Modeling analysis of chain transfer in reversible addition‐fragmentation chain transfer polymerization

The validity of simplifying the reversible addition‐fragmentation chain transfer (RAFT) polymerization as a degenerative chain transfer process was verified in this work. The simplified chain transfer mechanism enabled the direct modeling investigation of chain transfer coefficient in the RAFT polymerization. It also gave the analytical expressions for concentration, chain length, and polydispersity of various chain species. The comparison between the simulations based on chain transfer mechanism and those from general RAFT mechanism showed that this simplified mechanism can accurately predict RAFT polymerization in the absence of side reactions to adduct radicals other than fragmentation. However, significant errors are introduced at high conversion when side reactions to adduct are present. The chain transfer coefficient of RAFT agent is the key factor in RAFT polymerization. The polydispersity is more sensitive to chain transfer coefficient at low conversion. At high conversion, however, the polydispersity is mainly determined by termination, which can be controlled by RAFT agent concentration and the selection of initiator. At last, an analytical equation is derived to directly estimate chain transfer coefficient of RAFT agent from the experimental data. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.     

Reversible addition–fragmentation chain transfer polymerization of styrene with benzoimidazole dithiocarbamate as a reversible addition–fragmentation chain transfer agent

Two novel dithiocarbamates [2‐Y‐benzoimidazole‐1‐carbodithioic acid benzyl esters: Y = methyl (1b) or phenyl (1c)] were synthesized and successfully used in the reversible addition–fragmentation chain transfer (RAFT) polymerization of styrene in bulk with thermal initiation. The effects of the temperatures and concentration ratios of the styrene and RAFT agents on the polymerization were investigated. The results showed that the polymerization of styrene could be well controlled in the presence of 1b or 1c. The linear relationships between ln([M]₀/[M]) and the polymerization time (where [M]₀ is the initial monomer concentration and [M] is the monomer concentration) indicated that the polymerizations were first‐order reactions with respect to the monomer concentration. The molecular weights increased linearly with the monomer conversion and were close to the theoretical values. The molecular weight distributions [weight‐average molecular weight/number‐average molecular weight (M_w/M_n)] were very narrow from 5.3% conversion up to 94% conversion (M_w/M_n < 1.3). © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 560–564, 2006     

Functionalization of poly(ester‐urethane) surface by radiation‐induced grafting of N‐isopropylacrylamide using conventional and reversible addition–fragmentation chain transfer‐mediated methods

The functionalization of poly(ester‐urethane) (PUR) surface was conducted using radiation‐induced grafting. A thermosensitive layer constructed from N‐isopropylacrylamide (NIPAAm) was introduced onto a polyurethane film and characterized using attenuated total reflection Fourier transform infrared and X‐ray photoelectron spectroscopies and contact angle measurements. Size exclusion chromatography was used to analyse the PUR‐graft‐PNIPAAm copolymers and homopolymers formed in solution. Additionally, reversible addition–fragmentation chain transfer (RAFT) polymerization was performed in order to obtain PNIPAAm‐grafted surfaces with well‐defined properties. Atomic force microscopy was used to evaluate the surfaces synthesized via conventional and RAFT‐mediated grafting methods. The results of various techniques confirmed the successful grafting of NIPAAm from PUR film. © 2015 Society of Chemical Industry     

Low protein fouling polypropylene membrane prepared by photoinduced reversible addition‐fragmentation chain transfer polymerization

In this study, 2‐hydroxyethyl methacrylate and N‐isopropyl acrylamide was block grafted onto the polypropylene macroporous membrane surface by photo‐induced reversible addition‐fragmentation chain transfer (RAFT) radical polymerization with benzyl dithiobenzoate as the RAFT agent. The degree of grafting of poly(2‐hydroxyethyl methacrylate) on the membrane surface increased with UV irradiation time and decreased with the chain transfer agent concentration increasing. The poly(2‐hydroxyethyl methacrylate)‐ grafted membranes were used as macro chain transfer agent for the further block graft copolymerization of N‐isopropyl acrylamide in the presence of free radical initiator. The degree of grafting of poly(N‐isopropyl acrylamide) increased with reaction time. Furthermore, the poly(2‐hydroxyethyl methacrylate)‐ grafted membrane with a degree of grafting of 0.48% (wt) showed the highest relative pure water flux and the best antifouling characteristics of protein dispersion. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Synthesis of polydimethylsiloxane‐containing block copolymers via reversible addition fragmentation chain transfer (RAFT) polymerization

Low polydispersity polydimethylsiloxane (PDMS) was end functionalized with a reversible addition fragmentation chain transfer (RAFT) agent by the esterification of hydroxyl terminated PDMS with a carboxylic acid functional RAFT agent. These PDMS‐RAFT agents were able to control the free radical polymerization of styrene and substituted styrene monomers to produce PDMS‐containing block copolymers with low polydispersities and targeted molecular weights. A thin film of polydimethylsiloxane‐block‐polystyrene was prepared by spin coating and exhibited a microphase separated morphology from scanning force microscopy measurements. Controlled swelling of these films in solvent vapor produced morphologies with significant long‐range order. This synthetic route will allow the straightforward production of PDMS‐containing block copolymer libraries that will be useful for investigating their thin film morphological behavior, which has applications in the templating of nanostructured materials.© 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Reversible addition‐fragmentation chain transfer (RAFT) polymerization of styrene using novel heterocycle‐containing chain transfer agents

BACKGROUND: Controlled/‘living’ radical polymerization is a new and robust method to synthesize polymers with predetermined molecular weight, narrow polydispersity and tailored architecture. Several methods have been developed but reversible addition‐fragmentation chain transfer (RAFT) has several advantages over the other methods. It has been reported that the effectiveness of RAFT agents depends strongly on the nature of the Z and R groups. RESULTS: Three new dithiocarbamates, namely (2‐ethoxy carbonyl)‐prop‐2‐yl‐pyrrole‐1‐carbodithioate (CTA‐A), (1‐phenyl ethyl)‐pyrazole‐1‐carbodithioate (CTA‐B) and (2‐ethoxy carbonyl)‐prop‐2‐yl‐pyrazole‐1‐carbodithioate (CTA‐C), were synthesized for studying the effect of the Z and R group of a chain transfer agent on the RAFT polymerization of styrene, initiated by 2,2′‐azobisisobutyronitrile. Well‐controlled molecular weight with narrow polydispersity (1.10–1.46) was achieved. The increase in molecular weight with conversion is linear and follows first‐order kinetics. CONCLUSION: The detailed kinetic results show that the structure of the activating (Z) group of dithiocarbamates has significant effects on the reactivity of dithiocarbamates towards the polymerization of styrene. In the homopolymerization of styrene it was found that, from the polydispersity index of polystyrenes obtained and the kinetic results, the pyrazole‐based dithiocarbamates (CTA‐B and CTA‐C) are very effective compared to the pyrrole‐based dithiocarbamate (CTA‐A). All the polymerizations show controlled living characters. Copyright © 2007 Society of Chemical Industry     

Ab initio reversible addition–fragmentation chain transfer emulsion polymerization of styrene/butyl acrylate mediated by poly(acrylic acid)‐block‐polystyrene trithiocarbonate

Ab initio reversible addition–fragmentation chain transfer (RAFT) emulsion polymerization of styrene/butyl acrylate was investigated with the trithiocarbonate macro‐RAFT agent poly(acrylic acid)‐block‐polystyrene (PAA‐b‐PS) as a stabilizer and a RAFT agent. Influences of the amount of ammonium persulfate (APS), the amount of PAA‐b‐PS and the mass ratio of monomers on emulsion polymerization and film properties are discussed. The particle morphology exhibited spherical‐like structure with particles of about 90 nm in diameter and relatively narrow particle size distribution characterized using transmission electron microscopy and dynamic laser scattering. Fourier transform infrared and ¹H NMR spectra showed that the styrene/butyl acrylate emulsion was successfully synthesized. The monomer conversion increased initially with increasing amount of APS, from 0.4 up to 0.8 wt%, and then decreased. The particle size increased and its distribution decreased gradually with increasing amount of APS. The monomer conversion increased from 76.83 to 94.21% as the amount of PAA‐b‐PS increased from 3 to 4 wt%, and then decreased with further increase of PAA‐b‐PS. The particle size decreased and its distribution increased with increasing amount of PAA‐b‐PS. The water resistance and solvent resistance of the polymer films initially increased and then decreased with decreasing mass ratio of butyl acrylate to styrene. © 2014 Society of Chemical Industry     

Preparation of poly(tert‐butyl acrylate)‐poly(acrylic acid) amphiphilic copolymers via radiation‐induced reversible addition–fragmentation chain transfer mediated polymerization of tert‐butyl acrylate

Poly(tert‐butyl acrylate) (PtBA) is a versatile hydrophobic macromolecule usually preferred in the development of new materials for a host of applications. PtBA homopolymers with well‐defined structure and controlled molecular weight in a wide range were successfully synthesized via radiation‐induced reversible addition–fragmentation chain transfer (RAFT) polymerization in the presence of a trithiocarbonate type RAFT agent. The polymerization of tBA was performed under ⁶⁰Co γ‐irradiation in the presence of 2‐(dodecylthiocarbonothioylthio)‐2‐methylpropionic acid (DDMAT) as the RAFT agent in toluene at room temperature with three [tBA]/[DDMAT] ratios (400, 600 and 1000) and different irradiation times. Radiation‐induced polymerization of tBA displayed controlled free radical polymerization characteristics: a narrow molecular weight distribution (M_w/M_n ~ 1.1), pseudo first order kinetics and controlled molecular weights. The system followed the RAFT polymerization mechanism even at very low amounts of RAFT agent ([tBA]/[DDMAT] = 1000), and molecular weights up to 113 900 with narrow dispersity (Ð =1.06) were obtained. PtBA was further hydrolysed into different amphiphilic PtBA‐co‐poly(acrylic acid) (PAA) copolymers by low (27.5%) and high (77.3%) degrees of hydrolysis. The pH sensitivity of the two copolymers was investigated by dynamic light scattering at pH 2 and pH 9 (above and below the pK_a value of PAA) and their hydrodynamic diameters and zeta potential values were determined. © 2020 Society of Chemical Industry     

Kinetics of RAFT emulsion polymerization of styrene mediated by oligo(acrylic acid‐b‐styrene) trithiocarbonate

The kinetics of ab initio reversible addition‐fragmentation chain transfer (RAFT) emulsion polymerization of styrene using oligo(acrylic acid‐b‐styrene) trithiocarbonate as both polymerization mediator and surfactant were systematically investigated. The initiator concentration was set much lower than that in the conventional emulsion polymerization to significantly suppress the irreversible termination reaction. It was found that decreased rapidly but the nucleation efficiency of micelles increased with the decrease of the initiator concentrations due to the significant radical exit. The particle number ( ) did not follow the classic Smith–Eward equation but was proportional to [I]^?0.4[S]^0.7. It was suggested that RAFT emulsion polymerization could be fast enough for commercial use even at extremely low initiator concentrations and low macro‐RAFT agent concentrations due to the higher particle nucleation efficiency at lower initiator concentration. © 2016 American Institute of Chemical Engineers AIChE J, 62: 2126–2134, 2016     

Synthesis of well‐defined polystyrene‐graft‐poly(methyl methacrylate)

A well‐defined graft copolymer, polystyrene‐graft‐poly(methyl methacrylate), was synthesized in two steps. In the first step, styrene and p‐vinyl benzene sulfonyl chloride were copolymerized via reversible addition–fragmentation chain transfer polymerization (RAFT) in benzene at 60 °C with 2‐(ethoxycarbonyl)prop‐2‐yl dithiobenzoate as a chain transfer agent and 2,2′‐azobis(isobutyronitrile) as an initiator. In the second step, poly[styrene‐co‐p‐(vinyl benzene sulfonyl chloride)] was used as a macroinitiator for the atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) in toluene at 80 °C with CuCl as a catalyst and 2,2′‐bipyridine as a ligand. With sulfonyl chloride groups as the initiating sites for the ATRP of MMA, high initiation efficiencies were obtained. Copyright © 2006 Society of Chemical Industry     

Water‐dispersible porous polyisoprene‐block‐poly(acrylic acid) microspheres

Two polyisoprene‐block‐poly(tert‐butyl acrylate) (PI‐b‐PtBA) samples and a poly(tert‐butyl acrylate) (PtBA) homopolymer (hPtBA) were prepared by anionic polymerization and characterized by light scattering, size exclusion chromatography, and NMR. The tert‐butyl groups were removed from one of the diblocks to yield amphiphilic polyisoprene‐block‐poly(acrylic acid) (PI‐b‐PAA). PI‐b‐PAA was then used as the surfactant to disperse dichloromethane containing PI‐b‐PtBA and hPtBA at different weight ratios as oil droplets in water. Solid microspheres containing segregated polyisoprene (PI) and PtBA/hPtBA domains were obtained after dichloromethane evaporation. Permanent microspheres were obtained after PI domain crosslinking with sulfur monochloride. Porous microspheres were produced after the hydrolysis of PtBA and the extraction of the homopoly(acrylic acid) chains. The shape and connectivity of the poly(acrylic acid)‐lined pores were tuned by changes in the PtBA/hPtBA content in the precursor microspheres. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2785–2793, 2003     

Preparation of nano‐sized poly(ethylene oxide) star microgels via reversible addition‐fragmentation transfer polymerization in selective solvents

Poly(ethylene oxide) (PEO) star microgels with a cross‐linked polystyrene core were successfully prepared by reversible addition‐fragmentation transfer polymerization of styrene (St) and divinylbenzene (DVB) with dithiobenzoate‐terminated PEO monomethyl ether (DTB‐MPEO) as macro chain transfer agent in mixtures of ethanol and tetrahydrofuran (THF). The formation of star polymers was affected by polymerization time, solvents and St:DVB:DTB‐MPEO molar ratios. Narrow polydispersed star microgels with high molecular weight were obtained under appropriate polymerization conditions. Transmission electron micrographs suggest that PEO star polymers could form nano‐size spherical micelles in mixtures of water and THF, which further demonstrates the amphiphilic nature of the star polymers. Copyright © 2006 Society of Chemical Industry     

Synthesis and characterization of polystyrene/poly(4‐vinylpyridine) triblock copolymers by reversible addition–fragmentation chain transfer polymerization and their self‐assembled aggregates in water

Reversible addition–fragmentation chain transfer polymerization (RAFT) was developed for the controlled preparation of polystyrene (PS)/poly(4‐vinylpyridine) (P4VP) triblock copolymers. First, PS and P4VP homopolymers were prepared using dibenzyl trithiocarbonate as the chain transfer agent (CTA). Then, PS‐b‐P4VP‐b‐PS and P4VP‐b‐PS‐b‐P4VP triblock copolymers were synthesized using as macro‐CTA the obtained homopolymers PS and P4VP, respectively. The synthesized polymers had relatively narrower molecular weight distributions (M_w/M_n < 1.25), and the polymerization was controlled/living. Furthermore, the polymerization rate appeared to be lower when styrene was polymerized using P4VP as the macro‐CTA, compared with polymerizing 4‐vinylpyridine using PS as the macro‐CTA. This was attributed to the different transfer constants of the P4VP and PS macro‐CTAs to the styrene and the 4‐vinylpyridine, respectively. The aggregates of the triblock copolymers with different compositions and chain architectures in water also were investigated, and the results are presented. Reducing the P4VP block length and keeping the PS block constant favored the formation of rod aggregates. Moreover, the chain architecture in which the P4VP block was in the middle of the copolymer chain was rather favorable to the rod assembly because of the entropic penalty associated with the looping of the middle‐block P4VP to form the aggregate corona and tailing of the end‐block PS into the core of the aggregates. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1017–1025, 2003     

Poly(dimethylsiloxane‐b‐styrene) diblock copolymers prepared by reversible addition–fragmentation chain‐transfer polymerization: Synthesis and characterization

Well‐defined poly(dimethylsiloxane‐b‐styrene) diblock copolymers were prepared by reversible addition–fragmentation chain‐transfer (RAFT) polymerization. Monohydroxyl‐terminated polydimethylsiloxane was modified to form a functional polydimethylsiloxane/macro‐RAFT agent, which was reacted with styrene to form the diblock copolymers. The chemical compositions and structures of the copolymers were characterized by proton nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, and gel permeation chromatography. The surface properties and morphology of the copolymers were investigated with static water contact‐angle measurements, X‐ray photoelectron spectroscopy, transmission electron microscopy, and atomic force microscopy, which showed a low surface energy and microphase separation surfaces that were composed of hydrophobic domains from polydimethylsiloxane segments. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Polymeric N‐allyl vinylpyridinium salts as addition–fragmentation type initiators for cationic polymerization

Polymeric allyl pyridinium salts were synthesized from styrene and 4‐vinyl pyridine copolymers by quaternization and counteranion exchange reactions. The initiation capability of these copolymers, in conjunction with a photochemical free radical source such as benzoin, via an addition –fragmentation mechanism in the cationic polymerization of cyclohexene oxide is investigated. © 2001 Society of Chemical Industry     

Poly(dimethylsiloxane‐b‐styrene) diblock copolymers prepared by reversible addition‐fragmentation chain transfer polymerization: Kinetic model

Well‐defined polydimethylsiloxane‐block‐polystyrene (PDMS‐b‐PS) diblock copolymers were prepared by reversible addition‐fragmentation chain transfer (RAFT) polymerization using a functional PDMS‐macro RAFT agent. The RAFT polymerization kinetics was simulated by a mathematical model for the RAFT polymerization in a batch reactor based on the method of moments. The model described molecular weight, monomer conversion, and polydispersity index as a function of polymerization time. Good agreements in the polymerization kinetics were achieved for fitting the kinetic profiles with the developed model. In addition, the model was used to predict the effects of initiator concentration, chain transfer agent concentration, and monomer concentration on the RAFT polymerization kinetics. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Comparison of styrene reversible addition–fragmentation chain‐transfer polymerization in a miniemulsion system stabilized by ammonlysis poly(styrene‐alt‐maleic anhydride) and sodium dodecyl sulfate

In this study, we conducted the reversible addition–fragmentation chain‐transfer (RAFT) polymerization of styrene (St) in a miniemulsion system stabilized by two different stabilizers, ammonlysis poly(styrene‐alt‐maleic anhydride) (SMA) and sodium dodecyl sulfate (SDS), with identical reaction conditions. The main objective was to compare the polymerization kinetics, living character, latex stability, and particle morphology. The macro‐RAFT agent used in both systems was SMA, which was obtained by RAFT solution polymerization mediated by 1‐phenylethyl phenyldithioacetate. The experimental results show that the St RAFT miniemulsion polymerization stabilized by SDS exhibited a better living character than that stabilized by ammonlysis SMA. The final latices were very stable in two systems, but different stabilizers had an obvious effect on the polymerization kinetics, living character, and particle morphology. All of the particles obtained by RAFT miniemulsion polymerization stabilized by SDS were solid, but an obvious core–shell structure was observed in the miniemulsion system stabilized by ammonlysis SMA. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

One‐step synthesis of triarm block copolymers via simultaneous reversible‐addition fragmentation chain transfer and ring‐opening polymerization

One‐step synthesis of star copolymers by reversible addition–fragmentation chain transfer (RAFT) and ring‐opening polymerization (ROP) by using a novel dual initiator is reported. Triarm block copolymers comprising one polystyrene (or polyacrylamide) arm and two poly(β‐butyrolactone) arms were synthesized in one‐step by simultaneous RAFT polymerization of styrene (St) (or acrylamide, designated as AAm) and ROP of β‐butyrolactone (BL) in the presence of a novel trifunctional initiator, 1,2‐propanediol ethyl xanthogenate (RAFT‐ROP agent). This dual initiator was obtained through the reaction of 3‐chloro‐1,2‐propanediol with the potassium salt of ethyl xanthogenate. The principal parameters such as monomer concentration, initiator concentration, and polymerization time that affect the one‐step polymerization reaction were evaluated. The characterization of the products was achieved using Fourier‐transform infrared spectroscopy (FTIR), ¹H‐nuclear magnetic resonance (¹H‐NMR), ¹³C‐nuclear magnetic resonance (¹³C‐NMR), Gas chromatography–mass spectrometry (GC–MS), gel‐permeation chromatography (GPC), thermogravimetric analysis (TGA), and fractional precipitation (γ) techniques. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Synthesis of double‐hydrophilic poly(methylacrylic acid)–poly(ethylene glycol)–poly(methylacrylic acid) triblock copolymers and their micelle formation

The aim of the work reported was to synthesize a series of double‐hydrophilic poly(methacrylic acid)‐block‐poly(ethylene glycol)‐block‐poly(methacrylic acid) (PMAA‐b‐PEG‐b‐PMAA) triblock copolymers and to study their self‐assembly behavior. These copolymeric self‐assembly systems are expected to be potential candidates for applications as carriers of hydrophilic drugs. Bromo‐terminated difunctional PEG macroinitiators were used to synthesize well‐defined triblock copolymers of poly(tert‐butyl methacrylate)‐block‐poly(ethylene glycol)‐block‐poly(tert‐butyl methacrylate) via reversible‐deactivation radical polymerization. After the removal of the tert‐butyl group by hydrolysis, double‐hydrophilic PMAA‐b‐PEG‐b‐PMAA triblock copolymers were obtained. pH‐sensitive spherical micelles with a core–corona structure were fabricated by self‐assembly of the double‐hydrophilic PMAA‐b‐PEG‐b‐PMAA triblock copolymers at lower solution pH. Transmission electron microscopy and laser light scattering studies showed the micelles were of nanometric scale with narrow size distribution. Solution pH and micelle concentration strongly influenced the hydrodynamic radius of the spherical micelles (48–310 nm). A possible reason for the formation of the micelles is proposed. Copyright © 2010 Society of Chemical Industry