Study on Smectic Liquid Crystalline Structure in Main-Chain Polyester

点击翻译按钮获取中文摘要

The thermotropic liquid crystal nature of mainーchain polyesters that can be constructed by an alternative arrangement of the p,p'ーbibenzoate unit as a mesogenic group and the alkanediol as a flexible spacer. The polyesters are designated BB-n where n is the number of methylene units in the diol. This homolog ous series of BB-n (n = 3-9) invariably form smectic mesophases whose isotropization temperatures and entropies exhibit an evenーodd oscillation with the number of intervening methylene units, n. The evenーodd nature of the methylene unit also reflected the thickness of smectic layers, with a larger layer thickness in the even series. Comparing the observed thickness with the calculated ones based on the rotational isomeric state model, we concluded that the evenーodd nature is strongly related to the polymer chain conformations and that the different types of smectic structures can be formed between the two. In even numbered polyesters there is formed a normal smectic A phase in which both axes of the polymer chain and mesogenic group lie perpendicular to the layers. In oddーnumbered ones, in contrast, the smectic structure was found to be a type of smectic C in which the average chain axis of the polymer is perpendicular to the layer, but the mesogenic groups are tilted with respect to the layer normal. Such structural characteristics are also confirmed from the xーray and optical microscopic studies for the oriented smectic phases.