Acetal copolymers: Synthesis, chemical modification and degradation study.
Item
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Title
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Acetal copolymers: Synthesis, chemical modification and degradation study.
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Identifier
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AAI9510648
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identifier
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9510648
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Creator
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Cho, Kumhee.
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Contributor
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Adviser: Nan-Loh Yang
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Date
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1994
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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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The degradation of trioxane-dioxolane copolymer in DMSO-d{dollar}\sb6{dollar} solution at 120{dollar}\sp\circ{dollar}C caused by the addition of trifluoroacetic acid, AIBN, or Luperox was investigated by {dollar}\sp1{dollar}H NMR spectroscopy. The degradation mechanisms in both acidic and radical processes were proposed based on the kinetic behaviors for triad sequences of the degraded copolymer and the small molecules formed during the processes. Formaldehyde was released through {dollar}\beta{dollar}-scisson reactions of both cationic and radical chain ends. The rate constants estimated based on available (H{dollar}\sp+{dollar}) and (R{dollar}\sp.{dollar}) were 10 {dollar}\sp{lcub}-3{rcub}{dollar} (sec {dollar}\sp{lcub}-1{rcub}{dollar}) and 10 {dollar}\sp{lcub}-2{rcub}{dollar} (sec {dollar}\sp{lcub}-1{rcub}{dollar}) respectively. Cyclic acetals 1,3,5-trioxane, 1,3-dioxolane, 1,3,5,7-tetraoxane and 1,3,5-trioxepane were generated by backbiting of the cationic chain ends and intramolecular substitution of radical chain ends. The rate constant values for both reactions were about 10 {dollar}\sp{lcub}-3{rcub}{dollar} (sec {dollar}\sp{lcub}-1{rcub}{dollar}).;The estimated free energy changes for the formation of formaldehyde and cyclic acetals based on the enthalpy changes indicated that the formation of formaldehyde is more favored than cyclic acetals by 43 (kJ/mole). The difference of activation energies between formation of formaldehyde and cyclic acetals was calculated from the kinetic data. The difference in activation energy favoring the formation of formaldehyde over that of cyclic acetals was determined to be 4.5 (kJ/mole) and 9.8 (kJ/mole) in the acidic and radical degradation processes respectively. The smaller difference in the acidic process may be a consequence of lower activation energy for backbiting reaction involving stable tertiary oxonium ion and higher activation energy for the {dollar}\beta{dollar}-scisson involving heterolysis bond scission. The degradation rate of active chain end, evaluated in terms of the rate for elimination of monomer units per active chain, revealed that the radical chain end degrade at a rate more than eight times faster than the cationic one.;Trioxane copolymer carrying vicinal dibromo functional groups was synthesized and its chemical modifications were carried out for the introduction of amino and triple bond functional groups. The resulting copolymer with backbone -C{dollar}\equiv{dollar}C- group has been demonstrated to be not only more stable than the copolymer with backbone -C=C- against degrading agent, Br{dollar}\sb2{dollar}, but also in the oxidative thermal degradation. In the oxidative thermal degradation, the functionalized copolymer with pendant hindered phenol-amine group showed better stability than the copolymers with comparable incorporation of octylamine pendant group or with higher incorporations of backbone -C=C- and -C{dollar}\equiv{dollar}C- groups.
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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.
