The use of a cobalt porphyrin ((TPP)CoCl, 1) in combination with dimethylaminopyridine (DMAP) for the alternating copolymerization of CO 2 and epoxide is described. The (TPP)CoCl (1)-DMAP system quantitatively produced the alternating copolymer from CO 2 and cyclohexene oxide (CHO) under optimized conditions (50 atm, 80°C). This calatyst system also worked satisfactorily for the alternating copolymerization of CO 2 and a terminal epoxide, e.g., propylene oxide (PO), without formation of cyclic carbonate to give the polycarbonate. The alternating copolymerization of CO 2 and epoxide (CHO, PO) was achieved under very mild conditions, such as at ambient temperature and under CO 2 at 1 atm, by using the 1-DMAP catalyst system.