A bifunctional cyclic five-membered dithiocarbonate (DTC), having a bisphenol A structure, was found to be an effective accelerator for a epoxy-amine curing system comprised of bisphenol A diglycidyl ether and amine-terminated polypropylene glycol. The acceleration effect was evaluated by monitoring the time-dependence of the storage modulus of the reaction mixture with a dynamic mechanical analyzer. The reactions involved in the curing system were investigated in detail by performing a series of model reactions using the corresponding monofunctional monomers. This investigation revealed that (1) DTC reacted with amine rapidly, (2) the reaction afforded the corresponding adduct having a thiourethane and thiol moieties, and (3) the thiol reacted rapidly with epoxide. The thiourethane moiety incorporated into the resulting adduct effectively catalyzed the reaction of epoxide and amine, and this catalysis was the predominant mechanism for the acceleration effect arisen by the addition of DTC. (c) 2007 Wiley Periodicals, Inc.