DIELECTRIC-SPECTROSCOPY AND REGULARITIES OF THE LOCAL MOLECULAR MOBILITY IN THERMOTROPIC LINEAR-POLYMERS

Dielectric losses in some thermotropic linear polymers with alternatin g flexible spacers and mesogenic fragments of various structure in the chain were studied in the frequency range from 60 Hz to 70 MHz. The s tudies were performed for in the block state polymers (below the glass transition temperature) and in semidilute solutions. Two relaxation p rocesses related to local motions in the mesogenic fragments were disc overed far both states elf polymers. Mobility of the kinetic units in a mesogenic fragment, which are adjacent to the spacer, increases subs tantially with the spacer length. fn contrast, the parameters of the r elaxation process caused by mobility of the central part of the mesoge nic fragment are virtually independent of on the spacer length. The me chanism of motion within the mesogenic fragment is proposed. This mech anism involves a small-angle rotation of rigid groups, whose length is determined by the conditions of internal rotation. The relaxation tim es and the activation energies for the corresponding relaxation of the dipole polarization are the same for the block polymers and their sol utions; hence, the mechanisms of motion in the condensed state and in the individual macromolecules are identical.