Investigation of the properties and structure of semi-rigid closed-cellular polyimide foams with different diamine structures

Polyimide foam (PIF) has been extensively used as structural and thermal insulation materials. Five semi-rigid PIFs with different diamine structures were fabricated by unrestricted foaming process with polyester ammonium salt (PEAS) precursor powders. All PIFs exhibited a nearly homogeneous spherical closed pore structure with an average pore size of 123–335 μm and a high closed-cell rate (87.4–95.5%). Results indicated that the molecular structure, melt viscosity and foaming temperature were important factors that affected the foaming process and pore structure. The values of 10% compression strength of PIFs at both 25 and 200 °C were in the range of 0.16–0.35 and 0.09–0.16 MPa, respectively, with PIFBTDA-MDA and PIFBTDA-DMBZ exhibiting the best mechanical performance. All PIFs exhibited outstanding thermal stability, with glass transition temperatures of 312–378 °C and 5% weight loss temperatures of 504.5–564.5 °C in nitrogen and 501.8–562.0 °C in air, respectively. The prepared PIFs exhibited extremely low thermal conductivity and thermal diffusivity, which can be used as thermal insulation materials. Based on above findings, the prepared semi-rigid PIFs demonstrate a great potential for being utilized as thermal insulation and structural support materials in high-tech fields such as aerospace, marine transportation, and microelectronics. [Display omitted] •Lightweight semi-rigid PIFs were prepared using PEAS precursor foaming method.•The foaming behavior was affected by molecular structure and foaming temperature.•The melt viscosity of PEAS determined the cell structure of PIFs.•All PIFs exhibited superior mechanical and thermal properties.