Studies of Mesophase Transformations for Certain Schiff's Base Esters

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Abstract
Schiff's bases derived from esters of p-aminocinnamic acid continue to be of interest because of novel mesophase transformations that they exhibit. At Berlin, preliminary results for the homologous methyl to n-decyl 4-(p-phenylbenzylideneamino)cinnamates were described which indicated that smectic polymorphism was important in the series. Results of differential thermal analysis, optical microscopy and miscibility studies now presented show that most of the homologues give a smectic A, a smectic B and an uncharacterized smectic 3 phase. Regular changes in smectic-smectic transition temperatures occur along the series. Photomicrographs reveal differences in the fan and other textures of the three smectic phases, particularly for smectic 3, a tentative structure and assignment for which are discussed. Studies of di-(-)2-methylbutyl terephthalylidene-bis-p-aminobenzoate have shown that the “focal-conic” or plane texture of the cholesteric phase undergoes three reversible transformations in forming the amorphous liquid. Photographic evidence for these changes is presented and discussed. Following these observations, cholesteric to amorphous liquid transformations for two other types of cholesterogen (cholesteryl esters and (-)2-methylbutyl 4-(p-substituted-benzylideneamino)cinnamates) have been re-examined. Results are presented showing that the cholesteric mesophases of the three types of cholesterogen change to the amorphous liquid on heating and reform from the liquid on cooling in significantly different ways.