Dielectric relaxation of rigid-chain thermotropic LC polymers studies by the methods of dielectric losses and thermostimulated depolarization current

Relaxation transitions in a copolyester of p-hydroxybenzoic acid and PET (PEE-1) and a copolyester of p-hydroxybenzoic and 2,6-hydroxynaphthoic acids (PEE-2) were studied by the methods of dielectric relaxation and thermostimulated depolarization current in a wide range of frequencies and temperatures. Earlier unknown transitions at high and low temperatures were revealed, and their relation to the structure and structural peculiarities of LC polymers was considered. High-temperature transitions at 170-190 degrees C (at a frequency of 1 Hz) were explained by the processes of glass transition (PEE-1) as well as by their superposition with polymorphic transitions (PEE-2). At temperatures above the principal glass transition temperature, PEE-1 was shown to possess a higher molecular mobility as compared to PEE-2. The hindered rotational mobility of PEE-2 was preserved up to temperatures close to the melting temperature T-m of the crystalline regions of polymer.