Phosphorus-Siloxane Allyl Compound: Enhancing Bismaleimide Resin’s Toughness, Flame Retardancy, and Hydrophobicity without Compromising Strength/Thermal Properties

Bismaleimide/2,2’-diallylbisphenol A (BD) resin, a high-performance thermosetting resin, is widely used in various fields. However, its toughness and flame retardancy still need further improvement to meet the requirements of harsher service conditions. In this study, a phosphorus-containing siloxane-based allyl compound (ADOEG) was synthesized and incorporated into the BD resin system, yielding an improved BD/ADOEG (BDAD) resin. ADOEG incorporation effectively enhanced the toughness, flame retardancy, and hydrophobicity of BD resin while retaining its strength and thermal performance. Relative to cured BD resin, cured BDAD-5% (5 wt % ADOEG) showed 77.2%, 75.6%, and 226.5% increases in impact strength, critical stress intensity factor ( K IC ), and critical strain energy release rate ( G IC ), respectively, alongside 5.2% and 32.6% higher flexural and tensile strengths. Cured BDAD resin with 1 wt % ADOEG attained UL94 V-0 classification in vertical burning tests. At 7 wt % ADOEG, the cured resin’s limiting oxygen index rose from 29.3% (neat BD) to 34.5%, with peak heat release rate, total heat release, and total smoke production reduced by 31.6%, 15.2%, and 55.2%, respectively. Cured BDAD-5% exhibited a water contact angle of 103.8°, up from 89.8° for neat BD. Additionally, the cured BDAD resin’s initial thermal decomposition temperature and glass transition temperature were barely reduced relative to neat BD. This study offers an effective strategy for enhancing BD resin performance.