Epoxide-Modulated Ring-Opening Polymerization of β-Butyrolactone

Abstract

Poly(3-hydroxybutyrate) (P3HB) is a promising sustainable plastic alternative, valued for its inherent biodegradability, biocompatibility, and desirable material properties. While structural modification of P3HB has largely centered on side-chain functionalization, its end-group functionalization remains relatively unexplored. Herein, we demonstrate that modulation with epoxides in the trimetallic-catalyzed ring-opening polymerization of β-butyrolactone has enabled the synthesis of various end-functionalized P3HBs. In the trimetallic aluminum system, epoxides have switched the initiating group from chloride to alkoxide, thus transforming the propagating species from carboxylate to alkoxide. By contrast, the trimetallic chromium system has exhibited a three-fold enhancement in activity (TOF up to 800 h⁻¹) and five-fold rise in molecular weight (Mn = 47.6 kg/mol) upon epoxide addition, while maintaining a narrow dispersity (Đ ~ 1.26). Mechanistic insight reveals that epoxides have converted the chloride to alkoxide initiator, while the propagation still proceeded via a robust carboxylate species with configurational inversion at the methine carbon atom. This strategy offers a new route to prepare high-molecular-weight P3HB products with desired end-functionalization.