## 8 Knowledge Gaps  
The tuning of PCR materials with porogenic solvents results in products with remarkable properties but there are some knowledge gaps identified herein that are recommended for further study. One of the gaps is the discrepancy of some results that are yet unaccounted for by the SP criteria. Although this has recently been addressed by [PERSON] [50] by accounting for the initiator solubility in porogenic \begin{table}
\begin{tabular}{|l|c|c|c|} \hline
**Solvent** & **Fixed pore volume** & **Surface area** & **Average pore diameter (nm)** \\ \hline Diethyl phthalate & 0.47 & 149 & 12.6 \\ \hline Benzyl alcohol & 0.65 & 110 & 23.6 \\ \hline Diisobutyl phthalate & 0.57 & 83 & 27.5 \\ \hline Dioctyl phthalate & 0.88 & 75 & 46.9 \\ \hline Heptane & 0.99 & 68 & 58.2 \\ \hline Isoamyl acetate & 0.34 & 30 & 45.3 \\ \hline Isoamyl alcohol & 1.00 & 7 & 143 \\ \hline Toluene & 0.01 & 0 & – \\ \hline Acetophenone & 0.06 & 0 & – \\ \hline Methyl-isobutyl ketone & 0.06 & 0 & – \\ \hline Decaline & 0.12 & 0 & – \\ \hline Ethyl acetate & 0.13 & – & – \\ \hline Butyl acetate & 0.41 & – & – \\ \hline \end{tabular}
\end{table} 
Table 4: Porosity properties of styrene-_co_-divinylbenzene synthesized with different porogenic solvents. The parameters are obtained from nitrogen porosimetry (Data obtained from [34]). \begin{table}
\begin{tabular}{|c|c|c|c|c|c|} \hline \multicolumn{4}{|c|}{**One-component**} & \multicolumn{4}{|c|}{**Three-component**} \\ \hline
**Solvent** & \(|\Delta\delta|\)**MPa\({}^{\mathbf{a,5}}\)** & **Prediction** & **Solvent** & **RED** & **Prediction** \\ \hline Ethyl acetate & 0.2 & \multirow{2}{*}{“Good” solvents _i.e._, \(|\Delta\delta|<1.0\)} & \multirow{2}{*}{“Good” _i.e._, \(|\Delta\delta|<1.0\)} & Acetophenone & 0.28 & \\ \cline{1-2} \cline{5-6} Toluene & 0.4 & & Diisobutyl phthalate & 0.59 & \\ \cline{1-2} \cline{5-6} Diisobutyl phthalate & 0.4 & & Toluene & 0.65 & “Good” \\ \cline{1-2} \cline{5-6} Decaline & 0.6 & & Diethyl phthalate & 0.65 & solvents _i.e._, \(|\Delta\delta|<1.0\) \\ \hline Butyl acetate & 1.2 & \multirow{2}{*}{Intermediary solvents _i.e._, \(|\Delta\delta|<3.0\)} & Decaline & 0.73 & \(|\Delta\delta|<1.0\) \\ \cline{1-2} \cline{5-6} Methyl-isobutyl ketone & 1.4 & & Dioctyl phthalate & 0.75 & \\ \cline{1-2} \cline{5-6} Diethyl phthalate & 1.8 & & Benzyl alcohol & 0.87 & \\ \cline{1-2} \cline{5-6} Isoamyl alcohol & 1.9 & & Ethyl acetate & 0.90 & Intermediary solvents, _i.e._, \(|\Delta\delta|>3.0\) \\ \cline{1-2} \cline{5-6} Dioctyl phthalate & 2.4 & & Butyl acetate & 0.90 & \\ \cline{1-2} \cline{5-6} Isoamyl acetate & 2.6 & & Methyl-isobutyl ketone & 0.94 & 1.0 \(|\Delta\delta|<3.0\) \\ \hline Acetophenone & 3.1 & & Isoamyl alcohol & 0.98 & \\ \hline Heptane & 3.5 & “Bad” solvents _i.e._, \(|\Delta\delta|>3.0\) & & Heptane & 1.10 & “Bad” solvents _i.e._, \(|\Delta\delta|>3.0\) \\ \hline Benzyl alcohol & 6.1 & _i.e._, \(|\Delta\delta|>3.0\) & Isoamyl alcohol & 1.13 & _i.e._, \(|\Delta\delta|>3.0\) \\ \hline \end{tabular}
\end{table} 
Table 3: Prediction of porogenic solvents in terms of one- and three-component SP criteria; relative energy difference (RED) is calculated using Equation 3. (Data obtained from [34]). solvent(s), it is anticipated to play a major role in the kinetics and thermodynamics of polymerization phenomena. The relationship between the initiator solubility and the resin properties require further research to support [PERSON]'s results. [PERSON] and [PERSON] [34] pointed out that molar volume prevails as a criterion of the SP since it is a measure of the solvating strength; however, the research is limited by the systematic correlations between V\({}_{\textrm{m}}\) and SP. Secondly, the SP value is used for matching the resins and the solvent(s) at standard temperature conditions; however, polymerization often occurs at elevated temperatures \(\sim\)60-80 \({}^{\circ}\)C. Since the SP value is anticipated to change with temperature, a better matching of SP values should be calculated for _in-situ_ polymerization temperature conditions [36,51].