# Multifunctional Modifying Systems Based on Ionic Liquids for Epoxy Resin Systems and Composites
## 3 Results and Discussion
### Curing Properties of Modified Epoxy Resin Formulations  
DSC analysis was performed for all resin systems, the results of which are summarized in Table 3. All modified systems relative to the reference, containing only [EMIM] [dca] as a curing agent, showed a decrease in onset temperature values, even by 24-25% (C and E). At the same time, there was also a decrease in the temperature of the maximum thermal peak in all modified systems relative to the reference. A proposed explanation for this phenomenon is the aggregate increase in the concentration of 1-ethyl-3-methylimidazolium cation in the systems, thereby shifting the polymerization equilibrium toward cationic polymerization. This fact also seems to be confirmed by the decrease in intensity or even the almost complete disappearance of the second thermal peak observed in the case of thermograms for the modified systems, indicating the almost complete elimination of anionic polymerization (C and D, thermograms in Supplementary Materials). In addition, compounds with long alkyl chains introduced into the systems can also affect the reduction of the temperatures of thermal transformations occurring during the polymerization of the epoxy resin. In the case of the total enthalpy of the process, a decrease in its value was observed in all cases, with a marked change of 14% for system E.  
Similarly, according to the results obtained, a decrease in the glass transition temperature values of the modified systems was observed. The average decrease in the T\({}_{\text{g}}\) value was 41% with respect to the reference value, reaching the largest decrease for system B. At the same time, systems D and E, containing phosphonium ionic liquids, recorded the lowest decrease at 33 and 34%, respectively, regarding the reference. The results obtained allow us to conclude that, despite the generally observed plasticizing effect achieved by modifying the resin system with ILs, this phenomenon can be somewhat controlled and due to the long-chain alkyl compounds, be significantly reduced. The effect of modifying the resin system with ionic liquids on thermal stability was investigated using thermogravimetric analysis (TGA), the results of which are presented in Table 4. The following parameters were used in the analysis of the results: (i) the temperature at which the mass of the sample is reduced by 5% (T\({}_{\text{5\%}}\)), (ii) the temperature \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Epoxy System**} & \multirow{2}{*}{**CA**} & \multicolumn{2}{c}{**Modification Formulation**} & \multirow{2}{*}{**Mass of P**} & \multirow{2}{*}{**Mass of Si**} \\ \cline{3-3} \cline{5-5}  & & **[Si] IL (1 eq.)** & **[P] IL (1 eq.)** & & **[g/100 g]** \\ \cline{2-5}  & \multicolumn{2}{c}{**2 g/98 g of ER**} & \multicolumn{2}{c}{**10 g/90 g of ER with CA**} & \\ \hline R & [EMIM] [dca] & 0 & 0 & 0 \\ \hline A & [EMIM] [dca] & [TMSPrMIM] [Cl] & [EMIM] [dmp] & 0.5 & 0.5 \\ \hline B & [EMIM] [dca] & [TMSPrMIM] [Cl] & [EMIM] [dep] & 0.6 & 0.5 \\ \hline C & [EMIM] [dca] & [TMSPrMIM] [Cl] & [EMIM] [dbp] & 0.5 & 0.4 \\ \hline D & [EMIM] [dca] & [TMSPrMIM] [Cl] & [P\({}_{66614}\)] [btmp] & 0.5 & 0.2 \\ \hline E & [EMIM] [dca] & [TMSPrMIM] [Cl] & [P\({}_{66614}\)] [behp] & 0.6 & 0.3 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Composition of the epoxy systems with ionic liquids. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Sample**} & \multicolumn{2}{c}{**Onset Temperature**} & \multicolumn{2}{c}{**Maximum Peak**} & \multicolumn{2}{c}{**Total Enthalpy**} \\  & [\({}^{\circ}\)C] & [\({}^{\circ}\)C] & [J/gl] \\ \hline R & 147 & 162 & 520 \\ A & 117 & 150 & 508 \\ B & 133 & 151 & 507 \\ C & 111 & 124 & 486 \\ D & 127 & 169 & 484 \\ E & 110 & 121 & 446 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Characteristic of the curing process, determined with DSC. when 50% of the sample decays (T\({}_{50\%}\)), (iii) the maximum mass loss rate (dTG\({}_{\max}\)), and (iv) the maximum mass loss rate temperature (T\({}_{\mathrm{dTGmax}}\)).