Characterisation of low molar mass siloxanes extracted from crosslinked polydimethylsiloxanes exposed to corona discharges

Crosslinked polydimethylsiloxanes were exposed to corona discharges in dry air at normal pressure. Short-time solvent extraction and subsequent analys is of the extractables, by gas chromatography, mass spectrometry and size e xclusion chromatography showed that, oligomers consisting mainly of cyclics with 4-9 repeating units were formed during corona exposure. The size dist ribution of the oligomers was independent of the crosslink density and coro na exposure time. The amount of oligomers located at the surface increased, with increasing storage time, after the corona exposure in qualitative agr eement with the ongoing hydrophobic recovery process. Longer extractions pe netrated deeper into the samples, and, in addition to the cyclic oligomers, higher molar mass species (similar to 50,000 g mol(-1) for unexposed sampl es) were detected. Samples exposed to corona, treated in this way, showed a broadening of the high molar mass peak towards lower molar masses. (C) 200 1 Elsevier Science Ltd. All rights reserved.