NMR AND IR SPECTROSCOPIC INVESTIGATIONS OF THERMOOXIDATIVELY TREATED PAN FIBERS

During thermooxidative treatment of PAN fibres at temperatures between 180 and 320-degrees-C several chemical reactions take place. As a result of cyclization by means of N-bridges and dehydrogenation, connected with the formation of conjugated double bonds, aromatic rings are formed. Furthermore, carbonyl groups occur due to oxidation. The resulting product is insoluble and nonmeltable. Therefore the mentioned reactions as well as the composition of the final product may be investigated by means of only a limited number of methods, among which high-resolution C-13-solid state-NMR and infrared spectroscopy proved to be particularly suitable. The reaction starts at about 180-degrees-C, the first being dehydrogenation. Cyclization and oxidation follow as temperature further increases.