POLYMER DYNAMICS IN BINARY BLENDS

We develop a theory of the dynamics of flexible linear polymers in a melt composed of macromolecules of two molecular weights and of the same chemical species. A polymer is represented by a freely jointed chain that moves by two dynamical processes. The first is a local jump motion that may be blocked by obstacles, and the second is a slithering mode that mimics reptation. The dynamics of the obstacles are determined self-consistently by an ansatz that associates their relaxation with the dynamics of the slowest mode of conformational relaxation of a chain. The calculations of the autocorrelation function of the end-to-end vector and of the mean squared displacement of the center of mass are related exactly to the solution of a random walk problem with dynamical disorder. We calculate the necessary random walk propagator by applying the dynamical effective medium approximation. Calculations of the dependence of the self-diffusion coefficient of both components on blend composition and on molecular weights are presented. The theory is shown to provide a unified description of diffusion in the unentangled and entangled regimes.