Copolymerization of Carbon Dioxide and Epoxide

Alternating copolymerization of CO2 and epoxide to give aliphatic polycarbonate with high molecular weight proceeds under mild conditions by organometallic catalyst systems. The reaction product of diethylzinc with a polyhydric compound, such as water or polyhydric phenol, exhibits high catalytic activity. Elementary reactions for the copolymerization of CO2 and epoxide with an organozinc catalyst system is considered to be the reaction of a zinc alkoxide with CO2 to form a zinc alkyl carbonate, and the reaction of the zinc alkyl carbonate with epoxide to regenerate zinc alkoxide. The system of aluminum porphyrin such as (tetraphenylporphinato)aluminum chloride, coupled with a quaternary ammominum or phosphonium salt, such as ethyltriphenylphosphonium bromide, is a good catalyst for this copolymerization. Of much interest is the very narrow molecular weight distribution of the copolymer obtained by this system. Aluminum porphyrin and the quaternary salt forms a hexa-coordinate complex, and the copolymerization reaction is considered to proceed on both sides of the porphyrin ring. Some properties of the copolymer for possible application are described.