Abstract
The molecular mechanism of two kinds of absorption peaks, which were usually observed at 160_??_170°C (α1) and ca. 120°C (α2) in the dynamic loss tangent (tan δ)- temperature curve (100Hz.) for unoriented polyacrylonitrile (PAN) film, was studied. For this purpose, PAN samples of widely different crystallinity were prepared by using the following methods: (1) radiation-induced polymerization with and without urea-canal complex and conventional free radical polymerization, (2) different kinds of solvent (i.e., N, N′-dimethyl-formamide and 70% nitric acid) in the solvent casting process, (3) solution grown crystal, and (4) heat-treatment. The negative correlationships were found between the sum of intensities of both α1 and α2 absorptions and the crystallinity. Apparent activation energy of α1 and α2 absorptions were determined as 92.1 and 57.5Kcal/mol, respectively. α1 and α2 absorptions were attributed to the micro-Brownian movement of the chain in an amorphous region, suggesting that the fine structures of PAN solid could be reasonably expressed in terms of two amorphous phases and a single crystalline phase.
