Chain transfer to the aluminum cocatalyst was found to be the predominant chain transfer reaction in propylene polymerization mediated by the sterically hindered, highly isospecific rac-dimethylsilanediylbis(2-methyl-4-naphthyl)indenyl-zirconium dichloride (rac-Me2Si[2-Me-4-Naph-Ind](2)ZrCl2)/methylaluminoxane (MAO) catalyst system. By finely tuning the polymerization conditions including the polymerization temperature and Al/Zr ratio, this predominant aluminum transfer reaction was directed to prepare aluminum-terminated isotactic polypropylene (i-PP) with high end-group selectivity and controlled and narrowly distributed molecular weight. (c) 2005 Elsevier B.V. All rights reserved.