Thermo-sensitive ionic microgels via post quaternization cross-linking: fabrication, property, and potential application

Abstract

A post quaternized cross-linking strategy was reported to fabricate thermo-sensitive ionic microgels from thermo-sensitive linear copolymer poly(N-isopropylacrylamide-co-1-vinylimidazole) [P(NIPAm-co-VIM)] or poly(N-isopropylacrylamide-co-4-vinylpyridine) [P(NIPAm-co-4VP)] in aqueous solution at elevated temperature above its critical transition temperature (T c). 1,4-dibromobutane, 1,5-dibromopentane, or 1,6-dibromohexane were chosen as the quaternization cross-linker to quaternize the imidazole or pyridine moieties, leading to the formation of cross-linking and ionic network. Transmission electron microscopy (TEM), dynamic and static light scattering (DLS & SLS), electrophoretic light scattering (ELS), and UV-visible spectroscopy were used to systematically investigate the sizes, morphologies, and properties of the obtained microgels. The sizes, swelling properties, and uniformity of microgels could be tuned by selecting proper quaternization cross-linking reaction temperature and cross-linkers. The obtained ionic microgels showed capability to adsorb the heavy metal salts like K2Cr2O7 in aqueous solution via the anion exchange reactions. It was also demonstrated that other functional groups could be introduced into the microgel networks if the unquaternized moieties were available.