STABILIZED ZIRCONOCENE/ALUMINOXANE CATALYSTS AND PROCESS FOR THE PREPARATION THEREOF

Abstract: Zirconocene/aluminoxane polymerization/oligomerization catalysts are stabilized against aging prior to use as catalysts by use of at least 1 mol of an olefin R₁R₂R₃C-CH₂=CH₂ wherein R₁, R₂ and R₃ are C₁-C₂₀-alkyl, per mol of metallocene.

Description: The invention relates to a zirconocene/aluminoxane catalyst composition stabilized against aging during storage prior to use as a catalyst. The invention also relates to a process for the prepara­ tion of such stabilized compositions. Zirconocene/aluminoxane catalysts are known for producing polymers from olefins. European patent specification No. 128,045 deals with the use of titanocenes, zirconocenes, hafnocenes and vanadocenes in combination with aluminoxane to produce polyethy­ lene. In U.S. patent application Serial No. 896,700, filed on 15th August, 1986, is disclosed the use of certain zirconocenes and hafnocenes in combination with aluminoxane to produce dimers of alpha-olefins. U.S. patent specification 4,404,344 deals with the use of zirconocenes in combination with aluminoxanes to produce polymers. One problem with these zirconocene/aluminoxane catalysts is that they must be used relatively quickly after preparation or their performance as catalysts will suffer. It is an object of the present invention to stabilize these catalysts against aging during storage prior to use. Accordingly, the invention provides a zirconocene/aluminoxane catalyst composition stabilized against aging during storage prior to use as a catalyst which composition comprises a) a zirconocene of the general formula (cyclopentadienyl) n ZrY n wherein n is an integer from 1 to 4, and each Y individually represents a hydrogen or halogen atom or an alkyl group having in the range of from 1 to 5 carbon atoms or an aryl group having in the range of from 6 to 20 carbon atoms, b) an aluminoxane and c) at least 1 mol of a stabili­ zing olefin per mol of zirconocene, the stabilizing olefin having the general formula R₁R₂R₃CCH₂=CH₂ where R₁, R₂ and R₃ each repre­ sent an alkyl group having in the range of from 1 to 20 carbon atoms. The invention further provides a process for the preparation of said stabilized catalyst compositions which process comprises adding to a catalyst composition comprising a) a zirconocene of the general formula (cyclopentadienyl) n ZrY n wherein n is an integer from 1 to 4, and each Y individually represents a hydrogen or halogen atom or an alkyl group having in the range of from 1 to 5 carbon atoms or an aryl group having in the range of from 6 to 20 carbon atoms, and b) an aluminoxane, during or after said preparation at least 1 mol of a stabilizing olefin per mol of zirconocene, the stabilizing olefin having the general formula R₁R₂R₃CCH₂=CH₂ wherein R₁, R₂ and R₃ each represent an alkyl group having in the range of from 1 to 20 carbon atoms The zirconocene/aluminoxane catalysts to be stabilized by the process according to the present invention are prepared by reacting a suitable zirconocene with an aluminoxane. The aluminoxanes (also referred to as "alumoxanes") are well-known in the art and are polymeric aluminium compounds which can be represented by the general formula (R-Al-O) n which is a cyclic compound and R(R-Al-O) n AlR₂, which is a linear compound. In the general formula, R preferably represents a C₁-C₅ alkyl group such as, for example, methyl, ethyl, propyl, butyl or pentyl, and n is an integer from 1 to about 20. Preference is given to methyl and ethyl groups, particularly to methyl groups. Generally, in the preparation of aluminoxanes from trialkylaluminium compounds and water, a mixture of the linear and cyclic compounds are obtained. The aluminoxanes can be prepared in various ways. They are prepared by contacting water with a solution of trialkylaluminium in a suitable organic solvent. Illustrative examples of suitable trialkylaluminium compounds are trimethylaluminium, triethylalumi­ nium, tri-isopropylaluminium, tri-n-propylaluminium, tri-isobutyl­ aluminium and tri-n-pentylaluminium. For example, the trialkylalu­ minium compound is treated with water present in a moist solvent, or ultrasonically dispersed in a solvent as disclosed in U.S. patent application Serial No. 896,689 filed on 15th August, 1986 or dispersed in a solvent by high-speed stirring as disclosed in U.S. patent application Serial No. 896,701 filed on 15th August, 1986 or by contact with a hydrated salt such as hydrated copper sulphate or aluminium sulphate as described in U.S. patent specification 4,544,762. The inert solvents that can be used to dissolve the trialkyl­ aluminium or disperse or contain the water are well-known and include, for example, the saturated aliphatic compounds such as butane, pentane, hexane, heptane, octane, isoctane and the purified kerosenes; the cycloaliphatics such as cyclobutane, cyclopentane, cyclohexane, cycloheptane, methylcyclopentane and dimethylcyclo­ pentane; alkenes such as butene, hexene and octene; cycloalkenes such as cyclohexene; and the aromatic solvents such as benzene, toluene and the xylenes. The major requirements in the selection of a solvent are that it be liquid at the reaction temperature, that it does not react with the trialkylaluminium compound or with water or interfere with any subsequent reaction wherein the aluminoxanes are used in polymerization catalysts. The solvents must be oxygen-­ free. Hydroxyl groups, ether groups, carboxyl groups, keto groups and the like adversely affect preparation of the aluminoxanes. All or part of the solvent may be the stabilizing olefin having the general formula mentioned hereinbefore. In the general formula (cyclopentadienyl) n ZrY n mentioned hereinbefore n is preferably 2 and Y preferably represents a hydrogen or chlorine atom or a methyl group. It is understood that when n is 2-4 the Y's may be the same or different. Preferred zirconocenes are bis(cyclopentadienyl)zirconium dichloride, bis­ (cyclopentadienyl)zirconium hydrogen chloride and bis(cyclopenta­ dienyl)zirconium dimethyl. Within the definition of cyclopenta­ dienyl is included the lower alkyl(C₁-C₅)-substituted, preferably the methyl-substituted cyclopentadienyl. The ratio of aluminium in the aluminoxane to zirconium metal in the zirconocenes can be in the range of about 1:1 to about 10⁸:1. In general terms, the catalyst is prepared by adding the aluminoxane dissolved in an organic solvent, preferably the solvent utilized to prepare the aluminoxane, to a well stirred suspension of the zirconocene in a dry, inert, organic solvent, which solvent can suitably be the solvent described hereinbefore for the preparation of the aluminoxane. Preferably, the solvents are the same. When the stirred solution to which the aluminoxane has been added becomes homogeneous, the catalyst has been formed. Usually not more than 20 mol of the stabilizing olefin per mol of ziconocene are present in the catalyst compositions according to the present invention. The stabilizing olefins should be added during or shortly after preparation to prevent degradation. Typical­ ly, the stabilizing olefin is added less than an hour after prepara­ tion. Alternatively, the stabilizing olefin may be used in total or in part in the preparation of the aluminoxane or to suspend the zirconocene during catalyst preparation whereby at least 1 mol of stabilizing olefin is present per mol of zirconocene in the finish­ ed catalysts. Examples of stabilizing olefins are 3-methyl-3-ethyl-1-pen­ tene, 3,3-dimethyl-1-pentene and, which is preferred, 3,3-dime­ thyl-1-butene. The following Examples further illustrate the invention. Examples 1-3 and Comparative Experiments A and B In a nitrogen-filled dry box methylalumoxane was prepared by adding 8 mmol of trimethylaluminium as a 25% by weight solution in toluene to 2 mmol of copper sulphate pentahydrate slurried in toluene. After the reaction of the trimethylaluminium with the water in the copper sulphate was complete as evidenced by cessation of gas evolution, the solution of the resultant methylaluminoxane was transferred to a nitrogen-flushed, stirred flask containing 1 mmol of bis(cyclopentadienyl)zirconium dichloride and 2 mmol of the solvent/olefin listed in column 1 of Table 1 hereinafter. The catalysts thus formed were stored under nitrogen and at ambient temperature for several days after which time 320 mmol of 1-octene was added, and the system stirred and heated to 40 °C to effect dimerization of the 1-octene. Conversions of 1-octene were measured after 0.5 h and 2 h reaction times and are presented in Table 1.

Claims: 1. A zirconocene/aluminoxane catalyst composition stabilized against aging during storage prior to use as a catalyst which composition comprises a) a zirconocene of the general formula (cyclopentadienyl)nZrYn wherein n is an integer from 1 to 4, and each Y individually represents a hydrogen or halogen atom or an alkyl group having in the range of from 1 to 5 carbon atoms or an aryl group having in the range of from 6 to 20 carbon atoms, b) an aluminoxane and c) at least 1 mol of a stabilizing olefin per mol of zirconocene, the stabilizing olefin having the general formula R₁R₂R₃CCH₂=CH₂ where R₁, R₂ and R₃ each represent an alkyl group having in the range of from 1 to 20 carbon atoms. 2. A stabilized composition as claimed in claim 1 wherein n is 2 and Y represents a hydrogen or chlorine atom or a methyl group. 3. A stabilized composition as claimed in claim 1 or 2 wherein the zirconocene is bis(cyclopentadienyl)zirconium dichloride, bis(cyclopentadienyl)zirconium hydrogen chloride or bis(cyclopen­ tadienyl)zirconium dimethyl. 4. A stabilized composition as claimed in any one of the prece­ ding claims wherein the stabilizing olefin is 3,3-dimethyl-1-bu­ tene. 5. A process for the preparation of a stabilized catalyst composition as claimed in any one of the preceding claims which process comprises adding to a catalyst composition comprising a) a zirconocene of the general formula (cyclopentadienyl)nZrYn wherein n is an integer from 1 to 4, and each Y individually represents a hydrogen or halogen atom or an alkyl group having in the range of from 1 to 5 carbon atoms or an aryl group having in the range of from 6 to 20 carbon atoms, and b) an aluminoxane, during or after said preparation at least 1 mol of a stabilizing olefin per mol of zirconocene, the stabilizing olefin having the general formula R₁R₂R₃CCH₂=CH₂ wherein R₁, R₂ and R₃ each represent an alkyl group having in the range of from 1 to 20 carbon atoms

Inventors: SCHOENTHAL, GALEON WAYNE, SLAUGH, LYNN HENRY
Applicants: SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ B.V.
Application year: 1987
Main classification: C08F4
IPC codes: C08F4, C08F10