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.