While it has been recognized for some time that the polymerization of ethylene by Ziegler-Natta catalysts was somewhat different from that of propylene and other ∝ -olefins, it has often been assumed that the polymerization of all ∝ -olefins proceeds more or less in the same manner, irrespective of the particular monomer under investigation. Recent research1–4 however, indicates that this may not be so.