Thermotropic compounds having two terminal mesogenic units and central spacers. Part 7. Homologous α,ω-bis-[p-(4-alkoxyphenoxycarbonyl)phenoxy]alkanes

Abstract

A homologous series of α,ω-bis-[p-(4-alkoxyphenoxycarbony)Phenoxy] alkanes was prepared; their thermal and liquid crystalline properties were studied by differential scanning calorimetry and on the hotstage of a polarizing microscope. The nature of the liquid crystalline phase of the compounds depended greatly on the length of the central polymethylene spacer and on the terminal alkoxy groups. The ‘odd–even’ effect of the terminal alkoxy groups was observed neither for the melting nor for the clearing transition temperatures of the compounds. However, the changes in enthalpy and entropy for the isotropic transitions showed a zig-zag dependence on the number of methylene units in the alkoxy groups. Values for ‘even’ members were consistently higher than those for ‘odd’ ones, regardless of whether the central polymethylene spacer was odd-numbered or even-numbered.