Zinc bis-pyrrolide-imine complexes: Synthesis, structure and application in ring-opening polymerization of rac -lactide

A series of bis-ligated zinc complexes with pyrrole-imine ligands were successfully synthesized and characterized by 1H and 13C{1H} NMR, and by X-ray crystallography for Zn1 and Zn3. These zinc complexes were used as catalysts for the ring-opening polymerization of rac-lactide in a toluene solution, under bulk conditions, in the presence and absence of benzyl alcohol. The complexes proved to be active in the presence of benzyl alcohol as co-initiator and chain transfer agent. Polymers were formed with high conversions and with well-matched experimental and calculated molar mass values. Under solvent-free conditions, high conversions were obtained after 1 h with good molecular control and satisfactory polydispersity. The homo-decoupled 1H NMR spectra of the methine regions of the PLA samples were consistent with the formation of polymer chains with slightly tendency to heterotacticity.