Thermal stability of SiO2-based inorganic-organic hybrid materials

The hydrolysis-polycondensation of organicallly modified Si-alkoxides leads to the obtaining of inorganic-organic hybrid materials in which the organi c moieties remain as permanent groups bonded to the inorganic network. The molecular species previously determinated by GC-MS during the gelation process have been significantly different according to the type of the alko xide used. In the present work, thermal stability of SiO2-based inorganic-organic hybr id materials starting with TEOS (tetraethoxysilan), MTEOS (triethoxymethyls ilan), VTEOS (triethoxyvinylsilan) and MTMOS (trimethoxymethylsilan) was st udied. The molecular structure of the gels obtained determines differences in thei r thermal behaviour. Gels obtained starting with MTEOS show the highest the rmal stability, while gels obtained using VTEOS the lowest, among the subst ituted alkoxides. A particular behaviour presents the gel obtained with MTM OS that decomposes in four steps. This could be explained by the presence i n the gel of some prevalent types of molecular species with different therm al stability.