Preparation of tetraethoxysilane-based silica aerogels with polyimide cross-linking from 3, 3′, 4, 4′-biphenyltetracarboxylic dianhydride and 4, 4′-oxydianiline

Polyimide cross-linked silica aerogels with different weight percentages of polyimide were prepared through sol–gel technology and supercritical CO₂ fluid drying technology. Tetraethoxysilane (TEOS) was used as a silica source precursor, 3-aminopropyltriethoxysilane (APTES) end-capped polyimide was used as a cross-linking agent, derived from 3, 3′, 4, 4′-biphenyltetracarboxylic dianhydride (BPDA) and 4, 4′-oxydianiline (ODA). The acid produced during the imidization process catalyzed the hydrolysis reaction without additional catalyst. After condensation reaction catalyzed by ammonium hydroxide solution, the polyimide cross-linked silica gels were obtained and then dried in supercritical CO₂. The polyimide cross-linked silica aerogels have low density (0.132~0.187 g/cm³), high specific surface area (623–741 m²/g), low thermal conductivity (0.0306~0.0347 W/m K at room temperature), relatively high compressive strength (1.03~3.82 MPa) and high thermal decomposition temperature (360 °C). This research provided a simple and efficient method that used the polyimide as a strengthening phase to improve the mechanical properties of TEOS-based silica aerogels.