*2.1. Characterization of Synthesized PILs*

All six ammonium-based PILs in this work exist as liquids at room temperature. The ammonium cation, [EHA] and [BEHA] were combined with anions from organic acids, [C5], [C6] and [C7] through acid-base neutralization reactions. The NMR results and the water contents for all six ammonium-based PILs, [EHA][C5], [EHA][C6], [EHA][C7], [BEHA][C5], [BEHA][C6] and [BEHA][C7], are presented in this sub section while all NMR spectra of PILs (Figures S1–S12) are available in the Supplementary Materials. The reported water content for all PILs is between 1.04% and 8.70%. Based on reported data by Chen et al., PILs are highly hygroscopic and own higher hydrophilicity in comparison to aprotic ionic liquids [38]. Meanwhile, the presence of water molecules lowers the electrostatic attractions between the ions and consequently reduces the viscosity of ILs [39]. Nonetheless, the thermophysical properties of our PILs are solely reported by using these water content values.

[EHA][C5]: 1H NMR (500 MHz, CDCl3): δ 0.902 [t, 9H (R-CH3)], δ 1.518 [m, 13H (R-CH, R-CH2), δ 2.120 [t, 2H (COOH-CH2)], δ 2.710 [m, 2H (NH2-CH2)]. 13C NMR (125 MHz, CDCl3): δ 181.05, 42.48, 37.97, 37.82, 30.17, 28.66, 28.43, 23.22, 22.88, 22.76, 13.98, 13.91, 10.14. Water content: 6.37%.

[EHA][C6]: 1H NMR (500 MHz, CDCl3): δ 0.880 [t, 9H (R-CH3)], δ 1.516 [m, 15H (R-CH, R-CH2), δ 2.118 [t, 2H (COOH-CH2)], δ 2.690 [m, 2H (NH2-CH2)]. 13C NMR (125 MHz, CDCl3): δ 181.22, 42.61, 38.09, 37.97, 31.92, 30.20, 28.14, 23.22, 22.89, 22.54, 13.97, 13.88, 10.16. Water content: 8.70%.

[EHA][C7]: 1H NMR (500 MHz, CDCl3 δ 0.900 [t, 9H (R-CH3)], δ 1.508 [m, 17H (R-CH, R-CH2), δ 2.086 [t, 2H (COOH-CH2)], δ 2.688 [m, 2H (NH2-CH2)]. 13C NMR (125 MHz, CDCl3): δ 181.11, 42.51, 38.22, 38.02, 31.79, 30.19, 29.45, 28.44, 26.55, 23.21, 22.90, 22.58, 14.00, 13.97, 10.14. Water content: 8.43%.

[BEHA][C5]: 1H NMR (500 MHz, CDCl3): δ 0.836 [m, 15H (R-CH3)], 1.265 [m, 16H (R-CH2, -CH)], δ 1.523 [m, 4H (R-CH2)], δ 2.149 [t, 2H (CH2-COO-)], δ 2.576 [d, 4H (CH2- NH)]. 13C NMR (125 MHz, CDCl3): δ 179.31, 51.75, 37.15, 36.37, 30.80, 28.53, 28.02, 23.95, 22.96, 22.57, 14.02, 13.86, 10.38. Water content: 1.52%.

[BEHA][C6]: 1H NMR (500 MHz, CDCl3): δ 0.811 [m, 15H (R-CH3)], δ 1.282 [m, 18H (R-CH2, -CH)], δ 1.534 [m, 4H (R-CH2)], δ 2.124 [t, 2H (CH2-COO-)], δ 2.585 [d, 4H (CH2- NH)]. 13C NMR (125 MHz, CDCl3): δ 179.25, 51.74, 37.15, 36.71, 31.74, 30.79, 28.51, 25.63, 23.94, 22.96, 22.50, 14.01, 13.96, 10.35. Water content: 1.04%.

[BEHA][C7]: 1H NMR (500 MHz, CDCl3): δ 0.865 [m, 15H (R-CH3)], δ 1.280 [m, 20H (R-CH2, -CH)], δ 1.540 [m, 4H (R-CH2)], δ 2.126 [t, 2H (CH2-COO-)], δ 2.582 [d, 4H (CH2- NH)]. 13C NMR (125 MHz, CDCl3): δ 179.29, 51.65, 37.00, 36.85, 31.67, 30.74, 29.20, 28.48, 28.47, 25.93, 23.90, 22.92, 22.53, 13.96, 10.27. Water content: 1.37%.
