SYNTHESIS AND LIQUID-CRYSTALLINE PROPERTIES OF THERMOTROPIC POLY(ESTER-URETHANE)S

Seven new mesogenic diol monomers CmCn, consisting of two bis(p-oxyben zoyl) units interconnected by a polymethylene segment containing n met hylene groups and Ranked by two linear o-hydroxyalkyl segments contain ing m methylene groups were reacted with 1,6-hexamethylenediisocyanate (HDI) to give a new series of liquid-crystalline poly(ester-urethane) s HDI-CmCn. All of the precursors CmCn exhibited a nematic phase, and in two of them a smectic mesophase also occurred. Poly(ester-urethane) s HDI-CmCn were semicrystalline and formed a monotropic mesophase. The mesomorphic properties of the polymers were studied as a function of their chemical structure by changing alternatively m or n. The effect of the molecular weight of the polymers on the stability of the mesoph ase was also investigated for various samples of poly(ester-urethane) HDI-C6C6 (M(n) = 3000-22,000). It was found that a competition existed between the tendencies of the polymer to crystallinity and liquid-cry stallinity, and the molecular weight dependence of the crystallization temperature determined the onset of a monotropic mesophase.