Synergistic Effects of Boron‐Based Derivatives via Triple Char‐Forming Effects: Simultaneously Conferring High Flame Retardancy and Mechanical Toughening to Epoxy Resins

To overcome the flammability, poor charring, and brittleness of epoxy resin (EP), a flame‐retardant additive, BPD, was synthesized from N‐aminoethylpiperazine, 4‐acetylphenylboronic acid, and DOPO, and then incorporated into EP to obtain EP/BPD composites. With 3 wt% BPD, the LOI increased from 25.7% to 28.3%, and the UL‐94 rating improved from NR to V‐0. At 5 wt% BPD loading, pHRR, THR, SPR, TSR, COP, and CO 2 P decreased by 39.1%, 10.2%, 42.8%, 74.3%, 30.0%, and 39.3%, respectively, versus pure EP, demonstrating excellent flame retardancy, smoke suppression, and fire safety. Moreover, 1 wt% BPD raised impact strength to 28.79 kJ/m 2 (65.9% increase), while tensile (51.98 MPa) and flexural strengths (69.78 MPa) remained nearly unchanged, achieving a synergistic balance of flame retardancy and mechanical toughness.