Synthesis and properties of novel polyurethanes containing the mesogenic moiety of α-methylstilbene derivatives

4,4′-Bis(ω-hydroxyalkoxy)-α-methylstilbene with various spacer lengths (HMSn, where “n” is the carbon number of the hydroxyalkoxy group) and two series of novel thermotropic liquid crystalline polyurethanes containing the mesogenic core of 4,4′-bis(ω-hydroxyalkoxy)-α-methylstilbene were synthesized. One series was obtained by polyaddition reaction of 2,4-toluene diisocyanate (2,4-TDI) with HMSn, denoted as TDIn, and the other was obtained by the reaction of 4,4′-diphenylmethane diisocyanate (MDI) with HMSn, denoted as MDIn. The polyurethanes were investigated by IR spectroscopy, DSC, wide angle X-ray diffraction, polarizing microscope and thermogravimetric analysis. All the polyurethanes except for TDI11 exhibited enantiotropic smectic phases which are not similar to those of corresponding HMSn. The transition temperatures and the temperature ranges of mesophases changed with the length of alkoxy spacer and the kind of diisocyanate. The thermal degradation behaviours under nitrogen atmosphere depend on the spacer length but not much on the diisocyanate moiety.