Combining Microwave-Assisted Foaming and Post Curing Process to Prepare Lightweight Flexible Polyimide Foams for Thermal Insulation Applications

Lightweight flexible polyimide foams (PIFs) with different rigid-flexible molecular structure networks are prepared by microwave-assisted foaming of polyester ammonium salt (PEAS) precursor powders, followed by post curing process to complete final imidization. The optimum foaming temperatures of PEAS precursors range from 85 to 135 °C, and the melting rate of PEAS is adjusted to meet the volatile releasing rate to fabricate PIFs. Results show that PIFs with nearly fully open cell rate (99.99%), micron pore sizes (400–500 µm), and micro/nano multiscale structures exhibit excellent mechanical flexibility and elasticity. The prepared PIFs demonstrate exceptional thermal stability and heat resistance in both dynamic and static environments. The PIFs possess low thermal conductivity and superior thermal insulation properties that demonstrate potential applications in high-tech fields such as aerospace, marine use, and microelectronics among others.