Synthesis of bio-based polycarbonate via one-step melt polycondensation of isosorbide and dimethyl carbonate by dual site-functionalized ionic liquid catalysts

Abstract

The synthesis of green products using renewable bio-monomers has become a research trend with the requirement of sustainable development. In this work, we reported a green pathway to synthesize poly(isosorbide carbonate) (PIC) via one-step melt polycondensation of biomass-derived isosorbide (ISB) and CO₂-derived dimethyl carbonate (DMC) catalyzed by eco-friendly dual site-functionalized ionic liquids; a series of these catalysts were synthesized for the first time to the best of our knowledge and their effects on the molecular weight and terminal groups of PIC were systematically investigated. The results showed that the steric structure of cations and anions of catalysts could significantly influence their catalytic performance in polymer synthesis reactions. Meanwhile, it was found that the ability of catalysts to activate the reaction substrate gradually increased with decreasing steric hindrance of cations and anions. Among our exploited ionic liquid catalysts, the selectivity of carboxymethylated products was increased significantly by using bis-tetraethylammonium hydroquinone ([N₂₂₂₂]₂ [HQ]), and a PIC with a weight average molecular weight (M_w) of 53 600 along with an ISB conversion up to 99.0% was obtained. As far as we know, the catalyst of [N₂₂₂₂]₂ [HQ] was the most efficient catalyst for PIC one-step synthesis compared with the existing traditional ionic liquid catalysts. Besides, according to the detected intermediates of the reaction process and the results of various analytical means, a possible mechanism for the synergetic catalysis of cations–anions promoting the chain growth was proposed.