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  • superabsorbent  (2)
  • Fermi energy  (1)
  • 1
    Digitale Medien
    Digitale Medien
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 35 (1997), S. 799-806 
    ISSN: 0887-624X
    Schlagwort(e): allyl crosslinkers ; poly(acrylic acid) ; NMR ; superabsorbent ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Several new crosslinkers have been synthesized for evaluation in superabsorbent polymers. These crosslinkers are allyl endcapped polyethylene glycols (PEG) of 200, 600, and 3400 molecular weight. A branched polyethylene oxide of 600 molecular weight, initiated with glycerin, was also synthesized as a trifunctional crosslinker. The allyl functionality was chosen because it is less reactive during radical polymerization than acrylate crosslinkers, an attribute that was necessary to achieve a more uniform gel network. A synthesis route was devised to make the crosslinkers in high purity and yield. The purity of the crosslinkers was determined by 13C NMR, liquid chromatography, and size exclusion chromatography. Gels that were produced with the allyl crosslinkers gave excellent soluble polymer levels and swelling characteristics. The mechanism of incorporation of the allyl functionality was determined to be exclusively vinyl polymerization rather than through hydrogen abstraction. This was determined using NMR spectroscopy, monitoring the polymerization of a model system consisting of acrylic acid and allylacetate. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 799-806, 1997
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 35 (1997), S. 2029-2047 
    ISSN: 0887-6266
    Schlagwort(e): poly(acrylic acid) gel ; polymerization kinetics ; nuclear magnetic resonance ; crosslinking ; superabsorbent ; Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The kinetics of the isothermal polymerization of acrylic acid were determined utilizing 1H-NMR spectroscopy. The polymerization rate was observed to depend approximately on the \documentclass{article}\pagestyle{empty}\begin{document}$ \frac{3}{2} $\end{document} power of monomer and the \documentclass{article}\pagestyle{empty}\begin{document}$ \frac{1}{2} $\end{document} power of sodium persulfate concentration. This is consistent with a model in which the rate of initiation is itself dependent on the monomer concentration. The polymerization rate was also observed to have a strong dependence on percent neutralization, decreasing with increasing level of neutralization up to 75 to 100% neutralization, and then increasing again. The activation energy for the rate of polymerization was between 9 and 13 kcal/mol except for 100% neutralized acrylic acid, which had an activation energy of 18 kcal/mol. These data suggest that a transition in mechanism occurred at 100% neutralization. Increasing the ionic strength by the addition of sodium chloride also increased the rate. The dependence of the molecular weight on the above variables was also quantified for use in the model. It decreased with increasing conversion, decreasing ionic strength and increasing initiator. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 2029-2047, 1997
    Zusätzliches Material: 17 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    Surface and Interface Analysis 26 (1998), S. 606-614 
    ISSN: 0142-2421
    Schlagwort(e): XPS ; x-ray photoelectron spectroscopy ; calibration ; Fermi energy ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Physik
    Notizen: Calibration of the binding energy scale in x-ray photoelectron spectroscopy (XPS) requires location of the zero point. This zero point has previously been identified with the inflection point in the Fermi-edge region of a valence-band photoemission spectrum of nickel. Comparison of photoemission spectra of nickel and silver measured with monochromated x-rays shows that the inflection points near the Fermi edge differ by 45±5 meV (where the stated uncertainty indicates the standard uncertainty) at an instrumental energy resolution of 0.30 eV. This difference is due to differences in the valence-band densities of states (DOS) of the two metals. Simulations of the Ni photoemission spectrum have been performed based on the DOS calculated by Eckhardt and Fritsche, and the simulated spectrum agrees well with the measured spectrum in the near-edge region. Additional simulations of the Ni photoemission spectrum have been carried out with both monochromated Al x-rays and unmonochromated Mg and Al characteristic x-rays to determine how the Ni near-edge inflection point varies with the energy resolution of the electron energy analyzer in XPS. © 1998 John Wiley & Sons, Ltd.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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