EP3277738A1

EP3277738A1 - Star copolymer and use thereof as a viscosity improver

Info

Publication number: EP3277738A1
Application number: EP16711869.4A
Authority: EP
Inventors: Raphaele IOVINE; Grégory DESCROIX; Jean-François TASSIN; Damien CHAVEROUX
Original assignee: Total Marketing Services SA
Current assignee: TotalEnergies Marketing Services SA
Priority date: 2015-03-30
Filing date: 2016-03-29
Publication date: 2018-02-07
Also published as: JP2018514608A; FR3034421B1; US20180066096A1; FR3034421A1; CN107428885A; WO2016156323A1

Abstract

The present invention relates to a star copolymer (C) including at least 10 wt.% of units derived from styrene monomer and including arms that include a statistical copolymer (EP) including ethylene units and propylene units, and the method for preparing same. The invention also relates to the use thereof in lubricating compositions, in particular for improving the viscosity index, to the lubricating compositions thus obtained and to the uses thereof.

Description

Star copolymer and its use as a viscosity improver

The present invention relates to improvers of the viscosity index of the lubricating compositions, especially for motor vehicles. The invention relates more particularly to a star copolymer that can be used as a lubricant viscosity index improver of lubricating compositions and lubricant compositions thus obtained that can be used in particular for engines, gearboxes or vehicle bridge.

Engine developments and performance of engine lubricating compositions are inextricably linked. The more the engines have a complex design, the higher the efficiency and the optimization of the consumption, the more the engine lubricating composition is solicited and must improve its performance.

Very high compression in the engine, higher piston temperatures, particularly in the area of the upper piston ring, as well as very high temperatures in the engine space are increasingly soliciting lubricating compositions for modern engines.

The conditions of use of gasoline engines and diesel engines include extremely short journeys as well as long journeys.

The emptying intervals are also very variable, from 5,000 km for some small diesel engines to up to 100,000 km on modern commercial diesel engines.

The lubricating compositions used in these vehicles must therefore have improved properties and performance.

It is also appropriate to optimize the formulation of these lubricant compositions to reduce the energy loss caused by friction within the engine.

Another essential requirement of engine lubricating compositions is related to the environmental aspects. It has indeed become essential to reduce lubricant composition consumption and fuel consumption, particularly in order to reduce C0 ₂ emissions.

The nature of automotive engine lubricating compositions has an influence on pollutant emissions and fuel consumption. Engine lubricating compositions for energy-saving automobiles are often referred to as "fuel-eco" (FE). Given the predominantly urban operating conditions, including many engine start-ups and restarts, the fuel-eco properties of the lubricants must be effective at both low and high engine speeds. The reduction of energy losses is therefore a constant search in the field of automotive lubricants.

For their part, the lubricating gearbox or gearbox compositions, and more generally the gear lubricating compositions, must satisfy numerous requirements, particularly related to driving comfort (perfect gearshift, silent operation, trouble-free operation, high reliability), to the service life of the assembly (reduction of wear during the cold run, no deposits and high thermal stability, safety of lubrication at high temperatures, stable viscosity situation and absence of shear loss , long service life) as well as the consideration of environmental aspects (lower fuel consumption, reduced lubricant consumption, low noise, easy evacuation). These are requirements for lubricating compositions for manual gearboxes and axle gears.

Moreover, in the automotive field, the search for the reduction of C0 ₂ emissions makes it necessary to develop products that make it possible to reduce friction in gearboxes and in bridge differentials. This reduction of friction in the gearboxes and in the bridge differentials must be obtained for different operating conditions. These friction reductions must concern the internal friction of the lubricant composition but also the friction of the constituent elements gearboxes or bridge differentials, in particular the metal elements.

To meet these objectives, the viscosity of the lubricating compositions is of all importance. In particular, it is necessary to provide lubricating compositions having a high viscosity index (VI) and a low coefficient of traction. The desired lubricating compositions must have a high viscosity index in order to avoid cold energy losses due to friction but also to keep a sufficient lubricant film on the lubricated elements hot. A high viscosity index thus guarantees a lower drop in viscosity when the temperature increases. For this purpose, viscosity index improvers (VI improvers in English) are generally added to the lubricating compositions. The purpose of these viscosity improvers is to provide selective thickening of the lubricating composition as the temperature increases to partially remedy the fall of viscosity recorded hot. These viscosity index improvers are generally polymers, especially of poly (alkyl) methacrylate type, olefin copolymers, or hydrogenated styrene / diene copolymers.

However, these polymers may have insufficient VI, insufficient engine cleanliness performance, mechanical degradation or high costs related in particular to the need to use these polymers at high levels. In addition, these polymer chemistries do not exhibit any particular character or particular properties when cold. There is therefore an interest in providing novel VI improvers with high VI and improved cold properties.

There is also an interest in providing new VI improvers with a high VI that would not degrade engine cleanliness.

There is also an interest in providing new VI improvers that promote longer engine life and therefore lower engine wear. There is also an interest in providing novel VI improvers which make it possible to retain the properties of the lubricating composition, even under severe conditions of use (shearing, elongation, sliding, etc.).

There is also an interest in providing new VI improvers whose mechanical properties deteriorate very little or little over time whatever the solicitations and duration of these solicitations.

There is also interest in providing novel VI enhancers with high VI and improved cold properties, which persist over time.

There is also interest in providing new VI improvers to reduce the coefficient of friction of lubricating oils.

There is also an interest in providing VI improvers that can be absorbed to the surfaces to be lubricated and thus create a film thickness favorable to the protection of the surfaces to be lubricated and the limitation of friction.

There is also an interest in providing novel VI improvers having the above advantages and whose formulation in a lubricant composition is simple to implement.

There is also an interest in providing lubricating compositions that make it possible to reduce the fuel consumption of an engine, a vehicle equipped with a bridge or a gearbox, or a vehicle equipped with a transmission.

There is also an interest in providing lubricating compositions having "fuel Eco" properties both at low engine speed and in high engine speed. There is also an interest in providing lubricating compositions having "Fuel Eco" properties that persist over time while maintaining rheological and tribological properties, and ensuring maintenance of engine cleanliness. To meet these objectives, the present invention provides a star copolymer (C) comprising at least 10% by weight of units derived from styrene monomer and comprising arms comprising a random copolymer (EP) comprising ethylene units (E) and propylene units (P). In general, a star copolymer comprises a heart and arms at the periphery of the heart. Preferably, the star copolymer (C) of the invention comprises at least 3 arms. Preferably, the star copolymer (C) of the invention comprises from 3 to 25 arms, preferably from 3 to 20 arms, preferably from 3 to 15 arms, preferably from 3 to 10 arms, for example 4, 5, 6, 7 or 8 arms.

In a particular embodiment, the invention also relates to a star copolymer (C) comprising arms comprising an S block and an EP block

S represents a block comprising units derived from styrene monomer, EP represents a random copolymer comprising ethylene units (E) and propylene units (P),

the copolymer (C) comprising at least 10% by weight of units derived from styrene monomer.

In this particular embodiment, the arms may also comprise at least one other monomer or at least one other block between the block S and the block EP.

In the context of the present invention, the arms of the star copolymer (C) preferably comprise a copolymer of the general formula S-EP, in which

S represents a block comprising units derived from styrene monomer, EP represents a random copolymer comprising ethylene units (E) and propylene units (P).

A star copolymer (C) comprising arms comprising a copolymer of the general formula S-EP in which

It should be understood that the copolymer (EP) of each of the arms may be the same or different.

It should also be understood that the S-EP copolymer of each of the arms may be the same or different.

Preferably, EP represents a random copolymer consisting of ethylene units and propylene units. Preferably, EP represents a random copolymer comprising units derived from ethylene monomer (E) and units derived from propylene monomer (P).

Preferably, S represents a block consisting of units derived from styrene monomer.

Preferably, S represents a block consisting of units derived from styrene monomer and EP represents a random copolymer consisting of ethylene units (E) and propylene units (P).

Preferably, S represents a block consisting of units derived from styrene monomer and EP represents a random copolymer comprising units derived from ethylene monomer (E) and units derived from propylene monomer (P).

Particularly advantageously, the block S, if present, is at the periphery of the core of the star copolymer (C) and the EP copolymer is at the ends of the arms. Indeed, particularly advantageously, the block S of the arms, if present, can participate in forming the core of the star copolymer (C) of the present invention.

In a particular embodiment of the invention, the star copolymer (C) can be defined as comprising:

a crosslinked core comprising units derived from styrene monomer; and

arms comprising a random copolymer (EP) comprising ethylene units (E) and propylene units (P);

the copolymer (C) comprising at least 10% by weight of units derived from styrene monomer. In a particular embodiment of the invention, the star copolymer (C) can be defined as comprising:

a crosslinked core comprising units derived from styrene monomer; and

arms comprising a copolymer of the general formula S-EP, in which o represents a block comprising units derived from styrene monomer,

EP represents a random copolymer comprising ethylene units (E) and propylene units (P);

The crosslinked core may in particular be obtained by using a crosslinking agent (or coupling agent) whose patterns are found in the heart. The crosslinking agent may in particular be chosen from polyalkenyls, i.e. compounds having two non-conjugated alkenyl groups, they may be aliphatic, aromatic or heterocyclic. There may be mentioned dienes, for example divinylbenzene, norboradiene ...

In one embodiment of the invention, the arms comprising a random copolymer (EP) comprising ethylene units and the propylene units are bonded to the crosslinked core comprising units derived from styrene monomer by an L bond.

In a preferred embodiment of the invention, the link L is chosen from carbon groups comprising at least one halogen function or an oxygen function, for example an ester function, an alcohol function, an acid function, an ether function, an epoxide function or an anhydride function. acid and their derivatives; carbon groups comprising at least one nitrogen function, for example amine function, amide function, imide function; carbon groups comprising at least one phosphorus function, for example phosphonic acid, phosphoric acid function; carbon groups comprising at least one sulfur function, for example sulphonyl, for example the alkylene glycol polyethylene glycol, poly (ethylene-propylene) glycol, poly (ethylene-butylene) glycol.

In a more preferred embodiment of the invention, the bond L is chosen from among carbon groups comprising at least one halogen function or an epoxide function or an acid anhydride function, advantageously a maleic anhydride function. In a particularly preferred manner, the star copolymer (C) of the invention comprises from 10 to 60% by weight, relative to the total weight of the copolymer (C), of units derived from styrene monomer, preferably from 10 to 50 %, preferably from 10 to 40%, preferably from 10 to 30%, preferably from 20 to 60%, preferably from 20 to 50%, preferably from 20 to 40%, preferably from 20 to 30%, preferably from 15 to 60%, preferably from 15 to 50%, preferably from 15 to 40%, preferably from 15 to 35%, preferably from 15 to 30%, preferably from 25 to 60%, preferably from 25 to 50%, preferably 25 to 40%, preferably 25 to 35%, preferably 25 to 30%, preferably 30 to 60%, preferably 30 to 50%, preferably 30 to 50%, preferably 40%, preferably 30 to 35%.

In a particularly preferred manner, the star copolymer (C) of the invention comprises from 15 to 50%, preferably from 20 to 40%, preferably from 20 to 30% by weight, relative to the total weight of the copolymer (C). ), units derived from styrene monomer. In the context of the present invention, the expressions "from x to y" and "between x and y" should be understood to include the x and y terminals.

The star copolymer (C) of the present invention may be characterized by a mean mass (Mw) of between 90,000 and 15,000,000 g / mol, preferably between 90,000 and 1,000,000 g / mol, for example between 90,000 and 800,000 or between 90000 and 500000 or between 90000 and 300000 or between 90000 and 20000 g / mol.

In the star copolymer (C) of the present invention, each of the arms, identical or different, has a mean mass (Mw) of between 25,000 and 300,000 g / mol, preferably between 25,000 and 200,000 g / mol, more preferably between 25000 and 100000 g / mol.

In the star copolymer (C) of the present invention, the arms are all identical or different and the mean average mass (Mw) of the arms is preferably between 25,000 and 300,000 g / mol, preferably between 200,000 g mol, more preferably between 25000 and 100000 g / mol.

In the context of the present invention, the average masses (Mw) are obtained by GPC (Gel Permeation Chromatography). The star copolymer (C) of the present invention is defined as comprising arms comprising an ethylene-propylene random copolymer (EP copolymer). It should be understood that the EP copolymer of each of the arms may be identical or different and preferably comprises from 14 to 90% by weight of ethylene unit relative to the total weight of the EP copolymer, preferably from 30 to 90%, of preferably from 40 to 90%, preferably from 50 to 90%, preferably from 60 to 90%, preferably from 70 to 90%, preferably from 80 to 90%, preferably from 30 to 80%, preferably from 40 to 80%, preferably 50 to 80%, preferably 60 to 80%, preferably 70 to 80%.

Preferably, the copolymer EP of each of the arms may be identical or different and comprises from 50 to 80%, preferably from 60 to 80% by weight of ethylene unit relative to the total weight of the EP copolymer.

Preferably, the EP copolymers of each of the arms are identical or different and comprise, on average, from 14 to 90% by weight of ethylene unit relative to the total weight of the EP copolymer, preferably from 30 to 90%, preferably from 40 to 80% by weight. at 90%, preferably from 50 to 90%, preferably from 60 to 90%, preferably from 70 to 90%, preferably from 80 to 90%, preferably from 30 to 80%, preferably from 40 to 80%; %, preferably 50 to 80%, preferably 60 to 80%, preferably 70 to 80%.

Preferably, the EP copolymers of each of the arms are identical or different and comprise on average from 50 to 80%, preferably from 60 to 80% by weight of ethylene unit relative to the total weight of the EP copolymer.

In a particularly preferred manner, the star copolymer (C) of the invention:

has a mean mass (Mw) of between 90,000 and 1,000,000 g / mol, for example between 90,000 and 800,000 g / mol

- comprises from 15 to 50%, preferably from 20 to 40%, preferably from 20 to 30% by weight, based on the total weight of the copolymer (C), of units derived from styrene monomer; and

the EP copolymers of each of the arms are identical or different and comprise on average from 50 to 80%, preferably from 60 to 80% by weight of ethylene unit relative to the total weight of the EP copolymer; or the EP copolymer of each of the arms may be the same or different and comprises from 50 to 80%, preferably from 60 to 80% by weight of ethylene unit based on the total weight of the EP copolymer.

In a particularly preferred manner, the star copolymer (C) of the invention:

has a mean mass (Mw) of between 90,000 and 1,000,000 g / mol, for example between 90,000 and 800,000 g / mol - comprises from 15 to 50%, preferably from 20 to 40%, preferably from 20 to 30% by weight, based on the total weight of the copolymer (C), of units derived from styrene monomer;

the EP copolymers of each of the arms are identical or different and comprise on average from 50 to 80%, preferably from 60 to 80% by weight of ethylene unit relative to the total weight of the EP copolymer; or the EP copolymer of each of the arms may be the same or different and comprises from 50 to 80%, preferably from 60 to 80% by weight of ethylene unit based on the total weight of the EP copolymer; and

each arm, identical or different, has a mean mass (Mw) of between 25,000 and 200,000 g / mol, preferably between 25,000 and 100,000 g / mol; or the arms are all identical or different and the mean average mass (Mw) of the arms is between 25,000 and 150,000 g / mol, preferably between 25,000 and 100,000 g / mol.

In a particularly advantageous way, the inventors have also found that the star copolymer (C) of the present invention may also comprise at least one polar group located on at least one of the arms, preferably on the EP portion of the arms and preferably at the end of the EP chain. Without wishing to be bound by any theory, the polar groups interact with the surfaces to be lubricated, thus making it possible to improve the adhesion of the copolymer (C) of the invention, to ensure the presence of a sufficient film for the lubrication and therefore improve lubrication performance. The polar group can in particular be chosen from carbon groups comprising at least one oxygenated function, for example ester function, alcohol function, acid function, ether function, epoxide function, acid anhydride function and their derivatives; carbon groups comprising at least one nitrogen function, for example amine function, amide function, imide function; carbon groups comprising at least one phosphorus function, for example phosphonic acid, phosphoric acid function; carbon groups comprising at least one sulfur function, for example sulphonyl, for example the alkylene glycol polyethylene glycol, poly (ethylene-propylene) glycol, poly (ethylene-butylene) glycol.

Preferably the polar group is the group, Q representing the binding of the polar group to the star copolymer arm. The copolymer (C) of the invention may be in pure form or in the form of a dispersion in an anhydrous medium. Said anhydrous medium may in particular be an oil, preferably a base oil. The dispersion thus obtained may be added to a base oil to form a lubricating composition, in particular such as that described below.

The present invention also relates to a process for preparing a copolymer (C) as described above.

In a first embodiment, the copolymer (C) of the present invention can be obtained by a method (P1) comprising the steps of:

a) polymerization of styrene monomers in the presence of an anionic polymerization crosslinking agent;

b) oligomerization of a short butadiene block;

c) polymerization of the ethylene and propylene monomers to the copolymer obtained in step b) by Ziegler-Natta polymerization, for example in the presence of TiCl ₄ ; d) optionally hydrogenation of the polymer obtained in step c);

e) recovery of a star copolymer (C) according to the invention.

In a second embodiment, the copolymer (C) of the invention may be obtained by a process (P2) comprising the steps of:

a) Ziegler-Natta polymerization preparation of ethylene and propylene monomers;

b) deactivation of the polymer obtained in step a) with an inhibitor, preferably carrying a reactive functionalization, in particular of alcohol type;

c) esterification of the polymer obtained in b);

d) controlled radical polymerization of the polymer obtained in step c) with styrene monomers and a crosslinking agent;

e) optionally hydrogenation of the polymer obtained in step d);

f) recovering a star copolymer (C) according to the invention.

In a third embodiment, the copolymer (C) of the invention may be obtained by a process (P3) comprising the steps of:

a) preparation of a core by controlled radical copolymerization of styrene monomers in the presence of a crosslinking agent; b) functionalization of the core obtained in step a) by controlled radical polymerization by addition of ethylene and propylene monomers;

c) optionally adding, in the reaction medium obtained in step b), a polar polymerizable function;

d) optionally hydrogenation of the polymer obtained in step b) or c) if necessary;

e) recovery of a star copolymer (C) according to the invention.

In this particular embodiment, step c) makes it possible to graft onto the copolymer (C), preferably at the end of the chain of the EP copolymer as defined above, at least one group comprising at least one polar function.

In a fourth embodiment, the copolymer (C) of the invention can be obtained by a process (P4) comprising the steps of:

a) synthesis of a core by metallocene polymerization of styrene monomers in the presence of a crosslinking agent;

b) synthesis of ethylene-propylene copolymers by metallocene polymerization of ethylene and propylene monomers;

c) recovering a star copolymer (C) according to the invention.

In the processes described above, one skilled in the art is able, on the basis of this general knowledge, to determine the quantities of monomers to be used and the specific reaction conditions for obtaining the star copolymers (C). of the invention. In a fifth embodiment, the copolymer (C) of the invention can be obtained by a process (P5) comprising the steps of:

a) synthesizing an ethylene-propylene copolymer (EP);

b) synthesizing a compound capable of generating radicals comprising a group comprising at least one polar function and comprising a radical radical (for example chosen from nitroxide or xanthate);

c) reaction between the ethylene-propylene copolymer (EP) obtained in step a) and the compound capable of generating radicals obtained in step b);

d) copolymerizing the copolymer obtained in step c) with styrene monomers and a crosslinking agent;

e) optionally hydrogenation of the polymer obtained in step d); f) recovering a star copolymer (C) according to the invention preferably comprising at the end of the EP copolymer chain as defined above, at least one group comprising at least one polar function. In a sixth embodiment, the copolymer (C) of the invention may be obtained by a process (P6) comprising:

a) a random copolymer (EP) synthesis step comprising ethylene units, propylene units and residual double bonds;

b) a step of functionalization of the copolymer (EP) resulting from step a) by a reactive function with nucleophilic additions;

c) a step of polymerizing styrene monomers in the presence of a crosslinking agent;

d) a step of adding the polymer resulting from step c) onto the copolymer (EP) derived from step b);

e) a step of recovering the star copolymer (C) resulting from step d).

In a preferred embodiment of the invention, the copolymer (C) is obtained by the process (P6) as defined above. In a more preferred embodiment of the invention, the function reactive to the nucleophilic additions of step b) is chosen from carbon groups comprising at least one oxygenated function, for example ester function, alcohol function, acid function, function ether, epoxide function, acid anhydride function, a halogen function and their derivatives; carbon groups comprising at least one nitrogen function, for example amine function, amide function, imide function; carbon groups comprising at least one phosphorus function, for example phosphonic acid, phosphoric acid function; carbon groups comprising at least one sulfur function, for example sulphonyl, for example the alkylene glycol polyethylene glycol, poly (ethylene-propylene) glycol, poly (ethylene-butylene) glycol. Preferably, the reactive function is chosen from carbon groups comprising an epoxide function, acid anhydride, a halogen function, advantageously an epoxide or maleic anhydride function.

In another preferred embodiment of the invention, the method (P6) comprises a step b-1) after step b) and before step c), said step b-1) comprising a purification step of copolymer (EP) from step b). Advantageously, step b-1) is carried out by washing the copolymer (EP) with methanol and then solubilizing in toluene and evaporation.

This step makes it possible in particular for the copolymer (EP) to be anhydrous and free of trace acidity, in particular when the reactive function with the nucleophilic additions is chosen from carbon groups comprising at least one acid anhydride function.

In another preferred embodiment of the invention, the polymerization of step c) is anionic polymerization.

In a more preferred embodiment of the invention, the polymerization of step c) is anionic polymerization and in the presence of a crosslinking agent.

The crosslinking agent may be chosen from the group of compounds known as crosslinking agent for use in anionic polymerization.

Advantageously, the crosslinking agent is divinylbenzene.

In another preferred embodiment of the invention, the process (P6) comprises a step d-1) between step d) and step e), said step d-1) comprising a step of precipitating the copolymer from step d) in a polar solvent.

Advantageously, the polar solvent is methanol.

The present invention also relates to a lubricant composition comprising at least one base oil and at least one star copolymer (C) according to the invention.

In general, the lubricating composition according to the invention may comprise any type of mineral lubricating base oil, synthetic or natural, animal or vegetable, known to those skilled in the art.

The base oils used in the lubricant compositions according to the invention may be oils of mineral or synthetic origins belonging to groups I to V according to the classes defined in the API classification (or their equivalents according to the ATIEL classification) (Table A) or their mixtures. Content in the Index of

saturated sulfur viscosity (VI)

Group I

<90%> 0.03% 80 <VI <120 Mineral oils

Group II

> 90% <0.03% 80 <VI <120 Hydrocracked oils

Group III

Hydrocracked oils> 90 <0.03%> 120 or hydro-isomerized

Group IV Polyalphaolefines (PAO)

Esters and other bases not included in groups I

Group V

at IV

Table A

The mineral base oils according to the invention include all types of base oils obtained by atmospheric and vacuum distillation of crude oil, followed by refining operations such as solvent extraction, desalphating, solvent dewaxing, hydrotreatment, hydrocracking , hydroisomerization and hydrofinition.

Mixtures of synthetic and mineral oils can also be used.

There is generally no limitation on the use of different lubricating bases to make the lubricating compositions according to the invention, except that they must have properties, in particular viscosity, viscosity index, sulfur content. , oxidation resistance, suitable for use for engines or for vehicle transmissions.

The base oils of the lubricating compositions according to the invention may also be chosen from synthetic oils, such as certain carboxylic acid esters and alcohols, and from polyalphaolefins. The polyalphaolefins used as base oils are, for example, obtained from monomers comprising from 4 to 32 carbon atoms, for example from octene or decene, and whose viscosity at 100 ° C. is between 1, 5 and 15 mm ² . s ^"1 according to the ASTM D445 standard. Their average molecular weight is generally between 250 and 3000 according to the ASTM D5296 standard. Preferably, the base oils of the present invention are selected from the above base oils which the aromatic content is between 0 and 45%, preferably between 0 and 30% The aromatic content of the oils is measured according to the Burdett UV method Without being bound by any theory, the aromaticity of the oil basic is a character allowing to optimize the functioning of the polymer in temperature function. The choice of a low aromatic oil allows an optimum at a higher temperature.

Advantageously, the lubricant composition according to the invention comprises at least 50% by weight of base oils relative to the total mass of the composition.

More advantageously, the lubricating composition according to the invention comprises at least 60% by weight, or even at least 70% by weight, of base oils relative to the total mass of the composition.

More particularly advantageously, the lubricant composition according to the invention comprises from 60 to 99.5% by weight of base oils, preferably from 70 to 99.5% by weight of base oils, relative to total mass of the composition.

Many additives can be used for this lubricant composition according to the invention.

The preferred additives for the lubricant composition according to the invention are chosen from detergent additives, anti-wear additives, friction modifying additives, extreme pressure additives, dispersants, pour point improvers, anti-wear agents and anti-wear agents. foam, thickeners and mixtures thereof.

Preferably, the lubricating composition according to the invention comprises at least one antiwear additive, at least one extreme pressure additive or their mixtures.

Anti-wear additives and extreme pressure additives protect friction surfaces by forming a protective film adsorbed on these surfaces.

There is a wide variety of anti-wear additives. In a preferred manner for the lubricating composition according to the invention, the anti-wear additives are chosen from phosphosulfur additives such as metal alkylthiophosphates, in particular zinc alkylthiophosphates, and more specifically zinc dialkyldithiophosphates or ZnDTPs. The preferred compounds have the formula Zn ((SP (S) (OR ¹ ) (OR ² )) ₂ , in which R ¹ and R ² , which may be identical or different, independently represent an alkyl group, preferably an alkyl group containing from 1 to 18 carbon atoms.

Amine phosphates are also anti-wear additives which can be used in the lubricating composition according to the invention. However, the phosphorus provided by these additives can act as a poison of the catalytic systems of automobiles because these additives are ash generators. These effects can be minimized by partially substituting amine phosphates with non-phosphorus additives, such as, for example, polysulfides, especially sulfur-containing olefins. Advantageously, the lubricating composition according to the invention may comprise from 0.01 to 6% by weight, preferably from 0.05 to 4% by weight, more preferably from 0.1 to 2% by weight relative to the total weight of lubricating composition, antiwear additives and extreme pressure additives.

Advantageously, the lubricant composition according to the invention may comprise at least one friction-modifying additive. The friction modifying additive may be chosen from a compound providing metal elements and an ash-free compound. Among the compounds providing metal elements, mention may be made of transition metal complexes such as Mo, Sb, Sn, Fe, Cu and Zn, the ligands of which may be hydrocarbon compounds comprising oxygen, nitrogen, sulfur or phosphorus. The ashless friction modifier additives are generally of organic origin and may be selected from monoesters of fatty acids and polyols, alkoxylated amines, alkoxylated fatty amines, fatty epoxides, borate fatty epoxides; fatty amines or fatty acid glycerol esters. According to the invention, the fatty compounds comprise at least one hydrocarbon group comprising from 10 to 24 carbon atoms.

Advantageously, the lubricant composition according to the invention may comprise from 0.01 to 2% by weight or from 0.01 to 5% by weight, preferably from 0.1 to 1.5% by weight or 0.1 at 2% by weight relative to the total mass of the lubricant composition, friction modifier additive.

Advantageously, the lubricant composition according to the invention may comprise at least one antioxidant additive.

The antioxidant additive generally serves to retard the degradation of the lubricating composition in service. This degradation can notably result in the formation of deposits, the presence of sludge or an increase in the viscosity of the lubricant composition.

Antioxidant additives act in particular as radical inhibitors or destroyers of hydroperoxides. Among the antioxidant additives commonly used, mention may be made of antioxidant additives of phenolic type, antioxidant additives of amine type, antioxidant phosphosulfur additives. Some of these antioxidant additives, for example phosphosulfur antioxidant additives, can be ash generators. Phenolic antioxidant additives may be ash-free or may be in the form of neutral or basic metal salts. The antioxidant additives may especially be chosen from sterically hindered phenols, sterically hindered phenol esters and sterically hindered phenols comprising a thioether bridge, diphenylamines, diphenylamines substituted by at least one C 1 -C 12 alkyl group, and Ν, Ν '-dialkyl-aryl diamines and mixtures thereof. Preferably, according to the invention, the sterically hindered phenols are chosen from compounds comprising a phenol group in which at least one vicinal carbon of the carbon bearing the alcohol function is substituted with at least one alkyl group in the range of d-C ₁ 0, preferably one C ₁ -C ₆ alkyl group, preferably a C ₄ alkyl group, preferably by the ter-butyl group.

Amino compounds are another class of antioxidant additives that can be used, optionally in combination with phenolic antioxidant additives. Examples of amine compounds are aromatic amines, for example aromatic amines of formula NR ³ R ⁴ R ⁵ in which R ³ represents an optionally substituted aliphatic or aromatic group, R ⁴ represents an optionally substituted aromatic group, R ⁵ represents a hydrogen atom, an alkyl group, an aryl group or a group of formula R ⁶ S (O) _z R ⁷ in which R ⁶ represents an alkylene group or an alkenylene group, R ⁷ represents an alkyl group, a alkenyl group or an aryl group and z represents 0, 1 or 2.

Sulfurized alkyl phenols or their alkali and alkaline earth metal salts can also be used as antioxidant additives.

Another class of antioxidant additives is copper compounds, for example copper thio- or dithio-phosphates, copper and carboxylic acid salts, dithiocarbamates, sulphonates, phenates, copper acetylacetonates. Copper salts I and II, succinic acid or anhydride salts can also be used.

The lubricant composition according to the invention may contain all types of antioxidant additives known to those skilled in the art.

Advantageously, the lubricating composition comprises at least one ash-free antioxidant additive.

Also advantageously, the lubricating composition according to the invention comprises from 0.5 to 2% by weight relative to the total weight of the composition, of at least one antioxidant additive.

The lubricant composition according to the invention may also comprise at least one detergent additive.

The detergent additives generally make it possible to reduce the formation of deposits on the surface of the metal parts by dissolving the secondary oxidation and combustion products. The detergent additives that can be used in the lubricant composition according to the invention are generally known to those skilled in the art. The detergent additives may be anionic compounds comprising a long lipophilic hydrocarbon chain and a hydrophilic head. The associated cation may be a metal cation of an alkali metal or alkaline earth metal.

The detergent additives are preferably chosen from the alkali metal or alkaline earth metal salts of carboxylic acids, the sulphonates, the salicylates, the naphthenates and the phenate salts. The alkali and alkaline earth metals are preferably calcium, magnesium, sodium or barium.

These metal salts generally comprise the metal in stoichiometric amount or in excess, therefore in an amount greater than the stoichiometric amount. It is then overbased detergent additives; the excess metal bringing the overbased character to the detergent additive is then generally in the form of an oil insoluble metal salt, for example a carbonate, a hydroxide, an oxalate, an acetate, a glutamate, preferably a carbonate .

Advantageously, the lubricant composition according to the invention may comprise from 2 to 4% by weight of detergent additive relative to the total mass of the lubricating composition.

Also advantageously, the lubricant composition according to the invention may also comprise at least one pour point depressant additive.

By slowing the formation of paraffin crystals, pour point depressant additives generally improve the cold behavior of the lubricant composition according to the invention.

As examples of pour point depressant additives, mention may be made of alkyl polymethacrylates, polyacrylates, polyarylamides, polyalkylphenols, polyalkylnaphthalenes and alkylated polystyrenes.

Advantageously, the lubricant composition according to the invention may also comprise at least one dispersing agent.

The dispersing agent may be chosen from Mannich bases, succinimides and their derivatives.

Also advantageously, the lubricating composition according to the invention may comprise from 0.2 to 10% by weight of dispersing agent relative to the total mass of the lubricating composition.

The lubricating composition of the present invention may also comprise at least one additional viscosity index improving polymer. As examples of additional viscosity index-improving polymers, there may be mentioned esters polymers, homopolymers or copolymers, hydrogenated or non-hydrogenated, styrene, butadiene and isoprene, polymethacrylates (PMA).

The lubricating composition according to the invention can be in various forms. The lubricant composition according to the invention may in particular be an anhydrous composition. Preferably, this lubricating composition is not an emulsion.

The lubricating composition according to the present invention preferably comprises from 0.1 to 50% by weight of star copolymer (C) as defined above relative to the total weight of the lubricating composition, preferably from 0.5 to 30% in weight.

Preferably, in the context of motor use, the lubricating composition of the present invention comprises from 0.1 to 10% by weight of star copolymer (C) as defined above relative to the total weight of the lubricant composition preferably 0.5 to 5% by weight.

Preferably, in the context of a use in transmission, the lubricating composition of the present invention comprises from 5 to 50% by weight of star copolymer (C) as defined above relative to the total weight of the lubricant composition, preferably from 10 to 30% by weight. The present invention also relates to the use of a copolymer (C) according to the invention as improving the viscosity index of a lubricating composition. Preferably, the use of a copolymer (C) according to the invention makes it possible to reach viscosity indices of at least 200. The viscosity number is measured according to the ASTM D2270 or ISO standard.

Preferably, the copolymer (C) is used in a proportion of 0.1 to 50% by weight relative to the total weight of the lubricating composition, preferably from 0.5 to 30% by weight.

Preferably, in the context of a motor use, the copolymer (C) is used in a proportion of 0.1 to 10% by weight relative to the total weight of the composition, preferably from 0.5 to 5% by weight .

Preferably, in the context of a use in transmission, the copolymer (C) is used in a proportion of 0.1 to 50% by weight relative to the total weight of the composition, preferably from 0.5 to 30% by weight. weight.

The ranges indicated above apply to the pure copolymer or to the dispersion of the copolymer in an anhydrous medium as defined above. The present invention also relates to the use of a copolymer (C) as described above:

to reduce the coefficient of friction of a lubricating composition; or

in a lubricant composition for reducing the fuel consumption of an engine, in particular a vehicle engine; or

in a lubricant composition for reducing the fuel consumption of a vehicle equipped with a bridge or a gearbox; or

in a lubricating composition for reducing the fuel consumption of a vehicle equipped with a transmission; or

- To reduce the tensile coefficient of lubricating compositions including transmission or gearbox; or

to improve the Fuel Eco (FE) of a lubricating composition.

The ranges indicated above apply to the pure copolymer or to the dispersion of the copolymer in an anhydrous medium as defined above. The invention also relates to the use of a lubricant composition as defined above:

to reduce the fuel consumption of an engine, especially a vehicle engine; or

- to reduce the fuel consumption of a vehicle equipped with a bridge or gearbox; or

- to reduce the fuel consumption of a vehicle equipped with a transmission.

The invention also relates to a method for modifying the viscosity number of a lubricating composition comprising adding to said lubricant composition a star copolymer (C) according to the invention. As part of this process, the copolymer (C) is used in a proportion of 0.1 to 50% by weight relative to the total weight of the lubricating composition, preferably from 0.5 to 30% by weight.

The ranges indicated above apply to the pure copolymer or to the dispersion of the copolymer in an anhydrous medium as defined above.

The invention also relates to a method:

- reducing the coefficient of friction of a lubricant composition; or

- reducing the fuel consumption of an engine, including a vehicle engine; or

- reducing the fuel consumption of a vehicle equipped with a bridge or gearbox; or

- reducing the fuel consumption of a vehicle equipped with a transmission; or

- Reducing the tensile coefficient of lubricating compositions including transmission or gearboxes; or

- Improvement of Fuel Eco (FE) of a lubricating composition;

comprising adding to said lubricating composition, or to the lubricating composition implemented in said engine or said vehicles, a star copolymer (C) according to the invention.

As part of this process, the copolymer (C) is used in a proportion of 0.1 to 50% by weight relative to the total weight of the lubricating composition, preferably from 0.5 to 30% by weight.

Preferably, in the context of a use in transmission, the copolymer (C) is used in a proportion of 0.1 to 50% by weight relative to the total weight of the composition, preferably from 0.5 to 30% by weight. weight. The ranges indicated above apply to the pure copolymer or to the dispersion of the copolymer in an anhydrous medium as defined above.

The invention also relates to a method

- reducing the fuel consumption of an engine, including a vehicle engine; or

- reducing the fuel consumption of a vehicle equipped with a transmission;

comprising implementing a lubricant composition according to the invention.

By analogy, the particular, advantageous or preferred characteristics of the star copolymer (C) according to the invention or of the lubricating composition according to the invention define particular, advantageous or preferred uses according to the invention.

The invention will now be described using non-limiting examples.

Example 1 Preparation of a Star Copolymer (C) According to the Invention

The entire preparation process is carried out under a controlled atmosphere of nitrogen. Furthermore, all the monomers are purified on an activated neutral alumina column and are stored on molecular sieve 4A under an inert atmosphere. The sec-BuLi solution used is 1.4M in hexane.

2 ml of anhydrous toluene (azeotropic purification), 1.0 ml of styrene (8.7 mmol) and 1, are introduced into a 2 liter reactor equipped with mechanical stirring (anchor type) and a counterpoise. 20 ml of Ν, Ν, Ν ', Ν'-tetramethylethylenediamine (4.0 mmol). The solution obtained is then degassed by three vacuum / nitrogen cycles and cooled to -20 ° C. with stirring (200 rpm). The protic impurities are neutralized by a dropwise addition of sec-butyllithium to a persistent yellow / orange coloration (amount of sec-BuLi variable between 0.2 and 0.6 mL). The load of sec-BuLi is then added rapidly (2.85 mL, 4 mmol) under 350 rpm of stirring and 1.12 mL of divinylbenzene (8 mmol) are then added. The medium then quickly turns a dark red color. The medium is stirred for 30 min at -20 ° C (200 rpm). Styrene (15 mL, 130 mmol) is then added rapidly at -20 ° C. The medium is then heated at 50 ° C. for 2 hours and then brought back to ambient temperature (medium of bright orange color). Then one ethylene / propylene random copolymer solution comprising maleic anhydride functional groups (V4021 distributed by FUNCTIONAL PRODUCTS INC and hereinafter referred to as OCP / MAH) is added to the medium by canula under an inert atmosphere.

Before its introduction, the OCP / MAH is purified according to the following method: in a flask fitted with mechanical stirring are solubilized 30 g of OCP / MAH in 500 ml of toluene. The copolymer is dissolved in 16h with vigorous stirring at 35 ° C. The copolymer is then precipitated in 1.5 L of MeOH with vigorous stirring. The solid is washed with 500 mL of additional methanol by trituration. The solid is then dried under reduced pressure at 40 ° C. for 4 hours.

The OCP / MAH obtained (28.5 g) is then dissolved in 700 ml of toluene. The solution thus obtained is refluxed under nitrogen in a dean-stark type of assembly for 24 hours by regularly withdrawing the toluene / water binary in the dean-stark. The solution is then cooled to room temperature and analyzed by IR.

The addition is stopped as soon as the orange color disappears (pale yellow medium) (75% by volume of the solution, ie 21 g of OCP). 20 ml of methanol are added to quench the reaction. The copolymer obtained is then purified by precipitation and washed by trituration in 2L of methanol. The copolymer is dried under vacuum overnight at room temperature.

The copolymer (C) obtained is a star copolymer comprising 34% by weight of styrene units (measured by NMR spectroscopy) and arms comprising an ethylene / propylene random copolymer.

EXAMPLE 2 Evaluation of the Improving Properties of the Viscosity Index of a Star Copolymer (C) According to the Invention

The star copolymer of Example 1 is solubilized in the following base oils: base oil 1: Group I base oil (kinematic viscosity measured at 100 ° C. according to the ISO 3104 standard = 5.19 mm ² / s )

base oil 2: Group V base oil of alkylnaphthalene type (Synesstic 5 marketed by Exxonmobil)

For this purpose, 1 g of star copolymer of Example 1 is solubilized in 100 g of base oil and then subjected to magnetic hot plate stirring at 150 ° C. for 96 h.

Then each mixture is filtered and centrifuged. Mixtures 1 and 2 thus prepared are described in Table I (the values described corresponding to mass percentages):

Table I The viscosity number of mixtures 1 and 2 as well as base oils 1 and 2 are measured according to ISO 2909 and the results are described in Table II

Table II These results show that the star copolymer (C) according to the invention makes it possible to improve the viscosity index of a base oil, whatever the nature of the base oil. These results therefore demonstrate that the star copolymer according to the invention can therefore be used in a lubricant composition as a VI enhancer.

Claims

1. - Star copolymer (C) comprising at least 10% by weight of units derived from styrene monomer and comprising arms comprising a random copolymer (EP) comprising ethylene units and propylene units.

2. - Copolymer (C) according to claim 1, comprising arms comprising a copolymer of the general formula S-EP, in which:

S represents a block comprising units derived from styrene monomer;

EP represents a random copolymer comprising ethylene units and propylene units,

the star copolymer (C) comprising at least 10% by weight of units derived from styrene monomer.

3. - Copolymer (C) according to claim 1 comprising:

a crosslinked core comprising units derived from styrene monomer; and arms comprising a random copolymer (EP) comprising ethylene units (E) and propylene units (P);

4. - Copolymer (C) according to claim 2, wherein the S block of the S-EP copolymer is at the periphery of the core and the EP copolymer at the ends.

5. - Star copolymer (C) according to any one of claims 1 to 4, comprising from 10 to 60% by weight relative to the total weight of the copolymer (C) of units derived from styrene monomer, preferably from 10 to 60% by weight relative to the total weight of the copolymer (C) of units derived from styrene monomer, preferably from 10 to at 50%, preferably from 10 to 40%, preferably from 10 to 30%, preferably from 20 to 60%, preferably from 20 to 50%, preferably from 20 to 40%, preferably from 20 to 30%, preferably from 20 to 30%; %, preferably from 15 to 60%, preferably from 15 to 50%, preferably from 15 to 40%, preferably from 15 to 35%, preferably from 15 to 30%, preferably from 25 to 60%, preferably 25 to 50%, preferably 25 to 40%, preferably 25 to 35%, preferably 25 to 30%, preferably 30 to 60%, preferably 30 to 50%, preferably from 30 to 40%, preferably from 30 to 35%.

6. Star copolymer (C) according to any one of claims 1 to 5, of average weight (Mw) of between 90,000 and 15,000,000 g / mol, preferably from 90,000 to 1,000,000 g / mol, for example from 90,000 to 800,000 g / mol. 7. Star copolymer (C) according to any one of claims 1 to 6, comprising from 3 to 25 arms, preferably from 3 to 20 arms, preferably from 3 to 15 arms, preferably from 3 to 10 arms, preferably 4, 5, 6,

7 or 8 arms, preferably these arms are identical or different.

8. Star copolymer (C) according to any one of claims 1 to 7, wherein each arm, identical or different, have a mean mass (Mw) of between 25 000 and 300 000 g / mol, preferably between 25,000 and 100,000 g / mol.

9. - Star copolymer (C) according to any one of claims 1 to 8, wherein the arms are all identical or different and the average weight average (Mw) of the arms is between 25 000 and 300 000 g / mol, preferably between 25,000 and 100,000 g / mol.

10. - Star copolymer (C) according to any one of claims 1 to 9, wherein the EP copolymer in each of the arms is identical or different and comprises from 14 to

90% by mass of ethylene unit relative to the total mass of said EP copolymer, preferably from 30 to 90%, preferably from 40 to 90%, preferably from 50 to 90%, preferably from 60 to 90%, of preferably from 70 to 90%, preferably from 80 to 90%, preferably from 30 to 80%, preferably from 40 to 80%, preferably from 50 to 80%, preferably from 60 to 80%, preferably from 70 to 80%.

1 1. - Star copolymer (C) according to any one of claims 1 to 9, wherein the EP copolymers in each of the arms are all identical or different, and comprise on average from 14 to 90% by weight of ethylene unit relative to the average weight of the EP copolymers, preferably from 30 to 90%, preferably from 30 to 90%, preferably from 40 to 90%, preferably from 50 to 90%, preferably from 60 to 90%, preferably from 70 to 90%, at 90%, preferably from 80 to 90%, preferably from 30 to 80%, preferably from 40 to 80%, preferably from 50 to 80%, preferably from 60 to 80%, preferably from 70 to 80%; %.

12. - star copolymer (C) according to any one of claims 1 to 1 1, further comprising at least one group comprising at least one polar function on at least one of the arms, preferably on the EP portion of arm, preferably at the end of the chain of arms.

13. - Star copolymer (C) according to any one of claims 1 to 12 in the form of a dispersion in an anhydrous medium, preferably in an oil.

14. - Lubricating composition comprising at least one base oil and at least one star copolymer (C) according to any one of claims 1 to 13.

15. - lubricating composition according to claim 14 comprising from 0.1 to 50% by weight of star copolymer (C), according to any one of claims 1 to 13, relative to the total weight of the composition, preferably 0 , 5 to 30%.

16. - Use of a star copolymer (C) according to any one of claims 1 to 13 as improving the viscosity index of a lubricating composition.

17. - Use according to claim 16, wherein the star copolymer (C) is used in a proportion of 0.1 to 50% by weight relative to the total weight of the composition, preferably from 0.5 to 30%.

18. - Use of a star copolymer (C) according to any one of claims 1 to 13:

to reduce the coefficient of friction of a lubricating composition; or

to reduce the tensile coefficient of the lubricating compositions, especially transmission or gearboxes; or

to improve the Fuel Eco (FE) of a lubricating composition.

19. - Use of a lubricant composition according to claim 14 or 15:

to reduce the fuel consumption of an engine, especially a vehicle engine; or

- to reduce the fuel consumption of a vehicle equipped with a transmission.

20. - Process for the preparation of a star copolymer (C) according to any one of claims 1 to 13, comprising:

e) a step of recovering the star copolymer (C) resulting from step d).