EP1525259A1 - Rubber composition for tyre comprising a coupling agent with cyclic polysulphide function - Google Patents

Abstract

The invention concerns an elastomeric composition useable for making tyres, based on at least (i) one diene elastomer, (ii) one inorganic filler as reinforcing filler and (iii), as coupling agent (inorganic filler/diene elastomer), one organosilicon compound at least bifunctional capable of being grafted on the elastomer by means of a sulphur group with cyclic polysulphide function, of formula (I): Si (Z S)p A Q, wherein : Z is a linear or branched divalent binding group, enabling the cyclic polysulphide group to be bound to a silicon atom of the organosilicon compound ; p is equal to 0, 1 or 2 ; A represents a valence bond or a divalent saturated aleghatic hydrocarbon group ; Q represents a specific polysulphide carbocycle. The invention also concerns tyres and treads comprising such a composition.

Description

 RUBBER COMPOSITION FOR TIRE COMPRISING A COUPLING AGENT HAVING A CYCLIC POLYSULFIDE FUNCTION

The present invention relates to diene elastomer compositions reinforced with a white or inorganic filler, intended in particular for the manufacture of tires or semi-finished products for tires, in particular treads for these tires.

It relates more particularly to the use, in such compositions, of binding agents for the coupling of reinforcing inorganic fillers and diene elastomers.

It is generally known that to obtain the optimal reinforcement properties conferred by. a filler, the latter should be present in the elastomeric matrix in a final form which is both as finely divided as possible and distributed in the most homogeneous manner possible. However, such conditions can only be achieved insofar as the filler has a very good ability, on the one hand to be incorporated into the matrix during mixing with the elastomer and to disaggregate, on the other hand to disperse homogeneously in this matrix.

In a completely known manner, carbon black exhibits such aptitudes, which is generally not the case for inorganic fillers. Indeed, for reasons of reciprocal affinities, the particles of inorganic charge have an unfortunate tendency, in the elastomeric matrix, to agglomerate between them. These interactions have the harmful consequence of limiting the dispersion of the filler and therefore the reinforcing properties to a level substantially lower than that which it would be theoretically possible to achieve if all the bonds (inorganic filler / elastomer) capable of being created. during the mixing operation, were actually obtained. These interactions also tend to increase the viscosity in the raw state of the rubber compositions and therefore to make their implementation ("processability") more difficult than in the presence of carbon black.

Since ^'fuel economy and the need to protect the environment have become a priority, it turned out, however, necessary to produce tires with reduced rolling resistance, without adversely affecting their wear resistance. This was made possible in particular thanks to the discovery of new rubber compositions reinforced with specific inorganic fillers qualified as "reinforcing", capable of competing from the reinforcing point of view with a conventional carbon black of pneumatic grade, while offering these compositions a lower hysteresis, synonymous with a lower rolling resistance for the tires comprising them, as well as high grip properties on wet, snowy or icy conditions.

Such rubber compositions, comprising reinforcing inorganic fillers, for example of the silica or alumina type, have for example been described in patents or patent applications EP 501,227 or US 5,227,425, EP 735,088 or US 5,852,099, EP 810 258 or US 5 900 449, EP 881 252, WO99 / 02590, O99 / 06480, WOOO / 05300, O00 / 05301, WO02 / 10269. Mention will in particular be made of the documents EP 501 227, EP 735 088 or EP 881 252 which disclose diene rubber compositions reinforced with precipitated silicas with high dispersibility, such compositions making it possible to manufacture treads having a markedly improved rolling resistance, without affecting the other properties, in particular those of adhesion, endurance and resistance to wear. Such compositions having such a compromise of contradictory properties are also described in patent application EP 810 258, with, as reinforcing inorganic fillers, specific aluminas with high dispersibility.

The use of these specific, highly dispersible inorganic fillers has certainly reduced the difficulties of processing in the raw state the rubber compositions containing them, but this processing nevertheless remains more difficult than for the compositions loaded conventionally with black. of carbon.

In particular, it is necessary to use a coupling agent, also called a bonding agent, which has the function of ensuring the bond between the surface of the particles of inorganic filler and the elastomer, while facilitating the dispersion of this filler inorganic within the elastomeric matrix.

By “coupling” agent (inorganic filler / elastomer) is understood, in known manner, a compound capable of establishing a sufficient connection, of chemical and / or physical nature, between the inorganic filler and the diene elastomer; such a coupling agent, at least bifunctional, has for example as simplified general formula "Y-T-X", in which:

Y represents a functional group ("Y" function) which is capable of physically and / or chemically binding to the inorganic charge, such a bond being able to be established, for example, between a silicon atom of the coupling agent and the surface hydroxyl groups (OH) of the inorganic filler (for example surface silanols when it is silica);

X represents a functional group (“X” function) capable of physically and / or chemically bonding to the diene elastomer, for example via a sulfur atom;

T represents a divalent organic group making it possible to connect Y and X.

Coupling agents should in particular not be confused with simple inorganic charge covering agents which, in known manner, may contain the active Y function with respect to the inorganic charge but are devoid of the active X function with respect to - screw of the diene elastomer.

Coupling agents, in particular (silica / diene elastomer), have been described in numerous documents, the best known being bifunctional organosilanes carrying three organoxysilyl functions (in particular alkoxysilyl) as function Y, and, as function X , at least one function capable of reacting with the diene elastomer such as in particular a sulfur functional group (ie, comprising sulfur). Thus, it has been proposed in patent applications FR 2 094 859 or GB 1 310 379 to use a mercaptoalkoxysilane coupling agent for the manufacture of tire treads. It was quickly revealed and it is now well known that mercaptoalkoxysilanes are capable of providing excellent silica / elastomer coupling properties, but that the industrial use of these coupling agents is not possible due to the very high reactivity of the sulfur-thiols -SH type functions (functions

"X") leading very quickly during the preparation of the rubber compositions, in an internal mixer, to premature vulcanizations also called "scorching", at very high raw viscosities, at the end from account to compositions of

^" rubber almost impossible to work and to implement industrially. To illustrate this problem, mention may be made, for example, of documents FR 2 206 330, US 3 873 489,

US 4,002,594.

To remedy this drawback, it has been proposed to replace these mercaptoalkoxysilanes with polysulphurized alkoxysilanes, in particular bis- (alkoxylsilylpropyl) polysulphides as described in numerous documents (see for example FR 2 149 339, FR 2 206 330, US 3,842,111, US 3,873,489, US 3,997,581). Among these polysulphides, mention should be made in particular of bis 3-triethoxysilylpropyl tetrasulphide (abbreviated to TESPT) or bis 3-triethoxysilylpropyl disulphide (abbreviated to TESPD).

These polysulphurized alkoxysilanes, in particular TESPT, are generally considered to be the products providing, for vulcanizates comprising a reinforcing inorganic filler, in particular silica, the best compromise in terms of safety in roasting, ease of implementation and reinforcing power. As such, they are the most widely used coupling agents today in rubber compositions for tires.

However, the Applicants have discovered during their research that certain specific coupling agents, carrying a particular cyclic polysulfide group, make it possible, unexpectedly, to obtain an improved compromise of properties.

These coupling agents are organosilicon compounds which have the essential characteristic of carrying, as function X, a particular cyclic polysulfide functional group. They do not moreover pose the aforementioned problems of premature roasting and those of implementation linked to too high a viscosity of rubber compositions in the raw state, disadvantages posed in particular by mercaptosilanes.

Consequently, a first subject of the invention relates to an elastomeric composition which can be used for the manufacture of tires, comprising at least, as basic constituents, (i) a diene elastomer, (ii) an inorganic filler as a reinforcing filler and ( iii), as coupling agent (inorganic filler / diene elastomer), an at least bifunctional organosilicon compound graftable onto the elastomer by means of a cyclic polysulphide group, of formula:

(I) ≡ Si - (Z - S) _p - A - Q in which:

Z is a divalent linking group, linear or branched, making it possible to link the cyclic polysulphide group to a silicon atom of the organosilicon compound; p is 0, 1 or 2;

A represents a valence bond or a divalent saturated aléghatic hydrocarbon group;

Q represents the group of formula:

in which:

- the symbol B denotes a saturated monocyclic or polycyclic C ₅ -Cι ₈ carbocycle in which one or more of the carbon atoms can be replaced by an oxygen or sulfur atom, the two ends of the bridge -Sx- being linked to two contiguous carbon atoms of said carbocycle B; the symbols = O denote an oxygen atom which can constitute, with one of the atoms of S of the Sx bridge, a sulfinyl group> S = O; x is a whole or fractional number ranging from 2 to 6; q represents a number equal to 0 or 1.

A subject of the invention is also the use of a rubber composition in accordance with the invention for the manufacture of tires or for the manufacture of semi-finished products intended for such tires, these semi-finished products being chosen in particular in the group formed by the treads, the sub-layers intended for example to be placed under these treads, the crown reinforcement plies, the sides, the carcass reinforcement plies, the heels, the protectors , air chambers and waterproof inner liners for tubeless tires.

The invention also relates to these tires and these semi-finished products themselves, when they comprise an elastomeric composition in accordance with the invention, these tires being intended to equip passenger vehicles, 4x4 vehicles (with 4 wheel drive), SUV ("Sport Utility Vehicles"), two wheels (especially bicycles or motorcycles), as industrial vehicles chosen from vans, "Heavy goods vehicles" - Metro, buses, road transport vehicles (trucks , tractors, trailers), off-road vehicles -, agricultural or civil engineering machinery, airplanes, other transport or handling vehicles.

The invention relates in particular to tire treads, these treads being able to be used during the manufacture of new tires or for retreading used tires; thanks to the compositions of the invention, these treads have both a low rolling resistance, a very good grip and a high resistance to wear. The invention also relates to a process for preparing a rubber composition which can be used for the manufacture of tires, such a process comprising the following steps:

• incorporate into a diene elastomer, in a mixer, at least: - a reinforcing inorganic filler; as coupling agent (inorganic filler / diene elastomer), an at least bifunctional organosilicon compound which can be grafted onto the elastomer by means of a sulfur group,

. by thermomechanically kneading the whole, in one or more times, until reaching a maximum temperature of between 110 ° C and 190 ° C;

. cool the assembly to a temperature below 100 ° C;

. then incorporate a crosslinking system;

. knead everything up to a maximum temperature below 120 ° C,

and being characterized in that said sulfur group corresponds to the above formula (I).

Another subject of the invention is the use as a coupling agent (inorganic filler / diene elastomer), in a composition based on diene elastomer reinforced with an inorganic filler intended for the manufacture of tires, of a compound organosilicon at least bifunctional, graftable on the elastomer by means of a sulfur group with cyclic polysulfide function corresponding to the above formula (I).

The invention and its advantages will be easily understood in the light of the description and of the exemplary embodiments which follow, as well as of the single figure relating to these examples which represents rheograms (baking curves) for diene rubber compositions, whether or not in accordance with the invention.

I. MEASUREMENTS AND TESTS USED

The rubber compositions are characterized before and after curing, as indicated below.

A) Rheometry:

The measurements are carried out at 150 ° C. with an oscillating chamber rheometer, according to standard DIN 53529 - part 3 (June 1983). The evolution of the rheometric torque as a function of time describes the evolution of the stiffening of the composition as a result of the vulcanization reaction. The measurements are processed according to DIN 53529 - part 2 (March 1983): tj is the induction time, that is to say the time necessary for the start of the vulcanization reaction; t _α (for example t ₀ or t ₉₉ ) is the time necessary to reach a conversion of α%, i.e. α% (for example 90% or 99%, respectively) of the difference between the couples minimum and maximum. The conversion speed constant denoted K (expressed in min ^"1 ), of order 1, calculated between 30% and 80% conversion, is also measured, which makes it possible to assess the vulcanization kinetics. B) Tensile tests:

The stresses at break (in MPa) and the elongations at break (in%) are measured, in accordance with French standard NF T 46-002 (September 1988). All measurements are made under normal temperature (23 ± 2 ° C) and hygrometry (50 + 5% relative humidity) conditions, according to French standard NF T 40-101 (December 1979).

CONDITIONS FOR CARRYING OUT THE INVENTION

The rubber compositions according to the invention are based on at least each of the following constituents: (i) (at least) a diene elastomer, (ii) (at least) an inorganic filler as reinforcing filler, (iii) (at least) a specific organosilicon compound as a coupling agent (inorganic filler / diene elastomer).

Of course, by the expression composition "based on" is meant a composition comprising the mixture and / or the in situ reaction product of the various constituents used, some of these base constituents being capable of, or intended to react between them, at least in part, during the various phases of manufacturing the composition, in particular during its vulcanization.

II- 1. Diene elastomer

By "diene" elastomer or rubber is meant in known manner an elastomer derived at least in part (i.e. a homopolymer or a copolymer) from diene monomers (monomers carrying two carbon-carbon double bonds, conjugated or not).

In general, the term “essentially unsaturated” diene elastomer is understood here to mean a diene elastomer derived at least in part from conjugated diene monomers, having a rate of units or units of diene origin (conjugated dienes) which is greater than 15% (% in moles).

Thus, for example, diene elastomers such as butyl rubbers or copolymers of dienes and alpha-olefins of the EPDM type do not enter into the preceding definition and can be qualified in particular as "essentially saturated diene elastomers". "(rate of motifs of diene origin low or very low, always less than 15%).

In the category of “essentially unsaturated” diene elastomers, the expression “highly unsaturated” diene elastomer is understood in particular to mean a diene elastomer having a content of units of diene origin (conjugated dienes) which is greater than 50%.

These definitions being given, the term “diene elastomer capable of being used in the compositions according to the invention” is more particularly understood: (a) - any homopolymer obtained by polymerization of a conjugated diene monomer having from 4 to 12 carbon atoms;

(b) - any copolymer obtained by copolymerization of one or more dienes conjugated together or with one or more vinyl aromatic compounds having from 8 to 20 carbon atoms;

(c) - a ternary copolymer obtained by copolymerization of ethylene, of an α-olefin having 3 to 6 carbon atoms with a non-conjugated diene monomer having of 6 to 12 carbon atoms, such as for example the elastomers obtained from ethylene, propylene with a non-conjugated diene monomer of the aforementioned type such as in particular 1,4-hexadiene, ethylidene norbornene, dicyclopentadiene;

(d) - a copolymer of isobutene and isoprene (butyl rubber), as well as the halogenated, in particular chlorinated or brominated, versions of this type of copolymer.

Although it applies to any type of diene elastomer, a person skilled in the art of tires will understand that the present invention, in particular when the rubber composition is intended for a tire tread, is first put implemented with essentially unsaturated diene elastomers, in particular of the type (a) or (b) above.

By way of conjugated dienes, 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-di (C ₁ -C ₅ alkyl) -1,3-butadienes, such as for example, are suitable. 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, aryl-1,3-butadiene, 1,3-pentadiene, 2,4-hexadiene. Suitable vinyl-aromatic compounds are, for example, styrene, ortho-, meta-, para-methylstyrene, the commercial "vinyl-toluene" mixture, para-tertiobutylstyrene, methoxystyrenes, chlorostyrenes, vinyl mesitylene, divinylbenzene. , vinylnaphthalene.

The copolymers can contain between 99% and 20% by weight of diene units and between 1% and 80% by weight of vinyl-aromatic units. The elastomers can have any microstructure which is a function of the polymerization conditions used, in particular the presence or not of a ^" modifying and / or randomizing agent and the quantities of modifying and / or randomizing agent employed. The elastomers can be for example block, statistics, sequences, microsequences, and be prepared in dispersion or in solution; they can be coupled and / or stars or even functionalized with a coupling and / or star-forming or functionalization agent.

Preferably, polybutadienes are suitable and in particular those having a content of -1,2 units between 4% and 80% or those having a cis-1,4 content greater than 80%, polyisoprenes, butadiene copolymers- styrene and in particular those having a styrene content of between 5% and 50% by weight and more particularly between 20% and 40%, a content of -1,2 bonds in the butadiene part of between 4% and 65%, a content of trans-1,4 bonds of between 20% and 80%, butadiene-isoprene copolymers and in particular those having an isoprene content of between 5% and 90% by weight and a glass transition temperature (Tg, measured according to ASTM D3418-82) from -40 ° C to -80 ° C, isoprene-styrene copolymers and in particular those having a content of styrene between 5% and 50% by weight and a Tg between -25 ° C and -50 ° C. In the case of butadiene-styrene-isoprene copolymers, especially those having a styrene content of between 5% and 50% by weight and more particularly between 10%) and 40%), an isoprene content of between 15%) are suitable. and 60% by weight and more particularly between 10% and 50%, a butadiene content of between 5% and 50% by weight and more particularly between 20% and 40%, a content of -1.2 units of the butadiene part between 4% and 85%, ^r a content in trans units -1,4 of the butadienic part between 6% and 80%, a content of units -1,2 plus -3,4 of the isoprene part included between 5% and 70% and a content of trans units -1.4 of the isoprenic part of between 10% and 50%, and more generally any butadiene-styrene-isoprene copolymer having a Tg of between -20 ° C and -70 ° C.

In summary, in a particularly preferred manner, the diene elastomer of the composition in accordance with the invention is chosen from the group of highly unsaturated diene elastomers constituted by polybutadienes (BR), polyisoprenes (IR), natural rubber (NR) , butadiene copolymers, isoprene copolymers and mixtures of these elastomers. Such copolymers are more preferably chosen from the group consisting of butadiene-styrene copolymers (SBR), isoprene-butadiene copolymers (BIR), isoprene-styrene copolymers (SIR) and isoprene copolymers butadiene-styrene (SBIR).

The composition according to the invention is particularly intended for a tread for a tire, whether it is a new or used tire (in the case of retreading).

In the case of a tire for a passenger vehicle, the diene elastomer is for example an SBR, whether it is an SBR prepared in emulsion ("ESBR") or an SBR prepared in solution ("SSBR "), or of a blend (mixture) SBRBR, SBR / NR (or SBR / IR), or even BR / NR (or BR / IR). In the case of an SBR elastomer, use is in particular of an SBR having a styrene content of between 20% and 30%) by weight, a vinyl bond content of the butadiene part of between 15% and 65%, a content of trans-1,4 bonds between 15% and 75%> and a Tg between -20 ° C and -55 ° C. Such an SBR copolymer, preferably prepared in solution (SSBR), is optionally used in admixture with a polybutadiene (BR) preferably having more than 90% of cis-1,4 bonds.

In the case of a tire for a commercial vehicle, in particular for a heavy vehicle, the diene elastomer is in particular an isoprene elastomer; "Isoprene elastomer" means in a known manner an isoprene homopolymer or copolymer, in other words a diene elastomer chosen from the group consisting of natural rubber (NR), synthetic polyisoprenes (IR), different isoprene copolymers and mixtures of these elastomers. Among the isoprene copolymers, mention will be made in particular of isobutene-isoprene (butyl rubber - IIR), isoprene-styrene (SIR), isoprene-butadiene (BIR) or isoprene-butadiene-styrene copolymers (SBIR). This isoprene elastomer is preferably natural rubber or a synthetic cis-1,4 polyisoprene; among these synthetic polyisoprenes, polyisoprenes are preferably used having a rate (mol%) of cis-1,4 bonds greater than 90%, more preferably still greater than 98%. For such pneumatic for utility vehicle, the diene elastomer can also consist, in whole or in part, of another highly unsaturated elastomer such as, for example, an SBR elastomer.

According to another advantageous embodiment of the invention, in particular when it is intended for a tire sidewall, the composition according to the invention may contain at least one essentially saturated diene elastomer, in particular at least one EPDM copolymer, which this copolymer is for example used or not in admixture with one or more of the highly unsaturated diene elastomers mentioned above.

The compositions of the invention may contain a single diene elastomer or a mixture of several diene elastomers, the diene elastomer (s) being able to be used in combination with any type of synthetic elastomer other than diene, or even with polymers other than elastomers, for example thermoplastic polymers.

11-2. Reinforcing filler

The white or inorganic filler used as reinforcing filler can constitute all or only part of the total reinforcing filler, in the latter case associated for example with carbon black.

Preferably, in the rubber compositions according to the invention, the reinforcing inorganic filler constitutes the majority, that is to say more than 50% by weight of the total reinforcing filler, more preferably more than 80% by weight of this total reinforcing load.

In the present application, the term “reinforcing inorganic filler” is understood, in known manner, an inorganic or mineral filler, whatever its color and its origin (natural or synthetic), also called "white" filler or sometimes "clear" filler "in contrast to carbon black, this inorganic filler being capable of reinforcing on its own, without other means than an intermediate coupling agent, a rubber composition intended for the manufacture of tires, in other words capable of replacing, in its reinforcing function, a conventional charge of pneumatic grade carbon black.

Preferably, the reinforcing inorganic filler is a mineral filler of the silica (SiO ₂ ) or alumina (AI ₂ O ₃ ) type, or a mixture of these two fillers.

The silica used can be any reinforcing silica known to those skilled in the art, in particular any precipitated or pyrogenic silica having a BET surface as well as a CTAB specific surface, both less than 450 m ² / g, preferably from 30 to 400 m ² / g. Highly dispersible precipitated silicas (called "HDS") are preferred, in particular when the invention is implemented for the manufacture of tires having a low rolling resistance; the term “highly dispersible silica” is understood to mean, in known manner, any silica having a significant ability to disaggregate and to disperse in an elastomeric matrix, observable in known manner by electron or optical microscopy, on fine cuts. As nonlimiting examples of such preferred highly dispersible silicas, mention may be made of Perkasil KS 430 silica from Akzo, BV3380 silica from Degussa, Zeosil 1165 MP and 1115 MP silica from Rhodia, Hi-Silica 2000 from the company PPG, the silicas Zeopol 8741 or 8745 from the company Huber, precipitated silicas treated such as for example the silicas "doped" with aluminum described in application EP-A-0 735 088.

The reinforcing alumina preferably used is a highly dispersible alumina having a BET surface ranging from 30 to 400 m ² / g, more preferably between 60 and 250 m ² / g, an average particle size at most equal to 500 nm, more preferably at most equal to 200 nm, as described in the above-mentioned application EP-A-0 810 258. As nonlimiting examples of such reinforcing aluminas, mention may be made in particular of "Baikalox""A125","CR125","D65CR" aluminas from the company Baikowski.

The physical state in which the reinforcing inorganic filler is present is immaterial, whether in the form of powder, microbeads, granules, pellets, beads or any other densified form. Of course, the term reinforcing inorganic filler is also understood to mean mixtures of various reinforcing inorganic fillers, in particular of highly dispersible silicas and / or aluminas as described above.

When the rubber compositions of the invention are used as tire treads, the reinforcing inorganic filler used, in particular if it is silica, preferably has a BET surface area of between 60 and 250 m ² / g , more preferably between 80 and 200 m ² / g.

The reinforcing inorganic filler can also be used in cutting (mixing) with carbon black. As carbon blacks, all carbon blacks are suitable, in particular blacks of the HAF, ISAF, SAF type, conventionally used in tires and particularly in tire treads. By way of nonlimiting examples of such blacks, mention may be made of blacks NI 15, N134, N234, N339, N347, N375.

The quantity of carbon black present in the total reinforcing filler can vary within wide limits, this quantity of carbon black preferably being less than the quantity of inorganic reinforcing filler present in the rubber composition. "

In the compositions in accordance with the invention, in particular in the treads incorporating such compositions, it is preferred to use, in small proportion, a carbon black in association with the reinforcing inorganic filler, at a preferential rate of between 2 and 20 phr, more preferably included in a range of 5 to 15 phr. In the ranges indicated, we benefit from the coloring (black pigmentation agent) and anti-UV properties of carbon blacks, without, moreover, penalizing the typical performances provided by the reinforcing inorganic filler, namely low hysteresis (reduced rolling resistance) and high grip on wet, snowy or icy ground. Preferably, the rate of total reinforcing filler (reinforcing inorganic filler plus carbon black if applicable) is between 10 and 200 phr, more preferably between 20 and 150 phr, the optimum being different depending on the intended applications; in fact, the level of reinforcement expected on a bicycle tire, for example, is in known manner significantly lower than that required on a tire capable of traveling at high speed in a sustained manner, for example a motorcycle tire, a tire for a passenger vehicle or for a utility vehicle such as Truck.

For the treads of such tires capable of running at high speed, the quantity of reinforcing inorganic filler, in particular if it is silica, is preferably between 30 and 140 phr, more preferably within a range of 50 to 120 pce.

In the present description, the BET specific surface is determined in a known manner by gas adsorption using the Brunauer-Emmett-Teller method described in "The Journal of the American Chemical Society" Vol. 60, page 309, February 1938, more precisely according to French standard NF ISO 9277 of December 1996 [multi-point volumetric method (5 points) - gas: nitrogen - degassing: hour at 160 ° C - relative pressure range p / in: 0.05 at 0.17]. The CTAB specific surface is the external surface determined according to French standard NF T 45-007 of November 1987 (method B).

Finally, those skilled in the art will understand that, as an equivalent charge of the reinforcing inorganic filler described in this paragraph, a reinforcing organic filler could be used, in particular a carbon black, covered at least in part with an inorganic layer. , for example silica, requiring the use of a coupling agent to establish the connection with the elastomer.

II-3. Coupling agent (organosilicon compound)

As explained above, a coupling agent (inorganic filler / diene elastomer) is, in known manner, carrying at least two functions, denoted here "Y" and "X", allowing it to be able to be grafted, on the one hand on the reinforcing inorganic filler by means of the function Y, for example a hydroxyl group or a hydrolyzable group, on the other hand on the diene elastomer by means of the function X, for example a sulfur function.

An essential characteristic of the organosilicon compound used as coupling agent in the compositions in accordance with the invention is that this compound can be grafted onto the elastomer by means of a sulfur group with cyclic polysulfide function, of formula:

(I) s If - (Z— S) „- A - Q

in which:

Z is a group of. divalent, linear or branched bond, making it possible to link the cyclic polysulfide group to a silicon atom of the organosilicon compound; rp is 0, 1 or 2; A represents a valence bond or a divalent saturated aléghatic hydrocarbon group; Q represents the group of formula:

in which:

- the symbol B denotes a saturated monocyclic or polycyclic C ₅ -C ₁₈ carbocycle in which one or more of the carbon atoms can be replaced by an oxygen or sulfur atom, the two ends of the -Sx- bridge being linked to two contiguous carbon atoms of said carbocycle B; the symbols = O denote an oxygen atom which can constitute, with one of the S atoms of the -Sx- bridge, a sulfinyl group> S = O; x is a whole or fractional number ranging from 2 to 6; q represents a number equal to 0 or 1;

In formula (I) above, p is preferably equal to 0 or 1, it being understood that if p is equal to zero then q is preferably equal to 1. In this formula (I) and in the description which follows , p is chosen more preferably equal to 1.

According to the invention, in the case for example where x = 3 and q = 1, Q represents the group of formula:

which then designates one of the following three radicals, or a mixture of these in any proportions:

It is recalled here that by “organosilicon” (or “organosilicon”) compound must be understood, by definition, an organic compound containing at least one Carbon-Silicon bond.

In formula (I) above, in the case where the route of synthesis of the compound considered can give rise to only one kind of polysulfide group, the number x is then an integer ranging from 2 to 6, of preferably ranging from 2 to 4. However, those skilled in the art will readily understand that this number can be a fractional average number when the synthetic route gives rise to a mixture of polysulphurized groups each having a different number of sulfur atoms; in such a case, the cyclic polysulphide group synthesized is in fact constituted a distribution of polysulphides, ranging from disulphide S ₂ to heavier polysulphides, centered on an average value (in moles) of "x" (fractional number) ranging from 2 to 6, more preferably from 2 to 4.

The divalent group Z is preferably chosen from aliphatic, saturated or unsaturated hydrocarbon groups, carbocyclic, saturated, unsaturated and / and aromatic, monocyclic or polycyclic groups, and groups having an aliphatic, saturated or unsaturated hydrocarbon part and a carbocyclic part. as defined above.

In the present description, the term “aliphatic hydrocarbon group” means a linear or branched group, preferably comprising from 1 to 25 carbon atoms, optionally substituted. Advantageously, said aliphatic hydrocarbon group comprises from 1 to 12 carbon atoms, better still from 1 to 8 carbon atoms, more preferably still from 1 to 6 carbon atoms.

As saturated aliphatic hydrocarbon groups, mention may be made of alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, t-butyl, pentyl, isopentyl, neopentyl, 2-methylbutyl, 1 -ethylpropyl, hexyl, isohexyl, neohexyl, 1-methylpentyl, 3-methylpentyl, 1, 1-dimethylbutyl, 1,3-dimethylbutyl, 2-ethylbutyl, 1-methyl-1-ethylpropyl, heptyl, 1-methylhexyl, 1 -propylbutyl, 4,4-dimethylpentyl, octyl, 1-methylheptyl, 2-ethylhexyl, 5,5-dimethylhexyl, nonyl, decyl, 1-methylnonyl, 3,7-dimethyloctyl and 7,7-dimethyloctyl.

The unsaturated aliphatic hydrocarbon groups which can be used comprise one or more unsaturations, preferably one, two or three unsaturations of ethylenic type (double bond) and / or acetylenic type (triple bond). Examples are the alkenyl or alkynyl groups derived from the alkyl groups defined above by the removal of two or more hydrogen atoms. Preferably, the unsaturated aliphatic hydrocarbon groups comprise a single unsaturation.

By carbocyclic radical is meant a monocyclic or polycyclic radical, optionally substituted, preferably C ₃ -C ₅ o. Advantageously, it is a C ₃ -Cι ₈ radical, preferably mono-, bi- or tricyclic. When the carbocyclic radical comprises more than one cyclic nucleus (in the case of polycyclic carbocycles), the cyclic nuclei are condensed two by two. Two condensed nuclei can be orthocondensed or pericondensed. The carbocyclic radical can comprise, unless otherwise indicated, a saturated part and / or an aromatic part and / or an unsaturated part.

Examples of saturated carbocyclic radicals are cycloalkyl groups. Preferably, the cycloalkyl groups are C ₃ -C _{8 8} , better still C ₅ -C ₁₀ . Mention may in particular be made of the cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, adamantyl or norbornyl radicals.

The unsaturated carbocycle or any unsaturated part of the carbocyclic type has one or more ethylenic unsaturation, preferably one, two or three. It comprises advantageously from 6 to 50 carbon atoms, better still from 6 to 20, for example from 6 to 18 carbon atoms.

Examples of unsaturated carbocycles are C ₆ -C ₁₀ cycloalkenyl groups. Examples of aromatic carbocyclic radicals are the C ₆ -C ₁₈ aryl groups and in particular phenyl, naphthyl, anthryl and phenanthryl.

A group having both an aliphatic hydrocarbon part and a carbocyclic part as defined above is, for example, an arylalkyl group such as benzyl, or an alkylaryl group such as tolyl.

The substituents of the aliphatic hydrocarbon groups or parts and of the carbocyclic groups or parts are, for example, alkoxy groups in which the alkyl part is preferably as defined above.

By hydrolysable monovalent group which has been mentioned above with regard to the Y function, is meant groups such as, for example: halogen atoms, in particular chlorine; the groups -OR ¹ and -O-CO-R ¹ where R ¹ is chosen from the group consisting of aliphatic, saturated or unsaturated hydrocarbon groups, carbocyclic, saturated, unsaturated and / or aromatic, monocyclic or polycyclic groups, groups having an aliphatic, saturated or unsaturated hydrocarbon part and a carbocyclic part as defined above, R ¹ possibly being halogenated and / or substituted by one or more alkoxyl groups; the groups -ON = CR ² R ³ in which R ² and R ³ independently take any of the meanings given above for R ¹ , R ² and R ^{3 which} may be. halogens or / and optionally substituted by one or more alkoxyl groups; the groups - O-NR ² R ³ in which R ² and R ³ are as defined above.

Advantageously, such a hydrolysable monovalent group is an alkoxyl radical, linear or branched, C _j -C ₈ optionally halogenated and / or optionally substituted by one or more (C ₁ -C ₈ ) alkoxy; C ₂ -C ₉ acyloxy optionally halogenated or optionally substituted by one or more (C _j -C ₈ ) alkoxy; C ₅ -C ₁₀ cycloalkyloxy; or C ₆ -C ₁₈ aryloxy. By way of example, the hydrolyzable group is methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, methoxymethoxy, ethoxyethoxy, methoxyethoxy, β-chloropropoxy or β-chloroethoxy or, although still acetoxy.

Group Z preferably comprises from 1 to 18 carbon atoms, it more preferably represents an alkylene chain, a saturated cycloalkylene group, an arylene group, or a divalent group consisting of a combination of at least two of these groups. It is more preferably selected from alkylenes and Ci-Cjg arylene C ₆ -C _2; it can be substituted or interrupted by one or more heteroatoms, chosen in particular from S, O and. N. Even more preferably, Z is a Cι-C ₈ alkylene, better a C alkylene _! -C ₄ , in particular methylene, ethylene or propylene, more particularly propylene. Thus, according to a preferred embodiment of the invention, the cyclic polysulphide group corresponds to formula (I) in which at least one, preferably all of the following characteristics is verified:

Z represents a Cι ~ C ₁₈ alkylene or a C ₆ -Cι arylene; p is 0 or 1;

A represents a valence bond or an alkylene chain in -Cs;

B is chosen from a C ₅ -C ₆ monocyclic saturated aliphatic carbocycle and a C ₅ -Cι ₈ polycyclic saturated aliphatic carbocycle composed of two-by-two condensed monocyclic rings, at least one of which is a monocyclic ring

C5-C6; x is a whole or fractional number ranging from 2 to 4; the -Sx- chain, oxidized or not, is linked to a C ₅ -C ₆ monocyclic ring representing B or forming part of B;

According to a more preferred embodiment of the invention, the group equipped with a cyclic polysulfide corresponds to formula (I) in which:

Z represents a Cι-C ₈ alkylene; p is 0 or 1;

A represents a valence bond or a C ₁ -C alkylene chain; x is a number equal to 3;

Q is chosen from the group formed by the remainders (Q-1) to (Q-5) below:

(Ql) (Q2) (Q3)

(Q4) (Q5)

where R represents a hydrogen atom or a C ₁ -C ₄ alkyl group, and q represents 0 or 1.

According to an even more preferred embodiment of the invention, the cyclic polysulfide group corresponds to formula (I) in which at least one, even more preferably all of the following characteristics is verified:

Z is chosen from methylene, ethylene and propylene; p is 0 or 1;

A represents a valential bond or a divalent methylene or ethylene radical; x is a number equal to 3;

Q is chosen from the group formed by the particular remains (Q-6) and (Q-7) below:

(Q6) (Q7)

where q is 0 or 1.

A person skilled in the art will know how to adapt the nature of the function Y to the particular organosilicon compound considered on which the cyclic polysulphide group is grafted, this function Y possibly being different, for example a hydroxyl or hydrolyzable group, depending on the type of organosilicon compound considered, in particular a polyfunctional silane or polysiloxane.

Those skilled in the art will understand that by the expression "polyfunctional silane" is meant a silane carrying on the one hand a function Y consisting of one, two or three hydroxyl group (s) or monovalent group (s) ( s) hydrolysable (s) linked (s) to a silicon atom, and on the other hand of a function X consisting of a cyclic polysulfide group of formula (I). Those skilled in the art will also understand that, by the expression "polyfunctional polysiloxane", is meant a polysiloxane carrying, in the chain and / or at the chain end (s), as function Y, of at least one motif. siloxyl equipped with one, two or three OH group (s) or monovalent group (s) hydrolysable, and, as function X, at least one siloxyl unit equipped with a cyclic polysulfide group of formula (I).

Without this embodiment being limiting, the organosilicon compound of formula (I) is preferably a silane compound carrying, as function Y, one or more (maximum equal to 3) groups (OR) attached to an atom of Silicon, R representing hydrogen or a monovalent, linear or branched hydrocarbon group (in particular alkyl).

Thus, as organosilicon compound which is particularly suitable for the invention, a cyclic silane-polysulphide corresponding to the general formula can be used most preferably:

(II) (R ⁵ O) _a R ⁴ ₍₃ - _a) Si - (Z - S) _p - A - Q

in which:

R ⁴ represents a monovalent hydrocarbon group; - R ⁵ represents hydrogen or a monovalent hydrocarbon group, identical to or different from R ⁴ ; a is an integer equal to 1, 2 or 3; Z, p, A and Q have the meanings and values (main or preferential) given above, p being more preferably equal to 1.

Those skilled in the art will readily understand that such a bifunctional organosilicon compound of formula (II) comprises a (first) "Y" function [symbolized by the 1 to 3 groups (OR ⁵ ) attached to the silicon atom] connected to the cyclic polysulphide functional group of formula (I) [(second) function "X"].

The radicals R ⁴ and R ⁵ , which are identical or different, are hydrocarbon groups chosen in particular from aliphatic, saturated or unsaturated hydrocarbon groups, carbocyclic, saturated, unsaturated or / and aromatic, monocyclic or polycyclic groups, and groups having a aliphatic hydrocarbon part, saturated or unsaturated, and a carbocyclic part as defined above, preferably comprising from 1 to 18 carbon atoms, these various groups being able to be substituted or unsubstituted. 15

The radicals R ⁴ , identical or different if there are more than one, preferably represent an alkyl, a cycloalkyl or an aryl. They are more preferably chosen from the group consisting of Cι-C ₈ alkyls, C -Cιo cycloalkyls (in particular cyclohexyl) and phenyl. Even more preferably, R is chosen from the group consisting of Cι-C ₆ alkyls 20 (in particular methyl, ethyl, propyl, isopropyl).

The radicals R ⁵ , identical or different if there are more than one, preferably represent an alkyl, a cycloalkyl, an acyl or an aryl. They are more preferably chosen from the group consisting of Cj-C ₈ alkyls, optionally halogenated and / or optionally

25 substituted by one or more (C ₂ -C ₈ ) alkoxy, C ₂ -C acyls, optionally halogenated and / or optionally substituted by one or more (C ₂ -Cg) alkoxy, Cs-Cio cycloalkyls and aryls in C ₆ -Cι ₈ . Even more preferably, R ⁵ is chosen from the group consisting of Cι-C ₈ alkyls (in particular methyl, ethyl, n-propyl, isopropyl, n-butyl, β-cloropropyl, β-cloroethyl), optionally substituted by one or several (C -C ₈ ) alkoxy

30 (in particular methoxy, ethoxy, propoxy, isopropoxy), C ₅ -C ₁₀ cycloalkyls and phenyl.

According to the best known embodiment, R ⁴ and R ⁵ , identical or different, are both chosen (if a ≠ 3) from C ₁ -C ₄ alkyls, in particular from methyl and ethyl.

35 As more preferred organosilicon compounds which can be used in the compositions of the invention, mention will be made in particular of the silanes-polysulfide of formula (II) in which the group Z represents a Cι-C ₄ alkylene, in particular methylene, ethylene or propylene ( more preferably still propylene), the radicals R ⁴ and R ⁵ , which are identical or different, more preferably representing a C 1 -C 4 alkyl, in particular methyl or

W ethyl, and more particularly, among these compounds, the silanes for which x is equal to 3.

Thus, among these more preferred compounds of formula (II), mention will be made more particularly. alkoxysilanes-polysulfide in which:

5 - - R ⁴ and R ⁵ are each selected from the group consisting of -C ₆ alkyls; Z is chosen from Cι-C ₄ alkylene; p is equal to 0 or 1, more preferably equal to 1; A represents a valence bond or a C1-C8 alkylene chain;

B is chosen from a C ₅ -C ₆ monocyclic saturated aliphatic carbocycle and a C ₅ -Cι ₈ polycyclic saturated aliphatic carbocycle composed of two-by-two condensed monocyclic rings, at least one of which is a C ₅ -C ₆ monocyclic ring; x is a whole or fractional number ranging from 2 to 4; the -Sx- chain, oxidized or not, is linked to a C ₅ -C ₆ monocyclic ring representing B or forming part of B.

Even more preferably, the alkoxysilanes-polysulfide of formula (II) will be mentioned in which:

- R ⁴ and R ⁵ are both chosen from methyl, ethyl, propyl, isopropyl;

Z is chosen from methylene, ethylene and propylene; p is equal to 0 or 1, more preferably equal to 1;

A represents a valence bond or a Cι-C ₄ alkylene chain; x equal to 3; - Q is chosen from the group formed by the residues (Ql) to (Q-5) where R ⁵ represents a hydrogen atom or a C1-C4 alkyl, and q represents 0 or 1, q being more preferably chosen equal to 1 when p is equal to 0.

Thus, by way of a particularly preferred embodiment of the invention, an alkoxysilane-polysulfide of formula (II) is used in which:

R ⁴ and R ⁵ are chosen from methyl and ethyl; Z is propylene; p is equal to 0 or 1, more preferably equal to 1; - A represents a valential bond or a divalent methylene or ethylene radical; x equal to 3;

Q is chosen from the group formed by the particular residues (Q-6) and (Q-7) in which q is equal to 0 or 1, q being more preferably chosen equal to 1 when p is equal to 0.

such as, for example, silanes (oxidized or not oxidized polysulphide cycle) of particular formulas:

( ^Q -l)

(II-2)

(II-3)

where T ¹ is chosen from methyl and ethyl; T ² is chosen from methoxy and ethoxy.

The above polyfunctional coupling agents, bearing a cyclic polysulphide group, have shown very good reactivity with respect to the diene elastomers used in rubber compositions for tires, and have been found to be sufficiently effective on their own for the coupling of such elastomers and a reinforcing inorganic filler such as silica. Without this being limiting, they can advantageously constitute the only coupling agent present in the rubber compositions of the invention.

Taking into account the quantities expressed above, in general, the content of coupling agent will preferably be greater than 1 phr, more preferably between 2 and 20 phr. Below the minima indicated, the effect is likely to be insufficient, while beyond the recommended maximum, there is generally no longer any improvement in coupling, while the costs of the composition increase; for these various reasons, this content of coupling agent is still more preferably between 3 and 15 phr.

Those skilled in the art will be able to adjust this content of coupling agent as a function of the intended application, for example of the part of the tire for which the composition of the invention is intended, of the nature of the diene elastomer, of the amount of reinforcing inorganic filler used and the nature of the organosilicon compound considered.

Of course, in order to reduce the costs of the rubber compositions, it is desirable to use as little as possible, that is to say the amount necessary for sufficient coupling between the diene elastomer and the reinforcing inorganic filler. Its effectiveness makes it possible, in a large number of cases, to use the coupling agent at a preferential rate representing between 0.5% and 20% by weight relative to the amount of reinforcing inorganic filler; rates below 15% are more particularly preferred.

Finally, it will be noted that the organosilicon compound described above could be grafted beforehand (via the "Y" function) onto the reinforcing inorganic filler, the filler thus "precoupled" possibly being subsequently linked to the diene elastomer, via the free function "X".

II-4. Synthesis of the coupling agent (organosilicon compound)

By way of example, organosilicon compounds as described above can be prepared according to the preferred synthetic routes indicated below. The polyfunctional silanes of formula (II) where, for example, x = 3 and the polysulfide chain is oxidized, are prepared by oxidation of the corresponding compounds of formula (III):

(R ⁵ O) _a (R ⁴ ) _3-a Si - (Z - S) _p - A - Q (III),

Q then having the formula:

and R ⁴ , R ⁵ , a, Z, p, A and B having the definitions given above.

To do this, an organic peracid will preferably be chosen as the oxidizing agent. Examples of the best known peracids are peracetic acid, perbenzoic acid, and metachloroperbenzoic acid. Another preferred type of oxidizing agent is dimehyldioxyrane (DMD).

The oxidation is generally carried out in a solvent capable of dissolving the compound of formula (III) at a temperature ranging from -78 ° C to 10 ° C. When the oxidizing agent is a peracid, the temperature is suitably maintained between -20 ° C and 10 ° C, preferably between -5 ° C and + 5 ° C. When the oxidizing agent is DMD, a temperature of -78 ° C to -50 ° C is preferable.

A general method for preparing the compounds of formula (III) consists in reacting elemental sulfur with the corresponding compound of formula (IV):

(R ⁵ O) _a (R ⁴ ) ₃ .a Si - (Z - S) _p - A - Qo (IV)

Qo then having the formula:

and R ⁴ , R ⁵ , a, Z, p and A being such that - described above; Qo represents a carboxyl corresponding to B but comprising an ethylenic double bond, it being understood that none of the sp ₂ carbons of this double bond carries the divalent group A.

Suitable reaction conditions are in particular: a strongly polar aprotic solvent such as in particular an amide (and for example dimethylacetamide, formamide, dimethylformamide); an elevated temperature between 50 ° C and 200 ° C (and preferably between 90 ° C and 130 ° C); the presence of an organic base such as in particular an amine in the reaction medium.

Examples of amines which can be used are diethylamine, pyridine, 4-dimethylaminopyridine, 2,6-di-tertbutylpyridine, 1,8-diazabicyclo [5.4.0] -undec-7-ene (DBU), 1,5-diazabicyclo [4.3.0] non-5-ene (DBN), 1,4-diazabicyclo [2.2.2] octane (DABCO or triethylenediamine) and ammonia. Diethylamine and ammonia are preferred.

It is preferred to use dimethylformamide as the solvent.

The amount of sulfur required will be readily determined by those skilled in the art.

The preparation of the compounds of formula (IV) for which B ° represents, for example, a norbornene ring or includes such a nucleus is illustrated just below.

It can in particular take place by addition of Diels-Alder between a cyclopentadiene or a dicyclopentadiene and an ethylenic compound of formula (V):

(R ⁵ O) _a (R ⁴ ) ₃ . _a Si - (Z - S) _p - A - CH = CH ₂ (V),

in which R ⁵ , R ⁴ , a, Z, p and A are as defined above. This reaction is particularly appropriate in the case where p = 0 and A represents a valential bond.

The addition reaction of Diels-Alder reaction is a known reaction which can be implemented, in this case, by mixing the reactants at a temperature ranging from 75 to 225 ° C, preferably from 100 to 200 ° C. ^{' •}

As a variant, when p = 0 and A represents a valential bond, it is possible to prepare the compound (IV), where B ° has a general definition, by addition reaction between a silylated derivative of formula (VI):

(R ⁵ O) _a (R ⁴ ) _3-a Si - H (VI),

, in which R ⁵ , R ⁴ and a are as defined above with the appropriate compound of formula _. (VII):

in which B 'corresponds to B ° but also comprises a second endocyclic ethylenic double bond between the carbon bearing A in the targeted compound and a carbon adjacent thereto. Examples of such molecules B 'are in particular:

these cycles being optionally substituted as indicated above in the case of the general definition of B and that of saturated mono- or polycyclic carbocycles. The adjacent carbon can be exocyclic and belong to a substituent carried by the B 'ring. Examples of such molecules B 'are in particular:

In the case of these examples of molecules B ', we are led to a compound of formula (IV) where p = 0 and A is a divalent radical -CH ₂ - or -CH (CH ₃ ) -.

In the case where A represents an aliphatic hydrocarbon chain having 2 or more than 2 carbon atoms and p represents 0, the compound of formula (IV) can be prepared by addition of a compound (VIII):

CH ₂ = CH ~ A'— (β ° |

where B ° is as defined above and where CH = CH-A'- corresponds to the aliphatic chain -A- as defined above, on the silane of formula (VI) defined above.

The reaction conditions for the addition of the compound (VI) to the compound (VII) or to the compound (VIII) are in particular the use of a platinum-based catalyst. A suitable catalyst is in particular platinum deposited on alumina or on animal carbon, chloroplatinic acid, complexes of platinum with ligands of olefin, nitrile, amino and / or phosphine type. The catalyst is normally present in the reaction medium at a rate of 10 to 200 ppm of platinum metal relative to the total weight of the reactants.

The reaction can be carried out in the presence of a solvent or in the absence of a solvent. Suitable solvents are in particular hydrocarbons, preferably aromatic hydrocarbons, alcohols and ethers. The reaction temperature is advantageously fixed between room temperature (20-25 ° C) and 150 ° C.

The Diels-Alder reaction and the addition reaction in the presence of platinum are more precisely described in US-A-4,100,172.

When p = 1 and A represents a valence bond, the compounds of formula (IV) can be prepared by adding a thiol of formula (IX):

(R ⁵ O) _a (R ⁴ ) ₃ . _a Si - Z - S - H (IX),

on a compound of formula (VII) as defined above which is the carbocycle B 'comprising two endocyclic ethylenic double bonds, one of which between the carbon bearing S, in the targeted compound of formula (IV), and an adjacent endocyclic carbon . The presence of a radical reaction initiator is necessary in the reaction medium. Among these, mention may be made of azobisisobutyronitrile (AIBN) and peroxides such as tert-butyl peroxide. AIBN is preferred.

The solvent is preferably a polar aprotic solvent such as in particular a nitrile and more particularly acetonitrile.

More generally, the operating conditions for this reaction are defined in B. Boutevin et al., Journal of Fluorine Chemistry, 1986, 31, 437-450.

When p = 1 and A represents a hydrocarbon chain, the compounds of formula (TV) for which B represents for example a norbornene nucleus can be prepared by Diels-Alder reaction between an optionally substituted cyclopentadiene or a dicyclopentadiene and a compound of formula (X):

(R ⁵ O) _a (R ⁴ ) ₃ -aSi - Z - S - A "'- CH = CH ₂ (X),

in which R ⁵ , R ⁴ , a and Z are as defined above and -A "-CH ₂ = CH ₂ corresponds to the chain -A- of the compound of formula (IV) targeted.

This Diels-Alder reaction is carried out in a manner known per se, as described above, by heating the reagents to a temperature ranging from 75 ° C to 225 ° C, preferably from 100 ° C to 200 ° C .

II-5. Miscellaneous additives

Of course, the rubber compositions according to the invention also comprise all or part of the additives usually used in diene rubber compositions intended for the. manufacture of tires, such as for example plasticizers, extension oils, protective agents such as anti-ozone waxes, chemical anti-ozonants, anti-oxidants, anti-fatigue agents, adhesion promoters, activators of coupling as described for example in applications WO00 / 05300 and WO00 / 05301, reinforcing resins as described in O02 / 10269, a crosslinking system based either on sulfur or on sulfur and / or peroxide donors and / or bismaleimides, vulcanization accelerators, vulcanization activators, etc. The reinforcing inorganic filler can also be associated, if necessary, with a conventional white filler with little or no reinforcing, for example particles of clays, bentonite, talc, chalk, kaolin.

The rubber compositions in accordance with the invention may also contain, in addition to the organosilicon compounds described above, agents for recovery of the reinforcing inorganic filler, comprising for example the only function Y, or more generally agents for assisting in setting implemented in known manner, thanks to an improvement in the dispersion of the inorganic filler in the rubber matrix and to a lowering of the viscosity of the compositions, of improving their ability to be used in the raw state, these agents being for example alkylalkoxysilanes (in particular alkyltriethoxysilanes), polyols, polyethers (for example polyethylene glycols), primary, secondary or tertiary amines (for example trialcanol-amines), hydroxylated or hydrolyzable polyorganosiloxanes, for example, ω-dihydroxy-polyorganosiloxanes (in particular α , ω-dihydroxy-polydimethylsiloxanes).

II-6. Preparation of rubber compositions

The compositions are produced in suitable mixers, using two successive preparation phases well known to those skilled in the art: a first working or thermo-mechanical kneading phase (sometimes called a "non-productive" phase) at high temperature, up to a maximum temperature (noted T _max ) of between 110 ° C and 190 ° C, preferably between 130 ° C and 180 ° C, followed by a second phase of mechanical work (sometimes referred to as the "productive" phase) at a lower temperature, typically less than 110 ° C, for example between 60 ° C and 100 ° C, finishing phase during which the crosslinking or vulcanization system is incorporated; such phases have been described for example in applications EP 501 227, EP 735 088, EP 810 258, EP 881 252, WO00 / 05300, WOOO / 05301 or WO02 / 10269 mentioned above.

The manufacturing process according to the invention is characterized in that at least the reinforcing inorganic filler and the organosilicon compound are incorporated by kneading with the diene elastomer, during the first so-called non-productive phase, that is to say -to say that one introduces into the mixer and that one thermomechanically kneads, in one or more steps, at least these different basic constituents until reaching a maximum temperature of between 110 ° C and 190 ° C, preferably between 130 ° C and 180 ° C.

By way of example, the first (non-productive) phase is carried out in a single thermomechanical step during which all the necessary basic constituents are introduced into a suitable mixer such as a conventional internal mixer. (diene elastomer, reinforcing inorganic filler and organosilicon compound), then in a second step, for example after one to two minutes of mixing, any additional covering or implementing agents and other various additives, with the exception of the system vulcanization; when the apparent density of the reinforcing inorganic filler is low (general case of silicas), it may be advantageous to split its introduction into two or more parts. A second thermomechanical working step can be added to this internal mixer, after the mixture has fallen and intermediate cooling (cooling temperature preferably less than 100 ° C.), with the aim of subjecting the compositions to a complementary thermomechanical treatment, in particular to improve still the dispersion, in the elastomeric matrix, of the reinforcing inorganic filler and of its coupling agent. The total duration of the kneading, in this non-productive phase, is preferably between 2 and 10 minutes.

After the mixture thus obtained has cooled, the vulcanization system is then incorporated at low temperature, generally in an external mixer such as a cylinder mixer; the whole is then mixed (productive phase) for a few minutes, for example between 5 and 15 minutes. The final composition thus obtained is then calendered, for example in the form of a sheet, a plate or even extradited, for example to form a rubber profile used for the manufacture of semi-finished products such as treads, crown reinforcement plies, sidewalls, carcass reinforcement plies, heels, protectors, air chambers or waterproof inner liners for tubeless tires.

In summary, the process according to the invention for preparing an elastomeric composition which can be used for the manufacture of semi-finished products for tires, comprises the following stages:

incorporating into a diene elastomer, in a mixer, at least: a reinforcing inorganic filler; as coupling agent (inorganic filler / diene elastomer), an at least bifunctional organosilicon compound which can be grafted onto the elastomer by means of a sulfur group,

• by thermomechanically mixing everything, in one or more times, until reaching a maximum temperature between 1-10 ° C and 190 ° C; cool the assembly to a temperature below 100 ° C; • then incorporate a crosslinking or vulcanization system;

• mix everything up to a maximum temperature below 120 ° C,

said sulfur group being a group with a cyclic polysulfide function corresponding to the above formula (I), more particularly to formula (II) above.

Vulcanization (or baking) is carried out in a known manner at a temperature generally between 130 ° C and 200 ° C, preferably under pressure, for a sufficient time which can vary for example between 5 and 90 min depending in particular on the temperature curing, the vulcanization system adopted, the vulcanization kinetics of the composition considered or of the size of the tire.

The vulcanization system proper is preferably based on sulfur and a primary vulcanization accelerator, in particular an accelerator of the sulfenamide type. To this crosslinking system are added, incorporated during the first non-productive phase and / or during the productive phase, various known secondary accelerators or vulcanization activators such as zinc oxide, stearic acid, guanidine derivatives (especially diphenylguanidine), etc. Sulfur is used at a preferential rate of between 0.5 and 10 phr, more preferably of between 0.5 and 5.0 phr, for example between 0.5 and 3.0 phr when the invention is applied to a strip. tire bearing. The primary vulcanization accelerator is used at a preferential rate of between 0.5 and 10 phr, more preferably between 0.5 and 5.0 phr in particular when the invention applies to a tire tread.

The invention relates to the rubber compositions previously described both in the so-called "raw" state (ie, before baking) and in the so-called "baked" or vulcanized state (Le., After crosslinking or vulcanization). The compositions according to the invention can be used alone or as a blend (ie, as a mixture) with any other rubber composition which can be used for the manufacture of tires.

III. EXAMPLES OF EMBODIMENT OF THE INVENTION

III- 1. Synthesis of coupling agents

The coupling agents which can preferably be used in the compositions of the invention are cyclic silanes-polysulphide, more preferably alkoxysilanes corresponding to one of the aforementioned specific formulas (II), the synthetic methods of which are described below, by way of 'nonlimiting examples.

The melting points (Pf) expressed in degrees Celsius (° C) are determined by projection on a KOFFLER bench, previously calibrated (ΔT = ± 2 ° C). The boiling points (Eb _press i _on ) are given in millibars (mbar). The 250 MHz spectra of the proton ( ¹ H NMR) and of the carbon ( ¹³ C NMR) are recorded on a BRUCKER AC 250 spectrometer. The chemical shifts (δc and δh) are expressed in parts per million (ppm) relative to deuterochloroform ( CDC1 ₃ ). The coupling constants denoted J are expressed in Hz. The following abbreviations are used: s, singlet; yes, broad singlet; d, doublet; t, triplet; q, quadruplet; m, multiplet.

All manipulations with the ^compounds' organosilicon radicals comprising alkoxysilanes are made under inert atmosphere and under anhydrous conditions.

Example 1

This example describes the synthesis of 8-triethoxysilyl-4-oxo-3,4,5-trithiatricyclo [5.2.1.0] decane.

a) 8-triethoxysilyl-exo-3,4,5-trithiatricyclor5.2.1.Oldecane:

A mixture of sulfur 6.14 g (24 mmol of S ₈ ), 50 ml of DMF and 910 mg of triethylamine (9 mmol) is stirred for 30 minutes at room temperature. 2-Triethoxysilylbicyclo [2.2.1] hept-5-ene (60 mmol) is added and the mixture is then heated at 110 ° C. for 2 hours. The mixture is allowed to return to ambient temperature and the DMF is evaporated under reduced pressure. The product obtained is purified by distillation under reduced pressure.

Its formula below has been verified by spectral analysis (yield 85%; yellow oil appearance):

Eb _0j4 : 125 ° C 1 H NMR (CDC1 ₃ ) δ _H

0.75 (m, 1H); 1.23 (m, 9H); 1.35-1.45 (m, 2H); 1.60-1.75 (m, 2H);

2.45-2.55 (m, 2H); 3.66 (m 1H, CHS); 3.83 (m, 6H, OCH ₂ ); 3.96 (m 1H, CHS).

8.7 (CH); 18.2 (CH3); 29.2 (CH2); 41.1 (CH); 41.9 (CH); 46.5 (CH2);

58.6 (OCH ₂ ); 69.3 (CH-S); 72.8 (CH-S).

b) 8-triethoxysilyl-4-oxo-3,4,5-trithiatricyclor5.2.1.0] decane:

The method for preparing dimethyldioxyrane (DMD) is that presented in Chem. Ber. 1991, 124, 2377 by W. Adam et al.

Under an argon atmosphere, 111 ml of a 0.09 M solution of DMD in acetone is added dropwise to a solution of 10 mmol of the compound obtained in the preceding step in acetone cooled to -78 °. C. The reaction medium is stirred for one hour at this temperature and then the solvent is evaporated off under reduced pressure to give the thiosulfinate with a yield of 80%.

The compound obtained (crude yield 82%; orange oil appearance), as verified by spectral analysis, has the formula:

MM: 368 g mol ^"1 Mass spectrum, IE (70eV): m / z (%); 368 (4), 352 (45), 320 (68), 288 (100), 274 (40), 260 ( 20), 242 (26), 211 (12), 179 (9), 164 (50), 151 (10), 145 (55), 125 (36), 119 (70), 107 (60), 97 ( 60), 92 (80), 89 (65), 77 (58), 65 (60), 45 (75).

Example 2:

This example describes the synthesis of the sulfide of 8- (methyl-exo-3,4,5-trithiatricyclb [5.2.1.0] decyl and of 3'-trimethoxysilylpropyl).

a) 3-trimethoxysilylpropyl and prop-2-enyl sulfide:

A mixture of 19.6 g (0.1 mol) of 3-mercaptopropyltrimethoxysilane, 15.18 g (0.11 mol) of potassium carbonate in 250 ml of freshly distilled DMF is stirred for 30 minutes at room temperature. 13.31 g (0.11 mol) of allyl bromide are added dropwise and the mixture is then stirred for 24 hours at room temperature. Filtered on celite and then the DMF is evaporated under reduced pressure. The product is purified by vacuum distillation. _Is obtained (80% yield, colorless oil appearance, Eb _0d2 : 84 ° C) the intermediate compound of formula:

(CHgOfeSh

whose spectral analysis is as follows:

¹ H NMR (CDC1 ₃ ) δ _H

0.73 (t, 2H, Si-CH ₂ ); 1.65 (m, 2H, CH ₂ ); 2.46 (t, 2H, S-CH ₂ ); 3.08 (d, 2H, J = Hz, CH ₂ ); 3.55 (s, 9H, CH ₃ ); 5.09 (m, 2H, CH = CH ₂ ); 5.73 (m, 1H, CH = CH ₂ );

^{• 13} C NMR (CDC1 ₃ ) δ _c

8.5 (Si-CH; 22.6 (CH ₂ ); 33.6 (S-CH ₂ ); 34.6 (S-CH ₂ ); 50.5 (-OCH ₃ ); 116.6 (CH = CH ₂ ); 134.6 (CH = CH ₂ ).

b) sulfide of 3-trimethoxysilylpropyl and 5 '- (methylnorborn-2'-enyl):

A mixture of 11.81 g (50 mmol) of the compound obtained in the previous step and 66 g (250 mmol) of dicyclopentadiene is heated at 185 ° C for three hours. The reaction medium is allowed to return to ambient temperature and then the unreacted reagents are removed under reduced pressure and the substituted norbornene formed is distilled.

Yield: 50%) Eb _0; ι: 120 ° C Appearance: colorless oil

0.73 (t, 2H, Si-CH ₂ ); 1.25 (m, 1H); 1.40 (m, 1H); 1.64 (m, 4H); 1.91 (m, 1H); 2.28 (m, 2H);

2.53 (t, 2H, CH ₂ ); 2.78 (m, 1H); 2.89 (m, 1H); ); 5.97 (m, 1H, CH≈CH); 6.15 (m, 1H, CH = CH).

8.4 (Si-CH ₂ ); 22.9 (CH ₂ ); 32.7 (CH ₂ ); 35.3 (CH ₂ ); 37.0 (CH ₂ ); 38.8 (CH); 42.7 (CH); 45.3

(CH); 49.6 (CH ₂ ); 50.4 (-OCH ₃ ); 132.0 (CH = CH);

137.5 (CH = CH).

c) 8-methyl-exo-3A5-trithiatricvclo [5.2.1.0] decyl and 3'-trimethoxysilylpropyl sulfide:

The title compound is obtained by implementing a process identical to that of Example 1a), but starting from the compound obtained in the previous step.

Yield: 99% Appearance: oil 1 H NMR (CDC1 ₃ ) δ _H 0.75 (t, 2H, Si-CH ₂ ); 1.25 (m, 1H); 1.40 (m, 1H); 1.64 (m, 4H); 1.98 (m, 1H); 2.25 (m, 1H); 5 (s, 9H, CH ₃₀ ); 3.60 (m, 1H, CHS); 3.90 (m, 1H, CHS).

8.4 (Si-CH ₃ ); 22.9 (CH ₂ ); 33.1 (CH ₂ ); 34.8 (CH ₂ ); 35.3 (CH ₂ ); 38.5 (CH); 40.9 (CH); 44.0

(CH); 48.6 (CH ₂ ); 50.4 (-OCH3); 63.5 (CHS); 69.4 (CHS). IE mass spectrum (70eV): m / z (%): 398 (4), 333 (traces), 302 (traces), 294 (2), 270 (2), 256 (5), 229 (5), 204 (12), 197 (6),

179 (6), 163 (15), 140 (20), 131 (10), 121 (75), 106 (20), 91 (100), 86 (26), 79 (48), 66 (46), 59 (23)

31.

Example 3:

This example describes the synthesis of the sulfide of 8- (methyl-exo-3,4,5-trithiatricyclo [5.2.1.0] decyl and of 3'-triethoxysilylpropyl).

a) 3-triethoxysilylpropyl and prop-2-enyl sulfide:

The procedure is as indicated in Example 2a) above, starting from 0.1 mol of mercaptopropyltriethoxysilane. The intermediate compound of formula is obtained:

Yield: 79% Appearance: colorless oil Ebo.os: 99 ° C NMR Η CDCh) δ _H 0.72 (t, 2H, Si-CH ₂ ); 1.21 (t, 9H, CH ₃ ); 1.66 (m, 2H, CH ₂ ); 2.48 (t, 2H, S-CH ₂ ); 3.10 (d, 2H, (q, 6H, OCH ₂ ); 5.09 (m, 2H, CH = CH ₂ ); 5.78 (m, 1H, CH = CH ₂ ).

9.7 (Si-CH ₂ ); 18.3 (CH ₃ ); 22.8 (CH ₂ ); 33.8 (S-CH ₂ ); 34.6 (S-CH ₂ ); 58.4 (-OCH ₂ ); 116.6

(CH = CH2); 134.6 (CH = CH ₂ ).

b) 3-triethoxysilylpropyl and 5 '- (methylnorborn-2'-enyl) sulfide: The procedure is as indicated in Example 2b) above, starting from 50 mmol of the compound obtained at the end of the previous step. The compound of formula is obtained:

Yield: 50% Appearance: colorless oil Eb ₀ .ι: 155 ° C NMR Η (CDC1 ₃ ) δ _H

0.76 (t, 2H, Si-CH ₂ ); 1.23 (t, 9H, CH ₃ -CH ₂ ); 1.27 (m, 1H); 1.45 (m, 1H); 1.62 (m, 4H); 1.91 (m, 1H); 2.27 (m, 3H); 2.52 (t, 2H, CH ₂ ); 2.77 (m, 1H) 2.80 (m, 1H);

2.95 (t, 2H, S-CH ₂ ); 3.82 (q, 6H, CH ₃ -CH ₂ O); 5.96 (m, 1H, CH ^≈ CH); 6.15 (m, 1H, CH = CH). ¹³ C NMR (CDC1 ₃ ) δ _c

9.9 (Si-CH ₂ ); 18.3 (CH ₃ -CH ₂ ); 23.1 (CH ₂ ); 32.7 (CH ₂ ); 35.5 (CH ₂ ); 37.2 (CH ₂ ); 38.8 (CH); 42.7 (CH); 45.5 (CH); 49.6 (CH ₂ ); 58.4 (-OCH ₂ ); 132.1 (CH = CH); 137.6 (CH = CH). IR (KBr) cm ^"1 : 780, 920, 1085, 1110, 1450, 2400, 2825, 2840.

c) sulfide of 8- (methyl-exo-3A5-trithiatricyclo [5.2.1.0] decyl and of 3'-triethoxysilylpropyl):

The title compound is obtained by implementing a process identical to that of Example 1a) but starting from the compound obtained at the end of the preceding step:

Efficiency: 99%

Appearance: oil

¹ H NMR (CDC1 ₃ ) δ _H

0.75 (t, 2H, Si-CH ₂ ); 1.25 (m, 10H); 1.40 (m, 1H); 1.65 (m, 4H); 2.00 (m, 1H); 2.25 (m, 1H); 2.53 (m, 4H); 3.62 (m, 1H, CHS); 3.82 (q, 6H, CH ₂ 0) 3.93 (m, 1H, CHS).

¹³ C NMR (CDCI ₃ ) δ _c

9.6 (Si-CH ₂ ); 18.3 (CH ₃ ); 22.8 (CH ₂ ); 33.2 (CH ₂ ); 34.8 (CH ₂ ); 35.3 (CH ₂ ); 38.7 (CH); 41.1 (CH); 44.0 (CH); 48.7 (CH ₂ ); 58.5 (-OCH ₂ ); 63.5 (CHS); 69.4 (CHS).

III-2. Preparation of rubber compositions

The following tests are carried out as follows: the elastomer is introduced into an internal mixer, filled to 70%) and whose initial tank temperature is approximately 90 ° C. diene (or the mixture of diene elastomers, if applicable), the reinforcing filler, the coupling agent, then, after one to two minutes of kneading, the various other ingredients with the exception of the vulcanization system. A thermomechanical work (non-productive phase) is then carried out in two stages (total mixing time equal to approximately 7 min), until a maximum "fall" temperature of approximately 165 ° C. is reached. The mixture thus obtained is recovered, it is cooled and then the vulcanization system (sulfur and sulfenamide accelerator) is added on an external mixer (homo-finisher) at 30 ° C, mixing the whole (productive phase) for 3 to 4 minutes .

The compositions thus obtained are then calendered either in the form of plates (thickness of 2 to 3 mm) or of thin sheets of rubber for the measurement of their physical or mechanical properties, or in the form of profiles which can be used directly, after cutting and / or assembly to the desired dimensions, for example as semi-finished products for tires, in particular as tire treads.

In the following tests, the diene elastomer is an SBR / BR blend and the reinforcing inorganic filler (HDS silica) is used at a preferential rate comprised within a range of 50 to 120 phr.

III-3. Characterization of rubber compositions

The purpose of this test is to demonstrate the improved coupling performance (inorganic filler / diene elastomer) in a composition (C-2) in accordance with the invention, compared with a composition (Cl) of the prior art using a coupling agent. conventional :

composition C-1: conventional TESPT silane; composition C-2: silane-polysulfide synthesized in paragraph III-1 (example 3).

Recall that the TESPT is bis (3-triethoxysilylpropyl) tetrasulfide, of formula [(C ₂ H ₅ O) ₃ Si (CH ₂ ) ₃ S ₂ ] ₂ ; it is marketed for example by the company Degussa under the name Si69. The developed formula of TESPT is:

And

This formula is to be compared with that of the coupling agent synthesized above (Et = ethyl):

The two coupling agents are used at an isomolar rate in silicon, that is to say that whatever the composition is used, the same number of moles of functions Y (here Y = Si (OEt) s) reactive towards silica and its surface hydroxyl groups.

Relative to the weight of reinforcing inorganic filler, the level of coupling agent is in both cases less than 12 phr, which represents less than 15% by weight relative to the amount of reinforcing inorganic filler.

Tables 1 and 2 give the formulation of the two compositions (Table 1 - rate of the various products expressed in phr) as well as their properties before and after cooking (at the optimum cooking at 150 ° C.). The appended figure shows the evolution of the rheometric torque (in dN.m) as a function of time (in min), for a temperature of 150 ° C., the curves denoted Cl and C2 corresponding respectively to the compositions C-1 and C-2.

Examination of the various results in Table 2 shows, for the composition according to the invention C-2:

a higher vulcanization yield, as demonstrated by higher values of the maximum torque C _max and of (C _max - C _mm ); - faster vulcanization kinetics, illustrated both by a constant K of higher conversion speed, and by shorter times t „t ₉₉ , (t ₉ - 1,).

The rheometric curves of the appended figure confirm the superiority of the composition according to the invention (curve C2) in terms of a share of vulcanization kinetics (see slope K of the curve of increase in torque, after 8 to 10 min of cooking), on the other hand vulcanization yield (see maximum torque, for example after 20 min of cooking).

The tensile stress and elongation at break properties, measured after baking, are moreover identical between the control composition and that of the invention.

In conclusion, the coupling agent selected for the compositions in accordance with the invention gives the latter improved baking properties compared to those offered by the conventional TESPT, the coupling agent (inorganic filler / elastomer) which is the reference in the compositions. diene rubber reinforced with an inorganic filler such as a reinforcing silica.

The invention finds particularly advantageous applications in rubber compositions intended for the manufacture of tire treads having both a low rolling resistance and a high resistance to wear, in particular when these treads are intended tires for passenger vehicles, motorcycles or industrial vehicles of the Truck type. Table 1

(1) SBR with 59.5% of 1-2 polybutadiene units; 26.5% styrene; Tg = -29 ° C; 75 pce dry SBR extended with 28.1 pce of aromatic oil (a total of 103.1 pce);

(2) BR with 4.3% of 1 -2; 2.7% trans; 93% cis 1-4 (Tg ≈ - 104 ° C);

(3) silica type "HD" - "Zeosil 1165MP" from the company RHODIA in the form of microbeads (BET and CTAB: approximately 150-160 m ² / g);

(4) TESPT ("Si69" from DEGUSSA);

(5) silane cyclic polysulfide (see synthesis in III-1, example 3);

(6) diphenylguanidine ("Vulkacit D" from the company BAYER);

(7) N-cyclohexyl-2-benzothiazyl-sulfenamide ("Santocure CBS" from the company FLEXSYS).

Table 2

Claims

1. Elastomeric composition usable for the manufacture of tires, based on at least (i) a diene elastomer, (ii) an inorganic filler as a reinforcing filler and (iii), as a coupling agent (inorganic filler / diene elastomer), an organosilicon compound at least bifunctional graftable on the elastomer by means of a sulfur group with cyclic polysulfide function, of formula (I): (I) ≡ Si - (Z - S) _p - A - Q in which: Z is a divalent linking group, linear or branched, making it possible to link the cyclic polysulphide group to a silicon atom of the organosilicon compound; p is 0, 1 or 2; A represents a valence bond or a divalent saturated aléghatic hydrocarbon group; - Q represents the group of formula: in which: the symbol B denotes a saturated monocyclic or polycyclic Cs-Cis carbocycle in which one or more of the carbon atoms can be replaced by an oxygen or sulfur atom, the two ends of the -Sx- bridge being linked to two atoms contiguous carbon of said carbocycle B; the symbols = O denote an oxygen atom which can constitute, with one of the atoms of S of the Sx bridge, a sulfinyl group> S = O; x is a whole or fractional number ranging from 2 to 6; q represents a number equal to 0 or 1. 2. Composition according to claim 1, A representing a valence bond or an alkylene chain in Cι-C ₈ , preferably in Cj-C ₄ . 3. Composition according to claims 1 or 2, B representing a saturated C ₅ -C ₆ monocyclic aliphatic carbocycle or a saturated C ₅ -C ₁₈ polycyclic aliphatic carbocycle composed of two-by-two condensed monocyclic rings, at least one of which is a monocyclic ring is C ₅ -C ₆ . 4. Composition according to any one of claims 1 to 3, the -Sx- chain, oxidized or not, being linked to a C ₅ -C ₆ monocyclic ring representing B or forming part of B. 5. Composition according to any one of claims 1 to 4, x being included in a range from 2 to 4. 6. Composition according to any one of claims 1 to 5, Z representing a hydrocarbon group comprising from 1 to 18 carbon atoms and optionally one or more heteroatoms. 7. A composition according to claim 6, Z being chosen from alkylene en.Cι-C ₁₈ and arylene C ₆ -C] ₂ , 8. A composition according to claim 7, Z being chosen from Cι-C ₈ alkylene, preferably from methylene, ethylene and propylene. 9. Composition according to any one of claims 1 to 8, p being equal to 0 or 1, preferably equal to 1. 10. Composition according to any one of claims 1 to 9, the diene elastomer being chosen from the group consisting of polybutadienes, synthetic polyisoprenes, natural rubber, butadiene copolymers, isoprene copolymers and mixtures of these elastomers. 11. Composition according to any one of claims 1 to 10, the rate of reinforcing inorganic filler being between 10 and 200 phr (parts by weight percent of elastomer) and the rate of coupling agent between 1 and 20 phr . 12. Composition according to any one of claims 1 to 11, the organosilicon compound being a cyclic silane-polysulfide of formula: (II) (R ⁵ O) _a R ⁴ _(3-a) Si - (Z - S) _p - A - Q in which: R ⁴ represents a monovalent hydrocarbon group; R ⁵ represents hydrogen or a monovalent hydrocarbon group, identical to or different from R ⁴ ; a is an integer equal to 1, 2 or 3. 13. Composition according to claim 12, the group Z representing a C 1 -C alkylene and the radicals R ⁴ and R ⁵ , identical or different, a C ₁ -C ₆ alkyl. 14. Composition according to claim 13, Z being propylene, R ⁴ and R ⁵ , identical or different, being chosen from methyl and ethyl. 15. Composition according to any one of claims 1 to 14, x being equal to 3. 16. Composition according to any one of claims 12 to 14, Q being chosen from the group formed by the residues (Ql) to (Q-5) below: (Qi) (Q2) (Q3) (Q4) (Q5) where R ⁵ represents a hydrogen atom or a Cj-C alkyl group, and q represents 0 or 1. 17. Composition according to claim 16, Q being chosen from the group formed by the particular residues (Q-6) and (Q-7) below: (Q6) (Q7) 18. Composition according to any one of claims 1 to 17, the amount of coupling agent representing between 0.5%> and 20%> by weight relative to the amount of reinforcing inorganic filler. 19. Composition according to any one of claims 1 to 18, the reinforcing inorganic filler being predominantly silica. 20. Composition according to claim 19, the reinforcing inorganic filler forming the whole of the reinforcing filler. 21. Composition according to any one of claims 1 to 19, the reinforcing inorganic filler being used in admixture with carbon black. 22. Composition according to claim 21, the carbon black being present at a level of between 2 and 20 phr. 23. Composition according to any one of claims 10 to 22, the diene elastomer being a butadiene-styrene copolymer (SBR) having a styrene content of between 20% and 30% by weight, a content of vinyl bonds of the butadiene part included between 15% and 65%, a content of trans-1,4 bonds between 20% and 75% o and a glass transition temperature between -20 ° C and -55 ° C. 24. The composition of claim 23, the SBR being an SBR prepared in solution (SSBR), preferably used in admixture with a polybutadiene. 25. The composition of claim 24, the polybutadiene having more than 90% _> of cis-1,4 bonds. 26. Composition according to any one of claims 10 to 22, the diene elastomer being an isoprene elastomer, preferably natural rubber or a synthetic cis-1,4 polyisoprene. 27. Composition according to any one of claims 1 to 26, characterized in that it is in the vulcanized state. 28. Process for preparing an elastomeric composition usable for the manufacture of tires, comprising the following steps: . incorporating into a diene elastomer, in a mixer, at least: a reinforcing inorganic filler; as coupling agent (inorganic filler / diene elastomer), an at least bifunctional organosilicon compound which can be grafted onto the elastomer by means of a sulfur group,. by thermomechanically kneading the whole, eh one or more times, until reaching a maximum temperature of between 110 ° C and 190 ° C; • cool the assembly to a temperature below 100 ° C; . then incorporate a crosslinking system; knead everything up to a maximum temperature below 120 ° C, characterized in that said sulfur group comprises a cyclic polysulphide function and corresponds to formula (I): (I) ≡ Si - (Z - S) _p - A - Q in which: Z is a divalent linking group, linear or branched, making it possible to link the cyclic polysulphide group to a silicon atom of the organosilicon compound; - p is 0, 1 or 2; A represents a valence bond or a divalent saturated aléghatic hydrocarbon group; Q represents the group of formula: in which: the symbol B denotes a saturated monocyclic or polycyclic C ₅ -C ₁₈ carbocycle in which one or more of the carbon atoms can be replaced by an oxygen or sulfur atom, the two ends of the -Sx- bridge being linked to two contiguous carbon atoms of said carbocycle B; the symbols = O denote an oxygen atom which can constitute, with one of the atoms of S of the Sx bridge, a sulfinyl group> S = O; x is a whole or fractional number ranging from 2 to 6; q represents a number equal to 0 or 1. 29. Use of a rubber composition according to any one of claims 1 to 27 for the manufacture of tires or semi-finished products intended for tires, these semi-finished products being chosen in particular from the group consisting of treads, underlayments, crown reinforcement plies, sidewalls, carcass reinforcement plies, heels, protectors, air chambers and internal rubber compounds for tubeless tires. 30. A tire comprising a rubber composition according to any one of claims 1 to 27. 31. Semi-finished product for a tire comprising a rubber composition according to any one of claims 1 to 27, this product being chosen in particular from the group consisting of treads, undercoats, plies of crown reinforcement, sidewalls, carcass reinforcement plies, beads, protectors, air chambers and waterproof inner liners for tubeless tires. 32. Semi-finished product according to claim 31, consisting of a tire tread. 33. Tire tread according to claim 32, comprising a rubber composition according to any one of claims 23 to 26. 34. A tire comprising a tread according to claim 33. 35. Use as coupling agent (inorganic filler / diene elastomer), in a composition based on diene elastomer reinforced with an inorganic filler intended for the manufacture of tires, of an at least bifunctional organosilicon compound graftable on the elastomer by means of a sulfur group, characterized in that said sulfur group comprises a cyclic polysulfide function and corresponds to formula (I): (I) _≡ Si - (Z - S) _p - A - Q in which: Z is a divalent linking group, linear or branched, making it possible to link the cyclic polysulphide group to a silicon atom of the organosilicon compound; p is 0, 1 or 2; A represents a valence bond or a divalent saturated aléghatic hydrocarbon group; Q represents the group of formula: in which: the symbol B denotes a saturated monocyclic or polycyclic C ₅ -C ₁₈ carbocycle in which one or more of the carbon atoms can be replaced by an oxygen or sulfur atom, the two ends of the -Sx- bridge being linked to two contiguous carbon atoms of said carbocycle B; - the symbols = O denote an oxygen atom which can constitute, with one of the atoms of S of the Sx bridge, a sulfinyl group> S = O; x is a whole or fractional number ranging from 2 to 6; q represents a number equal to 0 or 1.