## 5 Influence of the Solvent (Porogen)
### Solvent Mixtures  
The preparation of PCR materials using polar co-monomers that do not dissolve in the solvent are the most solvating diluents. The use of non-solvating diluent affects the nature of the products. In this case, the most solvating diluent is mixed with the non-solvating or an intermediary solvating diluent. The prediction of the SP value is shown in Equation (6) [46]. \[\delta_{m}=(\varphi_{1}\delta_{1}^{\;2}+\varphi_{2}\delta_{2}^{\;2})^{0.5} \tag{6}\] \begin{table}
\begin{tabular}{|c|c|c|c|c|c|} \hline
**Polymer type** & **Porogen** & **Surface area** & **Pore volume** & **Porosity** & **Average pore diameter** & **Reference** \\  & & **(m\({}^{2}\)/g)** & **(cm\({}^{3}\)/g)** & **(\%)** & **(nm)** & \\ \hline Poly(styrene-co- & Cyclohexanone & 25 & 0.22 & & ND \({}^{*}\) \\  & 2-ethylhexanol & 242 & 1.13 & & 20–45 & \\  &  Toluene & 599 & 0.44 & & \(<\)4 & \\ \hline  & Octan-2-one & 174 & 1.31 & & & \\  & n-butyl acetate & 170 & 1.27 & & & \\ \cline{2-6} Glycidyl methacrylate-co- & \(p\)-xylene & 139 & 1.50 & & & \\ \cline{2-6} trimethylopropane trimethacrylate - 1:1 & Toluene & 145 & 1.02 & & \\ \cline{2-6}  & Ethyl acetate & 110 & 0.66 & & 10–100 & [15] \\ \cline{2-6} trimethacrylate - 1:1 & Benzonitrile & \(<\)1 & 0.07 & & \\ \cline{2-6}  & Cyclohexanone & 0.2 & 0.16 & & \\ \cline{2-6}  & Dodecan-1-ol & ND \({}^{*}\) & ND \({}^{*}\) & & \\ \hline Poly(hydroxyethyl methacrylate-co- ethylene glycoldimethoxy) – 1:20 & Cyclohexanol & 250 & 0.396 & & 6.3 & \\ \cline{2-6}  & & & & & \\ \cline{2-6}  & & & & & \\ \cline{2-6} Poly(divinylbenzene); mixtures of isomers & Dodecanol & 28 & 0.06 & & 8.6 & \\ \hline  & Heptane & 482 & \(\text{NM}^{*}\) & 45.3 \({}^{\text{a}}\) & 6.9 \({}^{\text{a}}\) & \\  & & & & & 69.0 \({}^{\text{b}}\) & 86.8 \({}^{\text{b}}\) \\ \cline{2-6}  & Cyclohexane & 640 & \(\text{NM}^{*}\) & 37.9 \({}^{\text{a}}\) & 3.8 \({}^{\text{a}}\) & \\  & Cyclohexane & 640 & \(\text{NM}^{*}\) & 47.7 \({}^{\text{b}}\) & 72.4 \({}^{\text{b}}\) & \\ \cline{2-6}  & & & & & \\ \cline{2-6}  & 1-chlorodecane & 720 & \(\text{NM}^{*}\) & 56.3 \({}^{\text{a}}\) & 7.2 \({}^{\text{a}}\) & \\  & & & & 66.7 \({}^{\text{b}}\) & 53.4 \({}^{\text{b}}\) & \\ \cline{2-6}  & & & & & \\ \cline{2-6}  & Toluene & 701 & \(\text{NM}^{*}\) & 35.9 \({}^{\text{a}}\) & 3.2 \({}^{\text{a}}\) & \\  & & & & 50.5 \({}^{\text{b}}\) & 68.1 \({}^{\text{b}}\) & \\ \cline{2-6}  & Dibutyl phthalate & 661 & \(\text{NM}^{*}\) & 37.1 \({}^{\text{a}}\) & 3.6 \({}^{\text{a}}\) & \\  & Cyclohexanol & 493 & \(\text{NM}^{*}\) & 61.8 \({}^{\text{b}}\) & 60.2 \({}^{\text{b}}\) & \\ \hline \end{tabular}
\end{table} 
Table 1: Surface area (from nitrogen porosimetry), pore-volume, pore-size and average pore diameter of porous copolymer resin (PCR) synthesized in presence of different types of solvent porogens. The synthesis properties are the same as indicated in Section 2.1.  
where \(\varphi_{1}\) and \(\varphi_{2}\) are the volume fractions of the two porogens, and \(\delta_{1}\)and \(\delta_{2}\) are the respective SP values. Tuning is done by mixing the two solvents at different volume fractions until the desired properties are achieved. Table 2 shows some of the examples studied for such mixtures. Reference [16] shows that a non-solvating medium such as dimethylformamide (DMF; \(\delta=24.8\) MPa\({}^{1/2}\)) was used as a diluent and mixed with 2-ethylhexanoic acid to yield a higher surface area material with a unimodal size distribution of 20 nm. The product obtained from toluene mixtures has a decreased surface area relative to pure toluene (_cf._ Table 1). To this point, it is assumed that a one-component SP value may explain differences in the product characteristics; whereas, the SP values of mixtures are calculated using Equation (6). The respective values are for 2-ethylhexanol:DMF (21.2 MPa\({}^{1/2}\)) and toluene/DMF (20.4 MPa\({}^{1/2}\)).