Toward Repairable, Recyclable, Strong, and Flame-Retardant Poly(urethane–urea) Cross-Linked via Dynamic Diels–Alder Reaction

Designing multifunctional polyurethane or polyurea elastomers that are simultaneously strong, recyclable, flame-retardant, and sustainable remains a major challenge in advanced elastomer research. Herein, a phosphorus-containing biobased diol (HMF–DOPO) was synthesized by the reaction between 5-hydroxymethylfurfural (HMF) and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO). Then, the tough, repairable, recyclable, and flame-retardant poly(urethane–urea) (PUA) elastomers cross-linked via reversible Diels–Alder (DA) bonds were developed. The synthesized elastomers exhibited excellent mechanical properties, while PUA–HMF-20% showed the best performance with a high tensile strength of 51.9 MPa and notable toughness of 167.6 MJ m –3 . The thermally reversible DA reaction endowed PUA materials with excellent repair and recycling properties. The cut pieces can be reformed into a complete film during hot pressing and solvent reprocessing. Due to the existence of the phosphorus-containing structure, PUA–HMF elastomers also exhibited excellent self-extinguishing capability, while PUA–HMF-40% showed the highest limiting oxygen index (LOI) value of 27% and reached a V-0 rating in the UL-94 vertical burning test. In the cone test, both the peak heat release rate (PHRR) and total heat release (THR) values of the PUA–HMF samples were significantly reduced. This work provides a promising strategy to expedite high-performance sustainable advanced elastomers and expand the industrial application.