Zinc Complexes of Guanidine– and Amidine–Phenolate Ligands for the Ring-Opening Polymerization of Lactide

A series of Zn complexes containing guanidine– and amidine–phenolate ligands were synthesized and evaluated as catalysts for the polymerization of rac-lactide at 130 °C, under solvent-free conditions, giving rate constants in the range of 0.71–4.37 × 10–4 s–1. Polymerization under identical conditions with the guanidine– and amidine–phenol proligands themselves used as catalysts gave values in the range of 0.30–2.45 × 10–4 s–1. The stereoselective production of polylactic acid from either the Zn complexes or the proligands was limited (Pr = 0.47–0.62). The molecular weight of the polymers was lower than expected for living polymerizations due to chain transfer and/or transesterification but were comparable to those obtained in control experiments with Sn(Oct)2.