Molecular Order of the Mesogens in Smectic Poly(ester imide) Fibers

Abstract

The molecular order of the mesogens in the smectic liquid-crystalline (LC) and smectic- crystalline phases of different poly(ester imide)s (PEI) with similar chemical structure is investigated by means of X-ray fiber patterns. During the fiber spinning from the melt, the smectic LC phase is frozen. Above the glass transition temperature, a transition into a higher-ordered smectic-crystalline phase occurs. The PEI which are based on aminobenzoic acid trimellitimide and long aliphatic spacers form exclusively orthogonal smectic phases (SA ,S B ,S E). In contrast, the PEI based on aminocinnamic acid trimellitimide and those derived from 4-hydroxyphthalic acid, aminophenol, and aliphatic dicarbon acids form tilted SC phases. The layer line broadening of the X-ray reflections indicates a poor lateral order of the smectic layers in the LC phase due to a frequent inversion of the staggering direction between adjacent mesogens. As a result of the equatorial smearing of the four-point-pattern, the splitting angle of the reflections is not identical with the tilt angle between the mesogens and the normal of the smectic layer plane. The order of the mesogens in the direction perpendicular to the fiber axis is evaluated on the basis of the paracrystallinity model. The resulting local tilt angle corresponds to an average staggering amount of the mesogens. Furthermore, the parameter , introduced by Porod, is interpreted as a probability for the inversion of the staggering direction.