Rheological Characterization of a Series of Thermotropic Liquid Crystalline Polymers

摘要

Dynamic rheological experiments were performed on a series of two copolymers and a homopolymer based on units of terephthaloyl chloride and isophthaloyl chloride at 90/10 and 75/25 mole ratios combined with 1.10-bis (4-hydroxyphenyl)-decane. Optical microscopy and wide angle X-ray diffraction (WAXD) confirmed that all of the polyesters in the present series formed nematic liquid crystals with nematic-to-isotropic temperatures in the range of 270-320 C with increasing terephthaloyl unit content. Broad nematic-to-isotropic transitions observed by differential scanning calorimetry (DSC) were indicative of biphasic regions where the nematic phase in the isotropic phase with shear thinning occuring in the former but Newtonian behavior in the latter. There were also some indications that nematic flow behavior could be induced in these polymers by dynamic oscillatory shear flow above the nematic-to-isotropic transition, T sub i. A form of hysteresis was observed with the homopolymer in that measurements of the dynamic viscosity eta* taken with ascending frequency sweeps were higher than those taken with descending frequency sweeps.