# Characteristics of Polycarbonate Soft Segment-Based Thermoplastic Polyurethane
## 3 Results and Discussion
### Phase Transition Regions  
The morphology of TPU presents a two-phase microstructure because the two dissimilar segment types are incompatible. Therefore, DSC thermograms of TPU are likely to display four transition regions as both phases crystallize. However, the structure and concentration of the hard and soft segments and the molecular weights and types of soft segments all influence the phase transition regions in DSC thermograms [44; 45; 46]. Therefore, not all phase transition regions are displayed on DSC thermograms. Figure 7a indicates the DSC thermograms of TPU-PTC and TPU-PHC with PDO and BDO, respectively. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Polyol or TPU-X-Y** & \(\mathbf{T_{di}}\)**a (°C)** & \(\mathbf{T_{d}}\)**5 wt\%**b (°C)** & \(\mathbf{T_{max}}\)**c (°C)** & \(\mathbf{T_{sl}}\)**d (°C)** & \(\mathbf{T_{s2}}\)**d (°C)** \\ \hline PTC & 182.2 & 212.0 & 251.7 & - & - \\ \hline PHC & 205.0 & 242.0 & 367.1 & - & - \\ \hline TPU-PTC-PDO & 224.3 & 243.5 & 263.9 & 322.8 & 438.8 \\ \hline TPU-PHC-PDO & 260.5 & 293.5 & 350.8 & 444.8 & - \\ \hline TPU-PTC-BDO & 247.7 & 270.4 & 298.1 & 344.5 & 441.0 \\ \hline TPU-PHC-BDO & 261.8 & 294.1 & 343.9 & 448.3 & - \\ \hline \hline \end{tabular}  
\end{table} 
Table 4: Characteristic temperatures of decomposition. Figure 6: Decomposition curves of (**a**) TPU-TG, (**b**) TPU-DTG, (**c**) polyols-TG, and (**d**) polyols-DTG. Figure 7: Second heating DSC thermograms of (**a**) TPU and (**b**) polyols. TPU-PHC copolymers had a phase transition region at 0-30 \({}^{\circ}\)C, which corresponds to the glass transition temperature of soft segments (T\({}_{\text{gs}}\)). On the other hand, the glass transition temperatures of hard segments (T\({}_{\text{gh}}\)) for the TPU-PTC and TPU-PHC copolymers were 100-160 \({}^{\circ}\)C. Thus, none of the samples exhibited a significant soft segment crystallization because of the effect of copolymer synthesis, though the PHC presented a melting temperature at approximately 42.2 \({}^{\circ}\)C (Figure 7b). Furthermore, the glass transition temperature of hard segments (T\({}_{\text{gh}}\)) and the melting temperature were not apparent on the thermograms because of the low content of hard segments. These results indicate that the TPU-PTC and TPU-PHC copolymers are amorphous copolymers [47; 48]. Dynamic mechanical analysis (i.e., DMA) can clearly determine the phase transition temperature and modulus of polymers. Chain extenders and polyols affect the T\({}_{\text{gs}}\) of TPU. As Figure 8a indicates, the TPU storage modulus dropped by two to three orders between \(-25\) and 50 \({}^{\circ}\)C, indicating the T\({}_{\text{gs}}\). In addition, the peak of the loss tangent (Figure 8b) is affected by the T\({}_{\text{gs}}\) of the TPU. The TPU copolymers using the BDO chain extender presented lower T\({}_{\text{gs}}\) than did the TPU with PDO (Table 5). In addition, the TPU copolymers with PHC soft segments displayed lower T\({}_{\text{gs}}\) than did the TPU with PTC. These results are attributed to the soft segments and chain extenders of long carbon chains having more conformations. Furthermore, the TPU-PTC-BDO had the lowest value of Tan \(\delta\), indicating it has low levels of damping behavior under the action of external force. By contrast, the TPU-PHC-PDO had the highest energy loss. This result suggests that the TPU-PTC-BDO is suitable for resisting external forces, whereas the TPU-PHC-PDO is suitable for recoil-resistant materials. Figure 8a shows that the storage modulus (E\({}^{\prime}\)) of TPU-PTC-BDO decreased rapidly between 50-75 \({}^{\circ}\)C. However, this decrease was not observed for TPU-PHC-BDO. The length of the plateau was associated with molecular mass, chain entanglement, and degree of crosslinking [49]. Because TPU-PTC-BDO and TPU-PHC-BDO have a similar molecular weight, the difference should probably be attributed to PHC molecular structure units having longer carbon chain lengths.