A method of synthesizing trimethylene carbonate is disclosed involving (a) reacting 1,3-propanediol and a compound chosen from phosgene and bis-chloroformates to form a polycarbonate intermediate having the structure: ##STR1## wherein n is at least 2; R.sup.1 is an end group chosen from H, R.sup.3 -Cl, R.sup.3 -OH and --C(O)Cl, where R.sup.3 is C.sub.1 -C.sub.6 linear or branched alkyl and R.sup.2 is an end group chosen from --OCH.sub.2 CH.sub.2 CH.sub.2 Cl, --OCH.sub.2 CH.sub.2 CH.sub.2 OH and Cl; and (b) providing a combination of temperature and pressure corresponding to vapor phase conditions for trimethylene carbonate.