Penultimate Effects and Chain Epimerization in Propene−Norbornene Copolymers byrac-Me2Si(2-Me-Ind)2ZrCl2C2-Symmetric Metallocene

The copolymerization of propene (P) and norbornene (N) by the catalytic system composed of rac-Me2Si(2-Me-Ind)2ZrCl2 (3) and methylaluminoxane (MAO) was investigated and compared with that by rac-Et(Ind)2ZrCl2 (1) and MAO. Methyl 2 substitution on the indenyl ligand in 3 has an unexpected and strong influence on the catalyst behavior in P−N copolymerization, causing a strong decrease in catalytic activity, molar fraction fN, Tg, and Mn values. P−N copolymers with maximum of 16 mol % of norbornene were obtained by 3-MAO in contrast with those highly alternating obtained by 1-MAO. The microstructural analysis by 13C NMR of the copolymers at triad level and reactivity ratios ri and rij obtained from diads and triads, respectively, give evidence of the tendency to alternate or not to alternate P and N comonomers and information on the probability of insertions of N and of the possible forms of P insertions (P12, P13, and P21). Penultimate effects were demonstrated as 3-MAO has difficulty in accommodating a no...