SEGMENTED POLYURETHANE ELASTOMERS WITH LIQUID-CRYSTALLINE HARD SEGMENTS .1. SYNTHESIS AND PHASE-BEHAVIOR

Segmented liquid crystalline polyurethanes (LCPUE) have been studied with hard segments composed of the mesogen 4,4'-bis(6-hydroxyhexoxy)biphenyl, 2,4-tolylene diisocyanate, and 2,6-tolylene diisocyanate and soft segments composed of poly(tetramethylene oxides). Differential scanning calorimetry and wide-angle X-ray scattering experiments show the existence of an enantiotropic mesophase in the hard domains of the elastomer. Compared with nonsegmented polyurethane containing the same mesogen, the isotropization temperature of the mesophase in the elastomer is depressed. This is a result of the oligomeric structure of the hard domains. The endotherm corresponding to the isotropization transition is also broadened, reflecting a lack of uniformity of the hard domains. Furthermore, the mesophase can be oriented by elastic deformation, and it forms a more ordered structure during this process. The tensile properties of these segmented polyurethanes are determined by their morphologies and can be manipulated by controlling the hard- and soft-segment concentration ratio.