## 3 Results
### Polar Free Interaction Energy of S-DVB Copolymer Modified by HMU with the Polar Probes  
Applying Equations (4) to (7), it was easy to determine the values of \(-\Delta G_{a}^{p}(T)\) of adsorbed polar molecules on the copolymer surfaces with the temperature. The obtained values were given in Table S1. The variations of \(-\Delta G_{a}^{p}(T)\) for polar molecules adsorbed on copolymer surfaces were plotted in Figure 3 versus temperature for various HMU percentages. Linear variations were obtained, allowing the values of polar enthalpy (\(-\Delta H_{a}^{p}\)) and entropy (\(-\Delta S_{a}^{p}\)) of adsorption. Table S1 and Figure 3 showed that the highest interaction was obtained with the highest HMU percentage (10%), showing that the polar free energy increased with the modifier percentage for all polar solvents. The lowest interaction was obtained with the S-DVB copolymer, meaning that the addition of HMU on the copolymer certainly increased the interaction capacity of the copolymer with the polar molecules. It can also be deduced that the lowest interaction for all materials was obtained with benzene and toluene solvents, whereas the highest adsorption was shown in Table S1 and Figure 3 for i-pentanol and i-butanol solvents, thus proving the highest effect of the hydroxyl group on the free polar interaction. Figure 3: _Cont._  
These conclusions can be obviously shown by Figure 4, which shows the variations of \(-\Delta G_{a}^{p}\) presented as a function of the HMU percentage in the copolymer at different temperatures. The maximum of the free interaction energy is shown for all polar solvents. Figure 3: Evolution of the free polar energy \(\left[-\Delta G_{a}^{p}(T)\right]\) of the various polar organic probes adsorbed on the different solid materials as a function of temperature for different HMU percentages. (**a**) Benzene, (**b**) toluene, (**c**) ethyl acetate, (**d**) ethanol, (**e**) i-propanol, (**f**) n-butanol, (**g**) i-butanol, (**h**) i-pentanol, and (**i**) dichloromethane. The determination of the polar enthalpy and entropy of adsorption for the different copolymers was obtained using Equation (8). The obtained results allowed determining the surface polar enthalpy and the entropy of adsorption, as well as the Lewis acid-base constants of the solid materials, as shown in the next section. Polar Enthalpy and Entropy of Adsorption, and Lewis Acid-Base Parameters of Dowex L-285 Modified by HMU  
The variations of \(-\Delta G_{a}^{p}(T)\) given in Table S1 and Figure 3, against temperature, allowed the values of \((-\Delta H_{a}^{p})\) and \((-\Delta S_{a}^{p})\) of the adsorbed polar solvents for the different modifier percentages, using Equation (9). The representation of the variations of \(\left(\frac{-\Delta H_{a}^{p}}{AN}\right)\) and \(\left(\frac{-\Delta S^{p}}{AN}\right)\) versus \(\left(\frac{DN^{\prime}}{AN^{\prime}}\right)\) of the polar solvents adsorbed on the various surfaces (Figure 5) led to the values of the Lewis acid-base parameters \(K_{A}\), \(K_{D}\), \(\omega_{A}\), and \(\omega_{D}\) relative to S-DVB-L-285 with different HMU percentages (from 1% to 10%). The obtained values are given in Table 3. The results proved the amphoteric character of the various copolymers. A stronger Lewis acidity than the Lewis basicity was observed in the case of the S-DVB copolymer, for a modifier percentage equal to 1%. However, this tendency was inverted for an HMU  
Figure 4: Variations in the free polar energy \(\left[-\Delta G_{a}^{p}(T)\right]\) of polar organic probes adsorbed on the different solid materials as a function of HMU percentage on Dowex L-285 at various temperatures. (**a**) Benzene, (**b**) toluene, (**c**) ethyl acetate, (**d**) ethanol, (**e**) i-propanol, (**f**) n-butanol, (**g**) i-butanol, (**h**) i-pentanol, and (i) dichloromethane. percentage higher than 3% where the Lewis basicity was shown to be two times higher than their Lewis acidity.