Direct synthesis of polycarbonate diols from atmospheric flow CO2 and diols without using dehydrating agents

Abstract

Polymer synthesis with CO₂ as a C1 chemical has attracted much attention from the viewpoint of green chemistry. The direct transformation of CO₂ and diols into polycarbonate diols is promising as an alternative method to the hazardous phosgene process, however, challenging due to the inert characteristic of CO₂ and thermodynamic limitation. Herein, we present the direct synthesis of polycarbonate diols from atmospheric pressure CO₂ and α,ω-diols using a heterogeneous CeO₂ catalyst and a CO₂ flow semi-batch reactor. The target alternating polycarbonate diol from CO₂ and 1,6-hexanediol was obtained with high yield (92%) and selectivity (97%) without using any dehydrating agents. Activation of atmospheric pressure CO₂ by a CeO₂ catalyst and the shift of equilibrium towards the product by removing the coproduced water (gas stripping) are responsible for the high yield. The flow reaction system with a CeO₂ catalyst was applicable to the reactions of CO₂ and primary mono-alcohols or 1,2-diols, giving the target organic carbonates in high selectivity (>99%).