Two series of poly(ether ether ketone)-block-poly(ether sulfone) (PEEK-b-PES) polymer precursors are successfully synthesized via two-step aromatic nucleophilic polycondensation reactions. Corresponding sulfonated PEEK-b-PES copolymers are prepared by the direct postsulfonation of the PEEK-b-PES precursors, and the activated methoxy groups enable the sulfonation occurrence on the PEEK segments. The degrees of sulfonation are evaluated by (1)H NMR spectroscopy and titration. All the membranes exhibit excellent thermal and dimensional stability, high proton conductivity and low methanol permeability. At 80 degrees C. the higher proton conductivities (>0.20 S cm(-1)) of the block polymers can be obtained in comparison with Nafion 117 (0.17 S cm(-1)). The methanol permeability values of the obtained membranes are in the range of 0.63-9.60 x 10(-7) cm(2) s(-1), which are much lower than the value of Nafion 117 (2.94 x 10(-6) cm(2) s(-1)). The TEM images of the block polymer membranes exhibit obvious phase separation morphology between ionic domains and hydrophobic domains. All the data prove that these block membranes obtained by the postsulfonation of block polymer precursors may be potential proton exchange membrane for fuel cells applications. (C) 2011 Elsevier B.V. All rights reserved.