Continuous solution copolymerization of ethylene with propylene using a constrained geometry catalyst system

Ethylene (E)/propylene (P) continuous solution copolymerization using the constrained geometry catalyst system, [CpMe4(SiMe2NtBu)]TiMe2 (CGC)/tris(pentafluorophenyl)boron/modified methylaluminoxane, was carried out at 3.45×103 kPa and 130, 140, and 150°C. Ethylene and propylene copolymers with a broad range of composition fractions were synthesized and characterized. The incorporation of propylene lowered the catalyst activity and increased chain termination reactions. The estimated reactivity ratios rE and rP were 2.89 and 0.324 at 130°C, 4.33 and 0.377 at 140°C, and 6.36 and 0.436 at 150°C, respectively. The relatively low rE and high rP values of CGC compared to other metallocene systems indicated a ready incorporation of propylene in ethylene/propylene copolymerization. The activation energies ΔEE and ΔEP were 56 and 21 kJ/mol, showing a more significant effect of polymerization temperature on rE than on rP. The reactivity ratios for normal propylene, inverted propylene, and ethylene were also estimated from the methylene sequence distributions.