Constructing rigid–flexible robust silicone aerogels via hyperconnected POSS networks for extreme thermal protection

Silica aerogels are widely regarded as promising candidates for high-performance thermal insulation, yet achieving a balanced combination of mechanical robustness and high-temperature stability remains a persistent challenge. In this work, we report a robust, thermally stable, and machinable silicone aerogel featuring a “rigid–flexible” integrated architecture, synthesized through the co-condensation of a POSS-based hyperbranched siloxane–amino/epoxy resin (POSS-SAE) with linear polymethylhydrosiloxane (PMS). Prepared via a temperature-controlled amine/epoxy addition–polycondensation process, the hyperbranched POSS-SAE incorporates a rigid POSS core, flexible long alkyl chains, and multiple reactive functional groups, achieving an intrinsic rigid–flexible molecular balance. Benefiting from this structural design, its copolymerization with long-chain PMS yields an aerogel with an ultrahigh-connectivity network, enabling a synergistic improvement in both mechanical strength and thermal performance. Consequently, the resulting POSS-PSA aerogel exhibits a compressive strength of 6.1 MPa, a low thermal conductivity of 0.036 W m−1 K−1 at room temperature, and an impressive char yield of 72.4% at 1000 °C under nitrogen. Furthermore, a low-density quartz fiber-reinforced composite (POSS-PSC) based on this aerogel matrix achieves a tensile strength of 27.8 MPa and delivers outstanding thermal insulation up to 1000 °C as well as excellent ablation resistance up to 1600 °C. Consequently, these exceptional properties make POSS-VPSC highly promising for demanding thermal protection applications, particularly in advanced aerospace thermal protection systems (TPSs), reusable launch vehicle insulation, and industrial thermal management.