Preparation of molecularly well-defined silicone resins based on trifluoropropyl-substituted trisilanol and their thermal, mechanical, and UV-resistance properties

Abstract

We prepared flexible free-standing films of trifluoropropyl-substituted open-cage silsesquioxane-pendant polysiloxane by optimizing the sol-gel reaction conditions of tris(dimethoxysilyl-ethyl-dimethylsiloxy)-heptatrifluoropropyl-substituted open-cage silsesquioxane (1). The polycondensation of 1 was fully achieved even at 50 °C for 6 h under vacuo. 29Si CP-MAS NMR analysis indicated that the flexible free-standing films, polycondensed at 50 °C and 180 °C, included cyclotrisiloxane (D3) and linear siloxane (Dlinear) structures. The elastic modulus and decomposition temperature at 5% mass weight loss (Td5) of the product by polycondensation at 180 °C under N2 were significantly greater than those for the 50 °C product. Significant changes in the UV‒vis spectra of the resulting transparent films were not observed even after 13 days of UV irradiation in air. In contrast, UV irradiation of the isobutyl-substituted counterpart under air clearly caused a decrease in its transmittance due to autoxidative degradation. Free-standing films of trifluoropropyl-substituted open-cage silsesquioxane-pendant polysiloxane by optimizing sol-gel reaction condition of tris(dimethoxysilyl-ethyl-dimethylsiloxy)-heptatrifluoropropyl-substituted open-cage silsesquioxane. Elastic modulus and the decomposition temperature for 5% weight loss under N2 of the product by polycondensation at 180 °C were significantly higher than that by polycondensation at 50 °C. Significant changes in the UV-vis spectra of the resulting transparent films were hardly observed even after 13 days of UV irradiation.