Enhancing mechanical, dielectric, fire-safety properties of bismaleimide and its glass fiber composites with a P–Si synergistic polysilsesquioxane (DVPOSS)

The growing demand for low-dielectric materials driven by advancements in communication technology has highlighted bismaleimide (BMI) resin and its glass fiber (GF) composites for its high-temperature resistance and low dielectric properties. However, its limited toughness and flame retardancy restrict its use in extreme environments. To overcome these challenges, we designed a cross-linkable P–Si synergistic flame-retardant (DVPOSS) to simultaneously improve the thermal stability, mechanical properties, dielectric performance, and fire safety of BMI resin and its fiber composites. In this work, DOPO was chemically incorporated into a silane coupling agent, followed by one-step co-condensation to synthesize a vinyl- and DOPO-functionalized polyhedral oligomeric silsesquioxane. Through thermal curing, DVPOSS formed a cross-linked interpenetrating network within the BMI and its GF composites. Benefiting from the hollow skeleton, ample free volume, excellent flame retardance and high chemical reactivity of DVPOSS, the BMI/DVPOSS-1.0 composite achieves optimal comprehensive properties. Specifically, its impact strength rises by 65.91% and flexural strength increases by 62.79%. Meanwhile, the dielectric constant (Dk) at 1 MHz drops to 2.64, accompanied by a 33.86% reduction in peak heat release rate (PHRR). The glass transition temperature (Tg) of BMI/DVPOSS/GF-1.0 increased by 26.96°C compared to the BMI/GF. This work offers a practical approach to balanced multifunctional performance in BMI/GF composites, enabling potential extreme-environment applications.