Study on rheological behavior of polystyrene‐polyisoprene‐polystyrene around viscous flow transformation: Effect of polystyrene block content and molecular weight

Abstract The flow behavior of triblock copolymer polystyrene‐polyisoprene‐polystyrene (SIS) was different below and above the viscous flow transition temperature ( T f ). The study investigated the relationship between molecular structure (molecular weight and polystyrene block content) and the macroscopic rheological properties of SIS melt around T f via capillary rheometer. The results indicated that below the T f , shear viscosity of SIS melt was controlled by the polystyrene (PS) block content. On the other hand, above the T f , shear viscosity was controlled by molecular weight. The rheological phenomena were explained based on the state change of the PS domains below and above T f . The effect of PS block content on the viscous flow activation energy ( E η ) and pressure drop of SIS melt was also investigated.