| Abstract
| - Ethylene−norbornene (E−N) copolymers were synthesized with the C2 metallocene rac-Me2Si(2-Me-[e]-benzindenyl)2ZrCl2 (3) and with the constrained geometry Me2Si(Me4Cp)(NtBu)TiCl2 (4)in the presence of methylaluminoxane. The E−N copolymerizations were carried out using a variety ofmonomer feed compositions. Copolymers were fully characterized by 13C NMR spectroscopy, gel permeationchromatography, and differential scanning calorimetry. Copolymer microstructures were analyzed indetail, through a procedure which accounts for the stoichiometric requirements of the copolymer chainas well as for the measured areas of 13C NMR signals. This analysis, which quantifies the differences insequence distribution and tacticity of the polymers, evidenced that mainly alternating stereoregular andstereoirregular copolymers were prepared with 3 and 4, respectively. The copolymer prepared with 4contains both meso and racemic NEN sequences and small amounts of meso and racemic NN diads, whilethe alternating copolymer prepared with 3 contains only meso NEN sequences and small amounts ofmeso NN diads. The formation of NN diads is disfavored with both catalysts. Surprisingly, a significantamount of norbornene (up to ∼10%) belonging to NNN triads (T) is obtained with the C2 catalyst.
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