Environmentally benign metal catalyst for the ring-opening copolymerization of epoxide and CO2: state-of-the-art, opportunities, and challenges

Abstract

Carbon dioxide (CO2) is the main greenhouse gas, whereas it is also a nontoxic, abundant, cheap carbon and oxygen resource. The copolymerization of CO2 with epoxide presents a sustainable approach to the synthesis of biodegradable polymers, which upcycles the waste into wealth. Metal complex catalyst plays the central role in the reaction, since it provides oxophilic and Lewis acidic active center both for monomer activation and chain end stabilization, and nucleophiles as Lewis base for initiation. However, heavy metal catalyst with certain toxicity such as cobalt undisputedly dominates the copolymerization catalysis which comprises the overall sustainability. To circumvent the potential environmental hazard, developing highly active catalyst composed of green metals is of great importance especially when the polymer was utilized for agriculture purpose. This work reviews the development of sustainable metal catalysts for the production of CO2 copolymer, centered by Al, Mg, Ti, Fe, generally acknowledged as low toxic, environmentally benign, biocompatible, and also abundant in earth's crust. Emphasis is placed in recent five years where several historic examples are also included to construct a full picture of the sustainable catalysis explored to date.