Preparation,characterization, and chiral recognition of optically active polymers containing pendent chiral units via reversible addition‐fragmentation chain transfer polymerization

Optically active polymers bearing chiral units at the side chain were prepared via reversible addition‐fragmentation chain transfer (RAFT) polymerization in the presence of 2,2′‐azobisisobutyronitrile (AIBN)/benzyl dithiobenzoate (BDB), using a synthesized 6‐O‐p‐vinylbenzyl‐1,2:3,4‐Di‐O‐isopropylidene‐D ‐galactopyranose (VBPG) as the monomer. The experimental results suggested that the polymerization of the monomer proceeded in a living fashion, providing chiral group polymers with narrow molecular weight distributions. The optically active nature of the obtained poly (6‐O‐p‐vinylbenzyl‐1,2:3,4‐Di‐O‐isopropylidene‐D ‐galactopyranose) (PVBPG) was studied by investigating the dependence of specific rotation on the molecular weight of PVBPG and the concentration of PVBPG in tetrahydrofuran (THF). The results showed the specific rotation of PVBPG increased greatly with the decrease of the concentration of the PVBPG homopolymer. In addition, the effect of block copolymers of PVBPG on the optically active nature was also investigated by preparing a series of diblock copolymers of poly(methyl methacrylate) (PMMA)‐b‐PVBPG, polystyrene (PS)‐b‐PVBPG, and poly(methyl acrylate) (PMA)‐b‐PVBPG. It was found that both the homopolymer and the diblock copolymers possessed specific rotations. Finally, the ability of chiral recognition of the PVBPG homopolymer was investigated via an enantiomer‐selective adsorption experiment. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3788–3797, 2007     

Reversible addition–fragmentation chain transfer polymerization of 2‐naphthyl acrylate with 2‐cyanoprop‐2‐yl 1‐dithionaphthalate as a chain‐transfer agent

The reversible addition–fragmentation chain transfer (RAFT) polymerizations of 2‐naphthyl acrylate (2NA) initiated by 2,2′‐azobisisobutyronitrile were investigated with 2‐cyanoprop‐2‐yl 1‐dithionaphthalate (CPDN) as a RAFT agent at various temperatures in a benzene solution. The results of the polymerizations showed that 2NA could be polymerized in a controlled way by RAFT polymerization with CPDN as a RAFT agent; the polymerization rate was first‐order with respect to the monomer concentration, and the molecular weight increased linearly with the monomer conversion. The polydispersities of the polymer were relatively low up to high conversions in all cases. The chain‐extension reactions of poly(2‐naphthyl acrylate) (P2NA) with methyl methacrylate and styrene successfully yielded poly(2‐naphthyl acrylate)‐b‐poly(methyl methacrylate) and poly(2‐naphthyl acrylate)‐b‐polystyrene block polymers, respectively, with narrow polydispersities. The P2NA obtained by RAFT polymerization had a strong ultraviolet absorption at 270 nm, and the molecular weights had no apparent effect on the ultraviolet absorption intensities; however, the fluorescence intensity of P2NA increased as the molecular weight increased and was higher than that of 2NA. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2632–2642, 2005     

Synthesis of chiral micelles and nanoparticles from amino acid based monomers using RAFT polymerization

Homopolymers of ^tbutyl acrylate (P^tBuA) and a monosubstituted acrylamide (PAM) having an amino acid moiety in the side chain, N‐acryloyl‐(L )‐phenylalanine methyl ester 1 , have been synthesized by Reversible Addition‐Fragmentation Chain Transfer (RAFT) polymerization. Diblock copolymers of these homopolymers were also synthesized by chain extending P^tBuA with monomer 1 and after modification, using simple acid deprotection chemistries of the acrylate block to afford a poly (acrylic acid) block, an optically active amphiphilic diblock copolymer was isolated. The optically active amphiphilic diblock copolymers, which contain chiral amino acid moieties within the hydrophobic segment, were then self‐assembled to afford spherical micelles which were subsequently crosslinked throughout the shell layer to afford robust chiral nanoparticles. The hydrodynamic diameters (D_h) of the block copolymer micelles and nanoparticles were measured by dynamic light scattering (DLS) and the dimensions of the nanoparticles were determined using tapping‐mode atomic force microscopy (AFM) and transmission electron microscopy (TEM). © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3690–3702, 2008     

Synthesis of enantiopure homo and copolymers by raft polymerization and investigation of their enantioselective lipase‐catalyzed esterification

Homo and copolymers were synthesized from enantionpure (R)‐ and (S)‐1‐(4‐vinylphenyl)ethanol by reversible addition‐fragmentation chain transfer polymerization. The polymerization conditions were optimized resulting in dioxane as the preferred reaction solvent. First‐order polymerization kinetics and well‐defined enantiopure homopolymers with low dispersities were obtained. In agreement with their enantiomeric composition, the (R) and (S)‐polymers gave opposite optical rotation of light. Polymer analogous esterification of the chiral hydroxy groups catalyzed by enantioselective Candida antarctica Lipase B was strongly (R)‐selective. Esterification on the homopolymer and copolymers could be achieved to a maximum of around 50 %. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Synthesis of ω‐sulfonated polystyrene via reversible addition fragmentation chain transfer polymerization and postpolymerization modification

The synthesis of chain‐end sulfonated polystyrene [PS (ω‐sulfonated PS)] by reversible addition fragmentation chain transfer (RAFT) polymerization followed by postpolymerization modification was investigated by two methods. In the first method, the polymer was converted to a thiol‐terminated polymer by aminolysis. This polymer was then sulfonated by oxidation of the thiol end‐group with m‐chloroperoxybenzoic acid (m‐CPBA) to produce a sulfonic acid end‐group. In the second method, the RAFT‐polymerized polymer was directly sulfonated by oxidation with m‐CPBA. After purification by column chromatography, ω‐sulfonated PS was obtained by both methods with greater than 95% end‐group functionality as measured by titration. The sulfonic acid end‐group could be neutralized with various ammonium or imidazolium counter ions through acid–base or ionic metathesis reactions. The effect of the ionic end‐groups on the glass transition temperature of the PS was found to be consistent with what is known for PS ionomers. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis and characterization of block copolymers containing poly(di(ethylene glycol) 2‐ethylhexyl ether acrylate) by reversible addition–fragmentation chain transfer polymerization

Reversible addition–fragmentation chain transfer (RAFT) polymerization has emerged as one of the important living radical polymerization techniques. Herein, we report the polymerization of di(ethylene glycol) 2‐ethylhexyl ether acrylate (DEHEA), a commercially‐available monomer consisting of an amphiphilic side chain, via RAFT by using bis(2‐propionic acid) trithiocarbonate as the chain transfer agent (CTA) and AIBN as the radical initiator, at 70 °C. The kinetics of DEHEA polymerization was also evaluated. Synthesis of well‐defined ABA triblock copolymers consisting of poly(tert‐butyl acrylate) (PtBA) or poly(octadecyl acrylate) (PODA) middle blocks were prepared from a PDEHEA macroCTA. By starting from a PtBA macroCTA, a BAB triblock copolymer with PDEHEA as the middle block was also readily prepared. These amphiphilic block copolymers with PDEHEA segments bearing unique amphiphilic side chains could potentially be used as the precursor components for construction of self‐assembled nanostructures. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5420–5430, 2007     

Controlled synthesis of carboxylic acid end‐capped poly(heptadecafluorodecyl acrylate) and copolymers with 2‐hydroxyethyl acrylate

1H,1H,2H,2H‐Heptadecafluorodecyl acrylate (AC8) was polymerized by reversible addition–fragmentation chain transfer and copolymerized with 2‐hydroxyethyl acrylate with the formation of random and block copolymers, respectively. The kinetics of the (co)polymerization was monitored with ¹H NMR spectroscopy and showed that the homopolymerization and random copolymerization of AC8 were under control. As a result of this control and the use of S‐1‐dodecyl‐S‐(α,α′‐dimethyl‐α″‐acetic acid)trithiocarbonate as a chain‐transfer agent, the copolymer chains were end‐capped by an α‐carboxylic acid group. Moreover, the controlled polymerization of AC8 was confirmed by the successful synthesis of poly(1H,1H,2H,2H‐heptadecafluorodecyl acrylate)‐b‐poly(2‐hydroxyethyl acrylate) diblock copolymers, which were typically amphiphilic compounds. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1499–1506, 2007     

End group transformations of RAFT‐generated polymers with bismaleimides: Functional telechelics and modular block copolymers

End group activation of polymers prepared by reversible addition‐fragmentation chain transfer (RAFT) polymerization was accomplished by conversion of thiocarbonylthio end groups to thiols and subsequent reaction with excess of a bismaleimide. Poly(N‐isopropylacrylamide) (PNIPAM) was prepared by RAFT, and subsequent aminolysis led to sulfhydryl‐terminated polymers that reacted with an excess of 1,8‐bismaleimidodiethyleneglycol to yield maleimido‐terminated macromolecules. The maleimido end groups allowed near‐quantitative coupling with model low molecular weight thiols or dienes by Michael addition or Diels‐Alder reactions, respectively. Reaction of maleimide‐activated PNIPAM with another thiol‐terminated polymer proved an efficient means of preparing block copolymers by a modular coupling approach. Successful end group functionalization of the well‐defined polymers was confirmed by combination of UV–vis, FTIR, and NMR spectroscopy and gel permeation chromatography. The general strategy proved to be versatile for the preparation of functional telechelics and modular block copolymers from RAFT‐generated (co)polymers. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5093–5100, 2008     

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     

Preparation of glycopolymer‐substituted gold nanoparticles and their molecular recognition

Glycopolymer‐substituted gold nanoparticles were prepared via living radical polymerization with a reversible addition‐fragmentation chain transfer (RAFT) reagent. Polyacrylamide derivatives with α‐mannose (α‐Man) and N‐acetyl‐β‐glucosamine (β‐GlcNAc) were synthesized and hydrogenated to obtain thiol‐terminated polymer. The thiol‐terminated glycopolymers were mixed with gold nanoparticles to yield the polymer substituted gold nanoparticles with various diameters, which aggregated on addition of saccharide‐recognition proteins (lectins). The aggregation properties were analyzed using transmission electron microscopy and UV spectra. Molecular recognition was studied with E. coli, which induced aggregation of the nanoparticles at the cell periphery. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1412–1421, 2009     

Controlled Radical Polymerization of 2,3‐Epithiopropyl Methacrylate

We report first results on the controlled radical polymerization of 2,3‐epithiopropyl methacrylate (ETMA) also known as thiiran‐2‐ylmethyl methacrylate. Reversible addition‐fragmentation chain transfer (RAFT) of ETMA was carried out in bulk and in solution, using AIBN as initiator and the chain transfer agents: cyanopropyl dithiobenzoate (CPDB) and cumyl dithiobenzoate (CDB). A linear increase of the number‐average molecular weight and decrease of the polydispersity with monomer conversion were observed using CPDB as transfer agent, indicating a controlled process. Atom transfer radical polymerization (ATRP) of ETMA was performed under different reaction conditions using copper bromide complexed by tertiary amine ligands and ethyl 2‐bromoisobutyrate (EBiB) or 2‐bromopropionitrile (BPN) as initiator. All experiments lead to a crosslinked polymer. Preliminary studies in the absence of initiator showed that the CuBr/ligand complex alone initiates the ring‐opening polymerization of thiirane leading to a poly(propylene sulfide) with pendant methacrylate groups.

     

Living free‐radical polymerization of sterically hindered monomers: Improving the understanding of 1,1‐disubstituted monomer systems

The sterically hindered, 1,1‐disubstituted monomers di‐n‐butyl itaconate (DBI), dicyclohexyl itaconate (DCHI), and dimethyl itaconate (DMI) were polymerized with reversible addition–fragmentation chain transfer (RAFT) free‐radical polymerization and atom transfer radical polymerization (ATRP). Cumyl dithiobenzoate, cumyl phenyl dithioacetate, 2‐cyanoprop‐2‐yl dithiobenzoate, 4‐cyanopentanoic acid dithiobenzoate, and S‐methoxycarbonylphenylmethyl dithiobenzoate were employed as RAFT agents to mediate a series of polymerizations at 60 °C yielding polymers ranging in their number‐average molecular weight from 4500 to 60,000 g mol^?1. The RAFT polymerizations of these hindered monomers displayed hybrid living behavior (between conventional and living free‐radical polymerization) of various degrees depending on the molecular structure of the initial RAFT agent. In addition, DCHI was polymerized via ATRP with a CuCl/methyl benzoate/N,N,N′,N″,N″‐pentamethyldiethylenetriamine/cyclohexanone system at 60 °C. Both the ATRP and RAFT polymerization of the hindered monomers displayed living characteristics; however, broader than expected molecular weight distributions were observed for the RAFT systems (polydispersity index = 1.15–3.35). To assess the cause of this broadness, chain‐transfer‐to‐monomer constants for DMI, DBI, and DCHI were determined (1.4 × 10^?3, 1.3 × 10^?3, and 1.0 × 10^?3, respectively) at 60 °C. Simulations carried out with the PREDICI program package suggested that chain transfer to monomer contributed to the broadening process. In addition, the experimental results indicated that viscosity had a pronounced effect on the broadness of the molecular weight distributions. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3692–3710, 2006     

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     

R‐RAFT approach for the polymerization of N‐isopropylacrylamide with a star poly(ε‐caprolactone) core

Reversible addition‐fragmentation chain transfer (RAFT) polymerization is a more robust and versatile approach than other living free radical polymerization methods, providing a reactive thiocarbonylthio end group. A series of well‐defined star diblock [poly(ε‐caprolactone)‐b‐poly(N‐isopropylacrylamide)]₄ (SPCLNIP) copolymers were synthesized by R‐RAFT polymerization of N‐isopropylacrylamide (NIPAAm) using [PCL‐DDAT]₄ (SPCL‐DDAT) as a star macro‐RAFT agent (DDAT: S‐1‐dodecyl‐S′‐(α, α′‐dimethyl‐α″‐acetic acid) trithiocarbonate). The R‐RAFT polymerization showed a controlled/“living” character, proceeding with pseudo‐first‐order kinetics. All these star polymers with different molecular weights exhibited narrow molecular weight distributions of less than 1.2. The effect of polymerization temperature and molecular weight of the star macro‐RAFT agent on the polymerization kinetics of NIPAAm monomers was also addressed. Hardly any radical–radical coupling by‐products were detected, while linear side products were kept to a minimum by careful control over polymerization conditions. The trithiocarbonate groups were transferred to polymer chain ends by R‐RAFT polymerization, providing potential possibility of further modification by thiocarbonylthio chemistry. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Hydrogen bonding driven self‐assembly of side‐chain amino acid and fatty acid appended poly(methacrylate)s: Gelation and application in oil spill recovery

We report an interesting class of fatty acid appended side‐chain phenylalanine (Phe) containing poly(methacrylate) homopolymers that undergo self‐assembly leading to gelation in selective organic hydrocarbons, due to association among the side‐chain functionalities. Fatty acids of different n‐alkyl chain lengths have been attached to the N‐terminal of the Phe‐based methacrylate and the corresponding homopolymers have been synthesized via reversible addition–fragmentation chain transfer polymerization. These homopolymers undergo gelation in selective organic hydrocarbons. The morphology of these organogels has been characterized by field emission scanning electron microscopy which revealed macroporous structure of the organogels. Viscoelastic properties of organogels and the thermoreversible gel‐to‐sol transition have been investigated by rheological measurements. Powder X‐ray diffraction study has been performed to understand the effect of long n‐alkyl chains on the gelation process. FTIR study reveals inter‐/intra‐chain hydrogen bonding which is the driving force of organogelation of the polymers in suitable solvents. In absence of hydrogen bonding interaction, hydrophobic association fails to direct the self‐assembly process and no gelation is observed. An interesting feature of the homopolymeric gelators is that it can selectively congeal the diesel part from an oil–water biphasic mixture, which might be useful in oil spill treatment. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 511–521     

Exploring amino acid‐tethered polymethacrylates as CO2‐sensitive macromolecules: A concealed property

Carbon dioxide (CO₂)‐responsive polymers have been gaining considerable interest because of their reactions with CO₂, giving rise to gas‐switchable properties, which can easily be reversed by mild heating or purging with inert gases. Herein, the synthesis of a series of side‐chain amino acids (alanine, leucine, isoleucine, phenylalanine, tryptophan) appending poly(meth)acrylates carrying primary amine (? NH₂) groups via reversible addition‐fragmentation chain transfer (RAFT) polymerization method was reported. It was found that alanine, leucine, isoleucine containing polymers displayed solubility–insolubility transition behavior and their associated property changes (solution transmittance, electrical conductivity, pH, zeta potential, and hydrodynamic diameter) in water upon alternate bubbling of CO₂/N₂ at room temperature. Among the three CO₂‐sensitive polymers only leucine based macromolecule was further chain extended with a thermoresponsive motif, di(ethylene glycol) methyl ether methacrylate (DEGMMA), via RAFT polymerization. CO₂‐tunable lower critical solution temperature and self‐assembling behavior of the diblock copolymer was carefully examined by UV–vis, ¹H NMR spectroscopy, dynamic light scattering (DLS), and field emission‐scanning electron microscopy (FE‐SEM) to establish dual thermo and gas‐tunable flip–flop micellizaion from the as‐synthesized block copolymer. Formation of polyammonium methacrylate bearing bicarbonate as counter anion is responsible for pendant primary amine containing polymer induced CO₂‐responsiveness. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2794–2803     

Dispersion of single‐walled carbon nanotubes using nucleobase‐containing poly(acrylamide) polymers

Single‐walled carbon nanotubes (SWNTs) possess extraordinary properties, but suffer from poor solubility and a lack of purity. Of the possible routes available to solubilize and purify nanotube samples, the use of noncovalent functionalization is ideal as carbon nanotube properties are not deleteriously affected. A multitude of different dispersants have been investigated thus far, but of particular interest is deoxyribonucleic acid (DNA), which has previously been demonstrated to effectively separate metallic and semiconducting carbon nanotubes. Here, we investigate the ability of synthetic nucleobase‐containing poly(acrylamide) polymers to produce stable nanotube dispersions in organic solvents. Polymers bearing different nucleobase and backbone structures, as well as block copolymers with different block sequences were investigated. Polymer:SWNT mass ratios and solvent compositions were optimized for the nucleobase‐functionalized polymers, and semiconducting and metallic SWNT populations were identified by a combination of UV‐Vis‐NIR absorption, Raman, and fluorescence spectroscopy. These results demonstrate the capacity for synthetic DNA analogues to disperse SWNTs in organic media. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2611–2617     

Experimental Requirements for an Efficient Control of Free‐Radical Polymerizations via the Reversible Addition‐Fragmentation Chain Transfer (RAFT) Process

Summary: Reversible addition‐fragmentation chain transfer (RAFT) polymerization is a recent and very versatile controlled radical polymerization technique that has enabled the synthesis of a wide range of macromolecules with well‐defined structures, compositions, and functionalities. The RAFT process is based on a reversible addition‐fragmentation reaction mediated by thiocarbonylthio compounds used as chain transfer agents (CTAs). A great variety of CTAs have been designed and synthesized so far with different kinds of substituents. In this review, all of the CTAs encountered in the literature from 1998 to date are reported and classified according to several criteria : i) the structure of their substituents, ii) the various monomers that they have been polymerized with, and iii) the type of polymerization that has been performed (solution, dispersed media, surface initiated, and copolymerization). Moreover, the influence of various parameters is discussed, especially the CTA structure relative to the monomer and the experimental conditions (temperature, pressure, initiation, CTA/initiator ratio, concentration), in order to optimise the kinetics and the efficiency of the molecular‐weight‐distribution control.

Schematic of the RAFT polymerization.     

Cyclopolymerization of α,ω‐heterodifunctional monomers containing styrene and maleimide moieties

A series of α,ω‐heterodifunctional monomers with styrene (St) and maleimide moieties bridged by a varied length of oligo‐ethylene glycol (OEG) linkers were synthesized. Cyclopolymerizations of these monomers through reversible addition–fragmentation chain transfer‐mediated alternating radical copolymerization between intramolecular St and maleimide moieties were investigated. For the monomers with three or more ethylene glycol (EG) units, their cyclopolymerizations can be realized properly in low monomer feeding concentrations, affording well‐defined cyclopolymers with crown ether encircled in their main chains. Importantly, the cyclopolymerizations of monomers with six or seven EG units in the presence of KPF₆ could be enhanced by the supramolecular effects between the OEG linkers and the potassium metal ion. Thus, the monomer feeding concentration could be largely improved, which may benefit preparation of the cyclopolymers with high degrees of copolymerization. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 330–338     

α‐Cyanobenzyl dithioester reversible addition–fragmentation chain‐transfer agents for controlled radical polymerizations

A series of new reversible addition–fragmentation chain transfer (RAFT) agents with cyanobenzyl R groups were synthesized. In comparison with other dithioester RAFT agents, these new RAFT agents were odorless or low‐odor, and this made them much easier to handle. The kinetics of methyl methacrylate radical polymerizations mediated by these RAFT agents were investigated. The polymerizations proceeded in a controlled way, the first‐order kinetics evolved in a linear fashion with time, the molecular weights increased linearly with the conversions, and the polydispersities were very narrow (～1.1). A poly[(methyl methacrylate)‐block‐polystyrene] block copolymer was prepared (number‐average molecular weight = 42,600, polydispersity index = 1.21) from a poly(methyl methacrylate) macro‐RAFT agent. These new RAFT agents also showed excellent control over the radical polymerization of styrenics and acrylates. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1535–1543, 2005