Structural-rheological behavior of binary polymer blends at the phase separation point

Features of the variation of structure and rheological properties of polymer blends in the vicinity of the point of phase separation are considered. The phase diagrams of polymer blends are characterized by the presence of an extended region of metastable states between the binodal and spinodal curves. This feature reflects a dual character of the polymer structure in these systems, with significantly different kinetic units-macromolecules and chain segments-involved in the liquid-liquid phase transition. The transient, incomplete character of the supermolecular structure of polymer blends at the phase separation point accounts for a sharp minimum of viscosity and the extremal character of variation of the other properties, as well as for a strong dependence of the phase transition temperature on the shear stress, molecular mass distribution, relaxation time, and some other factors.