Synthesis of isosorbide bis(methyl carbonate) by transesterification of isosorbide with dimethyl carbonate, and evidence of its usefulness as a monomer for manufacturing polycarbonates

Isosorbide bis(methyl carbonate) (IBMC) is a barely explored isosorbide derivative potentially useful as a monomer for synthesizing biobased polymers. In this paper, its synthesis by transesterification of isosorbide (IS) with dimethyl carbonate (DMC) at reflux temperature using potassium and cesium carbonates as catalysts is reported. Using a semicontinuous operation mode, a 97% yield was obtained with cesium carbonate as catalyst at a concentration of 0.2 mol% vs. IS, and a DMC/IS molar ratio of 30. Oligomerization by reaction between IS, the intermediate isosorbide mono(methyl carbonate) and IBMC is a severe competitive reaction. Oligomers formation is strongly suppressed at high molar ratios and low catalyst concentrations. Cesium carbonate leads to a lower oligomer formation than potassium carbonate which is explained by the “cesium effect”. Evidence of the usefulness of IBMC as a biobased monomer for polymer synthesis through its polycondensation with 1,4-butanediol (1,4-BDO) is provided. A poly(isosorbide-1,4-BDO carbonate) with a weight average molar mass of 1800 g/mol and a polydispersity of 1.43 is obtained in 63.4% yield using 3 mol% DBU vs. IBMC as a catalyst with an IBMC/1,4-BDO molar ratio of 1 at 130 °C.