## 3 Results and Discussion
### The Effect of the BA/BI Ratio of PBABA Copolymers with an EDTA Concentration of 0.1 mole%
The thermal properties are listed in Table 3. In the first cycle cooling curve, the heating crystallization peak (\(\Delta H_{\rm hc}\)) was observed clearly at all BA/BI ratios, suggesting that PBABI copolyesters were easy to pack in the ordered phase [51]. The melting crystallization peak of the BA/BI was found in a single sharp peak around 20-30 \({}^{\circ}\)C, at ratios of 10/0 and 9/1. When the IA concentration was increased to 20 mole%, a broader crystallization peak was obtained, implying that greater IA concentration could hinder the molecular chain from packing into the ordered state, and disrupt the crystallization region of the AA-rich domain. In Figure 3c, the \(T_{\rm m}\) was observed to be around 21.1-57.5 \({}^{\circ}\)C, and the melting peak (\(\Delta H_{\rm m}\)) appeared with a broader distribution at a ratio of BA/BI = 10/0 (heat PBA). After removing the thermal history, the melting peak of the PBABI copolyesters was shown to be in a continuous double peak, demonstrating that a competitive effect might exist in the crystallization zone of AA and IA, within the PBABI copolyesters, during melt polymerization. The TGA curve is shown in Figure 4, and the 5 wt % weight loss temperature (\(T_{\rm d.5\%}\)) of the PBABI copolyesters occurred around 313.6-342.1 \({}^{\circ}\)C, indicating that all synthesized PBABI copolyesters had excellent thermal stability since the \(T_{\rm d.5\%}\) of all PBABI copolyesters was over 300 \({}^{\circ}\)C. The thermal stability of the PBABI copolyesters decreased slightly, as the IA concentration increased, as can be seen in Table 3. Compared to the DSC results, all PBABI copolyesters displayed lower \(T_{\rm d.5\%}\) and \(T_{\rm m}\) values, than a neat PBA with EDTA of 0.1 mole%. Hence, an increase in the IA concentration could not improve the thermal stability of the PBABI copolyesters, as a result of the disruption of the crystallization region. Figure 5 shows the viscoelastic curves of the PBABI copolyesters. The second-order transition (\(T_{\rm g}\)) was not detected in the DSC measurement but was observed clearly via DMA, due to the  
Figure 4: TGA curves of PBABI copolyesters. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Item**} & * \(T_{\rm g}\) & \(T_{\rm c}\) & \(\Delta H_{\rm c}\) & \(T_{\rm m}\) & \(\Delta H_{\rm m}\) & \(T_{\rm d.5\%}\) & *\(\chi_{\rm c}\) \\  & (*C) & (*C) & (m)\(\cdot\)mg\({}^{-1}\) & (*C) & (m)\(\cdot\)mg\({}^{-1}\) & (*C) & (m)\(\cdot\)mg\({}^{-1}\) & (*C) & (\%) \\ \hline BA/BI = 10/0 & \(-\)55.8 & 29.5 & \(-\)46.1 & 57.5 & 40.4 & 342.1 & 39.4 \\ BA/BI = 9/1 & \(-\)55.9 & 22.7 & \(-\)56.3 & 52.2 & 60.3 & 331.8 & 36.7 \\ BA/BI = 8/2 & \(-\)53.6 & 6.5 & \(-\)32.5 & 33.8 & 32.0 & 323.9 & 34.1 \\ BA/BI = 7/3 & \(-\)54.8 & \(-\)6.7 & \(-\)33.2 & 21.1 & 32.2 & 313.6 & 37.9 \\ \hline \hline \end{tabular}  
* The \(T_{\rm g}\) is measured by DMA. # the \(\chi_{\rm c}\) is determined via XRD.  
\end{table} 
Table 3: Thermal property of the PBABI copolyesters. temperature-range setting. The \(T_{\text{g}}\) of the PBABI copolymers, obtained via DMA, maintained a stable value between \(-53.6\) and \(-55.9\)\({}^{\circ}\)C, as the IA concentration increased, as shown in Figure 5a. In contrast, the \(T_{\text{g}}\) was not affected by an increase in IA concentration with EDTA. The EDTA played an essential role in preserving the stability of the disordered region, even when the IA concentration was higher, due to the double-bond within IA, which maintained the amorphous zone. The \(\beta\)- and \(\gamma\)-relaxation were also measured around \(-100\) and \(-130\)\({}^{\circ}\)C, which was associated with the motion of the R-C=CH\({}_{2}\) group, within IA, and the motion of the R-CH\({}_{2}\) group within the aliphatic main-chain [64].