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  • 1985-1989  (7)
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  • 1
    Electronic Resource
    Electronic Resource
    Free radicals induced by adriamycin-sensitive and adriamycin-resistant cells: a spin-trapping study (1989)
    s.l. : American Chemical Society
    Biochemistry 28 (1989), S. 8653-8658 
    Details
    ISSN: 1520-4995
    Source: ACS Legacy Archives
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/bi00447a056
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Simultaneous evaluation of viscosity and retardation time in glassy polymers by a parallel-plate technique (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 642-646 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this work we describe a new experimental procedure for parallel-plate rheometry of glassy polymers above the glass-transition temperature range. This method has been used with an automated setup built by us which is linked to a HP-86 desk computer. Both our experimental procedure and experimental setup allow us not only to determine the Newtonian viscosity in the wide 104–109 Pa s range, but also the evaluation of a kind of retardation time. This is related to the time that the sample needs to reach the viscous behavior. Moreover, this time can be identified with the retardation time corresponding to the effects of the entanglements in the polymer melt, at least for the two polymers investigated here: polycarbonate and polysulfone.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.341954
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Study of the α and β relaxations on a commercial poly(vinyl chloride) by thermally stimulated creep and depolarization current techniques (1986)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 59 (1986), S. 3829-3834 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Thermally stimulated creep and depolarization current measurements have been carried out in a temperature range between −180 and 120 °C, on a pure commercial poly(vinyl chloride). Mechanical and dielectric relaxation times involved in α and β relaxations are obtained by fractional stresses/polarizations procedure. The distribution of the Arrhenius-like kinetic parameters, deduced from the relaxation times, is interpreted in terms of compensation laws. From the obtained results, a same molecular origin can be assumed for the mechanical and dielectric behavior in both α and β relaxations. Moreover, the compensation law analysis leads to two different relaxations modes, likely associated to two kinds of thermally activated molecular motions, in β relaxation. In the α region, the values of found kinetic parameters point out a high degree of cooperativeness of the involved molecular motions. Depolarization curve in this region shows a high temperature peak, not found in the mechanical one, whose evolution with the poling field allows us to assign it to a nondipolar process associated to the movement of free charge carriers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.336724
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Viscosity and relaxation times temperature behaviour above the glass transition in some glassy polymers (1987)
    Springer
    Polymer bulletin 18 (1987), S. 39-45 
    Details
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract We have performed mechanical and dielectric dynamic measurements above the glass-transition temperature range of two glassy-polymers: Poly(Hydroxyether of Bisphenol-A) and Poly(Carbonate of Bisphenol-A). From these measurements the temperature dependence of mechanical and dielectric mean relaxation times has been calculated. Results obtained have been compared with the viscosity temperature behaviour of the same polymers, which has been reported elsewhere. Both, relaxation times and viscosity temperature behaviour can well be described by Doolittle functional forms, exp{1/[αf(T-To)]}, with the same values of To but different values of the apparent free-volume expansion coefficient, αf. This difference in the experimental behaviour has been addresed in the framework of the free-volume model ideas. In this context, the different values of αf obtained from viscosity and relaxation times temperature behaviour can be understood assuming different values of critical volume controlling the molecular motions associated to viscosity and relaxation processes. Similar conclusions have also been obtained by means of a fine revision of the viscosity and relaxation times data of another two glassy-polymers: Poly(Arylate) and Poly(Sulfone of Bisphenol-A), reported previously.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00255820
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    Switching electrical power of bulk chalcogenide glassy semiconductors (1987)
    Springer
    Journal of materials science 6 (1987), S. 823-825 
    Details
    ISSN: 1573-4811
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01729025
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  • 6
    Electronic Resource
    Electronic Resource
    Theoretical interpretation of activation energies associated with the glass transition, obtained from td or DSC experiments (1987)
    Springer
    Journal of thermal analysis and calorimetry 32 (1987), S. 623-635 
    Details
    ISSN: 1572-8943
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Thermodilatometrische (TD) und differential-scanningkalorimetrische (DSC) Experimente mit verschiedenen Arten von Gläsern im Glastransitionsbereich werden unter Verwendung eines Computers mittels des kürzlich vorgeschlagenen theoretischen Modells des freien Volumens simuliert. Aus den erhaltenen Ergebnissen geht hervor, daß die oft benutzten empirischen Prozeduren zur Bestimmung der sich auf die Glastransition beziehenden ‚'Aktivierungsenergien“ theoretisch gerechtfertigt sind. Diese ‚'Aktivierungsenergien“ werden im Rahmen des benutzten Modells als mittlere Energien für die strukturellen Umordnungen im Glas interpretiert.
    Abstract: Резюме Термодилатометриче ские и ДСК измерения различных стекол в об ласти температур стеклообразования б ыли промоделированы на ЭВМ с помощью ранее предло женной модели теоретически свобод ного объема. Полученн ые результаты дали возм ожность теоретическ и обосновать эмпириче ские методы определе ния «энергий активации» процесса стеклообразования. Кроме того, в рамках ис пользованной модели, такие «энергии активации» интерпретированы как средние энергии с труктурных преобраз ований в стекле.
    Notes: Abstract Thermodilatometry (TD) and differential scanning calorimetry (DSC) experiments in the glass-transition region of different kinds of glasses have been simulated on a computer by means of a previously proposed theoretical free volume model. From the results obtained, the empirical procedures often used to obtain the values of “activation energies” associated with the glass transition are theoretically justified. Moreover, these “activation energies” are interpreted, in the framework of the model used, as average energies for the structural rearrangements in the glass.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01912715
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    Paper (German National Licenses)
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  • 7
    Electronic Resource
    Electronic Resource
    Determining viscosity temperature behavior of four amorphous thermoplastics using a parallel plate technique (1987)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 27 (1987), S. 810-815 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    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 temperature dependence of the Newtonian viscosity, ηo(T), of four structurally related amorphous thermoplastics (polyarylate, polysulfone, polycarbonate, and phenoxy) was measured in the temperature region between Tg and (Tg + 100 K) by means of a parallel plate technique. This offers a simple and quick alternate mode of measurement to traditional techniques. Values of ηo(T) measured, as well as some data obtained from literature and corresponding to the T 〉 (Tg + 100 K) range, were fitted to Vogel-Fulcher expressions. Fractional free volume at Tg was evaluated from Vogel-Fulcher parameters. The values obtained are similar for all polymers studied, and they are greater than those normally observed for other amorphous polymeric systems that are structurally simpler. From the results obtained we can conclude that the rheological behavior and, hence, the chain “stiffness” of polyarylate, polysulfone, and polycarbonate, at the temperature range of industrial processing, are very similar. However, phenoxy, which contains a greater number of nonaromatic flexible structures in its chain, has a different behavior with a lower activation energy for viscous flow in the same range of temperature.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760271107
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