Accessing a Carboxyl‐Anhydride Molecular Switch‐Mediated Recyclable PECT Through Upcycling End‐of‐Use PET

Poly(ethylene terephthalate) (PET), with an annual production of exceeding 70 million tons, is mainly utilized in disposable fields and subsequently contribute to severe environmental pollution. Conventional chemical recycling, which typically involves depolymerizing polymer into monomers, is limited due to the intricate recycling process, excess using unrecyclable solvents and low polymer conversion. Inspired by protein's molecular switches, we propose a novel polymer-to-polymer recycling strategy based on polycondensation principles upcycling waste PET to high-value recyclable poly(ethylene-co-1,4-cyclohexanedimethanol terephthalate) derivatives containing molecular switches. Upon deactivating the molecular switch, an acidification reaction occurs within the system, leading to a rapid and controllable reduction in molecular weight due to the imbalance of reactive group. Conversely, activating the molecular switch triggers a ring-closing reaction that detaches acid anhydrides, bringing about equal molar ratio of groups and thereby facilitating an increase in molecular weight. By simply incorporating a molecular switch into condensation products based on melt polycondensation, closed-loop recycling capability is achieved without necessitating excessive organic solvents or complex depolymerization processes. The present study not only presents a novel pathway for end-of-use PET upcycling but also introduces an innovative concept of molecular switching for the closed-loop recyclability of condensation polymers, thereby demonstrating significant potential for large-scale implementation.