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  • 1
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 20 (1980), S. 244-251 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    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: This paper is concerned with detecting crosslinking and changes in crosslink densities in cured polyimides. The methods used include diffusional weight gain and dynamic mechanical measurements on thin films of the cured polymers. In this study changes in diffusivities (D) for dimethylformamide (DMF) sorption into polyimide films as well as dynamic mechanical moduli and loss tangents are shown to be related to differences in polyimide cure schedule and composition. In all cases studied there is a β loss dispersion in the range 120 to 150°C and a γ loss dispersion in the range -50 to -80°C. The position and intensity of the β and γ relaxation processes vary primarily with cure cycle. There is a significant correlation between the magnitude of the diffusion coefficient and β and γ transition temperatures (Tβ and Tγ). Tβ increases and Tγ decreases with higher values of D so that T*, the difference Tβ - Tγ, is directly proportional to the diffusivity. By relating these results to data in the literature and the known curing behavior of polyimides, this trend is shown to be consistent with the presence of crosslinking and to be related to the crosslink density of the polymers. The data of this study indicate that measurements of diffusion coefficients for solvent sorption can be used to study changes in crosslink densities in glassy thermosetting polymers. Since the method is best suited for studying one dimensional diffusion, it also is suggested as a possibility for determining relative crosslink densities in adhesives bonded between substrates.
    Additional Material: 8 Ill.
    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 17 (1973), S. 2443-2455 
    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: Interpenetrating polymer networks (IPN's) of poly(alkyl methacrylates) and poly(alkyl acrylates) have been synthesized in latex form. Dynamic mechanical spectroscopy studies on these materials revealed extraordinarily broad glass transition regions, illustrating the semicompatible nature of these materials. In a true synergistic effect, the value of tan δ remains high and nearly constant over a broad temperature range for select compositions, emphasizing their potential value in noise and vibration damping applications. Compositionally identical latex IPN pairs were prepared by slow and rapid addition of monomer. The mechanical behavior of the resulting materials was similar and can be explained in terms of the core-shell model. A 50/50 isomeric homologous series of compositions was examined. After taking into account the relative difference between the glass transition temperatures of the methacrylic/acrylic pair, no substantial change in compatibility was noted throughout the series. Because the acrylic monomer II is roughly equally solvated by both the previously formed methacrylic polymer I and the nascent acrylic polymer II, extensive polymer I/polymer II mixing is encouraged, and sharp phase separation discouraged in these materials.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
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