Blends of isotactic polypropylene (PP), ethylene-propylene rubber copolymer (EPR), and ethylene-propylene crystalline copolymer (EPC) can be produced through in situ polymerization processes directly in the reactor and blends with different structure and composition can be obtained. In this work we studied the structure of five reactor-made blends of PP, EPR, and EPC produced by a Ziegler-Natta catalyst system. The composition of EPR was related to the ratio between ethylene and propylene used in the copolymerization step. The ethylene content in the EPR was in the range of 50-70 mol %. The crystallization behavior of PP and EPC in the blends was influenced by the presence of the rubber, and some specific interactions between the components could be established. By preparative temperature rising elution fractionation (P-TREF) analysis, the isolation and characterization of crystalline EPC fractions were made. (C) 2004 Wiley Periodicals, Inc.