Thermal properties of liquid-crystalline diols and corresponding bis-urethanes with mesogenic groups of various structures in side chains

The liquid-crystalline diols with mesogenic groups of different structures were synthetized and their temperature behavior and existence of mesophases were determined. These compounds were also reacted with phenylisocyanate to form bis-urethanes at the ratio of reactive groups [OH]/[NCO] = 1/1. The changes of phase transition temperatures due to the change of H-O-H to H-N-H interactions have been investigated. Generally, the introduction of a phenylurethane group into the molecule suppresses the occurence of mesophases; in the case of simple mesogens the mesophases disappear completely. Stiff substituents bound to mesogen as end groups (such as the phenyl group, alkoxy group, etc.) stabilize the mesophases to such a degree that the negative influence of urethane group is compensated and the LC properties are recovered.