Alkali Metal/Quaternary Ammonium Salt Synergistic Catalytic System for the Efficient Synthesis of Biobased Poly(Isosorbide Carbonate)

Biobased poly(isosorbide carbonate) (PIC) has received wide attention due to its excellent performance and biomass feedstocks. Herein, PICs were synthesized from isosorbide (ISB) and diphenyl carbonate (DPC) by melt polycondensation. Several alkali metal catalysts and a basic ionic liquid were screened to synthesize PICs with high conversions of DPC and high molar mass. The combination of LiCl and tetramethylammonium acetate ([TMA][Ac]) exhibited excellent catalytic performance and reduced the reactivity difference between endo-hydroxyl (endo-OH) and exo-hydroxyl (exo-OH) group of ISB. PIC with a high intrinsic viscosity of 0.55 dL/g and glass transition temperature of 171 °C was obtained with the total catalyst amount of 500 ppm (based on ISB). A possible transesterification mechanism referring to the synergetic effects of cation–anion interaction and hydrogen bonding was proposed based on the nuclear magnetic resonance analyses and density functional theory calculations. It is expected that these results can provide guidance for the industrial catalyst design of biobased PICs.