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  • 1990-1994  (3)
  • 1991  (3)
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  • 1990-1994  (3)
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  • 1
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The accuracy of the SEC/LALLS/RI method for measuring molecular weight and molecular weight distribution of the polymerizing system, consisting of a triisocyanate and a diol was examined. It has been found that both Mn and Mw were higher than theoretical up to about 60% conversion. Above this conversion Mw was considerably lower and molecular weight distribution narrower than predicted by gelation theory.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 42 (1991), S. 391-398 
    ISSN: 0021-8995
    Keywords: 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: A series of segmented polyurethanes from two polyols, 4,4′-diphenylmethane diisocyanate (MDI) and butane diol was synthesized. The degree of chemical crosslinking was controlled by varying the ratio of poly(oxypropylene) diol to poly(oxypropylene/oxyethylene) triol. The samples were prepared at the stoichiometric ratio of NCO to OH groups and at a constant concentration of hard segments (butane diol; MDI) equal 50 wt %. At low concentrations of the triol the molecular weight of the polyurethanes increases; at higher concentrations (above 9 mol %) crosslinked products are obtained. All samples show a distinct two-phase structure and in the region of 0-150°C the dynamic mechanical behavior is affected by the hard phase. Chemical crosslinking was found to increase the tensile strength and strain at break, but did not affect appreciably the tear strength, hardness, and soft segment glass transition. The stress relaxation rate at room temperature was found to depend both on the elongation and on the degree of crosslinking. A comparison of the sol fractions ws found for crosslinked samples with the predictions of the theory of branching processes proved that the achieved conversions of reactive groups in networks are high (∼ 0.98).
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 42 (1991), S. 779-790 
    ISSN: 0021-8995
    Keywords: 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: Five series of blends were obtained by mixing five polyurethanes (PUR), based on poly-propyleneoxide, MDI, and butanediol, with polypropylene (PP). The structure of PUR was varied by varying soft segment length (MW = 1000 and 2000) and soft segment concentration (50, 60, and 70%). It has been shown that interaction between PUR and PP was better in the case of PUR with the polyol of MW = 1000. The addition of lower molecular weight PUR produced an easy flowing material in the molten state, comparable with the “control rheology PP.” The morphology of the blends changed with PUR concentration. At 30% PUR the dispersed phase tended to agglomerate in the form of long cylinders. Mechanical properties generally were affected by the change of morphology.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
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