Synthesis of x-Sulfonated Polystyrene Via Reversible Addition Fragmentation Chain Transfer Polymerization and Postpolymerization Modification Lei Feng, 1 Kevin A. Cavicchi, 1 Bryan C. Katzenmeyer, 2 Chrys Wesdemiotis 2 1 Department of Polymer Engineering, The University of Akron, 250 S. Forge St, Akron, Ohio 44325-0301 2 Department of Chemistry, The University of Akron, 190 E. Buchtel Common, Akron, Ohio 44325-0301 Correspondence to: K. A. Cavicchi (E-mail: kac58@uakron.edu) Received 2 May 2011; accepted 25 August 2011; published online 15 September 2011 DOI: 10.1002/pola.24976 ABSTRACT: The synthesis of chain-end sulfonated polystyrene [PS (x-sulfonated PS)] by reversible addition fragmentation chain transfer (RAFT) polymerization followed by postpolymeri- zation 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 sec- ond method, the RAFT-polymerized polymer was directly sulfo- nated by oxidation with m-CPBA. After purification by column chromatography, x-sulfonated PS was obtained by both meth- ods with greater than 95% end-group functionality as meas- ured 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 tempera- ture of the PS was found to be consistent with what is known for PS ionomers. V C 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 5100–5108, 2011 KEYWORDS: ionomers; polystyrene; reversible addition frag- mentation chain transfer (RAFT); RAFT polymerization INTRODUCTION Polymers terminated with a sulfonate end- group (x-sulfonated polymers) are useful as model ionom- ers, modifiers for thin films and surfaces, and supramolecu- lar building blocks for linear and graft block copolymers. 1–10 A widely used method to produce these polymers is through anionic polymerization by termination with propane sul- tone. 11 While this approach generates well-defined polymers with quantitative yields of functional end-groups, it has limits to the range of polymers that can be produced due to the high purity reaction conditions and chemical require- ments of the polymerization technique. 12 The advent of controlled radical polymerization techniques has provided new routes for the synthesis of well-defined polymer systems. For example, nitroxide-mediated radical polymerization, atom transfer radical polymerization, and re- versible addition fragmentation chain transfer (RAFT) poly- merization have been used to synthesize polymers contain- ing sulfonate groups. 13–17 These provide a range of options for producing sulfonated polymers when considered in con- cert with other approaches, such as postpolymerization modification. 18,19 RAFT polymerization has also proven useful for producing polymers with well-defined functional groups. 20 The key to the polymerization is the addition of a dithioester RAFT agent, which is able to undergo reversible chain transfer reactions with the growing polymer chain to achieve con- trolled polymerization conditions. As a consequence of the chain transfer reactions, the dithioester group is incorpo- rated into the polymer chain. These polymers are converted to thiol-terminated polymers by treatment with primary amines. 21,22 These thiol-terminated polymers can be further functionalized or used as building blocks, for example, through thiol-ene chemistry or disulfide formation. 23–30 This article reports the synthesis of x-sulfonated polystyrene (PS-SO 3 H) through two methods. The first is the synthesis of PS by RAFT polymerization, aminolysis of the subsequent polymer to produce thiol-terminated PS, and subsequent oxi- dation of the thiol-terminated polymer with m-chloroperoxy- benzoic acid (m-CPBA). The oxidation reaction of thiols is commonly used in small molecule organic synthesis and has been used to introduce sulfonate groups along polymer back- bones, but to the authors knowledge has not been reported for modification of RAFT polymers. 31–33 The second method is the direct oxidation of the RAFT polymerization-prepared PS with m-CPBA. This route was based on a previous obser- vation by Zagorevskii et al. where x-sulfonated PS was detected by matrix-assisted laser desorption/ionization Additional Supporting Information may be found in the online version of this article. V C 2011 Wiley Periodicals, Inc. 5100 JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY 2011, 49, 5100–5108 ARTICLE WWW.POLYMERCHEMISTRY.ORG