Dimethylsilanone generation from pyrolysis of polysiloxanes filled with nanosized silica and ceria/silica

TL;DR

This study investigates how nanosized silica and ceria/silica fillers influence the thermal decomposition of PDMS, revealing that dimethylsilanone is generated at relatively low temperatures and is catalyzed by nano-oxides.

Contribution

It demonstrates that nano-oxides catalyze the formation of dimethylsilanone during PDMS pyrolysis and provides detailed mechanisms supported by DFT calculations.

Findings

Dimethylsilanone is generated from PDMS starting at 70°C.

Nano-oxides catalyze the pyrolysis process.

Multiple reaction channels produce dimethylsilanone and related compounds.

Abstract

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.