Thesis

Synthesis, characterisation and thermal degradation studies of carborane containing siloxane elastomers

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Awarding institution
  • University of Strathclyde
Date of award
  • 2012
Thesis identifier
  • T13217
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Abstract
  • The investigation of model siloxane then subsequent m-carborane, 1,7- bis(dimethylmethoxysilyl)-m-carborane-carborane and 1,7-diallyl-m-carborane filled siloxane elastomer systems was undertaken. Thermal degradation studies showed little difference in the degradation profile of all carborane containing elastomers compared to the model system. The major degradation products of these materials are siloxane ring structures. Use of different cross-linkers also showed little difference in the thermal degradation properties of both materials. Investigation of poly(dimethylsiloxane) (PDMS) polymerised by Lewis acid condensation catalysts to obtain a replacement catalyst for FeCl3 has been undertaken. Both FeCl3 and GaCl3 give rise to vulcanized material in which the catalyst is trapped in the matrix. AlCl3 and ZnCl2 give high molecular mass material determined by both GPC and NMR spectroscopy. Kinetic studies have been undertaken to determine the activation energy for the FeCl3 catalysed reaction. Carborane-siloxane network polymers have been produced using FeCl3 as the catalyst. These materials display unusually high thermal stability and have been shown to be crystalline in nature by DSC analysis. Thermal volatilisation studies show carborane dehydrogenates during thermal decomposition. Hydrosilylation has been employed to produce novel network carborane-siloxane materials. Samples have been produced where the molar ratio of carborane to PMDS has been varied from 1:1 to 6:1. Higher carborane containing materials have problems with volatile loss of unbound monomer. The materials have been studied using thermal volatilisation analysis and their degradation has changed remarkably from what was observed previously for carborane-siloxane elastomers. The majority of the degradation products observed are low molecular mass silanes. These form in part by the demethylation of the siloxane polymer promoted by platinum catalyst residues in the material The investigation of model siloxane then subsequent m-carborane, 1,7- bis(dimethylmethoxysilyl)-m-carborane-carborane and 1,7-diallyl-m-carborane filled siloxane elastomer systems was undertaken. Thermal degradation studies showed little difference in the degradation profile of all carborane containing elastomers compared to the model system. The major degradation products of these materials are siloxane ring structures. Use of different cross-linkers also showed little difference in the thermal degradation properties of both materials. Investigation of poly(dimethylsiloxane) (PDMS) polymerised by Lewis acid condensation catalysts to obtain a replacement catalyst for FeCl3 has been undertaken. Both FeCl3 and GaCl3 give rise to vulcanized material in which the catalyst is trapped in the matrix. AlCl3 and ZnCl2 give high molecular mass material determined by both GPC and NMR spectroscopy. Kinetic studies have been undertaken to determine the activation energy for the FeCl3 catalysed reaction. Carborane-siloxane network polymers have been produced using FeCl3 as the catalyst. These materials display unusually high thermal stability and have been shown to be crystalline in nature by DSC analysis. Thermal volatilisation studies show carborane dehydrogenates during thermal decomposition. Hydrosilylation has been employed to produce novel network carborane-siloxane materials. Samples have been produced where the molar ratio of carborane to PMDS has been varied from 1:1 to 6:1. Higher carborane containing materials have problems with volatile loss of unbound monomer. The materials have been studied using thermal volatilisation analysis and their degradation has changed remarkably from what was observed previously for carborane-siloxane elastomers. The majority of the degradation products observed are low molecular mass silanes. These form in part by the demethylation of the siloxane polymer promoted by platinum catalyst residues in the material.
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  • Strathclyde theses - ask staff. Thesis no. : T13217
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Date Created
  • 2012
Former identifier
  • 948090

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