A novel series of naphthalene-based poly(arylene ether ketone) copolymers containing methoxy groups and hexafluoroisopropylidene diphenyl moieties (6F-MNPAEK5) were successfully synthesized by aromatic nucleophilic polycondensation. Chain-type fluorinated and sulfonated naphthalene-based poly(arylene ether ketone) copolymers (6F-SNPAEKs) were subsequently synthesized by demethylation and sulfobutylation. The chemical structures of 6F-SNPAEKs were confirmed by H-1 NMR. The 6F-SNPAEKs in acid form showed excellent thermal stability at elevated temperatures. The 6F-SNPAEK membranes were easily obtained by solution casting and properties for fuel cells were investigated in detail. The water uptake, swelling ratio and proton conductivity increased with degree of sulfonation (DS) and temperature. 6F-SNPAEK-90 showed the highest conductivity of 0.181 S cm(-1) at 80 degrees C. The methanol permeability of the membranes was in the range of 0.238-6.49 x 10(-7) cm(2) s(-1), compared to 1.55 x 10(-6) cm(2) s(-1) for Nation 117. The membranes also showed excellent mechanical properties: the elongation at break was greater than 15%. These results indicate that the 6F-SNPAEK membranes are a promising candidate for use in direct methanol fuel cell (DMFC) applications. (C) 2012 Elsevier Ltd. All rights reserved.