EP1556425A1

EP1556425A1 - Synthetic branched polyisoprenes and method of obtaining same

Info

Publication number: EP1556425A1
Application number: EP03757962A
Authority: EP
Inventors: Philippe Laubry; Fanny Barbotin; Philippe Johnson; Jean-Luc Auger
Original assignee: Michelin Recherche et Technique SA Switzerland; Michelin Recherche et Technique SA France; Societe de Technologie Michelin SAS
Current assignee: Compagnie Generale des Etablissements Michelin SCA; Michelin Recherche et Technique SA France
Priority date: 2002-10-21
Filing date: 2003-10-13
Publication date: 2005-07-27
Also published as: US20050261453A1; KR20050074966A; BR0315509A; KR101075382B1; RU2005115468A; FR2845999A1; CN1705687A; US7319126B2; WO2004035638A1; AU2003273992B2; CA2503200A1; MXPA05004153A; BRPI0315509A8; AU2003273992A1; JP2006503935A; RU2330047C2; CN100365030C; JP5097918B2

Abstract

The invention relates to synthetic branched polyisoprenes having a macrostructure and a microstructure which are very similar to those of natural rubber. According to one aspect of the invention, said polyisoprenes have an apparent stress F/S0 which is equal to or greater than 0.4 MPa for an elongation alpha of 150 % which is applied to a dumb-bell-shaped test piece containing cross-linkable polyisoprene. According to another aspect of the invention, said polyisoprenes satisfy relation (i) Cotan delta = 0.3761. eta inh + 0.15, wherein: cotan delta is the cotangent of the loss angle of a sample of the polyisoprene, which is measured at 130 DEG C using a device with the trade name RPA2000, said sample being shear stressed at 10 % of deformation and at a stress frequency of 0.035 Hz; and eta inh is the inherent viscosity of the polyisoprene, which is measured in toluene at 25 DEG C and with a 0.1 g/dl concentration of polyisoprene in the toluene.

Description

Synthetic branched polyisoprenes and their process for obtaining:

The present invention relates to branched synthetic polyisoprenes having macrostructure and microstructure characteristics very close to those of natural rubber, and to a process for the synthesis of these polyisoprenes. These synthetic polyisoprenes can advantageously be used in rubber compositions for tires, replacing natural rubber.

Natural rubber (also called “natural polyisoprene”) is still widely used in rubber compositions for tires, despite the progress made in recent years in obtaining synthetic polyisoprenes capable of partially replacing natural rubber in certain locations of the tires.

Natural rubber being in particular characterized in the pure state by a rate of cis-1,4 chains equal to 100%, attempts have been made to synthesize polyisoprenes having a value of this rate which is as close as possible to 100%. The most significant advance in this field is described in the international patent document WO-A-02/38635 in the name of the applicants, which presents a catalytic system of “preformed” type based on at least:

- a conjugated diene monomer,

- a salt of one or more rare earth metals (metals having an atomic number between 57 and 71 in the periodic table of the elements of Mendeleev) of an organic phosphoric acid, said salt being in suspension in at least one solvent inert, saturated, aliphatic or alicyclic hydrocarbon,

- an alkylating agent consisting of an aluminum alkyl of formula A1R or HA1R ₂ , the molar ratio (alkylating agent / rare earth salt) having a value ranging from 1 to 5, and - a halogen donor consisting of 'an aluminum alkyl halide.

This catalytic system makes it possible to polymerize isoprene with satisfactory activity at polymerization temperatures which are less than or equal to 5 ° C., and to obtain at these low temperatures polyisoprenes, the cis-1,4 linkage rates, measured at once

- according to the technique of nuclear magnetic resonance of carbon 13 and according to the technique of metering by infrared means, are strictly greater than 99.0%. Natural rubber is also characterized in that it presents in the non-

_^ cross-linked (ie in the "raw" state, prior to any cooking) a very strong force-elongation curve

"Straightened" compared to those of synthetic polyisoprenes known to date (i.e.

^" respective slopes of the tangents to this curve for given relative elongations are much higher for natural rubber, for example at relative elongations of

300% and 400%), which results in the fact that natural rubber crystallizes much more in the non-crosslinked state than synthetic polyisoprenes, under the effect of a tension which is applied to it.

It results in particular from this insufficient crystallization under tension of the synthetic polyisoprenes that the mechanical properties of the rubber compositions incorporating them sometimes exhibit a strong decline during their implementation, which does not make these compositions suitable for replacing those based on rubber natural, at all tire manufacturing stations.

Natural rubber also differs from synthetic polyisoprenes known to date by its degree of branching or “branching” in the non-crosslinked state, which is very high in the case of natural rubber and which is on the contrary relatively reduced in the case of synthetic polyisoprenes.

A major drawback of synthetic polyisoprenes known to date is therefore that they do not exhibit, in the non-crosslinked state, the aforementioned characteristics of stress crystallization and branching which characterize in particular natural rubber.

The object of the present invention is to remedy this drawback, and it is achieved in that the applicants have discovered, surprisingly, that if homopolymerization of isoprene is carried out in an inert hydrocarbon polymerization solvent or in mass, by means of a “preformed” catalytic system based on at least:

- a conjugated diene monomer,

- a salt of one or more rare earth metals of an organic phosphoric acid, said salt being in suspension in at least one inert and saturated hydrocarbon solvent of aliphatic or alicyclic type which is included in said catalytic system, - an agent of alkylation consisting of an aluminum alkyl of formula A1R ₃ or HA1R ₂ , and

- a halogen donor consisting of an alkylaluminum halide, and if, following said homopolymerization, it is reacted by a cationic mechanism. Said catalytic system with at least one branching agent comprising an organic Lewis acid or not, then a polyisoprene is obtained with a high rate of cis-1 linkages , 4 and practically free from gel which has an apparent stress F / S ₀ equal to or greater than 0.4 MPa for a relative elongation α of 150%, applied to a dumbbell-shaped test piece which consists of crosslinkable polyisoprene (ie "Raw") and which is successively obtained by: forming a plate of thickness E = 2.5 mm made of said polyisoprene by pressure molding for 10 min. at 110 ° C. in a mold between two polyester sheets, - cooling under pressure of the plate thus formed for a period of 16 hours, extraction of said mold from the plate thus formed and cooled at the end of said period, - cutting of said test piece in the plate thus extracted, so that said test piece has two ends connected to each other by a rod of thickness E = 2.5 mm, of length L = 26 mm and of width W = 6 mm, this test piece then being subjected , at the latest 1 hour after said extraction, at a traction at a temperature of 23 ° C and at an air humidity level of 50%, by displacement at a constant speed of 100 mm / min. a movable jaw of a traction machine with the commercial name "INSTRON 4501" relative to a fixed jaw of said machine, said jaws respectively enclosing said ends with the same clamping pressure of 2 bars, with: α (%) = 100 x D / L (D being the measured displacement of said movable jaw in mm), and F / S ₀ (MPa) = tensile force F / initial section S ₀ (WE in mm ² ) of the test piece. Reference is made to the attached annex 1, paragraph II, for the precise conditions for obtaining this apparent stress as a function of the deformation.

It will be noted that the polyisoprenes according to the invention thus obtained have a force-elongation curve in the non-crosslinked state which is characterized by an apparent stress value F / S ₀ much higher than that of known synthetic polyisoprenes, for

~ given elongations, and which is relatively close to the force-elongation curves in the uncrosslinked state of known natural rubbers. This “straightening” in the uncrosslinked state of the force-elongation curve attests to an increased ability of the polyisoprenes according to the invention to crystallize under tension, compared with known synthetic polyisoprenes.

Advantageously, said apparent stress F / S ₀ of the polyisoprenes according to the invention is equal to or greater than 0.5 MPa for said relative elongation α of 150% and, even more advantageously, it is equal to or greater than 0.6 MPa for this same relative elongation.

It will be noted that these latter values of apparent stress at 150% relative elongation give the synthetic polyisoprenes according to the invention force-elongation curves in the non-crosslinked state which are extremely close to the force-elongation curves in the non-crosslinked state. crosslinked from known natural rubbers. As a result, these polyisoprenes crystallize under tension in much the same way as natural rubber.

Preferably, these synthetic polyisoprenes according to the invention are obtained by carrying out said homopolymerization at a temperature of between -55 ° C and 55 ° C. Also for preference, a ratio is used for this homopolymerization

(polymerization solvent / isoprene monomer) which is between 5 and 20.

Preferably, said branching agent belongs to the group consisting of halogenated metal compounds and halogenated organometallic compounds. According to a preferred embodiment of the invention, said branching agent is a halogenated metal compound of formula MX _m , M being a metal of the groups IN or N, X a halogen represented by fluorine, chlorine, bromine or iodine and m an integer equal to 3 or 4.

Even more preferably for this preferred example, said branching agent is titanium tetrachloride, tin tetrachloride or phosphorus trichloride. According to another preferred embodiment of the invention, said branching agent is a halogenated organometallic compound of formula R _n M'X ₄ - _n , being an aliphatic, alicyclic or aromatic hydrocarbon group, M 'a metal from groups IN or V , X a halogen represented by fluorine, chlorine, bromine or iodine and n an integer ranging from 1 to 3.

It will be noted that the branching agent according to the invention can be used, following the polymerization, according to a mass ratio (branching agent / neodymium salt) ranging for example from 2 to 20. According to an alternative embodiment of the invention, the synthetic polyisoprenes according to the invention are obtained, following said hopolymerization and prior to the addition of said branching agent, by the addition of an additional quantity of said catalytic system. In accordance with this alternative embodiment, it is possible, for example, to vary the quantity of rare earth metal from 200 μmol to 600 μmol per 100 g of isoprene monomer to carry out the homopolymerization then, during the additional addition of the catalytic system , varying the quantity of rare earth metal added from 500 μmol to 100 μmol per 100 g of said monomer. In the case where the entire catalytic system is introduced for the purpose of homopolymerization, it is possible, for example, to vary the quantity of rare earth metal from 500 μmol to 2500 μmol per 100 g of said monomer.

According to another aspect of the present invention, the applicant has also surprisingly discovered that if one proceeds to said homopolymerization of isoprene by means of said catalytic system in said polymerization solvent or in bulk and if, following to this polymerization, the polymerization medium is reacted with said branching agent, then a polyisoprene is obtained with a high rate of cis-1,4 linkages which is very branched, like natural rubber, because '' it satisfies the following relation: (i) Cotan δ ≥ 0.3761. η _inh + 0.15, where cotan δ is the cotangent of the angle of loss of a sample of said polyisoprene, measured at 130 ° C by means of an apparatus with the commercial name "RPA2000", said sample being stressed in shear at 10% deformation and at a stress frequency of 0.035 Hz (see Annex 2 to this description), and where ηι _n is the intrinsic viscosity of said polyisoprene, measured in toluene at 25 ° C and at a concentration of said polyisoprene in toluene of 0.1 g / dl (see appendix 3 of this description).

The relation (i), established from the variation of the modules G 'and G "as a function of the imposed frequency, accounts for dynamic shear properties of the polyisoprene according to the invention, cotan δ representing the ratio of modules G' / G ", where G 'is the real modulus, also called elastic or in phase, and where G '' is the imaginary module, also called loss or quadrature module (cotan δ represents an index of viscoelasticity of polyisoprene).

It will be noted that this relation (i) makes it possible to relate the rheological properties of polyisoprene to its macrostructure and in particular to its degree of branching, which, for a given intrinsic viscosity, is appreciated by the value of cotan δ. Indeed, we know that an elastomer is all the more branched or "connected" that this value of cotan δ is higher, for a given value of its inherent viscosity η; _n .

As it has been possible to verify that the synthetic polyisoprenes according to the invention are characterized by a cotan value δ which is much higher than that of known synthetic polyisoprenes, this for a given inherent viscosity, it follows that the polyisoprenes according to invention are significantly more branched than known synthetic polyisoprenes. Advantageously, the branched polyisoprenes according to the invention satisfy the relationship: (ii) Cotan δ ≥ 0.3761. η _inh + 0.60.

Even more advantageously, these branched polyisoprenes satisfy the relationship: (iii) Cotan δ ≥ 0.3761. η _inh + 1.0.

Advantageously, the polyisoprenes according to the invention have an inherent viscosity ηi _nh , measured at 0.1 g / dl in toluene according to annex 3 attached, which is equal to or greater than 4 dl / g and, even more advantageously , which is equal to or greater than 4.5 dl / g, like the synthetic polyisoprenes commercially available with the highest inherent viscosities.

According to a particularly advantageous embodiment of the invention, a molar ratio (alkylating agent / rare earth salt) is used in the catalytic system which has a value ranging from 1 to 7 and, even more advantageously , ranging from 1 to 5, so that the polyisoprene obtained according to the invention has a cis-1,4 linkage rate, measured according to the assay technique by infrared means (see section 4 for the description of this technique), which either equal to or greater than 98.0% and, advantageously, which is strictly greater than 98.5%.

According to a preferred example of this embodiment of the invention, said polymerization reaction of isoprene is carried out at a temperature below 0 ° C., so that said polyisoprene has a rate of cis-1,4 sequences, measured according to the technique of _* metering by infrared means, which is strictly greater than 99.0%.

According to another even more preferred example of this embodiment of the invention, said polymerization reaction of isoprene is carried out at a temperature less than or equal to -10 ° C., so that said polyisoprene has a level of cis-1,4 sequences, measured using the infrared assay technique, which is equal to or greater than 99.3%.

It will be noted that these cis-1,4 chain rate values are very close to the value of 100% which characterizes natural rubber. The cis-1,4 chain rate domain measured according to the present invention takes account of measurements established by means of the infrared assay technique after a calibration of the polyisoprene samples carried out by ¹³ C NMR analysis (at uncertainty measurement near plus or minus 0.1% which is inherent in said technique). The precision of these cis-1,4 chain rate values is thus notably increased, compared to that of the rates which have been mentioned in the prior art to date.

It will also be noted that the very high rate of cis-1,4 sequences obtained for the polyisoprenes according to the invention is independent of the amount of catalytic system used.

As the conjugated diene monomer which can be used to "preform" the catalytic system according to the invention, mention may be made of 1, 3-butadiene, preferably.

Mention may also be made of 2-methyl 1, 3-butadiene (or isoprene), the 2, 3-di (C1-C5 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 8 carbon atoms.

It will be noted that, in said catalytic system, the molar ratio (conjugated diene monomer / rare earth salt) may have a value ranging from 15 to 70 and, preferably, ranging from 25 to 50. According to another characteristic of the invention, the rare earth salt consists of a non-hygroscopic powder having a slight tendency to agglomerate at room temperature.

According to a preferred embodiment of the invention, the inert hydrocarbon solvent in which said rare earth salt is in suspension is an aliphatic or alicyclic solvent of low molecular weight, such as cyclohexane, methylcyclohexane, n-heptane, or a mixture of these solvents.

According to another embodiment of the invention, the solvent used for the suspension of the rare earth salt is a mixture of an aliphatic solvent of high molecular weight comprising a paraffinic oil, for example petrolatum oil, and a low molecular weight solvent such as those mentioned above (for example methylcyclohexane).

This suspension is produced by dispersive grinding of the rare earth salt in this paraffinic oil, so as to obtain a very fine and homogeneous suspension of the salt.

According to another characteristic of the invention, said catalytic system comprises said rare earth metal (s) at a concentration ranging from 0.01 mol / 1 to 0.06 mol / 1, preferably ranging from 0.015 mol / 1 to 0.025 mol .l.

According to a preferred embodiment of the invention, a tris [bis (2-ethylhexyl) phosphate] of the rare earth metal (s) is used as the salt in said catalytic system.

Even more preferably, said rare earth salt is neodymium tris [bis (2-ethylhexyl) phosphate].

As alkylating agent which can be used in the catalytic system according to the invention, mention may be made of aluminum alkyls such as:

- trialkylaluminiums, for example triisobutylaluminium, or

- dialkylaluminum hydrides, for example diisobutylaluminum hydride. It will be noted that this alkylating agent preferably consists of diisobutylaluminum hydride (called HDiBA in the remainder of this description). Mention may be made, as halogen donor usable in the catalytic system according to the invention, of aluminum alkyl halides, preferably diethyl aluminum chloride (called CDEA in the remainder of the present description).

It will be noted that the molar ratio (halogen donor / rare earth salt) can have a value ranging from 2.0 to 3.5 and preferably ranging from 2.6 to 3.0.

According to the invention, the process for preparing said catalytic system consists of:

in a first step, carrying out a suspension of said salt in said solvent,

- in a second step, adding said conjugated diene monomer to the suspension, - in a third step, adding said alkylating agent to the suspension comprising said monomer to obtain an alkylated salt, and

- In a fourth step, adding said halogen donor to the alkylated salt.

The aforementioned characteristics 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, said description being made in relation to the attached drawings, among which:

Fig. 1 is a graph of the apparent stress curves F / S ₀ (MPa) - deformation (%) relating to non-crosslinked test pieces which have been obtained according to the method described in annex 1 attached, paragraph II, and which are respectively constituted :

- branched synthetic polyisoprenes according to the invention, obtained by means of different catalytic systems and of the same branching agent according to the invention,

- linear synthetic polyisoprenes not in accordance with the invention, obtained by means of the same catalytic system according to the invention, but without branching agent,

- commercially available synthetic polyisoprenes, and

- natural rubbers also commercially available; Fig. 2 is a graph of the apparent stress curves F / S ₀ (MPa) -

"Deformation (%) relating to test pieces which have been obtained according to the method described in annex 1, paragraph II /, and which consist respectively of non-crosslinked rubber compositions, loaded with carbon black, and comprising respectively: synthetic branched polyisoprenes according to the invention, obtained by means of various catalytic systems and branching agents according to the invention, and

- a commercially available natural rubber;

Fig. 3 is a graph illustrating, for given inherent viscosity values (in dl / g), the respective cotangent values of the loss angle (cotan δ) corresponding to:

- branched synthetic polyisoprenes according to the invention, obtained by means of various catalytic systems and branching agents according to the invention,

- a linear synthetic polyisoprene not in accordance with the invention, obtained by means of a catalytic system according to the invention but without branching agent, and - synthetic polyisoprenes commercially available;

Fig. 4 is a schematic front view of the specimen geometry used to obtain the stress-strain curves of FIG. 1 and of FIG. 2

Fig. 5 is a schematic side view of the test tube of FIG. 4 in which the thickness of said test piece is particularly visible,

Fig. 6 illustrates a front view of the application of the traction machine to said test piece, and

Fig. 7 also illustrates in side view the application of said traction machine on said test piece. I. PREPARATION OF CATALYTIC SYSTEMS ACCORDING TO THE INVENTION:

1) Synthesis of an organic phosphate salt of neodymium according to the invention:

A plurality of tests have been carried out for the synthesis of this salt. The same synthesis method was used for each of these tests, which is detailed below.

a) Synthesis of an aqueous solution of neodymium NdCK 6H ₂ O:

A given quantity of Nd O ₃ is introduced into a reactor. 31.25 kg of demineralized water are added per kg of Nd O ₃ . 1.56 l of concentrated HCl 36% by weight (d = 1.18) per kg of Nd ₂ O _{3 are} added slowly at room temperature.

The Nd ₂ O ₃ + 6 HC1 + 9 H ₂ O → 2 NdCl ₃ , 6H ₂ O reaction is very exothermic. When all the hydrochloric acid has been added, the solution is brought to the boil with stirring for 30 minutes, to remove the excess hydrochloric acid. The aqueous solution of NdCl ₃ is clear and purple in color. There remains no insoluble product (Nd ₂ O ₃ ).

The pH of the solution, measured at 25 ° C., is corrected by adding sodium hydroxide to 2 moles per liter. The final pH is around 4.5.

b) Synthesis of an organic sodium phosphate of formula [ROIiPCO. We have

, R = 2-éthylhexyl_:

27.8 kg of demineralized water per kg of Nd O ₃ from the synthesis of paragraph a) above are introduced into an empty reactor. 0.708 kg of NaOH is dissolved in pellets per kg of Nd ₂ O from said paragraph a). In another reactor is added, still per kg of initial Nd O,

10.4 1 of acetone and 5.819 kg of an organic phosphoric acid (bis (2-ethylhexyl) phosphoric acid, listed in the work "Aldrich" under the reference 23,782-5).

At room temperature, the solution of said organic phosphoric acid is poured into the NaOH solution. The reaction is as follows: [RO] ₂ P (O) OH + NaOH → [RO] ₂ P (O) ONa + H ₂ O. This reaction is slightly exothermic, and a homogeneous solution of yellowish color is obtained. The pH of the solution, measured at 25 ° C, is 5.4.

c) Synthesis of a phosphate salt of neodymium of formula ITROl P. O) OfeNd:

The aqueous solution of NdCl, 6H ₂ O obtained in paragraph a) above is poured with vigorous stirring and at a temperature of 36 ° C. onto the organic phosphate solution of Na obtained in paragraph b) above. The addition can, as the case may be, be carried out in reverse order. A very fine white precipitate immediately forms. The mixture obtained is kept under stirring for 15 min., After the addition of all the organic phosphate of Na: 3 [RO] ₂ P (O) ONa + NdCl ₃ , 6H ₂ O - Nd [OP (O) [OR ] ₂ ] ₃ + 3 NaCl + 6 H ₂ O. The neodymium phosphate salt thus obtained is recovered by sedimentation and it is washed with a mixture of 45 liters of demineralized water and 15 liters of acetone for 15 minutes. The phosphate salt of neodymium is then recovered by centrifugation. The pH of "mother" waters is between 3 and 4 at 25 ° C. These "mother" waters are colorless and clear. On the last wash water, the qualitative analytical test for chlorides is almost negative (the reaction is: NaCl + AgNO (HNO ₃ medium) -> AgCl ^ + NaNO ₃ ). The neodymium salt thus washed is dried in an oven at 60 ° C, under vacuum and with air flow for 72 hours.

2) Synthesis of seven “preformed” catalytic systems according to the invention:

a) Composition of these seven catalytic systems:

Each of these systems comprises a neodymium phosphate salt as synthesized according to paragraph 1) above, which is in suspension in an inert low molecular weight hydrocarbon solvent (consisting of methylcyclohexane, "MCH" for short below).

These catalytic systems are characterized by the following relative molar ratios, - relative to the neodymium salt: Nd salt / butadiene (Bd) / HDiBA / CDEA = 1/30 or 50 / 1.8 or 3 / 2.6 or 3 .

The final Nd concentration of these catalytic systems is 0.02 M. b Process for the synthesis of each of these seven catalytic systems:

- First stage :

In order to obtain these catalytic systems, a given quantity of neodymium salt, in the powder state, is poured into a reactor previously cleaned of its impurities. This salt is then subjected to nitrogen sparging through the bottom of the reactor, for 15 min.

- Second step:

About 90% (mass fraction) of the solvent mentioned in paragraph is introduced.

2) a) above in the reactor containing the neodymium salt, the duration of contacting the neodymium salt with this solvent being 30 min, the contacting temperature being 30 ° C.

- Third step :

Butadiene is then introduced into the reactor (according to the salt / butadiene molar ratio of 1/50 or 1/30 mentioned in paragraph 2) a) above) at a temperature of 30 ° C, for the purpose of "preformation" of each catalytic system. - Fourth step:

HDiBA is then introduced into the reactor as an alkylating agent for the neodymium salt, at a concentration of approximately 1 M in the MCH. The duration of the alkylation is 30 min. and the temperature of the alkylation reaction is 30 ° C.

- Fifth step: CDEA is then introduced into the reactor as a halogen donor, at a concentration of approximately 1 M in the MCH. The temperature of the reaction medium is brought to 60 ° C.

- Sixth step:

A “preformation” (or aging) of the mixture thus obtained is then carried out while maintaining this temperature of 60 ° C. for a period of 2 hours.

- Seventh step:

A solution of the catalytic system is thus obtained. The reactor is emptied and this solution is transferred to a 750 ml "Steinie" bottle, previously washed, dried and sparged with nitrogen. Finally, the catalytic solution is stored under a nitrogen atmosphere in a freezer, at a temperature of -15 ° C. Table 1 below contains the characteristics of each catalytic system 1 to 7 and its preparation process.

Table 1:

II. SYNTHESIS OF POLYISOPRENES VIA THESE CATALYTIC SYSTEMS:

1) Synthesis process used:

On the one hand, 16 branched polyisoprenes A to P according to the present invention were prepared which were synthesized by means of catalytic systems and branching agents according to the invention, and, on the other hand, three linear polyisoprenes Q, R, S not in accordance with the present invention which have been synthesized by means of a catalytic system according to the invention but without the addition of branching agent. For the synthesis of branched polyisoprenes A, B, C, D, E, F, G, H, M, N, O, P and of the first linear polyisoprene Q, a 250 ml “Steinie” bottle was used. For the synthesis of the second linear polyisoprene R, a 750 ml “Steinie” bottle was used (the tightness of the “Steinie” bottle is ensured by an assembly of "pierced joint-capsule" type allowing the injection of the catalytic system. using a syringe). For the synthesis of branched polyisoprenes I, J, K, L and of the third linear polyisoprene T, a stirred 100 liter reactor was used.

With regard to the polymerizations carried out in the bottle, each polymerization reaction was carried out dynamically with stirring in a water tank or in a glycol tank (for a polymerization carried out at a temperature below 0 ° C.).

A C5 naphtha steam cracking cup was used in order to extract isoprene having a purity close to 100%. To this end, a conventional purification was carried out in the laboratory, consisting successively of:

- a distillation of this C5 cut on maleic anhydride to remove the residual cyclopentadiene, followed

- a passage over an alumina column to remove the polar impurities, and

- bubbling with nitrogen for 20 min., just before the polymerization reaction. The mass fraction of the isoprene extracted from this C5 cut, which is close to 99%, was determined by the gas chromatography technique (GC). For each test A to S carried out, the polymerization reaction of isoprene was carried out using 10 g or 50 g of isoprene when the polymerization is carried out in said 250 ml or 750 ml “Steinie” bottle, respectively, or else 8,469 g of isoprene when the polymerization is carried out in said agitated reactor of 100 1. For a polymerization temperature equal to or greater than 0 ° C., cyclohexane is used as polymerization solvent whereas, for a temperature of polymerization below 0 ° C (tests D and E only), methylcyclohexane is used.

Furthermore, the mass ratio of polymerization solvent / monomer (S / M) under an inert nitrogen atmosphere is equal to 9, except for test R where this ratio is equal to 7 and for tests I, J, K, Where said ratio is between 10 and 20.

The catalytic base of neodymium was varied in these polymerization tests from 100 μmol to 1750 μmol per 100 g of monomer (amount of neodymium in μMcm below).

To obtain each of the branched polyisoprenes in the polymerization tests A to L, a branching agent according to the invention (consisting of titanium or tin tetrachloride) is added to the "living" polymer, after 100% conversion. a mass ratio (branching agent / neodymium salt) of between 2 and 15.

To obtain each of the branched polyisoprenes in the M, N, O, P polymerization tests (see asterisk "*" in Table 2), a specific quantity is again added to the "living" polymer, after 100% conversion. (400 μMcm for each test M, N, O and 450 μMcm for test P) of the same catalytic system previously used for the polymerization (in an amount of 300 μMcm for each test M, N, O and 250 μMcm for l 'test P), then said branching agent according to the invention is added according to a mass ratio (branching agent / neodymium salt) ranging from 10 to 20.

For tests A, B, C, G, H, I, J, K, L, M, N, P, the branching agent is used at a concentration of 0.2 mol / 1 in cyclohexane and, for the tests D, E, F and O, at 0.1 mol / 1 in methylcyclohexane (tests D and E) or in cyclohexane (tests F, O).

Acetylacetone ("acac" below) is used as a stopping agent and N-1,3-dimethylbutyl-N'-phenyl-p-phenylenediamine (6PPD for short) is used as a protective agent ("Acac / Nd "designating the mass ratio (acetylacetone / neodymium)). The polymer solution obtained is then stripped with steam for 30 min> in the presence of calcium tamolate. Finally, the drying is carried out in an oven at 60 ° C under vacuum (200 mm Hg) with a slight stream of nitrogen for about 48 hours.

In Table 2 below, the term “syst.cat. »The catalytic system used, by« conv. »The conversion rate of the polymerization reaction, by“ S / P ”the Solvent / Polymer mass ratio, and by“ Sn / Nd ”or“ Ti / Nd ”the mass ratio (tin / neodymium) or (titanium / neodymium ).

Table 2

Regarding each of tests I and J, the concentration of TiCl ₄ or SnCl ₄ in the polymerization medium was 0.0935 mol / l.

Regarding tests K and L, this concentration of TiCl ₄ or SnCl was 0.17 mol / l and 0.12 mol / l, respectively.

2. Results obtained:

The inherent viscosity η _mh at 0.1 g / dl in toluene (measured according to annex 3 attached), the Mooney viscosity ML (l + 4) at 100 ° C (measured according to standard ASTM D-1646), the molecular weight distribution by the SEC technique (measured according to annex 5 attached) and the rate of gel or insoluble on grid (measured according to annex 6 attached) characterize the macrostructure of each polyisoprene according to the invention.

To determine the microstructure of these polyisoprenes, the MIR technique (medium infrared) was used, as detailed in annex 4 attached. This technique made it possible to establish, with an uncertainty of 0.1%, the rates of cis-1,4 and 3,4.

It will be noted that the MIR technique is very precise for determining the rate of units 3,4, because it uses polyisoprene samples having been previously calibrated for the ¹³ C NMR analysis.

Table 3 below compares the characteristics of macrostructure and microstructure: - of said synthetic polyisoprenes branched IR A to IR P according to the invention,

- said linear synthetic polyisoprenes IR Q to IR S not in accordance with the invention (obtained by means of a catalytic system of the invention but without branching agent), and linear synthetic polyisoprenes IR1 to IR 6 commercially available :

- IR 1: marketed by Nizhnekamsk under the name "SKI3S" or "IR 6596", - IR 2: marketed by Nippon Zeon under the name "IR 2200L",

- IR 3: marketed by Japan Synthetic Rubber under the name "JSR 2200",

- IR 4: marketed by Goodyear under the name "NATSYN 2200",

- IR 5: marketed by Nizhnekamsk under the name "SKI3S" or "IR 6596",

- IR 6: marketed by Nippon Zeon under the name "IR 2200". Table 3:

First series of "raw" tensile tests:

In accordance with the description of annex 1 attached, paragraph II, and in Figs. 4 and 5, non-crosslinked test pieces 1 were prepared, respectively consisting of: - three synthetic branched polyisoprenes IR A, IR D and IR E according to the invention, two linear synthetic polyisoprenes IR R and IR S not in accordance with l invention (but obtained by a catalytic system according to the invention), six synthetic polyisoprenes IR 1 to IR 6 commercially available, and two natural rubbers NR1 and NR2 with the common name "TSR20". “Raw” tensile tests were carried out on these uncrosslinked test pieces 1. This appendix 1, paragraph II, details the method and the traction device used for these tests, in relation to FIGS. 6 and 7. FIG. 1 illustrates the results obtained in the form of apparent stress curves F / S ₀ (MPa) as a function of the deformation (%).

This Fig. 1 shows that the branched polyisoprenes according to the invention IR A, IR D and IR E each have, for a relative elongation α of 150% applied to the dumbbell-shaped test piece which consists of the corresponding polyisoprene, an apparent stress F / S ₀ which is, on the one hand, much superior to those of “commercial” polyisoprenes IR 1 to IR 6 and to those of linear polyisoprenes not in accordance with the invention IR R and IR S, and which is, on the other hand share, close to those of the known natural rubbers NR1 and NR2. It can be seen that these branched polyisoprenes according to the invention IR A, IR D and IR E have an apparent stress F / S ₀ greater than 0.4 MPa, for this relative elongation of 150%. It will be noted that the apparent stress F / S ₀ of the polyisoprene IR E according to the invention is substantially equal to 0.5 MPa for this relative elongation, and that that of the polyisoprene IR D according to the invention is greater than 0.6 MPa for this same relative elongation. Fig. 1 shows that the non-crosslinked force-elongation curve of these polyisoprenes according to the invention IR A, IR D and IR E is relatively close to the corresponding curves of natural rubber comius.

This “straightening” in the uncrosslinked state of the force-elongation curve with respect to the known polyisoprenes IR 1 to IR 6 and IR R, IR S shows an increased ability of the polyisoprenes according to the invention to crystallize under tension, by compared to these known synthetic polyisoprenes. Second series of "raw" tensile tests:

Non-crosslinked rubber compositions A to F were prepared, the elastomeric matrices of which are respectively made of said IR A to IR F polyisoprenes according to the invention, as well as a reference non-crosslinked rubber composition T incorporating only natural rubber NR1 of denomination "TSR20" as an elastomeric matrix, with the aim of carrying out "raw" tensile tests of test pieces 1 (shown diagrammatically in FIGS. 4 and 5) which consist respectively of these compositions A to F and T. Reference is made to the attached annex 1, paragraph 11 / for the detailed description of each rubber composition A to F and T, of each test piece 1 and of the tensile tests carried out (see FIGS. 6 and 7).

The results of the tensile tests are illustrated in Fig. 2, in the form of apparent stress curves F / S ₀ as a function of the deformation (%). Table 4 below presents the results obtained from apparent stress F / S ₀ for relative elongations of 400% and 300%.

Table 4:

These results show that the synthetic polyisoprenes IR A to IR F according to the invention,

_^ when they constitute the elastomer matrix of a charged and non-crosslinked rubber composition, confer on this composition, for a relative elongation of 400% of the test piece

1, an apparent stress F / S ₀ greater than 1.0 MPa, possibly even greater than 1.5 MPa.

It will be noted that this apparent stress may even be greater than 2.0 MPa and even greater than 3.0 MPa, for this relative elongation of 400%.

These results also show that the synthetic polyisoprenes IR A to IR F according to the invention, when they constitute the elastomer matrix of a non-crosslinked rubber composition, confer on this composition, for a relative elongation of 300% of the test piece 1, an apparent stress F / So greater than 0.7 MPa, possibly greater than 1.2 MPa.

It will be noted that this apparent stress may even be greater than 1.7 MPa for this relative elongation of 300%.

In view of these results, it also appears that these synthetic polyisoprenes according to the invention give this non-crosslinked composition an F / S ₀ curve - elongation very close to that which natural rubber gives to an identical composition (elastomer matrix excepted) . This confirms that the synthetic polyisoprenes according to the invention have an ability to crystallize under tension which is analogous to that of natural rubber.

Degree of branching of the polyisoprenes according to the invention:

In order to characterize the degree of branching of the synthetic polyisoprene samples IR B to IR P according to the invention, the evolution of their cotangent of angle of losses was compared (see appendices 2 and 3), according to their inherent viscosity, the evolution of this same cotangent in the case of samples of said synthetic polyisoprenes

"Commercial" IR 1 to IR 6 and of said linear polyisoprene IR Q not in accordance with the invention.

To do this, each of these samples was dynamically stressed in shear at 10% deformation and at a stress frequency of 0.035 Hz (see annex 2 of this description for the details of the conditions of these stresses).

The cotangent loss angle measurements as a function of the inherent viscosity, carried out in accordance with appendices 2 and 3, are illustrated in FIG. 3. As can be seen in this Fig. 3, the synthetic polyisoprenes IR B to IR P according to the invention, for an inherent viscosity ηj _nh varying substantially from 2.5 dl / g to 5.5 dl / g, are characterized in that they have a value of cotan δ which is equal to or greater than 0.3761. ηi _n + 0.15.

Indeed, we can see in Fig. 3 that the coordinate points _. y≈cotan δ) which characterize these branched polyisoprenes IR B to IR P are all located clearly above the line of equation y = 0.3761 x + 0.15, unlike the corresponding points which characterize the polyisoprenes of "commercial" synthesis IR 1 to IR 6 and linear polyisoprene IR Q.

It is deduced therefrom that the synthetic polyisoprenes according to the invention, like natural rubber, are notably more branched than the known synthetic polyisoprenes.

It will be noted that these polyisoprenes according to the invention can have a wide range of inherent viscosities, which can in particular be of the same order as those of the most viscous "commercial" synthetic polyisoprenes, ie close to 5 dl / g. ANNEX 1

Obtaining force-elongation curves of non-crosslinked specimens based on synthetic or natural polyisoprenes.

1 / First series of tests on test pieces made of known synthetic polyisoprenes, according to the invention or natural rubbers:

1) Forming of polyisoprene plates in the non-crosslinked state:

Each 2.5 mm thick polyisoprene plate E is formed in a mold by pressure molding, between two polyester sheets, for 10 minutes at 110 ° C.

Each plate thus formed is kept under pressure for cooling for a period of 16 hours, then it is extracted from the mold at the end of these 16 hours.

2. Making of test pieces 1 from these plates:

Each test piece 1 is then immediately cut according to a dumbbell shape in one of the plates thus extracted from the mold, so that it has two ends connected to each other by a rod of thickness E = 2.5 mm, of length L = 26 mm and width

W = 6 mm. The cutting is carried out in such a way that the longitudinal direction L of the test piece 1 is parallel to the direction of the calendering.

3) Packaging of the plates obtained:

In order to avoid the appearance of air bubbles in the polyisoprene plates or test pieces, the tensile tests are carried out within a reduced time after extraction from the mold, this time being at most equal to 1 hour. 4) Tensile tests:

At least three identical test pieces 1 are tested under the same conditions for each of the tensile tests carried out. Each tensile test consists in subjecting a test piece 1 to constant speed traction and recording the evolution of the tensile force as a function of the displacement of a movable jaw of a traction machine 2 of the name "INSTRON 4501". This machine 2 is equipped with a force sensor and a means for measuring the displacement of this movable jaw. Each test piece 1 is held in its widest part under a clamping pressure P equal to 2 bar (see Fig. 5).

Each tensile test is carried out at room temperature, in a laboratory conditioned at 23 ° C and at 50% humidity. The constant speed of movement of the movable jaw is 1000 mm / minute. The variations in the tensile force and the displacement of the movable jaw are recorded during each test.

For each test piece 1, the following parameters are calculated: - Relative deformation α (%) = 100 x D / L (D is the displacement of the movable jaw in mm), measured by the machine sensor during each test and L - 26 mm is the initial length of the test piece 1 imposed by the "cookie cutter"), and - Apparent stress F / S ₀ (MPa), which represents the ratio of the force (in N) measured by the sensor of the machine, on the initial section S ₀ of the test piece (S ₀ = W. E in mm ² , W = 6 mm being the width imposed by the "punch" and E = 2.5 mm l ' thickness of test piece 1 before traction).

For each level of relative strain, the average of the corresponding stresses has been calculated for three identical test pieces 1, and a stress (average over three measurements) - deformation graph has been drawn for each of the test pieces tested. 11 / Second series of tests on test pieces consisting of compositions based on synthetic polyisoprenes according to the invention or natural rubber:

1) Making of plates made up of non-crosslinked rubber compositions:

The rubber composition intended to constitute each plate contains, per 100 g of synthetic polyisoprene or natural rubber:

- 50 g of carbon black N375

- 5 g of ZnO - 2 g of stearic acid

- 1 g of antioxidant with the name "Santoflex 13"

- 1.2 g of soluble sulfur "2H"

- 1.2 g of CBS (N-cyclohexyl-benzothiazyl-sulfenamide).

The mixing of these ingredients is carried out in an internal mixer with the name "Brabender", the useful volume of which is 87 cm ³ , under the following conditions:

- Tank temperature = 60 ° C

- Pallet rotation speed = 50 revolutions / minute

- Filling coefficient = 65% The ingredients are introduced in the following order:

- 0 minute: polyisoprene

- 1 minute: carbon black, ZnO, stearic acid, antioxidant

- 5 minutes: sulfur and CBS

- 6 minutes: fall (performed before 6 minutes if the temperature reaches 105 ° C). The mixture is then homogenized on a calender whose cylinders are at 75 ° C, so as to obtain a sheet 2.9 mm thick.

This sheet is pressure molded in a mold for 10 minutes at 110 ° C between two polyester sheets, then extracted from the mold and finally cooled in the open air. A 2.5 mm thick plate is thus obtained. 2. Packaging of the plates obtained:

Between the time of their preparation and that of the tensile test, each plate is stored in an ambient atmosphere for a duration at least equal to 5 hours and not to exceed 8 days.

3) Making of test pieces 1 from these plates:

We proceed as indicated in paragraph II 2) above.

4) Tensile tests:

We proceed as indicated in paragraph 1/4) above.

APPENDIX 2: Dynamic shear properties of the polyisoprenes obtained.

1) Device used:

The device used is marketed by the company Alpha Technologies under the name "RPA2000" ("Rubber Process Analyzer"). It allows the measurement of the dynamic properties of elastomers and of the rubber compositions incorporating them.

2) Preparation of samples:

The mass of polyisoprene sample is 4.5 +/- 0.5 grams. The protection of the “RPA2000” trays (see below) is ensured by the use of interlayer films which are obtained from a roll of “Nylon® Dartek f0143” film and which are placed between these trays and the sample.

3. Description of the test:

The sample is preheated for three minutes at 130 ° C in the thermally stabilized "RPA" chamber, before carrying out 10 cycles of dynamic stress at 0.035 Herz, 10% deformation at 130 ° C. The calculation of the results is an average over the last five cycles.

ANNEX 3: Determination of the inherent viscosity of the polyisoprenes obtained.

PRINCIPLE:

The inherent viscosity is determined by measuring the flow time t of the polyisoprene solution and the flow time t ₀ of toluene in a capillary tube. The method is broken down into 3 main steps:

- »step 1: preparation of the measurement solution at 0.1 g / dl in toluene; - step 2: measurement of the flow times t of the polyisoprene solution and t ₀ of toluene at 25 ° C. in a “Ubbelohde” tube;

- »step 3: calculation of the inherent viscosity.

STEP 1 - Preparation of the measurement solution from the dry polyisoprene

0.1 g of dry polyisoprene is introduced into a 250 ml bottle, washed and steamed at 140 ° C. for a minimum of 10 hours (use of a scale precision scale e = 0.1 mg) and 100 ml of toluene purity greater than 99.5%.

The bottle is placed on a shaker for 90 min. (or even more if the polyisoprene is not dissolved).

STEP 2 - Measurement of the flow times t, of the toluene and t of the polyisoprene solution at 25 ° C:

1. Material:

- 1 tank with a thermostatically controlled bath at 25 ° C ± 0.1 ° C provided with a cooling system with running water. The tank is filled with VA of running water and VA of demineralized water.

- 1 "PROLABO" type alcohol thermometer, placed in the thermostatically controlled bath with an uncertainty of ± 0.1 ° C - 1 "Ubbelohde" viscometer tube intended to be placed in a vertical position in the 1st thermostatically controlled bath.

Characteristics of the tubes used: - capillary diameter: 0.46 mm;

- capacity: 18 to 22 ml.

2. Measurement of the flow time t ₀ of toluene:

- rinse the tube by washing with toluene; -introduce the quantity of toluene (purity greater than 99.5%) necessary for the measurement;

-check that the thermostatically controlled bath is at 25 ° C; -determine the flow time t ₀ .

3. Measurement of the flow time of the polyisoprene solution t

rinse the tube by washing with polyisoprene solution;

-introduce the quantity of polyisoprene solution necessary for the measurement;

-check that the thermostatically controlled bath is at 25 ° C.

- determine the flow time t.

STEP N ° 3 - Calculation of the inherent viscosity:

The inherent viscosity is obtained by the following relation:

with

C: concentration of the toluene polyisoprene solution in g / dl; t: flow time of the toluene polyisoprene solution in hundredths of a min .; t ₀ : toluene flow time in hundredths of a min .;

Tji _nh : inherent viscosity expressed in dl / g. APPENDIX 4: Determination of the microstructure of the polyisoprenes obtained.

1) Preparation of the samples according to the ¹³ C NMR technique:

2 g of polyisoprene are extracted with acetone at reflux for 8 hours. The extracted polyisoprene is then dried at room temperature and under vacuum for 24 hours. Then this dried polyisoprene is redissolved in chloroform. The polyisoprene solution is filtered and the solvent is removed on a rotary evaporator for 4 hours (the bath temperature is 40 ° C).

2) Metering technique by infrared medium (MIR):

a) Preparation of samples:

This MIR technique is calibrated by means of samples as prepared in paragraph 1) above. As for the samples to be analyzed according to this MIR technique, a polyisoprene solution at 10 g / l exactly in CC1 _{4 is used} , which is analyzed using a KBr cell of 0.2 mm thick.

b) Apparatus:

- Spectrophotometer sold under the name "NECTOR 22".

- Recording conditions: beam opening: maximum; resolution: 2 cm ^"1; frequency of the moving mirror: 10 kHz; detector: DTGS; accumulations: 64 scan; purge time: 3 min; spectral window: 4000 to 400 cm ^"1; spectra recorded in transmittance; - Processing of spectra: transfer to microcomputer; treatment with “OPUS” software from “BRUKER”.

vs. Spectrum peak allocation:

Spectral studies and the content of the following documents have made it possible to determine the characteristic bands of the different chaining modes:

- Y. Tanaka, Y. Takeuchi, M. Kobayashi, H. Tadokoro, Journal ofPolymer Science,

PartA-2, 1971, 9 (1), 43-57.

- J.P. Kistel, G. Friedman, B. Kaempf, Bulletin de la Société Chimique de France, 1967, n ° 12.

- F. Asssioma, J. Marchai, C. R. Acad. Se. Paris, Ser C, 1968, 266 (22), 1563-6 and Ser D, 1968, 266 (6), 369-72.

- T.F. Banigan, AJ. Nerbiscar, T.A. Oda, Rubber Chemistry and technology, 1982, 55 (2), 407-15.

The conformation 3 ^ 4 has two characteristic bands: - a band at 880 cm ^"1 of high intensity corresponding to the deformation vibrations out of the plane (δ CH) of the terminal hydrogens of the vinyl group (= CH ₂ ).

- a band at 3070 cm ^"1 corresponding to the elongations v CH of this same group (= CH ₂ ).

The 1-4 cis conformation has a characteristic band around 3030 cm ^"1. This band corresponds to the vibrations of elongation v CH of the group = CH.

The band corresponding to the symmetrical deformation vibrations of the methyl groupings (δ CH ₃ ) is a complex band which integrates the three conformations. The absorption corresponding to δ CH ₃ of the 1-4 trans conformation is maximum around 1385 cm ^"1 ; it is - a shoulder of this band. d) Integration method:

The bands of 3-4 and 1-4 cis are integrated according to the tangential surface mode. The maximum absorption of 1-4 trans is located at the shoulder of the intense band of δ CH ₃ . The most suitable method in this case is the measurement of the strip height with the tangent of the des CH strip as the base line.

e) Calibration curves:

Expression of Beer-Lambert's law:

Do (v or δ) = ε (v or δ) e c with:

Do (v or δ) = optical density of the band v or δ; ε (v or δ) = molar extinction coefficient of the analyte responsible for the band v or δ; c = molar concentration of the analyte; and e = thickness of the sample.

Commercial polyisoprenes (sold under the names “IR305”, “NATSYN 2200” and “SKI-3S”), polyisoprene synthesized in the laboratory (MC78) and natural rubber (NR) are taken as standards. Compared to iso-concentration (solutions), the law can therefore be written:

Dx = K X with:

Dx = value of the integration of the band corresponding to the motif X, X = rate of motif X in the gum (determined by ¹³ C NMR), and

K = calibration constant.

The calibration curves Dx = f (X) can therefore be plotted for each of the patterns. APPENDIX 5: Determination of the molecular mass distribution of the elastomers obtained by the size exclusion chromatography (SEC) technique.

at. Principle of measurement:

Size exclusion chromatography (SEC) makes it possible to physically separate the macromolecules according to their size in the swollen state on columns filled with porous stationary phase. The macromolecules are separated by their hydrodynamic volume, the largest being eluted first.

Without being an absolute method, the SEC makes it possible to apprehend the molecular weight distribution of a polymer. From commercial standard products, the various average masses in number (Mn) and in weight (Mw) can be determined and the polydispersity index calculated (Ip = Mw / Mn).

b) Preparation of the polymer:

There is no special treatment of the polymer sample before analysis. This is simply dissolved in tetrahydrofuran at a concentration of about 1 g / 1.

c) SEC analysis:

The apparatus used is a “WATERS ALLIANCE” chromatograph. The elution solvent is tetrahydrofuran, the flow rate of 0.7 ml / min, the system temperature of 35 ° C and the analysis time of 90 min. A set of four columns is used, with the trade names "STYRAGEL HMW6E", "STYRAGEL HMW7" and two "STYRAGEL

HT6E ”, placed in this order.

The injected volume of the polymer sample solution is 100 μl. The detector is a "WATERS 2140" differential refractometer and the operating software for the chromatographic data is the "WATERS MILLENIUM" system. APPENDIX 6: Determination of the insoluble rate on a polyisoprene grid.

1) Field of application:

This method makes it possible to determine the insoluble rate on a grid of polymers for values greater than 0.3%. It applies to all polymers whose inherent viscosity (in toluene at 25 ° C and 0.1 g / dl) is less than 5.5 dl / g.

Unless otherwise indicated, the measurement is made in toluene.

2) Principle:

A known quantity of polymer is stirred at room temperature in toluene under determined conditions and the insoluble material is filtered through a metal filter, dried and then weighed.

3) Material:

Shaker shaker

Capper - Rubber seals and capsules

500 ml Steinie bottles

Vacuum oven for drying set at 100 ° C

Dryer

Stainless steel mesh filter (10 cm x 10 cm). Mesh size: 125 μm - Balance to the nearest 0.1 mg

Pair of scissors

Aluminum trays.

4) Reagent:

Toluene suitable for polymerization. 5) Procedure:

In a previously tared aluminum tray, weigh 1.0 g (P) to 0.1 mg near the polymer cut into small pieces. Introduce the polymer into a 500 ml Stemie bottle containing 200 ml of toluene. Cap the bottle. Place it horizontally on the shaker and shake for at least 6 hours at the speed of 100 to 120 back and forth per minute. Filter immediately on a metal filter previously washed with toluene, dried in an oven for 1 h, cooled, stored in a desiccator and tared immediately after desiccant to the nearest 0.1 mg (PI). Rinse the bottle twice with 50 ml of toluene and pour the rinsing toluene over the filter.

Dry the metal filter for 1 hour in the vacuum oven at 100 ° C. Leave to cool for 30 minutes in the desiccator and weigh to the nearest 0.1 mg (P2).

6. Calculation:

Let:

P expressed in grams the weight of polymer analyzed

PI expressed in grams the weight of the metal filter before filtration P2 expressed in grams the weight of the metal filter after filtration

The insoluble level T, expressed in%, is given by the formula:

T = 100 (P2 - P1) / P (%)

Round the result to the nearest multiple of 0.1.

Note :

It is possible that in special cases, the polymer remains stuck to the walls of the Steinie bottle; it is therefore essential to peel it off using a spatula and place it on the metal filter.

Claims

1) Synthetic crosslinkable polyisoprene, characterized in that it has an apparent stress F / S ₀ equal to or greater than 0.4 MPa for a relative elongation α of 150%, applied to a dumbbell-shaped test piece (1) which consists of said crosslinkable polyisoprene and which is obtained by:

- Forming a plate of thickness E - 2.5 mm made of said polyisoprene by pressure molding for 10 min. at 110 ° C. in a mold between two sheets of polyester,

- cooling under pressure of the plate thus formed for a period of 16 hours, - extraction of said mold from the plate thus formed and cooled at the end of said period,

cutting of said test piece (1) in the plate thus extracted, so that said test piece (1) has two ends connected together by a rod of thickness E = 2.5 mm, of length L = 26 mm and of width W = 6 mm, said test piece (1) then being subjected, at the latest 1 hour after said extraction, to traction at a temperature of 23 ° C. and to an air humidity level of 50%, by displacement at a constant speed of 100 mm / min. a movable jaw of a traction machine (2) with the commercial name "INSTRON 4501" relative to a fixed jaw of said machine, said jaws respectively enclosing said ends with the same clamping pressure of 2 bars, with: α (%) = 100 x D / L (D being the measured displacement of said movable jaw in mm), and

F / S ₀ (MPa) = tensile force F / initial section S ₀ (WE in mm ² ) of the test piece (1).

2) Synthetic polyisoprene according to claim 1, characterized in that the apparent stress F / S ₀ is equal to or greater than 0.5 MPa for said relative elongation α of 150%.

3) Synthetic polyisoprene according to claim 2, characterized in that the apparent stress F / S ₀ is equal to or greater than 0.6 MPa for said relative elongation α of 150%. 4) Synthetic polyisoprene according to one of the preceding claims, characterized in that it satisfies the relation (i): Cotan δ> 0.3761. η _inh + 0.15, where cotan δ is the cotangent of the angle of loss of a sample of said polyisoprene, measured at 130 ° C by means of an apparatus with the commercial name "RPA2000", said sample being stressed in shear at 10% deformation and at a stress frequency of 0.035 Hz, and where ηin _h is the inherent viscosity of said polyisoprene, measured in toluene at 25 ° C and at a concentration of said polyisoprene in toluene of 0.1 g / dl .

5) Synthetic polyisoprene according to claim 4, characterized in that it also satisfies relation (ii): Cotan δ> 0.3761. ηj _nh + 0.60

6) Synthetic polyisoprene according to claim 5, characterized in that it also satisfies relation (iii): Cotan δ> 0.3761. ηj _nh + 1.0

7) Synthetic polyisoprene according to one of the preceding claims, characterized in that it has an inherent viscosity ηi _nh , measured at 0.1 g / dl in toluene according to annex 3 attached, which is equal to or greater than 4 dl / g.

8) Synthetic polyisoprene according to one of the preceding claims, characterized in that it has a rate of cis-1,4 sequences, measured according to the assay technique by infrared means, which is equal to or greater than 98.0%.

9) Synthetic polyisoprene according to claim 8, characterized in that said rate of cis-1,4 sequences is strictly greater than 99.0%.

10) Synthetic polyisoprene according to claim 9, characterized in that said rate of cis-1,4 sequences is equal to or greater than 99.3%. 11) Process for the synthesis of a polyisoprene according to one of claims 1 to 10, comprising the reaction of a catalytic system in the presence of isoprene to polymerize said isoprene, characterized in that said process comprises the reaction of polymerization of said isoprene in a inert or bulk hydrocarbon polymerization solvent, said catalytic system being based on at least:

- a conjugated diene monomer,

a salt of one or more rare earth metals of an organic phosphoric acid, said salt being in suspension in at least one inert and saturated hydrocarbon solvent of aliphatic or alicyclic type which is included in said catalytic system,

an alkylating agent consisting of an aluminum alkyl of formula A1R ₃ or HA1R, and

- A halogen donor consisting of an aluminum alkyl halide, and in that said process comprises, following said polymerization, a cationic reaction between said catalytic system and at least one branching agent comprising an organic Lewis acid or not.

12) Process for the synthesis of a polyisoprene according to claim 11, characterized in that said process comprises, following said polymerization and prior to the addition of said branching agent, the addition of an additional quantity of said catalytic system.

13) Synthesis process according to claim 11 or 12, characterized in that said branching agent belongs to the group consisting of halogenated metal compounds and halogenated organometallic compounds.

14) Synthesis process according to claim 13, characterized in that said branching agent is a halogenated metallic compound of formula MX _m , M being a metal of groups IN or N, X being a halogen represented by fluorine, chlorine, bromine or iodine and m being a natural integer equal to 3 or 4.

15) Synthesis process according to claim 14, characterized in that said branching agent is titanium tetrachloride. 16) Synthesis process according to claim 14, characterized in that said branching agent is tin tetrachloride.

17) Synthesis process according to claim 13, characterized in that said branching agent is a halogenated organometallic compound of formula R _n M'X ₄ - _n ,

R being an aliphatic, alicyclic or aromatic hydrocarbon group, M 'being a metal of groups IV or V, X being a halogen represented by fluorine, chlorine, bromine or iodine and n being a natural integer ranging from 1 to 3.

18) Synthesis process according to one of claims 11 to 17, characterized in that, in said catalytic system, the molar ratio (alkylating agent / rare earth salt) has a value ranging from 1 to 7, for obtaining of a polyisoprene having a rate of cis-1,4 sequences, measured according to the assay technique by infrared means, which is equal to or greater than 98.0%.

19) Synthesis process according to claim 18, characterized in that it comprises the implementation of said polymerization reaction of isoprene at a temperature below 0 ° C, so that said polyisoprene has a rate of cis sequences -1.4, measured using the infrared assay technique, which is strictly greater than 99.0%.

20) Synthesis process according to claim 19, characterized in that it comprises the implementation of said isoprene polymerization reaction at a temperature less than or equal to -10 ° C, so that said polyisoprene has a rate of 'cis-1,4 sequences, measured using the infrared medium assay technique, equal to or greater than 99.3%.

21) Synthesis process according to one of claims 11 to 20, characterized in that said salt is a tris [bis (2-ethylhexyl) phosphate] of rare earth (s).

22) Synthesis process according to claim 21, characterized in that said salt is neodymium tris [bis (2-ethylhexyl) phosphate]. 23) Synthesis process according to one of claims 11 to 22, characterized in that said catalytic system comprises said rare earth metal (s) at a concentration ranging from 0.01 mol / 1 to 0.06 mol / 1.

24) Synthesis process according to one of claims 11 to 23, characterized in that, in said catalytic system, the molar ratio (halogen donor / salt) has a value ranging from 2.0 to 3.5.

25) Synthesis process according to one of claims 11 to 24, characterized in that, in said catalytic system, the molar ratio (conjugated diene monomer / salt) has a value ranging from 15 to 70.

26) Synthesis process according to one of claims 11 to 25, characterized in that said conjugated diene monomer is butadiene.

27) Synthesis process according to one of claims 11 to 26, characterized in that said alkylating agent is diisobutylaluminum hydride.

28) Synthesis process according to one of claims 11 to 27, characterized in that said halogen donor is diethylaluminum chloride.