An efficient strategy for achieving controlled ring-opening polymerization of O-carboxyanhydrides via amine initiation in collaboration with metal-alkoxide catalysis

Abstract

The ring-opening polymerization (ROP) of O-carboxyanhydrides (OCAs) is a versatile alternative for generating well-defined functional poly(α-hydroxy acids) (PAHAs). In contrast to the ROP of lactides, which has countless successful examples, exploring new catalysts and polymerization pathways for the controlled ROP of OCAs remains an attractive challenge. Considering the polymerization characteristics of OCAs, we herein describe an effective catalytic system containing Zn(C₆F₅)₂ and amines that mediates the controlled ROP of OCAs. The strong nucleophilic attack of the amines combined with the effective switching of Zn(C₆F₅)₂ to Zn alkoxide during polymerization provides a collaborative catalytic pathway of amine initiation and metal-alkoxide-promoted chain propagation for the ROP of OCAs. The ROP of OCAs catalyzed by Zn(C₆F₅)₂ and amines enables the controlled polymerization of PAHA, as evidenced by the afforded homopolymers and block polymers with the expected molecular weights and narrow molecular weight distributions (M_w/M_n < 1.1). Careful analysis of the polymerization system and computational studies verify a Lewis pair composed of amines and Zn(C₆F₅)₂ for polymerization initiation and functionality switch from Zn(C₆F₅)₂ to a metal-alkoxide species for coordination–insertion chain propagation.