Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F297/00—Macromolecular compounds obtained by successively polymerising different monomer systems using a catalyst of the ionic or coordination type without deactivating the intermediate polymer
  • C08F297/06—Macromolecular compounds obtained by successively polymerising different monomer systems using a catalyst of the ionic or coordination type without deactivating the intermediate polymer using a catalyst of the coordination type
  • C08F297/08—Macromolecular compounds obtained by successively polymerising different monomer systems using a catalyst of the ionic or coordination type without deactivating the intermediate polymer using a catalyst of the coordination type polymerising mono-olefins
  • C08F297/083—Macromolecular compounds obtained by successively polymerising different monomer systems using a catalyst of the ionic or coordination type without deactivating the intermediate polymer using a catalyst of the coordination type polymerising mono-olefins the monomers being ethylene or propylene
  • C08F297/086—Macromolecular compounds obtained by successively polymerising different monomer systems using a catalyst of the ionic or coordination type without deactivating the intermediate polymer using a catalyst of the coordination type polymerising mono-olefins the monomers being ethylene or propylene the block polymer contains at least three blocks
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F210/00—Copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond
  • C08F210/02—Ethene

Definitions

• the field of the present invention is that of processes for the synthesis of block polymers based on 1,3-diene and ethylene which contain at least three blocks. More particularly, the field of the invention is that of block polymers which comprise at least a first block comprising units of a 1,3-diene and two other blocks comprising ethylene units, each block comprising units of ethylene being attached to a separate end of the first block.
• Document EP 2599809 Al describes the synthesis of block polymers based on ethylene and 1,3-butadiene. They are synthesized by a first step of polymerization of ethylene, followed by a step of polymerization of 1,3-butadiene. Multiblock polymers are also synthesized by repeating several times the sequence composed of the polymerization of a first monomer charge of ethylene and the polymerization of a second monomer charge of 1,3-butadiene. As the polymerization is carried out in the presence of a metallocene, the constituent blocks of the block polymer have a typical microstructure of a catalytic polymerization, in particular a high cis content for the 1,3-butadiene units.
• each additional block after the synthesis of a first block requires the addition of a new monomer charge in the polymerization medium.
• the synthesis of a triblock polymer requires the use of three monomer charges, the synthesis of a pentablock five monomer charges, and so on.
• each new addition of a monomer charge in a polymerization medium during the polymerization reaction complicates the synthesis process and is generally accompanied by a deactivation of part of the active sites which participate in the polymerization reaction. , which has the effect of forming polymer species other than the targeted block polymer.
• a first object of the invention is a process for the preparation of a block polymer which comprises the polymerization of ethylene or of a monomer mixture containing ethylene and a first 1,3-diene in the presence of a catalytic system based on at least one metallocene of formula (Ia) or (Ib),
• Cp 1 , Cp 2 , Cp 3 and Cp 4 identical or different, being chosen from the group consisting of fluorenyl groups, cyclopentadienyl groups and indenyl groups, the groups being substituted or unsubstituted,
• R B being different from R A ,
• R B being a group comprising a benzene ring substituted by the magnesium atom, one of the carbon atoms of the benzene ring ortho to the magnesium being substituted by a methyl, an ethyl, an isopropyl or forming a ring with the atom carbon which is its closest neighbor and which is meta to the magnesium, the other carbon atom of the benzene ring ortho to the magnesium being substituted by a methyl, an ethyl or an isopropyl,
• R A being a polymer chain of a second 1,3-diene or of a second 1,3-diene and of styrene
• m being a number greater than or equal to 1, preferably equal to 1.
• the invention also relates to a block polymer capable of being obtained by the process in accordance with the invention.
• the block polymer is of formula A-B-A, the symbol A designating a terminal block and representing a polymer chain containing ethylene units and units of a first 1,3-diene, the symbol B designating a central block and representing a polymer chain of a second 1,3-diene or a copolymer chain of a second 1,3-diene and styrene, the total rate of 1,2 units and 3,4 units in the central block representing more than 7% by mole of the units of the second 1,3-diene constituting the polymer chain of the central block B.
• any interval of values denoted by the expression “between a and b” represents the range of values greater than “a” and less than “b” (i.e. limits a and b excluded) while any interval of values denoted by the expression “from a to b” means the range of values going from “a” to “b” (that is to say including the strict limits a and b).
• the expression “based on” used to define the constituents of a catalytic system or of a composition is meant the mixture of these constituents, or the product of the reaction of part or all of these constituents between them.
• the rates of the units resulting from the insertion of a monomer in a polymer are expressed in molar percentage with respect to all of the monomer units which constitute the polymer.
• the compounds mentioned in the description can be of fossil origin or biosourced. In the latter case, they can be, partially or totally, derived from biomass or obtained from renewable raw materials derived from biomass. In the same way, the compounds mentioned can also come from the recycling of materials already used, that is to say they can be, partially or totally, from a recycling process, or obtained from materials raw materials themselves from a recycling process.
• the expression “based on” used to define the constituents of the catalytic system means the mixture of these constituents, or the product of the reaction of some or all of these constituents with each other.
• metallocene an organometallic complex whose metal, in this case the rare earth atom, is bonded to two Cp 3 and Cp 4 groups or to a ligand molecule consisting of two Cp 1 and Cp 2 interconnected by a P bridge.
• Cp 1 , Cp 2 , Cp 3 and Cp 4 groups which are identical or different, are chosen from the group consisting of fluorenyl groups, cyclopentadienyl groups and indenyl groups, these groups possibly be substituted or unsubstituted.
• the rare earths are metals and designate the elements scandium, yttrium and the lanthanides whose atomic number varies from 57 to 71.
• the metallocene used as base constituent in the catalytic system corresponds to the formula (la)
• Y denotes a group containing a rare earth atom
• Cp 1 and Cp 2 are chosen from the group consisting of fluorenyl groups, cyclopentadienyl groups and indenyl groups, the groups being substituted or unsubstituted,
• P is a group bridging the two Cp 1 and Cp 2 groups, and comprising a silicon or carbon atom.
• the metallocene used as base constituent in the catalytic system in accordance with the invention corresponds to the formula (Ib)
• Cp 3 and Cp 4 are chosen from the group consisting of fluorenyl groups, cyclopentadienyl groups and indenyl groups, the groups being substituted or unsubstituted.
• substituted cyclopentadienyl, fluorenyl and indenyl groups mention may be made of those substituted by alkyl radicals having 1 to 6 carbon atoms or by aryl radicals having 6 to 12 carbon atoms or alternatively by trialkylsilyl radicals such as SiMe3.
• the choice of the radicals is also oriented by the accessibility to the corresponding molecules which are the substituted cyclopentadienes, fluorenes and indenes, because the latter are commercially available or easily synthesized.
• substituted fluorenyl groups mention may be made of those substituted in position 2,7, 3 or 6, particularly 2,7-ditertiobutyl-fluorenyl, 3,6-ditertiobutyl-fluorenyl.
• Positions 2, 3, 6 and 7 respectively designate the position of the carbon atoms of the cycles as shown in the diagram below, position 9 corresponding to the carbon atom to which the bridge P is attached.
• Position 2 designates the position of the carbon atom which is adjacent to the carbon atom to which the P bridge is attached, as shown in the diagram below.
• Position 2 designates the position of the carbon atom which is adjacent to the carbon atom to which is attached the bridge P, as shown in the diagram below.
• the metallocene is of formula (Ia).
• Cp 1 and Cp 2 are identical and are chosen from the group consisting of substituted fluorenyl groups and the unsubstituted fluorenyl group of formula C13H8.
• the catalytic system according to this preferred embodiment has the particularity of leading to copolymers of butadiene and ethylene which also comprise ethylene monomer units and butadiene units, cyclic units, 1,2-cyclohexane units of the following formula:
• the mechanism for obtaining such a microstructure is for example described in the document Macromolecules 2009, 42, 3774-3779.
• Cp 1 and Cp 2 are identical and each represents an unsubstituted fluorenyl group of formula C13H8, represented by the symbol Flu.
• the symbol Y represents the Met-G group, with Met denoting the rare earth atom and G denoting a group comprising the borohydride unit BH4 or denoting a halogen atom chosen from the group consisting of chlorine, fluorine, bromine and iodine.
• G denotes a chlorine atom or the group of formula (III):
• N represents a molecule of an ether, x, whole number or not, is equal to or greater than 0, y, whole number, is equal to or greater than 0.
• G designates the group of formula (III).
• Suitable ether is any ether which has the power to complex the alkali metal, in particular diethyl ether and tetrahydrofuran.
• the metallocene metal useful for the purposes of the invention is preferably a lanthanide whose atomic number ranges from 57 to 71, from more preferably neodymium, Nd.
• the bridge P connecting the Cp 1 and Cp 2 groups preferably corresponds to the formula ZR 1 R 2 , in which Z represents a silicon or carbon atom, R 1 and R 2 , which are identical or different, each represent an alkyl group comprising from 1 to 20 carbon atoms, preferably methyl.
• ZR 1 R 2 Z advantageously represents a silicon atom, Si.
• the metallocene useful for the synthesis of the catalytic system can be in the form of crystallized powder or not, or even in the form of monocrystals.
• the metallocene can be in a monomer or dimer form, these forms depending on the mode of preparation of the metallocene, as for example described in patent application WO 2007054224 or WO 2007054223.
• the metallocene can be prepared in a traditional way by a process analogous to that described in patent application WO 2007054224 or WO 2007054223, in particular by reaction under inert and anhydrous conditions of the salt of an alkali metal of the ligand with a rare earth borohydride in a suitable solvent, such as an ether, such as diethyl ether or tetrahydrofuran or any other solvent known to those skilled in the art. After reaction, the metallocene is separated from the reaction by-products by techniques known to those skilled in the art, such as filtration or precipitation in a second solvent. The metallocene is finally dried and isolated in solid form.
• a suitable solvent such as an ether, such as diethyl ether or tetrahydrofuran or any other solvent known to those skilled in the art.
• the metallocene is of formula (III-1), (III-2), (III-3), (III-4) or (III-5):
• R B is a group comprising a benzene nucleus substituted by the magnesium atom , one of the carbon atoms of the benzene ring ortho to magnesium being substituted by methyl, ethyl, isopropyl or forming a ring with the carbon atom which is its nearest neighbor and which is meta to magnesium, the other atom of carbon of the benzene ring ortho to the magnesium being substituted by a methyl, an ethyl or an isopropyl, R A is a polymer chain of a 1,3-diene or of a 1,3-diene and of styrene, m is a number greater than or equal to 1, preferably equal to 1.
• the organomagnesium of formula (II) therefore has the characteristic of comprising two magnesium atoms, each magnesium atom being bonded to two carbon atoms.
• two magnesium atoms each share a first bond with a first carbon atom belonging to R B and a second bond with a second carbon atom belonging to R A .
• the first carbon atom is constitutive of the benzene ring of R B .
• the second carbon atom is a constituent of the aliphatic hydrocarbon chain R A which may contain within its chain one or more heteroatoms chosen from oxygen and sulfur or else one or more arylene groups.
• m is equal to 1
• each magnesium atom therefore shares a first bond with a first carbon atom of R B and a second bond with a second carbon atom of R A .
• R B has the essential characteristic of comprising a benzene ring substituted by the magnesium atom.
• the two carbon atoms of the benzene ring of R B ortho to the magnesium carry a substituent, identical or different.
• one of the two carbon atoms of the benzene ring of R B ortho to the magnesium can bear a substituent, the other carbon atom of the benzene ring of R B ortho to the magnesium can form a cycle.
• the substituent is methyl, ethyl or isopropyl.
• the second carbon atom of the benzene ring of R B ortho to magnesium is not substituted by an isopropyl.
• the carbon atoms of the benzene ring of R B ortho to the magnesium are substituted by a methyl or an ethyl. More preferably, the carbon atoms of the benzene ring of R B ortho to the magnesium are substituted by a methyl.
• the organomagnesium of formula (II) corresponds to the formula (IV-m) in which m is a number greater than or equal to 1, Ri and Rs, which are identical or different, represent a methyl or an ethyl, preferably a methyl, R 2 , R 3 and R 4 , which are identical or different, represent a hydrogen atom or an alkyl and R A is the polymer chain of a second 1,3-diene or d 'a second 1,3-diene and styrene.
• Ri and R 5 each represent a methyl.
• the organomagnesium of formula (IV-m) is of formula (IV-1) in the case where m is equal to 1.
• R1, R3 and R5 are identical in formula (IV-m), in particular in formula (IV-1).
• R2 and R4 represent a hydrogen and R1, R3 and R5 are identical.
• R2 and R4 represent hydrogen and R1, R3 and R5 represent methyl.
• m is preferably equal to 1 in formula (II), in particular in formula (IV-m).
• R A is a polymer chain of a 1,3-diene or of a 1,3-diene and of styrene .
• second monomer is used to designate the monomer or monomers constituting the polymer chain R A .
• second 1,3-diene is also used to designate the 1,3-diene constituting the polymer chain R A .
• the organomagnesium useful for the purposes of the invention as a cocatalyst can be prepared by reaction of a living anionic polymer of formula LiR A Li with a halide of an organomagnesium of formula R B -Mg-X,
• X being a halogen chosen from the group consisting of chlorine, fluorine, bromine and iodine, R B and R A being as defined above.
• X is preferably a bromine atom or a chlorine atom. X is more preferably a bromine atom.
• the halides of an organomagnesium compound with the formula R B -Mg-X are well-known compounds. They may be commercially available or prepared like any Grignard reagent by reacting magnesium metal with the corresponding halide, for example using the procedures described in the collection of volumes of “Organic Synthesis”.
• the living anionic polymer of formula LiR A Li is typically a polymer chain having at each of its two chain ends a carbon-lithium bond.
• the living anionic polymer is generally referred to as a dilithium polymer.
• the living anionic polymer of formula LiR A Li is prepared by the anionic polymerization of the second monomer in the presence of a dilithium initiator, generally in a solvent, called polymerization solvent. 1,3-dienes and styrene are well known to polymerize or copolymerize anionically and to form living anionic polymer or copolymer chains. The polymerization processes of these monomers are also well known and widely described.
• the anionic polymerization solvent can be any hydrocarbon solvent known to be used in the polymerization of 1,3-diene monomers and styrene.
• the anionic polymerization solvent is preferably a hydrocarbon solvent, better still an aliphatic solvent such as hexane, cyclohexane or methylcyclohexane.
• the anionic polymerization solvent may include an additive to control the microstructure of the polymer chain and the rate of the polymerization reaction. This additive can be a polar agent such as an ether or a tertiary amine.
• the ratio between the quantity of solvent and the quantity of monomer useful for the formation of the dilithium polymer is chosen by those skilled in the art according to the desired viscosity of the solution of dilithium polymer. This viscosity depends not only on the concentration of the polymer solution, but also on many other factors such as the length of the polymer chains, the complexing power of the solvent, the temperature of the polymer solution. Consequently, those skilled in the art adjust the amount of solvent on a case-by-case basis.
• the dilithium initiator useful in the anionic polymerization is typically a compound which comprises two carbon-lithium bonds, the carbon atoms and the lithium atoms being distinct.
• Dilithium initiators and their syntheses are well known to those skilled in the art in the field of anionic polymerization. They are for example described in patent applications WO 02/20623 A1 and WO 89/04843 A1, in the documents Macromolecules 2, 453 (1969) and Macromolecules 27, 1680 (1994).
• the adduct of the reaction between lithium metal or an alkyllithium and a compound bearing two ethenylidene groups such as 1,1-diphenylethylene, l,3-bis(l-phenyléthenyl)benzene, divinylbenzene or 1,3-diisopropenylbenzene.
• the initiator is preferably the adduct of the reaction between sec-butyllithium and 1,3-diisopropenylbenzene.
• the initiator is used in an amount chosen according to the desired chain length of the dilithium polymer and can therefore vary to a large extent.
• the amount of dilithium initiator used to react with the monomer to be polymerized is indexed to the mass of monomer converted into polymer for a target number-average molar mass value Mn of the polymer to be synthesized. It is determined in a well-known manner from equation (1) which connects the targeted Mn, the mass of monomer converted into polymer in grams and the number of moles of initiator.
• Target Mn mass of converted monomer/moles of initiator (1)
• the quantity of dilithium initiator used to react with the monomer to be polymerized varies preferentially from 0.34 mmol to 33.00 mmol of dilithium initiator per 100 g of polymerized monomer, more preferentially from 0.50 mmol to 20.00 mmol of dilithium initiator per 100 g of monomer polymerized.
• the quantity of dilithium initiator used to react with the monomer to be polymerized varies from 2.00 mmoles to 33.00 mmoles of dilithium initiator per 100 g of polymerized monomer.
• the quantity of dilithium initiator used to react with the monomer to be polymerized varies from 0.40 mmol to 2.00 mmol, preferably from 0.67 mmol to 2.00 mmol of dilithium initiator per 100 g of polymerized monomer.
• the polymerization temperature to form the dilithium polymer can vary widely. It is chosen as a function in particular of the stability of the carbon-lithium bond in the polymerization solvent, of the relative rate coefficients of the initiation reaction and of the propagation reaction, of the target microstructure of the dilithium polymer. Traditionally, it varies in a range ranging from -20 to 100°C, preferably from 20 to 70°C.
• the dilithium polymer can be a homopolymer in the case where the second monomer is a 1,3-diene or else a copolymer in the case where the second monomer is a mixture of a 1,3-diene and styrene.
• the copolymer can be random or block, since the incorporation of the comonomers can be controlled by known operating conditions of anionic polymerization processes. For example, it is known that the polarity of the polymerization reaction medium and the mode of supply of the co-monomers in the polymerization medium influence the relative incorporation of the co-monomers in the growing polymer chain.
• the dilithium polymer is a dilithium polymer obtained by anionic polymerization of 1,3-butadiene, isoprene, styrene or a mixture of at least two of them.
• the second 1,3-diene is preferably 1,3-butadiene, isoprene or their mixture.
• the dilithium polymer typically has a total content of 1,2 units and of 3,4 units greater than 7% by mole of the units of the second 1,3-diene.
• the total content of 1,2 units and 3,4 units in the dilithium polymer represents more than 20% by mole of the units of the second 1,3-diene, preferably more than 30% by mole of the units of the second 1 ,3-diene, more preferably more than 40% by mole of the units of the second 1,3-diene.
• the bringing into contact of the living anionic polymer with the halide of an organomagnesium is preferably done by adding a solution of the living anionic polymer of formula LiR A Li to a solution halide of an organomagnesium compound of formula R B -Mg-X.
• the solution of the living anionic polymer of formula LiR A Li is generally a solution in a solvent hydrocarbon, preferably aliphatic such as n-hexane, cyclohexane or methylcyclohexane.
• the solution of the halide of an organomagnesium compound of formula R B -Mg-X is generally a solution in an ether, preferably diethyl ether or dibutyl ether or methyltetrahydrofuran.
• the concentration of the living anionic polymer of formula LiR A Li is preferably from 0.01 to 1 mole of lithium equivalent/L, more preferably from 0.05 to 0.2 mole of lithium equivalent/L, that of the solution of the halide of a organomagnesium of formula R B -Mg-X preferably from 1 to 5 mol/L, more preferably from 2 to 3 mol/L.
• the reaction between the living anionic polymer of formula LiR A Li and the halide of an organomagnesium compound of formula R B -Mg-X is typically carried out at a temperature ranging from 0°C to 60°C.
• the contacting is preferably carried out at a temperature between 0°C and 23°C.
• the contacting and the reaction take place under anhydrous conditions under an inert atmosphere.
• solvents and solutions are used under anhydrous nitrogen or argon.
• the different stages of the process are generally carried out with stirring.
• the organomagnesium useful as a cocatalyst is formed, it is generally recovered in solution after filtration carried out under an inert and anhydrous atmosphere.
• the solution of the organomagnesium useful as a cocatalyst is typically stored before its use in sealed containers, for example capped bottles, at a temperature between -25°C and 23°C.
• the organomagnesium of formula R B -(Mg-R A ) m -Mg-R B useful as a cocatalyst can be in the form of a monomeric entity (R B -(Mg-R A ) m -Mg-R B )i or in the form of a polymer entity (R B -(Mg-R A ) m -Mg-R B ) p , p being an integer greater than 1, in particular dimer (R B - (Mg-R A ) m -Mg-R B )2, m being as previously defined.
• a monomer or polymer entity can also be in the form of an entity coordinated with one or more molecules of a solvent, preferably an ether such as diethyl ether, tetrahydrofuran or methyltetrahydrofuran.
• a solvent preferably an ether such as diethyl ether, tetrahydrofuran or methyltetrahydrofuran.
• the catalytic system useful for the purposes of the invention can be prepared in a traditional manner by a process analogous to that described in patent application WO 2007054224 or WO 2007054223.
• the organomagnesium compound of formula R B is reacted in a hydrocarbon solvent.
• -Mg-R A -Mg-R B useful as a cocatalyst and the metallocene typically at a temperature ranging from 20 to 80° C. for a period of between 5 and 60 minutes.
• the amounts of cocatalyst and metallocene reacted are such that the ratio between the number of moles of Mg of the cocatalyst and the number of moles of rare earth metal of the metallocene preferably ranges from 1 to 200, more preferably from 1 less than 20.
• the range of values from 1 to less than 20 is in particular more favorable for obtaining polymers of high molar masses.
• the catalytic system is generally prepared in a hydrocarbon solvent, aliphatic like methylcyclohexane or aromatic like toluene. Generally after its synthesis, the catalytic system is used as it is in the process for synthesizing the polymer in accordance with the invention.
• the synthesis of the metallocene, the synthesis of the organomagnesium useful as a cocatalyst and the synthesis of the catalytic system take place under anhydrous conditions under an inert atmosphere.
• the reactions are carried out from solvents and anhydrous compounds under anhydrous nitrogen or argon.
• the catalytic system generally comes in the form of a solution in a hydrocarbon solvent.
• the hydrocarbon solvent can be aliphatic like methylcyclohexane or aromatic like toluene.
• the hydrocarbon solvent is preferably aliphatic, more preferably methylcyclohexane.
• the catalytic system is stored in the form of a solution in the hydrocarbon solvent before being used in polymerization. We can then speak of a catalytic solution which comprises the catalytic system and the hydrocarbon solvent.
• the concentration of the catalyst solution is typically defined by the metallocene metal content in the solution.
• the metallocene metal concentration has a value preferably ranging from 0.0001 to 0.2 mol/L, more preferably from 0.001 to 0.03 mol/L.
• the catalyst system is used in a process for polymerizing ethylene or a monomer mixture containing ethylene and a 1,3-diene to form a polymer chain of a first monomer.
• first monomer is used to designate ethylene or a monomer mixture containing ethylene and a 1,3-diene.
• first 1,3-diene is also used to designate the 1,3-diene of the monomer mixture containing ethylene and a 1,3-diene.
• the first 1,3-diene can be any 1,3-diene having 4 to 24 carbon atoms such as 1,3-butadiene and isoprene.
• the first 1,3-diene is 1,3-butadiene, isoprene or a mixture thereof.
• the first monomer is ethylene
• the first monomer is a mixture of a 1,3-diene and ethylene.
• the first monomer is a mixture of a 1,3-diene, ethylene and styrene.
• the first monomer is a monomer mixture containing ethylene and a 1,3-diene, in particular a mixture of ethylene and a 1,3-diene, advantageously the monomer mixture contains more than 50% by mole of ethylene.
• the first 1,3-diene is preferably 1,3-butadiene.
• the first monomer is ethylene or a monomer mixture of ethylene and 1,3-butadiene.
• the polymerization of the first monomer is preferably carried out in solution, continuously or discontinuously.
• the polymerization solvent can be a hydrocarbon, aromatic or aliphatic solvent.
• polymerization solvent mention may be made of toluene and methylcyclohexane.
• the first monomer can be introduced into the reactor containing the polymerization solvent and the catalytic system or conversely the catalytic system can be introduced into the reactor containing the polymerization solvent and the first monomer.
• the first monomer and the catalytic system can be introduced simultaneously into the reactor containing the polymerization solvent, in particular in the case of continuous polymerization.
• the polymerization is typically carried out under anhydrous conditions and in the absence of oxygen, in the optional presence of an inert gas.
• the polymerization temperature generally varies within a range ranging from 40 to 150°C, preferably 40 to 120°C. It is adjusted according to the first monomer to be polymerized. If the first monomer is a mixture of monomers containing ethylene, the copolymerization is preferably carried out at constant ethylene pressure.
• the polymerization of the first monomer is the polymerization of a monomer mixture of ethylene and a 1,3-diene in a polymerization reactor
• a continuous addition of ethylene and 1,3-diene can be carried out in the polymerization reactor, in which case the polymerization reactor is a fed reactor.
• This embodiment is particularly suitable for a random or random incorporation of ethylene and 1,3-diene.
• the quantity of the first monomer used in the polymerization reaction of the first monomer is chosen according to the desired mass proportion of the first monomer in the block polymer. It can vary to a large extent and is adjusted by those skilled in the art according to the desired properties of the block polymer and the intended application of the block polymer, which generally determines its composition.
• the polymerization reaction is stopped by cooling the polymerization medium or by adding a terminating agent, such as for example a compound having an acidic proton , such as an alcohol, for example ethanol.
• a terminating agent such as for example a compound having an acidic proton , such as an alcohol, for example ethanol.
• the polymer prepared according to the process in accordance with the invention can be recovered, in particular by separating it from the reaction medium, for example by coagulating it in a solvent causing it to coagulate or by eliminating the polymerization solvent and any residual monomer under reduced pressure or under the effect of steam distillation (stripping operation).
• the process in accordance with the invention implements the polymerization of the first monomer in the presence of a catalytic system which comprises a cocatalyst of formula (II) and knowing that R A represents a polymer chain of the second monomer, the polymer chain of the second monomer and the polymer chain resulting from the polymerization of the first monomer both constitute the polymer synthesized by the process in accordance with the invention.
• the polymerization of the first monomer also results in the growth of a polymer chain of the first monomer from each of the ends of the polymer chain of the second monomer.
• the polymers synthesized by the process in accordance with the invention are therefore block polymers having a central block and two terminal blocks as their characteristic, each of the two terminal blocks having one end attached to a distinct end of the central block.
• Each of the blocks which constitute the synthesized polymers and which is formed from different monomers, whether it is terminal or central, can itself be random or block.
• the process in accordance with the invention therefore allows the synthesis of a block polymer of formula A-B-A, the symbol A designating a terminal block and representing an ethylene polymer chain or a polymer chain containing ethylene units and units of the first 1,3-diene, the symbol B designating a central block and representing a polymer chain of the second 1,3-diene or a copolymer chain of the second 1,3-diene and styrene.
• the process leads to the synthesis of a block polymer which is an elastomer or a thermoplastic elastomer (TPE) when the terminal block is for example a polyethylene, which block polymer can be used in a rubber composition, for example for tyres.
• TPE thermoplastic elastomer
• the process leads to the synthesis of an original block polymer.
• the central block and the terminal blocks have microstructures which are not accessible by the same polymerization route, the central block having a microstructure accessible by anionic polymerization, the terminal blocks a microstructure accessible by catalytic polymerization.
• a wide range of glass transition temperature can be reached for the central block while a range of crystallinity of the terminal blocks is also possible.
• the method makes it possible to operate the parameters of the anionic polymerization and those of the catalytic polymerization independently, such as the relative quantities of the second monomer with respect to that of the initiator for the anionic polymerization, the relative quantities of the first monomer with respect to that of the catalytic system to prepare respectively the central block and the terminal blocks of the block polymers.
• the process therefore offers the possibility of preparing the synthesis of a wide variety of block polymers which can be differentiated from each other not only by the composition of their blocks, but also by the length of the blocks.
• the process also has the advantage of preparing such block polymers with a relatively low catalytic cost due to good catalytic activity.
• the block polymer another object of the invention capable of being obtained by the process in accordance with the invention, has the formula ABA, the symbol A designating a terminal block and representing a polymer chain containing ethylene units and units of a first 1,3-diene, the symbol B designating a central block and representing a polymer chain of a second 1,3-diene or a copolymer chain of a second 1,3-diene and styrene, the total rate of 1,2 units and 3,4 units in the central block representing more than 7% by mole of the units of the second 1,3-diene present in the central block.
• the microstructure of the block polymer is original, since the block polymer contains a block of microstructure typical of an anionic polymerization, the two ends of which are each connected to a distinct block of microstructure typical of a catalytic polymerization, block which contains units ethylene and a 1,3-diene.
• the symbol A represents a polymer chain which is a random copolymer chain.
• the first 1,3-diene can be any 1,3-diene having 4 to 24 carbon atoms such as 1,3-butadiene and isoprene.
• the first 1,3-diene is preferably 1,3-butadiene.
• the second 1,3-diene can be any 1,3-diene polymerizable by anionic polymerization, preferably 1,3-butadiene, isoprene or their mixture.
• the polymer chain containing ethylene units and units of a first 1,3-diene contains units having a 1,2-cyclohexane unit, these preferably represent at most 15% by mole of the monomer units of the polymer chain containing ethylene units and units of a first 1,3-diene.
• the total rate of 1,2 units and 3,4 units in the central block represents more than 20% by mole of the units of the second 1,3-diene present in the central block. , preferably more than 30% by mole of the units of the second 1,3-diene present in the central block, more preferably more than 40% by mole of the units of the second 1,3-diene present in the central block.
• the 1,2 units and the 3,4 units are monomer units well known to those skilled in the art in the polymers obtained by polymerization reaction of 1,3-dienes, as described for example in the work "Principles of Polymerization” by G. Odian , 4th Edition, John Wiley & Sons, Inc., 2004, page 627.
• the polymer chain represented by the symbol A is a copolymer chain of ethylene and of a 1,3-diene, in this case the first 1,3-diene.
• the polymer chain represented by the symbol A is a random copolymer chain of ethylene and of the first 1,3-diene.
• the invention is advantageously implemented according to any one of the following embodiments 1 to 39:
• Mode 1 Process for the preparation of a block polymer which comprises the polymerization of ethylene or of a monomer mixture containing ethylene and a first 1,3-diene in the presence of a catalytic system based at least of a metallocene of formula (Ia) or (Ib),
• Cp 1 , Cp 2 , Cp 3 and Cp 4 identical or different, being chosen from the group consisting of fluorenyl groups, cyclopentadienyl groups and indenyl groups, the groups being substituted or unsubstituted,
• R B being different from R A ,
• R B being a group comprising a benzene ring substituted by the magnesium atom, one of the carbon atoms of the benzene ring ortho to the magnesium being substituted by a methyl, an ethyl, an isopropyl or forming a ring with the atom carbon which is its closest neighbor and which is meta to the magnesium, the other carbon atom of the benzene ring ortho to the magnesium being substituted by a methyl, an ethyl or an isopropyl,
• R A being a polymer chain of a second 1,3-diene or of a second 1,3-diene and of styrene
• m being a number greater than or equal to 1, preferably equal to 1.
• Mode 2 Process according to mode 1 in which Cp 1 and Cp 2 are identical and are chosen from the group consisting of substituted fluorenyl groups and the unsubstituted fluorenyl group of formula C13H8.
• Mode 3 Process according to mode 1 or 2 in which Cp 1 and Cp 2 are identical and each represents an unsubstituted fluorenyl group of formula C13H8.
• Mode 4 Process according to any one of modes 1 to 3 in which the symbol Y represents the Met-G group, with Met denoting the rare earth atom and G denoting a group comprising the borohydride unit BH 4 or denoting a halogen atom selected from the group consisting of chlorine, fluorine, bromine and iodine.
• Mode 5 Process according to mode 4 in which G denotes a chlorine atom or the group of formula (III) (BH 4 )(i + y)-Ly-N x (III) in which
• L represents an alkali metal chosen from the group consisting of lithium, sodium and potassium,
• N represents a molecule of an ether, x, whole number or not, is equal to or greater than 0, y, whole number, is equal to or greater than 0.
• Mode 6 Process according to mode 4 or 5 in which G denotes the group of formula (III)
• L represents an alkali metal chosen from the group consisting of lithium, sodium and potassium,
• N represents a molecule of an ether, x, whole number or not, is equal to or greater than 0, y, whole number, is equal to or greater than 0.
• Mode 7 Process according to any one of modes 5 to 6 in which N represents a molecule of diethyl ether or of tetrahydrofuran.
• Mode 8 Process according to one of modes 1 to 7 in which the rare earth is a lanthanide whose atomic number varies from 57 to 71.
• Mode 9 Process according to any one of modes 1 to 8 in which the rare earth is neodymium.
• Mode 10 Process according to any one of modes 1 to 9 in which the bridge P corresponds to the formula ZR 1 R 2 , Z representing a silicon or carbon atom, R 1 and R 2 , identical or different, each representing an alkyl group comprising 1 to 20 carbon atoms.
• Mode 11 Process according to mode 10 in which Z represents a silicon atom.
• Mode 12 Process according to mode 10 or 11 in which R 1 and R 2 each represent a methyl.
• Mode 13 Process according to any one of modes 1 to 12 in which the metallocene is of formula (III-1), (111-2), (111-3), (111-4) or (111-5) :
• Mode 14 Process according to any one of modes 1 to 13 in which the compound of formula (II) is prepared by reaction of a living anionic polymer of formula LiR A Li with a halide of an organomagnesium compound of formula R B - Mg-X,
• X being a halogen chosen from the group consisting of chlorine, fluorine, bromine and iodine
• R B being a group comprising a benzene ring substituted by the magnesium atom, one of the carbon atoms of the benzene ring in ortho of magnesium being substituted by a methyl, an ethyl, an isopropyl or forming a ring with the carbon atom which is its closest neighbor and which is meta to magnesium, the other carbon atom of the benzene ring in ortho magnesium being substituted by methyl, ethyl or isopropyl,
• R A being a polymer chain of a second 1,3-diene or of a second 1,3-diene and styrene.
• Mode 15 Process according to mode 14 in which X is a bromine atom or a chlorine atom.
• Mode 16 Process according to mode 14 or 15 in which X is a bromine atom.
• Mode 17 Process according to mode 16 in which the living anionic polymer of formula LiR A Li is prepared by the anionic polymerization of the second 1,3-diene or of a mixture of the second 1,3-diene and styrene in the presence of a dilithium initiator.
• Mode 18 Process according to any one of modes 1 to 17 in which if one of the 2 carbon atoms of the benzene ring of R B ortho to magnesium is substituted by an isopropyl, the second carbon atom of the benzene ring of R B ortho to magnesium is not substituted by isopropyl.
• Mode 19 Process according to any one of modes 1 to 18 in which the carbon atoms of the benzene ring of R B ortho to the magnesium are substituted by a methyl or an ethyl, preferably a methyl.
• Method 20 Process according to any one of modes 1 to 19 in which the compound of formula (II) is of formula (IV-m) m)
• Ri and R5 identical or different, representing a methyl or an ethyl, preferably a methyl,
• R 2 , R 3 and R 4 identical or different, being a hydrogen atom or an alkyl
• R A being the polymer chain of a second 1,3-diene or of a second 1,3-diene and of styrene, m being a number greater than or equal to 1.
• Mode 21 Process according to any one of modes 1 to 20 in which m is equal to 1.
• Mode 22 Process according to any one of modes 20 to 21 in which R1 and Rs each represent a methyl.
• Mode 23 Process according to any one of modes 20 to 22 in which R 2 and R 4 each represent a hydrogen atom.
• Mode 24 Process according to any one of modes 20 to 23 in which R 1 , R 3 and R 5 are identical.
• Mode 25 Process according to any one of modes 1 to 24 in which the monomer mixture containing ethylene and a first 1,3-diene is a mixture of ethylene and a first 1,3-diene.
• Mode 26 Process according to any one of modes 1 to 25 in which the monomer mixture containing ethylene and a first 1,3-diene contains more than 50% by mole of ethylene.
• Mode 27 Process according to any one of modes 1 to 26 in which the first 1,3-diene is 1,3-butadiene, isoprene or their mixture.
• Mode 28 Process according to any one of modes 1 to 27 in which the first 1,3-diene is 1,3-butadiene.
• Mode 29 Process according to any one of modes 1 to 28 in which the second 1,3-diene is 1,3-butadiene, isoprene or their mixture.
• Mode 30 Process according to any one of modes 1 to 29 in which the ratio between the number of moles of Mg of the cocatalyst and the number of moles of rare earth metal of the metallocene ranges from 1 to 200.
• Mode 31 Process according to any one of modes 1 to 30 in which the ratio between the number of moles of Mg of the cocatalyst and the number of moles of rare earth metal of the metallocene ranges from 1 to less than 20.
• Mode 32 Block polymer of formula ABA, the symbol A designating a terminal block and representing a polymer chain containing ethylene units and units of a first 1,3-diene, the symbol B designating a central block and representing a polymer chain of a second 1,3-diene or a copolymer chain of a second 1,3-diene and styrene, the total content of 1,2 units and 3,4 units in the central block representing more than 7% by mole of the units of the second 1,3-diene constituting the polymer chain of the central block B.
• Mode 34 Block polymer according to mode 33 in which the units having a 1,2-cyclohexane unit represent at most 15% by mole of the monomer units of the polymer chain containing ethylene units and units of a first 1 ,3-diene.
• Mode 35 Block polymer according to any one of modes 32 to 34 in which the total rate of 1,2 units and 3,4 units in the central block represents more than 20% by mole of the units of the second 1,3 -diene.
• Mode 36 Block polymer according to any one of modes 32 to 34 in which the total rate of 1,2 units and 3,4 units in the central block represents more than 30% by mole of the units of the second 1,3 -diene.
• Mode 37 Block polymer according to any one of modes 32 to 34 in which the total rate of 1,2 units and 3,4 units in the central block represents more than 40% by mole of the units of the second 1,3 -diene.
• Mode 38 Block polymer according to any one of Modes 32 to 37 in which the polymer chain containing ethylene units and units of a first 1,3-diene is a random copolymer chain.
• Mode 39 Block polymer according to any one of Modes 32 to 38 in which the polymer chain containing ethylene units and units of a first 1,3-diene is a copolymer chain of ethylene and the first 1 ,3-diene.
• HT SEC High Temperature Size Exclusion Chromatography
• Viscotek apparatus Malvern Instruments
• 3 columns PLgel Olexis 300 mm x 7 mm ID from Agilent Technologies
• 3 detectors ref. differential ctometer and viscometer, and light scattering. 200 ⁇ L of a sample solution at a concentration of 3 mg mL 1 was eluted in 1,2,4-trichlorobenzene using a flow rate of 1 mL min 1 at 150°C.
• the mobile phase was stabilized with 2,6-di(tert-butyl)-4- methylphenol (400 mg L 1 ).
• OmniSEC software was used for data acquisition and analysis.
• the number-average molar masses (Mn) of the copolymers of ethylene and butadiene synthesized are calculated using a universal calibration curve calibrated from standard polystyrenes (Molar masses at peak p : 672 to 12,000,000 g mol -1 ) of Polymer Standard Service (Mainz) using the refractometer detector.
• Size Exclusion Chromatography SEC/RI
• Size exclusion chromatography allows the fractionation of polymer chains in a solvent according to their hydrodynamic volume.
• the technique is based on the elution of a solute (the polymer) through a column containing a stationary phase.
• the system is composed in this order: a solvent reservoir, a pumping system, an injector, a set of columns and detectors.
• the measurement chain is equipped with a Waters Alliance e2695 module and a Waters fRI410 refractometer.
• the mobile phase is eluted with a flow rate of 1 mL/min.
• the polymer is dissolved in THF in the presence of 1% wt of diisopropylamine and 1% wt of triethylamine at a concentration of 1 g/L.
• a volume of 100 ⁇ l is injected through a set of 3 AGILENT brand steric exclusion chromatography columns (MIXED B LS). The columns are thermostated in an oven at 35°C.
• the stationary phase of the columns is based on a polystyrene divinylbenzene gel with controlled porosity.
• the polymer chains are separated according to the hydrodynamic volume they occupy when they are dissolved in the solvent.
• the mobile phase is eluted with a flow rate of 1 mL/min.
• the polymer is dissolved in THF at a concentration of 1.5 g/L.
• a volume of 100 ⁇ L is injected through a set of 4 AGILENT brand steric exclusion chromatography columns (2 MIXED D and 2 MIXED E). The columns are thermostated in an oven at 35°C.
• the stationary phase of the columns is based on a polystyrene divinylbenzene gel with controlled porosity.
• the polymer chains are separated according to the hydrodynamic volume they occupy when they are dissolved in the solvent. The larger the volume they occupy, the less the pores of the columns are accessible to them and the shorter their elution time.
• Detection is ensured by a refractometer (RI) thermostated at 35°C.
• RI refractometer
• Each elution volume is associated with a mass via the Moore calibration (passage of certified standard: polystyrenes standards (Molar masses at peak Mp: 162 to 66,000 g mol-1) from Polymer Standard Service GmbH.
• the nuclear magnetic resonance (NMR) spectra are acquired on a Brüker Avance III 500 MHz spectrometer equipped with a BBIz-grad 5 mm “broadband” cryoprobe.
• the samples are dissolved in 1,2-dichlorobenzene d4.
• the calibration is carried out on the protonated impurity of 1,2-dichlorobenzene at 7.20 ppm in 1H NMR.
• the quantitative 1H NMR experiment uses a simple 30° pulse sequence and a repetition delay of 5 seconds between each acquisition.
• the chemical shift comprised between 5.36-5.10 ppm is attributed to the 1,4 units of the butadiene units
• the signal comprised between 5.63 and 5.36 ppm is attributed to the 1,2 units of the butadiene units.
• the signal at 1.18 ppm is assigned to ethylene units.
• the thermal characterizations were carried out with a Mettler Toledo DSC3+ NETZSCH device.
• the sample (about 10 mg) is weighed and sealed in a 40 pL aluminum crucible.
• the crucible is pierced with a fine needle just before the measurement.
• Dry helium is used as purge gas (with a flow of 40 mL min -1 ) and as protective gas (with a flow of 200 mL/min).
• the sample is heated as well as an empty reference crucible from 25°C to 200°C at 20°C min 1 .
• the temperature is maintained for 1 minute at 200° C., then reduced from 200° C. to -180° C. to 15° C. min -1 .
• Two successive cycles of heating and cooling are carried out and only the second is considered for the measurements.
• the glass transition temperature is measured by means of a differential calorimeter ("Differential Scanning Calorimeter") according to standard ASTM D3418 (1999).
• the melting temperature is measured by means of a differential calorimeter ("Differential Scanning Calorimeter").
• the melting temperature corresponds to the apex of the melting peak.
• the metallocene ⁇ Me2SiFlu2Nd(p-BH4)2Li(THF) ⁇ (also represented by the formula Me2Si(Ci3H8)2Nd(BH4)2Li.THF) is prepared according to the procedure described in patent application WO 2007054224 Al.
• Ethylene of at least N25 quality, comes from Air Liquide and is used without prior purification.
• the 1,3-butadiene is purified on alumina guards.
• the methylcyclohexane (MCH) solvent is dried and purified on an alumina column in a solvent fountain from mBraun and used in an inert atmosphere after degassing the solvent with nitrogen.
• the toluene solvent is dried and purified on an alumina column in a solvent fountain from mBraun and used in an inert atmosphere after degassing the solvent with nitrogen.
• the polymerizations of ethylene or a mixture of ethylene and 1,3-butadiene are carried out in a reactor with a 500 mL disposable glass tank (Schott bottles) equipped with a stirring paddle. Stainless steel. Temperature control is ensured by a thermostatically controlled oil bath connected to a double polycarbonate envelope. This reactor has all the inputs or outputs necessary for the manipulations.
• Step 1 Preparation of a cocatalyst of formula (II):
• 192 mL of methylcyclohexane (MCH) are introduced into a 750 mL Steinie bottle.
• 175 mL of sec-BuLi dosed at 1.15 M in cyclohexane (0.2 mol, 1 equivalent) are introduced into the Steinie bottle containing the MCH.
• 17.1 mL of 1.3 diisopropenylbenzene (0.1 mol, 0.5 equivalent) are introduced into the bottle containing the MCH and the sec-BuLi at 23°C.
• the bottle is shaken immediately for a few seconds.
• the solution turns yellow and a slight rise in temperature is observed (approximately 40° C.).
• TEDA tetramethylethylenediamine
• 150 mL of methylcyclohexane are introduced into a 250 mL Steinie bottle.
• the bottle is bubbled under nitrogen for ten minutes.
• 7.7mL of 1,3-butadiene are introduced into the bottle, then 1.85mL of the dilithium initiator solution prepared at 0.54 mol/L.
• the bottle is kept at 50° C. for 1 h.
• 0.1mL of a 1mol/L solution of mesitylmagnesium bromide in diethyl ether is introduced into the bottle containing the dilithium polybutadiene. The solution is stirred for 15 min at room temperature.
• Step 2 Polymerization of a mixture of ethylene and 1,3-butadiene:
• the contents of the bottle containing the metallocene Me2Si(Ci3H8)2Nd(BH4)2Li.THF and the cocatalyst is then introduced into the reactor of polymerization using a double needle.
• the reactor is partially placed under vacuum and then the reactor is pressurized to 3 bars with a gaseous mixture containing 80% molar ethylene and 20% molar 1,3-butadiene.
• the polymerization is stopped with methanol when 5.6 g of the monomer mixture has been consumed.
• the polymer is recovered after drying in an oven at 60° C. under vacuum under nitrogen sweeping.
• the catalytic activity is measured at 28 kg/mol. h.
• Step 1 Preparation of a cocatalyst of formula (II):
• the cocatalyst is prepared according to the procedure of step 1 described in example 1.
• Step 2 Polymerization of ethylene:
• the polymerization is carried out according to the procedure of stage 2 described in example 1 with this difference that the reactor is pressurized to 3 bars of ethylene.
• the polymerization is stopped with methanol when the reaction medium has consumed 7.9 g of ethylene.
• the polymer is recovered after drying in an oven at 60° C. under vacuum under nitrogen sweeping.
• the catalytic activity is measured at 76 kg/mol. h.
• Step 1 Preparation of a dilithium cocatalyst having a polymer chain:
• MCH methylcyclohexane
• Step 2 Polymerization of ethylene:
• Step 1 Preparation of a dilithium cocatalyst having a polymer chain:
• Step 2 Polymerization of ethylene and 1,3-butadiene:
• 60 mg (93.8 ml) of metallocene Me2Si(Ci3H8)2Nd(BH4)2Li.THF are weighed into a 250 mL Steinie bottle in a glove box.
• 15mL (93.8pmol) of the dilithium cocatalyst solution synthesized beforehand in step 1 is added using a syringe to the bottle containing the metallocene under inert conditions.
• the content of the bottle containing the metllocene Me2Si(Ci3H8)2Nd(BH4)2Li.THF and the dilithium cocatalyst is diluted with 285mL of previously degassed methylcyclohexane, then transferred to the polymerization reactor under inert conditions.
• the reactor is partially placed under vacuum, pressurized to 3 bars with a gaseous mixture containing 80% molar ethylene and 20% molar 1,3-butadiene.
• the polymerization is stopped with methanol when the reaction medium has consumed 5.3 g of the monomer mixture.
• the catalytic activity is measured at 1.3 kg/mol. h.
• Step 1 Preparation of a cocatalyst, reaction product between the dilithium initiator and the mesitylmagnesium bromide:
• Step 2 Polymerization of a mixture of ethylene and 1,3-butadiene:
• Half of the contents of the 750 mL bottle is introduced into a inerted reactor with stirring (400 revolutions per minute) at 77°C.
• the 250 mL bottle containing the metallocene and the cocatalyst is introduced into the reactor, then the rest of the 750 mL bottle is also introduced into the reactor.
• the reactor is degassed under vacuum until gas bubbles form, then pressurized to 3 bars with a gaseous mixture containing 80% molar ethylene and 20% molar 1,3-butadiene.
• the ballast pressure shows the pressure drop corresponding to 9 g of monomers, the reactor is degassed with 3 vent/nitrogen cycles.
• the reaction medium is deactivated with a few mL of ethanol, then emptied into an aluminum tray and dried under vacuum at 50° C. in an oven for 24 h.
• Approximately 2 g of polymer are dissolved in 20 mL of MCH, then precipitated in approximately 150 mL of acetone.
• the operation is repeated 3 times in succession in order to wash the polymer.
• the washed polymer is dried in an oven at 60° C. under vacuum under nitrogen sweeping.
• the catalytic activity measured is equal to 108 kg/mol/h.
• the polymer is a random copolymer of ethylene and 1,3-butadiene which contains 77.9% by mole of ethylene unit. Its number-average molar mass determined by the SEC/RI method described above is 272500 g/mol, the dispersity being equal to 1.64.
• Example 5 differs from example 4 in that 48.2 mg (75.4 pmol) of metallocene are used and the pressure drop corresponds to 4 g of monomers.
• the catalytic activity measured is equal to 95 kg/mol/h.
• the polymer is a random copolymer of ethylene and 1,3-butadiene which contains 75.5 mole % ethylene unit. Its number-average molar mass determined by the SEC/RI method described above is 128500 g/mol, the dispersity being equal to 1.43.
• Example 1 A single population of block polymers characterized by a relatively narrow dispersity of 1.23 is obtained in the process in accordance with the invention (Example 1) while two populations of polymers of respective dispersity 1.11 and 1.22 and of very distinct number-average molar masses are obtained in Example 3 which does not conform.

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