Stabilization behavior of poly(acrylonitrile) with different stereoregularities

The effect of stereoregularity of poly (acrylonitrile) (PAN) on the stabilization mechanism was investigated by TG/DTA measurements, Infra-red spectroscopy, and gas chromatography-mass spectroscopy (GC-MS). The stabilization of atactic PAN (at-PAN) with lower stereoregularity occurred at a lower temperature than that of isotactic PAN (iso-PAN) with higher stereoregularity. The weight loss during stabilization was derived from the evolution of ammonia, hydrogen cyanide and compounds related with nitrile groups, having molecular weights between 41 and 147, formed by the bond cleavage reactions of PAN. The amount of gases evolved from iso-PAN was greater than that from at-PAN. These results revealed that the stabilization reactions proceeded more steadily in at-PAN than in iso-PAN. However, the IR spectra of the PAN samples with different stereoregularities recorded at the initial stage of the stabilization revealed significant differences in their chemical structures. The initial stage of the stabilization reaction in at-PAN occurred preferentially at the disordered chain configuration. However, the stereoregularity of iso-PAN stayed constant during the initial stage of stabilization reaction, showing that there exists no selectivity of the reactive site as opposed to at-PAN. No difference in the chemical structure could be found after the stabilization of at-PAN and iso-PAN.