Process for the continuous polymerization of a diene elastomer

Abstract

A process for the continuous synthesis of a diene elastomer by n reactors r1 to rn, n ranging from 2 to 15, is provided. The reactor r1 is fed by an input solution comprising a solvent, one or more monomers, an anionic polymerization initiator and a polar agent, one or more of the reactor(s) r2 to rn also being fed by reinjection of a purified solution comprising solvent and/or monomer(s), the purity of the or of each reinjected solution being such that the proportion of the number of dead chains in the output stream from the reactor rn is less than 30%, of the number of living chains initiated in the reactor r1, the temperature of each reactor ranging from 20 to 150 C. and being greater than or equal to the temperature of the reactor which immediately precedes it, the diene elastomer having a polydispersity index of 1.1 to 2.

Claims

1. A process for the continuous synthesis of a diene elastomer by means of n reactors r1 to rn, n being the number of reactors, equipped with an internal stirring system, and arranged in series, n ranging from 2 to 15, the reactor r1 being fed by an input solution comprising a solvent, one or more monomers, an anionic polymerization initiator and a polar agent, one or more of the reactor(s) r2 to rn also being fed by reinjection of a purified solution comprising solvent and/or monomer(s), the purity of the reinjected solution fed to one or more of the reactors being such that the proportion of the number of dead chains in an output stream from the reactor rn is less than 30%, of the number of living chains initiated in the reactor r1, the temperature of each reactor ranging from 20 to 150 C., and being greater than or equal to the temperature of the reactor which immediately precedes it, the temperature of the reactor rn being greater than the temperature of the reactor r1, the weight amount W.sub.1 of monomer(s) introduced into the reactor r1 being such that $0.1<\frac{W1}{\underset{i=1}{\overset{n}{.Math.}}\mathrm{Wi}}1$ the weight amount We of monomer(s) reinjected into the reactor ri, when W.sub.i0, i ranging from 2 to n, being such that $0\frac{{\mathrm{Wi}}^{}}{\underset{1}{\overset{n}{.Math.}}\mathrm{Wi}}<0.9$ and such that Wi represents from 5% to 100% by weight of the weight of the solution reinjected into the reactor ri, when W.sub.i0, where Wi is the weight amount of monomer(s) introduced into the reactor ri, i ranging from 1 to n, the weight amount of all of the monomers entering the reactors r1 to rn representing 5% to 25% by weight of the sum of the total weight inputs of the reactors r1 to rn, the overall weight conversion Ci in each reactor ri being such that $\frac{\mathrm{Cn}}{n}-0.2<\frac{{\mathrm{Ci}}^{}}{i^{}}<\frac{\mathrm{Cn}}{n}+0.2$ where ${\mathrm{Ci}}^{}=\frac{{\mathrm{Pi}}^{}}{\underset{1}{\overset{n}{.Math.}}\mathrm{Wi}}$ where Pi is the weight of polymer formed at the output of the reactor ri, i ranging from 1 to n1, Cn is the overall weight conversion in the reactor rn, with $\mathrm{Cn}=\frac{\mathrm{Pn}}{\underset{1}{\overset{n}{.Math.}}\mathrm{Wi}}$ where Pn is the weight of total polymer at the output of the reactor rn, the diene elastomer obtained having a polydispersity index ranging from 1.1 to 2.

2. A process according to claim 1, wherein n ranges from 2 to 3.

3. A process according to claim 1, wherein the reinjected solution fed to one or more of the reactors contains the polar agent.

4. A process A process according to claim 1, wherein at least one constituent of the reinjected solution fed to one or more of the reactors is, before reinjection, purified independently by adsorption, liquid/liquid extraction, gas/liquid extraction, or distillation.

5. A process according to claim 4, wherein the chemical adsorption is carried out on zeolite or on alumina.

6. A process according to claim 4, wherein the chemical washing is washing by liquid/liquid extraction by means of sodium hydroxide.

7. A process according to claim 4, wherein the gas/liquid extraction is carried out by means of a stream of air or nitrogen.

8. A process according to claim 4, wherein the purification is carried out by distillation.

9. A process according to claim 8, wherein the distillation is a single-stage distillation without reflux or a column distillation.

10. A process according to claim 4, wherein residues of the purification process(es) for the at least one constituent are reinjected into the input solution feeding the first reactor.

11. A process according to claim 10, wherein residues of the purification process(es) of the at least one constituent constitute an extra contribution of monomer and/or of solvent to the input solution.

12. A process according to claim 10, wherein residues of the process(es) for purifying the at least one constitute the sole source of monomer and/or of solvent of the input solution.

13. A process according to claim 1, wherein the residence time in the reactor ri, i ranging from 1 to n, is between 1 and 60 minutes.

14. A process according to claim 1, wherein the diene elastomer is a copolymer of butadiene and of a vinyl aromatic monomer.

15. A process according to claim 1, wherein the polymerization initiator is chosen from ethyllithium, n-butyllithium and isobutyllithium.

16. A process according to claim 1, wherein the output stream which is from the reactor rn and which contains the living chains is brought into contact with one or more agents for stopping polymerization, injected into the process continuously.

17. A process according to claim 1, wherein the living diene elastomer included in the output stream from the reactor n is reacted with one or more agents for stopping polymerization and one or more functionalizing, coupling or star-branching agents.

18. A process according to claim 1, wherein the living diene elastomer included in the output stream from the reactor n is reacted with one or more functionalizing, coupling or star-branching agents.

Description

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

(1) The expression weight amount of all of the monomer(s) entering the reactors r1 to rn is intended to mean the sum of the weight amount of monomer(s) introduced into the reactor r1 by the input solution and of the weight amounts of the monomer(s) reinjected into one or more of the reactors r2 to rn.

(2) The term polydispersity index is intended to mean the weight-average molecular weight/number-average molecular weight ratio. The weight-average and number-average molecular weights are measured by size exclusion chromatography.

(3) The process according to the invention makes it possible to control the polydispersity index of the polymer synthesized, through the controlling of the conversion in each reactor and through the number of reactors.

(4) The conversion in each reactor is controlled by the temperature, the residence time, the amount of polar agent and the amount of monomer entering into each reactor.

(5) The equilibration of the conversions in each reactor, as indicated above, makes it possible to minimize the polydispersity index.

(6) By working at increasing temperature according to the invention, the propagation in the subsequent reactors is accelerated and the conversions are thus equilibrated.

(7) The optional reinjection of a part of the monomers into one of the reactors from the second has an impact on the amount of monomers present in the reactor and the residence time in said reactor. Thus, these reinjections, which constitute an advantageous implementation of the process of the invention, also contribute to the equilibration of the conversions and, as explained above, to the control of the polydispersity index.

(8) Advantageously, the very high purity of the monomers reinjected makes it possible to reduce the impact of the side reactions which have a tendency to widen the molecular distribution of the polymer formed.

(9) The residence times and the temperatures are also chosen so as not to promote these side reactions.

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

(11) Preferably, the number of reactors is equal to 2 or 3, preferably 2.

(12) When the number of reactors is equal to 2, the process according to the invention has at least one of the following characteristics and preferably all of the following characteristics: a reinjection of a solution comprising monomer(s) is carried out in the reactor r2, the purity of the solution reinjected into the reactor r2 is such that the proportion of the number of dead chains in the output stream from the reactor r2 is less than 10%, preferentially less than 5% of the number of living chains initiated in the reactor r1, the temperature of the reactors r1 and r2 ranges 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 weight amount of monomer(s) introduced into the reactor r1 is greater than 10% and less than 100% of the total weight amount of the monomers introduced into the reactors r1 and r2, the weight amount 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, the weight amount of all of the monomers entering the reactors r1 to rn representing 5% to 25% by weight of the sum of the weight inputs of the reactors r1 and r2, the overall weight conversion in the reactor 1 is equal to half the overall weight conversion in the reactor 2, +/20%.

(13) 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 in the following way:

(14) ${}_i=\frac{V_i}{Q_{\mathrm{Vn}}}$

(15) with: Vi, reaction volume Ri, i ranging from 1 to n QVn=flow rate by volume leaving the reactor n.

(16) As explained above, a solution comprising monomer(s) can be reinjected into one or more of the reactors r2 to rn.

(17) One or more of the reinjected solutions can contain a polar agent.

(18) The purity of each reinjected solution is such that the proportion of the number of dead chains in the output stream from the reactor rn is, relative to the number of living chains initiated in the reactor r1, less than 30% by number, preferably less than 10% by number and more preferentially less than 5% by number.

(19) The term purity of a reinjected solution is intended to mean the weight proportion of optional monomer(s), and of optional solvent and of optional polar agent, relative to the total weight of the reinjected solution.

(20) Each reinjected solution contains purified solvent and/or purified monomers.

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

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

(23) The adsorption can be carried out on zeolite or on alumina.

(24) The liquid/liquid extraction can be carried out by means of sodium hydroxide.

(25) The gas/liquid extraction can be carried out by means of a stream of air or nitrogen.

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

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

(28) Regardless of the purification process chosen for each constituent, the purified phase is used to constitute the stream to be reinjected.

(29) According to one embodiment, the residues of the purification process(es) for the or for each constituent are reinjected into the input solution feeding the first reactor. These residues consist of the monomers and/or the solvent with a high concentration of impurities. The residues can then either constitute an extra contribution of monomer and/or of solvent to the input solution, or can constitute the sole source of monomer and/or of solvent of the input solution. This embodiment makes it possible to limit the loss of material in the case of reinjection.

(30) The term diene elastomer should be understood, in a known way, as meaning an (one or more is understood) elastomer resulting at least in part (i.e., a homopolymer or a copolymer) from diene monomers (monomers bearing two conjugated or non-conjugated carbon-carbon double bonds). More particularly, diene elastomer is understood as meaning any homopolymer obtained by polymerization of a conjugated diene monomer having from 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 vinylaromatic monomers having from 8 to 20 carbon atoms. In the case of copolymers, the latter contain from 20% to 99% by weight of diene units and from 1% to 80% by weight of vinylaromatic units.

(31) The following in particular are suitable as conjugated dienes which can be used in the process in accordance with the invention: 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-di(C.sub.1 to C.sub.5 alkyl)-1,3-butadienes, such as, for example, 2,3-dimethyl-1,3-butadiene, 2,3-diethyl-1,3-butadiene, 2-methyl-3-ethyl-1,3-butadiene or 2-methyl-3-isopropyl-1,3-butadiene, phenyl-1,3-butadiene, 1,3-pentadiene and 2,4-hexadiene, etc.

(32) The following in particular are suitable as vinylaromatic monomers: styrene, ortho-, meta- or para-methylstyrene, the vinyltoluene commercial mixture, para-(tert-butyl)styrene, methoxystyrenes, vinylmesitylene, divinylbenzene and vinylnaphthalene, etc.

(33) The diene elastomer is preferably selected from the group of highly unsaturated diene elastomers consisting of polybutadienes (BRs), synthetic polyisoprenes (IRs), butadiene copolymers, in particular copolymers of butadiene and of a vinylaromatic monomer, isoprene copolymers and the mixtures of these elastomers. Such copolymers are more particularly butadiene/styrene copolymers (SBRs), isoprene/butadiene copolymers (BIRs), isoprene/styrene copolymers (SIRs) and isoprene/butadiene/styrene copolymers (SBIRs). Among these copolymers, butadiene/styrene copolymers (SBRs) are particularly preferred.

(34) The diene elastomer is generally prepared by anionic polymerization in the presence of a polymerization initiator. The polymerization initiator is included in the input solution.

(35) Use may be made, as polymerization initiator, of any known monofunctional anionic initiator. However, an initiator comprising an alkali metal, such as lithium, is preferably used.

(36) Use may be made, as polymerization initiator, of any known monofunctional anionic initiator. However, an initiator comprising an alkali metal, such as lithium, is preferably used. Those comprising a carbon-lithium bond are suitable in particular as organolithium initiators. Representative compounds are aliphatic organolithium compounds, such as ethyllithium, n-butyllithium (n-BuLi), isobutyllithium, etc.

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

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

(39) As explained above, the input solution, and also optionally one or more of the reinjected solutions, used in the process according to the invention comprise(s) a polar agent.

(40) By way of chelating polar agents that can be used in the process in accordance with the invention, agents comprising at least one tertiary amine function or at least one ether function and preferentially agents of tetrahydrofurfuryl ethyl ether or tetramethyl ethylenediamine type in particular are suitable.

(41) According to a first particular embodiment, the output stream which is from the reactor n and which contains the living chains is brought into contact with one or more agents for stopping the polymerization as known per se, injected into the process continuously.

(42) In this first embodiment, the living diene elastomer included in the output stream from the reactor n can be reacted with, in addition, one or more functionalizing, coupling or star-branching agents, which can act as an additional agent for stopping the polymerization. The particular feature of these additional agents is that they can either interact with a reinforcing filler (this is the case with functionalizing agents, coupling agents and certain star-branching agents) or confer a given structure on the polymer (this is the case with certain star-branching or coupling agents).

(43) According to a second particular embodiment, the living diene elastomer included in the output stream from the reactor n is reacted with one or more functionalizing, coupling or star-branching agents. These agents then also act as stopping agent.

(44) Regardless of the embodiment, any agent known per se can be envisaged as functionalizing, coupling or star-branching agent.

(45) The abovementioned characteristics of the present invention, and also others, will be better understood on reading the following description of several exemplary embodiments of the invention, given by way of illustration and without limitation.

(46) Measurements and Tests Used

(47) Glass Transition Temperature

(48) In these examples, the glass transition temperatures (Tg) of the elastomers are determined using a differential scanning calorimeter.

(49) Polydispersity Index

(50) The polydispersity index of the polymer is determined by means of SEC (size exclusion chromatography).

(51) The SEC (Size Exclusion Chromatography) technique makes it possible to separate macromolecules in solution according to their size through columns filled with a porous gel. The macromolecules are separated according to their hydrodynamic volume, the bulkiest being eluted first.

(52) Without being an absolute method, SEC makes it possible to comprehend the distribution of the molar masses of a polymer. The various number-average molar masses (Mn) and weight-average molar masses (Mw) can be determined from commercial standards and the polydispersity index (PI=Mw/Mn) can be calculated via a Moore calibration.

(53) There is no specific treatment of the polymer sample before analysis. The latter is simply dissolved in the elution solvent at a concentration of approximately 1 g.Math.l.sup.1. The solution is then filtered through a filter with a porosity of 0.45 m before injection.

(54) The apparatus used is a Waters Alliance chromatographic line. The elution solvent is either tetrahydrofuran or tetrahydrofuran+1 vol % of diisopropylamine+1 vol % of triethylamine, the flow rate is 1 ml.Math.min.sup.1, the temperature of the system is 35 C. and the analysis time is 30 min. A set of two Waters columns with the Styragel HT6E trade name is used. The volume of the solution of the polymer sample injected is 100 l. The detector is a Waters 2410 differential refractometer and the software for making use of the chromatographic data is the Waters Empower system.

(55) The calculated average molar masses are relative to a calibration curve produced for SBRs having the following microstructure: 25% by weight of units of styrene type, 23% by weight of units of 1,2-type and 50% by weight of units of trans-1,4-type.

(56) Conversion

(57) The conversions are measured by weighing dry extract of the solution containing the polymer. In this method, solution containing the polymer is sampled at the reactor output. This solution is introduced into a pre-tared punnet. The weight of solution is thus weighed.

(58) The sample is dried at 140 C., under a reduced pressure of 200 mmHg for 15 minutes. The punnet is then placed in a desiccator containing silica gel, for two minutes. Weighing of the punnet then makes it possible to determine the weight of polymer of the sample taken. It is then possible, via the monomer concentration, to work back to the conversion at the output of the reactor.

(59) $C=\frac{\frac{w_{\mathrm{dry}\mathrm{extract}}}{w_{\mathrm{sample}}}}{\frac{\underset{1}{\overset{n}{.Math.}}\mathrm{Wi}}{\underset{1}{\overset{n}{.Math.}}\mathrm{Qi}}}.Math.100$

(60) with
.sub.1.sup.nWi

(61) which represents the sum of all the weight inputs of monomers in the total process (reactors 1 to n)

(62) and
.sub.1.sup.nQi

(63) which represents the sum of all the weight inputs in the total process (reactors 1 to n) (Solvant, monomers, catalysts, etc. . . . ),

(64) the ratio

(65) $\frac{\underset{1}{\overset{n}{.Math.}}\mathrm{Wi}}{\underset{1}{\overset{n}{.Math.}}\mathrm{Qi}}$
corresponding to the % by weight of monomers

(66) Elastomer Microstructure

(67) The microstructure of the elastomers is characterized by the near-infrared (NIR) spectroscopy technique.

(68) Near-infrared spectroscopy (NIR) is used to quantitatively determine the content by weight of styrene in the elastomer and also its microstructure (relative distribution of the 1,2-, trans-1,4- and cis-1,4-butadiene units). The principle of the method is based on the Beer-Lambert law generalized for a multicomponent system. As the method is indirect, it involves a multivariate calibration [Vilmin, F., Dussap, C. and Coste, N., Applied Spectroscopy, 2006, 60, 619-29] carried out using standard elastomers having a composition determined by .sup.13C NMR. The styrene content and the microstructure are then calculated from the NIR spectrum of an elastomer film having a thickness of approximately 730 m. The spectrum is acquired in transmission mode between 4000 and 6200 cm.sup.1 with a resolution of 2 cm.sup.1 using a Brker Tensor 37 Fourier-transform near-infrared spectrometer equipped with an InGaAs detector cooled by the Peltier effect.

(69) Content of living chains in the Elastomer at Output from the Reactors

(70) In the examples, the solution of living polymer at the output from the polymerization reactors is continuously brought into contact with the DEAB (diethylaminobenzophenone) functionalizing agent in excess with a contact time sufficient for total reaction of all the living chains with the functionalizing agent. The determination of the content of grafted DEAB (function content in the examples) is carried out by NMR analysis. This determination is carried out relative to the amount of elastomer. In this way, the results obtained can be expressed as mol %, as meq/kg of elastomer or as phr (gram percent of elastomer).

(71) The samples (approximately 25 mg of elastomer) are dissolved in approximately 1 ml of carbon disulfide (CS2). 100 l of deuterated cyclohexane are added for the Lock signal.

(72) The spectra are acquired on a Bruker Avance 500 MHz spectrometer fitted with a Bruker broad band BBI z-grad 5 mm probe.

(73) The quantitative .sup.1H NMR experiment uses a 30 single pulse sequence and a repetition time of 5 seconds between each acquisition. 256 accumulations are carried out at ambient temperature.

(74) The .sup.1H NMR signals of the 8 protons quantified (protons bound to the carbons identified 1 to 4 in FIG. 1) of the grafted DEABs corresponds to an unresolved peak at the chemical shift of 3.2 ppm.

(75) The edited HSQC .sup.1J .sup.1H/.sup.13C 2D NMR correlation spectrum makes it possible to verify the nature of the unit grafted by means of the chemical shifts of the carbon atoms and protons. The signal of carbons 1 to 4 has a chemical shift at 44.4 ppm.

(76) The .sup.1H NMR spectrum makes it possible to quantify the grafted DEAB units by integration of the signal unresolved peaks described above: H1, H2 for the dehydrated DEAB form and H3, H4 for the DEAB carbinol form.

(77) The grafted diethylaminobenzophenone, dehydrated and carbinol forms, has the formula below:

(78) ##STR00001##

(79) The chemical shifts are calibrated relative to the protonated impurity of the carbon disulfide ppm 1H at 7.18 ppm referenced on the TMS ( ppm 1H at 0 ppm) and ppm 13C at 192 ppm referenced on the TMS ( ppm 13C at 0 ppm).

(80) The simple-pulse .sup.1D .sup.1H NMR spectrum makes it possible to quantify the units of the polymer by integration of the characteristic signal unresolved peaks. Example, for an SBR (styrene butadiene rubber), the unresolved peaks in question for the calculation are 5H (protons) styrene between 7.4 ppm and 6.0 ppm, 2H PB (polybutadiene) 1-4+1H PB1-2 between 5.8 ppm and 4.9 ppm and 2H PB1-2 between 4.9 ppm and 4.3 ppm.

(81) Thus, as a function of the content of living chains at the output from the polymerization reactors, it is possible to determine by difference the degree of dead chains in the elastomer.

EXAMPLES

(82) Methylcyclohexane, butadiene, styrene and tetrahydrofurfuryl ethyl ether are continuously introduced, according to the proportions described in each example, into a pilot facility for continuous polymerization containing several stirred continuous reactors, assumed to be perfectly stirred according to those skilled in the art. n-Butyllithium (n-BuLi) is introduced in a sufficient amount in order to neutralize the protic impurities introduced by the different constituents present in the line inlet. The samples for the characterization are taken after stabilization of the process. The stability is taken to be a period of time which is the sum of 3 residence times per polymerization reactor. For example, for 3 reactors i in series:

(83) $T_{\mathrm{Imb}}=3.Math.\underset{i=1}{\overset{3}{.Math.}}{\mathrm{Tds}}_i$

(84) For examples 1 to 3, a purification of the reinjected solution of butadiene and/or of solvent is carried out continuously by means of an alumina column. This column is packed with a fixed bed of aluminas of Axsorb 920 type.

(85) The minimum fixed-bed L/D ratio is 4.

(86) The column diameter/minimum mean alumina particle diameter ratio is 10.

(87) The empty-tank Reynolds number is greater than 2.

(88) The minimum residence time of the fluid in the packed fixed bed is 5 minutes.

(89) The column is maintained under the following conditions: Temperature=10 C. Pressure=5 bar.

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

Example 1

(91) A synthesis of butadiene/styrene polymer is carried out according to a comparative process using 9 stirred reactors, assumed to be perfectly stirred in series.

(92) The reinjected butadiene is purified by alumina column.

(93) The operating conditions are specified in Table 1

(94) TABLE-US-00001 TABLE 1 Operating conditions Value Unit Reactor Number of 9 reactors Volume of 1.83 1 reactors 2.411 2 2.411 3 2.411 4 2.411 5 2.411 6 4.441 7 4.441 8 4.441 9 % Styrene (1) 45 % Wt % 12.5 % monomers (2) Polar agent 8.2 10.sup.7 Mol/m.sup.3 9 (tetrahydrofurfuryl ethyl ether) Active 5.1 10.sup.7 Mol/m.sup.3 9 initiator (n- butyllithium) Residence 6.53 Min 9 time Temperature 60 C. 1, 2, 3, 4, 5, 6, 7, 8, 9 Reinjection 8 % 7 butadiene (3) Overall 8 % 1 weight 27.8 % 3 conversion (4) 46.7 % 6 69.3 % 9 (1) by weight relative to the sum of all the weight inputs of monomers of the process (2) by weight relative to the sum of all the weight inputs of the process (3) by weight relative to the total weight of the monomers injected into all of the reactors (4) overall weight conversion in the reactor

(95) The characteristics of the polymer obtained at the output from reactor 9 are given in Table 2.

(96) TABLE-US-00002 TABLE 2 Vinyl content (5) 23.4 % Styrene content (6) 28.8 % Tg 46.2 C. PI 1.24 Mn 126.1 kg/mol Amount of functions 7.41 mmol/kg Living polymer content (7) 96.9 % (5) by weight of the total weight of the butadiene units introduced into all of the reactors (6) by weight of the total weight of the monomers introduced into all of the reactors (7) Molar ratio of the amount of functions determined by NMR to the amount of active initiator introduced.

Example 2

(97) A synthesis of styrene/butadiene polymer is carried out according to a process according to the invention using 6 stirred reactors, assumed to be perfectly stirred in series.

(98) The reinjected butadiene is purified by alumina column. The operating conditions are specified in Table 3.

(99) TABLE-US-00003 TABLE 3 Operating conditions Value Unit Reactor Number of reactors 6 Volume of reactors 2.411 L 1 2.411 2 2.411 3 4.441 4 4.441 5 4.441 6 % Styrene (1) 45 % Wt % monomers (2) 12.5 % Polar agent 8.2 10.sup.7 Mol/m.sup.3 6 (tetrahydrofurfuryl ethyl ether) Active initiator (n- 5.1 10.sup.7 Mol/m.sup.3 6 butyllithium) Residence time 9.49 Min 6 Temperature 55 C. 1 55 2 55 3 65 4 65 5 65 6 Reinjection butadiene (3) 8 % 4 Overall weight conversion (4) 9.8 % 1 33.4 % 3 64.8 % 6 (1) by weight relative to the sum of all the weight inputs of monomers of the process (2) by weight relative to the sum of all the weight inputs of the process (3) by weight relative to the total weight of the monomers injected into all of the reactors (4) overall weight conversion in the reactor

(100) The characteristics of the polymer obtained at the output from reactor 6 are given in Table 4.

(101) TABLE-US-00004 TABLE 4 Vinyl content (5) 23.5 % Styrene content (6) 29.1 % Tg 45.7 C. Mn 122.2 kg/mol PI 1.27 Amount of functions 7.89 mmol/kg Living polymer content (7) 95.4 % (5) by weight of the total weight of the butadiene units introduced into all of the reactors (6) by weight of the total weight of all of the monomers introduced into all of the reactors (7) Molar ratio of the amount of functions determined by NMR to the amount of active initiator introduced.

(102) Thus, this example shows that it is possible to synthesize a functional polymer with a reduced polydispersity index, using a polythermal process comprising 6 reactors in series.

(103) Thus, this example shows that it is possible to synthesize, using a polythermal process comprising 6 reactors in series, a functional polymer with a reduced polydispersity index equivalent to that obtained by the synthesis with 9 reactors of Example 1, which is however, a priori, more effective for reducing the PI because of the higher number of reactors.

(104) The temperature gradient makes it possible to maintain a reduced polydispersity index by decreasing the number of reactors. This has a strong impact on the cost of the process and therefore on the economic aspect of the industrialization thereof.

Example 3

(105) The object of this example is to compare two syntheses of a functionalized butadiene/styrene polymer carried out by means of two stirred polymerization reactors, assumed to be perfectly stirred polymerization reactors, in series, and of a functionalization reactor.

(106) During the first synthesis of functionalized polymer, the polymerization does not comprise any reinjection of monomer into the second reactor.

(107) The second synthesis of functionalized polymer is carried out with reinjection of monomers according to a process according to the invention. The solvent and the butadiene that are reinjected into the second reactor during the polymerization are purified on alumina columns.

(108) The operating conditions are specified in Table 5

(109) TABLE-US-00005 TABLE 5 Operating Value Value conditions synthesis 1 synthesis 2 Unit Reactor Number of 2 2 reactors Volume of 14 14 L 1 reactors 14 14 2 % Styrene (1) 40 40 % Wt % monomers (2) 13 13 % 1 Polar agent 5.8 10.sup.7 5.8.107 Mol/m.sup.3 2 (tetrahydrofurfuryl ethyl ether) Active initiator 8.5 10.sup.7 8.5 10.sup.7 Mol/m.sup.3 2 (n-butyllithium) Residence time 30 30 Min 2 Temperature 50 50 C. 1 Temperature 60 60 C. 2 Reinjection 0 10 % 2 solvent (3) Reinjection 0 50 % 2 butadiene (4) Weight conversion 76.2 56.4 % 1 of monomers (5) 96.3 93.3 % 2 (1) by weight relative to the sum of all the weight inputs of monomers of the process (2) by weight relative to the sum of all the weight inputs of the process (3) by weight relative to the sum of all the inputs of solvent of the process (4) by weight relative to the total weight of the monomers injected into all of the reactors (5) overall weight conversion in the reactor

(110) The characteristics of the polymers obtained at the output from reactor 2 are given in Table 6.

(111) TABLE-US-00006 TABLE 6 Synthesis 1 Synthesis 2 Unit Vinyl content (6) 49.3 48.8 % Styrene content (7) 39.1 39.8 % Tg 14.4 13.9 C. Mn 111.5 112.2 kg/mol PI 1.67 1.52 Function content 8.95 8.81 mmol/kg Living polymer 97.3 95.7 % content (8) (6) by weight of the total weight of the butadiene units introduced into all of the reactors (7) by weight of the total weight of the monomers introduced into all of the reactors (8) Molar ratio of the amount of functions quantitatively determined by NMR to the amount of active initiator introduced.

(112) The synthesis 2 to the invention exhibits equilibrated conversions between reactor 1 and reactor 2.

(113) In this way, the functionalized polymer synthesized by means of synthesis 2 with reinjection of monomers has a lower PI than that of synthesis 1 carried out without reinjection of monomers.

Example 4

(114) The object of this example is to quantify the impact of the purification of butadiene on the living polymer content at the polymerization output.

(115) The first synthesis comprises a reinjection of an unpurified butadiene during the polymerization. The unpurified butadiene contains, as major impurity, tert-butyl catechol (TBC) in an amount of 300 ppm.

(116) The second synthesis comprises, during the polymerization, a reinjection of butadiene that has been flash-purified under the following temperature and pressure conditions:

(117) P=1.1 bar

(118) T=50 C.

(119) The solvent reinjected in the two syntheses is purified by alumina column as described above for Examples 1 to 3. The operating conditions are specified in Table 7

(120) TABLE-US-00007 TABLE 7 Operating Value Value conditions synthesis 1 synthesis 2 Unit Reactor Number of 2 2 reactors Volume of 32.5 32.5 L 1 reactors 32.5 32.5 2 % Styrene (1) 35 35 % Wt % monomers (2) 13 13 % 1 Polar agent 1.9 10.sup.7 1.9 10.sup.7 Mol/m.sup.3 2 (tetrahydrofurfuryl ethyl ether) Active initiator 7.6 10.sup.7 7.6 10.sup.7 Mol/m.sup.3 2 (n-butyllithium) Residence time 30 30 Min 2 Temperature 40 40 C. 1 Temperature 70 70 C. 2 Reinjection 10 10 % 2 solvent (3) Reinjection 19.5 19.5 % 2 butadiene (4) Weight conversion 38.5 38.0 % 1 of monomers (5) 85.9 86.1 % 2 (1) by weight relative to the sum of all the weight inputs of monomers of the process (2) by weight relative to the sum of all the weight inputs of the process (3) by weight relative to the sum of all the inputs of solvent of the process (4) by weight relative to the total weight of the monomer is injected into all of the reactors (5) overall weight conversion in the reactor

(121) The characteristics of the polymers obtained at the output from reactor 2 are given in Table 8.

(122) TABLE-US-00008 TABLE 8 Synthesis 1 Synthesis 2 Unit Vinyl content (6) 36.8 37.0 % Styrene content (7) 29.2 29.8 % Tg 36.8 35.8 C. Mn 110.5 110.2 kg/mol PI 1.51 1.51 Function content 8.05 8.81 mmol/kg Living polymer content (8) 90.1 98.8 % (6) by weight of the total weight of the butadiene units introduced into all of the reactors (7) by weight of the total weight of the monomers introduced into all of the reactors (8) Molar ratio of the amount of functions determined by NMR to amount of active initiator introduced.

(123) It can thus be seen that the purification of the butadiene has a strong impact on the living polymer content measured by the method described above.