Double-Decker Silsesquioxane-Grafted Polysilsesquioxane Hybrid Films as Thermal Insulation Materials

The development of thermal insulators possessing high thermal insulating properties and thermal stability is desired for realizing a sustainable society. In polysilsesquioxanes (PSQs), which are promising as next-generation thermal insulation materials, the introduction of cross-linking units allows improving the thermal insulating properties through formation of intramolecular void spaces. However, this is usually accompanied by a loss of transparency and stability. To circumvent this issue, the hydrosilylation reaction between hydrodimethylsilylated oligomethylsilsesquioxane and vinyl-functionalized double-decker silsesquioxane (vinyl-DDSQ), which is a highly thermally stable unit, was conducted to obtain aggregation-free DDSQ-grafted PSQ films. The high miscibility of the double-decker silsesquioxane (DDSQ) molecule allowed introducing a high amount of vinyl-DDSQ, and colorless and transparent DDSQ-grafted PSQ films were obtained without aggregation of DDSQ molecules. The thermal diffusivities of the DDSQ-grafted PSQ films decreased from 1.21 × 10–7 to 1.02 × 10–7 m2/s with increasing the DDSQ amount from 5 to 25 mol %. Although a similar trend was observed for the previously reported polyhedral oligomeric silsesquioxane-containing hybrid films, the hardness of the DDSQ-grafted PSQ films decreased with increases in the vinyl-DDSQ content, and their thermal stability was higher (over 400 °C), with higher 5% mass loss temperature and 10% mass loss temperature values of 438–463 °C and 495–523 °C, respectively. Therefore, the high thermal insulating properties and thermal stability of the DDSQ-grafted PSQ films render them promising materials for next-generation thermal insulators.