POLYMERS FROM MULTIFUNCTIONAL ISOCYANATES .5. SYNTHESIS OF LIQUID-CRYSTALLINE POLYURETHANES FROM METHYL-SUBSTITUTED DIISOCYANATO-SUBSTITUTED BENZOATES

A number of new aromatic or cycloaliphatic diisocyanato-substituted benzoates: 4-isocyanatophenyl 4-isocyanatobenzoate, trans-4-isocyanatocyclohexyl 4-isocyanatobenzoate, and several derivatives with lateral methyl substituents were synthesized by the reaction of appropriate (trimethylsiloxy)phenyl or cyclohexyl isocyanates and isocyanatobenzoyl chlorides. They were reacted with 3-methyl-1,5-pentanediol and mixtures of two different diols to give hard-segment type polyurethanes. The influence of the substituents on the thermal behavior of the polyurethanes was studied and compared to the parent isocyanates. Monotropic nematic liquid-crystalline phases could be observed with polyurethanes from the unsubstituted 4-isocyanatophenyl 4-isocyanatobenzoate. In the case of the other polyurethanes, the melting points could be lowered, but this decrease was accompanied by the loss of liquid-crystalline properties.