INFLUENCE OF CRYSTALLINITY ON THE DIELECTRIC-RELAXATION BEHAVIOR OF POLY(ETHER ETHER KETONE)

The dielectric relaxation characteristics of amorphous and semicrystalline poly(ether ether ketone) have been investigated as a function of crystallization history; both the glass-rubber (alpha) relaxation and a sub-glass (beta) relaxation were examined. The characteristics of the alpha relaxation were highly sensitive to crystallinity owing to the constraint imposed on the amorphous phase dipoles by the presence of the crystalline phase. The magnitude of the alpha relaxation strength indicated an immobilized rigid amorphous phase fraction in the semicrystalline samples which appeared to relax at temperatures above T(g); finite rigid amorphous fractions were observed for both cold-crystallized and melt-crystallized specimens. The sub-glass (beta) relaxation was also sensitive to the presence of crystallinity: the isochronal loss maxima measured for the cold-crystallized samples were offset to higher temperatures as compared to the wholly-amorphous material, and a disproportionate decrease in the beta relaxation strength with the degree of crystallinity was observed. The influence of the crystalline phase on the beta relaxation thus appears to extend well into the amorphous material, suggesting sub-glass motions which encompass a larger segmental length scale as compared to more flexible polymers.