Toward the design of superabsorbent materials for non-polar organic solvents and oils: ionic content dependent swelling behaviour of cross-linked poly(octadecyl acrylate)-based lipophilic polyelectrolytes

Oil spills and other industrial chemical leaks to natural environments can cause long-term impact on ecosystems, and the use of polymer-based absorbent materials for such media is a promising technique for cleaning up contaminated sites. Here, we prepared a set of poly(octadecyl acrylate)-based lipophilic polyelectrolyte gels bearing tetraalkylammonium tetrakis(3,5-bis(trifluoromethyl)phenyl) borate (TFPB) with different contents of the ionic groups from 1.0 mol% (EG18(1%)) to 10 mol% (EG18(10%)), and investigated their swelling behaviours in organic solvents and oils. The swelling degrees of the polymer gels in non- or less-polar media (3 < epsilon < 14) increased both with increasing the contents of TFPB salt on the polymer chain and increasing the dielectric constants of the solvents. The swelling degrees of EG18(10%) in dichloromethane and 1,2-dichloroethane showed over 300 times as much as its dry weight. In nonpolar media (epsilon < 3) such as toluene and hexane, however, EG18(10%) collapsed and showed low swelling degrees owing to their low dielectric constants. But, the addition of ethanol (epsilon = 24.6) to them increased the solvent polarities as mixtures, resulting in the high swelling degrees over 100 times by polyelectrolyte effects. The lipophilic polyelectrolyte gels could find applications as protective barriers for volatile organic compounds (VOCs) spilled in the environment and as absorbents for waste oil.