Ethylene/Norbornene Copolymerizations with Titanium CpA Catalysts

Group 4 ansa-cyclopentadienylamido (CpA) complexes [Me2Si(Cp')(NR)]MCl2 (R = alkyl, M = Ti, Zr) efficiently copolymerize ethylene with a variety of α-olefins. Ethylene/norbornene copolymerization reactivity ratios were determined at 40 °C for CpA catalysts [Me2Si(Cp')(NtBu)]TiCl2 (Cp' = Me4Cp, 2,4-Me2Cp, 3-tBuCp, Ind), and the resulting values are low (r1 = 2.0−5.1, r2 → 0), suggesting a tendency toward alternating comonomer insertion at high norbornene/ethylene feed ratios. As reaction temperature is increased and norbornene concentration is decreased, productivity increases and norbornene incorporation decreases. No more than 46 mol % norbornene is incorporated into the copolymer using these CpA catalysts even at low feed ratios (E/N ≥ 0.02), and norbornene homopolymerizations with [Me2Si(Me4Cp)(NtBu)]TiCl2 proceed to very low conversion (<1%). 13C NMR spectroscopy of CpA-derived poly(ethylene-co-norbornene)s shows the copolymers contain virtually no consecutive norbornene sequences, and the microstructure of the resulting ethylene norbornene copolymers is dependent on catalyst geometry.