Mechanically flexible polyimide foams with different chain structures for high temperature thermal insulation purposes

Mechanically flexible polyimide foams (PIFs) with exceptional high temperature thermal insulation properties were fabricated by microwave-assisted foaming and post thermal imidization process, using polyester ammonium salt (PEAS) precursor powders which consisted of different molecular chain structures as the derivatives. A comparison of foaming behavior, pore morphology, mechanical and thermal insulation properties between PIFs prepared with mono-dianhydride and copolymerized dianhydride structures was systematically studied. Results showed that the optimum foaming temperatures of PEASs was in the range of 85–150 °C, which correlated with the volatilization of solvents such as H2O, tetrahydrofuran and methanol. The introduction of copolymerized dianhydride structure altered the chain rigidity and melt viscosity of PEAS, which improved the cellular structure and mechanical flexibility of PIFs. Moreover, the micron-scale cellular structure of PIFs was determined by melt viscosity, chain rigidity, volatile content and foaming temperatures. The PIFs exhibited low apparent densities (25–30 kg/m3), high open cell rate (95–97%) and mechanical flexibility (compression/release recover rate: 96–99%). All PIFs possessed exceptional thermal stability and thermal insulation properties which can be targeted for thermal insulation applications in the fields of aerospace, transportation, and microelectronics among others.