Synthesis and Properties of Thermotropic Compounds with Two Terminal Mesogenic Units and a Central Spacer Ⅲ. Homologous Series of $\alpha,\omega$-Bis[4-(p-nitrobenzoyloxy)phenoxy]alkanes

Synthesis and Properties of Thermotropic Compounds with Two Terminal Mesogenic Units and a Central Spacer Ⅲ. Homologous Series of $\alpha,\omega$-Bis[4-(p-nitrobenzoyloxy)phenoxy]alkanes

A series of new liquid crystalline compounds having two identical mesogenic terminal units, the 4-(p-nitrobenzoyloxy)phenoxy group, attached to both ends of a central polymethylene spacer of various lengths was prepared. The mesomorphic properties of the compounds were investigated by differential scanning calorimetry (DSC) and by polarizing microscopy. Almost all of the compounds formed monotropic nematic mesophases. The trimethylene spacer compound was found to be non-liquid crystalline, while the one with the hexamethylene central spacer was enantiotropic. A thermodynamic analysis was performed for the phase transitions of the compounds and the results are discussed in relation to their liquid crystal properties.