Alternating copolymerization of CO2 with propylene oxide and terpolymerization with aliphatic epoxides by bifunctional cobalt Salen complex

Abstract

A novel N,N′-[2,2′-bis(nitrilomethylidyne)]bis[α-methyl-4-(morpholin-1-ylmethyl)-6-tert-butyl phenolato]-1,2-diaminocyclohexane CoIII (2,4-dinitrophenoxy) complex (complex 1) was designed and used to couple carbon dioxide (CO2) and propylene oxide (PO) as a single-component catalyst. Systematic investigation revealed that complex 1 was highly active and selective in the coupling of CO2/PO and that complete consumption of PO was accomplished with high copolymer selectivity. A high molecular weight of up to 108.6 kg mol−1 was achieved with an appropriate combination of all variables. Matrix-assisted laser desorption ionization–time-of-flight mass spectrometer analysis implied that a chain-end control mechanism controls the copolymerization. In addition, complex 1 could operate very efficiently in the terpolymerization of PO and cyclohexene oxide (CHO) with CO2 to provide polycarbonates with a narrow polydispersity. The Tg of the PO/CHO/CO2 terpolymer can be easily adjusted between 40 and 118.9 °C. A bifunctional cobalt Salen complex containing a Lewis acid metal center and two covalent bonded Lewis base units on the ligand was designed and used for the coupling of carbon dioxide (CO2) and epoxides at mild conditions. The Tg of the propylene oxide/cyclohexene oxide/CO2 terpolymer can be easily adjusted between 40 and 118.9 °C.