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dc.contributor.authorWang, Fengen
dc.date.accessioned2014-03-14T20:22:28Zen
dc.date.available2014-03-14T20:22:28Zen
dc.date.issued1998-04-23en
dc.identifier.otheretd-72698-13572en
dc.identifier.urihttp://hdl.handle.net/10919/30687en
dc.description.abstractThis thesis addresses the systematic modification of poly(tetramethylene oxide) (PTMO), polyether based segmented thermoplastic polyurethane with a secondary aminoalkyl functional polydimethylsiloxane (PDMS), which was intended to improve the fire resistance of polyurethane systems. The PDMS oligomer was successfully incorporated into the polyurethane backbone via one step solution polymerization. The effect of PDMS content on thermal stability, morphology, surface composition, mechanical properties, and fire resistance of polyurethane was investigated. These polymers displayed a complex two phase morphology and composition-dependant mechanical properties. The PDMS segment microphase separated from other polyurethane segments and varying microphase separation morphologies were observed with differing PDMS content. Spherical dispersed complex phases and co-continuous phases occurred when the PDMS content was 15wt% and 55wt%, respectively. Similar thermal stability was observed for both the polyurethane control and the PDMS modified polyurethanes, but the later displayed increased char yield in air with increased PDMS concentration. Quantitative measurements of the fire resistance of the modified polyurethanes by cone calorimetry showed that the peak heat release rate of the 15wt% siloxane modified samples dropped 67wt%, compared with the polyurethane control. However, the peak heat release rate did not further change with increasing siloxane content. Excellent mechanical properties, in terms of tensile strength and elongation, were found for the modified polyurethane with 15wt% of PDMS. Higher PDMS levels did reduce tensile strength, probably because of the reduction in strain crystallizing PTMO content. The PDMS modification, which resulted in improved fire resistance and excellent mechanical properties, is attributed to the low surface energy of the PDMS segment that tended to migrate to the surface of the polymer. It could be oxidized into a partially silicate-like material upon heating in air. In addition, the syntheses of primary and secondary aminoalkyl functional PDMS based segmented polyureas are described herein. Two-phase morphology was observed for all the polyurea samples, even when the hard segment concentration was as low as 6wt%. All these polyureas formed clear transparent films that exhibited good mechanical properties even with very high PDMS content, up to 94wt%. They also demonstrated similar thermal stability, independent of the PDMS end group. However, the nature of the end group, i.e. primary or secondary aminoalkyl, had a dramatic effect on mechanical and morphological properties of these PDMS based polyureas, which was interpreted in terms of the level of hydrogen bonding.en
dc.publisherVirginia Techen
dc.relation.haspartDisswhl2.pdfen
dc.rightsIn Copyrighten
dc.rights.urihttp://rightsstatements.org/vocab/InC/1.0/en
dc.subjectfire resistancyen
dc.subjectpolydimethylsiloxaneen
dc.subjectpolyureaen
dc.subjectpolyurethaneen
dc.subjectsegmented copolymeren
dc.titlePolydimethylsiloxane Modification of Segmented Thermoplastic Polyurethanes and Polyureasen
dc.typeDissertationen
dc.contributor.departmentChemistryen
dc.description.degreePh. D.en
thesis.degree.namePh. D.en
thesis.degree.leveldoctoralen
thesis.degree.grantorVirginia Polytechnic Institute and State Universityen
thesis.degree.disciplineChemistryen
dc.contributor.committeechairMcGrath, James E.en
dc.contributor.committeememberAnderson, Mark R.en
dc.contributor.committeememberDillard, John G.en
dc.contributor.committeememberShultz, Allan R.en
dc.contributor.committeememberRiffle, Judy S.en
dc.contributor.committeememberMcGrath, James E.en
dc.identifier.sourceurlhttp://scholar.lib.vt.edu/theses/available/etd-72698-13572/en
dc.date.sdate1998-04-23en
dc.date.rdate1998-08-31en
dc.date.adate1998-08-31en


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