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IR spectroscopy showed that in nitrile copolymers and fibres containing units based on itaconic acid, these units can exist in different modifications. The formation and set of modifications are a function of the conditions of preparation of the copolymer and fibre, especially their hydrophilicity. The existence of different modifications of itaconic acid fragments (in both the initial samples and in the samples formed in the initial stages of heat treatment) affects the rate of the subsequent processes of thermooxidative decomposition of the objects and the set of polyconjugated systems formed and consequently also the supermolecular structure. These findings should be taken into consideration both in the analysis of the corresponding copolymers and in the technology of their fabrication and processing.

The dichroic ratios of a series of absorption bands of the spectra of oriented PAN films and a number of acrylonitrile copolymers treated thermally for different times have been calculated. The orientation of the polyconjugated structures formed in the polymer chains as a result of thermal treatment is evaluated. The high rate of formation of the polyconjugated structures in the copolymers studied as compared with PAN is due not only to chemical initiation of their formation because of the influence of the functional groups of other components but to the manifestation of qualitatively new physical conditions for flattering the fragments of the chains with nitrile units.

The methods of IR spectroscopy, X-ray structural analysis and DTA were applied to study changes in the molecular and super-molecular structure of polyacrylonitrile subjected to a short intense energy pulse-laser irradiation or thermal impact. Both actions lead to the formation of conformers with absorption bands at 965 cm−1, and of a collection of polyconjugated structures. The chemical reactions proceeding during such action do not affect the ordered domains of the polymer. Three ranges were revealed in the temperature dependence of layer spacing. By a short energy impact, interchain interactions are enhanced due to improved packing of the structure, leading to a displacement of the high-temperature transition to higher temperatures. This results in improved thermostability of crystallites in the samples (this effect is the highest with laser irradiation). By DTA an additional maximum was detected, caused by the difference in the temperature range for cyclization processes in amorphous and crystalline polymer domains.

Preliminary irradiation of technical polyacrylonitrile tow with CO2 laser radiation leads to initiation of cyclization processes on subsequent heat treatment and to a decrease in oxidation time.

The results of IR spectroscopy studies on polyacrylonitrile and some model nitrile polymers subjected to the action of temperature and a laser are systemized. The spectroscopic features of polyconjugated structures, i.e. conjugations along the chain resulting from nitrile group opening and the formation of naphytyridine rings formed in the polyacrylonitrile macromolecules during thermooxidative degradation are established.