Imino phenoxide complexes of group 4 metals: synthesis, structural characterization and polymerization studies

Abstract

A complete library of new alkoxides containing group 4 metals and the imino phenol ligand were synthesized in high yields and purity. These compounds showed catalytic activity towards the polymerization of L-lactide (L-LA), rac-lactide (rac-LA), ε-caprolactone (CL), δ-valerolactone (VL), rac-β-butyrolactone (rac-BL), ethylene and propylene. The zirconium catalysts were found to yield better polymerization results in comparison to the titanium and hafnium analogues. The number average molecular weight (Mn) values of the polymers are very high for LA and CL with controlled molecular weight distributions (MWDs). Analyses of MALDI-TOF and 1H NMR spectra of low Mn oligomers reveal that the ligand initiates the ring-opening polymerization (ROP). For ethylene and propylene polymerization, we have achieved moderate to good activity using MAO as a co-catalyst.