Multiblock copolymers 1a (M-n = 31,500-47,400) of sulfonated poly(aryl ether)s were synthesized by polycondensation of 4,4'-difluorobenzophenone (DFBP), bis(4-hydroxyphenyl)sulfone (BHPS), and an hydroxy-terminated sulfonated oligomer, which was synthesized from DFBP and 2,2',3,3',5,5'-hexaphenyl-4,4'-dihydroxybiphenyl a. The copolymerization of trimeric monomer b with DFBP and BHPS gave a series of copolymers 1b (M-n = 26,200-45,900). The copolymers were then sulfonated with chlorosulfonic acid to give ionomers 3a with hydrophilic multiblock segments and ionomers 3b with segments containing clusters of 18 sulfonic acid groups. The proton exchange membranes cast from ionomers 3a and 3b were characterized with regard to thermal stability, water uptake, proton conductivity, and morphology. Transmission electron microscopy images of 3a-1 and 3b-1 revealed a phase separation similar to that of Nafion that may explain their higher proton conductivities compared with randomly sulfonated copolymers. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4762-4773, 2009