High Thermal Resistance of Epoxy/Cyanate Ester Hybrids Incorporating an Inorganic Double-Decker-Shaped Polyhedral Silsesquioxane Nanomaterial

In this study, we prepared a difunctionalized cyanate ester double-decker silsesquioxane (DDSQ-OCN) cage with a char yield and thermal decomposition temperature (T-d) 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 (T-d), and char yield (166 degrees C, 427 degrees 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 T-d 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.

Automated summary

In this study, a difunctionalized cyanate ester double-decker silsesquioxane (DDSQ-OCN) cage was prepared to improve the thermal behavior of epoxy resin. The covalently bonded network structure formed by the copolymerization of epoxy and OCN units, as well as the hydrogen bonding between the OH groups of epoxy and the SiOSi moieties of DDSQ units, enhanced the physical properties of the material. The addition of Cu(II)-acac accelerated the thermal polymerization process but decreased the thermal stability.