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

Thermogravimetry, differential thermal analysis, and IR spectroscopy were u sed to investigate the process of thermal destruction of adsorbed polydimet hylsiloxane (PDMS) in air. The disperse adsorbents were pristine fumed sili ca and modified fumed silica whose surface contained oxygen compounds of ph osphorus. It was shown that under the given experimental conditions the thermal destr uction of PDMS on the fumed silica surface was accompanied by the complete transformation of the adsorbed PDMS to SiO2. In the case of phosphorus-cont aining 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 remov al of volatile products of the reaction. However, the remaining part of the adsorbed PDMS interacted with the modified silica surface to form chemisor bed dimethylsilyl structures. The thermal destruction of the chemisorbed fr agments of PDMS in air was initiated at 400 degreesC or above for both type s of silica investigated.