Synthesis of diblock copolymers containing poly(N‐vinylcarbazole) by reversible addition‐fragmentation chain transfer polymerization

The reversible addition‐fragmentation chain transfer (RAFT) polymerization of N‐vinylcarbazole (NVK) mediated by macromolecular xanthates was used to prepare three types of block copolymers containing poly(N‐vinylcarbazole) (PVK). Using a poly(ethylene glycol) monomethyl ether based xanthate ( PEG‐X ), the RAFT polymerization of NVK proceeded in a controlled way to afford a series of PEG‐b‐PVK with different PVK chain lengths. Successive RAFT polymerization of NVK and vinyl acetate (VAc) with a small molecule xanthate ( X1 ) as the chain transfer agent was tested to prepare PVK‐b‐PVAc. Though both monomers can be homopolymerized in a controlled manner with this xanthate, only by polymerizing NVK first could give well‐defined block copolymers. The xanthate groups in the end of PVK could be removed by radical‐induced reduction using tributylstannane, and PVK‐b‐PVA was obtained by further hydrolysis of PVK‐b‐PVAc under basic conditions. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Poly(N‐vinyl pyrrolidone)‐block‐Poly(N‐vinyl carbazole)‐block‐poly(N‐vinyl pyrrolidone) triblock copolymers: Synthesis via RAFT/MADIX process,self‐assembly behavior,and photophysical properties

Poly(N‐vinyl pyrrolidone)‐block‐poly(N‐vinyl carbazole)‐block‐poly(N‐vinyl pyrrolidone) (PVP‐b‐PVK‐b‐PVP) triblock copolymers were synthesized via sequential reversible addition‐fragmentation chain transfer/macromolecular design via the interchange of xanthate (RAFT/MADIX) process. First, 1,4‐phenylenebis(methylene)bis(ethyl xanthate) was used as a chain transfer agent to mediate the radical polymerization of N‐vinyl carbazole (NVK). It was found that the polymerization was in a controlled and living manner. Second, one of α,ω‐dixanthate‐terminated PVKs was used as the macromolecular chain transfer agent to mediate the radical polymerization of N‐vinyl pyrrolidone (NVP) to obtain the triblock copolymers with various lengths of PVP blocks. Transmission electron microscopy (TEM) showed that the triblock copolymers in bulks were microphase‐separated and that PVK blocks were self‐organized into cylindrical microdomains, depending on the lengths of PVP blocks. In aqueous solutions, all these triblock copolymers can self‐assemble into the spherical micelles. The critical micelle concentrations of the triblock copolymers were determined without external adding fluorescence probe. By analyzing the change in fluorescence intensity as functions of the concentration, it was judged that the onset of micellization occurred at the concentration while the FL intensity began negatively to deviate from the initial linear increase with the concentration. Fluorescence spectroscopy indicates that the self‐assembled nanoobjects of the PVP‐b‐PVK‐b‐PVP triblock copolymers in water were capable of emitting blue/or purple fluorescence under the irradiation of ultraviolet light. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1852–1863     

RAFT/MADIX copolymerization of vinyl acetate and 5,6‐benzo‐2‐methylene‐1,3‐dioxepane

The synthesis of well‐defined degradable poly(vinyl acetate) analogues is achieved by RAFT copolymerization of 5,6‐benzo‐2‐methylene‐1,3‐dioxepane (BMDO) and vinyl acetate (VAc) using methyl (ethoxycarbonothioyl)sulfanyl acetate (MEA) as controlling agent. Several monomer mixtures with low BMDO contents (<30 mol %) are employed to prepare different copolymers. In all the cases, the evolution of molar masses and the dispersity values (<1.26) confirm the controlled feature of the polymerization. The livingness of the obtained chains is demonstrated by successful chain extension experiments with VAc, although the presence of dead chains is also shown. The introduction of ester groups into the main chain of these P(VAc‐co‐BMDO) copolymers allows their degradation when treated with a mixture of KOH/MeOH in reflux during 2.5 h. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 104–111     

Synthesis of poly(tert‐butyl acrylate‐block‐vinyl acetate) copolymers by combining ATRP and RAFT polymerizations

The synthesis of poly(tert‐butyl acrylate‐block‐vinyl acetate) copolymers using a combination of two living radical polymerization techniques, atom transfer radical polymerization (ATRP) and reversible addition‐fragmentation chain transfer (RAFT) polymerization, is reported. The use of two methods is due to the disparity in reactivity of the two monomers, viz. vinyl acetate is difficult to polymerize via ATRP, and a suitable RAFT agent that can control the polymerization of vinyl acetate is typically unable to control the polymerization of tert‐butyl acrylate. Thus, ATRP was performed to make poly(tert‐butyl acrylate) containing a bromine end group. This end group was subsequently substituted with a xanthate moiety. Various spectroscopic methods were used to confirm the substitution. The poly(tert‐butyl acrylate) macro‐RAFT agent was then used to produce (tert‐butyl acrylate‐block‐vinyl acetate). © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7200–7206, 2008     

One‐step synthesis of poly(N‐vinylpyrrolidone)‐b‐poly(l‐lactide) block copolymers using a dual initiator for RAFT polymerization and ROP

Amphiphilic, biocompatible poly(N‐vinylpyrrolidone)‐b‐poly(l ‐lactide) (PVP‐b‐PLLA) block polymers were synthesized at 60 °C using a hydroxyl‐functionalized N,N‐diphenyldithiocarbamate reversible addition–fragmentation chain transfer (RAFT) agent, 2‐hydroxyethyl 2‐(N,N‐diphenylcarbamothioylthio)propanoate (HDPCP), as a dual initiator for RAFT polymerization and ring‐opening polymerization (ROP) in a one‐step procedure. 4‐Dimethylamino pyridine was used as the ROP catalyst for l ‐lactide. The two polymerization reactions proceeded in a controlled manner, but their polymerization rates were affected by the other polymerization process. This one‐step procedure is believed to be the most convenient method for synthesizing PVP‐b‐PLLA block copolymers. HDPCP can also be used for the one‐step synthesis of poly(N‐vinylcarbazole)‐b‐PLLA block copolymers. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1607–1613     

One-step synthesis of poly(alkyl methacrylate)-b-polyester block copolymers via a dual initiator route combining RAFT polymerization and ROP

One-step synthesis of well-defined poly(alkyl methacrylate)-b-polyester block copolymers was successfully performed at 30?°C using a dual initiator for reversible addition–fragmentation chain transfer (RAFT) polymerization and ring-opening polymerization (ROP). 4-Cyano-1-hydroxypent-4-yl dithiobenzoate, a hydroxyl-functionalized RAFT agent, was used as a dual initiator for the RAFT polymerization of methacrylic monomers and the ROP of lactones. Diphenyl phosphate (DPP) was used as a catalyst for ROP. The two polymerization reactions proceeded in a controlled manner without mutual interference. DPP was found to be a suitable catalyst for a dual initiator route combining RAFT polymerization and the ROP of lactones.     

Synthesis and characters of hyperbranched poly(vinyl acetate) by RAFT polymeraztion

Reversible addition-fragmentation chain transfer (RAFT) polymerization of VAc in the presence of ECTVA, which capable of both reversible chain transferable through a xanthate moiety and propagation via a vinyl group, led to highly branched copolymers by a method analogous to self-condensing vinyl polymerization (SCVP). The ECTVA acted as a vinyl acetate AB^∗ inimer. It was copolymerized with vinyl acetate (VAc) in ratios selected to tune the distribution and length of branches of resulting hyperbranched poly(vinyl acetate). The degree of branching increased with chain ECTVA concentration, as confirmed by NMR spectroscopy. The polymer structure was characterized via MALDI–TOF. Retention of the xanthate compound during the polymerization was evidenced by successful chain extension of a branched (PVAc) macroCTA by RAFT polymerization. The branched PVAc led to better dissolution as compared to linear PVAc, an effect attributed primarily to an increased contribution of end groups.     

Amphiphilic block copolymer self‐assemblies of poly(NVP)‐b‐poly(MDO‐co‐vinyl esters): Tunable dimensions and functionalities

Functional, degradable polymers were synthesized via the copolymerization of vinyl acetate (VAc) and 2‐methylene‐1,3‐dioxepane (MDO) using a macro‐xanthate CTA, poly(N‐vinylpyrrolidone), resulting in the formation of amphiphilic block copolymers of poly(NVP)‐b‐poly(MDO‐co‐VAc). The behavior of the block copolymers in water was investigated and resulted in the formation of self‐assembled nanoparticles containing a hydrophobic core and a hydrophilic corona. The size of the resultant nanoparticles was able to be tuned with variation of the hydrophilic and hydrophobic segments of the core and corona by changing the incorporation of the macro‐CTA as well as the monomer composition in the copolymers, as observed by Dynamic Light Scattering, Static Light Scattering, and Transmission Electron Microscopy analyses. The concept was further applied to a VAc derivative monomer, vinyl bromobutanoate, to incorporate further functionalities such as fluorescent dithiomaleimide groups throughout the polymer backbone using azidation and “click” chemistry as postpolymerization tools to create fluorescently labeled nanoparticles. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2699–2710     

Preparation of miktoarm star‐block copolymers PSn‐b‐PVAc4‐n via combination of ATRP and RAFT polymerization

Three tetrafunctional bromoxanthate agents (Xanthate₃‐Br, Xanthate₂‐Br₂, and Xanthate‐Br₃) were synthesized. Initiative atom transfer radical polymerizations (ATRP) of styrene (St) or reversible addition fragmentation chain transfer (RAFT) polymerizations of vinyl acetate (VAc) proceeded in a controlled manner in the presence of Xanthate₃‐Br, Xanthate₂‐Br₂, or Xanthate‐Br₃, respectively. The miktoarm star‐block copolymers containing polystyrene (PS) and poly(vinyl acetate) (PVAc) chains, PS_n‐b‐PVAc_4‐n (n = 1, 2, and 3), with controlled structures were successfully prepared by successive RAFT and ATRP chain‐extension experiments using VAc and St as the second monomers, respectively. The architecture of the miktoarm star‐block copolymers PS_n‐b‐PVAc_4‐n (n = 1, 2, and 3) were characterized by gel permeation chromatography and ¹H NMR spectra. Furthermore, the results of the cleavage of PS₃‐b‐PVAc and PVAc₂‐b‐PS₂ confirmed the structures of the obtained miktoarm star‐block copolymers. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Latices of poly(fluoroalkyl mathacrylate)‐b‐poly(butyl methacrylate) copolymers prepared via reversible addition–fragmentation chain transfer polymerization

Poly(fluoroalkyl mathacrylate)‐block‐poly(butyl methacrylate) diblock copolymer latices were synthesized by a two‐step process. In the first step, a homopolymer end‐capped with a dithiobenzoyl group [poly(fluoroalkyl mathacrylate) (PFAMA) or poly(butyl methacrylate) (PBMA)] was prepared in bulk via reversible addition–fragmentation chain transfer (RAFT) polymerization with 2‐cyanoprop‐2‐yl dithiobenzoate as a RAFT agent. In the second step, the homopolymer chain‐transfer agent (macro‐CTA) was dissolved in the second monomer, mixed with a water phase containing a surfactant, and then ultrasonicated to form a miniemulsion. Subsequently, the RAFT‐mediated miniemulsion polymerization of the second monomer (butyl methacrylate or fluoroalkyl mathacrylate) was carried out in the presence of the first block macro‐CTA. The influence of the polymerization sequence of the two kinds of monomers on the colloidal stability and molecular weight distribution was investigated. Gel permeation chromatography analyses and particle size results indicated that using the PFAMA macro‐CTA as the first block was better than using the PBMA RAFT agent with respect to the colloidal stability and the narrow molecular weight distribution of the F‐copolymer latices. The F‐copolymers were characterized with ¹H NMR, ¹⁹F NMR, and Fourier transform infrared spectroscopy. Comparing the contact angle of a water droplet on a thin film formed by the fluorinated copolymer with that of PBMA, we found that for the diblock copolymers containing a fluorinated block, the surface energy decreased greatly, and the hydrophobicity increased. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 471–484, 2007     

Copolymerization of N-Vinylcarbazole and Vinyl Acetate via Reversible Addition-Fragmentation Chain Transfer (RAFT) Polymerization

Summary: The reversible addition–fragmentation chain transfer (RAFT) random copolymerization of N-vinylcarbazole (NVC) and vinyl acetate (VAc) was carried out using s-benzyl-o-ethyl dithiocarbonate (BED) as the chain transfer agent and 2,2′-azoisobutyronitrile (AIBN) as the initiator in 1,4-dioxane solution at 70 °C. The polymerization showed the characteristics of ‘living’ free radical polymerization behaviors: first order kinetics, linear relationships between molecular weight and conversion, and narrow polydispersity of the polymers. The reactivity ratios of NVC and VAc were calculated via the Kelen–Tudos (KT) and non-linear error in variable (EVM) methods and showed as r₁ = 1.938 ± 0.191, r₂ = 0.116 ± 0.106. The thermal behavior of the copolymers with different content of NVC and VAc was investigated by DSC and TGA. The results showed that the introduction of a VAc segment into copolymer significantly reduced the T_g of the NVC homopolymers. FT-IR spectra, fluorescence spectra, and cyclic voltammetric behavior of these copolymers were also measured and compared with those of NVC homopolymers. The copolymers showed similar oxidative behavior to the NVC homopolymer. However, there was only one reductive potential peak shown for the copolymers at about 0.058 V.     

Fabrication and cytocompatibility evaluation for blood‐compatible polyethersulfone membrane modified by a synthesized poly (vinyl pyrrolidone)‐block‐poly (acrylate‐graft‐poly(methyl methacrylate))‐block‐poly‐(vinyl pyrrolidone)

Polyethersulfone (PES) membrane, one of the most important polymeric materials because of its good chemical resistance, thermal stability, mechanical, and film‐forming properties, has already been used in hemodialysis, tissue engineering, and artificial organs. In order to improve the blood compatibility of PES membrane, many amphiphilic block copolymers have been synthesized and used as additives for surface modification. The object of this study is to develop a hydrophilic PES membrane by blending a comblike amphiphilic block copolymer poly (vinyl pyrrolidone)‐block‐poly [acrylate‐graft‐poly (methyl methacrylate)]‐block‐poly‐(vinyl pyrrolidone) [PVP‐b‐P (AE‐g‐PMMA)‐b‐PVP] synthesized by RAFT polymerization. The cytocompatibility performance of PVP‐b‐P (AE‐g‐PMMA)‐b‐PVP modified PES membrane was evaluated, which showed better cytocompatibility compared with that of pristine PES membrane. Endothelial cells cultured on the modified membranes present improved growth in terms of scanning electron microscope observation, MTT assay, and confocal laser scanning microscope observation. These results indicate that the modified membrane has great potential application in blood‐contact fields such as hemodialysis and bio‐artificial liver supports. Copyright © 2015 John Wiley & Sons, Ltd.     

Mn2(CO)10‐induced controlled/living radical copolymerization of vinyl acetate and methyl acrylate: Spontaneous formation of block copolymers consisting of gradient and homopolymer segments

The controlled/living radical polymerization of vinyl acetate (VAc) and its copolymerization with methyl acrylate (MA) were investigated in bulk or fluoroalcohols using manganese complex [Mn₂(CO)₁₀] in conjunction with an alkyl iodide (R? I) as an initiator under weak visible light. The manganese complex induced the controlled/living radical polymerization of VAc even in the fluoroalcohols without any loss of activity. The R? I/Mn₂(CO)₁₀ system was also effective for the copolymerization of MA and VAc, in which MA was consumed faster than VAc, and then the remaining VAc was continuously and quantitatively consumed after the complete consumption of MA. The ¹H and ¹³C NMR analyses revealed that the obtained products are block copolymers consisting of gradient MA/VAc segments, in which the VAc content gradually increases, and homopoly(VAc). The use of fluoroalcohols as solvents increased the copolymerization rate, controllability of the molecular weights, and copolymerizability of VAc. The saponification of the VAc units in poly(MA‐grad‐VAc)‐block‐poly(VAc) resulted in the corresponding poly(MA‐co‐γ‐lactone)‐block‐poly(vinyl alcohol) due to the intramolecular cyclization between the hydroxyl and neighboring carboxyl groups in the gradient segments. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1343–1353, 2009     

Aspects of Living Radical Polymerization Mediated by Cobalt Porphyrin Complexes

Living radical polymerization (LRP) of methyl acrylate (MA), acrylic acid (AA), and vinyl acetate (VAc) mediated by cobalt(II) porphyrin complexes ((TMP)Co^II·, (TMPS)Co^II·) are reported. The polymeric products with relatively low polydispersity and controlled number average molecular weight (M_n) based on one polymer chain per cobalt complex demonstrate the living characters of the polymerization process. The formation of block copolymers of poly(methyl acrylate)‐b‐poly(vinyl acetate) (PMA‐b‐PVAc) and poly(methyl acrylate)‐b‐poly(vinyl pyrrolidone) (PMA‐b‐PVP) demonstrate another important feature of LRP and extend the application of cobalt porphyrin mediated radical polymerization to a wider array of functionalized monomers. Kinetic studies using ¹H NMR to follow the formation of orGano‐cobalt complexes reveal that two mechanisms, reversible termination (RT) and degenerative transfer (DT), occur during the polymerization process. MA and VAc polymerization mediated by cobalt porphyrin complexes are used to illustrate the properties of these two LRP pathways and evaluate the kinetic and thermodynamic properties for several of the central reactions.     

Phosphonate‐terminated poly(vinyl acetate) synthesized by RAFT/MADIX polymerization

Four different xanthates containing either phosphonate or bisphosphonate moieties were synthesized with high degree of purity. These xanthates were used as chain transfer agents (CTA) in the RAFT/MADIX polymerization of vinyl acetate (VAc) to prepare end‐capped poly(VAc). The rate of VAc polymerization in the presence of these new CTAs was shown to be similar to that obtained with conventional xanthate, that is, (methyl ethoxycarbonothioyl) sulfanyl acetate. Good control of VAc polymerization was also obtained since the molecular weight increased linearly with monomer conversion for each phosphonate‐containing xanthate. Low‐PDI values were obtained, ascribed to efficient exchange during RAFT/MADIX polymerization. C_ex value was therefore calculated to about 25, based on RAFT/MADIX of VAc in the presence of rhodixan A1/VAc adduct. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

A cyclic selenium‐based reversible addition‐fragmentation chain transfer agent mediated polymerization of vinyl acetate

A cyclic selenium‐based reversible addition‐fragmentation chain transfer (RAFT) agent, 5,5‐dimethyl‐3‐phenyl‐2‐selenoxo‐1,3‐selenazolidin‐4‐one (RAFT‐Se), was synthesized and utilized in the RAFT polymerizations of vinyl acetate (VAc). Its analog, 5,5‐dimethyl‐3‐phenyl‐2‐thioxothiazolidin‐4‐one (RAFT‐S), was also used in RAFT polymerizations for comparison under identical conditions. The RAFT polymerizations of VAc with RAFT‐Se were moderately controlled evidenced by the increase of molecular weights with conversion, despite the slightly high M_w/M_n (less than 1.90), whereas the molecular weights were poorly controlled in the presence of RAFT‐S (2.00 < M_w/M_n < 2.30). Thanks to its unusual cyclic structure of RAFT‐Se, one or more RAFT‐Se species was incorporated into the resultant poly(VAc) as revealed by the results of cleavage of polymer and atomic absorption spectroscopy. Considering the biorelated functions of both poly(VAc) and Se element, this work undoubtedly provided a successful methodology of how to incorporate high content of Se into a molecular weight controlled poly(VAc). © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Double hydrophilic diblock copolymers containing a poly(ionic liquid) segment: Controlled synthesis, solution property, and application as carbon precursor

In this contribution, we demonstrate the controlled synthesis of double hydrophilic block copolymers comprising a hydrophilic poly(ionic liquid) (PIL) segment via the RAFT/MADIX process. The non-ionic segment is made up from either poly(N-isopropylacrylamide) (PNIPAAm) or poly(N,N-dimethylacrylamide) (PDMA), due to their favorable controllable solubility in water at room temperature. They were employed as macro-chain transfer agents (macro-CTAs) for the RAFT polymerization of four different 1-vinylimidazolium ionic liquid monomers possessing different alkyl substitutes and anions. The block copolymers of PNIPAAm-b-PIL are dual stimuli-responsive copolymers that can respond to the changes in temperature and ionic strength in aqueous solution. This special property facilitated a facile anion exchange of the PIL segment. In addition, one copolymer could successfully be employed as carbon precursor for the preparation of mesoporous graphitic nanostructures in the presence of metal salts.     

Cobalt‐mediated radical polymerization routes to poly(vinyl ester) block copolymers

Cobalt‐mediated radical polymerizations (CMRPs) utilizing redox initiation are demonstrated to produce poly(vinyl ester) homopolymers derived from vinyl pivalate (VPv) and vinyl benzoate (VBz), and their block copolymers with vinyl acetate (VAc). Combining anhydrous Co(acac)₂, lauroyl peroxide, citric acid trisodium salt, and VPv at 30 °C results in controlled polymerizations that yield homopolymers with M_n = 2.5–27 kg/mol with M_w/M_n = 1.20–1.30. Homopolymerizations of scrupulously purified VBz proceed with lower levels of control as evidenced by broader polydispersities over a range of molecular weights (M_n = 4–16 kg/mol; M_w/M_n = 1.34–1.65), which may be interpreted in terms of the decreased nucleophilicity of these less electron donating propagating polymer chain ends. Based on these results, we demonstrate that sequential CMRP reactions present a viable route to microphase separated poly(vinyl ester) block copolymers as shown by small‐angle X‐ray scattering analyses. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Investigation of the influence of the architectures of poly(vinyl pyrrolidone) polymers made via the reversible addition–fragmentation chain transfer/macromolecular design via the interchange of xanthates mechanism on the stabilization of suspension polymerizations

Linear, star, and block copolymers based on poly(vinyl pyrrolidone) (PVP) were synthesized with the macromolecular design via the interchange of xanthates (MADIX) process for use as potential stabilizers in suspension polymerization. The design of the leaving group of the dithioxanthate‐based transfer agent was shown to be key to the successful preparation of well‐defined PVP architectures. A linear correlation of the monomer conversion and molecular weight was found in the synthesis of star polymers, whereas the molecular weight distribution remained narrow (polydispersity index < 1.3). Significant side reactions, which typically broaden the molecular weight distribution when R‐designed MADIX agents are used, were absent. The living behavior of the PVP polymerization was furthermore confirmed via chain extension with vinyl acetate, which resulted in the formation of PVP–PVAc block copolymers [where PVAc is poly(vinyl acetate)]. The prepared polymers were used as stabilizers in suspension polymerization to prepare crosslinked poly(vinyl neodecanoate)/ethylene glycol dimethacrylate microspheres. The ratio of the interfacial tension of the aqueous and monomer phases and the overall viscosity were found to have an effect on the diameter of the particles, with PVP star polymers as stabilizers resulting in smaller particles. A smaller interfacial tension, measured when star polymers and block copolymers were used, resulted in the appearance of smaller particles, probably because of more breakup events of the monomer droplets and the enhanced stabilization of the particle surface area. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4372–4383, 2006     

Reversible addition–fragmentation transfer (RAFT) copolymerization of methyl methacrylate and styrene in miniemulsion

In the reversible addition–fragmentation transfer (RAFT) copolymerization of two monomers, even with the simple terminal model, there are two kinds of macroradical and two kinds of polymeric RAFT agent with different R groups. Because the structure of the R group could exert a significant influence on the RAFT process, RAFT copolymerization may behave differently from RAFT homopolymerization. The RAFT copolymerization of methyl methacrylate (MMA) and styrene (St) in miniemulsion was investigated. The performance of the RAFT copolymerization of MMA/St in miniemulsion was found to be dependent on the feed monomer compositions. When St is dominant in the feed monomer composition, RAFT copolymerization is well controlled in the whole range of monomer conversion. However, when MMA is dominant, RAFT copolymerization may be, in some cases, out of control in the late stage of copolymerization, and characterized by a fast increase in the polydispersity index (PDI). The RAFT process was found to have little influence on composition evolution during copolymerization. The synthesis of the well‐defined gradient copolymers and poly[St‐b‐(St‐co‐MMA)] block copolymer by RAFT miniemulsion copolymerization was also demonstrated. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 6248–6258, 2004