Polymerization mechanism study of poly(4-methyl-1,3-pentadiene) and poly(4-methyl-1-pentene) prepared by using rac-[CH2(3-tert-butyl-1-indenyl)2]ZrCl2/13C enriched methylaluminoxane

13C NMR analysis of poly(4-methyl-1,3-pentadiene) (poly(4-MPD)) obtained by using the C2symmetric zirconocene based catalytic system: rac-[CH2(3-tert-butyl-1-indenyl)2]ZrCl2(1)/13C enriched methylaluminoxane (MAO) shows strong differences between the microstructure of the first inserted monomer unit and the in-chain inserted ones. The first insertion step results regiospecific, but not stereospecific, while the propagation step is regio- and stereoselective producing 1,2 syndiotactic poly(4-MPD). This feature is justified by assuming a “chain end” controlled mechanism working for the propagation step of polymerization.13C NMR analysis of isotactic poly(4-methyl-1-pentene) (poly(4-MP)) obtained by using the same catalytic system shows that the first monomer insertion is partially enantioselective.