Polymer blending offers an efficient strategy to develop materials with optimal properties superior to that of the components. By varying the polymers, their composition and processing routes, blends with a wide range of morphologies can be generated for tuning the final properties. Paradoxically, the inherent immiscibility of most polymers mandates their compatibilization to refine and stabilize the biphasic morphology. The classical strategy to improve the blends compatibility is the incorporation of premade block polymers.More recently, compatibilzation by nanoparticles has proven to be a successful alternative route. Here we describe a novel compatibilization strategy by employing novel compatibilizers, in particular short unentangled poly(styrene) (PS) polymers, in phase separating poly[(methyl styrene)-co-acrylonitrile]/poly(methyl methacrylate) (PMSAN/PMMA) blends or immiscible PS/PMMA blends. The compatibilization effectiveness of the PS polymers is assessed by in-situ characterization of the matrix-droplet morphology as a function of coalescence time using a flow-induced coalescence protocol. Below the entanglement molecular weight (Me), there is good compatibilization, discerned from the decrease in the interfacial tension and increase in the extent of coalescence suppression of the PMMA droplets in 85/15 PMSAN/PMMA and PS/PMMA blends. However, compatibilization significantly decreases if the molecular weight (Mw) of the PS polymers is increased above Me. The compatibilization effects are independent of the functionalization of the PS terminal groups and also hold when the compatibilizer has exactly the same chemical composition as one of the blend components, thus demonstrating the occurrence of self-compatibilization.