INFLUENCE OF THE EXTERNAL (ELECTRIC OR MECHANIC) FIELD ON THE DIELECTRIC-RELAXATION IN LIQUID-CRYSTALLINE SIDE-CHAIN POLYMERS

The effect of orienting fields on the relaxation of dipole polarizatio n in siloxane nd methacrylate liquid crystalline polymers with cyanobi phenyl groups in side chains has been investigated. The temperature-fr equency dependences of dielectric losses of comb-like polymers with th e main siloxane chain were studied in the mesomorphic state (in bulk). Two relaxation processes, alpha and delta, were established. They are related to the reorientation of the transverse and longitudinal compo nents of the dipole moment of the mesogenic group. Similarity of the t emperatures of the alpha- and delta-processes and of the glass transit ion are due to the dependence of the main chain segment motion on the interaction between side mesogenes, with the segmental mobility occurr ing only when the mesogenes move. The effect of the external orienting field leading to homeotropic orientation of mesogenic fragments resul ts in the increasing intensity of delta-transition and the suppression of alpha-transition. The relaxation times and the activation energies of the delta-transition remain unchanged. On the basis of dielectric data the order parameter of mesogenic groups was evaluated. Three rela xation regions of dipole polarization were detected on the temperature -frequency dependences of dielectric losses in a comb-like polymer wit h the methacrylate main chain in a chloroform solution. Two of them we re related to intramolecular mobility of polar kinetic elements in sid e chains, whereas the third region was associated with the cooperative mobility of mesogenic groups in the macromolecular coil. Only the thi rd process was shown to be influenced by the external electric field.