Molecular dynamics simulation of reactive compatibilization of polymer blends

Molecular dynamics simulations of reactive compatibilization of polymer blends are performed for a wide range of chain lengths and densities of reactive groups ρ_o. We directly observe the predicted diffusive growth as well as the saturation at later times. The crossover to the saturation regime is consistent with theoretical predictions. There is also a separate transition from second to first-order reaction kinetics. However, the crossover to first-order kinetics does not agree with predictions. Although a depletion layer builds up on a time scale ∝ ρ_o^-2, we find that, for times less than the Rouse time τ_g, the copolymer per area is a function only of tρ_o³ for a wide range of ρ_o implying an additional crossover time scale which scales as ρ_o^-3. The interface is unstable at later times for sufficiently large ρ_o. The surface tension vanishes before the interface roughens showing that the instability is initiated mainly by the vanishing surface tension. The time required for the surface tension to vanish scales as ρ_o^-3. A dilute limit model is introduced to study the behavior for small ρ_o. In this limit, ∑(t) grows linearly with time asymptotically and the reaction rate is a slowly decreasing function of Z in agreement with theoretical predictions. For times less than τ_g there is a logarithmic correction to the linear growth.