MXPA97005210A

MXPA97005210A - Catalyst system and process for the production of a polim

Info

Publication number: MXPA97005210A
Application number: MXPA/A/1997/005210A
Authority: MX
Inventors: R Hawley Gil; Richard Fahey Darryl; Lee Halterman Ronald; Michael Ramsey Timothy
Original assignee: Phillips Petroleum Company
Priority date: 1996-07-17
Filing date: 1997-07-10
Publication date: 1998-04-01

Abstract

The present invention relates to: A catalyst system comprising bis (2- (para-methoxyphenyl) tetrahydroindenyl) zirconium dichloride and a cocatalyst. It also describes a process for the polymerization of olefins, which has 3 or more carbon atoms, when using the catalyst system.

Description

CATALYST SYSTEM AND PROCESS FOR THE PRODUCTION OF A POLYMER Field of the invention The present invention relates to the polymerization of olefins by using metallocenes. In particular, the present invention relates to the isotactic stereo-selective polymerization of olefins having at least 3 carbon atoms.

BACKGROUND OF THE INVENTION It is well known that olefins having 3 or more carbon atoms have the possibility of being polymerized to form polymers having different types of stereospecific microstructure. In general, syndiotactic polymers are considered to have a stereochemical structure in which the monomeric units have an enantiomorphic configuration of the asymmetric carbon atoms that follow each other alternately and regularly in the polymer backbone. It is generally described that isotactic polymers have long sequences of monomer units with the same relative configuration of the tertiary carbon atoms. In atactic polymers the stereo centers are positioned disorderly. Polymers having high levels of isotactic or syndiotactic character are generally crystalline solids and are insoluble in xylene. Atactic polymers are generally soluble in xylene and are gums or liquids.

REF: 25211 For particular applications, it is desirable to have high levels of isotactic structure in the polymer. Very few specific types of metallocenes have been found that have isotactic stereoselectivity. Examples include bis (indenyl) zirconium dichlorides with racemic ethylene and tetrahydroindenyl zir mio pcpbBadD can etilax, racrarao. Efetes racemic racemic metallocene isomers should be isolated, however, from racemic mixtures and meso-isomers in order to produce a catalytic material which is stereoselective isotactic. This separation can be difficult and expensive. As far as is known, only a non-stressed metallocene has been reported as capable of producing high levels of isotactic microstructure. That metallocene is bis (tmethyl fluorenyl) zirconium dichloride as described in U.S. Patent No. 5,304,523. The present invention provides a new method for polymerizing olefins. The invention also provides a method for producing polymer from olefins having at least 3 carbon atoms with high levels of isotactic microstructure by using an unstained metallocene which is prepared more easily than petrified metallocenes. The invention further provides a metallocene which is stereoselective without having to separate racemic and meso-isomeric isomers.

BRIEF DESCRIPTION OF THE INVENTION In accordance with the present invention, there is provided a process for the polymerization of olefins having at least 3 carbon atoms, comprising contacting the olefin with a metallocene and an appropriate cocatalyst, wherein the metallocene is bis (2-para-methoxyphenyl) tetrahydroindenyl zirconium dichloride. Techniques for producing some metallocenes of this type are described in article J. Orgomet, Chem., 465, 175-179 (1994). The above metallocene is suitable for producing polymers from olefins in which ethylene is included and particularly for producing molecules having isotactic microstructure by using olefins having 3 or more carbon atoms. Examples of olefins having 3 or more carbon atoms include propylene, 1-butene, 1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl -pentene, 3-etii-β-butene, 1-heptene , 1-octene, 1-decene, 4,4-dimetih-pentene, 4,4-diethyl-1-hexene, 3,4-dimetiM-hexene and the like. It is within the scope of the present invention to employ catalyst systems in the preparation of homopolymers. It is also within the scope of the present invention to employ catalyst systems or the polymerization of mixtures of two or more such alpha-olefins. It is also within the scope of the present invention to employ the catalyst systems in the polymerization of one or more of the alpha-olefins in combination with ethylene. Usually, if ethylene is used in an amount such that the resulting polymer contains less than 80% by weight of ethylene, a polymer is obtained which is generally referred to as a thermoelastomer instead of a thermoplastic. A classic example would be an ethylene-propylene copolymer having at least 20% by weight of the incorporated propylene monomer. The metallocene can be activated to produce an appropriate catalyst system for the polymerization of olefin monomers by using an appropriate cocatalyst. It is contemplated that the metallocene can be activated by using in general any of the techniques that in the past have been appropriate to activate other similar metallocenes, which include using a stable non-coordinating counter ion, as described in the U.S. patent. 5,155,080, this is a triphenyl carbenium tetrakis (pentafluorophenyl) boronate. Such polymerizations can be carried out in a homogeneous system in which the catalyst and the cocatalyst are both soluble; however, it is also within the scope of the present invention to carry out suspension polymerization or gas phase conditions. Supported forms of the catalyst and / or cocatalyst can be employed. It is generally preferred that the support be a material that is insoluble in the polymerization medium that is employed. Examples of conventional cocatalysts include in general any of those organometallic cocatalysts which have been used in the past with olefin polymerization catalysts containing transition metals. Some classical examples include organometallic compounds of metals of group IA, HA and IIIB of the periodic table. Examples of such compounds that have included organometallic halide compounds, organometallic hydride compounds and metal hydrides. Some specifically preferred examples include triethylaluminum, triisobutylaluminum, diethylaluminum chloride, diethylaluminum hydride and the like. The most currently preferred cocatalyst is an aluminoxane.

Such compounds include those compounds having repeating units of the formula wherein R is an alkyl group having in general from 1 to 5 carbon atoms. Such aluminoxanes, also sometimes referred to as poly (hydrocarbylaluminum oxides), are well known in the art and are generally prepared by reacting an organohydrocarbylaluminum compound with water. Such preparation techniques are described in U.S. Patents 3,242,099 and 4,808,561. The currently preferred cocatalysts are prepared either from trimethylaluminum or triethylaluminum. Such aluminoxanes are frequently referred to as poly (methyl aluminoxide) or poly (diethyl aluminoxide) respectively. It is also within the scope of the present invention to use an aluminoxane in combination with a trialkylaluminum, as described in U.S. Patent No. 4,794,096. As indicated above, the catalyst can be formed after the metallocene mixture with an aluminoxane. The catalyst system can be prepared as an unsupported catalyst by mixing the required metallocene and aluminoxane in an appropriate diluent, either in the presence or absence of monomers. Polymerization with the use of unsupported catalysts can be carried out either by solution or suspension polymerization processes. The catalyst system can also be prepared and used as a heterogeneous catalyst by the required gauging of the metallocene required and / or the aluminoxane components on a catalyst support material such as silica gel, alumina or other organic or inorganic support material. appropriate. The support material for preparing a heterogeneous catalyst can be a fine polyolefin powder or a finely divided solid porous inorganic support, such as talc, silica, alumina, silica-alumina or mixtures thereof. Other inorganic oxides which can be used either alone or in combination with silica or silica-alumina are magnesia, titania, zirconia and the like. The inorganic oxides must be dehydrated, as is well known in the art, to separate the water. If desired the residual hydroxyl groups of the surface in the inorganic solid porous support can be removed by further heating or by reaction with dehydroxylating agents such as alkyl lithium, silyl chlorides, aluminum alkyl or preferably aluminoxane. A preferred catalytic support is a dehydrated inorganic oxide treated with an aluminoxane, more preferably methylaluminoxane. A suitable support material is a dehydrated silica gel which is then treated with methylaluminoxane. The metallocene and the aluminoxane normally soluble in hydrocarbon can be used as a heterogeneous sustained catalyst by deposition on a support material, such as a dehydrated silica gel treated with methylaluminoxane. A suitable silica gel would have a particle diameter in the range of 1-600 microns, preferably 10-100 microns; a surface area of 50-1000 m2 / g, preferably 100-500 m2 / g; and a pore volume of 0.5-3.5 cm3 / g. The silica gel can be heat treated at a temperature of 100 ° C-1000 ° C, preferably 300 ° C-800 ° C for a period of 1-100 hours, preferably 3-24 hours to ensure its use in the dehydrated. The catalyst system obtained by contacting the metallocene and the aluminoxane cocatalyst can be formed before the introduction of these components into the reactor or alternatively can be formed in the reactor. In the case where the active system is formed in the reactor, the molar ratio of aluminum to zirconium in the reactor is soefele in the range of 10-5000, preferably 20-4000 and preferably 20-1000. In the case where the active system is formed outside the reactor, the preferred ratio of aluminum to zirconium is in the range of 1-200, desirably 20-200. In this case, additional aluminoxane cocatalyst can be used in the reactor, such that the total ratio of aluminum to zirconium in the reactor is in the range of 10-5000, preferably 20-4000 and more preferably 20-1000. Also, in this case, a small amount of another alkylaluminum compound, such as triethylaluminum or triisobutylaluminum, may be added to the reactor together with, or in place of, additional aluminoxane, for the purpose of purifying the impurities or for other benefits. In all of the above, the catalyst or cocatalyst can be contacted in the reactor with one of the components already present on an appropriate support. In a preferred technique for preparing a screened catalyst system, a dehydrated silica gel is contacted with aluminoxane and subsequently with zirconocene. If desired, however, the zirconocene can be added to a dehydroxylated support material before contacting the support material with an aluminoxane. In accordance with the preferred embodiment of this invention, the aluminoxane dissolved in an appropriate inert hydrocarbon solvent is added to the support material either dry or suspended therein or other appropriate hydrocarbon liquid and thereafter the zirconocene is added to the suspension , preferably after the drying of the support under vacuum and resuspension in a light hydrocarbon. In such an embodiment, the zirconocene is added to the suspension in an amount sufficient to provide from about 0.02 to about 5.0 wt.% Zirconium metal based on the total weight of the catalyst. The zirconocene is more preferably added in an amount to provide from about 0.10 to about 1.0 wt.% Zirconium metal based on the total weight of the catalyst. The treatment of the support material, as mentioned above, is carried out in an inert solvent. The same inert solvent or a different inert solvent is also used to dissolve zirconocene and aluminoxanes. Preferred solvents include the various hydrocarbons which are liquid at the treatment temperatures and at the treatment pressures and in which the individual ingredients are soluble. Illustrative examples of useful solvents include the alénes such as propane, butane, pentane, isopentane, hexanes, heptanes, octanes and nonanes; cycloalkanes such as cyclopentane and cyclohexane; and aromatic compounds such as benzene, toluene, xylene, ethylbenzene and diethylbenzene. Sufficient solvent should be used to provide an appropriate heat transfer of the catalyst components during the reaction and to allow good mixing. The temperature used during the production of the catalytic system can vary widely, such as, for example, from 0 ° C to 100 ° C. Higher or lower temperatures may also be used. The reaction between the aluminoxane and the support material is fast, however, that the aluminoxane is contacted with the support material for about half an hour up to eighteen hours or longer. Preferably, the reaction is maintained for about one hour as 25 ° C-100 ° C. At all times, the individual ingredients as well as the recovered catalytic components must be protected from oxygen and moisture. Accordingly, the reactions are carried out in an atmosphere free of oxygen and moisture and the catalyst is recovered in an atmosphere free of oxygen and moisture. Preferably, therefore, the reactions are carried out in the presence of an inert anhydrous gas such as, for example, nitrogen. The recovered solid catalyst is maintained in the inert gas atmosphere. After the completion of the deposition of zirconocene and aluminoxane on the support, the solid material can preferably be treated with a small amount of monomer, for example, ethylene to form a quantity of polymer on the solid catalyst materials to increase the weight of the catalyst at least 50%, desirably from about 100 to about 500% based on the total weight of the catalyst and the support material. Such treatment is subsequently referred to herein as prepolymerization of the catalyst. Then, the solid material as such or as prepolymerized, can be recovered by any well known technique. For example, the solid catalytic material can be recovered from the liquid by filtration, vacuum evaporation or decantation. After this the solid is dried under a stream of pure anhydrous nitrogen or dried under vacuum. The prepolymerization of the solid catalytic material aids in the production of an EPC elastomer produced therefrom during suspension polymerization in the form of well-defined particles. The prepolymerized catalyst can be rinsed with a hydrocarbon to provide the good granular particle shape. The prepolymerization also greatly reduces the requirement for aluminoxane. For example, a relation of a pini: zi? Enium of about 1000: 1 or greater for aiuraroxa D: zirconocene is needed for high activity when the aluminoxane is added to the liquid phase of the reactor, but a ratio less than about 100: 1 may be sufficient when the aluminoxane is incorporated into the catalyst prepolymerized For a prepolymerized catalyst, the ratio of aluminum to zirconium would normally fluctuate from about 1 to 500: 1 and more preferably from about 20: 1 to 100: 1 and still high activities would be obtained. More preferably, the catalyst sepa-tai) is prepared in the following manner: 1) formation of a suspension by the addition of the aluminoxane dissolved in an appropriate solvent, toluene for example, to the support; 2) stirring the suspension at a temperature of 60-80 ° C for 30-60 minutes; 3) separating the solvent under vacuum with sufficient heating to produce a dry powder; 4) addition of a light hydrocarbon, pentane for example, to suspend the powder; 5) addition of a solution of zirconocene in pertan or a minimum amount of toluene and stirring for 15-60 minutes at a temperature of 20-60cC, 6) prepolymerization with ethylene or another olefin in the suspension of pentane and then collection, rinsing and drying of the catalyst. For the best particle form, it is preferred not to add aluminoxane to the reactor beyond what is on the prepolymerized catalyst. An alkylaluminum, such as triethylaluminum or triisobutylaluminum can also be employed in the catalyst system. A heterogeneous form of the catalyst system is particularly suitable for a suspension polymerization process. According to a preferred method of this invention, it is possible to use the alpha olefin monomers in the liquid state as the polymerization diluent. As a practical limitation, the polymerization in the suspension is carried out in liquid diluents in which the product of the polymer is substantially insoluble. Preferably, the diluent for a suspension polymerization consists of one or more hydrocarbons with less than 5 carbon atoms. If desired, saturated hydrocarbons such as ethane, propane, or butane may be used in whole or in part as the diluent. Also, the alpha-olefin monomer or a mixture of different alpha-olefin monomers can be used in whole or in part as the diluent. More preferably, the diluent consists mostly of the alpha-olefin monomer or monomers to be polymerized. A further understanding of the present invention and its object and advantages will be provided by the following examples.

Example 1 Bis (2- (para-methoxyphenyl) tetrahydroindenyl) zirconium chloride A solution is prepared by combining 1.3 mmoles of 2- (para-methoxyphenyl) tetrahydroindene in diethyl ether. To the solution at a temperature of 0 ° C under an argon atmosphere in a Schlenk apparatus equipped with a side arm, 1.46 mmoles of n-butyllithium is slowly added in a heptane solution to obtain a white suspension which is allowed to warm up at room temperature for 2 hours. Then 0.6 mmoles of zirconium tetrachloride is added via the side arm and the reaction mixture is allowed to stir at room temperature for 24 hours. The crude product is purified by tituiaa? with hexane, filtration under argon atmosphere and vacuum separation of the solvent to yield 533 mg of a yellow solid which is identified as bis (2- (parathytoxyphenyl) tetrahydroindenyl zirconium dichloride.

Example II Polymerization reactions are carried out to evaluate the effectiveness of the metallocene of Example I in the polymerization of propylene. The catalytic systems were prepared in an argon atmosphere in a glove box by placing the solid or solid in a Diels Alder tube which was then sealed. Then 7.5 ml of a 10% by weight solution of methylaluminoxane was added to the tube via a syringe at room temperature.

Then the tube is stirred until the solid dissolves. The polymerizations were carried out in a 4 liter stainless steel autoclave reactor equipped with a mechanical stirrer and temperature tomatic control. The catalytic system was extracted from the Diels tube Alder using a syringe and charged to the purged, clean reactor, through a small orifice with a flow to aartraaarriepte of propylene gas. Then the reactor was sealed and filled with two-thirds of liquid propylene at room temperature. In some runs, hydrogen was also added.

Then the temperature of the mixture was raised to the desired level by indirect heat transfer by using steam heat. Then the reactor temperature was maintained at this level for two hours and then the polymerization reaction was terminated by venting the liquid propylene to a torch. Ventilation was carried out for a few seconds. Then the reactor is opened and the polymer is removed. The polymer is dried in a vacuum oven for one hour and then weighed. Productivities of the catalyst were determined from the zirconium levels in the polymer as determined by X-ray fluorescence. Molecular weights are determined by gel permeation chromatography. A series of runs involved a series of polymerizations using each catalyst system prepared using 8 mg of bis (2- (para-methoxyphenyl) tetrahydroindenyl zirconium dichloride.) The results of those runs are summarized in Table 1.

The results of Table 1 demonstrate that the metallocene dichloride bis (2- (para-methoxyphenyl) tetrahydroindenyl) zirconium is capable of producing polypropylene homopolymer having relatively high levels of isotactic microstructure. It seems that the level of isotactic microstructure is inversely related to temperature. A comparison of runs 3 and 5 indicates that hydrogen reduces the molecular weight of the polymer and reduces the production of the isotactic microstructure. Runs carried out without hydrogen produced a polymer having a molecular weight distribution that was broader than would be expected in general from a single-site metallocene catalyst. The polymers have melting points in the range of 152.5 to 157CC and melting heat values in the range of 51.2 to 70.5 J / g.

It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention. Having described the invention as above, property is claimed as contained in the following

Claims

Claims 1. A catalyst system, characterized in that it is prepared by the combination of bis (2- (para-methoxyphenyl) tetrahydroindenyl) zirconium dichloride as a cocatalyst.
2. A catalyst system according to claim 1, characterized in that the cocatalyst is an organometallic compound of a metal of group IA, HA or IIIB of the periodic table.
3. A catalyst system according to claim 2, characterized in that the cocatalyst comprises an alkylaluminoxane or triphenylcarbenium tetrakis (pentafluorophenyl) boronate.
4. A catalyst system according to claim 3, characterized in that the cocatalyst comprises an aluminoxane which is methylaluminoxane.
5. A process for producing a polymer in which the isotactic microstructure exceeds the atactic microstructure, characterized in that it comprises contacting at least one olefin having at least three carbon atoms with a catalyst system according to any of the preceding claims .
6. A process according to claim 5, characterized in that the polymerization is conducted under particulate conditions, such that the polymer of the final product is insoluble in the polymerization medium.
7. A process according to claim 5 or 6, characterized in that the polymerization is conducted at a temperature in the range of about 40 ° C to about 70 ° C.
8. A process according to claims 5-7, characterized in that it is conducted in the absence of added oxygen.
9. A process according to claims 5-8 characterized in that propylene is polymerized.
10. A process according to claim 9, characterized in that propylene is homopolymerized.
11. A process according to claim 10, characterized in that it is carried out to produce a propylene homopolymer having a [mm] as determined from 13 C NMR of at least about 62.8%.
12. A process according to claim 11, characterized in that it is carried out to produce a propylene homopolymer having a [mm] as determined from 13 C NMR of at least about 70%.