Poly(pyridylene/phenylene-ethynylene) polymers of controlled rigidity/flexibility were synthesized and used as molecularly dispersed reinforcing components in ionomer blends with partially sulfonated polystyrene. Homogeneous ionomer blends were formed due to acid-base interactions between the two blend components. The complete protonation of the poly(pyridylene/phenylene-ethynylene) in the acid/base ionomer blends has been proven by UV-VIS absorption and emission spectroscopy. Furthermore, the complete miscibility of the blend components in the ionomer blends was revealed from DSC analysis and transmission electron microscopy. The mechanical properties of the synthesized ionomer blends were determined by stress-strain measurements. The Young modulus of the blends was found to systematically vary with the rigidity/flexibility of the reinforcing polymer i.e. the molecular conformation of the reinforcing polymers as determined by small angle X-ray scattering. (C) 2004 Elsevier Ltd. All rights reserved.