Terpolymerization of Propylene Oxide, CO₂, and <i>p</i>-Toluenesulfonyl Isocyanate for the Synthesis of Poly(urethane-carbonate): <i>p</i>-Toluenesulfonyl Isocyanate Acts as a Backbiting Suppressor

Terpolymerization of propylene oxide, CO2, and p-toluenesulfonyl isocyanate (TsNCO) was catalyzed by bifunctional AlIII porphyrin catalysts to afford polyurethane-poly(propylene carbonate), PU-PPC, with high CO2 contents of up to 39 wt %. TsNCO acted as a backbiting suppressor at the initial stage of the terpolymerization, contributing to the selective formation of PU-PPC. In contrast to the high electrophilicity of TsNCO, the carbamate anion generated by the reaction of TsNCO with the alkoxide intermediate has modest nucleophilicity owing to the tosyl group, which allows for the smooth formation of the PU units and the subsequent elongation of the PPC units on the catalyst to selectively produce PU-PPC. Terpolymers having the PU and PPC units in a 1:1 ratio had glass transition temperature (Tg) of 86–104 °C, while those with higher PPC contents had Tg values of 39–40 °C. Block copolymer PU-b-PPC, which was synthesized in a one-pot two-step manner, showed two Tg values at 45 and 76 °C. Pure PU showed 10% weight loss temperature (Td10) at 230 °C, while PU-PPC with high PPC contents showed Td10 at 236–254 °C. They were degradable upon UV light irradiation and heat treatment, while they were resistant to acid. The terpolymerization strategy using TsNCO as a backbiting suppressor potentially enables one to create CO2-based polymers such as plastics and elastomers with degradability controlled by UV light or heat.