Hybrid Polyimide\nFoams with Hyperbranched Organosilicon\nfor High-Temperature Sound Absorption

Lightweight\nand flexible polyimide foams (PIFs) with superior thermal\nand acoustic properties are high in demand for advanced aerospace\nand industrial machinery, however, traditional foams cannot offer\nboth satisfactory acoustic and thermal insulation simultaneously.\nIn this study, we successfully develop a new class of flexible PIFs\nby incorporating amino-functionalized hyperbranched polysiloxanes\n(NH<sub>2</sub>–HBPSi) into ammonium salt oligomer (PAES) through\na thermal foaming process. The complex viscosity (η*), microfoaming\nbehavior of PAES and cell morphology of the resulting PIFs are precisely\ncontrolled by tuning the ratio of NH<sub>2</sub>–HBPSi/4,4′-diaminodiphenyl\nether (ODA). Significantly, PIF<sub>HBPSi</sub>-4, a hybrid PIF with\na NH<sub>2</sub>–HBPSi loading of 33.3% and exceptional thermal\nproperty (<i>T</i><sub>5%</sub> exceeded 480 °C), exhibits\na normalized compressive strength of 3.47 kPa/(kg·m<sup>–3</sup>) at room temperature (over 10 times higher than commercial PIFs)\nand a noise reduction coefficient (NRC) of 0.375, which substantially\nimproved compared to previously reported polyimide composites. Additionally,\nNH<sub>2</sub>–HBPSi can form a dense oxide layer at high temperatures,\nimpeding the transmission of heat. This allows PIF<sub>HBPSi</sub>-4 to withstand a 10 min exposure to a high heat flux of 50 kW/m<sup>2</sup> without any significant erosion. These lightweight, flexible,\nthermally resistant, and acoustically superior hybrid PIFs have the\npotential to revolutionize applications in high-tech fields such as\naerospace, acoustics, and aviation.