Polymerization of rac-lactide catalyzed by group 4 metal complexes containing chiral N atoms

Abstract

The hydroxyl- and phenoxy-bridged dinuclear zirconium and hafnium complexes, 1 and 2, containing a chiral N atom in the N2O2 ligand (H2L = 2-(((2-pyridylmethyl)(2-hydroxyphenyl)amino)methyl)-4,6-di(tert-butyl)phenol) were used as catalysts for the ring-opening polymerization of rac-lactide. Experiments prove that 1 and 2 are living and controlled catalytic systems with activity up to 3.25 gpol mmolini−1 h−1. The isotactic-rich polylactides in a narrow polydispersity (Mw/Mn = 1.01–1.13) were produced with enantiomeric complexes 1 and 2 (Pm = 0.65–0.73). The kinetic studies show a first-order dependency in both monomer and initiator. The initiation mechanism is discussed on the basis of the MALDI-TOF MS and 1H NMR spectra of the rac-LA oligomer prepared by 1.