Concentration effects of methylalumoxane, palladium and nickel pre-catalyst and monomer in the vinyl polymerization of norbornene

Summary

The vinyl polymerization of norbornene with di-μ-chloro-bis-(6-methoxybicyclo-[2.2.1]hept-2-ene-5σ,2π)-palladium(II), Ni(acetylacetonate)₂ and Ni(2-ethylhexanoate)₂ in combination with methylalumoxane (MAO) was investigated by varying the molar MAO:metal-complex ratio, the norbornene:metal ratio and the metal concentration. The effects on the catalyst activity could be explained with a complexation equilibrium for the active homogeneous complex. Activity data in combination with polymer analyses suggest that at low, yet economical Al(MAO):metal ratios of 100 the fraction of active metal centers is less than 15%. The turnover frequency for the monomer insertion was found to reach 50 s⁻¹. Polydispersities around M_w/M_n= 2 indicate a coordination polymerization with chain transfer and a single-site character of the active centers.