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  • 1
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 34 (1994), S. 203-208 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The relaxed potential energy surfaces of chitobiose were calculated based on the MM3-force field by optimizing dimer structures on a 10° grid spacing of the torsional angles about the glycosidic bonds (Φ,Ψ). The 36 conformations; the four combinations of the hydroxymethyl group orientations coupled with the nine of the secondary group ones -  were assumed for each Φ,Ψ conformation. The four conformations, each differing in the hydroxymethyl group orientations, were considered for the whole Φ,Ψ space, and all the 36 conformations, for the restricted space of low energy. While the resulting energy map and the structures of the energy minima were similar to those proposed for cellobiose in many respects, more restricted energy profile was suggested for the relaxed map of chitobiose where differences in the energy level between the global minimum and the local minima were within 5.4 kcal/mol, compared with the equivalent value of 3.6 kcal/mol for cellobiose. Further depression of the global minimum occurred when the acidic residue was used. The Monte Carlo samples of the chitosan chain were generated based on the relaxed map to predict the unperturbed coil dimension in solution. The chitosan chains showed Gaussian behavior at x = 500 (x, degree of polymerization) and gave the characteristic ratio Cx, of about 70, which was much larger than the experimental values observed for the chitosan and cellulosic chains. © 1994 John Wiley & Sons, Inc.
    Additional Material: 7 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 13 (1975), S. 73-86 
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Extrudates of solid linear polyethylene prepared under proper pressure and temperature conditions have a high c axis orientation along the extrusion direction, with lamellar crystals and amorphous layers stacked alternately along the extrusion direction. Kink bands were formed by compressing the oriented extrudate at room temperature along the extrusion direction. Inspection of the kink bands by wide-angle and small-angle x-ray diffraction and electron microscopy revealed that the fiber axis was rotated from the original axis direction by 70-75° and that the lamellar crystals were inclined to the fiber axis in the kink band by 55-60° and stacked nearly parallel to the kink boundary. The superstructural change during the formation of the kink band could not be interpreted in terms of uniform c axis shear alone. In addition to such a mechanism, it was necessary to take into account intermicrofibril and/or intercrystallite slip.
    Additional Material: 11 Ill.
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  • 3
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Molekulare Struktur und Kristallstruktur von Polytetrahydrofuran wurden durch eine Röntgenbeugungsanalyse bestimmt. Die Elementarzelle besitzt die Abmessungen a = 5,48, b = 8,73, c (Faserachse) = 12,07 Å und β = 134,2°. Die Raumgruppe ist C2/c - C62h. Zwei Molekülketten durchlaufen die Elementarzelle. Die Ketten liegen in einer ebenen Zick-zack-Konformation vor; die dadurch definierte Ebene fällt mit der kristallographischen (100)-Ebene zusammen.Der Infrarot-Dichroismus und -Pleochroismus wurden gemessen und eine versuchsweise Zuordnung der Absorptionsbanden angegeben und diskutiert.
    Notes: The molecular and crystal structure of polytetrahydrofuran has been determined by X-ray diffraction analysis. The unit cell dimensions are a = 5.48, b = 8.73, c (fiber axis) = 12.07 Å., and β = 134.2°. The space group is C2/c - C62h. Two molecular chains pass through the unit cell. The skeleton of the molecular chain has a planar zig-zag conformation and the zig-zag plane is parallel to the (100)-plane.The infrared dichroism and pleochroism were measured, and the tentative assignments for the infrared absorption bands were given and discussed.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
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