Phenoxy-imine based Mononuclear Zn(II) Compounds: Applications as Polymerization Catalysts

The production of aliphatic polyesters (via ROP of cyclic esters) and aliphatic polycarbonates (via ROCOP of CO2/epoxide) is an important synthetic pathway for the production of biodegradable and biocompatible polymers. The study focuses on the catalytic activity and selectivity of phenoxy-imine based zinc compounds for the ROP of cyclic esters (rac-LA and -CL) and ROCOP of carbon dioxide and CHO/PO. The monoligated and bisligated zinc compounds have the same coordination number (four) but differed from each other in the binding mode of the ligand to the metal center (tridentate for monoligated and bidentate for bisligated compounds) and thus the compounds adopt different symmetry. For the ROP of rac-LA, the monoligated zinc compounds gave isotactic-enriched PLA while the bisligated zinc compounds gave heterotactic-enriched PLA. For the ROCOP of epoxide/CO2, isotactic-enriched polycarbonates were obtained with a notable difference in catalytic activity with the variation of the number of ligands attached to the zinc center. In addition, a correlation is established between the percentage of carbonate linkage in the polycarbonate chain and the substituent attached to the phenolate core.