Molecular design and properties of a P‐N synergistic flame retardant epoxy resin curing agent

The utilization of epoxy resin (EP) is widespread across various industries. Nevertheless, its combustibility restricts its broader utilization. Additive flame retardants have proven effective in enhancing EP flame retardancy in recent decades. However, poor weather and aging resistance have always been the defects of added flame retardants. A reactive flame retardant (VPD) was synthesized from 3, 5‐diamino‐1, 2, 4‐triazole and phenylphosphonic dichloride, and was used to prepare VPD/EP flame retardant epoxy thermosets. The mechanical properties of the VPD/EP flame retardant epoxy thermosets are lower than those of pure epoxy, because the distance between molecules of VPD is increased compared with that of DDM, the cross‐linking density of the polymer after curing is decreased, and the intermolecular force is reduced. The VPD/EP flame retardant epoxy thermosets have a 40% reduction in total heat release compared to pure EP, an increase in limiting oxygen index value from 24.7% (pure EP) to 29.4%, and a V‐1 rating in UL‐94 testing. The obtained EP has not only good flame retardancy but also better weather resistance and aging resistance than additive flame retardants. Highlights An intrinsic flame‐retardant P and N coacting EP was designed and synthesized. The intrinsic flame‐retardant EP has excellent weather and aging resistance. The presence of the P, the residual char generated by combustion is denser. Schematic diagram of synthesis and flame retardant mechanism of EP containing P and N.