Vinylbenzyl S-thioacetate (1) was prepared from thioacetic acid and chloromethylstyrene. Although bulk polymerization of 1 afforded a crosslinked polymer, solution polymerization in chlorobenzene afforded a corresponding soluble polymer. The S-thioacetate group did not react during the radical polymerization of 1. Bulk copolymerization of 1 with styrene afforded a soluble copolymer when the feed ratio of 1 was lower than 30 mol %. Soap-free emulsion copolymerization of 1, St, divinylbenzene, and 2-hydroxyethyl methacrylate (66 : 28 : 1 : 5) was carried out in water using 2,2’-azobis (N,N’-dimethyleneisobutyramidine) dichloride as an initiator to afford uniform spherical microgel 2, whose average diameter was 135 nm. Aminolysis of 2 with an excess amount of butylamine in the presence of sodium tetrahydridoborate followed by treatment with hydrochloric acid resulted in complete removal of the acetyl group to give a slightly distorted spherical microgel (MG-SH) bearing mercapto group. The average diameter of MG-SH was 165 nm. Trans-esterification of p-nitrophenyl acetate (3) in the presence of triethylamine was efficiently accelerated by the addition of MG-SH. The radical polymerization of methyl methacrylate (MMA) in the presence of suspended MG-SH in chlorobenzene afforded the MMA-grafted microgel. Although MG-SH is a crosslinked gel, it acts as a soluble polymer bearing mercapto group.