Chemisorption and thermally induced transformations of polydimethylsiloxane on the surface of nanoscale silica and ceria/silica

Dimethylsilanone Generation from Pyrolysis of Polysiloxanes Filled with Nanosized Silica and Ceria/Silica

“…In the present work we observe this ion at relatively low temperatures for some samples. However, the radical reaction mechanism required for methyl group migrations to occur (a possible path to permethylated silanes), is known to require higher temperatures . This suggests that the formation of dimethylsilanone is much more likely than the formation of permethylated silanes under the present experimental conditions.…”

“…On the basis of previous work, the ion with m/z =207 can be attributed to the characteristic fragment of HMCTS, the pentamethylcyclotrisiloxane ion radical (depicted in Figure ) . HMCTS desorption starts at 140 °C and continues up to 750 °C (Figure ).…”

“…An increase in the ceria content in the sample (PDMS/CeO 2 /SiO 2 _high) was found to induce the catalytic action even more prominently: (CH 3 ) 2 Si=O generation starts already at 42 °C and continues up to 750 °C, passing through three maxima at 75, 369, and 637 °C in the process (Figure ). The maximum at 260 °C can be ignored as it is related to the release of trimethylsilanol …”

“…Although the TPD MS technique is not inherently quantitative in an absolute sense, it is still possible to estimate the fraction of dimethylsilanone generated with respect to the other products by comparing the areas under the TPD curves for the ions of interest. According to the current literature, under vacuum conditions, thermal degradation of PDMS results primarily in depolymerization and formation of cyclic oligomers as products . The trimer hexamethylcyclotrisiloxane (HMCTS) is known to be the most abundant compound among these products.…”

“…Kinetic parameters (reaction order n , activation energy E ≠ , pre‐exponential factor v 0 , and activation entropy dS ≠ ) of the dimethylsilanone formation reaction were determined from the TPD MS data by using the Arrhenius plot method. The detailed procedure for obtaining the kinetic parameters has been described previously . We were able to obtain the kinetics only for the high‐temperature stage of the dimethylsilanone release for the samples PDMS, PDMS/CeO 2 /SiO 2 _low, and PDMS/CeO 2 /SiO 2 _high (as the other desorption maxima for these samples have ambiguous forms, some of the peaks overlap); see Table .…”