Rheology and phase separation of poly(styrene-co-maleic anhydride)/poly (methyl methacrylate) blends

The effects of shear flow on the phase behavior of a polymer blend with high glass transition temperature, Tg, constituents and small dynamic asymmetry (T,g contrast) were investigated using shear and capillary rheometry, complemented by differential scanning calorimetry and analysis of the extrudates. This blend is a lower critical solution temperature mixture of a random copolymer of styrene and maleic anhydride, SMA, and poly(methyl methacrylate), PMMA. Both shear-induced mixing, at low and very high shear rates, and shear-induced demixing, at moderate shear rates, were observed. A way to detect and isolate the degradation effects, which are predominant in SMA at high temperatures, and result in opaque but not necessarily phase-separated samples, is also presented. The methodology presented here for the determination of the shear-phase diagram in a flowing polymer blend should be applicable to any industrial mixture, and it is of particular value for assessing the effects of strong shear flow, relevant in processing applications. Furthermore the method of solution preparation, i.e., solution-cast versus melt-mixed samples, did not affect the Theologically determined demixing temperatures. Finally, a simple general thermodynamic model within the framework of Flory's statistical mechanical lattice model is presented for predicting the shear-induced phase changes in polymer fluids. Theoretical predictions of the shear-induced phase diagrams agree reasonably well with selected experiments with the systems polystyrene/dioctyl phthalate and poly(styrene-comaleic anhydride)/poly(methyl methacrylate).Applied Science, Faculty ofChemical and Biological Engineering, Department ofGraduat