Azaborolinyl metal complexes as olefin polymerization catalysts

Details Azaborolinyl metal complexes as olefin polymerization catalysts Azaborolinyl metal complexes as olefin polymerization catalysts

1999-04-27

2001-05-08

Wu, David W. (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C526S132000, C526S348000, C526S348600, C526S352000, C526S133000, C502S103000, C502S117000, C502S162000

Reexamination Certificate

active

06228958

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to catalysts useful in homo- and co-polymerizing ethylene and other olefinic hydrocarbons. In particular, it relates to catalysts containing a transition metal &pgr;-bonded to a ligand that contains an azaboroline ring.
Until recently, polyolefins have been primarily made with conventional Ziegler catalyst systems. These catalysts typically consist of transition metal-containing compounds and one or more organometallic compound. For example, polyethylene has been made using Ziegler catalysts such as titanium trichloride and diethylaluminum chloride, or a mixture of titanium tetrachloride, vanadium oxytrichloride, and triethylaluminum. These catalysts are inexpensive but they have low activity and therefore must be used at high concentrations. As a result, it is sometimes necessary to remove catalyst residues from the polymer, which adds to production costs. Neutralizing agents and stabilizers must be added to the polymer to overcome the deleterious effects of the catalyst residues. Failure to remove catalyst residues leads to polymers having a yellow or grey color and poor ultraviolet and long term stability. For example, chloride-containing residues can cause corrosion in polymer processing equipment. Furthermore, Ziegler catalysts produce polymers having a broad molecular weight distribution, which is undesirable for some applications such as injection molding. They are also poor at incorporating &agr;-olefin co-monomers. Poor co-monomer incorporation makes it difficult to control the polymer density. Large quantities of excess co-monomer may be required to achieve a certain density and many higher &agr;-olefins, such as 1-octene, may be incorporated at only very low levels, if at all.
Although substantial improvements in Ziegler catalyst systems have occurred since their discovery, these catalysts are now being replaced with the recently discovered metallocene catalyst systems. A metallocene catalyst typically consists of a transition metal compound which has one or more cyclopentadienyl ring ligands. They have low activities when used with organometallic compounds, such as aluminum alkyls, which are used with traditional Ziegler catalysts, but very high activities when used with aluminoxanes as cocatalysts. The activities are generally so high that catalyst residues need not be removed from the polymer. Furthermore, they produce polymers with high molecular weights and narrow molecular weight distributions. They also incorporate &agr;-olefin co-monomers well. However, at higher temperatures metallocene catalysts tend to produce lower molecular weight polymers. Thus, they are useful for gas phase and slurry polymerizations of ethylene, which are conducted at about 80° C. to about 95° C., but they do not generally work well in solution polymerizations of ethylene, at about 150° C. to about 250° C. The polymerization of ethylene in solution is desirable because it allows great flexibility for producing polymers over a wide range of molecular weights and densities as well as the use of a large variety of different co-monomers. One can produce polymers that are useful in many different applications. For example, high molecular weight, high density polyethylene (PE) film useful as a barrier film for food packaging and low density ethylene co-polymers with good toughness and high impact strength.
SUMMARY OF THE INVENTION
We have found a new class of catalysts based on an azaboroline ring structure and containing a transition metal. The catalysts of this invention have unusually high activities, which means that they can be used in very small quantities. They are also very good at incorporating co-monomers into the polymer. They have good activity at higher temperatures and are therefore expected to be useful in solution polymerizations of ethylene.
We have also discovered that the hydrogen response of monomers polymerized with the catalysts of this invention is better than with other catalysts. That is, when the catalysts of this invention are used to polymerize monomers, small variations in the amount of hydrogen present have a large effect on the molecular weight of the resulting polymer.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The catalysts of this invention have the general formula
where L is a ligand having the formula
L′ is L, Cp, Cp*, indenyl, fluorenyl, NR
2
, OR, or halogen, L can be bridged to L′, X is halogen, NR
2
, OR, or alkyl from C
1
to C
12
, M is titanium, zirconium, or hafnium, R is alkyl from C
1
to C
12
or aryl from C
6
to C
12
, R
1
is R, alkaryl from C
6
to C
12
, aralkyl from C
6
to C
12
, hydrogen, or Si(R)
3
, R
2
is R
1
, halogen, COR, COOR, SOR, or SOOR, R
3
is R
2
, OR, N(R)
2
, SR, or a fused ring system, Cp is cyclopentadienyl, and Cp* is pentamethylcyclopentadienyl.
The L′ ligand is preferably Cp, Cp*, or L as those compounds are easy to make and have good activity. The X group is preferably halogen and most preferably chlorine as those compounds are more readily available. The R group is preferably alkyl from C
1
, to C
4
, the R
1
group is preferably alkyl from C
3
to C
12
or aryl, the R
2
group is preferably t-butyl or trimethylsilyl, and the R
3
group is preferably hydrogen or methyl as those compounds are easier to make. Examples of fused ring structures that can be used for R
3
include
The metal N is preferably zirconium, as the zirconium catalysts offer a good combination of activity and stability.
Optionally, L can be bridged to L′. Groups that can be used to bridged the two ligands include methylene, ethylene, 1,2-phenylene, dimethylsilyl, diphenylsilyl, diethylsilyl, and methylphenylsilyl. Normally, only a single bridge is used in a catalyst. It is believed that bridging the ligands changes the geometry around the catalytically active transition metal and improves the catalyst activity and other properties, such as comonomer incorporation and thermal stability.
In the general formula, L
B
is an optional Lewis base. Up to an equimolar amount (with M) of base can be used. The use of the Lewis base is generally not preferred because it tends to decrease catalyst activity. However, it also tends to improve catalyst stability, so its inclusion may be desirable, depending upon the process in which the catalyst is to be used. The base may be residual solvent from the preparation of the azaboroline containing compound or it may be added separately in order to enhance the properties of the catalyst. Examples of bases that can be used in this invention include ethers such as diethylether, dibutylether, tetrahydrofuran, 1,2-dimethoxyethane, esters such as n-butylphthalate, ethylbenzoate, and ethyl p-anisate, tertiary amines such as triethylamine, and phosphines such as triethyl phosphine, tributyl phosphine, and triphenyl phosphine.
The catalysts of this invention can be prepared from commercially available starting materials. Specific starting materials that may not be commercially available can be prepared by techniques well-known in the literature as exemplified by the following. The azaboroline ligand precursor for the catalysts can be prepared from allyl amine by reacting its dianion (generated by a strong base) with an alkyl boron dihalide as described in the literature (J. Schulze, G. Schmid, J. Organomet. Chem., 193, 1980, p. 83).
Examples of strong bases that can be used include alkyl lithium compounds such as n-butyl lithium, methyl lithium, and hydrides such as sodium hydride and potassium hydride. Two moles of base are used per mole of the allyl amine. This reaction will occur at room temperature in several hours in a hydrocarbon solvent such as pentane or hexane. Tetramethylethylene diamine in a 1:1 molar ratio with the allyl amine can be used to stabilize the alkyl lithium. The product can be isolated by vacuum and distilled to purify.
In the next step, the product is reacted with a base such as a hindered lithium reagent (e.g., lithium tetramethylpiperidide) to generate the azaborolinyl anion as described in the literature (G. Schmid et al

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