VISCOELASTIC PROPERTIES OF BLENDS OF POLY(ACRYLONITRILE-CO-STYRENE) AND POLY[STYRENE-CO-(N-PHENYLMALEIMIDE)]

Dynamic viscoelastic properties for miscible polymer blends of poly[styrene-co-(N-phenylmaleimide)] (SMI) and three kinds of poly(acrylonitrile-co-styrene)s (AS) with the same composition but different molecular weights (AS-2, AS-3, and AS-4, in increasing molecular weight) are measured by using a concentric cylinder-type rheometer. It is found that the time-temperature superposition principle can be applied over the entire temperature range for the blends. The temperature dependence of the shift factors can be expressed by the WLF equation log aT = -8.86(T - Ts)/(101.6 + Τ - Τs). The Ts and, in other words, the glass transition temperature of the blends increase linearly with an increase in the mole fraction of SMI. The zero-shear viscosities at constant temperatures increase concavely with the SMI content for SMI/AS-2, have a minimum at 20 wt % SMI for SMI/AS-3, and hardly depend on the SMI content for SMI/AS-4. When compared at the same free volume fractions, the zero-shear viscosities decrease convexly with SMI content for all blends. Such compositional dependences of the zero-shear viscosities can be interpreted by the change in the number of entanglement couplings, without any change in each entanglement molecular weight in the component copolymers. It means that the relaxation behavior of the miscible SMI/AS blends is similar to that of a blend consisting of homologous polymers with different molecular weights. It is emphasized that the viscoelastic functions of miscible blends should be compared at the isofree volume condition. © 1990, American Chemical Society. All rights reserved.