Terpolymerization of carbon dioxide (CO2), propylene oxide (PO), and epoxide with bulky side groups (styrene oxide (SO), cyclohexylethylene oxide (CyEO), tert-butylethylene oxide (tBuEO), or 1-adamantylethylene oxide (AdEO)) was conducted by using a tetraphenylporphyrinatocobalt(III) chloride ((TPP)CoCl)/4-dimethylamino pyridine (DMAP) catalyst system. Compared with the copolymerizations of CO2 and epoxides with bulky side groups, it took less than half (AdEO) or even one-third (CyEO and tBuEO) of the polymerization time to synthesize polycarbonates with degrees of polymerization of 100 or above. In this (TPP)CoCl/DMAP system, a highly random terpolymer of CO2, PO, and SO was realized for the first time, which has not been observed in other catalyst systems, such as cobalt salen complex systems. In contrast, gradient terpolymers were formed in the cases of CyEO, tBuEO, and AdEO. The glass transition temperatures (Tgs) of these terpolymers are tunable between that of the copolymer of CO2 with PO (34 °C) and that of the copolymer of CO2 with the corresponding epoxide with bulky side groups by changing the initial ratio of PO to epoxide with bulky side groups.