Various molecular weights of poly(propylene oxide) diamines oligomers/Nafion (R) acid-base blend membranes were prepared to improve the performance of Nafion (R) membranes in direct methanol fuel cells (DMFCs). The acid-base interactions were studied by Fourier transform infrared spectroscopy (FT-IR) and differential scanning calorimetry (DSC). The performance of the blend membranes was evaluated in terms of methanol permeability, proton conductivity and cell performance. The proton conductivity was slightly reduced by acid-base interaction. The methanol permeability of the blend D2000/Nafion (R) was 8.61 x 10(-1) cm(2) S-1, which was reduced 60% compared to that of pristine Nafion (R). The cell performance of D2000/Nafion (R) blend membranes was enhanced significantly compared to pristine Nafion (R). The current densities that were measured with Nafion (R) and 3.5 wt% D2000/Nafion (R) blend membranes were 62.5 and 103.5 mA cm(-2). respectively, at a potential of 0.2 V. Consequently, the blend poly(propylene oxide) diamines oligomers/Nafion (R) membranes critically improved the single-cell performance of DMFC. (C) 2008 Published by Elsevier B.V.