In Situ Polyimide Modified Polymethylsilsesquioxane Aerogels for Thermal Insulation

The inherent brittleness of silica aerogels severely limits their practical application in thermal protection. To address this issue, polymethylsilsesquioxane (PMSQ) wet gels were fabricated via an aqueous sol–gel method, and polyimide (PI) was introduced through in situ polymerization to construct an inorganic–organic continuous framework with PI in situ bridging and interfacial coating, thus successfully preparing the Si/PI composite aerogel. This composite achieves synergistic enhancements in mechanical, thermal insulation, hydrophobic and flame-retardant properties. The flexible PI network effectively alleviates stress concentration, and the compressive modulus of the composite aerogels increased with the PI content, reaching 7.52 MPa for Si/PI-80 and 23.78 MPa for Si/PI-100. The thermal conductivity stays below 0.036 W·m−1·K−1 with favorable low thermal conduction stability. The Si–CH3 groups in PMSQ provide excellent hydrophobicity with a maximum water contact angle of 145.6°. Meanwhile, the char-forming effect of PI at high temperatures counteracts the negative impact of methyl groups on flame retardancy, endowing the aerogel with self-extinguishing behavior and high thermal stability. This work offers a novel strategy for designing high-strength multifunctional silica-based aerogels, which exhibit promising application prospects in aerospace, building energy conservation and high-end thermal protection.