Preparation and properties of polysilsesquioxanes. Function and characterization of coating agents and films

Coating characteristics of polysilsesquioxanes with various molecular weights prepared by acid-catalyzed hydrolytic polycondensation of trimethoxysilane RSi(OMe)3 (R=Me, Vinyl) were investigated in relation to the structure. Homogeneous, smooth and crack-free coating films of thickness from 0.25 to 0.95 μm were prepared by 1–10 times dip-coating of an acetone–methanol solution of polysilsesquioxanes on polymer, metal and ceramic substrates. Their mechanical, optical and electrical properties were investigated. The adhesion and hardness of coating films showed the maximum values based on the evaluation of JIS (Japanese Industrial Standard) K5400. They also increased with increasing molecular weight, T3 unit of polysilsesquioxanes, heating time and sintering temperature. The coating films were revealed to be thermally stable on heating to 800°C. The refractive index of coating films decreased gradually with increasing temperatures up to about 800°C. The transmittance of coating films was higher than 98% at 500 nm. The surface resistivity of the coating films increased with the increase of sintering temperature.