Pyrolysis-gas chromatographic studies on poly-dimethyl-siloxanes and poly-dimethyl-sil-alkylene-siloxanes

M. blazsó, G. Garzó, T. Székely

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28 Citations (Scopus)

Abstract

The investigated linear polymers consisted partly of dimethyl-siloxane units-[Me2SiO]n-and partly of regularly alternating tetramethyl-disiloxane and short hydrocarbon chain segments. The results of pyrolysis-gas chromatographic experiments performed either with dimethyl-poly-siloxanes of different molecular weight terminated with -OH, -OR, -OK and -OSiMe3 groups, or with poly-dimethyl-sil-ethylene-siloxane and poly-dimethyl-sil-propylene-siloxane samples respectively, were utilized for the evaluation of the thermal degradation mechanism of these polymers. All the significant peaks on the pyrograms were identified and the relative amounts of the pyrolysis products were estimated at different pyrolysis temperatures. Based on present experimental results, decomposition of the polydimethyl-siloxanes may proceed on two different ways. In the presence of catalytic amounts of potassium ions the heterolytic cleavage of the silicon-oxygen bond is initiated at the polymer chain terminals, resulting in the formation of rings consisting of 3-8 dimethyl-siloxane units. Noncatalyzed thermal degradation, however, is not affected by the terminal groups. The main degradation product, the hexamethyl-cyclo-trisiloxane is formed via a fourcentered intramolecular transition complex, arising from spiralization of the polymer chain. The poly-dimethylsil-alkylene-siloxanes may also decompose by this latter (siloxane-type) degradation, yielding cyclic monmers of the[Figure not available: see fulltext.] type. Nevertheless, a competing reaction, namely radical-type splitting of the C-C or Si-C bond in the hydrocarbon segment of the polymer chain, followed by an intermolecular radical transfer and subsequent β-scission takes place simultaneously. We observed, that the reproducibility of relative amounts of the components on the pyrograms was fairly good on comparison of products of the same decomposition path-way, but was poor if decomposition products of different competitive reactions were related.

Original languageEnglish
Pages (from-to)485-492
Number of pages8
JournalChromatographia
Volume5
Issue number9
DOIs
Publication statusPublished - Sep 1 1972

ASJC Scopus subject areas

  • Analytical Chemistry
  • Biochemistry
  • Clinical Biochemistry
  • Organic Chemistry

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