A series of novel partially fluorinated statistical (ABAC type) co-poly(arylene ether sulfone)s on the basis of decafluorobiphenyl (DFBP, monomer A) and different mole fractions of 2,2-bis(4-hydroxyphenyl)hexafluoropropane (BHPHFP, monomer B, x= 0, 0.25, 0.50, 0.75, 1,00, x = mole fraction of BBFHFP) and 2,2-bis(4-hydroxyphenyl)sulfone (BHPS, monomer C,y= 1-x,y = mole fraction of BHPS) has been prepared and characterised by H-1, C-13 and F-19 NMR spectroscopy, gel permeation chromatography (GPC) and thermogravimetric analysis (TGA). All statistical (ABAC type) co-poly (arylene ether sulfone)s were sulfonated by fuming sulfuric acid (65% sulfur trioxide) and used for acid-base blending with polybenzimidazole (PBI). The comparison of these PBI blend membranes among one another and with those of the corresponding homo-polymers (x = 0, 1.0) revealed that the water uptake and proton conductivity of the PBI blend membranes can be controlled by the ratio of the two different bisphenol monomers (BHPHFP/ BM;), whereof the specific resistance decreases and the water uptake increases with increasing content of BHPS. (C) 2007 Elsevier B.V. All rights reserved.