Chiral C{sub 1}-symmetric group 4 metallocenes as catalysts for stereoregular {alpha}-olefin polymerization. Metal, ancillary ligand, and counteranion effects
- Northwestern Univ., Evanston, IL (United States)
Chiral C{sub 1}-symmetric Zr and Hf complexes of the novel, chelating, cyclopentadienyl-based, Me{sub 2}SiCp{double_prime}(R{sup *}Cp) ancillary ligand have been synthesized. The diastereoselectivity in the initial synthetic complexation reaction is found to be insensitive to reaction conditions and chiral auxiliary. For the (-)-menthyl derivatives, optically pure metallocene may be isolated in good yield after a single recrystallization of the initial complexation and alkylation reaction products. However, the (+)-neomenthyl derivative has only been isolated as a pseudoracemate due to cocrystallization of both the (R) and (S) isomers in the same crystal lattice. The metallocenes are found to be configurationally stable in donor solvents at ambient and elevated temperatures. Active polymerization catalysts are prepared by reaction of the various metallocenes with a variety of cocatalysts. For propylene polymerization, relatively high isotacticities (>95% mmmm pentad content) are observed, which rival or exceed those of many axially- and C{sub 2}-symmetric catalyst systems. Significantly, polymer isotacticities and molecular weight have been found to depend markedly on the quantity and structure of the cocatalyst. Further, these ion-pairing effects offer additional means to modulate polymer stereoregularity and molecular weight. 66 refs., 5 figs., 5 tabs.
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- FG02-86ER13511
- OSTI ID:
- 171385
- Journal Information:
- Journal of the American Chemical Society, Vol. 117, Issue 49; Other Information: PBD: 13 Dec 1995
- Country of Publication:
- United States
- Language:
- English
Similar Records
Catalyst system for the polymerization of alkenes to polyolefins
Catalyst system for the polymerization of alkenes to polyolefins