Importance of Molecular Coupling for Mechanical Performance of Block Copolymer Compounds

Abstract

AbstractMixtures of polystyrene‐block‐polyisoprene‐block‐polystyrene (SIS) triblock copolymer and various styrenic block copolymers (having diblock and triblock architectures) as well as polystyrene homopolymer (PS) were prepared via solution blending to determine the influence of molecular coupling on the large strain mechanical performance of the block copolymers. The techniques used were transmission electron microscopy (TEM) as well as scanning electron microscopy (SEM) for the morphological characterization and uniaxial tensile testing for the determination of mechanical properties. In the block copolymer blends, it was possible to tailor the mechanical properties as long as the molecular coupling was present among the outer polystyrene blocks. The mechanical performance of the triblock copolymer was found to deteriorate by the presence of dangling chains in the microphase‐separated domains. In the blends comprising an SIS triblock copolymer and polystyrene homopolymers, the macrophase‐separated compounds containing PS having molar mass exceeding the entanglement molar mass showed the optimum mechanical properties. The observed mechanical behaviour has been correlated with the fracture surface morphology of the corresponding blends.