A polyimide (PI) aerogel with excellent combined thermal and dielectric properties was successfully prepared by the polycondensation of 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA), 5-amino-2-(4-aminophenyl)benzoxazole (APBO) and octa(amino-phenyl)silsesquioxane (OAPS) crosslinker, followed by a supercritical carbon dioxide (scCO 2 ) drying treatment. The developed PI aerogel exhibited an ultra-low dielectric constant (k) of 1.15 at a frequency of 2.75 GHz, a volume resistivity of

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... 0 14 Ω·cm, and a dielectric strength of 132 kV/cm. The flexible PI aerogel exhibited an openpore microstructure consisting of three-dimensional network with tangled nanofibers morphology with a porosity of 85.6% (volume ratio), an average pore diameter of 19.2 nm, and a Brunauer-Emmet-Teller (BET) surface area of 428.6 m 2 /g. In addition, the PI aerogel showed excellent thermal stability with a glass transition temperature (T g ) of 358.3°C, a 5% weight loss temperature over 500°C, and a residual weight ratio of 66.7% at 750°C in nitrogen.