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  • 1
    ISSN: 1435-1536
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Zusammenfassung Dieγ-Bestrahlung des Nylon-6-Films in der Anwesenheit von wäßriger Acrylsäure und Cuprichlorid bei konstanten Konzentrationen wurde bei verschiedenen Strahlungsintensitäten (I) untersucht, wobei die folgenden Beziehungen ermittelt wurden:R H ∞I 1,0 undR G ∞I 0,7.R H undR G bezeichnen hier die Anfangsgeschwindigkeiten der Homopolymerisation bzw. Pfropfung. Die Werte der Exponenten, 1,0 und 0,7, zeigen, daß der Abbruch bei Homopolymerisation hauptsächlich durch Cupri-Ionen hervorgerufen wird; im Gegensatz dazu haben wir bei der Pfropfung eine Mischform des Abbruches, nämlich durch Cupri-Ionen einerseits und durch bimolekulare Reaktion zwischen wachsenden Ketten andererseits. Der Einfluß der Film-Dicke, die Quellungsgeschwindigkeit gepfropfter und ungepfropfter Filme und der Effekt wiederholten Pfropfens bereits gepfropfter Filme wurden experimentell untersucht. Die Ergebnisse zeigen, daß eine hohe Geschwindigkeit des Pfropfens bei gleichzeitiger geringer Geschwindigkeit der monomeren Diffusion in diesem System nicht besteht und dies daher kein bestimmender Faktor in dem beobachteten Absinken der Pfropf kurve ist.
    Notes: Summary Theγ-irradiation of nylon-6 film in the presence of aqueous acrylic acid and cupric chloride at constant concentrations has been studied at different radiation intensities,I, and the following relationships found:R H ∞I 1.0 andR G ∞I 0.7. Here,R H andR G denote the initial rates of homopolymerisation and grafting respectively. The values of the exponents, 1.0 and 0.7, indicate that in homopolymerisation the termination is mainly by cupric ions, whereas in grafting there is a mixed form of termination, viz. by cupric ions and by bimolecular reaction between growing chains. Experiments have been conducted on the influence of film thickness, the rates of swelling of grafted and ungrafted films and the effect of regrafting to grafted films. The results show that a fast rate of grafting ac companied by a slower rate of monomer diffusion does not prevail in this system, and hence it is not a contributory factor to the fall-off observed in the grafting curves.
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  • 2
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Apparatus and technique have been described for the polymerization of 1,3-butadiene in the vapor phase with sodium as catalyst. Research grade butadiene or that obtained from alcohol is necessary for production of high molecular weight polymers by this method. Unmodified polymerizations with increased sodium surface go faster and produce polymers of lower gel content and inherent viscosity. Increase in polymerization temperature reduces the rate, gel content, and inherent viscosity. The chemical structure of the modifier seems to be the predominant factor in its efficiency within a concentration range of 0.1 to 1.0 %. Ethyl chloride is the most powerful modifier of those examined, followed in order by dimethylamine, acetaldehyde, and acetoue. Gelfree polymers with average inherent viscosities of the whole sol between 0.4 and 4.6 were vulcanized and evaluated. The weight distribution was found to be rather narrow for the low viscosity polymers but to become broader as the average inherent viscosity of the polymer increased. Optimum processing and tensile properties were obtained on the polymers of medium viscosity. The dynamic properties of the vulcanizates improve with increase in average inherent viscosity of the raw polymer; the ethyl chloride modified polymer is exceptionally good. The physical properties of the vulcanizate of a blend of equal parts of five polymers of inherent viscosity 1.0 to 4.6 were near those of the lowest molecular weight polymer.
    Additional Material: 2 Ill.
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  • 3
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    ISSN: 0449-296X
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The grafting of acrylic acid in aqueous solution to nylon 6 film has been studied in the presence of ferrous, ferric, and cupric salts. The mutual irradiation technique was adopted using a 60Co source. The anions were found to have no effect on the grafting or homopolymerization, but both of these processes were suppressed by the cations in the following order of effectiveness: Cu2+ 〉 Fe2+ 〉 Fe3+. The rate constant for the capture of hydroxyl radicals by acrylic acid has been determined as 6 × 109 1. mole-1 sec-1 by pulse radiolysis using the CNS- competition method. By invoking this result, mechanisms have been suggested for the process of chain termination by metal cations.
    Additional Material: 3 Ill.
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  • 4
    ISSN: 0360-6376
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Aqueous acrylic acid in the presence of cupric chloride has been subjected to γ-irradiation under various reaction conditions and the molecular weights of the resultant poly(acrylic acid) measured. The results, taken in conjunction with previous findings on the dependence of the rate of polymerization on intensity, monomer concentration, and cupric chloride concentration, indicate chain termination solely by cupric ion (rate constant ktCu) and chain transfer to polymer (rate constant kf). Values have been obtained for ktCu/kp, kf/kp and G(radical) of acrylic acid. On the basis of these data a theoretical chain-length distribution has been derived which agrees well with distribution measured by gel-permeation chromatography.
    Additional Material: 10 Ill.
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  • 5
    ISSN: 1432-2242
    Keywords: Triticum urartu ; Sitopsis ; Tetraploids ; Differentiation ; Diploidization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The genomes of the diploid wheats Triticum boeoticum and T. urartu are closely related, giving 7II in the f1 hybrid (TbTu) and 8.4 (0–14) II + 2.5 (0–7) IV in the derived amphiploid (TbTbTuTu). The genomes of the tetraploid wheats are also closely related, giving up to 7II at the polyhaploid level (AB) in the absence of the gene Ph but 14II at the tetraploid level (AABB) in the normal presence of Ph. If the amphiploid is the progenitor of the tetraploids, one or the other homoeologue (Tb or Tu) in each of the 7 homoeologous groups (the 7 potential IV) must have differentiated with respect to pairing affinity in order to account for 14II in the tetraploid. Consequently, in tetraploid X amphiploid hybrids (TbTuAB) carrying the Ph gene from the tetraploid, the seven differentiated chromosomes (B) would be expected to give 7I while, on the basis of their observed chiasma frequency, Tb, Tu and the less differentiated A would be expected to give 4.17I + 3.57II + 3.23III), assuming homoeologous pairing. The expected chromosomal configuration freqencies at MI (11.17I + 3.57II + 3.23III) closely fit the observed values (11.22I + 3.45II + 3.19III + 0.071IV) for such hybrids (X2 = 0.0046; P〉0.99). Thus diploidization of the boeoticum-urartu amphiploid clearly could account for the origin of the tetraploid wheats. Furthermore, T. aestivum X amphiploid hybrids (TbTuABD) with and without Ph indicated that B as well as A chomosomes tended to pair with their presumed TbTu homologues in the absence of Ph. Other tests showed that the tetraploid wheats could not plausibly have originated from any postulated Triticum-Sitopsis (TTSS) parental combinations with or without such chromosomal differentiation.
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  • 6
    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: In the γ-irradiation in vacuo of nylon 6 film in the presence of aqueous acrylic acid and different concentrations of cupric chloride, the following relationships have been obtained: RH ∝ [CuCl2]-1.0 and RG ∝ [CuCl2]-0.3 Here [CuCl2] is the concentration of cupric chloride in the bulk solution, and RH and RG denote the initial rates of homopolymerization and grafting, respectively. The values of -1.0 and -0.3 for the exponents indicate that the cupric ion is a less effective chain terminator in the film on account of its lower concentration there. Analyses of films grafted in different media demonstrate the copper content of a film to be independent of both the concentration of monomer in the solution and the degree of swelling. The copper content is primarily a function of the total poly(acrylic acid) present, i.e., (grafted species plus occluded homopolymer). Thus, at high doses, where the total poly(acrylic acid) associated with a film is significant, the grafting curves exhibit a falling off, and complex formation between cupric ion and a growing chain is considered a likely contributory factor.
    Additional Material: 5 Ill.
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  • 7
    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: Samples of nylon 6 have been prepared by the hexamethylene diamine-initiated polymerization of ∊-caprolactam at 220°C. Fractionation of these with m-cresol-diethyl ether at 26°C yielded 15 amino-terminated fractions of M̄n of 337-10,940 determined conductometrically. Below M̄n = 4,306 the Mark-Houwink parameters in m-cresol at 30°C are K = 3.0 × 10-3 dl/g and v = 0.53 ± 0.02. Thereafter v exhibits a pronounced increase. The value of K is similar to the values of Kθ derived from Stockmayer-Fixman plots of published data in good solvents. The findings thus corroborate a current hypothesis that fractionated, low molecular weight polymers in good solvents tend to behave viscometrically, as if they were under θ conditions (i.e., K = Kθ and v = 0.50).
    Additional Material: 1 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 216 (1967), S. 859-862 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] A method for identifying the C and D genome donors of Ae. cylindrica (CCDD) from the electrophoretic pattern of protein mixtures of Ae. caudata (CC) and Ae. squarrosa (DD) types may be useful confirming the B genome donor of ...
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  • 9
    ISSN: 1520-5045
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1520-5045
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Type of Medium: Electronic Resource
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