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  • Polymer and Materials Science  (4)
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  • 1
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 28 (1983), S. 1137-1146 
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The dielectric loss behavior of crosslinked polyethylene has been determined over the frequency range 10-5 kHz and over the temperature range -150 to 100°C. Major loss effects occur at the lower temperatures and are caused by libration of the organic byproducts of the crosslinking agent, dicumyl peroxide. Analog materials prepared from linear low density polyethylene by blending in of either acetophenone or 2-phenyl-2-propanol confirm the hypothesis. The effects of concentration of by products and of orientation of the polymer have been studied. Activation energy analyses suggest that room temperature losses will occur in the microwave region. The behavior is significantly affected by curing with steam, typical loss peaks being an order of magnitude lower than for dry cured specimens. A new loss region appears close to but below, 0°C.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 23 (1985), S. 2483-2498 
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The dielectric and viscoelastic relaxation behavior of linear low-density polyethylene has been investigated. All three usual relaxation regions occur; however, the α process is more dominant than in conventional low-density polyethylene made dielectrically active through the introduction of carbonyl groups. The observed behavior is very sensitive to orientation and morphology. There are significant differences between oriented samples (stretching or extrusion) and a single-crystal texture specimen. Effects are caused by dipolar orientation and dipolar immobilization, the relative importance of each effect varying with specimen preparation. Active dipolar groups are not carbonyls, or any common organic species, but appear to be due to chain ends having residual dipoles caused by the catalyst used in synthesis.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 24 (1986), S. 1259-1269 
    ISSN: 0887-6266
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Dielectric relaxation studies have been used as a means of investigating the behavior of aromatic molecules dissolved in a semicrystalline polymer. All molecules show a relaxation in the vicinity of the γ loss peak of polyethylene, while several show an additional peak at lower temperatures. The latter is interpreted as an indicator of molecular motions below the glass transition and the former is to be associated with the onset of molecular motions on a local scale as the glass transition is approached. The α loss process of polyethylene is seemingly unaffected by the presence of the molecules. Integration of loss curves shows that, at most, 50% of the molecules are able to relax but that the fraction relaxing increases with increasing temperature, suggesting the presence of a wide distribution of sites within the polymer.
    Additional Material: 9 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 27 (1989), S. 1333-1347 
    ISSN: 0887-6266
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Stretched polyethylene has been used for several years by organic spectroscopists as a means of orienting isolated aromatic molecules. Dielectric relaxation studies are reported which consider dipolar aromatic molecules dissolved in stretched polyethylene in order to learn more about the environment of these oriented molecules. The research builds on earlier studies of the dielectric relaxation behavior of dipolar aromatic molecules dissolved in unoriented low density polyethylene. Studies demonstrate that molecules in the amorphous phase are oriented at temperatures below the glass transition, both the β and γ relaxations being orientation dependent. It is shown through studies of oriented rods that large numbers of the orientable molecules are immobilized by the oriented polyethylene and cannot relax. An essential criterion for immobilization to occur is that molecules exhibit geometrical symmetry.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
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