# Characteristics of Polycarbonate Soft Segment-Based Thermoplastic Polyurethane
## 3 Results and Discussion
### Decomposition Properties  
A typical TPU is thermally unstable. Thus, thermogravimetric analysis was used to measure the decomposition characteristics of the copolymers. Figure 6a,b displays the thermogravimetry (TG) and differential thermogravimetry (DTG) curves for the TPU copolymers. The TG curves of TPU-PTC-PDO and TPU-PTC-BDO revealed three distinct regions of weight loss, which are reflected in three peaks on the DTG curve. This result implies that both copolymers possess at least three significant stages of decomposition. However, the TPU-PTC-PDO and TPU-PTC-BDO presented only two significant stages of decomposition. Typical TPU is composed of hard and soft segments, which usually represent two stages of decomposition. The first stage is related to the hard segments, and the second to the soft segments. The temperatures of initial decomposition (T\({}_{\text{di}}\)) for the TPU copolymers were approximately 220 to 260 \({}^{\circ}\)C (Table 4), possibly due to the decomposition of urethane segments caused by MDI and a chain extender, or by MDI and a polyol [40]. Subsequently, the decompositions of the TPU exhibited obvious differences at 5 wt% of weight loss (T\({}_{\text{d 5 wt}}\)). The temperatures of T\({}_{\text{d 5 wt}}\) for TPU-PTC-BDO and TPU-PTC-BDO herein were higher than those of TPU-PTC-PDO and TPU-PTC-BDO. This result may be due to the effect of the decomposition of soft segments. To confirm the decomposition properties of polyol monomers, their decomposition temperatures were also examined (Figure 6c,d). As may be observed from Figure 6c, the temperature regions of decomposition for the PTC and PHC were respectively from 180 to 325 \({}^{\circ}\)C and from 200 to 400 \({}^{\circ}\)C. Furthermore, the decomposition temperature of the maximum rate (T\({}_{\text{max}}\)) for the PHC was 367.1 \({}^{\circ}\)C, obviously exceeding that of the PTC. Therefore, the T\({}_{\text{d 5 wt}}\) of the TPU-PHC copolymers were higher than those of the TPU-PTC copolymers because the decomposition temperature of PHC is higher than that of PTC [41; 42]. The TPU-PTC copolymers (i.e., TPU-PTC-PDO and TPU-PTC-BDO) on the TG curve presented their first and second shoulder peak from 270 to 375 \({}^{\circ}\)C and from 375 to 470 \({}^{\circ}\)C, which are reflected in the two peaks on the DTG curve, as shown in Figure 6a,b. The decomposition of the region was possibly related to the decomposition of soft polycarbonate segments (PTC), including the decomposition, cyclization, and re-decomposition for the cyclic compounds [43]. The decomposition of the TPU-PHC copolymers (i.e., TPU-PHC-PDO and TPU-PHC-BDO) presented only one shoulder peak between 400 and 500 \({}^{\circ}\)C, which was related to the decomposition of soft polycarbonate segments (PHC), which also involves cyclization and re-decomposition of the cyclic compounds. The PHC polyol on the DTG curves displays a T\({}_{\text{max}}\) peak at 300 to 400 \({}^{\circ}\)C; therefore, the TPU-PHC presented only one shoulder peak. The T\({}_{\text{d 5 wt}}\) of the TPU-PTC copolymers was lower than that of the TPU-PHC copolymers, but their decomposition properties were sufficient to withstand the processing temperature. The TPU-PHC samples also had favorable processability, which is investigated in the section on rheological behavior.  
Figure 6: _Cont._