Asymmetric PS-block-(PS-co-PB)-block-PS block copolymers: morphology and deformation behavior of star block copolymer/PS blends

The morphology and deformation behavior of blends comprising an asymmetric styrene/butadiene star block copolymer and polystyrene homopolymer (hPS) were investigated by means of transmission electron microscopy (TEM) and uniaxial tensile testing. The hPS samples used had a wide range of molecular weights. In spite of the high polystyrene (PS) content, the star block copolymer exhibited a morphology consisting apparently of a rubbery matrix, attributable to its asymmetric architecture and presence of polystyrene/polybutadiene random copolymer (PS-co-PB) as soft rubbery blocks. In the blends, depending on the molecular weight and modality of the added hPS and on the composition of the mixtures, different morphologies (ranging from microphase-separated and macrophase-separated ones to a combination of both of them) were observed. Consequently, it was possible to tailor the tensile mechanical properties based on the nature of the nanoscopic morphology of the star block copolymer/PS blends. Copyright (c) 2005 John Wiley T Sons, Ltd.