# Characteristics of Polycarbonate Soft Segment-Based Thermoplastic Polyurethane
## 3 Results and Discussion
### Tensile Strength  
The molecular weight of a polymer is a key factor affecting its tensile strength. As mentioned in Section 3.3, the TPU copolymers using the same chain extender had comparable molecular weights. Thus, the molecular weight can be ignored in the analysis of tensile strength. As Table 6 indicates, the TPU had high elongations at break (above 460%), and both the TPU-PTC-PDO and TPU-PTC-BDO had moderate strain at break. However, the TPU-PTC-BDO and TPU-PTC-PDO differed considerably in terms of the strain at break. The results are possibly affected by hydrogen bonding. According to the FT-IR results in Section 3.1 (Scheme 1a), the TPU-PTC-BDO and TPU-PTC-PDO had strong intermolecular hydrogen bonds in the TPU-PTC-BDO; because the regularity of the molecular chains was poor (atactic) and the intermolecular attraction weak, poor strength resulted. Notably, TPU-PTC-PDO uses an odd-numbered polyol and chain extender to cause regular molecular chains (isotactic), stacking well, and more secondary bonds (such as hydrogen bonds, benzene \(\pi-\pi\) stacking, and dipole-dipole interactions) (Scheme 1b). Both of the copolymers had the same number of the hydrogen bonds per unit in Scheme 1b, and whereas we can see that Scheme 1b focuses on the blue and red squares in the soft segments, TPU-PTC-PDO could have possible dipole-dipole force (\(\delta^{+}\) to \(\delta^{-}\)) and TPU-PTC-BDO does not (\(\delta^{-}\) to \(\delta^{-}\)). More dipole interactions for TPU copolymers can drive better mechanical strength. According to the literature, the storage modulus increases with dipole interactions under a glassy state [51]. We also saw this phenomenon in this study, and Figure 8a in the manuscript revealed that the storage modulus of TPU-PTC-PDO was higher than TPU-PTC-BDO., It can be compared to Scheme 1b to prove that TPU-PTC-PDO has more dipole interactions than TPU-PTC-BDO. Thus, it has a high tensile strength close to TPU-PTC-BDO and TPU-PTC-PDO (Table 6). The regularity of molecular chains also affected the stretching process. As is shown in Figure 9a,b, the stress of the TPU samples presented a rapid rise at approximately 300% of elongation, except in the case of TPU-PTC-BDO. This was because TPU-PTC-BDO is an odd-numbered carbon chain (a long chain of three carbons) corresponding to an even-numbered carbon chain (a short chain of four carbons), and it cannot be arranged regularly after stress as is expected in strain-induced crystallization [52; 53; 54; 55]. Therefore, the intermolecular hydrogen bonding effect for the TPU-PTC-BDO was lower than for other samples. Accordingly, the TPU-PTC-BDO presented the lowest stress but the highest elongation.  
\begin{table}
\begin{tabular}{c c c c c} \hline
**TPU-X-Y** & **Elongation at Break** & **Modulus at 100\%** & **Modulus at 300\%** & **Tensile Strength** \\  & **(\%)** & **Deformation (MPa)** & **Deformation (MPa)** & **(MPa)** \\ \hline TPU-PTC-PDO & 571.6 \(\pm\) 27.2 & 6.73 \(\pm\) 0.12 & 15.18 \(\pm\) 0.19 & 41.1 \(\pm\) 10.8 \\ TPU-PTC-PDO & 466.6 \(\pm\) 11.8 & 4.92 \(\pm\) 0.03 & 13.68 \(\pm\) 0.03 & 37.9 \(\pm\) 16.9 \\ TPU-PTC-BDO & 613.3 \(\pm\) 25.5 & 5.62 \(\pm\) 0.07 & 8.19 \(\pm\) 0.03 & 13.4 \(\pm\) 0.8 \\ TPU-PTC-BDO & 482.2 \(\pm\) 21.7 & 5.86 \(\pm\) 0.18 & 14.30 \(\pm\) 0.27 & 37.9 \(\pm\) 10.8 \\ \hline \end{tabular}
\end{table}
Table 6: Mechanical properties of the TPU copolymers.