Fabrication of Rigid Polyimide Foams by Constructing Dual Crosslinking Network Structures

Herein, lightweight rigid polyimide foams (PIFs) with excellent mechanical and thermal properties were fabricated by constructing dual crosslinking structures combined with the thermal foaming of polyester ammonium salt (PEAS) precursor powders. The dual crosslinking network relied on the self-crosslinking of pararosaniline base (PA) and active crosslinking derived from the breakage of C= C bonds in 5-norbornene-2, 3-dicarboxylic anhydride (NA) under heating. The results showed that melt viscosity and micro-foaming behavior of PEASs and the cell morphology of PIFs could be regulated by varying the molar ratio of PA/NA and the number of repeating units amid crosslinking points. The compressive strength of PIF(P1BMN3-)5 (density: 165.5 kgmiddotm(-3)) with dual crosslinking structures at 10% strain reached 1.36 MPa at room temperature and 0.75 MPa at 200 degrees C. The PIFs exhibited outstanding thermal properties with the initial thermal degradation temperature falling in a temperature range of 458.2-503.0 degrees C and the glass-transition temperatures exceeding 310 degrees C. In addition, PIFs exhibited excellent thermal insulation properties since the thermal conductivity of PIFs was between 0.048 and 0.065 Wmiddotm(-1) K-1, and the temperature increase of the top surface of the cubic sample block (height: 15 mm) was approximately 20 degrees C when they were placed on a preheated hot stage at 200 degrees C for 30 min. Thus, mechanically strong rigid PIFs with dual crosslinking structures were successfully prepared, which show promising applications as lightweight, high-temperature resistant structural materials in high-end engineering fields.