Direct synthesis of polycarbonate diols from atmospheric flow CO2 and diols without using dehydrating agents†
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%).