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 PIF BTDA-MDA and PIF BTDA-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.