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dc.contributor.authorHoyt-Lalli, Jennifer K.en_US
dc.date.accessioned2014-03-14T20:20:01Z
dc.date.available2014-03-14T20:20:01Z
dc.date.issued2002-08-05en_US
dc.identifier.otheretd-12092002-150514en_US
dc.identifier.urihttp://hdl.handle.net/10919/30007
dc.description.abstractThe scope of this research entailed the synthesis of novel polyorganosiloxanes with pendent phosphine, phosphine oxide, nitrile and carboxylic acid moieties. Such polysiloxanes were prepared with controlled concentrations of both the polar moieties and hydrido or vinyl pendent crosslinkable sites to afford precursor materials for well-defined networks. The intention was to generate stable microcomposite dispersions with very high concentrations of polar thermally conductive fillers. Lightly crosslinked elastomeric networks with controlled amounts of polar moieties were prepared via a hydrosilation curing mechanism. High concentrations of thermally conductive micro-fillers were dispersed throughout the resins and the microcomposites were investigated as thermally conductive adhesives. Random polysiloxane copolymers containing controlled number average molecular weights (Mns) and compositions with systematically varied concentrations of hydridomethylsiloxy- or vinylmethylsiloxy- units were prepared via ring-opening equilibrations of cyclosiloxane tetramers. These precursors were functionalized with precise concentrations of polar pendent moieties via hydrosilation (nitrile) or free radical addition reactions (phosphine and carboxylic acids). Valuable additions to the family of polysiloxanes were prepared by oxidizing the phosphine moieties to form phosphine oxide containing polysiloxanes. Defined concentrations of residual hydrido- or vinyl- reactive sites were crosslinked via hydrosilation to yield elastomeric adhesives. Specific interactions between the nitrile and phosphine oxide substituted polysiloxanes and the acidic proton of chloroform were shown using 1H NMR. The magnitude of the shift for the deshielded chloroform proton increased with the degree of hydrogen bonding, and was larger for the phosphine oxide species. The polar polysiloxane resins were filled with high concentrations of thermally conductive fillers including silica-coated AlN, Al spheres, BN and Ag flake, then hydrosilated to form microcomposite networks. Microcomposite adhesive strengths, thermal properties (glass transition temperature (Tg) and high temperature stability), and thermal conductivities were studied. An unfilled polysiloxane network containing only 15 mole percent phosphine oxide exhibited a dramatic improvement (46 N/m) in adhesive strength to Al adherends relative to a control polydimethylsiloxane network (2.5 N/m). Importantly, stable polysiloxane micro-dispersions were obtained with up to 67 volume percent (86 weight percent) silica-coated AlN. TEM data confirmed the dispersion homogeneity and XPS demonstrated that the particle surfaces were well-coated with the functionalized polysiloxanes. A microcomposite comprised of 67 volume percent silica-coated AlN and a polysiloxane containing only 9 molar percent nitrile groups had a thermal conductivity of 1.42 W/mK. The glass transition temperatures of the microcomposites were controlled by the amounts of polar functional moieties on the resins and the network crosslink densities. All of the microcomposites exhibited Tgs lower than -44°C and the materials remained stable in dynamic TGA measurements to approximately 400°C in both air and nitrogen.en_US
dc.publisherVirginia Techen_US
dc.relation.haspart01hoyt.pdfen_US
dc.rightsI hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to Virginia Tech or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report.en_US
dc.subjectthermally conductiveen_US
dc.subjectequilibrationen_US
dc.subjectnitrileen_US
dc.subjectnetworksen_US
dc.subjectphosphine oxideen_US
dc.subjectmicrocompositeen_US
dc.subjectcarboxylic aciden_US
dc.subjectadhesivesen_US
dc.subjecthydrosilationen_US
dc.subjectpolysiloxaneen_US
dc.titleSynthesis of Functionalized Polysiloxanes and Investigation of Highly Filled Thermally Conductive Microcompositesen_US
dc.typeDissertationen_US
dc.contributor.departmentChemistryen_US
dc.description.degreePh. D.en_US
thesis.degree.namePh. D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.grantorVirginia Polytechnic Institute and State Universityen_US
thesis.degree.disciplineChemistryen_US
dc.contributor.committeechairRiffle, Judy S.en_US
dc.contributor.committeememberShultz, Allan R.en_US
dc.contributor.committeememberDillard, John G.en_US
dc.contributor.committeememberMcGrath, James E.en_US
dc.contributor.committeememberEsker, Alan R.en_US
dc.identifier.sourceurlhttp://scholar.lib.vt.edu/theses/available/etd-12092002-150514/en_US
dc.date.sdate2002-12-09en_US
dc.date.rdate2008-10-15
dc.date.adate2002-12-10en_US


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