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  • 1
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Macromolecules 23 (1990), S. 2365-2370 
    ISSN: 1520-5835
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0887-6266
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Stress relaxation after a simple elongational step strain, creep under a constant simple elongational stress, and stress build-up under a constant Hencky strain rate have been measured for ultrahigh-molecular-weight polyethylene (UHMW-PE) fibers. The data from the various experiments are consistent with the Boltzman superposition principle in the experimental region of small strains or short times. This leads to a simple constitutive equation in which temperature can be incorporated via time-temperature superposition. The measured power-law relaxation of the UHMW-PE fiber leads to analytical expressions for the dynamic quantities in simple elongation.The constitutive equation is the one-dimensional equivalent of the gel equation derived for cross-linking gels at the gel point. The similarity between the rheological behavior of fibers and cross-linking gels at the transition point might lead to an enhanced understanding of the molecular processes occurring during deformation.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 0887-6266
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The influence of initial polymer concentration in solution (c), weight-average molecular weight (Mω), and drawing temperature on the solid-state drawing behavior of linear polyethylenes was investigated. Optimum conditions, with respect to maximum attainable draw ratio, are observed in isothermal drawing experiments. Moreover, it is shown that high maximum attainable draw ratios can also be obtained upon multistage drawing of UHMW-PE (ultrahigh-molecular-weight polyethylene, Mω 〉 106 g/mol) gel films cast from concentrated solutions. The high maximum attainable draw ratio in combination with the high molecular weight (Mω 〉 106 g/mol) and polymer concentration (c = 10% w/v) is of particular interest because it results in tapes or fibers with a high Young's modulus (100 GPa) and tensile strength (2.5-3.5 GPa). It is also shown that the maximum attainable draw ratio of polyethylenes scales with the Bueche parameter (c · Mω) to the -0.5 power. This experimental observation indicates that intermolecular interactions not only dominate the rheological properties of polyethylene melts and concentrated solutions, but also strongly influence the solid-state drawing behavior of linear polyethylenes.
    Additional Material: 4 Ill.
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  • 4
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: High-strength/high-modulus structures such as fibres, tapes and rods can be produced currently on the basis of intrinsically flexible macromolecules. The prime example amongst these new developments is gelspinning of high-molecular-weight polyethylene resulting in fibrous structures possessing tenacities of 3-4 GPa and corresponding moduli up to appr. 150 GPa. The basic aspects of chain-extension for polyethylene will be discussed in relation to the various routes toward oriented/extended PE structures as well as recent developments concerning the utilization of other flexible polymeric systems for the production of high-strength/high-modulus fibres.
    Additional Material: 5 Ill.
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  • 5
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Two new polymeric materials (polymers A and B) containing covalently bound iodine were prepared. These polymers were evaluated with respect to their possible use as radiopaque implant biomaterials - that is, materials that are visible in a noninvasive manner using routine X-ray absorption imaging techniques. Polymer A is a copolymer of methyl methacrylate (MMA) and 1 (80 and 20 mol%, respectively). Polymer B was prepared from MMA, 1, and 2-hydroxyethyl methacrylate (HEMA) (mol ratio 65:20:15, respectively). Compound 1 was synthesized from 4-io-dophenol and methacryloyl chloride. The resulting polymers were characterized with GPC, DSC, NMR, and by measuring both the advancing and receding contact angles. Thrombogenicity of the polymers was determined by an in vitro thrombin generation test procedure. The maximum concentration of free thrombin was 76 ± 1 nM for polymer A, and 64 ± 3 nM for polymer B. The lag times (i.e., time onset of thrombin generation) were 392 seconds for polymer A and 553 seconds for polymer B. For PVC-T, which is known as a passive material, a lag time of 583 seconds was found. This indicates that polymer B is comparable to PVCT, and more passive than polymer A. Polymer A exhibited minor activation of platelets. Polymer B did not induce platelet activation at all. The polymers exhibited, even as fibers with a diameter of ca. 0.3 mm, good radiopacity with routine imaging X-ray techniques in the clinic. It is argued that polymers A and B - which actually represent a whole family of radiopaque polymeric biomaterials - exhibit promising properties with respect to applications as construction materials for a new generation of endovascular stents. © 1994 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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