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An NMR Study of Microvoids in PolymersAn understanding of polymer defect structures, like microvoids in polymeric matrices, is most crucial to their fabrication and application potential. In this project guest atoms are introduced into the microvoids in PMR-15 and NMR is used to determine microvoid sizes and locations. Xenon is a relatively inert probe that would normally not be found naturally in polymer or in NMR probe materials. There are two NMR active Xenon isotopes, Xe-129 and Xe-131. The Xe atom has a very high polarizability, which makes it sensitive to the intracrystalline environment of polymers. Interactions between the Xe atoms and the host matrix perturb and Xe electron cloud, deshielding the nuclei, and thereby expanding the range of the observed NMR chemical shifts. This chemical shift range which may be as large as 5000 ppm, permits subtle structural and chemical effects to be studied with high sensitivity. The Xe-129-NMR line shape has been found to vary in response to changes in the pore symmetry of the framework hosts in Zeolites and Clathrasil compounds. Before exposure to Xe gas, the PMR-15 samples were dried in a vacuum oven at 150 C for 48 hours. The samples were then exposed to Xe gas at 30 psi for 72 hours and sealed in glass tubes with 1 atmosphere of Xenon gas. Xenon gas at 1 atmosphere was used to tune up the spectrometer and to set up the appropriate NMR parameters. A series of spectra were obtained interspersed with applications of vacuum and heating to drive out the adsorbed Xe and determine the role of Xe-Xe interactions in the observed chemical shift.
Document ID
19960052321
Acquisition Source
Legacy CDMS
Document Type
Conference Paper
Authors
Toy, James
(Norfolk State Univ. VA United States)
Mattrix, Larry
(Norfolk State Univ. VA United States)
Date Acquired
August 17, 2013
Publication Date
July 1, 1996
Publication Information
Publication: HBCUs Research Conference Agenda and Abstracts
Subject Category
Nonmetallic Materials
Report/Patent Number
Paper-25
Accession Number
96N35518
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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