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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.