Fabrication of rigid polyimide foams via thermal foaming of nadimide-end-capped polyester-amine precursor

This work provides a method for fabricating rigid polyimide foams via thermal foaming method of nadimide-end-capped polyester-amine oligomer (NPEAO) precursor particles, which were synthesized by reaction of benzophenone-3,3′,4,4′-tetracarboxylic dianhydride and cis-5-norbornene-endo-2,3-dicarboxylic anhydride (NA) with different diamines. The foaming mechanism of the rigid PI foams was systematically investigated. The experiment demonstrates that the pre-treatment of the NPEAO precursor particles and foaming temperature are two pivotal factors that determine the foaming processes. The densities of the prepared rigid PI foams are mainly in the range of 40–200 kg m⁻³. Moreover, the density and morphology of the PI foams can be effectively controlled by adjusting these two factors. Besides, the obtained rigid PI foams present excellent mechanical and thermal properties, specifically, the flexural and compressive strength reaches as high as to 1.42 MPa and 0.47 MPa, respectively, with the density of 0.076 g cm⁻³, which are superior to common PI foams and aerogels that of reported in the literature. Therefore, these superior mechanical and thermal properties make obtained rigid PI foams promising candidates as structural materials in the advanced manufacturing industry.