Poly(ionic liquid)-Based\nHydrogel for Emerging Pollutant\nRemoval and Controlled Drug Delivery

In this study, we report the synthesis and characterization\nof\na set of poly(ionic liquid) (PIL)-based gel membranes formed by the\nreaction of poly(4-vinylpyridine) (P4VPy) with a terminal dibrominated\npoly(ethylene glycol) (PEG), which led to the formation of quaternized\npyridines as cross-linking joints. First, for hydrogel synthesis,\nPEG terminal hydroxyls were brominated and subsequently reacted with\nP4VPy, resulting in the formation of ionic liquid (IL)-like moieties\nwithin the hydrogel network. Modified PEG and PIL-based membranes\nwere characterized by Nuclear Magnetic Resonance (NMR), Fourier-Transform\nInfrared (FT-IR), thermogravimetric analysis (TGA), and differential\nscanning calorimetry (DSC), as well as their swelling and adsorption\nproperties. FT-IR spectroscopy confirmed the quaternization of the\npyridine pendant groups of P4VPy by the appearance of a band at 1639\ncm<sup>–1</sup> due to the presence of pyridinium units. Thermal\ncharacterization revealed a decrease in the thermal stability of the\nmembranes with respect to the starting materials, probably ascribed\nto the presence of charged species inside the cross-linked matrix.\nFurthermore, DSC characterization revealed that the P4VPy:PEG ratio\nand degree of cross-linking strongly affected the amount of non-freezable\nwater. Swelling experiments of the hydrogels revealed a swelling ratio\nvalue (% SW) near 297% after 2 h of hydration, showing remarkable\nrecyclability over multiple hydration and drying cycles. Finally,\nsodium diclofenac (DCl) and methyl orange (MO) adsorption experiments\nrevealed the remarkable ability of the hydrogels to remove pollutants\nfrom water, with <i>q</i><sub>max</sub> values of 166.7\nand 218.8 mg/g, respectively. Finally, a hydrogel loaded with DCl\nwas used as a model system for drug release experiments, in which\nthe hydrogel was able to release almost 70% of DCl to the medium within\n1 day of exposure. This process is controlled mainly by a polymer\nrelaxation mechanism and influenced by the temperature of the experiment,\nshowing great potential for reuse in further experiments and also\nas an interesting platform for controlled drug release.