Influence of phase separation on the linear viscoelastic behavior of a miscible polymer blend

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Abstract
The influence of phase separation on the linear viscoelastic response has been studied in miscible blends of polystyrene and poly(vinyl methyl ether) with a lower critical solution temperature near 110 °C. At temperatures between 25 and 155 °C, and for compositions in the range 20% to 60% polystyrene, the complex moduli G’ and G‘ were measured at frequencies in the range of 0.01 to 100 rad/s. Time–temperature superposition was applied in the single phase region to obtain the complex modulus over eight decades of frequency. Increasing the polystyrene content resulted in an increase in the zero‐shear viscosity and a shift of the terminal behavior to lower frequencies or longer times. The phase separation above the lower critical solution temperature was measured as a sudden increase in the fluorescence intensity of an anthracene‐labeled polystyrene (approximately 1 wt % in the blend), using an optical probe in the rheometer fixture. For the 20/80 and 40/60 PS/PVME samples, the terminal zone was in the accessible frequency window and phase separation was accompanied with a large increase in G’ and G‘. In contrast, the complex modulus of the 60/40 PS/PVME blend could not be measured near the terminal zone and the G’ and G‘ did not exhibit any significant changes near the phase transition temperature.

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