Polymer blends comprising a polystyrene-block-polybutadiene-block-polystyrene (SBS) block copolymer and atactic homopolystyrene (hPS) were investigated using injection molded and solution cast samples. The morphology of the materials was studied by means of transmission electron microscopy (TEM) and scanning force microscopy (SFM). Dynamic mechanical analysis (DMA) was used to characterize the phase behavior and the morphology formation of the block copolymer as well as of the SBS/hPS blends. The glass transition temperatures seem to strongly depend on the homogeneity of the corresponding phases. A distinct difference was found between the morphologies of the blends prepared by different methods. While the SBS block copolymer always shows a lamellar morphology in injection molded or as-cast samples, the injection molded blends show a disturbance in the morphology consisting of alternating layers. In contrast, in the case of as-cast samples, added hPS forms polystyrene domains dispersed in a matrix of the pure block copolymer. Regarding the change in the glass transition temperature, in the effective volume and in the interfacial volume obtained from DMA curves, the morphology formation of the injection molded samples (pure SBS block copolymer and the corresponding blends) was investigated. Two different structural models for the blends are proposed. (C) 2004 Society of Plastics Engineers.