Increasing hydrophobicity multiblock copolymers were synthesized by altering the copolymer composition of the hydrophobic segments. A series of nitrile-containing hydrophobic oligomers consisting of bisphenol A (Bis A), dimethylbisphenol A (DMBPA), and tetramethylbisphenol A (TMBPA) moieties were reacted with a disulfonated poly (arylene ether sulfone) hydrophilic segment to form the multiblock copolymer series. H-1 and F-19 NMR spectroscopy were used to monitor the progress of the copolymerization reactions and confirm the desired compositions. Membranes cast from the resultant multiblock copolymers had high molecular weight as measured by size-exclusion chromatography (SEC), and showed strong mechanical properties. As the hydrophobicity of the polymers increased from the Bis A, to the DMBPA, and to the TMBPA systems, the membranes showed a corresponding decrease in water uptake. The reduced water uptake and limited fluorine content produced membranes with significantly reduced methanol permeabilities over that of Nafion or other similar multiblock copolymer membranes. Electrochemical testing showed that the more hydrophobic TMBPA systems showed improved performance at higher methanol concentrations. (C) 2014 The Electrochemical Society.