Morphologies of PBS/PBA blends varying in blend ratio at different crystallization temperatures of PBS component were studied using optical and atomic force microscopies. It was found that interspherulitic phase segregation of PBA takes place at high temperature, e.g. 100 degrees C, for all blend compositions due to the high diffusion length. On the contrary, no interspherulitic phase segregation of PBA at 75 degrees C occurs at all, consistent with a shorter diffusion length. It was further found that the PBA melt acted as a diluter, affecting the morphology of PBS, which in turn influenced the phase separation behavior of PBA remarkably. At 100 degrees C, with increasing PBA concentration, the resultant open structure of PBS caused by the diluting effect of the PBA melt makes it necessary to retain some portion of the PBA melt between the PBS lamellae. This leads to the concurrence of interlamellar and interspherulitic phase segregations. An even higher PBA content results in the occurrences of all three phase separation options, i.e. interlamellar, interfibrillar and interspherulitic phase segregations. At 75 degrees C, in blends with PBA as a minority phase, mainly interlamellar segregation of PBA occurs. For a 50/50 blend, interlamellar and interfibrillar phase segregations take place simultaneously. For a PBA in-rich blend, PBS forms only a spherulitic framework, filled in with the PBA lamellar crystals, indicating that interfibrillar mode is the main phase separation process. (C) 2008 Elsevier Ltd. All rights reserved.