CA1128920A - Polymerization of alpha-olefins with a dual organo titanium-chromium catalyst - Google Patents

Abstract

Abstract of the Disclosure Dual transition metal catalysts exhibiting high activity for the polymerization of .alpha.-olefins are prepared by reacting a tetravalent hydrocarbyloxy titanium halide with chromium oxide and combining the resulting product, preferably in the presence of an inert solid catalyst support, with an organo-metallic activating agent such as trialkyl aluminum.

Description

l~Z8920 POLYMERIZATION OF a-OLEFINS WITH A DUAL
ORGANO TITANIUM-CHROMIUM CATALYST

The present invention concerns dual tran-sition metal compositions useful in the preparationof catalysts, and the resulting catalysts and process for polymerization of a-olefins employing these catalysts.

Dual transition metal compounds prepared by reacting a tetraorgano titanate with chromium oxide have been employed in the preparation of catalysts for olefin polymerization as described in Boone U.S.
Patents 3,752,795 and 3,847,957. It has now been dis-covered that dual transition metal compounds prepared from chromium oxide and a tetravalent organoxy titanium halide can be employed in catalysts suitable for the polymerization of a-olefins.

One aspect of the present invention concerns dual transition metal compounds which are the reaction product of chromium oxide and a tetravalent hydrocarbyloxy titanium halide. Another aspect concerns a catalyst for polymerizing a-olefins which comprises (a) such a reac-tion product, (b) a solid catalyst support, and (c) an organometallic activating agent or cocatalyst. Another aspect is a process for polymerizing ~-olefins which 27,724-F
.' ~.

'llZ8920 comprises conducting the polymerization in the pre-sence of such a catalyst.

Suitable titanium compounds which can be employed in the preparation of the compounds of the present invention containing both chromium and titanium include those represented by the formula ~RO)n TiX4_n wherein R is a monovalent hydrocarbyl group, X is a halogen such as chlorine, bromine, iodine, preferably chlorine or bromine, and n has a value of from 1 to 3, preferably 2.
.
These titanium compounds are readily prepared by the admixture of a titanium tetrahalide (TiX4) and a titanate (Ti(OR)4), preferably in the presence of an inert solvent. The reaction proceeds presumably as follows:

; nTi(OR)4 + (4-n) TiX4 ~ 4Ti(oR)nX4 n ,.,~
as shown in THE ORGANIC CHEMISTRY OF TITANIUM, Raoul ; Feld and Peter L. Cowe, Butterworth & Co. Ltd., 1965, page 49 where X is chlorine.

The term "hydrocarbyl" as employed herein means alkyl, cycloalkyl, aryl, aralkyl, alkenyl and similar hydrocarbon radicals having from 1 to 20 carbon atoms wlth C1-C10 alkyl being especially preferred.

Particularly suitable tetra~alent titanium compounds include, for example, dibutoxy titanium dichloride, dibutoxy titanium dibromide, diethoxy titanium dichloride, :
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""'`'` il28920 diethoxy titanium dibromide, dipropoxy titanium dichloride, dipropoxy titanium dibromide, diphenoxy titanium dichloride, - 5 diphenoxy titanium dibromide, ethoxy titanium trichloride, ethoxy titanium tribromide, propoxy titanium trichloride, propoxy titanium tribromide, butoxy titanium trichloride, phenoxy titanium trichloride, phenoxy titanium tribromide, triethoxy titanium chloride, triethoxy titanium bromide, tripropoxy titanium chloride, tripropoxy titanium bromide, tributoxy titanium chloride, tributoxy titanium bromide, triphenoxy titanium chloride, triphenoxy titanium bromide, and mixtures thereof.

The chromium oxide employed is hexavalent chromium oxide, CrO3.

The reaction between the hydrocarbyloxy titanium compound and the chromium oxide is preferably carried out in the presence of a suitable hydrocarbon solvent or diluent at temperatures of from 0C to 120C, preferably from 20C to 90C at pressures of from 1 to 100 atmopheres.
The reaction is most preferably conducted at 25C to 50C
at atmospheric pressure, e.g. 14.7 psi (1.03 kg/cm2).
The time depends upon the reaction temperature, but usually from 0.5 to 72 hours, preferably from 1 to 24 hours, is sufficient.

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~ ~'lZ89~0 : The molar ratio of chromium oxide to hydro-carbyloxy titanium halide is from 0.25:1 to 6:1, preferably from 0.5:1 to 2:1. At ratios lower than 0.25:1 very small amounts of product are formed and at quantities above about 6:1, quantities of chromium oxide are wasted.

While the exact structure of the reaction product (A) is not known, it is believed to be that . represented by the formulas (I) ~ X O X
R ~ Ti-O-Cr-O ~ Ti-OR
~' " J
Q ~ n Q
,:
and 15 (II) ~ X ~
OmCrt-o-Ti~Q
~ Q P

wherein each Q is independently a halogen atom or a -OR group, each X is independently a halogen atom, each R is independently a hydrocarbyl group, n has an average value of from 1 to 6, preferably from about 1 ` to 2, m has an average value of from zero to 2, preferably 1 to 2, p has an average value of from 1 to 6, preferably from 2 to 4, and ~-(2m + p) is equal to the valence of chromium.

The preferred reaction products are those which are hydrocarbon soluble, e.g. those wherein the average value of n is less than 5, preferably less than 3.
,~

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Suitable inert solid support materials IB) which can be employed include, for example, silica, titania, zirconia, magnesium oxide, zinc chloride, and magnesium chloride mixtures thereof. A particularly suitable inert support material is prepared by reacting an organomagnesium component with a halide source.

A suitable organomagnesium component is a hydrocarbon soluble complex of the formula MgR"2 xMR'Iy wherein each R" is independently hydrocarbyl or hydro-carbyloxy, M is aluminum, zinc or mixtures thereof,x is about 0.001 to 10, especially from about 0.15 to about 2.5, and y is the number of hydrocarbyl groups corresponding to the valence of M. The hydrocarbyl and hydrocarbyloxy groups are monovalent hydrocarbon radicals, preferably, alkyl, cycloalkyl, aryl, aralkyl, alkenyl and similar hydrocarbon radicals having 1 to 20 carbon atoms. Cl-C10 alkyl groups are-especially preferred. Likewise, preferably, hydrocarbyloxy is alkoxy, cycloalkyloxy, aryloxy, aralkyloxy, alkenyloxy and similar oxyhydrocarbon radicals having 1 to 20 carbon atoms, with alkyloxy having 1 to 10 carbon atoms being preferred. Hydrocarbyl is preferred over hydrocarbyloxy.

This complex is prepared by reacting particulate magnesium such as magnesium turnings, or magnesium particles with about a stoichiometric amount of hydrocarbyl or hydro-carbyloxy halide R'X. The resulting hydrocarbon insoluble MgR"2 is solubilized by adding the organometallic compound such as AlR"3 or mixtures thereof with ZnR"2. The amount of organometallic compound added should be enough to ' 30 solubilize a significant amount of MgR"2, e.g., at least 5 weight percent, preferably at least 50 weight percent, and especially preferred all the MgR"2. When employing 27,724-F
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~Z89ZO

a mixture of AlR"3 and ZnR"2 to solubilize MgR"2, the atomic ratio of Zn to Al is from 3000:1 to 0.1:1, pre-ferably from 350:1 to 1:1.

In order to obtain maximum catalyst efficiency at polymerization temperatures above 180C, it is desirable to minimize the amount of aluminum in the complex as well as in the total catalyst. Accordingly, for catalysts having Al:Ti atomic ratios less than 120:1, it is desirable to have a Mg:Al atomic ratio more than 0.3:1, preferably from 0.5:1 to 10:1.

Organometallic compounds, other than AlR"3, ZnR"2 or mixtures thereof, can be used to solubilize the organo-magnesium compound in hydrocarbons, usually in an amount sufficient to produce an atomic ratio of metal in the organometallic compounds to magnesium of 0.01;1 to 10:1.
Examples of such other organometallic compounds include boron trialkyls such as boron triethyl, alkyl silanes such as dimethyl silane and tetraethyl silane, alkyl tin and alkyl phosphorous compounds.

Alternatively, organomagnesium compounds can be rendered soluble in hydrocarbon by addition of ether, amine, etc. More recently, such compounds have been made hydrocarbon soluble as taught in Kamienski et al. U.S. 3,646,231. These hydrocarbon - 25 soluble organomagnesium compounds are particularly desirable.

Preferably the organomagnesium compound is a ffldrocarbon soluble dihydrocarbylmagnesium such as the magnesium dialkyls and the magnesium diaryls. Exemplary 27,724-F

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suitable magnesium dialkyls include particularly n-butyl--sec-butyl magnesium, diisopropyl magnesium, di-n-hexyl magnesium, isopropyl-n-butyl magnesium, ethyl-n-hexyl magnesium, ethyl-n-butyl magnesium, di-n-octyl magnesium and others wherein alkyl has from l to 20 carbon atoms.
Exemplary suitable magnesium diaryls include diphenyl-magnesium, dibenzylmagnesium, and particularly ditolyl-magnesium. Also suitable are alkyl and aryl magnesium alkoxides and aryloxides and aryl and alkyl magnesium halides with the halogen-free organomagnesium compounds being more desirable.

The halide source is suitably an active non-metallic halide of the formula R'X wherein R' is hydrogen or a monovalent organic radical and X is halogen. Alternatively, the halide source is a metallic halide corresponding to the formula MRy aXa wherein M is a member of Groups IIB, IIIA or IVA of Mendeleev's Periodic Table of the Elements, R is a monovalent organic radical usually hydrocarbyl or hydrocarbyloxy, X is halogen, y is a number corresponding to the valence of M, and a is a number from l to y.

The preferred halide sources are the active non-metallic halides including hydrogen halides and active organic halides such as t-alkyl halides, allyl halides, benzyl halides and other active hydrocarbyl halides. By an active organic halide is meant a hydrocarbyl halide that contains a labile halogen at least as active, i.e., as easily lost to another com-pound, as the halogen of sec-butyl chloride and pre-ferably as active as t-butyl chloride. Active organic dihalides, trihalides and other polyhalides are also suitably employed. Examples of preferred active non--metallic halides include hydrogen chloride, hydrogen '' .

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bromide, t-butyl chloride, t-amyl bromide, allyl chloride, benzyl chloride, crotyl chloride, methylvinyl carbinyl chloride, ~-phenylethyl bromide, and diphenyl methyl chloride. Most preferred are hydrogen chloride, t-butyl chloride, allyl chloride and benzyl chloride.

Suitable metallic halides are organometallic halides and metal halides wherein the metal is in Group IIB, IIIA or IVA, of Mendeleev's Periodic Table of Elements.
Preferred metallic halides are aluminum halides of the formula AlR3 aXa wherein each R is independently hydrocarbyl such as alkyl, X is a halogen, and a is a number from 1 to 3.
Most preferred are alkylaluminum halides such as ethylaluminum sesquichloride, diethylaluminum chloride, ethylaluminum dichloride, and diethylaluminum bromide, with ethylaluminum dichloride being especially preferred. Alternatively, a metal halide such as aluminum trichloride or a combination of aluminum trichloride with an alkyl aluminum halide or a trialkyl aluminum compound may be suitably employed.

A sufficient guantity of the halide source is employed to provide a small amount in excess of that required to completely react with the solid support material, if such occurs as in the reaction of a dialkyl magnesium compound with the halide source.

The organic moieties of the aforementioned organomagnesium, e.g., R", and the organic moieties of the halide source, e.g., R and R', are suitably any other organic radical provided that they do not contain functional groups that poison conventional Ziegler catalysts.
Preferably such organic moieties do not contain active ~- 30 hydrogen, i.e., those sufficiently active to react with the Zerewitinoff reagent.

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:, , ' ' : ' ~ ' ~` 1;~2ss2a In those instances where the halide source does not contain a reducing metal such as aluminum or contains an insufficient quantity thereof, then an organometallic compound is added so as to provide the desired quantity of reducing metal as an activator or co-catalyst (C). Any reducing component commonly employed in Ziegler polymerization may be used.
Preferred are alkyl aluminum compounds having at least two alkyl groups per aluminum, e.g., aluminum trialkyls or dialkyl aluminum halides. Examples include aluminum triethyl, aluminum triisobutyl, aluminum tripropyl, aluminum trimethyl, diethyl aluminum chloride and others wherein alkyl has from l to 12 carbons and halide is preferably chloride or bromide. Preferably, the organometallic reducing compound is present in concentrations sufficient to provide an atomic ratio of reducing metal to tran-sition metal in the range from 0.3:1 to 2000:1, pre-ferably from 1:1 to 100:1, especially from 10:1 to 5~

Such activating agents or cocatalysts are generated in situ when an aluminum alkyl halide is employed as the halide source in preparing the inert solid support from an organomagnesium compound.

To maximi~e catalyst efficiency, the catalyst is prepared by mixing the components of the catalyst in an inert liquid diluent in the following especially pre-ferred order: (1) the inert support material (B) preferably prepared in situ by reacting an organo-magnesium compound with an active halide source, (2) the reducing component or activator (C), and (3) the organo titanium-chromium reaction product (A). The 27,724-F

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concentration~ of catalyst components are preferably such that when the essential components are combined, the resultant slurry is from 0.005 to 1.0 molar (moles/-liter) based on magnesium.

By way of example, suitable inert organic diluents or solvents include liquefied ethane, propane, isobutane, n-butane, n-hexane, the various isomeric hexanes, isooctane, paraffinic mixtures of alkanes having from 8 to 12 carbon atoms, cyclohexane, methylcyclopentane, dimethylcyclohexane, dodecane, as well as industrial solvents composed of saturated or aromatic hydrocarbons such as kerosene, naphthas, etc., especially when freed of any olefin compounds and other impurities. Also suitable are aromatic diluents like benzene, toluene, ethylbenzene, cumene, and decalin. Preferred are liquid diluents having boiling points in the range from -50 to 200C.

Mixing of the components to provide the desired catalyst is advantageously carried out under an inert atmosphere such as nitrogen, argon or other inert gas at temperatures in the range from -100 to 200C, preferably from 0 to 100C. The mixing time is not critical as the catalyst usually forms in one minute or less. Also in the preparation of the catalyst, it is usually not necessary to separate hydrocarbon soluble and insoluble components.

In preparing the catalysts, the proportions of the components are such that the atomic ratios of the metallic elements are:

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~:Z8920 Ms:Ti is from 0.1:1 to 1000:1, preferably from 10:1 to 100:1 and most preferably from 20:1 to 40:1;

Mr:Ti is from 0.3:1 to 2000:1, preferably from 1:1 to 100:1 and most preferably from 10:1 to 50:1; and x'sX:Mr is from 0.01:1 to 100:1, preferably from 0.1:1 to 10:1 and most preferably from 0.4:1 to 1:1;

where Ms is the metallic element of the inert solid support such as Zn, Si, Ti, Zr, and preferably Mg.

Mr is the metal of the organometallic activating agent or cocatalyst; and x'sX is the excess halide above that theoretically required lS to convert the organomagnesium compound or other reactable support compound to the corresponding halide.

Polymerization of a-olefins is effected by ; contacting a catalytic amount of the catalyst composition and the a-olefin monomer at temperatures in the range from 0 to 300C, preferably at solution polymerization tempera-tures, e.g., from 130 to 250C for a residence time of about a few seconds to 48 hours or more, preferably 15 seconds to 2 hours. It is generally desirable to carry out the polymerization in the absence of moisture and oxygen using an inert organic liquid diluent. Diluents used in the catalyst preparation are particularly suit-able.

. , ,~

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'~

~i28920 ~ suitable amount of the catalyst i8 generally within the range fr~m 0.0001 to 0.1 millimole titanium per liter of diluent. However, the most advantageous catalyst concentration will depend upon polymerization conditions such as temperature, pressure, solvent and presence of catalyst poisons.

Olefins which are suitably homopolymerized or copolymerized in the practice of this invention are a-olefins such as ethylene or a mixture of ethylene and a higher a-olefin such as hexene-1 and octene-1, or other ethylenically polymerizable monomer. Most benefits are realized in the polymerization of ali-phatic a-monoolefins particularly ethylene and mix-tures of ethylene and hexene-l, octene-l, or similar lS higher a-olefins.

To optimize catalyst yields in the polymeri-zation of ethylene, it is preferable to maintain an ethylene concentration in the solvent in the range from l to lO weight percent, most advantageously 1.2 to 2 weight percent. To achieve this, when an excess of ethylene is fed into the system, a portion of the ethylene can be vented.
, To realize the full benefit of the high efficiency catalyst, care must be taken to avoid oversaturation of the solvent with polymer. For best results, it is preferred that the amount of polymer in the liquid carrier not exceed about 50 weight percent based on the total weight of the reaction mixture.

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The polymerization pressures preferably employed are relatively low, e.g., from 50 to 1000 psig (3.4 to 68.0 atm), especially from 100 to 600 psig ~6.8 to 40.8 atm). ~owever, polymerization within the scope of the present invention can occur at pres-sures from atmospheric to the pressure limits of the reactor. During polymerization, it is desirable to stir the reactant mixture to obtain better tempera-ture control and uniform polymerization conditions.

Hydrogen can be employed to lower the molecular weight of the polymer. For this purpose, it is beneficial to employ hydrogen in amounts ranging from 0.001 to 1 mole per mole of monomer. The larger amounts of hydrogen produce generally lower molecular weight polymers.
lS Hydrogen can be added with a monomer stream or separately to the reactor before, during or after addition of the monomer, or by other conventional means.

The monomer or mixture of monomers is contacted with the catalyst in any conventional manner, preferably by bringing the catalyst and monomer together with intimate agitation. With more active catalysts, means can be provided for refluxing monomer and solvent, if any, to remove the heat of reaction or otherwise dissipate the exothermic heat of polymerization.

If desired, a gaseous monomer can be contacted with the solid catalyst in the presence or absence of liquid diluent.

Polymerization can be effected in a batch or continuous manner, such as, for example, by passing the reaction mixture through an elongated reaction tube 27,724-F

l~Z8920 contacted externally with suitable cooling medium to maintain the desired reaction temperature, or by passing the reaction mixture through an equilibrium overflow reactor or a series thereof.

The polymer is recovered from the polymeri-zation mixture by removing any unreacted monomer and solvent. Generally, no further purification is required, thus eliminating catalyst residue removal steps. In some instances, however, it may be desirable to add a small amount of a conventional catalyst deactivating reagent. The resultant polymer normally contains insignificant amounts of catalyst residue and possesses a relatively broad molecular weight distribution.

The following examples are given to further illustrate the invention. All parts and percentages are by weight unless otherwise indicated. The melt index values I2 and I1o were determi~ed by ASTM
D-1238-70 and the density values were determined by ASTM D-1248-74.

ExAMæLE 1 A Pre~aration of Dual Transition Metal Compounds 1. In a nitrogen-filled dry box 3.4 ml (0.01 mole) of tetra-n-butyl titanate and 1.1 ml (0.01 mole) of titanium tetrachloride were added to 50 ml of Isopar~ E (a mixture of C7-Cg hydrocarbon) in a 500 ml reaction flask. Two grams (0.02 mole) of powdered chromium (VI) oxide (CrO3) was then added followed by an additional 50 ml of Isopar~ E. The reaction flask was sealed, removed from the dry box to a lab hood, and fitted with a condenser and a nitrogen inlet means. The contents were heated at 27,724-F

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~ ' ` 1128920 50C to 60C f~r 24 hours under nitrogen. The resultant red-brown solution was filtered from a pink precipitate in a nitrogen-filled dry box.
The red-brown filtrate contained by X-ray emission spectroscopy and titrimetric analysis with silver nitrate, 0.95% Ti, 0.13% Cr, and 1.12% Cl.

2. The procedure of A-l was repeated with the filtrate analysis being 0.95% Ti, 0.11% Cr and 0.63%
Cl.

3. The procedure of A-l was repeated employing 2.98 ml (0.01 mole) of tetraisopropyl titanate in place of 3.4 ml (0.01 mole) of tetra-n-butyl titanate.
After five hours of reaction, the product was predomi-nately a brown precipitate. The reaction mixture was filtered in a dry box yielding a brown powder and a clear yellow solution. The brown powder was found, after analysis, to contain 24% Ti, 8.2% Cr and 15.2% Cl.

B. Pre~aration of Catalyst 1. In a nitrogen filled dry box, a 4 oz (118 ~- cc) catalyst bottle containing 95.5 ml of Isopar~ E
` was added 1.5 ml (0.75 millimole) of a 0.5 M solution of ethyl aluminum dichloride in Isopar~ E. While stirring, 1.5 ml (0.6 millimole) of 0.4 M di-n-hexyl magnesium was added followed by the addition of 1.5 ml of a mixture prepared from 5 ml of the filtrate from A-l and 95 ml of Isopar~ F. The catalyst bottle was fitted with a rubber septum and removed from the dry box. The catalyst had the following atomic ratios: 67 Al, 53.6 Mg, 0.125 Cr, and 1 Ti.

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.~ , , ~, i ~' ,, :', ' 2. The procedure of B-l was repeated employing 3 ml of the diluted filtrate from A-l instead of 1.5 ml. The atomic ratios of the resultant catalyst was 33.5 Al, 26.8 Mg, 0.125 Cr, and 1 Ti.

C. Polymerization 1. To a stirred 5 liter batch reactor at 150C
containing 2 liters (20 psig vapor pressure; 1.4 atm) of Isopar~ E purified by passing through molecular sieves was added 1 psig (0.06 atm) of chromatographic grade hydrogen and 175 psig (11.`9 atm) of ethylene purified with molecular sieves. 20 ml of the slurried catalyst from B-l containing 12 mg of solid catalyst was syringed into a 75 ml pressure bomb under a nitro-gen purge. The bomb was then pressured to 250 psig (17.0 atm) and the catalyst vented into the reactor where the ethylene was polymerized at 150C for 31 minutes. The polymer was remove~ from the reactor and dried in a vacuum oven at 80C. The 65 g of recovered polymer had an I2 melt index of 0.18, an Ilo melt index of 3.78, an Ilo/I2 of 21.0, a density of 0.9762 and a catalyst efficiency of 5420 g polymer per g of solid catalyst or 0.62 x 106 g polymer per g of Ti.

2. The procedure of C-l was repeated except that 25 ml of the slurried catalyst prepared in B-l containing 15 mg of solid catalyst was employed and the polymerization was conducted for 34 minutes. The resultant 49 g of polymer had a melt index I2 of 1.17, an Ilo melt index of 13.53, an Ilo/I2 ratio of 11.56, a density of 0.950, a catalyst efficiency of 3270 g of polymer per g of solid catalyst or 0.37 x 106 g of polymer per g of Ti.

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89'~0 3. The procedure of C-1 was repeated except that the temperature was 140C which provided a solvent vapor pressure of about lS psig (1.0 atm), about 2 psig (0.12 atm) of hydrogen was added to the reactor and lS ml (9.5 mg of solid catalyst~
of the catalyst slurry from B-2 was employed at a polymerization time of 34 minutes. The resultant 89 g of recovered polymer had a melt index I2 of 1.21, a melt index Ilo of 10.15, an Ilo/I2 a density of 0.9696, and a catalyst efficiency of 9370 g of polymer per gram of solid catalyst or 0.56 x 106 g of polymer per g of Ti.

4. The procedure of C-l was employed except that the temperature employed was 170C which provided a solvent vapor pressure of about 35 psig (2.4 atm), about 2 psig (0.14 atm) hydrogen was employed and 20 ml (12.7 mg of solid catalyst) of the slurried catalyst of B-l was employed.
The polymerization was conducted for 38 minutes.
The 22 g of recovered polymer had a melt index I2 of 5.46, a melt index Ilo of 45.10, an Ilo/I2 ratio of 8.26, a density of 0.9557 and a catalyst efficiency of 1730 g of polymer per g of solid catalyst or 0.106 x 106 g of polymer per g of Ti.

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Claims (10)

1. As a composition of matter, the reaction product of (1) a tetravalent hydrocarbyloxy titanium halide of the formula: (Ro)nTix4-n wherein each R
is independently a hydrocarbyl group having from 1 to about 20 carbon atoms, X is chlorine or bromine, and n has a value of from 1 to 3, and (2) CrO3 in a mole ratio of CrO3 to hydrocarbyloxy titanium halide of from 0.25 to 6:1.

2. The composition of Claim 1 wherein each R is independently a hydrocarbyl group having from 1 to 10 carbon atoms, n has a value of 2, and the mole ratio of CrO3 to titanium halide is 0.5 to 2Ø

3. The composition of Claim 2 wherein the hydro-carbyloxy titanium halide is the reaction product of (a) tetraisopropyl titanate, tetra-n-butyl titanate or a mixture thereof with (b) titanium tetrachloride.

4. A catalyst suitable for the polymerization of an .alpha.-olefin or mixture thereof which catalyst comprises (a) an inert solid catalyst support containing metal (Ms) selected from the group Mg, Zr, Zn, Si, Ti and mixtures thereof; (b) the reaction product of a tetravalent hydro-carbyloxy titanium halide or mixture of such compounds 27,724-F

and CrO3 in a mole ratio of CrO3 to hydrocarbyloxy titanium halide of from 0.25 to 6:1; and (c) an organoaluminum reducing agent suitable for use in Ziegler polymerization; provided that the proportions of these components are such that the atomic ratio of Ms:Ti is from 0.1 to 1000 and the ratio of Al:Ti is from 0.3 to 2000.

5. The catalyst of Claim 4 wherein the said solid catalyst support (a) is the reaction product of an organomagnesium compound and a halide source; the hydro-carbyloxy titanium halide (b) is a compound of the formula (Ro)nTiX4-a wherein each R is independently a hydrocarbyl group having from 1 to 10 carbon atoms, X is chlorine or bromine, and n has a value of from 1 to 3; and the organo-aluminum compound (c) is an aluminum trialkyl, a dialkyl aluminum halide or a mixture thereof, wherein the alkyl groups independently have from 1 to 12 carbon atoms; and wherein the atomic ratio of Mg:Ti is from 10:1 to 100:1, of Al:Ti is from 1:1 to 100:1, and of x'sX:Al is from 0.01:1 to 100:1.

6. The catalyst of Claim 5 wherein the organomagnesium compound is a hydrocarbon soluble dialkyl magnesium compound; the halide source is an aluminum alkyl halide; and the organoaluminum compound is generated in situ from the reaction of the dialkyl magnesium compound and the aluminum alkyl halide; and wherein the atomic ratio of Mg:Ti is from 20:1 to about 40:1; of Al:Ti is from 10:1 to 50:1 and of x'sX:Al is from 0.01:1 to 10:1.

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7. The catalyst of Claim 5 wherein the organomagnesium compound is di-n-hexyl magnesium, the halide source is ethyl aluminum dichloride; and the x'sX:Al ratio is from 0.4:1 to 1:1.

8. A process for polymerizing .alpha.-olefins under conditions characteristic of Ziegler polymerization by contacting the .alpha.-olefin monomer at temperatures in the range from 0° to 300°C with a catalytic amount of the supported catalyst composition of Claim 4.

9. The process of Claim 8 wherein the a-olefin is ethylene or a mixture of ethylene and a copolymerizable higher .alpha.-olefin, the inert solid catalyst support (a) is the reaction product of a hydrocarbon soluble dialkyl magnesium compound and a halide source, and the process is conducted under solution polymerization conditions.

10. The process of Claim 8 wherein ethylene or a mixture thereof with hexene-l or octene-l is polymerized under solution polymerization conditions using a catalyst comprising (a) an inert support prepared by reaction of di-n-hexyl magnesium with ethyl aluminum dichloride and (b) the reaction product of (l) tetraisopropyl titanate, tetra-n-butyl titanate, or a mixture thereof, (2) titanium tetrachloride, and (3) chromium oxide, said catalyst having an atomic ratio of Mg:Ti of 20:1 to 40:1, Al:Ti of 10:l to 50:1, and x'sX:Al of 0.4:1 to l.0:1.

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