Multiphase Structure of a Segmented Polyurethane: Effects of Temperature andAnnealing. (Reannouncement with New Availability Information)

摘要

The multiphase structure and related relaxations of a segmented polyurethane werecharacterized by using a combination of differential scanning calorimetry (DSC) and synchrotron small-angle X-ray scattering (SAXS). The results showed a soft-segment glass transition temperature (Tg,s) which is significantly higher than the Tg,s (-84 deg C) of the corresponding pure soft segment, suggesting an incomplete phase-separation behavior for the soft segment. The specimen lost its mechanical strength at above 200 deg C while DSC indicated an endotherm at 195 deg C due to the hard-segment domain dissolution into the soft-segment matrix. Synchrotron SAXS scanning from 26 to 250 deg C indicated that the sample structure remained stable with increasing temperature. A small change around 75 deg C was attributed to the glass transition of the amorphous hard-segment domain. Phase mixing took place when the temperature was above 190 deg C, in agreement with the DSC results. Synchrotron SAXS was also used to study the post-annealing effects on the segmented polyurethane with a well-defined thermal history. The structural changes were irreversible upon annealing. Thermal post-annealing did not have a significant effect on the multiphase structure once the structure development had reached equilibrium and interactions among the hard segments had reached a certain degree of strength. However, post-annealing could promote perfection inside the hard-segment domain or further phase separation of some hard segments inside the soft-segment matrix. The structures from the samples which have not reached equilibrium or have very weak interactions among the hard segments could be changed dramatically by post-annealing.