|Systematic (IUPAC) name|
|Trade names||Sodium salt: Kayexalate, Kionex, Resonium A, sodium polystyrene sulfonate
Calcium salt: Calcium Resonium, Sorbisterit, Resikali, Calcium Resonium, Sorbisterit, Resikali
|Routes||Oral, retention enema|
|(what is this?)|
Polystyrene sulfonates are polymers derived from polystyrene but containing sulfonic acid or sulfonate functional groups. The linear polymer is white when very pure and is water-soluble. The crosslinked material (called a resin) does not dissolve in water and typically appears amber in color. These polymers are classified as polysalts and ionomers. They are widely used to remove ions from a solution in technical or medical applications.
Production and chemical structure
- (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.
Alternative sulfonation methods
Double substitutions of the phenyl rings are known to occur, even with conversions well below 100%. Crosslinking reactions are also found, where condensation of two sulfonic acid groups yields a sulfonyl crosslink. On the other hand, the use of milder conditions such as acetyl sulfate leads to incomplete sulfonation. Recently, the atom transfer radical polymerization (ATRP) of protected styrenesulfonates has been reported, leading to well defined linear polymers, as well as more complicated molecular architectures.
Water softening is achieved by percolating hard water through a bed of sodium form of cross-linked polystyrene sulfonate. The hard ions such as calcium (Ca2+) and magnesium (Mg2+) adhere to the sulfonate groups, displacing sodium ions. The resulting solution of sodium ions is softened.
For medical applications, polystyrene sulfonate is usually supplied in the sodium and calcium form. Its use is indicated as potassium binders in acute and chronic kidney disease for patients suffering from hyperkalaemia (abnormal high blood serum potassium levels), which may, e.g., result in weakness or irregular heartbeat. Excess blood potassium also arises due to digoxin toxicity, although there is concern about possible side effects when it is mixed with sorbitol.
Polystyrene sulfonates are administered orally (with a meal) or rectally, by retention enema. In the large intestines, potassium derived from food is exchanged for sodium or calcium ions, respectively. Finally, the indigestible potassium polystryene sulfonate complex is excreted with the feces, preventing the absorption of potassium into the blood stream. Hence, the serum potassium level decreases.
Intestinal disturbances are common, including loss of appetite, nausea, vomiting, and constipation. In rare cases, it has been associated with colonic necrosis. Changes in electrolyte blood levels may occur such as hypermagnesemia, hypercalcemia, and hypokalemia.
Sodium polystyrene sulfonate is used as a superplastifier in cement, as a dye improving agent for cotton, and as proton exchange membranes in fuel cell applications. In their acid form, the resin is used as a solid acid catalyst in organic synthesis.
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