UV-Resistant Trifluoropropyl-Substituted Open-Cage Silsesquioxane-Pendant Polysiloxanes

Abstract

We prepared three types of tris(dimethoxysilyl)-heptatrifluoropropyl-substituted open-cage silsesquioxanes, namely hepta(3,3,3-trifluoropropyl)-substituted open-cage silsesquioxanes (IC-POSSs) attached to three dimethoxysilyl groups by linkers of variable lengths at the opening vertex (TFP-Hdi, TFP-Vdi, and TFP-Adi). The dimethoxysilyl groups allowed subsequent hydrolysis and polycondensation under mild conditions to form flexible siloxane bonds. The structures of the resulting trifluoropropyl-substituted open-cage silsesquioxane-pendant polysiloxanes (P-H, P-V, and P-A) could be tuned by polycondensation temperature and the linker lengths of the tris(dimethoxysilyl)-heptatrifluoropropyl-substituted open-cage silsesquioxanes. The hybrid structure of the trifluoropropyl-substituted open-cage silsesquioxane-pendant polysiloxanes exhibited a low glass transition temperature, good thermal stability, hydrophobicity, optical transparency, and ultraviolet (UV) resistance. In particular, the transmittance of P-H exhibited no significant changes even after 11 days of UV irradiation with an average transmittance of >90% (250–600 nm). On the other hand, the transmittance of sulfur-containing P-V and P-A initially decreased after 2 days of irradiation due to oxidation of sulfur atoms to sulfoxide. Sulfoxide presence was then validated by XPS measurements. However, the transmittance remained largely unchanged during further consistent irradiation, indicating no further changes.