ISSN:
0360-6376
Schlagwort(e):
Physics
;
Polymer and Materials Science
Quelle:
Wiley InterScience Backfile Collection 1832-2000
Thema:
Chemie und Pharmazie
Notizen:
The oxidative degradation of isotactic polypropylene films coated on well-defined Cu(Cu2O), CuO0.67, and CuO films in a temperature range of 90-120°C in a quartz-spoon-gauge-reaction vessel was studied. This catalytic reaction has been compared with the oxidation of polypropylene without copper or oxide films. The reaction vessel contained, if needed, P2O5 and/or KOH as “getters” for H2O and CO2, these substances could be menitored continuously. Cu(Cu2O) films were transformed during oxidation of the polymer to yellow CuO0.67 below 100°C and above this temperature to black CuO in the presence of H2O and CO2, whereas in the absence of these compounds CuO was formed below 100°C and CuO0.67 at 120°C. Characteristic autoxidation curves obtained in the absence of H2O and CO2 showed induction periods that were shorter for copper oxide-polymer interfaces than for glass-polymer interfaces (i.e., for uncatalyzed oxidation). Abnormalities were observed for Cu(Cu2O)-polymer interfaces because of further oxidation of Cu during the reaction. The rates of oxygen consumption were faster for CuO0.67-polymer and CuO-polymer than for the uncatalyzed reaction; the catalytic action of CuO0.67 was somewhat larger than that of CuO. The important observation was made that the mechanism of oxidation is not the same in the absence and presence of reaction products; that is, H2O and CO2. This was confirmed by ion beam scattering experiments, which also revealed that an oxidation-reduction process takes place at Cu and their oxide interfaces. A mechanism for the catalytic oxidation process, based on the ease by which copper ions are released from the metal oxides at the interface, was formulated. These ions diffuse subsequently as actions of carboxylate anions into the bulk of the polymer. Arrhenius equations of oxygen consumption are given for all cases; the energy of activation calculated for the initiation of the uncatalyzed oxidation agrees with its literature value. The energy of activation for the initiation of the catalyzed reaction was a few kilocalories lower than that for the uncatalyzed reaction. Catalytic action is mainly operative for the initiation reaction at the interface and for the decomposition of hydroperoxides by copper ions. Preventing the delivery of copper ions to the polymer would be the most efficient way of inhibiting the catalysis.
Zusätzliches Material:
29 Ill.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1002/pol.1979.170170523
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