No abstract

No abstract

Positron-lifetime measurements have been made in undoped and polymers 0.8 wt%iodine-doped polyacrylonitrile (PAN) under annealing from room temperature to 160'C. From the measured lifetimes, the free-volume size is calculated following the treatment of Nakanishi, Jean, and collaborators. The variation in free-volume size as function of temperature seems to suggest molecular-chain-folding processes in amorphous regions of the polymer, positron trapping at kink-type defects, and at the interface between crystalline and amorphous regions at lower temperatures. This study indicates that in the undoped state, the polymer has a glass transition temperature at 90'C which is shifted toward lower temperature in the doped state by 30'C. The results also suggest the degradation of the polymer in the two states after 100'C and the effect of annealing is only on the size but not on the density of free-volume sites.

No abstract

No abstract