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Abstract
The dielectric relaxation behavior of a series of ethylene-vinylacetate (EVA) copolymers was investigated by measuring the complex dielectric permittivity in a broad frequency and temperature range. Crystallinity of EVA copolymers was estimated by differential scanning calorimetry (DSC) and wide-angle X-ray scattering (WAXS). The shape of the higher temperature relaxation, appearing above the glass transition temperature T g depends on the VA content. It was found that this relaxation was asymmetric for VA concentrations higher than 40 wt% and changed to a symmetric shape at lower VA values. Concurrently, as the VA content decreased, a major broadening of the relaxation over a wide frequency range was observed. It is found that the dielectric relaxation was preserved on going through the melting range of the semicrystalline samples, although it exhibited changes of its characteristic parameters that are typical for segmental relaxation appearing at T g. This finding allows one to associate this relaxation to the segmental motions at T g in the amorphous phase and not to the existence of interfacial regions.
ACKNOWLEDGMENT
We are indebted to DGICYT (grant PB 94–0049) and to Comunidad de Madrid (07N/0063/998), Spain, for generous support of this investigation. I. Š. thanks AECI (Spain) for the fellowship. We thank Dr. F. Ania for providing the samples investigated in this work.