## 5 Influence of the Solvent (Porogen)
### Solvent Volume  
The volume of the porogenic solvent plays a major role in the structure and morphology of the resins. Previous research indicates that the copolymer resin prepared in the presence of larger amounts of porogen have a looser structure than those obtained with reduced levels of porogen [39; 43; 44; 45]. In terms of pore formation, Figure 4[42] illustrates three types of resins produced with higher porogen  
\begin{table}
\begin{tabular}{c|c|c|c|c|c} \hline \multirow{2}{*}{**Polymer type**} & \multirow{2}{*}{**Porogen A**} & **Surface area** & **Pore volume** & **Average pore** & \multirow{2}{*}{**Reference**} \\  & & **(m\({}^{2}\)/g)** & **(cm\({}^{3}\)/g)** & & **diameter (nm)** & \\ \hline \multirow{4}{*}{Poly(styrene-_co_-divinylbenzene) – 1:3} & 2-ethylhexanol: DMF (70\%:30\%) & \multirow{4}{*}{375} & \multirow{4}{*}{NM \({}^{*}\)} & 20.0 & \multirow{4}{*}{[16]} \\  & DMF (70\%:30\%) & & & & \\ \cline{1-1} \cline{4-5}  & Toluene: DMF (70\%:30\%) & \multirow{2}{*}{555} & \multirow{2}{*}{NM \({}^{*}\)} & \multirow{2}{*}{NM \({}^{*}\)} & \\ \cline{1-1} \cline{4-5}  & & Cyclohexanone : & & & \\ \cline{1-1} \cline{4-5}  & trimethyllopropate trimethacrylate – 1:1 & Cyclohexanone : & & & \\ \cline{1-1} \cline{4-5}  & & Dodecan-1-ol (9:1) & \multirow{2}{*}{140} & \multirow{2}{*}{1.13} & \multirow{2}{*}{10–100} & \multirow{2}{*}{[15]} \\ \hline \multirow{4}{*}{2-vinylpyridine-_co_-styrene-_co_-} & \multirow{4}{*}{heptane : Toluene (100\%:0\%)} & \multirow{2}{*}{ND \({}^{*}\)} & \multirow{2}{*}{ND \({}^{*}\)} & \multirow{2}{*}{ND \({}^{*}\)} & \\ \cline{1-1} \cline{4-5}  & divinylbenzene – 1:20 & \multirow{2}{*}{heptane : Toluene (70\%:30\%)} & \multirow{2}{*}{131} & \multirow{2}{*}{0.5845} & \multirow{2}{*}{21.9} & \\ \cline{1-1} \cline{4-5}  & & NM \({}^{*}\) = Not Measured, ND \({}^{*}\) = Not Detected. & & & \\ \hline \end{tabular}
\end{table}
Table 2: Surface area (from nitrogen porosimetry), pore-volume, pore-size and average pore diameters of PCR materials synthesized in presence of various solvent mixtures. The synthesis conditions were outlined in Section 2.1.  
levels which result in a shift of the PSD toward larger pores (to the right) with greater pore abundance (higher peaks). The resin HS (poly(2-hydroxyethyl methacrylate-_co_-styrene)) has particles with smaller pores; whereas, HN (poly(2-hydroxyethyl methacrylate-_co_-_N_-vinyl-2-pyrrolidone)) particles possess larger pores. Therefore, pore size may be controlled by adjusting the relative porogen ratio. The authors conclude from their results that a lower porogen volume ratio generates fewer pores with a reduced pore size; whereas, a higher volume ratio of porogen contributes to greater numbers of pores with greater pore size. These results are further supported by [PERSON] _et al_. [46] where greater concentration of 1-chlorodecane reveals that the precipitated phase exhibits limited swelling and the polymer aggregates behave as an immiscible \"solid\" polymer, similar to bulk microspheres prepared in the absence of porogen. The resulting final pore volume between aggregates should be close to the volume of the non-solvating porogen. In contrast, low levels of 1-chlorodecane yield a precipitated phase that undergoes swelling with a final pore volume less than that of the non-solvating porogen. The relative tuning of solvent porogen composition represents a good technique for tuning PSD.