E(0) - 0 M1(10) HTPU (PTMG) 10 M2(10) ATPU (PTMG) 10 B1 (10) HTPU (PBA) 10 B2(10) ATPU (PBA) 10
Figures 4, 5, and 6 show the temperature dependence of loss tangent of HTPU (PBA), HTPU (PTMG) and ATPU (PTMG) modified cured epoxy resins, respectively.
In the ATPU (PTMG)-modified resin system [ILLUSTRATION FOR FIGURE 6 OMITTED], the [Beta]-relaxation peak of tan [Delta] in M2(15) decreased toward a lower temperature and had increased amplitude as compared with the control.
Figure 8a-c shows the post-failure appearance of CT specimens of HTPU (PTMG)- and ATPU (PTMG)modified epoxy under the scanning electron microscope at low magnification (100 x).
The presence of large particles ([greater than] 4 [[micro]meter]) in the ATPU (PTMG)-modified epoxy indicates that microgelation might occur during the pre-reaction because of the presence of the amine-terminal group.
For example, we have prepared good ATPUs
with lower than Shore 50A hardness using 7,000 and 11,000 molecular weight PPGs.