The IR laser‐induced degradations of liquid polydimethylsiloxane (PDMS) vapor and of hexamethyldisiloxane vapor have been studied in order to determine whether the high temperature thermal properties of the dimethylsiloxane unit is best represented by SiO bond rearrangement (the conventional pyrolysis mechanism) or SiC bond cleavage (the thermodynamic reaction pathway). The volatile products of these pulsed laser experiments with various viscosities of PDMS are methane, ethane, ethylene, and hydrogen. These results are consistent with SiC bond cleavage to form methyl radicals, which can then recombine to form ethane or abstract a hydrogen atom from a matrix molecule to form methane. The presence of ethylene and hydrogen can be explained by the decomposition of hot ethane molecules. No evidence of SiO bond cleavage was observed. Reaction temperatures are estimated with computer modeling using heat capacity data.
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Manders et al. (1985) studied this question.
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