SMECTIC POLYMORPHISM OF SOME BIS-(4,4'-NORMAL-ALKOXYBENZYLIDENE)-1,4-PHENYLENEDIAMINES UP TO 3 KBARS BY DIFFERENTIAL THERMAL-ANALYSIS

The T-p phase diagrams of four homologues of the bis-(4,4'-n-alkoxybenzylidene)-1,4-phenylenediamine series (C//5H//1//1O equals PENTOBPD, C//6H//1//3O equals HEXOBPD, C//7H//1//5O equals HEPTOBPD and C//8H//1//7O equals OOBPD) have been determined by high pressure differential thermal analysis (dta) up to 3 kbars and in the temperature range 300 K to 600 K. From the areas of the dta peaks the transition enthalpies were determined up to 2. 4 kbars. By means of these values and the slopes of the T-p transition curves at different pressures the transition volumes could be additionally calculated. A phase theoretical analysis of the results demonstrates that for this homologous series pressure increase has a similar influence on the T-phase diagrams as it would have a shortening of the alkoxy chains at a constant (e. g. normal) pressure; a similar effect has been found for the transition enthalpies.