Structure–Thermal Property Relationships of Polysilsesquioxanes for Thermal Insulation Materials

For the development of polysilsesquioxanes (PSQs) as organic–inorganic hybrid materials for efficient thermal insulators, gaining a better understanding on the structure–thermal property relationship of PSQ gel films is essential. With this aim, PSQs were prepared via the sol–gel method to investigate the influence of residual alkoxy groups and substituents on the thermal insulation property of PSQ freestanding gel films. The thermal diffusivities of gel films prepared from polymethylsilsesquioxanes having ethoxy and isobutoxy groups increased with increasing the amount of these residual groups. However, compared with the ethoxy group, the bulky isobutoxy group decreased the thermal diffusivity of the corresponding polymethylsilsesquioxanes gel films. The thermal insulation property of the PSQ films was affected by the amount of residual alkoxy groups mainly due to their bulkiness. The presence of a phenyl group bonded to the silicon atom apparently decreased the thermal diffusivity of a gel film prepared from polyphenylsilsesquioxane compared with that of a polymethylsilsesquioxane gel film. Meanwhile, the thermal stability of the polyphenylsilsesquioxane gel film was significantly higher than that of polymethylsilsesquioxane gel film. Overall, the organic substituents on the silicon atom affected the thermal insulation property and thermal stability of PSQ films.