Thermal properties of polymethylvinylborosiloxanes

New branched polymethylvinylborosiloxanes (PMVBSs) with random structures were prepared, and their chemical structures were studied by spectroscopic methods (FTIR, 1H-, 29Si-, and 11B-NMR) and elemental analysis (% C, % H, % Si, and % B). Average molecular weights M w and M n were determined by a size exclusion chromatography (SEC), and dynamic viscosities were measured in Brookfield cone–plate reoviscometer HBDV-II+cP. Thermal properties of PMVBSs were studied under air and under nitrogen atmosphere. Thermal curves were interpreted from the point of view of physical and chemical transitions, taking place during the heating process of PMVBSs. Parameters of their thermal stabilities and glass transition temperatures (T g) were determined. The synthesized PMVBSs are characterized by low glass transition temperatures (T g: from −122 to −137 °C) which depend on their chemical structures. It was concluded that gaseous products (such as volatile siloxanes, silanes, CO2, H2O, CH2O, methanol, and formic acid), which could be liberated during the heating process of PMVBSs, promote ceramization processes, leading to the formation of the ceramics of a type SiBCO—a borosilicate glass and silica.