‘Rigid-flexible hybrid’ epoxy resin with superior curing performance, fire safety, and toughness

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The rapid advancement of aerospace, electronics, and electrical industries has imposed increasingly stringent requirements on the fire safety and mechanical properties of epoxy (EP) resins. However, traditional additive flame retardants suffer from low efficiency, and their excessive incorporation often leads to deterioration in the mechanical properties of EP. Therefore, the development of intrinsically flame-retardant EP has emerged as an important research direction. Herein, a flame-retardant co-curing agent, N-(2-(bis(2-aminoethyl)amino)ethyl)-P, P-diphenylphosphinic amide (BADP), was synthesized and introduced into the EP matrix to construct a “rigid-flexible hybrid” crosslinking network. When the phosphorus content was only 0.6wt.%, the resultant EP sample (EPBP4) achieved a vertical burning (UL-94) V-0 rating with a limiting oxygen index of 36.3%. Compared with pure EP, the peak heat release rate and total heat release of EPBP4 declined by 43.3% and 24.9%, respectively. These results demonstrate a significant enhancement in fire safety performance, which can be attributed to the char‑forming promotion effect of BADP. In addition, EPBP4 exhibited 113.0% and 34.7% improvements in impact strength and flexural strength, owing to the construction of a ‘rigid-flexible hybrid’ network. Overall, EPBP4 achieved an excellent balance between flame retardancy and mechanical properties, demonstrating strong potential for applications in electrical and electronic, aerospace, and other emerging advanced industries.