A Phosphorus‐Nitrogen Synergistic Bio‐Based Monomer Imparts Intrinsic Flame Retardancy and Smoke Suppression to Vinyl Ester Composites

Vinyl ester resin (VER) and its composites suffer from high flammability and dense smoke emission, posing significant fire hazards. While incorporating additive flame retardants is common, it often compromises mechanical properties and processability. To address this, a novel phosphorus/nitrogen‐containing intrinsically flame‐retardant bio‐based monomer (HDBMA) was rationally designed and synthesized from vanillin through the formation of a Schiff base (CH N ) intermediate, followed by a straightforward addition of diethyl phosphite (DEP). HDBMA demonstrates excellent solubility in ethylene glycol dimethacrylate (EGDMA), enabling the convenient preparation of a cross‐linked resin (HDBMAR) and its fiberglass‐reinforced composite (GFHDBMAR). The resulting materials exhibit significantly enhanced flame retardancy and smoke suppression. HDBMAR achieves a limiting oxygen index (LOI) of 23.8% and shows 37.3% and 48.5% reductions in total heat release (THR) and total smoke production (TSP), respectively, compared to a commercial resin (VER901). More notably, GFHDBMAR attains a high LOI of 35.3%, with 25.2% lower THR and 49.2% lower TSP than a commercial composite (GFVER901). Systematic characterization reveals that the phosphorus‐nitrogen synergistic effect endows HDBMAR and GFHDBMAR with a dual‐phase flame‐retardant mechanism. This work provides a viable molecular design strategy for developing sustainable high‐performance VER composites with intrinsic fire safety.