Reversible addition‐fragmentation chain transfer polymerization of methacrylates containing hole‐ or electron‐transporting groups

The controlled/living radical polymerization of 2‐(N‐carbazolyl)ethyl methacrylate (CzEMA) and 4‐(5‐(4‐tert‐butylphenyl‐1,3,4‐oxadiazol‐2‐yl)phenyl) methacrylate (t‐Bu‐OxaMA) via reversible addition‐fragmentation chain transfer polymerization has been studied. Functional polymers with hole‐ or electron‐transfer ability were synthesized with cumyl dithiobenzoate as a chain transfer agent (CTA) and AIBN as an initiator in a benzene solution. Good control of the polymerization was confirmed by the linear increase in the molecular weight (MW) with the conversion. The dependence of MW and polydispersity index (PDI) of the resulting polymers on the molar ratio of monomer to CTA, monomer concentration, and molar ratio of CTA to initiator has also been investigated. The MW and PDI of the resulting polymers were well controlled as being revealed by GPC measurements. The resulting polymers were further characterized by NMR, UV‐vis spectroscopy, and cyclic voltammetry. The polymers functionalized with carbazole group or 1,3,4‐oxadiazole group exhibited good thermal stability, with an onset decomposition temperature of about 305 and 323 °C, respectively, as determined by thermogravimetric analysis. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 242–252, 2007     

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     

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     

Living free‐radical polymerization (reversible addition–fragmentation chain transfer) of 6‐[4‐(4′‐methoxyphenyl)phenoxy]hexyl methacrylate: A route to architectural control of side‐chain liquid‐crystalline polymers

Side‐chain liquid‐crystalline polymers of 6‐[4‐(4′‐methoxyphenyl)phenoxy]hexyl methacrylate with controlled molecular weights and narrow polydispersities were prepared via reversible addition–fragmentation chain transfer (RAFT) polymerization with 2‐(2‐cyanopropyl) dithiobenzoate as the RAFT agent. Differential scanning calorimetry studies showed that the polymers produced via the RAFT process had a narrower thermal stability range of the liquid‐crystalline mesophase than the polymers formed via conventional free‐radical polymerization. In addition, a chain length dependence of this stability range was found. The generated RAFT polymers displayed optical textures similar to those of polymers produced via conventional free‐radical polymerization. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2949–2963, 2003     

Living free‐radical polymerization of styrene under a constant source of γ radiation

Living polymerization of styrene was observed using γ radiation as a source of initiation and 1‐phenylethyl phenyldithioacetate as a reversible addition–fragmentation chain transfer (RAFT) agent. The γ radiation had little or no detrimental effect on the RAFT agent, with the molecular weight of the polymer increasing linearly with conversion (up to the maximum measured conversions of 30%). The polymerization had kinetics (polym.) consistent with those of a living polymerization (first order in monomer) and proportional to the square root of the radiation‐dose rate. This initiation technique may facilitate the grafting of narrow polydispersity, well‐defined polymers onto existing polymer surfaces as well as allow a wealth of kinetic experiments using the constant radical flux generated by γ radiation. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 19–25, 2002     

Controlled radical polymerization of a trialkylsilyl methacrylate by reversible addition–fragmentation chain transfer polymerization

The reversible addition–fragmentation chain transfer (RAFT) polymerization of a hydrolyzable monomer (tert‐butyldimethylsilyl methacrylate) with cumyl dithiobenzoate and 2‐cyanoprop‐2‐yl dithiobenzoate as chain‐transfer agents was studied in toluene solutions at 70 °C. The resulting homopolymers had low polydispersity (polydispersity index < 1.3) up to 96% monomer conversion with molecular weights at high conversions close to the theoretical prediction. The profiles of the number‐average molecular weight versus the conversion revealed controlled polymerization features with chain‐transfer constants expected between 1.0 and 10. A series of poly(tert‐butyldimethylsilyl methacrylate)s were synthesized over the molecular weight range of 1.0 × 10⁴ to 3.0 × 10⁴, as determined by size exclusion chromatography. As strong differences of hydrodynamic volumes in tetrahydrofuran between poly(methyl methacrylate), polystyrene standards, and poly(tert‐butyldimethylsilyl methacrylate) were observed, true molecular weights were obtained from a light scattering detector equipped in a triple‐detector size exclusion chromatograph. The Mark–Houwink–Sakurada parameters for poly(tert‐butyldimethylsilyl methacrylate) were assessed to obtain directly true molecular weight values from size exclusion chromatography with universal calibration. In addition, a RAFT agent efficiency above 94% was confirmed at high conversions by both light scattering detection and ¹H NMR spectroscopy. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5680–5689, 2005     

Are o‐nitrobenzyl (meth)acrylate monomers polymerizable by controlled‐radical polymerization?

We report on the controlled‐radical polymerization of the photocleavable o‐nitrobenzyl methacrylate (NBMA) and o‐nitrobenzyl acrylate (NBA) monomers. Atom transfer radical polymerization (ATRP), reversible addition‐fragmentation chain transfer polymerization (RAFT), and nitroxide‐mediated polymerization (NMP) have been evaluated. For all methods used, the acrylate‐type monomer does not polymerize, or polymerizes very slowly in a noncontrolled manner. The methacrylate‐type monomer can be polymerized by RAFT with some degree of control (PDI ∼ 1.5) but leading to molar masses up to 11,000 g/mol only. ATRP proved to be the best method since a controlled‐polymerization was achieved when conversions are limited to 30%. In this case, polymers with molar masses up to 17,000 g/mol and polydispersity index as low as 1.13 have been obtained. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6504–6513, 2009     

Well‐controlled polymerization of 2‐azidoethyl methacrylate at near room temperature and click functionalization

A functional monomer with a pendant azide moiety, 2‐azidoethyl methacrylate (AzMA), was polymerized via reversible addition‐fragmentation chain transfer (RAFT) polymerization with excellent control over the molecular weight distribution (PDI = 1.05–1.15). The subsequent copper‐catalyzed Huisgen 1,3‐dipolar cycloadditions of phenyl acetylene with polyAzMA was achieved at room temperature with high conversion. The resulting functional polymer exhibited identical ¹H NMR and IR spectra with the polymer of the same molecular structure but prepared by a prefunctionalization approach, confirming the retention of the azide side chains during the RAFT polymerization of AzMA. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4300–4308, 2007     

Long‐lived intermediates in reversible addition–fragmentation chain‐transfer (RAFT) polymerization generated by γ radiation

A novel experimental procedure is presented that allowed probing of reversible addition–fragmentation chain‐transfer (RAFT) free‐radical polymerizations for long‐lived species. The new experimental sequence consisted of gamma irradiation of a mixture of initial RAFT agent (cumyl dithiobenzoate) and monomer at ambient temperature, a subsequent predetermined waiting period without initiation source also at ambient temperature, and then heating of the reaction mixture to a significantly higher temperature. After each sequence step, the monomer conversion and molecular weight distribution were determined, indicating that controlled polymer formation occurs only during the heating period. The results indicated that stable intermediates (either radical or nonradical in nature) are present in such experiments because thermal self‐initiation of the monomer can be excluded as the reason for polymer formation. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1058–1063, 2002     

Controlled polymerization of 2‐(diethylamino)ethyl methacrylate and its block copolymer with N‐isopropylacrylamide by RAFT polymerization

Poly(2‐(diethylamino)ethyl methacrylate) (PDEAEMA) homopolymers with low polydispersities were synthesized by reversible addition fragmentation chain transfer (RAFT) radical polymerization. The performances of two chain transfer agents, 2‐cyanoprop‐2‐yl dithiobenzoate and 4‐cyanopentanic acid dithiobenzoate (CPADB), were compared. It was found that the polymerization of 2‐(diethylamino) ethyl methylacrylate was under good control in the presence of CPADB with 4,4′‐azobis(4‐cyanopentanoic acid) (ACPA) as initiator in 1,4‐dioxane at 70 °C. The kinetic behaviors were investigated under different CPADB/ACPA molar ratios. A long polymerization inhibition period was observed at high [CPADB]/[ACPA] ratio. The influences of [CPADB]/[ACPA] ratio, monomer/[CPADB] ratio, and temperature were studied with respect to monomer conversion, molecular weight control, and polydispersity index (PDI). The PDI decreased from 1.21 to 1.12, as the CPADB/ACPA molar ratio changed from 2 to 10. The molecular weight of PDEAEMA could be controlled by monomer/CPADB molar ratio. The control over MW and PDI was improved as the temperature increased from 60 to 70 °C; however, an additional increase to 80 °C led to a loss of control. Using PDEAEMA macroRAFT agent, pH/thermo double‐responsive block copolymers of PDEAEMA and poly(N‐isopropylacrylamide) (PDEAEMA‐b‐PNIPAM) with narrow polydispersity (PDI, 1.24) were synthesized. The lower critical solution temperature of PDEAEMA‐b‐PNIPAM block copolymer depended on the environmental pH. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3294–3305, 2008     

Modeling the reversible addition–fragmentation transfer polymerization process

A kinetic model has been developed for reversible addition–fragmentation transfer (RAFT) polymerization with the method of moments. The model predicts the monomer conversion, number‐average molecular weight, and polydispersity of the molecular weight distribution. It also provides detailed information about the development of various types of chain species during polymerization, including propagating radical chains, adduct radical chains, dormant chains, and three types of dead chains. The effects of the RAFT agent concentration and the rate constants of the initiator decomposition, radical addition, fragmentation, disproportionation, and recombination termination of propagating radicals and cross‐termination between propagating and adduct radicals on the kinetics and polymer chain properties are examined with the model. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1553–1566, 2003     

Highly efficient and well‐controlled ambient temperature RAFT polymerization of glycidyl methacrylate under visible light radiation

A range of well‐defined poly(glycidyl methacrylate) (PGMA) polymers and their corresponding block copolymers were synthesized via 2‐cyanoprop‐2‐yl(4‐fluoro) dithiobenzoate or CPFDB‐mediated ambient temperature reversible addition fragmentation chain transfer radical polymerization or RAFT polymerization under environmentally friendly visible light radiation (λ = 405–577 nm), using a (2,4,6‐trimethylbenzoyl) diphenylphosphine oxide photoinitiator. As comparison, CPFDB‐mediated ambient temperature RAFT polymerizations of glycidyl methacrylate (GMA) under both full‐wave radiation (λ = 254–577 nm) and long‐wave radiation (λ = 365–577 nm) were also studied in this article. The results indicated that CPFDB moieties were significantly photolyzed under either full‐wave radiation or long‐wave radiation, thus undermining the controlled behavior of these RAFT processes. Whereas this photolysis was significantly suppressed under visible light radiation, thus CPFDB functionalities exerted well control over RAFT process, leading to a remarkably living behavior up to 90% GMA monomer conversions. This strategy facilitates the facile synthesis of well‐defined PGMA polymers. More importantly, under visible light radiation, a relatively high initial molar ratio of GMA to CPFDB and TPO led to shortening initialization period of RAFT process and accelerating overall polymerization rate. These effects are remarkably in favor of the facile synthesis of well‐defined PGMA polymers and PGMA‐based copolymers with high molecular weights. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5091–5102, 2007     

Synthesis of comb‐like polystyrene with poly(N‐phenyl maleimide‐alt‐p‐chloromethyl styrene) as macroinitiator

The copolymerization of N‐phenyl maleimide and p‐chloromethyl styrene via reversible addition–fragmentation chain transfer (RAFT) process with AIBN as initiator and 2‐(ethoxycarbonyl)prop‐2‐yl dithiobenzoate as RAFT agent produced copolymers with alternating structure, controlled molecular weights, and narrow molecular weight distributions. Using poly(N‐phenyl maleimide‐alt‐p‐chloromethyl styrene) as the macroinitiator for atom transfer radical polymerization of styrene in the presence of CuCl/2,2′‐bipyridine, well‐defined comb‐like polymers with one graft chain for every two monomer units of backbone polymer were obtained. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2069–2075, 2006     

Block copolymers based on 2‐vinyl‐4,4‐dimethyl‐5‐oxazolone by RAFT polymerization: Experimental and computational studies

The ability of 2‐vinyl‐4,4‐dimethyl‐5‐oxazolone (VDM), a highly reactive functional monomer, to produce block copolymers by reversible addition fragmentation chain transfer (RAFT) sequential polymerization with methyl acrylate (MA), styrene (S), and methyl methacrylate (MMA) was investigated using cumyl dithiobenzoate (CDB) and 2‐cyanoisopropyl dithiobenzoate (CPDB) as chain transfer agents. The results show that PS‐b‐PVDM and PMA‐b‐PVDM well‐defined block copolymers can be prepared either by polymerization of VDM from PS‐ and PMA‐macroCTAs, respectively, or polymerization of S and MA from a PVDM‐macroCTA. In contrast, PMMA‐b‐PVDM block copolymers with controlled molecular weight and low polydispersity can only be obtained by using PMMA as the macroCTA. Ab initio calculations confirm the experimental studies. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Influence of a reversible addition–fragmentation chain transfer agent in the dispersion polymerization of styrene

Dispersion polymerization was applied to the controlled/living free‐radical polymerization of styrene with a reversible addition–fragmentation chain transfer (RAFT) polymerization agent in the presence of poly(N‐vinylpyrrolidone) and 2,2′‐azobisisobutyronitrile in an ethanol medium. The effects of the polymerization temperature and the postaddition of RAFT on the polymerization kinetics, molecular weight, polydispersity index (PDI), particle size, and particle size distribution were investigated. The polymerization was strongly dependent on both the temperature and postaddition of RAFT, and typical living behavior was observed when a low PDI was obtained with a linearly increased molecular weight. The rate of polymerization, molecular weight, and PDI, as well as the final particle size, decreased with an increased amount of the RAFT agent in comparison with those of traditional dispersion polymerization. Thus, the results suggest that the RAFT agent plays an important role in the dispersion polymerization of styrene, not only reducing the PDI from 3.34 to 1.28 but also producing monodisperse polystyrene microspheres. This appears to be the first instance in which a living character has been demonstrated in a RAFT‐mediated dispersion polymerization of styrene while the colloidal stability is maintained in comparison with conventional dispersion polymerization. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 348–360, 2007     

Reversible addition–fragmentation transfer polymerization of p‐nitrophenyl acrylate and synthesis of diblock copolymers poly(p‐nitrophenyl acrylate)‐b‐polystyrene

Poly(p‐nitrophenyl acrylate)s (PNPAs) with different molecular mass and narrow polydispersity were successfully synthesized for the first time by reversible addition–fragmentation transfer (RAFT) polymerization with azobisisobutyronitrile (AIBN) as an initiator and [1‐(ethoxy carbonyl) prop‐1‐yl dithiobenzoate] as the chain‐transfer agent. Although the molecular mass of PNPAs can be controlled by the molar ratio of NPA to RAFT agent and the conversion, a trace of homo‐PNPA was found, especially at the early stage of polymerization. The dithiobenzoyl‐terminated PNPA obtained was used as a macro chain‐transfer agent in the successive RAFT block copolymerization of styrene (St) with AIBN as the initiator. After purification by two washings with cyclohexane and nitromethane to remove homo‐PSt and homo‐PNPA, the pure diblock copolymers, PNPA‐b‐PSt's, with narrow molecular weight distribution were obtained. The structural analysis of polymerization products by ¹H NMR and GPC verified the formation of diblock copolymers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4862–4872, 2004     

Copper(0)‐mediated living radical polymerization of acrylonitrile: SET‐LRP or AGET‐ATRP

Cu(0)‐mediated living radical polymerization was first extended to acrylonitrile (AN) to synthesize polyacrylonitrile with a high molecular weight and a low polydispersity index. This was achieved by using Cu(0)/hexamethylated tris(2‐aminoethyl)amine (Me₆‐TREN) as the catalyst, 2‐bromopropionitrile as the initiator, and dimethyl sulfoxide (DMSO) as the solvent. The reaction was performed under mild reaction conditions at ambient temperature and thus biradical termination reaction was low. The rapid and extensive disproportionation of Cu(I)Br/Me₆‐TREN in DMSO/AN supports a mechanism consistent with a single electron transfer‐living radical polymerization (SET‐LRP) rather than activators generated by electron transfer atom transfer radical polymerization (AGET ATRP). ¹H NMR analysis and chain extension experiment confirm the high chain‐end functionality of the resultant polymer. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Reversible addition–fragmentation chain transfer polymerization of alkyl‐2‐cyanoacrylates: An assessment of livingness

Alkyl 2‐cyanoacrylates (CAs) are primarily used as instant adhesives, including those sold under the Loctite brand. The adhesive action can be inhibited with acid stabilizers allowing radical polymerization to be employed. The following article details the first attempted controlled/living radical polymerization of alkyl CAs: Reversible addition fragmentation chain transfer (RAFT) polymerization mediated by a poly(methyl methacrylate) dithiobenzoate macroRAFT agent for three different CA monomers (ethyl 2‐cyanoacrylate, n‐butyl 2‐cyanoacrylate, and 2‐phenylethyl cyanoacrylate) allowed the preparation of the first block copolymers of this challenging but commercially important monomer class. Nevertheless, GPC with UV detection indicated significant loss of the RAFT end‐group for all three CAs limiting control/living character. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 1397–1408     

Controlled radical polymerization of N‐vinylcaprolactam mediated by xanthate or dithiocarbamate

Controlled radical polymerization of N‐vinylcaprolactam (NVCL) via reversible addition‐fragmentation chain transfer (RAFT) polymerization or macromolecular design via the interchange of xanthate (MADIX) was described, employing 2‐diphenylthiocarbamoylsulfanyl‐2‐methyl‐propionic acid (CTA1), ((O‐ethylxanthyl)methyl)benzene (CTA2) and (1‐(O‐ethylxanthyl)ethyl)benzene (CTA3) as chain transfer agents (CTA). It was found that all the CTAs led to controlled radical polymerization of NVCL, with the molecular weight increased along with the conversion of monomer and a relatively narrow molecular weight distribution could be obtained, as determined with matrix‐assisted laser desorption and ionization time‐of‐flight (MALDI‐TOF) and gel permeation chromatography (GPC), the polydispersity indices, as determined by MALDI‐TOF, were typically on the order of 1.24, but the polymerization did not proceed in a strictly living manner. The chain transfer ability of these CTAs was in the following order: CTA1 ≈ CTA2 < CTA3. MALTI‐TOF measurement showed that the major population of polymer retained the chain‐end functional group, but minor population deactivated by radical coupling. In preparation of the block copolymer of NVCL and vinyl acetate (VAc) by sequential polymerization, the sequence of monomer addition was important. Using VAc as the first monomer could lead to a block copolymer presenting a unimodal GPC trace and a narrow PDI index, and if NVCL was used as the first monomer, the polymerization was less well controlled. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3756–3765, 2008     

(Thiocarbonyl‐α‐thio)carboxylic acid derivatives as transfer agents in reversible addition–fragmentation chain‐transfer polymerizations

Ethyl S‐(thiobenzoyl)thioacetate, ethyl S‐thiobenzoyl‐2‐thiopropionate, and S‐(thiobenzoyl)thioglycolic acid were used as chain‐transfer agents for the reversible addition–fragmentation chain‐transfer (RAFT) polymerizations of styrene, methyl methacrylate, and butyl acrylate. Of these polymerizations, only those of styrene and butyl acrylate with any of the transfer agents showed molecular weight control corresponding to controlled/living polymerizations. The best molecular weight control was observed for the polymerizations of styrene and butyl acrylate with ethyl (S)‐thiobenzoyl‐2‐thiopropionate. Semiempirical PM3 calculations were performed for the investigation of the relative heats of reaction of the chain‐transfer equilibria between the aforementioned chain‐transfer agents and dimer radicals of the three monomers. The molecular weight control of the polymerizations correlated with the stability trend of the leaving‐group radical of the chain‐transfer agent. This relatively simple computational model offered some value in determining which transfer agents would show the best molecular weight control in RAFT polymerizations. © 2002 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 555–563, 2002; DOI 10.1002/pola.10143