A series of novel hexene-1-propylene random copolymers with isotactic sequence of propylene was synthesized with a MgCl2-supported Cr(acac)3 catalyst. The molecular weight distribution of copolymers and homopolymers was considerably narrower than that of typical polyolefins produced by heterogeneous Ziegler-Natta catalysts. The crystallizability of the copolymers having a propylene-unit content of more than 50 mol % drastically decreased with decreasing propylene-unit content, and the copolymers with a propylene content of less than 50 mol % were completely amorphous. In the present novel type of random copolymers with crystallizable and noncrystallizable units, a single glass transition was observed between pure polypropylene and polyhexene-1, and a major component was found to govern the final morphology and the mechanical characteristics. (C) 2004 Wiley Periodicals, Inc.