Patent ID: 8012539

Claim:
A process for preparing sulfonated block polymers, comprising the steps of: (a) providing a precursor block copolymer having at least two end blocks A and at least one interior block B, wherein each A block is a polymer block resistant to sulfonation and each B block is a polymer block susceptible to sulfonation; (b) reacting the precursor block polymer with a C2 to C8 acyl sulfate in a reaction mixture further comprising at least one non-halogenated aliphatic solvent to form a sulfonated block polymer, therein resulting in the formation of a solution of a sulfonated block copolymer and a residual carboxylic acid; and (c) subsequently reacting the residual carboxylic acid contacted with a C1 to C4 alcohol or mixture thereof in a molar ratio of alcohol to residual carboxylic acid of at least 0.9:1 to form the corresponding alkyl esters of the carboxylic acid and to reduce the residual level of the organic residual acid to less than 2.0 wt % based on the total weight of the solution, wherein the reaction mixture is free of any halogenated solvent.