Synthesis of a P/N/B‐Containing Halogen‐Free Modifier for High‐Efficiency Flame Retardancy, Reinforcement and Toughening of Epoxy Thermosets

ABSTRACT Although epoxy resins (EP) have been widely used in many fields, performing halogen‐free flame‐retardant modification on them while improving their mechanical properties still holds significant research value. Herein, a halogen‐free P/N/B‐containing modifier (DVB) was synthesized via mild nucleophilic substitution, esterification, and Schiff base reactions using diphenylphosphinyl chloride, vanilline, phenylboronic acid, and 3‐amino‐1,2‐propanediol as precursors. Its efficacy on bisphenol A epoxy resin/4,4′‐diaminodiphenylmethane thermosets was systematically evaluated, with comparisons to a phosphorus‐only intermediate (DV). At 3 wt% DVB loading (0.18 wt% P content), the modified EP exhibited a limiting oxygen index of 28.5% and achieved UL‐94 V‐0 classification. Relative to pristine EP, EP/5% DVB demonstrated a reduction of 41.8% in peak heat release rate, 27.7% in total heat release, and 30.0% in total smoke production, outperforming EP/5% DV (17.8%, 15.8%, and 12.2% reductions, respectively). Furthermore, EP/DVB thermosets displayed maximal improvements of 37.0% in flexural strength and 59.4% in impact strength, coupled with a glass transition temperature retention rate of 98%. Collectively, DVB presents considerable application potential for synergistically enhancing the flame retardancy and mechanical performance of epoxy resins.