High Performance Polyimide Composites with 3D Boron Nitride Networks

Efficient thermal management is a critical challenge for high-power-density electronics, particularly in the aerospace sector. This work presents a hierarchical composite film with exceptional thermal conductivity and robust electrical insulation, fabricated by hot-pressing electrospun boron nitride-polyimide (BN/PI) papers with a BN-rich bismaleimide (BMI) adhesive. This unique multilayer architecture establishes a three-dimensional (3D) BN network, where the BN-enriched adhesive layers serve as thermal bridges to minimize interfacial thermal resistance. Consequently, the composite film achieves a high through-plane thermal conductivity of 7.62 W/(m·K), a 38.1-fold enhancement compared to pure PI, while maintaining an excellent breakdown strength of 204.7 kV/mm and low dielectric loss (<0.02). The enhanced electrical insulation is attributed to the strong Maxwell–Wagner–Sillars (MWS) interfacial polarization at the heterogeneous PI/BN-BMI interfaces, which homogenizes the electric field and suppresses charge transport. The scalable design strategy proposed in this study achieves a synergistic improvement in thermal conductivity and insulation and offers a promising material solution for advanced thermal management in next-generation aerospace systems.