Chromium allyl and alkyl catalysts for the vinyl polymerization of norbornene and ethylene-norbornene copolymerizations

The catalytic behavior of Cr(II) and Cr(IV) catalyst precursors for the polymerization of ethylene and norbornene are compared. Cr(allyl)2/MAO catalysts polymerize norbornene but not ethylene, whereas Cr(II) undergoes one-electron transfer with B(C6F5)3 to generate [CrIII(allyl)2]+ which readily polymerizes ethylene. By contrast, the Cr(IV) complex Cr(CH2SiMe3)4/MAO oligomerizes norbornene but is highly active for ethylene/norbornene copolymerizations to high molecular weight copolymers with up to 60 mol% norbornene content. Significantly, activity increases with norbornene concentration.