Copolymerization of ethylene and norbornene by zirconium complexes containing symmetrically tuned trianionic ligands

Abstract

Homo and copolymerization of ethylene and cyclic olefins were carried out using C 3 symmetric N[CH2CH(Ph)O]3ZrCl (1-ZrCl) and also pseudo-C s symmetric N[CH2CH(Ph)O]3ZrCl (2-ZrCl) catalyst systems upon activation with MAO. Incorporation of comonomer into the polyethylene back bone was mainly governed by catalyst symmetry. Norbornene (NB) incorporation was as high as 40% in the ethylene–norbornene copolymer (ENC) using C 3 symmetric 1-ZrCl/MAO catalyst system and 25% in the case of the pseudo-C s symmetric analogue 2-ZrCl. Unlike the more efficient titanium analogues, the copolymerization of ethylene and NB showed a marginal decrease in catalyst activity and NB incorporation on switching over to the Zr analogues. The aluminum to metal ratio required for catalyst activation was higher for the Zr catalysts compared to that of its Ti analogues. 13C NMR spectral studies on the copolymer clearly indicated the incorporation of NB in an alternating manner.