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  • 1
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 35 (1997), S. 213-223 
    ISSN: 0887-6266
    Keywords: stress-strain ; yield ; crystallite ; ethylene copolymer ; superstructure ; lamellae ; Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Nominal stress-strain curves of a series of random ethylene-hexene copolymers having narrow composition and most probable molecular weight distributions were investigated. A series of such molecular weight copolymers with a constant concentration of branches were crystallized under a variety of conditions. In each molecular weight series the level of crystallinity was approximately constant. Particular attention was focused on the yield region and the nature of the yielding process. It was found, quite surprisingly, that the yield stress was not solely dependent on the crystallinity level. Moreover, the shape of the force-elongation curve in the yield region was very dependent on the molecular weight and the crystallization mode. These changes in yielding correlated quite well with the overall crystallite structure that was characterized by thin section transmission electron microscopy. The orthorhombic unit cell of polyethylene was maintained in all the samples despite the changes that occurred in the overall crystallite structure. © 1997 John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
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  • 2
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 15 (1977), S. 1189-1198 
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Previous work on the small-angle light scattering of polyethylene films, to determine the supermolecular structure, has been continued. One of the main efforts has been the study of a binary mixture whose low molecular weight component forms well defined spherulites and whose high molecular weight component yields a poorly defined rod-like morphology. The addition of the high molecular weight fraction causes a progressive deterioration of the initial spherulitic morphology; a relatively small amount of the high molecular weight species causes a major decrease in the spherulitic size. However, there are no indications of any spherulitic structures when the weight fraction of the high molecular weight species is 0.5 or greater. The isothermal crystallization of a fraction M = 6.6 × 105 was also studied. Spherulites were formed at low crystallization temperatures while at the higher crystallization temperatures the morphology became nondistinct. Preliminary studies with solvents indicate that high molecular fractions, which do not form spherulites when crystallized in the pure state, do so when crystallized from highly swollen solutions.
    Additional Material: 6 Ill.
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  • 3
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 16 (1978), S. 1583-1592 
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: There are several reports in the literature to the effect that when isotactic polystyrene crystallizes from moderately dilute solution, lamellas (precipitate) form at high crystallization temperatures and gels at low temperatures. We report here the occurrence of a very similar phenomenon during the crystallization of ethylene-butene-1 copolymers. The observations for the latter system can be given a straightforward explanation based on the demonstrated compositional fractionation that occurs on crystallization. Low co-unit content copolymers are associated with lamellas. Gels invariably contain much higher co-unit content. A generalization of these findings is invoked to explain the previous polystyrene results. A new resonance detected by 13C NMR experiments in this polymer can be ascribed to head-head sequences.
    Additional Material: 3 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 20 (1982), S. 641-650 
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Carbon-13 nuclear magnetic resonance relaxation parameters have been obtained as a function of temperature for a set of branched polyethylenes whose β transition temperatures were determined independently. Resolvable spectra could be obtained at temperatures either corresponding to or very close to the temperature of the β transition. Together with results for other systems, these observations preclude the indentification of the β transition with the glass temperature. From the measured spin relaxation times and nuclear Overhauser enhancements average correlation times were calculated as a function of temperature. The average correlation times were calculated as a function of temperature. The average correlation time is on the order of 10-8-10-9 s at the β transition. These results argue strongly against it being assigned to the glass temperature.
    Additional Material: 5 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 21 (1983), S. 29-43 
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The first-, third-, and fifth-order low-frequency, Raman-active, longitudinal acoustical modes of the n-alkane C94H190 and different morphological forms of semicrystalline polyethylene have been obtained. An analysis of the results shows that the correction needed to obtain the extended planar-zigzag ordered sequence length is maximum for the n-alkane and very small for the polymer systems. These represent solution crystals as well as bulk-crystallized material. For the latter, samples were prepared so that the crystallite thickness is either comparable to or very much smaller than the extended chain length. An approximate method is also developed which enables the natural linewidth to be determined.
    Additional Material: 4 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 16 (1978), S. 1135-1138 
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Additional Material: 3 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 18 (1980), S. 2347-2367 
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Replicas and thin-section electron microscopic studies were made of fractions of linear polyethylene covering the molecular weight range 2.78 × 104 to 6.0 × 106 for a variety of crystallizing conditions. Lamellar crystallites were found under all circumstances; and the supermolecular structure, or crystalline morphology, is in agreement with that previously reported from an analysis of the small-angle light-scattering patterns of the same samples under similar crystallization conditions. Details of the crystalline microstructure are also described, which range from truncated hollow pyramids which degenerate as the molecular weight or the undercooling are increased. From these results, it is possible to describe the mechanism of formation of polyethylene spherulites.
    Additional Material: 15 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 19 (1981), S. 1769-1790 
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Replica and thin-section electron microscopy was performed on a linear polyethylene fraction (Mw = 1.89 × 105, Mn = 1.79 × 10 5) which was either isothermally crystallized or quenched at difference temperatures. The results are numerically analyzed in such a manner so as to give the distribution of the total long spacing and of the crystallite and amorphous thicknesses. The quantitative information about the maximum and minimum values for these parameters at each crystallization temperature yields important clues as to possible molecular processes involved. Qualitative information regarding general morphology, molecular tilt with respect to the lamellar surface, and possible crystallographic faults are also discussed.
    Additional Material: 15 Ill.
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  • 9
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Wide-angle neutron scattering studies have been made of a series of mixed crystal blends of polyethylene and deuterated polyethylene in the range 0.68 ≤ K = 4πλ-1 sinθ ≤ 2.02 Å-1. Recent calculations by Stamm have shown that regularly folded subunits of small numbers (two to ten) of stems should produce an observable modulation of the diffuse scattering pattern of such mixtures in this K range. For both melt- and solution-crystallized blends, no extra signal was observed above the background scattering level. The data are used to place an upper limit (of about four) on the number of stems that could be regularly folded in the (100) and (010) planes for these materials.
    Additional Material: 10 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 21 (1983), S. 285-294 
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: An analysis of the Raman internal modes of dilute-solution-crystallized homopolymers and co-polymers of ethylene has been made, similar to the work previously reported for the bulk-crystallized polymers. The crystallite structure can be described in terms of the relative amounts of the crystalline orthorhombic phase, the liquidlike amorphous phase, and the interfacial region. These quantities change with the molecular constitution of the chains and the crystallization conditions. The level of crystallinity decreases significantly with increasing counit content as would be expected. In addition, an appreciable interfacial structure develops in copolymers as compared with the homopolymers. A possible relationship between the interfacial content and the relaxation transitions in polyethylene is discussed.
    Additional Material: 1 Ill.
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