Synthesis and characterization of new side-chain liquid crystalline polyoxazolines

Side-chain liquid crystalline (LC) polyoxazolines with different contents of mesogens and spacer lengths were synthesized by the reaction of partially hydrolyzed poly(N-acetylethylenimine)s with cyanobiphenyl mesogens having carboxylic acid group in the presence of DCC as a condensing agent. The obtained LC polyoxazolines seem to have broader LC phase than the corresponding cyanobiphenyl mesogenic compounds. The melting temperature and LC phase range decreased as the methylene units in the spacer increased. It was found that their liquid crystallinities were closely dependent on the degrees of substitution and the length of the spacer group incorporated into the portion of the ethylenimine. The critical percentage which the LC phase can be observed is above 27 mol% of cyanobiphenyl moiety introduced to hydrolyzed polyoxazolines. From optical polarizing microscopy, the nematic texture of all the prepared cyanobiphenyl compounds changed into the smectic texture of the LC polyoxazolines except LC polyoxazolines with decamethylene spacer.