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  • Chemistry  (144)
  • Spacecraft Design, Testing and Performance  (24)
  • Biochemistry and Biotechnology  (20)
  • Meteorology and Climatology  (17)
  • 1
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An optimized potential function for base-stacking interaction is constructed. Stacking energies between the complementary pairs of a dimer are calculated as a function of the rotational angle and separation distance. Using several different sets of atomic charges, the electrostatic component in the monopole-monopole approximation (MMA) is compared to the more refined segmented multipole-multipole representation (SMMA); the general features of the stacking minima are found to be correctly reproduced with IEHT or CNDO atomic charges. The electrostatic component is observed to control the location of stacking minima. The MMA, in general, is not a reliable approximation of the SMMA in regions away from minima; however, the MMA is reliable in predicting the location and nature of stacking minima. The attractive part of the Lennard-Jones 6-12 potential is compared to and parameterized against the expression for the second-order interaction terms composed of multipole-bond polarizability for the polarization energy and transition-dipole bond polarizabilities for approximation of the dispersion energy. The repulsive part of the Lennard-Jones potential is compared to a Kitaygorodski-type repulsive function; changing the exponent from its usual value of 12 to 11.7 gives significantly better agreement with the more refined repulsive function. Stacking minima calculated with the optimized potential method are compared with various perturbation-type treatments. The optimized potential method yields results that compare as well with melting data as do any of the more recent and expensive perturbation methods.
    Additional Material: 1 Ill.
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  • 2
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: dl-β-Bulnesene (1) and dl-1-epi-α-bulnesene (15) have been synthesized starting from the bromide 4 (Schemes 2 and 3). In the key step 9→10 the bonds of the final product were formed by an intramolecular photoaddition. The synthesis was completed by the fragmentation 12→14 and the Wittig reaction 14→15+1.
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 1363-1374 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Absolute rate constants for the addition of the highly nucleophilic 2-hydroxy-2-propyl radical to eight fast-reacting 1- and 1,1-disubstituted alkenes in MeOH at room temperature have been determined by laser flash photolysis. Also the absorption spectra of the 2-hydroxy-2-propyl and the benzylic and alkyl-type adduct radicals are presented. The rate constants were obtained using various methods for the analysis of the kinetic traces and support earlier findings.
    Additional Material: 11 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 175 (1974), S. 833-841 
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: N-Alkylmaleimide vom N-Methyl-bis zum N-Octadecyl-Derivat wurden durch γ-Strahlung im festen Zustand polymerisiert. Die Polymerisation weist während der Bestrahlung im allgemeinen eine S-förmige Umsatzkurve auf, mit hohen Geschwindigkeiten und quantitativem Umsatz bei Temperaturen von 10°C unterhalb des Schmelzpunktes. Die Geschwindigkeiten waren nach der Bestrahlung niedriger und zeigten eine typische Annäherung an einen Grenzumsatz. Die Polymerisationsgeschwindigkeiten nahmen mit der Temperatur und der Bestrahlungsdosis sowie mit der Länge der Alkylkette zu. N-Methylmaleimid zeigte eine hohe Geschwindigkeit bei der Polymerisation in Substanz, die der Flüchtigkeit des Monomers zugeschrieben wurde.
    Notes: N-alkylmaleimides from the N-methyl to the N-octadecyl derivative were polymerized in the solid state by γ-radiation. Polymerization during irradiation generally showed sigmoidal conversion curves with high rates and complete conversion 10°C below the melting point. Post-irradiation rates were lower and showed the typical approach to a “limiting” conversion. The polymerization rates increased with temperature and radiation dose and with the length of the alkyl chain. N-methylmaleimide had a high rate of in-source polymerization which was attributed to the volatility of the monomer.
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  • 5
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 179 (1978), S. 2323-2326 
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Additional Material: 1 Tab.
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  • 6
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Whereas the radiation-induced polymerization of crystalline barium methacrylate monohydrate has been well established there have been conflicting reports concerning barium methacrylate anhydrate. We have now shown that the yields of high molecular weight polymer are negligible if adequate precautions are taken to prevent polymerization occurring during the separation of polymer from residual monomer. However, monomer losses of up to 80% have been observed by titration of C=C bonds with bromine and confirmed by decreases in the appropriate infrared absorptions. X-ray diffraction studies showed that the crystalline lattice was largely destroyed during the reaction. ESR spectra indicate that initial trapped radicals are converted into propagating radicals with a different conformation than has been reported for the monohydrate.
    Additional Material: 7 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 11 (1967), S. 133-136 
    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: Certain homopolymer-polyol mixtures, after treatment with a free-radical generating agent or ionizing radiation, will produce polyurethane elastomers of nearly twice the stiffness and tensile properties compared to control elastomers made with untreated mixtures. Specific examples of these mixtures include the homopolymers of acrylonitrile and vinyl chloride with a poly(oxypropyl) triol of about 3000 molecular weight as the polyol in each case. The marked improvement in the stiffness and tensile properties of elastomers made with the treated mixtures over those of the untreated controls indicates a grafting process occurring between the polyol and homopolymer upon the generation of free radicals. In the present work, grafting could occur by a chain-transfer hydrogen-abstraction mechanism, whereby a free-radical site is generated on both the homopolymer and polyol chains. Coupling of these two free-radical sites would thus result in the establishment of a polymer-polyol graft bond.
    Additional Material: 1 Tab.
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  • 8
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 27 (1982), S. 4623-4635 
    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: The solution viscosity of polymer thickened hydrocarbons normally decreases markedly as temperature is increased. It has been observed that metal sulfonate ionomers, such as sulfonated ethylene propylene terpolymer, or sulfo-EPDM, when dissolved in a mixed solvent behave much differently. Specifically, sulfonated ionomers, dissolved in xylene or paraffinic oils with low levels of a polar cosolvent, can provide solutions whose viscosities are either relatively constant or can actually increase with increasing temperature. This isoviscosity effect can be manifested over broad temperature ranges and is mechanistically different from the behavior of conventional polymer solutions. This unusual behavior is explained on the basis of a simple equilibrium involving solvated ion pairs and is shown to be a specific example of a general phenomenon.
    Additional Material: 10 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 5 (1991), S. 503-521 
    ISSN: 0886-9383
    Keywords: Antagonism ; Bounded ordinal scale ; Herbicide interaction ; Inter block comparisons ; Non-parametric ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Studies of interactions among bioactive compounds are often difficult to interpret unambiguously. A priori assumptions about the nature of such interactions can seriously distort analysis of the data. By applying a rank order analysis appropriate to the naturally ordinal scale of response to xenobiotic insult, several co-herbicides were successfully identified from among numerous candidates in an experiment involving multiple blocks, rates and species. Moreover, underlying herbicide interactions were substantiated and identified which were not apparent by more traditional parametric analysis.
    Additional Material: 6 Ill.
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  • 10
    ISSN: 0887-6134
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Fast atom bombardment (FAB) mass spectrometry was used to characterize the pyochelin complexes of iron and zinc. Ferripyochelin readily forms the [M + H]+ and [2M + H]+ ions in a glycerol matrix. The molecular ion was 2.5 fold more abundant when acetic acid was present. Iron was shown to be present in the iron-pyochelin complex as the ferric ion by wet chemical methods. Differentiation between ferric and ferrous ions by FAB was not successful owing to the FAB reducing environment. Ferric ions were reduced by FAB to ferrous ions in the following model salts - ferric chloride, ferric nitrate and ferric sulfate - when dissolved in either glycerol, thioglycerol or the magic bullet matrix. Ferric and ferrous chloride salts gave virtually identical spectra with a glycerol/acetic acid matrix. Zinc-pyochelin readily forms the [M + H]+ and [2M + H]+ ions, but only when acetic acid was present in the glycerol matrix. The FAB mass spectrum of zinc-pyochelin exhibited various fragmentations which can be used in structural analysis. Linked-scan at constant B/E and accurate mass data were used to characterize the fragmentations of the zinc-pyochelin complex. Metastable analysis allowed the fragmentation pathway of zinc-pyochelin to be determined.
    Additional Material: 7 Ill.
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