Integrating Flame Retardancy and Recyclability through Molecularly Synergistic Design: Dual-Dynamic Thermosetting Polymers Based on Diels–Alder Chemistry

The structural design of phosphorus-containing moieties and the construction of covalent adaptable networks (CANs) have emerged as effective strategies for simultaneously addressing the challenges of flame retardancy and recyclability in thermosetting polymers. Different from conventional curing approaches, this work reports an in situ integrated dual-dynamic network design strategy. Initially, furfurylamine (diene) was employed to chain-extend epoxy resin, yielding a furan-terminated linear prepolymer; then, a phosphorus-containing bismaleimide (dienophile) was introduced as a DA cross-linker to construct the three-dimensional network. The resulting resin subsequently exhibited excellent flame retardancy, achieving a 40.9% reduction in the peak heat release rate compared to the pristine sample. Moreover, the dual-dynamic network endowed the material with favorable dynamic responsiveness, enabling distinct thermal healing behavior under mild conditions without external force and retaining 88.9% of its mechanical properties after thermomechanical reprocessing. Furthermore, adhesives prepared by coating this resin onto various substrates maintained over 80% of their original adhesion strength after multiple debonding-rebonding cycles, demonstrating the potential for application in reversible and thermally responsive adhesives. Overall, this design approach provides a feasible pathway to achieve integrated performance for multifunctional materials in practical applications.