Ring-Opening Polymerization of Lactides Initiated by Zinc Alkoxides Derived from NNO-Tridentate Ligands

A new series of dinuclear zinc complexes of the types [LZnEt] 2 and [LZn(μ-OBn)] 2 (where L = NNO-tridentate Schiff base ligand) have been prepared. The activities of zinc alkoxides, [LZn(μ-OBn)] 2, toward the ring-opening polymerization of l -lactide have been investigated. Experimental results indicate that the reactivity of [LZn(μ-OBn)] 2 was dramatically affected by both the electronic and steric effect of the substituents on the Schiff base. The polymerization kinetics using [L 1 Zn(μ-OBn)] 2 ( 2a ) as an initiator were also studied, and the experimental results reveal that the rate of reaction is first-order, which depends on both [LA] and [L 1 Zn(μ-OBn)] 2 . Furthermore, the heterotactic PLA with Pr up to 91% can be achieved by initiating of [L 5 Zn(μ-OBn)] 2 in CH 2 Cl 2 at −55 °C.