## 3 Results and Discussion
### The Effect of Varying EDTA Concentrations at BA/BI = 8/2 of PABBI Copolymers  
Section 3.2 discussed the role of the EDTA concentration with the BA/BI of the PABBI copolyesters, supported by measurements of the thermal behavior and mechanical properties. Figure 11 shows the DSC trace for the PABBI copolyesters, to investigate the thermal response. In the first cycle of the heating procedure for DSC measurement in Figure 11a, the onset of \(T_{\mathrm{m}}\) tended to lower the temperature as the EDTA concentration increased from 0.001 to 0.2 mole%, and all melting point peaks with different EDTA concentrations shifted to the left. The results confirmed that the thermal property was associated with the EDTA concentration, and the lowest onset temperature of \(T_{\mathrm{m}}\) was located at an EDTA value of 0.2 mole%. The crystallization of each ratio of the PABBI copolyesters occurred from first cooling (as shown in Figure 11b). Crystallization was initiated at a higher temperature with an EDTA concentration of 0.2 mole%, and also had a larger enthalpy of crystallization (\(\Delta H_{\mathrm{c}}\)), implying the crystallization behavior was correlated with the amount of EDTA. The aliphatic molecular chain could be driven to pack into an ordered state, due to the limiting influence that a higher EDTA concentration had on the main-chain movement. The subsequent reheating procedure was displayed in Figure 11c, and the thermal history of the PABBI copolyesters was eliminated to precisely measure the \(T_{\mathrm{m}}\) and \(\Delta H_{\mathrm{m}}\). The onset temperature and peak position of the melting point obtained similar curves, and the peak melting point was divided into two continuous peaks, representing the competitive effect between the AA and the IA, in the crystallization region. Additionally, the \(\Delta H_{\mathrm{m}}\) (as shown in Table 6) had a significant bell-shaped trend--\(\Delta H_{\mathrm{m}}\) increased when EDTA concentration increased from 0.001 to 0.05 mole%, and then decreased at an EDTA ratio of 0.2 mole%. The results indicated that  
Figure 10: The torsional angle distribution of (**a**) N–C–C–N within the EDTA and (**b**) N–C–C–O between the EDTA and the 1,4-BDO. increased gradually as EDTA concentration increased, when there was a small amount of EDTA. However, more EDTA concentration as a node could decrease the freedom of the molecular chain, to hinder backbone packing into a crystal regime, thus, decreasing the enthalpy of crystallization. \begin{table}
\begin{tabular}{l l l l l l l} \hline \hline \multirow{2}{*}{**Item**} & \multicolumn{1}{c}{\({}^{*}\)\(T_{\text{g}}\)} & \(T_{\text{c}}\) & \(\Delta H_{\text{c}}\) & \(T_{\text{m}}\) & \(\Delta H_{\text{m}}\) & \(T_{\text{d-5\%}}\) \\  & \multicolumn{1}{c}{(\({}^{\circ}\)C)} & \multicolumn{1}{c}{(\({}^{\circ}\)C)} & \multicolumn{1}{c}{(\({}^{\circ}\)C)} & \multicolumn{1}{c}{(\({}^{\circ}\)C)} & \multicolumn{1}{c}{(\({}^{\circ}\)C)} & \multicolumn{1}{c}{(\({}^{\circ}\)C)} \\ \hline BA/BI = 8/2—0.001 & \(-\)52.8 & 4 & \(-\)37.6 & 30.6, 39.7 & 35.6 & 333.4 \\ BA/BI = 8/2—0.01 & \(-\)52.9 & 4.8 & \(-\)39.4 & 30.9, 40.8 & 38.2 & 325.5 \\ BA/BI = 8/2—0.05 & \(-\)53.4 & 9.3 & \(-\)43.8 & 32.0, 40.7 & 42.6 & 331.9 \\ BA/BI = 8/2—0.1 & \(-\)55.5 & 6.6 & \(-\)40.8 & 30.5, 40.6 & 39.7 & 323.7 \\ BA/BI = 8/2—0.2 & \(-\)56.1 & 8.9 & \(-\)39.3 & 31.9, 40.9 & 38.4 & 324.9 \\ \hline \hline \end{tabular}  
* The \(T_{\text{g}}\) is measured via DMA.  
\end{table} 
Table 6: Thermal properties of the PABBI copolyesters at different concentrations of EDTA. Figure 11: _Cont._  
Figure 12 displays the TGA curves of the PBABI copolyesters, with varying concentrations of EDTA. Results suggest that the \(T_{\text{d-5\%}}\) of the PBABI copolyesters decreased slightly between 333.4 to 323.7 \({}^{\circ}\)C, as the EDTA ratio increased, implying that using a higher EDTA concentration to enhance the degree of partial cross-linking was not suitable for improving the thermal degradation temperature of the PBABI copolyesters, since it disrupted crystallization.