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  • 1
    Electronic Resource
    Electronic Resource
    Lewis acid properties of phosphenium and arsenium cations: Study of their adducts with pyridine (1992)
    New York, NY [u.a.] : Wiley-Blackwell
    Heteroatom Chemistry 3 (1992), S. 157-162 
    Details
    ISSN: 1042-7163
    Keywords: Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In the growing field of dicoordinated Group 15 cations, the quantitative study of the Lewis acid properties of phosphenium or arsenium cations has not yet been undertaken. Moreover, there are only a few described examples of syntheses of arsenium cations. The aim of this work is to enhance this series and to develop a quantitative comparative study of their complexation with Lewis bases such as pyridine. The observation of the 13C NMR C-4 variation in the pyridine ring is a good probe to obtain the apparent equilibrium constant Kc and thus a Lewis acidity scale. Phosphenium cations are more acidic than arsenium cations.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hc.520030212
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  • 2
    Electronic Resource
    Electronic Resource
    An efficient synthesis of phosphenimidous esters, RO—P=N—Ar (1992)
    New York, NY [u.a.] : Wiley-Blackwell
    Heteroatom Chemistry 3 (1992), S. 453-458 
    Details
    ISSN: 1042-7163
    Keywords: Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Trimethylsilyltrifluoromethane sulfonate is shown to be an efficient catalyst for the elimination of Me3SiCl from N-trimethylsilyl-N-(2,4,6-tri-tert-butylphenyl)amidochlorophosphites la-f, leading to the phosphenimidous esters 3a-f. The crystal structures of phosphites 1a and 1d provide a stereochemical explanation for the better thermal stability of 1d On the basis of these observations a convenient and general synthesis of phosphenimidous esters 3a-f is presented.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hc.520030423
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  • 3
    Electronic Resource
    Electronic Resource
    SnS—Sno2 conversion of chemically deposited SnS thin films (1992)
    New York, NY [u.a.] : Wiley-Blackwell
    Advanced Materials for Optics and Electronics 1 (1992), S. 117-121 
    Details
    ISSN: 1057-9257
    Keywords: Tin(II) sulphide ; Tin(IV) oxide ; Photoconductor ; Air annealing ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: The thermal decomposition of chemically deposited SnS thin films to SnO2 films by air annealing at temperatures up to 400°C is discussed. The conversion of a 0.7 μm thick SnS thin film to an SnO2 film involves the creation of non-stoichiometric SnS, SnS + SnS2 mixed phase and non-stoichiometric SnO2 (i.e. SnO2 — x), as concluded from X-ray diffraction patterns, optical transmission spectra and electrical characteristics. The SnO2 thin films obtained in this manner are photoconductive, with a lowest sheet resistance (in the dark) of about 105 Ω/□ and an activation energy (Ea) of 0.1 eV for the electrical conductivity observed for the SnS films annealed at 325°C. This was found as the onset temperature for conversion of the SnS + SnS2 phase to the non-stoichiometric SnO2 - x film. Elevation of the annealing temperature to 400°C results in an elevation of the sheet resistance to about 109 Ω/□ with the value of Ea at 1.3 eV, indicating an improvement in the degree of stoichiometry.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/amo.860010303
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  • 4
    Electronic Resource
    Electronic Resource
    Determination of the kinetic parameters for the polymerization of a polyurethane using an improved method of differential scanning calorimetry (1992)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 46 (1992), S. 571-580 
    Details
    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 kinetic parameters for the polymerization reactions of two polyurethane systems were determined by using an improved method of differential scanning calorymetry (DSC). The calculated activation energy, reaction order, and Arrhenius prefactor show good correlation with the experimental results. The method used here shows several improvements as respects to other DSC methods: the three kinetic parameters can be calculated directly; it is more accurate than other DSC methods; and it requires only one heating rate, during the calorimetric experiments, to determine the activation energy.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1992.070460402
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  • 5
    Electronic Resource
    Electronic Resource
    Influence of reprocessing on the mechanical properties of a commercial polysulfone/polycarbonate blend (1992)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 861-867 
    Details
    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: Commercial polysulfone/polycarbonate (PSU/PC) polymer blends were reprocessed up to five times to determine the influence that reprocessing has on their structure and physical properties. All the high strain properties, mainly ductility, significantly decreased under harsh processing conditions, such as five cycles at 320°C. The results of reprocessing the blends at 320°C have been compared with results at a lower temperature and also with those of the separate components with the aim of clarifying the origin of the degradation. These results plus Fourier transform infrared spectroscopy (FTIR), dynamic mechanical analysis, and melt flow index measurements (MFI) indicate that the presence of the two polymers together clearly decreases the resistance to degradation of each component. Moreover, degradation under the stated conditions is mainly thermal and does not change the chemical nature of the blends. However, a clear decrease in molecular weight was observed both by viscosimetry and MFI measurements as was a shift to higher temperatures of the low temperature secondary transition of both PC and PSU. Both molecular weight and secondary transition changes usually deteriorate mechanical properties but not in the degree observed here. This probably means that the fine and difficult-to-observe structure of the blend has also changed.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760321305
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  • 6
    Electronic Resource
    Electronic Resource
    Theory of hydrogen bonding in supercritical fluids (1992)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 38 (1992), S. 1243-1253 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The degree of hydrogen bonding and macroscopic thermodynamic properties for pure and mixed fluids are predicted with the hydrogen bonding lattice fluid (LFHB) equation of state over a wide range in density encompassing the gas, liquid and supercritical states. The model is successful for molecules forming complex self-associated networks, in this case pure methanol, ethanol, and water, and the mixture 1-hexanol-SF6. In supercritical water, significant hydrogen bonding is still present despite all the thermal energy and is highly pressure- and temperature-dependent. A fundamental description of pressure and temperature effects on hydrogen bonding is presented for a well-defined case, the formation of a complex between a donor and acceptor in an inert solvent, where no self-association is present. The partial molar enthalpy and volume change on complexation both become pronounced near the critical point, where the density is highly variable with temperature and pressure.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690380811
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  • 7
    Electronic Resource
    Electronic Resource
    Design and evalution of control strategies for high cell density fermentations (1992)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 39 (1992), S. 293-304 
    Details
    ISSN: 0006-3592
    Keywords: control ; fermentation ; baker's yeast ; high cell density ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A methodology for the design and evalution of bioprocess control strategies is presented. The strategies manage nutrient supply with demand and vary with the metabolic condition and phase of fermentation operation. Six carbon source addition strategies are based on different combinations of available measurements; they are described and evaluated under different operating conditions for yeast cultivation. It is concluded that a single control strategy is not the most appropriate under all possible operating conditions. An oxygen uptake rate-based control strategy performs better with a mean respiratory quotient (RQ) value less than 1.1 during an oxygen limitation than an ethanol control strategy which had a mean RQ of 14. The designed strategies and an approach of applying the strategy that best matches fermentation conditions consistently enables achievement of high cell densities 78.7 g DCW/L and yields 0.50 g DCW/g glucose as the mean values for three fermentations.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260390307
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  • 8
    Electronic Resource
    Electronic Resource
    Study of solid-state polymerization by positron lifetime measurements (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 30 (1992), S. 1-9 
    Details
    ISSN: 0887-6266
    Keywords: polymerization, solid-state, positron lifetime technique for study of ; acrylamide, positron lifetime study of ; acrylamide, solid-state polymerization of ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The positron lifetime measurement technique was applied to analyze the structural changes occurring in solid-state polymerization of acrylamide and trioxane. Positronium (Ps) parameters, τ2 and I2, which show a marked change as a function of the γ-ray irradiation dose, signaled the presence of three clearly defined stages in the polymerization process: initiation, propagation, and saturation. The initial increase in τ2, may very well be the result of efficient trapping of Ps in vacancies created around the polymer nuclei. The complicated behavior of I2 may be explained as a chemical reaction between Ps precursors and the radiolysis products of this polymerization process.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1992.090300101
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  • 9
    Electronic Resource
    Electronic Resource
    Functionalization of dextran: Incorporation of carboxy groups by O-succinoylation (1992)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 194 (1992), S. 79-89 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Die Modifizierung von Dextran rnit Bernsteinsaureanhydrid unter Verwendung von Pyridin als Katalysator und DMF/LiCl als Liisungsmittel wurde untersucht und die Struktur der gebildeten Polymeren IH- und 13C-NMR-spektroskopisch bestimmt. Es wurde eine lineare Abhangigkeit zwischen der Reaktionsgeschwindigkeit und der Bernsteinsaureanhydrid-Konzentration gefunden, wobei die Reaktion beziiglich Pyridin erster und beziiglich des Polymeren zweiter Ordnung war. Die Aktivierungsenergie betrug 69,O kUmol. Die I3C-NMR-Spektren von teilweise, d. h. rnit nur einer SuccinatGruppe pro Anhydroglucose-Einheit modifiziertem Dextran wurden untersucht, um die Selektivitat der Reaktion von Dextran rnit Bernsteinsaureanhydrid in homogener Phase abzuschatzen. Die Analyse der Ring-Kohlenstoffatome der Anhydroglucose-Einheit zeigte, dal3 die Reaktivitat der einzelnen Hydroxy-Gruppen in der Reihenfolge C-2 3 C-3 〉 C-4 abnimmt; Proben rnit einem hoheren Substitutionsgrad, d. h. rnit mehr als einer Succinat-Gruppe pro Anhydroglucose-Einheit, zeigten die umgekehrte Reihenfolge C-4 〉 C-3 〉 C-2. Dieses Ergebnis ist vermutlich auf intramolekulare Wasserstoffbriicken Bindungen in Verbindung rnit sterischen Effekten zuriickzufiihren.
    Notes: The modification reaction of dextran with succinic anhydride using pyridine as catalyst and N,N-dimethylformamide/lithiumchloride system as solvent was studied. The structure of the resulting polymers was determined by means of 1H and 13C NMR spectroscopy. A linear dependence of the reaction rate on succinic anhydride concentration was found. The orders with respect to pyridine and polymer concentrations were 1 and 2, respectively. The activation energy was found to be 69.0 kJ/mol. 13C NMR spectra at 75.4 MHz of partially modified dextran with monosuccinate groups were studied in order to evaluate the selectivity of the reaction of dextran with succinic anhydride in the homogeneous phase. Analysis of the spectra of ring carbons in the anhydroglucose units shows that the reactivity of individual hydroxy groups decreases in the order C-2 ∽ C-3 〉 C-4. For samples with higher degree of substitution the order is C-4 〉 C-3 〉 C-2. The results were explained by considering the formation of intramolecular hydrogen bonds as well as by steric considerations.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1992.051940107
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  • 10
    Electronic Resource
    Electronic Resource
    Role of ionic strength in the kinetics of formation of the monochelate of nickel(II) with heptane-3,5-dione (1992)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992), S. 359-368 
    Details
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The kinetics and mechanism of the reaction of Ni(II) with heptane-,5-dione (Hhptd) have been investigated in concentrated sodium perchlorate aqueous solutions at 298 K. The kinetic data in the different media are consistent with a mechanism in which Ni(II) reacts with the enol form of the ligand. The observed positive salt effect on the rate of the reaction of formation of the complex Nihptd+ is rationalized taking into account the increase of the rate of water exchange from the first solvation sphere of the metal ion to the bulk solvent when increasing salt concentration.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/kin.550240405
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