Preparation of poly(ionic liquid) nanoparticles and their novel application as flocculants for water purification

Abstract

New methods for preparing polymeric nanoparticles are actively being investigated such as self-assembly of amphiphilic block copolymers, self-crosslinking of single-chain macromolecules, nanoprecipitation or emulsion–miniemulsion polymerizations. However, most methods require multi-step synthesis, controlled polymerization mechanisms and tedious purification processes. In this work, amphiphilic poly(ionic liquid) random copolymers that self-assemble into polymeric nanoparticles were prepared in water through a simple partial anion exchange process. This method was demonstrated for different cationic polyelectrolytes such as poly(1-vinyl-3-ethyl imidazolium bromide), poly(diallyldimethylammonium chloride) and poly(allylamine hydrochloride). Their partial anion exchange was conducted by the addition of lithium bis(trifluoromethanesulphonyl)imide to the aqueous solution of the polymer. It was found out that the amphiphilic poly(ionic liquid)s containing small amounts (1–10%) of bis(trifluoromethanesulfonimide) anion self-assemble into spherical nanoparticles as revealed by dynamic light scattering and transmission electron microscopy. The nanoparticle size ranged from 100 nm to 600 nm depending on the extent of partial anion exchange and the nature of the polyelectrolyte. As an application, the poly(ionic liquid) nanoparticles were used as flocculants for water purification. The use of amphiphilic poly(ionic liquid)s as flocculants enhanced the evolution rate of the sediment considerably in comparison with the parent polyelectrolytes.