Polystyrene sulfonic acid, the acid whose salts are the polystyrene sulfonates, has the idealized formula {{chem2|(CH2CHC6H4SO3H)_{
n} }}. The material is prepared by
sulfonation of
polystyrene: :{{chem2|(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: :{{chem2|(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 styrene sulfonates has been reported, leading to well defined linear polymers, as well as more complicated molecular architectures. ==Chemical uses==