AbstractThe flow properties of saturated rubber‐modified polymer melts were studied using a capillary rheometer. The two‐phase polymer consists of styrene–acrylonitrile copolymer as matrix and ethylene–vinyl acetate copolymer (EVA) as rubber component. When the rubber concentration increases, melt viscosity of the polymer increases appreciably and activation energy for the viscous flow decreases. When the degree of grafting of EVA rubber increases, melt viscosity of the polymer increases, but activation energy is nearly constant at a given shear rate. It is shown that the superposition principle of shear rate–temperature is applicable to polymer containing from 0 to 12 wt‐ rubber at a temperature from 180 to 280°C and that the superposition principle of shear rate–concentration is also applicable only in the shear rate range of above 70 sec−1. Die swell ratio decreases monotonically with increasing rubber concentration. A master curve is obtained for the reduced variables of die swell ratio and shear rate using the method described by Petraglia et al. Assuming the polymer melt as a generalized Maxwell body, relaxation spectra were evaluated from die swell ratio and dependence of viscosi
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