In this research, the reinforcement of polypropylene (PP) was studied using a new method that is more practical for synthesizing polypropylene-block-poly(ethylene-propylene) copolymer (PP-co-EP), which can be used as a rubber toughening agent. This copolymer (PP-co-EP) could be synthesized by varying the feed condition and changing the feed gas in the batch reactor system using Ziegler-Natta catalysts system at a copolymerization temperature of 10 degrees C. The C-13-NMR tested by a 21.61-ppm resonance peak indicated the incorporation of ethylene to propylene chains that could build up the microstructure of the block copolymer chain. Differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and dynamic mechanical analysis (DMA) results also confirmed these conclusions. Under these conditions, the morphology of copolymer trapped in PP matrix could be observed and the copolymer T-g would decrease when the amount of PP-co-EP was increased. DMA study also showed that PP-co-EP is good for the polypropylene reinforcement at low temperature. Moreover, the PP-co-EP content has an effect on the crystallinity and morphology of polymer blend, i.e., the crystallinity of polymer decreased when the PP-co-EP content increased, but tougher mechanical properties at low temperature were observed. (c) 2006 Wiley Periodicals, Inc.