Title of Invention

"A PROCESS FOR OBTAINING A POLYISOPRENE"

Abstract The present invention relates to a process for obtaining a polyisoprene from a steam-cracked C5 naphtha fraction enriched with isoprene, wherein said enriched C5 fraction comprises aliphatic and alicyclic mono-olefins, wherein it consists of using a C5 fraction enriched with isoprene in which the mass ratio (aliphatic and alicyclic mono-olefins isoprene) is less than or equal to 50%, wherein said process essentially consists of essentially reacting a catalytic system in the presence of said enriched C5 fraction at a temperature from -55°C to 55°C, using: * a C5 fraction enriched with isoprene such that the mass fraction of isoprene in said enriched fraction lies within a range of from 30% to 95%, and * a catalytic system based on at least: - a conjugated diene monomer, - an organic phosphoric acid salt of at least one rare earth metals such as herein described, - an alkylating agent consisting of an alkylauminium of the formula AIR3 or HAIR2, and a halogen donor consisting of an alkylaluminium halide such as herein described, said salt being suspended in at least one inert saturated hydrocarbon solvent of aliphatic or alicyclic type such as herein described which is included in at least one inert saturated hydrocarbon solvent of aliphatic or alicyclic type which is included in said catalytic system, and the molar ratio (alkylating agent : rare earth salt) being in a range of from 1 to 5, the molar ratio (halogen donor : salt) being within a range of from 2.6 to 3, and the molar ratio (conjugated diene monomer : salt) being within a range of from 25 to 50.
Full Text The present invention relates to a process for obtaining a polyisoprene.
The present invention relates to a process for obtaining a polyisoprene having a high cis-1,4 linkage content, from a steam-cracked C5 naphtha fraction enriched with isoprene.
Steam-cracked C5 naphtha fractions conventionally contain isoprene in a mass fraction of substantially from 10% to 30%. Furthermore, they contain in particular the following compounds:
- mono-olefins (α-olefins and ß-olefins), in a mass fraction of from 20% to 40%,
1 dienes such as cyclopentadiene, 1,3-pentadiene (also referred to as piperylene) and other pentadienes, in a mass fraction of conventionally from 20% to 30%, alkanes,
- limonene (dimer of isoprene) and, in a minority proportion,
- acetylene and aromatic compounds.
In order to be able to effect selective polymerisation of isoprene with high activity from such a steam-cracked C5 naphtha fraction, the latter must first be enriched with isoprene so that the mass fraction of isoprene in the enriched fraction is close to 100%. In fact, it turns out that the other aforementioned compounds adversely affect the yield of the isoprene polymerisation reaction. In particular, this enriched fraction must be practically devoid of cyclopentadiene, which is a poison to catalytic systems.
In known manner, this enriching with isoprene of the steam-cracked C5 naphtha fraction may be obtained by implementing the following operations.
First and foremost, fractional or extractive distillation (byjneans of a polar solvent) is effected, followed by distillation on maleic anhydride, in order practically to remove the cyclopentadiene from the initial fraction. Hereafter, for example distillation is effected over diisobutylduminium hydride, to make practically all the acetylene compounds of the fraction disappear. Finally, the residual polar impurities are removed, for example by passing over alumina.
JP 58 154705 discloses a process for selectively polymerizing butadiene, isoprene and 1,3-pentadiene from a hydrocarbon mixture in the presence of a two component catalytic system based on a rare earth metal compound, such as a rare earth metal phosphate, and a trialkylaluminum compound. When isoprene and 1,3-pentadiene are copolymerized, the hydrocarbon mixture can be an C5 naphta fraction.

EP 1 048 675 discloses a catalytic suspension polymerization of a conjugated diene in hydrocarbon mixtures comprising a fraction by volume greater than 80% of C4 hydrocarbons. This C4 fraction can originate directly from a steam cracker without other purification or concentration stage than removing the alkynes. Although butadiene and isoprene are intended in this document, the process is essentially directed to the polymerization of butadiene. If isoprene is to be polymerized, the neat monomer appears to be added to the hydrocarbon mixture.
EP 0 846 707 discloses a process for obtaining a conjugated diene polymer from a pure monomer solution in the presence of a catalyst system based on an organic compound containing a rare earth, a trialkylaluminum compound and a halogen-containing compound.
EP 0 304 088 discloses a process for obtaining a diene oligomer starting from a monomer mixture containing at least one conjugated diene compound and at least one vinyl aromatic compound, to further produce a high impact vinyl aromatic polymer.
As is known, polyisoprenes having a high cis-1,4 linkage content may be obtained using a catalytic system based on titanium tetrachloride and an alkylaluminium. The article by
E. Schoenberg, H.A. Marsh, S.J. Walters, W.M. Saltman, Rubber Chemistry and Technology, 1979, vol. 52, pp. 564-565, indicates that, if this catalytic system is used for the polymerisation of isoprene, the steam-cracked C5 naphtha fraction must have previously been enriched so as to comprise a mass fraction of isoprene of at least 97%.
More precisely, this article teaches that the mass fraction of mono-olefins in the enriched fraction must be at most 3.8% (of which 1% at most for the a-olefins and 2.8% at most for the p-olefins), and that that of the limonene must be at most 0.1%. Furthermore, the mass fraction of cyclopentadiene must be at most 1 ppm (ppm: parts per million), that of piperylene at most 80 ppm, and that of the acetylene compounds at most 50 ppm.

As is also known, polyisoprenes having a high cis-1,4 linkage content may be obtained using catalytic systems based on:
- a rare earth salt in solution in a hydrocarbon solvent,
- an alkylating agent of this salt consisting of an alkylaluminium, and
- an alkylaluminium halide.
It is known, for example from the document "Report of the Academy of Sciences of the USSR, volume 234, no. 5, 1977 (Y.B. Monakov, Y.R. Bieshev, A.A. Berg, S.R. Rafikov)", to use a catalytic system comprising:
- a bis(2-ethylhexyl)phosphoric acid salt of neodymium or praseodymium, as the rare earth salt, in solution in toluene,
- triisobutylaluminium as the alkylating agent, in a molar ratio (alkylating agent : rare earth salt) of 20, and
- diethylaluminium chloride as the alkylaluminium halide.
As in the case of catalytic systems based on titanium, it turns out that the selective polymerisation of isoprene with high activity can only be contemplated from a C5 fraction which has been enriched so that it will comprise isoprene in a mass fraction close to 100%.
This extraction from the C5 fraction of practically pure isoprene has the disadvantage of requiring the implementation of a complex separation process and, consequently, of involving relatively high operating costs for the polymerisation of isoprene.


The object of the present invention is to overcome this drawback, and it is achieved in that the Applicant has unexpectedly discovered that a catalytic system based on at least:
- a conjugated diene monomer,
- an organic phosphoric acid salt of one or more rare earth metals (metals with
an atomic number between 57 and 71 in Mendeleev's periodic table),
- an alkylating agent consisting of an alkylaluminium of the formula AIRs or
HA1R2, and
- a halogen donor consisting of an alkylaluminium halide,
said salt being suspended in at least one inert saturated hydrocarbon solvent of aliphatic or alicyclic type which is included in said catalytic system, and the molar ratio (alkylating agent: rare earth salt) being in a range from 1 to 5,
permits the selective polymerisation of isoprene with high catalytic activity to obtain a polyisoprene having a high cis-1,4 linkage content, from a steam-cracked C5 naphtha fraction which has been only slightly enriched with isoprene, comprising a mass fraction of isoprene which is as low as 30%.
This C5 fraction which is only slightly enriched with isoprene may be obtained by implementing a simplified enrichment process consisting successively:
- of simple or extractive distillation to remove the major part of the dienes other than
isoprene, in particular cyclopentadiene,
- of distillation over maleic anhydride to remove practically any residual
cyclopentadiene,
- of removal of the vinylacetylene compounds (residual "true" alkynes) by distillation
on diisobutylaluminium hydride (DiBAH), and
- of passing over alumina or over a molecular sieve to remove the residual polar
impurities.
According to a variant embodiment of the invention, this C5 fraction which is only slightly enriched with isoprene may also be obtained by implementing a simplified enrichment process consisting successively:
- of the aforementioned simple or extractive distillation to remove the major part of the
dienes other than isoprene, in particular cyclopentadiene,

- of removal of the vinylacetylene compounds (residual "true" alkynes) by a selective
catalytic hydrogenation reaction,
- of distillation over maleic anhydride to remove practically any residual
cyclopentadiene, and
- of passing over alumina or over a molecular sieve to remove the residual polar
impurities.
It will be noted that this selective polymerisation of high yield takes place a fortiori from a C5 fraction which is more enriched with isoprene, that is to say in which the mass fraction of isoprene is greater than 30%, the latter advantageously lying within a range of between 30% and 70%, Of course, this mass fraction of isoprene may adopt even higher values, for example reaching 95%.
The possibility of simplifying the purification operation of this C5 fraction results in a possibility of substantially lowering the overall cost of obtaining polyisoprenes.
According to another advantageous characteristic of the invention, this enriched C5 fraction comprises aliphatic and alicyclic mono-olefins, the mass ratio (aliphatic and alicyclic mono-olefins : isoprene) possibly being less than or equal to 50% and being for example between 4% and 50% and, preferably, between 20% and 50%.
According to another advantageous characteristic of the invention, this enriched C5 fraction comprises, as mono-olefins, a-olefms and p-olefins, the mass ratio (a-olefins : isoprene) possibly being less than or equal to 30%, for example between 1% and 30%, and the mass ratio (p-olefins : isoprene) possibly being less than or equal to 20%, for example between 3% and 20%.
It will be noted that said enriched C5 fraction furthermore comprises:
1,3-pentadiene, the mass ratio (1,3-pentadiene : isoprene) possibly being less than or equal to 0.5% and being for example between 0.01% and 0.5%, - disubstituted alkynes, the mass ratio (disubstituted alkynes : isoprene) possibly being less than or equal to 0.7%, for example between 0.01% and 0.7%,

vinylacetylene compounds (also referred to as "true" alkynes), the mass ratio (vinylacetylenes : isoprene) possibly being less than or equal to 15 ppm (parts per million) and being for example between 1 ppm and 15 ppm, 1,4-pentadiene, the mass ratio (1,4-pentadiene : isoprene) possibly being less than or equal to 0.2% and being for example between 1 ppm and 2000 ppm, cyclopentadiene, the mass ratio (cyclopentadiene : isoprene) possibly being less than or equal to 5 ppm and being for example between 1 ppm and 5 ppm, and limonene, the mass ratio (limonene : isoprene) possibly being less than or equal to 2% and being for example between 0.1 % and 2%.
It will be noted that the constituents other than isoprene in the enriched C5 fraction according to the invention may be present in this fraction in mass fractions which are very much higher than those of the same constituents of the C5 fractions which have been enriched with isoprene in known manner for the polymerisation of the latter, such as the enriched C5 fraction featured in the aforementioned article by E. Schoenberg, H.A. Marsh, S.J. Walters, W.M. Saltman, Rubber Chemistry and Technology, 1979, vol. 52, p. 565, while permitting the selective polymerisation of isoprene with a high catalytic activity with a polyisoprene having a high cis-1,4 linkage content being obtained.
It will also be noted that the polyisoprenes thus obtained have high viscosities.
Advantageously, the polyisoprenes obtained by means of this catalytic system and this C5 fraction enriched with isoprene have cis-1,4 linkage contents, measured in accordance with carbon-13 nuclear magnetic resonance and mid-infrared analysis, which lie within a range of from 98.0% to 99.6%.
It will be noted that when the polymerisation operations are effected at temperatures of from 25°C to 55°C, the polyisoprenes obtained by means of the catalytic system according to the invention have cis-1,4 linkage contents, measured by one and the other of these techniques, which lie within a range from 98.0% to 98.5%.
Advantageously, when the polymerisation operations are effected at temperatures of less than or equal to 5°C, the polyisoprenes obtained by means of said catalytic system have

cis-1,4 linkage contents, measured in accordance with carbon-13 nuclear magnetic resonance and mid-infrared analysis, which lie within a range of from 99.0% to 99.6%.
It will be noted that such low-temperature polymerisation operations can be implemented in an inert hydrocarbon solvent, or alternatively without a solvent.
More precisely, this catalytic system makes it possible, at polymerisation temperatures of from -55°C to -20°C, to obtain polyisoprenes the cis-1,4 linkage contents of which, measured by one and the other of the aforementioned techniques, lie in a range from 99.3% to 99.6%.
Particularly advantageously, this catalytic system makes it possible, at polymerisation temperatures of from -55°C to -45°C, to obtain polyisoprenes the cis-1,4 linkage contents of which, also measured by one and the other of the aforementioned techniques, are equal to 99.6%.
It will be noted that these latter values of cis-1,4 linkage contents which are close to the value of 100% which characterises natural rubber have never really been achieved to date.
It will also be noted that the aforementioned values of cis-1,4 linkage contents take into account measurements established by means of, on one hand, mid-infrared analysis after calibration of the samples of polyisoprene which is effected within the scope of C-NMR analysis and, on the other hand, of 13C-NMR analysis, the measurements obtained by one of these techniques being confirmed by the other (disregarding the inaccuracy of measurement of +/- 0.1%, which is inherent in each of these two techniques). The accuracy of these values of cis-1,4 linkage contents is thus increased, relative to that of the values of the contents which have been mentioned in the prior art to date.
It will furthermore be noted that the particularly high cis-1,4 linkage content obtained for the polyisoprenes according to the invention is independent of the quantity of catalytic system used.
It should be noted that the catalytic systems according to the invention are characterised by a molar ratio (alkylating agent : rare earth salt) which is extremely low compared with the molar ratios equal to or greater than 20 which have been used to date which, surprisingly, makes it possible to increase significantly the activity of these catalytic systems according to the invention.

Preferably, the catalytic system according to the invention is such that the molar ratio (alkylating agent: rare earth salt) has a value ranging from 1 to 2.
1,3-Butadiene may be mentioned as a preferred conjugated diene monomer usable for "preforming" the catalytic system of the invention.
Mention may also be made of 2-methyl-l,3-butadiene (or isoprene), 2,3-di(Cl to C5 alkyl)-l,3-butadienes such as, for instance, 2,3-dimethyl-l,3-butadiene, 2,3-diethyl-l,3-butadiene, 2-methyl-3-ethyl-l,3-butadiene, 2-methyl-3-isopropyl-l,3-butadiene, phenyl-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 the molar ratio (monomer : rare earth salt) may have a value ranging from 25 to 50.
According to another characteristic of the invention, said rare earth salt consists of a non-hygroscopic powder having a slight tendency to agglomerate at ambient temperature.
- According to a preferred embodiment of the invention, the inert hydrocarbon solvent
in which said rare earth salt is suspended is a low molecular weight aliphatic or alicyclic
solvent, such as cyclohexane, methylcyclohexane, n-heptane or a mixture of these solvents.
- According to another embodiment of the invention, the solvent used to suspend the
rare earth salt is a mixture of a high molecular weight aliphatic solvent comprising a
paraffinic oil, for example petrolatum oil, and of a low molecular weight solvent such as those
mentioned above (for example methylcyclohexane).
This suspension is prepared by dispersive grinding of the rare earth salt in this paraffinic oil in such a manner as to obtain a very fine and homogeneous suspension of the salt.
According to another characteristic of the invention, said catalytic system comprises the rare earth metal in a concentration equal to or substantially equal to 0.02 mol/1.
According to a preferred embodiment of the invention, a tris[bis(2-ethylhexyl)phosphate] salt of said rare earth metal or metals is used as the salt.

Even more preferably, said rare earth salt is neodymium tris[bis(2-ethylhexyl)phosphate].
Alkylating agents usable in the catalytic system of the invention which may be mentioned are alkylaluminiums such as:
- trialkylaluminiums, for example triisobutylaluminium, or
- dialkylaluminium hydrides, for example diisobutylaluminium hydride.
It will be noted that this alkylating agent is preferably formed of diisobutylaluminium hydride (referred to as DiBAH in the rest of the present description).
Halogen donors usable in the catalytic system according to the invention which may be mentioned are alkylaluminium halides, preferably diethylaluminium chloride (referred to as DEAC in the rest of the present description).
It will be noted that the molar ratio (halogen donor : rare earth salt) may have a value ranging from 2.6 to 3.
According to the invention, the process for the preparation of said catalytic system consists:
- in a first stage, of preparing a suspension of said rare earth salt in said solvent,
- in a second stage, of adding said conjugated diene monomer to the suspension,
- in a third stage, of adding said alkylating agent to the suspension comprising said
monomer to obtain an alkylated salt, and
- in a fourth stage, of 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 examples of embodiment of the invention, which are given by way of illustration and not of limitation.
For each of the examples hereafter, a steam-cracked C5 naphtha fraction (fraction not enriched with isoprene) was initially used, the composition of which is as follows:
Isoprene 24%
Alkanes 14%

Mono-olefins 36%, of which a-olefms 17%
p-olefms 19%
Acetylenes 1%
Aromatics 2%
Dienes 23%, of which 1,4-pentadiene 3%
piperylene 11 %
cyclopentadiene 8%
other dienes 1 %.
EXAMPLE 1: Synthesis of polyisoprenes from a first C5 fraction enriched with isoprene.
I. Obtaining a first C5 fraction enriched with isoprene according to the invention:
The initial C5 fraction was subjected to a series of stages of enrichment in isoprene, in order to obtain an enriched C5 fraction in which the mass fraction of isoprene is only 62%.
In a first enrichment stage, simple distillation of the initial C5 fraction on a 50-plate column was effected, so that the mass fraction of cyclopentadiene in the fraction is reduced to 600 ppm.
In a second enrichment stage, distillation over maleic anhydride of the fraction obtained following said first stage was effected, using a molar ratio (maleic anhydride : cyclopentadiene) substantially equal to 30, so that the mass fraction of cyclopentadiene in the fraction is reduced to a value of less than 5 ppm. Furthermore, the mass fraction of residual "true" alkynes (vinylacetylenes) in the fraction is reduced to 750 ppm.
In a third enrichment stage, distillation of the fraction obtained following said second stage was performed over diisobutylaluminium (DiBAH), so that the mass fraction of the vinylacetylenes is reduced to 10 ppm in the fraction. A molar ratio (DiBAH : vinylacetylenes) substantially equal to 40 is used for this distillation.
In a fourth enrichment stage, the fraction thus obtained is passed over alumina, in order to remove practically all the residual polar compounds.
Analysis by gas phase chromatography (GPC, see Appendix 3) made it possible to determine the composition of the enriched C5 fraction following these four stages (expressed in mass fractions of constituents in the fraction):
1-pentene 3%
2-methyl-1 -butene 8%
pentane 21 %
isoprene 62%
others 3%
2-pentene 3%.
It will be noted that the relative mass ratio (mono-olefins : isoprene) is substantially equal to 22.6% in this example of embodiment.
As for the relative mass ratios (a-olefins : isoprene) and (p-olefins : isoprene), they are substantially equal to 17.7% and 4.8%, respectively.
It. Preparation of a catalytic system 1 according to a first example of embodiment of the invention for the polymerisation of isoprene:
1) Synthesis of an organic phosphate salt of neodymium for the preparation of this catalytic system 1;
a) Synthesis of an aqueous solution of neodymium NdCl^, 6H?O:
96 g of Nd2O? (sold by RHODIA), which has been determined by complexation analysis to have an Nd content of 85.3% (theoretical value 85.7%), so amounting to 0.57 mol of Nd, are weighed out into a "tall" form 600 ml beaker.
80 ml of demineralised water are added. Under a fume hood, 150 ml of 36% by weight concentrated HCl (d = 1.18), namely 1.75 mol of HC1 (molar ratio HC1 : Nd -1.75:0.57 -=~~ 3.07), are slowly added at ambient temperature while the mixture is stirred with a magnetic stirrer.
The reaction Nd2O3 + 6 HCl + 9 H2O -> 2 NdCl3, 6H2O is highly exothermic.
Once all the hydrochloric acid has been added, the solution is raised to boiling while being stirred with a magnetic stirrer, in order to remove the excess hydrochloric acid. The aqueous NdC^ solution is clear and mauve in colour. No insoluble product (Nd2O3) remains.
This solution is then evaporated until a volume of approximately 130 ml remains in the beaker. The solution of NdCh, 6H2O is then highly concentrated (it crystallises at ambient temperature).
The concentrated solution of NdCl3 is then poured into a 10 litre drum containing 4500 ml of demineralised water at ambient temperature while the mixture is stirred (using a motor with an anchor agitator).
The pH of the solution, measured at 25°C, is close to 4.
1 500 ml of technical grade acetone are then added to the solution. No insoluble product remains, and the resultant solution is pink in colour.
b) Synthesis of an organic sodium phosphate of formula (R = 2-ethylhexyl):
68 g, or 1.70 mol, of NaOH flakes are dissolved in a 5 litre beaker containing 1 500 ml of demineralised water. 554 g of an organic phosphoric acid (bis(2-ethylhexyl)phosphoric acid, listed in the "Aldrich" catalogue under number 23,782-5), namely 1.72 mol of this acid, are dissolved in another 3 litre beaker containing 500 ml of acetone. The molar ratio NaOH : organic phosphoric acid is 1 .70: 1 .72 or 0.99.
At ambient temperature and while stirring the mixture by hand with a glass stirrer, the solution of said organic phosphoric acid is poured into the NaOH solution. The reaction is as follows:
[RO]2P(O)OH + NaOH -> [RO]2P(O)ONa + H2O.
The reaction is slightly exothermic and a homogeneous solution of a yellowish colour is obtained. The pH of the solution, measured at 25°C, is close to 7.
c) Synthesis of a phosphated neodymium salt of the formula [[RO]?P(O)O]rNd:
- At ambient temperature and while the mixture is being vigorously stirred (motor with anchor agitator), the organic Na phosphate salt obtained in section b) above is poured into the aqueous solution of NdCl3,6H2O obtained in section a) above.
A very fine white precipitate forms immediately. Stirring of the resultant mixture is continued for 30 minutes once all the organic Na phosphate has been added (in a molar ratio (RO)2P(O)ONa : NdCl3 = 1.70:0.57 = 2.98). The reaction is as follows:
3 [RO]2P(0)ONa + NdCl3,6H2O -> Nd[OP(O)[OR]2]3 + 3 NaCl + 6 H2O.
- The resultant phosphated neodymium salt is recovered and washed in a centrifuge equipped with a "sock".
The pH of the mother liquors is between 3 and 4 at 25°C. These mother liquors are colourless and clear.
The salt obtained is divided into two samples, then each sample is washed with an acetone/demineralised water mixture, performing the washing cycle described below three times in order to remove all the chlorides.
Each washing cycle is performed in a 10 litre plastic bucket initially containing 2 litres of acetone. Each sample is then homogenised with the acetone using an "Ultra-Turrax" homogeniser for approx. 1 minute in order to obtain a milky solution.
4 litres of demineralised water are then added to the bucket and the resultant mixture is homogenised for 3 minutes using the same homogeniser.
The resultant mixture is centrifuged and the phosphated neodymium salt is recovered in the "sock".
The qualitative analytic test for chlorides is virtually negative for the final washing water (the reaction is as follows: NaCl + AgNO3 (HNO3 medium) —> AgCl -I + NaNO3).
The neodymium salt thus washed is dried in an oven at 60°C, under a vacuum and with an air current for approximately 80 hours.
The final yield for each of the synthesis tests performed is between 95% and 98%, depending upon the losses arising during washing. In each case, approx. 600 g of dry phosphated neodymium salt are obtained.
The mass contents of neodymium, determined both by complexometric back titration with ethylenediaminetetraacetic acid (EDTA) and by inductively-coupled plasma atomic emission spectrometry (abbreviated to 1CP-AES), are substantially between 12.5% and 12.8%

(with a theoretical content i of 13.01% where T = [144.24 / 1108.50] x 100, where 144.24 g/mol = molar mass of neodymium).
For each of these two methods, the neodymium content measurements were performed after wet acid mineralisation of the salt, either in a sand bath in an open system or in a microwave oven in a closed system.
The complexometric back titration with EDTA involves back titration with complexation of neodymium with an excess of EDTA (ethylenediaminetetraacetic acid), in which the excess EDTA is determined at pH = 4.6 with zinc sulphate.
A coloured indicator was used with photometric detection of the equivalence point.
Inductively-coupled plasma atomic emission spectrometry is an elemental analytical method based on the observation of the radiation emitted by atoms raised to an excited state in a plasma.
The emitted radiation used for analysis of neodymium corresponds to wavelengths of 406.109nmand401.225nm.
This spectrometric method was implemented by previously calibrating the system with "control" neodymium salts having a known neodymium content.
The following table shows the Nd contents obtained by means of these two methods (the number of tests performed on each salt sample is shown in brackets).
(Table Remove) The results obtained by the two methods are comparable (relative deviation 2) Synthesis of the catalytic system 1:
a) Composition of this catalytic system 1:
The catalytic system 1 comprises a phosphated neodymium salt as synthesised in section 1) above, which is suspended in a low molecular weight inert hydrocarbon solvent (formed of methylcyclohexane, abbreviated to "MCH" hereafter).
This catalytic system 1 is characterised by the following relative molar ratios, with respect to the neodymium salt:
Nd salt: butadiene (Bd hereafter) : DiBAH : DEAC = 1 : 25 : 1.8 : 2.6.
b) Process for synthesising this catalytic system 1:
- First stage:
In order to obtain this catalytic system 1, 15.6 g of the neodymium salt, in powder form, is poured into a 1 litre reactor from which the impurities have been removed
beforehand. This salt is then subjected to nitrogen bubbling from the bottom of the reactor for a period of 15 minutes.
- Second stage:
90% (mass fraction) of the methylcyclohexane (used as solvent) is introduced into the reactor containing the neodymium salt.
The duration of contact of the neodymium salt with the methylcyclohexane is 30 min., and the temperature of contact is 30°C.
- Third stage:
Butadiene is then introduced into the reactor (in the molar ratio salt : butadiene of 1 : 25 mentioned in section a) above), at a temperature of 30°C, for "preforming" the catalytic system.
- Fourth stage:
Diisobutylaluminium hydride (DiBAH) is then introduced into the reactor as the alkylating agent for the neodymium salt in a concentration of approx. 1 M, together with a quantity of methylcyclohexane corresponding to a mass fraction of 5% of the entire quantity of said solvent. The duration of the alkylation is 15 min. and the temperature of the alkylation reaction is 30°C.
- Fifth stage:
Diethylaluminium chloride (DEAC) is then introduced into the reactor as the halogen donor in a concentration of approx. 1 M, together with a quantity of methylcyclohexane corresponding to the remaining mass fraction of 5% of the entire quantity of this solvent. The temperature of the reaction medium is adjusted to 60°C.
- Sixth stage:
"Preforming" (or ageing) of the mixture thus obtained is then carried out by maintaining this temperature of 60°C for a period of 2 hours.
- Seventh stage:
In this manner, approximately 700 ml of a solution of catalytic system 1 is obtained. The reactor is emptied and this solution is transferred to a 750 ml "Steinie" bottle, which has beforehand been washed, dried and subjected to nitrogen bubbling.
Finally, the catalytic solution is stored under a nitrogen atmosphere in a freezer at a temperature of -15°C.
III. Preparation of polyisoprenes by means of the catalytic system 1, from the enriched C5 fraction in accordance with this first example:
The polymerisation reactor is a 250 ml "Steinie" bottle, which contains 10 g isoprene and the tightness of which is ensured by a "septum/open-top seal" assembly which permits addition of the catalytic system 1 using a syringe.
The polymerisation of the isoprene is carried out in cyclohexane at 50°C in an inert atmosphere (nitrogen), by subjecting the bottle to stirring in a water tank.
Several polymerisation tests were carried out consisting of preparing polyisoprenes, on one hand, from the enriched C5 fraction in accordance with section I. above and, on the other hand, from practically pure isoprene ("control" polyisoprene).
This practically pure isoprene was extracted conventionally in a laboratory from a steam-cracked C5 naphtha fraction, by effecting:
- distillation of the initial C5 fraction over maleic anhydride to remove any residual
cyclopentadiene, followed by
- passage through an alumina column to remove polar impurities, and
- nitrogen bubbling for 20 min, immediately prior to the polymerisation reaction.
The mass fraction of isoprene extracted from this C5 fraction was determined, by gas phase chromatography (GPC, see Appendix 3), and is 99.2%.
Given quantities of neodymium catalyst base were used (approximately 300 micromoles per 100 grammes of monomer, quantities expressed in uMcm).
It will be noted that the tests were carried out with a mass ratio S : M (solvent : monomer) which is equal to 9, the mass fraction of isoprene in the polymerisation medium being equal to 25%.
Acetylacetone was used as a polymerisation reaction shortstopping agent (1 ml of an acetylacetone solution of a concentration of 1M in cyclohexane), and N-l,3-dimethylbutyl-N'-phenyl-p-phenylenediamine (abbreviated to 6PPD) as a protection agent (in a volume of 1 ml at a concentration of 20 g/1 in cyclohexane, giving a mass of 0.02 g).
Then the polyisoprene is extracted from each polymer solution obtained by steam stripping for 30 min., in the presence of calcium tamolate (using 2 ml of tamol and 50 ml of CaCl2 at 30 g/1). Then each extracted solution was dried for approximately 18 hours in an oven at 60°C under a vacuum (at a pressure of 200 mm Hg), under a gentle stream of nitrogen.
The conversion rate of isoprene to polyisoprene as a function of reaction time is measured to describe the polymerisation kinetics for each test.
The inherent viscosity at 0.1 g/dl in toluene, measured at 25°C, characterises the macrostructure of each polyisoprene obtained.
Table I hereafter shows the results obtained for each polymerisation test.
TABLE I:

(Table Remove) These results show that the catalytic system 1 according to the invention permits the selective polymerisation of isoprene from a steam-cracked C5 naphtha fraction enriched to only 62% isoprene, with a reaction rate analogous to that relating to the polymerisation of practically pure isoprene ("control").
Furthermore, the polyisoprenes which are prepared at a temperature of 50°C from said C5 fraction enriched to 62%, just like the "control" polyisoprenes, all have the same cis-1,4

linkage content, measured by the C-NMR technique and the MIR technique (see Appendix 1), which is equal to 98.0%.
It will be noted that the polyisoprenes obtained have particularly low polymolecularity indices, which vary from 2.1 to 2.3 (see the attached Appendix 2 for the SEC measurement method).
EXAMPLE 2: Synthesis of polyisoprenes from a second C5 fraction enriched with isoprene.
I. Obtaining of a second C5 fraction enriched with isoprene according to the invention:
The initial C5 fraction was subjected to a series of stages of enrichment in isoprene, in order to obtain an enriched C5 fraction in which the mass fraction of isoprene is 56%.
The procedure was as described in section I. of Example 1, except for the fact that:
- the first stage of distillation on the 50-plate column is of "extractive" type, being implemented by means of a polar extraction solvent (consisting of dimethyl formamide at a concentration of 3%);
the mass fraction of cyclopentadiene following this first stage is 150 ppm; the mass fraction of vinyl acetylenes following the second distillation stage over maleic anhydride is 950 ppm.
Analysis by gas phase chromatography (see Appendix 3) made it possible to determine the composition of the enriched C5 fraction following these four stages (expressed in mass fractions of constituents in the fraction):

1 -pentene 5%
2-methyl-l-butene 11%
pentane 20%
isoprene 56%
others 3%
2-pentene 5%.
It will be noted that the relative mass ratio (mono-olefms : isoprene) is substantially equal to 37.5% in this example of embodiment.
As for the relative mass ratios (a-olefins : isoprene) and (P-olefins : isoprene), they are substantially equal to 28.6% and 8.9%, respectively.
II. Preparation of a catalytic system 2 according to a second example of embodiment of the invention for the polymerisation of isoprene:
The catalytic system 2 comprises a phosphated neodymium salt as synthesised in Example 1, and differs from the catalytic system 1 of Example 1 by:
the relative molar ratios Nd salt : butadiene (Bd hereafter) : DiBAH : DEAC,
respectively 1 : 30 : 1.8 : 2.6,
the duration of the alkylation stage, which is 30 min., and
the duration of the "preformation" stage with DEAC, which is one hour.
III. Preparation of polvisoprenes by means of the catalytic system 2. from the enriched C5 fraction in accordance with this second example of embodiment:
As in Example 1, polymerisation tests were carried out, on one hand, starting from this enriched C5 fraction in accordance with this second example and, on the other hand, from 99.2% pure isoprene ("control" tests).
The conditions of polymerisation and recovery of the polyisoprenes are the same as those described in Example 1.

Table II below sets forth the results obtained.
TABLE II

(Table Remove) These results show that the catalytic system 2 according to the invention permits the selective polymerisation of isoprene from a steam-cracked C5 naphtha fraction enriched to only 56% isoprene, with a reaction rate analogous to that relating to the polymerisation of practically pure isoprene ("control").
As mentioned in Example 1, the polyisoprenes which are prepared at a temperature of 50°C from the C5 fraction enriched to 56% isoprene, just like the "control" polyisoprenes, all have the same cis-1,4 linkage content, measured by the 13C-NMR technique and by the MIR technique (see Appendix 1), which is equal to 98.0%.
It will be noted that the polyisoprenes obtained have particularly low polymolecularity indices, which vary from 2.1 to 2.3 (see the attached Appendix 2 for the SEC measurement method).
EXAMPLES: Synthesis of polyisoprenes from third C5 fractions enriched with isoprene.
1. Obtaining of two third C5 fractions enriched with isoprene according to the invention:
The initial C5 fraction was subjected to a series of stages of enrichment in isoprene, in order to obtain each of the two enriched C5 fractions in which the mass fraction of isoprene is 57%.
The procedure was as described in section I. of Example 2, except for the fact that said first stage of "extractive" distillation on the 50-plate column (implemented by means of a polar extraction solvent consisting of dimethyl formamide in a concentration of 3%) is followed by the sequence of the following three stages:
two successive catalytic hydrogenation operations which are such that the mass fraction of the vinylacetylenes ("true" alkynes) is reduced to 10 ppm in each of the two fractions (the mass fraction of vinylacetylenes before these catalytic hydrogenation operations being 950 ppm, just as in Example 2 before the stage of distillation over DiBAH), then
distillation over maleic anhydride so that the mass fraction of cyclopentadiene in the fraction is reduced to a value less than 5 ppm (distillation implemented in the same manner as in Examples 1 and 2), then
passing the fraction thus obtained over alumina or over a molecular sieve of type "3A", respectively to obtain the two C5 fractions in accordance with this third example of the invention, in order to remove practically all the residual polar compounds.
The aforementioned two catalytic hydrogenation operations are carried out using one and the same Lindlar catalyst (comprising palladium in a mass fraction of 5%, on calcium carbonate "poisoned" with lead).
The operating conditions for these hydrogenation operations are as follows:
reactor: 250 ml "Steinie" bottle, with stirring in a water tank (tightness of the bottle
being ensured by a "septum/open-top seal" assembly permitting introduction of
hydrogen by means of a needle);
treated volume: 100 ml, or 68 g;
Lindlar catalyst: 70 mg;
hydrogen pressure in the reactor: 3 bar for each hydrogenation operation;
reaction time: 6 hours for each hydrogenation operation;
reaction temperature: 60°C.
Each C5 fraction thus hydrogenated is then filtered, by means of a filter of "HPLC" jality.
Following these two hydrogenation operations, it will be noted that the mass fraction ui vinylacetylenes (10 ppm) present in each C5 fraction is substantially the same as that obtained in Examples 1 and 2, after distillation over DiBAH.
Analysis by gas phase chromatography (see Appendix 3) made it possible to determine the composition of each enriched C5 fraction in accordance with this third example of embodiment of the invention following the aforementioned four stages (expressed in mass fractions of constituents in each fraction):
1-pentene 5%
2-methyl-1-butene 12%
pentane 21 %
isoprene 57%
others 2%
2-pentene 3%.
It will be noted that the relative mass ratio (mono-olefins : isoprene) is substantially equal to 35.1 % in this third example of embodiment.
As for the relative mass ratios (a-olefins : isoprene) and (p-olefins : isoprene), they are substantially equal to 29.8% and 5.3%, respectively.
II- Preparation of a catalytic system 3 according to a third example of embodiment of the invention for the polymerisation of isoprene:
The catalytic system 3 comprises a phosphated neodymium salt as synthesised in Example 1, and differs from the catalytic system 1 of Example 1 by:
the relative rnolar ratios Nd salt : butadiene (Bd hereafter) : DiBAH : DEAC,
respectively 1 : 30 : 1,8 : 2,6, and
the duration of the alkylation stage, which is 30 min.
III. Preparation of polvisoprenes by means of the catalytic system 3, from the two enriched C5 fractions in accordance with this third example of embodiment:
As in Example 1, polymerisation tests were carried out, on one hand, starting from the two enriched C5 fractions in accordance with this third example and, on the other hand, from 99.2% pure isoprene ("control" test).
The sole differences from the tests of Example 1 are as follows:
the mass fraction of isoprene in the polymerisation medium is 10%, the tests having been carried out with a mass ratio S : M (solvent : monomer) which is equal to 9;
a quantity of neodymium catalyst base was used which is 440 micromoles per 100 grammes of monomer for each of the two tests in accordance with this third example according to the invention, and which is 400 micromoles per 100 grammes of monomer for said "control" test (quantities expressed in u,Mcm). The conditions of polymerisation and recovery of the polyisoprenes are the same as those described in Example 1.
Table ID below sets forth the results obtained.
TABLE III:

(Table Remove) These results show that the catalytic system 3 according to the invention permits the iclective polymerisation of isoprene from steam-cracked C5 naphtha fractions which have :ach been enriched to 57% isoprene, by carrying out a catalytic hydrogenation reaction in >rder to reduce the amount of vinylacetylenes, with a reaction rate analogous to that relating o the polymerisation of practically pure isoprene ("control").
As mentioned in Examples 1 and 2, the polyisoprenes which are prepared at a etnperature of 50°C from each enriched C5 fraction in accordance with this third example, ust like the "control" polyisoprene, all have the same cis-1,4 linkage content measured by the 3C-NMR technique and by the MIR technique (see Appendix 1), which is equal to 98.0%.
It will be noted that the polyisoprenes obtained have particularly low polymolecularity indices, which vary from 2.1 to 2.3 (see the attached Appendix 2 for the SEC measurement method).

APPENDIX 1:
Determination of the microstructure of the polvisoprenes.
1) By carbon-13 nuclear magnetic resonance analysis (13C-NMR analysis):
a) Preparation of the samples:
2 g of polyisoprene are extracted in refluxing acetone for 8 hours. The extracted polyisoprene is then dried at ambient temperature under vacuum for 24 hours. This dried polyisoprene is then redissolved in chloroform. The polyisoprene solution is filtered and the solvent removed in a rotary evaporator for 4 hours (bath temperature is 40°C).
For the purposes of the analysis, approximately 600 mg of the polyisoprene thus prepared is solubilised in CDCla (2 ml), directly in a 13C-NMR tube.
b) Characteristics of the apparatus:
- Spectrophotometer sold under the name "BRUKER AM250".
- Resonance frequency (SFO) = 62.9 MHz.
- Pulse program: INVGATE.AU (suppression of the "NOE" effect for quantitative
NMR analysis of I3C).
- Pulse duration: Mus (90°).
- Relaxation time: 10 s.
- Cumulative number of scans (NS) = 8192.
c) Assignment of the peaks of the spectrum:
The peaks were identified in accordance with:
Quang Tho Pham, R. Petiaud, H. Waton, M.F. Llauro Barricades, "Proton and NMR Spectra of Polymers", 1991, Penton Press.

d) Integration method:
- No 1,2 structural units detected.
- The ratio between the contents of 3,4 and of 1,4 is determined by means of the
ethylenic carbons. The content of trans-1,4 and cis-1,4 linkages in the polyisoprene is
calculated from the aliphatic carbons.
2) By mid-infrared (MIR) analysis:
a) Preparation of the samples:
The polyisoprene as prepared in section 1) above is used for this infrared analysis, while for NMR the sample is extracted with acetone and then dried in an oven.
A polyisoprene solution of exactly 10 g/1 in CCU is analysed using a KBr cell with a pathlength of 0.2 mm.
b) Apparatus:
- Spectrophotometer sold under the name "BRUKER IFS88".
- Recording conditions:
beam aperture: maximum;
resolution: 2 cm"1'
speed of the moving mirror: 0.639 cm.s"1'
detector: DTGS;
accumulations: 64 scans;
purge time: 3 min;
spectral window: 4000 to 400 cm"1;
transmission spectra recorded;
reference: CCU solvent.

- Processing of the spectra:
transfer to microcomputer;
processing with "OPUS" software from "BRUKER".
c) Assignment of the peaks of the spectrum:
Spectral studies and the contents of the following documents made it possible to determine the characteristic bands of the various linkage modes:
- Y. Tanaka, Y. Takeuchi, M. Kobayashi, H. Tadokoro, Journal of Polymer Science,
PartA~2, 1971, 9(1), 43-57.
- J.P. Kistel, G. Friedman, B. Kaempf, Bulletin de la Societe Chimique de
France, 1967, No. 12.
- F. Assioma, J. Marchal, C. R. Acad. Sc. Paris, Ser C, 1968, 266(22), 1563-6
and SerD, 1968, 266(6), 369-72.
- T.F. Banigan, AJ. Verbiscar, T.A. Oda, Rubber Chemistry and technology,
1982, 55(2), 407-15.
The 3_4 conformation exhibits two characteristic bands:
- a high intensity band at 880 cm" corresponding to the out-of-plane
deformation vibrations (8 C-H) of the terminal hydrogens of the vinyl group (=CHi).
- a band at 3070 cm"1 corresponding to the v C-H stretching of this same group
(=CH2).
The 1-4 cis conformation has a characteristic band around 3030 cm"1. This band corresponds to the v C-H stretching vibrations of the =CH group.
The band corresponding to the symmetrical deformation vibrations of the methyl groups (5 CHj) is a complex band which incorporates all three configurations. The absorption corresponding to the 5 CHj of the trans-1.4 conformation is at its maximum around 1385 cm" '; this is a shoulder of this band.

d) Integration method:
The cis-3,4 and 1,4 bands are integrated by the tangential area method. The absorption maximum of the trans- 1 ,4 is located on the shoulder of the intense 5 band. The most suitable method in this case is to measure the height of band using the tangent of the 8 CHa band as baseline.
e) Calibration curves:
Statement of the Beer-Lambert law:
Do(v or 8) - s(v or 8) e c where:
Do(v or 8) = optical density of the band v or 8;
e(v or 8) = molar extinction coefficient of the analyte responsible for the band v or 8;
c = molar concentration of the analyte; and
e = thickness of the sample.
Commercial polyisoprenes (sold under the names "IR305", "NATSYN 2200" and "SKI-3S"), a polyisoprene synthesised in the laboratory (MC78) and natural rubber (NR) are used as standards. Compared at isoconcentration (solutions), the law may thus be written:
Dx =•- K X
where:
Dx = integration value of the band corresponding to the structural unit X,
X - amount of structural unit X in the rubber (determined by I3C-NMR), and
K = calibration constant.
The calibration curves Dx = f(X) may therefore be plotted for each of the structural units.

APPENDIX 2:
Determination of the distribution of the molecular weights of the elastomers obtained by size exclusion chromatography (SEC).
a) Principle of the measurement:
Size exclusion chromatography or SEC makes it possible physically to separate macromolecules according to their size in the swollen state in columns filled with porous stationary phase. The macromolecules are separated by their hydrodynamic volume, the bulkiest being eluted first.
Although not an absolute method, SEC does enable an assessment to be made of the molecular weight distribution of a polymer. On the basis of commercially available standards, the various number-average (Mn) and weight-average (Mw) molecular weights can be determined and the polydispersity index calculated (Ip = Mw/Mn).
b) Preparation of the polymer:
There is no particular treatment of the sample of polymer before analysis. It is simply solubilised in tetrahydrofuran, at a concentration of approx. 1 g/1.
c) SEC analysis:
The apparatus used is a "WATERS model 150C" chromatograph. The elution solvent is tetrahydrofuran, the flow rate is 0.7 ml/min, the temperature of the system is 35°C and the duration of analysis is 90 min. A set of four columns in series is used, of the trade names "SHODEX KS807", "WATERS type STYRAGEL HMW7" and two "WATERS STYRAGEL HMW6E".
The volume of polymer sample solution injected is 100 u,l. The detector is a "WATERS model RI32X" differential refractometer and the chromatographic data processing software is "WATERS MILLENNIUM" (version 3.00).

APPENDIX 3:
Determination of the composition of the "control" steam-cracked C5 naphtha fraction and the fraction enriched according to the invention, by gas phase chromatography (GPC).
a) GPC!£TO analysis:
Analysis of each enriched C5 fraction according to the invention and of the "control" C5 fraction (with a mass fraction of isoprene close to 100%) is effected from traces injected without prior dilution, in order not to saturate the response of the flame ionisation detector (FID) used.
b) Chromatographic conditions used:
Chromatograph HP6890
Carrier gas: nitrogen
Pressure at the head of the column: 6.6 psi
Constant flow rate: 0.8 ml/min.
Method of injection: "split"
Ratio of "split": 50/1
Temperature of the injector: 250°C
Injected volume: traces
Column HP 1: methyl silicone phase
length: 60 m
internal diameter: 0.32 mm
thickness of the film: 1.0 urn
Temperature program: T1=30°C
Dl = 17min.
Pl-20°C/min.
T2 = 280°C
D2 = 20min.

FID temperature: 300°C. c) Results;
Semi-quantitative analysis was performed by calculating the relative proportion of the areas of the peaks of each chromatogram, in order to obtain a distribution. The differences in responses of the eluted compounds were not taken into consideration, as the FID did not detect signals due to the presence of non-eluted and eluted compounds . The proportion in % of a compound i is given by the following expression:
100
where A; = area relative to the compound i, and
ZAj = total of all the eluted compounds i (identified and non-identified).

WE CLAIM;
1. A process for obtaining a polyisoprene from a steam-cracked C5 naphtha fraction enriched with isoprene, wherein said enriched C5 fraction comprises aliphatic and alicyclic mono-olefins, wherein it consists of using a C5 fraction enriched with isoprene in which the mass ratio (aliphatic and alicyclic mono-olefins isoprene) is less than or equal to 50%, wherein said process essentially consists of essentially reacting a catalytic system in the presence of said enriched C5 fraction at a temperature from -55°C to 55°C, using:
* a C5 fraction enriched with isoprene such that the mass fraction of isoprene in said enriched fraction lies within a range of from 30% to 95%, and
* a catalytic system based on at least:

- a conjugated diene monomer,
- an organic phosphoric acid salt of at least one rare earth metals such as herein described,
- an alkylating agent consisting of an alkylauminium of the formula AIR3 or HAIR2, and
- a halogen donor consisting of an alkylaluminium halide such as herein described,
said salt being suspended in at least one inert saturated hydrocarbon
solvent of aliphatic or alicyclic type such as herein described which is
included in at least one inert saturated hydrocarbon solvent of aliphatic or
alicyclic type which is included in said catalytic system, and
the molar ratio (alkylating agent : rare earth salt) being in a range of from 1
to 5,
the molar ratio (halogen donor : salt) being within a range of from 2.6 to 3
and
the molar ratio (conjugated diene monomer : salt) being within a range of
from 25 to 50.

2. A process for obtaining a polyisoprene as claimed in claim 1, wherein it consists of using a molar ratio (alkylating agent : rare earth salt) which lies within a range of from 1 to 2.
3. A process for obtaining a polyisoprene as claimed in claims 1 or 2, wherein it consists of using, as catalytic system, a system which is such that said rare earth salt is a rare earth tris[bis(2-ethylhexyl)phosphate].
4. A process for obtaining a polyisoprene as claimed in claim 3, wherein it consists of using, as catalytic system, a system which is such that said rare earth salt is neodymium tris[bis(2-ethylhexyl)phosphate].
5. A process for obtaining a polyisoprene as claimed in one of the preceding claims, wherein it consists of using, as catalytic system, a system comprising said rare earth metal(s) in a concentration equal or substantially equal to 0.02 mol/1.
6. A process for obtaining a polyisoprene as claimed in one of the preceding claims, wherein it consists of using, as catalytic system, a system which is such that said conjugated diene monomer is butadiene.
7. A process for obtaining ,a polyisoprene as claimed in one of the preceding claims, wherein it consists of using, as catalytic system, a system which is such that said alkylating agent is diisobutylaluminium hydride.
8. A process for obtaining a polyisoprene as claimed in one of the preceding claims, wherein it consists of using, as catalytic system, a system which is such that said halogen donor is diethylaluminium chloride.
9. A process for obtaining a polyisoprene as claimed in one of the preceding claims, wherein it consists of using a C5 fraction enriched with

isoprene in which the mass fraction of isoprene lies within a range of from 30% to 70%.
10. A process for obtaining a polyisoprene as claimed in claim 1, wherein it consists of using a C5 fraction enriched with isoprene in which the mass ratio (aliphatic and alicyclic mono-olefins : isoprene) is between 20% and 50%.
11. A process for obtaining a polyisoprene as claimed in claim 1 said mono-olefins comprising a-olefins and (^-olefins, wherein it consists of using a C5 fraction enriched with isoprene in which the mass ratio (a-olefins : isoprene) is less than or equal to 30%, and in which the mass ratio (^-olefins : isoprene) is less than or equal to 20%.
12. A process for obtaining a polyisoprene as claimed in one of the preceding claims, wherein it consists of using a C5 fraction enriched with isoprene in which the mass ratio (1,3-pentadiene isoprene) is less than or equal to 0.5%.
13. A process for obtaining a polyisoprene as claimed in one of the preceding claims, wherein it consists of using a C5 fraction enriched with isoprene in which the mass ratio (disubstituted alkynes : isoprene) is less than or equal to 0.7%.
14. A process for obtaining a polyisoprene as claimed in one of the preceding claims, wherein it consists of using a C5 fraction enriched with isoprene in which the mass ratio (vinylacetylene compounds isoprene) is less than or equal to 15 ppm (parts per million).
15. A process for obtaining a polyisoprene as claimed in one of the preceding claims, wherein it consists of using a C5 fraction enriched with

isoprene in which the mass ratio (1,4-pentadiene : isoprene) is less than or equal to 0.2%.
16. A process for obtaining a polyisoprene as claimed in one of the preceding claims, wherein it consists of using a C5 fraction enriched with isoprene in which the mass ratio (cyclopentadiene : isoprene) is less than or equal to 5 ppm.
17. A process for. obtaining a polyisoprene as claimed in one of the preceding claims, said C5 fraction comprising limonene, wherein it consists of using a C5 fraction enriched with isoprene in which the mass ratio (limonene : isoprene) is less than or equal to 2%.

Documents:

00782-delnp-2003-abstract.pdf

00782-delnp-2003-claims.pdf

00782-delnp-2003-correspondence-others.pdf

00782-delnp-2003-description (complete)-18-06-2008.pdf

00782-delnp-2003-description (complete)-30-05-2008.pdf

00782-delnp-2003-description (complete).pdf

00782-delnp-2003-form-1.pdf

00782-delnp-2003-form-18.pdf

00782-delnp-2003-form-2.pdf

00782-delnp-2003-form-3.pdf

00782-delnp-2003-form-5.pdf

00782-delnp-2003-gpa.pdf

00782-delnp-2003-pct-notificatian.pdf

00782-delnp-2003-pct-search report.pdf

782-DELNP-2003-Abstract (30-05-2008).pdf

782-DELNP-2003-Abstract-(18-06-2008).pdf

782-DELNP-2003-Claims (30-05-2008).pdf

782-DELNP-2003-Claims-(18-06-2008).pdf

782-DELNP-2003-Correspondence-Others (30-05-2008).pdf

782-DELNP-2003-Form-1 (30-05-2008).pdf

782-DELNP-2003-Form-2 (30-05-2008).pdf

782-DELNP-2003-Form-3 (30-05-2008).pdf

782-DELNP-2003-GPA (30-05-2008).pdf

782-DELNP-2003-Petition-137 (30-05-2008).pdf

782-DELNP-2003-Petition-138 (30-05-2008).pdf


Patent Number 221589
Indian Patent Application Number 00782/DELNP/2003
PG Journal Number 31/2008
Publication Date 01-Aug-2008
Grant Date 25-Jun-2008
Date of Filing 21-May-2003
Name of Patentee SOCIETE DE TECHNOLOGIE MICHELIN
Applicant Address 23 RUE BRESCHET, F-63000 CLERMONT-FERRAND, CEDEX 09, FRANCE
Inventors:
# Inventor's Name Inventor's Address
1 PHILIPPE LAUBRY 4, RUE DE LA POMMERRAIE, F-63200 MARSAT, FRANCE
PCT International Classification Number C08F 36/08
PCT International Application Number PCT/EP01/13928
PCT International Filing date 2001-11-28
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 00/16456 2000-12-14 France