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-separa ted polymer with submicron mesophases as physical cross-links, and its theological study indicates a broad transition from a viscoelastic so lid to a viscoelastic liquid at the isotropization temperature of the mesophase. Furthermore, it has been found that time-temperature superp osition applies in the isotropic state (160 to 110 degrees C). We conc lude that the aggregation of liquid crystalline hard segments does enh ance the connectivity of the molecular structure, and this is supporte d by the results of a kinetic study with dynamic mechanical spectrosco py (DMS). Physical gelation studies identify a liquid/solid transition when cooled to 106 degrees C or below and show the characteristic cri tical behavior at the gel point with a power law relaxation spectrum a t low frequencies. Estimates are given for the relaxation exponent and the stiffness of the critical gel.