Direct Synthesis of Polycarbonate Diols with Tunable Molecular Weights from Atmospheric Flow CO ₂ and Diols

The synthesis of polycarbonates with various molecular weights, which are effective as precursors for producing functional plastics and polyurethanes, is essential to meet diverse applications. In our previous work, we have reported the direct synthesis of polycarbonate diols from atmospheric flow CO2 and diols over CeO2 without dehydrating agents, where the average molecular weight of polycarbonate diols is around 3500 g mol–1. In this study, we synthesize polycarbonates from CO2 and 1,6-hexanediol with molecular weights of up to 7700 g mol–1. The molecular weights are tunable within 1500–5500 g mol–1 by controlling the reaction solvent systems, such as the solvent types, ratios, and amounts. Low water affinity of solvents and high 1,6-hexanediol concentrations are preferable for a high reaction rate, whereas their impact on molecular weight variation remains marginal. The effect of solvents on the molecular weight becomes pronounced when the solvent amounts are reduced, where evaporation of 1,6-hexanediol is facilitated to result in water elimination, thereby enhancing the conversion of 1,6-hexanediol and accelerating the polycarbonate chain growth.