During the melt-processing of polymer blends the final morphology is determined by composition, viscosity and elasticity ratio, and interfacial tension between the components. If two components of a blend have the same viscosity, the component with the lowest volume fraction will form the dispersed phase. When the amount of the dispersed phase is increased, the particles will become larger due to increased coalescence. Finally, the amount of dispersed phase will reach a maximum, and subsequently the blend morphology will become co-continuous and phase inversion will occur. Avgeropoulus [6] observed on EPDM/BR blends (50/50 vol%) that it is possible to shift the phase inversion by lowering the viscosity of one of the components. Jordhamo et al. [7] developed an empirical model based on the melt-viscosity ratio, ηd/ηm, and the volume fractions φ, of each phase for predicting the phase inversion region in immiscible polymer blends. According to this model, phase inversion should occur when the following equation holds: