Effects of orientation on the dielectric glass–rubber relaxation of amorphous networks

Abstract

AbstractThe effects of the orientation on the dielectric glass–rubber relaxation of elongated poly(diethylene glycol isophthalate) networks, are studied. Orientation of the chains shifts the maximum of the α peak, at any frequency, to slightly lower temperature, as occurs in the case of mechanical relaxations. The dielectric behavior is interpreted in terms of the free volume theory. It is found that the ratio of the relative free volume to the parameter B at the glass transition temperature, where B is related to the minimum hole size required for local segmental motions, is almost independent of the elongation ratio λ. Cole–Cole diagrams are circular in the low‐frequency region, but at high frequencies the curves approach the abscissa along straight lines, which are nearly parallel for different values of λ. The difference between the dielectric constant at zero and infinite frequencies (ε0 − ε∞) is a linear function of the elongation ratio, and the Frölich theory suggests strong correlations between the relaxing species. The dielectric behavior of oriented networks is interpreted by using both the coupling model and a model which assumes the presence of defects around which the relaxation processes take place.