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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: The nucleophilic substitution of the chlorine atoms of poly(vinyl chloride) with sodium thiophenate is assumed to obey an SN2 mechanism with inversion of configuration and a steric control according to which reactivities R of the triads follow the order Rmm 〉 Rmr ≫ Rrr. Such a reaction cannot be described by simple differential equations, but a Monte Carlo simulation, first generating a random Bernouillian chain and then simulating random attack of the chain by the reactant according to the triad reactivities, allows a good agreement with the experimental results of both the kinetics of a reaction carried out in cyclohexanone solution at 40°C and the evolution of the 13C and 1H NMR spectra of the tertiary carbon atoms, assuming the following parameters: Bernouillian probability for a meso placement in the initial chain: 0.431; relative reactivities of the mm, mr and rm, rr triads: 1, 0.5, and 0., respectively. The agreement is excellent until the reaction is about three-quarters complete; this shows a limiting level of about 60% substitution. Better agreement can be obtained up to the limit, if a secondary process of steric control by the substituant in a partially substituted mr triad is assumed. Other possibilities for that secondary process are discussed.
    Additional Material: 21 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Nucleophilic substitution of PVC with sodium thiophenate was carried out in cyclohexanone solution at 5, 25, 40, 60, and 70°C. The initial rate obeys an Arrhenius law from 25 to 60°C, with an activation energy of 70 kJ/mol. Conversion limits are observed which strongly depend on the temperature. The stereoselectivity of the reaction with respect to the configurational triads does not depend on the temperature: the distribution of configurations is only dependent on the conversion. Assuming an SN2 substitution mechanism governed by steric factors, the Monte Carlo simulation procedure described in a prior study is shown to give a good account for all temperatures above 40°C assuming for the mm, mr or rm, and rr triads a reactivity such as Rmm = 2 Rmr and Rrr nil at low temperature and very low at temperatures ≥ 40°C. The low conversion limits observed at 5 and 25°C cannot be explained by a limited accessibility of a part of the polymer. Finally, it is shown that the elimination reaction, which remains limited, does not interfere with the substitution process.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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  • 3
    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: A new technique, based on the formation of reversible gels is proposed for the separation of grafted copolymer from the homopolymer corresponding to the grafts. The method is developed particularly with respect to its application to ABS resins.It is shown that, if the main chain carrying the grafts (polybutadiene) is supplied with COOH groups, reversible cross-linking can be obtained by dipolar association of neutralized COOH groups (e.g. by CH3ONa). When dissolved in a mixture of an apolar solvent and a solvent (CH3OH) solvating the COONa associates, such a polymer forms a gel, if the solvating agent is eliminated. This cross-linking by association of COONa dipols leads to a nearly total insolubility of the carboxylated polymer.Renewed addition of the solvating agent leads to a dissolution of the gel phase. The mixture benzene/CH3OH has been chosen for effectuating the cycles gelation-dissolution; methanol being easily eliminated by azeotropic distillation at ordinary temperature.Optimal conditions for the reversible gel formation have been given.This sol-gel separation technique can be applied for the purification of graft copolymers.
    Notes: Une nouvelle technique, basée sur la formation de gels réversibles, est proposée pour la séparation d'un copolymère greffé de l'homopolymère correspondant aux greffons. La mise au point de la méthode a été faite en vue de son application aux résines ABS.On montre ainsi que si le tronc porteur des greffons (polybutadiène) a été muni de groupes COOH, une réticulation réversible peut être obtenue par association dipolaire des groupes COOH salifiés (p. ex. par CH3ONa). A partir d'un tel polymère, en solution dans un mélange de solvant apolaire et d'un solvatant (CH3OH) des associats COONa, on provoque la gélification par élimination du solvatant. Cette réticulation par association entre dipoles COONa permet l'insolubilisation presque totale du polymère carboxylé.Une nouvelle addition de solvatant provoque la dissolution de la phase gel.Le mélange benzène/CH3OH a été choisi pour effectuer les cycles gélification-dégélification, le méthanol pouvant être éliminé aisément par distillation azéotropique à température ordinaire.Les conditions optimales de formation du gel réversible ont pu être définies.Cette technique de séparation sol-gel peut être transposée aux copolymères greffés, en vue de leur purification.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 4
    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: For the separation of graft copolymers, especially for ABS (acrylonitrile, butadiene, styrene), we propose a new technique based on the formation of reversible gels. For carboxylated polybutadiene, reversible crosslinking may be obtained by dipole associations of COOH groups, neutralized with a monovalent metal derivative (e.g. CH3ONa). Under these conditions, by sol-gel separations, the graft copolymer can be isolated rapidly from the polymer not fixed on polybutadiene.The efficiency of the method is shown for 4 different ABS, by using a radioactif AS copolymer as a tracer.The graft copolymer, isolated after 3 successive sol-gel separation steps, contains as low as 0,03% to 0,85% non grafted AS, depending on the initial ABS. This method presents the advantage to give evidence for low graft contents and may so be suitable for kinetic studies at low degrees of conversion.This separation technique can also be applied to other systems, if COONa groups can be fixed selectively, before or after grafting, either on the polymer backbone of the graft or on the polymer forming the grafts.
    Notes: Une nouvelle technique, basée sur la formation de gels réversibles, est proposée pour la séparation de copolymères greffés, spécialement dans le cas des ABS (acrylonitrile, butadiène, styrène). Par carboxylation du polybutadiène une réticulation réversible peut être obtenue par associations dipolaires des groupes COOH salifiés par un composé d'un métal monovalent (ex.: CH3ONa). Dans ces conditions, des séparations sol-gel permettent d'isoler rapidement le copolymère greffé du polymère non fixé sur le polybutadiène.L'efficacité de la méthode a été montrée pour 4 ABS différents, en utilisant comme traceur un copolymère AS radioactif.Le copolymère greffé, isolé après 3 séparations successives sol-gel, ne contient plus qu'une proportion d'AS non greffé variant de 0,03% à 0,85%, suivant les ABS analysés. Cette méthode, qui présente l'avantage de pouvoir mettre en évidence des taux de greffage faibles, permet d'aborder l'étude cinétique des greffages, notamment aux taux de conversion faibles.Ce principe de séparation peut être appliqué à d'autres systèmes, à condition de pouvoir fixer sélectivement avant ou après greffage, des groupes COONa sur le polymère tronc ou le polymère formant les greffons.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: In order to assign all —CH2Cl resonances observed by 1H NMR in poly(vinyl chloride), (PVC), a preliminary study of the diastereoisomers of molecular models for the groups CH2Cl—CHCl— [II] and is used, in conjunction with spin echo experiments. The complex region [3,5-4,0 ppm] which corresponds to saturated —CH2Cl chloromethyl protons is completely assigned. A separate evaluation of —CHCl—CH2Cl [II], —CH2—CH2Cl [III] and is proposed and tested on raw PVC samples. The main interest of this 1H NMR determination is the fact that raw PVC can be used and that it gives the ratio [II]/[III] which is not accessible by 13C NMR on reduced samples.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: 4-Chloro-3-chloromethylheptane (2) and 1,2,4-trichloropentane (3) were synthesized and analysed by means of 1H NMR. These compounds  -  with two asymmetric carbon atoms  -  are models for two types of structure involving chloromethyl groups present in poly(vinyl chloride): short chloromethyl branches and chain end groups resulting from reinitiation by a chlorine atom. The spectra of these compounds allow a better understanding of the corresponding resonance region observed in standard PVC.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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