REACTION OF CHLOROMETHYLSILANES WITH SILICA - A LOW-FREQUENCY INFRARED STUDY

By employing a thin film technique in transmission infrared spectroscopy, we have been able to observe bands due to chemisorbed chloromethylsilanes on Aerosil silica in the low-frequency region below 1300 cm-1. At 300-degrees-C the chloromethylsilanes react with surface silanol groups and produce bands due to surface Si-O-Si,Si-C, CH3 rocking, and Si-Cl stretching modes and these provide direct spectral evidence for the various types of adsorbed methylsilyl species. The bands due to Si-Cl stretching modes are especially useful in determining the structure of the absorbed species anchored to the surface. The reaction of trichloromethylsilane (TCMS) gave rise to Si-Cl bands at 574 cm-1 (assigned to the nonsymmetric stretch of the monofunctionally adsorbed species-SiCH3-Cl2) and at 473 cm-1 (assigned to the stretching mode of the difunctionally adsorbed species = SiCH3-Cl). The reaction of dichlorodimethylsilane (DCDMS) produced one Si-Cl band at 485 cm-1 assigned to the stretch mode of the species -Si(CH3)2-Cl and the reaction of chlorotrimethylsilane (CTMS) gave rise to a single Si-Cl band at 622 cm-1, which is due to a surface Si(S)-Cl species. The reaction of the adsorbed species with water was determined by monitoring changes in the bands located in the low frequency region.