A new Co(III) salen betaine functional catalyst is reported which displays high activity and high selectivity for the copolymerization reaction of oxirane and carbon dioxide. Importantly, this catalyst system is not only effective for propylene oxide and CO2 but also efficient for more difficult epoxides to selectively provide copolymers. For example, styrene oxide and 2-vinyloxirane are readily coupled with CO2 to provide the corresponding completely alternating copolymers. This catalyst system is thereby able in several instances to avoid the use of tediously prepared bifunctional Co(III) salen catalysts. Through a combination of control experiments, MALDI-TOF measurements, and DFT computations, the addition of a cocatalyst is shown to play a significant role in this process.