X-ray Analysis of Chiral Thermotropic Liquid Crystal Copolyesters Based on Linear and Nonlinear Aromatic Ester Triads

Abstract

A series of chiral thermotropic liquid crystalline copolyesters, based on linear mesogenic triads and nonlinear nonmesogenic triads consisting of two p-oxybenzoyl units coupled by a terephthaloyl or phthaloyl residue respectively, is studied by X-ray diffraction. Complementary data of differential calorimetry and polarizing microscopy are presented. The degree of crystallinity is found to depend significantly on the relative content of the nonlinear counit and to vary with thermal history. The occurrence of cholesteric phases is established, whose stability and breadth can be modulated on the basis of appropriate chemical compositions. The structural data of the investigated copolymer samples are compared with those previously obtained for an analogous series of copolymer samples based on the same linear aromatic triad and an isomeric triad containing a central isophthaloyl residue.

Keywords: liquid crystalline polymers, chiral thermotropic polymers, cholesteric copolyesters, 4,4'-(terephthaloyldioxy)dibenzoate mesogen, X-ray diffraction