Lightweight Copolymerized Polyimide Foams Containing Trifluoromethyl and Siloxane Moieties for Thermal Insulation and Hydrophobic Applications

Lightweight porous materials with integrated cushioning and shock absorption, excellent thermal insulation, and hydrophobicity demonstrate a broad application prospect in high-end engineering sectors. Herein, the fabrication of lightweight polyimide foams (PIFs) containing trifluoromethyl and siloxane moieties was proposed by adopting copolymerization and microwave-assisted foaming processes. The synthesis and preparation of fluorine- and silicon-containing polyester ammonium salt (PEAS) precursor powders and subsequent PIFs, as well as the relationship and mechanism between structure and properties, were systematically explored. The construction of the anisotropic pore structure was attributed to the "bottom-up" directional foaming behavior of the microwave-assisted foaming process, which endowed PIFs with different traits with respect to the pore growth direction. The resulting copolymerized PIFs displayed low density (18.3-27.7 kg/m³), enhanced mechanical flexibility (compressive strength improvement of 26.2%, compression response rate between 97.5 and 99.1%), excellent thermal stability (<i>T</i>_5% > 485.2 °C), and thermal insulation performance. Combining the micro/nano pore structure with the presence of hydrophobic trifluoromethyl and siloxane moieties, PIFs exhibited exceptional hydrophobicity with the water contact angle, reaching as high as 145.9° in the vertical direction (parallel to pore growth direction) and 136.3° in the horizontal direction (perpendicular to pore growth direction). Therefore, lightweight, mechanically flexible, thermally insulating, and hydrophobic PIFs were successfully prepared by the proposed approach, which demonstrate potential applications in the aerospace, transportation, microelectronics, and nuclear energy sectors, among others.