The mechanical properties of Nafion (R) membranes that were degraded after periods of open circuit voltage (OCV) conditions in a fuel cell were studied. Severe decreases in membrane modulus and ductility at 80 degrees C and 100% relative humidity were observed. Stress-at-break values for 45 and 72 h degraded membrane-electrode assemblies (MEAs) were 6 and 9 times lower, respectively, while strain-at-break was 24 and 28 times lower, respectively, than that of a control MEA. Contractile stresses developed in constrained hydrated membranes that were then dried were conducted as a function of drying time. A pre-OCV degraded MEA, when subjected to creep deformation at 10 MPa, showed surface cracks which were not present in the control MEA. The 72 h-degraded MEA exhibited wider cracks than those of the 45 h-degraded MEA sample. Spectroscopic analysis of degraded membranes showed various small molecule fragments associated with side chain degradation. (C) 2010 Elsevier B.V. All rights reserved.