Viscoelastic Properties of Miscible Poly(methyl methacrylate)/Poly(styrene-co-acrylonitrile) Blends in the Molten State

Dynamic viscoelastic properties for three kinds of miscible blends of poly(methyl methacrylate) (PMMA) and poly(styrene- co -acrylonitrile) (SAN) have been measured. 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 a T = −8.86( T − T s )/(101.6 + T − T s ). The T s increases linearly with an increase in the weight fraction of PMMA. The zero-shear viscosity versus blend composition curves deviate positively from linear additivity for the blends at both constant temperature and free volume fraction. The plateau modulus, determined as the storage modulus G ‘ in the plateau zone at the frequency where tan δ is at a minimum, varies linearly with blend composition for the PMMA-7 ( M w = 7.2 × 10 4 )/SAN-18 ( M w = 11.6 × 10 4, AN = 18.4 wt %) and PMMA-7/SAN-27 ( M w = 8.4 × 10 4, AN = 27.0 wt %) blends, but concavely with the blend composition for the PMMA-60 ( M w = 59.3 × 10 4 )/SAN-18 blends. It is considered that the above method to determine the plateau modulus cannot be applicable for the PMMA-60/SAN-18 blends, because of the great difference in the concentration of entanglements. It is concluded that the relaxation behavior of the PMMA/SAN blends is similar to that of a blend consisting of homologous polymers, and the entanglement molecular weights in PMMA/SAN blends are identical with those in the component polymers.