Thermotropic Polyurethanes Prepared from 2,5-Tolylene Diisocyanates and 1,4-Bis(.omega.-hydroxyalkoxy)benzenes Containing No Mesogenic Unit

Thermotropic liquid-crystalline polyurethanes were synthesized by the polyaddition reaction of para-substituted 2,5-tolylene diisocyanate (2,5-TDI) with 1,4-bis(ω-hydroxyalkoxy)benzenes (BHBm : HO(CH 2 ) m OC 6 H 4 O(CH 2 ) m OH ; m is the carbon number of the hydroxyalkoxy group). Intrinsic viscosities of the polymers were in the range of 0.22-0.41 dL/g. Polyurethanes 2,5-TDI/BHBm's (m = 3, 5, 6, 8) prepared from BHBm and 2,5-TDI, exhibited monotropic liquid crystallinity, although these polyurethanes contained no mesogenic core unit. For example, polyurethane 2,5-TDI/BHB5 with [η] = 0.33 prepared from 1,4-bis(5-hydroxypentoxy)benzene (BHB5) and 2,5-TDI exhibited an anisotropic phase from 119 to 51 °C. In contrast, for the series of 1,4-PDI/BHBm (m = 2, 3, 5, 6, 8, 11) having no substituent in a phenylene unit, no explicit mesomorphic behavior was observed by DSC measurement and polarized microscopic observation.