# 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  
A more detailed insight into the chemical nature of the sulfonic resins can be obtained with solid state CP-MAS NMR (Figures 5-7). For the sake of comparison, the NMR spectrum of the starting cross-linked polymer has also been collected (Figure 8). The occurrence of isotropic chemical shifts vs. spinning sidebands has been checked for, by comparing spectra registered at different MAS speeds. Deconvolution of the observed signals has been carried out taking into account the chemical non-equivalence of the different carbon atoms. \begin{table}
\begin{tabular}{c c} \hline \hline
**Peak/Band (cm\({}^{-1}\))** & **Assignment** \\ \hline
1599, 1495, 1413 & Skeleton stretching vibrations of the benzene ring \\ \hline
1451 & scissor vibration of CH\({}_{2}\) group \\ \hline
1348 & antisymmetric stretching vibration of the S=O bonds \\ \hline
1033 & symmetric stretching vibration of the -SO\({}_{3}\)\({}^{-}\) ion \\ \hline
1126, 1097 & in-plane skeleton vibration of the benzene ring. Bands characteristic of disubstituted benzene rings \\ \hline
1004 & in-plane bending vibrations of the CH groups for benzene ring \\ \hline
836/831 & out-of-plane vibration of the pairs of CH groups in the p-substituted benzene ring (in comparison with p-toluenesulfonic acid, 817 cm\({}^{-1}\)) \\ \hline
772 & out-of-plane vibration of four CH groups in the o-substituted benzene ring (as the term of comparison, 765 cm\({}^{-1}\) for o-toluenesulfonic acid) \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Diagnostic signals of sulfonic poly(styrene-divinylbenzene) materials, with the pertinent assignments. Figure 5: \({}^{1}\)H-\({}^{13}\)C CP MAS spectrum of \(Gel\_H_{2}SO_{4}\). Contact time 1 ms, MAS rate 10 kHz, T = 25 \({}^{\circ}\)C.  
Figure 6: \({}^{1}\)H-\({}^{13}\)C MAS spectrum of \(Gel\_oleum\). Contact time 1 ms, MAS rate 10 kHz, T = 25 \({}^{\circ}\)C.  
The signals at 41.10 ppm and 45.58 ppm in the spectrum of the starting material (Figure 8) can be assigned to the backbone carbons. The signal at 146.29 ppm is due to the quaternary carbon of the aromatic rings, whereas the signals at 128.72 and 126.30 ppm have been attributed to non-functionalized aromatic carbons [16]. Figure 8: \({}^{1}\)H \({}^{13}\)C MAS spectrum of the starting gel-type poly(styrene-divinylbenzene) (2% mol DVB). Contact time 1 ms, MAS rate = 10 kHz, T = 25 \({}^{\circ}\)C.  
Figure 7: \({}^{1}\)H \({}^{13}\)C MAS spectrum of _Gel_HCISO\({}_{3}\)_. Contact time 1 ms, MAS rate 10 kHz, T = 25 \({}^{\circ}\)C.  
The signals of sulfonic resins, summarized in Table 4, have been assigned according to the literature [28; 29; 30]. The positions of the carbon atoms of the aromatic rings given hereafter will be referred to the position of the polymeric chain. The spectra of alkylbenzenes or 1,3-diphenylpropane and of p-toluenesulfonic acid in CDCl\({}_{3}\)[31] can be used to attribute the signals in the aromatic region by comparison. Accordingly, the aromatic carbon atom directly attached to the polymeric chain (ipso) resonates in the 146-150 ppm in all the materials. In the parent gel resin (non-sulfonic) the resonances of the ortho and meta carbon are superimposed at 128.7 ppm (128.39 and 128.26 ppm in 1,3-diphenylpropane) and the signal at 126.3 ppm is assigned to the para- carbon atom. A signal in the 124.5-126.3 ppm range is found also in the sulfonic polymers, but in this case, it can be attributed to the meta carbon atom, by analogy with p-toluenesulfonic acid (125.45 ppm). The para position is the preferred one for the sulfonation of polystyrene [28; 29; 30; 32] and the carbon atom bearing the sulfonic group resonates in the 134.4-137.8 ppm range. Not only is this signal absent in the spectrum of the parent gel resin, but its position is also consistent with the solution-state spectrum (CDCl\({}_{3}\)) of p-toluenesulfonic acid, where the sulfonated carbon atoms resonate at 138.49 ppm.