THE PHOTOCHEMISTRY OF POLYENYL RADICALS AND ITS APPLICATION TO UHMWPE FOR USE IN ARTIFICIAL CARTILAGE

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dc.contributor.advisorAl-Sheikhly, Mohamaden_US
dc.contributor.authorKasser, Michael Jacoben_US
dc.contributor.departmentMaterial Science and Engineeringen_US
dc.contributor.publisherDigital Repository at the University of Marylanden_US
dc.contributor.publisherUniversity of Maryland (College Park, Md.)en_US
dc.date.accessioned2009-10-06T06:20:55Z
dc.date.available2009-10-06T06:20:55Z
dc.date.issued2009en_US
dc.description.abstractThe use of UV light as an alternative to thermal treatments above the melting point (150 °C) to remove free radicals in irradiated UHMWPE was explored. It was found that, in contrast to the allyl free radical which is converted by 258 nm light to alkyl free radicals, polyenyl radicals are not converted to alkyl radicals by UV light. None-the-less, by sandwiching UV light treatments between low temperature thermal anneals (100 °C), it was possible to reduce free radical concentrations by 30%. This reduction was achievable for depths up to one millimeter. However, this reduction did not have a significant effect on oxidation due to an increase in oxidation susceptibility because of the concurrent increase in concentration of easily abstracted allylic hydrogens. By photoirradiating for the optimal amount of time, it was possible, for the first time, to synthesize a polyethylene sample whose residual free radicals consisted of almost entirely dienyl free radicals. This allowed unambiguous identification and simulation of dienyl free radical's EPR spectra to be a singlet containing nine peaks separated by 9 G hyperfine separation. Detailed studies of photoirradiation of UHMWPE containing free radicals revealed that photoirradiation with a continuous spectrum above 200 nm causes the decay of diene unsaturations and allyl free radicals, a reduction in the overall amount of free radicals, and an increase in the degree of unsaturation of polyenyl free radicals. Upon longer photoirradiation times, polyenyl radicals were converted from lower to higher degrees of unsaturation. This effect was identical in the presence and absence of oxygen, but was suppressed by hydrogen gas. These results showed that the conversion does not occur by a linear alkyl radical addition mechanism wherein alkyl radicals migrate to stable polyene unsaturations and polyenyl radicals thereby increasing their order, as previously suggested. The valid mechanism appears to be the direct photoconversion of diene unsaturations to dienyl radicals and lower order polyenyl radicals to higher order polyenyl radicals.en_US
dc.format.extent2413780 bytes
dc.format.mimetypeapplication/pdf
dc.identifier.urihttp://hdl.handle.net/1903/9592
dc.language.isoen_US
dc.subject.pqcontrolledEngineering, Materials Scienceen_US
dc.subject.pqcontrolledChemistry, Radiationen_US
dc.subject.pquncontrolledfree radicalen_US
dc.subject.pquncontrolledphotochemistryen_US
dc.subject.pquncontrolledpolyenylen_US
dc.subject.pquncontrolledPolyethyleneen_US
dc.subject.pquncontrolledreplacement jointsen_US
dc.subject.pquncontrolledUHMWPEen_US
dc.titleTHE PHOTOCHEMISTRY OF POLYENYL RADICALS AND ITS APPLICATION TO UHMWPE FOR USE IN ARTIFICIAL CARTILAGEen_US
dc.typeDissertationen_US

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