The present invention relates to an activator solid support for metallocene catalysts used for the polymerization of olefins, to a process for preparing such a support, to the corresponding catalytic system and to the suspension or gas-phase polymerization of olefins using such a catalytic system.
It is well known to (co)polymerize ethylene and xcex1-olefins in the presence of a metallocene/aluminoxane catalyst system. The first very active catalytic system of this type that was discovered is that based on zirconocene: Cp2ZrCl2/aluminoxane. Metallocene/aluminoxane catalyst systems are soluble in the polymerization medium. The extension of research in this field has led to the discovery of other metallocene catalysts, such as bridged metallocenes which are capable, in the case of the copolymerization of ethylene with xcex1-olefins, of leading to better uniformity in the distribution of the comonomers in the molecular chains.
However, aluminoxanes, in particular methylaluminoxane which is the most commonly used, have the drawbacks of being expensive and unstable substances which are partly responsible for the poor morphology of the polymers, a situation which causes fouling of the reactors and which makes the conveying process very complicated.
The Applicants have sought to solve this problem for the purpose of providing a metallocene-based catalytic system, which is active for the polymerization of olefins and does not use aluminoxane, or uses less aluminoxane than in the past.
It is now accepted that a metallocene complex has a cationic nature in its active form. This has been confirmed by several spectroscopic methods and by the equivalence of the properties of two polymers, one produced by the metallocene/aluminoxane system and the other produced by metallocene/stable cationic salt systems. The role of the aluminoxane is assumed to be the alkylation of the metallocene, the activation of the methylated species by the formation of a cationic complex and the stabilization of this active species. Many non-coordinating counteranions have been proposed for replacing the aluminoxane in its activator role [J. Ewen, M. Elder, R. Jones, L. Haspeslagh, J. Atwood, S. Bott and K. Robinson, Makromol. Chem. Macromol. Symp. 48/49, 253 (1991) and M. Bochmann and S. Lancaster: Organometallics, 12, 633 (1993)].
The Applicants have discovered that the counteranion of the active cationic complex could consist of a solid support, advantageously having a defined and controlled structure comparable to that of the supports employed in conventional Ziegler-Natta catalysis in order to allow physical development of the polymerization, the said support being functionalized in order to create acid sites which activate the metallocene without complexing it.
The solid support according to the invention, as defined below, constitutes an activator support which has made it possible to reach levels of activity, in the polymerization of olefins, at least equal to, but often greater than, the activity displayed by a purely homogeneous system.
The subject of the present invention is therefore firstly an activator solid support for metallocenes as catalysts in the polymerization of olefins, characterized in that it consists of a group of support particles for a solid catalytic component, which are formed from at least one porous mineral oxide, the said particles having been modified in order to carry, on the surface, aluminium and/or magnesium Lewis-acid sites of formula: 
or xe2x80x94Mgxe2x80x94F, the 
groups coming from a functionalization agent having reacted with xe2x80x94OH radicals carried by the base particles of the support, the functionalization reaction having been followed by a fluorination reaction.
The direct use of aluminium and/or magnesium fluorides presents difficulties which are barely surmountable in terms of forming a support having suitable particle-size and porosity properties.
The porous mineral oxides are advantageously chosen from silica, alumina and mixtures thereof.
The porous mineral oxide particles preferably have at least one of the following characteristics:
they include pores having a diameter ranging from 7.5 to 30 nm (75 to 300 xc3x85);
they have a porosity ranging from 1 to 4 cm3/g;
they have a specific surface area ranging from 100 to 600 m2/g; and
they have an average diameter ranging from 1 to 100 xcexcm.
Before it is modified, the support has xe2x80x94OH radicals on its surface, in particular from 0.25 to 10, and even more preferably from 0.5 to 4 xe2x80x94OH radicals, per nm2. After it has been modified, the said support has as many at least partially fluorinated aluminium and/or magnesium Lewis-acid sites per nm2.
The support may be of various kinds. Depending on its nature, its state of hydration and its ability to retain water, it is possible to make it undergo dehydration treatments of greater or lesser intensity depending on the desired surface content of xe2x80x94OH radicals.
Those skilled in the art may determine, by routine tests, the dehydration treatment that should be applied to the support that they have chosen, depending on the desired surface content of xe2x80x94OH radicals.
For example, if the support is made of silica, which is in accordance with a preferred embodiment of the invention, the silica may be heated between 100 and 1000xc2x0 C. and preferably between 140 and 800xc2x0 C., with purging by an inert gas such as nitrogen or argon, at atmospheric pressure or under a vacuum, for example of an absolute pressure of 1xc3x9710xe2x88x922 millibars, for at least 60 minutes, for example. For this heat treatment, the silica may be mixed, for example, with NH4Cl so as to accelerate the dehydration.
If this heat treatment is between 100 and 450xc2x0 C., it is conceivable to follow it with a silanization treatment. This kind of treatment results in a species derived from silicon being grafted on the surface of the support in order to make this surface more hydrophobic. This silane may, for example, be an alkoxytrialkylsilane, such as methoxytrimethylsilane, or a trialkylchlorosilane, such as trimethylchlorosilane or triethylchlorosilane.
This silane is generally applied to the support by forming a suspension of this support in an organic silane solution. This silane may, for example, have a concentration of between 0.1 and 10 mol per mole of OH radicals on the support. The solvent for this solution may be chosen from linear or branched aliphatic hydrocarbons, such as hexane or heptane, alicyclic hydrocarbons, optionally substituted, such as cyclohexane, and aromatic hydrocarbons, such as toluene, benzene or xylene. The treatment of the support by the silane solution is generally carried out between 50xc2x0 C. and 150xc2x0 C., for 1 to 48 hours, and with stirring.
After silanization, the solvent is removed, for example, by siphoning or filtration, the support then being washed, preferably thoroughly, for example using 0.3 1 of solvent per gram of support.
The surface xe2x80x94OH radical content of the support may be assayed using known techniques such as, for example, by reacting an organomagnesium compound such as CH3MgI with the support and by measuring the amount of methane given off [McDaniel, J. Catal., 67, 71 (1981)]; by reacting triethylaluminium with the support and by measuring the amount of ethane given off [Thesis of Vxc3xa9ronique Gachard-Pasquet, Universitxc3xa9 Claude Bernard, Lyon 1, France, 1985, pages 221-224].
According to the present invention, the said at least partially fluorinated aluminium and/or magnesium Lewis-acid sites are formed by the reaction of xe2x80x94OH radicals carried by the support base particles with at least one functionalization agent chosen from:
compounds of formula (I):
Al(R1)3xe2x80x83xe2x80x83(I)
xe2x80x83in which the R1 groups, which are identical or different, each represent a C1-C20 alkyl group;
compounds of formula (II):
Mg(R2)2xe2x80x83xe2x80x83(II)
xe2x80x83in which the R2 groups, which are identical or different, each represent a C1-C20 alkyl group; and
compounds of formula (III): 
xe2x80x83in which:
the R3 groups, which are identical or different, each represent a C1-C12 alkyl group or a C1-C12 alkoxy group;
the R4 groups, which are identical or different, each represent a C1-C12 alkyl group or a C1-C12 alkoxy group;
Y represents Al or Si, m having a value of 2 if Yxe2x95x90Al and 3 if Yxe2x95x90Si; and
n has a value of 0 or is an integer from 1 to 40, n preferably having a value of 0 or being an integer from 1 to 20;
compounds of formula (IV): 
xe2x80x83in which:
the R5 groups each represent a C1-C8 alkyl group; and
p is an integer from 3 to 20,
the said functionalization reaction having been followed by a fluorination reaction.
By way of examples of compounds (I), mention may be made of those in which the R1 groups represent methyl, ethyl, butyl and hexyl, it being possible for the aluminium to carry 1, 2 or 3 different groups; a preferred compound (I) is triethylaluminium.
By way of examples of compounds (II), mention may be made of those in which R2 represents methyl, ethyl and butyl; a preferred compound (II) is (n-butyl)(sec-butyl)magnesium.
By way of examples of compounds (III), mention may be made of dibutoxyaluminoxytriethoxysilane (C2H5O)3Sixe2x80x94Oxe2x80x94Alxe2x80x94(OC4H9)2, tetraisobutyldialuminoxane (iBu)2Alxe2x80x94Oxe2x80x94Al(iBu)2 and linear alkylaluminoxane oligomers, in particular those in which R3 and R4 are methyl groups.
Compounds (IV) are cyclic alkylaluminoxane oligomers; in particular, mention may be made of those in which R5 is a methyl group.
The present invention also relates to a fluorinated functionalized support, as described above, in the state in which it is pre-impregnated with a metallocene catalyst, the said metallocene catalyst having been subjected, if required, to a prealkylation treatment carried out before or after the said support has been pre-impregnated.
The present invention also relates to a process for preparing an activator solid support for metallocenes as catalysts in the polymerization of olefins, characterized in that a group of support particles for a solid catalytic component, which are formed from at least one porous mineral oxide and carry, on the surface, xe2x80x94OH radicals, undergoes functionalization by using a functionalization agent capable of grafting aluminium and/or magnesium Lewis-acid sites on the said particles; the said support particles thus grafted are then subjected to a fluorination treatment.
In order to implement this process, it is possible to use the support particles such as those described above and the functionalization agents such as those described above.
In a preferred method of implementing this process, the functionalization is carried out by treating a suspension of the said particles in a solvent medium with the said functionalization agent at a temperature ranging from xe2x88x92150xc2x0 C. to +150xc2x0 C. for a period of time ranging from 1 minute to 12 hours, and then by recovering the grafted particles after washing. The solvent is especially chosen from aliphatic, alicyclic and aromatic hydrocarbons, and more preferred temperature and time conditions are from 30 to 100xc2x0 C. and from 1 to 3 hours. In particular, from 0.5 to 20 mmol of functionalization agent per g of particles are used.
After functionalization, a heat treatment in an inert gas (such as argon or nitrogen) may optionally be carried out, preferably in a bed fluidized by the said inert gas, the said treatment being intended to remove the alkoxy groups present on the surface, which groups could come from the functionalization agent carrying R3 and/or R4 alkoxy radicals. This heat treatment, or pyrolysis, is advantageously carried out at approximately 200-600xc2x0 C. for approximately 1-10 hours. If the treatment were not carried out, the alkoxy groups could be the cause of water forming by reaction with oxygen during an oxidation treatment which may be intended before the final fluorination. This is because it is desirable to remove any trace of water since water is likely to adversely affect or poison the solid support.
The oxidation treatment indicated above may advantageously consist of a heat treatment of the functionalized support particles, in a bed fluidized by oxygen, for example at 200-600xc2x0 C. for 1-10 hours. This treatment makes it possible to increase the acidity of the surface of the support and, consequently, the performance of the catalytic system.
The radicals R1, R2, R3, R4 and R5 are at least partially replaced by F during the final fluorination step. The fluorination treatment may be carried out by bringing the functionalized support particles into contact with gaseous hydrofluoric acid, if necessary after heat treatment in an inert gas and/or after oxidation, this contacting step being carried out for a period of time ranging from 1 minute to 24 hours, at a temperature ranging from 20 to 800xc2x0 C.; however, the hydrofluoric acid may advantageously be replaced by (NH4)2SiF6, in which case the functionalized support particles are mixed with powdered (NH4)2SiF6, if necessary after heat treatment in an inert gas and/or after oxidation; the actual fluorination treatment with (NH4)2SiF6 consists especially in gently fluidizing the aforementioned mixture of support particles and (NH4)2SiF6 with an inert gas, such as argon or nitrogen, and in carrying out a heat treatment at a temperature of approximately 300 to 500xc2x0 C. for approximately 1 to 10 hours. In general, especially from 1 to 5% by weight, in particular 3 to 5% by weight, of fluorine with respect to the said support particles are used for the fluorination (above the value of 5% by weight, the support undergoes degradation).
The present invention also relates to a catalytic system for the polymerization of olefins, comprising:
(a) a metallocene catalyst, which has, if required, been subjected to a prealkylation treatment;
(b) a cocatalyst; and
(c) an activator solid support for metallocene, as defined above or prepared by the process as defined above,
it being possible for the cocatalyst (b) to be absent if the metallocene catalyst (a) has been prealkylated, it being possible for the support (c) to have been impregnated with the metallocene catalyst (a), which catalyst has, if required, been subjected to a prealkylation treatment carried out either before or after the said support has been pre-impregnated.
The metallocene catalyst (a) generally consists of a compound of formula (V):
MLxxe2x80x83xe2x80x83(V)
in which:
M represents a transition metal belonging to Group 4b of the Periodic Table of Elements according to the Handbook of Chemistry and Physics, 61st edition;
L represents a ligand coordinated to the transition metal, at least one ligand L being a group having a cycloalkadienyl-type backbone; and
x is equal to the valency of the transition metal, the ligands L, the number of which is equal to the valency of the transition metal M, being identical or different.
In particular, M is Ti, Zr or Ef.
The expression xe2x80x9cgroup having a cycloalkadienyl-type backbonexe2x80x9d should be understood to mean the cycloalkadienyl group itself or a substituted cycloalkadienyl group.
Preferably, a cycloalkadienyl group is a cyclopentadienyl group.
When the compound of formula MLx contains at least two groups having a cycloalkadienyl-type backbone, at least two of these groups may be linked together by a divalent radical. Each divalent radical may be an alkylene radical, such as the methylene radical (xe2x80x94CH2xe2x80x94), the ethylene radical (xe2x80x94CH2CH2xe2x80x94) or the trimethylene radical (xe2x80x94CH2CH2CH2xe2x80x94), it being possible for this alkylene radical also to be substituted, for example by at least one hydrocarbon group, such as the isopropylidene radical; the divalent radical may also be a silylene (xe2x80x94SiH2) group, optionally substituted, for example by at least one hydrocarbon group, as is the case with dialkylsilylene (dimethylsilylene), diarylsilylene (diphenylsilylene) or alkylarylsilylene (methylphenylsilylene) radicals.
When a cycloalkadienyl group is substituted, the substituents are especially chosen from C1-C20 alkyl, C2-C20 alkenyl, aryl and aralkyl groups. Two substituents which are in adjacent positions on the same cycloalkadienyl ring may be linked together, forming an aromatic or non-aromatic ring condensed on the said cycloalkadienyl ring. If the latter is a cyclopentadienyl ring, the resulting condensed cycle may be an indenyl, tetrahydroindenyl, fluorenyl or octahydrofluorenyl ring.
Moreover, at least one ligand L may be chosen from:
groups of formula: xe2x80x94Oxe2x80x94; xe2x80x94Sxe2x80x94; xe2x80x94NR6xe2x80x94; or xe2x80x94PR6 (where R6 represents hydrogen or a group chosen from the silyl, alkyl or aryl groups, the latter two being optionally halogenated), one of the free valencies of which is linked to the transition metal M atom and the other free valency of which is linked to a divalent radical which is itself linked to a ligand L having a cycloalkadienyl backbone; and
groups of formula: xe2x80x94OR7; xe2x80x94SR7; xe2x80x94NR72; or xe2x80x94PR72 (R7 having the same meaning as R6 above), the free valency of which is linked to a divalent radical which is itself linked to a ligand L having a cycloalkadienyl backbone;
examples of divalent radicals having been indicated above in the description of the agents carrying two cycloalkadienyl ligands.
Ligands L differing from those mentioned above may be chosen from:
hydrocarbon groups containing from 1 to 20 carbon atoms, such as linear or branched alkyl groups (such as methyl, ethyl, propyl, isopropyl and butyl); cycloalkyl groups (such as cyclopentyl and cyclohexyl); aryl groups (such as phenyl); alkaryl groups (such as tolyl); and aralkyl groups (such as benzyl);
alkoxy groups, such as methoxy, ethoxy, butoxy and phenoxy; and
halogens, such as fluorine, chlorine, bromine and iodine.
By way of examples, the metallocene catalyst may be chosen from the following compounds:
bis (cyclopentadienyl) dichlorozirconium (Cp2ZrCl2);
bis(indenyl)dichlorozirconium (Ind2ZrCl2);
bis(n-butylcyclopentadienyl)dichlorozirconium [(nBuCp)2ZrCl2];
ethylenebis(4,5,6,7-tetrahydro-1-indenyl)dichlorozirconium [Et (THInd)2ZrCl2];
ethylenebis(indenyl)dichlorozirconium [Et(Ind)2ZrCl2];
isopropylidene(cyclopentadienyl, fluorenyl)dichlorozirconium [ipr(Cp)(Flu)ZrCl2];
isopropylidenebis(tert-butylcyclopentadienyl)dichlorozirconium [iPr(tBuCp)2ZrCl2];
dimethylsilyl(3-tert-butylcyclopentadienyl, fluorenyl)dichlorozirconium;
dimethylsilylbisindenyldichlorozirconium [Me2Si (Ind)2ZrCl2];
bis(cyclopentadienyl)dimethylzirconium;
bis(indenyl)dimethylzirconium (Ind2ZrMe2);
ethylenebis(4,5,6,7-tetrahydro-1-indenyl)dimethylzirconium;
ethylenebis(indenyl)dimethylzirconium;
isopropylidene(cyclopentadienyl, fluorenyl)dimethylzirconium;
dimethylsilyl(3-tert-butylcyclopentadienyl, fluorenyl)dimethylzirconium;
bis(cyclopentadienyl)diphenylzirconium;
bis(cyclopentadienyl)dibenzylzirconium;
dimethylsilyl(tetramethylcyclopentadienyl, tertbutylamino)dichlorozirconium, the latter compound having the formula (CH3)2Si ((CH3)4C5, (CH3)3CN) ZrCl2; dimethylsilyl(tetramethylcyclopentadienyl, tertbutylamino)-dimethyltitanium, this compound having the formula (CH3)2Si((CH3)4C5, (CH3)3CN)Ti(CH3)2;
bis(cyclopentadienyl)dichlorotitanium;
ethylenebis(4,5,6,7-tetrahydro-1-indenyl)dichlorotitanium;
ethylenebis(indenyl)dichlorotitanium;
isopropylidene(cyclopentadienyl, fluorenyl)dichlorotitanium;
dimethylsilyl (3-tert-butylcyclopentadienyl, fluorenyl)dichlorotitanium;
bis(cyclopentadienyl)dimethyltitanium;
ethylenebis(4,5,6,7-tetrahydro-1-indenyl)dimethyltitanium;
ethylenebis(indenyl)dimethyltitanium;
isopropylidene(cyclopentadienyl, fluorenyl)dimethyltitanium;
dimethylsilyl(3-tert-butylcyclopentadienyl, fluorenyl)dimethyltitanium;
dimethylsilyl(tetramethylcyclopentadienyl, tert-butylamino)dichlorotitanium, the latter compound having the formula (CH3)2Si ((CH3)4C5, (CH3)3CN) TiCl2.
With regard to the cocatalysts (b), they are especially chosen from:
(b1) alkylaluminiums of formula (Ia):
Al(R8)3xe2x80x83xe2x80x83(Ia)
xe2x80x83in which the R8 groups, which are identical or different, represent a substituted or unsubstituted alkyl, containing from 1 to 12 carbon atoms such as ethyl, isobutyl, n-hexyl and n-octyl; an alkoxy; an aryl; a halogen; hydrogen or oxygen; at least one R8 group representing an alkyl;
(b2) aluminium sesquihalides;
(b3) compounds of formula (IIIa) consisting of compounds of formula (III) as defined above, in which Yxe2x95x90Al; and
(b4) compounds of formula (IV) as defined above.
By way of examples of cocatalyst (b), mention may be made of methylaluminoxane, triisobutylaluminium and triethylaluminium.
As was mentioned above, the metallocene catalyst may be pre-impregnated on the activator support. This pre-impregnation may be carried out as follows:
The activator support is put into suspension, in a solvent chosen from aliphatic, alicyclic or aromatic hydrocarbons, with the metallocene. The operation is carried out between 0 and 140xc2x0 C. for 1 hour to 10 hours. The proportion of metallocene represents between 0.01 and 20% by mass with respect to the activator support. At the end of the operation, the mixture is decanted in order to remove the supernatant liquid. The support is then washed several times, between 20 and 140xc2x0 C., with a quantity of solvent of between 50 and 300 ml per gram of support.
Moreover, as already mentioned above, the metallocene (a) may have been subjected to prealkylation; if the activator support is pre-impregnated with the metallocene (a), this prealkylation may take place either before or after the pre-impregnation.
The prealkylation may be carried out using an alkylizing agent, such as an alkyllithium or an alkylmagnesium, the straight-chain or branched alkyl group having from 1 to 20 carbon atoms, under the following conditions:
The metallocene or the impregnated solid support are placed in a Schlenk tube containing from 10 to 50 ml of a solvent, chosen from aliphatic, alicyclic or aromatic hydrocarbons, per gram of support or per 10 milligrams of metallocene. The temperature of the mixture is taken to between xe2x88x92100 and 0xc2x0 C. Between 1 and 5 mol of alkylizing agent per mole of metallocene are then introduced. After they have been introduced, the reaction mixture is left so as to come slowly back to room temperature. The complete operation lasts between 1 and 10 hours.
In the catalytic system according to the invention, the Al molar ratio of the cocatalyst (b1) or (b2) to the transition metal of the metallocene is especially from 1 to 10,000, in particular from 1 to 2000; and the Al molar ratio of the cocatalyst (b3) or (b4) to the transition metal of the metallocene (a) is especially from 1 to 10,000, in particular from 10 to 200. Moreover, the activator solid support is used especially in an amount ranging from 0.01 to 2000 mg, in particular from 0.01 to 200 mg, per xcexcmole of metallocene catalyst.
The present invention also relates to a process for homopolymerizing or copolymerizing olefins, in suspension or in the gas phase, in the presence of a catalytic system as defined above.
The olefins which can be used for the polymerization (homopolymerization and copolymerization) are, for example, the olefins containing from two to twenty carbon atoms and, in particular xcex1-olefins of this group. Mention may be made of ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-octene, 1-hexene, 3-methyl-1-pentene, 3-methyl-1-butene, 1-decene and 1-tetradecene, or mixtures thereof as the olefin. In particular, the olefin is ethylene.
If the polymerization process is carried out in suspension, it may be performed in the following manner: a suspension in an inert medium, such as an aliphatic hydrocarbon, of the catalytic system is introduced into a reactor, the concentration of the metallocene (a) being from 0.5 xcexcmol/l to 10 xcexcmol/l, that of the cocatalyst (b) being from 0.01 to 5 mmol/l, the amount of activator solid support being from 0.5 to 1000 mg/l, and then the olefin or olefins are introduced at a pressure ranging from 1 to 250 bar, the (co)polymerization being carried out at a temperature ranging from xe2x88x9220xc2x0 C. to 250xc2x0 C. for a period of time ranging from 5 minutes to 10 hours.
It is possible to use n-heptane, n-hexane, isohexane, isopentane or isobutane as the aliphatic hydrocarbon.
The preferred conditions are as follows:
pressure ranging from 0.5 to 60 bar;
temperature ranging from 10xc2x0 C. to a temperature slightly below the melting point of the polymer (5xc2x0 C. below this melting point).
If the polymerization is carried out in the gas phase, it may be performed as follows: the olefin or olefins are injected at a pressure of 1-60 bar, at a temperature ranging from 10 to 110xc2x0 C., into a reactor having a stirred bed and/or a fluidized bed of the catalytic system. In this case, the metallocene catalyst has been impregnated into the activator support and the cocatalyst is introduced by injection into the reactor or by impregnation of a solid charge injected into the reactor.
The aforementioned polymerization processes may involve a chain-transfer agent so as to control the melt flow index of the polymer to be produced. Hydrogen may be used as the chain-transfer agent, this being introduced in an amount which can range up to 90% and preferably lies between 0.01 and 60% in terms of moles of the olefinihydrogen combination injected into the reactor.
If it is desired to have excellent morphological control of the polymer particles, it is recommended to carry out a suspension, or, preferably gas-phase prepolymerization step on the catalytic system of the invention and then to introduce the prepolymer particles thus obtained into the suspension or gas-phase (co)polymerization process proper. The prepolymerization is carried out to a degree tailored to the polymerization process in which the prepolymer will subsequently be used.