electrostatic properties due to the difference in dielec. permittivity of the polyelectrolyte layer and the aq. electrolyte soln. We find that ion partitioning enhances electrostatic potential in the region between two charged soft surfaces and hence increases the electrostatic interaction between two charged soft surfaces. Ion partitioning effect on osmotic pressure is enhanced not only by an increase in the thickness of polyelectrolyte layer and Debye length but also by a decrease in ion radius.
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      Miller, John F.; Schaetzel, Klaus; Vincent, Brian
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      An app. is described that can det. electrophoretic mobilities of polar and nonpolar colloidal dispersions down to 1 × 10-12 m2 s-1 V-1, with typical resolns. of 0.5 to 5%, depending on the nature of the dispersion being studied. The diffusion coeff. and settling/convection velocity of the sample may be detd. simultaneously with the electrophoretic mobility in real time. The technique, phase anal. light scattering (PALS), is based upon classical laser-Doppler electrophoresis, but employs signal processing of the time domain phase information within the scattered light signal, rather than anal. of its frequency spectrum. This allows much smaller elec. field strengths to be employed, thereby alleviating the usual heating problems assocd. with electrophoretic studies of nonpolar dispersions. The PALS measurements of typical aq. latex dispersions with large mobilities and some nonpolar dispersions with very small mobilities are presented to illustrate the versatility of this technique.
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      Warren, N. J.; Muise, C.; Stephens, A.; Armes, S. P.; Lewis, A. L. Near-Monodisperse Poly(2-(Methacryloyloxy)Ethyl Phosphorylcholine)-Based Macromonomers Prepared by Atom Transfer Radical Polymerization and Thiol-Ene Click Chemistry: Novel Reactive Steric Stabilizers for Aqueous Emulsion Polymerization. Langmuir 2012, 28, 2928– 2936,  DOI: 10.1021/la204083z
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      Near-Monodisperse Poly(2-(methacryloyloxy)ethyl phosphorylcholine)-Based Macromonomers Prepared by Atom Transfer Radical Polymerization and Thiol-Ene Click Chemistry: Novel Reactive Steric Stabilizers for Aqueous Emulsion Polymerization
      Warren, Nicholas J.; Muise, Carl; Stephens, Alex; Armes, Steven P.; Lewis, Andrew L.
      Langmuir (2012), 28 (5), 2928-2936CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
      Poly(2-(methacryloyloxy)ethyl phosphorylcholine) (PMPC) macromonomers have been prepd. by the atom transfer radical polymn. (ATRP) of 2-(methacryloyloxy)ethyl phosphorylcholine (MPC) using a bifunctional disulfide-based initiator. To attach a terminal polymerizable methacrylate group, the central disulfide bond was cleaved and the resulting thiols were conjugated to 3-(acryloyloxy)-2-hydroxypropyl methacrylate using tris(2-carboxyethyl)phosphine (TCEP) in water. Here TCEP serves as both the disulfide cleavage agent and also the catalyst for the subsequent Michael addn., which is highly selective for the acrylate group. The resulting methacrylate-terminated macromonomers were used as a reactive steric stabilizer for the aq. emulsion polymn. of styrene, yielding near-monodisperse PMPC-stabilized polystyrene (PS) latexes of around 100-200 nm in diam. As a comparison, the disulfide-contg. PMPC homopolymer precursor and the intermediate thiol-functional PMPC homopolymer (PMPC-SH) were also evaluated as potential steric stabilizers. Interestingly, near-monodisperse latexes were also obtained in each case. These three sterically-stabilized latexes, prepd. using either PMPC macromonomer, disulfide-based PMPC homopolymer, or PMPC-SH homopolymer as a reactive steric stabilizer, remained colloidally stable after both freeze-thaw expts. and the addn. of an electrolyte, indicating that a coronal layer of PMPC chains prevented flocculation in each case. In contrast, both a charge-stabilized PS latex prepd. in the absence of any steric stabilizer and a PS latex prepd. in the presence of a nonfunctional PMPC homopolymer exhibited very poor colloidal stability when subjected to a freeze-thaw cycle or the addn. of an electrolyte, as expected.
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      Williams, M.; Penfold, N. J. W.; Armes, S. P. Cationic and Reactive Primary Amine-Stabilised Nanoparticles via RAFT Aqueous Dispersion Polymerisation. Polym. Chem. 2016, 7, 384– 393,  DOI: 10.1039/C5PY01577D
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      Cationic and reactive primary amine-stabilized nanoparticles via RAFT aqueous dispersion polymerisation
      Williams, M.; Penfold, N. J. W.; Armes, S. P.
      Polymer Chemistry (2016), 7 (2), 384-393CODEN: PCOHC2; ISSN:1759-9962. (Royal Society of Chemistry)
      The synthesis of primary amine-functionalized diblock copolymer nanoparticles via polymn.-induced self-assembly (PISA) using a RAFT aq. dispersion polymn. formulation is reported. The primary amine steric stabilizer is a macromol. chain transfer agent (macro-CTA) based on 2-aminoethyl methacrylate AMA, which can be readily polymd. in its hydrochloride salt form with good control (Mw/Mn < 1.30) using RAFT aq. soln. polymn. Subsequent chain extension of this macro-CTA with 2-hydroxypropyl methacrylate (HPMA) leads to the formation of relatively monodisperse spherical nanoparticles (68 to 288 nm) at pH 6. However, worms or vesicles could not be obtained, because strong lateral repulsion between the highly cationic PAMA stabilizer chains impedes the formation of these higher order copolymer morphologies. Deprotonation of the primary amine stabilizer chains at or above pH 9 results in flocculation of these spherical nanoparticles as the PAMA block becomes uncharged. Diblock copolymer spheres, worms or vesicles can be synthesized that remain stable at pH 9 by supplementing the PAMA macro-CTA with a poly(glycerol monomethacrylate) (PGMA) macro-CTA, since this non-ionic block confers effective steric stabilization in alk. media. A series of diblock copolymer nanoparticles with the general formula ([1 - n]PGMAx + nPAMAy)-PHPMAz can be synthesized by optimizing: (i) the mean degree of polymn. (DP, or x) of the PGMA block, (ii) the PHPMA core-forming DP (or z); (iii) the mol. fraction (n) of the PAMA stabilizer; and (iv) the copolymer concn. These spheres, worms and vesicles are both cationic at low pH and colloidally stable at high pH. Furthermore, deprotonation of the protonated primary amine groups on the PAMA stabilizer chains at high pH renders these particles susceptible to epoxy-amine conjugation. This is demonstrated by the reaction between the primary amine groups on (0.8PGMA101 + 0.2PAMA96)-PHPMA1000 diblock copolymer spheres, and epoxide-functionalised diblock copolymer nanoparticles in aq. soln. at pH 8.
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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, 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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    51. 51
      Derry, M. J.; Fielding, L. A.; Warren, N. J.; Mable, C. J.; Smith, A. J.; Mykhaylyk, O. O.; Armes, S. P. In Situ Small-Angle X-Ray Scattering Studies of Sterically-Stabilized Diblock Copolymer Nanoparticles Formed during Polymerization-Induced Self-Assembly in Non-Polar Media. Chem. Sci. 2016, 7, 5078– 5090,  DOI: 10.1039/C6SC01243D
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      In situ small-angle X-ray scattering studies of sterically-stabilized diblock copolymer nanoparticles formed during polymerization-induced self-assembly in non-polar media
      Derry, Matthew J.; Fielding, Lee A.; Warren, Nicholas J.; Mable, Charlotte J.; Smith, Andrew J.; Mykhaylyk, Oleksandr O.; Armes, Steven P.
      Chemical Science (2016), 7 (8), 5078-5090CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
      Reversible addn.-fragmentation chain transfer (RAFT) dispersion polymn. of benzyl methacrylate (BzMA) is utilized to prep. a series of poly(stearyl methacrylate)-poly(benzyl methacrylate) (PSMA-PBzMA) diblock copolymer nano-objects at 90°C directly in mineral oil. Polymn.-induced self-assembly (PISA) occurs under these conditions, with the resulting nanoparticles exhibiting spherical, worm-like or vesicular morphologies when using a relatively short PSMA13 macromol. chain transfer agent (macro-CTA), as confirmed by transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS) studies. Only kinetically-trapped spherical nanoparticles are obtained when using longer macro-CTAs (e.g. PSMA18 or PSMA31), with higher mean ds.p. (DPs) for the PBzMA core-forming block simply producing progressively larger spheres. SAXS is used for the first time to monitor the various morphol. transitions that occur in situ during the RAFT dispersion polymn. of BzMA when targeting either spheres or vesicles as the final copolymer morphol. This powerful characterization technique enables the evolution of particle diam., mean aggregation no., no. of copolymer chains per unit surface area (Sagg) and the distance between adjacent copolymer chains at the core-shell interface (ditt) to be monitored as a function of monomer conversion for kinetically-trapped spheres. Moreover, the gradual evolution of copolymer morphol. during PISA is confirmed unequivocally, with approx. 'lifetimes' assigned to the intermediate pure sphere and worm morphologies when targeting PSMA13-PBzMA150 vesicles. Within vesicle phase space, the membrane thickness (Tm) increases monotonically with PBzMA DP. Furthermore, a combination of dynamic light scattering (DLS), TEM and post mortem SAXS studies indicate that the lumen vol. is reduced while the overall vesicle dimensions remain essentially const. Thus the constrained vesicles grow inwards, as recently reported for an aq. PISA formulation. This suggests a universal vesicle growth mechanism for all PISA formulations.
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    52. 52
      Byard, S. J.; Williams, M.; McKenzie, B. E.; Blanazs, A.; Armes, S. P. Preparation and Cross-Linking of All-Acrylamide Diblock Copolymer Nano-Objects via Polymerization-Induced Self-Assembly in Aqueous Solution. Macromolecules 2017, 50, 1482– 1493,  DOI: 10.1021/acs.macromol.6b02643
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      Preparation and Cross-Linking of All-Acrylamide Diblock Copolymer Nano-Objects via Polymerization-Induced Self-Assembly in Aqueous Solution
      Byard, Sarah J.; Williams, Mark; McKenzie, Beulah E.; Blanazs, Adam; Armes, Steven P.
      Macromolecules (Washington, DC, United States) (2017), 50 (4), 1482-1493CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      Various carboxylic acid-functionalized poly(N,N-dimethylacrylamide) (PDMAC) macromol. chain transfer agents (macro-CTAs) were chain-extended with diacetone acrylamide (DAAM) by reversible addn.-fragmentation chain transfer (RAFT) aq. dispersion polymn. at 70 °C and 20% wt./wt. solids to produce a series of PDMAC-PDAAM diblock copolymer nano-objects via polymn.-induced self-assembly (PISA). TEM studies indicate that a PDMAC macro-CTA with a mean d.p. (DP) of 68 or higher results in the formation of well-defined spherical nanoparticles with mean diams. ranging from 40 to 150 nm. In contrast, either highly anisotropic worms or polydisperse vesicles are formed when relatively short macro-CTAs (DP = 40-58) are used. A phase diagram was constructed to enable accurate targeting of pure copolymer morphologies. Dynamic light scattering (DLS) and aq. electrophoresis studies indicated that in most cases these PDMAC-PDAAM nano-objects are surprisingly resistant to changes in either soln. pH or temp. However, PDMAC40-PDAAM99 worms do undergo partial dissocn. to form a mixt. of relatively short worms and spheres on adjusting the soln. pH from pH 2-3 to around pH 9 at 20 °C. Moreover, a change in copolymer morphol. from worms to a mixt. of short worms and vesicles was obsd. by DLS and TEM on heating this worm dispersion to 50 °C. Postpolymn. crosslinking of concd. aq. dispersions of PDMAC-PDAAM spheres, worms, or vesicles was performed at ambient temp. using adipic acid dihydrazide (ADH), which reacts with the hydrophobic ketone-functionalized PDAAM chains. The formation of hydrazone groups was monitored by FT-IR spectroscopy and afforded covalently stabilized nano-objects that remained intact on exposure to methanol, which is a good solvent for both blocks. Rheol. studies indicated that the cross-linked worms formed a stronger gel compared to linear precursor worms.
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      Parker, B. R.; Derry, M. J.; Ning, Y.; Armes, S. P. Exploring the Upper Size Limit for Sterically Stabilized Diblock Copolymer Nanoparticles Prepared by Polymerization-Induced Self-Assembly in Non-Polar Media. Langmuir 2020, 36, 3730– 3736,  DOI: 10.1021/acs.langmuir.0c00211
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      Exploring the Upper Size Limit for Sterically Stabilized Diblock Copolymer Nanoparticles Prepared by Polymerization-Induced Self-Assembly in Non-Polar Media
      Parker, Bryony R.; Derry, Matthew J.; Ning, Yin; Armes, Steven P.
      Langmuir (2020), 36 (14), 3730-3736CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
      Reversible addn.-fragmentation chain transfer (RAFT) dispersion polymn. of benzyl methacrylate is used to prep. a series of well-defined poly(stearyl methacrylate)-poly(benzyl methacrylate) (PSMA-PBzMA) diblock copolymer nanoparticles in mineral oil at 90°C. A relatively long PSMA54 precursor acts as a steric stabilizer block and also ensures that only kinetically trapped spheres are obtained, regardless of the target d.p. (DP) for the core-forming PBzMA block. This polymn.-induced self-assembly (PISA) formulation provides good control over the particle size distribution over a wide size range (24-459 nm diam.). 1H NMR spectroscopy studies confirm that high monomer conversions (≥96%) are obtained for all PISA syntheses while transmission electron microscopy and dynamic light scattering analyses show well-defined spheres with a power-law relationship between the target PBzMA DP and the mean particle diam. Gel permeation chromatog. studies indicate a gradual loss of control over the mol. wt. distribution as higher DPs are targeted, but well-defined morphologies and narrow particle size distributions can be obtained for PBzMA DPs up to 3500, which corresponds to an upper particle size limit of 459 nm. Thus, these are among the largest well-defined spheres with reasonably narrow size distributions (std. deviation ≤20%) produced by any PISA formulation. Such large spheres serve as model sterically stabilized particles for anal. centrifugation studies.
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      Cunningham, V. J.; Armes, S. P.; Musa, O. M. Synthesis, Characterisation and Pickering Emulsifier Performance of Poly(Stearyl Methacrylate)-Poly(N-2-(Methacryloyloxy)Ethyl Pyrrolidone) Diblock Copolymer Nano-Objects via RAFT Dispersion Polymerisation in n-Dodecane. Polym. Chem. 2016, 7, 1882– 1891,  DOI: 10.1039/C6PY00138F
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      Synthesis, characterisation and Pickering emulsifier performance of poly(stearyl methacrylate)-poly(N-2-(methacryloyloxy)ethyl pyrrolidone) diblock copolymer nano-objects via RAFT dispersion polymerization in n-dodecane
      Cunningham, V. J.; Armes, S. P.; Musa, O. M.
      Polymer Chemistry (2016), 7 (10), 1882-1891CODEN: PCOHC2; ISSN:1759-9962. (Royal Society of Chemistry)
      A near-monodisperse poly(stearyl methacrylate) macromol. chain transfer agent (PSMA macro-CTA) was prepd. via reversible addn.-fragmentation chain transfer (RAFT) soln. polymn. in toluene. This PSMA macro-CTA was then utilized as a stabilizer block for the RAFT dispersion polymn. of a highly polar monomer, N-2-(methacryloyloxy)ethyl pyrrolidone (NMEP), in n-dodecane at 90 °C. 1H NMR studies confirmed that the rate of NMEP polymn. was significantly faster than that of a non-polar monomer (benzyl methacrylate, BzMA) under the same conditions. For example, when targeting a PSMA14-PNMEP100 diblock copolymer, more than 99% NMEP conversion was achieved within 30 min, whereas only 19% BzMA conversion was obtained on the same time scale for the corresponding PSMA14-PBzMA100 synthesis. The resulting PSMA-PNMEP diblock copolymer chains underwent polymn.-induced self-assembly (PISA) during growth of the insol. PNMEP block to form either spherical micelles, highly anisotropic worms or polydisperse vesicles, depending on the target DP of the PNMEP chains. Systematic variation of this latter parameter, along with the solids content, allowed the construction of a phase diagram which enabled pure morphologies to be reproducibly targeted. Syntheses conducted at 10% wt./wt. solids led to the formation of kinetically-trapped spheres. A monotonic increase in particle diam. with PNMEP DP was obsd. for such PISA syntheses, with particle diams. of up to 462 nm being obtained for PSMA14-PNMEP960. Increasing the copolymer concn. to 15% wt./wt. solids led to worm-like micelles, while vesicles were obtained at 27.5% wt./wt. solids. High (≥95%) NMEP conversions were achieved in all cases and 3 : 1 chloroform/methanol GPC anal. indicated relatively high blocking efficiencies. However, relatively broad mol. wt. distributions (Mw/Mn > 1.50) were obsd. when targeting PNMEP DPs greater than 150. This indicates light branching caused by the presence of a low level of dimethacrylate impurity. Finally, PSMA14-PNMEP49 spheres were evaluated as Pickering emulsifiers. Unexpectedly, it was found that either water-in-oil or oil-in-water Pickering emulsions could be obtained depending on the shear rate employed for homogenization. Further investigation suggested that high shear rates lead to in situ inversion of the initial hydrophobic PSMA14-PNMEP49 spheres to form hydrophilic PNMEP49-PSMA14 spheres.
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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, 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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      Pedersen, J. S. Form Factors of Block Copolymer Micelles with Spherical, Ellipsoidal and Cylindrical Cores. J. Appl. Crystallogr. 2000, 33, 637– 640,  DOI: 10.1107/S0021889899012248
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      Form factors of block copolymer micelles with spherical, ellipsoidal and cylindrical cores
      Pedersen, Jan Skov
      Journal of Applied Crystallography (2000), 33 (3, Pt. 1), 637-640CODEN: JACGAR; ISSN:0021-8898. (Munksgaard International Publishers Ltd.)
      The form factor of a micelle model with a spherical core and Gaussian polymer chains attached to the surface has previously been calcd. anal. by Pedersen and Gerstenberg. Non-penetration of the chains into the core region was mimicked in the anal. calcns. by moving the center of mass of the chains Rg away from the surface of the core, where Rg is the radius of gyration of the chains. In the present work, the calcns. have been extended to micelles with ellipsoidal and cylindrical cores. Non-penetration was also for these taken into account by moving the center of mass of the chains Rg away from the core surface. In addn. results for worm-like micelles, disk-shape micelles and micelles with a vesicle shape are given.
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      Muratov, A.; Moussäd, A.; Narayanan, T.; Kats, E. I. A Percus-Yevick Description of the Microstructure of Short-Range Interacting Metastable Colloidal Suspensions. J. Chem. Phys. 2009, 131, 054902  DOI: 10.1063/1.3179667
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      A Percus-Yevick description of the microstructure of short-range interacting metastable colloidal suspensions
      Muratov, A.; Moussaid, A.; Narayanan, T.; Kats, E. I.
      Journal of Chemical Physics (2009), 131 (5), 054902/1-054902/11CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
      We present a revised form of the Percus-Yevick approach applicable to dispersions of interacting colloidal particles such as colloid-polymer mixts. and square-well attractive colloids. Our approach is suitable for treating short-range interparticle potentials including excluded vol. hard-sphere repulsion, short-range depletion attraction, and square-well attraction. In all these cases, the Ornstein-Zernike equation for the pair correlation function can be satisfied by a trial function, which generalizes the and ansatz. Structure factors (or x-ray scattering intensities) calcd. by this method are in good agreement with exptl. data for colloid-polymer mixts. over a range of parameters pertaining to the stable fluid phase and the metastable state with moderate attraction. On the same footing, we have detd. the stability limits and analyzed contributions to the scattered intensity from particle aggregates appearing prior to the phase sepn. for sufficiently strong short-range attraction. Similar features are obsd. in the case of square-well attractive colloids when the attraction is turned on. (c) 2009 American Institute of Physics.
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      Chu, B.; Liu, T. Characterization of Nanoparticles by Scattering Techniques. J. Nanoparticle Res. 2000, 2, 29– 41,  DOI: 10.1023/A:1010001822699
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      Characterization of nanoparticles by scattering techniques
      Chu, Benjamin; Liu, Tianbo
      Journal of Nanoparticle Research (2000), 2 (1), 29-41CODEN: JNARFA; ISSN:1388-0764. (Kluwer Academic Publishers)
      A review with 39 refs. basic principles and applications of different scattering techniques (including static and dynamic light scattering (SLS and DLS), small-angle X-ray scattering (SAXS), wide-angle X-ray diffraction (WAXD) and small-angle neutron scattering (SANS)) on the characterization of nanoparticles. By choosing a suitable scattering technique or a combination of different techniques for nanoparticle characterization, the particles' mol. wt., radius of gyration, hydrodynamic radius, size distribution, shape and internal structure as well as interparticle interactions of nanoparticles, can be detd. Examples, including some sophisticated colloidal systems, are presented.
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      Tan, B. H.; Tam, K. C.; Dupin, D.; Armes, S. P. Rheological Behavior of Acid-Swellable Cationic Copolymer Latexes. Langmuir 2010, 26, 2736– 2744,  DOI: 10.1021/la9027699
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      Rheological Behavior of Acid-Swellable Cationic Copolymer Latexes
      Tan, Beng H.; Tam, Kam C.; Dupin, Damien; Armes, Steven P.
      Langmuir (2010), 26 (4), 2736-2744CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
      2-Vinylpyridine (2VP) was copolymd. with four different cross-linker densities ranging from 0.05 to 0.31 wt % divinylbenzene (DVB) via aq. emulsion polymn. to produce a series of submicrometer-sized, lightly cross-linked P2VP latexes. Protonation of the 2VP residues leads to a latex-to-microgel transition due to interchain electrostatic repulsion, as confirmed by dynamic light scattering. The DVB content of these pH-responsive copolymer particles strongly affects their rheol. behavior. The particle size and viscosity of the swollen cationic microgels exhibit a max. at ∼0.11 wt % DVB. Static light scattering results confirm this d. as the min. amt. of DVB required to ensure that all P2VP chains are crosslinked (i.e. that there is no sol. fraction), thus allowing optimal swelling of the microgels. Viscosity studies shows that the soln. viscosity of a P2VP microgel at low pH follows two models, depending on its concn. For vol. fractions below 0.30, the P2VP microgels behave as hard spheres, as predicted by the Batchelor equation. For more concd. P2VP microgels (vol. fractions above 0.30), the rheol. behavior can be predicted using the Krieger-Dougherty model for strong particle-particle interactions; thus, this semiempirical approach provides a useful description of the aq. soln. behavior of microgel.
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      Jesson, C. P.; Pearce, C. M.; Simon, H.; Werner, A.; Cunningham, V. J.; Lovett, J. R.; Smallridge, M. J.; Warren, N. J.; Armes, S. P. H2O2 Enables Convenient Removal of RAFT End-Groups from Block Copolymer Nano-Objects Prepared via Polymerization-Induced Self- Assembly in Water. Macromolecules 2017, 50, 182– 191,  DOI: 10.1021/acs.macromol.6b01963
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      H2O2 Enables Convenient Removal of RAFT End-Groups from Block Copolymer Nano-Objects Prepared via Polymerization-Induced Self-Assembly in Water
      Jesson, Craig P.; Pearce, Charles M.; Simon, Helene; Werner, Arthur; Cunningham, Victoria J.; Lovett, Joseph R.; Smallridge, Mark J.; Warren, Nicholas J.; Armes, Steven P.
      Macromolecules (Washington, DC, United States) (2017), 50 (1), 182-191CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      RAFT-synthesized polymers are typically colored and malodorous due to the presence of the sulfur-based RAFT end-group(s). In principle, RAFT end-groups can be removed by treating molecularly dissolved copolymer chains with excess free radical initiators, amines or oxidants. Herein we report a convenient method for the removal of RAFT end-groups from aq. dispersions of diblock copolymer nano-objects using H2O2. This oxidant is relatively cheap, has minimal impact on the copolymer morphol. and produces benign side-products that can be readily removed via dialysis. We investigate the efficiency of end-group removal for various diblock copolymer nano-objects prepd. with either dithiobenzoate- or trithiocarbonate-based RAFT chain transfer agents. The advantage of using UV GPC rather than UV spectroscopy is demonstrated for assessing the kinetics and extent of end-group removal.
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      Liu, X.; Chen, D.; Yue, Y.; Zhang, W.; Wang, P. Dispersion Copolymerization of Acrylamide with Acrylic Acid in an Aqueous Solution of Ammonium Sulfate: Synthesis and Characterization. J. Appl. Polym. Sci. 2006, 102, 3685– 3690,  DOI: 10.1002/app.24259
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      Dispersion copolymerization of acrylamide with acrylic acid in an aqueous solution of ammonium sulfate: synthesis and characterization
      Liu, Xiaoguang; Chen, Dongnian; Yue, Yumei; Zhang, Wende; Wang, Pixin
      Journal of Applied Polymer Science (2006), 102 (4), 3685-3690CODEN: JAPNAB; ISSN:0021-8995. (John Wiley & Sons, Inc.)
      Dispersion copolymn. of acrylamide with acrylic acid in an aq. soln. of ammonium sulfate using poly(sodium 2-acrylamido-2-methylpropanesulfonate) as the stabilizer and ammonium persulfate (APS) as the initiator was investigated. The influence of initiator concn., stabilizer concn., ammonium sulfate (I) concn., chain-transfer agent concn., and polymn. temp. on the copolymn. was discussed. Varying the I concn. could affect the particle size and the intrinsic viscosity of the copolymer significantly. With increasing stabilizer concn., the particle size of the copolymer decreased first, and then increased, meanwhile the intrinsic viscosity of the copolymer decreased. The increase of initiator concn., chain-transfer agent concn., and polymn. temp. resulted in the increase in the particle size. Polydisperse spherical particles were formed in the system, and the kinetics for the dispersion copolymn. were discussed.
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      Lu, J.; Peng, B.; Li, M.; Lin, M.; Dong, Z. Dispersion Polymerization of Anionic Polyacrylamide in an Aqueous Salt Medium. Pet. Sci. 2010, 7, 410– 415,  DOI: 10.1007/s12182-010-0086-9
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      Dispersion polymerization of anionic polyacrylamide in an aqueous salt medium
      Lu, Jiao; Peng, Bo; Li, Mingyuan; Lin, Meiqin; Dong, Zhaoxia
      Petroleum Science (2010), 7 (3), 410-415CODEN: PSECCF; ISSN:1995-8226. (Editorial Office of Petroleum Science)
      Anionic polyacrylamide dispersions were prepd. by dispersion polymn. in an aq. salt medium, using acrylamide(AM) and acrylic acid(AA) as monomers and anionic polyelectrolytes as stabilizer. Effects of salt concn., and mol. wt. and concn. of stabilizers on the stability of the dispersions were investigated using a HAAKE rheometer and optical microscopy. The results showed that stable anionic polyacrylamide dispersions, consisting of smooth, spherical, polydisperse particles, could be obtained under the conditions of salt concn. ranging from 26 wt% to 30 wt%, concn. of stabilizers from 1.2 wt% to 1.8 wt%, and intrinsic viscosity of stabilizers from 2.98 dL·g-1 to 3.74 dL·g-1. The apparent viscosity of the stable dispersions changed very little with the shear rate, showing Newton fluid behavior.
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      Bai, S.; Wang, Y.; Liu, B.; Zhu, Y.; Guo, R. Dispersion Copolymerization of Acrylamide and Sodium 2-Acrylamido-2-Methylpropanesulfonate in Aqueous Salt Solution Stabilized with a Macro-RAFT Agent. Colloids Surf., A 2018, 553, 446– 455,  DOI: 10.1016/j.colsurfa.2018.05.082
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      Dispersion copolymerization of acrylamide and sodium 2-acrylamido-2-methylpropanesulfonate in aqueous salt solution stabilized with a macro-RAFT agent
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