Phosphonium cation-containing polymers: From ionic liquids to polyelectrolytes

Phosphonium cation-based ionic liquids (ILs) are a readily available family of ILs that often offer superior properties compared to ammonium cation-based ILs. Recently investigated applications include extraction solvents, electrolytes in batteries and super-capacitors, and corrosion protection. At the same time, the range of cation–anion combinations available commercially has also increased in recent years. Polymerized ionic liquids and polyelectrolytes play major roles in a broad range of biological applications including antimicrobials, non-viral gene delivery, synthetic enzymes, metal chelation, and drug delivery. Ammonium- and phosphonium-containing macromolecules will be reviewed with a focus on structure–property relationships of these polyelectrolytes and ionic liquids. Phosphonium-containing macromolecules often display enhanced performance compared to ammonium analogs.