Cost-Effective Synthesis of High Molecular Weight Biobased Polycarbonate via Melt Polymerization of Isosorbide and Dimethyl Carbonate

Green synthesis of poly(isosorbide carbonate) (PIC) with remarkable properties is a huge challenge in industrial applications due to low molecular weight and harsh reaction conditions. We reported a novel pathway to synthesize high molecular weight PIC through melt polymerization of isosorbide (ISB) and dimethyl carbonate (DMC), which are derived from the biomass and CO2, respectively. The effects of metal ion-containing compound catalyst on chemical structures, terminal groups, and molecular weight of PIC in the process of melt polycondensation were studied. Compared with the best reported catalyst lithium acetylacetonate, the weight-average molecular weight (M-w) of PIC was increased by using our preferred catalyst sodium tert-butoxide from 46 500 to 55 100 with the ISB conversion up to 99.0%, and the reaction time was decreased from 12 h to only 2.5 h, as far as we know, which is the highest M-w value and the most efficient catalyst achieved by one-step method. According to the results of the experiment and simulation, we found that high catalytic performance was ascribed to the weak interaction energy of anion-cation of catalyst and the strong proton acceptance ability of the anion of the catalyst. Meanwhile, increasing the interaction energy of anion-cation of the catalyst could inhibit the occurrence of the methylation side reaction and interestingly the activated endohydroxyl groups of ISB were found to be more easily methylated. Finally, based on the captured and detected intermediates of the two-stages of the reaction, a possible mechanim for the synergetic effects of cation-anion through hydrogen bond formation was proposed.