The trifunctional five-membered cyclic carbonate 2 and dithiocarbonate 3 were successfully synthesized by the reaction of trifunctional epoxide 1 with carbon dioxide and carbon disulfide, respectively. The crosslinking reactions of 2 with p-xylylenediamine or hexamethylenediamine were carried out in dimethyl sulfoxide at 100 degreesC for 48 h to produce the corresponding crosslinked poly(hydroxyurethane)s quantitatively. The crosslinking reactions of 3 with both p-xylylenediamine and hexamethylenediamine, followed by acetylation of thiol moiety, produced the corresponding crosslinked poly(thioester-thiourethane)s quantitatively. The obtained crosslinked poly(hydroxyurethane)s were thermally more stable than the analogous crosslinked poly(thioester-thiourethane)s, probably because of less thermal stability of thiourethane moiety than hydroxyurethane moiety. (C) 2004 Wiley Periodicals, Inc.