A trinuclear [Zn3(L)2(OAc)2] complex based on the asymmetrical bis-Schiff-base ligand H2L for ring-opening copolymerization of CHO and MA

Based on asymmetrical bis-Schiff-base ligand H2L from o-vanillin and the half-unit Schiff-base precursor HL synthesized from 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone (PMBP) and o-phenylenediamine, a trinuclear [Zn3(L)2(OAc)2] (1) is obtained. In complex 1, the unsaturated five and four-coordinate coordination environment for the catalytic active centers (Zn2 + ions) permits the monomer insertion for the effective bulk or solution copolymerization of CHO (cyclohexene oxide) and MA (maleic anhydride) in the presence of co-catalyst of DMAP (4-(dimethylamino)pyridine), TPP (triphenylphosphine) or n-Bu4NBr. All the bulk copolymerizations afford poly(ester-co-ether)s, while some of the solution copolymerizations produce perfectly alternating polyester copolymers. Of the three co-catalysts, DMAP is found to be the most efficient, while an excess thereof is detrimental for chain growth of the copolymers.