High strength microcellular thermoplastic polyimide/carbon fiber composite foams containing flexible ether amine, rigid diaminodiphenyl ether, and triaminopyrimidine moieties: Synthesis and fabrication

In this study, pyromellitic dianhydride (PMDA) and polyetheramine D230 were used as the primary polymerization monomers, with 2,4,6-triamino pyrimidine (TAP) as a chain extender. By introducing aromatic ring-containing 4,4′-diaminodiphenyl ether (ODA) and precisely controlling its molar ratio with D230, a highly branched, high-temperature-resistant thermoplastic polyimide (TPI), was successfully developed. The optimal thermal imidization temperature was determined to be 250 °C. Incorporating surface-modified short carbon fibers (SCF) via melt blending significantly improved the mechanical properties, with tensile and impact strengths increasing fourfold and sevenfold, respectively, at 10 phr of SCF. TPI foam prepared using supercritical carbon dioxide (scCO2) foaming technology exhibited excellent performance, achieving a regular hexagonal structure, cell sizes of 10.19 μm, and a cell density of 1.68 × 1010 cells/cm3 at an ODA to D230 molar ratio of 1:9. The TPI/SCF composite foam, with 3 phr SCF under 20 MPa saturation pressure and 120 °C foaming temperature, achieved a 90 % closed-cell ratio and a 300 % increase in compression strength at the same foam density. Compared to traditional thermoset PI foams, TPI/SCF foam offers smaller cell sizes and higher compression strength, demonstrating significant commercial potential. Backward differentiation shows that TPIF compression is constant at 0.035 ± 0.005 in the [0,0,1] lattice direction. This research provides theoretical and practical insights for preparing high-performance TPI foam for high-temperature applications.