Hyper-Cross-Linked Polymers with Dual Functionality: Enhancing Flame Retardancy and Thermal Insulation in Epoxy Resin Composites

The development of multifunctional materials integrating superior thermal insulation and flame retardancy remains a critical challenge for energy-efficient construction. Herein, we present hyper-cross-linked polymers (HCP-X) synthesized via Friedel–Crafts alkylation using 9-bromophenanthrene (9BP) and octavinyl-T8-silsesquioxane (OVS) under anhydrous conditions. The resulting HCP-X exhibit hierarchical micro-/mesoporous structures and exceptional thermal stability, as evidenced by a residual mass of >75% at 600 °C. As HCP-X were introduced to epoxy resin (EP), the resulting HCP/EP composites demonstrate remarkable performance. Specifically, HCP/EP 20 achieves a 97.90% reduction in thermal conductivity, while HCP/EP 5.0 shows a 49.9% decrease in peak heat release rate via microscale combustion calorimetry. The synergistic flame-retardant mechanism involves (1) gas-phase inhibition through bromine-derived radicals and (2) condensed-phase char formation via the Si–O–Si framework. This work provides a scalable strategy for designing high-performance composites with dual functionality, offering significant potential for fire-safe insulation applications.