Polystyrene sulfonates are polymers derived from polystyrene by the addition of sulfonate functional groups. They are widely used as ion-exchange resins to remove ions such as potassium, calcium, and sodium from solutions in technical or medical applications.
Linear ionic polymers are generally water-soluble, whereas cross-linked materials (called resins) do not dissolve in water. These polymers are classified as polysalts and ionomers.
Polystyrene sulfonic acid has the idealized formula (CH2CHC6H4SO3H)n. The material is prepared by sulfonation of polystyrene:
(CH2CHC6H5)n + n SO3 → (CH2CHC6H4SO3H)n
Several methods exist for this conversion, which can lead to varying degree of sulfonation. Usually the polystyrene is crosslinked, which keeps the polymer from dissolving. Since the sulfonic acid group (SO3H) is strongly acidic, this polymer neutralizes bases. In this way, various salts of the polymer can be prepared, leading to sodium, calcium, and other salts:
(CH2CHC6H4SO3H)n + n NaOH → (CH2CHC6H4SO3Na)n + n H2O
These ion-containing polymers are called ionomers.
Polystyrene sulfonates release sodium or calcium ions in the stomach in exchange for hydrogen ions. When the resin reaches the large intestine the hydrogen ions are exchanged for free potassium ions; the resin is then eliminated in the feces. The net effect is lowering the amount of potassium available for absorption into the blood and increasing the amount that is excreted via the feces. The effect is a reduction of potassium levels in the body.
NaSS is widely used to improve dyeability of acrylic and polyester fibers. Other applications include reactive emulsifiers for water-borne coatings and anti-static agents for textiles, plastics, and papers. Fields of application include water treatment, photography and paper manufacturing.