Existence of highly ordered smectic structures in a series of main-chain liquid-crystalline polyethers

[[abstract]]©1997 Elsevier - A series of polyethers has been synthesized from 1-(4-hydroxy-4'-biphenyl)-2-(4-hydroxyphenyl)propane and α,ω-dibromoalkanes having both odd and even numbers of methylene units [TPP(n = odd)s and TPP(n = even)s]. These polymers exhibit multiple thermodynamic first-order transitions during cooling and heating which demonstrate little supercooling dependence at different rates. The transition thermodynamic properties (enthalpy and entropy changes at the transitions) are studied by means of differential scanning calorimetry experiments. The contributions of the mesogenic groups and methylene units to each ordering process can be separated and indicate the characteristics of these processes, thereby providing estimations of the transition types. To construct the phase diagrams for both TPP(n = odd)s and TPP(n = even)s, identification of each phase structure can be obtained from wide-angle X-ray diffraction powder and fiber patterns at different temperatures as well as from electron diffraction experiments. In addition to the nematic liquid-crystalline phase, highly ordered smectic F, smectic crystal G and H phases have been identified. These phase assignments are also supported by 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 applicable to main-chain liquid-crystalline polymers.[[department]]化學工程學