INFLUENCE OF LIQUID-CRYSTALLINE ORDER ON THE DIELECTRIC-RELAXATION OFRANDOM COPOLYESTERS OF PET, PEN, AND PHB

The dielectric constant and dielectric loss values for random copolyes ters of poly(ethylene terephthalate) (PET), poly(ethylene 2,6-naphthal enedicarboxylate) (PEN), and poly(p-hydroxybenzoic acid) (PHB) have be en determined in the 10(3)-10(6) Hz frequency range. The variation of the dielectric properties with temperature has been related mainly to two processes: (1) The alpha relaxation, which is associated to the gl ass transition and which has been shown to be dependent on the molecul ar order of the systems. Copolymers with liquid crystalline order exhi bit an alpha relaxation process occurring at lower temperatures than t he amorphous ones. (2) The beta process which has been assigned to a l ocal motion of the ester groups attached to both sides of the aromatic rings. The beta process also depends on the molecular order. The exis tence of a liquid crystalline state increases the dipolar correlation of both the beta and the alpha relaxation processes.