Isotactic polypropylene has been reactively blended with an ethylene-octene copolymer so as to improve mechanical and rheological properties. Free radical polymerization of styrene and a multifunctional acrylate during melt extrusion has resulted in the formation of unique features in both amorphous and crystalline phases. Transmission electron microscopy images show that the elastomer domains are less than 200 nm in diameter, whereas grafting leads to the appearance of clusters of polymeric particles, ranging in size from several nanometers up to 200 nm. Differential scanning calorimetry (DSC) shows that grafting creates lamellar crystals that melt at much lower temperatures and recrystallize at much higher temperatures than binary blends. From wide angle X-ray diffraction and DSC, grafting has been shown to limit the maximum crystal size and perfection, as well as broaden the size distribution of the crystals. Grafting causes significant changes in the a crystalline phase of polypropylene and promotes the formation of the beta phase. Scanning electron microscopy reveals a unique cross-hatch structure of small crystals in the reactive blend, with tangential and radial lamellae appearing as crosslinked material of about the same aspect ratio. Polarized light microscopy gives evidence that grafting and branching within this blend causes a gelation-like recrystallization.