Poly(pyridyl/phenyl-ethinylene) polymers of tuned rigidity/flexibility were synthesized and their molecular conformations in solution determined by small-angle X-ray scattering. These polymers were used as molecularly dispersed reinforcing components in ionomer blends with partially sulfonated polystyrene. Homogeneous ionomer blends were formed by acid-base interactions between the two blend components. Small-angle X-ray scattering revealed that in the case of rodlike or semiflexible poly(pyridyl/phenyl-ethinylenes) an elongation-induced orientational ordering is obtained. However, blend samples prepared with flexible poly(pyridyl/phenyl-ethinylene) polymers do not show any observable orientation. The orientation parameter varied systematically with the rigidity/flexibility of the reinforcing component, as did the Young modulus determined from stress-strain measurements.