Multi-Site Organoboron Catalysts Enable Sequence-Regulated Terpolymerization of Epoxides, CO2, and β-Propiolactone via Intermolecular Chain Shuttling.

Abstract

Sequence regulation in synthetic polymers is essential for tailoring material properties; however, achieving precise control in polycarbonate-polyhydroxyalkanoate (PC-PHA) terpolymers derived from epoxides, CO₂, and β-lactones remains challenging. Current metal-based catalysts lack multisite strategies for sequence diversification, limiting the formation of gradient architectures. This study employed mononuclear (catalyst 1) and dinuclear (catalyst 2) organoboron catalysts to mediate the terpolymerization of epoxides, CO₂, and β-propiolactone (BPL). Kinetic analysis, NMR spectroscopy, and a chain-shuttling approach with mixed catalysts were utilized to regulate sequences. Key findings indicated: i) Catalyst 1 preferentially promoted β-propiolactone ring-opening polymerization (ROP), forming tapered P3HP-b-PC blocks, whereas catalyst 2 enhanced epoxide/CO₂ ring-opening copolymerization (ROCOP), yielding PC-b-P3HP; ii) Boron centers kinetically suppressed ROP but increased ROCOP efficiency; iii) Mixed 1 and 2 catalysts enabled intermolecular chain shuttling, synthesizing gradient PC-grad-P3HP terpolymers; and iv) Terpolymer compositions modulated thermal properties from amorphous to crystalline. This work establishes the first metal-free, chain-shuttling platform for sequence-regulated PC-PHA terpolymers, extending the scope of programmable biodegradable materials beyond metal-catalyzed systems.