Synthesis and Thermal. Properties of Cholesteryl 4-n-Alkoxy-3-methoxybenzoates

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Abstract
A homologous series of new liquid crystalline compounds, cholesteryl 4-n-alkoxy-3-methoxybenzoate were synthesized from vanillin and their mesomorphic properties were studied by differential scanning calorimetry, polarizing microscopy and x-ray diffractometry. Each of the homologues from cholesteryl 3,4-dimethoxybenzoate (n = 1) to cholesteryl 4-n-hexyloxy-3-methoxybenzoate (n = 6) showed a cholesteric-nematic phase (NCh). The other higher homologues (from n=7 to n=18) indicated smectic A (SA) and NCh phases. The temperature region of smectic phases increased with the increase of the chain length of the n-alkoxyl group. Transition temperatures in each of the homologues were lower than those in a corresponding non-3-methoxy substituted benzoate ester, due to the destabilizing effect of the lateral methoxyl group. The effect was more significant on the homologues having a shorter n-alkoxyl chain. It was also found that these esters formed a glassy state by quenching from mesophases and/or the isotropic liquid phase. The change of the glass transition temperature on each homologue (from n = 1 to n = 6) suggested the effect of the chain length of the n-alkoxyl group on the formation of the glassy state.