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  • 1
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Cis (CP) and trans (TP) isomers of 1,3-pentadiene (piperylene) were homo and copolymerized with acrylonitrile (A) in bulk and emulsion, at 50°C, using azobisisobutyronitrile and potassium persulfate as free radical initiators. The cis isomer reacts more rapidly than the trans monomer. The copolymer compositions were determined from nitrogen analysis, 100-MHz 1H-NMR and 25-MHz 13C-NMR spectra. The results thus obtained show that both the bulk and emulsion processes yield copolymers characterized by a very similar composition. Data plotted according to the Kelen-Tüdös method indicate that the terminal-unit model is applicable to the piperylene-acrylonitrile system. Reactivity ratios for bulk copolymerization were as follows: rA = 0.079, rTP = 0.114, and rA = 0.033, rCP = 0.188. These values are very small and hence suggest a strong alternating tendency for acrylonitrile and 1,3-pentadiene in both comonomer systems. This latter conclusion is corroborated by the comparison of the NMR spectra of the synthesized copolymers with that of a standard alternating sample. The reactivity (Q) and electronegativity (e) of the 1,3-pentadiene isomers calculated from the reactivity ratios by the Alfrey - Price equations were QTP = 0.56, eTP = -0.97 and QCP = 1.215, eCP = -1.055 for trans and cis dienes, respectively.
    Additional Material: 8 Ill.
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  • 2
    ISSN: 0935-6304
    Keywords: Chiral discrimination ; 2,3,6-Tri-O-methyl)-β-cyclodextrin ; Capillary Gas Chromatography ; ?-Alkyl-5-methylhydantoin ; Thermodynamic parameters ; Molecular modeing ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Permethylated β-cyclodextrin (hereafter designated perMe-β-CD), dililuted or not in polysiloxane, is an efficient chiral discriminant for native, 3-methylated, and 1,3-dimethylated series of 5-methyl-5-(CnH2n + 1)hydantoins. From thermodynamic data obtained with pure perMe-β-CD and with the aid of molecular modeling, it is concluded that: (i) For native hydantoin derivatives having a carbon chain at the 5-position varying from ethyl to nonyl (2≤n≤9), the retention time is related to their H-bonding capability. The resolution is poor for derivatives with n≤4. For n≤5, the resolution is considerably improved and this increase in resolution is attributed to the long alkyl chain being capable of being buried inside the cyclodextrin cavity. (ii) For 1,3-dimethylhydantion derivatives having a carbon chain at the 5-position varying from ethyl to hexyl(2≤n≤6), the retention time is mainly determined by a steric fit between the solute and the inner volume of the macrocyclic cavity. For n = 2, a particular behavior is observed, consistent with a total inclusion of the solutes inside the cavity. By contrast with the native hydantoins, the selectively is high for light derivatives. Thus, the selectivity does not correlate with a strong docking energy (such as the presence of H-bonds postulated with native derivatives). (iii) For 3-methylhydantoin derivatives having a carbon chain at the 5-position varying from ethyl to octyl (2≤n≤8), as expected, retension time and selectivity are intermediate between that of native hydantoins and 1,3-dimethylhydantoins. For all three series, where n≤5, the increase in chain length (n) does not bring about substantial changes in the chromatographic results. Therefore, for these long alkyl chain derivatives, similar dominant interactions with perMe-β-CD are postulated.
    Additional Material: 5 Ill.
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  • 3
    ISSN: 0935-6304
    Keywords: High performance size exclusion chromatography ; molecular weight ; lignin derivatives ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---No abstract
    Additional Material: 4 Ill.
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  • 4
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The microstructure of diene units was investigated in radical homopolymers of the cis and trans isomers of 1,3-pentadiene and copolymers with acrylonitrile, synthetized in bulk and emulsion. Experiments were carried out by infrared spectroscopy, 100 MHz 1H-NMR, and 25 MHz 13C-NMR studies. No difference between the bulk and emulsion samples was noted. The microstructure of poly(1,3-pentadiene) is practically independent of the cis or trans configuration of the diene monomer and is as follows: 56-59% trans-1,4, 15-17% cis-1,4, 16-20% trans-1,2 7-10% cis-1,2 and 0% 3,4. On the other hand, up to about 30% of incorporated acrylonitrile (10% in the feed), the microstructure of the pentadiene fraction in the copolymers is not affected. This finding suggests that the penultimate unit has very little influence on the polymerization process involving the terminal pentadienly unit. Beyond 10% of acrylonitrile in the feed, the proportions of the structural units were linearly dependent upon the acrylonitrile content: trans-1,4 content increased whereas the amounts of cis-1,4 trans-1,2 and cis-1,2 decreased (except the cis-1,2 fraction, constant in the copolymers from the cis-diene). These results are discussed on the assumption that the microstructure of pentadiene residues is strongly associated with the acrylonitrile comonomer in the feed.
    Additional Material: 9 Ill.
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  • 5
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Local mass transfer studies have been carried out in an external loop airlift reactor and indicated the existence of significant non-uniformities in aeration capacity in the various sections of the reactor. The traditional assumption of a single well mixed unit with a single kL a value for external loop airlift reactors was found to be poor and cannot represent adequately the reactor as a whole. The liquid head in the gas/liquid separator was found to have a significant negative negative effect on the local mass transfer coefficient kL a. Visualization of flow patterns showed the existence of strong vortices in the riser and downcomer which contributed to a reduction in local aeration capacity. Mass transfer experiments in an aerated tank showed that the aeration capacity can be reduced by half in viscous media but improved significantly in the presence of salts.
    Additional Material: 9 Ill.
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  • 6
    ISSN: 0749-1581
    Keywords: 119Sn NMR ; nJ(119Sn, 1H) values ; 2D 13C—1H and 119Sn—1H non-refocused COLOC (TPPI) correlation methods ; Organotin derivatives ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: nJ(119Sn, 1H) coupling constants were determined by 2D 13C—1H and 119Sn—1H non-refocused COLOC (TPPI) correlation methods. As the 2D 13C—1H method only gives access to coupling constants directly measured from the spectra, the proposed non-refocused COLOC technique is more general since it allows measurements in the case of satellites which are non-observable in 13C NMR spectra. An optimization method for the τ value in COLOC experiments is also proposed.
    Additional Material: 2 Ill.
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  • 7
    ISSN: 0570-0833
    Keywords: bridging ligands ; magnetic properties ; manganese ; metalloenzymes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1052-9306
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The biotransformation of 6-benzoyl benzoxazolinone (6-BB), a non-narcotic peripheral analgesic, was studied in eight healthy volunteers after oral administration of a single dose of 1 g. Urinary metabolites were extracted either with ethyl acetate at different pH values or by percolating at pH 5 through Amberlite XAD 2 ion-exchange resin. Eluates were concentrated under vacuum, purified by thin-layer chromatography and analysed by gas chromatography/mass spectrometry or direct insertion probe mass spectrometry. Metabolites were identified with reference to the mass spectra of various synthesized compounds assumed to be metabolites of 6-BB, as N-methylated or monohydroxylated compounds. Another metabolic pathway was cleavage of the benzoxazolinone heterocycle giving 2-amino-5-benzoyl phenol after hydrolysis and decarboxylation. N-methyl, N-acetyl and hydroxylated metabolites having an amino-5-benzoyl phenol structure were also found.
    Additional Material: 6 Ill.
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  • 9
    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 Anionenaustauscheigenschaften von Polyurethanfilmen wurden als Funktion ihres Stickstoffgehalts untersucht. Quellungs-, Wasserdampfdurchlässigkeits-, Anionenaustauscherkapazitäts-, spezifische Ionenleitungswiderstands- und Permselektivitätsmessungen zeigen, daß sich diese Filme tatsächlich wie Membranen mit durchschnittlichen Eigenschaften verhalten. Hinsichtlich der stöchiometrischen Zusammensetzung aus beiden Komponenten bringt die Herabsetzung des Stickstoffgehaltes eine Verminderung der Korrosionsschutzeigenschaften des Filmes. Andererseits müßte der Stickstoffgehalt erheblich erhöht werden, um die Schutzeigenschaften merklich zu verbessern. Eine solche Erhöhung ginge jedoch zu Lasten der mechanischen Eigenschaften des Anstrichs.
    Notes: Les propriétés de membranes échangeuses d'anions de films de résines de polyuréthannes ont été examinées, en fonction de leur teneur en azote. Les mesures de gonflement, de perméabilité à la vapeur d'eau, de capacité d'échange d'anions, de résistivité ionique transversale et de permsélectivité montrent que ces pellicules peuvent ětre effectivement considérées comme de médiocres membranes. Par rapport à la composition correspondant à la stoechiométrie des deux réactifs, un abaissement de la teneur en azote conduit à un affaiblissement des qualités de protection anti-corrosion; en revanche, il faudrait une élévation considérable de cette teneur pour améliorer sensiblement ces qualités, au détriment des propriétés mécaniques du revětement.
    Additional Material: 9 Ill.
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  • 10
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Four oligomers of α-L-glutamic acid with ends blocked by nonionizable protecting groups were studied in 0.1M NaClO4 solution using potentiometric measurements. The titrations were analyzed using a pit-mapping method. The results are compared with those obtained with the corresponding polymer. The successive dissociation constants of the carboxylic side chains are obtained for oligomers with degrees of polymerization varying from 1 to 6. Then the successive stability constants corresponding to the association Cu2+-oligomer are given, and the MpHqLr distribution is calculated for each oligomer introducing MHqL complexes.
    Additional Material: 6 Ill.
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