Chemical Synthesis of CO2-Based Polymers with Enhanced Thermal Stability and Unexpected Recyclability from Biosourced Monomers

The development of completely recyclable polymers has become an emerging frontier in polymer chemistry; however, the efficient synthesis of monomers or/and polymers with desirable physical properties and mechanical strengths required for practical uses from renewable feedstocks under environmentally friendly conditions still represents a challenge. Herein, we report five types of completely recyclable polycarbonates made from CO2 and biosourced epoxide featuring different substituents on the carbamate group. It is discovered that the judicious installation of various alkyl substituents can drastically enhance the thermal stability and crystalline capacity of the resultant polymers, while the stable five-membered pyrrolidine ring can execute the complete chemical recyclability. For example, CO2-based polycarbonates with a tBu substituent feature with a Tg value of up to 152 °C, close to those of the BPA-based polycarbonates and iBu-substituted CO2 polycarbonates are thermally stable up to ∼300 °C, while Me- and Bn-substituted copolymers become crystalline. Remarkably, all of the reported CO2-based polycarbonates can be recycled back into the epoxide monomers in quantitative yields under mild conditions. This represents a rare example of a CO2-based polycarbonate featuring biosourced characteristics and unique recyclability.