*3.4. Thermal Stability Analysis*

To investigate the thermal stability of WPU-SS films, thermogravimetric analysis (TGA) was carried out at 30~800 ◦C in a nitrogen atmosphere. Figure 5 shows the typical TGA and the first derivative curve DTG, respectively. The characteristic thermal degradation data display in Table 2. From the TGA curve, the thermal stability of WPU-SS films was improved with the decrease of short chain disulfide bond content and the enhancement of long chain PTMG content. In particular, the 50% weight loss temperature (Td50%) increased from 361 ◦C to 382 ◦C. In the region of 230~440 ◦C, there are two obvious degradation stages for WPU-SS films. The partial weight loss at 230~350 ◦C can be attributed to the rupture of the amino ester bond in the hard segment isocyanate, and the thermal stability of the hard segment is poor, which can be decomposed into primary amines (or secondary amines), alkenes and carbon dioxide [28–30]. In contrast, polyether has better thermal stability, 350~440 ◦C weight loss is mainly the decomposition of the soft segment [31–33].

**Figure 5.** TGA curves and DTG curves of different WPU-SS films.


**Table 2.** Particular thermal degradation dates of diifferent WPU samples.
