Abstract Today, the use of immiscible polymer blends is ubiquitous, nevertheless the principal technical hurdle to developing a novel blend material remains the effective compatibilization of the interface. In order to be effective, the compatibilizer must locate at the interface of the phases, saturate the interface, occupy an optimal interfacial areal density (number of modifier molecules per unit area of interface), Σ, and possess an optimal molecular weight to ensure an appropriate level of entanglement. This work examines these issues by considering the results of numerous papers published by this laboratory over the years. It will be shown that a general relationship exists between Rg, the radius of gyration or Mn, the molecular weight of the interfacial modifier, and Σ of interfacial modifier at interfacial saturation using data from a wide range of systems. The results reported here indicate very little stretching of the modifier molecules at the interface for these systems. The obtained master curve can be used to generally predict the critical concentration required for interfacial saturation for a wide range of systems.