Part II. Pyrolysis of a tetrafluoroethylene–acrylonitrile copolymer

The pyrolysis of copolymers obtained by radiation-induced grafting of acrylonitrile onto polytetrafluoroethylene has been studied. Infrared spectroscopy shows disappearance of ? C?N and appearance ? C?N? absorptions, indicative of the conjugation of the nitrile groups in the polyacrylonitrile segments. Aromatization is suggested by the appearance of aromatic C? H absorption and by the disappearance of aliphatic C? H absorption in the infrared spectra, as well as by the decrease of the C/H ratio and the constancy of the N content during exposure to 280°C. shown by elementary analysis. Melting and remelting was studied by differential thermal analysis with respect to temperature, extent, and shape of peak area. An increase in the melting temperature proportional to the content of acrylonitrile in the copolymer was explained in terms of entropy effects. The melting peak obtained after grafting appears as a doublet. The latter disappears after annealing for 14 hr. at 300°C. and does not reappear on crystallization or on remelting. In addition, the areas obtained on first and repeated meltings shows a decrease which is proportional to the content of grafted polyacrylonitrile. These results are taken as an indication of an exothermic reaction involving crosslinking. The rate of disappearance of the ? C?N absorption reaches a maximum at the melting temperature. It seems that the exothermic reaction occurring in the crystalline region is identical with “propagation crosslinking” suggested by Grassie and Hay. It is concluded that an interesting new type of polymeric material has been found.