ISSN:
0449-296X
Schlagwort(e):
Physics
;
Polymer and Materials Science
Quelle:
Wiley InterScience Backfile Collection 1832-2000
Thema:
Chemie und Pharmazie
Notizen:
The thermal stability of the isomeric poly-1,2,4-oxadiazole (PO-2) and poly-1,3,4-oxadiazole (PO-3) was investigated. The isomerism of the ring substantially influenced polymer thermostability. The weight losses in PO-2 occur above 220-230°C. in vacuo, but PO-3 degrades only at 280-300°C. The weight changes in isomeric polyoxadiazole at lower temperatures are connected with the completion of the cyclization process. At higher temperatures degradation of the oxadiazole ring takes place, and as a result carbon and nitrogen oxides, 4,4′-dicarboxy (diphenyl ether) dinitrile and other products are evolved. The mechanism of polymer thermal degradation is examined; it is shown that the weakest bonds are C—O and N—O. These data are in a good agreement with the results of calculation of the π-electron systems of unsubstituted oxadiazole cycles in the framework of the molecular orbital treatment in the Hückel approximation. It is shown that the oxygen in the oxadiazole ring oxidizes the products of thermal degradation of polymers and a cell effect takes place. The thermal oxidation of isomeric polyoxadiazoles does not differ essentially from the degradation in vacuo. It was found that the formation of intermediate products such as peroxides and hydroperoxides does not take place, and oxygen does not act as an initiator of polymer degradation.
Zusätzliches Material:
8 Ill.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1002/pol.1968.150060526
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