Topological constraint-enabled high-temperature creep resistance and mechanical robustness in organic-inorganic IPN-like PMI aerogels

High-performance aerospace core materials are required to combine low thermal conductivity and high load-bearing capacity at low density, while maintaining dimensional stability under thermo-mechanically coupled conditions. However, it remains challenging to simultaneously achieve low density, high mechanical strength, excellent thermal stability and reliable flame retardancy within a single-material system. To address this issue, an inorganic silicate and an aminosilane coupling agent were introduced into the polymethacrylimide (PMI) system. Through in situ hydrolysis and condensation, a continuous Si-O-Si inorganic skeleton was constructed. Meanwhile, interfacial chemical coupling between the organic and inorganic phases was promoted by the aminosilane, enabling efficient molecular-level integration of the rigid inorganic network with the flexible organic matrix and thereby generating an organic-inorganic interpenetrating polymer network (IPN)-like PMI aerogel. Benefiting from this unique interpenetrating topology, the aerogels exhibit outstanding mechanical performance, with a stress of 11.19 MPa at 70% strain, excellent high-temperature dimensional stability, with an accumulated strain of 2.96% over 3 h at 200 °C under a constant stress of 0.2 MPa, and a low thermal conductivity of 0.0492 W·m −1 ·K −1 at room temperature. In addition, the aerogels show good intrinsic flame retardancy, with the limiting oxygen index (LOI) increasing from 29.6% to 31.1% as the inorganic silicate content increases from 7 wt% to 10 wt%, which is attributed to the protective effect of the inorganic siloxane network during combustion. These results provide useful design guidance for the development of integrated load-bearing and thermal-insulating materials for extreme conditions.