The mechanical properties of polymer blends made from sulfonated polyetheretherketone and sulfonated and/or silylated polyphenylsulfone (PPSU) are reported. Elastical modulus and maximum strength of membranes increase strongly by addition of silylated PPSU, whereas sulfonated PPSU softens the materials. A correlation is established between the water uptake coefficient measured after immersion in water and the elastic modulus of the membranes. The relation with membrane swelling during fuel cell operation is discussed. (C) 2007 Elsevier B.V. All rights reserved.