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  • 1
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The crystallization behaviour of the series of hydrogenated poly(butadiene-alt-ethene) to poly[butadiene-alt-(1-hexadecene)] copolymers was investigated with the aid of differential scanning calorimetry (DSC) and X-ray measurements. Hydrogenated poly(butadiene-alt-ethene) corresponds to polyethylene and crystallizes in the same way. Hydrogenated copolymers poly(butadiene-alt-propene) through poly[butadiene-alt-(1-decene)] are completely amorphous. In these cases the large branching degree prevents crystallization of the main chains, whereas the side chains are too short to be able to crystallize above the glass transition temperature. The critical length is obviously reached in case of hydrogenated poly[butadiene-alt-(1-dodecene)]. The part of the series with large side chains (hydrogenated poly[butadiene-alt-(1-dodecene)] through poly[butadiene-alt-(1-hexadecene)], shows the most interesting effects, especially hydrogenated poly[butadiene-alt-(1-dodecene)], which shows crystallization depending on thermal history. In these substances the side chains are long enough to cause side-chain crystallization, which becomes more pronounced with increasing length of the side chains. The crystal structure is not excactly to be determined, but some data indicate a model, in which the side chains are packed in a manner as in unbranched alkanes, but are also possible orthorhombic. However, the quality of the crystals formed is not very good, so these regions are better described as ordered domains rather than as crystallites.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Poly[(butadiene-alt-ethene)-co-(butadiene-alt-1-olefin)] terpolymers were synthesized by Ziegler-Natta polymerization using VO(O-neopentyl)2Cl/Al(i-Bu)3 catalyst system in toluene. Variation of the 1-olefin/ethene ratio in the monomer feed produces terpolymers with mixed units of butadiene-alt-ethene and butadiene-alt-1-olefin. After hydrogenation one obtains model substances for LLDPE with a special distribution of methylene sequences between branching points. Differential scanning calorimetry (DSC) was used to determine the degree of crystallinity and the melting behavior. From the melting temperature region, the thickness distribution of the crystal lamellac, and thus the average number of C-atoms between the alkyl branches, can be determined. From detailed X-ray diffractometry, the mean crystallite size, the lattice distortions and the degree of crystallinity was determined for those products which show distinct reflections. The crystallization behavior can only be described by a three-phase model.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 0959-8103
    Keywords: blend ; molecular dynamics ; dielectric investigation ; DSC measurements ; glass relaxation process ; local process ; molecular weight ; compatibility ; polystyrene ; tetramethyl polycarbonate ; Chemistry ; Polymer and Materials Science
    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: Dielectric and calorimetric measurements have been carried out for tetramethyl polycarbonate/polystyrene (TMPC/PS) blends with different compositions. The effect of varying the molecular weight of the weakly polar component (PS) on the molecular dynamics of the polar segments of TMPC has been thoroughly studied over wide ranges of frequency (10-2-105 Hz), temperature (50-220°C) and number average molecular weight, M̄n, (6500-560 000 g mol-1). All blends were found to be compatible regardless of the composition ratio and the molecular weight of PS. Some new and interesting experimental findings have been observed concerning the effect of molecular weight on the glass temperature and on the broadness of the glass transition and relaxation. Neither the kinetics nor the distribution of relaxation times of the local process observed in pure TMPC was affected by blending with PS, regardless of the composition ratio or the molecular weight of PS. It has been concluded that the mixing of the polymeric components to form a homogeneous single phase (compatible blend) does not take place on a segmental level but on a structural one. The size of this structural level has been suggested to have the same volume as the cooperative dipoles, which is assumed to be the minimum volume responsible for a uniform glass transition (10-15 nm). The molecular weight dependence of the relaxation characteristics of the glass process and temperature could be attributed to the variation in the size and packing of the structural units.
    Additional Material: 18 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Acta Polymerica 42 (1991), S. 357-359 
    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: Ein neues Modell für die Kristallstruktur der Form II des Poly(vinylidenfluorid)s (PVDF) wird vorgeschlagen, das auf Fehlordnung bezüglich der Symmetric beruht. Die Fehlordnung bewirkt, daß der Kristall keine einheitliche Raumgruppe besitzt, sondern aus monoklinen Bereichen mit der Raumgruppe P21/c und orthorhombischen Bereichen mit der Raumgruppe Pbc21 bestcht. Das Verhältnis zwischen dem Anteil monokliner zu orthorhombischen Bereichen ändert sich in Abhängigkeit von den Bedingungen der Probenpräparation. Dieses Modell erklärt alle in der Literatur publizierten experimentellen Daten. Theoretische Berechungen bestätigen die Richtigkeit des neuen Modells.
    Notes: A new model based on disorder phenomenon concerning the symmetry is proposed for the crystalline structure of form II of poly(vinylidene fluoride) (PVDF). The disorder has the effect that the crystal possesses no unique space group but it consists alternately of monoclinic regions with space group P21/c and orthorhombic regions with space group Pbc21. The ratio between monoclinic and orthorhombic parts changes depending on the conditions of sample preparation. This model explains all experimental data published in literature. Theoretical calculations confirm the correctness of the new model.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 0009-286X
    Keywords: Wandreibung ; Schüttgut ; Haftkräfte ; Scherversuche ; Fließeigenschaften ; Silo ; Dimensionierung ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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