Green Polycarbonates Prepared by CO₂ and Bio-Based Epoxides

The synthesis of aliphatic polycarbonates from carbon dioxide (CO₂) not only utilizes cheap and renewable CO₂ resources, but also enables the preparation of fully biodegradable polymer materials, providing us a promising green and sustainable polymer material synthetic route. However, the researches in this field have mainly focused on the copolymerization of CO₂ with some petroleum-derived alkylene oxides (such as propylene oxide, cyclohexene oxide, etc.), and have not completely shed the dependence on petroleum resources. In 2004, Coates developed a non-petroleum route towards CO₂-based copolymer for the first time via the copolymerization of CO₂ and limonene epoxide (LO) using β-diiminate zinc complexes. Afterwards, the use of bio-based epoxides combined with CO₂ to achieve fully bio-based polymer materials has gradually turned to be a research focus in this area. The structural diversity of bio-based products and their derivatives also provides more possibilities for enriching the divercities of CO₂-based polymer family, as well as for expending the properties and the application ranges of the materials. However, due to the feature of the copolymerization of CO₂ and epoxide, the structure and the purity of epoxides are crucial to the activity and selectivity of the reaction. Many bio-based epoxides exhibit very low copolymerization activity with CO₂, or only forming cyclic carbonates. In current stage, the main bio-based monomers which can copolymerize with CO₂ include limonene epoxides, furfural-based epoxides, and vegetable oil-derived epoxides. Herein, recent advances in the copolymerization of CO₂ and bio-based epoxides are reviewed, and the future development trends in this field are also prospected.