AbstractA modified‐polypropene‐supported Ziegler catalyst was prepared using polypropene containing a small amount of poly(7‐methyl‐1,6‐octadiene) as a starting polymer for bromination, lithiation, and reaction with TiCl4. The polymerization of ethene was carried out using the catalyst with Al(C2H5)3in toluene at 60°C up to 100 h. The polymer yield increased linearly with polymerization time, which indicates that the active sites of the modified‐polypropene‐supported Ziegler catalyst are practically stable without deactivation even for 100 h and are able to propagate further polymeriza