Ionic liquid [Bmim][Lac]-catalyzed melt polycondensation for bisphenol A-based polycarbonate synthesis

Abstract

Bisphenol A-based polycarbonate (BPA-PC) green synthesis via melt polycondensation is a significant field, while traditional metal catalysts suffer from severe side reactions and metal residue issues. Herein, metal-free ionic liquid [Bmim][Lac] was used to catalyze the melt polycondensation of bisphenol A (BPA) and diphenyl carbonate (DPC). Under optimal conditions, BPA-PC with a number-average molecular weight of up to 48.4 kDa was successfully synthesized, which exhibits superior thermal properties, melt processability and mechanical strength (>43 MPa) relative to commercial BPA-PC. in situ NMR revealed a synergistic nucleophilic–electrophilic mechanism of [Bmim][Lac]: imidazolium cations activate DPC and lactate anions activate BPA via hydrogen bonding. Copolymerization with diphenyl terephthalate, diphenyl isophthalate, 9,9-bis(4-hydroxyphenyl)fluorene and phenolphthalein verified the catalytic system's versatility, and the resulting copolycarbonates showed elevated glass transition temperature (T_g, up to 150.9 °C) and thermal stability (T_d,5% > 424 °C). This work provides a green metal-free catalytic strategy for BPA-PC and functional copolycarbonate synthesis, expanding the application of ionic liquids in melt polycondensation.