Recycling homocarbon backbone polymers toward a circular materials economy

Global plastic waste has reached a critical level, posing serious hazards to ecosystems and human health because of its persistent presence in landfills, oceans, and natural environments. Unlike heteroatom-backbone polymers, which feature a heterochain structure, homocarbon backbone polymers with nonpolar C–C backbones exhibit unprecedented durability and resistance to environmental factors, making them less prone to degradation. Consequently, the conversion of such plastic waste into valuable chemicals via chemical recycling presents a crucial solution to address the issues stemming from plastic waste. This review aims to summarize the latest developments in the closed-loop recycling and upcycling of homocarbon backbone polymers with a specific focus on the conversion of waste plastics into their original monomers and/or value-added chemicals through bio-, thermo-, and photocatalysis, which promotes a circular economy. Notably, the development of highly active catalysts and related depolymerization systems accelerates the evolution of plastic degradation and enhances product controllability, rendering the recycling of plastic waste feasible and affordable.