Temperature transitions and structural changes in polyacrylonitrile

The temperature transitions and structural changes in polyacrylonitrile, associated with activation of molecular motion in the amorphous and crystalline regions of the polymer are studied by X-ray diffraction analysis, IR spectroscopy, and DSC. There are two transitions in the temperature region ∼ 340–370 K. The first is due to freezing of the segmental motion in the amorphous regions of the polymer and is the reason for precrystallization and splitting off of α-hydrogen. At ∼ 370 K activation of the tortional vibrations in the crystals is observed, as a result of which structural reorganizations take place in them. The high temperature transition in the region of 440–450 K, associated with the activation of bending vibrations, is also revealed and studied. There are two processes which are a consequence of this, i.e. recrystallization and ring closure. Ring closure above 450 K includes not only the amorphous regions of the polymer but also the crystalline regions.