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 weig...