Integrated Design of Flame Retardancy and Toughening for Bismaleimide Resins Based on Reactive Linear Polyphosphazene

A maleimide-functional linear polyphosphazene (PHMP) was developed to address the challenge of achieving simultaneous toughening and flame retardancy in bismaleimide (BMI) resins. PHMP was introduced into the diallyl bisphenol A / 4,4'-bismaleimidodiphenylmethane (DBA/BDM) resin system to achieve integrated regulation of flame retardancy, smoke suppression, and toughening. Owing to its reactive side groups and phosphorus-nitrogen backbone, PHMP can participate in the curing network while imparting flame retardancy. The results show that PHMP significantly improves the mechanical and fire-safety performance of the resin while maintaining good heat resistance. With the addition of only 4% (mass fraction) PHMP, the impact strength of the modified resin increases by 124.6% compared to that of DBA/BDM resin, while the total heat release and total smoke production decrease by 41.0% and 32.1%, respectively. Moreover, the limiting oxygen index reaches 35.5% and the material achieves a UL-94 V-0 rating. This study provides a new strategy for the multi-functional integrated modification of BMI resins.