SYNCHROTRON SAXS STUDIES OF THE PHASE-SEPARATION KINETICS IN A SEGMENTED POLYURETHANE

Synchrotron small-angle X-ray scattering (SAXS) was used to investigate the kinetics of phase separation of a segmented polyurethane which was quenched from the homogeneous melt state to lower temperatures. The phase-separation process in the segmented polyurethane was very slow at most of the annealing temperatures, owing to the high viscosity of the system and low mobility of the hard segment. The phase-separation rate depended strongly on the annealing temperature, with the maximum rate being at an annealing temperature of around 80-107-degrees-C. Further increase in the annealing temperature reduced the rate. The rate decrease could be attributed to an increase in the hard- and soft-segment compatibility at higher temperatures. The interdomain spacing did not change throughout the whole annealing process, a characteristic of segmented copolymers. However, the interdomain spacing increased with increasing annealing temperature. Both the phase-separation process and the peak intensity changes could be analyzed according to an equation of relaxation, which indicated that the phase separation in the segmented polyurethane system behaved like a relaxation process. The results are compared with the more restrictive Hashimoto theory.