## 3 Results and Discussion
### Characteristics of the Porous Structure  
Table 3 presents porous structure parameters of the prepared polymers. The highest values of the specific surface area (S\({}_{\text{BET}}\)) and total pore volume (V\({}_{\text{tot}}\)) were obtained for pDVB. The materials whose porosity was regulated by the presence of phenol, trichlorophenol or their mixture had the specific surface areas 2-5% lower and pore volumes 5-18% lower than unmodified pDVB.  
The lowest values were observed for pDVB-SO\({}_{3}\)H. Due to a steric effect caused by bulky sulphonic groups some pores become not available for nitrogen molecules. If -SO\({}_{3}\)H group is placed inside mesopore, its width apparently decreases that is observed as the narrowing of pores and formation of micropores. The scheme of the described process is shown in Figure 3.  
The confirmation of this explanation can also be found in Figure 4 where nitrogen adsorption-desorption isotherms and pore size distributions (PSD) are shown. The location of pDVB-SO\({}_{3}\)H isotherm indicates the decrease of porous structure parameters values. It is evident when the PSD plots of pDVB-SO\({}_{3}\)H and pDVB are compared. A peak at 3.75 nm is a little higher for pDVB-SO\({}_{3}\)H than that for pDVB, proving increase in the number of narrow mesopores. Next peak corresponding to broader mesopores in the case of pDVB-SO\({}_{3}\)H has it apex at 6.5 nm and half-height width in the range of 4.8-7.7 nm, while that for pDVB has the top at ca 7 nm and its half-height width is 4.2-9 nm.  
Figure 3: The process of narrowing of pores and micropore formation during the pDVB sulphonation.  
\begin{table}
\begin{tabular}{c c c c c c} \hline
**Polymer** & **S\({}_{\text{BET}}\) (m\({}^{2}\)/g)** & **V\({}_{\text{tot}}\) (cm\({}^{3}\)/g)** & **S\({}_{\text{mi}}\) (m\({}^{2}\)/g)** & **V\({}_{\text{mi}}\) (cm\({}^{3}\)/g)** & **W (nm)** \\ \hline pDVB & 560 & 0.717 & 1 & 0 & 3.75 and 7.15 \\ pDVB -P & 553 & 0.677 & 5 & 0 & 3.75 and 6.35 \\ pDVB - T & 529 & 0.591 & 9 & 0 & 3.75 and 4.75 \\ pDVB - M & 548 & 0.584 & 1 & 0 & 4.89 \\ pDVB-SO\({}_{3}\)H & 444 & 0.518 & 60 & 0.025 & 3.75 and 6.50 \\ \hline \end{tabular}
\end{table}
Table 3: The porous structure parameters.  
Moreover, the heights of both peaks are different demonstrating loss of pore volume as a consequence of sulphonation taking place inside wider mesopores.  
Equally interesting is the comparison of the isotherms obtained for other materials. According to IUPAC classification, isotherms of type IV-H2 are characteristic for materials with complex pore system, in which pores are interconnected, have irregular shapes and narrow entrances [28]. Such structure is typical of polymeric networks, therefore the shapes of hysteresis loops are very similar in all cases. The differences in porous structure can be discussed on the basis of PSDs.  
Replacement of 1 mL of toluene with phenol (pDVB-P) results in not only increase in the number of narrow pores (3.75 nm), but also wider mesopores. However, the latter are more homogeneous in comparison to those in pDVB. Even greater uniformity of wider mesopores was obtained by replacing 1 mL of toluene with trichlorophenol (pDVB-T). In the case of this material both peaks (3.75 and 4.75 nm) are high and narrow and the maximum pore width does not exceed 7 nm. The hardest to explain seems to be the result obtained for pDVB-M. The usage of the mixture of phenol and trichlorophenol instead of 1 mL of toluene resulted in the polymer with the most uniform porosity. PSD in this case has only one narrow peak with apex at 4.9 nm and half-height width in the range of 3.5-5.7 nm. The observed changes in the formation of porous structure can be explained by the fact that trichlorophenol is better soluble in toluene than phenol and the latter has a tendency to create dimers and more complex systems in solution due to strong hydrogen interactions [29].