Design of styrene-based polysilsesquioxanes (STPOSS) and its improvement in mechanical strength, dielectric properties, fire safety of bismaleimide resins and composites

Bismaleimide resin (BMI) and its fiber-reinforced composites show great promise in the field of electronic communication and aerospace, but the limitations of BMI in terms of mechanical, dielectric, and fire-safety properties limit its development in high-precision fields. The addition of glass fiber (GF) can enhance the mechanical strength of composites; however, it compromises the dielectric and fire-retardant properties of BMI materials. To address these issues, a new halogen-free and phosphorus-free styrene-based POSS (STPOSS) was designed and synthesized. Due to the internal inorganic Si-O cavity skeleton structure and external organic functional groups, STPOSS possesses high hardness, superior thermal stability, strong reactivity, and a large free volume. STPOSS significantly enhances the mechanical strength, dielectric properties, and fire safety of BMI and its fiber composites. At a 2 % loading, the impact strength and flexural strength increased by 76.15 % and 71.01 %, respectively. The dielectric constants of the BMI and its fiber composites decreased from 2.84 and 2.57 to 2.42 and 2.38, respectively. Furthermore, the total heat release (THR) of the resin was reduced from 71.97 MJ/m² to 31.11 MJ/m², corresponding to a 56.70 % reduction. Easy application of STPOSS could overcome the key limitations of BMI resin in mechanical, dielectric, and fire-safety properties, making a foundation for the wider application of bismaleimide resin.