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  • 1980-1984  (2)
  • 1950-1954  (1)
  • Chemistry  (3)
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  • 1
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 17 (1981), S. 290-295 
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Natural abundance proton-coupled 15N NMR spectra have been observed for pyridine and a series of mono- and disubstituted pyridines using polarization transfer achieved by the selective population transfer method. The magnitudes and signs of the 15N—1H spin-spin coupling constants between the ring-nitrogen and ring-protons are determined from complete iterative spectral analysis and/or selective population transfer experiments. Substituent effects on the 15N—1H coupling constants are discussed and compared with those for 13C—1H couplings in substituted benzenes.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    Journal of Polymer Science 6 (1951), S. 681-689 
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Excellent reproducibility of an emulsion polymerization of styrene has been obtained in a nitrogen atmosphere and a technique and apparatus have been described to obtain this reproducibility. The rate of polymerization for this system has been shown to be proportional to the square root of the catalyst concentration and to increase with higher catalyst concentrations. Average molecular weights were higher with higher concentration of catalyst within the catalyst concentrations studied and polymerization occurred without significant pH changes.In contrast, reproducibility of the emulsion polymerization in air atmosphere was unsatisfactory. The presence of air (oxygen) increased the induction period, decreased the rate of polymerization and decreased the average molecular weight of the polymer. Since the time necessary for polymerization was increased, the decrease in pH was considerable during the polymerization.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 0272-8397
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The dynamic mechanical properties of carbon-fiber-reinforced, epoxy-matric-composite laminates subjected to loading perpendicular to the plane of lamination and of neat epoxy resin are reported. The dynamic mechanical measurements were performed in the frequency range from 0.1 to 40 Hz and at temperatures between 20° and 200°C at deformation levels within the linear viscoelastic region by the use of a Dynastat apparatus. It is found that thein-phase and out-of phase stiffnesses superpose to form master curves covering a frequency range of 12 decades. By a suitable scaling procedure of the master curves, it is found that thein-phase stiffiness has tbe same shape and the out-of-phase stiffness has the same dispersion for all laminates irrespective of the stacking sequence and are nearly identical to those for neat epoxy resin, An empirical function for the relaxation modulus is developed that, when converted to dynamic modulus, gives a good overall agreement for both components of the dynamic stiffness as a function of frequency. Absorbed moisture is found to cause a reduction in thhe elevated temperature mechanical properties of a laminate due to a reduction in the glass-transition temperature of the resin. It is also found thatthemositure absorption is a reversible process, in the sense that the initially dry properties of the laminate are recovered afterredrying the wet sample.
    Additional Material: 18 Ill.
    Type of Medium: Electronic Resource
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