Synthesis of zwitterionic block copolymers via RAFT polymerization

A series of poly [2-(dimethylamino)ethyl methacrylate (DMA)-sodium acrylate (SA)] diblock copolymers were synthesized using reversible addition-fragmentation chain transfer (RAFT) polymerization. The polymerization exhibits controlled characters: well-controlled molecular weight, narrow molecular weight distribution, molecular weight increasing with polymerization time. The zwitterionic diblock copolymers show rich solution behaviors. Dynamic light scattering (DLS) indicated the formation of micelles and reverse micelles of copolymers is affected by net charge density of copolymers. Microcalorimetry studies showed that the lower critical solution temperature (LCST) increases with incorporation of hydrophilic segments in buffer.     

RAFT polymerization kinetics and polymer characterization of P3HT rod–coil block copolymers

Here an in‐depth analysis of reversible addition–fragmentation chain transfer (RAFT) polymerization kinetics is reported in order to provide better definition of poly(3‐hexylthiophene) (P3HT) rod–coil block copolymers thru a more thorough understanding of the RAFT polymerization of the coil block. To this end, a new P3HT macroRAFT agent is synthesized and utilized to prepare rod–coil block copolymers with P3HT and poly(styrene), poly(tert‐butylacrylate), and poly(4‐vinylpyridine), and the RAFT polymerization kinetics of each system are fully detailed. This is achieved by a comprehensive analysis of characterization data from ¹H nuclear magnetic resonance spectroscopy, gel permeation chromatography, and matrix‐assisted laser desorption ionization time of flight spectroscopy, which are used as complementary techniques in order to address difficulties in accurately characterizing the synthesized polymer systems. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 3575–3585     

RAFT mediated polysaccharide copolymers

Graft copolymers were prepared using the RAFT process via a Z-group approach, where xanthate esters were formed directly on a cellulosic substrate. Grafting of vinyl acetate onto the modified cellulosic materials was then carried out via the reversible addition fragmentation chain transfer (RAFT) process. The xanthate RAFT agents on the backbone of the cellulosic materials were identified by Fourier-transform infrared spectroscopy (FT-IR) and ultraviolet-visible spectroscopy (UV-vis). The number average molar masses of the graft copolymers were determined using size exclusion chromatography (SEC) and further characterization was conducted via liquid adsorption chromatography (LAC). The chromatographic results showed that the modified cellulosic materials were successfully grafted with polyvinyl acetate in a controlled manner. Grafted polyvinyl acetate (on the surface) and nongrafted polyvinyl acetate (in the solution) have almost the same molar mass and polydispersity index.     

Facile synthesis of comb,star, and graft polymers via reversible addition–fragmentation chain transfer (RAFT) polymerization

Reversible addition–fragmentation chain transfer (RAFT) polymerization has been shown to be a facile means of synthesizing comb, star, and graft polymers of styrene. The precursors required for these reactions were synthesized readily from RAFT‐prepared poly(vinylbenzyl chloride) and poly(styrene‐co‐vinylbenzyl chloride), which gave intrinsically well‐defined star and comb precursors. Substitution of the chlorine atom in the vinylbenzyl chloride moiety with a dithiobenzoate group proceeded readily, with a minor detriment to the molecular weight distribution. The kinetics of the reaction were consistent with a living polymerization mechanism, except that for highly crowded systems, there were deviations from linearity early in the reaction due to steric hindrance and late in the reaction due to chain entanglement and autoacceleration. A crosslinked polymer‐supported RAFT agent was also prepared, and this was used in the preparation of graft polymers with pendant polystyrene chains. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2956–2966, 2002     

Facile synthesis of temperature-sensitive ABA triblock copolymers by dispersion RAFT polymerization

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Controlled radical copolymerization of styrene and maleic anhydride and the synthesis of novel polyolefin‐based block copolymers by reversible addition–fragmentation chain‐transfer (RAFT) polymerization

Reversible addition–fragmentation chain transfer (RAFT) was applied to the copolymerization of styrene and maleic anhydride. The product had a low polydispersity and a predetermined molar mass. Novel, well‐defined polyolefin‐based block copolymers were prepared with a macromolecular RAFT agent prepared from a commercially available polyolefin (Kraton L‐1203). The second block consisted of either polystyrene or poly(styrene‐co‐maleic anhydride). Furthermore, the colored, labile dithioester moiety in the product of the RAFT polymerizations could be removed from the polymer chain by UV irradiation. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3596–3603, 2000     

Mechanism and kinetics of dithiobenzoate‐mediated RAFT polymerization. I. The current situation

Investigations into the kinetics and mechanism of dithiobenzoate‐mediated Reversible Addition–Fragmentation Chain Transfer (RAFT) polymerizations, which exhibit nonideal kinetic behavior, such as induction periods and rate retardation, are comprehensively reviewed. The appreciable uncertainty in the rate coefficients associated with the RAFT equilibrium is discussed and methods for obtaining RAFT‐specific rate coefficients are detailed. In addition, mechanistic studies are presented, which target the elucidation of the fundamental cause of rate retarding effects. The experimental and theoretical data existing in the literature are critically evaluated and apparent discrepancies between the results of different studies into the kinetics of RAFT polymerizations are discussed. Finally, recommendations for further work are given. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5809–5831, 2006     

RAFT polymerization of alternating styrene‐pentafluorostyrene copolymers

Reversible addition‐fragmentation chain‐transfer (RAFT) polymerization was used to control the alternating copolymerization of styrene and 2,3,4,5,6‐pentaflurostyrene. The RAFT polymerization yields a high degree of control over the molecular weight of the polymers and does not significantly influence the reactivity ratios of the monomers. The controlled free‐radical polymerization could be initiated using AIBN at elevated temperatures or using a redox couple (benzoyl peroxide/N,N‐dimethylaniline) at room temperature, while maintaining control over molecular weight and dispersity. The influence of temperature and solvent on the molecular weight distribution and reactivity ratios were investigated. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1555–1559     

Controlled/living radical polymerization of vinylcyclicsilazane by RAFT process and their block copolymers

High molecular weight poly(vinyl)silazane were synthesized successfully by reversible addition fragmentation chain transfer (RAFT) polymerization in toluene at 120 °C, using dithiocarbamate derivatives and 2,2′‐azobis‐isobutyrylnitrile (AIBN) as the RAFT agents and thermal initiator, respectively. The polymerization of a vinylcyclicsilazane oligomer with 82.5% conversion was readily controlled to increase the molecular weight from 1000 to 12,000 g/mol with a narrow polydispersity <1.5. The resulting polymer showed a high ceramic yield of 70 wt % at 1000 °C. Moreover, the approach was extended successfully to the synthesis of poly(vinyl)silazane‐block‐polystyrene as an inorganic–organic diblock copolymer. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4594–4601, 2008     

Synthesis and characterizations of 1,2,3-triazole containing polymers via reversible addition-fragmentation chain transfer (RAFT) polymerization

A novel monomer containing triazole and naphthalene ring, 2-(1-naphthalen-1-ylmethyl-1H-[1,2,3]triazol-4-yl)-ethyl methacrylate (NTEMA), was designed and synthesized via “click” chemistry method. The RAFT polymerization of NTEMA was successfully carried out using 2-cyanoprop-2-yl dithiobenzoate (CPDB) as a RAFT agent, 2,2′-azobisisobutyronitrile (AIBN) as an initiator in tetrahydrofuran (THF) solution. The results showed that the polymerizations exhibited “living”/controlled characteristics. The obtained poly(2-(1-naphthalen-1-ylmethyl-1H-[1,2,3]triazol-4-yl)-ethyl methacrylate) homopolymers, PNTEMAs, were further coordinated with samarium ion to prepare rare earth containing polymers (PNTEMA-Sm(III) complexes) which were characterized by FT-IR, DSC and ICP-AES. The characterization data confirmed that triazole in side chain of the polymer could coordinate with Sm(III). The fluorescence property of the polymers and polymer Sm(III) complexes were investigated in solution and in film.     

Synthesis of natural rubber-based telechelic cis-1,4-polyisoprenes and their use to prepare block copolymers via RAFT polymerization

A new trithiocarbonate functionalized cis-1,4-polyisoprene was obtained from oxidative degradation of natural rubber followed by reductive amination and amidation. The structure of the resulting functionalized cis-1,4-polyisoprene was confirmed by a combination of ¹H NMR spectroscopy, ¹³C NMR spectroscopy, MALDI-TOF mass spectrometry and FTIR spectroscopy. ¹H NMR spectroscopy showed that the trithiocarbonate functionality was equal to one. The well-defined trithiocarbonyl-end functionalized cis-1,4-polyisoprene was used as a macromolecular chain transfer agent (macroCTA) to mediate the RAFT polymerization of t-BA using AIBN as the initiator ([t-BA]₀/[macroCTA]₀/[AIBN]₀ = 250/1/0.2) in toluene at 60 °C. The resulting PI-b-P(t-BA) diblock copolymer presents an unimodal SEC trace shifted toward higher molecular weight in comparison with the SEC trace of the macroCTA, indicating that the polymerization of the second block is effective. The characteristics of the copolymer were determined by SEC = 26,000 g mol⁻¹, PDI = 1.76) and ¹H NMR spectroscopy ( (PI) = 62 and (P(t-BA)) = 87).     

Thermoresponsive NIPAM block copolymers containing densely grafted poly(vinyl ether) brushes synthesized by a combination of living cationic polymerization and RAFT polymerization

Diblock copolymers consisting of a multibranched polymethacrylate segment with densely grafted poly[2‐(2‐methoxyethoxy)ethyl vinyl ether] pendants and a poly(N‐isopropylacrylamide) segment were synthesized by a combination of living cationic polymerization and RAFT polymerization. A macromonomer having both a poly[2‐(2‐methoxyethoxy)ethyl vinyl ether] backbone and a terminal methacryloyl group was synthesized by living cationic polymerization. The sequential RAFT copolymerizations of the macromonomer and N‐isopropylacrylamide in this order were performed in aqueous media employing 4‐cyanopentanoic acid dithiobenzoate as a chain transfer agent and 4,4′‐azobis(4‐cyanopentanoic acid) as an initiator. The obtained diblock copolymers possessed relatively narrow molecular weight distributions and controlled molecular weights. The thermoresponsive properties of these polymers were investigated. Upon heating, the aqueous solutions of the diblock copolymers exhibited two‐stage thermoresponsive properties denoted by the appearance of two cloud points, indicating that the densely grafted poly[2‐(2‐methoxyethoxy)ethyl vinyl ether] pendants and the poly(N‐isopropylacrylamide) segments independently responded to temperature. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Living radical miniemulsion polymerization by RAFT in the presence of beta-cyclodextrin

Living radical polymerization of styrene in a miniemulsion by reversible addition–fragmentation chain transfer (RAFT) was successfully realized in the presence of beta-cyclodextrin (CD), using sodium dodecyl sulfate and hexadecane as surfactant and costabilizer, respectively. The drawback of instability (red layer formation) encountered in the living radical polymerization in emulsion or miniemulsion was overcome. The linear relationship between the monomer conversion and the molecular weight, as well as lower molecular weight distribution (MWD), shows that the polymerization process was under control. The addition of CD was found to have little influence on the polymerization rate. However, MWD of the polymer synthesized is obviously decreased. The mechanism of stability and controllability improvement in the presence of CD proposed that the complex formation between CD and RAFT agent or RAFT agent-ended oligomer increased their diffusion ability from monomer droplet to polymerization locus and improved the homogeneity of the RAFT agent level among the polymerization loci.     

Macromolecular design via reversible addition–fragmentation chain transfer (RAFT)/xanthates (MADIX) polymerization

Among the living radical polymerization techniques, reversible addition–fragmentation chain transfer (RAFT) and macromolecular design via the interchange of xanthates (MADIX) polymerizations appear to be the most versatile processes in terms of the reaction conditions, the variety of monomers for which polymerization can be controlled, tolerance to functionalities, and the range of polymeric architectures that can be produced. This review highlights the progress made in RAFT/MADIX polymerization since the first report in 1998. It addresses, in turn, the mechanism and kinetics of the process, examines the various components of the system, including the synthesis paths of the thiocarbonyl‐thio compounds used as chain‐transfer agents, and the conditions of polymerization, and gives an account of the wide range of monomers that have been successfully polymerized to date, as well as the various polymeric architectures that have been produced. In the last section, this review describes the future challenges that the process will face and shows its opening to a wider scientific community as a synthetic tool for the production of functional macromolecules and materials. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43:5347–5393, 2005     

Radical addition fragmentation chain transfer (RAFT) polymerization of ferrocenyl (Meth)acrylates

We report on the controlled free radical homopolymerization of 1‐ferrocenylethyl acrylate as well as of three new ferrocene bearing monomers, namely 4‐ferrocenylbutyl acrylate, 2‐ferrocenylamido‐2‐methylpropyl acrylate, and 4‐ferrocenylbutyl methacrylate, by the RAFT technique. For comparison, the latter monomer was polymerized using ATRP, too. The ferrocene containing monomers were found to be less reactive than their analogues free of ferrocene. The reasons for the low polymerizability are not entirely clear. As the addition of free ferrocene to the reaction mixture did not notably affect the polymerizations, sterical hindrance by the bulky ferrocene moiety fixed on the monomers seems to be the most probable explanation. Molar masses found for 1‐ferrocenylethyl acrylate did not exceed 10,000 g mol^?1, while for 4‐ferrocenylbutyl (meth)acrylate molar masses of 15,000 g mol^?1 could be obtained. With PDIs as low as 1.3 in RAFT polymerization of the monomers, good control over the polymerization was achieved. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

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     

Facile synthesis of star‐shaped copolymers via combination of RAFT and ring opening polymerization

Reversible addition fragmentation chain transfer (RAFT) polymerization and bifunctional sparteine/thiourea organocatalyst‐mediated ring opening polymerization (ROP) were combined to produce poly(L ‐lactide) star polymers and poly(L ‐lactide‐co‐styrene) miktoarm star copolymers architecture following a facile experimental procedure, and without the need for specialist equipment. RAFT was used to copolymerize ethyl acrylate (EA) and hydroxyethyl acrylate (HEA) into poly(EA‐co‐HEA) co‐oligomers of degree of polymerization 10 with 2, 3, and 4 units of HEA, which were in turn used as multifunctional initiators for the ROP of L ‐lactide, using a bifunctional thiourea organocatalytic system. Furthermore, taking advantage of the living nature of RAFT polymerization, the multifunctional initiators were chain extended with styrene (poly((EA‐co‐HEA)‐b‐styrene) copolymers), and used as initiators for the ROP of L ‐lactide, to yield miktoarm star copolymers. The ROP reactions were allowed to proceed to high conversions (>95%) with good control over molecular weights (ca. 28,000‐230,000 g/mol) and polymer structures being observed, although the molecular weight distributions are generally broader (1.3–1.9) than those normally observed for ROP reactions. The orthogonality of both polymerization techniques, coupled with the ubiquity of HEA, which is used as a monomer for RAFT polymerization and as an initiator for ROP, offer a versatile approach to star‐shaped copolymers. Furthermore, this approach offers a practical approach to the synthesis of polylactide star polymers without a glove box or stringent reaction conditions. The phase separation properties of the miktoarm star copolymers were demonstrated via thermal analyses. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6396–6408, 2009     

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     

RAFT试剂N-咔唑二硫代甲酸1,4-对二甲基苯双酯的合成及应用

以咔唑和对二氯甲基苯为原料, 合成了以咔唑为Z基团的双功能团RAFT聚合链转移试剂N-咔唑二硫代甲酸1,4-对二甲基苯双酯(PXCBD). 以PXCBD为链转移试剂, 以苯乙烯、丙烯酸甲酯及N,N-二丁基丙烯酰胺为单体, 考察了PXCBD在RAFT聚合中合成多嵌段共聚物上的应用, 并研究了PXCBD及由其合成的聚合物的荧光特性. 研究结果表明, PXCBD是一种性能优异的双功能团RAFT聚合链转移试剂, 可用于合成特殊结构并且带有荧光标识的功能高分子材料.