EFFECT OF THE LENGTH OF FLEXIBLE CHAIN FRAGMENTS ON THE CURVATURE ELASTICITY CONSTANTS OF THERMOTROPIC NEMATIC LIQUID-CRYSTALS OF AROMATIC POLYESTERS

The orientational elastic distortions induced by a magnetic field in t he nematic phase of linear aromatic polyesters with different lengths of a flexible ethylene glycol fragment separating rigid mesogenic core s are studied using the method of the Freedericksz threshold transitio ns. The temperature dependences of the birefringence Delta n and the s play and bend elastic constants (K-1 and K-3, respectively) are obtain ed. For polymeric nematic liquid crystals, the ratio K-3/K-1 does not vary as the length of the flexible fragment increases by a factor of t wo, whereas for the low-molecular-mass model compounds, K-3/K-1 increa ses considerably with increasing length of flexible terminal groups.