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  • Articles  (1,789)
  • Articles: DFG German National Licenses  (1,789)
  • Chemistry  (1,775)
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  • 1995-1999  (685)
  • 1980-1984  (712)
  • 1970-1974  (392)
  • Physics  (1,789)
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  • Articles  (1,789)
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  • 1
    ISSN: 1075-4261
    Keywords: cholelithiasis ; gallstone ; bile salts ; periodic precipitation ; fractal precipitation ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Physics
    Notes: This is the first observation that both chaotic and periodic patterns are formed in metal ions-deoxycholate-gel systems. It is an in vitro model for approximating the conditions present during gallstone formation. The experimental results suggest that a nonlinear scientific concept such as the “butterfly effect” should be considered in understanding gallstone formation. This effect suggests that a butterfly flapping its wings in Beijing today may lead to a thunderstorm in New York months later. Applying this concept to biology, minor changes in the local chemical environment within biological systems may lead to large variations in the structure and morphology of gallstone through changes in the behavior of biological mineralization process. © 1997 John Wiley & Sons, Inc. Biospect 3: 195-205, 1997
    Additional Material: 13 Ill.
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  • 2
    ISSN: 1432-0649
    Keywords: 33 ; 82.50
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 17 (1973), S. 269-282 
    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 development of gel permeation chromatography (GPC) has provided a convenient tool for the rapid determination of molecular weight distribution. The question has arisen as to the suitability of the method for specification purposes. The present work, suggested by the Naval Air Systems Command, represents an attempt to assess the precision of the method through a series of tests carried out by a number of laboratories using identical procedures on the same samples. Ten laboratories agreed to take part. Naval Ordnance Station, Indian Head, worked out standard conditions for operation of the chromatograph, for calibration of the columns, and for analysis of the GPC curves. Two samples of polystyrene were used by the various organizations for calibration of their instruments. Number-average molecular weight, heterogeneity index, and cumulative molecular weight distribution curves were determined on four samples of carboxyl-terminated polybutadiene (CTPB) and two samples of hydroxyl-terminated polybutadiene (HTPB), all unidentified except by letter code. All laboratories used identical directions for setting up CTPB and HTPB calibration curves which were based on curves determined from vapor-pressure osmometer molecular weights and GPC count numbers of fractionated material. Variation among the different laboratories was 0.15 in heterogeneity index, and a maximum of 1200 in molecular weight provided one aberrant set of values was eliminated. The six samples had heterogeneity indices from 1.15 to 1.54, while molecular weight varied from approximately 3000 to 6000. The average coefficient of variation of the molecular weight values was 6.2 ± 0.7%, which is quite acceptable. Variation in heterogeneity index was too great for specification purposes when considered among the different laboratories, but may be sufficiently good when measured by any one laboratory.
    Additional Material: 7 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 16 (1972), S. 3353-3360 
    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: Two independently derived distribution function methods validate both the calibration curve and the dispersion correction of the “effective linear calibration” method used in gel permeation chromatography (GPC). Experimental conditions are specified for making the method more useful by permitting linear extrapolation of the calibration line, \documentclass{article}\pagestyle{empty}\begin{document}$ V_R = C_1 + C_2 \log M, $\end{document} and for using a minimum number of standards. The independent methods quantitatively relate known differential of integral distribution functions for standard samples to their respective chromatograms. As such, they are useful calibration methods also, but are limited in scope and range.
    Additional Material: 5 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 169 (1973), S. 177-189 
    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: Die elektroinitiierte Polymerisation von N-Vinylcarbazol (VCZ) wurde in Aceton bei 25°C mit Zinkbromid als Katalysator unter Verwendung von Platinelektroden eingehend untersucht. Die Polymerisationsgeschwindigkeit erwies sich als direkt abhängig von der Stromstärke, der Zinkbromid-Konzentration und dem anfänglichen Wassergehalt des Solvens.Die Molekulargewichte der entstandenen Polymeren (1000-6000) sind unabhängig von der Stromstärke, der Zinkbromid-Konzentration und dem Umsetzungsgrad des Monomeren zum Polymeren, werden jedoch beeinflußt durch Wasser, die Monomerkonzentration und das Elektrodenmaterial. Die chemische Zusammensetzung der Polymeren ändert sich nicht mit der Stromstärke, der Zinkbromid-Konzentration, dem Umsetzungsgrad und dem Elektrodenmaterial. Sie ändert sich jedoch ein wenig mit dem Wassergehalt des Acetons.
    Notes: The electroinitiated polymerization of N-vinylcarbazole (VCZ) in acetone solvent at 25°C with zinc bromide, as catalyst, and platinum electrodes was investigated in detail. The polymerization rate was found to be directly dependent on current strength, zinc bromide concentration and the initial water content of the solvent.The molecular weights of the formed polymers (1000-6000) are independent of current strength, zinc bromide concentration and degree of conversion of monomer to polymer, but are affected by water, monomer concentration, and by the type of electrodes used. The chemical composition of the polymer is invariant with current strength, zinc bromide concentration, degree of conversion, and electrode material but does vary slightly with the water content of acetone.
    Additional Material: 2 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 33 (1995), S. 1545-1557 
    ISSN: 0887-6266
    Keywords: NMR relaxation ; PMR polyimides ; thermal degradation ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: We have studied cross-linking and thermal degradation of high-performance first-and second-generation PMR-15 polyimides, both thermoset and thermoplastic versions, by performing nonspectroscopic NMR solid echo T*2 relaxation measurements at temperatures up to 430°C using probes built for this purpose. We employ signal averaging and automated decomposition of the relaxation decays into two Gaussian components, the slower of which gradually appears above 300°C. Tracking the molecular mobility spectrum in terms of the relative intensity of the components and their relaxation times as temperature is cycled, we detect essentially no irreversible effects below the glass transition, measure permanent mobility reductions attributable to completion of cure, and find that exposure to temperatures above 380°C on the order of 1 h is required for substantial thermal degradation to occur. These results are closely supported by thermal and mechanical measurements on parallel specimens. Second-generation PMR resins appear to have higher microscopic rigidity and reduced viscous fraction at high temperatures. ©1995 John Wiley & Sons, Inc.
    Additional Material: 10 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 56 (1995), S. 1673-1677 
    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: A series of oxazoline-modified styrene-acrylonitrile (SAN) copolymers was prepared through the reaction of amino alcohols onto preformed SAN copolymers. Consequently, a variety of reactive copolymers were synthesized. The major focus of this study was to examine the influence of reaction conditions, i.e., the nature of the catalyst and amino alcohol structure, on reactivity. The ability to incorporate oxazoline groups onto preformed polymers is dependent on whether homogeneous reaction conditions are met. For example, the use of nonreactive solubilizing agents, i.e., cosolvent, is effective. However, optimum conditions are obtained when the catalyst is completely soluble in the reaction mixture containing the amino alcohol and SAN copolymer. With these restrictions, zinc stearate is quite effective. Our results show that controlled and reproducible levels of oxazoline can be incorporated (typically at a rate of 2 mol %/h) up to high levels. These results are general and therefore are applicable to a wide variety of nitrile-containing polymers. © 1995 John Wiley & Sons, Inc.
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  • 8
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Rapid Communications in Mass Spectrometry 9 (1995), S. 712-716 
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: A variety of ionophores have been studied by packed column supercritical-fluid chromatography combined with mass spectrometry. One of the ionophores, lasalocid, provided particularly good multiple-reaction monitoring signal-to-noise responses when analysed by tandem mass spectrometry and this approach shows considerable potential for the analysis of this compound in medicated animal feeds. A capillary supercritical-fluid chromatograph has been interfaced to an unmodified benchtop quadrupole mass spectrometer and this combination has enabled the molecular weight determination of the sodium salt of an ionophore.
    Additional Material: 8 Ill.
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  • 9
    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: Novel EPDM (ethylenepropylenediene monomer) and polybutadiene polyols can be synthesized by a two-step process of controlled hydroformylation and then reduction of the formyl groups to place a desired amount of pendant alcohol groups along the polymer chain. The degree of functionalization can be controlled by measuring gas uptake from a calibrated reservoir during hydroformylation. Hydroformylation can be performed in solution or under simulated melt-phase conditions using either HRh(CO)(PPh3)3 or Rh(acac) (CO)2 as catalysts. Reduction of the polyaldehyde by NaBH4 generates the polymeric alcohol without further reaction of the remaining double bonds. Polymer functionalization and further modifications were followed by H-NMR and FTIR. These unique hydrophobic polyols can be reacted further to produce other polymer systems. As an example, urethanes have been made with these polyols by reaction with diisocyanates. © 1995 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 62 (1996), S. 1819-1833 
    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: Multiblock copolymers offer the possibility to combine the properties of different polymers. Thus, new materials with tailor-made unique properties are available by coupling of different suitable polymeric segments. The goal of the work discussed in this paper was to combine advantageous properties of liquid-crystalline polymers (LCP) with those of polysulfone (PSU). Therefore, liquid crystalline poly(ethylene terephthalate-co-1,4-oxybenzoates) were connected with PSU oligomers. Chemically homogeneous multiblock copolymers with high molecular weight were obtained by a melt transesterification procedure. It was demonstrated by wide angle x-ray scattering (WAXS), polarizing microscopy, transmission electron microscopy (TEM), and differential scanning calorimetry (DSC) that the properties of the multiblock copolymers (solid phase structure, phase behavior, morphology, glass transition, and melting behavior) can be balanced by the segment length of the incorporated blocks. The investigations clearly reveal the existence of a two-phase structure. However, a change of properties compared to the corresponding homopolymers refers to certain interactions between the phase due to the chemical connection of the LCP and PSU segments. © 1996 John Wiley & Sons, Inc.
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