Preparation of phenylsilsesquioxane thick films using thermal softening behavior

Transparent films with a thickness of more than 100 μm of phenylsilsesquioxane (PhSiO_3/2) were prepared via thermal softening of PhSiO_3/2 gel, which was obtained by a two-step acid-base catalyzed sol–gel process. The gel was applied to a substrate and subjected to a heat treatment at 200 °C, which resulted in the thermal softening of the gel and the attainment of fluidity. Upon cooling to ambient temperature, transparent films were obtained. The hardness of the films was slightly increased through the addition of colloidal silica in the preparation of PhSiO_3/2 gel, which was also synthesized via a two-step acid-base catalyzed sol–gel process. The resulting gel containing colloidal silica also displayed fluidity upon heating, and crack-free films were obtained in a larger-thickness region with the addition of SiO₂ filler.