## 3 Results
### Hypercrosslinking of PolyHIPEs  
Hypercrosslinking of polyHIPEs was performed by an established procedure, applying a Friedel-Crafts type electrophilic aromatic substitution process [6]. Generally, a chloromethyl group tethered to the polymer chain can react either with a benzene ring or another VBC moiety creating methylene bridges or cyclical type connections. DCE has been used as a solvent in which styrene-type polymers are swollen, while being effective in dissolving FeCl\({}_{3}\), which serves as a catalyst for Friedel-Crafts alkylation reactions. The effect of this procedure was apparent both in the drop of chlorine content due to conversion of a part of chloromethyl groups into crosslinking methylene bridges and in a substantial increase of the BET surface area (Table 2). In most cases, the residual chlorine content after hypercrosslinking was 10-15 wt.%. Somewhat surprisingly, higher values of residual chlorine (suggesting lower efficiency of the hypercrosslinking) were found in samples with the highest VBC or DVB content. In these samples, there is greater probability that within the polymer network some chloromethyl groups could be located in less accessible places. A very profound effect of the hypercrosslinking is evident in the surface area values. Before hypercrosslinking all the polymers exhibited low surface area only, corresponding with the area of the macro pores created by emulsification of the monomer mixture. The hypercrosslinking porosity modification does not modify the macroporous polyHIPE features (Figure 2). Figure 1: PolyHIPE preparation. Substantially higher BET surface of the hypercrosslinked polymers indicates the formation of new porosity. However, hypercrosslinking is known to produce microporosity with pores smaller than 2 nm [47]. Such narrow pores are filled with the sorbate sooner than the BET equation-described multilayer adsorption begins. Standard evaluation of the BET surface of such materials interprets the sorbate amount filling the micropores as a part of the BET multilayer, which produces incorrect BET surface area data. It is possible to distinguish between micropore volume and external surface area using the \(t\)-plot method, which is plotting the adsorbed amount against thickness of the adsorbed layer computed by the \(t\)-plot method. The \(t\)-plot method is able to distinguish between micropore volume and external surface area using the \(t\)-plot method, which is plotting the adsorbed amount against thickness of the adsorbed layer computed by the \(t\)-plot method. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & \multicolumn{2}{c}{**Before Hypercrosslinking**} & \multicolumn{2}{c}{**After Hypercrosslinking**} \\ \cline{2-6}  & **Cl Content, wt.\%** & **BET Surf. ** & **Cl Content, Are, m\({}^{2}\)/g** & **Cl Content, wt.\%** & **Residual Cl, \% of Orig. ** & **BET Surf. ** \\ \hline A93 & 21.90 \(\pm\) 0.20 & 2.40 & 3.70 \(\pm\) 0.03 & 16.9 & 709 \\ A73 & 18.00 \(\pm\) 0.40 & 3.20 & 1.70 \(\pm\) 0.03 & 9.4 & 636 \\  
from adsorption on a flat surface. The software used in this study is based on the Harkins and Jura thickness equation [48]. The linear part of such a plot (usually corresponding to relative pressures 0.05-0.35) can be considered as the region of the adsorption on flat surface. The Y-intercept of such a line corresponds to the micropore volume and the slope is proportional to the external (outside micropores) surface area [49]. T-plot analyses of the polymers before hypercrosslinking show zero or slightly negative values of the micropore volumes (\(-0.008\)-\(0\) cm\({}^{3}\)/g) and external surface areas in the range of 0.8-8.8 m\({}^{2}\)/g, slightly higher than the BET surfaces. However, considering the completely different theoretical background of these two methods, the agreement is very good. In the hypercrosslinked polymers, both the amount of micropores and the external surface area varied in dependence of the VBC content of the polymer (Figure 3).