Green synthesis of isosorbide-based polycarbonate via dimethyl carbonate by dual imidazolate ionic liquid catalyst

Abstract

Addressing the increased demand for the development of bio-based polymers from renewable resources, a pathway for synthesizing poly(isosorbide carbonate) (PIC) via melt polycondensation catalyzed by ionic liquid (IL) was proposed from CO₂-based dimethyl carbonate (DMC) and bio-based isosorbide (ISB) as reactants. 1-Ethyl-3-methylimidazolium imidazolate ([Emim][Im]) with imidazole acted as both an anion and a cation was designed and the highest activity with an ISB conversion of 98 % and PIC molecular weight of 52600 g·mol⁻¹ was achieved for the PIC synthesis compared to other catalysts with single imidazole cation or anion. High catalytic activity of [Emim][Im] can be attributed to its exceptionally high cationic electrostatic potential (+53.05 kcal/mol) and remarkably low anionic electrostatic potential (−76.12 kcal/mol), which collectively result in the strongest relative electrophilicity and nucleophilicity. Furthermore, the reduced electrostatic complementarity weakens the ion-pair interactions between the cation and anion, thereby enhancing the accessibility of active sites during the catalytic process. This process will promote the sustainable production of bio-based polymers.