MALDI-TOF/MS characterisation of LMW PDMS in high voltage HTV silicone rubber insulators

This paper reports the results of the characterisation of low molecular weight polydimethylsiloxane (LMW PDMS) extracted from four different brands of high temperature vulcanised (HTV) silicone rubber insulators designed for high voltage applications. LMW PDMS material was obtained from the insulators by sequential soxhlet extractions and mass changes were recorded for each extraction. The insulator extracts were thoroughly characterised using matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF/MS), which provides identification of individual molecular species allowing differences in molecular structure to be identified. The extracts were found to contain both linear and cyclic species. Some variations in end groups of the linear species were also noted. These spectra were used to calculate the relative proportions of these species as well as the average molecular weights of the extracts. Significant differences were observed in molecular composition and the speed of recovery of the insulators studied.