US Patent 7862983 Process for preparing stable photoresist compositions

A composition of matter consisting of a stable solution containing a polymer derived from a solution of a polymer containing trace metals, the derived method comprising the steps of:(a) providing a polymer solution containing a polymer, a first solvent and trace metals;(b) passing said polymer solution through an acidic cation ion exchange material to remove said trace metals therefrom and thereby forming a polymer solution containing free acid radicals;(c) precipitating said polymer from said polymer solution of step b by contacting with a second solvent wherein the polymer is substantially insoluble therein;(d) filtering said solution and said second solvent to thereby form a solid polymer cake; and(e) contacting said cake from step d with sufficient quantities of additional said second solvent in order to remove free acid radicals therefrom.