## 3 Results and Discussion
### Chemical Structure Analysis  
The deterioration in the mechanical properties of the AEMs is attributable to the degradation of the PVC skeleton. The PVC was extracted in THF via Soxhlet extraction, whereas changes in the molecular weight and the polydispersity of the polymeric fraction (Extract A) were determined via GPC, as shown in Figure 10. Both the number-average molecular weight (\(M_{\text{n}}\)) and weight-average molecular weight (\(M_{\text{w}}\)) decreased as the alkali treatment time progressed. Meanwhile, the polydispersity (\(M_{\text{w}}\)/\(M_{\text{n}}\)) increased with the treatment time. The obtained results suggest the random scission of the PVC chain under alkali treatment conditions. Rapid PVC degradation appeared to have occurred in the first 5 min, from 175 to 80 kDa in \(M_{\text{w}}\); thereafter, the molecular weight decreased less with a constant polydispersity. This might be because only a hexane-insoluble polymeric fraction was collected by the extraction (Extract A), whereas the significantly lower molecular weight PVC in Extract B was outside of the analysis targets. However, the GPC results suggested that the PVC degradation in such high pH conditions resulted primarily in a change in the mechanical properties of the AEMs. The PVC degradation owing to the alkali treatment was investigated via \({}^{1}\)H and \({}^{13}\)C NMR. Figure 11a shows the \({}^{1}\)H NMR spectra of pristine PVC in an IEM, an extract from the AMX membrane without alkali treatment, and an extract from the AMX membrane after alkali treatment for 30 min in 1 M NaOH at 80 \({}^{\circ}\)C. In all cases, two significant proton peaks were observed at 2.1-2.6 and 4.3-4.7 ppm, which were assigned to methylene (CH\({}_{2}\)) and methine (CHCI) protons of the PVC backbone, respectively. Hence, it was confirmed that the extracts via Soxhlet extraction were PVC. Figure 10: Changes in the molecular weights and dispersity of PVC by alkali treatment. Furthermore, small peaks at 5.5-6.5 ppm were discovered only after the alkali treatment (Figure 11b), indicating allyl protons [7]. In addition to the AEMs becoming darker by the treatment, C=C double bonds were generated by dehydrochlorination to form a polyene structure along the polymer backbone. Meanwhile, Figure 11c shows the \({}^{13}\)C NMR spectra of the corresponded specimens. The absence of peaks between 80 and 160 ppm confirmed the absence of other serious degradations that could lead to different chemical structures. In addition to the peaks of the PVC carbon skeleton (44-47 and 55-57 ppm), it was difficult to verify the polyene structure because of the low sensitivity of \({}^{13}\)C in comparison to those of the protons from the \({}^{1}\)H NMR spectra. Figure 11: (**a,b**) \({}^{1}\)H NMR and (**c**) \({}^{13}\)C NMR spectra of PVC, an extract from the AMX membrane without alkali treatment, and an extract from the AMX membrane after alkali treatment for 30 min in 1 M NaOH at 80 \({}^{\circ}\)C. Panel (**b**) is an enlarged view of the polyene region of (**a**). Furthermore, the effect of alkali treatment time on the mechanical properties of the AEMs was investigated via tensile testing. Figure 11(a) shows the tensile properties before Soxhlet extraction. The value of the pristine sample was expressed as the dashed line. The tensile stress and tensile strain decreased monotonically as the treatment time progressed. Meanwhile, the properties after the extraction are shown in Figure 11(b). The residues extracted from the pristine membrane and following the five-minute treatments were a fibrous powder that could not tolerate the subsequent tensile testing because the PVC skeleton was removed via extraction. In other words, a membrane cannot be formed solely using the CMS-DVB copolymer; however, the shape of the membrane can be maintained using an IPN structure of PVC and CMS-DVB co-polymers. However, the residues after 10 and 30 min of alkali treatment retained their original shape such that tensile testing could be realized.