## 3 Results and Discussion
### XPS Analysis  
After modification, PVA was characterized by XPS. Figure 3 shows the survey spectra of unmodified PVA and of PVA after each chemical modification. The elements compositions from each spectrum were calculated and listed in Table 1.  
For unmodified PVA, only characteristic peaks of C and O can be found. After tosylation (Figure 3b), the XPS spectrum showed two additional peaks at 169 eV and 233 eV which are assigned to the binding energy of S\({}_{2p}\) and S\({}_{2s}\) respectively. These peaks are related to the presence of the tosyl group.  
For the tosylation we measured the degree of substitution (DS) from the XPS data using the following method:  
% [Ts] = % [S] = 3.27  
% [O\({}_{TS}\)] = 2 \(\times\) 3.27 = 6.54 (each molecule of Ts contains 2 Oxygen atoms)9% [O\({}_{\text{VA}}\)] = % [1 VA] = \(24.81-6.54\) = \(18.27\) (VA = unit of polyvinyl alcohol; each molecule of VA contains 1 Oxygen atom)  
Finally the DS of tosylation is obtained by dividing % [tos] per % [One VA]  
DS = [Ts]/[1 VA] = 0.1789  
This value is in good agreement with the literature [10].  
After aidation, the characteristic peaks of S disappeared in the XPS spectrum (Figure 3c) suggesting the consumption of the tosyl group. In addition, the XPS spectrum showed an additional peak at 401 eV which is assigned to the binding energy of N\({}_{\text{1s}}\). This peak suggested the introducing of the azide group on PVA polymer chains. After click reaction, (Figure 3d) XPS spectra showed the same chemical composition (presence of C, O and N) with different atomic percentage. In order to confirm the click reaction, a comparison between the high resolution spectrum of the N\({}_{\text{1s}}\) before and after click reaction was shown in Figure 4.  
In Figure 4a we observed the characteristic N\({}_{\text{3}}\) peak doublet at 404.48 eV and 400.76 eV with a peak area of 2:1. The larger intensity peak at 400.76 eV results from the two outer nitrogen atoms of the azide functional group, and the smaller peak at 404.8 eV (assigned to azides) is characteristic of the electron poor middle nitrogen [20,21]. After click reaction (Figure 4b), the peak at 404.48 eV is  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Sample** & **C\%** & **O\%** & **S\%** & **N\%** \\ \hline PVA & 69.95 & 30.05 & - & - \\ PVA-Ts & 71.92 & 24.81 & 3.27 & - \\ PVA-N\({}_{\text{3}}\) & 77.42 & 17.74 & - & 4.84 \\ PVA-NH\({}_{\text{2}}\) & 72.15 & 23.82 & - & 4.03 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Elements compositions of unmodified PVA and PVA after each chemical functionalization.  
Figure 3: XPS spectra of (**a**) unmodified PVA; (**b**) tosylated PVA (PVA-Ts); (**c**) azidated PVA (PVA-N\({}_{\text{3}}\)) and (**d**) PVA after click reaction with proparglamine (PVA-NH\({}_{\text{2}}\)).  
reduced and the peak at 400.76 eV is shifted to 400.49 eV, which corresponds to the appearance of the triazole. This modification of the Ni\({}_{\text{s}}\), in good agreement with the literature, indicated the formation of the triazole [22; 23; 24].  
The XPS results complement the FTIR analysis, providing strong evidence in support of each step of PVA chemical modification.