Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2002-12-18
2004-06-01
Lu, Caixia (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C502S152000
Reexamination Certificate
active
06743872
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to processes for preparing olefin catalysts and, more particularly, to a method of synthesizing a novel class of alpha-olefin polymerization catalysts comprising titanacarbocycles.
BACKGROUND OF THE INVENTION
The combination of metal alkyls of Groups 1, 2 or 13 metals of the Periodic Table with metal halides, or salts of Groups 4 or 5 metals at ambient temperatures in hydrocarbon media, has long been known to function as an effective catalyst system for the polymerization of olefins, conjugated dienes, or acetylenes. These catalysts were discovered and reported by Karl Ziegler and coworkers in 1952. The resulting catalysts formed in a heterogeneous phase are further capable of the stereoregular polymerization of alpha-olefins, 1, 3-alkadienes and alkynes, as was observed and reported by Giulio Natta and coworkers in 1953. The revolutionary impact that these dual discoveries exerted on the polymer industry worldwide has been evident in the thousands of patents issued in the last 50 years that describe so-called Ziegler-Natta technology and in the joint conferral of the Nobel Prize in Chemistry on these two pioneers in 1963. An admirably thorough review of the scientific and patent literature of Ziegler-Natta polymerization technology before 1978 has been published (J. Boor, Jr.,
Ziegler
-
Natta Catalysts and Polymerizations
, Academic Press, New York, 1979).
The specific interaction of either lithium alkyls (RLi) or aluminum alkyls (R
3
A1) at room temperature with titanium(IV) chloride can lead to the exchange of one or two chloro ligands of TiCl
4
(1) for alkyl groups of RLi (Eqs. 1 and 2) to yield alkyltitanium derivatives 2 and 3:
The polymerizing action of the heterogeneous reaction mixture of TiCl
4
and RLi has been ascribed either to compounds 2 and 3, which precipitate from the reaction mixture along with the by-product LiCl, and/or to the TiCl
3
(4) or TiCl
2
(5) generated by the homolyses of 2 and 3 (Eqs. 3 and 4).
Many studies and patents corroborate that preformed TiCl
3
, combined with a main-group metal alkyl activator, and preformed TiCl
2
, with or without a metal alkyl activator, can effect the polymerization of ethylene and of alpha-olefins, as well as the isotactic polymerization of alpha-olefins. All such polymerizations apparently occur in a heterogeneous phase and are proposed to ensue by repeated insertions of the olefin monomer (7) into a preexisting carbon-titanium bond (e.g., 6), where the oxidation state of the titanium, n, could be 2, 3 or 4 (Eq. 5).
In light of the novel catalyst system described herein, it is important to note that a hydrocarbon solution of titanium(IV) chloride (in alkane or arene medium), when treated at room temperature with 2 equivalents of n-butyllithium (cf. Eq. 2) immediately takes on a brown color and over a period of an hour rapidly darkens as a black solid precipitates. Finally, the supernatant liquid is colorless, and solid TiCl
2
and LiCl have formed quantitatively, as analyses have shown (Eq. 6). Thus any intermediate, such as di-n-butyltitanium
dichloride 8a has completely decomposed to 5 under these conditions. With reference to the works of Friedlander and Oita, who polymerized ethylene (
Ind. Eng. Chem
., 49, 1885 (1957)), and of Max Frankel and coworkers, who polymerized ethylene and propylene (
J. Polymer Sci
., 28, 387 (1958) and 40, 149 (1959)) by forming their catalyst by combining various ratios of TiCl
4
and BuLi at ambient temperatures, it is most likely that what was actually being generated was either TiCl
2
or TiCl
3
as the active catalysts, and not 8a. Moreover, these previous workers generally prepared their catalysts and conducted their polymerizations at room temperature and under an atmosphere of nitrogen gas. Our laboratory has now shown that catalysts such as 8a are not stable at 25° C. under nitrogen but are destroyed by the nitrogen, ultimately reducing the nitrogen to ammonia. Of necessity, therefore we prepare catalyst 8
a
and 8
b
at −78° C. and under an argon atmosphere.
The present invention describes the synthesis of a novel family of olefin polymerization catalysts that can be readily generated by the preparation and utilization of di-n-butyltitanium dichloride (8
a
) or di-t-butyltitanium dichloride (8b), that are generated as a suspension with LiCl at −78° C. in alkane, cycloalkane, or aromatic hydrocarbon media (Eq. 7).
Under these conditions, 8 is sufficiently stable to undergo a remarkable, unprecedented reaction whereby the TiCl
2
-moiety of 8 is efficiently transferred to a substrate like diphenylacetylene (9), to generate three-membered titanacycle 10 (Eq. 8), most likely via the octahedral transition state 11.
Similar reactions will be discussed hereinafter with reference to intermediates comprising such titanacyclopropanes or titanacyclopropenes. These olefin catalysts comprise a class of. three-membered titanacarbocycles, which have high activity and stereoregularity in olefin polymerization, and can be easily prepared from di-n-butyltitanium dichloride or di-t-butyltitanium dichloride when combined with either olefins or acetylenes through a novel process termed epimetalation-by-transfer and exemplified in Eq. 8.
Some advantages of synthesizing and using these novel catalysts are the following: they are relatively inexpensive to synthesize because they can be generated from commercially readily available starting materials; their synthesis is straightforward because the catalyst preparation uses common laboratory or pilot-plant apparatus; the structure of the specific catalyst can be varied widely by changing the nature of the specific acetylene, olefin or diolefin employed; polymerization proceeds with acceptable reaction rates, even at lower temperatures and pressures; polymerization of alpha-olefins may be made to proceed in an isotactic manner; and the inventive catalyst system can be employed for the copolymerization of two or more olefin monomers.
The only possible disadvantage of the present inventive catalysts is their sensitivity to traces of moisture and active-hydrogen organic compounds like alcohols, acids, 1-alkynes and to oxygen, or peroxides, all of which can destroy the carbon-titanium bond and thereby inactivate the catalyst. However, such chemical sensitivities are shared with other Ziegler-Natta polymerization catalysts as well.
Titanacycles are the key polymerization intermediates formed when a dibutyltitanium dichloride (8
a
or 8
b
) is generated by mixing titanium tetrachloride and butyllithium together (Eq. 7), then exposing them to either ethylene or propylene gas. Such titanacycles, in hexane or toluene solution, but in the absence of THF, initiate the polymerization of ethylene into polyethylene and of propylene into isotactic polypropylene.
DISCUSSION OF RELATED ART
To the best of present knowledge and belief, polymerization catalysts for olefins and other related compounds having titanacycles as an essential part of their structure have not been previously reported.
SUMMARY OF THE INVENTION
In accordance with the present invention, a novel family of olefin polymerization catalysts comprising three-membered titanacarbocycles is illustrated. The titanacarbocycles can be readily synthesized by utilizing di-n-butyltitanium dichloride or di-t-butyltitanium dichloride, prepared at −78° C. in alkane, cycloalkane, or aromatic hydrocarbon media. These procatalysts exhibit sufficient stability below 0° C. that they can undergo a remarkable, unprecedented reaction whereby the titanium dichloride moiety is efficiently transferred to a substrate, such as ethylene, an alpha-olefin, acetylene or a mono- or disubstituted acetylene, or similar compounds, in order to generate the corresponding three-membered titanacarbocycles.
It is an object of this invention to provide a new class of olefin polymerizing catalysts.
It is another object of the present invention to provide novel polymerization catalysts for olefins that can be conveniently and inexpensively synthesized.
DESCRIPTIO
Eisch John J.
Gitua John N.
Lu Caixia
Mark Levy & Associates
The Research Foundation of the State University of New York
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