Salicylaldimine Copper(II) complex catalyst: Pioneer for ring opening Polymerization of Lactide

Abstract

Salicylaldimine copper complex has been synthesized and its reactivity for the ring-opening polymerization (ROP) of lactide has been studied. This monomeric copper complex was prepared by the reaction of copper(II) solution with one molar equivalent of salicylaldimine Schiff-base ligand in methanol under nitrogen atmosphere. This copper complex has been characterized by different spectroscopic methods, which showed square planar geometry. The molecular structure of the salicylaldimine Schiff-base has been determined by X-ray diffraction studies. The complex was tested as the initiator for the ring-opening polymerization of lactide, with variation in diamine group in ligand. The rate of polymerization is dependent on the diamine group in the following order: ethylene > propylene > phenyl. The salicylaldimine copper complex allows controlled ring-opening polymerization as indicated by the linear relationship between the percentage conversion and the number-average molecular weight. On the basis of literature reports, a mechanism for ROP of lactide has been proposed.