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The influence of the extrusion process on the morphology and micromechanical behavior of an asymmetric polystyrene‐block‐(polystyrene‐co‐butadiene)‐block‐polystyrene (SBS) star block copolymer and its blends with general‐purpose homopolystyrene (hPS) was studied with films prepared with a single‐screw extruder. The techniques used were transmission electron microscopy and uniaxial tensile testing. Unlike the pure SBS block copolymer possessing a gyroid‐like morphology, whose deformation was found to be insensitive to the processing conditions, the mechanical properties of the blends strongly depended on the extrusion temperature as well as the apparent shear rate. The deformation micromechanism was primarily dictated by the blend morphology. The yielding and cavitation of the nanostructures were the principal deformation mechanism for the blends having a droplet‐like microphase‐separated morphology, whereas cavitation dominated for the blends containing macrophase‐separated layers of polystyrene. The mechanical properties of the blends were further examined with respect to the influence of the temperature and shear rate on the phase behavior of the blends. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007 [ABSTRACT FROM AUTHOR]