Solvent-Assisted CO₂ Foaming Induced Ultralarge Pore Span Hierarchically Porous Polyimide

Inspired by natural materials, constructing hierarchically porous composite materials can better meet the increasingly demanding needs of engineering materials. Currently, lightweight polyimide components commonly used in aerospace and deep-sea applications are difficult to combine with cross-scale pores due to limitations in performance stability and porogenic strategies. Finding an efficient, environmentally friendly, convenient, and highly controllable method to prepare hierarchically porous polyimide (HPPI) to utilize structural advantages for functional suitability remains a huge challenge. Here, we propose a solvent-assisted supercritical CO₂ foaming strategy to develop ultralarge pore span polyimide (ODA-ODPA). This strategy can not only realize the construction of HPPIs, but also regulate the porosities span from 15 to 75%. The HPPI mechanical parts prepared by controlling the foaming conditions can improve the oil storage and supply capacity and reduce the material quality while maintaining excellent dimensional stability thanks to the combination of micro- and nanopore. The prepared lightweight HPPI foam also shows excellent high-temperature-resistant mechanical properties. Additionally, the versatility of this strategy has been successfully demonstrated in other thermoplastic polyimide systems. This work not only provides a new method for preparing hierarchically porous materials, but also provides more possibilities for further expanding the application areas of special engineering polymers, for example, maintenance-free components for human deep space exploration and high-temperature-resistant fall buffers.