Effects of Branching of the Ester Alkyl Chain on the Liquid Crystalline Properties of Alkyl 4-(4-Alkoxybenzylideneamino)- benzoates

Abstract

The liquid crystalline properties of alkyl 4-(4-alkoxybenzylideneamino)benzoates, where the ester alkyl groups are propyl, isobutyl, neopentyl, racemic 2-methylbutyl, pentyl, 1-methylpentyl, 2-methylpentyl, 3-methylpentyl, and 4-methylpentyl, have been studied by thermal microscopy and differential scanning calorimetry. The alkoxyl group includes all the members from methoxyl to decyloxyl in most of the series. Chain branching of the purely smectogenic five propyl, two butyl, and six pentyl esters produces nematic behavior. All the resulting nematogens but one are the 2-methyl derivatives in which two are neopentyl esters. The smectic B phases observed for many propyl esters are not found for the isobutyl and neopentyl esters. Similarly, the smectic B and C phases of the butyl esters are eliminated by a 2-methyl substituent. On the other hand, smectic B behavior not exhibited by the pentyl esters appears in a few early homologs and smectic C behavior is thermally enhanced in some higher homologs of the 3- and 4-methyl derivatives.