AbstractCarbon dioxide and propylene oxide (PO) were copolymerized using diethylzinc in addition with benzenedi‐ and triols, aliphatic diols and triols, and aminophenols as catalyst systems. A large amount of CO2/PO alternating copolymer, {poly(propylene carbonate), poly(oxycarbonyloxypropylene), of high molecular weight was obtained using the homogeneous (C2H5)2Zn/pyrogallol (2:1 by mole) system (1). The (C2H5)2Zn/o‐aminophenol system (2) (also homogeneous) appeared to be much less active in the copolymerization of CO2with PO than the former one. From the other studied systems, that appeared to be heterogeneous, (C2H5)2Zn/resorcinol (1:1 by mole) was the most active one, but less active than the system1.Further, the copolymerization of CO2and PO was studied in the presence of the (C2H5)2Zn/resorcinol (1:1 by mole) system at various temperatures and in reaction media of different basicity.On the basis of the obtained results of the copolymerization of CO2with PO and of measurements of the quantity of ethane evolved in the reactions between the catalytic systems' components, structures of several catalysts, particularly homogeneous ones, are suggested and some aspects of the copolymerization mechanism are discus