Multiphase structure of a segmented polyurethane: effects of temperature and annealing

: The multiphase structure and related relaxations of a segmented polyurethane were characterized by using a combination of differential scanning calorimetry (DSC), dynamical mechanical analysis (DMA), stress-strain test, thermally stimulated discharge current (TSDC), and synchrotron small-angle X-ray scattering (SAXS). The polymers studied consisted of 4,4'-diphenylmethane diisocyanate (MDI), 1,4'-butanediol (BD) hard segments with soft segments comprised of PTMO end-capped with PPO at a 70/30 PTMO/PPO weight ratio. 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 segments. The specimen lost its mechanical strength at above 200 deg C while DSC indicated an endotherm ca. 195 deg C due to the hard segment domain consisting of dissolution into the soft segment matrix. TSDC showed interfacial polarization due to the multiphase characteristics. Synchrotron SAXS scanning from 26 deg C 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 and DMA results. Polyurethanes, Elastomers, X-ray scattering, Multiphase structure, Thermal analysis, Morphology, Annealing effects, Microphase, Glass transition.