Synergistic Flame Retardancy and Mechanical Enhancement of Vinyl Ester Resin via Chemically Bonded <scp>ADOTP</scp> and Carbon Fiber Reinforcement

ABSTRACT This study proposes a chemical bonding strategy to integrate bifunctional phosphorus‐based flame retardant a difunctional 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide derivative (ADOTP) into vinyl ester resin (VER), addressing migration issues of conventional flame retardants. Synergistic effects of ADOTP on flame retardancy and mechanical properties in VER (ADOTP‐VER) and carbon fiber‐reinforced composites (ADOTP‐VER/CF) are investigated. At 15 phr (parts per hundred resin), ADOTP boosts VER's limiting oxygen index (LOI) from 20.0% to 30.5%, with 20/25 phr formulations achieving UL94 V‐1 (Underwriters Laboratories Standard 94 vertical burning test rating V‐1). Cone calorimetry shows 25ADOTP‐VER reduces peak heat release rate (PHRR) by 57.3% and fire growth rate (FIGRA) by 28.0%, via gas‐phase radical quenching and condensed‐phase char reinforcement. In ADOTP‐VER/CF, LOI reaches 59.0% at 25 parts per hundred resin (phr), but fiber wicking and char layer fracturing cause UL94 failure. Thermogravimetric analysis confirms “sacrificial protection” with char residue increasing from 0.1% to 6.1%. Mechanically, ADOTP enhances the flexural and tensile modulus of ADOTP‐VER by 14.3% via crosslink densification, while carbon fibers counteract matrix brittleness through stress transfer and crack bridging, increasing flexural strength by 10.2% (from 1278.9 to 1410.0 MPa) and maintaining interlaminar shear strength (ILSS) above 75.0 MPa, confirming the stability of the fiber‐resin interfaces. This study establishes ADOTP as a dual‐function crosslinker/flame retardant, offering a multi‐scale strategy for fire‐safe, high‐performance VER composites in marine/new energy applications.