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Dynamic viscoelastic properties for miscible blends of poly(⑀-caprolactone) (PCL) and poly(styrene-co-acrylonitrile) (SAN) were measured. It was found that the time-temperature superposition principle is applicable over the entire temperature range studied for the blends. The temperature dependency of the shift factors a T can be expressed by the Williams-Landel-Ferry equation: log a T ϭ Ϫ8.86(T Ϫ T s )/(101.6 ϩ T Ϫ T s ). The compositional dependency of T s represents the Gordon-Taylor equation. The zero-shear viscosities are found to increase concavely upward with an increase in weight fraction of SAN at constant temperature, but concavely downward at constant free volume fraction. It is concluded that the relaxation behavior of the PCL/SAN blends is similar to that of a blend consisting of homologous polymers. It is emphasized that the viscoelastic functions of the miscible blends should be compared in the iso-free volume state.

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