Abstract
The series of novel symmetric and asymmetric salphen cobalt (III) complexes with different counteranions (trichloroacetate, dinitrophenolate, pentafluorobenzoate and acetate) was synthesized and used as catalysts in copolymerization of CO2 with propylene oxide (PO) and cyclohexene oxide (CHO). Hexacoordinated structure of complexes adducts was found in solid phase.
The effect of catalyst structure, temperature, CO2 pressure, catalyst/cocatalyst ratio on overall activity and selectivity was investigated. Synthesized salphen-Co (III) complexes were effective for both PO/CO2 and CHO/CO2 highly alternating copolymerization.
Substitution of phenylene framework of salphen ligand by chlorine atom led to decrease of activity in PO/CO2 copolymerization. Complexes with trichloroacetate counteranion were shown to be the most active and selective in PO/CO2 copolymerization leading to poly(propylenecarbonate) with highest molar mass.
On contrary, catalytic performance of salphen Co (III) complexes in CHO/CO2 copolymerization was almost independent on ligand structure and counteranion. Excellent selectivity to poly(cyclohexenecarbonate) was achieved even at 0.1 MPa CO2.
MALDI-TOF analysis of polycarbonates was used to investigate the initiation step of the copolymerization.