An isotope substitution -NMR study of trioxane /dioxolane copolymerization.
Item
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Title
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An isotope substitution -NMR study of trioxane /dioxolane copolymerization.
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Identifier
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AAI9986321
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identifier
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9986321
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Creator
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Dunn, Patrick A.
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Contributor
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Adviser: Nan Loh Yang
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Date
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1998
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Language
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English
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Publisher
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City University of New York.
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Subject
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Chemistry, Polymer
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Abstract
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On the subject of the trioxane (TOX)/dioxolane (DOL) copolymerization, the present work represents the first attempt to apply extensively the method of isotope substitution in conjunction with state of the art NMR spectroscopy to gather hitherto unattainable detailed mechanistic information. A systematic compilation of data from in-situ 13C, 1H, and DEPT NMR spectra of cationic initiated TOX/DOL copolymerization with isotope labeling of three coreactants was accomplished. Replacing TOX with TOX-d6 as comonomer resulted in a much enhanced dynamic range for resonance detection and remarkably improved overall resolutions of 1H NMR spectra, including direct pentad detection for the first time. Three distinct stages of reaction marked by the changes in formation rates of copolymer sequences can be distinguished. In the first stage, activated DOL preferentially reacts with CD2O to produce deuterium labeled trioxepane (TOP-2,2-d2). Concurrently, TOP-(2,2-d 2) generates all the observed sequences and additional comonomers simultaneously. In the second stage, the TOP-(2,2-d2)/DOL copolymerization results in the increased formation of pentads with two ethylene oxides, "E", units. In the third stage, transacetalization involving pentad sequences with two and three "E" plays a major role. Replacing DOL with DOL-(2,2-d 2) as comonomer resulted in significantly improved resolution in the methylene oxide, "M", region of 1H NMR spectra due to the elimination of the intense DOL acetal proton peak. Kinetic curves approach those with natural isotopic abundance since only 10% of the "M" units are deuterium substituted. Four distinct stages of copolymerization marked by increased generation of specific sequences and information in addition to the TOX-d6 system was observed. The first stage also includes the copolymerization of excess formaldehyde with TOP resulting in the overall increase in the generation of "M-centered" sequences. Before the second stage, TOX/TOP-(2,2-d2) copolymerization was observed resulting in the increased generation of "one E-pentads" and DOL. In the second stage, DOL/TOP-(2,2-d2) copolymerization results in the increased generation of "two E-pentads" as noted in the TOX-d 6 system, while transacetalization accounts for the increase rate of generation of "one E-pentads". Stage three marks the dominance of TOX-d6 and CD2O in generating "five-M pentads" and "one E-pentads" via transacetalization and polymerization reactions. In the polymerization systems with C13H3OCH 2OC13H3 as chain transfer agent, the early initiation of TOP was verified.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
