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  • Computational Chemistry and Molecular Modeling  (3)
  • Polymer and Materials Science  (3)
  • Wiley-Blackwell  (6)
  • 1990-1994  (6)
  • 1
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 411-418 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A theoretical prediction of the absorption spectra in n-doped semiconductors due to donor pairs is extended further to investigate its contribution to the refractive index of phosphorus-doped silicon. Such a contribution yields a polarization catastrophe at the metal-nonmetal transition. The alternant molecular orbital with a many-valley character of the host material is used in the calculation. The results show good agreement with experiments.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 41 (1992), S. 517-524 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The density of states is calculated for a random distribution of donor-pairs of hydrogenlike impurities in three- and two-dimensional systems. Recent investigations of the hydrogen molecule in the alternant-molecular-orbital approximation are here extended. We found that the lowest excited state 1Σu (i.e., H+H-), which is optically connected to the ground state, plays a relevant role in the absorption spectra of semiconductor systems.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 1137-1147 
    ISSN: 0887-624X
    Keywords: Ziegler-Natta catalysts ; propylene polymerization ; catalysts characterization ; supported catalysts ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In this article we present the results of the preparation and characterization of two Ziegler-Natta precatalysts: MgCl2/Ethyl benzoate (EB)/TiCl4 and MgCl2/2,2,6,6 tetramethylpiperidine (TMPiP)/TiCl4 by means of FTIR, X-ray diffraction, SEM, BET surface area measurements, and other techniques applied at different steps of their preparation procedures.The precatalysts were prepared by impregnating with TiCl4 a given amount of MgCl2, which was previously ball-milled with the electron donor chosen.Prior to impregnation, the ball-milled material presented different surface compounds depending on the electron donor used: [(MgCl2)2] · 2EB, MgCl2 · EB, or a salt of the amine. The solid milled with EB is more homogeneous than the one milled with the TMPiP.Titanium is better retained in the solid milled with EB. This precatalyst has better morphological properties and larger BET surface area. By means of FTIR, we found evidences that an adequate surface structure for the formation of stereospecific sites in MgCl2/TMPiP/TiCl4 was formed. © 1994 John Wiley & Sons, Inc.
    Additional Material: 10 Ill.
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  • 4
    ISSN: 0003-3146
    Keywords: polyethylene ; photo-oxidation ; weathering ; mechanism ; kinetics ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The kinetics of the natural and accelerated photo-oxidation of low-denisty polyethylene (LDPE) films have been studied; different geographical locations have been selected for the natural tests, and a range of temperatures used in the accelerated experiments in a specially built temperature-controlled ultraviolet radiation enclosure. A meaningful correlation between natural and accelerated weathering results was established, by means of an adequate superposition of the effects of UV radiation exposure and temperature. Reasonably detailed and accurate, lumped-parameter, kinetic models of the photo-oxidation process have also been developed, to interpret and predict the results of measurements of carbonyl, hydroperoxide and vinyl absorbances as functions of time and temperature; the models predict the general experimental behaviour, and also that both the formation of hydroperoxides and carbonyl Norrish-I reactions are important initiation steps. More complex models have the potential of interpreting other fine details of the degradation behaviour, namely the generation of other chemical species, and the chain scission and cross-linking process which are directly related to changes in the mechanical properties.
    Additional Material: 10 Ill.
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  • 5
    ISSN: 0142-2421
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: The partial decomposition of PF6- during pyrrole electropolymerization in methanol and acetonitrile on Fe and Pt electrodes is demonstrated using XPS analysis. A complex mixture of PF6-, fluorides of phosphorus and metal oxides is shown to exist in the interfacial region, probably resulting in a weak cohesive layer unfavourable to the adhesion of polymer films.
    Additional Material: 3 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 12 (1991), S. 885-890 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The use of principal components as a basis for a graphical procedure to analyze polar tensor data is proposed. Molecular orbital and experimental polar tensor data for all possible sign combinations of the ∂p/∂Qj of CHCl3 and CDCl3 are represented graphically as principal component scores facilitating sign selection for the ∂p/∂Qj. The graphs are particularly useful in analyzing an apparent conflict in ∂p/∂Qj sign choices based on the isotopic invariance criterion and molecular orbital results for the A1 symmetry species of these molecules. The numerical impacts of individual sign ambiguities for the ∂p/∂Qj on the polar tensor data are measured by the variances associated with the principal components. Assuming the ∂p/∂Qj sign sets with indeterminate signs provide replicated results for the polar tensor elements, their errors are estimated and compared with errors obtained previously by propagating intensity uncertainties through the polar tensor equations.
    Additional Material: 2 Ill.
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