Odd–even effect in miscibility of main-chain liquid crystal polymers with low molar mass nematogens

Abstract

Qualitative phase diagrams were constructed using the contact method for binary mixtures of several chemically-distinct low molar mass nematogens (LMMN) with a main chain liquid crystal polymer (TPB-x) which has a mesogenic group, 1-(4-hydroxy-4′-biphenyl)-2-(4-hydroxy phenyl) butane, separated by flexible alkyl spacers of variable length, x. Several interesting effects were observed. TPB-x was found to exhibit an odd-even variation in miscibility in the nematic state (2n + 1 = miscible, 2n=immiscible) with 4′-pentyl-4-cyanobiphenyl (5CB), but not with 4′-pentyloxy-4-cyanobiphenyl (5OCB) in which most polymers were completely miscible. On prolonged isothermal annealing in the biphasic region in 5CB, TPB-2n exhibited spherulitic crystallization of the liquid crystal polymer. These observations are shown to be qualitatively consistent with a modification of the Flory-Huggins theory by Brochard et al.