A novel functional poly(propylene oxide)-backboned diamine of M-w 400 (abbreviated as D400) was grafted with sulfonic acid (abbreviated as D400-PS) to improve the performance of Nafion((R)) membranes in direct methanol fuel cells (DMFCs). The interaction of the D400-PS with Nafion((R)) was studied by Fourier transform infrared spectroscopy (FT-IR) and differential scanning calorimetry (DSC). The performance of the blend Nafion((R))/D400-PS membranes was evaluated in terms of methanol permeability, proton conductivity and cell performance. The proton conductivity of the blend membrane was slightly reduced by rendering proton conductivity to D400 by functionalized with an organic sulfonic acid. The methanol permeability of the blend membrane decreased with increasing of D400-PS content. The methanol permeability of the blend Nafion((R))/D400-PS with the composition 3/1 (-SO3H/-NH2) was 1.02 x 10(-6) cm(2) S-1, which was reduced 50% compared to that of pristine Nafion((R)). The current densities 2 that were measured with Nafion((R))/D400-PS blend membranes in the ratio 1/0 and 5/1 (-SO3H/-NH2), were 51 and 72 mA cm(-2), respectively, at a potential of 0.2 V Consequently, the blend Nafion((R))/D400-PS membranes critically improved the single-cell performance of DMFC. (c) 2007 Published by Elsevier B.V.