Hydrogenated linear polydiene copolymers as base stocks for lubricant compositions or lubricant additives

Abstract

The present invention relates to hydrogenated linear copolymers comprising butadiene and isoprene monomer units, and to a process for preparing these copolymers. The present invention also relates to lubricating oil compositions comprising one or more hydrogenated linear copolymers according to the invention, and to the use of the above copolymers as lubricant additives or synthetic base fluids for lubricant compositions, in particular in gear oils, transmission oils, hydraulic oils, engine oils, greases, marine oils or industrial lubricants.

Description

Technical Field

[0001] The present invention relates to hydrogenated linear copolymers comprising butadiene and isoprene monomer units, and to a process for preparing these copolymers. The present invention also relates to lubricating oil compositions comprising one or more hydrogenated linear copolymers according to the invention, and to the use of the above copolymers as lubricant additives or synthetic base fluids for lubricant compositions, in particular in gear oils, transmission oils, hydraulic oils, engine oils, greases, marine oils or industrial lubricants. Background Art

[0002] The present invention relates to the field of lubrication. Lubricants are compositions that reduce friction between surfaces. In addition to allowing freedom of movement between two surfaces and reducing mechanical wear of the surfaces, lubricants can also inhibit corrosion of the surfaces and / or can inhibit damage to the surfaces due to heat or oxidation. Examples of lubricant compositions include, but are not limited to, gear oils, transmission oils, hydraulic oils, engine oils, greases, marine oils, and industrial lubricants.

[0003] Typical lubricant compositions include a base fluid and optionally one or more additives. Conventional base fluids are naturally occurring hydrocarbons, such as mineral oils, or synthetic compositions, such as poly-alpha olefins, poly(meth) alkyl acrylates, and ethylene-propylene copolymers. The terms "base oil" or "base fluid" are often used interchangeably. Here, "base fluid" is used as a general term.

[0004] Depending on the intended use of the lubricant, various additives can be combined with the base fluid. Examples of lubricant additives include, but are not limited to, oxidation inhibitors, corrosion inhibitors, dispersants, high pressure additives, defoamers, and metal passivators. In order to improve viscosity measurement performance, viscosity index improvers (VII) and thickeners can be used. These viscosity modifiers are typically polymeric types.

[0005] However, a disadvantage of adding polymeric additives to lubricant formulations is that they experience shear stress and mechanical degradation over time. Polymers with higher molecular weights are better thickeners, but they are more susceptible to shear stress, resulting in polymer degradation. By reducing the molecular weight of the polymer, a more shear-stable polymer is obtained. However, these shear-stable low molecular weight polymers are no longer very effective thickeners and must be used in larger concentrations in the lubricant in order to achieve the desired viscosity. These low molecular weight polymers typically have a molecular weight below 20,000 g / mol and are also referred to as synthetic high viscosity base fluids.

[0006] Typical polymeric additives on the market, such as polyalkyl (meth)acrylates (PAMA), have various disadvantages in different lubricating oil compositions. One example is that a large amount of PAMA product is required in these compositions to achieve the desired viscometric performance. Another example is the solubility problem of PAMA products with different types of base oils. Another disadvantage of conventional PAMA-based lubricant additives is poor traction performance.

[0007] Alternatively, some lubricant additives are based on isoprene and butadiene, such as in US 7,163,913 B2, which discloses linear, radial and star-shaped statistical copolymers of isoprene and butadiene, wherein at least 70 wt. % of butadiene is incorporated into the polymer and the weight ratio of isoprene to butadiene is in the range of 90:10 to 70:30, which are suitable for use as viscosity index improvers for lubricating oil compositions.

[0008] There remains a need to find new lubricant additives which not only combine high thickening efficiency, good oil solubility, good shear stability, a high viscosity index in lubricating oil compositions, but also improve the traction properties of said lubricating oil compositions. Summary of the invention

[0009] It is therefore an object of the present invention to provide a synthetic base fluid or lubricant additive for lubricating oil compositions which is highly efficient compared to the prior art. The object of these new polymers is to provide excellent performance in lubricating oil compositions, in particular in terms of thickening efficiency, shear stability and traction. The shear-stable polymers described should be able to thicken the oil to the desired viscosity using lower amounts of polymer than the typically used poly(meth)alkyl acrylates. In addition, the polymers should show a high viscosity index in lubricating oil compositions, as well as excellent solubility in typical base fluids. SUMMARY OF THE INVENTION

[0011] After intensive studies, the inventors of the present invention surprisingly found that the hydrogenated linear copolymer composed of butadiene, isoprene and optionally alkyl (meth)acrylate monomer units as defined in claim 1 provides excellent performance in the lubricating oil composition, particularly in terms of thickening efficiency and traction performance, when added to the lubricating oil composition.

[0012] A first object of the present invention is therefore a hydrogenated linear copolymer as defined in claim 1 and its dependent claims.

[0013] A second object of the present invention relates to a process for preparing the hydrogenated linear copolymers according to the invention.

[0014] A third object of the present invention is a lubricating oil composition comprising the hydrogenated linear copolymer according to the invention.

[0015] A fourth object of the present invention is the use of the hydrogenated linear copolymers of the present invention as synthetic base fluids in lubricating oil compositions or as lubricating additives in synthetic base fluids, in particular in gear oil compositions, transmission oil compositions, hydraulic oil compositions, engine oil compositions, marine oil compositions, industrial lubricating oil compositions, or in greases.

[0016] Another object of the present invention is a method for improving the traction coefficient of a lubricating oil composition, wherein said method comprises the step of adding a hydrogenated linear copolymer as defined in the present invention to the base oil of the lubricating oil composition. DETAILED DESCRIPTION OF THE INVENTION

[0018] The hydrogenated polybutadiene-isoprene copolymer according to the present invention

[0019] According to a first aspect of the present invention, the present invention relates to a hydrogenated linear copolymer obtainable by polymerizing a monomer composition consisting of the following monomers:

[0020] a) 10 to 60 mol % of 1,3-butadiene monomer,

[0021] b) 40 to 90 mol % of isoprene,

[0022] c) 0 to 40 mol % of one or more (meth)acrylic acids C 1 -C 6 Alkyl esters, and

[0023] d) 0 to 30 mol % of one or more (meth)acrylic acids C 7 -C 24 Alkyl esters,

[0024] Based on the total amount of monomers in the monomer composition,

[0025] wherein the total amount of monomers a) and b) amounts to at least 60 mol % of the total amount of the monomer composition, and

[0026] The hydrogenated linear copolymer has a weight average molecular weight in the range of 2,000 g / mol to 30,000 g / mol and has a degree of hydrogenation greater than 95%.

[0027] In fact, the inventors of the present invention surprisingly found that the combination of the specific amounts of butadiene and isoprene defined above leads to the formation of hydrogenated linear copolymers with good solubility in oil. According to the present invention, the total amount of butadiene (monomer a) and isoprene (monomer b) in the hydrogenated polybutadiene-isoprene copolymer must add up to at least 60 mol% of the total amount of the monomer composition, and the amount of butadiene should not exceed 60 mol% based on the total amount of the monomer composition. On the contrary, as shown in the experimental part of the present invention, pure hydrogenated polyisoprene or copolymers containing isoprene and butadiene that do not meet the ratio of monomer units defined in claim 1 do not have good comprehensive properties, in particular with respect to having a high thickening efficiency while maintaining good traction properties. Therefore, it is unexpected to achieve excellent performance in oil when the two dienes are combined according to the ratio defined in claim 1.

[0028] According to a preferred embodiment of the present invention, the hydrogenated copolymer has a weight average molecular weight ranging from 3,000 g / mol to 20,000 g / mol, more preferably from 4,000 g / mol to 18,000 g / mol, and most preferably from 5,000 g / mol to 15,000 g / mol. Polymers having this weight average molecular weight have particularly good shear resistance and provide excellent improvements in the viscosity measurement properties of the lubricant composition, even at low amounts of the copolymer.

[0029] Preferably, the copolymers of the present invention have a very low degree of crosslinking and a narrow molecular weight distribution, which further contributes to their shear resistance. The low degree of crosslinking and the narrow molecular weight are reflected in the polydispersity index of the copolymer. Preferably, the polydispersity index (PDI) of the copolymers according to the present invention is in the range of 1.0 to 4.0, more preferably in the range of 1.0 to 3.3. For most industrial applications, a polydispersity index in the range of 1.0 to 3.3 is considered to be optimal with respect to the shear resistance of the copolymer. The polydispersity index is defined as the ratio of the weight average molecular weight to the number average molecular weight (Mw / Mn).

[0030] The weight-average and number-average molecular weights are determined by gel permeation chromatography using commercially available polybutadiene calibration standards. The determination is preferably carried out in accordance with DIN 55672-1 by gel permeation chromatography using THF as eluent.

[0031] According to a preferred embodiment of the present invention, the hydrogenated linear copolymer is a statistical copolymer or a block copolymer, preferably a statistical copolymer.

[0032] monomer

[0033] In the present invention, isoprene may also be referred to as 2-methyl-1,3-butadiene.

[0034] In the present invention, butadiene may also be referred to as 1,3-butadiene.

[0035] According to a preferred embodiment, the hydrogenated linear copolymers according to the invention may optionally comprise, in addition to the monomers a) and b), monomers derived from (meth)acrylic acid C 1 -C 6 As monomer c), monomers of alkyl esters derived from (meth) acrylic acid C 7 -C 24 As monomers d) monomers of alkyl esters or mixtures thereof.

[0036] The term "(meth)acrylic acid" refers to acrylic acid, methacrylic acid and a mixture of acrylic acid and methacrylic acid; preferably methacrylic acid. The term "(meth)acrylate" refers to an ester of acrylic acid, an ester of methacrylic acid or a mixture of an ester of acrylic acid and an ester of methacrylic acid; preferably an ester of methacrylic acid.

[0037] The term "(meth)acrylic acid C 1-6 "(meth)acrylic acid alkyl ester" refers to an ester formed from (meth)acrylic acid and a straight chain or branched alcohol having 1 to 6 carbon atoms. The term includes a single (meth)acrylic acid ester formed with an alcohol of a specific length, and also includes a mixture of (meth)acrylic acid esters formed with alcohols of different lengths. Similarly, the term "(meth)acrylic acid C 7-24 The term "alkyl ester" refers to an ester formed from (meth)acrylic acid and a straight-chain or branched alcohol having 7 to 24 carbon atoms.

[0038] Suitable (meth)acrylic acids C for monomer c) 1-6 The alkyl esters include, for example, methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate and tert-butyl (meth)acrylate. 1-6 The alkyl ester is methyl (meth)acrylate, butyl (meth)acrylate or a mixture of methyl (meth)acrylate and butyl (meth)acrylate. More preferably, the butyl (meth)acrylate is n-butyl (meth)acrylate.

[0039] Suitable (meth)acrylic acids C for monomer d) 7-24The alkyl esters include, for example, 2-butyloctyl(meth)acrylate, 2-hexyloctyl(meth)acrylate, decyl(meth)acrylate, 2-butyldecyl(meth)acrylate, 2-hexyldecyl(meth)acrylate, 2-octyldecyl(meth)acrylate, undecyl(meth)acrylate, 5-methylundecyl(meth)acrylate, dodecyl(meth)acrylate, 2-methyldodecyl(meth)acrylate, 2-hexyldodecyl(meth)acrylate, 2-octyldodecyl(meth)acrylate, tridecyl(meth)acrylate, 5-methyltridecyl(meth)acrylate, tetradecyl(meth)acrylate, 2-decyl(meth)acrylate, In a particularly preferred embodiment, the monomer d) comprises one or more of C (meth)acrylic acid, ... 10 -C 16 Alkyl esters, which refer to esters formed from (meth)acrylic acid and linear or branched alcohols having 10 to 16 carbon atoms. Preferably, monomer d) comprises lauryl (meth)acrylate (linear C 12 -C 15 alkyl esters).

[0040] Monomer composition

[0041] As indicated above, the present invention relates to hydrogenated linear copolymers obtainable by polymerizing a monomer composition consisting of:

[0042] a) 10 to 60 mol % of 1,3-butadiene monomer,

[0043] b) 40 to 90 mol % of isoprene,

[0044] c) 0 to 40 mol % of one or more (meth)acrylic acids C 1 -C 6 Alkyl esters, and

[0045] d) 0 to 30 mol % of one or more (meth)acrylic acids C 7 -C 24 Alkyl esters,

[0046] Based on the total amount of monomers in the monomer composition,

[0047] wherein the total amount of monomers a) and b) amounts to at least 60 mol % of the total amount of the monomer composition, and

[0048] The hydrogenated copolymer has a weight average molecular weight in the range of 2,000 g / mol to 30,000 g / mol and has a degree of hydrogenation greater than 95%.

[0049] In a preferred embodiment, the monomer composition indicated above consists of the following monomers:

[0050] a) 10 to 60 mol % of 1,3-butadiene monomer,

[0051] b) 40 to 90 mol % of isoprene,

[0052] c) 0 to 20 mol % of one or more (meth)acrylic acids C 1 -C 6 Alkyl esters, and

[0053] d) 0 to 20 mol % of one or more (meth)acrylic acids C 7 -C 24 Alkyl esters,

[0054] Based on the total amount of monomers in the monomer composition.

[0055] According to a preferred embodiment, the monomer composition defined above may further comprise an alkyl (meth)acrylate monomer c) or d) or a mixture thereof.

[0056] In a preferred embodiment, the monomer composition consists of the following monomers:

[0057] a) 10 to 60 mol % of 1,3-butadiene monomer,

[0058] b) 40 to 90 mol % of isoprene,

[0059] c) 1 to 30 mol % of one or more (meth)acrylic acids C 1 -C 6 Alkyl esters, and

[0060] d) 0 to 30 mol % of one or more (meth)acrylic acids C 7 -C 24 Alkyl esters,

[0061] Based on the total amount of monomers in the monomer composition.

[0062] In a preferred embodiment, the monomer composition consists of the following monomers:

[0063] a) 10 to 60 mol % of 1,3-butadiene monomer,

[0064] b) 40 to 90 mol % of isoprene,

[0065] c) 1 to 20 mol % of one or more (meth)acrylic acids C 1 -C 6 Alkyl esters, and

[0066] d) 0 to 30 mol % of one or more (meth)acrylic acids C 7 -C 24 Alkyl esters,

[0067] Based on the total amount of monomers in the monomer composition.

[0068] In another preferred embodiment, the monomer composition consists of the following monomers:

[0069] a) 10 to 60 mol % of 1,3-butadiene monomer,

[0070] b) 40 to 90 mol % of isoprene,

[0071] c) 1 to 20 mol % of one or more (meth)acrylic acids C 1 -C 6 Alkyl esters, and

[0072] d) 5 to 20 mol % of one or more (meth)acrylic acids C 7 -C 24 Alkyl esters,

[0073] Based on the total amount of monomers in the monomer composition.

[0074] According to a preferred embodiment, in the preferred monomer compositions defined above, the one or more (meth)acrylic acids C 1 To C 6 The alkyl ester monomer c) is selected from methyl (meth)acrylate, butyl (meth)acrylate or a mixture thereof, and the one or more (meth)acrylates C 7 To C 24 The alkyl ester monomer d) is lauryl (meth)acrylate.

[0075] Process for preparing the copolymer of the present invention

[0076] As explained above, the hydrogenated polybutadiene-isoprene copolymer of the present invention is prepared according to a method comprising the following steps:

[0077] (i) providing a monomer composition as defined above,

[0078] (ii) initiating solution polymerization in the monomer composition to obtain a copolymer, and

[0079] (iii) hydrogenating the copolymer of step (ii).

[0080] Polymerization step (ii)

[0081] According to a preferred embodiment, the polymerization of step (ii) is a free radical polymerization in solution or an anionic polymerization, more preferably a free radical polymerization in solution.

[0082] Free Radical Polymerization

[0083] Standard free-radical polymerization is described in detail in, inter alia, Ullmann's Encyclopedia of Industrial Chemistry, 6th edition. In general, polymerization initiators and optionally chain transfer agents are used for this purpose.

[0084] The copolymers of the invention can be obtained via the ATRP process. This reaction scheme is described, for example, by J.-S. Wang et al. in J. Am. Chem. Soc, Vol. 117, pp. 5614-5615 (1995) and by Matyjaszewski in Macromolecules, Vol. 28, pp. 7901-7910 (1995). In addition, patent applications WO 96 / 30421, WO 97 / 47661, WO 97 / 18247, WO 98 / 40415 and WO 99 / 10387 disclose variants of the ATRP described above.

[0085] In addition, the copolymers of the invention can also be obtained via the RAFT process. The RAFT process is described in detail, for example, in WO 98 / 01478 and WO 2004 / 083169.

[0086] According to a preferred embodiment, the statistical copolymers of the present invention are prepared by free radical solution polymerization, in which case the reaction mixture during step (ii) preferably comprises the monomer composition (step (i)), one or more free radical initiators, a solubilizing support medium as described below and optionally one or more chain transfer agents.

[0087] Solution polymerization is a preferred method for carrying out the process of the present invention because it allows the concentration of the monomer composition in the reaction mixture to be adjusted by adding more or less solubilizing carrier medium. By choosing the correct concentration of the monomer composition in the reaction mixture, the molecular weight and polydispersity index of the resulting copolymer can be controlled.

[0088] Preferably, the total amount of the monomer composition in the reaction mixture is 5 to 95 wt %, more preferably 10 to 70 wt %, even more preferably 20 to 55 wt %, most preferably 35 to 50 wt %, based on the total weight of the reaction mixture. On an industrial scale, monomer concentrations above 20 % are generally preferred. A monomer composition concentration in the range of 20 to 55 wt %, preferably 35 to 50 wt %, based on the total weight of the reaction mixture is considered optimal because it produces statistical copolymers having low weight average molecular weights in the range of 2,000 to 30,000 g / mol and low polydispersity indices in the range of 1.0 to 3.3.

[0089] The polymerization is preferably carried out at a temperature of 20 to 200°C, more preferably 50 to 150°C, the reaction pressure is preferably 1 to 30 bar, more preferably 10 to 28 bar, and the total reaction time of the free radical polymerization is 1 to 10 hours.

[0090] Preferably, the solubilizing carrier medium used is selected from mineral oils, synthetic oils, ketones, ester solvents, aromatic hydrocarbons, alicyclic hydrocarbons and aliphatic hydrocarbons or mixtures thereof.

[0091] Examples of mineral oils are paraffinic oils, naphthenic oils, solvent refined oils, high VI oils containing isoparaffins, and high VI oils of hydrocracking. Examples of synthetic oils are organic esters, such as diesters and polyesters, such as carboxylic acid esters and phosphates; organic ethers, such as silicone oils, perfluoroalkyl ethers, and polyalkylene glycols; and synthetic hydrocarbons, especially polyolefins and gas-to-liquids (GTLs). Examples of ketones are butanone and methyl ethyl ketone. Examples of ester solvents are fatty oils, and synthetic ester lubricants (e.g., C4-12 dicarboxylic acid di-C4-12 alkyl esters, such as dioctyl sebacate and dioctyl adipate, polyol poly-C4-12 alkanoates, such as pentaerythritol tetrahexanoate; and tri-C4-12 alkyl phosphates, such as tri-2-ethylhexyl phosphate, (dibutyl) (phenyl) phosphate, (di-2-ethylhexyl) (phenyl) phosphate, (2-ethylhexyl) (diphenyl) phosphate, and tricresyl phosphate). Examples of aromatic hydrocarbons are benzene, toluene, xylene, ethylbenzene, trimethylbenzene, ethyltoluene and mixtures thereof. Examples of alicyclic hydrocarbons are cyclohexane, methylcyclohexane and alicyclic terpenes. Examples of aliphatic hydrocarbons are n-pentane, n-hexane, n-heptane, 1-decene and aliphatic terpenes.

[0092] In a preferred embodiment, the solubilizing carrier medium is an alicyclic or aliphatic or aromatic hydrocarbon, preferably cyclohexane or toluene.

[0093] Step (ii) involves adding a free radical initiator.

[0094] Suitable free radical initiators are, for example, azo initiators, such as azobisisobutyronitrile (AIBN), 2,2'-azobis(2-methylbutyronitrile) (AMBN) and 1,1-azobiscyclohexanecarbonitrile, and peroxide compounds, such as methyl ethyl ketone peroxide, acetylacetone peroxide, lauryl peroxide, ketone peroxide, tert-butyl peroctoate, methyl isobutyl ketone peroxide, cyclohexanone peroxide, dibenzoyl peroxide, tert-butyl peroxybenzoate, tert-butyl peroxyisopropyl carbonate, 2,5-bis(2-ethylhexanoylperoxy)-2,5-dimethylhexane, tert-butyl peroxy-3,5,5-trimethylhexanoate, dicumyl peroxide, 1,1-bis(tert-butylperoxy)cyclohexane, 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane, cumyl hydroperoxide, tert-butyl hydroperoxide and bis(4-tert-butylcyclohexyl)peroxydicarbonate.

[0095] Preferably, the free radical initiator is selected from 2,2'-azobis(2-methylbutyronitrile), 2,2-bis(tert-butylperoxy)butane, 1,1-di-tert-butylperoxy-3,3,5-trimethylcyclohexane, tert-butyl peroxybenzoate and tert-butyl peroxy-3,5,5-trimethylhexanoate. In a particularly preferred embodiment, the free radical initiator is 2,2-bis(tert-butylperoxy)butane.

[0096] Preferably, the total amount of free radical initiator is from 0.01 to 5 wt%, more preferably from 0.02 to 1 wt%, most preferably from 0.05 to 0.5 wt%, relative to the total weight of the monomer mixture.

[0097] The total amount of the free radical initiator can be added in a single step, or the free radical initiator can be added in multiple steps during the polymerization reaction. For example, a portion of the free radical initiator can be added to initiate free radical polymerization, and a second portion of the free radical initiator can be added 0.5 to 3.5 hours after the initial dose. Preferably, the free radical initiator is added in a single step.

[0098] Step (ii) optionally comprises the addition of a chain transfer agent. Examples of chain transfer agents are sulfur-containing compounds, such as mercaptans, for example n-dodecyl mercaptan, tert-dodecyl mercaptan, 2-mercaptoethanol and mercaptocarboxylates, for example methyl 3-mercaptopropionate, or longer chain olefins. Preferred chain transfer agents are olefins having up to 20 carbon atoms, in particular up to 15 carbon atoms and more preferably up to 12 carbon atoms.

[0099] After the free radical polymerization is complete, the product is preferably filtered to remove any impurities present in the reaction mixture followed by evaporation of any volatile solvents.

[0100] Anionic polymerization

[0101] An alternative way to carry out step (ii) of the process is by preparing the polybutadiene-isoprene polymers of the present invention via living anionic polymerization of butadiene and isoprene monomers.

[0102] This type of reaction is very well established and is described in detail in HLHsieh, RP Quirk, Anionic Polymerization, Principles and Practical Applications, 1996, Marcel Dekker, Inc. New York.

[0103] According to the invention, for the living anionic polymerization of 1,3-butadiene and isoprene, processes of batch or semi-batch type are preferred. Living polymerization in a continuous process is also conceivable.

[0104] The polymerization is usually carried out in an aliphatic, alicyclic or aromatic hydrocarbon solvent. Examples of aliphatic hydrocarbon solvents are hexane or heptane. Examples of alicyclic hydrocarbon solvents are cyclohexane or methylcyclohexane. Examples of aromatic hydrocarbon solvents are benzene or toluene. Polar heteroaliphatic solvents such as tertiary amines and / or ethers and / or cyclic ethers can also be used as solvents or cosolvents. Examples of tertiary amines are tetramethylenediamine or N,N,N',N",N"-pentamethyldiethylenediamine. Examples of ethers or cyclic ethers are diethyl ether and tetrahydrofuran. Solvent mixtures of aliphatic, alicyclic or aromatic hydrocarbon solvents and polar heteroaliphatic solvents are usually used.

[0105] Common initiators are organometallic reagents, wherein the metal is from the alkali metal class or from the alkaline earth metal class. Typical examples are mono- or difunctional organic sodium, organic lithium or organic potassium as initiators, such as n-butyl lithium, sec-butyl lithium, tert-butyl lithium, 1,1-diphenylhexyl lithium, diphenylmethyl lithium, 1,1,4,4,-tetraphenyl-1,4-dilithium butane, lithium naphthalene and their sodium and potassium homologues. Preferably, an organic lithium initiator is used, more preferably an n-butyl lithium initiator is used.

[0106] The living character of anionic polymerization provides excellent control over the resulting molecular weight and polydispersity index (PDI) in the absence of oxygen and protic agents.

[0107] Typically, the polymerization reaction is terminated using a protic agent such as methanol, ethanol, 2-propanol or water to neutralize the macromolecular anion.

[0108] Typical reaction temperatures range between 10°C and 120°C, and typical reaction pressures range between 1 and 100 bar.

[0109] Hydrogenation step (iii)

[0110] On an industrial scale for use in the present invention, it is desirable to provide a hydrogenated copolymer without double bonds, since the presence of double bonds would reduce the reactivity of the copolymer against chemical oxidation, crosslinking or other undesirable side reactions. Therefore, in step (iii), the inventors of the present invention have carried out a selective hydrogenation of the diene units, as described below.

[0111] According to the invention, the monomer units derived from butadiene and isoprene are hydrogenated. A high degree of hydrogenation of the polyisoprene-butadiene copolymer of more than 95% relative to the polymerized units derived from butadiene and isoprene is desirable in order to improve the stability against oxidation. The hydrogenation is selective and does not affect the monomer units c) and d) derived from the optional (meth)acrylate.

[0112] The selectivity of the hydrogenation can be determined, for example, by quantitative 1 H NMR ( 1 The degree of hydrogenation of the copolymers according to the present invention is determined by HPLC in a deuterated chloroform solution using dimethyl terephthalate as a standard. 1 The measurements are carried out by H NMR spectroscopy. The chemical shift is calibrated using the solvent signal. To determine the degree of hydrogenation, the corresponding signal integral of the standard is correlated with the signal integral of the olefinic protons. For each sample, in order to define a degree of hydrogenation of 0%, the measurement and determination must be repeated using a non-hydrogenated reference sample.

[0113] The selective hydrogenation of the copolymer of the present invention is usually carried out in the presence of at least one solubilizing carrier medium, using hydrogen or other hydrogen sources as a reducing agent, either using an insoluble supported metal or metal complex catalyst to carry out in a heterogeneous form, or using a soluble organic metal catalyst to carry out in a homogeneous form. A detailed description of homogeneous catalytic hydrogenation can be found, for example, in US 3,541,064 and GB 1,030,306. Because it provides economic advantages, heterogeneous catalysis using insoluble supported metals as catalysts is widely used in industrial selective hydrogenation methods, and is generally superior to other methods. Preferably, the selective hydrogenation method is a heterogeneous catalytic method using an insoluble supported metal as a catalyst.

[0114] Typical catalytically active metals for heterogeneous catalysis of the selective hydrogenation according to the present invention include, but are not limited to, Ru, Rh, Pd, Ir, Pt, Mn, Cr, Fe, Co, Ni, U, Cu, Nd, In, Sn, Zn, Ag, Cr and alloys of one or more of these metals.

[0115] Typical catalyst supports include but are not limited to oxides (Al 2 O 3 、TiO 2 、SiO 2 or other oxides), carbon, diatomaceous earth or other supports.

[0116] Furthermore, the heterogeneous catalyst can be used, for example, in the form of pellets or powder.

[0117] In a preferred embodiment, the selective hydrogenation process is preferably carried out using a heterogeneous carbon-supported Pd catalyst in powder form. The use of a carbon-supported Pd catalyst is preferred because it performs hydrogenation of double bonds derived from butadiene and isoprene with high selectivity and reactivity.

[0118] The amount of the catalytically active metal supported on the carrier is preferably 0.1 to 10% by weight, more preferably 1 to 10% by weight, based on the total weight of the supported catalyst.

[0119] In the case where hydrogen is used as the reducing agent, the reaction pressure is preferably 5 to 1500 bar, either as a constant pressure or as a gradient pressure. More preferably, the reaction pressure is 5 to 500 bar, even more preferably 5 to 250 bar, and most preferably 10 to 90 bar.

[0120] In the hydrogenation step (iii), the concentration of the statistical copolymer in the solubilizing support medium may typically be in the range of 5 to 95 wt %. Preferably, the concentration of the statistical copolymer in the solubilizing support medium is 10 to 70 wt % of the statistical copolymer based on the total weight of the copolymer and the support medium.

[0121] In a preferred embodiment, the hydrogenation is carried out in the presence of a cycloaliphatic or aliphatic hydrocarbon, preferably cyclohexane.

[0122] The reaction temperature in the hydrogenation step (iii) is preferably from 0 to 200°C, more preferably from 20 to 150°C, even more preferably from 20 to 120°C.

[0123] In a particularly preferred embodiment, the hydrogenation is carried out at a temperature of 20 to 120° C., at a pressure of 10 to 90 bar, in the presence of a carbon-supported Pd catalyst, and in the presence of cyclohexane as the solubilizing support medium. These conditions have been found to be optimal for the preparation of the above-mentioned copolymers, since they lead to high reactivity and selectivity in the selective hydrogenation of the double bonds derived from the conjugated diene.

[0124] Lubricating oil composition

[0125] The present invention also relates to a composition comprising

[0126] (x) one or more base oils, and

[0127] (y) One or more of the above-mentioned hydrogenated linear copolymers of the present invention.

[0128] The lubricant composition of the present invention preferably has a viscosity index greater than 140. The viscosity index can be measured according to ASTM D2270.

[0129] Preferably, the lubricating oil composition comprises 0.5 to 80 wt. %, more preferably 1 to 50 wt. %, even more preferably 1 to 30 wt. %, most preferably 1 to 15 wt. % of the one or more hydrogenated linear copolymers, and 20 to 99.5 wt. %, more preferably 50 to 99 wt. %, even more preferably 70 to 99 wt. %, most preferably 85 to 99 wt. % of the one or more base oils, based on the total amount of the lubricating oil composition.

[0130] If the lubricant composition according to the invention is used as an engine oil, it preferably comprises from 0.5 to 20 wt. % of the copolymer according to the invention, based on the total weight of the lubricant composition, which results in a viscosity at 3 mm according to ASTM D445. 2 / s to 10mm 2 Kinematic viscosity at 100°C in the range of 1.5 / s.

[0131] If the lubricant composition according to the invention is used as an automotive gear oil, it preferably comprises 2 to 35 wt. % of the copolymer according to the invention, based on the total weight of the lubricant composition, which results in a relative humidity of 20 % at 2 mm according to ASTM D445. 2 / s to 15mm 2 Kinematic viscosity at 100°C in the range of 1.5 / s.

[0132] If the lubricant composition according to the invention is used as automatic transmission oil, it preferably comprises in the base oil from 1 to 25% by weight of the copolymer according to the invention, based on the total weight of the lubricant composition, which results in a viscosity of 100 % to 200 % at 2 mm according to ASTM D445. 2 / s to 9mm2 Kinematic viscosity at 100°C in the range of 1.5 / s.

[0133] If the lubricant composition according to the invention is used as an industrial gear oil, it preferably comprises from 15 to 80% by weight of the copolymer according to the invention, based on the total weight of the lubricant composition, which results in a relative humidity of 100% at 10 mm according to ASTM D445. 2 / s to 130mm 2 Kinematic viscosity at 100°C in the range of 1.5 / s.

[0134] If the lubricant composition of the invention is used as a hydraulic oil, it preferably comprises 1 to 20 wt. % of the copolymer according to the invention, based on the total weight of the lubricant composition, which results in a viscosity at 3 mm according to ASTM D445. 2 / s to 20mm 2 Kinematic viscosity at 100°C in the range of 1.5 / s.

[0135] Preferably, the amounts of (x) and (y) add up to 100 wt. %, based on the total weight of the lubricant composition.

[0136] Base oil

[0137] The base oil that can be used in the composition preferably comprises one or more oils of lubricating viscosity. Such oils correspond to lubricant base fluids suitable for their application / selected according to the intended use, mineral, synthetic or natural, animal or vegetable oils.

[0138] The base fluids used to formulate the lubricating oil composition according to the present invention include, for example, conventional base stocks selected from the API (American Petroleum Institute) base stock categories, which are referred to as Group I, Group II, Group III, Group IV and Group V. The Group I and Group II base stocks are mineral oil materials (such as paraffinic base oils and naphthenic oils) having a viscosity index (or VI) of less than 120. Group I is further distinguished from Group II in that the latter contains greater than 90% saturated materials, while the former contains less than 90% saturated materials (i.e., greater than 10% unsaturated materials). Group III is considered to be the highest level of mineral base fluids, having a VI greater than or equal to 120 and a saturate level greater than or equal to 90%. Group IV base fluids are polyalphaolefins (PAOs). Group V base fluids are esters and any other base fluids not included in the Group I to IV base fluids. These base fluids can be used alone or as a mixture.

[0139] Preferably, the one or more base oils (x) are selected from polyalphaolefin base oils, API Group III base oils or mixtures thereof.

[0140] Additional additives

[0141] The lubricating oil composition according to the present invention may further comprise any other additional additive (z) suitable for use in the formulation. These additives are selected from viscosity index improvers, pour point improvers, dispersants, demulsifiers, lubricity additives, detergents, defoamers, corrosion inhibitors, friction modifiers, antioxidants, anti-wear additives, extreme pressure additives, anti-fatigue additives, dyes, odorants or mixtures thereof. Preferably, the lubricating oil composition according to the present invention comprises a pour point depressant (PPD) to reduce the minimum temperature at which the fluid will flow or can be poured. Such additives are well known. Typical PPDs include ethylene-vinyl acetate copolymers, chlorinated paraffin-naphthalene condensates, chlorinated paraffin-phenol condensates, polymethacrylates, polyalkylstyrenes. Polymethacrylates having a mass average molecular weight of 5,000 to 200,000 g / mol are preferred.

[0142] Preferably, the amounts of components (x), (y) and (z) add up to 100 wt. %, based on the total weight of the lubricating oil composition.

[0143] Use of the hydrogenated linear copolymer according to the invention

[0144] The present invention relates to the use of the hydrogenated linear copolymers according to the invention as lubricant additives or synthetic base fluids, depending on the treat rate in a lubricant oil composition, preferably in a gear oil composition, a transmission oil composition, a hydraulic oil composition, an engine oil composition, a marine oil composition, an industrial lubricant oil composition, or in a grease.

[0145] As demonstrated in the experimental part below, the use of the hydrogenated linear copolymers according to the invention in lubricating oil compositions allows the traction coefficient of said lubricating oil compositions to be improved while maintaining excellent thickening efficiency and shear stability in said compositions.

[0146] The present invention also relates to a method for improving the traction coefficient of a lubricating oil composition, wherein said method comprises the step of adding a hydrogenated linear copolymer according to the present invention and as described above in detail to a base oil.

[0147] As demonstrated in the experimental section below, due to the advantageous effects of the hydrogenated linear copolymers according to the invention, there are excellent improvements in the traction coefficient as well as the thickening efficiency in lubricating oil compositions. In addition, the hydrogenated linear copolymers as defined in the present invention maintain a high viscosity index, good shear stability, excellent low temperature properties and excellent solubility in typical base fluids. DETAILED DESCRIPTION

[0148] Experimental Section

[0149] The present invention is hereinafter further illustrated in detail with reference to Examples and Comparative Examples, without any intention of limiting the scope of the present invention.

[0150] abbreviation

[0151] PMMA Polyalkyl (meth)acrylate

[0152] MMA Methacrylate C 1 -Alkyl ester = methyl methacrylate

[0153] BMA Methacrylate C 4 -Alkyl ester = n-butyl methacrylate

[0154] LMA Methacrylate C 12 / 14 -Alkyl ester = Lauryl methacrylate

[0155] KRL Kegelrollenlager (= tapered roller bearing)

[0156] KV 40 Kinematic viscosity at 40°C measured according to ASTM D445

[0157] KV 100 Kinematic viscosity at 100°C measured according to ASTM D445

[0158] M n Number average molecular weight

[0159] M w Weight average molecular weight

[0160] NB3030 Nexbase , a Group III base oil from Neste with a KV of 3.0 cSt 100

[0161] NB3043 Nexbase , a Group III base oil from Neste with a KV of 4.3 cSt 100

[0162] PDI polydispersity index, via M w / M n Calculated molecular weight distribution

[0163] PSSI100 Permanent Shear Stability Index (based on KV before and after shearing 100 calculate)

[0164] VI Viscosity index measured according to ASTM D2270

[0165] GPC Gel Permeation Chromatography

[0166] MTM Micro Traction Tester

[0167] PP Pour point measured according to ASTM D 97.

[0168] T g Glass transition temperature measured by differential scanning calorimetry

[0169] BF Brookfield viscosity measured at -40°C according to ASTM D 2983

[0170] Sample preparation

[0171] Polymer synthesis

[0172] Copolymers 1 to 8 and Comparative Examples 10 to 12 of the present invention were prepared by free radical solution polymerization using the monomer compositions shown in Table 1 below. The monomers were mixed with toluene in a 5-liter autoclave at a temperature of 20° C. and a pressure of 10 bar, so that the monomer concentration relative to the total weight of the mixture was 40% by weight. The temperature was raised to 130° C. using a heating rate of 5.5° C. / min, and then an initiator, 2,2-bis(tert-butylperoxy)butane (50% by weight in liquid paraffin) was added. Free radical copolymerization was carried out at a reaction temperature of 130° C., a reaction pressure of about 20 bar, and a reaction time of 3 hours. The discharge was filtered and the volatile solvent was evaporated. The copolymer obtained was then subjected to selective hydrogenation.

[0173] Hydrogenation of copolymers

[0174] For the selective hydrogenation, 1.5 liters of a 40 wt. % solution of the unsaturated copolymer in cyclohexane were charged to a 2 liter autoclave and 0.15 wt. % of Pd per polymer of a 5 % Pd / C catalyst powder were introduced. At a reaction temperature of 90° C. and a pressure of 90 bar H 2 Hydrogenation was carried out under stirring at reaction pressure until a degree of hydrogenation of 95% or more was achieved. The discharge was filtered and the volatile components were evaporated. All polymeric units except those derived from conjugated dienes (butadiene and isoprene) were not converted during the selective hydrogenation. All copolymers 1 to 8 of the present invention and comparative examples 10 to 12 were hydrogenated according to this operating procedure.

[0175] Examples (as also shown in Table 1 below)

[0176] Examples 1 to 4 of the present invention are based on a monomer composition of butadiene and isoprene.

[0177] Examples 5 and 6 of the invention are based on a monomer composition of butadiene, isoprene and methyl (meth)acrylate.

[0178] Examples 7 and 8 of the present invention are based on a monomer composition of butadiene, isoprene, methyl (meth)acrylate, butyl (meth)acrylate, and lauryl (meth)acrylate.

[0179] Comparative Example 9, PAMA, is C synthesized according to Example 1 in US2013 / 0229016A1 12-15 Copolymers of methacrylates.

[0180] Comparative Example 10 is a copolymer of 80 mol % (76 wt %) butadiene and 20 mol % (24 wt %) isoprene, such as disclosed in US 7,163,913 B2.

[0181] Comparative Example 11 Monomer composition based on butadiene, methyl (meth)acrylate, butyl (meth)acrylate and lauryl (meth)acrylate. The product was synthesized using the same method as in the example of the present invention.

[0182] Comparative Example 12 is based on pure polyisoprene and is synthesized using the same method as the examples of the present invention.

[0183] Bulk polymer properties

[0184] Test Method

[0185] The weight average molecular weight M of the hydrogenated linear copolymer of the present invention is w The polydispersity index PDI was determined using a Tosoh EcoSEC GPC system "HLC-8320" equipped with a PSS SDV 5 μm precolumn and a 30 cm PSS SDV 5 μm linear S separation column, and an RI detector at a flow rate of 0.3 mL / min at T = 40°C using tetrahydrofuran (THF) as eluent, relative to a polybutadiene calibration standard.

[0186] The weight average molecular weight of the polyalkyl (meth)acrylate of Comparative Example 9 was determined by gel permeation chromatography (GPC) using polymethyl methacrylate calibration standards and THF as eluent.

[0187] The composition of the copolymers of the present invention, the degree of hydrogenation and the selectivity of the hydrogenation process are determined by means of 1 Determined by H-NMR spectroscopy.

[0188] The glass transition temperature was measured on a Mettler-Toledo DSC1 via differential scanning calorimetry. The analysis was performed using Mettler Toledo STARe 10.00 software. Indium and cyclohexane were used as standards. In two heating / cooling cycles, 8 to 10 mg of the sample were cooled to -80°C at a cooling rate of 20 K / min. After 10 minutes, the sample was heated to 200°C at a heating rate of 10 K / min. The glass transition temperature was obtained from the second heating cycle.

[0189] As reflected in Table 1 below, the bulk properties of the hydrogenated linear copolymers of the present invention are all very satisfactory, with low PDI values, Mw and glass transition temperatures. In addition, a high level of control was observed during the synthesis process, as the PDI values ​​of the hydrogenated copolymers of the present invention were all below 3.3.

[0190] Additionally, the hydrogenated linear copolymers of the invention obtained all have a high level of hydrogenation (more than 96% of the isoprene and butadiene are hydrogenated). The degree of hydrogenation is calculated as described above in the section on hydrogenation.

[0191]

[0192] Evaluation of lubricant compositions

[0193] The use of the copolymers according to the invention as lubricant additives was demonstrated in two different lubricant formulations with different hydrogenated linear copolymers according to the invention.

[0194] Test Method

[0195] The formulations in Table 3 had a KV100 target value of 7.0 cSt - the viscosity loss at 100°C relative to the kinematic viscosity of fresh oil at 100°C was measured after 40 hours at 80°C in the tapered roller bearing test (KRL) according to CEC-L-45-A-99.

[0196] The formulations in Table 4 had fixed VIs - KV40 with a target value of 26 cSt and KV100 with a target value of 5.5 cSt. The traction coefficient was measured on a micro traction tester using a 3 / 4 inch ball loaded on a disc with the following conditions as shown in Table 2 below:

[0197] Table 2:

[0198]

[0199] Kinematic viscosity was measured according to ASTM D 445.

[0200] The viscosity index is determined according to ASTM D2270.

[0201] The Brookfield viscosities reported in the lubricant formulation examples in Table 3 were measured according to ASTM D 2983 at a temperature of -40°C.

[0202] The pour points (PP) of the examples shown in Table 3 were measured according to ASTM D97.

[0203] Lubricating oil formulation 1 (KV100 = 7.0 cSt)

[0204] As shown in Table 3 below, several lubricating oil compositions were prepared comprising an API Group III base fluid (Nexbase 3030), a commercially available additive package, and any of the inventive copolymers 1 to 8 or Comparative Examples 9 and 10. To compare the individual lubricating oil compositions, the kinematic viscosity at 100°C was adjusted to 7.0 cSt.

[0205] For each composition, viscometric properties were measured as well as shear stability (KRL) and low temperature properties.

[0206] An advantage of the present invention is that low dosages (treat rates) of the inventive copolymers 1 to 8 are sufficient to achieve good kinematic viscosity and good viscosity index. In contrast, the formulation comprising comparative PAMA additive 9 achieves similar results to the inventive formulation, but with a treat rate of more than 20 wt.-% (twice the amount of the inventive formulation).

[0207] Thus, unexpectedly, even though the additives of the present invention have a low molecular weight, they are still very effective thickeners, even at low concentrations in the lubricant formulation.

[0208] Although similar results to those of the inventive examples were observed in terms of treatment rate and VI in the case of Comparative Example 10, the low temperature properties of Comparative Example 10 did not meet the requirements for industrial applications. Therefore, it was shown that copolymers having a high butadiene to isoprene ratio are not suitable for preparing good lubricant additives.

[0209]

[0210]

[0211] Lubricating oil formulations (fixed VI)

[0212] As shown in Table 4 above, a second type of lubricating oil formulations were prepared and the traction coefficient was measured for each formulation containing copolymers 1 to 8 according to the invention and comparative polymers 9 to 12. The lubricating oil formulations of Table 4 are all based on a mixture of Group III base fluids (Nexbase 3030 and Nexbase 3043), a commercially available additive package and a copolymer of the invention or any of the comparative examples.

[0213] In order to directly compare the individual lubricating oil compositions, the kinematic viscosity at 100°C of each composition was adjusted to 5.5 cSt, and the kinematic viscosity at 40°C of each composition was adjusted to 26.0 cSt.

[0214] For each composition, viscometric properties and traction coefficient were determined (see Table 4 above).The lubricant composition containing the PAMA additive showed inferior traction performance and therefore served as a reference point for comparing the different traction results of the other lubricant compositions.

[0215] As shown in Table 4 above, the traction coefficients of the inventive examples are superior compared to the comparative examples, demonstrating the additional beneficial effects of using the lubricant additives according to the present invention.

[0216] In summary, it has been demonstrated that the hydrogenated copolymers of the invention meet the requirements of the field of lubricant technology due to the lower treat rates which are always sought in order to avoid thickening of the lubricant formulation and to reduce the risk of incompatibilities with other components in the lubricant formulation. In addition, there is also a clear beneficial effect on the traction properties of the lubricant formulations comprising the lubricant additive according to the invention.

Claims

1. A hydrogenated linear copolymer obtained by polymerizing a monomer composition consisting of: a) 10 to 60 mol % of 1,3-butadiene monomer, b) 40 to 90 mol % of isoprene, c) 1 to 30 mol % of one or more C1-C6 alkyl (meth)acrylates, and d) 0 to 30 mol % of one or more (meth)acrylic acids C7-C 24 Alkyl esters; Based on the total amount of monomers in the monomer composition, The total amount of monomers a) and b) is at least 60 mol% of the total amount of the monomer composition. The sum of the mole percentage contents of monomers a), b), c) and d) is 100 mole %, and The hydrogenated linear copolymer has a weight average molecular weight in the range of 2,000 g / mol to 30,000 g / mol and has a degree of hydrogenation greater than 95%.

2. The hydrogenated linear copolymer according to claim 1, wherein the hydrogenated linear copolymer has a weight average molecular weight in the range of 3,000 g / mol to 20,000 g / mol.

3. The hydrogenated linear copolymer according to claim 2, wherein the hydrogenated linear copolymer has a weight average molecular weight in the range of 4,000 g / mol to 18,000 g / mol.

4. The hydrogenated linear copolymer according to any one of claims 1 to 3, wherein the hydrogenated linear copolymer has a PDI of 1.0 to 4.

0.

5. The hydrogenated linear copolymer according to claim 4, wherein the hydrogenated linear copolymer has a PDI of 1.0 to 3.

3.

6. The hydrogenated linear copolymer according to any one of claims 1 to 3, wherein the hydrogenated linear copolymer is a statistical copolymer or a block copolymer.

7. The hydrogenated linear copolymer according to any one of claims 1 to 3, wherein the monomer composition consists of the following monomers: a) 10 to 60 mol % of 1,3-butadiene monomer, b) 40 to 90 mol % of isoprene, c) 1 to 20 mol % of one or more C1-C6 alkyl (meth)acrylates, and d) 5 to 20 mol % of one or more (meth)acrylic acids C7-C 24 Alkyl esters; Based on the total amount of monomers in the monomer composition, The sum of the molar percentage contents of monomers a), b), c) and d) is 100 mol %.

8. The hydrogenated linear copolymer according to any one of claims 1 to 3, wherein the one or more C1 to C6 alkyl (meth)acrylate monomers c) are selected from methyl (meth)acrylate, butyl (meth)acrylate or mixtures thereof.

9. The hydrogenated linear copolymer according to any one of claims 1 to 3, wherein the one or more (meth)acrylic acids C7 to C 24 The alkyl ester monomer d) is lauryl (meth)acrylate.

10. A process for preparing a hydrogenated linear copolymer according to any one of claims 1 to 9, wherein the process comprises the following steps: (i) providing a monomer composition as defined in any one of claims 1 to 9, (ii) initiating solution polymerization in the monomer composition to obtain a copolymer, and (iii) hydrogenating the copolymer of step (ii).

11. A process according to claim 10, wherein the polymerisation in step (ii) is a free radical or anionic solution polymerisation.

12. A lubricating oil composition comprising: (x) one or more base oils, and (y) one or more hydrogenated linear copolymers according to any one of claims 1 to 9.

13. The lubricating oil composition according to claim 12, wherein the one or more base oils are selected from polyalphaolefin base oils, API Group III base oils or mixtures thereof.

14. The lubricating oil composition according to claim 12 or 13, wherein the lubricating oil composition comprises 0.5 to 80 wt% of the one or more hydrogenated linear copolymers (y) and 20 to 99.5 wt% of the one or more base oils (x), based on the total amount of the lubricating oil composition.

15. Use of the hydrogenated linear copolymer according to any one of claims 1 to 9 as lubricant additive or synthetic base fluid in a lubricating oil composition or in a lubricating grease.

16. The use according to claim 15, wherein the lubricating oil composition is selected from the group consisting of a gear oil composition, a transmission oil composition, a hydraulic oil composition, an engine oil composition and a marine oil composition.

17. The use according to claim 15, wherein the lubricating oil composition is an industrial lubricating oil composition.

18. Method for improving the traction coefficient of a lubricating oil composition according to any one of claims 12 to 14, wherein said method comprises the step of adding one or more hydrogenated linear copolymers (y) to said one or more base oils (x).

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