Vibrational spectra of phenyltriethoxysilane, phenyltrimethoxysilane and their sol–gels

Raman and infrared spectra of phenyltriethoxysilane and phenyltrimethoxysilane have been recorded. These silane coupling agents (SCAs) have been used as precursors to prepare sol–gels using acid or base as catalyst under different solution conditions. From the vibrational spectroscopic identification, it was found that the major sol–gel products obtained from different catalysts and different solvents were essentially the same. Vibrational assignments for the SCAs, sol–gel and xerogel have been made based on the group frequencies, the spectral variation collected at different physical and chemical states and the previous spectroscopic studies of similar molecules. The compositions of xerogels after thermal treatments at different temperatures have been analyzed and identified by using infrared spectroscopic method along with thermal gravimetric analysis. Results from the experimental treatments for the xerogels indicated that the xerogel baking at 118 °C served to evaporate the sample moisture, the curing at 225 °C helped to complete the condensation reaction, and the treatment at 600 °C caused the decomposition of the organic group but the siloxane net-work remained essentially unchanged.