Neutral Bidendate Guanidine-Based Zinc Complexes for the Ring Opening Polymerization of Lactide

Herein is reported the synthesis and structure elucidation of three novel zinc complexes bearing neutral bidentate guanidine ligands for the ring opening polymerization (ROP) of lactide to PLA. Ligand and complex structures were obtained computationally and leveraged against single-crystal studies to develop a method for predicting solid state structures of future complexes. The catalysts were tested for ring opening polymerization of lactide to PLA. The most active complex displayed a rate constant for propagation, kp, of 26 M-1h-1. The catalyst showed some stereoselectivity with a heterotactic bias in the polymer (Pr = 0.60). The polymer number average molecular weight was determined to be ~4700 g mol-1. The end analysis of the MALDI-TOF mass spectrum suggested water activation for the polymerization. The polydispersity index of the polymer was determined by gel permeation chromatography to be 1.10, indicating a well-behaved polymerization.