Liquid‐crystalline polyurethanes, 4. Polyurethanes containing an azobenzene group in the side chain

Polyurethanes with azobenzene side groups attached via an alkyl spacer of different length were synthesized from N-[4-phenylazophenyl]-ω-[bis(2-hydroxyethyl)amino]alkanamides (5) and equimolar amounts of diisocyanates such as hexamethylene diisocyanate (HDI), 4,4′-methylenedicyclohexyl diisocyanate, 1,3-cyclohexylenedimethyl diisocyanate, 2,4-toluylene diisocyanate, and 4,4′-methylenediphenyl diisocyanate. Polyurethanes obtained from diols 5 with HDI have a mesomorphic phase as determined by DSC and polarizing microscopy and are crystalline at room temperature as evidenced by X-ray studies.