Ring-opening polymerization of lactide with Zr complexes of {ONSO} ligands: From heterotactically inclined to isotactically inclined poly(lactic acid)

摘要

Six members of a new family of {ONSO}-type ligands - the tetradentate-diainionic imine-thiobis(phenolate) ligands - were prepared by a two-step synthesis. Their [{ONSO}Zr(O ~tBu) _2] complexes formed as single diastereomers with different degrees of fluxionality that depended on the substitution pattern of the two phenolate rings. The complexes were active in polymerization of l-lactide and rac-lactide. The tacticity of the poly(lactic acid) prepared from rac-lactide changed gradually from heterotactically inclined through atactic to isotactically inclined. The most flexible complex and the most rigid complex gave the highest degrees of heterotacticity and isotacticity, respectively.