Patent ID: 8377515

Claim:
A process for preparing a membrane, comprising: (a) applying a fluid composition of sulfonated block copolymer, ester of residual carboxylic acid and non-halogenated aliphatic solvents onto the surface of a substrate, said fluid composition prepared by the steps of: i. 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; ii. 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 iii. 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, (b) spreading the fluid composition to form a uniform thickness layer on the substrate, and (c) allowing the solvent to evaporate from the fluid composition resulting in a solid membrane.