A pre-cursor block copolymer for sulfonation which, prior to hydrogenation, has the general configuration A-B-A, A-B-A-B-A, (A-B-A)nX, (A-B)nX, A-D-B-D-A, A-B-D-B-A, (A-D-B)nX, (A-B-D)nX or mixtures thereof, wherein A, B and D blocks do not contain any significant levels of olefinic unsaturation. Each A and D block is a polymer block resistant to sulfonation, and each B block is a polymer block susceptible to sulfonation. Each A block is a segment of one or more polymerized para-substituted styrene monomers, each B block contains segments of one or more vinyl aromatic monomers selected from polymerized (i) unsubstituted styrene monomers, (ii) ortho-substituted styrene monomers, (iii) meta-substituted styrene monomers, (iv) alpha-methylstyrene, (v) 1,1-diphenylethylene, (vi) 1,2-diphenylethylene and (vii) mixtures thereof, and each D block contains polymers having a glass transition temperature less than 20° C. and a number average molecular weight of between 1,000 and 50,000.