Bifunctional phosphazene-thiourea/urea catalyzed ring-opening polymerization of cyclic esters

Abstract

A series of new bifunctional phosphazene-thiourea/urea catalysts have been designed and applied to ring-opening polymerization (ROP) of rac-lactide, δ-valerolactone and ε-caprolactone. The ROPs were promoted efficiently, delivering the corresponding polyesters with controlled molecular weights, narrow molecular weight distributions, well-defined end group fidelities and without undesired epimerization of rac-lactide. Kinetic experiment of rac-LA confirmed the controlled/living nature of the ROP process. The isoselective polymerization of rac-LA was achieved with a highest Pm value of 0.79 (based on Bernouillan statics) under mild conditions. In addition, the ROPs of δ-VL and ε-CL were also smoothly achieved with high conversions and narrow molecular weight distributions. These catalysts exhibit a broad monomer scope of lactones, providing a facile synthesis methodology of metal-free and applicable polyester materials.