Dynamic decrosslinking enables self-healing, reprocessability, and upcycling in polyurethane networks.

Thermosetting polymers are widely used for their high mechanical performance and long-term structural reliability, but their permanent crosslinked networks prevent reprocessing and recycling, leading to persistent environmental challenges. Existing dynamic covalent and supramolecular strategies offer partial solutions, yet often suffer from performance loss after repeated recycling due to incomplete reversibility and the accumulation of defects. Here, we present a strategy for the decrosslinking and upcycling of post-service thermosets based on a dynamic polyurethane network containing hindered urea bonds (HUBs). The elastic network exhibits high mechanical strength, self-healing, and thermal reprocessability. Upon exposure to small-molecule amines, the HUBs undergo exchange reactions that enable controlled network disassembly, allowing the thermosets to be transformed into reprocessable thermoplastics. The decrosslinked derivatives facilitate high-value composites-toughening glass fiber matrices by 229% through interfacial reinforcement and achieving commercial-grade electromagnetic shielding (28.1 dB) via optimized carbon nanotube integration. This molecularly engineered decrosslinking-upcycling paradigm establishes a viable pathway for circular thermoset utilization, advancing sustainable polymer technologies.