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
  • C08F136/00—Homopolymers of compounds having one or more unsaturated aliphatic radicals, at least one having two or more carbon-to-carbon double bonds
  • C08F136/02—Homopolymers of compounds having one or more unsaturated aliphatic radicals, at least one having two or more carbon-to-carbon double bonds the radical having only two carbon-to-carbon double bonds
  • C08F136/04—Homopolymers of compounds having one or more unsaturated aliphatic radicals, at least one having two or more carbon-to-carbon double bonds the radical having only two carbon-to-carbon double bonds conjugated
  • C08F136/06—Butadiene

Definitions

• the present invention relates to a catalytic system for the stereospecific polymerization of conjugated dienes favoring the 1,4-trans insertion of the monomers.
• the invention relates more particularly to a polymetallic catalytic system for the stereospecific polymerization of conjugated dienes favoring the 1,4-trans insertion of the monomers.
• the invention also relates to a process for the synthesis of diene polymers with a high 1,4-trans linking rate using a polymetallic catalytic system for the polymerization of the monomers.
• the article Macromolecules 2017, 50, 7887-7894 "Regulation of the cis-1,4- and trans-l,4-Polybutadiene Multiblock Copolymers via Chain Shuttling Polymerization Using a Ternary Neodymium Organic Sulfonate Catalyst", Quanquan Dai et al., describe the synthesis of polybutadienes allowing to regulate the ratio of 1,4-cis and 1,4-trans levels to achieve a balance between tolerance to deformation (attributed to the cis-1,4 part of the polybutadiene) and stiffness (attributed to the crystallinity of the trans-1,4-part of the polybutadiene).
• EP0091287 describes a catalytic system for the polymerization of butadiene comprising in particular didymium versatate and a dibutylmagnesium making it possible to achieve stereoregular polybutadiene with a high level of 1,4-trans.
• the technical problem that arises in the context of the present invention is to have a process for the synthesis of stereoregular diene polymers, particularly stereoregular polymers of butadiene, promoting the formation of 1,4-trans linkages, and also making it possible to limit the formation of sequences 1.2.
• the invention makes it possible to solve this problem by proposing a preformed catalytic system combining a neodymium organophosphate and an organic magnesium compound which, used for the polymerization of 1,3-dienes, has a stereospecificity with respect to the insertion 1 ,4-trans while maintaining satisfactory polymerization reaction conversion.
• the use of the catalytic system according to the invention in a process for the synthesis of a diene polymer makes it possible to obtain diene polymers having high levels of 1,4-trans linkage, with in particular values of at least 65% by weight relative to the diene part of the polymer, and a low 1,2-linking rate, in particular with values less than or equal to 10% by weight relative to the diene part of the polymer.
• the use of the preformed catalytic system according to the invention in a process for the polymerization of butadiene allows the synthesis of a polybutadiene having the following characteristics:
• the invention relates to such a preformed catalytic system.
• the invention relates to a method of synthesizing a diene polymer using such a preformed catalyst system.
• R 1 R 2 Mg an organic magnesium compound of formula R 1 R 2 Mg, in which R 1 and R 2 represent, independently of each other, an aliphatic radical in Ci-Cio, substituted or not, an aromatic radical in C6- C20, substituted or not.
• R 1 and R 2 represent, independently of each other, an aliphatic radical in Ci-Cio, substituted or not, an aromatic radical in C6- C20, substituted or not.
• the aliphatic radical in the definition of R 1 and R 2 is a Ci-Cio alkyl radical chosen from a methyl or ethyl radical, propyl, butyl, pentyl, hexyl, heptyl radicals , octyls, nonyls and decyls.
• the preformation monomer is a conjugated diene monomer having 4 to 15 carbon atoms.
• the preformation monomer is a 1,3-diene monomer having 4 to 15 carbon atoms, preferably 1,3-butadiene.
• neodymium salt of an organic phosphoric acid is a neodymium tris(organophosphate).
• the 12- Catalytic system according to any one of the preceding embodiments in which the molar ratio (preformation monomer/neodymium) has a value of at least 5/1, preferably of at least 15/1.
• the organic phosphoric acid salt of neodymium is a phosphoric acid diester of neodymium, preferably tris [bis (2-ethylhexyl) phosphate] of neodymium,
• the preformation monomer is 1,3-butadiene
• the organic magnesium compound is n-butylethylmagnesium or n-butyloctylmagnesium
• the molar ratio (R 1 R 2 Mg / neodymium) has a value of at most 15/1, preferably of at most 12/1, more preferably of at most 11/1, - the molar ratio (preformation monomer/neodymium) has a value of at least 5/1, preferably of at least 15/1.
• the molar ratio (organic magnesium compounds / neodymium) is at most 15/1, preferably at most 12/1, more preferably at most 11/1, the molar quantity of organic magnesium compounds being the sum of the molar quantities of the magnesium compounds R 1 R 2 Mg and R 3 R 4 Mg.
• the conjugated diene monomer to be polymerized is a 1,3-diene monomer having 4 to 15 carbon atoms, preferably butadiene or isoprene, more preferably butadiene .
• conjugated diene monomer to be polymerized is copolymerized with at least one other monomer chosen from conjugated diene monomers having 4 to 15 carbon atoms.
• the conjugated diene monomer to be polymerized is a 1,3-diene having 4 to 15 carbon atoms, preferably 1,3-butadiene,
• the neodymium organic phosphoric acid salt of the preformed catalytic system is the neodymium tris[bis(2-ethylhexyl)phosphate],
• the preformation monomer is 1,3-butadiene
• the organic magnesium compound of the preformed catalytic system is n-butylethylmagnesium or n-butyloctylmagnesium
• the molar ratio (R 1 R 2 Mg / neodymium) has a value of at most 15/1, preferably of at most 12/1, more preferably of at most 11/1 ,
• the molar ratio (preformation monomer/neodymium) has a value of at least 5/1, preferably at least 15/1,
• an organic magnesium compound R 3 R 4 Mg in which each of R 3 and R 4 represents, independently of one another, an aliphatic radical in Ci-Cio, substituted or not, an aromatic radical in C6- C20, substituted or not, preferably n-butylethylmagnesium or n-butyloctylmagnesium, is added to the reactor independently of the catalytic system provided that the molar ratio (organic magnesium compounds / neodymium) is at most 15/1, preferably of at most 12/1, more preferably of at most 11/1, the molar quantity of organic magnesium compounds being the sum of the molar quantities of the magnesium compounds R 1 R 2 Mg and R 3 R 4 Mg .
• the percentages (%) expressing the microstructure of the diene polymer are percentages by weight relative to the diene part of the polymer .
• a 1,4-trans linking rate of more than 65% in a diene polymer corresponds to a 1,4-trans diene unit rate of more than 65% by weight relative to the weight of the diene part of the polymer .
• high level of 1,4-trans linkage means a level of 1,4-trans linkage of more than 65% by weight relative to the weight of the diene part of the polymer.
• any interval of values denoted by the expression “between a and b” represents the domain of values going from more than a to less than b (i.e. limits a and b excluded) while any interval of values denoted by the expression “from a to b” signifies 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 the catalytic system is meant the mixture of these constituents and/or the product of the reaction between these constituents.
• the compounds comprising carbon mentioned in the description can be of fossil origin or biobased. 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. Are concerned more particularly in the present application in particular the monomers.
• the butadiene can advantageously be derived in a known manner directly from biomass or be obtained from a biosourced precursor, for example biosourced ethanol.
• the isoprene can advantageously be derived in a known manner directly from biomass or be obtained from a biosourced precursor, for example from biosourced isobutene.
• the styrene can, for example, advantageously be obtained in a known manner directly from biomass or else from the recycling of polystyrene.
• the subject of the invention is a preformed catalytic system based on at least
• R 1 R 2 Mg an organic magnesium compound of formula R 1 R 2 Mg, in which R 1 and R 2 represent, independently of each other, an aliphatic radical in Ci-Cio, substituted or not, an aromatic radical in C6- C20, substituted or not.
• the catalytic system according to the invention is based on at least one neodymium salt of an organic phosphoric acid.
• the organic phosphoric acid salt of neodymium is advantageously a tris(organophosphate) of neodymium, the organophosphate being able to be chosen from the diesters of phosphoric acid of general formula (R'0)(R"0)P0(OH), in which R' and R", which are identical or different, represent a C 1 -C 10 alkyl radical or a C 6 -C 20 aryl or C 7 -C 25 alkylaryl radical.
• the organic phosphoric acid salt of neodymium is neodymium tris[bis(2-ethylhexyl)phosphate].
• the neodymium salt can be in the form of a powder, of a solution in an inert hydrocarbon solvent, of a suspension in an inert hydrocarbon solvent or else of a gel in an inert hydrocarbon solvent.
• neodymium is present in the catalytic system in a concentration equal to or greater than 0.005 mol/l and at most 0.1 mol/l, more particularly at most 0.08 mol/l.
• the catalytic system according to the invention is also based on at least one organic magnesium compound of formula R 1 R 2 Mg
• R 1 R 2 Mg, R 1 and R 2 can be identical or different.
• R 1 R 2 Mg at least one of R 1 and R 2 can be a Ci-Cio aliphatic radical, substituted or not.
• an aliphatic radical mention may be made of C 1 -C 10 alkyl groups, C 2 -C 10 alkenyl groups and C 2 -C 10 alkynyl groups, whether cyclic or non-cyclic.
• R 1 and R 2 when one of R 1 and R 2 is an aliphatic radical, it is a noncyclic C 1 -C 10 alkyl radical chosen from the methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyls, nonyls and decyls.
• R 1 R 2 Mg at least one of R 1 and R 2 can be a C -C aromatic radical, substituted or not.
• aromatic radical mention may be made of C -C aryl groups.
• substituted aliphatic radical or substituted aromatic radical is meant a radical substituted by one or more hydrocarbon groups having from 1 to 10 carbon atoms.
• R 1 and R 2 each denote a non-cyclic C -C alkyl radical.
• the organic magnesium compound of formula R 1 R 2 Mg is n-butylethylmagnesium or n-butyloctylmagnesium.
• the molar ratio (R 1 R 2 Mg/neodymium) in said catalytic system has a value of at least 1/2, preferably of at least 1/1. There is no maximum value for this ratio which is linked to the 1,4-trans linkage rate to be achieved. Nevertheless, so that the achievement of a high level of 1,4-trans linkage greater than 65% by weight relative to the diene part of the polymer does not occur to the detriment of the 1,2- linkage level, the molar ratio (R 1 R 2 Mg/neodymium) in said catalytic system is preferably at most 15/1.
• the molar ratio (R 1 R 2 Mg / neodymium) is at most 12/1 to maintain a 1,2 linking rate of less than 10% by weight relative to the diene part of the polymer, more preferably still of at most 11/1.
• the molar ratio (R 1 R 2 Mg/neodymium) in said catalytic system advantageously has a value of at least 1/1, or even preferably of at least 2/ 1.
• the molar ratio (R 1 R 2 Mg/neodymium) in said catalytic system advantageously has a value of at most 12/1, even more preferably of at most 11/ 1.
• the molar ratio (R 1 R 2 Mg / neodymium) in said catalytic system has a value of at least 1/1, preferably of at least 2/1, and at most 12/1, more preferably at most 11/1.
• the catalytic system according to the invention is also based on at least one diene monomer intended for the preformation of the catalytic system.
• diene monomer which can be used to preform the catalytic system according to the invention, mention may be made of conjugated diene monomers and very particularly conjugated diene monomers having 4 to 15 carbon atoms.
• Suitable as preformation diene monomer are in particular 1,3-butadiene, 2-methyl-
• 1,3-butadiene or isoprene
• 2,3-di(C 1 to C 5 alkyl) 1,3-butadiene such as for example 2,3-dimethyl-1,3-butadiene, 2,3-diethyl -1,3-butadiene, 2-methyl-3-ethyl-1,3-butadiene, 2-methyl-3-isopropyl-1,3-butadiene, phenyl-1,3-butadiene, 1,3 -pentadiene, 2,4-hexadiene, or any other conjugated diene having between 4 and 12 carbon atoms.
• the preforming diene monomer is a conjugated diene monomer having 4 to 12 carbon atoms, particularly isoprene or
• 1,3-butadiene preferably butadiene.
• the molar ratio (preformation monomer/neodymium) can have a value of at least 5/1, more particularly of at least 15/1.
• the quantity of preformation monomer is mainly linked to the process for manufacturing the catalytic system and to its exothermic nature which is difficult to control industrially.
• the catalytic system preferably comprises a hydrocarbon solvent.
• the catalytic system can be in the form of a solution when it is in the presence of a hydrocarbon solvent.
• the hydrocarbon solvent can be a low molecular weight aliphatic hydrocarbon solvent, such as for example cyclohexane, methylcyclohexane, n-heptane, or a mixture of these solvents, or else in an aromatic solvent such as toluene. It should be noted that non-aromatic solvents are particularly preferred.
• 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.
• the catalytic system is bimetallic and therefore contains as metallic compounds only the neodymium salt and the organic magnesium compound.
• the catalytic system is ternary and therefore only contains, apart from a possible solvent as mentioned above, the neodymium salt, the preformation monomer and the compound organic magnesium.
• the organic phosphoric acid salt of neodymium is a phosphoric acid diester of neodymium, preferably tris [bis (2-ethylhexyl) phosphate] of neodymium,
• the preformation diene monomer is a conjugated diene monomer having 4 to 15 carbon atoms, preferably 1,3-butadiene,
• the organic magnesium compound R 1 R 2 Mg is n-butylethylmagnesium or n-butyloctylmagnesium
• the molar ratio (R 1 R 2 Mg / neodymium) has a value of at most 15/1, preferably of at most 12/1, more preferably of at most 11/1,
• the molar ratio (preformation monomer/neodymium) has a value of at least 5/1, preferably of at least 15/1.
• the catalytic system according to the invention can be prepared in a conventional manner.
• the method for preparing the catalytic system according to the invention comprises the following steps a) and b):
• the organic phosphoric acid salt of neodymium used for the preparation of the catalytic system can be in the form of a powder; said salt is then previously placed in suspension or in solution in the hydrocarbon solvent.
• Stage b) corresponds to the preformation stage of the catalytic system.
• the hydrocarbon solvent used in the preparation of the catalytic system is generally an aliphatic hydrocarbon solvent such as methylcyclohexane or an aromatic solvent such as toluene. Most often, it is identical to the solvent of the catalytic solution defined previously. Indeed, the hydrocarbon solvent used in the preparation of the catalytic system is, preferably, also the solvent of the catalytic solution.
• step a) the neodymium salt can be added to the hydrocarbon solvent, then the organic magnesium compound.
• Step a) can take place at a temperature ranging from 10 to 60°C.
• the reaction time of step a) can vary between 5 and 60 minutes, more preferably from 10 to 20 minutes.
• step b) the preforming monomer is added to the reaction product of step a).
• Step b) can be carried out at a temperature ranging from 20 to 70°C.
• the reaction time of step b) can typically vary from 10 minutes to 24 hours, preferably from 20 minutes to 12 hours.
• Stage b) can be followed by a degassing stage to eliminate the preformation monomer which would not have reacted during stage b).
• the synthesis takes place under anhydrous conditions under an inert atmosphere both for step a) and for step b) and, where appropriate, the degassing step.
• the reactions are carried out starting from solvents and anhydrous monomers under anhydrous nitrogen or argon.
• Steps a) and b) are generally carried out with stirring.
• the catalytic system thus obtained in solution can be stored under an inert atmosphere, for example under nitrogen or argon, in particular at a temperature ranging from ⁇ 20° C. to ambient temperature (of the order of 23° C. ).
• the catalytic system according to the invention can be advantageously used in a diene polymer synthesis process, which process is also the subject of the present invention. Indeed, it turns out that the catalytic system according to the invention, used in such a process, promotes the 1,4-trans insertion of 1,3-diene monomers, thus making it possible to obtain diene polymers having a rate of high 1,4-trans linkage.
• the synthesis process using a catalytic system according to the invention makes it possible in particular to obtain butadiene polymers having 1,4-trans linkage rates greater than or equal to 65% and having a linkage rate
• a subject of the invention is therefore also a process for the synthesis of a diene polymer comprising a stage of polymerization of at least one conjugated diene monomer in the presence of a preformed catalytic system as described above.
• the conjugated diene monomer to be polymerized is most particularly a monomer
• 1,3-diene monomer in accordance with the invention, mention may very particularly be made of 1,3-diene monomers having 4 to 15 carbon atoms.
• 1,3-diene monomer butadiene, isoprene, 2,3-di(C 1 to C 5 alkyl)-l,3-butadiene such as for example 2,3-dimethyl-l ,3-butadiene, 2,3-diethyl-l,3-butadiene, 2-methyl-3-ethyl-l,3-butadiene, 2-methyl-3-isopropyl-l,3-butadiene, phenyl-l ,3-butadiene, 1,3-pentadiene, or any other 1,3-diene monomer having 4 to 12 carbon atoms.
• 2,3-dimethyl-l ,3-butadiene 2,3-diethyl-l,3-butadiene, 2-methyl-3-ethyl-l,3-butadiene, 2-methyl-3-isopropyl-l,3-butadiene, phenyl-l ,3-butadiene, 1,3-pentad
• any non-cyclic terpene is also suitable, such as in particular a non-cyclic monoterpene (C10H16) such as myrcene, a non-cyclic sesquiterpene (C15H24) such as farnesene, etc.
• C10H16 non-cyclic monoterpene
• C15H24 non-cyclic sesquiterpene
• the conjugated diene monomer to be polymerized is butadiene or isoprene, advantageously butadiene.
• the polymerization step of the process is a homopolymerization step of a conjugated diene monomer in the presence of a catalytic system as described above.
• the polymerization step of the process is a step of copolymerization of at least one conjugated diene monomer in the presence of a catalytic system as described above.
• the conjugated diene monomer is then copolymerized with at least one other monomer.
• conjugated diene monomer having 4 to 15 carbon atoms as defined above, different from the first conjugated diene monomer.
• conjugated diene monomer suitable in particular 1,3-butadiene, 2-methyl-l,3-butadiene (or isoprene), 2,3-di (C 1 to C 5 alkyl) 1,3-butadiene such than for example 2,3-dimethyl-1,3- butadiene, 2,3-diethyl-1,3-butadiene, 2-methyl-3-ethyl-1,3-butadiene, 2-methyl-3-isopropyl-1,3-butadiene, phenyl-1, 3-butadiene, 1,3-pentadiene, 2,4-hexadiene, or any other conjugated diene having between 4 and 12 carbon atoms.
• conjugated diene monomer mention may also be made of non-cyclic terpene conjugated diene monomers, more particularly
• a vinylaromatic compound is also suitable.
• vinyl aromatic monomer mention may be made of a vinylaromatic monomer having from 8 to 20 carbon atoms, such as for example styrene, ortho-, meta-, para-methylstyrene, 2,4,6-trimethylstyrene, divinyl benzene and vinylnaphthalene, preferably the vinylaromatic monomer is styrene.
• the polymerization step can be carried out in known manner, continuously or discontinuously, in bulk or in solution, generally and in known manner at a temperature between 40°C and 120°C.
• the polymerization step can be carried out in an organic solvent conventionally used for the polymerization of diene monomers.
• organic solvent is meant according to the invention an inert hydrocarbon solvent which can be for example an aliphatic or alicyclic hydrocarbon such as pentane, hexane, heptane, iso-octane, cyclohexane, methylcyclohexane, or a aromatic hydrocarbon such as benzene, toluene, xylene, or mixtures of these solvents.
• non-aromatic solvents are particularly preferred.
• the preformed catalytic system as described above is introduced into a reactor and used for the polymerization of at least one conjugated diene monomer in a reaction medium comprising the monomers to be polymerized and, where appropriate, the solvent of polymerization.
• the catalytic system is used in proportions varying from 20 to 2000 pmol of rare earth metal per 100 g of monomers, preferably from 20 to 1000 pmol, even more preferably from 50 to 1000 pmol .
• the polymerization step of the process is preceded by the addition to the polymerization medium, independently of the introduction of the preformed catalytic system used for the polymerization reaction and in a staggered manner, a quantity of at least one organic magnesium compound of formula R 3 R 4 Mg. That is to say that the addition is made in the polymerization medium not at the same time and, therefore, either before, or after, or partly before and partly after, with respect to the introduction of the system preformed catalyst used to catalyze the polymerization reaction.
• the addition can advantageously take place before the introduction of the monomers in order to avoid degassing.
• the quantity of organic magnesium compound of formula R 3 R 4 Mg is such that the molar ratio (organic magnesium compounds/neodymium) is preferably at most 15/1, and more preferably of at most 12/1 with a view to maintaining a 1,2 linking rate of less than or equal to 10%, more preferably of at most 11/1. It is necessary to understand here by molar quantity of organic magnesium compounds the sum of the molar quantity of magnesium compound R 3 R 4 Mg used during the polymerization and of the molar quantity of magnesium compound R 1 R 2 Mg of the catalytic system.
• the organic magnesium compound of formula R 3 R 4 Mg may be identical to or different from the organic magnesium compound of formula R 1 R 2 Mg of the catalytic system.
• each of R 3 and R 4 represents, independently of one another, an aliphatic radical in Ci-Cio, substituted or not, an aromatic radical in C 6 -C 20 , substituted or not.
• the aliphatic and aromatic radicals are defined above in relation to R 1 and R 2 . More particularly, each of R 3 and R 4 is a noncyclic C 1 -C 10 alkyl radical chosen from a methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl and decyl radical.
• the organic magnesium compound of formula R 3 R 4 Mg is preferably n-butylethylmagnesium or n-butyloctylmagnesium.
• At least one of the following characteristics is observed, at least two, at least three, at least four, at least five, at least six and preferably all:
• the conjugated diene monomer to be polymerized is a 1,3-diene monomer having 4 to 15 carbon atoms, preferably 1,3-butadiene,
• the neodymium organic phosphoric acid salt of the catalytic system is a neodymium phosphoric acid diester, preferably neodymium tris [bis (2-ethylhexyl) phosphate],
• the preformation diene monomer of the catalytic system is a conjugated diene monomer having 4 to 15 carbon atoms, preferably 1,3-butadiene,
• the organic magnesium compound of the catalytic system is n-butylethylmagnesium or n-butyloctylmagnesium
• the molar ratio (R 1 R 2 Mg / neodymium) is at most 15/1, preferably at most 12/1, more preferably at most 11/1,
• the molar ratio (preformation monomer / neodymium) is at least 5/1, preferably at least 15/1
• each of R 3 and R 4 represents, independently of one another, a C 1 -C 10 aliphatic radical, substituted or not, an aromatic C 6 radical -C 20 , substituted or unsubstituted, preferably n-butylethylmagnesium or n-butyloctylmagnesium, is added to the polymerization medium independently of the catalytic system at a rate such that the molar ratio (organic magnesium compounds/neodymium) is less than 15/ 1, preferably at most 12/1, more preferably at most 11/1, the molar amount of organic magnesium compounds being the sum of the molar amount of R 3 R 4 Mg and the molar amount of R 1 R 2 Mg.
• the process for synthesizing a diene polymer according to the invention can be continued in a manner known per se.
• the polymerization can be stopped, optionally after a step of post-polymerization modification of the diene polymer.
• the process then continues in a manner known per se with the separation and recovery of the diene polymer prepared. Unreacted monomers can be removed by methods known to those skilled in the art, as can the solvent.
• NIR Near infrared spectroscopy
• NIR Near infrared
• the principle of the method is based on the Beer-Lambert law generalized to a multi-component system. The method being indirect, it calls upon a multivariate calibration [Vilmin, F.; Dussap, C.; Coste, N. Applied Spectroscopy 2006, 60, 619-29] produced using standard elastomers with a composition determined by 13 C NMR.
• the microstructure is then calculated from the NIR spectrum of an elastomer film of about 750 pm thick. Spectrum acquisition is carried out in transmission mode between 7800 and 3900 cm 1 with a resolution of 2 cm 1 , using a Fourier transform near infrared spectrometer equipped with an InGaAs detector cooled by the Peltier effect.
• the conversion is calculated by the ratio between the mass of the polymer isolated at the end of the reaction and the mass of butadiene introduced into the reactor.
• c m polybutadiene _ 100 m butadiene rri butadiene which represents the mass of butadiene introduced into the reactor, mp oiybutadiene which represents the mass of polybutadiene obtained.
• Neodymium tris[bis(2-ethylhexyl)phosphate] is dissolved for 12 hours in methylcyclohexane.
• the reaction medium is heated at 30° C. for 60 minutes.
• the quantities of the reactants (molar ratios) are mentioned in the table below.
• Table 2 presents the degree of conversion of the polymerization reactions with the various catalytic systems AX, as well as the microstructures of the polybutadienes obtained.
• Catalyst 400 pmol Nd/100g monomer to be polymerized nd the quantity of polymer synthesized is insufficient to be able to carry out the microstructure measurements by NIR.
• the 1,4-trans level in the polybutadiene decreases and the 1,2 linking level increases with an increasing Mg ca taiyseur/Nd molar ratio in the catalytic system. It is thus possible to modulate the 1,4-trans linking rate by varying the Mgc a t a iyseuri/Nd molar ratio with a preferential maximum value of the order of 10/1 in order to maintain a linking rate of 1 .2 to a value less than or equal to 10%.
• Table 3 shows the microstructures of the polybutadienes obtained by varying the amount of organic magnesium compound added to the reaction medium outside the catalytic system.
• the 1,2-linkage rate increases with an increasing Mg to t ai / Nd molar ratio while maintaining a high 1,4-trans linking rate, Mg to t ai being the total molar amount of organomagnesium compound comprising the magnesium compound added during the polymerization process and the magnesium compound which enters into the composition of the catalytic system.
• the Mg totai / Nd molar ratio is preferably lower to 12/1, or even at most 11/1.

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