Several ansa C1-symmetric cyclopentadienyl-fluorenyl metallocenes based on
zirconium have been prepared with different substituents at position 3 on the
cyclopentadienyl ring. Isotactic polypropylene production from these systems depends
highly on the size of these substituents. Therefore, large groups such as 1-methyl-4-tbutylcyclohexyl
(metallocene 6), 1-methyl-cyclohexyl (metallocene 7), 1,3,3,5-
tetramethylcyclohexyl (metallocene 8), and 2,3,4-trimethyl-3-pentyl (metallocene 9)
have been investigated. In combination with methylaluminoxane (MAO), they showed
good activity and produced high molecular weight of isotactic polypropylene. In terms
of the tacticity of the polymers, metallocene 6 made the best isotactic polypropylene
with ~88% mmmm pentad content. Also, it has been found that if the size of this
substituent is large as in 2,3,4-trimethyl-3-pentyl (metallocene 9), then it will block the
polymerization active site which will deactivate the metallocene.
New synthetic pathways for the synthesis of cyclopentadienyl-fluorenyl
metallocenes based on titanium have been achieved. Anchoring these types of ligands
onto titanium by following the conventional method of using TiCl4 in the metallation
step has failed for the production of Me2C(3-(diphenylmethyl)-C5H3)(C13H8)TiCl2
(metallocene 12), Ph2C(C5H4)(C13H8)TiCl2 (metallocene 14), and
Ph2C(C5H4)(C13H8)TiMe2 (metallocene 15); this is possibly due to the high reactivity of
TiCl4. Therefore, TiCl4·2THF has been prepared and used in that step to produce these
new titanocenes with good yields.
A new ansa-C2-symmetric substituted bis-indenyl metallocene for isotactic
polypropylene production has been successfully prepared. It is known that ansa-C2-
symmetric metallocenes are good catalysts for isotactic polypropylene production, but in
general, their synthesis suffers from the production of the meso Cs-stereoisomer of these
catalysts, which generally produces only atactic polypropylene. Therefore, the meso
stereoisomers must be removed and this is considered a loss of the material that
increases the cost of the catalysts. Addition of bulky substituents on the indenyl groups
as in Me2Si(5,5,8,8-tetramethyl-5,6,7,8-tetrahydrobenz(f)indenyl)2ZrCl2 (metallocene 5)
has prevented the meso stereoisomer production. 5/MAO produces isotactic
polypropylene with up to ~80% mmmm pentad content.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/3061 |
| Date | 12 April 2006 |
| Creators | Al-Bahily, Khalid A |
| Contributors | Miller, Stephen |
| Publisher | Texas A&M University |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Thesis, text |
| Format | 1319336 bytes, electronic, application/pdf, born digital |
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