## 3 Results and Discussion  
### The Effect of the BA/BI Ratio of PBABA Copolymers with an EDTA Concentration of 0.1 mole%  
The chemical structure and comonomer composition of PBABI copolymers were first confirmed by NMR spectroscopy. The \({}^{1}\)H NMR spectra of PBABI copolymers are displayed in Figure 1. The resonance peaks of the PBABI copolymers were identified and assigned in H1 (1.838-2.169 ppm, 3, 4-CH\({}_{2}\) of adipic acid), H2 (1.923-2.231 ppm, 2, 3-CH\({}_{2}\) of 1.4-butanediol), H3 (2.015-2.545 ppm, -CH\({}_{2}\) between two nitrogen of Ethylenediaminetetraacetic acid), H4 (2,579-2.922 ppm, 2, 5-CH\({}_{2}\) of adipic acid), H5 (3.632-3.948 ppm, 2-CH\({}_{2}\) of itaconic acid), H6 (4.361-4.675 ppm, 1, 4-CH\({}_{2}\) of 1.4-butanediol), H7 (6.044-6.343 ppm, -C=CH\({}_{2}\) of itaconic acid), and H8 (6.626-6.942 ppm, -C=CH\({}_{2}\) of itaconic acid). All individual values of resonance peaks, the integral ratio, and the calculated composition of IA, within the PBABI copolymers, are summarized in Table 1. From the ratio of the integral area of \({}^{1}\)H NMR resonance peaks of the PBABI copolymers, the calculated rates of C=C of IA in BA/BI = 9/1, 8/2, and 7/3 were obtained at 4.51%, 11.41%, and 15.01%, because the C=C double-bond of the IA might isomerize into 2-methyl fumarate, which has a significantly lower reactivity and cannot be observed in NMR measurements [60]. Moreover, the catalyst selectivity in the esterification stage could cause the IA concentration to copolymerize into PBABI copolymers [40; 61]. The concentration of the C=C bond of IA can be maintained near 50%, in each PBABI copolymers, through high-temperature melt polymerization, with the DBTEL catalyst, and T\({}_{\rm i}\)(OBu\({}_{4}\))\({}_{4}\), which could participate in the successive UV curing procedure, to adjust the hardness of the PBABI copolymers through the UV curing time. Figure 2 shows the FT-IR spectra of PABBI copolyesters, for which the absorption peaks associated with the asymmetry and symmetry C-H stretch have been identified at 2958 and 2874 cm\({}^{-1}\), respectively. The stretching vibration of the C=O of the ester bond was observed at 1727 cm\({}^{-1}\), a C-H bond absorption peak was seen at a value of 1462 cm\({}^{-1}\), and a band in 1256 cm\({}^{-1}\), related to the C-O of the ester bond. The most significant peak was identified and observed at 1659 and 816 cm\({}^{-1}\), which was attributed to the stretching vibration of the C=C in the IA. The intensity of these two absorption peaks increased as the concentration of IA increased, demonstrating that the IA molecule was successfully copolymerized into the main-chain of the PABBI copolyesters. Moreover, the C=C bond of IA was protected by a radical inhibitor, 4-methoxyphenyl, even through melt polymerization at a temperature of 230 \({}^{\circ}\)C, with  
Figure 1: \({}^{1}\)H NMR spectra of PABBI copolyesters at (a) BA/BI = 10/0, (b) BA/BI = 9/1, (c) BA/BI = 8/2, and (d) BA/BI = 7/3. further UV curing, to control the hardness of the PBABI copolyesters. This aligns with the results from [PERSON] and his colleague [62], who found that IA-based polyester could form a cross-linked structure, through C=C of IA, using methyl methacrylate (MMA) as an initiator to improve the mechanical property, after irradiation under UV light; but, fumarate and maleate-based polyesters could not be induced by the UV curing process. The results of gel permeation chromatography (GPC) analysis are shown in Table 2, and the PBABI copolyesters were dissolved in HFIP, for further measurement. The I.V. values of PBABI copolyesters in phenol and tetrachloroethane cosolvents (50/50, wt %) were estimated at 0.98, 1.02, 1.14, and 1.22 for BA/BI = 10/0, 9/1, 8/2, and 7/3, respectively [63]. Meanwhile, the \(M_{\mathrm{n}}\) between 16,696 to 35,171 g-mole\({}^{-1}\) indicated that the BA/BI = 9/1 had a better reactivity than other BA/BI ratios, under the same operating conditions.