Patent Description:
The present invention relates to the field of lubrication. Lubricants are compositions that reduce friction between surfaces. In addition to allowing freedom of motion between two surfaces and reducing mechanical wear of the surfaces, a lubricant also may inhibit corrosion of the surfaces and/or may inhibit damage to the surfaces due to heat or oxidation. Examples of lubricant compositions include, but are not limited to, engine oils, transmission fluids, gear oils, industrial lubricating oils, greases and metalworking oils.

Lubricants typically contain a base fluid and variable amounts of additives. The terminology base oil, base stock or base fluid is commonly used interchangeably. Here, base fluid is used as a general term.

High viscosity base fluids are used to lift the viscosity index (VI) and to thicken lubricant formulations with demanding shear stability requirements. A typical application are gear oils which have very demanding requirements due to high mechanical stress and a broad temperature range in operation.

A wide variety of additives may be combined with the base fluid, depending on the intended use of the lubricant. Examples of lubricant additives include, but are not limited to, viscosity index improvers, thickeners, pour point depressants, oxidation inhibitors, corrosion inhibitors, dispersing agents, high pressure additives, anti-foaming agents and metal deactivators.

The most common thickener used in mineral oil based industrial gear oils is bright stock. Bright stock is a product of Group I base oil refineries which are technologically outdated so future supply is unknown. Replacement with alternative thickeners is difficult as typical polyolefin thickeners such as polyisobutylene (PIB), olefin copolymers (OCP) and polyalphaolefins (PAO) are very apolar, which causes compatibility issues (<NPL>; <NPL>; <NPL>). Viscosity of bright stock is also limited so high ISO viscosity grades like <NUM> or <NUM> require a more powerful thickener in combination with bright stock.

Alternatively, thickeners having a higher polarity can also be used, which have the advantage that these polar high viscosity base fluids do not need the addition of nonpolar low viscous fluids, such as esters or high alkylated naphthalenes, as compatibilizers for the polar lubricant additives. Furthermore, polar high viscosity fluids usually do not cause problems with coatings and seals in comparison with polar low viscous fluids. Such thickeners with higher polarity are for example copolymers of alpha-olefins with maleates (e.g. <CIT>), acrylates (e.g. <CIT> or <CIT>), methacrylates (e.g. <CIT>) or terpolymers based on the aforementioned monomers (e.g. <CIT>).

Alternatively, oil compatible polyesters (e.g. <CIT> or <CIT>), polyvinylethers (<CIT>), polyacrylates (e.g. <CIT>), or polyalkyl (meth)acrylate (PAMA) can be applied.

More specifically, polyalkyl (meth)acrylate base fluids (PAMA base fluids) are mainly used and designed as thickeners for very high performing synthetic or semi-synthetic formulations, which have similar performance parameters as polyalphaolefin base fluids (PAO base fluids). PAMA base fluids are commonly used in most demanding applications, such as wind turbine gear oils. The document <CIT> discloses polyalkyl (meth)acrylates for use in lubricants with high viscosity index and good anti-wear performance, particularly in wind turbine transmissions. To achieve this targeted purpose, the polyalkyl (meth)acrylate polymers disclosed in <CIT> are prepared using a monomer mixture comprising from <NUM> to <NUM>% by weight of linear and branched C<NUM>-C<NUM> alkyl (meth)acrylates, wherein the amount of branched alkyl (meth)acrylates is from <NUM> to <NUM>% by weight, preferably from <NUM> to <NUM>% by weight, based on the total weight of C<NUM>-C<NUM> alkyl (meth)acrylates. All examples are based on a careful balance of linear and branched monomers to provide high viscosity index (VI), while preventing crystallization at low temperatures. It is described that the transmission lubricants must comprise at least <NUM>% by weight of polyalkyl (meth)acrylates, which is a very high treat rate. However, for less demanding applications, the required high treat rate of PAMA to reach the viscometric performance makes them less attractive compared to polyolefins, such as PIB.

Monomers with aromatic or non-aromatic alicyclic side chains are well known for providing high glass temperature properties to the polymers they are incorporated in, and are therefore commonly used in polymers for optical components, resins, adhesives, or coatings (Ullmann's Encyclopedia of Industrial Chemistry, Edition <NUM>, Chapter "Polymethacrylates" on page <NUM>; <CIT>; <CIT>).

<CIT> relates to copolymers prepared with a mixture of monomers having a cyclic chain (Formula <NUM> to <NUM>) and branched (meth)acrylate monomers (Formula <NUM>), and their use, as additives, in a lubricating oil composition. It is described that these lubricating oil additives have good properties in thick oil film forming capability and wear resistance. The examples provided are prepared in Yubase <NUM> and <NUM> API Group III base oils with a kinematic viscosity at <NUM> up to <NUM><NUM>/s and the lubricating oil compositions all have a targeted kinematic viscosity at <NUM> of <NUM><NUM>/s. Due to their low viscosities, such thin gear oil formulations require additional measures to protect the surfaces from damage. One concept is the formation of sticky films on the surface as described in <CIT>. These film formers ideally have little impact on the bulk viscosity of the formulation in order to avoid unnecessary thickening which either limits the amount of additive or requires thinner base oils for the formulation.

<CIT> relates to additives for diesel fuel, in which the additives are copolymers prepared with bicyclic (meth)acrylate ester (e.g. IBOMA) and C<NUM>-C<NUM> (meth)acrylate, and optionally at least one aromatic vinyl monomer, and/or other ethylenically unsaturated monomers. The copolymers have a weight-average molecular weight above <NUM>,<NUM> Dalton and up to <NUM>,<NUM>,<NUM> Dalton and are used as additive package for fuels.

There is still the need to provide highly shear stable polymeric synthetic base fluids or lubricating oil polymeric additives, which have a positive influence on oil solubility and component solubility. Furthermore, the new polymers should be able to thicken an oil to a desired viscosity, even at low treat rates. The polymers should have good viscometric performance, including low temperature and viscosity index performance to reduce the effect of changes in viscosity with temperature, when used in lubricant oil compositions.

Surprisingly, it has been found that the polyalkyl (meth)acrylate polymer, comprising a certain amount of alicyclic methacrylate monomer units a) as defined in claim <NUM>, can meet the viscometric targets of industrial gear oils at treat rates close to simple well-known polyolefins, such as ethylene-propylene copolymers or polyisobutylenes, usually used in the lubricant market. In addition, they have the advantages of a polar high viscous base fluid, e.g. compatibilization of additives with the base fluid, which allows a full or partial replacement of bright stock in the formulation.

Accordingly, a first aspect of the invention is a polyalkyl (meth)acrylate polymer as defined in claim <NUM> and its dependent claims.

A second aspect of the invention is a method for preparing the polyalkyl (meth)acrylate polymers according to the invention.

A third aspect of the invention is a lubricating oil composition comprising at least one base oil and at least one polyalkyl (meth)acrylate polymer according to the invention.

A fourth aspect of the invention is a method of thickening a lubricating oil composition by adding a polyalkyl (meth)acrylate polymer according to the present invention, as a lubricant additive or a synthetic base fluid, to said lubricating oil composition, preferably a gear oil composition, a transmission oil composition, a hydraulic oil composition, an engine oil composition, a marine oil composition, an industrial lubricating oil composition or in grease.

The present invention relates to a polyalkyl (meth)acrylate polymer obtainable by polymerizing a monomer composition comprising:.

In the present invention, the term "alkyl methacrylate" refers to esters of methacrylic acid and the term "alkyl acrylate" refers to esters of acrylic acid. The term "(meth)acrylate" refers to esters of acrylic acid, esters of methacrylic acid or a mixture of esters of acrylic acid and methacrylic acid.

Within the meaning of the present invention, the monomer composition corresponds to the monomers used to prepare the polymer according to the present invention (not including the other reactants such as initiators, chain transfer agents).

Within the meaning of the present invention, the term "average carbon number of alkyl chains R<NUM>, R<NUM> and R<NUM> of monomers a), b) and c) in the monomer composition" corresponds to the average carbon number of the alkyl chains of monomers a), and optionally monomers b) and/or monomers c) when also present in the monomer composition.

According to the preferred aspect of the invention, the polyalkyl (meth)acrylate polymer has a kinematic viscosity from <NUM>,<NUM> to <NUM>,<NUM><NUM>/s at <NUM> according to ASTM D445. More preferably, the polyalkyl (meth)acrylate polymer has a kinematic viscosity from <NUM>,<NUM> to <NUM>,<NUM><NUM>/s at <NUM> according to ASTM D445, even more preferably from <NUM>,<NUM> to <NUM>,<NUM><NUM>/s at <NUM> according to ASTM D445.

According to the present invention, the polyalkyl (meth)acrylate polymer comprises at least <NUM>% by weight of monomer a) selected from the group consisting of an alkyl methacrylate with the formula (I) or a mixture thereof, wherein R<NUM> is a substituted or unsubstituted alicyclic radical. Preferably, the polyalkyl (meth)acrylate polymer comprises from <NUM>% to <NUM>% by weight of monomer a), more preferably at least <NUM>% by weight of monomer a), more preferably from <NUM>% to <NUM>% by weight, even more preferably from <NUM>% to <NUM>% by weight, most preferably from <NUM>% to <NUM>% by weight, most preferably from <NUM>% to <NUM>% by weight, based on the total weight of the monomer composition.

Preferably, the monomer a) is selected from the group consisting of cyclohexyl methacrylate, isobornyl methacrylate, <NUM>,<NUM>,<NUM>-trimethylcyclohexyl methacrylate, <NUM>-tert-butylcyclohexyl methacrylate, cyclopentyl methacrylate, dicyclopentanyl methacrylate, or a mixture thereof. More preferably, the monomer a) is selected from the group consisting of cyclohexyl methacrylate, isobornyl methacrylate, <NUM>,<NUM>,<NUM>-trimethylcyclohexyl methacrylate, dicyclopentanyl methacrylate, or a mixture thereof.

According to the present invention, the monomer composition to prepare the polyalkyl (meth)acrylate polymer comprises from <NUM> to <NUM>% by weight, preferably from <NUM> to <NUM>% by weight, more preferably from <NUM> to <NUM>% by weight, even more preferably from <NUM> to <NUM>% by weight, most preferably from <NUM> to <NUM>% by weight, of monomer b) of formula (II), based on the total weight of the monomer composition.

Preferably, the monomer b) of formula (II) is selected from the group consisting of <NUM>-octyl methacrylate, isooctyl methacrylate, <NUM>-ethylhexyl methacrylate, isononyl methacrylate, <NUM>,<NUM>-dimethyl-<NUM>-heptyl methacrylate, <NUM>-propylheptyl methacrylate, isodecyl methacrylate, or a mixture thereof.

According to another preferred aspect of the present invention, the monomer composition to prepare the polyalkyl (meth)acrylate polymer may further comprises alkyl methacrylate monomer c) of formula (III) having a linear or a branched alkyl chain from <NUM> to <NUM> carbon atoms, preferably alkyl methacrylate monomer c) having a linear or a branched alkyl chain from <NUM> to <NUM> carbon atoms, or a mixture thereof. The alkyl methacrylates c) refer to esters of methacrylic acid with linear or branched chain alcohols having from <NUM> to <NUM> carbon atoms. The term "esters of methacrylic acid with linear or branched chain alcohols having <NUM> to <NUM> carbon atoms" encompasses individual methacrylic esters with an alcohol of a particular length, and likewise mixtures of methacrylic esters with alcohols of different lengths. Most preferred alkyl methacrylate c) is lauryl methacrylate (alkyl methacrylates having a C<NUM>-C<NUM> linear alkyl group).

According to the present invention, the monomer composition to prepare the polyalkyl (meth)acrylate polymer comprises from <NUM> to <NUM>% by weight of monomer c) of formula (III), preferably from <NUM> to <NUM>% by weight, more preferably from <NUM> to <NUM>% by weight, even more preferably from <NUM> to <NUM>% by weight, most preferably from <NUM> to <NUM>% by weight, of monomer c), based on the total weight of the monomer composition.

According to the present invention, the monomer composition to prepare the polyalkyl (meth)acrylate polymer comprises from <NUM>% by weight or more of monomers a), b) and c), based on the total weight of the monomer composition. It means that the total amount of monomers a), and optionally b) and c) since monomers b) and c) are optional according to the present invention, is at least <NUM>% by weight in the monomer composition, based on the total weight of the monomer composition. In other words, the monomer composition to prepare the polyalkyl (meth)acrylate polymer comprises from <NUM> to <NUM>% by weight of monomers a), b) and c), based on the total weight of the monomer composition. Preferably, the total amount of monomers a), b) and c) in the monomer composition sums up to <NUM>% by weight or more, based on the total weight of the monomer composition. In other words, the monomer composition to prepare the polyalkyl (meth)acrylate polymer preferably comprises at least <NUM>% by weight of monomers a), optionally b) and c) since monomers b) and c) are optional according to the present invention, based on the total weight of the monomer composition. Preferably, the monomer composition to prepare the polyalkyl (meth)acrylate polymer preferably comprises from <NUM> to <NUM>% by weight of monomers a), b) and c), based on the total weight of the monomer composition.

According to a preferred aspect of the invention, the monomer composition to prepare the polyalkyl (meth)acrylate polymer may further comprise a monomer d) selected from the group consisting of alkyl (meth)acrylate having a linear alkyl chain from <NUM> to <NUM> carbon atoms, alkyl acrylates having an alkyl chain from <NUM> to <NUM> carbon atoms, or a mixture thereof, based on the total weight of the monomer composition. Most preferred monomer d) is selected from the group consisting of methyl methacrylate, methyl acrylate, butyl methacrylate, butyl acrylate, ethyl methacrylate, ethyl acrylate, <NUM>-ethylhexyl acrylate, <NUM>-propylheptyl acrylate, lauryl acrylate, isotridecyl acrylate, stearyl acrylate, or a mixture thereof.

Preferably, the monomer composition to prepare the polyalkyl (meth)acrylate polymer comprises from <NUM> to <NUM>% by weight, more preferably from <NUM> to <NUM>% by weight, of monomer d), based on the total weight of the monomer composition.

According to a preferred aspect of the invention, the total amount of monomers a), b), c) and d) in the monomer composition to prepare the polyalkyl (meth)acrylate polymer sums up to at least <NUM>% by weight, more preferably sums up to <NUM>% by weight, based on the total weight of the monomer composition. When the total amount of monomers a), b), c) and d) in the monomer composition to prepare the polyalkyl (meth)acrylate polymer sums up to <NUM>% by weight, it means that the monomer composition to prepare the polyalkyl (meth)acrylate polymer consists of a mixture of monomers a), and optionally monomers b), c) and d).

According to the present invention, the average carbon number of the alkyl chains R<NUM>, R<NUM> and R<NUM> of monomers a), and optionally b) and/or c) present in the monomer composition is from <NUM> to <NUM> carbon atoms, preferably from <NUM> to <NUM> carbon atoms, more preferably from <NUM> to <NUM> carbon atoms.

According to the present invention, the polyalkyl (meth)acrylate polymer according to the invention has a weight-average molecular weight from <NUM>,<NUM> to <NUM>,<NUM>/mol, preferably from <NUM>,<NUM> to <NUM>,<NUM>/mol, more preferably from <NUM>,<NUM> to <NUM>,<NUM>/mol, according to DIN <NUM>-<NUM>.

In the present invention, the weight-average molecular weights (Mw) or number-average molecular weights (Mn) of the copolymers were determined by gel permeation chromatography (GPC) using PMMA calibration standards according to DIN <NUM>-<NUM> using the following measurement conditions:.

Preferably, the polymers of the invention have a very low degree of cross-linking and a narrow molecular weight distribution, which further contributes to the shear resistance. The low degree of crosslinking and the narrow molecular weight are reflected in the polydispersity index of the polyalkyl (meth)acrylate polymers. Preferably, the polydispersity index (PDI) of the copolymers according to the invention is in the range of from <NUM> to <NUM>, more preferably in the range of from <NUM> to <NUM>. The polydispersity index is defined as the ratio of weight-average molecular weight to number-average molecular weight (Mw/Mn).

According to the invention, the polyalkyl (meth)acrylate polymer is an amorphous statistical polymer, wherein the monomer units a) and optionally monomers b) and/or c) and/or d) are distributed randomly, and sometimes unevenly, in the polymer.

According to the present invention, the above-mentioned polymers are prepared following the method comprising the steps of:.

The polyalkyl (meth)acrylates can preferably be obtained by free-radical polymerization. Accordingly, the proportion by weight of the respective repeat units that these polymers have is calculated from the proportions by weight of corresponding monomers used for preparation of the polymers.

The preparation of the polyalkyl (meth)acrylates from the above-described compositions is known per se. For instance, these polymers can be obtained especially by free-radical polymerization, and also related processes, for example ATRP (= Atom Transfer Radical Polymerization) or RAFT (= Reversible Addition Fragmentation Chain Transfer).

One comprehensive description, more particularly with further references, of these methods is given in <NPL>, to which explicit reference is made for the purposes of the disclosure.

The free-radical polymerization of the ethylenically unsaturated compounds can be affected in a manner known per se. Customary free-radical polymerization is described inter alia in Ullmann's Encyclopedia of Industrial Chemistry, Sixth Edition.

In the context of the present invention, the polymerization is initiated using at least one polymerization initiator for free-radical polymerization. These include the azo initiators widely known in the specialist field, such as <NUM>,<NUM>'-azobisisobutyronitrile, <NUM>,<NUM>'-azobis(<NUM>,<NUM>-dimethylvaleronitrile) and <NUM>,<NUM>-azobiscyclohexanecarbonitrile, organic peroxides such as dicumyl peroxide, diacyl peroxides such as dilauroyl peroxide, peroxydicarbonates such as diisopropyl peroxydicarbonate, peresters such as tert-butyl peroxy-<NUM>-ethylhexanoate, and the like.

According to the invention, very particular preference is given to polymerization initiators having a half-life of <NUM> hour at a temperature in the range from <NUM> to <NUM>, preferably in the range from <NUM> to <NUM>, especially in the range from <NUM> to <NUM>. Particularly preferred polymerization initiators are peroxidic polymerization initiators, more preferably tert-butylperoxy-<NUM>-ethylhexanoate.

In preferred processes, the at least one polymerization initiator for the free-radical polymerization is added preferably in one step, more preferably in multiple addition steps, even more preferably in at least two addition steps, most preferably in three addition steps. The polymerization initiator can preferably be added all at once in each addition step. More preferably, the polymerization initiator can be metered in each addition step, even more preferably continuously, especially with a constant metering rate.

The polymerization initiator can be added in each step in undiluted form or in diluted form, preferably dissolved in a solvent, especially in the form of a <NUM>% by weight to <NUM>% by weight solution in at least one mineral oil, in a polyalphaolefin and/or in the starting material monomers, more preferably in monomer a), monomer b), monomer c), monomer d), or a mixture thereof.

For the purpose of the present invention, it has been found to be very particularly appropriate to add the polymerization initiator in three steps, in which case, the amount of initiator added in the third step is greater than the amount of initiator added in the first step and in the second step. More preferably, the amount of polymerization initiator added in the third step is greater than the amount added in the second step, based on the total weight of the polymerization initiator added in the second step. More preferably, the amount of polymerization initiator added in the third step is at least <NUM>% by weight, even more preferably from <NUM>% to <NUM>% by weight, most preferably from <NUM>% to <NUM>% by weight, based on the total weight of the polymerization initiator added in the second step.

In the third step, the polymerization initiator is appropriately added all at once. Alternatively, it is also preferable to meter in the polymerization initiator in the third step, preferably continuously, especially with a constant metering rate. In a very particularly preferred embodiment of the present invention, the polymerization initiator is metered in continuously in the first, in the second and in the third step, favorably with a constant metering rate in each case, the mean metering rate of the third step preferably being greater than the mean metering rate of the second step, and the mean metering rate of the second step preferably being greater than the mean metering rate of the first step. The ratio of the mean metering rate of the third step to the mean metering rate of the second step is preferably greater than <NUM>:<NUM>, preferably in the range from <NUM>:<NUM> to <NUM>:<NUM>, more preferably greater than <NUM>:<NUM>, even more preferably greater than <NUM>:<NUM>, especially greater than <NUM>:<NUM>.

The third step is preferably started at a time at which <NUM> to <NUM>% by weight, more preferably <NUM> to <NUM>% by weight, even more preferably <NUM> to <NUM>% by weight of the total amount of the polymerization initiator added during the second step, is consumed.

The process detailed above allows a rapid and extremely effective polymerization of ethylenically unsaturated compounds and leads to polymers with comparably low residual monomer contents. Nevertheless, it has occasionally been found to be extremely favorable to provide further initiation toward the end of the reaction in order to lower the residual monomer content of the reaction mixture still further. Further initiation is preferably provided at a time at which at least <NUM>% by weight, appropriately at least <NUM>% by weight and especially at least <NUM>% by weight of the total amount of the polymerization initiator added during the last step has been consumed. Preference is given to adding in a further <NUM>% by weight to <NUM>% by weight of polymerization initiator, based on the total amount of polymerization initiator added beforehand.

The total amount of initiator is preferably in the range from <NUM> to <NUM>% by weight, and more preferably in the range from <NUM> to <NUM>% by weight, based on the total weight of the monomers (namely, the total weight of the monomer composition).

The process can be performed either in the presence or in the absence of a chain transfer agent. The chain transfer agents used may be typical species described for free-radical polymerizations, as known to those skilled in the art.

The sulfur-free chain transfer agents include, for example, without any intention that this should impose a restriction, dimeric α-methylstyrene (<NUM>,<NUM>-diphenyl-<NUM>-methyl-<NUM>-pentene), enol ethers of aliphatic and/or cycloaliphatic aldehydes, terpenes, β-terpinene, terpinolene, <NUM>,<NUM>-cyclohexadiene, <NUM>,<NUM>-dihydronaphthalene, <NUM>,<NUM>,<NUM>,<NUM>-tetrahydronaphthalene, <NUM>,<NUM>-dihydrofuran, <NUM>,<NUM>-dimethylfuran and/or <NUM>,<NUM>-dihydro-<NUM>-pyran, preference being given to dimeric α-methylstyrene.

The sulfur-containing chain transfer agents used may preferably be mercapto compounds, dialkyl sulfides, dialkyl disulfides and/or diaryl sulfides. The following chain transfer agents are mentioned by way of example: di-n-butyl sulfide, di-n-octyl sulfide, diphenyl sulfide, thiodiglycol, ethylthioethanol, diisopropyl disulfide, di-n-butyl disulfide, di-n-hexyl disulfide, diacetyl disulfide, diethanol sulfide, di-t-butyl trisulfide and dimethyl sulfoxide. Compounds used with preference as chain transfer agents are mercapto compounds, dialkyl sulfides, dialkyl disulfides and/or diaryl sulfides. Examples of these compounds are ethyl thioglycolate, <NUM>-ethylhexyl thioglycolate, pentaerythritol tetrathio-glycolate, cysteine, <NUM>-mercaptoethanol, <NUM>,<NUM>-mercapto-propanol, <NUM>-mercaptopropane-<NUM>,<NUM>-diol, <NUM>,<NUM>-mercaptobutanol, mercaptoacetic acid, <NUM>-mercaptopropionic acid, thioglycolic acid, mercaptosuccinic acid, thioglycerol, thioacetic acid, thiourea and alkyl mercaptans such as n-butyl mercaptan, n-hexyl mercaptan, t-dodecyl mercaptan or n-dodecyl mercaptan. Polymerization regulators used with particular preference are mercapto alcohols and mercapto carboxylic acids. In the context of the present invention, very particular preference is given to the use of n-dodecyl mercaptan and tert-dodecyl mercaptan as chain transfer agents.

In a particular aspect of the present invention, it is possible to use mixtures of chain transfer agents, preferred mixtures comprising especially sulfur-containing chain transfer agents such as the abovementioned mercaptan derivatives and sulfur-free chain transfer agents such as terpinolene, terpinene and derivatives thereof, and suitable transition metal complexes. More preferably, the chain transfer agents are selected from the group consisting of n-dodecyl mercaptan, tert-dodecyl mercaptan, terpinolene or a mixture thereof.

The chain transfer agents are used preferably in amounts of <NUM> to <NUM>% and especially <NUM> to <NUM>% by weight and more preferably <NUM> to <NUM>% by weight, based on the total weight of the monomers used in the polymerization (namely, the total weight of the monomer composition).

Further information can be found by the person skilled in the art in the specialist literature, especially the publications <NPL>; <NPL> and <NPL>.

Processes of particular interest are especially those in which a majority of the monomers is initially charged and the polymerization initiators, as explained above, are added in several steps over the polymerization time. Preferably, at least <NUM>% by weight, especially at least <NUM>% by weight, more preferably at least <NUM>% by weight and most preferably at least <NUM>% by weight of the monomers can be initially charged in a reactor. Subsequently, the initiators mentioned can be added at the polymerization temperature. The chain transfer agents may either be initially charged or added with the initiator, the chain transfer agents being initially charged in preferred processes. Particular preference here is given to processes in which at least <NUM>% by weight, especially at least <NUM>% by weight, more preferably at least <NUM>% by weight and most preferably at least <NUM>% by weight of the total weight of chain transfer agent are initially charged in a reactor.

The polymerization can be performed at standard pressure, reduced pressure or elevated pressure. The polymerization temperature is also uncritical. In general, however, it is in the range of from <NUM> to <NUM>, preferably from <NUM> to <NUM> and more preferably from <NUM> to <NUM>. In the case of performance of a free-radical polymerization, higher polymerization temperatures may be preferable; for instance, the polymerization temperature in the case of stepwise addition of the initiator may preferably be in the range from <NUM> to <NUM>, more preferably <NUM> to <NUM>. Particular preference is given here to processes in which the polymerization is performed at a temperature in the range from <NUM> to <NUM> above the reaction temperature, at which the half-life of the initiator is <NUM> minutes.

The polymerization can be performed with or without solvent. The term "solvent" should be understood here in a broad sense. The solvents to be used include hydrocarbon solvents, for example aromatic solvents such as toluene, benzene and xylene, saturated hydrocarbons, for example cyclohexane, heptane, octane, nonane, decane, dodecane, which may also be present in branched form. These solvents can be used individually or else as a mixture. Particularly preferred solvents are mineral oils, natural oils and synthetic oils, and mixtures thereof.

In a preferred embodiment, the proportion of solvent can be kept low, preferred embodiments of the process according to the invention having the feature that, after the polymerization has ended, there is no need to remove solvent from the composition, for example by distillation, in order to obtain a useable polymer mixture. Accordingly, the total amount of solvent, which is used in the polymerization reaction, is preferably in the range from <NUM> to <NUM>% by weight, more preferably <NUM> to <NUM>% by weight, even more preferably <NUM> to <NUM>% by weight based on the total weight of the monomer composition.

The measures detailed above, especially the stepwise addition of the initiator to a reactor comprising relatively large amounts of the monomers, can give surprising advantages. One of these is more particularly that the reaction can be performed without any great amounts of solvents. This allows the reaction to be conducted very inexpensively. It is surprisingly possible to obtain, more particularly, very narrow molecular weight distributions with a low polydispersity index without any need to use costly processes such as ATRP. In addition, the reaction time and initiator consumption can be minimized.

As indicated above, the present invention also relates to a lubricating oil composition comprising at least one base oil and at least one polyalkyl (meth)acrylate polymer as defined in the present invention.

The base oils correspond to lubricant base oils, mineral, synthetic or natural, animal or vegetable oils suited to their use/chosen depending on the intended use.

The base oils used in formulating the lubricating oil compositions according to the present invention include, for example, conventional base stocks selected from API (American Petroleum Institute) base stock categories known as Group I, Group II, Group III, Group IV and Group V. The Group I and II base stocks are mineral oil materials (such as paraffinic and naphthenic oils) having a viscosity index (or VI) of less than <NUM>. Group I is further differentiated from Group II in that the latter contains greater than <NUM>% saturated materials and the former contains less than <NUM>% saturated material (that is more than <NUM>% unsaturated material). Group III is considered the highest level of mineral base oil with a VI of greater than or equal to <NUM> and a saturates level greater than or equal to <NUM>%. Group IV base oils are polyalphaolefins (PAO). Group V base oils are esters and any other base oils not included in Group I to IV base oils. These base oils can be used individually or as a mixture.

Preferably, the base oil included in the lubricating oil composition of the present invention is selected from the group of mineral oils consisting of API Group I base oils, API Group II base oils, API Group III base oils or a mixture thereof. Most preferably, the lubricant composition comprises an API Group I base oil, API Group II base oil or a mixture thereof.

According to a preferred embodiment of the invention, the lubricating oil composition comprises at least one base oil selected from an API Group I base oil, API Group II base oil or a mixture thereof, with a kinematic viscosity at <NUM> according to ASTM D445 of <NUM><NUM>/s or more, and at least one polyalkyl (meth)acrylate polymer as defined in the present invention.

Preferably, the lubricating oil composition comprises from <NUM> to <NUM>% by weight, more preferably from <NUM> to <NUM>% by weight, and even more preferably from <NUM> to <NUM>% by weight of polyalkyl (meth)acrylate polymer according to the invention, based on the total weight of the lubricating oil composition.

Preferably, the lubricating oil composition according to the invention comprises from <NUM> to <NUM>% by weight, more preferably from <NUM> to <NUM>% by weight, and even more preferably from <NUM> to <NUM>% by weight of base oil, based on the total weight of the lubricating oil composition.

All preferred aspects of the polymer, base oil and amounts as listed above apply for this lubricating oil composition.

The lubricating oil compositions according to the present invention may also comprise any other additional additives suitable for use in the formulations. These additives include additional viscosity index improvers, pour point depressants, dispersants, demulsifiers, defoamers, lubricity additives, friction modifiers, antioxidants, detergents, dyes, corrosion inhibitors and/or odorants.

According to a preferred aspect of the invention, the total content of the polyalkyl (meth)acrylates and base oil in the lubricant composition sums up from <NUM>% by weight or more, sums up from <NUM>% by weight or more, based on the total weight of the lubricant composition.

The invention also relates to the use of the polyalkyl (meth)acrylate polymer according to the present invention, as defined herein above, as a lubricant additive or a synthetic base fluid, by adding said polyalkyl (meth)acrylate polymer to a lubricating oil composition.

Preferably, the lubricating oil composition is a gear oil composition, a transmission oil composition, a hydraulic oil composition, an engine oil composition, a marine oil composition, an industrial lubricating oil composition or a grease.

The invention also relates to a method of thickening a lubricating oil composition by adding a polyalkyl (meth)acrylate polymer according to the present invention, as a lubricant additive or a synthetic base fluid, to said lubricating oil composition.

Thus, the invention relates to a method of optimizing the rheological properties of a lubricating oil composition by adding a polyalkyl (meth)acrylate polymer according to the present invention, as a lubricant additive or a synthetic base fluid, to said lubricating oil composition.

In the experimental part, the examples demonstrate that, even at low treat rates, the polyalkyl (meth)acrylate polymer according to the present invention provides a very good thickening effect when added to the lubricating oil composition, while maintaining good shear stability. Furthermore, the polymers have good viscometric performance, including low temperature and viscosity index performance to reduce the effect of changes in viscosity with temperature, when used in lubricating oil compositions. The polymeric additives also have a positive influence on component solubility thanks to their chemical structure.

The invention is further illustrated in detail hereinafter with reference to examples and comparative examples, without any intention to limit the scope of the present invention. All percentages in relation to monomers or base fluids given in the tables below are weight percentages (wt%).

A round-bottom flask equipped with a glass stir rod, nitrogen inlet, thermometer and reflux condenser were initially charged with the monomers as defined in Table <NUM>. For the inventive example Ex. <NUM>, <NUM> of EHMA, <NUM> of LMA and <NUM> of CHMA were charged to the flask together with <NUM> (<NUM> wt% relative to the total amount of monomers) of dodecyl mercaptan (DDM) and <NUM> (<NUM> wt% relative to the total amount of monomers) of tert-dodecyl mercaptan (TDDM). The mixture was heated to <NUM>, while stirring and nitrogen bubbling for inertion. Thereafter, <NUM> of tert-butylperoxy-<NUM>-ethylhexanoat (<NUM> wt% relative to the total amount of monomers) was dissolved in <NUM> of EHMA. The initiator solution was metered in within three hours, with addition of <NUM> wt% of the amount specified within the first hour, <NUM> wt% within the second hour and <NUM> wt% within the third hour. After the feed ended, the mixture was stirred for an additional hour.

Inventive examples Ex. <NUM> to Ex. <NUM> and Ex. <NUM> to Ex. <NUM>, as well as comparative examples Ex. <NUM>*, Ex. <NUM>*, Ex. <NUM>* and Ex. <NUM>* to Ex. <NUM>* were prepared in the same way as inventive example <NUM>, except that the amounts of reactants and/or other reaction conditions were changed as listed in Table <NUM>.

<NUM>, <NUM> IDMA and <NUM> of IBOMA were charged to the flask together with <NUM> Chevron 600R, <NUM> (<NUM> wt% relative to the total amount of monomers) of DDM and <NUM> (<NUM> wt% relative to the total amount of monomers) of TDDM. The mixture was heated to <NUM>, while stirring and nitrogen bubbling for inertion. Thereafter, <NUM> of tert-butylperoxy-<NUM>-ethylhexanoat (<NUM> wt% relative to the total amount of monomers) was dissolved in <NUM> of Chevron 600R. The initiator solution was metered in within three hours, with addition of <NUM> wt% of the amount specified within the first hour, <NUM> wt% within the second hour and <NUM> wt% within the third hour. After the feed ended, the mixture was stirred for an additional hour, before an initiator chaser shot (<NUM> of tert- butylperoxy-<NUM>-ethylhexanoat, <NUM> wt% relative to the total amount of monomers) was added. After three hours, a second initiator chaser shot (<NUM> of tert-butylperoxy-<NUM>-ethylhexanoat, <NUM> wt% relative to the total amount of monomers) was added. Subsequently, the mixture was stirred for another <NUM> hours.

The inventive examples Ex. <NUM> to Ex. <NUM> and comparative example Ex. <NUM>*, Ex. <NUM>* and Ex. <NUM>* were prepared in a similar way as inventive example Ex. <NUM>, except that the amounts of reactants and/or other reaction conditions were changed as listed in Table <NUM>. <NUM> to Ex. <NUM>, the initiator was dissolved in monomer instead of oil and the dilution with oil was done after polymerization.

Details regarding the polymer composition of the individual examples, prepared according to the above-indicated procedures A and B, are provided in Tables <NUM> and <NUM>, together with basic properties of the polymers. The main amount of the monomer is always first charged to the flask. A solution of the initiator in the remaining amount of monomer or oil is then fed at <NUM> over a set period of time. For copolymers with monomer mixtures, all monomers are mixed and charged to the reactor before feeding the initiator. The amount of chain transfer agent is adjusted as listed in Table <NUM> to control the molecular weight of the polymer. All polymers were synthesized with <NUM> wt% initiator relative to the total amount of monomers.

In the present invention, the bulk viscosity (BV) of the polymer (product obtained from polymerization reaction) corresponds to the kinematic viscosity (KV) of the resulting product of the polymerization measured in accordance with ASTM D445. Thus, the bulk viscosity of the polymers (BV100) as shown in Table <NUM> below, were measured as kinematic viscosity at <NUM> in accordance with ASTM D445. For inventive examples Ex. <NUM> to Ex. <NUM>, the polymer was diluted in Chevron 600R oil to simplify handling of the polymers. Thus, the bulk viscosity corresponds to the KV100 of the polymer diluted in oil.

The thickening of each polymer in oil was tested by mixing <NUM>% by weight of polymer in <NUM>% by weight of Chevron 600R base oil (Group II base oil). The results for the kinematic viscosity at <NUM> and <NUM> were measured in accordance with ASTM D445 and are listed in Table <NUM>.

Formulations comprising the inventive and comparative polymers of Table <NUM> were then prepared. Formulation composition and properties such as viscosity index, kinematic viscosity, PP and shear loss are shown in Tables <NUM> and <NUM>, Table <NUM> and Table <NUM>. Formulations were prepared in API Group II base oil targeting a KV40 of <NUM><NUM>/s. Examples according to the invention are listed in Tables <NUM>, comparative examples in Table <NUM>. Table <NUM> lists formulations with inventive and comparative examples for formulations targeting a KV40 of <NUM><NUM>/s in a mixture of API Group II base oil and bright stock AP/E Core™ <NUM>.

As shown in Table <NUM> above, the polymers according to the invention have very high BV100 values (Ex. <NUM> to Ex. <NUM>) in contrast to the comparative polymers. This is also reflected in the comparison of the thickening of <NUM>% by weight of each polymer in Group II base oil as listed in Table <NUM>. The KV40 value is most relevant for the thickening power as the viscosity at <NUM> defines the ISO class of the fluid. All inventive examples have a higher KV40 value than the comparative examples. Especially the inventive examples with high amounts of cyclic comonomer (≥ <NUM> wt%) such as Ex. <NUM> and Ex. <NUM> exhibit the highest thickening with KV40 values above <NUM><NUM>/s in the example formulation.

The effect of the cyclic monomer on the thickening power can be observed when comparing inventive Ex. <NUM> with Ex. <NUM>* or inventive Ex. <NUM> with Ex. <NUM>*, wherein even the replacement of <NUM> wt% EHMA, which provides itself already high thickening power, with CHMA shows a good increase of KV40 values. The effect correlates to the content of cyclic monomers as it can be observed when comparing Ex. <NUM>*, Ex. <NUM>* and Ex. <NUM> for IDMA/CHMA combinations or Ex. <NUM> to Ex. <NUM> for IDMA/IBOMA combinations. Larger bulky side chains allow incorporation of more cyclic monomer into the polymers while maintaining the solubility in oil (e.g. Ex. <NUM> with <NUM>% TMCHMA). Those results confirm that the average carbon number of the alkyl chains R<NUM>, R<NUM> and R<NUM> of monomers a), b) and c) in the monomer composition to prepare the polymer must be higher than <NUM> to maintain solubility in common base oil systems.

As shown in Table <NUM> and <NUM> above, the formulations with KV40 of <NUM><NUM>/s comprising polymers according to the invention deliver a reduction in treat rate of at least <NUM> wt% up to <NUM> wt% in comparison to the comparative examples shown in Table <NUM> (Ex. <NUM>*, <NUM>*, <NUM>* used in F-<NUM>* to F-<NUM>*, respectively). The treat rates are even further reduced by using polymers comprising higher amounts of cyclic monomers a). With the inventive polymers according to the invention, low treat rates are achieved while fulfilling the viscometric performance required in the industry (Lubricants and industrial oils industry norm ISO <NUM>-<NUM>:<NUM>). Advantageously, small shear losses at <NUM> of less than <NUM>% are observed.

As shown in Table <NUM>, similar observations are made for formulations with higher KV40, such as <NUM><NUM>/s, in a Group I+II base oil mixtures. The inventive examples Ex. <NUM> and Ex. <NUM> have lower treat rates (F-<NUM> to F-<NUM>) compared to the comparative examples Ex. <NUM>*, Ex. <NUM>*, Ex. <NUM>* (F-<NUM>* to F-<NUM>*).

Claim 1:
A polyalkyl (meth)acrylate polymer obtainable by polymerizing a monomer composition comprising:
a) at least <NUM>% by weight of monomer a) selected from the group consisting of an alkyl methacrylate of formula (I) or a mixture thereof, based on the total weight of the monomer composition,
<CHM>
wherein R<NUM> is a substituted or unsubstituted alicyclic radical,
b) from <NUM> to <NUM>% by weight of monomer b) selected from the group consisting of an alkyl methacrylate of formula (II) or a mixture thereof, based on the total weight of the monomer composition,
<CHM>
wherein R<NUM> is a branched alkyl radical having <NUM> to <NUM> carbon atoms and wherein from <NUM>% to <NUM>% by weight of the R<NUM> radicals are branched, based on the total amount of methacrylate monomers b) of formula (II),
c) from <NUM> to <NUM>% by weight of monomer c) selected from the group consisting of an alkyl methacrylate monomer of formula (III) or a mixture thereof, based on the total weight of the monomer composition,
<CHM>
wherein R<NUM> is a linear or branched alkyl radical having <NUM> to <NUM> carbon atoms,
wherein the total amount of monomers a), b) and c) sums up to <NUM>% by weight or more, based on the total weight of the monomer composition, and
wherein the average carbon number of the alkyl chains R<NUM>, R<NUM> and R<NUM> of monomers a), b) and c) in the monomer composition is from <NUM> to <NUM> carbon atoms, and
wherein the polyalkyl (meth)acrylate polymer has a weight-average molecular weight from <NUM>,<NUM> to <NUM>,<NUM>/mol according to DIN <NUM>-<NUM>.