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  • 1
    Electronic Resource
    Electronic Resource
    Conformational Behavior of the Spacer in a Liquid Crystalline Main-Chain Polymer in Its Nematic and Glassy States (1995)
    s.l. : American Chemical Society
    Macromolecules 28 (1995), S. 6937-6941 
    Details
    ISSN: 1520-5835
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ma00124a033
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  • 2
    Electronic Resource
    Electronic Resource
    Nonexponential relaxation functions above T"g analysed by multidimensional NMR and novel spin-echo decay techniques
    Amsterdam : Elsevier
    Physica A: Statistical Mechanics and its Applications 201 (1993), S. 79-87 
    Details
    ISSN: 0378-4371
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0378-4371(93)90402-P
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  • 3
    Electronic Resource
    Electronic Resource
    Geometry and time scale of the complex rotational dynamics of amorphous polymers at the glass transition by multidimensional nuclear magnetic resonance (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 7088-7096 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present a new multidimensional NMR exchange experiment, three dimensional difference correlated exchange spectroscopy (DICO), which allows one to extract detailed information about the time scale as well as the geometry of rotational processes simultaneously. In contrast to experiments presently available the geometric information specified by a dynamic order parameter is independent of a specific model. Among others full isotropisation can be directly seen from the spectrum via a symmetry criterion. We apply this method to study the chain motion of polystyrene slightly above the glass transition. The DICO spectra prove that a typical chain segment performs small angle fluctuations as well as large angle jumps which can neither be described as random jumps nor tetrahedral jumps. A typical jump angle can be estimated to be of the order of 30°−40°. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472511
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  • 4
    Electronic Resource
    Electronic Resource
    Molecular dynamics at the glass transition: One dimensional and two dimensional nuclear magnetic resonance studies of a glass-forming discotic liquid crystal (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 3749-3759 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The molecular dynamics of the aromatic core as well as the hydrocarbon side chains have been studied in a new kind of glass-forming discotic liquid crystal, based on a triphenylene core. It serves as a model compound in which only a limited number of degrees of freedom is activated at the glass transition. Slow motion with non-Arrhenius temperature dependence (α process) is associated with the axial motion of the discs around the column axis. The geometry of this rotation is found to be neither a simple threefold jump as suggested by the pseudo threefold symmetry of the substituted triphenylene core nor does it correspond to small-step rotational diffusion, established as a prominent feature of the rotational motions of polymers at the glass transition. Instead ill-defined angular displacements with pseudo threefold symmetry are detected by two-dimensional exchange NMR. A simple model combining small-step diffusion and rotational jumps is presented that quantitatively accounts for the angular displacements observed. The motional behavior and the conformational order of the side chains were also studied. This shows that the high frequency β process detected previously by dielectric spectroscopy indeed can be associated with side chain motions. Moreover evidence is presented that the axial motion of the discs is a cooperative process, where adjacent molecules within the column rotate in a correlated fashion without changing the conformation of the side chains in the immediate neighborhood of the core.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462956
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  • 5
    Electronic Resource
    Electronic Resource
    Rotational dynamics of substituted phthalocyaninatopolysiloxanes as measured by 2D solid-state NMR spectroscopy (1993)
    Weinheim : Wiley-Blackwell
    Acta Polymerica 44 (1993), S. 31-38 
    Details
    ISSN: 0323-7648
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Das rotationsdynamische Verhalten eines Polymers vom “hairy rod”-Typ wurde im festen Zustand gemessen. Für diese Untersuchungen wurden am aromatischen Kern selektiv deuterierte Octa-(alkoxy)-phthalocyaninatopolysiloxane synthetisiert. Die bilden eine hexagonale säulenförmige Struktur, die im Temperaturbereich von 170 bis 470 K keine Phasenänderungen zeigt. Durch Festkörper-Echo 2H-NMR-Spektroskopie konnten thermisch aktivierte uniaxiale Rotationen der Phthalocyanateinheit um die Längsachse des Polymers nachgewiesen werden. Die zweidimensionale NMR-Spektroskopie zeigt, daß der Bewegungsprozeß 90°-Sprünge mit beträchtlicher Verbreiterung des Reorientierungspotentials umfaßt, was die Vierfachsymmetrie der Elementareinheit widerspiegelt. Dies weist darauf hin, daß die Moleküle eher um ihre covalenten Si-O-Bindungen rotieren anstatt als ganze Siliconphthalocyanin-Einheiten um die Säulenachse.
    Notes: The rotational dynamic behaviour of a polymer of the hairy rod type has been investigated in the solid state. Octa-(alkoxy)-phthalocyaninatopolysiloxanes have been synthesized selectively deuterated at the aromatic core positions for this study. They form a hexagonal columnar structure without any phase change in the temperature range from 170 to 470 K. Thermally activated uniaxial rotation involving the phthalocyanato moiety around the long axis of the polymer is detected by solid-echo 2H-NMR spectroscopy. Two-dimensional NMR spectroscopy shows that the motional process involves 90° jumps with considerable broadening of the reorientation potential, reflecting the four-fold symmetry of the repeat unit. This indicates that the siliconphthalocyanine moieties can rotate around their covalent Si-O bond within a single macromolecule, rather than the molecules as a whole around their columnar axes.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/actp.1993.010440105
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