Engineering Phosphorus–Iron Coordination Complexes for Simultaneously Fire‐Retardant and Enhanced Epoxy Resins

ABSTRACT FD is prepared by an aqueous coordination reaction between 10‐hydroxy‐9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPA) and iron sulfate, with deionized water as the solvent in the coordination step. The comprehensive characterization demonstrates the formation of FD and a uniform distribution of elements. Incorporating merely 5 wt.% FD into epoxy resin enables exceptional flame retardancy, achieving UL‐94 V‐0 classification and 33% limiting oxygen index (LOI). Cone calorimetry analysis demonstrates remarkable fire hazard suppression: 31.5% reduction in peak heat release rate, 19.6% decrease in total heat release, and 17.8% reduction in total smoke production. The addition of FD promotes formation of a coherent, graphitized char layer that effectively restricts heat/mass transfer while maintaining mechanical performance. This green strategy provides a sustainable pathway for high‐performance epoxy composites balancing fire safety and mechanical integrity.