In this study, we synthesized bismaleimide into a functionalized double-decker silsesquioxane (DDSQ) cage. This was achieved by hydrosilylation of DDSQ with nadic anhydride (ND), reacting it with excess p-phenylenediamine to obtain DDSQ-ND-NH2, and treating with maleic anhydride (MA), which finally created a DDSQ-BMI cage structure. We observed that the thermal decomposition temperature (Td) and char yield were both increased upon increasing the thermal polymerization temperature, and that these two values were both significantly higher than pure BMI without the DDSQ cage structure since the inorganic DDSQ nanoparticle could strongly enhance the thermal stability based on the nano-reinforcement effect. Based on FTIR, TGA, and DMA analyses, it was found that blending epoxy resin with the DDSQ-BMI cage to form epoxy/DDSQ-BMI hybrids could also enhance the thermal and mechanical properties of epoxy resin due to the organic/inorganic network formation created by the ring-opening polymerization of the epoxy group and the addition polymerization of the BMI group due to the combination of the inorganic DDSQ cage structure and hydrogen bonding effect. The epoxy/DDSQ-BMI = 1/1 hybrid system displayed high Tg value (188 °C), Td value (397 °C), and char yield (40.4 wt%), which was much higher than that of the typical DGEBA type epoxy resin with various organic curing agents.

This work synthesizes a new bifunctional furan derivative (PDMS‐FBZ) through a sequence of hydrosilylation of nadic anhydride (ND) with polydimethylsiloxane (PDMS), reaction of the product with p‐aminophenol to form PDMS‐ND‐OH, and its subsequent Mannich reaction with furfurylamine and CH2O. Then, the main chain‐type copolymer PDMS‐DABZ‐DDSQ is prepared through a Diels–Alder (DA) cycloaddition of PDMS‐FBZ with the bismaleimide‐functionalized double‐decker silsesquioxane derivative DDSQ‐BMI. Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectroscopy confirm the structure of this PDMS‐DABZ‐DDSQ copolymer; differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and dynamic mechanical analysis (DMA) reveal it to have high flexibility and high thermal stability (Tg = 177 °C; Td10 = 441 °C; char yield = 60.1 wt%); contact angle measurements reveal a low surface free energy (18.18 mJ m−2) after thermal ring‐opening polymerization, because the inorganic PDMS and DDSQ units are dispersed well, as revealed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). This PDMS‐DABZ‐DDSQ copolymer possesses reversible properties arising from the DA and retro‐DA reactions, suggesting its possible application as a functional high‐performance material.