Segmental melting

Figure 5. Dynamic shear modulus-temperature behavior (torsion pendulum, 1 Hz) of 50% w/w HS copolyurethanes based on diisocyanates FDI-a (F) and MDI (M). Soft segment glass transition and hard-segment melting are in the temperature regions indicated, respectively, by and Tm.

At a ratio of 6 1, however, Tg jumps dramatically to -18 C as a result of phase mixing. In this system (6 1), the hard segment melts at a higher temperature which is an indication that the purity of the phase and crystal size is increasing as the hard segment content increases. 

Figure 4 and 5 and Table III show the DSC data for these RIM specimens. It is seen that AH for the hard segment melting In the unannealed/wlthout PEDA specimens increases on annealing (for both the 18 Eg and 30 Eg series) and essentially the same Increase occurs in the unannealed/with PEDA specimens. These effects corrleate with the X-ray data showing a similar increase in the crystalline perfection of the hard domains with annealing or with the use of PEDA. 

Figure 13. Variation of tensile stress (300%) with hard-segment melting point in PTMEG-T copolyesters A = 2GT A = 3GT Q = 4GT =...

The crystalline hard segment melting, crystallisation and heats of transition observed during the DSC analysis are given in Table 8.14. 

Higher thermal stability due to high crystalline hard segment melting. High flexibility due to low Tg. 

The dynamics of structure development during the experiment may be observed in the contour plots in Figure 11. SAXS and WAXS contours are in arbitrary levels of I(q) and 1(26) respectively. The peak position in the SAXS pattern has been marked vnih a bold line, q, and remains constant up to 120 °C after which the structure starts to change continuously by lamella thickening. This process involves melting, diffusion and some recrystaUisation and is manifest as a shift in q to lower values of q the weak WAXS pattern is relatively insensitive to these dynamic processes. Eventually the hard segments melt ( 210 °C) and mix with the soft segment, the SAXS peak... 

Subsequent off-line DSC experiments show the as-prepar polyurethane to have a hard segment melting point of 178 °C and a heat of fusion of 20J/g whereas the... 

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