  Polydimethylsiloxane (PDMS) is a widely used organosilicon polymer often
employed in formulations with fine oxide particles for various high temperature
applications. Although PDMS is considered to be thermally stable and chemically
inert, it is not always clear how the oxide filler influences its
thermoresistance, decomposition chemistry and what reactive products are formed
in the underlying thermal reactions. In this work we use temperature programmed
desorption mass spectrometry (TPD MS) to study the pyrolysis of PDMS and its
composites with nanosized silica and ceria/silica. Our results suggest that the
elusive organosilicon compound - dimethylsilanone is generated from PDMS over a
broad temperature range (in some cases starting at 70${\deg}$C). The presence
of nano-oxides catalyzed this process. Ions characteristic of the fragmentation
of dimethylsilanone under electron ionization were assigned with the aid of DFT
structure calculations. Possible reaction mechanisms for generating
dimethylsilanone were discussed in the context of the calculated kinetic
parameters. Observed accompanying products of PDMS pyrolysis, such as
tetramethylcyclodisiloxane and hexamethylcyclotrisiloxane, indicate that
multiple channels are involved in the dimethylsilanone release.
