Multi-scale cooperatively tuned sol-gel kinetics of hierarchical nanoporous phthalonitrile aerogel for thermal insulation and high-temperature dimensional stability

Molecular rigidity and nanofiller hybridization regulate sol-gel kinetics and optimize nanoporous structure. • The aerogel shows ultralow thermal conductivity (0.036 W m - ¹ K - ¹) and high compressive strength (4.67 MPa). • The aerogel maintains dimensional stability at 300 °C for 3000 s with Td₅ % reaching 527.8 °C. • The material shows strong ablation resistance and self-extinguishing ability for aerospace thermal insulation. The development of high-performance polymers has facilitated the emergence of polymer aerogels, which integrate lightweight characteristics, mechanical strength, and excellent heat resistance. This advancement overcomes the brittleness of inorganic aerogels, fulfilling the requirements for high-temperature applications. Here, phthalonitrile (PN) aerogels are prepared via the sol-gel method. A systematic study is conducted on the fundamental process underlying PN aerogel formation. It was found that molecular rigidity and crosslinking density are the key factors that regulate the sol-gel process and affect the macroscopic performance. By introducing phenolic hydroxyl and amino fillers, the nucleation and growth of PN molecules are regulated, enabling the tailored design of hierarchical nanoporous structures. The hybrid PN aerogel exhibits ultralight characteristics (0.22 g cm −3 ), high specific surface area (575.57 m 2 g −1 ), low thermal conductivity (0.036 W m −1 K −1 ), excellent mechanical strength (4.67 MPa), and high-temperature resistance ( T d5%  = 527.8°C). It also demonstrates exceptional thermal dimensional stability, maintaining almost unchanged dimensions up to 300°C for 3000 s. Moreover, it exhibits ablation resistance and self-extinguishing properties. This novel aerogel extends the limits of thermal resistance and thermal insulation compared with existing thermosetting aerogels. This work holds significant potential for extreme-environment applications such as thermal sealing for aerospace vehicles and thermal insulation for engine components. High-temperature-resistant phthalonitrile aerogels are developed via the sol-gel process, accompanied by rigid phenolic chain design and aminated silica nanoparticle hybridization. This cooperative regulation reduces the effective crosslinking sites and enhances the spatial hindrance, which ultimately refines pore sizes to the nanoscale and optimizes the hierarchical porosity. It results in ultralight aerogels (0.22 g cm -3 ) with high surface area (575.57 m² g -1 ), low thermal conductivity (0.036 W m -1 K -1 ), excellent mechanical strength (4.67 MPa), and superior thermal stability (T 5%  = 527.8 °C, negligible shrinkage at 300 °C). Moreover, it also exhibits excellent ablation resistance and self-extinguishing properties. Download: Download high-res image (293KB) Download: Download full-size image