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  • 1
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-2: Polymer Physics 9 (1971), S. 531-541 
    ISSN: 0449-2978
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Dilatometric and calorimetric studies have been made of the fusion process of linear polyethylene crystallized by stirring xylene solutions at elevated temperatures. It is shown that the melting point of the crystals increases rapidly from 139.5°C to 145°C in the crystallization temperature range of 100-103°C and levels off to 146 ± 0.5°C, provided that very slow heating rates are employed. Stirrer-crystallized samples treated with fuming nitric acid show higher crystalline contents. Comparison of their enthalpies of fusion and melting points indicate that higher molecular order along the fiber axis is associated with higher crystallization temperatures. This is in general agreement with corresponding results of other modes of crystallization. The attack of fuming nitric acid on stirrer crystals is characterized by weight-loss curves similar to those of dilutesolution crystals and bulk polyethylene. The linear molecular weight dependence on time of exposure to nitric acid suggests that the oxidation proceeds mainly from the chain ends at a constant rate for samples stirred in the lower crystallization range, but an increased rate is observed for a sample stirred from xylene at 105°C. It is suggested that the lamellar overgrowths, most evident at low crystallization temperatures, are epitaxially attached to the fiber axis, whereas the smaller crossbandings observed at higher crystallization temperatures are possibly made up of elements of chains that are only partly incorporated in the highly ordered fibrous core.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Enzyme-purified elastin from bovine ligamentum nuchae was digested with elastase in the presence of sodium dodecyl sulfate. Chromatographic fractionation of the digest, after removal of the detergent, resulted in the high-yield isolation of two peptide fractions (F2 and F3) that differed in size and composition. The larger, F2, which accounted for about 55% of the starting material, was subjected to sedimentation-equilibrium analysis in three chaotropic solvents. Comparison of the distribution of point-average molecular weights (Mw and Mz) with protein concentration in the three systems lead to the conclusion that significant self-association of peptides occurred in the absence of 6M guanidinium hydrochloride. In this solvent, the molecular-weight distribution was between 25,000 and 34,000, a range of values in agreement with an intrinisic viscosity of 13.1 cc g-1 determined in the same solvent. Assessment of chain weight by N- and C-terminal analysis was consistent with F2 being a multichain molecule comprising four polypeptide chains linked by three polyfunctional amino acids. Results are interpreted in terms of an anisotropic ultrastructural model of the protein, in which four polypeptide chains constitute the primary filament visualized by electron microscopy in the intact fiber.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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