Chemical closed-loop recyclable thermosetting polymers based on dynamic covalent bonds

Conventional thermosetting plastics have faced the dilemma of non-degradability and recycling, leading to waste accumulation and a huge burden on the global environment and economy. Realizing recycling, reusing and repurposing plastics is a meaningful mileage for the development of sustainable ecological energy. Closed-loop recycling represents an emerging strategy for achieving the circular “waste-to-starting value-to-polymeric plastics” in recent years. Dynamic covalent chemistry (DCC) offers an attractive and efficient targeted design concept for closed-loop recyclable thermosetting polymers. In this review, the features and mechanisms of various DCC including Schiff bases, B–O bonds, sulfide- or selenide-based linkages, acetal linkages, etc., are discussed in the construction of recyclable polymers. Based on the reversible cleavage and reformation of dynamic covalent bonds, chemically closed-loop recyclable polymers with multi-functions have been raised and developed as promising circular materials. Furthermore, we highlight and analyze the process, conditions and mechanisms of the depolymerization of polymers and recovery of monomers, as well as the remanufacture of cycled polymer networks. Significantly, the reported closed-loop recyclable thermosetting polymers exhibit potential applications in multiple fields, while providing an advanced aspect for resolving plastic waste pollution and promoting the circularity in polymeric materials. Finally, existing challenges and opportunities such as the limited production process, high costs, harsh recycling conditions, and the maintenance of comprehensive performance of thermosetting polymers in the process of implementing the practical use are proposed and discussed.