The effect of external orienting electric field on dielectric relaxation of segmented polyesters in dilute solution

Abstract

A comparative study of dipole polarization relaxation in the absence and in the presence of an external orienting electric field was performed for linear segmented polyesters with alternating rigid (oxyfumaroylbis-4-oxybenzoates) and flexible (methylene-CH2-, ethylene oxide-CH2CH2-O-, and dimethylsiloxane-Si(CH3)2-O-Si(CH3)2-) fragments in dilute solutions. Polyesters that do not display mesomorphic properties in the bulk show several regions of dielectric absorption with relaxation character. These regions are associated with the motions via the local mobility mechanisms of different polar fragments of the macromolecule. In solutions of polyesters that possess LC properties in the bulk, large-scale dipole polarization relaxation with long relaxation times and high activation energies was revealed along with local dielectric relaxation transitions. This process is associated with the cooperative motion of mesogenic fragments in their associates. In an external orienting electric field, the intensity of dielectric absorption usually increases for all types of dielectric transition; relaxation times and activation energies experience changes only for large-scale processes.