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Acrylonitrile‐styrene‐acrylate (ASA) toughened plastics based on block copolymers are successfully prepared via RAFT emulsion polymerization and various molecular structures are designed to have different morphologies in order to investigate the relationship between morphologies and mechanical properties. All materials prepared by blending exhibit sea‐island morphology. Promoting particles dispersion and increasing spherical particle size shorten surface‐to‐surface interparticle distance and help to improve tensile properties of materials. Enlarging particles through crosslinked structures are found to be a more effective method to improve tensile toughness, at the cost of a slight reduction in tensile yield strength. Larger spherical particles with crosslinked structures are found to help improving the Izod notched impact strength of materials. However, the existence of a SAN core decreases the material's ability to withstand impact. Compared to blended samples, triblock copolymer materials display higher flexural strength with equal flexural modulus. POLYM. ENG. SCI., 59:389–395, 2019. © 2018 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

ABSTRACT: Pickering emulsion technique has been demonstrated a simple method to fabricate the microcapsules. However, the resulted microcapsules are often fragile. This limits their applications. Here, we report that the microcapsules with the nanostructured shell of poly(acrylic acid‐b‐styrene‐b‐isoprene‐b‐styrene) (ASIS), which is of high toughness and elasticity, could be fabricated via Pickering emulsions using ASIS nanoparticles as stabilizing particles. The surfactant‐free ASIS latex (with theoretical molecular weight for each block: 1.5k–15k–55k–10k) was synthesized by reversible additional fragmentation transfer (RAFT) emulsion polymerization using amphiphilic macro‐RAFT agent [poly(acrylic acid)20‐b‐polystyrene5 trithiocarbonate] as both reactive surfactant and polymerization mediator. It was found that the ASIS nanoparticles were able to self‐assemble on oil/water interface to stabilize Pickering emulsion of hexadecane in the pH range from 8 to 12. The droplet diameter was finely tuned from 17 to 5 µm by increasing the ASIS particle levels from 0.13 to 12 wt % based on the mass of the ASIS aqueous dispersions. With toluene as a coalescing aid, the capsules with a coherent and nonporous shell were obtained with the dispersed phase volume percentage as high as 50%. The toluene treated capsules were so mechanically strong to survive the utrasonic treatment. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46700. [ABSTRACT FROM AUTHOR]

The kinetics of ab initio reversible addition-fragmentation chain transfer (RAFT) emulsion polymerization of styrene using oligo(acrylic acid-b-styrene) trithiocarbonate as both polymerization mediator and surfactant were systematically investigated. The initiator concentration was set much lower than that in the conventional emulsion polymerization to significantly suppress the irreversible termination reaction. It was found that [ABSTRACT FROM AUTHOR]

The comparison between methyl methacrylate (MMA) and styrene (St) RAFT emulsion polymerization using oligo(methacrylic acid41-b-methyl methacrylate8) RAFT agent (oligo(MAA41-b-MMA8) RAFT) as surfactant is investigated in order to gain a better understanding on RAFT emulsion polymerization of MMA. It is found that the colloidal stability during MMA emulsion polymerization is much more sensitive to the initiator concentrations and temperature than that of St polymerization. The coagulum-free latex of highly living PMMA can be achieved only at 80 °C and low initiator concentrations. The final PDI is higher in RAFT emulsion polymerization of MMA than that of St. It is revealed that about 40% acid groups of oligo(MAA41-b-MMA8) RAFT should be buried within the final particles of PMMA, indicating that particle coagulation should occur in the very beginning of the polymerization. The poorer performance of the MMA polymerization could be well explained by the homogeneous nucleation mode of particles combined with relatively slow transporting rate of oligo(MAA41-b-MMA8) RAFT molecules from the partly frozen micelles to the newly-born particles. [ABSTRACT FROM AUTHOR]

ABSTRACT Reversible addition-fragmentation chain transfer (RAFT) emulsion polymerization is becoming an important technique to synthesize the latex of block copolymers. A previous study showed that in the synthesis of polystyrene- b-poly(butyl acrylate)- b-polystyrene triblock copolymer via RAFT emulsion polymerization using amphiphilic oligo(acrylic acid-styrene) macroRAFT as surfactant and mediator, the molecular weight distribution could be much broadened to PDI higher than 2. In this study, an in-depth investigation was performed to decrease PDI. It was found that long-chain branches could be formed in the synthesis of triblock block copolymer, leading to the appearance of a higher molecular weight shoulder in the GPC curve of the final product. The lower neutralization degree of acrylic acid (AA) units on the macroRAFT and shorter AA chains would help to suppress the formation the long-chain branches, leading to PDI around 1.5. It is evidenced that the successful suppression is due to the promotion of radical entry as a result of decreased interfacial transport impedance. It is also evidenced that the presence of styrene during the polymerization of butyl acrylate could promote the formation of long chain branches. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 1464-1473 [ABSTRACT FROM AUTHOR]

ABSTRACT The mechanical properties of linear and V-shaped compositional gradient copolymer of styrene and n-butyl acrylate with composition of around 55 wt % styrene were investigated by comparing with their block copolymer counterparts. Compared with their block copolymer counterparts, the gradient copolymers showed lower elastic modulus, much larger elongation at break, and similar ultimate tensile strength at room temperature. This performance could be ascribed to that the local moduli continuously change from the hardest nanodomains to the softest nanodomains in the gradient copolymer, which alleviates the stress concentration during tensile test. Compared with the V-shaped gradient (VG) copolymer, the linear gradient copolymer showed much higher elastic modulus but lower elongation at break. The mechanical properties of the gradient copolymers were more sensitive to the change in temperature from 9 °C to 75 °C. With recovery temperature increased from 10 °C to 60 °C, the strain recovery of VG copolymer would change steadily from 40% to 99%. However, the elastic recovery of linear and triblock copolymer was poor even at 60 °C. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 860-868 [ABSTRACT FROM AUTHOR]

Reversible addition fragmentation chain transfer (RAFT) ab initio emulsion polymerization of styrene using poly(acrylic acid)-b-polystyrene trithiocarbonate (AA x-b-St y macroRAFT) as both mediator and surfactant was investigated with systematically changed y from 0 to 7 and x from 15 to 30. A well-controlled polymerization in terms of little coagulum, well predicted molecular weight and low polydispersity (PDI) (≈1.2) could only be achieved by using the macroRAFTs of hydrophile-lipophile balance (HLB) values between 13 and 20. The final latex particle size could be tuned from 80 to 172 nm in diameter simply by changing x and y values while the molecular weight was targeted the same (30 K). [ABSTRACT FROM AUTHOR]

It was demonstrated that gel-free styrene–butadiene–styrenetriblock copolymer (SBS) latex with a molecular weight about 90 kg/moland styrene composition about 34% could be synthesized by reversibleaddition–fragmentation chain transfer miniemulsion polymerization.The resulted SBS might be an excellent thermoplastic elastomer asindicated by its mechanical properties with ultimate tensile strengthof 16 MPa and about 800% elongation at break. [ABSTRACT FROM AUTHOR]

Abstract: Oligomer of styrene and maleic anhydride synthesized by bulk RAFT polymerization (SMA-RAFT) was used to construct a novel strategy for robust nanoencapsulation via interfacially confined controlled/living radical miniemulsion polymerization. After ammonolysis, SMA-RAFT becomes amphiphilic and can be used as a surfactant to prepare miniemulsion. The ammonolyzed SMA-RAFT molecules would self-assemble on the interface of water/droplets. This self-assembly property combining with the RAFT living polymerization chemistry demands the polymer chains to grow inwards gradually in particles, leading to the formation of a polymer shell. The hydrophilicity of ammonolyzed SMA-RAFT agent tuned by the ammonolyzed degree or structures of SMA-RAFT agent was found to play a key role in the final morphology. The well-defined nanocapsules with little solid particles can be obtained by using partially ammonolyzed SMA-RAFT with 0.5wt% SDS as a co-surfactant. [Copyright &y& Elsevier]

Abstract: The RAFT polymerization of styrene in miniemulsion using 1-phenylethyl phenyl-dithioacetate (PEPDTA) as a RAFT agent was investigated, in attempt to reveal the mechanism for the often observed inferior performance such as low polymerization rate, broad molecular weight distribution and particle size distribution in the RAFT miniemulsion polymerization with regular levels of surfactant and co-stabilizer (1wt% sodium dodecyl sulfate and 2wt% hexadecane). It is strongly evident that a few of large oligomer particles consisting of oligomer, RAFT agent (RAFT agent refers to the original RAFT agent), and monomer would be formed in the early stage of the polymerization due to the superswelling of the first nucleated droplets. With the regular levels of surfactant and co-stabilizer, the observed low polymerization rate, broadened molecular weight distribution, slow conversion of the RAFT agent, lower N p, and broadened particle size distribution could be well explained by the formation of these large oligomer particles and their prolonged existence. When the formation of the oligomer particles was suppressed by increasing surfactant and co-stabilizer levels and wise selection of types of RAFT agent, the molecular weight distribution could be narrowed to around 1.3 and particle size distribution could be close to that of the conventional non-living miniemulsion polymerization. [Copyright &y& Elsevier]

We designed and used a cyclohexenyl-functionalizedamphiphilicmacromolecular reversible addition–fragmentation chain transfer(macro-RAFT) agent as surfactant and polymerization mediator for (mini)emulsionpolymerization of styrene (St), aiming at synthesizing nanoparticleswith vinyl-enriched surface and well-defined polymer chains. Unexpectedly,the pendent cyclohexenyl units in the macro-RAFT agent were foundto undergo significant copolymerization with St exclusively duringthe nucleation period in the ab initio emulsion polymerization, leadingto the consumption of cyclohexenyl groups, positive deviation of molecularweights, and broad molecular weight distributions. By contrast, inminiemulsion polymerization, the radical polymerization exhibitedsuperb selectivity toward St monomers relative to the pendent cyclohexenevinyl units just as in the solution polymerization. The obtained polymerchains retained designed molecular weights, low polydispersity indexes,and quantitative cyclohexenyl functionalities confined to the particlesurface. Thus, PSt particles with vinyl-enriched surface were obtainedvia miniemulsion polymerization. [ABSTRACT FROM AUTHOR]

Abstract: RAFT ab initio emulsion copolymerization of γ-methyl-α-methylene-γ-butyrolactone (MeMBL) and styrene with various monomer ratios was investigated with PAA20-PS5 trithiocarbonate being mediator and surfactant at 70 °C. The polymerization was fully controlled as evidenced by stable latexes, well predicted molecular weights and low PDIs about 1.2 when [MeMBL]:[St] ≤ 1:2. However, in the case of [MeMBL]:[St] = 1:1, the molecular weight became out of control due to gel effect of RAFT reactions. The relatively water-soluble MeMBL was found to dramatically influence the polymerization kinetics and copolymer properties, as evidenced by (1) No inhibition period was observed; (2) The copolymer compositions in the early stage of polymerization were much higher than those predicted by the Mayo-Lewis equation in the case of [MeMBL]:[St] = 1:2, leading to the formation of linear gradient copolymer. (3) T gs of the copolymers from emulsion copolymerization were higher than those from bulk copolymerization. It was concluded that we could synthesize the gradient copolymer with preset molecular weight and low PDI in RAFT emulsion polymerization, T g of which should be much higher than 100 °C. [Copyright &y& Elsevier]