Olefin polymerization catalyst system, producing and using it

Details Olefin polymerization catalyst system, producing and using it Olefin polymerization catalyst system, producing and using it

1998-09-21

2001-05-01

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...

C526S089000, C526S160000, C526S943000, C502S104000, C502S117000, C502S152000

Reexamination Certificate

active

06225423

ABSTRACT:

The invention relates to an olefin polymerization catalyst system comprising a reaction product of a transition metal compound. The invention also relates to a process for the polymerization of olefins by polymerizing one or more olefins, using an olefin polymerization catalyst system that comprises a reaction product of a transition metal compound. The invention relates also to a process for producing the transition metal compound's reaction product for the olefin polymerization catalyst system.
Ethylenically unsaturated monomers, especially olefins, are commonly polymerized by systems called Ziegler-Natta catalyst systems. These catalyst systems comprise a transition metal compound and most often an organometallic compound which functions synergetically with the transition metal compound, and often also one or more electron donors.
The Ziegler-Natta catalyst systems can be divided according to their physical states, into heterogenous and homogenous catalyst systems. The heterogenous Ziegler-Natta catalyst systems are solid catalysts with or without carrier. The homogenous Ziegler-Natta catalyst systems are catalyst systems that function in solution.
In catalyst systems based on alkyl aluminium cocatalysts, the transition metal component is usually based on titanium, vanadinium, chromium or nickel. Thus homogenous catalyst systems based on chromium are used, among other things, for the polymerization of dienes. Homogenous catalyst systems based on nickel are suitable for the oligomerization of ethylene. &agr;-olefins have been polymerized using metallocene-type and vanadinium-based catalyst systems, where alkyl aluminium compounds have functioned as cocatalysts.
There are catalyst systems known in the art, which are based on vanadinium and wherein a vanadinium compound, combined with an alkyl aluminium compound, has been used as a catalyst system for polymerizing propene. Such catalyst systems have also been utilized for homopolymerizing higher &agr;-olefins and copolymerizing higher &agr;-olefins with ethylene.
Homogenous Ziegler-Natta catalyst systems based on metallocenes form a group of their own in the art. They usually comprise a &pgr;-cyclopentadiene complex of a transition metal, such as titanium or zirconium, and a synergistically functioning organoaluminium complex, such as alkyl aluminium or aluminium oxane (aluminoxane, alumoxane), which is a reaction product of alkyl aluminium and water. Characteristic to these homogenous catalyst systems is a medium polymerizing activity, a narrow molecular weight distribution of the polymer product and that the activity of the catalyst systems is rapidly lost. The deactivation of the catalyst system has been studied using kinetic and spectroscopic methods. It was possible to demonstrate that the part that was active in the polymerization of ethylene comprised the transition metal in oxidation state +IV. The short life time of the active part is thought to be due to rapid deactivation processes, such as alkyl exchange, hydrogen exchange reaction and reduction reactions. See S. S. Reddy and S. Siwaram,
Prog. Polym. Sci.
20 (1995), 313.
The newest group of homogenous Ziegler-Natta catalyst systems in the art is based on cationic metallocenes. As ligand there is usually a cyclopentadienyl or its derivative, and the metal is usually titanium or zirconium, and the compound comprises an aluminium-free pair of ions that functions as the active centre of the polymerization. The polymerizing activity of this type of cationic metallocenes is usually medium or low.
An important characteristic of homogenous catalyst systems, i.e., catalyst systems that function in solution, is that in them, all the active centres or catalysts are similar i.e. the catalyst is a single-site one. Thus the polymerization forms macromolecules of various lengths according to a narrow distribution called the Schultz-Flory distribution. These single site catalyst systems are often layered on a carrier to improve the morphology of the polymer obtained and to facilitate the feeding of the catalyst into the polymerization reactor. Since the morphology of the catalyst repeats itself in the polymer (replica phenomen), a polymer with a Schultz-Flory molecular weight distribution and with a favourable morphology is obtained as a result.
As mentioned above, previous homogenous catalyst often have the impediments of low or medium activity and a very short active life. The present invention intends to remove these impediments. It is known to treat Ziegler-Natta catalyst systems with an olefin before they are fed into the polymerization reactor.
The dry and prepared catalyst, impregnated according to a known process, is treated with an olefin before it is fed into the reactor, to provide a more controlled initial activity for the catalyst system and thus prevent uncontrolled local exotermic polymerization reaction. The presence of an olefin leads to a process called prepolymerization and it can be carried out either in reactors located prior to the actual polymerization reactor or in the actual polymerization reactor. The prepolymerization is usually carried out until the catalyst particle is decomposed and the size of the prepolymerization particle thus formed is manyfold in comparison with the original catalyst particle. This type of prepolymerization can also be carried out in order to retain the essential chemicals in a solid catalyst particle.
The publication WO 94/28034 proposes a process of this type, in which methylalumoxane, di-methylsilane-diyl-bis-(2-methyl-4,5-benzo-indenyl)zirconiumdichloride and dehydrated silica are brought into contact in toluene, after which the toluene is removed by evaporation, and the ethylene is prepolymerized in an isopentane medium, using the solid catalyst system obtained. Using the prepolymerized solid catalyst system obtained, the actual polymerization is then carried out using propene with triethylaluminium as cocatalyst.
According to another process, the homogenous catalyst system is transformed into a heterogenous one by prepolymerizing a homogenous, single-site catalyst system in a solvent, in which case an insoluble polymer is produced, with which some catalytically active material is precipitated. This catalyst system precipitated during the prepolymerization is subsequently used for the actual polymerization.
Specification EP-A2-0 354 893 proposes a precipitating prepolymerization, wherein a toluene solution of a metallocene and aluminoxane is fed into a polymerization reactor, after which propene is added and the catalyst system is allowed to prepolymerize for five minutes. After that an actual propene polymerization is carried out with the solid prepolymer obtained. The reaction time is about ½-4 hours. Specification EP-A2-0 519 236 proposes bringing into contact dicyclopentadienyl zirconium chloride and methyl aluminoxane in a toluene solution. Heptane and a viscosity-enhancing polymer are then added to suspend the catalyst system, after which ethylene is added in order to carry out a prepolymerization. Finally, the prepolymer is separated from the suspension, and used in a normal ethylene polymerization.
A third way to transform a homogenous single-site catalyst system into a heterogenous, but still single-site system, has been proposed in U.S. Pat. No. 5,416,179. In this process, methyl aluminoxane is precipitated by adding hexane to a toluene solution thereof. The prepicitated methyl aluminoxane and bis(n-butyl-cyclopentadienyl)zirconiumdichloride are suspended in hexane, after which the product is filtered and dried. The catalyst system obtained is then added into the polymerization reactor together with isobutene and ethylene monomers. According to the specification, adding isobutene comonomer increases the ethylene polymerization activity of the catalyst.
The intention of the heterogenization of the homogenous catalyst systems mentioned has been to obtain solid catalysts which have single-site active centres and are also stable, have advantageous particle shape and are sufficiently active.
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