Identification of highly ordered smectic phases in a main-chain liquid-crystalline polyethers

A series of polyethers have been synthesized from 1-(4-hydroxy-4'-bipbenyl)-2-(4-hydroxyphenyl)propane and alpha,omega-dibromoalkanes having different numbers of methylene units [TPPs]. Both odd- and even-numbered TPPs [TPP(n=odd)s and TPP(n=even)s] exhibit multiple transitions during cooling and heating and they show little supercooling dependence. The phase diagrams for both TPP(n=odd)s and TPP(n=even)s have been constructed and the phase identification is the central part of this publication. The transition thermodynamic properties (enthalpy and entropy changes during the transitions) are studied based on differential scanning calorimetry experiments. The contributions of the mesogenic groups and methylene units to each ordering process can be separated and they indicate the characteristics of these processes thereby providing estimations of the transition types. Structural information can be obtained via wide angle X-ray diffraction powder and fiber patterns at different temperatures, Tn addition to the nematic liquid crystalline phase. highly ordered smectic F, G and II phases have been identified. These phase assignments are also supported by the morphological observations in the liquid crystals under polarized light and transmission electron microscopy. The concepts of the liquid crystalline phases defined For small-molecule liquid crystals are also applicable to main-chain liquid crystalline polymers.