The use of a metallocene catalyst in combination with alumoxanes as a co-catalyst to polymerize ethylene, propylene and other olefins is well-known in the art. U.S. Pat. No. 4,769,510 (Kaminsky et al.) discloses the use of a metallocene catalyst with an alumoxane co-catalyst in polymerizing ethylene. In Kaminsky, polymerization is carried out by using a dilute solution of metallocene catalyst/alumoxane in toluene. The solution is formed by mixing 360 milligrams of methylalumoxane in 330 milliliters of toluene and then adding 3.3.times.10.sup.-6 moles of racemic zirconium dichloride metallocene catalyst. The propylene to be polymerized is then condensed into the solution. In Kaminsky, polymerization is carried out by mixing a methylalumoxane with a zirconium dichloride catalyst and then subsequently condensing propylene into the solution. This patent does not disclose the amount of time which lapsed between the mixing of the methylalumoxane and the catalyst and the addition of the propylene to the mixture. Another patent which discloses the use of a metallocene catalyst and an alumoxane as a co-catalyst is U.S. Pat. No. 4,892,851 (Ewen et al.). Ewen et al discloses the use of a metallocene-alumoxane-co-catalyst in a process for preparing syndiotatic polyolefins.
The amounts of milligrams of catalyst used per milliliter of alumoxane and toluene ranges from one milligram of catalyst per milliliter of alumoxane in toluene to 0.05 milligrams of catalyst per one milliliter of alumoxane in toluene. The catalyst was precontacted for 20 minutes with a toluene solution containing 10.7% by weight of metallocene-alumoxane with an average molecular weight of about 1300. The catalyst and co-catalyst solution was then added to a zipper-clave reactor followed by the addition of 1 liter of liquid propylene. The polymerization reaction was then allowed to run for 60 minutes during which time the reactor was maintained at the polymerization temperature of 20 deg. C. In Ewen '851, the metallocene catalyst and alumoxane co-catalyst were mixed in toluene immediately prior to the time of its injection into a zipper-clave reactor which was then followed by the addition of the propylene. None of the examples in Ewen teach that the catalyst and co-catalyst were precontacted for more than a period of 20 minutes.
U.S. Pat. No. 4,912,075 (Chang) is yet another patent which teaches the use of a metallocene-alumoxane catalyst for the use of polymerizing olefins. In Chang, a silica gel is used as a support for the metallocene and alumoxane co-catalysts. Chang discloses a process whereby methylalumoxane in toluene was slowly added to dehydrated silica gel and was stirred for one hour at room temperature. Thereafter, 300 milliliters of a 13% weight toluene solution of zirconium dichloride catalyst was slowly added to the stirred suspension of silica gel solids and stirring continued for 0.5 hours at 75 deg. C. Thereafter, the volatile solvent was evaporated with the resulting free-flowing powder comprised of a metallocene-alumoxane catalyst complex supported on a silica gel with the ratio of aluminum to zirconium of 50:1. The free-flowing powder was then utilized as a catalyst for the gas-phase polymerization of ethylene. The process disclosed in Chang uses a support medium to pre-contact the metallocene and alumoxane. The polymerization process was carried out by adding 5 grams of the catalyst to a vile. Subsequent to that, ethylene gas was injected into the vile wherein polymerization was allowed to proceed for one hour. The process disclosed in Chang involves a metallocene/alumoxane powder and therefore is very difficult to monitor and regulate in a continuous reactor system because the powder is not in solution.
U.S. Pat. No. 4,935,474 (Ewen et al.) also discloses a process which uses a metallocene/alumoxane co-catalyst to polymerize ethylene or higher alpha olefins. In Ewen et al. '474, the alumoxane solution was injected into a vessel followed by the injection of 0.091 mg. of zirconium dimethyl metallocene catalyst dissolved in 1 milliliter of toluene and was allowed to react for 1 minute. Thereafter, ethylene was injected into the reaction vessel wherein polymerization of the ethylene occurred.
The process of using metallocene catalyst and alumoxane as a co-catalyst in Ewen et al. '474 does not disclose any systems whereby the metallocene and alumoxane as a composition can be conveniently stored in solution for long periods of time which would be an advantage for monitoring and pumping purposes in a continuous reactor system.
The use of a continuous loop reactor system in a bulk process using a heterogenous Ziegler-Natta supported catalyst system which uses an aluminum alkyl as a co-catalyst is also well known in the art. Generally, the olefin to be polymerized is continuously fed into the reactor system and serves as both monomer and diluent. When polymerization of the olefin is desired, the catalyst which is typically suspended in a suitable diluent is activated by contacting with the aluminum alkyl co-catalyst and then injected into the reactor where polymerization then occurs. The heterogeneous Ziegler-Natta catalyst systems are not preactivated because Ziegler-Natta catalysts begin decomposing within hours after being contacted with the aluminum alkyl co-catalyst.
The prior art adequately discloses both use of homogeneous metallocene-alumoxane catalyst systems and the use of the continuous loop reactor system in a bulk process with the traditional heterogeneous Ziegler-Natta-aluminum alkyl catalyst systems. However, the prior art does not describe, teach or even imply any process or composition which would provide for the metallocene and alumoxane co-catalyst to be precontacted in a concentrated solution for a long period of time. Without the advantage of having a composition of metallocene-alumoxane solution which is capable of being stored for long periods of time, the processes and compositions disclosed by the prior art make it very difficult to efficiently monitor and pump the metallocene and alumoxane solutions. This disadvantage is remedied by the present invention.