We report on multiblock copolymers consisting of highly sulfonated hydrophilic poly(arylene sulfone) (SPAS) blocks combined with hydrophobic poly(arylene ether sulfone) (PAES) blocks. Thiol-terminated precursor blocks of sulfonated poly(arylene thioether sulfone) (SPATS) were first prepared via polycondensations involving a novel tetrasulfonated dichlorotetraphenyldisulfone monomer, followed by coupling with pentafluorophenyl end-capped PAES precursor blocks under mild conditions to form SPATS-PAES block copolymers. The thioether bridges of the SPATS blocks were then selectively oxidized to obtain the SPAS-PAES copolymers with hydrophilic blocks containing exclusively sulfone bridges. Thus, the SPAS blocks were designed for high chain stiffness and stability toward desulfonation and had an ion exchange capacity (IEC) of 4.2 mequiv g(-1). Membranes of the SPAS-PAES copolymers were phase separated on the nanoscale and showed an increased thermal stability and decreased water uptake in relation to the corresponding SPATS-PAES membranes. Meta-connectivity in the sulfonated blocks gave slightly higher water uptake than pure para-connectivity. At 80 degrees C and 30% relative humidity, the proton conductivity of a SPAS-PAES membrane with an IEC of 1.8 mequiv g(-1) reached 5.1 mS cm(-1), which was comparable to that of Nafion and far exceeded that of a sulfonated statistical copolymer membrane with a similar IEC. This class of block copolymers possesses very attractive properties and has great prospective to meet the demands of various electrochemical applications.