The base‐catalyzed transformation of polyacrylonitrile

In an effort to produce high‐molecular‐weight, linear ladder polymer by linking the nitrile groups within the molecule of polyacrylonitrile, polyacrylonitrile homopolymers were heat treated in N,N‐dimethylformamide and N,N‐dimethylacetamide solutions, in the presence of tertiary alkylamine catalysts. The products were soluble in formic acid, had relatively low molecular weight, and could be cast into brittle films. The infrared spectra indicated that the polymerization of the nitrile groups is initiated by a self‐initiation mechanism based on the active methine groups in polyacrylonitrile, as proposed by Grassie and Hay, and that the reaction is complicated by molecular weight degradation via reverse Michael addition, as proposed by Hamada and Takahashi. The inherent viscosities of the products increase with increasing catalyst concentration, and further increases can be achieved by the addition of anionic chain coinitiators of phenolic nature. Density measurements indicated that the ladder structures undergo rearrangement into a more stereoregular form after formation, and that some aromatization occurs when the reaction is carried out in the presence of air.