EP3727880A1

EP3727880A1 - Composition comprising a polysulfide compound

Info

Publication number: EP3727880A1
Application number: EP18836488.9A
Authority: EP
Inventors: Anne-Frédérique SALIT; Sophie GANDER; Adeline JASSELIN; Anne-Lise THUILLIEZ
Original assignee: Compagnie Generale des Etablissements Michelin SCA
Current assignee: Compagnie Generale des Etablissements Michelin SCA
Priority date: 2017-12-19
Filing date: 2018-12-18
Publication date: 2020-10-28
Also published as: WO2019122688A1

Abstract

The invention relates to a composition based on at least one unsaturated polymer and a polysulfide compound of general formula (I) wherein: A and B together form a covalent bond or else A is a hydrogen atom and B is an -S-R₁-(S)_m-R₂-SH group or a hydrogen atom; m is a number within a range from 1 to 3; - n is a number greater than or equal to 3; - p is a number greater than or equal to 1; R₁ and R₂, represent, independently of each other, identical or different divalent hydrocarbon-based groups comprising from 1 to 18 carbon atoms, optionally interrupted by a heteroatom. The invention also relates to a method for producing this composition and to the use of a polysulfide compound of general formula (I) as an agent for crosslinking unsaturated polymers.

Description

COMPOSITION COMPRISING A POLY SULPHIDE COMPOUND

The present invention relates to the field of crosslinking of unsaturated polymers, in particular elastomers, and more particularly diene elastomers. The present invention particularly relates to compositions comprising unsaturated polymers and polysulfide compounds which may be crosslinking agents.

[002] Unsaturated polymers are part of the constitution of many objects of everyday life, such as tires, shoe soles, seals, glues, foam articles, profiles for the automobile, etc. These are macromolecules having carbon-carbon double bonds, also called unsaturations, in their main chain and / or in their side chain (s).

[003] It is known to increase or modify the mechanical properties of these unsaturated polymers by creating bridges between their chains (crosslinking). There are a number of methods for creating these bridges, the best known being vulcanization.

[004] The principle of vulcanization, also called sulfur crosslinking, lies in the creation of sulfur bridges between different chains of macromolecules by reaction on the double bonds of these chains of a vulcanizing agent. The vulcanizing agent, also called sulfur donor, is a compound that is capable of releasing sulfur by heating to the vulcanization temperature. The most known and most commonly used vulcanizing agent is elemental sulfur.

However, it is known that vulcanization with elemental sulfur has the disadvantage of leading to a limited resistance vulcanisais obtained due to thermal aging of the latter ("thermal aging"). When used, the vulcanizates undergo many stresses, including thermal stresses. These thermal stresses are the effect of overcuring, which when the temperature of the vulcanizate reaches a value close to the vulcanization temperature, causes a phenomenon of reversion. Reversion is a rupture of the network of crosslinking by destruction or shortening of the bridges of sulfur created during vulcanization; that is to say a reduction of the polysulphide bridges in favor of monosulphide or disulfide bridges. This rupture of the network adversely modifies the mechanical properties of the vulcanisai. Thus, the use of elemental sulfur leads to constraints on the process for vulcanizing compositions comprising unsaturated polymers, in particular elastomers, in particular diene elastomers, with respect to the vulcanization temperature, the baking time and the elongation modulus. [006] There remains therefore a need for a composition of unsaturated polymers, in particular elastomers, in particular diene elastomers, which does not exhibit a phenomenon of reversion or is limited to high crosslinking temperatures while retaining or even improving the breaking elongation properties.

Several solutions have been developed in order to meet the disadvantages of an elemental sulfur crosslinking system. There may be mentioned, for example, the use of specific additives called anti-reversion agents which make it possible to thermally stabilize the vulcanisais.

Another solution has been to develop new crosslinking agents for the formation of sulfur bridges between the macromolecule chains while limiting the phenomenon of reversion. By way of example, the document US2002 / 107338 describes the synthesis of a crosslinking agent: 1,2,3,4-tetrathiecane. However, this crosslinking agent has a low crosslinking kinetics.

[009] It is therefore interesting for manufacturers to have compositions comprising unsaturated polymers capable of being crosslinked at high temperature, in order to save time, without their elongation breaking properties being reduced.

[0010] The Applicant has now discovered that the aforementioned objectives can be achieved, in part or in full, by using a new crosslinking agent which will be detailed hereinafter.

Thus according to a first aspect, the invention relates to a composition based on at least one unsaturated polymer and at least one polysulfurized compound of general formula (I).

in which :

A and B together form a covalent bond or A represents a hydrogen atom and B represents a group -S-Ri - (S) _m -R ₂ -SH or a hydrogen atom;

m is a number in a range from 1 to 3;

n is a number greater than or equal to 3;

p is a number greater than or equal to 1; R 1 and R ₂ represent, independently of one another, identical or different divalent hydrocarbon groups containing from 1 to 18 carbon atoms, optionally interrupted by a heteroatom.

It has indeed been found that the use of a polysulfide compound of general formula (I) allows, surprisingly, to crosslink at high temperatures compositions based on at least one unsaturated polymer, in particular at least one elastomer and more particularly at least one diene elastomer while limiting the phenomenon of reversion and improving the elongation properties of these compositions and in particular their kinetics of crosslinking.

Thus, advantageously, the vulcanisais obtained from the compositions of the invention have the advantage of being more thermally stable, especially at high temperatures. The compositions of the invention also have the advantage of being produced more rapidly without a reduction in their mechanical properties, in particular without reducing their breaking elongation properties.

According to a second aspect, the invention relates to an article comprising at least one composition as definie above. Preferably, this article is a tire.

According to a third aspect, the invention relates to a process for the manufacture of a composition comprising at least one unsaturated polymer, at least one filler and at least one polysulfurized compound of general formula (I)

in which :

m is a number in a range from 1 to 3;

n is a number greater than or equal to 3;

p is a number greater than or equal to 1;

R 1 and R ₂ represent, independently of one another, identical or different divalent hydrocarbon groups containing from 1 to 18 carbon atoms, optionally interrupted by a heteroatom.

said method comprising at least the following steps: a) the filler is mixed with the unsaturated polymer in a mixer; b) the mixture of step (a) is mechanically kneaded one or more times until a maximum temperature of less than or equal to 200 ° C. is reached; ,

c) cooling the mixture obtained at the end of step (b) to a temperature below 100 ° C;

d) is incorporated in the mixture obtained at the end of step (c) said polysulfurized compound of general formula (I) and,

e) kneading the mixture obtained at the end of step (d) to a temperature below 120 ° C.

According to a fourth aspect, the invention relates to the use of at least one polysulfide compound of general formula (I) as a crosslinking agent for unsaturated polymers.

in which :

m is a number in a range from 1 to 3;

n is a number greater than or equal to 3;

p is a number greater than or equal to 1;

According to a fifth aspect, the invention relates to a process for crosslinking unsaturated polymers, said process comprising at least the following steps:

Mixing at least one unsaturated polymer and at least one polysulfurized compound of general formula (I)

in which

A and B together represent a covalent bond or when A represents a hydrogen atom and B represents a group -S-Ri- (S) _{m -} R ₂ ^~ SH or a hydrogen atom;

m is a number in a range from 1 to 3; n is a number greater than or equal to 3;

p is a number greater than or equal to 1;

R 1 and R ₂ represent, independently of one another, identical or different divalent hydrocarbon groups containing from 1 to 18 carbon atoms, optionally interrupted by a heteroatom; and heating the mixture obtained above to a temperature greater than or equal to 130.degree. C., preferably lying in the range 130.degree. C. to 200.degree.

According to a sixth aspect, the invention relates to a crosslinking system comprising at least one vulcanization accelerator and at least one polysulfurized compound of general formula (I)

in which

A and B together form a covalent bond or A represents a hydrogen atom and B represents a -S-R- (S) _m -R ₂ -SH group or a hydrogen atom;

m is a number in a range from 1 to 3; n is a number greater than or equal to 3;

p is a number greater than or equal to 1;

The invention as well as its advantages will be readily understood in the light of the description and examples of embodiment. 1 - MEASURING METHODS USED

1.1 Rheometry

The measurements are carried out at 150 ° C. or at 190 ° C. with an oscillating chamber rheometer, according to the standard DIN53529 - part 3 (June 1983). The evolution of the rheometric torque as a function of time describes the evolution of the stiffening of the composition following the crosslinking reaction. The measurements are processed according to DIN53529 - Part 2 (March 1983): the minimum and maximum torques, measured in dN.m (deciNewton.meter) are respectively named C _min and C _max , the distance noted ACouple ( in dN.min) between C _max and C _min which makes it possible to assess the crosslinking efficiency. The conversion rate constant expressed in min ¹ , of order 1, calculated between 30% and 80% of conversion is also measured which makes it possible to assess the kinetics of crosslinking.

The reversion rate expressed in% is calculated according to the equation below:

The percentage of reversion is calculated from the vulcanization isotherm measured by the method DIN-53529. The value of C _max corresponds to the maximum torque in dN.m reached during the ascending phase of vulcanization. When there is a phenomenon of reversion, then the measured torque decreases with time. On the basis of the DIN53529 standard method, the percentage of reversion that appears 5 minutes after reaching the C _max torque has been calculated: it therefore corresponds to the rheometric torque measured according to the vulcanization isotherm, 5 minutes after the C _max has been reached.

1.2 Tensile tests

The measured properties are the modules of the compositions, as determined in tensile tests. These tests make it possible to determine the elastic stress and the properties at break. They are carried out in accordance with the French standard NF T 46-002 of September 1988. The elongations at break (in%) are measured in second elongation (ie after an accommodation cycle). The measurements of elongation at break (denoted AR) are carried out under the normal conditions of temperature (23 ± 2 ° C.) and hygrometry (50 ± 5% relative humidity), according to the French standard NF T 40- 101 (December 1979), and also at 100 ° C. Nominal secant moduli (or apparent stresses, in MPa, referred to strain, without unit) at 10%, 100% or 300% elongation (denoted MA10, MA100 and MA300) and the true stresses at break (in MPa) can also be measured.

2 - DETAILED DESCRIPTION OF THE INVENTION

The invention and its advantages will be readily understood in light of the description and examples of embodiment.

In the present description, unless otherwise expressly indicated, all the percentages (%) indicated are percentages by weight.

[0025] On the other hand, any range of values designated by the expression "between a and b" represents the range of values from more than "a" to less than "b" (i.e. a and b excluded) while any range of values referred to as "a to b" means the range of values from "a" to "b" (ie including strict bounds a and b).

In the present application, the term "phr" (usually "phr" in English) the part by weight of a constituent per hundred parts by weight of the elastomer or elastomers, that is to say the total weight of or elastomers.

When the objects of the present invention comprise elastomer-free compositions, it will be understood by those skilled in the art that the term "phr" refers to the portion by weight of a constituent of the composition per hundred parts by weight. unsaturated polymer (s) of this composition.

In the context of the invention, the carbon-containing products mentioned in the description may be of fossil origin or biobased. In the latter case, they can be, partially or totally, derived from biomass or obtained from renewable raw materials derived from biomass. These include polymers, plasticizers, fillers, etc.

2.1 Composition

A first subject of the invention relates to a composition based on at least one unsaturated polymer and at least one polysulfurized compound of general formula (I)

in which : A and B together form a covalent bond or A represents a hydrogen atom and B represents a group -S-Ri - (S) _m -R ₂ -SH or a hydrogen atom;

m is a number in a range from 1 to 3;

n is a number greater than or equal to 3;

p is a number greater than or equal to 1;

By the expression "composition based on" is meant a composition comprising the mixture and / or the reaction product in situ of the various basic constituents used, some of these constituents being able to react and / or being intended for react with each other, at least partially, during the various phases of manufacture of the composition, or during the subsequent firing, modifying the composition as it was initially prepared. Thus, the compositions as implemented for the invention may be different in the uncrosslinked state and in the crosslinked state.

Unsaturated polymer

As indicated above, the composition of the invention comprises at least one unsaturated polymer, that is to say a single unsaturated polymer or a mixture of unsaturated polymers.

[0032] Preferably, the unsaturated polymer is an elastomer.

More preferably still, the unsaturated polymer is a diene elastomer.

By elastomer (or "rubber", the two terms being considered as synonymous) of the "diene" type, it is recalled here that must be understood in a known way (one or more) elastomeric origin at least in part ( ie, a homopolymer or copolymer) of diene monomers (monomers bearing two carbon-carbon double bonds, conjugated or otherwise).

The diene elastomers can be classified in two categories: "essentially unsaturated" or "essentially saturated".

The term "essentially unsaturated" is generally understood to mean a diene elastomer derived at least in part from conjugated diene monomers, having a proportion of units or units of diene origin (conjugated dienes) which is greater than 15% (% by weight). moles). In the category of "essentially unsaturated" diene elastomers, we mean in particular by diene elastomer "highly unsaturated" a diene elastomer having a ratio of units of diene origin (conjugated dienes) which is greater than 50% (mol%).

The term "essentially saturated" is generally understood to mean a diene elastomer derived at least in part from conjugated diene monomers, having a proportion of units or units of diene origin (conjugated dienes) which is less than 15% (% by weight). moles), such as butyl rubbers or copolymers of dienes and alpha-olefins EPDM type.

These definitions being given, the term "diene elastomer" can be understood more particularly to be used in the compositions according to the invention:

(a) any homopolymer obtainable by polymerization of a conjugated diene monomer having from 4 to 12 carbon atoms;

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

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

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

The invention applies to any type of diene elastomer. When the composition is intended for the preparation of pneumatic tires, those skilled in the art will understand that the present invention is preferably carried out with essentially unsaturated diene elastomers, in particular of the type (a) or (b) above.

By way of conjugated dienes 1,3-butadiene,

1,3-butadiene (or isoprene), 2,3-di (C 1 -C 5) alkyl-1,3-butadienes such as, for example, 2,3-dimethyl-1,3-butadiene, 2,3-diethyl 1,3-butadiene, 2-methyl-3-ethyl-

1,3-butadiene, 2-methyl-3-isopropyl-1,3-butadiene, aryl-1,3-butadiene, 1,3-pentadiene, 2,4-hexadiene. Suitable vinylaromatic compounds are, for example, styrene, ortho-, meta-, para-methylstyrene, the commercial mixture "vinyl-toluene", para-tert-butylstyrene, methoxystyrenes, chlorostyrenes, vinylmesitylene, divinylbenzene, vinylnaphthalene.

The copolymers may contain between 99% and 20% by weight of diene units and between 1% and 80% by weight of vinylaromatic units. The elastomers may have any microstructure which is a function of the polymerization conditions used, in particular the presence or absence of a modifying and / or randomizing agent and amounts of modifying agent. and / or randomizing used. The elastomers can be for example block, statistical, sequenced, microsequenced, and be prepared in dispersion or in solution; they may be coupled and / or starred or functionalized with a coupling agent and / or starring or functionalization. For coupling with carbon black, there may be mentioned, for example, functional groups comprising a C-Sn bond or amine functional groups such as aminobenzophenone for example; for coupling to a reinforcing inorganic filler such as silica, mention may be made, for example, of silanol or polysiloxane functional groups having a silanol end (as described, for example, in FR 2,740,778, US 6,013,718 and WO 2008/141702), alkoxysilane groups (as described for example in FR 2,765,882 or US 5,977,238), carboxylic groups (as described for example in WO 01/92402 or US 6,815,473, WO 2004/096865 or US 2006/0089445). ) or polyether groups (as described for example in EP 1 127 909, US 6,503,973, WO 2009/000750 and WO 2009/000752). As other examples of functionalized elastomers, mention may also be made of elastomers (such as SBR, BR, NR or IR) of the epoxidized type. These functionalized elastomers may be used in a blend with each other or with unfunctionalized elastomers. For example, a functionalized silanol or polysiloxane elastomer having a silanol end, in admixture with a coupled and / or stanned tin elastomer (described in WO 11/042507), may be used, the latter representing a rate of from 5 to 50 %, for example from 25 to 50%.

Polybutadienes and in particular those having a content (mol%) in units -1.2 of between 4% and 80% or those having a content (mol%) of cis-1,4, of greater than 80%, are suitable. polyisoprenes, butadiene-styrene copolymers and in particular those having a Tg (glass transition temperature Tg, measured according to AS TM D3418) of between 0 ° C. and -70 ° C. and more particularly between -10 ° C. and -60 ° C. ° C, a styrene content of between 5% and 60% by weight and more particularly between 20% and 50%, a content (mol%) in -1,2 bonds of the butadiene part of between 4% and 75%, a content (mol%) in trans-1,4 bonds of between 10% and 80%, butadiene-isoprene copolymers and in particular those having an isoprene content of between 5% and 90% by weight and a Tg of -40 At -80 ° C., the isoprene-styrene copolymers and in particular those having a styrene content of between 5% and 50% by weight and a Tg included e between -5 ° C and -60 ° C. In the case of butadiene-styrene-isoprene copolymers are especially suitable those having a styrene content of between 5% and 50% by weight and more particularly of between 10% and 40%, an isoprene content of between 15% and 60%. by weight and more particularly between 20% and 50%, a butadiene content of between 5% and 50% by weight and more particularly between 20% and 40%, a content (mol%) in -1,2 units of the butadiene part between 4% and 85%, a content (mol%) in trans-1,4 units of the butadiene part of between 6% and 80%, a content (mol%) in units -1,2 plus -3,4 of the isoprenic part between 5% and 70% and a content (mol%) in trans-1,4 units of the isoprene part of between 10% and 50%, and more generally any butadiene-styrene-isoprene copolymer having a Tg between -20 ° C and -70 ° C.

Preferably, the diene elastomer of the composition of the invention is chosen from the group of highly unsaturated diene elastomers consisting of polybutadienes (abbreviated to BR), synthetic polyisoprenes (IR) and natural rubber (NR). , butadiene copolymers, isoprene copolymers and mixtures of these diene elastomers. Such copolymers are more preferably selected from the group consisting of butadiene-styrene copolymers (SBR), isoprene-butadiene copolymers (BIR), isoprene-styrene copolymers (SIR), isoprene-copolymers of butadiene-styrene (SBIR), butadiene-acrylonitrile copolymers (NBR), butadiene-styrene-acrylonitrile copolymers (NSBR) or a mixture of two or more of these compounds. In the case of an SBR elastomer (ESBR or SSBR), an SBR having an average styrene content, for example between 20% and 35% by weight, or a high styrene content, for example 35 to 35% by weight, is used in particular. 45%, a vinyl ring content of the butadiene part of between 15% and 70%, a content (mol%) of trans 1,4 bonds of between 15% and 75% and a Tg of between -10 ° C. and 55 ° C; such an SBR can be advantageously used in admixture with a BR preferably having more than 90% (mol%) of 1,4 cis bonds. More preferably still, the diene elastomer is natural rubber or a synthetic polyisoprene.

The diene elastomers, whether functionalized or not, may be used in blending (mixing) with each other. Thus, the compositions in accordance with the invention may preferably contain a single diene elastomer, functionalized or not, or a mixture of several diene elastomers, functionalized or not, this or these diene elastomers may be used in combination with any type of elastomer synthetic other than diene, or with polymers other than elastomers, for example thermoplastic polymers.

Preferably, the level of diene elastomer in the composition is more than 50 phr (that is to say 50 to 100 phr), more preferably at least 60 phr (that is to say 60 to 100 phr), more preferably at least 70 phr (that is to say from 70 to 100 phr), more preferably still at least 80 phr (i.e. from 80 to 100 phr) and very preferably at least 90 phr (that is to say from 90 to 100 phr). In particular according to this embodiment, the level of diene elastomer is very preferably 100 phr. Polysulfide compound

As seen above, the composition of the invention comprises at least one polysulfurized compound of general formula (I)

in which :

m is a number in a range from 1 to 3;

n is a number greater than or equal to 3;

p is a number greater than or equal to 1;

The polysulfide compound of general formula (I) has the function of crosslinking the unsaturated polymer chains, in particular the chains of the elastomers, in particular the chains of the diene elastomers. This polysulfurized compound of general formula (I) may be a crosslinking agent. It can advantageously replace the elemental sulfur usually used in a crosslinking. Thus, according to a preferred embodiment, the composition of the invention does not comprise elemental sulfur or comprises elemental sulfur at a level of less than 1 phr, preferably less than or equal to 0.5 phr.

By the expression "A and B together form a covalent bond" is meant that the sulfur atoms adjacent to A and B respectively are connected directly by a covalent bond. In this case, the polysulfurized compound of general formula (I) is cyclic.

For the purposes of the present invention, the term "divalent hydrocarbon group" means a group comprising carbon and hydrogen atoms. This group may optionally be interrupted by at least one heteroatom. The hydrocarbon group may be optionally branched, in particular substituted with C ₁ -C ₆ alkyl groups, with phenyl or with benzyl. The grouping hydrocarbon may also and preferably be linear, that is to say, it is not branched. It can also be cyclical. Whatever its linear, cyclic or branched form, it may optionally comprise one or more carbon-carbon double bonds.

By "heteroatom" is meant in the sense of the present invention, the sulfur atoms, the nitrogen atoms, the silicon atoms and the phosphorus atoms.

Preferably, in the general formula (I), R 1 and R ₂ represent, independently of one another, alkylene radicals containing from 1 to 18 carbon atoms, preferably from 2 to 10 carbon atoms, more preferably still from 2 to 8 carbon atoms.

According to a preferred embodiment, Ri and R ₂ are identical.

More preferably, R 1 and R ₂ represent, independently of one another, identical or different groups, preferably identical, selected from the group formed by -CH ₂ -CH ₂ -; -CH ₂ -CH ₂ -CH ₂ -; -CH ₂ -CH ₂ -CH ₂ -CH ₂ -; -CH _2- (CH ₂ ) ₃ -CH _2- ; -CH _2- (CH ₂ ) ₄ -CH _2- ; -CH _2- (CH ₂ ) ₅ -CH _2- ; -CH _2- (CH ₂ ) ₆ -CH _2-,

Preferably, in the general formula (I), m represents a number included in a range from 1 to 2, preferably m is equal to 1.

Preferably in the general formula (I), n represents a number included in a range from 3 to 8, preferably from 3 to 6, more preferably is equal to 3 or 4.

Preferably, in the general formula (I), p represents a number in a range from 1 to 30, preferably from 1 to 15, more preferably from 1 to 3.

Among the polysulphurized compounds of general formula (I), the polysulphurized compounds of which n = 3 or n = 4 are preferred with R 1, R ₂ , A, B, m and p as defined above, including their favorite variants.

More preferably still, among the polysulfurized compounds of general formula (I), the polysulfurized compounds of which m = 1 and n = 3 or n = 4 are among the preferred ones with R 1, R ₂ , A, B and p as defined. above including their preferred variants.

According to a preferred embodiment, A and B form a covalent bond. In this embodiment, the polysulfide compound of general formula (I) is a cyclic compound.

According to another preferred embodiment, A represents a hydrogen atom and B represents a hydrogen atom or a group -S-Ri - (S) _m -R ₂ -SH; of preferably A represents a hydrogen atom and B represents a group -S-Ri - (S) _m -R ₂ -SH. In this embodiment, the polysulfide compound of general formula (I) is a non-cyclic compound.

The polysulfide compounds of general formula (I), including their preferred variants, may be mixtures of polysulfide compounds of general formula (I) in which case the indices n, m and p are average values. These indices can therefore be integers like fractional numbers. Also, the polysulfurized compound of general formula (I) can be in the form of a mixture of cyclic and non-cyclic form.

Very preferred embodiments are those in which the compound of general formula (I) is such that A and B together form a covalent bond, Ri and R ₂ , which are identical, are alkylene radicals containing from 2 to 10 atoms. carbon, more preferably still 2 to 8 carbon atoms, m ranging from 1 to 3, preferably m = 1, n = 3 and p = 1.

Other very preferred embodiments are those in which the compound of general formula (I) is such that A represents a hydrogen atom, B represents a group -S-Ri - (S) _m -R ₂ - SH, Ri and R ₂ , identical, are alkylene radicals containing from 2 to 10 carbon atoms, more preferably still from 2 to 8 carbon atoms, m ranging from 1 to 3, preferably m = 1, n = 3; and p represents a number ranging from 1 to 30.

Other very preferred embodiments are those in which the compound of general formula (I) is a mixture of polysulphurized compounds, the mixture comprising at least one compound of general formula (I) in which A represents an atom of hydrogen, B represents a group -S-R- (S) _m -R ₂ -SH, Ri and R ₂ , which are identical, are alkylene radicals containing from 2 to 10 carbon atoms, more preferably still from 2 to 8 atoms; of carbon, m ranging from 1 to 3, preferably m = 1, n = 3 and p represents a number ranging from 1 to 30 and at least one other compound of general formula (I) in which A and B together form a bond covalent, Ri and R ₂ , identical, are alkylene radicals containing from 2 to 10 carbon atoms, more preferably still from 2 to 8 carbon atoms, m ranging from 1 to 3, preferably m = 1, n = 3 and p = 1.

Preferably, the level of the polysulfurized compound of general formula (I) in the composition is in a range from 0.5 to 10 phr, preferably ranging from 0.5 to 5 phr, preferably ranging from 0, 5 to 3 pce.

The polysulfide compound of general formula (I) may be used alone in the composition of the invention or in combination with one or more co-crosslinking agents. These co-crosslinking agents are well known to those skilled in the art and may be incorporated during the first non-productive phase and / or during the productive phase of manufacture of the composition as described later.

These co-agents, optional, may be vulcanization activators, vulcanization accelerators, well known to those skilled in the art.

As vulcanization activators, mention may be made of zinc oxide and stearic acid derivatives. The term "stearic acid derivative", stearic acid or a salt of stearic acid, both of which are well known to those skilled in the art. As an example of a stearic acid salt that may be used in the context of the present invention, there may be mentioned in particular zinc or magnesium stearate.

As vulcanization accelerators well known to those skilled in the art, one will preferably choose from the group consisting of thiazoles, sulfenamides, guanidines, amines, aldehyde-amines, dithiophosphates, xanthates thiurams, dithiocarbamates and mixtures thereof.

In particular, it is preferred for the present invention, benzothiazyl-2-cyclohexyl sulfenamide (CBS), benzothiazyldicyclohexy-1 sulfenamide (DCBS), benzothiazoyl-2-tert.-butyl sulfenamide (TBBS), 2- mercaptobenzothiazole (MBT), benzothiazole disulfide (MBTS), zinc or sodium salt of 2-mercaptobenzothiazole (ZMBT), benzothiazyl-2-sulfene morpholide (MBS), guanidine diphenyl (DPG), triphenyl guanidine (TPG), diorthotolyl guanidine (DOTG), o-tolylbiguanide (OTBG), benzothiazole disulfide (MBTS), tetramethylthiuram disulfide (TMTD), tetrabenzylthiuram disulfide (TBzTD), zinc dibenzyldithiocarbamate (ZBEC) , zinc N, N'-dimethylcarbamodithioates (ZDMC), zinc N, N'-diethylcarbamodithioates (ZDEC), zinc N, N'-dibutylcarbamodithioates (ZDBC), zinc N, N'-dibenzylcarbamodithioates (ZDBC), zinc isopropylxanthate (ZIX) and mixtures thereof.

According to a preferred embodiment, the composition of the invention comprises at least one complementary vulcanization accelerator, different from the accelerator described above, selected from the group consisting of diphenyl guanidine (DPG), triphenyl guanidine (TPG), diorthotolyl guanidine (DOTG), o-tolylbiguanide (OTBG), benzothiazole disulfide (MBTS), tetramethylthiuram disulfide (TMTD), tetrabenzylthiuram disulfide (TBzTD), zinc dibenzyldithiocarbamate (ZBEC) ), zinc N, N'-dimethylcarbamodithioates (ZDMC), zinc N, N'-diethylcarbamodithioates (ZDEC), zinc N, N'-dibutylcarbamodithioates (ZDBC), zinc N, N'-dibenzylcarbamodithioates (ZDBC), zinc isopropylxanthate (ZIX), and mixtures thereof. Very preferably, the complementary vulcanization accelerator, different from the accelerator described above, is zinc dibenzyldithiocarbamate (ZBEC). Those skilled in the art can adjust the level of these co-agents, activators and vulcanization accelerators in the composition of the invention as a function of the various constituents of this composition and depending on the use of the composition.

The polysulfide compounds of general formula (I) useful for the invention, if they are not commercially available, may be prepared by any means known to those skilled in the art. For example, a process generally comprising a step of reacting a sulfur compound with a compound of formula (II) according to the following reaction scheme can be used:

wherein in the general formula (II), R 1, R ₂ and m have the same definitions (and same preferred variants) as those mentioned in the general formula (I).

For example, the polysulfide compounds of general formula (I) may in particular be obtained by an oxidative coupling reaction of the alkylthiol precursors, corresponding arylthiols. The reactions described in the following references make it possible to obtain polysulphide compounds by oxidative coupling. R. Hunter, M. Caira, N. Stellenboom, J. Org. Chem., 2006, 71, 8268-8271. R. Hunter, M. Caira, N. Stellenboom, J. Org. Chem., 2006, 71, 8268-8271. S. Antoniow, D. Witt, Synthesis, 2007, 363-366. M. Szymelfejnik, S. Demkowicz, J. Rachon, D. Witt, Synthesis, 2007, 3528-3534. M. Bao, M. Shimizu, Tetrahedron, 2003, 59, 9655-9659. C. K. Maurya, A. Mazumder, A. Kumar, P. K. Gupta, Synlett, 2016, 27, 409-411. . Kirihara, Y. Asai, S. Ogawa, T. Noguchi, A. Hatano, Y. Hirai, Synthesis, 2007, 3286-3289. A. Khazaei, M. A. Zolfigol, A. Rostami, Synthesis, 2004, 2959-2961.

Optional ingredients

Charge

The compositions according to the invention with only the ingredients described above are sufficient to respond to the technical problem, particularly that of obtaining compositions having improved kinetics of crosslinking while limiting or suppressing the phenomenon of reversion to high temperatures of 50.degree. vulcanization.

However, the compositions of the invention may further comprise additional ingredients. For example, in a preferred embodiment, the composition of the invention further comprises at least one filler; that is to say a single charge or a mixture of several charges.

As a filler, mention may be made of reinforcing fillers, semi-reinforcing fillers and inert fillers.

According to a preferred embodiment, the compositions of the invention comprise a reinforcing filler or a mixture of several reinforcing fillers.

For the purposes of the present invention, the term "reinforcing filler" is intended to mean any type of filler known for its ability to reinforce a rubber composition that can be used in particular for the manufacture of a tire, for example an organic filler such as black carbon or even a reinforcing inorganic filler.

Preferably, the reinforcing filler is selected from carbon black, a reinforcing inorganic filler (preferably silica) and mixtures thereof.

According to a preferred embodiment, the reinforcing filler comprises carbon black.

As carbon blacks are suitable all carbon blacks, including the black type HAF, ISAF, SAF conventionally used in tires (so-called pneumatic grade black). Among these, the reinforcing carbon blacks of the 100, 200 or 300 series (ASTM grades), for example the N115, N134, N234, N326, N330, N339, N347 or N375 blacks, or even targeted applications, blacks of higher series (eg N660, N683, N772). The carbon blacks could for example already be incorporated into an isoprene elastomer in the form of a masterbatch (see for example WO 97/36724 or WO 99/16600).

As carbon blacks are preferentially suitable reinforcing carbon blacks having a specific surface CTAB (determined according to the French standard NF T 45-007 November 1987, method B) greater than or equal to 90 m ² / g. More preferably, carbon blacks having a CTAB upper surface area greater than or equal to 120 m ² / g, more preferably a CTAB specific surface area in a range of from 120 m ² / g to 180 m ² / g, are more preferable.

Preferably, the reinforcing filler may comprise an organic filler other than carbon black. As examples of organic fillers other than carbon blacks, mention may be made of the functionalized polyvinyl organic fillers as described in applications WO-A-2006/069792, WO-A-2006/069793, WO-A-1 2008/003434 and WO-A-2008/003435.

According to another preferred embodiment of the composition of the invention, the reinforcing filler may comprise a reinforcing inorganic filler, preferably a silica.

By "reinforcing inorganic filler" must be understood in the present application, by definition, any inorganic or mineral filler (whatever its color and its origin (natural or synthetic), also called "white" charge, charge "Clear" or "non-black filler" as opposed to carbon black, capable of reinforcing on its own, with no other means than an intermediate coupling agent, a rubber composition for manufacturing tire, in other words able to replace, in its reinforcing function, a conventional carbon black pneumatic grade, such a charge is generally characterized, in known manner, by the presence of hydroxyl groups (-OH) at its area.

The physical state in which the reinforcing inorganic filler is present is indifferent, whether in the form of powder, microbeads, granules, beads or any other suitable densified form. Of course, the term "reinforcing inorganic filler" also refers to mixtures of different reinforcing inorganic fillers, in particular highly dispersible siliceous and / or aluminous fillers as described below.

As reinforcing inorganic fillers are particularly suitable mineral fillers of the siliceous type, in particular of silica (SiO ₂ ), or of the aluminous type, in particular of alumina (Al 2 O 3).

Preferably, the composition may contain a type of silica or a blend of several silicas. The silica used may be any reinforcing silica known to those skilled in the art, in particular any precipitated or fumed silica having a BET specific surface and a CTAB specific surface area both less than 450 m ² / g, preferably from 30 to 400 m ² / g. The BET surface area is determined by gas adsorption using the method of Brunauer-Emmett-Teller described in "The Journal of the American Chemical Society" (Vol 60, page 309, February 1938), and more specifically according to a method adapted from standard NF ISO 5794-1, appendix E of June 2010 [multipoint volumetric method (5 points) - gas: nitrogen - vacuum degassing: one hour at 160 ° C - relative pressure range p / po: 0 , 05 to 0.2] As highly dispersible precipitated silicas (referred to as "HDS"), there may be mentioned, for example, "Ultrasil 7000" and "Ultrasil" silicas. 7005 "from Evonik, the" Zeosil "silicas 1165MP, 1135MP and 1115MP from Solvay, the silica" Hi-Sil EZ150G "from PPG, the" Zeopol "silicas 8715, 8745 and 8755 from Huber, treated precipitated silicas such as, for example, the "aluminum doped" silicas described in application EP-A-0735088 or the silicas with a high surface area as described in application WO003016387.

When a reinforcing inorganic filler is present in the composition, in particular a silica, it is possible to use, in known manner, a coupling agent (or bonding agent) at least bifunctional intended to ensure a sufficient connection, of a chemical nature and or physical, between the inorganic filler (surface of its particles) and the diene elastomer, in particular organosilanes or bifunctional polyorganosiloxanes.

In particular, polysulfide silanes, called "symmetrical" or "asymmetrical" according to their particular structure, are used, as described for example in the applications W003 / 002648 (or US 2005/016651) and W003 / 002649 (or US 2005 / 016650).

When the rubber compositions in accordance with the invention contain coupling agents, their level is preferably in a range from 4 to 12 phr, more preferably from 3 to 8 phr.

These compositions may optionally also contain, in addition to the coupling agents, coupling activators, inorganic charge-covering agents or, more generally, processing aid agents that are capable in a known manner, by means of a improvement of the dispersion of the filler in the rubber matrix and a lowering of the viscosity of the compositions, to improve their ability to use in the green state, these agents, well known to those skilled in the art , being, for example, hydrolysable silanes such as alkylalkoxy silanes, polyols, fatty acids, polyethers, primary, secondary or tertiary amines, hydroxylated or hydrolysable polyorganosiloxanes. In particular, polysulfide silanes, called "symmetrical" or "asymmetrical" silanes according to their particular structure, are used, as described, for example, in claims WO 03/002648 (or US 2005/016651) and WO 00/002649 (or US 2005/016650).

Those skilled in the art understand that as an equivalent load of the reinforcing inorganic filler described above, could be used a reinforcing filler of another nature, especially organic, since this reinforcing filler is covered with an inorganic layer such as silica, or has on its surface functional sites, in particular hydroxylated sites, requiring the use of a coupling agent to establish the bond between the filler and the elastomer. The person skilled in the art knows how to adapt the total rate of total reinforcing filler (carbon black, silica or possibly a mixture of carbon black and silica), depending on the use of the composition which is envisaged. Preferably, especially when the composition is used for the manufacture of a tire, this total content of reinforcing filler is in a range from 5 to 250 phr, preferably from 40 to 200 phr.

According to a preferred embodiment of the composition of the invention, the reinforcing filler (or a reinforcing filler mixture) comprises mainly by weight of carbon black. The carbon black used as a reinforcing filler is predominant in weight; that is to say, it represents the highest rate in phr among the reinforcing fillers of the composition. Preferably, the carbon black represents more than 50% by weight (> 50% by weight) of the total weight of the reinforcing filler, preferably more than 60% by weight. Other types of reinforcing filler may be used in a minor minority relative to carbon black in the compositions according to the invention, in particular other reinforcing organic fillers or reinforcing inorganic fillers such as silica. A reinforcing inorganic filler is a minority when its weight does not represent the highest level in phr of the reinforcing fillers of the composition; that is to say, the reinforcing inorganic filler represents less than 50% by weight (<50% by weight) of the total weight of the reinforcing filler, preferably less than 40% by weight.

According to this embodiment, the level of carbon black in the composition of the invention is then preferably in a range from 20 to 150 phr, preferably from 30 to 90 phr, more preferably from 35 to 80 phr. pce, the optimum being of course differ depending on the particular applications targeted. In this embodiment, the silica content in the composition is preferably less than 10 phr.

According to another preferred embodiment of the composition of the invention, the reinforcing filler (or a reinforcing filler mixture) comprises predominantly by weight of the silica. The silica used as a reinforcing filler is predominant in weight; that is to say, it represents the highest rate in phr among the reinforcing fillers of the composition. Preferably, the silica represents more than 50% by weight (> 50% by weight) of the total weight of the reinforcing filler, preferably more than 60% by weight. Other types of reinforcing filler may be used in a minor proportion to the silica in the compositions according to the invention, in particular other reinforcing organic fillers such as carbon black. Carbon black is a minority when its weight does not represent the highest level in phr of the reinforcing fillers of the composition; that is, carbon black is less than 50% by weight (<50% by weight) of the total weight of the reinforcing filler, preferably less than 40% by weight.

According to this embodiment, the level of silica in the composition of the invention is then preferably in a range from 20 to 150 phr, preferably from 30 to 90 phr, more preferably from 35 to 80 phr, the optimum being of course differ according to the particular applications concerned. In this embodiment, the content of carbon black in the composition is preferably less than 10 phr, and more preferably 5 phr. (

As seen above, according to a preferred embodiment, the composition of the invention may comprise at least one semi-reinforcing filler. The semi-reinforcing fillers are not capable of reinforcing by themselves a rubber composition intended for the manufacture of tires, in other words they are not able to replace, in its reinforcing function, a conventional carbon black of pneumatic grade, however they allow an increase in tensile modulus of a rubber composition in which they are incorporated, that is why they are called "semi-reinforcing". As a semi-reinforcing filler, mention may be made of graphite.

According to another embodiment, the composition of the invention may comprise at least one inert filler. The inert fillers that may be used in the compositions of the invention may be chosen from chalk, clay, bentonite, talc, kaolin, glass microbeads, glass flakes and a mixture of these compounds.

Other additives

The compositions of the invention may optionally additionally comprise all or part of the usual additives usually used in elastomer compositions, for example pigments, protective agents such as anti-ozone waxes, chemical ozonants, antioxidants, plasticizing agents such as plasticizing oils or hydrocarbon resins well known to those skilled in the art, reinforcing resins, acceptors (for example phenolic novolak resin) or methylene donors ( for example HMT or H3M).

It goes without saying that the invention relates to compositions in the said state "raw" or uncrosslinked (ie before crosslinking) or in the state said "cooked" or crosslinked (ie after crosslinking). 2.2 - Article

The compositions of the present invention can be used for the preparation of articles.

Thus another object of the present invention relates to an article comprising at least one composition as defined above.

By way of an article, mention may be made of a pneumatic object, a semi-finished product for a tire, a foam article, conveyor belts, particularly sealing seals, automobile profiles, shock absorbers. , layers for the manufacture of cables, shoe soles etc.

For the purpose of the present invention, the term "pneumatic object" means any object which takes its usable form when it is inflated with a gas (or gases) for inflation such as air for example.

Examples of such pneumatic objects include pneumatic boats, pneumatic tires, balls or balls used for play or sport.

[00111] Preferably, the article comprising at least one composition as described above is a pneumatic object a tire. This tire may be intended to equip including non-motorized vehicles such as bicycles, tourism-type motor vehicles, SUV (Sport Utility Vehicles), two wheels (including motorcycles), aircraft, industrial vehicles chosen among vans, heavy goods vehicles (ie metro, buses, road machinery (trucks and trailers)), off-road vehicles, such as agricultural or civil engineering machinery, others transport or handling vehicles.

Another article may be a semi-finished product for a pneumatic tire. It can be any type of rubber, such as in particular treads, underlays, sidewalls, layers of beads, layers of protectors, sheets of underlays, sheets of rubber blocks .

[00113] Mention may also be made of foam articles based on the above composition and of blowing agents having insulating, soundproofing, anti-vibration or reinforcement properties, used in the field of sports and leisure-like structure. of balloon, epaulette of protection. By "foam" or "foam structure" is meant an object or article or material of lower density than that of the starting material. 2.3 - Obtaining the composition

The compositions are manufactured in appropriate mixers, using for example two successive preparation phases according to a general procedure well known to those skilled in the art: a first phase of work or thermomechanical mixing (sometimes referred to as "non-phase" phase). at high temperature, up to a maximum temperature of between 130.degree. C. and 200.degree. C., preferably between 145.degree. C. and 185.degree. C., followed by a second phase of mechanical work (sometimes referred to as a productive phase). ) At a lower temperature, typically below 120 ° C, for example between 60 ° C and 100 ° C, finishing phase during which is incorporated the crosslinking agent or the crosslinking system.

Thus another object of the present invention relates to a method of manufacturing a composition comprising at least one unsaturated polymer, at least one filler, preferably at least one reinforcing filler as described above and at least one a polysulfide compound of general formula (I)

in which :

A and B together form a covalent bond or A represents a hydrogen atom and B represents a group -S-Ri - (S) _{m -} FL - SH or a hydrogen atom;

m is a number in a range from 1 to 3;

n is a number greater than or equal to 3;

p is a number greater than or equal to 1;

R 1 and R ₂ represent, independently of one another, identical or different divalent hydrocarbon groups containing from 1 to 18 carbon atoms, optionally interrupted by a heteroatom;

said method comprising at least the following steps:

a) the filler is mixed with the unsaturated polymer in a mixer; b) the mixture of step (a) is mechanically kneaded one or more times until a maximum temperature of less than or equal to 200 ° C. is reached; ,

c) cooling the mixture obtained at the end of step (b) to a temperature below 100 ° C; d) is incorporated in the mixture obtained at the end of step (c) said polysulfurized compound of general formula (I) and,

The method may further comprise a step (f) during which the composition obtained at the end of step e) is extruded or calendered.

The method may further comprise a step (g) during which the mixture obtained is heated at the end of step (e) or the extruded or calendered composition obtained at the end of step (f) at a temperature greater than or equal to 130 ° C, preferably in the range of 130 ° C to 200 ° C.

For example, the first phase (non-productive) is conducted in a single thermomechanical step during which is introduced into a suitable mixer such as a conventional internal mixer, all the necessary constituents, the possible complementary coating or processing agents and other various additives, except for the polysulfide compound of the general formula (I), (including these preferred embodiments and its preferred variants) or the crosslinking system comprising the compound polysulfide of general formula (I), (including these preferred embodiments and its preferred variants) and the co-agent. After cooling the mixture thus obtained during the first non-productive phase, the polysulfurized compound of general formula (I) (including these preferred embodiments and its preferred variants) or the crosslinking system comprising the compound is then incorporated. polysulfide of general formula (I), (including these preferred embodiments and its preferred variants) and the co-agent at low temperature (ie a temperature of less than or equal to 120 ° C., generally in an external mixer such as roll mixer, the whole is then mixed (productive phase) for a few minutes, for example between 5 and 15 minutes The final composition thus obtained can then be calendered, for example in the form of a sheet, a plate or still extruded.

The crosslinking (or baking) is conducted according to any procedure known to those skilled in the art, at a temperature, at a pressure and for a suitable duration depending on the nature and use of the composition. For example, the crosslinking is carried out in a known manner at a temperature generally greater than or equal to 130.degree. C., in a range from 130.degree. C. to 200.degree. C., for a sufficient time which may vary for example between 5 and 90 minutes. . 2.4 Use of the Compound of General Formula (I) and Crosslinking Process

Another object of the invention relates to the use of at least one polysulfurized compound of general formula (I) as crosslinking agent for unsaturated polymers.

in which :

A and B together form a covalent bond or A represents a hydrogen atom and B represents a group -S-Ri - (S) _{m -} R ₂ -SH or a hydrogen atom;

m is a number in a range from 1 to 3;

n is a number greater than or equal to 3;

p is a number greater than or equal to 1;

R 1 and R ₂ represent, independently of one another, identical or different divalent hydrocarbon groups containing from 1 to 18 carbon atoms, optionally interrupted by a heteroatom

The embodiments and preferred variants of the polysulfide compounds of general formula (I) also apply to this use as a crosslinking agent for unsaturated polymers.

[00122] Preferably, in this use, the polymers are elastomers, more preferably diene elastomers, as described above.

Another object of the present invention relates to a process for crosslinking unsaturated polymers, said process comprising at least the following steps:

Mixing at least one unsaturated polymer and at least one polysulfurized compound of general formula (I), including its embodiments and its preferred variants) previously described,

• heating the mixture obtained above at a temperature greater than or equal to 130 ° C, preferably in a range from 130 ° C to 200 ° C.

2.5 Crosslinking system

Another object of the present invention relates to a crosslinking system comprising at least one vulcanization accelerator and at least one polysulfide compound of general formula (I) as described above, including its embodiments and its variants. previously described. [00125] Vulcanization accelerators are well known to those skilled in the art and have been described above.

Preferably, the vulcanization accelerator is selected from the group consisting of thiazoles, sulfenamides, guanidines, amines, aldehyde amines, dithiophosphates, xanthates, thiurams, dithiocarbamates and mixtures thereof.

In particular, it is preferred for the present invention to choose a vulcanization accelerator from benzothiazyl-2-cyclohexyl sulfenamide (CBS), benzothiazyldicyclohexy-1 sulfenamide (DCBS), benzothiazoyl-2-tert-butyl. sulfenamide (TBBS), 2-mercaptobenzothiazole (MBT), benzothiazole disulfide (MBTS), 2-mercaptobenzothiazole zinc or sodium salt (ZMBT), benzothiazyl-2-sulfene morpholide (MBS), diphenyl guanidine (DPG), triphenyl guanidine (TPG), diorthotolyl guanidine (DOTG), o-tolylbiguanide (OTBG), benzothiazole disulfide (MBTS), tetramethylthiuram disulfide (TMTD), tetrabenzylthiuram disulfide (TBzTD) , zinc dibenzyldithiocarbamate (ZBEC), zinc N, N'-dimethylcarbamodithioates (ZDMC), zinc N, N'-diethylcarbamodithioates (ZDEC), zinc N, N'-dibutylcarbamodithioates (ZDBC), zinc N, N dibenzylcarbamodithioates (ZDBC), zinc isopropylxanthate (ZIX) and mixtures thereof.

According to a preferred embodiment, the crosslinking system comprises a complementary vulcanization accelerator, different from the accelerator described above, selected from the group consisting of diphenyl guanidine (DPG), triphenyl guanidine (GPT). , diorthotolyl guanidine (DOTG), o-tolylbiguanide (OTBG), benzothiazole disulfide (MBTS), tetramethylthiuram disulfide (TMTD), tetrabenzylthiuram disulfide (TBzTD), zinc dibenzyldithiocarbamate (ZBEC), zinc N, N'-dimethylcarbamodithioates (ZDMC), zinc N, N'-diethylcarbamodithioates (ZDEC), zinc N, N'-dibutylcarbamodithioates (ZDBC), zinc N, N'-dibenzylcarbamodithioates (ZDBC), zinc isopropylxanthate ( ZIX), and mixtures thereof. Very preferably, the complementary vulcanization accelerator, different from the vulcanization accelerator described above, is zinc dibenzyldithiocarbamate (ZBEC).

The vulcanization accelerators are commercially available from many suppliers such as Nocil, Lanxess, Flexsys for example.

Preferably, the crosslinking system of the invention may further comprise a stearic acid derivative and zinc oxide. The term "stearic acid derivative", stearic acid or a salt of stearic acid, both of which are well known to those skilled in the art. As an example of stearic acid salt useful in the context of the present invention include zinc stearate or magnesium.

The person skilled in the art knows how to adjust the level of the polysulfide compound of general formula (I) as well as the vulcanization accelerator (s) and activator (s) in the crosslinking system of the invention as a function of the use of this system for crosslinking unsaturated polymers, especially elastomers, in particular diene elastomers.

3 - EXAMPLES

The following example illustrates the invention without limiting it. Its purpose is to demonstrate the improvement of the crosslinking kinetics of a composition when a polysulfurized compound of general formula (I) is used with respect to the use of a crosslinking agent of the prior art. .

For this, three compositions are compared comprising an unsaturated polymer reinforced with carbon black, these compositions differing from each other by the following technical characteristic:

the composition Cl is a non-compliant composition comprising elemental sulfur as a crosslinking agent;

composition C2 is a non-conforming composition comprising a polysulfide compound of formula different from general formula (I): 1,2,3,4-tetrathiecane; and

the composition C3 is a composition in accordance with the invention comprising a polysulfurized compound of general formula (I): compound A.

3.1 - Synthesis of 1,2,3,4-tetrathiecane

1,2,3,4-Tetrathiecane is synthesized according to Reaction Scheme No. 1 and according to the following synthesis protocol:

Reaction Scheme No. 1

To a solution of 1,6-hexanedithiol (8.0 g, 0.053 mol) in ethyl ether (150 ml) at -3 ° C. (bath temperature) is added for 60 minutes, dropwise, a solution of S2Cl2 (7.19 g, 0.053 mmol) in ethyl ether (80 mL). The temperature of the reaction medium is brought to room temperature (at 23 ° C.) over 1.5 hours. Then, the medium is heated for 1.5 hours at 30 ° C. (bath temperature). The precipitate formed is filtered and then solubilized in dichloromethane (200 ml) at 40 ° C. The dichloromethane is evaporated under reduced pressure (1-2 mbar, 35-40 ° C.).

After drying the product for 6 hours under vacuum (1-2 mbar, 40 ° C), a very viscous oil is obtained (8.61 g, 77% yield).

The molar purity is greater than 98 mol%. (1H NMR).

The distribution of x is as follows: 0.3% for x = 2; 1.2% for x = 3; 98.5% for x> 4

3.2 - Synthesis of compound A

Compound A is synthesized according to Reaction Scheme 2 and the following synthesis protocol:

Reaction scheme no. 2 A solution of 2,2'-thiodiethanethiol (10 g, 0.0648 mol, 1 ee, Aldrich, commercial purity) in diethyl ether (400 mL) is cooled to 0-2 ° C (temperature). bath). The solution of S2Cl2 (8.93 g, 0.0661 mol, 1.02 eq.) In anhydrous diethyl ether (200 mL) is added dropwise over 1 hour. Gradually the reaction mixture becomes cloudy and then a white solid is formed. After the addition of all the reagents, the reaction mixture is stirred at room temperature for 1 hour and finally the mixture is refluxed for 2 hours. Then, after returning to ~ 25 ° C, the white solid obtained is filtered, washed with petroleum ether (twice for 25 mL) and dried at room temperature under atmospheric pressure.

The product is then taken up in chloroform (6 mL of the solvent to 1 g of product) and is heated at 50 ° C (bath temperature) for 3 hours. An insoluble fraction and a soluble fraction are obtained.

Compound A is thus obtained in the form of a mixture of the cyclic form (insoluble fraction) and of the open form (soluble fraction). The proportion of the reactants is such that the value of the index n is centered on 3.

The insoluble fraction (cyclic form) is filtered and washed on the filter with chloroform (50 mL) and dried at room temperature under atmospheric pressure. At the end of this treatment, a white polymer product (9.8 g) is obtained. This product being insoluble in the usual solvents, it has not been characterized. The soluble fraction (open form) is in turn concentrated and analyzed by NMR (see NMR characterization below). The product obtained contains oligomers in which the index p has a value in the range from 12 to 23.

The NMR data are as follows:

The chemical shifts in 1 H and ¹³ C for the reasons 1, 2, 3 and 4 are approximate as they change according to the number of sulfur (S) _n 3.3 - Formulation and Preparation of the compositions

The formulation of compositions C1 to C3 is presented in Table I. The amounts are expressed in parts per 100 parts of elastomers (phr). The compositions are formulated with iso-mole of sulfur.

Table I

(1) Natural rubber grade TSR20;

(2) Carbon black marketed by Cabot grade ASTM N335;

(3) Industrial grade zinc oxide marketed Umicore company;

(4) Stearin "Pristerene 4931" marketed by Uniqema;

(5) N- (1,3-dimethylbutyl) -N'-phenyl-p-phenylenediamine ("Santoflex 6-PPD") marketed by Flexsys; (6) N-tert-butyl-2-benzothiazol sulfenamide ("VULKACIT®NZ" from the company Lanxess

(7) 1,2,3,4-tetrathienane obtained according to the synthesis method described in section 4.1;

(8) Compound A obtained according to the synthesis method described in section 4.2. For the preparation of these compositions, the procedure is as follows: is introduced into an internal mixer of 400 cm ³ with "Banburry" type pallets, filled to 70% and whose initial tank temperature is about 60 ° C, diene elastomer, carbon black, anti-oxidant G, zinc oxide and stearic acid. Thermomechanical work is conducted until the temperature of the mixture is about 100 ° C. A first shot of pestle, bringing chaos in the mixture, is then achieved. When the mixture reaches about 140 ° C, a second pestling is performed. Thermomechanical work is continued for about 4 minutes to reach a maximum "fallout" temperature of 160 ° C.

the mixture thus obtained is recovered and cooled on an external mixer at room temperature (23 ° C.). The polysulfurized compound of general formula (I) ((7) or (8) depending on the composition) and the crosslinking accelerator are incorporated into the mixture on the external mixer (homofilizer), then twelve passes in the portfolio are made to homogenize The mixture.

The compositions are then calendered in the form of rubber plates with a thickness of 2 to 3 mm for measuring the rheometric and mechanical properties.

[00148] Unless otherwise indicated, the mechanical properties of the compositions indicated below are those measured after firing (or crosslinking) at t ₉₀ (cf method DIN 53529) at 150 ° C. or at 190 ° C. 3.4 - Results

Rheometry measurements are carried out in accordance with paragraph 1.1 and those of mechanical properties in accordance with paragraph 1.2 The results obtained are presented in Table IL. Table II

[00150] The examination of Table II shows that the composition C1 not according to the invention comprising elemental sulfur as crosslinking agent has a reversion phenomenon at high temperatures (firing temperature at 190 ° C).

Surprisingly, the composition C3 according to the invention comprising a polysulfide compound of general formula (I) instead of elemental sulfur (composition C1 not in accordance with the invention) does not exhibit a reversion phenomenon at high temperatures. Cooking. Moreover, the composition C3 according to the invention has elongation properties greater than those of the composition Cl, regardless of the firing temperature.

Furthermore, it may be noted that the composition C3 according to the invention has a higher firing kinetics than the composition C2 not according to the invention comprising a polysulfide compound of formula different from that of the formula (I), whatever the cooking temperature.

Claims

1. Composition based on at least one unsaturated polymer and at least one polysulfurized compound of general formula (I)

in which :

m is a number in a range from 1 to 3;

n is a number greater than or equal to 3;

p is a number greater than or equal to 1;

The composition of claim 1, wherein the unsaturated polymer is an elastomer.

3. The composition of claim 2, wherein the unsaturated polymer is a diene elastomer.

The composition of claim 3, wherein the diene elastomer is selected from the group consisting of natural rubber, synthetic polyisoprenes, polybutadienes, isoprene copolymers, butadiene copolymers and mixtures of these diene elastomers.

5. Composition according to any one of claims 1 to 4, wherein R 1 and R ₂ represent, independently of one another, alkylene radicals containing from 1 to 18 carbon atoms, preferably from 2 to 10 carbon atoms. carbon, more preferably still 2 to 8 carbon atoms.

6. Composition according to any one of claims 1 to 5, wherein m represents a number in a range from 1 to 2, preferably m is equal to 1.

7. Composition according to any one of claims 1 to 6, wherein n represents a number in a range from 3 to 8, preferably from 3 to 6, more preferably is equal to 3 or 4.

8. Composition according to any one of claims 1 to 7, wherein p represents a number in a range from 1 to 30, preferably from 1 to 15, more preferably from 1 to 3.

9. A composition according to any one of claims 1 to 8, wherein A and B form a covalent bond.

10. Composition according to any one of claims 1 to 8, wherein A represents a hydrogen atom and B represents a group-S-Ri- (S) _m -R ₂ -SH or a hydrogen atom.

11. Composition according to any one of claims 1 to 8, wherein A represents a hydrogen atom and B represents a group-S-Ri- (S) _{m -} R ₂ -SH.

12. Composition according to any one of claims 1 to 11, wherein the level of the polysulfide compound of general formula (I) is in a range from 0.5 to 10 phr, preferably from 0.5 to 5 phr. preferably from 0.5 to 3 phr.

13. Composition according to any one of claims 1 to 12, further comprising a filler.

The composition of claim 13, wherein the filler is a reinforcing filler.

15. The composition of claim 14, wherein the reinforcing filler is selected from an inorganic reinforcing filler, carbon black and their mixture.

16. The composition of claim 14 wherein the reinforcing filler comprises predominantly by weight of carbon black.

17. The composition of claim 14, wherein the reinforcing filler comprises predominantly by weight of the silica.

18. Composition according to any one of claims 1 to 17, which does not include elemental sulfur.

19. Composition according to any one of claims 1 to 17, further comprising elemental sulfur at a rate of less than 1 phr, preferably less than or equal to 0.5 phr.

20. Article comprising at least one composition as defined in any one of claims 1 to 19.

21. Article according to claim 20, characterized in that it is a tire.

22. Process for the manufacture of a composition comprising at least one unsaturated polymer, at least one filler and at least one polysulfurized compound of general formula (I)

in which :

m is a number in a range from 1 to 3;

n is a number greater than or equal to 3;

p is a number greater than or equal to 1;

said method comprising at least the following steps:

23. Use of at least one polysulfide compound of general formula (I) as crosslinking agent for unsaturated polymers

(I) P in which :

m is a number in a range from 1 to 3;

n is a number greater than or equal to 3;

p is a number greater than or equal to 1;

24. A process for crosslinking unsaturated polymers, said process comprising at least the following steps:

At least one unsaturated polymer and at least one polysulfurized compound of general formula (I)

P

(I)

in which

m is a number in a range from 1 to 3; n is a number greater than or equal to 3;

p is a number greater than or equal to 1;

R 1 and R ₂ represent, independently of one another, identical or different divalent hydrocarbon groups containing from 1 to 18 carbon atoms, optionally interrupted by a heteroatom; and • heating the mixture obtained above to a temperature greater than or equal to greater than or equal to 130 ° C, preferably in a range from 130 ° C to 200 ° C.

25. Crosslinking system comprising at least one vulcanization accelerator and at least one polysulfurized compound of general formula (I)

in which :

m is a number in a range from 1 to 3; n is a number greater than or equal to 3;

p is a number greater than or equal to 1;

The crosslinking system of claim 25, wherein the vulcanization accelerator is selected from the group consisting of thiazoles, sulfenamides, guanidines, amines, aldehyde amines, dithiophosphates, xanthates, thiurams, dithiocarbamates and mixtures thereof.

27. The crosslinking system of claim 25 or 26, further comprising a derivative of stearic acid and zinc oxide.