Innovative Synthesis of PPC-P-co-PLA Multi-block copolymers via One-pot copolymerization and transesterification catalysed by Alkyl Boron and Diverse Lewis Bases

Abstract

Carbon dioxide (CO2) has been utilized for synthesizing biodegradable polymers to promote sustainable energy conservation and mitigate emissions. Nonetheless, the low glass transition temperature of amorphous CO2-based polyester-polycarbonate (PPC-P) significantly impedes its practical application. Herein, semi-crystalline copolymers, PPC-P-co-PLA, were successfully synthesized via copolymerization of propylene oxide (PO), phthalic anhydride (PA), and CO2 in combination with PLA through transesterification catalysed by Lewis acid-base pairs in a one-pot/one-step method. Metal-free catalysts were utilized for the first time to catalyse both ring-opening copolymerization and transesterification reactions for copolymer synthesis. The mechanism study of PLA transesterification catalysed by triethyl borane (TEB)/Lewis bases revealed that effective depolymerization and transesterification of PLA hinge on α-H chemical shift alterations induced by Lewis bases. Lewis acid-base pairs facilitate the formation of PPC-P-co-PLA multi-block copolymers by terminating one end of PPC-P with PLA segments via continuous transesterification reactions. Compared to PPCP, copolymers exhibit an increase in glass transition temperature by 5-7°C and an elevation in thermal decomposition temperature by 18-45°C. The optimal mechanical and rheological properties of PPC-P-co-PLA multi-block copolymers are achieved at a PLA concentration of 8 wt%. This study opens new avenues for the synthesis of semi-crystalline polyester-polycarbonate-based copolymers with high glass transition temperatures, thereby enriching the theoretical foundation for the synthesis of block copolymers.