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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.