PHASE AND RELAXATION TRANSITIONS IN THERM OTROPIC LIQUID-CRYSTALLINE COPOLYESTERS BASED ON P-HYDROXYBENZOIC ACID AND ETHYLENE TEREPHTHALATE

Phase and relaxation transitions in thermotropic LC copolyesters based on n-hydroxybenzoic acid and ethylene terephthalate were studied by m eans of X-ray analysis, differential scanning calorimetry, and dynamic mechanical relaxation. Copolymers with the ratio between components o f 80:20, 60:40, and 50:50 mol % were examined both in isotropic state and as highly oriented fibers. In the latter case, the samples were te sted immediately after spinning and annealing of the as-spun fibers fo r several hours at elevated temperatures. Glass transition temperature of copolyesters, which is controlled by the mobility of most rigid st ructural units, was found to be independent of the composition and was equal to similar to 70 degrees C. At temperatures below the temperatu re of transition to viscous LC state, the above copolyester was charac terized by a well-pronounced two-phase structure. One of the phase com ponents was provided by crystalline phase. At temperatures below the g lass transition temperature, this phase showed an orthorhombic crystal line structure, whereas at higher temperatures, it assumed hexagonal p acking. As a result of annealing at optimal temperatures, the attainme nt of maximal crystallinity was observed, and the degree of crystallin ity was estimated to be as high as 15%. The second phase was found to exist in the LC smectic state with an aperiodic arrangement of smectic layers.