Constructing a Salen‐Polyphosphazene/Organically Modified <scp>LDH</scp> Hybrid for Flame‐Retardant Epoxy Resins

ABSTRACT Epoxy resin (EP) is widely used in aerospace, electronics, and coatings because of its excellent mechanical properties, chemical resistance, and electrical insulation. However, its inherent flammability severely limits its broader applications. Layered double hydroxides (LDHs) have garnered significant attention in flame‐retardant research due to their controllability of interlayer cations and the exchangeability of interlayer anions. Despite their promise, the flame‐retardant effect of pure LDHs, which are purely inorganic compounds, remains insufficient for many applications. In this study, DOPO‐derived phosphate species were synthesized by reacting DOPO with hydroxyethyl acrylate and phosphorus oxychloride, and subsequently used to modify LDHs. The modified LDHs were then compounded with Salen‐based polyphosphazene microspheres to create a novel flame retardant designed to further improve the flame‐retardant performance of EP composites. Experimental results demonstrate that the addition of just 5% of the flame retardant allows the EP composite to achieve a UL‐94 V‐0 rating, with a limiting oxygen index (LOI) of 29.1%, a peak heat release rate (PHRR) reduced to 188.82 W/g, and a total heat release (THR) reduced to 22.69 kJ/g, indicating a significant enhancement in flame retardancy.