Chemical closed-loop recycling of polymers realized by monomer design.

The development of modern society is closely related to polymer materials. However, the improper disposal of the polymer wastes not only squanders resources but also intensifies the environmental issues, despite that energy recovery, physical recycling and chemical recycling pathways have been developed to tackle the recycle and reuse of polymers. Among them, chemical recycling is considered as the most pivotal solution, as it can depolymerize the polymer wastes back to monomers, which then repolymerize into polymer materials. Recently, remarkable progress has been made in the development of chemically recyclable polymers through monomer design to shift "polymerization-depolymerization" equilibrium to realize the selective depolymerization of the polymers into monomers, and to achieve chemical recycling closed-loop. This article reviews the closed-loop polymers such as polyesters, polycarbonates, sulfur-containing polymers, vinyl monomer-based polymers as well as other types of polymers. Moreover, the challenges and prospects in this field are also discussed.