In this study, we prepared a difunctionalized cyanate ester double-decker silsesquioxane (DDSQ-OCN) cage with a char yield and thermal decomposition temperature (Td) which were both much higher than those of a typical bisphenol A dicyanate ester (BADCy, without the DDSQ cage) after thermal polymerization. Here, the inorganic DDSQ nanomaterial improved the thermal behavior through a nano-reinforcement effect. Blending the inorganic DDSQ-OCN cage into the epoxy resin improved its thermal and mechanical stabilities after the ring-opening polymerization of the epoxy units during thermal polymerization. The enhancement in the physical properties arose from the copolymerization of the epoxy and OCN units to form the organic/inorganic covalently bonded network structure, as well as the hydrogen bonding of the OH groups of the epoxy with the SiOSi moieties of the DDSQ units. For example, the epoxy/DDSQ-OCN = 1/1 hybrid, prepared without Cu(II)-acac as a catalyst, exhibited a glass transition temperature, thermal decomposition temperature (Td), and char yield (166 °C, 427 °C, and 51.0 wt%, respectively) that were significantly higher than those obtained when applying typical organic curing agents in the epoxy resin. The addition of Cu(II)-acac into the epoxy/BADCy and epoxy/DDSQ-OCN hybrids decreased the thermal stability (as characterized by the values of Td and the char yields) because the crosslinking density and post-hardening also decreased during thermal polymerization; nevertheless, it accelerated the thermal polymerization to a lower curing peak temperature, which is potentially useful for real applications as epoxy molding compounds.

In this study, a monofunctionalized bio‐based benzoxazine monomer (VAnBZ‐CN) is synthesized by condensation of vanillin, formaldehyde, and aniline, and a bifunctional epoxy‐functionalized poly(dimethylsiloxane) (PDMS‐epoxy) is also prepared through hydrosilylation reactions with allyl glycidyl ether. By blending the inorganic PDMS‐epoxy with the VAnBZ‐CN benzoxazine monomer, an organic/inorganic hybrid material is formed, which exhibited enhanced thermal stability after thermal curing polymerization. The improved thermal stability observed in the hybrid material can be attributed to a combination of the formation of the triazine structure by VAnBZ‐CN and the presence of the inorganic part of PDMS‐epoxy on the surface. For example, the PDMS‐epoxy/VAnBZ‐CN = 1/1 hybrid showed the thermal decomposition temperature (Td10) of 309 °C, the glass transition temperature (Tg) of 165 °C, and the char yield of 54 wt.% after the thermal curing polymerization process conducted at 240 °C based on thermogravimetric (TGA) and dynamic mechanical analyses (DMA). Furthermore, the char yield of the hybrid material with PDMS‐epoxy/VAnBZ‐CN = 1/3 is higher than that both of pure VAnBZ‐CN and PDMS‐epoxy after the thermal curing polymerization process. This result indicates that the addition of PDMS‐epoxy resin can improve the formation of a char residue and then enhance the resistance to thermal decomposition for their overall thermal stabilities.