We investigated the effects of solvent type (mono-ester vs. di-ester solvent) and aging on the structural development in the poly(vinyl chloride)/butyl benzoate (PVC/BB) and PVC/dibutyl phthalate(DBP) gels, as well as on their viscoelastic and mechanical behaviors. It was found that aged PVC/DBP gels held at RT for 7 days exhibit an improvement of about 100% in storage modulus (G') compared to fresh gels, with a sudden drop in G' around 50 degrees C, whereas the storage moduli of the PVC/BB gels decrease monotonically with temperature, irrespective of the postaging time. These different behaviors of the PVC/BB and PVC/DBP gels arise mainly because of the difference in the network structure produced by the formation of the polymer-solvent complex between the C = O groups of the solvent and the polarized hydrogen moieties of PVC, as was confirmed with small angle X-ray scattering and uniaxial tensile experiments. (C) 2007 Wiley Periodicals, Inc.