Fabrication of rigid polyimide foams with overall enhancement of thermal and mechanical properties

Polyimide (PI) foams have been developed for decades and widely used as thermal insulation materials. However, the limited mechanical and thermal properties continually being a serious problem that restrict their further applications. In this study, a series of rigid PI foams with excellent mechanical and thermal performance were fabricated by the reaction of benzophenone-3,3',4,4'-tetracarboxylic dianhydride (BTDA) with two diamines of 2–(4-aminophenyl)-5-aminobenzimidazole (BIA) and 4,4'-diaminodiphenyl ether (ODA) with various molar ratios, and the cis-5-norbornene-endo-2,3-dicarbox-ylic acid (NA) was introduced as end-capping and foaming agent. The results demonstrate that the foaming degree decreases with increasing the BIA molar ratio in the polymer chains owing to the elevated melt viscosity of precursor. Furthermore, the prepared rigid PI foams exhibit excellent thermal and mechanical properties. When the BIA contend up to 40 mol%, the glass transition temperature (T_g) and the temperature at 10% of weight loss (T_d ^10%) of PI foam increased ∼80°C and ∼35°C in comparison with the pristine PI-0, respectively. In addition, the compressive strength and modulus at 10% strain of PI-4 reached to 5.48 MPa and 23.8 MPa, respectively. For the above-mentioned advantages, the prepared rigid PI foams are promising candidates as thermal insulation and structure support composite materials in the aerospace and aviation industries.