AbstractThe properties of solution‐mixed blends of isotactic polypropylene (iPP) and an amorphous ethylene‐propylene copolymer (EPM), containing 40 wt.‐% of ethylene, were studied throughout the composition range. The techniques used were differential scanning calorimetry (DSC), dynamic mechanical spectroscopy, and optical microscopy. Morphological examination revealed a heterogeneous structure. The dynamic mechanical technique at isochronous conditions (110 Hz) between ‐120 and 160°C confirmed the heterophase nature of the blends and revealed limited phase mixing of the amorphous components of the two constituents. DSC measurements of specimens quenched at 0°C, indicated that EPM rubber promotes crystallization of the iPP phase.Appropriate mechanics models tested in the complete composition range led to the conclusion that the system is incompatible, with rubber spherical inclusion strongly adhering to the iPP matrix, up to an EPM volume fraction Φ (EPM) ≃ 0.70. At higher EPM compositions, matrix reversal occurs — a fact corroborated by the available mechanical data