Lightweight, Radiation-Resistant, and Flexible Polyimide Foams with an Anisotropic Porous Structure for Efficient Thermal Insulation Applications

Flexible polyimide foams (PIFs) with an anisotropic porous structure were prepared by a facile strategy, possessing exceptional mechanical robustness and thermal insulation performances. A comparison of the foaming and rheological behavior, microstructure, and mechanical and thermal and radiation-resistant properties of copolymerized and blended PIFs was conducted. Besides, the formation mechanism of the anisotropic structure and its influence on the mechanical and thermal insulation properties were explored in depth. By reasonably regulating the molecular structure, melt viscosity, melt volatile content, and foaming temperature, a favorable microscopic morphology and structure can be achieved. PIFs with regular porous near-spherical appearance and aligned ellipsoidal strip structures exhibited anisotropic mechanical performance. Meanwhile, PIFs showed anisotropic thermal insulation behavior, which possessed a minimum thermal conductivity (λ) of 0.0314 W/m·K along the pore growth direction (i.e., vertical direction) and a λ as low as 0.0279 W/m·K in the horizontal direction. The anisotropic thermal conduction behavior endowed PIFs with intelligent thermal protection and infrared stealth performance. In addition, the PIFs presented an exceptional thermal stability and compressive strength retention rate after experiencing a radiation dose of 10027.5 kGy. Therefore, a facile strategy for rapid fabrication of PIFs that can be positioned for structural design, thermal insulation, and radiation-resistant applications in high-end engineering sectors was proposed.