Structure/selectivity studies of zirconium catalysts in ethylene/alpha-olefin copolymerization: Kinetic strategies for controlling copolymer microstructure.

摘要

The effects of metallocene structural characteristics on ethylene/α-olefin copolymerization behavior were investigated to enable rational catalyst design for the production of novel ethylene/α-olefin copolymer architectures.; A systematic study of the influence of cyclopentadienyl ligand substituents on the ethylene/I-hexene copolymerization behavior of unbridged zirconocenes activated with methylaluminoxane was carried out. Unbridged bis(2-phenylindenyl)zirconium dichloride, (2-Ph-Ind)₂ZrCl₂, showed higher selectivity for the incorporation of α-olefin than its unsubstituted bridged and unbridged analogues. Comonomer selectivity of the mixed ligand compound, (Cp)(2-Ph-Ind)ZrCl ₂, was much lower than that of (2-Ph-Ind)₂ZrCl₂. For unbridged bis-indenyl metallocenes, the nature of the 2-substituent influenced comonomer selectivity; (2-Me-Ind)₂ZrCl₂ and (2-Ph-ethynyl-Ind) ₂ZrCl₂ exhibited higher 1-hexene incorporation than (Ind) ₂ZrCl₂, but lower than (2-Ph-Ind)₂ZrCl₂.; Ethylene/α-olefin copolymerizations with 1,2′-bridged metallocenes were investigated and compared to results reported for 1,1 ′ and 2,2′-bridged complexes to determine the influence of ligand substitution as well as bridge type and placement on comonomer incorporation and distribution. The nature of the bridge had a significant effect on both the incorporation and sequence distribution of the α-olefin. Substitution of a phenyl group at the 2-position of the indene gave a significant increase in α-olefin incorporation as well as enhancement of α-olefin homosequences compared to unsubstituted complexes.; Ethylene/1-hexene copolymerizations with disiloxane-bridged metallocenes, rac and meso-1,1,3,3-tetramethyldisiloxanediyl-bis(I-indenyl)zirconium dichloride, were carried out to investigate the influence of conformational dynamics on comonomer selectivity. The relatively high 1-hexene selectivity, high product of reactivity ratios, and ability to separate the resulting copolymers into fractions with different ethylene contents suggest that the active species of the meso isomer exhibits multi-site behavior populating conformations with different comonomer selectivity during the copolymerization.; Five structurally varied amine bis(phenolate)zirconium dibenzyl complexes, [ONDO]ZrBn2, were studied in ethylene/1-hexene copolymerization. All five complexes were active in copolymerization but had activities almost an order of magnitude lower than those observed for metallocenes. The C _s-symmetric complex, [ONNO]ZrBn₂, showed lower α-olefin incorporation and a blockier distribution of comonomers compared to its C_s-symmetric analogue which gave a more alternating distribution. The nature of substituents on the aryl ring as well as the identity of the pendant donor group in the series of C_s-symmetric complexes had little influence on copolymerization selectivity.