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 H2OThese 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
Polystyrene sulfonates are useful because of their ion exchange properties. 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. Water softening
Water softening is achieved by percolating hard water through a bed of the 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. Other uses
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 its acid form, the resin is used as a solid acid catalyst in organic synthesis. == References ==
Parapsoriasis refers to one of a group of skin disorders that are characterized primarily by their resemblance to psoriasis (red, scaly lesions), rather than by their underlying cause. Neoplasms can develop from parapsoriasis. For example, it can develop into cutaneous T-cell lymphoma. The word "parapsoriasis" was formed in 1902. Classification
The parapsoriasis groups, described and debated for nearly a century, has spawned a confusing nomenclature. There are some authors who prefer to limit the term "parapsoriasis" to large- and small-plaque variants only. However, the following classification scheme is now generally accepted:: 450 
Large-plaque parapsoriasis
Small-plaque parapsoriasis
Pityriasis lichenoides
Pityriasis lichenoides chronica
Pityriasis lichenoides et varioliformis acuta
Lymphomatoid papulosis

See also
Poikiloderma vasculare atrophicans
List of cutaneous conditions

References


== External links ==