A SEGMENTED POLYURETHANE ELASTOMER WITH LIQUID-CRYSTALLINE HARD SEGMENTS .2. RHEOLOGICAL STUDY

The Linear viscolastic properties of a segmented polyurethane referred to as LCPUE-1000 have been studied. LCPUE-1000 is a microphase-separated polymer with submicron mesophases as physical cross-links, and its theological study indicates a broad transition from a viscoelastic solid to a viscoelastic liquid at the isotropization temperature of the mesophase. Furthermore, it has been found that time-temperature superposition applies in the isotropic state (160 to 110 degrees C). We conclude that the aggregation of liquid crystalline hard segments does enhance the connectivity of the molecular structure, and this is supported by the results of a kinetic study with dynamic mechanical spectroscopy (DMS). Physical gelation studies identify a liquid/solid transition when cooled to 106 degrees C or below and show the characteristic critical behavior at the gel point with a power law relaxation spectrum at low frequencies. Estimates are given for the relaxation exponent and the stiffness of the critical gel.