Synthesis and degradation of terpolymers of cyclohexene oxide, cyclopentene oxide, and carbon dioxide using organoboron catalysts

Abstract

Copolymerization or terpolymerization involving carbon dioxide to form materials with excellent properties has received much attention in the context of carbon peak and carbon neutrality. Previous reports have shown that mononuclear organoboron catalysts can catalyze the copolymerization of cyclohexene oxide (CHO) with carbon dioxide but not cyclopentene oxide (CPO) with carbon dioxide, and dinuclear organoboron catalysts can catalyze the degradation of poly(cyclopentene carbonate) (PCPC) but not efficiently poly(cyclohexene carbonate) (PCHC). In this work, we first synthesize a series of terpolymers of CHO, CPO, and carbon dioxide using organoboron catalysts, achieving high conversion and selectivity (TOF_(CPO) = 18.1 h⁻¹, CPO selectivity of 95.8%, TOF_(CHO) = 114.0 h⁻¹, CHO selectivity of 99.9%). The molecular weights of these terpolymers range from 5 to 17 kg mol⁻¹, and the molecular weight distributions are all less than 1.3. Then, we investigated the properties of the terpolymers and found that these properties were intermediate between those of PCHC and PCPC (85 °C < T_g < 106 °C, T_d ≈ 300 °C). Further experiments reveal that simple blending of two polymers also promotes the degradation of PCHC. Finally, we find that the degradation of the terpolymer is superior to that of the simple blend of the two polymers. As demonstrated in our study on PCPC/PCHC, combining these two polymers into a single copolymer improves the unfavorable properties of each component and enhances the overall performance of the copolymer. This study supplements the reaction mechanisms of terpolymerization and degradation catalyzed by organoboron catalysts. This report may help improve the development of chemical recycling of plastics through the introduction of another polymer.