PURPOSE:To obtain the titled copolymer, having high rigidity and impact strength, and low brittle temperature, and giving an extrudate with excellent surface, by polymerization in the presence of a solid TiCl3 catalyst complex and an organoaluminum compound, in two steps. CONSTITUTION:In two-step polymerization by use of a catalyst system primarily composed of an organoaluminum compound and a solid TiCl3 catalyst complex, of an atomic ratio of Al to Ti =0.15, containing a complexing agent, in the first step, propyrene is polymerized in the presence of liquefied propylene and H2, to produce 70-95wt%, based on the total polymer, of a propylene homopolymer of melt flow index 1-150, and in the second step, propylene and ethylene are copolymerized at 25-70 deg.C in the presence of liquefied propylene, in a vapor phase, containing H2, of prophylene/(propylene+ethylene) ratio of 50-80mol% and H2/(propylene+ ethylene) ratio of 0.5-30mol%, to produce 5-30wt%, based on the total polymer prepared, of a propylene-ethylene copolymer of melt flow index 10-7-0.1.
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