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  • Chemistry  (3)
  • 1980-1984  (1)
  • 1975-1979  (2)
  • 1
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 47 (1975), S. 61-77 
    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: When the ozonisation of bulk or suspension poly(vinylchloride) is carried out in tetrachloroethane solution between 0-120°C the molecular weight decreases continuously and the rate of breaking of chains deduced from the intrinsic viscosity variation is constant under isothermal conditions. Whatever the time and temperature of ozonisation may be, at every breaking, β and α chlorinated acid groups are introduced which have been characterized by infrared spectroscopy, high resolution NMR spectroscopy and potentiometric titration in dimethylformamide. Besides these functions, peroxide groups have also been identified and their concentration has been determined for different times and temperatures of ozonisation.This study permits to propose two mechanisms to explain the breaking of chains. The first implies the previous dehydrochlorination of the polymer and the second the formation of unstable peroxides which by decomposition cause the breaking of chains.
    Notes: Quelle que soit la nature du polychlorure de vinyle (masse ou suspension) l'action de l'ozone en milieu homogène dans le tétrachloroéthane provoque la décroissance continue de la masse moléculaire dans le domaine de température 0-120°C et la vitesse de coupure des chaînes déduite des variations de viscosité est constante en conditions isothermes.Quels que soient le temps et la température d'ozonisation, à chaque point de coupure apparaissent des fonctions acides α et β chlorées qui ont été caractérisées par spectroscopie infra-rouge, RMN haute résolution et dosage potentiométrique en milieu diméthylformamide. Outre ces fonctions, des peroxydes ont égé également identifiés dans le polymère et on a suivi leur concentration en fonction des conditions d'ozonisation.Cette étude permet de proposer deux mécanismes pour expliquer la coupure des chaînes, l'un suppose une déhydrochloruration préalable du polymère et l'autre la formation de peroxydes instables qui en se décomposant provoqueraient la coupure des chaînes.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 2
    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: Whatever the state of the iron compounds as smoke suppressant during the combustion of poly(vinyl chloride), they lead rapidly to native αFe2O3 in the char residue left after dehydrochlorination. It causes incandescence of the char residue and catalyzes its oxidation into carbon monoxide and carbon dioxide that contributes to decreasing the amount of available carbon for the soot formation after self-ignition. FeCl2 and FeCl3 are the precursors of αFe2O3, which is the true compound as smoke suppressant. Nevertheless, as intermediate, iron chlorides are able to modify the degradation processes, and they favor the formation of light tars instead of heavy tars. For that reason the iron compounds cause the formation of smoke at lower temperature than for pure PVC, but, as αFe2O3 is formed, the smoke production levels off and then decreases. The higher the ease of the iron compounds to give chlorides through reaction with HCI and further native αFe2O3, the higher the ease of the additive to cause the oxidation of the char residue sooner and in consequence to decrease the smoke level. In the PVC combustion three main steps may be distinguised: dehydrochlorination step between 200-300°C; tars aerosols formation from the char residue between 300°C and self-ignition; at temperature higher than self-ignition, formation of soot from the previous tars as precursors.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 0360-6384
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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