Ring-opening copolymerization of cyclohexene oxide and maleic anhydride catalyzed by mononuclear [Zn(L)(H2O)] or binuclear [Zn2(L)(OAc)2(H2O)] complex based on the Salen-type Schiff-base ligand

From the self-assembly of the typical Salen-type Schiff-base ligand H (2) L and Zn(OAc)(2)center dot 2H(2)O in the molar ratio of 1:1 or 1:2, the mononuclear [Zn(L)(H2O)] (1) or binuclear [Zn-2(L)(OAc)(2)(H2O)] (2) are obtained, respectively. For both complexes 1 and 2, the unsaturated five-coordinate coordination environment to the catalytic active centers (Zn2+ ions) permits the monomer insertion for the effective solution copolymerization of cyclohexene oxide and maleic anhydride. All the solution copolymerizations afford poly(ester-co-ether)s, while lower catalyst and co-catalyst concentrations are helpful for the formation of alternating polyester. Of the three co-catalysts, 4-(dimethylamino)pyridine is found to be the most efficient, while an excess thereof is detrimental for chain growth of the copolymers.