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Effect of the dimethylsilyloxy co-monomer “D” on the chemistry of polysiloxane pyrolysis to SiOC
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SYSNO ASEP 0461612 Document Type J - Journal Article R&D Document Type Journal Article Subsidiary J Článek ve WOS Title Effect of the dimethylsilyloxy co-monomer “D” on the chemistry of polysiloxane pyrolysis to SiOC Author(s) Havelcová, Martina (USMH-B) RID, ORCID
Strachota, Adam (UMCH-V) RID, ORCID
Černý, Martin (USMH-B) RID, ORCID, SAI
Sucharda, Zbyněk (USMH-B)
Šlouf, Miroslav (UMCH-V) RID, ORCIDSource Title Journal of Analytical and Applied Pyrolysis. - : Elsevier - ISSN 0165-2370
Roč. 117, JAN (2016), s. 30-45Number of pages 16 s. Publication form Print - P Language eng - English Country NL - Netherlands Keywords silicon oxycarbide ; siloxane ; pyrolysis ; composites ; fibers Subject RIV CD - Macromolecular Chemistry Institutional support USMH-B - RVO:67985891 ; UMCH-V - RVO:61389013 UT WOS 000370105000004 EID SCOPUS 84954286957 DOI 10.1016/j.jaap.2015.12.018 Annotation The effect of the dimethylsilyloxy co-monomer "D" on the chemistry of polysiloxane pyrolysis to silicon oxycarbide (SiOC) glass was studied with the aim of its optimization for the preparation of refractory composites with ceramic fibers. Reasonably small weight losses (shrinkage), but also some temporary plasticity of the material during its pyrolysis was sought. The pyrolysis chemistry was varied by preparing precursors from methyltriethoxysilane (T; main monomer) and dimethyldiethoxysilane (D; co-monomer) in different ratios, but also by using an alternative composition based on tetraethoxysilane (Q) and D. Pyrolysis temperatures between 300 and 1000 degrees C were studied, and the escaping gases-polar, as well as non-polar-were analysed by means of chromatography/mass spectrometry. It was demonstrated, that the co-monomer D, which undergoes thermal elimination and subsequent reactions with the siloxane skeleton, seems to be responsible for the generally useful "micro-creep" ability of the pyrolyzing material. At higher D contents, where the pyrolysis weight losses strongly increase, the pyrolysis gases were shown to contain also polycyclic oligomers, which consist not only of D, but of the branching T or Q "main" monomers as well. The Si-O/Si-C exchange reactions of escaping D with the skeleton were found to be highly efficient not only in T/D, but also in Q/D polysiloxanes. It was further found, that the SiOC products after completed pyrolysis at 1000 degrees C still can release gases detectable by GC/MS upon repeated heating, although no significant weight losses are observed: this indicates the presence of small amounts of pyrolysable sediments in micro-and nano-pores of the SiOC glass. Workplace Institute of Rock Structure and Mechanics Contact Iva Švihálková, svihalkova@irsm.cas.cz, Tel.: 266 009 216 Year of Publishing 2017
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