Photo-enhanced Dual-Functional Polyurethane: Balancing Flame Retardancy with Improved Mechanical and Self-Healing Properties

Polyurethane (PU) holds significant promise for industrial applications, such as electronic encapsulation and aerospace, where a combination of safety (flame retardancy and mechanical strength) and long-term durability (self-healing capability) is paramount. However, the integration of traditional flame retardants often compromises the mechanical integrity of the polymer. In this study, a phosphorus–nitrogen diol chain extender (DPDF) was synthesized as a flame retardant, which was strategically incorporated together with a UV-responsive coumarin-based chain extender (HNA) into a polyurethane backbone to form a series of dual-responsive elastomers (DPHx-PU). Accordingly, the flame retardancy of DPH1/1-PU was significantly enhanced, with a limiting oxygen index (LOI) of 29.2% and an improved UL-94 rating of V-1 compared to the samples without the flame retardant, with the LOI at 23.6% and the fire rating at V-2. Cone calorimetry tests confirmed a substantial reduction in heat release and smoke production rates. Besides, after irradiation with 365 nm UV light, the tensile strength of DPH1/1-PU significantly increased by 30.2% to 26.7 MPa, effectively compensating for the typical mechanical degradation associated with flame-retardant additives. Furthermore, the dynamic cross-links from the coumarin motifs endowed the material with promising self-healing capabilities. This work provides a viable strategy for developing high-performance PU elastomers that successfully integrate superior flame retardancy, robust and tunable mechanical properties, and additional multifunctionality. This innovative approach paves the way for developing next-generation high-performance PUs that simultaneously meet rigorous safety and durability demands for advanced industrial applications.