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 Bright stock is a product of Group I base oil refineries which are technologically outdated so future supply is unknown.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.

The advantage of using alternative thickeners having a higher polarity is that these polar high viscosity base fluids do not need the addition of nonpolar low viscous fluids, such as esters, 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 where 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 make them less attractive compared to polyolefins, such as PIB.

<CIT> discloses PAMA viscosity index improvers (VII) prepared by free-radical polymerization using at least <NUM> to <NUM>% by weight of methyl (meth)acrylate (MMA) and <NUM> to <NUM>% by weight of a C<NUM> to C<NUM> alkyl (meth)acrylate. Polar monomers like MMA reduce the coil size in solution and contribute to a strong coiling/uncoiling effect which lifts the VI. As a consequence, the thickening power of these polymers is reduced, especially at lower temperatures.

<CIT> discloses PAMA-based viscosity index improvers prepared using different combinations of C<NUM> to C<NUM> alkyl (meth)acrylates, C<NUM> to C<NUM> alkyl (meth)acrylates branched in the C<NUM> position of the alkyl radical and at least one monomer from the group of C<NUM> to C<NUM> alkyl (meth)acrylates, vinyl aromatic compounds and nitrogen-containing vinyl monomers. The amount of alkyl (meth)acrylates with not more than <NUM> carbon atoms in the alkyl side chain is no more than <NUM>% by weight, preferably no more than <NUM>% by weight, even more preferably no more than <NUM>% by weight.

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. Last, but not least, it is desired that the polymers should not have any negative effect on the foaming properties of the lubricant oil composition they are added to. Ideally, no foam or only very little foam with quick collapse times should be observed to meet the requirements of the industry.

Surprisingly, it has been found that mid-chain polyalkyl (meth)acrylates, comprising a high amount of branched alkyl methacrylate monomer units, 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. Furthermore, they do not have any negative effect on the foaming properties of the lubricant oil composition they are added to.

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 lubricant 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 the use of these polyalkyl (meth)acrylate polymers as lubricant additive or synthetic base fluid in a lubricating 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 lubricating oil composition or in grease.

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

wherein more than <NUM>% by weight of the monomers a), b) and c) in the monomer composition are branched, 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>.

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).

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. According to another 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 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, most 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 linear or a branched alkyl radical having <NUM> or <NUM> carbon atoms and wherein from <NUM>% to <NUM>% by weight of the R<NUM> radicals are branched, based on the weight of the total amount of methacrylate monomers a) of formula (I). Preferably, the polyalkyl (meth)acrylate polymer comprises from <NUM>% to <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, based on the total weight of the monomer composition.

Preferably, the monomers a) are selected from the group consisting of isononyl methacrylate, <NUM>,<NUM>-dimethyl-<NUM>-heptyl methacrylate, <NUM>-propylheptyl methacrylate, isodecyl methacrylate, or a mixture thereof. More preferably, the monomers a) are selected from the group consisting of isononyl 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 further comprises alkyl methacrylate monomer b) having a linear or a branched alkyl chain from <NUM> to <NUM> carbon atoms, preferably alkyl methacrylate monomer b) having a linear or a branched alkyl chain from <NUM> to <NUM> carbon atoms, or a mixture thereof. The alkyl methacrylates b) 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 straight 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 preferable alkyl methacrylate b) is lauryl methacrylate (alkyl methacrylates having a C<NUM>-C<NUM> linear alkyl group).

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

Preferably, the monomer composition to prepare the polyalkyl (meth)acrylate polymer further comprises monomer c) 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. Most preferred monomer c) 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 of monomer c), based on the total weight of the monomer composition.

According to the present invention, the polyalkyl (meth)acrylate polymer has a weight-average molecular weight from <NUM>,<NUM> to <NUM>,<NUM>/mol, according to DIN <NUM>-<NUM>. Preferably, the polyalkyl (meth)acrylate polymer has a weight-average molecular weight 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>, even more preferably in the range of from <NUM> to <NUM>. A polydispersity index in the range of <NUM> to <NUM> is considered optimal for most industrial applications with regard to the shear resistance of the copolymers. The polydispersity index is defined as the ratio of weight-average molecular weight to number-average molecular weight (Mw/Mn).

According to another preferred aspect of the invention, the total content of monomer units derived from monomers a) and b) in the polyalkyl (meth)acrylate polymer of the invention sums up to at least <NUM>% by weight, more preferably sums up to at least <NUM>% by weight, even more preferably sums up to at least <NUM>% by weight, most preferably sums up to <NUM>% by weight, based on the total weight of the polyalkyl (meth)acrylate polymer.

According to another preferred embodiment of the invention, the monomer composition to prepare the polyalkyl (meth)acrylate polymer according to the invention consists of methacrylate monomers a) of formula (I), in which case the resulting polymer is a polyalkyl methacrylate polymer.

According to the preferred embodiment of the invention, the monomer composition to prepare the polyalkyl (meth)acrylate polymer according to the invention consists of, based on the total weight of the monomer composition:.

According to another preferred embodiment of the invention, the monomer composition to prepare the polyalkyl (meth)acrylate polymer according to the invention consists of, based on the total weight of the monomer composition:.

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) are distributed randomly, and sometimes unevenly, in the polymer.

According to a preferred embodiment of the invention, the preferred polyalkyl (meth)acrylate polymers according to the invention are poly isononyl methacrylate, poly <NUM>-propylheptyl methacrylate and poly isodecyl methacrylate. All preferred aspects of the polymer as listed above apply for these preferred polymers.

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 <NPL>on.

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), 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>% and more preferably in the range from <NUM> to <NUM>% by weight, based on the weight of the monomers.

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 proportion of solvent which is used overall is preferably in the range from <NUM> to <NUM>% by weight, more preferably <NUM> to <NUM>% by weight and most preferably in the range from <NUM> to <NUM>% by weight. The solvent here may especially serve for dissolution of the initiator added over the course of the reaction.

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.

Preferably, the lubricating oil composition for use in accordance with 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 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 <NUM> to <NUM>% by weight, preferably <NUM> to <NUM>% by weight, and most preferably <NUM> to <NUM>% by weight of base oil, based on the total weight of the lubricating oil composition.

In a preferred embodiment of the invention, the lubricating oil composition comprises polyisononyl methacrylate, poly-<NUM>-propylheptyl methacrylate, polyisodecyl methacrylate or a mixture thereof, and a base oil. 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 the base oil in the lubricant composition sums up to <NUM>% by weight or more, more preferably sums up to <NUM>% by weight or more by weight, 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 a monomer (mixture) as defined in Table <NUM>. For the inventive example Ex. <NUM>, <NUM> of INMA 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). <NUM> of tert-butylperoxy-<NUM>-ethylhexanoat (<NUM> wt% relative to the total amount of monomers) was dissolved in <NUM> of INMA. 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 another hour, a second initiator chaser shot (<NUM> of tert-butylperoxy-<NUM>-ethylhexanoat, <NUM> wt% relative to the total amount of monomers) was added. Finally, the mixture was stirred for at least an additional hour.

The inventive examples and comparative examples 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> or described in the following.

For inventive examples Ex. <NUM>, as well as comparative examples Ex. <NUM>*, Ex. <NUM>*, and Ex. <NUM>* to Ex. <NUM>* the initiator solution was added with <NUM> wt% of the amount specified within the first hour, <NUM> wt% within the second hour and <NUM> wt% within the third hour. For inventive examples Ex. <NUM> and Ex. <NUM>, the initiator solution was added with <NUM> wt% of the amount specified within the first hour, <NUM> wt% within the second hour and <NUM> wt% within the third hour. For comparative example Ex. <NUM>*, the initiator solution was added with <NUM> wt% of the amount specified within the first hour, <NUM> wt% within the second hour and <NUM> wt% within the third hour.

For inventive examples Ex. <NUM> and Ex. <NUM>, as well as comparative examples Ex. <NUM>*, Ex. <NUM>*, and Ex. <NUM>* to Ex. <NUM>* no chaser shots were added and the whole amount of initiator (<NUM> wt% initiator relative to the total amount of monomer) dissolved in monomer was added with the feed. <NUM> and comparative Ex. <NUM>* and additional distillation step at <NUM> mbar and <NUM> was included at the end.

Details regarding the polymer composition of the individual examples, prepared according to the above-indicated procedure, 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 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 monomer.

<NUM> of DBPO (<NUM> wt% relative to the acrylate in the feed) dissolved in <NUM> EHA was slowly fed to <NUM> of Chevron 600R under nitrogen at <NUM> within <NUM> hours. After the feed had been finalized and stirring for <NUM> hours at <NUM>, the resulting clear and colorless polymer solution was cooled down.

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. 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 inventive polymers and comparative polymers of Table <NUM> were then prepared. The amounts of components along with the properties of the different formulations such as viscosity index, kinematic viscosity and shear loss are shown in Table <NUM> for formulations using Group II base oil adjusted to a kinematic viscosity of approximately <NUM><NUM>/s at <NUM>.

Table <NUM> shows the amounts of components along with the viscosities and viscosity index of formulations adjusted to a kinematic viscosity of approximately <NUM><NUM>/s or <NUM><NUM>/s at <NUM> in a mixture of a Group I and Group II base oil.

As shown in Table <NUM> above, the inventive polymers according to the invention all have a high BV100 in contrast to the comparative polymers Ex. <NUM>* to <NUM>*. Only comparative Ex. <NUM>* and Ex. <NUM>*, prepared with EHMA and OCMA (C8 alkyl methacrylate), show a high BV100. 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>. KV40 is most relevant for the thickening power as the viscosity at <NUM> defines the ISO class of the fluid. Especially the comparative example Ex. <NUM>*, which is pure EHA, compared to the inventive examples Ex. <NUM> and <NUM>, which are pure INMA of similar weight-average molecular weight, demonstrates the higher thickening of methacrylates compared to acrylates. Furthermore, comparative Ex. <NUM>* and Ex. <NUM>* demonstrate that already <NUM>% by weight of short-chain methacrylates, such as MMA or BMA, in the polymer composition is detrimental to the target of high thickening. <NUM>* and Ex. <NUM>* show lower KV40 values in the <NUM>% by weight in Group II base oil mixture, thus poorer thickening, compared to the polymers according to the present invention.

As shown in Table <NUM> above, the formulations with KV40 of <NUM><NUM>/s comprising polymers according to the invention (Ex. <NUM> used in F-<NUM> to F-<NUM>, respectively) deliver a reduction in treat rate of at least <NUM> wt% up to <NUM> wt% in comparison to the comparative examples (Ex. <NUM>*, Ex. <NUM>* used in F-<NUM>* and F-<NUM>*, respectively). The lower treat rate is achieved while maintaining good viscometrics with a VI of more than <NUM>, small shear losses at <NUM> of less than <NUM>% and comparable pour points. Similar observations are made for formulations with higher KV40, such as <NUM> or <NUM><NUM>/s, in a Group I+II base oil mixtures as shown in Table <NUM>. The inventive example Ex. <NUM> has significantly lower treat rates (F-<NUM> and F-<NUM>), compared to the comparative example Ex. <NUM>* (F-<NUM>*, F-<NUM>*). Using the inventive examples, the treat rates are <NUM> wt% and <NUM> wt% lower as for the comparative example for the VG460 and VG680, respectively.

The comparative polymer examples with higher amounts of methacrylate monomer units having a linear alkyl chain, such as Ex. <NUM>* to Ex. <NUM>* and Ex. <NUM>*, are poorer in thickening efficiency and are not able to reduce the treat rate in the same amount as the examples according to the present invention. Furthermore, also the comparative example Ex. <NUM>*, similar to Example <NUM> of <CIT>, with <NUM>% by weight of a C<NUM>-C<NUM> methacrylate monomer (<NUM>% branched and <NUM>% linear alkyl chains), is not able to achieve the treat rate advantage. <CIT> also describes the use of the monomer IDMA. However, the corresponding IDMA-containing polymers disclosed in <CIT> all contain a maximum of <NUM>% by weight of this monomer (Example <NUM> in <CIT>). It can be observed that the comparative example Ex. <NUM>*, similar to Example <NUM> of <CIT>, with a high amount of linear alkyl methacrylate monomer units is poor in thickening efficiency. Additionally, the comparative example Ex. <NUM>*, containing <NUM>% by weight of MMA, therefore similar to the polymer composition of <CIT>, shows a lower KV40 value than the polymers according to the present invention.

When used in lubricant oil compositions, the polymers should not only be able to thicken an oil to a desired viscosity, even at low treat rates as shown in Tables <NUM> and <NUM> above, but they should also not have any negative impact on the foaming properties of the lubricant oil composition they are added to. Ideally, no foam or only very little foam with quick collapse times should be observed to meet the requirements of the industry.

Formulations in Group II base oil adjusted to a kinematic viscosity of approximately <NUM><NUM>/s at <NUM> were prepared to test foaming properties according to ASTM D892-<NUM> (Standard Test Method for Foaming Characteristics of Lubricating Oils from <NUM>). The test procedure used within this patent application uses Option A for sample preparation and a cylindrical gas diffuser. According to ASTM D892-<NUM>, the test includes three sequences at <NUM>, at <NUM> and <NUM>, wherein for each sequence the volume of foam is recorded directly after the blowing period and then again after <NUM> minutes of settling. In case, foam formation is observed but disappears within the <NUM> minutes, a collapse time is calculated. The amounts of components along with the properties such as viscosity index, kinematic viscosities and foam behavior are shown in Table <NUM> below.

Norms such as ISO12925 have a limit of <NUM> foam direct after blowing period and a limit of <NUM> foam after <NUM> minutes, for each sequence. Inventive formulation F-<NUM> outperforms because no foam formation is observed at all (all values at OmL). Inventive formulations F-<NUM> and F-<NUM> have also very good foam test results and would comply with the ISO12925 norm requirements. In contrast, the comparative formulations F-<NUM>* and F-<NUM>*, comprising a polyalkyl (meth)acrylate polymer from pure C8 methacrylate monomer units (polymers Ex. <NUM>* and Ex. <NUM>*), show poor foam test results since it is observed a significant foam formation and long collapse times.

In Table <NUM> above, the low temperature performance of the formulations has also been tested. The kinematic viscosity at -<NUM> /KV-<NUM>) of both comparative formulations F-<NUM>* and F-<NUM>*, comprising a polyalkyl (meth)acrylate polymer from pure C8 methacrylate monomer units (polymers Ex. <NUM>* and Ex. <NUM>*), were not measurable as the samples became solid at -<NUM>. In contrast, formulations F-<NUM> to F-<NUM> comprising the inventive polymers according to the invention, show better low temperature performance at -<NUM>.

Claim 1:
A polyalkyl (meth)acrylate polymer obtainable by polymerizing a monomer composition consisting of:
a) 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, based on the total weight of the monomer composition,
<CHM>
wherein R<NUM> is a linear or a branched alkyl radical having <NUM> or <NUM> carbon atoms and wherein from <NUM>% to <NUM>% by weight of the R<NUM> radicals are branched, based on the weight of the total amount of methacrylate monomers a) of formula (I),
b) from <NUM> to <NUM>% by weight of monomer b) selected from the group consisting of an alkyl methacrylate monomer having a linear or a branched alkyl chain from <NUM> to <NUM> carbon atoms, or a mixture thereof, based on the total weight of the monomer composition,
c) from <NUM> to <NUM>% by weight of monomer c) 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,
wherein more than <NUM>% by weight of the monomers a), b) and c) in the monomer composition are branched, 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>.