# Effect of the Sulfonation on the Swollen State Morphology of Styrene Cross-Linked Polymers
## 3 Results and Discussion
### Solid State CP-MAS \({}^{13}\)C-NMR Characterization
Hence, in view of the degree of sulfonation obtained from the mass balance of sulfur, no unsubstituted para carbon atoms should be present hence. As shown above in _Gel_oleum_, ca. 33% of the aromatic rings are doubly sulfonated, but its spectral pattern is practically the same of the other two sulfonic resins. We therefore speculate that the sulfonated carbon atoms resonate at the same frequency irrespective of their position or that their resonances are so close that they cannot be resolved. The second sulfonation of the aromatic rings of _Gel_oleum_ most likely occurs in the ortho- position, which is favoured by the orienting effects of both the (alkyl) polymeric chain and of the first \"sulfo\" group, assuming that the para position is sulfonated first. This is consistent with the well-know regiochemistry of aromatic electrophilic substitutions. In fact, the polymer chains can be considered as alkyl substituents of the phenyl rings at the ipso carbon atoms. Alkyls are electron-donating, para- and ortho-directing groups. As the polymeric chains are very bulky, the para- position should be preferred for the first sulfonation. In addition, the first sulfonic group introduced in the phenyl ring, which is electron withdrawing, is meta- directing (with respect to its own position). Thus, it should also contribute to the sulfonation of the ortho- position with respect to the ipso carbon atom. This is qualitatively confirmed by the analysis of the peak intensity in the spectra of the sulfonic resins (Table 5; for sake of clarity the carbon atoms are also numbered according to the structural scheme represented in Figure 9). \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & **C\({}_{ipso}\) (1)** & **C\({}_{para}\) (4)** & **C\({}_{ortho}\) (2)** & **C\({}_{meta}\) (3)** & **C\({}_{aliphatic}\)** \\ \hline Parent Gel resin & 146.3 & 126.3 & 128.7 & 128.7 & 45.6 & 41.1 \\ _Gel\({}_{o}\)beam_ & 147.7 & 134.7 & 128.7 & 124.7 & 38.7 & 38.3 \\ _Gel\({}_{H2 SO}\)\({}_{4}\)_ & 148.8 & 134.4 & 128.1 & 124.5 & 40.6 & 38.2 \\ _Gel\({}_{HClSO}\)\({}_{3}\)_ & 149.7 & 137.8 & 130.4 & 126.3 & 42.7 & 40.0 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Signal attribution of \({}^{1}\)H \({}^{13}\)C MAS spectra of the sulfonic samples (\(\delta\), ppm). \begin{table}
\begin{tabular}{c c c c} \hline \hline  & _Gel\({}_{H2 SO}\)\({}_{4}\)_ & _Gel\({}_{o}\)beam_ & _Gel\({}_{HClSO}\)\({}_{3}\)_ \\ \hline A\({}_{ipso}\) (1) & 723.785 & 1476.143 & 3467.159 \\ A\({}_{sulfonated}\) (2) & 834.452 & 2831.201 & 3574.537 \\ A\({}_{ortho}\) (3) & 1229.298 & 1716.835 & 4811.788 \\ A\({}_{meta}\) (4) & 2542.258 & 5038.13 & 9517.451 \\ A\({}_{sulfonated}\)/A\({}_{ortho}\) (4/1) & 0.68 & 1.66 & 0.75 \\ A\({}_{meta}\)/A\({}_{ortho}\) (3/1) & 2.1 & 2.87 & 1.99 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Integrated intensities (absolute units) of the signals of aromatic carbon atoms. Although the intensity of cross-polarized signals cannot be directly related to the number of resonating spins, the ratio between the areas of selected signals can be compared for similar samples. For _Gel_H\({}_{2}\)SO\({}_{4}\)_ and _Gel_HCISO\({}_{3}\)_, which have no doubly-sulfonated aromatic rings, the intensity ratios ortho/sulfonated and meta/sulfonated are similar. By contrast, for _Gel_oleum_ the intensity ratios ortho/sulfonated and meta/sulfonated are much lower and much higher, respectively. This suggests, at least qualitatively, that the number of carbon atoms in ortho to the polymeric chain is smaller in _Gel_oleum_ and supports the hypothesis of the second sulfonation of its aromatic rings in this position. A complete sulfonation in the ortho- position is anyway ruled out by the NMR data and also by the presence of the signal at 836 cm\({}^{-1}\) in the IR spectra of the sulfonic resins.