Fabrication of recast Nafion (R)-117 membrane using the dipolar aprotonic solvent will normally lead to a random matrix. On the contrary, when a designed amount of vinyl-pendant octasiloxane (Q(8)M(8)(v)) cubic molecules was included into the Nafion (R) matrix during the recasting process and then subjected to polymerization, a nonrandom matrix was obtained. This paper provides an insight into the matrix-formatting role of rigid poly(Q(8)M(8)(v)) blocks, generated in situ in Nafion (R) matrix, according to thermal analyses (thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA) and Differential Scanning Calorimetry (DSC)) and electron microscopic images of the resulting composite matrix. The P(Q(8)M(8)(v)) played a role in restricting random extensions of proton-conducting channels (PCCs) and promoted ordered assembling of NafionO molecules. As a result, compared with the recast pristine NafionO membrane, the composite membranes containing P(Q(8)M(8)(v)) of 5-15 wt.% manifested obvious improvement on both repression of methanol permeability and promotion of power density output of the single direct methanol fuel cell (DMFC). (C) 2008 Elsevier B.V. All rights reserved.