Entangledlike chain dynamics in nonentangled polymer blends with large dynamic asymmetry

We discuss simulations of a simple model for polymer blends in the framework of the Rouse model. At odds with standard predictions, large dynamic asymmetry between the two components induces strong nonexponentiality of the Rouse modes for the fast component. Despite chains being much shorter than the entanglement length, it also induces dynamic features resembling a crossover to entangledlike chain dynamics. This unusual behavior is associated with strong memory effects which break down the assumption of time uncorrelation of the external forces acting on the tagged chain.