Advancements in the Development of Polyimide-Based Aerogels for Extreme Thermal Environments: A Critical Review

Polyimide-based aerogels are being considered as one of the most promising classes of advanced porous materials for extreme thermal environments, owing to their ultralow density, high porosity, tunable mechanical strength, and excellent thermal stability. In recent years, significant progress has been made in understanding how monomer selection, cross-linking strategy, solvent interactions, and drying methods govern the structural development and extreme-temperature performance of these aerogels. This Review systematically examines the design principles of high-temperature polyimide aerogels, emphasizing strategies to overcome critical challenges such as thermal shrinkage, structural collapse, brittleness, and limited scalability. Particular attention is given to the role of rigid and flexible diamine and dianhydride combinations, bulky substituents, cross-linkers, nanofillers, and fiber reinforcements in enhancing dimensional stability and maintaining pore structure under prolonged thermal aging. The impacts of solvent polarity, percentage solid content, and drying conditions on the microstructure development and shrinkage control are also highlighted. Emerging insights into isothermal aging, long-term thermal degradation mechanisms, and high-temperature mechanical behavior reveal the strong potential of these aerogels for aerospace, aviation, energy, electrical insulation, and other demanding applications. By incorporating current advancements with unresolved research gaps, this Review outlines a forward-looking perspective for developing next-generation polyimide aerogels with superior processability, structural integrity, and multifunctional performance for extreme hot operating conditions.