RAFT Polymerization of Vinyl Sulfonate Esters for the Controlled Synthesis of Poly(lithium vinyl sulfonate) and Sulfonated Block Copolymers

Four vinyl sulfonate ester derivatives, neopentyl ethenesulfonate (NES), 1-butyl ethenesulfonate (BES), isopropyl ethenesulfonate (IPES), and phenyl ethenesulfonate (PES), were polymerized by conventional radical polymerization and reversible addition fragmentation chain transfer (RAFT) polymerization. Three xanthate-type chain transfer agents (CTAs), a dithiocarbamate-type CTA, and a dithioester-type CTA were compared for these RAFT polymerizations. Among various CTAs, O-ethyl-S-(1-methoxycarbonyl) ethyldithiocarbonate was the most efficient to obtain poly(NES) and poly(BES) having low polydispersities. The effects of several parameters, such as temperature and CTA to initiator molar ratio, were examined in order to determine the conditions, leading to optimal control of the polymerization. With the xanthate-type CTA under suitable conditions, reasonable control of the polymerization of NES was confirmed by the formation of the relatively low polydispersity products, linear increase in the molecular weight with the conversion, and feasibility in the control of the molecular weight based on the ratio of monomer consumed to the amount of CTA used. The polymerization behavior of BES was comparable to that of NES. Deprotection of the neopentyl group of the poly(NES) proceeded smoothly to give water-soluble poly(lithium vinyl sulfonate). Synthesis of the well-defined block copolymer involving the poly(lithium vinyl sulfonate) segment was conducted by RAFT polymerization of NES using poly(N-vinylcarbazole) macro-CTA, followed by deprotection.