Preparation and Physical Properties of Polyurethane Elastomers Containing Mesogenic Moieties*

The mesogenic diols containing azobenzene, benzophenone and biphenyl moieties with an alkoxy flexible spacer were synthesized, and the linear polyurethanes were prepared by the polyaddition of these diols with diisocyanates such as 2,4-toluene diisocyanate and 4,4'-diphenylmethane diisocyanate. From the measurement of DSC and polarizing optical microscopy with the hot stage, it was found that most resulting polyurethanes revealed a thermotropic liquid crystalline behaviour and the temperature of mesomorphic phase was effected significantly by the molecular structure of diisocyanates and the chain length of flexible spacers. On the other hand, the segmented polyurethanes were prepared by the chain extension of isocyanate-terminated prepolymers with these mesogenic diols. As the results, it was found that the incorporation of mesogenic moieties to the hard segment of the polyurethanes contributed to the enhancement of thermal stability and mechanical properties.