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Design and synthesis of novel group IV metallocenes for the Ziegler -Natta type polymerization of alpha-olefins
Four new substituted indenyl-fluorenyl asymmetric ethylene bridged ligands have been prepared from the reaction of 1-(9-fluorenyl)-2-bromoethane and the lithium salt of the desired indenyl moiety. The ligands have been converted to the corresponding substituted asymmetric ethylene-bridged metallocenes (M = Zr, Hf). The metallocenes have been evaluated as Ziegelr-Natta type catalyst precursors for the polymerization of ethylene and propylene. The zirconocene complexes 19-21 showed very high activity for both monomers. The influence of substitution on the selectivity of the propylene polymerization has been studied. The metallocene 1-(9-fluorenyl)-2-[(2,4,7-trimethyl)-1-indenyl] ethane zirconium dichloride (21) was found to produce highly isotactic polypropylene with [mmmm] of 89%. ^ The dimethylsilylene bridged analog of 21 (31) was prepared and was found to be less active and less stereoselective than the ethylene bridged precursor. A detailed study of the propylene polymerization behavior of the zirconocene complexes (19-21, 31) was carried out and the mechanistic aspects of polymerization are discussed. ^ Three new zirconocenes bearing 2,4-disubstitution on the indenyl moiety have been synthesized and evaluated as (x-olefin polymerization catalysts. For the new complex, ethylene-1-(9-fluorenyl)-2-[1-(2-methyl4-phenyl)indenyl]zirconium dichloride (42), highly isotactic polypropylene with [mmmm] = 91% and Mw = 1.1 x 105 was produced in very high yield. The dimethylsilylene analog (44) while less active, gave similar results in terms of stereoregularity with a two-fold increase in MW. ^ Two new asymmetric complexes with partially or fully substituted fluorenyl ligands have been synthesized. Dimethylsilylene-[1-(2-methyl-4-phenyl)indenyl-(9-tetrahydrofluorenyl) zirconium dichloride (51) and the octahydrofluorenyl analog 52 were highly active catalyst precursors for ethylene and propylene polymerizations with activities approaching 108 g polymer/[(mol Zr) [monomer] h]. The polypropylenes produced at room temperature were highly isotactic. ^ Several new, novel bridged and unbridged bis-tetrahydrofluorenyl zirconocenes were synthesized. The complexes were found to be highly stable compared to some bis-fluorenylzirconocenes. Polypropylene and polyethylene were produced in good yield using the new catalyst precursors with MAO or Trityl/TIBA as co-catalysts. ^
Emma Jane Thomas,
"Design and synthesis of novel group IV metallocenes for the Ziegler -Natta type polymerization of alpha-olefins"
(January 1, 2000).
Doctoral Dissertations Available from Proquest.