High ionic conductivity for ionic and poly ionic liquids based on 1-(hydroxyethyl)-3-vinylimidazolium cation: Asymmetric acidic anion contribution of hydrogen sulfate and dihydrogen phosphate

• Asymmetric acidic anion affects the ionic conductivity of monomeric MILs and PILs. • [EtOHVIM][HSO 4 ], good thermal stability and low glass transition temperature with a significant direct current (DC) conductivity. • The hydrophilic ionic liquid [P-EtOHVIM][H 2 PO 4 ] showed good thermal stability, low glass transition temperature, and decomposition at higher temperatures. • [P-EtOHVIM][H 2 PO 4 ] stands out among polyionic liquids due to its exceptional ionic conductivity (σ RT = 1.99 × 10 –5 S.cm -1 ). The outstanding characteristics of ionic liquids (ILs), combined with the mechanical stability of polymeric systems, give rise to a novel class of materials known as polymeric ionic liquids (PILs) with transformative potential applications. The study aimed to investigate the influence of asymmetric acidic anions on the ionic conductivity of monomeric ionic liquid MILs and PILs. Therefore, an anion exchange reaction was carried out on 1-hydroxyethyl-3-vinylimidazolium chloride [EtOHVIM]Cl, resulting in the formation of 1-hydroxyethyl-3-vinylimidazolium hydrogen sulfate [EtOHVIM][HSO 4 ]. Since a previous investigations highlighted the intriguing characteristics of dihydrogen phosphate anion, an additional anion exchange reaction was performed on Poly(1-hydroxyethyl-3-vinylimidazolium) chloride [P-EtOHVIM]Cl, which gave rise to the formation of Poly(1-hydroxyethyl-3-vinylimidazolium) dihydrogen phosphate [P-EtOHVIM][H 2 PO 4 ], resulting in the formation of Poly (1-hydroxyethyl-3-vinylimidazolium) dihydrogen phosphate [P-EtOHVIM][H 2 PO 4 ]. The molecular structures were confirmed using 1 H NMR, 13 C NMR, and Infrared (ATR/FTIR) spectroscopy. The obtained ionic liquids were analysed using Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA), and Derivative Thermogravimetry (DTG). The findings revealed that these compounds have intriguing thermal properties, including a low glass transition temperature and good thermal stability. Furthermore, Broadband Dielectric Spectroscopy (BDS) analysis and thermal characterisations were combined to unravel the interplay between charge transport and glassy dynamics.