WO2018115169A1

WO2018115169A1 - Method for continuous polymerisation of diene elastomer with lithium amide initiator

Info

Publication number: WO2018115169A1
Application number: PCT/EP2017/083898
Authority: WO
Inventors: Marie-Hélène DESSENDIER; Charlotte Dire; Claire FAUVARQUE-NUYTTEN
Original assignee: Compagnie Generale Des Etablissements Michelin
Priority date: 2016-12-21
Filing date: 2017-12-20
Publication date: 2018-06-28
Also published as: FR3060580A1

Abstract

The invention relates to a method for continuous synthesis of a diene elastomer by means of n reactors r1 to rn, provided with an internal stirring system, assumed to be perfectly stirred, arranged in series, n ranging from 2 to 15, preferably from 2 to 9, the reactor r1 being supplied with an input solution comprising a solvent, one or more monomers, an anionic polymerisation initiator chosen among the lithium amides and a polar agent, one or more reactors r2 to rn optionally also being supplied by re-injection of a purified solution comprising solvent and/or one or more monomers and/or polar agent, the temperature of each reactor ranging from 20°C to 150°C, preferably ranging from 30°C to 120°C and being no lower than the temperature of the reactor that immediately precedes same, the temperature of the reactor rn being higher than the temperature of the reactor r1, the diene elastomer obtained having a polymolecularity index ranging from 1.1 to 1.7.

Description

Process for continuous polymerization of diene elastomer with initiator lithium amide

The present invention relates to a process of continuous synthesis, by means of several reactors in series, making it possible to obtain a diene elastomer having a narrow molecular weight distribution and a high level of living polymer, in the case of a initiation with a lithium amide.

Since fuel savings and the need to protect the environment have become a priority, it is desirable to produce polymers having good mechanical properties and as low a hysteresis as possible in order to be able to use them in the form of rubber compositions. useful for the manufacture of various semi-finished products used in the construction of tire casings such as, for example, underlays, bonding gums between rubbers of different kinds or coating of metal or textile reinforcements, sidewall rubbers or treads and obtain tires with improved properties, including reduced rolling resistance.

Reducing the hysteresis of mixtures is a permanent objective of the tire industry in order to limit fuel consumption and thus preserve the environment. However, this must be done while maintaining the mixing ability of the mixtures intact.

To achieve the hysteresis reduction objective, many solutions have already been tested. In particular, mention may be made of modifying the structure of the polymers and diene copolymers at the end of polymerization by means of functionalising, coupling or starring agents in order to obtain a good interaction between the polymer thus modified and the charge, whether it is carbon black or a reinforcing inorganic filler. It may also be mentioned that the use of a functional initiator has a functional group that is interactive with the charge. As an illustration of this prior art, mention may be made of the use of diene elastomers functionalized with alkoxysilane compounds and amine compounds.

One can cite JP4655706B2 patent which proposes to combine the functionalization of the living end of chain with an alkoxysilane type compound carrying an amine function at initiation with a functional amino alkyl ester in order to minimize hysteresis. Similarly, in the patent application US20120245275A 1, it is proposed to combine the functionalization of the living end-chain with an alkoxysilane compound carrying an amine function at initiation with a lithium amide but also with a functional monomer of the vinylamino silane type. Finally, in the patent applications WO2015063 161 A1, WO2015044225A1, WO201501 8772A1 and WO201501 8600A1, it is proposed to combine the initiation with a lithium amide with the reaction of the living end-chain with compounds of the following type. alkoxysilanes having different groups having an affinity for silica.

As illustrated above, the use of functional initiators having a silica-interactive moiety such as amino functional alkyl lithium amides or lithium amides is of interest in decreasing the rolling resistance by decreasing the energy dissipation associated with the ends. free chain. It is therefore interesting to use them on an industrial scale in competitive elastomer synthesis processes.

It is known to those skilled in the art that continuous synthesis processes are more competitive than batch synthetic processes for which frequent shutdowns and restarts are required. But whereas the use of a lithium amide initiator leads to the joint production of high monomer conversions (greater than 85%) and higher levels of living polymer chains in the form of C Li ^{+ +} in the batch process (higher or lower). 90%>), a high conversion to monomers (greater than 85%>) is associated with a low level of living polymer chains (less than 60%) and a high level of polymer chains. (greater than or equal to 90%) is associated with a low monomer conversion (less than 70%>) in the case of a conventional continuous reactor process.

The reduction of the molecular weight distribution prior to functionalization of the elastomer also makes it possible to improve the compromise hysteresis / implementation of the material.

The synthesis of elastomers with a batch-type process is preferable in this respect, since this type of method allows a control of the molecular distribution in order to obtain diene copolymers with a narrow molecular weight distribution before functionalization, unlike of a continuous process which gives access to a wide distribution of molecular weight.

By way of example, US Pat. No. 6,313,232, EP 13,182,172 and EP 1 829 906 claim that products with a low polydispersity are favorable for reduced hysteresis. Linear polymers with narrow mo lecular distributions also have an improved implementation.

No. 5,587,420 discloses a method for the polymerization of diene monomers in hydrocarbon solvent solution using as initiator a batch organolithium compound. An organotin compound is added during or at the end of the batch. This type of batch process is less productive and less economical than a continuous process. This is described in US Pat. No. 6,313,232, which describes a continuous process with a first polymerization step in the presence of a compound derived from tin followed by a step of functionalization with tin at the outlet of the production reactor. of a diene polymer with improved physical properties, including the decrease in hysteresis. But the polydispersity values of polymers synthesized with this method are not indicated.

Moreover, as previously explained, in order for the polymer obtained to be recovered, the synthesis process must be competitive and economical. In this sense, a continuous type process is preferable. However, this type of process with a reactor perfectly stirred does not allow a control of the polymoecularity index as the discontinuous type processes.

Numerous patents describe the synthesis of functional elastomers in a continuous process. Patent JP 1988-235305 (63-235305 JP) which describes a continuous process of economic polymerization in which the polymer obtained has a broad molecular distribution.

EP 1 829 906 discloses a continuous process for the production of aromatic diene and vinyl copolymers in the presence of a polarity modifying agent (THFA-ethyl) in order to obtain a statistical incorporation of the monomers. The synthesis is done by means of at least two reactors in series. The copolymer obtained has a polymolecularity index of between 1.6 and 2.5.

Reference may also be made to US Pat. No. 6,337,263B1, which describes a continuous process for the polymerization of styrene and butadiene in two series reactors, in which all the styrene is introduced into the first reactor with only part of the butadiene, the remainder of the butadiene being introduced into the second reactor. This method makes it possible to synthesize low vinyl content random elastomers with an absence of styrene blocks.

The aim of the invention is therefore to identify a continuous synthesis process which makes it possible to obtain a high conversion of monomers (greater than 70% by weight) and a high level of living polymer chains (higher or higher). equal to 90% by number) at the end of the polymerization step in the case of an initiation with a lithium amide. A high level of living polymer at the end of the polymerization step is desirable in order to be able to functionalize, couple or to star the polymer chains as desired. The synthesis method must also make it possible to synthesize diene elastomers having a low molecular weight distribution prior to functionalization which allows a gain on the compromise hysteresis / implementation of the material thus synthesized.

The inventors have now surprisingly discovered that the objects of the invention can be obtained by a method of continuous synthesis comprising several reactors in series, monomer, solvent or a polar agent being optionally reinjected in one or more reactors other than the first, the intrinsic mass conversion in the first reactor being less than 70%, the polymerization being continued in such a way that the total mass conversion at the outlet of the last reactor is greater than 70%>, the diene elastomer obtained having a polymolecularity index ranging from 1.1 to 1.7, and a low level of dead chains .

The object of the invention is therefore to provide a process for the continuous synthesis of a diene elastomer by means of n rn reactors equipped with an internal stirring system, which are supposed to be perfectly stirred, arranged in series, n varying from 2 to 15, preferably 2 to 9, the reactor r1 being fed with an input solution comprising a solvent, one or more monomers, an anionic polymerization initiator selected from lithium amides and a polar agent, one or more the reactor (s) r2 to rn optionally being further supplied by reinjection of a purified solution comprising solvent and / or monomer (s) and / or polar agent, the temperature of each reactor varying from 20 to 150 ° C, preferably ranging from 30 to 120 ° C, and being greater than or equal to the temperature of the reactor immediately preceding it, the temperature of the reactor rn being greater than the temperature of the reactor r1,

the mass quantity Mi of monomer (s) introduced into the reactor r1 being such that

the mass quantity Mi of monomer (s) reinjected in the reactor ri, when Mi ≠ 0, i varying from 2 to n, being such that

and such that Mi represents from 5 to 100% by weight of the mass of the solution injected into the reactor ri, when Mi ≠ 0,

where Mj is the mass quantity of monomer (s) introduced into the reactor rj, j varying from 1 to n,

the mass quantity of all the monomers entering the reactors at rn representing 5 to 25% by weight of the sum of the total mass inputs of the reactor 1rs to rn,

the intrinsic intrinsic conversion Cintrinsque, 1 in the first reactor being less than 70%,

where Cintrinsque, 1 = P 1 / M l

where P i is the mass of polymer formed in the reactant, the total mass conversion Ctot at the outlet of the reactor rn being greater than or equal to 70%>,

or

where Pi is the mass of polymer formed in the reactor ri, the overall mass conversion Cglobal i in each reactor ri, i ranging from 1 to n being such that

and

Or

where Pi is the mass of polymer formed in the reactor ri, i ranging from 1 to n, the diene elastomer obtained having a polymolecularity index ranging from 1.1 to 1.7, preferably ranging from 1.2 to 1.6.

In the context of the present application, it is called reinj ection repeating the inj ection action in a reactor ri, different from the reactor r 1, already fed by the stream from ri 1. The reinjection, when it takes place, can be done directly in one or more of the reactors, or, advantageously, by mixing with the stream coming from one or more reactors. Reinjection can be done with flows of composition identical or different from the feed stream of r 1. When the reinjection takes place in at least two reactors, the natures of these reinjections can be identical or different. The reinjected monomer is the monomer injected into the non-stream from the stream.

Thus, by mass quantity Mi of monomer (s) introduced into the reactor ri, is meant, when i = 1, the amount of monomer (s) contained in the inlet solution and introduced (s). ) in this way in the reactor 1, and when i = 2 to n, the amount of monomer (s) possibly reinjected (s) in the reactor i.

By controlling the conversion in each reactor and by the number of reactors, the continuous process according to the invention makes it possible to obtain, at the outlet of the last reactor, a level of living chains greater than or equal to 90% by number relative to the number total living chains initiated by lithium amide in reactor 1. However, the reinjected solution (s) must be purified so as not to degrade the living polymer.

In the case of anionic polymerization, the living chain is a carbanion. Carbanion is a very reactive species. It reacts with protic species or electrophilic species.

Also if the charge of the first reactor contains protic impurities (alcohols, water, acids ...) or electrophilic (carbonyls, ...), the initiator will react first with these impurities to lead to inactive species (alcoholates) unable to initiate polymerization of the monomers. The difference between the quantity of initiator introduced at the inlet of the reactor 1 and the quantity of initiator having reacted with the impurities in the reactor is the amount of active initiator. The number of living chains initiated in reactor 1 is equivalent to this amount of active initiator in reactor 1.

On the other hand, for any subsequent reinjections between the reactors, the neutralization of the impurities introduced by reinfection will be by the polymer carbanion. This neutralization prevents the polymer chain from propagating and the chain thus becomes dead, that is to say inactive towards the polymerization but also the functionalization. This species is no longer reactive with the agents of stoppage, functionalisation, coupling or starring possible.

That is why, apart from the charge of the first reactor, it is necessary to control the purity of each reinjected solution in order to guarantee a dead polymer content at the outlet of the reactor rn as low as possible, ie less than 10% in number relative to the total number of chains initiated in the reactor r 1.

By mass quantity of all the monomers (s) entering the reactors r 1 to rn, is meant the sum of the mass quantity of monomer (s) introduced into the reagent by the input solution and the mass quantities of the monomers optionally reinjected in one or more reactors r2 to rn.

Sum of the total mass inputs of the reactors rn is the sum of the mass quantity of the input solution and the mass quantities of the solutions possibly reinjected.

By polymoecularity index, also referred to as polydispersity index, is meant the ratio of the weight average molecular weight to the number average molecular weight. The average molecular weight and number of masses are measured by size exclusion chromatography.

The process according to the invention also makes it possible to control the polymoecularity index of the synthesized polymer by controlling the conversion, balancing the temperatures in each reactor and the number of reactors. The control of the conversion in all the reactors, in particular in the first and the last reactor, is ensured by the temperature, the residence time, the quantity of polar agent and the quantity of monomer entering these reactors, the concentration in living polymer. The skilled person knows how to vary these different parameters to control the conversions in the different reactors.

Working at increasing temperature accelerates the propagation in the reactors. Therefore, preferably, the temperature in at least one reactor is greater than the temperature of the reactor 1, preferably the temperature of each reactor is greater than the temperature of the reactor. to n.

The optional reinjection of a part of the monomers in one or more of the reactors from the second impacts the amount of monomers present in the reactor and the residence time therein. Thus, these reinjections, which constitute an advantageous implementation of the method according to the invention, also contribute to the balancing of the conversions, and as previously explained, to the control of the polymo-uniformity index.

Advantageously, the very high purity of the monomers reinjected reduces the impact of side reactions which tend to widen the molecular distribution of the polymer formed.

The residence times and temperatures are also chosen not to favor these side reactions.

Preferably, the reactors are equipped with an internal stirring mechanism.

Preferably, the intrinsic intrinsic mass conversion C 1 in reactor 1 is less than 65%, preferably less than 60%. Preferably, the total mass conversion Ctot at the outlet of the reactor rn is greater than or equal to 80%, preferably greater than or equal to 85%.

Preferably, the number of reactors is equal to 2 or 3, preferably 2. When the number of reactors is equal to 2, the process according to the invention preferably has at least one of the following characteristics and, more preferably, all the following characteristics:

a reinjection of a solution comprising monomer (s) is carried out in reactor r2,

the purity of the solution possibly reinjected into the reactor r2 is such that the level of impurities in the reinjected solution is minimized to a value less than or equal to 5% of the number of living chains initiated in the reactor r1,

the temperature of the reactors r1 and r2 varies from 20 to 150 ° C, preferably from 30 ° C to 120 ° C, the temperature of the reactor r2 being greater than the temperature of the reactor r1,

the mass quantity of monomer (s) introduced into the reactor r1 is greater than 10% and less than 100% of the total mass quantity of the monomers introduced into the reactors r1 and r2, when a reinjection is performed in r2 ,

the mass quantity of monomer (s) reinjected into the reactor r2 is less than 90% by weight of the total weight of monomer (s) injected into the reactor r1 and reinjected into the reactor r2 , when a reinjection is performed in r2,

the mass quantity of all the monomers entering the reactors r1 to r2 representing 5 to 25% by mass of the sum of the mass inputs of the reactors r1 and r2, when a reinjection is carried out in r2,

the intrinsic mass conversion in the reactor 1 is preferably less than 65%, more preferably less than 60%.

Preferably, the residence time in the reactor ri is between 1 and 60 minutes, preferably between 5 and 60, more preferably between 10 and 50 minutes. It is calculated as follows:

with: Vi, reactor volume Ri, i ranging from 1 to n

- Qvi = volumetric flow out of the reactor i.

As previously explained, a solution comprising solvent and / or monomer (s) and / or polar agent is optionally reinjected into one or more reactors r2 to rn.

As previously explained, the purity of each reinjected solution must be controlled.

By purity of a reinjected solution, is meant the mass proportion of monomer (s), if any, and possible solvent and polar agent, relative to the total mass of the reinjected solution.

The purification step consists in eliminating in the reinjected solution the protic compounds (water, alcohol, acids, ...) and electrophilic compounds (carbonyl, ...) which can deactivate the end of the living chain so as to reduce their quantity. in this solution reinjected at a content less than or equal to 5 mol. % of the active initiator, preferably less than or equal to 2 mo. % of the active initiator. Each reinjected solution contains purified solvent and / or purified monomers and / or purified polar agent.

The constituent or each constituent of the reinjected solution (s) may be, before reinjection, purified independently by any purification means usually used to purify the constituents, for example by adsorption, liquid / liquid extraction, gas / liquid extraction or distillation. .

In particular, the solvent and / or the monomer (s) and / or the polar agent can be purified independently by adsorption, liquid / liquid extraction, gas / liquid extraction or distillation.

Alternatively, the solution (s) to be reinjected, comprising all or part of all of its constituents, may be, before reinjection, purified by any purification means usually used to purify the constituents. for example by adsorption, liquid / liquid extraction, gas / liquid extraction or distillation.

The adsorption can be done on zeolite or on alumina. The liquid / liquid extraction can be done by means of soda. The gas / liquid extraction can be done by means of a flow of air or nitrogen.

The distillation may be a single-stage distillation without reflux (or flash) or column distillation optionally under vacuum.

The flash is carried out by means of an evaporation compartment. The column distillation is carried out by means of a distillation column.

Whatever the purification method chosen for each constituent or for the solution to be reinjected, the purified phase is used to constitute the flow to be reinjected.

According to one embodiment, the residues of the purification process (es) of the or each constituent or of the solution (s) to be reinjected are reinjected in the inlet solution supplying the first reactor. These residues consist of monomers and / or solvents with a high concentration of impurities. The residues may then either be a monomer and / or solvent additive and / or polar agent additive to the input solution or be the sole source of monomer and / or solvent and / or polar agent. the entrance solution. This embodiment makes it possible to limit the loss of material in the case of reinjection.

By diene elastomer, it is to be understood in a known way (one means one or more elastomers) derived at least in part (ie, a homopolymer or a copolymer) from monomers dienes (monomers bearing two carbon-carbon double bonds, conjugated or not). More particularly, diene elastomer is any homopolymer obtained by polymerization of a conjugated diene monomer having 4 to 12 carbon atoms, or any copolymer obtained by copolymerization of one or more conjugated dienes with one another or with one or more monomers. vinylaromatic compounds having 8 to 20 carbon atoms. In the case of copolymers, these contain from 20% to 99% by weight of diene units, and from 1 to 80% by weight of vinylaromatic units. As conjugated dienes which can be used in the process according to the invention, 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-di (C 1 to C ₅ ) -alkyl are especially suitable. , 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 and 2,4-hexadiene, etc.

As vinylaromatic monomers are especially suitable styrene, ortho-, meta, para-methylstyrene, the commercial mixture "vinylto luene", para-tert-butylstyrene, methoxystyrenes, vinylmesitylene, divinylbenzene and vinylnaphthalene, etc.

The diene elastomer is preferably chosen from the group of highly unsaturated diene elastomers consisting of polybutadienes (BR), synthetic polyisoprenes (IR) and butadiene copolymers, in particular copolymers of butadiene and of a vinyl aromatic monomer, copolymers of isoprene and mixtures of these elastomers. Such copolymers are more particularly butadiene-styrene copolymers (SBR), isoprene-butadiene copolymers (BIR), copolymers of isoprene-styrene (SIR) and copolymers of isoprene-butadiene-styrene (SBIR). . Among these copolymers, butadiene-styrene copolymers (SBR) are particularly preferred.

The diene elastomer is prepared by anionic polymerization in the presence of a lithium amide polymerization initiator included in the input solution.

Lithium amides are the reaction products of an organolithium compound, preferably alkyl lithium, and an acyclic or cyclic, preferably cyclic, secondary amine.

As a secondary amine used to prepare the initiators, mention may be made of dimethylamine, diethylamine, dipropylamine, di-n-butylamine, di-sec-butylamine, dipentylamine, dihexylamine, di-n-octylamine, di- (2-ethylhexyl) ) amine, di-cyclohexylamine, N-methylbenzylamine, diallylamine, morpholine, piperazine, 2,6-dimethylmorpho line, 2,6-dimethylpiperazine, 1 - ethylpiperazine, 2-methylpiperazine, 1-benzylpiperazine, piperidine, 3,3-dimethylpiperidine, 2,6-dimethylpiperidine, 1-methyl-4-

(methylamino) piperidine, 2,2,6,6-tetramethylpiperidine, pyrrolidine, 2,5-dimethylpyrrolidine, azetidine, hexamethyleneimine, heptamethyleneimine, 5-benzyloxyindole, 3-azaspiro [5,5] undecane, 3-aza-bicycle [ 3.2.2] nonane, carbazole, bistrimethylsilylamine, pyrrolidine and hexamethyleneamine.

The secondary amine, when cyclic, is preferably selected from pyrrolidine and hexamethyleneamine.

The alkyl lithium compound is preferably ethyllithium, n-butyllithium (n-BuLi), isobutyl lithium, and the like.

The polymerization is carried out in the presence of a solvent included in the input solution.

The solvent used in the process according to the invention is preferably an inert hydrocarbon solvent which may be, for example, an aliphatic or alicyclic hydrocarbon such as pentane, hexane, heptane, isooctane, cyclohexane. methylcyclohexane or an aromatic hydrocarbon such as benzene, toluene, xylene.

As previously explained, the inlet solution, as well as optionally one or more of the recycled solutions used in the process according to the invention comprises / comprise a polar agent.

As chelating polar agents that may be used in the process according to the invention, agents comprising at least one tertiary amine function or at least one ether function and preferably tetrahydrofurfuryl ethyl ether or tetramethyl ethylenediamine agents are especially suitable.

According to a first particular embodiment, the stream leaving the reactor n and containing the living chains is brought into contact with one or more polymerization stopper agents as known per se, injected into the process in a continuous manner. .

In this first embodiment, the living diene elastomer included in the flow at the outlet of the reactor n may, in advance at the stoppage, be reacted with one or more functionalising, coupling or starring agents. The peculiarity of these functionalising, coupling or starring agents is that they can either modify the elastomer so as to improve the interaction with a reinforcing filler (this is the case with functionalising, coupling and some starch agents) give the polymer a given structure (this is the case of certain starch and coupling agents).

According to a second particular embodiment, the living diene elastomer included in the outlet stream of the reactor n is reacted with one or more functionalising, coupling or starring agents also acting as a polymerization stopper agent. It is then not necessary to add a conventional conventional stopper to terminate the polymerization.

Whatever the embodiment, as functionalising, coupling or starring agent, it is possible to envisage any agent known per se.

The aforementioned features of the present invention, as well as others, will be better understood on reading the following description of several embodiments of the invention, given by way of illustration and not limitation.

Measurements and tests used Conversion

The conversions are measured by dry weight weighings of the solution containing the polymer. In this method, solution containing the polymer is withdrawn at the outlet of the reactor. This solution is introduced into a previously tared container. The mass of solution is thus weighed.

The sample is dried at 140 ° C under the reduced pressure of 200 mmHg for 15 minutes. The tray is then placed in a desiccator containing silica gel for 2 minutes. The weighing of the tray then makes it possible to determine the mass of polymer of the sample taken.

We then go back to the different conversions as follows:

with,

Ml is the mass flow rate in monomers introduced into the reactor 1,

Ql is the sum of all the mass flow rates of the species entering the reactor 1,

With,

Qi the sum of all the mass flow rates of the species entering the reactor i.

Glass Transition Temperature In these examples, the glass transition temperatures (Tg) of the elastomers are determined using a differential scanning calorimeter according to ASTM E1356-08 (2014). Microstructure elastomers

The microstructure of elastomers is characterized by the technique of near infrared spectroscopy (NIR). Near infrared spectroscopy (NIR) is used to quantitatively determine the mass content of styrene in the elastomer as well as its microstructure (relative distribution of 1,2-butadiene 1,4-trans and 1,4-cis units). The principle of the method is based on the Beer-Lambert law generalized to a multicomponent system. The method being indirect, it uses a multivariate calibration [Vilmin, F .; Dussap, C; Coste, N. Applied Spectroscopy 2006, 60, 619-29] carried out using standard elastomers of composition determined by ¹³ C NMR. The styrene content and the microstructure are then calculated from the NIR spectrum of a film. elastomer approximately 730 μιη thick. The acquisition of the spectrum is carried out in transmission mode between 4000 and 6200 cm ^"1 with a resolution of 2 cm ^-1 , using a Bruker Tensor 37 Fourier transform infrared near-infrared spectrometer equipped with a cooled InGaAs detector. by Peltier effect.

Number-average molar mass and polymolecularity index

The number average molar mass and the polymolecularity index of the polymer are determined using a SEC (size exclusion chromatography).

The SEC (Size Exclusion Chromatography) technique separates macromolecules in solution according to their size through columns filled with a porous gel. The macromolecules are separated according to their hydrodynamic volume, the larger ones being eluted first.

The SEC makes it possible to apprehend the average molar masses and the molar mass distributions of a polymer. From commercial standard products, the various average molar masses by number (Mn) and by weight (Mw) can be determined and the polymolecularity index (Ip = Mw / Mn) calculated via a so-called MOORE calibration.

There is no particular treatment of the polymer sample before analysis. This is simply solubilized in the elution solvent at a concentration of about 1 gL ^{-1, and} then the solution is filtered through a 0.45 μm porosity filter before injection.

The equipment used is a chromatographic chain "WATERS alliance". The eluting solvent is either tetrahydrofuran or tetrahydrofuran + 1% vol. of diisopropylamine + 1% vol. of triethylamine, the flow rate of 1 mL.min- ¹ , the system temperature of 35 ° C. and the analysis time of 30 min.A set of two WATERS columns with the trade name "STYRAGEL HT6E" is used. of the solution of the polymer sample is 100 μί The detector is a differential refractometer "WATERS 2410" and the chromatographic data exploitation software is the system "WATERS EMPOWER".

The calculated average molar masses relate to a calibration curve produced for SBR with the following microstructure: 28% by weight of styrene type units, 18% by mass of type 1-2 units, 31% by mass of type 1-4 trans units, and 23% by mass of units type 1-4 cis.

Live chain rate in the elastomer at the reactor outlet

In the examples, the living polymer solution at the outlet of the polymerization reactors is contacted continuously with the excess functionalizing agent DEAB (diethylaminobenzophenone) with a contact time sufficient for the total reaction of all the living chains with the functionalization agent. The determination of the degree of grafted DEAB (functional level in the examples) is carried out by NMR analysis. This determination is made with respect to the amount of elastomer. In this way the results obtained can be expressed in% molar, in mmol / kg of elastomer or in phr (per hundred grams of elastomer)

The samples (approximately 25 mg of elastomer) are solubilized in Carbon Disulfide (CS ₂ ) in approximately 1 ml. Ι ΟΟμί of deuterated cyclohexane are added for the Lock signal.

The spectra are acquired on a Bruker 500 MHz Avance spectrometer equipped with a Bruker BBI z-grad 5 mm broadband probe.

The NMR experiment ^! Quantitative H uses a simple 30 ° pulse sequence and a 5 second repeat delay between each acquisition. 256 accumulations are made at room temperature.

The 1 H NMR signals of the 8 quantized protons (protons bound to the identified carbons 1 to 4 in FIG. 1) of the grafted DEAB correspond to a chemical shift mass of 3.2 ppm.

The 2D NMR correlation spectrum H / ⁿ C ^! J HSQC edited allows to verify the nature of the grafted pattern through chemical shifts of carbon atoms and protons. The signal from carbons 1 to 4 has a chemical shift at 44.4 ppm.

The NMR spectrum ^! H makes it possible to quantify the grafted DEAB motifs by integration of the signal massings described above: H 1, H 2 for the dehydrated DEAB form and H 3, H 4 for the DEAB carbino form.

The grafted diethylaminobenzophenone, dehydrated forms and carbino l, has the following formula:

Figure 1 The chemical shifts are calibrated with respect to the protonated impurity of Carbon Disulfide δ ppm ¹ H to 7. 1 8 ppm referenced on the TMS (δppm ¹ H at 0 ppm) and δppm 13 C at 192 ppm referenced on the TMS ( ¹ ppm at 0 ppm).

The single-pulse 1 D ¹ H NMR spectrum makes it possible to quantify the polymer units by integrating the characteristic signal masses. For example for a SBR (Styrene butadiene rubber), the mass considered for the calculation are 5H (protons) styrene between 7.4ppm and 6. Oppm, 2H PB (polybutadiene) 1 -4 + 1H PB 1-2 between 5.8 ppm and 4.9ppm and 2H PB 1-2 between 4.9 ppm and 4.3 ppm.

Thus, knowing the total amount of chains by the value of Mn obtained SEC analysis, it is possible to determine the level of living chains corresponding to the level of functionalized chains DEAB.

HMN Initiated Channel Rates

The determination of the level of HMN initiated chains is carried out by NMR analysis.

The samples (about 200 mg) are solubilized in about 1 mL of carbon disulfide (CS ₂ ). 100% of deuterated cyclohexane are added to the solution for the lock of the spectrometer.

The spectra are acquired on a BRUKER 500 MHz Avance spectrometer equipped with a BBIz-grad 5mm wide band probe cryo.

The NMR quantitative ^J H experiment uses a sequence simp the 30 ° pulse and a repetition time of 5 seconds between each acquisition. 64 to 1024 accumulations are made. Two-dimensional H / ¹³ C experiments were performed to determine the structure of the functional polymers. The proton chemical shifts are calibrated against the proton impurity of C S2 at 7.18 ppm.

In the case of a homopolymer of butadiene, ie a polybutadiene, the measurement NMR 1 D ¹ H simple quantitative pulse allows to observe two masses (2, 8 ppm at 3, 0 ppm and 2.3 ppm at 2.5 ppm) corresponding to protons 1 and 2.

The integration of the protons 2 makes it possible to estimate the quantity of HMN units grafted on a butadiene 1, 4 and the integration of the protons 1 makes it possible to estimate the total quantity of HMN units grafted onto the polybutadiene chains.

In the case of a copolymer of butadiene and styrene, the simple quantitative 1 D ¹ H NMR measurement makes it possible to observe a single mass (2.8 ppm to 3.0 ppm) corresponding to the protons 2.

The integration of protons 2 makes it possible to estimate the quantity of patterns

HMN grafted on butadiene 1, 4 only. The proton signal 1 is masked by the aliphatic signal of the SBR matrix. In the case of an SBR, only the quantity of HMN units grafted to a butadiene 1, 4 can be estimated.

So, knowing the total amount of strings by the value of

Mn obtained by SEC analysis, it is possible to determine the level of HMN initiated chain (only the HMN units linked to a butadiene unit 1, 4 are quantifiable in the case of copolymers of butadiene and styrene).

Examples of elastomer preparation

In a continuous polymerization pilot plant containing one or more stirred continuous reactors, presumed to be perfectly stirred according to the person skilled in the art, methylcyclohexane, butadiene, styrene and tetrahydrofurfurylethyl ether are introduced continuously in the proportions described in each example. . N-Butyllithium is introduced in sufficient quantity to neutralize the protic impurities provided by the various constituents present in the line inlet and then lithiated hexamethyleneimine is introduced to initiate the polymer chains. The synthesis of lithiated hexamethyleneimine is carried out in situ continuously by reacting one equivalent of hexamethyleneimine and 1.02 equivalent of butyl lithium in a perfectly stirred reactor.

For the D example, a purification of the reinjected solution of butadiene is carried out continuously by means of a column of aluminas. This column is furnished with a fixed bed of Axsorb 920 type aluminas.

The L / D ratio of the minimum fixed bed is 4

The ratio Coil diameter / average particle diameter minimum alumina is 10

The Reyno lds in empty cask is greater than 2.

The minimum residence time of the fluid in the full column is 5 minutes.

The column is maintained under the following conditions:

- Temperature = 10 ° C

- Pressure = 5 bar.

The residence times and the concentrations indicated as examples are calculated from the flow rates of the various constituents entering into the polymerization process.

Example A - Comparative - 1 reactor continuous process

A synthesis of butadiene / styrene polymer is carried out according to a comparative method using only 1 stirred reactor, supposed to be perfectly stirred.

The operating conditions are specified in Table 1. Table 1

(1) by weight relative to the sum of all mass inputs of process monomers

(2) by weight in relation to the sum of all mass inputs of the process

(3) mass conversion to monomers in the reactor

The characteristics of the polymer obtained at the outlet of the reactor are given in Table 2. Table 2

(4) by weight relative to the butadiene units present in the polymer chains

(5) by weight relative to butadiene and styrene units

(6) the ratio between the quantity of HMN functions determined by NMR and the number of chain ends calculated from the value of Mn measured on the elastomer recovered at the end of the functionalization step with DEAB.

(7) the ratio between the quantity of DEAB functions determined by NMR and the number of chain ends calculated from the value of Mn measured on the elastomer recovered at the end of the step of functionalization with DEAB.

Thus, this comparative example shows that a low living polymer level and a larger weight distribution are obtained than the targeted one.

Example B - According to the invention - 2 reactors in series without reinjection

A styrene / butadiene polymer synthesis is carried out according to a process according to the invention using two agitated reactors, supposed to be perfectly stirred in series.

The operating conditions are specified in Table 3.

Table 3

(1) by weight relative to the sum of all mass inputs of process monomers

(2) by weight in relation to the sum of all mass inputs of the process

The characteristics of the polymer obtained at the outlet of the reactor 2 are given in Table 4. Table 4

(3) by weight relative to the butadiene units present in the polymer chains

(4) by weight relative to butadiene and styrene units

(5) the ratio between the quantity of HMN functions determined by NMR and the number of chain ends calculated from the value of Mn measured on the elastomer recovered at the end of the step of functionalization with DEAB.

(6) the ratio between the quantity of DEAB functions determined by NMR and the number of chain ends calculated from the value of Mn measured on the elastomer recovered at the end of the step of functionalization with DEAB.

Thus, this example shows that it is possible to obtain concomitantly with the continuous process according to the invention a high conversion, a high level of living polymer and a narrow distribution of molecular masses.

Example C - Comparative - 2 reactors in series with reinjection of unpurified butadiene

A styrene / butadiene polymer synthesis is carried out according to a process according to the invention using two agitated reactors, supposed to be perfectly stirred in series. Butadiene reinjected is not purified. The operating conditions are specified in Table 5.

Table 5

by weight relative to the sum of all the mass inputs of monomers of the process

(2) by weight in relation to the sum of all mass inputs of the process

(3) by weight relative to the total weight of the monomers injected in all the reactors

The characteristics of the polymer obtained at the outlet of the reactor 2 are given in Table 6. Table 6

(4) by weight relative to the butadiene units present in the polymer chains

(5) by weight relative to butadiene and styrene units

(7) the ratio between the quantity of DEAB functions determined by NMR and the number of chain ends calculated from the value of Mn measured on the elastomer recovered at the end of the step of functionalization with DEAB. Thus, this example shows that if the reinjection solution is not purified then it is not possible to obtain the target level of living polymer and therefore a high level of functionalized chains.

Example D - According to the invention - 2 reactors in series with reinjection of purified butadiene

A styrene / butadiene polymer synthesis is carried out according to a process according to the invention using two agitated reactors, supposed to be perfectly stirred in series. The reinjected butadiene is purified by column of alumina. The operating conditions are specified in Table 7

Table 7

(1) by weight relative to the sum of all mass inputs of process monomers

(2) by weight in relation to the sum of all mass inputs of the process

The characteristics of the polymer obtained at the outlet of the reactor 2 are given in Table 8. Table 8

(4) by weight relative to the butadiene units present in the polymer chains

(5) by weight relative to butadiene and styrene units

Example E - According to the invention - 3 reactors in series with temperature ramp and without reinjection of butadiene

A synthesis of butadiene / styrene polymer is carried out according to a process according to the invention using 3 agitated reactors, supposed to be perfectly stirred in series. The operating conditions are specified in Table 1 1.

Table 1 1

(1) by weight relative to the sum of all mass inputs of process monomers

(2) by weight in relation to the sum of all mass inputs of the process

The characteristics of the polymer obtained at the outlet of the reactor 3 are given in Table 12. Table 12

(3) by weight relative to the butadiene units present in the polymer chains

(4) by weight relative to butadiene and styrene units

Claims

1. Process for the continuous synthesis of a diene elastomer by means of n reactors r1 to rn, equipped with an internal stirring system, supposed to be perfectly agitated, arranged in series, n varying from 2 to 15, preferably from 2 to at 9, the reactor r1 being fed with an input solution comprising a solvent, one or more monomers, an anionic polymerization initiator chosen from lithium amides and a polar agent, one or more of the reactors r2 to rn. optionally further being fed (s) by reinjection of a purified solution comprising solvent and / or monomer (s) and / or polar agent, the temperature of each reactor ranging from 20 to 150 ° C, preferably varying from 30 to 120 ° C, and being greater than or equal to the temperature of the reactor immediately preceding it, the temperature of the reactor rn being greater than the temperature of the reactor r1,

the mass quantity Mi of monomer (s) reinjected into the reactor ri, when Mi ≠ 0, i ranging from 2 to n, being such that

and such that Mi represents from 5 to 100% by weight of the mass of the solution reinjected into the reactor ri, when Mi ≠ 0,

where Mj is the mass quantity of monomer (s) introduced into the reactor rj, j varying from 1 to n, the mass quantity of all the monomers entering the reactors r1 to rn representing 5 to 25% by weight of the sum of the total mass inputs of the reactors r1 to rn,

where Cintrinsque, 1 = P 1 / Ml

where PI is the mass of polymer formed in the reactor r1, the total mass conversion Ctot at the outlet of the reactor rn being greater than or equal to 70%>,

or

where Pi is the mass of polymer formed in the reactor ri, the overall mass conversion Cglobal i in each reactor ri, with i ranging from 1 to n, being such that

and

or

where Pi is the mass of polymer formed in the reactor ri, i ranging from 1 to n,

the diene elastomer obtained having a polymolecularity index ranging from 1.1 to 1.7, preferably ranging from 1.2 to 1.6.

2. Method according to claim 1, characterized in that the temperature in at least one reactor ri is greater than the temperature of the reactor ri- 1, preferably the temperature of each reactor ri is greater than the temperature of the reactor ri- 1, i ranging from 2 to n.

3. Method according to claim 1 or 2, characterized in that n ranges from 2 to 3, preferably n = 2.

4. Process according to any one of the preceding claims, characterized in that the intrinsic intrinsic mass conversion C 1 in reactor r 1 is less than 65%, preferably less than 60%.

5. Method according to any one of the preceding claims, characterized in that the total mass conversion Ctot at the outlet of the reactor rn is greater than or equal to 80%>, preferably greater than or equal to 85%>.

6. Method according to any one of the preceding claims, characterized in that one or more of the reactor (s) r2 to rn is further fed (s) by reinjection of a purified solution comprising santvant and / or monomer (s) and / or polar agent,

7. Process according to any one of the preceding claims, characterized in that the solution (s) to be reinjected, or independently, the or each constituent of the solution (s) reinjected is / are, before reinjection, purified. (s) adsorption, liquid / liquid extraction, gas / liquid extraction or distillation.

8. Process according to claim 7, characterized in that the residues of the purification process (es) of the or each constituent or of the solution (s) to be reinjected are reinjected in the inlet solution supplying the first reactor.

9. Process according to claim 8, characterized in that the residues of the purification process (es) of the or each constituent or of the solution (s) to be reinjected constitute an additional monomer and / or solvent and / or agent. polar to the input solution.

10. Process according to claim 8, characterized in that the residues of the purification process (es) of the or each constituent or of the solution (s) to be reinjected constitute the sole source of monomer and / or solvent and / or as polar agent of the entry solution.

1 1. Process according to any one of the preceding claims, characterized in that the residence time in reactor ri, ranging from 1 to n, is between 1 and 60 minutes, preferably between 5 and 60 minutes, more preferably between 10 and 60 minutes. and 50 minutes.

12. Method according to any one of the preceding claims, characterized in that the flow at the outlet of the reactor rn and containing the living chains is brought into contact with one or more polymerization stopper agents injected (s) continuously in the process.

13. Process according to claim 12, characterized in that the living diene elastomer included in the stream leaving the reactor n, before reaction with the stoppage agent, is reacted with one or more functionalization, coupling or starring.

14. Process according to any one of Claims 1 to 1 1, characterized in that the living diene elastomer comprised in the stream leaving the reactor n is reacted with one or more functionalization, coupling or starring agents. .