We use a multiscale computational approach to study reactive compatibilization in an immiscible binary AB blend that contains A-like and B-like interacting molecules. These molecules are modeled as spherical particles that react at the A/B interface to form A-B dumbbells. Through these simulations, we investigate the reaction kinetics and interfacial morphology of the system as a function of time for different densities of reacting molecules and diffusivities of the dumbbells. The results provide insight into the factors that affect the structural evolution of the interface between the incompatible A and B domains. In particular, we find that for sufficiently high densities of reacting molecules, the initially flat interface is unstable at later times. The instability is initiated by a vanishing of the surface tension, but the amplification of the initial instability is determined by the Brownian motion of the dumbbells. The interfacial width (defined as the root-mean-square variation of the interfacial position) grows as t(1/2) and the domains form a lamellar structure at long times.(C) 2003 American Institute of Physics.