Relation between the thermal behavior of polyacrylonitrile and polymerization factors

In order to clarify the mechanism to produce the large dispersion of the exothermic peak temperature (T_pk) of polyacrylonitrile, a systematic and quantitative study was made by means of the differential thermal analysis and the viscosity measurment. General tendency between T_pk and the polymerization methods was reconfirmed. Under a controlled condition (i.e., aqueous solution system), presence of N,N-dimethyl formamide or isopropyl alcohol produced a lower T_pk of resulting polymer, while presence of activator produced a higher T_pk. Thus, the large dispersion of T_pk (250–300°C) can be explained inclusively in terms of a single reaction factor, i.e., chain transfer mechanism. Particularly in the above third case it was shown that owing to strong and rapid chain transfer to activator, some kind of secondary reaction (caused by propagating chain end radical), probably chain branching which deteriorates the higher thermal quantity of molecule, is restrained effectively. Furthermore, some specific behaviors (i.e., cooperativeness and dynamic character, etc.) were observed in this reaction of PAN in solid amorphous phase.