Use of a polyalkoxysiloxane base oil as a lubricating agent

Abstract

The present invention relates to the use of a polyalkoxysiloxane base oil of formula (I) [Chem.1] in which each R1 is independently a C1-C4 alkyl group or a phenyl group, each R2 is independently a C2-C22 alkyl or alkenyl group or a phenyl group, R3 is either a methyl group or a CH2 group linked to the other R3 group by a single bond, thus forming a ring in which the two terminal silicon atoms are linked by a CH2-CH2 bridge, x is an integer from 0 to 50, y is an integer from 1 to 500, and such that the ratio y / x is strictly greater than 0.5, or of a mixture of polyalkoxysiloxane base oils of formula (I), as a lubricating agent. Figure for abstract: No figure

Description

Title of the invention: Use of a polyalkoxysiloxane base oil as a lubricating agent technical field

[0001] The present invention relates to the technical field of lubricants, in particular base oils for lubricating applications. TECHNOLOGICAL BACKGROUND

[0002] In this field, a lubricating composition is generally composed of a base oil to which a number of additives are added to adjust properties such as, for example, foaming, corrosion resistance, oxidation resistance (via antioxidants) and wear resistance (via anti-wear or extreme pressure additives).

[0003] Silicone oils, also known as polydimethylsiloxanes (PDMS), are used as base oils in certain industrial applications, particularly as lubricants or dielectric fluids, in cosmetics, and in instrumentation. Their main advantage lies in their good fluidity, especially at low temperatures, which is characterized by a high viscosity index. Silicone chemistry is also recognized for its excellent thermal resistance and fire behavior, offering users a very high level of safety during operation.

[0004] Moreover, this type of chemistry is also distinguished by a significantly improved toxicological aspect compared to that of other chemistries such as PolyAlphaOlefins (some grades of which can be fatal if ingested and enter the respiratory tract) or Phosphate esters which, moreover, are carcinogenic category 2 because of n-tributylphosphate.

[0005] However, silicone oils, particularly PDMS, exhibit very low lubricating power, as described in particular in the publication by E.D. Brown, "Methyl Alkyl Silicones, A New Class of Lubricants," Asie Trans. 1966, 9, 31-35. Furthermore, silicone oils, especially PDMS, exhibit poor compatibility with other components, notably very poor compatibility with additives commonly used in this field. Thus, it is difficult to substantially modify the properties of silicone oils by adding additives, as is generally the case in the field of lubricating compositions.

[0006] In this context, the Applicant has developed a new family of polyalkoxysiloxane derivatives having significantly better lubrication properties than polydimethylsiloxanes, while retaining other interesting physicochemical properties in ranges close to those Polydimethylsiloxanes, for example, exhibit high viscosity index, high thermal resistance, and non-flammability. These polyalkoxysiloxane derivatives also demonstrate compatibility with other components, particularly additives and other families of synthetic and mineral base oils, unlike conventional polydimethylsiloxanes. This allows for a significant expansion of their use by offering the possibility of modifying, adjusting, and / or optimizing the properties of lubricating compositions whose base oil contains such a polyalkoxysiloxane. Summary of the invention

[0007] The present invention relates to the use of a polyalkoxysiloxane base oil of formula (I):

[0008] [Chem.l] RI RI Me RS —:Sïr O “J- Si ~O jy [- SI- O —k S R3 Me R1 O Me

[0009] in which

[0010] each RI is independently an alkyl group at Cl to C4 or a phenyl,

[0011] each R2 is independently an alkyl or alkenyl group at C2 to C22 or a phenyl,

[0012] R3 is either a methyl group or a CH2 group linked to the other R3 group by a single bond, thus forming a ring in which the 2 terminal silicon atoms are linked by a CH2-CH2 bridge,

[0013] x is an integer between 0 and 50,

[0014] y is an integer between 1 and 500 and such that the ratio y / x is strictly greater than 0.5,

[0015] or a mixture of polyalkoxysiloxane base oils of formula (I),

[0016] as a lubricating agent.

[0017] Other non-limiting and advantageous features of use according to the invention, taken individually or in all technically possible combinations, are as follows:

[0018] x is equal to 0 and each RI is chosen independently from among the methyl, ethyl and phenyl groups;

[0019] each R2 is independently an alkyl or alkenyl group at C4 to C18, preferably at C4 to C12;

[0020] each R3 is a methyl group;

[0021] The polyalkoxysiloxane is chosen from the group consisting of polyalkoxysiloxanes of formula (I) in which:

[0022] x=0, y is between 1 and 140, each RI is a methyl, each R3 is a methyl and each R2 is an n-butyl chain, x=0, y is between 1 and 140, each RI is a methyl, each R3 is a methyl and each R2 is a heptyl chain, x=0, y is between 1 and 140, each RI is a methyl, each R3 is a methyl and each R2 is a dodecyl chain, x=0, y is between 1 and 140, each RI is a methyl, each R3 is a methyl and each R2 is a tetradecyl chain, and x=0, y is between 1 and 140, each RI is a methyl, each R3 is a methyl and each R2 is chosen from the group consisting of octadecenyl and hexadecyl chains;

[0023] The polyalkoxysiloxane base oil of formula (I) is used as a dielectric fluid, coolant fluid or as a hydraulic fluid;

[0024] The polyalkoxysiloxane base oil of formula (I) is used in a mixture with at least one other base oil, as a co-base.

[0025] The invention also relates to a lubricating composition comprising a polyalkoxysiloxane base oil of formula (I) as described above and at least one additive.

[0026] Preferably, said at least one additive is chosen from the group consisting of extreme-pressure additives, anti-wear additives, detergent additives, viscosity-modifying additives, anti-foaming additives, antioxidant additives, flame retardants, corrosion inhibitors and a combination of at least two of said additives.

[0027] Advantageously, said composition includes at least one flame retardant additive, so as to obtain a non-flammable hydraulic fluid.

[0028] The invention also relates to polyalkoxysiloxanes of formula (II):

[0029] [Chem.2]

[0030] in which

[0031] each RI is independently an alkyl group at Cl to C4 or a phenyl,

[0032] each R2 is independently an alkyl or alkenyl group at C4 to C16 or a phenyl,

[0033] x is an integer between 0 and 50,

[0034] y is an integer between 1 and 500, and such that the ratio y / x is strictly greater than 0.5.

[0035] The invention also relates to particular polyalkoxysiloxanes, selected from the group consisting of polyalkoxysiloxanes of formula (II) in which:

[0036] x=0, y is between 1 and 140, preferably between 40 and 80, each RI is a methyl, and each R2 is an n-butyl chain (PAS4),

[0037] x=0, y is between 1 and 140, preferably between 40 and 80, each RI is a methyl, and each R2 is a heptyl chain (PAS7),

[0038] x=0, y is between 1 and 140, preferably between 40 and 80, each RI is a methyl, and each R2 is a dodecyl chain (PAS 12),

[0039] x=0, y is between 1 and 140, preferably between 40 and 80, each RI is a methyl, each R3 is a methyl group and each R2 is a tetradecyl chain (PAS 14), and

[0040] x=0, y is between 1 and 140, preferably between 40 and 80, each RI is a methyl, and each R2 is chosen from the group consisting of octadecenyl and hexadecyl chains (PAS16-18).

[0041] In the present invention, unless otherwise specified, the term "comprise" and its derivatives shall be understood as non-limiting and not excluding the presence of other components or steps. In certain particular embodiments, the term "comprise" may be understood as "consisting essentially of" or "being made up of".

[0042] Unless otherwise specified, the intervals mentioned in the present invention are understood to include the limits.

[0043] Of course, the different features, variants and embodiments of the invention can be combined with each other in various ways insofar as they are not incompatible or mutually exclusive. BRIEF DESCRIPTION OF THE FIGURE

[0044] In addition, various other features of the invention become apparent from the attached description made with reference to the drawings which illustrate non-limiting embodiments of the invention and where:

[0045] [Fig. 1] presents the results of friction coefficient measurement for different polyalkoxysiloxanes according to the invention. DETAILED DESCRIPTION OF THE INVENTION

[0046] The present invention relates first of all to the use of a polyalkoxysiloxane base oil of formula (I)

[0047] [Chem.l] Ms R1 RI Me R3 -SR SHD Me RI O 1 Me i 02 «

[0048] in which

[0049] each RI is independently an alkyl group at Cl to C4 or a phenyl,

[0050] each R2 is independently an alkyl or alkenyl group at C2 to C22 or a phenyl,

[0051] R3 is either a methyl group or a CH2 group linked to the other R3 group by a single bond, thus forming a ring in which the 2 terminal silicon atoms are linked by a CH2-CH2 bridge,

[0052] x is an integer between 0 and 50,

[0053] y is an integer between 1 and 500 and such that the ratio y / x is strictly greater than 0.5,

[0054] or a mixture of polyalkoxysiloxane base oils of formula (I),

[0055] as a lubricating agent.

[0056] By "alkyl group in the C1 to C2 region" is meant a saturated hydrocarbon group, linear, branched, or cyclic, comprising i to j carbon atoms, and optionally interrupted by one or more heteroatoms, such as O or S. Examples of alkyl groups in the C1 to C2 region include methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, iso-butyl, tert-butyl, n-pentyl, n-hexyl, cyclohexyl, n-heptyl, n-octyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl, n-tetradecyl, n-hexadecyl, and n-octadecenyl. In general, an alkyl group in the C1 to C2 region according to the invention is a linear saturated group or a branched saturated group, preferably a linear saturated group.

[0057] By "C1 to C1 alkenyl group" is meant an unsaturated, linear, branched, or cyclic hydrocarbon group comprising i to j carbon atoms, and optionally interrupted by one or more heteroatoms, such as O or S. The alkenyl group may include one or more unsaturations such as double bonds between two carbon atoms. Preferably, the alkenyl group comprises a single unsaturation. Preferably, the unsaturation(s) of the alkenyl group are double bonds between two carbon atoms. Examples of C2 to C1 alkenyl groups include ethenyl, propenyl, butenyl, pentenyl, hexenyl, cyclohexenyl, heptenyl, octenyl, nonenyl, decenyl, undecenyl, dodecenyl, tetradecenyl, hexadecenyl, and octadecenyl. Preferably, an alkenyl group according to the invention is linear or branched, in particular linear.

[0058] According to the invention, "phenyl" is commonly understood to mean a univalent group of benzene comprising six carbon atoms bonded to five hydrogen atoms.

[0059] In one embodiment, each RI is independently selected from the group consisting of a methyl group, an ethyl group, and a phenyl group. Preferably, all the RIs are methyl groups, or all the RIs are ethyl groups, or all the RIs are phenyl groups. In particular, all the RIs are methyl groups.

[0060] In one embodiment, each R2 is independently an alkyl or alkenyl group at C2 to C22, preferably at C2 to Cl8, preferably at C4 to Cl8, preferably at C4 to C16, preferably at C4 to C12.

[0061] In one embodiment, each R2 is independently an alkyl group in C2 to C22, preferably in C2 to Cl8, preferably in C4 to Cl8, preferably in C4 to C16, preferably in C4 to C12.

[0062] According to the invention, by a group comprising a number of carbons from "C2 to C22", the following values ​​are understood to mean, or any other interval between these values: 2; 3; 4; 5; 6; 7; 8; 9; 10; 11; 12; 13; 14; 15; 16; 17; 18; 19; 20; 21; 22.

[0063] The R2 chains may all be identical in the same compound of formula (I), but they may also be different in pairs. In particular, the use of R2 chains of different lengths in the same compound of formula (I) can combine the advantages in terms of the properties of compounds of formula (I) with R2 chains of each length.

[0064] In one embodiment, each R3 is a methyl group.

[0065] x is an integer between 0 and 50, y is an integer between 1 and 500.

[0066] According to the invention, a range "between 0 and 50" means the following values ​​or any interval between these values: 1; 2; 3; 4; 5; 6; 7; 8; 9; 10; 11; 12; 13; 14; 15; 16; 17; 18; 19; 20; 21; 22; 23; 24; 25; 26; 27; 28; 29; 30; 31; 32; 33; 34; 35; 36; 37; 38; 39; 40; 45; 50. Similarly, according to the invention, a range "between 1 and 500" means the following values ​​or any interval between these values: 1; 2; 3; 4; 5; 6; 7; 8; 9; 10; 11; 12; 13; 14; 15; 16; 17; 18; 19; 20; 21; 22; 23; 24; 25; 26; 27; 28; 29; 30; 31; 32; 33; 34; 35; 36; 37; 38; 39; 40; 45; 50; 55; 60; 65; 70; 75; 80; 85; 90; 95; 105; 110; 115; 120; 125; 130; 135; 140; 145; 150; 155; 160; 165; 170; 175; 180; 185; 190; 195; 200; 205; 210; 215; 220; 225; 230; 235; 240; 245; 250; 260; 270; 280; 290; 300; 310; 320; 330; 340; 350; 360; 370; 380; 390; 400; 410; 420; 430; 440; 450; 460; 470; 480; 490; 500.

[0067] Preferably, x is between 0 and 25.

[0068] In general, y is between 1 and 150, in particular between 1 and 140. Typically, y is between 1 and 80. Preferably, the sum x+y is between 1 and 500.

[0069] The molar mass of polyalkoxysiloxane of formula (I) is typically between 300 g / mol and 200,000 g / mol, preferably between 300 g / mol and 30,000 g / mol. The molar mass can notably be measured by gel permeation chromatography (GPC).

[0070] In one embodiment, x is 0. This means that the polyalkoxysiloxane comprises only alkoxylated (or phenoxylated) units. In a preferred embodiment, x is zero and y is between 1 and 140, in particular x is zero and y is between 1 and 80.

[0071] According to the invention, the polyalkoxysiloxane oil may comprise a mixture of derivatives of formula (I) of different lengths, i.e., for which the values ​​of x and / or y are not all the same. In this case, it is possible for a polyalkoxysiloxane oil according to the invention to define an average value of x and / or an average value of y. Preferably, the average value of y in a polyalkoxysiloxane oil according to the invention is between 50 and 60.

[0072] According to the invention, the polyalkoxysiloxane oil may comprise a mixture of polyalkoxysiloxane base oils of formula (I) having different substitutions among R1, R2, or R3. According to one feature of the invention, the mixture of polyalkoxysiloxane base oils of formula (I) may correspond to and / or is obtained from a physical mixture of different oils previously synthesized separately. According to another feature of the invention, the mixture of polyalkoxysiloxane base oils of formula (I) may be obtained during the same chemical synthesis, for example, when a mixture of alcohols having varying chain lengths is used.Thus, during the same synthesis, a mixture of polyalkoxysiloxane base oils of formula (I) is obtained, the R2 group of which varies between the oils (it is thus possible to obtain a mixture of polyalkoxysiloxane base oils of formula (I) which may include a first polyalkoxysiloxane oil whose R2 group is a hexadecyl group (Cl6) and a polyalkoxysiloxane oil whose R2 group is an octadecenyl group (Cl8)).

[0073] The polyalkoxysiloxane of formula (I) may be, in the case where x is different from 0, a block polymer, an alternating polymer, a random or statistical polymer. Preferably, the polyalkoxysiloxane of formula (I) is an alternating, random or statistical polymer.

[0074] By "lubricating agent" is meant an agent which, when used alone or in a composition, reduces friction between two surfaces moving relative to each other.

[0075] The Applicant unexpectedly discovered that the polyalkoxysiloxane base oils of formula (I) according to the invention have lower coefficients of friction (CoF) than polysiloxanes, such as PDMS and polyalphaolefins (PAOs), and even lower than those of other organophosphate-based fluids used in hydraulics, under specific conditions. This confirms their superior lubricity compared to these other fluids. In particular, the CoF measured for the polyalkoxysiloxanes of formula (I) is less than 0.1, indicating good performance. Under the same conditions, the CoF measured for the reference polydimethylsiloxanes, organophosphates (marketed, for example, under the brand name Skydrol®), and polyalphaolefins is greater than or equal to 0.1.The specific conditions are as follows: mixed lubrication system, speed 100 mm / s, pure sliding, load of 40 N (pressure 1.02 GPa), temperature 75°C.

[0076] The term "coefficient of friction (CoF)" refers to a dimensionless characteristic intrinsic to a base oil and indicating the ability of a base oil film to reduce friction between two surfaces. The value of the coefficient of friction, also known as lubricating power, is highly dependent on the lubrication regime. The coefficient of friction can be measured using a tensile testing machine such as a Mini Traction Machine (MTM) equipped with an AISI 52100 steel ball and disc. In particular, tests can be carried out at a speed of 100 mm / s, in pure sliding (Sliding Rolling Ratio of 200%), under a load of 40 N equivalent to a contact pressure of 1.02 GPa and at a temperature of 75°C, for one hour.

[0077] Friction is a force that opposes the relative motion of two surfaces in contact. It depends on several factors such as the surface condition, temperature, normal power, sliding speed, etc. Significant friction between two surfaces (characterized by a high coefficient of friction) will lead to wear of the moving parts. The best way to reduce this risk is to add a lubricant between the surfaces, so that, in a hydrodynamic lubrication regime, they are not in direct contact. The coefficient of friction is a function of the system's characteristics, and its evolution is graphically illustrated by the Stribeck curve.

[0078] The choice of the hydrodynamic regime makes it possible to characterize the lubricating power of a base oil under conditions of pressure, temperature and speed relatively standard for undemanding lubrication systems such as pumps and other accessories found in hydraulic circuits.

[0079] Polyalkoxysiloxane base oils of formula (I) have high viscosity indices, in particular viscosity indices greater than 200, preferably greater than 300, approaching those recorded for PDMS (>350) and significantly higher than those of polyalphaolefins in particular. This means that the polyalkoxysiloxane base oils according to the invention have high fluidity over a wide temperature range, particularly at low temperatures. Low temperature is preferably defined as a temperature below -40°C, in particular below -50°C. The viscosity index can be measured by any technique known in the art. It is preferably measured according to the standardized method known as ASTMD2270.

[0080] Polyalkoxysiloxane base oils of formula (I) may be used either alone, or as a mixture of at least two polyalkoxysiloxane base oils of formula (I), or in a mixture with at least one other base oil, as a co-base or major base, preferably as a co-base. Preferably, the polyalkoxysiloxane base oil of formula (I) is used in the absence of another base oil.

[0081] Other base oils that can be blended with the polyalkoxysiloxane base oils according to the invention include polyalphaolefins, polydimethylsiloxanes, and synthetic esters, particularly diesters. These other base oils are known to those skilled in the art and will therefore not be described in detail below.

[0082] Indeed, the polyalkoxysiloxane base oils according to the invention are, unlike polydimethylsiloxanes, compatible with these various other base oils, particularly at high temperatures, but also with certain other base oils at low temperatures, notably with other low-viscosity base oils. The polyalkoxysiloxane base oil according to the invention and the other base oil can be used in the mixture in any mass proportion from 100:0 to 0:100 (excluding limits), preferably from 10:90 to 90:10 (including limits), and thus encompassing the following mass proportions (including limits): 10:90, 50:50 or 90:10.

[0083] The polyalkoxysiloxane base oils of formula (I) according to the invention can also be used as a dielectric fluid. Indeed, their physicochemical characteristics, such as their insulating properties, pour point, kinematic viscosity, flash point, fire point, and / or auto-ignition temperature, are perfectly suited for these base oils to constitute a good dielectric fluid. Also, according to the present invention, the polyalkoxysiloxane base oil of formula (I) preferably simultaneously performs the functions of lubrication and dielectric power. This is particularly suitable when the polyalkoxysiloxane base oil of formula (I) according to the invention is used as a lubricant in a system requiring electrical insulation, cooling, arc extinguishing and / or limitation, and / or reduction of partial discharges, such as for example electrical transformers: traction transformers, power transformers, wind turbine transformers, offshore transformers, distribution transformers, etc.

[0084] In addition, the polyalkoxysiloxane base oil of formula (I) according to the invention is perfectly suited for lubricating hydraulic systems, whether for small, independent systems such as actuators (a few liters of fluid), or for large, centralized hydraulic systems transmitting commands (>100L of fluid). It can also be adapted to fluids found in landing gear, radar fluids, and other dielectric fluids used in military or space applications. Thanks to its low coefficient of friction (CoF), the polyalkoxysiloxane base oil of formula (I) according to the invention can, in particular, perfectly lubricate the pumps of a hydraulic system, providing a level of protection against long-term wear and, consequently, ensuring excellent longevity of the equipment and mechanical components.

[0085] Due to their advantageous technical characteristics as previously mentioned, the polyalkoxysiloxane base oils of formula (I) according to the invention can also be used as hydraulic fluids. The performance level of these alternative formulations can easily be justified as being equivalent to or superior to that of reference fluids such as, for example, phosphate esters, which are widely used in commercial aviation (see Example 2 below).

[0086] The polyalkoxysiloxanes of formula (I) according to the invention can be synthesized by any technique known to those skilled in the art. In particular, the polyalkoxysiloxanes of formula (I) can be synthesized by processes such as those described in patent applications EP0475440 and WO2014099497. However, the Applicant has observed that replacing the reported catalytic systems (palladium or platinum catalysts, possibly with the additional addition of carboxylic acids) with bases well known to those skilled in the art (e.g., cesium fluoride CsF) can advantageously improve the conversion rate and therefore the reaction yield as well as its selectivity. The invention also relates to a lubricating composition comprising a polyalkoxysiloxane base oil of formula (I) as defined above, or a mixture thereof, and at least one additive.

[0087] By "additive", we mean in particular a chemical product which is added to the lubricating composition to improve certain properties of it for its application as a lubricating agent.

[0088] At least one additive included in the lubricating composition according to the invention may be chosen from among the additives well known to those skilled in the art. In particular, it may be chosen from the group consisting of additives suitable for extreme pressures, anti-wear additives, detergent additives, viscosity-modifying additives, anti-foaming additives, amine and phenolic antioxidant additives, corrosion inhibitors, flame-retardant additives and a combination of at least two of said additives.

[0089] Examples of additives suitable for extreme pressures include zinc dithiophosphate and MoS2 or molybdenum disulfide.

[0090] Examples of anti-wear and / or extreme-pressure additives include sulfides, chlorides, organophosphates, aryl and / or alkyl phosphates and metallic phosphates, for example zinc dialkyldithiophosphates (ZDDP).

[0091] Examples of anti-foaming additives include silicones.

[0092] Examples of flame-retardant additives include organophosphates with a high auto-ignition point.

[0093] Examples of antioxidant additives include phenols, aromatic amines, and sulfur-containing additives such as zinc dithiophosphates. Additives marketed under the names Vanlube 81® and Naugalube® 438 (4,4'-dioctyldiphenylamine), and Irganox® LO6 (octylated N-phenyl-l-naphthylamine) are examples of aromatic organic amines. Additives marketed under the names Irganox® L109 (hexamethylene glycol bis(3,5-di-tert-butyl-4-hydroxyhydrocinnamate)) and Ionol® 220 AH (4,4'-methylenebis(2,6-di-tert-butylphenol)) are examples of phenolic antioxidant additives.

[0094] Examples of oil-soluble corrosion inhibitors include zinc-based agents, sulfonates, sorbitan esters, phosphates, and amine phosphates.

[0095] Examples of detergent and / or viscosity-modifying additives are well known to those skilled in the art.

[0096] In one embodiment, the lubricating composition according to the invention comprises at least two, at least three, at least four, at least five, at least six, different additives.

[0097] In one embodiment, the composition comprises fewer than ten additives or ten different additives.

[0098] Each of the additives present in the lubricating composition according to the invention is advantageously present in an amount ranging from 0.001% to 35% by weight, and preferably between 0.1% and 15% by weight, relative to the total weight of said lubricating composition.

[0099] The lubricating composition according to the invention advantageously comprises an amount of polyalkoxysiloxane base oil according to the invention ranging from 50% to 99.9999% by weight relative to the total weight of the lubricating composition, preferably an amount of polyalkoxysiloxane base oil according to the invention of 60% to 99%, in particular 75% to 95%. The other components of said composition are preferably selected from other base oils and additives, in particular additives as described above or other types of additives known in Art.

[0100] Other base oils that can be mixed with a base oil according to the invention or that can be included in a lubricating composition according to the invention are the same as those mentioned above and may in particular be mineral lubricating oils, or synthetic lubricating oils such as synthetic esters, or polyalphaolefins.

[0101] The lubricating composition according to the invention can be used in various fields, including industry, energy, marine, automotive, and / or aerospace. Specifically, it can be used as a hydraulic fluid, engine oil, power transfer oil, and / or turbine lubricant. It can advantageously be used in all fields where silicone oils are employed, while generally offering more advantageous characteristics.

[0102] The invention also relates to a polyalkoxysiloxane of formula (II)

[0103] [Chem.2] RI RI ye

[0104] in which:

[0105] each RI is independently an alkyl group in Cl to C4 or a phenyl, each R2 is independently an alkyl or alkenyl group in C4 to C16 or a phenyl, x is an integer between 0 and 50, and y is an integer between 1 and 500 and such that the ratio y / x is strictly greater than 0.5.

[0106] According to the invention, by C4 to C16 alkyl or alkenyl group, a group comprising from 4 to 16 carbon atoms or any range between: 4; 5; 6; 7; 8; 9; 10; 11; 12; 13; 14; 15; 16.

[0107] Polyalkoxysiloxanes of formula (II) constitute a particular subgroup of polyalkoxysiloxanes of formula (I) as previously defined.

[0108] In one embodiment, each RI in formula (II) is independently selected from the group consisting of a methyl group, an ethyl group, and a phenyl group. Preferably, all the RIs are methyl groups, all the RIs are ethyl groups, or all the RIs are phenyl groups. In particular, all the RIs are methyl groups.

[0109] In one embodiment, each R2 in formula (II) is independently an alkyl or alkenyl group, preferably alkyl, at C4 to C14, preferably at C4 to C12.

[0110] In one embodiment, each R2 in formula (II) is independently an alkyl group at C4 to C14, preferably at C4 to C12.

[0111] The R2 chains may all be identical in the same compound of formula (II), but they may also be different in pairs.

[0112] In formula (II), x is an integer between 0 and 50, y is an integer between 1 and 500. Preferably, x is between 0 and 25. Preferably, y is between 1 and 150, preferably between 1 and 140. In particular, y is between 1 and 80. Preferably, the sum x+y is between 1 and 500.

[0113] According to the invention, by a range "between 0 and 50", the following values ​​or any interval between these values ​​are meant: 1; 2; 3; 4; 5; 6; 7; 8; 9; 10; 11; 12; 13; 14; 15; 16; 17; 18; 19; 20; 21; 22; 23; 24; 25; 26; 27; 28; 29; 30; 31; 32; 33; 34; 35; 36; 37; 38; 39; 40; 45; 50.Similarly, according to the invention, a range "between 1 and 500" means the following values ​​or any interval between these values: 1; 2; 3; 4; 5; 6; 7; 8; 9; 10; 11; 12; 13; 14; 15; 16; 17; 18; 19; 20; 21; 22; 23; 24; 25; 26; 27; 28; 29; 30; 31; 32; 33; 34; 35; 36; 37; 38; 39; 40; 45; 50; 55; 60; 65; 70; 75; 80; 85; 90; 95; 105; 110; 115; 120; 125; 130; 135; 140; 145; 150; 155; 160; 165; 170; 175; 180; 185; 190; 195; 200; 205; 210; 215; 220; 225; 230; 235; 240; 245; 250; 260; 270; 280; 290; 300; 310; 320; 330; 340; 350; 360; 370; 380; 390; 400; 410; 420; 430; 440; 450; 460; 470; 480; 490; 500.

[0114] The molar mass of polyalkoxysiloxane of formula (II) is typically between 300 g / mol and 200,000 g / mol, preferably between 300 g / mol and 30,000 g / mol.

[0115] In one embodiment, x is 0 in formula (II). This means that the polyalkoxysiloxane comprises only alkoxylated (or phenoxylated) units. In a preferred embodiment, x is zero and y is between 1 and 140 in formula (II), in particular x is zero and y is between 1 and 80.

[0116] The invention also relates to particular polyalkoxysiloxanes, selected from the group consisting of polyalkoxysiloxanes of formula (II) in which:

[0117] x=0, y is between 1 and 140, each RI is a methyl, and each R2 is a n-butyl chain (PAS4),

[0118] x=0, y is between 1 and 140, each RI is a methyl, and each R2 is a heptyl chain (PAS7),

[0119] x=0, y is between 1 and 140, each RI is a methyl, and each R2 is a dodecyl chain (PAT 12),

[0120] x=0, y is between 1 and 140, each RI is a methyl, and each R2 is a tetradecyl chain (PAS 14), and

[0121] x=0, y is between 1 and 140, each RI is a methyl group, and each R2 is chosen in the group consisting of octadecenyl and hexadecyl chains (PAS 16-18).

[0122] In one embodiment, independently for each of the particular polyalkoxysilanes according to the invention, y is between 1 and 80. In another embodiment, independently for each of the polyalkoxysiloxanes according to the invention, an average value of y is between 50 and 60. EXAMPLES

[0123] The following examples are intended to illustrate the invention without limiting its scope.

[0124] Example 1: Synthesis of polyalkoxysiloxanes according to the invention

[0125] The synthesis of polyalkoxysiloxanes according to the invention is carried out following the following protocol: - Conditions

[0126] The synthesis of polyalkoxysiloxane compounds according to the invention is carried out imperatively under anhydrous conditions requiring the washing and drying of all the elements of the assembly under nitrogen purging; - Device

[0127] In order to carry out the synthesis of polyalkoxysiloxanes according to the invention, a 6L cylindrical "Schott" type grooved flanged neck reactor marketed by the company Belleville SA.

[0128] The reactor is equipped with a water condenser to allow the alcohol vapors to condense during the reaction and is maintained under a flow of nitrogen;

[0129] - Summary

[0130] a) an alcohol (as defined in Table 1 below) is introduced in excess (approximately 10% by mass relative to the stoichiometric amount corresponding to the number of moles of Si-H contained in a PolyMethylHydroSiloxane which will be used (see below) in the reactor and maintained under a nitrogen flow up to a temperature of 75-80°C;

[0131] b) when the reaction medium is anhydrous, the catalyst (Cesium Fluoride CsF) is introduced (ideally 0.005% by mass relative to the total mass of the reaction medium);

[0132] c) Polymethylhydrosiloxane (PMHS), called Silres® BS 94 (marketed by Wacker), is then added drop by drop, controlling the flow rate to avoid a runaway reaction;

[0133] d) the precise progress of the reaction can be determined by infrared by checking the decrease, then the disappearance of the characteristic band “Si—H” (“2170cm *);

[0134] e) once the reaction is complete, the catalyst is extracted from the reaction medium by filtration and the excess alcohol is then distilled under vacuum.

[0135] The polyalkoxysiloxanes according to the invention which were synthesized following the above protocol are presented in Table 1 below.

[0136] [Tables 1] PAS Alcohol introduced into the synthesis RI R2 R3 X Polymeric fraction not present in PAS4 n-methyl butanol n-butyl methyl 0 1 to 140 PAS5 n-methyl pentanol n-pentyl methyl 0 1 to 140 PAS6 n-methyl hexanol n-hexyl methyl 0 1 to 140 PAS7 n-methyl heptanol n-heptyl methyl 0 1 to 140 PAS8 n-methyl octanol n-octyl methyl 0 1 to 140 PAS9 n-methyl nonanol n-nonyl methyl 0 1 to 140 PAS10 n-methyl decanol n-decyl methyl 0 1 to 140 PAS12 lauryl alcohol methyl n-dodecyl methyl 0 1 to 140 PAS16- 18 Mixture of methyl n-hexadecyl n-octate cenyl methyl (N AFOL 1 618) 0 1 to 140

[0137] The average value of y for each of the polyalkoxysiloxane oils in Table 1 is between 50 and 60.

[0138] Example 2: Characterization of polyalkoxysiloxanes. Characteristics tested

[0139] * The Coefficient of Friction

[0140] The coefficient of friction (CoF) was measured for each polyalkoxylsiloxane synthesized in Example 1, under the following conditions: mixed lubrication regime, speed 100 mm / s, pure sliding, load of 40 N (pressure 1.02 GPa), temperature 75°C.

[0141] In particular, the coefficient of friction is measured using a Mini Traction Machine (MTM) equipped with an AISI 52100 steel ball and disc, at a speed of 100 mm / s, in pure sliding (Sliding Rolling Ratio of 200%), under a load of 40 N equivalent to a contact pressure of 1.02 GPa and at a temperature of 75°C, for one hour.

[0142] * Kinematic viscosity

[0143] The kinematic viscosity at different temperatures (100°C, 40°C, -40°C) was measured according to ASTM D445 / 2532.

[0144] * The viscosity index

[0145] The viscosity index was measured according to the ASTM D2270 method standard.

[0146] * Flashpoint

[0147] The flash point was measured according to ASTM D92

[0148] * Fire point

[0149] The point of ignition was measured according to ASTM D92.

[0150] The auto-ignition point was measured according to ASTM E659.

[0151] * The pour point*

[0152] The pour point was measured according to ASTM D97.

[0153] * Mechanical shear stability KRL after 100h

[0154] The mechanical shear stability KRL after lOOh was measured according to the modified CEC L 45-A-99 method.

[0155] Results

[0156] Fig. 1 presents the measurement results of the coefficient of friction, as well as the measurement results for the reference oils PDMS 20 and PAO 8 and for three reference hydraulic fluids (FH2 (PAO / ester mixture), FH42 (PAO / ester mixture), Skydrol® type V (organophosphate-based aeronautical hydraulic fluid)) respectively approved according to the military standards MIL-PRF-83282, MIL-PRF-87257 and civil standard BMS 3-11 Type V. PAO8 designates a polyalphaolefin with a kinematic viscosity of 8 cSt at 100°C.

[0157] Under these conditions, the coefficient of friction values ​​of the polyalkoxysiloxanes according to the invention are less than 0.1 and are, therefore, significantly more favorable in terms of lubricity than the reference aeronautical hydraulic fluid used in commercial aviation, namely Skydrol V (BMS 3-11 type V). Among the best polyalkoxysiloxanes in the prepared series, some achieve coefficients of friction (CoF) close to or even below 0.05, representing a very substantial improvement compared to the reference military fluids MIL-PRF-83282 & MIL-PRF-87257. This test demonstrates that the polyalkoxysiloxane compounds of the invention make it possible to consider better protection of hydraulic systems (less and slower wear of moving mechanical parts in contact with each other).

[0158] Table 2 below sets together the results of the measurements of the physicochemical properties for the polyalkoxysiloxanes synthesized in Example 1, and the corresponding values ​​for reference lubricants: PDMS20 and PAO8.

[0159] [Tables2] Characteristics Reference Oils Base Oils According to the Invention PDMS20 PAO8 PAS4 PAS5 PAS6 PAS7 Coefficient of Friction (CoF) >0.25 0.100 0.049 0.061 0.087 0.056 Kinematic Viscosity at (cSt): 100°C 6.30 8 6.48 5.57 5.59 6.24 40°C 14.70 48 20.24 15.89 17.24 18.9 -40°C 19000 460 256 421 730 Viscosity Index 467 139 324 345 312 325 Flash Point COC (°C) 248 260 152 160 194 220 Pour Point (°C) <-72 -48 <-72 -93 -93 <-72 Base Oils According to the Invention PAS8 PAS9 PAS10 PAS12 PAS16-18 Coefficient of Friction (CoF) 0.068 0.096 0.091 0.041 Kinematic Viscosity at (cSt): 100°C 7.11 7.49 7.76 9.31 14.0 40°C 25.77 28.12 28.91 37.8 69.4 -40°C 1390 solid solid Viscosity Index 262 254 259 242 211 Flash Point COC (°C) 216 266 248 Pour Point (°C) -60 -39 -6 9

[0160] The grey boxes in Table 2 correspond to measurements that were not carried out or could not be carried out in view of the behavior of the oil under the measurement conditions.

[0161] The coefficient of friction (CoF) values ​​demonstrate the superiority in terms of lubricating power of the polyalkoxylsiloxanes according to the invention compared to polydimethylsiloxane oils and polyalphaolefins.

[0162] The kinematic viscosity and viscosity index values ​​demonstrate that the polyalkoxysiloxane oils according to the invention possess a very interesting fluidity relatively close to that of polydimethylsiloxane oils over a wide thermal range.

[0163] The pour point values, in particular those below -45°C, kinematic viscosity values, in particular those below 28 cSt at 40°C and / or those below 15000 cSt at -40°C, and flash point values ​​demonstrate that the polyalkoxysiloxane oils according to the invention can advantageously combine their lubricating properties with dielectric fluid properties for use at very low temperature compatible with very cold regions (Russia, Canada, etc.).

[0164] [Tables3] Characteristic Unit Base Oil PAS 7 Phosphate Ester (Skydrol® Type V product) Flash Point °C 220 166 Fire Point °C 246 192 Mechanical Shear Stability KRL after 100h (CEC-L-45-A-99) * Change in Kinematic Viscosity at 40°C % 3.0 -26.4 * Change in Kinematic Viscosity at 100°C % -0.9 -32.7 * Change in Viscosity Index — -17 -136

[0165] These results in Table 3 show that the base oil according to the invention possesses safety and shear stability characteristics (simulating the severe mechanical stresses exerted on the fluid, particularly in pumps operating in a pressurized environment) superior to those of the reference hydraulic fluid used in commercial aviation (e.g., Skydrol®), making it a prime candidate for potential substitution. It should be noted that the compounds of the invention exhibit very high performance under shear stress compared to Skydrol® type V (the reference fluid used in commercial aviation). aeronautical market) for which the rheology decreases very significantly after only 100h of shear (the drop in the viscosity index indicating here a drastically different behavior at high and low temperatures).

[0166] Example 3: Study of compatibility with other base oils

[0167] Mixtures of a base oil according to the invention with various other base oils were prepared, and their compatibility was studied for different proportions of base oil according to the invention: other base oil (0:100, 10:90, 50:50, 90:10 and 100:0), and at different temperatures (100°C, room temperature, 5.9°C and -30°C). The base oil according to the invention is an oil of formula (I) with R1=methyl, R2=heptyl, R3=methyl, x=0 and y=1 at 140.

[0168] An absence of cloudiness or separation demonstrating very good compatibility of the base oil according to the invention with the other base oil was observed for mixtures in all proportions and at all temperatures with polyalphaolefins of kinematic viscosity at 100°C of 4, 6 and 8 cSt respectively, designated PAO4, PAO6 and PAO8.

[0169] Similarly, very good compatibility of the base oil according to the invention has been demonstrated at high temperature (100°C) in all proportions with the polyalphaolefin PAO 100 of kinematic viscosity at 100°C of 100 cSt.

[0170] Finally, very good compatibility of the base oil according to the invention has been demonstrated at 100°C, ambient temperature and 5.9°C in all proportions with the paraffinic mineral oils known under the names 150 Neutral Solvent®, 600 Neutral Solvent® and BSS® (Bright Stock Solvent).

[0171] Example 4: Study of compatibility with anti-wear additives

[0172] In this example, the compatibility of the polyalkoxysiloxane base oil according to the invention (here, the PAS7 compound described in Example 1) with the following anti-wear additives was measured:

[0173] a) tri(methyl silyl) phosphate,

[0174] b) tris(trimethylsiloxy)bore

[0175] c) (diethylphosphatoethyl)triethoxysilane.

[0176] by measuring, in particular, mechanical performance according to ASTM D4172 (4-ball wear, Ih, 40kg, 75°C 1200 revolutions per minute).

[0177] The results are presented in Table 4 below:

[0178] [Tables4] 1 2 3 4 5 6 7 Composition PAS7 PAS7 PAS7 PAS7 PAS7 PAS7 PAS7 (oil se + + + + + + ule) a) 1% a) 3% b) 1% b) 3% c) 1% c) 3% Mechanical performance (wear diameter) 1.54 1.06 0.85 1.3 1.26 1.12 0.93

[0179] This example shows that adding anti-wear additives to the polyalkoxysiloxane base oil according to the invention makes it possible to form a lubricating composition with significantly improved mechanical performance.

[0180] Example 5: Study of compatibility with flame-retardant additives

[0181] In this example, the compatibility of the polyalkoxysiloxane base oil according to the invention (here, the PAS7 compound described in Example 1) with flame-retardant additives as listed below was measured, as well as their effects on the auto-ignition temperature of the mixtures obtained.

[0182] The results are presented in Table 5 below:

[0183] [Tables5] Base oil Flame retardant Mass content of flame retardant additive Auto-ignition temperature (°C) Organophosphates (HYJET V) NANA 391 Organophosphates (SKYDROL® PE 5) NANA 396 PAS7 none 0% 385 PAS7 Isodecyl diphenyl phosphate 5% 393 PAS7 Isodecyl diphenyl phosphate 10% 403 PAS7 Isodecyl diphenyl phosphate 15% 407 PAS7 Phenol, isobutylene phosphate (3:1) 5% 390 PAS7 Phenol, isobutylene phosphate (3:1) 15% 409

[0184] This example shows that the addition of flame-retardant additives is chemically possible and allows the polyalkoxysiloxane base oil according to the invention to form a lubricating composition having an auto-ignition point higher than that of the base oil (PAS7) as well as those of reference hydraulic fluids such as Skydrol® type V and Hyjet V. This is undeniably a very advantageous (fire) safety feature.

[0185] Of course, various other modifications can be made to the invention within the scope of the annexed claims.

Claims

Demands

1. Use of a polyalkoxysiloxane base oil of formula (I) [Chem.l] RI RI Ri Si ]x[ & O -|y s. R3 ue RI Q in which each RI is independently an alkyl group in C4-Cl, each R2 is independently an alkyl or alkenyl group in C2-C22 or a phenyl, R3 is a methyl group, x is an integer from 0 to 50, y is an integer from 1 to 500 and such that the ratio y / x is strictly greater than 0.5, or of a mixture of polyalkoxysiloxane base oils of formula (I), as a lubricating agent.

2. Use according to claim 1, wherein x is 0 and each RI is chosen independently from the methyl and ethyl groups.

3. Use according to claim 1 or 2, wherein each R2 is independently an alkyl or alkenyl group in C4 to Cl8, preferably in C4 to C12.

4. Use according to any one of claims 1 to 3, wherein the polyalkoxysiloxane is selected from the group consisting of polyalkoxysiloxanes of formula (I) in which: x=0, y is from 1 to 140, each RI is a methyl group, and each R2 is an n-butyl chain; x=0, y is from 1 to 140, each RI is a methyl group, and each R2 is a heptyl chain; x=0, y is from 1 to 140, each RI is a methyl group, and each R2 is a dodecyl chain; x=0, y is from 1 to 140, each RI is a methyl group, and each R2 is a tetradecyl chain; and x=0, y is between 1 and 140, each RI is a methyl, and each R2 is chosen from the group consisting of octadecenyl and hexadecyl chains.

5. Use according to any one of claims 1 to 4, wherein the polyalkoxysiloxane base oil of formula (I) is used as a lubricating agent for formulating a dielectric fluid, a coolant fluid or a hydraulic fluid.

6. Use according to any one of claims 1 to 5, wherein the polyalkoxysiloxane base oil of formula (I) is used in mixture with at least one other base oil, as a cobase.

7. Lubricating composition, characterized in that it comprises a polyalkoxysiloxane base oil of formula (I) according to any one of the preceding claims and at least one additive.

8. Lubricating composition according to claim 7, wherein said at least one additive is selected from the group consisting of extreme-pressure additives, anti-wear additives, detergent additives, viscosity-modifying additives, anti-foaming additives, antioxidant additives, flame retardants, corrosion inhibitors and a combination of at least two of said additives.

9. Lubricating composition according to claim 7 or 8, wherein said composition comprises at least one flame retardant additive, so as to obtain a non-flammable hydraulic fluid.

10. Polyalkoxysiloxane of formula (II): [Chem.2] Me RI RI Me Me RT Q " Me H2 pi; wherein each RI is independently a C4 Cl alkyl group, each R2 is independently a C4 to C16 alkyl or alkenyl group or a phenyl, x is an integer from 0 to 50, y is an integer from 1 to 500, and such that the ratio y / x is strictly greater than 0.

5.

11. Polyalkoxysiloxane of formula (II) according to claim 10, selected from the group consisting of polyalkoxysiloxanes of formula (II) in which: x=0, y is between 1 and 140, each RI is a methyl, and each R2 is an n-butyl chain, x=0, y is between 1 and 140, each RI is a methyl, and each R2 is a heptyl chain, x=0, y is between 1 and 140, each RI is a methyl, and each R2 is a dodecyl chain, x=0, y is between 1 and 140, each RI is a methyl, and each R2 is a tetradecyl chain, and x=0, y is between 1 and 140, each RI is a methyl, and each R2 is selected from the group consisting of octadecenyl and hexadecyl chains.

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