VISCOELASTIC EFFECTS ON THE EARLY STAGES OF PHASE-SEPARATION IN POLYMER BLENDS

We modify the Cahn-Hilliard theory of concentration fluctuation dynami cs to account for the short-time networklike nature of high molecular weight polymers. We propose an additional term in the free energy, due to elastic energy arising from the finite lifetime of entanglements. If we assume a single-exponential decay time for the entanglements, th e equation of motion is governed by two exponential modes. For quenche s into the two-phase region, the faster mode always decays with time, and the slower mode grows. The theory successfully accounts for data f rom spinodal decomposition of polymer blends containing at least one c omponent of very high molecular weight.