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  • Chemistry  (23)
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  • 1990-1994  (24)
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  • 1993  (24)
  • 1
    Electronic Resource
    Electronic Resource
    Dextran functionalized by cyclic carbonate groups as supports of bioactive compounds (1993)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 206 (1993), S. 77-85 
    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: Es werden Aspekte der Reaktion von Dextran mit Ethyl-chlorformiat und Triethylamin als Katalysator behandelt. Mittels 1H- und 13C NMR-Spektroskopie wurden in den gebildeten modifizierten Dextranen cyclische und acyclische Carbonatgruppen nachgewiesen. Vorversuche zeigten, daß die Reaktion cyclischer Carbonatgrupen mit verschiedenen Amin-Modellverbindungen stark vom Basencharakter des Amins abhängt. Phenethylamin und Tyramin wurden quantitativ an aktiviertes Dextran mit cyclischen Carbonatgruppen gebunden. Die Dextran-Phenethylamin- und Dextran-Tyramin-Addukte werden unter den angewendeten Bedingungen (pH 1,0 oder 9,1 bei 37°C) nicht heterogen hydrolysiert.
    Notes: This work deals with some features of the reaction of dextran with ethyl chloroformate using triethylamine as catalyst. The presence of cyclic and acyclic carbonate groups in the resulting modified dextrans was demonstrated by IR, 1H and 13C NMR spectroscopy. Preliminary experiments have shown that the reaction of cyclic carbonate groups with several model amines is greatly dependent on the basic character of the amine. Model amino type drugs (Phenethylamine and tyramine) were quantitatively bound to activated dextran with cyclic carbonate groups. The heterogeneous hydrolysis of dextran-phenethylamine or dextran-tyramine adducts showed that no hydrolysis takes place under the applied conditions.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1993.052060108
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  • 2
    Electronic Resource
    Electronic Resource
    Experimental design optimization of the separation of the aromatic compounds in petroleum cuts by supercritical fluid chromatography (1993)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 16 (1993), S. 169-174 
    Details
    ISSN: 0935-6304
    Keywords: Experimental design optimization ; Supercritical fluid chromatography ; Aromatic content ; Petroleum cuts ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A experimental design optimization method is demonstrated for evaluation of the resolution of the performance mixture used in the proposed ASTM test to determine the aromatic content of aviation fuels. The method uses a Doehlert experimental matrix test to optimize the resolution and analysis time by varying the pressure and temperature of the supercritical carbon dioxide mobile phase. The separation between saturated and aromatic compounds was optimized using only seven experiments. With this procedure, the analysis time required for determination of the total aromatic content of more complex samples can be reduced to less than 10 min.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jhrc.1240160308
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  • 3
    Electronic Resource
    Electronic Resource
    The effect of the trifluoropropyl group in polysiloxane stationary phases used for capillary gas chromatography (1993)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 16 (1993), S. 721-724 
    Details
    ISSN: 0935-6304
    Keywords: Capillary GC ; Selectivity of stationary phases ; Poly(methyltrifluoropropyl siloxane) ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Four poly(methyl 3,3,3-trifluoropropyl siloxanes) with trifluoro-propyl group content (group substitution) between 8 and 35 percent have been synthesized and characterized as stationary phases for gas chromatography in borosilicate glass capillary columns. Results are compared with those from two commercial stationary phases-a polydimethylsiloxane and a poly(methyl 3,3,3-trifluoropropyl siloxane) with a fifty percent trifluoropropyl group content (group substitution).Retention index values, McReynolds constants, polarity (as defined by McReynolds) and retention polarity (as defined by Takács) increase regularly with the trifluoropropyl group content of the stationary phase. The temperature coefficient of the retention indices of the McReynolds probes, and that of the polarities, have been determined at temperatures between 60 and 180 °C. Specific retention volumes do not follow the linear dependence on trifluoropropyl group content observed for retention indices or polarities. Substances with electron-donor groups show maximum retention for a trifluoropropyl group content of ca 30%, whereas the retention of hydrocarbons, halogenated compounds, and alcohols decreases as the degree of trifluoropropyl group substitution increases from 0 to 50%. It is felt that a polysiloxane with a trifluoropropyl group content of ca 30 to 35% would be the best choice for the separation of ketones, nitro compounds or amines.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jhrc.1240161210
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  • 4
    Electronic Resource
    Electronic Resource
    Determination of chromium(VI) and chromium(III) by using a diphenylcarbazide-modified carbon paste electrode (1993)
    Weinheim : Wiley-Blackwell
    Electroanalysis 5 (1993), S. 155-163 
    Details
    ISSN: 1040-0397
    Keywords: Chromium ; Modified Electrode ; Voltammetry ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A carbon paste electrode modified with diphenylcarbazide has been prepared in order to improve the analytical determination of chromium(VI) and chromium(III) using voltammetric techniques. Several parameters, such as carbon/diphenylcarbazide ratio, carbon/Nujol ratio, scan rate, accumulation time, etc., have been explored. A voltammetric study of both chemical species and an explanation of the chemical and electrochemical mechanism are presented. When applied to assays of soil samples, the results compared favorably to those of a polarographic method.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/elan.1140050211
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  • 5
    Electronic Resource
    Electronic Resource
    Improvement to the lattice-fluid prediction of gas solubilities in polymer liquids (1993)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 31 (1993), S. 273-277 
    Details
    ISSN: 0887-6266
    Keywords: gas solubility ; polymers ; Henry's law ; solubility parameters ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Previously we have shown that the Lattice Fluid (LF) model can quantitatively predict, without adjustable parameters, gas solubilities for hydrocarbon and chlorinated hydrocarbon vapors in nonpolar polymers. For polar polymers, the model can also predict, with reasonable success, the solubilities of polar and aromatic vapors. However, the solubilities in polar/nonpolar combinations of gas and polymer are systematically overestimated. These are cases in which the geometric mean approximation for the interaction parameter is not expected to be valid. This paper demonstrates that with the addition of a simple empirical correlation for the interaction parameter based on Hansen's three-dimensional solubility parameters, the LF model is then able to quantitatively predict solubilities in all types of gas/polymer systems (excluding strongly self-associating systems, such as alcohols). No adjustable parameters are used; only the pure component equation-of-state and solubility parameters are required. © 1993 John Wiley & Sons, Inc.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1993.090310305
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  • 6
    Electronic Resource
    Electronic Resource
    Thermal degradation study of poly(vinyl chloride): Kinetic analysis of thermogravimetric data (1993)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 50 (1993), S. 1565-1573 
    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 thermal degradation of a poly(vinyl chloride) (PVC) resin was studied using a non-isothermal thermogravimetric technique. Kinetic parameters such as activation energies, reaction orders, and preexponential factors are calculated using integral and differential methods reported in the literature. Advantages and disadvantages of these methods are discussed in order to characterize PVC. © 1993 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1993.070500910
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  • 7
    Electronic Resource
    Electronic Resource
    Modification of the dark and photoconductivity and the optical transmittance of solution-grown CdS thin films (1993)
    New York, NY [u.a.] : Wiley-Blackwell
    Advanced Materials for Optics and Electronics 2 (1993), S. 133-141 
    Details
    ISSN: 1057-9257
    Keywords: CdS ; Chemical deposition ; Photodetector ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Very interesting behaviour is shown by chemically deposited CdS thin films for optoelectronic applications after air and vacuum (10-5 Torr) annealing. Vacuum annealing of samples at about 100°C caused the dark conductivity to improve by five orders of magnitude. The dark and photoconductivity of air-annealed (at around 200°C) samples increased by seven and two orders of magnitude respectively. Air-annealed (at 350°C for about 2 min) samples exhibited a very quick photoresponse (〈2 s for two decades of photocurrent decay) with σp/σd ≈ 105 for a bias of 10 V, which may be exploited for photodetector applications. Air or vacuum annealing of samples for a minimum of 10-15 min caused the optical transmittance above the band edge to increase by 10%-15% and annealing the sample at 200°C caused the absorption edge to shift towards the longer-wavelength region compared with the as-prepared and 100 and 350°C annealed films.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/amo.860020306
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  • 8
    Electronic Resource
    Electronic Resource
    Poly(benzylsulfonic acid) siloxane as proton-conducting electrolyte (1993)
    New York, NY : Wiley-Blackwell
    Polymers for Advanced Technologies 4 (1993), S. 99-105 
    Details
    ISSN: 1042-7147
    Keywords: Proton-conducting polymer ; Sol-gel process ; Battery ; Supercapacitor ; 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
    Notes: A new proton-conducting polymer electrolyte - poly-(benzylsulfonic acid)siloxane (PBSS) - has been prepared by sol-gel process. Both the hydrolysis and the condensation reactions of triethoxybenzylsilane have been studied under different catalysis conditions. The basic material - polybenzylsiloxane (PBS) - is always soluble, no matter what the experimental conditions, reaching an average molecular weight - Mw - of 20,000 and a polydispersity index close to 5. Good yields of a water-soluble polyelectrolyte - PBSS-thermally stable up to 300°C in air according to thermogravimetric analysis (TGA), and for which the exchange capacity is close to 4.4, can be obtained by sulfonation of PBS. Conductivities ranging from 2 × 10-3 to 10-2 S/cm at room temperature have been determined by a.c. impedance spectroscopy. These high conductivities, as well as the tensile strength of the PBSS, allow its use in several electrochemical devices.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pat.1993.220040207
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  • 9
    Electronic Resource
    Electronic Resource
    Ceramic thin films deposited on Si(100) by laser ablation: Application as buffer layers for YBa2Cu3O7 films (1993)
    New York, NY [u.a.] : Wiley-Blackwell
    Advanced Materials for Optics and Electronics 2 (1993), S. 99-103 
    Details
    ISSN: 1057-9257
    Keywords: Buffer layers ; Laser ablation ; Superconducting films ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Ceramic thin films of yttria-stabilised zirconia (YSZ), SrTiO3(STO) and CeO2 have been deposited on Si(100) substrates by laser ablation. The films have been characterized by X-ray diffractometry, field emission scanning electron microscopy and secondary ion mass spectrometry (SIMS). The effects of the oxygen partial pressure during deposition and the substrate temperature were studied. All the films have preferential orientation: (h00) and (hh0) for STO and (hhh) for CeO2 and YSZ. The films show a low density of particulates and a very smooth surface. SIMS profiles indicate a low interdiffusion between film and silicon. One of the applications of these materials is their use as a buffer layer for the growth of YBCO on silicon. Because both materials are highly reactive, it is necessary to put a barrier between YBCO and silicon. For this purpose we used the ceramic films previously deposited in order to obtain superconducting YBCO films. The deposited YBCO films present good superconducting properties with zero resistance at temperatures between 80 and 85 K.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/amo.860020113
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  • 10
    Electronic Resource
    Electronic Resource
    Physical properties and structure of unreacted PC/PBT blends (1993)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 50 (1993), S. 995-1005 
    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: Unreacted PC/PBT blends have been obtained by melt blending in all the composition ranges. The followed processing method produced partially miscibilized and crystalline blends. The plot of the density of the amorphous part of the blends against its composition indicates that this parameter is more important than the crystallinity level in determining the mechanical properties of the blends. The blends exhibited an overall improvement of mechanical properties with a combination of behaviors that are close to linearity and are synergistic. © 1993 John Wiley & Sons, Inc.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1993.070500609
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