Thermal destruction of polydimethyl-siloxane on a phosphorus-containing silica surface

Thermogravimetry, differential thermal analysis, and IR spectroscopy were used to investigate the process of thermal destruction of adsorbed polydimethylsiloxane (PDMS) in air. The disperse adsorbents were pristine fumed silica and modified fumed silica whose surface contained oxygen compounds of phosphorus. It was shown that under the given experimental conditions the thermal destruction of PDMS on the fumed silica surface was accompanied by the complete transformation of the adsorbed PDMS to SiO2. In the case of phosphorus-containing silica, the thermal destruction proceeded in a different way. It was found that at 140-300 degreesC depolymerization of the siloxane chains of a certain part of the adsorbed polymer took place with the concurrent removal of volatile products of the reaction. However, the remaining part of the adsorbed PDMS interacted with the modified silica surface to form chemisorbed dimethylsilyl structures. The thermal destruction of the chemisorbed fragments of PDMS in air was initiated at 400 degreesC or above for both types of silica investigated.