Perfectly Alternating Copolymerization Of Propylene Oxide And Co2 Over Salenco/Salencr Complexes

Schiff-cobalt (salenCo) and Schiff-chromate (salenCr) were synthesized and used as catalysts for copolymerizing of propylene oxide (PO) and CO2. The alternating copolymer of polycarbonate was successfully obtained under mild conditions in the presence of 4-(dimethylamino)-pyridine (DMAP) cocatalyst. The influences of DMAP amount, polymerization time, temperature, and CO2 pressure on the copolymerization efficiency and selectivity to polycarbonate were investigated in the presence of catalysts. Under the optimized conditions, salenCo/DMAP exhibited an excellent catalytic efficiency with perfectly alternating copolymerization products (99% carbonate and more than 99% polycarbonate with head-to-tail linkage) and high selectivity to polycarbonate over cyclic carbonate (more than 99% polymeric product) without byproduct (polyether). While only 76% selectivity to polymer, 95% carbonate linkage, and 80% head-to-tail connection unit were obtained over salenCr/DMAP catalyst. Furthermore, the catalytic activity of salenCo was superior to that of salenCr, resulting in higher molecular weight, more regular microstructure, and higher stability of copolymer.