Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2001-05-21
2002-11-26
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...
C526S134000, C526S160000, C526S161000, C526S943000, C526S348000, C502S152000, C502S155000, C502S167000
Reexamination Certificate
active
06486276
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a solution polymerization process for the preparation of ethylene propylene elastomers using a comparatively inexpensive single site catalyst system. The catalyst of the present process is an unbridged Group 4 organometallic complex having a cyclopentadienyl ligand and a monosubstituted nitrogen ligand. A boron activator is also required.
BACKGROUND OF THE INVENTION
Ethylene propylene (EP) elastomers are widely available items of commerce which are prepared by copolymerizing ethylene, propylene and (optimally) a small amount of a diene monomer. Copolymers which contain at least 20 weight % of randomly distributed propylene units are substantially less crystalline than typical thermoplastic polyethylene or polypropylene homopolymers. A combination of low crystallinity and high molecular weight generally provides elastomeric properties in these polymers. These elastomers are used in many applications such as membranes (for roofing or for pond liners); blending components for the preparation of “toughed” thermoplastics (such as “toughened” polypropylene and toughened nylon) and, in particular, automotive parts. Examples of automotive parts which are made from ethylene propylene elastomers include belts, seals, hoses and tire sidewalls.
Ethylene propylene elastomers may also include a small amount of a diene. This leaves residual unsaturation in the elastomer which may be usefully employed to prepare “vulcanized” or “cured” compounds. Such elastomers are typically referred to as “EPDM”.
EP and/or EPDM elastomers generally require a weight average molecular weight (“Mw”) of at least 60,000 in order to provide sufficient tensile strength for use in automotive applications. These elastomers may be produced in slurry and solution polymerization processes.
Slurry polymerization processes are particularly suitable for preparing extremely high molecular weight ethylene propylene (diene) elastomers.
Solution polymerization processes are somewhat less suitable for the preparation of high molecular weight ethylene propylene (diene) elastomers because the high solution viscosity of high molecular weight elastomers makes such solutions difficult to handle. This problem may be mitigated by increasing the solution temperature. However, the use of higher polymerization temperatures generally increases the rate of chain termination reactions and thereby lowers the molecular weight of the polymer.
Conventional EP and EPDM elastomers are typically prepared with a Ziegler catalyst system comprising a Group 4 or 5 metal and an alkyl aluminum (halide) cocatalyst. Vanadium is the generally preferred metal because it provides elastomers having high molecular weight. Exemplary vanadium compounds include vanadium halides (especially vanadium chloride), vanadium alkoxides and vanadium oxy halides (such as VOCl
3
). These vanadium compounds are inexpensive but are not particularly active.
More recently, the use of “single site catalysts” such as metallocene catalysts has been proposed for the preparation of EP or EPDM elastomers. These catalysts are generally more expensive than the simple vanadium components described above. In particular, high catalyst costs are incurred due to the cost of synthesizing the organometallic catalyst complexes and/or when large amounts of alumoxane cocatalysts are used. Accordingly, high polymerization activity (as well as the capability to produce high molecular weight EP and EPDM polymers) is required if these new catalysts are to provide economically viable alternatives to the vanadium compounds.
Bridged metallocene catalysts (i.e. catalysts having a bridging group which is bonded to two cyclopentadienyl or indenyl or fluorenyl ligands) have been proposed for the preparation of EP elastomers. See for example, U.S. Pat. No. 4,871,705 (Hoel; to Exxon), U.S. Pat. No. 5,229,478 (Floyld et al.; to Exxon) and U.S. Pat. No. 5,491,207 (Hoel; to Exxon).
The use of bridged metallocene is potentially desirable because such catalysts may be more stable (i.e. less prone to decomposition) than unbridged catalysts under ethylene propylene polymerization conditions. However, bridged metallocenes are comparatively difficult and expensive to synthesize. Moreover, such catalysts can lead to the formation of isotactic polypropylene sequences in ethylene propylene polymers (as disclosed in European Patent Application (EPA) 374,695; Davis et al; to Polysar Ltd.) which is not desirable for products that are intended for use as elastomers.
Similarly, U.S. Pat. No. 5,696,213 (Schiffino et al.; to Exxon) teaches the preparation of EP and EPDM in a solution process using a cyclic monocyclopentadienyl Group 4 metallocene catalyst (i.e. a catalyst having a bridged (or “cyclic”) ligand in which the cyclopentadienyl group forms part of the “bridge” (or “cyclic”) ligand with another atom—such as a group 15 heteroatom being bonded both to the cyclopentadienyl ligand and the Group 4 metal so as to form the rest of the cyclic ligand. This patent also teaches the use of a bridged bis indenyl hafnium catalyst.
SUMMARY OF THE INVENTION
A process for the preparation of an elastomeric ethylene-propylene polymer wherein said process is characterized by being undertaken under solution polymerization conditions in the presence of a catalyst system which comprises:
1) an unbridged catalyst having a single cyclopentadienyl ligand and a monosubstituted nitrogen ligand; and
2) a boron activator;
wherein said catalyst is defined by the formula:
wherein Y is selected from the group consisting of:
ai) a phosphorus substituent defined by the formula:
wherein each R
1
is independently selected from the group consisting of a hydrogen atom, a halogen atom, C
1-20
hydrocarbyl radicals which are unsubstituted by or further substituted by a halogen atom, a C
1-8
alkoxy radical, a C
6-10
aryl or aryloxy radical, an amido radical, a silyl radical of the formula:
—Si—(R
2
)
3
wherein each R
2
is independently selected from the group consisting of hydrogen, a C
1-8
alkyl or alkoxy radical, C
6-10
aryl or aryloxy radicals, and a germanyl radical of the formula:
—Ge—(R
2′
)
3
wherein R
2′
is independently selected from the group consisting of hydrogen, a C
1-8
alkyl or alkoxy radical, C
6-10
aryl or aryloxy radicals, and a germanyl radical; and
aii) a substituent defined by the formula:
wherein each of Sub
1
and Sub
2
is independently selected from the group consisting of hydrocarbyls having from 1 to 20 carbon atoms; silyl groups, amido groups and phosphido groups.
Cp is a ligand selected from the group consisting of cyclopentadienyl, substituted cyclopentadienyl, indenyl, substituted indenyl, fluorenyl and substituted fluorenyl;
X is an activatable ligand and n is 1 or 2, depending upon the valence of M and the valence of X; and
M is a group 4 metal selected from the group consisting of titanium, hafnium and zirconium.
Preferred elastomeric polymers have a weight average molecular weight of at least 60,000 and a propylene content of at least 20 weight %.
As noted above, the process of this invention must employ a boron activator. As described later and illustrated in the examples, it is particularly preferred to use a small amount of the activator (especially an equimolar amount of the catalyst and activator). This can provide a cost advantage in comparison to the more conventional use of large molar excesses of alumoxane cocatalyst. In addition, whilst not wishing to be bound by theory, it is believed that large molar excesses of alumoxane may lead to the degradation of the catalysts of this invention under the conditions required for the solution polymerization of ethylene propylene elastomers. (More particularly, it is postulated that large molar excesses of alumoxane may lead to undesirable interactions or reactions with the metal-nitrogen bond of the catalysts of this invention, such as the formation of bridging groups and/or cleavage of the metal-nitrogen bond.)
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Part 1. Description of Catalysts
The catalys
Brown Stephen John
Wang Qinyan
Harlan R.
Johnson Kenneth H.
Nova Chemicals (International) S.A.
Wu David W.
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