Fabrication of Rigid Polyimide Foams with Superior Compressive Properties

Rigid polyimide foams (PIFs) with excellent compressive and thermal properties were fabricated by thermal foaming of polyester ammonium salts (PEAS) precursors which were terminated by 5-norbornene-2,3-dicarboxylic anhydride (NA). The melt viscosities of PEAS precursors were found essential to obtaining PIFs with high closed cell ratios and improved interactions between foam cells, which were indispensable to improving mechanical properties. The room temperature compressive strength and compressive modulus of PIF (density: 146.3 kg m–3) with four repeating units reached 1.55 and 23.3 MPa, which were 7 and 9 times higher than that of PIF-∞ (230.9 kg m–3), respectively. Furthermore, the room temperature compressive strength of PIFs with foam densities of 358.3 kg m–3 reached 9.79 MPa. The PIFs demonstrated outstanding thermal properties with initial thermal degradation and glass transition temperatures higher than 450 and 290 °C, respectively. The thermal conductivities of PIFs fell in a range of 0.071–0.073 W m–1 K–1, which showed promising applications in the fields of aerospace, aeronautics, and marine use as high temperature-resistant structural materials.