The compatibilizing effect of polypropylene (PP) grafted with hyperbranched polymers (PP-HBP) has been investigated in PP/polyamide-6 (PA-6) blends. Because of its high reactivity and diffusitivity, PP-HBP has been shown to be a more effective compatibilizer in decreasing the interfacial tension than the commonly used maleic anhydride-grafted polypropylene (PP-MAH). This article describes the influence of PP-HBP and PP-MAH on the interfacial tension between PP and PA-6, as measured by the deformed drop-retraction method (DDRM). Overall, PP-HBP yielded lower interfacial tension values between PP and PA-6, which resulted in a finer particle size of the secondary phase. The time dependence of the interfacial tension can be monitored by DDRM, enabling evaluation of the diffusitivity and reactivity of the compatibilizer. A model based on particle coarsening has been developed to describe the time dependence of the interfacial tension. This model showed that the diffusitivity and reactivity for PP-HBP was higher than that of PP-MAH. Therefore, PP-HBP has strong potential as a compatibilizer in diffusitivity-dependant processes such as film coextrusion and fusion bonding.