WO2012076676A1

WO2012076676A1 - A viscosity index improver comprising a polyalkyl(meth)acrylate polymer

Info

Publication number: WO2012076676A1
Application number: PCT/EP2011/072268
Authority: WO
Inventors: Boris Eisenberg; Torsten Stöhr; Thomas Schimmel; Christopher Paul Radano; Justin August Langston; Peter Moore; Mandi J Mcelwain
Original assignee: Evonik Rohmax Additives Gmbh
Priority date: 2010-12-10
Filing date: 2011-12-09
Publication date: 2012-06-14

Abstract

The present invention describes a viscosity index improver comprising a polyalkyl(meth)acrylate polymer having a polydispersity Mw/Mn in the range of 1.05 to 2.0. In addition thereto, the present invention discloses a lubricant comprising the viscosity index improver of the present invention.

Description

A viscosity index improver comprising a polyalkyl(meth)acrylate polymer The present application relates to a viscosity index improver comprising a

polyalkyl(meth)acrylate polymer. Furthermore the present invention describes a lubricant comprising such a viscosity index improver.

For more than 50 years, the lubricant industry has sought for efficient ways to modify the viscosity of various fluids to improve the overall lubricity of a fluid for applications in crankcase fluids, transmission fluids, gear oils, and hydraulic oils. The viscosity index (VI) of a fluid, refers to the ability for a fluid to maintain viscosity and lubricity over a specified temperature range, most often between 40 °C and 100 °C. Increasing the VI of a fluid not only leads to enhanced lubrication, but also can introduce many additional benefits finding usefulness in the lubricant industry and distinguishing the overall performance of one fluid versus another. These benefits include but are not limited to reduced viscosities at colder temperatures thus improving low temperature performance and improvements in hydraulic pump efficiency for various hydraulic systems, which can ultimately lead to reduced fuel consumption.

The viscosity index of a lubricant formulation may be modified by addition of a viscosity modifier or by altering the composition of the base fluid. Viscosity index of formulated lubricating oil can be improved by the choice of base oil as well as the viscosity modifier. The base oils used are generally selected from a class of mineral base oils (Groups l-lll) or synthetic oils such as poly alpha-olefins (Group IV) or ester-based oils (Group V). The viscosity index of these base fluids generally increase as the fluid changes from a Group I to Group III. Synthetic base fluids (Groups IV-V) are beneficial for their favorable low temperature properties and their high viscosity index. Viscosity modifiers are generally selected from a class of polymers such as polyolefins and polymethacrylates. Poly(alkylmethacrylates) (PAMAs) are conventionally employed as VI improvers to obtain favorable viscosity profiles in lubricating oils at high and low temperature. Chemical modification of poly(alkylmethacrylates), such as, for example, compositional modifications, molecular weight/shear stability adjustments and solvent selection may affect performance of the polymer as a VI improver in a lubricant composition. Poly(alkylmethacrylates) (PAMA) represent a class of VI improvers that have been used for many years and boast favorable viscosity profiles in lubricating oils at high and low temperature. Due to ever increasing demands on lubricants, in particular, hydrocarbon oil based lubricants, for better performance which would contribute to reduced fuel consumption and reduced frictional wear leading to increased engine or pump performance lifetime, the industry is continuously exploring new methods and technologies to improve lubricant performance and increase the VI of the lubricant formulation. The need for increasing viscosity index is important for many applications requiring lubrication, where incremental increases can result in vast improvements in performance and efficiency.

There have been many approaches known in the prior art in order to stabilize and/or to further improve the viscosity index of lubricants by adding suitable polymers to the lubricant, such as WO 2009/145823 discloses the combination of base oils to give a favorable shear stability and viscosity index. US 6,746,993 B2 reports improved VI from higher polar monomer incorporation in the viscosity modifier wherein these polymers comprised a considerable amount of a uniquely branched Guerbet ester to overcome solubility in oil.

The most important parameters to improve the viscosity index of lubricating oils have been adjustments of the molecular weight and of the molecular composition. Molecular weight increases alone improve viscosity index, but at the expense of fluid shear stability, thereby limiting the end use applications. GB 1 333 733 p.e. discloses the time dependent decomposition of high molecular weight polymers due to shearing forces which leads to smaller molecules with lower molecular weights having conclusively lower viscosity and viscosity index values.

Molecular compositional modifications can improve the viscosity index, but are limited by their solubility and compatibility in fully formulated lubricating oils. While adjustments in VI improver compositions can generally maintain shear stability, the solubility of the viscosity modifier reaches a limit in oil formulations. Such compositional changes can result in sharp differences in polarity which then lead to incompatibility and immiscibility with standard detergent-inhibitor package components.

WO 2006/047398 A2, WO 2008/058108 A2, WO 2007/025837 A1 and EP 0 814 097 A2 disclose the structures of star polymers and their uses in lubricating oils.

Unfortunately, addressing these techniques and approaches individually may not deliver optimal viscometric performance. There have been some approaches to narrow the polydispersity of the polymers used.

Bataille P., Lubrication Engineering, 1995, 51 , 12, 996-1005 discloses the preparation of viscosity index improvers based on copolymers of vinyl 2-ethyl hexanoate and 2- ethyl hexyl acrylate wherein one polymer sample has been fractionated to narrow its polydispersity. The viscosity index values could be improved thereby but without indicating whether the shear stability has been changed or not.

CA 2 514 499 A1 discloses in one embodiment a method for improving the viscosity index of a lubricant composition comprising mixing with the lubricant composition from about 5 to about 30 percent by weight of an additive comprising a shear stable olefin copolymer derived from a copolymer having a number average molecular weight ranging from about 50000 to about 250000, wherein the shear stable olefin copolymer has a shear stability index of less than about 40, a polydispersity of not more than about 1.5, and a thickening efficiency of greater than about 1.8, and wherein the amount of shear stable olefin copolymer in the lubricant composition is based on a total weight of the lubricant composition. Herein, the oil and copolymer mixtures have been cycled between 1 and 10 times through a homogenizer to narrow the polydispersity of the used copolymer samples. The example data listed in Tables 3 and 4 exhibits that with increasing number of homogenizer cycles the viscosity index decreases drastically.

US 6,403,745 B1 , WO 01/40333 A1 and US 6,391 ,996 B1 provide examples of improved pour point and low temperature viscosity using a polymer with controlled radical polymerization chemistry such as with ATRP. No hints are suggesting the use of these polymers as VI improvers. The known polymers show a good efficiency as viscosity index improvers. Accordingly, most of these polymers exhibit a satisfactory property profile. However, there is a permanent effort to improve the relationship of thickening, viscosity index and shear stability in order to achieve a desired viscosity with minimum use of additive in lubricant oils over a wide temperature range without impairing this property through premature degradation of the polymers.

Furthermore, the polymers should be producible in a simple and inexpensive manner, and especially commercially available components should be used. In this context, they should be producible on the industrial scale without new plants or plants of complicated construction being required for this purpose.

These objects and also further objects which are not stated explicitly but are

immediately derivable or discernible from the connections discussed herein by way of introduction are achieved by a viscosity index improver having all features of claim 1. Appropriate modifications to the viscosity index improver are protected in the claims referring back to claim 1.

The present invention accordingly provides a viscosity index improver comprising a polyalkyl(meth)acrylate polymer characterized in that the polyalkyl(meth)acrylate polymer comprises a polydispersity Mw/Mn in the range of 1.05 to 2.0.

Preferably, the present polyalkyl(meth)acrylate polymer comprises at least 40 % by weight of repeating units being derived from alkyl (meth)acrylates having 10 to 15 carbon atoms in the alkyl residue.

The present polymers provide a high efficiency as viscosity index improvers while retaining high shear stability. At the same time, the inventive polymers allow a series of further advantages to be achieved. These include:

The inventive polymers have a particularly high viscosity index-improving effectiveness in lubricant oils. These properties are achieved by low treating rates and high shear stabilities. The polymers of the present invention can be prepared in a particularly easy and simple manner. It is possible to use customary industrial scale plants. Furthermore, the present polymers impart fuel efficiency to vehicles using the inventive lubricants. In addition, hydraulic fluids comprising the present polymers show very low fuel consumption and improved power output. Moreover, the present polymers have a high compatibility with very different base oils. This is especially true with regard to high performance base oils.

Moreover, the present polymers show an astonishing low temperature performance.

The adjusting of the molecular weight distribution of the viscosity modifier results in a greater lubrication benefit over a broader temperature range, without sacrificing shear stability or viscosity modifier solubility. This approach has enabled to expand the available techniques which improve the viscosity index which has been demonstrated for methacrylate polymers across a broad range of compositions, polarity, and molecular weight. The present invention describes polymers which preferably have a high oil solubility. The term "oil-soluble" means that a mixture of a base oil and a polyalkyl(meth)acrylate polymer is preparable without macroscopic phase formation, which has at least 0.1 % by weight, preferably at least 0.5% by weight, of the polymers. The polymer may be present in dispersed and/or dissolved form in this mixture. The oil solubility depends especially on the proportion of the lipophilic side chains and on the base oil. This property is known to those skilled in the art and can be adjusted readily for the particular base oil via the proportion of lipophilic monomers.

The alkyl(meth)acrylate polymers exhibit a polydispersity, given by the ratio of the weight average molecular weight to the number average molecular weight Mw/Mn, in the range of 1.05 to 2.0, preferably 1.10 to 1.65 more preferably 1.15 to 1.4.

The weight average molecular weight of the polyalkyl(meth)acrylate polymer is preferably in the range from 15,000 to 1 ,500,000, especially from 20,000 to 1 ,000,000, preferably 40,000 to 500,000, more preferably from 80,000 to 250,000 g/mol. The polydispersity and the weight average molecular weight may be determined by gel permeation chromatography (GPC) using a polymethyl methacrylate standard.

Preferably, the polyalkyl(meth)acrylate polymer may comprise a Chi parameter in the range from 0.2 to 0.60, more preferably in the range from 0.3 to 0.43 and most preferably in the range from 0.34 to 0.41. The Chi (χ) parameter is well known in the art and describes the solubility of the polymers. The calculation of the Chi parameter is based on the Hoy method. Useful information are provided in Polymer Handbook (4^th Edition, Editors. Bransdrup, Immergut, Gruike, 1999, VII/675). The values can easily be calculated based on the following formulae exemplifying a copolymer comprising two or three monomers:

Chi (A/B) = [wt. fraction A (delta A-delta solvent)² + wt. fraction B (delta B - delta solvent)² - wt. fraction A x wt. fraction B (delta A - delta B)² ]/6

Chi (A/B/C) = [wt. fraction A (delta A-delta solvent)² + wt. fraction B (delta B - delta solvent)² + wt. fraction C (delta C - delta solvent)² - wt. fraction A x wt. fraction B (delta A - delta B)² - wt. fraction A x wt. fraction C (delta A - delta C)² - wt. fraction B x wt. fraction C (delta B - delta C)² ]/6 The delta values for the monomers A, B and C, respectively are provided by the reference mentioned above or can easily be calculated using the group addition rules such as in the method of Hoy described in Krevelen D.W. Van, Properties of Polymers, published by Elsevier, 3^rd completely revised edition, 1990; K.L. Hoy, J. Paint Technol. 42, 76 (1970) and Polymer Handbook (4^th Edition, Editors, Bransdrup, Immergut, Gruike, 1999, VII/675), especially on Table 2, page 684 (Hoy).

The delta value for the solvent can preferably be assumed to be the delta value of isooctane and calculated to be 6.8 cal^{1 2}cm^{"3 2}. The previously mentioned interaction parameter Chi correlates to the Hildebrand solubility parameter through an extensive and detailed derivation of the following equation:

Chi = V(5_a - 5_S)²/RT

The Hildebrand solubility parameter can be used as a useful guide to determine the solubility of polymers in a specific medium. A detailed summary of this parameter is provided in the chapter entitled "Solubility Parameter Values", by E. A. Gruike in the Polymer Handbook, Fourth Edition, ed. J. Brandrup, E. J. Immergut, and E. A. Gruike, John Wiley & Sons, New York, 1999. The viscosity index improver of the present invention may comprise a

polyalkyl(meth)acrylate polymer preferably comprising at least 40 % by weight of repeating units being derived from alkyl (meth)acrylates having 10 to 15 carbon atoms in the alkyl residue.

The term "repeating unit" is widely known in the technical field. The present polyalkyl(meth)acrylate polymer can preferably be obtained by means of free-radical polymerization of monomers and the controlled radical process techniques of ATRP, RAFT and NMP, which will be explained later, being preferred, without any intention that this should impose a restriction. In these processes, double bonds are opened up to form covalent bonds. Accordingly, the repeat unit is obtained from the monomers used. The polyalkyl(meth)acrylate polymers may preferably contain at least 40 % by weight, especially at least 60 % by weight and more preferably at least 70 % by weight of repeating units derived from alkyl (meth)acrylate monomers having 10 to 15 carbon atoms, preferably 1 1 to 14 carbon atoms and more preferably 12 to 14 carbon atoms in the alcohol part.

The polyalkyl(meth)acrylate polymer may preferably contain at least 1 %, more preferably at least 5% by weight, especially at least 10 % by weight and most preferably at least 12% by weight of repeat units derived from alkyl (meth)acrylate monomers having 1 to 4 carbon atoms, more preferably 1 or 2 carbon atoms in the alcohol part. Furthermore, polyalkyl(meth)acrylate polymers are preferred having at most 40%, more preferably at most 30% by weight, especially at most 25 % by weight and most preferably at most 22% by weight of repeat units derived from alkyl

(meth)acrylate monomers having 1 to 4 carbon atoms, more preferably 1 or 2 carbon atoms in the alcohol part.

In addition, the polyalkyl(meth)acrylate polymer may contain 0 to 60% by weight, especially 1 to 40% by weight, preferably 5 to 30% by weight, more preferably 10 to 25% by weight and most preferably 12 to 22% by weight, of repeat units derived from alkyl (meth)acrylate monomers having 1 to 4 carbon atoms in the alcohol part. Preferably, the polyalkyl(meth)acrylate polymer may contain repeating units derived from alkyl (meth)acrylate monomers having 16 to 4000 carbon atoms, preferably 16 to 300 carbon atoms. The polyalkyl(meth)acrylate polymer may preferably contain at least 1 %, more preferably at least 5% by weight, especially at least 10 % by weight and most preferably at least 15% by weight of repeat units derived from alkyl (meth)acrylate monomers having 16 to 4000 carbon atoms in the alcohol part. Furthermore, polyalkyl(meth)acrylate polymers are preferred having at most 40%, more preferably at most 30% by weight, especially at most 25 % by weight and most preferably at most 20% by weight of repeat units derived from alkyl (meth)acrylate monomers having 16 to 4000 carbon atoms in the alcohol part.

According to a preferred embodiment the polymer may comprise repeating units derived from alkyl (meth)acrylate monomers having 16 to 4000 carbon atoms, preferably 16 to 300 carbon atoms and more preferably 16 to 30 carbon atoms in the alcohol part, and repeating units derived from alkyl (meth)acrylate monomers having 10 to 15 carbon atoms in the alcohol part. In a particular aspect, the polyalkyl(meth)acrylate polymer may contain 0 to 60% by weight, preferably 1 to 40% by weight and more preferably 5 to 20% by weight of repeat units derived from alkyl (meth)acrylate monomers having 16 to 4000, preferably 16 to 30 carbon atoms in the alcohol part. Preferably, the polymer may comprise repeating units derived from alkyl (meth)acrylate monomers having 23 to 4000 carbon atoms, preferably 23 to 400 carbon atoms and more preferably 23 to 300 carbon atoms in the alcohol part.

The polyalkyl(meth)acrylate polymer comprises preferably at least 40% by weight, more preferably at least 60% by weight, especially preferably at least 80% by weight and very particularly at least 95% by weight of repeat units derived from ester monomers.

Mixtures from which the inventive polyalkyl(meth)acrylate polymer are obtainable may contain 0 to 60% by weight, especially 1 to 40% by weight, preferably 5 to 30% by weight and more preferably 10 to 22% by weight of one or more alkyl(meth)acrylate monomers of the formula (I)

in which R is hydrogen or methyl, R¹ means a linear or branched alkyl residue with 1 to 4 carbon atoms, especially 1 to 3 and preferably 1 to 2 carbon atoms.

Examples of component (I) include

((meth)acrylates which derived from saturated alcohols such as methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, and tert-butyl (meth)acrylate. Preferably, the polymer comprises units being derived from methyl methacrylate..

The compositions to be polymerized preferably contain at least 40 % by weight, especially at least 60 % by weight and more preferably at least 70 % by weight of one or more alkyl(meth)acrylate monomers of the formula (II)

in which R is hydrogen or methyl, R² means a linear, branched or cyclic alkyl residue with 10 to 15, preferably 1 1 to 15 and more preferably 12 to 14 carbon atoms.

Examples of component (II) include:

(meth)acrylates, which derive from saturated alcohols, such as decyl (meth)acrylate, 2- propylheptyl (meth)acrylate, undecyl (meth)acrylate, 5-methylundecyl (meth)acrylate, dodecyl (meth)acrylate, 2-methyldodecyl (meth)acrylate, tridecyl (meth)acrylate, 5-methyltridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate; (meth)acrylates which derive from unsaturated alcohols, for example oleyl

(meth)acrylate;

cycloalkyl (meth)acrylates such as 3-butylcyclohexyl (meth)acrylate, trimethylbornyl (meth)acrylate. In addition, preferred monomer compositions comprise 0 to 60% by weight, preferably 1 to 40% by weight and more preferably 5 to 20% by weight of one or more

alkyl(meth)acrylate monomers of the formula (III)

in which R is hydrogen or methyl, R³ means a linear, branched or cyclic alkyl residue with 16-4000 carbon atoms, preferably 16 to 400 carbon atoms and more preferably 16 to 30 carbon atoms.

Examples of component (III) include (meth)acrylates which derive from saturated alcohols, such as hexadecyl (meth)acrylate, 2-methylhexadecyl (meth)acrylate, heptadecyl (meth)acrylate, 5-isopropylheptadecyl (meth)acrylate, 4-tert-butyloctadecyl (meth)acrylate, 5-ethyloctadecyl (meth)acrylate, 3-isopropyloctadecyl (meth)acrylate, octadecyl (meth)acrylate, nonadecyl (meth)acrylate, eicosyl (meth)acrylate, cetyleicosyl (meth)acrylate, stearyleicosyl (meth)acrylate, docosyl (meth)acrylate and/or

eicosyltetratriacontyl (meth)acrylate;

cycloalkyl (meth)acrylates such as 2,4,5-tri-t-butyl-3-vinylcyclohexyl (meth)acrylate, 2,3,4,5-tetra-t-butylcyclohexyl (meth)acrylate.

Furthermore, the monomers according formula (III) especially include long chain branched (meth)acrylates as disclosed inter alia in US 6,746,993, filed 07.08.2002 with the United States Patent Office (USPTO) having the application number 10/212,784; and US 2004/077509, filed 01.08.2003 with the United States Patent Office (USPTO) having the application number 10/632, 108. The disclosure of these documents, especially the (meth)acrylate monomers having at least 16, preferably at least 23 carbon atoms are enclosed herewith by reference.

In addition thereto, the Ci₆-C₄₀oo alkyl (meth)acrylate monomers, preferably the Ci₆-C₄₀o alkyl (meth)acrylate monomers include polyolefin-based macromonomers. The polyolefin-based macromonomers comprise at least one group which is derived from polyolefins. Polyolefins are known in the technical field, and can be obtained by polymerizing alkenes and/or alkadienes which consist of the elements carbon and hydrogen, for example C₂-Ci₀-alkenes such as ethylene, propylene, n-butene, isobutene, norbornene, and/or C₄-Ci₀-alkadienes such as butadiene, isoprene, norbornadiene. The polyolefin-based macromonomers comprise preferably at least 70% by weight and more preferably at least 80% by weight and most preferably at least 90% by weight of groups which are derived from alkenes and/or alkadienes, based on the weight of the polyolefin-based macromonomers. The polyolefinic groups may in particular also be present in hydrogenated form. In addition to the groups which are derived from alkenes and/or alkadienes, the alkyl (meth)acrylate monomers derived from polyolefin-based macromonomers may comprise further groups. These include small proportions of copolymerizable monomers. These monomers are known per se and include, among other monomers, alkyl (meth)acrylates, styrene monomers, fumarates, maleates, vinyl esters and/or vinyl ethers. The proportion of these groups based on copolymerizable monomers is preferably at most 30% by weight, more preferably at most 15% by weight, based on the weight of the polyolefin-based macromonomers. In addition, the polyolefin-based macromonomers may comprise start groups and/or end groups which serve for functionalization or are caused by the preparation of the polyolefin-based macromonomers. The proportion of these start groups and/or end groups is preferably at most 30% by weight, more preferably at most 15% by weight, based on the weight of the polyolefin-based macromonomers. The number-average molecular weight of the polyolefin-based macromonomers is preferably in the range from 500 to 50 000 g/mol, more preferably from 700 to 10 000 g/mol, in particular from 1500 to 8000 g/mol and most preferably from 2000 to 6000 g/mol. In the case of preparation of the comb polymers via the copolymerization of low molecular weight and macromolecular monomers, these values arise through the properties of the macromolecular monomers. In the case of polymer-analogous reactions, this property arises, for example, from the macroalcohols and/or

macroamines used taking account of the converted repeat units of the main chain. In the case of graft copolymerizations, the proportion of polyolefins formed which have not been incorporated into the main chain can be used to conclude the molecular weight distribution of the polyolefin.

The polyolefin-based macromonomers preferably have a low melting point, which is measured by means of DSC. The melting point of the polyolefin-based macromonomers is preferably less than or equal to -10°C, especially preferably less than or equal to 20°C, more preferably less than or equal to -40°C. Most preferably, no DSC melting point can be measured for the repeat units which are derived from the polyolefin-based macromonomers in the polyalkyl(meth)acrylate copolymer.

Polyolefin-based macromonomers are disclosed in the publications DE 10 2007 032 120 A1 , filed 09.07.2007 at the German Patent Office (Deutsches Patentamt) having the application number DE102007032120.3; and DE 10 2007 046 223 A1 , filed

26.09.2007 at the German Patent Office (Deutsches Patentamt) having the application number DE 102007046223.0; which documents are enclosed herein by reference.

The ester compounds with a long-chain alcohol part, especially components (II) and (III), can be obtained, for example, by reacting (meth)acrylates and/or the

corresponding acids with long-chain fatty alcohols, which generally gives rise to a mixture of esters, for example (meth)acrylates with different long-chain hydrocarbons in the alcohol parts. These fatty alcohols include Oxo Alcohol® 7911 , Oxo Alcohol® 7900, Oxo Alcohol® 1100; Alfol® 610, Alfol® 810, Lial® 125 and Nafol® types (Sasol);

Alphanol® 79 (ICI); Epal® 610 and Epal® 810 (Afton); Linevol® 79, Linevol® 911 and Neodol® 25E (Shell); Dehydad®, Hydrenol® and Lorol® types (Cognis); Acropol® 35 and Exxal® 10 (Exxon Chemicals); Kalcol® 2465 (Kao Chemicals).

The weight ratio of units derived from alkyl (meth)acrylate monomers having 10 to 15 carbon atoms, preferably of the formula (II), to the units derived from alkyl

(meth)acrylate monomers having 16 to 4000 carbon atoms, preferably of the formula (III), may be within a wide range. The weight ratio of repeat units derived from alkyl (meth)acrylate monomers having 10 to 15 carbon atoms in the alcohol part to repeat units derived from alkyl (meth)acrylate monomers having 16 to 4000 carbon atoms in the alcohol part is preferably in the range from 30: 1 to 1 : 1 , more preferably in the range from 10:1 to 1 ,5: 1 , especially preferably 5: 1 to 2: 1.

The polymer may contain units derived from comonomers as an optional component. These comonomers include alkyl(meth)acrylate monomers having 5 to 9 carbon atoms in the alkyl residue like pentyl (meth)acrylate, hexyl (meth)acrylate, cyclopentyl, (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, heptyl (meth)acrylate, 2-tert-butylheptyl (meth)acrylate, octyl (meth)acrylate, 3-isopropylheptyl (meth)acrylate, nonyl

(meth)acrylate; aryl (meth)acrylates like benzyl (meth)acrylate or phenyl (meth)acrylate, where the acryl residue in each case can be unsubstituted or substituted up to four times;

(meth)acrylates of halogenated alcohols like 2,3-dibromopropyl (meth)acrylate, 4- bromophenyl (meth)acrylate, 1 ,3-dichloro-2-propyl (meth)acrylate, 2-bromoethyl (meth)acrylate, 2-iodoethyl (meth)acrylate, chloromethyl (meth)acrylate; nitriles of (meth)acrylic acid and other nitrogen-containing (meth)acrylates like N- (methacryloyloxyethyl)diisobutylketimine, N-

(methacryloyloxyethyl)dihexadecylketimine, (meth)acryloylamidoacetonitrile, 2- methacryloyloxyethylmethylcyanamide, cyanomethyl (meth)acrylate; vinyl halides such as, for example, vinyl chloride, vinyl fluoride, vinylidene chloride and vinylidene fluoride; vinyl esters like vinyl acetate; vinyl monomers containing aromatic groups like styrene, substituted styrenes with an alkyl substituent in the side chain, such as a-methylstyrene and a-ethylstyrene, substituted styrenes with an alkyl substituent on the ring such as vinyltoluene and p- methylstyrene, halogenated styrenes such as monochlorostyrenes, dichlorostyrenes, tribromostyrenes and tetrabromostyrenes; vinyl and isoprenyl ethers; maleic acid and maleic acid derivatives such as mono- and diesters of maleic acid, maleic anhydride, methylmaleic anhydride, maleinimide, methylmaleinimide; fumaric acid and fumaric acid derivatives such as, for example, mono- and diesters of fumaric acid; methacrylic acid and acrylic acid.

According to a special aspect of the present invention, the polyalkyl(meth)acrylate polymer may comprise dispersing monomers.

Dispersing monomers are understood to mean especially monomers with functional groups, for which it can be assumed that polymers with these functional groups can keep particles, especially soot particles, in solution (cf. R.M. Mortier, S . Orszulik (eds.): "Chemistry and Technology of Lubricants", Blackie Academic & Professional, London, 2^nd ed. 1997). These include especially monomers which have boron-, phosphorus-, silicon-, sulfur-, oxygen- and nitrogen-containing groups, preference being given to oxygen- and nitrogen-functionalized monomers.

Appropriately, it is possible to use especially heterocyclic vinyl compounds

ethylenically unsaturated, polar ester compounds of the formula (IV)

in which R is hydrogen or methyl, X is oxygen, sulfur or an amino group of the formula - NH- or -NR^a- in which R^a is an alkyl radical having 1 to 40 and preferably 1 to 4 carbon atoms, R⁴ is a radical which comprises 2 to 1000, especially 2 to 100 and preferably 2 to 20 carbon atoms and has at least one heteroatom, preferably at least two

heteroatoms, R⁵ and R⁶ are each independently hydrogen or a group of the formula - COX'R⁴ in which X' is oxygen or an amino group of the formula -NH- or -NR^a- in which R^a is an alkyl radical having 1 to 40 and preferably 1 to 4 carbon atoms, and R⁴ is a radical comprising 1 to 100, preferably 1 to 30 and more preferably 1 to 15 carbon atoms, as dispersing monomers.

The expression "radical comprising 2 to 1000 carbon" denotes radicals of organic compounds having 2 to 1000 carbon atoms. Similar definitions apply for corresponding terms. It encompasses aromatic and heteroaromatic groups, and alkyl, cycloalkyl, alkoxy, cycloalkoxy, alkenyl, alkanoyi, alkoxycarbonyl groups, and also heteroaliphatic groups. The groups mentioned may be branched or unbranched. In addition, these groups may have customary substituents. Substituents are, for example, linear and branched alkyl groups having 1 to 6 carbon atoms, for example methyl, ethyl, propyl, butyl, pentyl, 2-methylbutyl or hexyl; cycloalkyl groups, for example cyclopentyl and cyclohexyl; aromatic groups such as phenyl or naphthyl; amino groups, hydroxyl groups, ether groups, ester groups and halides.

According to the invention, aromatic groups denote radicals of mono- or polycyclic aromatic compounds having preferably 6 to 20 and especially 6 to 12 carbon atoms. Heteroaromatic groups denote aryl radicals in which at least one CH group has been replaced by N and/or at least two adjacent CH groups have been replaced by S, NH or O, heteroaromatic groups having 3 to 19 carbon atoms.

Aromatic or heteroaromatic groups preferred in accordance with the invention derive from benzene, naphthalene, biphenyl, diphenyl ether, diphenylmethane,

diphenyldimethylmethane, bisphenone, diphenyl sulfone, thiophene, furan, pyrrole, thiazole, oxazole, imidazole, isothiazole, isoxazole, pyrazole, 1 ,3,4-oxadiazole, 2,5-diphenyl-1 ,3,4-oxadiazole, 1 ,3,4-thiadiazole, 1 ,3,4-triazole, 2,5-diphenyl- 1 ,3,4-triazole, 1 ,2,5-triphenyl-1 ,3,4-triazole, 1 ,2,4-oxadiazole, 1 ,2,4-thiadiazole, 1 ,2,4-triazole, 1 ,2,3-triazole, 1 ,2,3,4-tetrazole, benzo[b]thiophene, benzo[b]furan, indole, benzo[c]thiophene, benzo[c]furan, isoindole, benzoxazole, benzothiazole, benzimidazole, benzisoxazole, benzisothiazole, benzopyrazole, benzothiadiazole, benzotriazole, dibenzofuran, dibenzothiophene, carbazole, pyridine, bipyridine, pyrazine, pyrazole, pyrimidine, pyridazine, 1 ,3,5-triazine, 1 ,2,4-triazine, 1 ,2,4,5-triazine, tetrazine, quinoline, isoquinoline, quinoxaline, quinazoline, cinnoline, 1 ,8-naphthyridine, 1 ,5-naphthyridine, 1 ,6-naphthyridine, 1 ,7-naphthyridine, phthalazine, pyridopyrimidine, purine, pteridine or quinolizine, 4H-quinolizine, diphenyl ether, anthracene, benzo- pyrrole, benzoxathiadiazole, benzoxadiazole, benzopyridine, benzopyrazine, benzopyrazidine, benzopyrimidine, benzotriazine, indolizine, pyridopyridine, imidazopyrimidine, pyrazinopyrimidine, carbazole, aciridine, phenazine,

benzoquinoline, phenoxazine, phenothiazine, acridizine, benzopteridine,

phenanthroline and phenanthrene, each of which may also optionally be substituted.

The preferred alkyl groups include the methyl, ethyl, propyl, isopropyl, 1-butyl, 2-butyl, 2-methylpropyl, tert-butyl radical, pentyl, 2-methylbutyl, 1 , 1-dimethylpropyl, hexyl, heptyl, octyl, 1 , 1 ,3,3-tetramethylbutyl, nonyl, 1-decyl, 2-decyl, undecyl, dodecyl, pentadecyl and the eicosyl group. The preferred cycloalkyl groups include the cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl and the cyclooctyl group, each of which is optionally substituted with branched or unbranched alkyl groups.

The preferred alkanoyl groups include the formyl, acetyl, propionyl, 2-methylpropionyl, butyryl, valeroyl, pivaloyl, hexanoyl, decanoyl and the dodecanoyl group.

The preferred alkoxycarbonyl groups include the methoxycarbonyl, ethoxycarbonyl, propoxycarbonyl, butoxycarbonyl, tert-butoxycarbonyl, hexyloxycarbonyl,

2-methylhexyloxycarbonyl, decyloxycarbonyl or dodecyloxycarbonyl group.

The preferred alkoxy groups include alkoxy groups whose hydrocarbon radical is one of the aforementioned preferred alkyl groups.

The preferred cycloalkoxy groups include cycloalkoxy groups whose hydrocarbon radical is one of the aforementioned preferred cycloalkyl groups.

The preferred heteroatoms which are present in the R⁴ radical include oxygen, nitrogen, sulfur, boron, silicon and phosphorus, preference being given to oxygen and nitrogen.

The R⁴ radical comprises at least one, preferably at least two, preferentially at least three, heteroatoms. The R⁴ radical in ester compounds of the formula (IV) preferably has at least 2 different heteroatoms. In this case, the R⁴ radical in at least one of the ester compounds of the formula (IV) may comprise at least one nitrogen atom and at least one oxygen atom.

Examples of ethylenically unsaturated, polar ester compounds of the formula (IV) include aminoalkyl (meth)acrylates, aminoalkyl (meth)acrylamides, hydroxyalkyl

(meth)acrylates, (meth)acrylates of ether alcohols, heterocyclic (meth)acrylates and/or carbonyl-containing (meth)acrylates. The hydroxyalkyl (meth)acrylates include

2- hydroxypropyl (meth)acrylate,

3.4- dihydroxybutyl (meth)acrylate,

2-hydroxyethyl (meth)acrylate,

3- hydroxypropyl (meth)acrylate,

2.5- dimethyl-1 ,6-hexanediol (meth)acrylate and

1 ,10-decanediol (meth)acrylate. (Meth)acrylates of ether alcohols include tetrahydrofurfuryl (meth)acrylate,

methoxyethoxyethyl (meth)acrylate, 1-butoxypropyl (meth)acrylate, cyclohexyloxyethyl (meth)acrylate, propoxyethoxyethyl (meth)acrylate, benzyloxyethyl (meth)acrylate, furfuryl (meth)acrylate, 2-butoxyethyl (meth)acrylate, 2-ethoxy-2-ethoxyethyl

(meth)acrylate, 2-methoxy-2-ethoxypropyl (meth)acrylate, ethoxylated (meth)acrylates, 1-ethoxybutyl (meth)acrylate, methoxyethyl (meth)acrylate, 2-ethoxy-2-ethoxy-2- ethoxyethyl (meth)acrylate, esters of (meth)acrylic acid and methoxy polyethylene glycols.

Appropriate carbonyl-containing (meth)acrylates include, for example,

2-carboxyethyl (meth)acrylate,

carboxymethyl (meth)acrylate,

oxazolidinylethyl (meth)acrylate,

N-(methacryloyloxy)formamide,

acetonyl (meth)acrylate,

mono-2-(meth)acryloyloxyethyl succinate,

N-(meth)acryloylmorpholine,

N-(meth)acryloyl-2-pyrrolidinone,

N-(2-(meth)acryloyloxyethyl)-2-pyrrolidinone,

N-(3-(meth)acryloyloxypropyl)-2-pyrrolidinone,

N-(2-(meth)acryloyloxypentadecyl)-2-pyrrolidinone,

N-(3-(meth)acryloyloxyheptadecyl)-2-pyrrolidinone and

N-(2-(meth)acryloyloxyethyl)ethyleneurea.

2-Acetoacetoxyethyl (meth)acrylate The heterocyclic (meth)acrylates include

2- (1-imidazolyl)ethyl (meth)acrylate, 2-(4-morpholinyl)ethyl (meth)acrylate and

1- (2-(meth)acryloyloxyethyl)-2-pyrrolidone. Of particular interest are additionally aminoalkyl (meth)acrylates and aminoalkyl (meth)acrylatamides, for example

dimethylaminopropyl (meth)acrylate,

dimethylaminodiglykol (meth)acrylate,

dimethylaminoethyl (meth)acrylate,

dimethylaminopropyl(meth)acrylamide,

3- diethylaminopentyl (meth)acrylate and

3-dibutylaminohexadecyl (meth)acrylate.

In addition, it is possible to use phosphorus-, boron- and/or silicon-containing

(meth)acrylates as dispersing units, such as

2- (dimethylphosphato)propyl (meth)acrylate,

2-(ethylenephosphito)propyl (meth)acrylate,

dimethylphosphinomethyl (meth)acrylate,

dimethylphosphonoethyl (meth)acrylate,

diethyl(meth)acryloyl phosphonate,

dipropyl(meth)acryloyl phosphate, 2-(dibutylphosphono)ethyl (meth)acrylate,

2,3-butylene(meth)acryloylethyl borate,

methyldiethoxy(meth)acryloylethoxysilane,

diethylphosphatoethyl (meth)acrylate.

The (meth)acrylate monomers may be branched or linear.

The preferred heterocyclic vinyl compounds include 2-vinylpyridine, 3-vinylpyridine, 2- methyl-5-vinylpyridine, 3-ethyl-4-vinylpyridine, 2,3 dimethyl-5-vinylpyridine, vinylpyrimidine, vinylpiperidine, 9-vinylcarbazole, 3-vinylcarbazole, 4-vinylcarbazole,

1- vinylimidazole, N-vinylimidazole, 2-methyl-1-vinylimidazole, N-vinylpyrrolidone,

2- vinylpyrrolidone, N-vinylpyrrolidine, 3-vinylpyrrolidine, N-vinylcaprolactam,

N-vinylbutyrolactam, vinyloxolane, vinylfuran, vinylthiophene, vinylthiolane, vinylthiazoles and hydrogenated vinylthiazoles, vinyloxazoles and hydrogenated vinyloxazoles, particular preference being given to using N-vinylimidazole and

N-vinylpyrrolidone for functionalization.

The monomers detailed above can be used individually or as a mixture.

Of particular interest are especially polyalkyl(meth)acrylate polymers being obtained using 2-hydroxypropyl methacrylate, 2-hydroxyethyl methacrylate, mono-2- methacryloyloxyethyl succinate, N-(2-methacryloyloxyethyl) ethyleneurea,

2-acetoacetoxyethyl methacrylate, 2-(4-morpholinyl)ethyl methacrylate,

dimethylaminodiglycol methacrylate, dimethylaminoethyl methacrylate and/or dimethylaminopropylmethacrylamide.

Special improvements can be achieved with polyalkyl(meth)acrylate polymers being obtained using N-vinyl-2-pyrrolidine and/or N-vinyl-2-pyrrolidone.

The dispersing and non-dispersing monomers can be statistically distributed within the polyalkyl(meth)acrylate polymer. The proportion of dispersing repeat units in a statistical polymer, based on the weight of the polyalkyl(meth)acrylate polymers, is preferably in the range from 0 % by weight to 20% by weight, more preferably in the range from 1 % by weight to 15% by weight and most preferably in the range from 2.5% by weight to 10% by weight.

More preferably, the dispersing repeating unit can be selected from

dimethylaminopropylmethacrylamide (DMAPMA) and/or

dimethylaminoethylmethacrylate (DMAPMA) and the amount of dispersing repeating based on the weight of the polyalkyl(meth)acrylate polymers, is preferably in the range from 0.5 % by weight to 10% by weight, more preferably in the range from 1.2 % by weight to 5% by weight. More preferably, the dispersing repeating unit can be selected from

2-(4-morpholinyl)ethylmethacrylate (MOEMA), 2-hydroxyethyl (meth)acrylate (HEMA) and/or hydroxypropylmethacrylate (HPMA) and the amount of dispersing repeating based on the weight of the polyalkyl(meth)acrylate polymers, is preferably in the range from 2 % by weight to 20% by weight, more preferably in the range from 5 % by weight to 10% by weight. According to another aspect of the present invention, the polyalkyl(meth)acrylate polymer may comprise only a low amount of dispersing repeating units. According such aspect, the proportion of the dispersing repeat units is preferably at most 5 %, more preferably at most 2 % and most preferably at most 0.5 %, based on the weight of the polyalkyl(meth)acrylate polymers.

According to a special aspect of the present invention, the lubricant may preferably comprise a mixture of polymers and at least one of the polymers comprises a considerable amount of dispersing repeating units and at least one of the polymers comprises a low amount of dispersing repeating units as mentioned above.

According to a preferred embodiment of the present invention, the

polyalkyl(meth)acrylate polymer is a graft copolymer having an non-dispersing alkyl (meth)acrylate polymer as graft base and an dispersing monomer as graft layer.

Preferably non-dispersing alkyl (meth)acrylate polymer essentially comprises

(meth)acrylate monomer units according formulae (I), (II) and (III) as defined above and below. The proportion of dispersing repeat units in a graft or block copolymer, based on the weight of the polyalkyl(meth)acrylate polymers, is preferably in the range from 0 % by weight to 20% by weight, more preferably in the range from 1 % by weight to 15% by weight and most preferably in the range from 2.5% by weight to 10% by weight.

The dispersing monomer preferably is a heterocyclic vinyl compound as mentioned above and below.

According to a further aspect of the present invention the polyalkyl(meth)acrylate polymer is an alkyl (meth)acrylate polymer having at least one polar block and at least one hydrophobic block. Preferably, the polar block comprises at least three units derived from monomers of the formula (IV) and/or from heterocyclic vinyl compounds, which are bonded directly to one another.

Preferred polymers comprise at least one hydrophobic block and at least one polar block, said polar block having at least eight repeat units and the proportion by weight of dispersing repeat units in the polar block being at least 30%, based on the weight of the polar block.

The term "block" in this context denotes a section of the polymer. The blocks may have an essentially constant composition composed of one or more monomer units. In addition, the blocks may have a gradient, in which case the concentration of different monomer units (repeat units) varies over the segment length. The polar blocks differ from the hydrophobic block via the proportion of dispersing monomers. The

hydrophobic blocks may have at most a small proportion of dispersing repeat units (monomer units), whereas the polar block comprise a high proportion of dispersing repeat units (monomer units).

The polar block may preferably comprise at least 8, especially preferably at least 12 and most preferably at least 15 repeat units. At the same time, the polar block comprise at least 30% by weight, preferably at least 40% by weight, of dispersing repeat units, based on the weight of the polar block. In addition to the dispersing repeat units, the polar block may also have repeat units which do not have any dispersing effect. The polar block may have a random structure, such that the different repeat units have a random distribution over the segment length. In addition, the polar block may have a block structure or a structure in the form of a gradient, such that the non- dispersing repeat units and the dispersing repeat units within the polar block have an inhomogeneous distribution.

The hydrophobic block may comprise a small proportion of dispersing repeat units, which is preferably less than 20% by weight, more preferably less than 10% by weight and most preferably less than 5% by weight, based on the weight of the hydrophobic block. In a particularly appropriate configuration, the hydrophobic block comprises essentially no dispersing repeat units. The hydrophobic block of the polyalkyl(meth)acrylate polymers may have 40 to 100% by weight, especially 50 to 98% by weight, preferably 60 to 95 and most preferably 70 to 92% by weight of repeat units derived from alkyl(meth)acrylate monomers having 10 to 15 carbon atoms in the alcohol radical. In a particular aspect, the hydrophobic block of the polyalkyl(meth)acrylate polymers may have 0 to 60% by weight, preferably 0.5 to 40% by weight, more preferably 2 to 30% by weight and most preferably 5 to 20% by weight of repeat units derived from alkyl(meth)acrylate monomers having 16 to 4000 carbon atoms in the alcohol radical.

In addition, the hydrophobic block of the polyalkyl(meth)acrylate polymers may have 0 to 40% by weight, preferably 1 to 30% by weight and more preferably 2 to 22% by weight of repeat units derived from alkyl(meth)acrylate monomers having 1 to 4 carbon atoms in the alcohol radical.

The hydrophobic block of the polyalkyl(meth)acrylate polymer comprises preferably at least 40% by weight, more preferably at least 60% by weight, especially preferably at least 80% by weight and most preferably at least 90% by weight of repeat units derived from alkyl(meth)acrylate monomers.

The length of the hydrophobic and hydrophobic blocks may vary within wide ranges. The hydrophobic block preferably possess a weight-average degree of polymerization of at least 10, especially at least 40. The weight-average degree of polymerization of the hydrophobic block is preferably in the range from 20 to 5000, especially from 50 to 2000.

The proportion of dispersing repeat units, based on the weight of the

polyalkyl(meth)acrylate polymers, is preferably in the range from 0.5% by weight to 20% by weight, more preferably in the range from 1.5% by weight to 15% by weight and most preferably in the range from 2.5% by weight to 10% by weight. At the same time, these repeat units preferably form a segment-like structure within the

polyalkyl(meth)acrylate polymer, such that preferably at least 70% by weight, more preferably at least 80% by weight, based on the total weight of the dispersing repeat units, are part of a polar block.

Preferably, the weight ratio of said hydrophobic block and said polar block is in the range from 100: 1 to 1 : 1 , more preferably in the range from 30: 1 to 2:1 and most preferably in the range from 10: 1 to 4: 1. The preparation of the polyalkyl(meth)acrylate polymers from the above-described compositions is known per se. Thus, these polymers can be obtained in particular by free-radical polymerization and related processes, for example ATRP (= Atom Transfer Radical Polymerization) or RAFT (= Reversible Addition Fragmentation Chain

Transfer).

Customary free-radical polymerization is described, inter alia, in Ullmann's

Encyclopedia of Industrial Chemistry, Sixth Edition. In general, a polymerization initiator and a chain transfer agent are used for this purpose. The usable initiators include the azo initiators widely known in the technical field, such as AIBN and 1 , 1- azobiscyclohexanecarbonitrile, and also peroxy compounds such as methyl ethyl ketone peroxide, acetylacetone peroxide, dilauryl peroxide, tert-butyl per-2- ethylhexanoate, ketone peroxide, tert-butyl peroctoate, methyl isobutyl ketone peroxide, cyclohexanone peroxide, dibenzoyl peroxide, tert-butyl peroxybenzoate, tert- butyl peroxyisopropylcarbonate, 2,5-bis(2-ethylhexanoylperoxy)-2,5-dimethylhexane, tert-butyl peroxy-2-ethylhexanoate, tert-butyl peroxy-3,5,5-trimethylhexanoate, dicumyl peroxide, 1 , 1 -bis(tert-butylperoxy)cyclohexane, 1 , 1 -bis(tert-butylperoxy)-3,3,5- trimethylcyclohexane, cumyl hydroperoxide, tert-butyl hydroperoxide, bis(4-tert- butylcyclohexyl) peroxydicarbonate, mixtures of two or more of the aforementioned compounds with one another, and mixtures of the aforementioned compounds with compounds which have not been mentioned but can likewise form free radicals.

Suitable chain transfer agents are in particular oil-soluble mercaptans, for example n- dodecyl mercaptan or 2-mercaptoethanol, or else chain transfer agents from the class of the terpenes, for example terpinolene.

The ATRP process is known per se. It is assumed that it is a "living" free-radical polymerization, without any intention that the description of the mechanism should impose a restriction. In these processes, a transition metal compound is reacted with a compound which has a transferable atom group. This transfers the transferable atom group to the transition metal compound, which oxidizes the metal. This reaction forms a radical which adds onto ethylenic groups. However, the transfer of the atom group to the transition metal compound is reversible, so that the atom group is transferred back to the growing polymer chain, which forms a controlled polymerization system. The structure of the polymer, the molecular weight and the molecular weight distribution can be controlled correspondingly. This reaction is described, for example, by J-S. Wang, et al., J. Am. Chem. Soc, vol. 1 17, p. 5614-5615 (1995), by Matyjaszewski, Macromolecules, vol. 28, p. 7901-7910 (1995). In addition, the patent applications WO 96/30421 , WO 97/47661 , WO

97/18247, WO 98/40415 and WO 99/10387 disclose variants of the ATRP explained above.

In addition, the inventive polymers may be obtained, for example, also via RAFT methods. This process is presented in detail, for example, in WO 98/01478 and WO 2004/083169, to which reference is made explicitly for the purposes of disclosure.

In addition, the inventive polymers are obtainable by NMP processes (nitroxide- mediated polymerization), which are described, inter alia, in US 4581429. These methods are described comprehensively, in particular with further references, inter alia, in K. Matyjaszewski, T.P. Davis, Handbook of Radical Polymerization, Wley Interscience, Hoboken 2002, to which reference is made explicitly for the purposes of disclosure. In order to achieve polymers having low polydispersity, methods of Controlled Free Radical Polymerization (CFRP) or Living Free Radical Polymerization (LFRP) such as ATRP (= Atom Transfer Radical Polymerization) RAFT (= Reversible Addition

Fragmentation Chain Transfer) or NMP processes are preferred. The polymerization may be carried out at standard pressure, reduced pressure or elevated pressure. The polymerization temperature is generally in the range of -20° - 200°C, preferably 0° - 160°C and more preferably 60° - 140°C.

The polymerization can be carried out with or without solvents. The term solvent is to be broadly understood here. Illustrative of suitable solvents are hydrocarbon solvents, for example, aromatic solvents (aromatic C₆-is hydrocarbons, such as benzene, toluene, xylene, ethylbenzene, C₉.i₅ alkyl benzenes, trimethyl benzene, ethyl toluene and mixtures of them), mineral oils (such as paraffinic oils, naphthenic oils, solvent- refined oils, isoparaffin-containing high VI oils and hydrocracked high VI oils), and synthetic hydrocarbon lubricants (such as poly-a-olefin synthetic lubricant); ketone solvents, such as butanone and methyl ethyl ketone; and ester solvents, including, fatty oils, and synthetic ester lubricants (for example, di-C₄.i₂ alkyl C₄_i₂ dicarboxylates, such as dioctyl sebacate and dioctyl adipate, polyol poly-C₄_i₂ alkanoates, such as pentaerythritol tetra-caproate; and tri-C₄.i₂ hydrocarbyl phosphates, such as tri-2- ethylhexyl phosphate, dibutyl phenyl phosphate, di-2-ethylhexyl phenyl phosphate, 2- ethylhexyl diphenyl phosphate and tricresyl phosphate).

According to a preferred embodiment, the polymer is obtainable by a polymerization in API Group I, Group II, Group III, Group IV or Group V oils.

According to a special aspect of the present invention, the polyalkyl(meth)acrylate polymer is not a polymer comprising about 25 % by weight methyl methacrylate and about 73 % by weight alkyl methacrylates having 12 to 15 carbon atoms in the alkyl residue and having a weight average molecular weight of about 37900 g/mol. In addition thereto, a polymer may be excluded from the present invention comprising about 13.2 % by weight methyl methacrylate and about 84.6 % by weight alkyl methacrylates having 12 to 15 carbon atoms in the alkyl residue and having a weight average molecular weight of about 36900 g/mol. The lubricant may preferably comprise a polyalkyl(meth)acrylate polymer and a olefinic polymer which preferably have a viscosity index-improving or thickening effect.

These polyolefins include in particular polyolefin copolymers (OCP) and hydrogenated styrene/diene copolymers (HSD).

The polyolefin copolymers (OCP) to be used according to the invention are known per se. They are primarily polymers synthesized from ethylene, propylene, isoprene, butylene and/or further olefins having 5 to 20 C atoms, as are already recommended as VI improvers. Systems which have been grafted with small amounts of oxygen- or nitrogen-containing monomers (e.g. from 0.05 to 5% by weight of maleic anhydride) may also be used. The copolymers which contain diene components are generally hydrogenated in order to reduce the oxidation sensitivity and the crosslinking tendency of the viscosity index improvers. The molecular weight Mw is in general from 10 000 to 300 000, preferably between 50 000 and 150 000. Such olefin copolymers are described, for example, in the German Laid-Open Applications DE-A 16 44 941 , DE-A 17 69 834, DE-A 19 39 037, DE-A 19 63 039 and DE-A 20 59 981.

Ethylene/propylene copolymers are particularly useful and terpolymers having the known ternary components, such as ethylidene-norbornene (cf. Macromolecular Reviews, Vol. 10 (1975)) are also possible, but their tendency to crosslink must also be taken into account in the aging process. The distribution may be substantially random, but sequential polymers comprising ethylene blocks can also advantageously be used. The ratio of the monomers ethylene/propylene is variable within certain limits, which can be set to about 75% for ethylene and about 80% for propylene as an upper limit. Owing to its reduced tendency to dissolve in oil, polypropylene is less suitable than ethylene/propylene copolymers. In addition to polymers having a predominantly atactic propylene incorporation, those having a more pronounced isotactic or syndiotactic propylene incorporation may also be used.

Such products are commercially available, for example under the trade names Dutral^® CO 034, Dutral^® CO 038, Dutral^® CO 043, Dutral^® CO 058, Buna^® EPG 2050 or Buna^® EPG 5050.

The hydrogenated styrene/diene copolymers (HSD) are likewise known, these polymers being described, for example, in DE 21 56 122. They are in general hydrogenated isoprene/styrene or butadiene/styrene copolymers. The ratio of diene to styrene is preferably in the range from 2: 1 to 1 :2, particularly preferably about 55:45. The molecular weight Mw is in general from 10 000 to 300 000, preferably between 50 00 and 150 000. According to a particular aspect of the present invention, the proportion of double bonds after the hydrogenation is not more than 15%, particularly preferably not more than 5%, based on the number of double bonds before the hydrogenation.

Hydrogenated styrene/diene copolymers can be commercially obtained under the trade name ^®SHELLVIS 50, 150, 200, 250 or 260. Within the context of the present invention, all ranges above and below include explicitly all subvalues between the upper and lower limits.

The inventive polymer can preferably be used in a lubricant oil composition. A lubricant oil composition comprises at least one type of lubricant oil. The lubricant oils include especially mineral oils, synthetic oils and natural oils. Especially preferred hydrocarbon oils are mineral oil of Group I, II or III or a poly-alpha-olefin of Group IV.

Preferably, the lubricant oil is based on mineral oil from API Group I, II, or III. According to a preferred embodiment of the present invention, a mineral oil containing at least 90 % by weight saturates and at most about 0.03 % sulfur measured by elemental analysis is used. Especially, API Group II or Group III oils are preferred.

Mineral oils are known per se and commercially available. They are generally obtained from mineral oil or crude oil by distillation and/or refining and optionally further purification and finishing processes, the term mineral oil including in particular the higher-boiling fractions of crude or mineral oil. In general, the boiling point of mineral oil is higher than 200° C, preferably higher than 300° C, at 5000 Pa. The production by low-temperature carbonization of shale oil, coking of bituminous coal, distillation of brown coal with exclusion of air and also hydrogenation of bituminous or brown coal is likewise possible. Accordingly, mineral oils have, depending on their origin, different proportions of aromatic, cyclic, branched and linear hydrocarbons. In general, a distinction is drawn between paraffin-base, naphthenic and aromatic fractions in crude oils or mineral oils, in which the term paraffin-base fraction represents longer-chain or highly branched isoalkanes, and naphthenic fraction represents cyclo-alkanes.

Valuable information with regard to the analysis of mineral oils and a list of mineral oils which have a different composition can be found, for example, in Ullmann's Encyclopedia of Industrial Chemistry, 5th Edition on CD-ROM, 1997, under "lubricants and related products".

Synthetic oils are, among other substances, organic esters, for example diesters and polyesters, like carboxylic esters and phosphate esters; organic ethers like silicone oils, perfluoro-alkyl ethers and polyalkylene glycol; and synthetic hydrocarbons, especially polyolefins and Gas to liquids oils (GTL), among which preference is given to polyalphaolefins (PAO) and GTL oils. They are for the most part somewhat more expensive than the mineral oils, but they have advantages with regard to performance.

Especially polyalphaolefins (PAO) are preferred. These compounds are obtainable by polymerization of alkenes, especially alkenes having 3 to 12 carbon atoms, like propene, hexene-1 , octene-1 , and dodecene-1. Preferred PAOs have a number average molecular weight in the range of 200 to 10000 g/mol, more preferably 500 to 5000 g/mol. Furthermore, GTL oils are useful as base fluid. These synthetic oils are obtained by a special refinery process converting natural gas or other gaseous hydrocarbons into longer-chain hydrocarbons such as gasoline or diesel fuel.

Natural oils are animal or vegetable oils, for example neatsfoot oils or jojoba oils.

For an explanation reference is made to the 5 API classes of base oil types (API: American Petroleum Institute).

American Petroleum Institute (API) Base Oil Classifications

Base oils preferably have a kinematic viscosity (hereinafter referred to as KV) of 1-15 mm²/s, particularly 2-5 mm²/s, at 100° C.

Base oils preferably have a VI of at least 80, particularly at least 100 and preferably at least 120. Especially, the VI of the base oil may be 180 or less, particularly 150 or less and more preferably 140 or less. Base oils preferably have a cloud point (defined in J IS K2269) of -5° C. or less, particularly -10° C. or less, more particularly -15° C. or less, in view of low-temperature viscosity behavior, with little wax deposition at low

temperature.

These lubricant oils may also be used as mixtures and are in many cases commercially available. The concentration of the polyalkyl(meth)acrylate polymer in the lubricant oil composition is preferably in the range from 0.5 to 40% by weight, especially in the range from 1 to 25% by weight, more preferably in the range from 2 to 13% by weight, based on the total weight of the composition. The amount of base oil in the lubricant is usually at least 60 % by weight, more preferably at least 75 % by weight.

Surprisingly, the inventive effect can be improved by adjusting the polarity of the polyalkyl(meth)acrylate polymer and the amount of the polymer used within the lubricant. Preferably the lubricant may comprise a polyalkyl(meth)acrylate polymer having repeating units being derived from alkyl (meth)acrylates having 1 to 4 carbon atoms in the alkyl residue and the amount of polyalkyl(meth)acrylate polymer in the lubricant and the amount of repeating units being derived from alkyl (meth)acrylates having 1 to 4 carbon atoms in the alkyl residue in the polymer is selected such that the lubricant preferably comprises 0.1 to 5 %, especially 0.3 to 3.2, more preferably 0.5 to 3 % and most preferably 0.8 to 2.5 % by weight of repeating units being derived from alkyl (meth)acrylates having 1 to 4 carbon atoms in the alkyl residue based on the total weight of said lubricant.

In addition to the aforementioned components, a lubricant oil composition may comprise further additives.

These additives include antioxidants, corrosion inhibitors, antifoams, antiwear components, dyes, dye stabilizers, detergents, pour point depressants and/or Dl additives.

In addition, these additives encompass further viscosity index improvers, dispersing assistants and/or friction modifiers, which are more preferably based on a

polyalkyl(meth) acrylate. These polyalkyl(meth)acrylates are different to the present polymers and are described especially in the prior art discussed by way of introduction, and these polymers may have dispersing monomers. Preferred polymers useful as viscosity improvers and methods for their preparation are disclosed in US

2003/0104955 filed August 3, 2002 with the USPTO having the application number US 10/212784 and JP 2008-031459 A filed June 29, 2007 with the Japanese Patent Office having the application number JP 2007-172420, both of which are incorporated herein by reference.

According to a special aspect of the present invention, the lubricant of the present invention may comprise only a low amount of ester oils. Preferably, the amount of ester oil is limited to about 10 % by weight of the lubricant composition, more preferably to about 5 % by weight. According to a preferred embodiment, the amount of ester oil is limited to about 2 % by weight of the lubricant composition, more preferably to about 1 % by weight. Very preferred, the lubricant comprises no essential amounts of ester oils. The ester oil include in particular phosphoric esters, esters of dicarboxylic acids, esters of monocarboxylic acids with diols or polyalkylene glycols, esters of neopentylpolyols with monocarboxylic acids (cf. Ullmanns Encyclopadie der Technischen Chemie

[Ullmann's Encyclopaedia of Industrial Chemistry], 3rd edition, Vol. 15, pages 287-292, Urban & Schwarzenberg (1964)).

Preferred lubricant oil compositions have a viscosity, measured at 40°C to ASTM D 445, in the range of 10 to 120 mm²/s, more preferably in the range of 20 to

100 mm²/s. The kinematic viscosity KV₁₀o measured at 100°C is preferably at least 3.5 mm²/s, especially at least 4.0 mm²/s, more preferably at least 5.0 mm²/s and most preferably at least 5.4 mm²/s.

In a particular aspect of the present invention, preferred lubricant oil compositions have a viscosity index, determined to ASTM D 2270, in the range from 100 to 400, more preferably in the range from 150 to 350 and most preferably in the range from 200 to 300.

Furthermore, lubricant compositions of the present invention may preferably comprise a High Temperature High Shear (HTHS) viscosity of at least 2.4 mPas, more preferably at least 2.6 mPas as measured at 150°C according to ASTM D4683. According to a further aspect of the present invention the lubricant may preferably comprise a high temperature high shear of at most 10 mPas, especially at most 7 mPas more preferably at most 5 mPas as measured at 100°C according to ASTM D4683. The difference between the High Temperature High Shear (HTHS) viscosities as measure at 100°C and 150°C HTHS100 - HTHS150 preferably comprises at most 4 mPas, especially at most 3.3 mPas and more preferably at most 2.5 mPas. The ratio of the High Temperature High Shear (HTHS) viscosity measured at 100°C (HTHS1₀₀) to the High Temperature High Shear (HTHS) viscosity measured at 150°C (HTHSi₅₀) HTHS1₀₀/HTHS15₀ preferably comprises at most at most 2.0 mPas, especially at most 1.9 mPas. High Temperature High Shear (HTHS) viscosity can be determined according to D4683.

In addition thereto, the lubricant may comprises a high shear stability index (SSI). According to a useful embodiment of the present invention, the shear stability index (SSI) as measured according to ASTM D5621 (40 minutes sonic treatment) could preferably amount to 35 or less, especially to 20 or less more preferably to 15 or less. Preferably, lubricants comprising a shear stability index (SSI) as measured according to DIN 51381 (30 cycles Bosch-pump) of at most 5, especially at most 2 and more preferably at most 1 could be used. The present lubricant composition can be used, for example, as engine oils (oils used in engines such as an engine for means of transportation and engine for machine tools); gear oils; transmission lube oils, particularly automatic transmission fluid (ATF), such as stepped automatic transmission fluid and continuously variable transmission fluid (CVTF); and traction oils, shock-absorber oils, power steering oils, hydraulic oils and the like.

The fuel saving (compared to 15W-40 reference motor oil RL 191) for use in passenger motor vehicles can be determined in Europe generally according to test method CEC L-54-T-96 ("Mercedes-Benz M 11 1 Fuel Economy Test"; CEC=Coordinating European Council for Development of Performance Tests for Transportation Fuels, Lubricants and Other Fluids). More recent results (K. Hedrich, M. A. Mueller, M. Fischer:

"Evaluation of Ashless, Phosphorus Free and Low Sulfur Polymeric Additives that Improve the Performance of Fuel Efficient Engine Oils" in Conference Proceedings of the International Tribology Conference (ITC 2005) at Kobe/Japan; K. Hedrich, G.

Renner: "New Challenge of VI Improver for Next Generation Engine Oils" in

Conference Proceedings of the International Tribology Conference (ITC 2000) at Nagasaki/Japan) show that another test method ("RohMax test") can also afford comparable results. Here, not a 2.0 L gasoline engine but rather a 1.9 L diesel engine (81 kW at 4150 rpm) is used. The setup of this engine corresponds essentially to the setup described in the test method CEC L-78-T-99 ("Volkswagen Turbocharged Dl

Diesel Piston Cleanliness and Ring Sticking Evaluation"). Exact maintenance of the oil temperature according to CEC L-54-T-96 necessitates additional cooling in the setup. Additional information regarding the evaluation of methods to determine the ability of fuel savings are provided in US 2010/0190671 being incorporated by reference herein.

Surprising efficiency improvements in fuel efficiency can be achieved by using the lubricant composition as gear oil or transmission lube oil. These improvements can be evaluated according to the methods as defined in HOHN, B.-R., et al.

"Wirkungsgradtest fur Getriebeole". Mineraloltechnik (2003) 10, S. 1 - 30; WIENECKE, D,„Prufung des Wirkungsgradeinflusses von Getriebeolen, VW-Prufvorschrift Nr. PV 1456, 1997; and DOLESCHEL, A.„Wirkungsgradtest, Vergleichende Beurteilung des Einflusses von Schmierstoffen auf den Wirkungsgrad bei Zahnradgetrieben", FVA Forschungsheft Nr. 710, 2002. According to a special aspect of the present invention, the lubricant composition is a hydraulic fluid having ISO VG 15, VG 22, VG 32, VG 46, VG 68, VG 100, VG 150, VG 1500 and VG 3200 fluid grades. The viscosity grades as mentioned above can be considered as prescribed ISO viscosity grade. Preferably, the ISO viscosity grade is in the range of 15 to 3200, more preferably 22 to 150.

According to a further aspect of the invention the preferred ISO viscosity grade is in the range of 150 to 3200, more preferably 1500 to 3200.

Astonishingly, the lubricant composition provides a low noise level, especially in a hydraulic fluid. The use of such fluids can eliminate the need for silencers and/or insulation, reducing the complexity and cost of a hydraulic system.

In addition thereto, the lubricant composition may reduce torque ripple, especially in a hydraulic system by at least 2%, more preferably at least 3 % and more preferably at least 10%, compared to the torque ripple of a system using a monograde hydraulic fluid having a VI of about 100 operating at the same pressure and temperature with identical mechanical power input from the engine or electric motor. Although equal amounts of energy are consumed (fuel or electricity) for both fluids, the system using the high VI fluid will produce less torque ripple and have higher and more consistent power output. According to a further aspect of the present invention, the lubricant composition provides an improved air release. The air release performance of fluids and lubricants is typically measured by the test methods ASTM D3427 or DIN 51 381. These methods are nearly identical, and are the most widely referenced test methods used in the major regional hydraulic fluid quality standards, such as ASTM D 6158 (North America), DIN 51524 (Europe), and JCMAS HK (Japan). These methods are also specified when measuring the air release properties of turbine lubricants and gear oils.

The lubricant of the present invention can be used for high pressure applications.

Preferred embodiments can be used at pressures between 0 to 700 bar, and specifically between 70 and 400 bar. Furthermore, preferred lubricant of the present invention have a low pour point, which can be determined, for example, in accordance with ASTM D 97. Preferred fluids have a pour point of -30°C or less, especially -40°C or less and more preferably -45°C or less.

The lubricant of the present invention can be used over a wide temperature range. For example the fluid can be used in a temperature operating window of -40°C to 120°C, and meet the equipment manufactures requirements for minimum and maximum viscosity. A summary of major equipment manufacturers viscosity guidelines can be found in National Fluid Power Association recommended practice T2.13.13-2002.

The lubricant of the present invention are useful e.g. in industrial, automotive, mining, power generation, marine and military hydraulic fluid applications. Mobile equipment applications include construction, forestry, delivery vehicles and municipal fleets (trash collection, snow plows, etc.). Marine applications include ship deck cranes.

The lubricants of the present invention are useful in power generation hydraulic equipment such as electrohydraulic turbine control systems.

Furthermore, the lubricants of the present invention are useful as transformer liquids or quench oils.

Astonishingly, the present lubricant provides an improvement of the energy efficiency of a system, especially a hydraulic system. The expression energy efficiency means a better effectiveness of the energy provided to a system in order to achieve a defined result. Particularly, the energy consumption of a hydraulic system may be lowered at least 5%, more preferably at least 10 % and more preferably at least 20%, based upon the energy consumption of a system using a monograde hydraulic fluid having a VI of about 100 and providing the same work or result of the system. The type of energy usually depends on the unit providing mechanical energy to the hydraulic system. Additionally, the energy consumption based upon a defined period of time can be improved. Furthermore, the system performance of a hydraulic system can be improved. The expression system performance means the work productivity being done by the hydraulic system within a defined period of time. Particularly, the system performance can be improved at least 5%, more preferably at least 10 % and more preferably at least 20%. The type of work depends on the hydraulic system. In preferred systems, the work cycles per hour are improved. The improvement of energy consumption and system performance can be observed at all typical engine or electrical motor operating speeds. Preferentially, the improvement of energy consumption and system

performance can be determined at the about 90% of the maximum performance of the unit providing mechanical energy to the hydraulic system, e.g. 90% throttle, if a combustion engine is used.

Preferentially, engine speed can be reduced to decrease load and stress while delivering the same amount of hydraulic power.

Furthermore, the present lubricant provides an improvement of the power output of a hydraulic system. The expression "power output" means energy usable as work, typically measured and quantified as output torque from a rotary hydraulic motor in horsepower or kilowatts.

Preferably, the fluid of the present lubricant is effective in increasing the power output of the hydraulic system by at least 3%, more preferably at least 5 % and more preferably at least 10%, compared to the power output of a system using a monograde hydraulic fluid having a VI of about 100 operating at the same pressure and

temperature with identical mechanical power input from the engine or electric motor. Therefore, equal amounts of energy are consumed (fuel or electricity), however, the system using the high VI fluid will produce more usable output power in an equal period of time. According to a preferred embodiment of the present invention, the volume output is increased. Preferably, the fluid of the present invention is effective in increasing the volume output of the hydraulic system by at least 3%, more preferably at least 5 % and more preferably at least 10%, compared to the volume output of a system using a monograde hydraulic fluid having a VI of about 100 operating at the same pressure and temperature with identical mechanical power input from the engine or electric motor. The expression "volume output" means volume provided to a hydraulic motor usable as work at a specific pressure difference, typically measured and quantified in m³ or liter.

The present lubricant could additionally provide a method for improving the constancy of the power output. Surprisingly, the constancy of the power output can also be increased at the maximum load. For example, the drop of the power output after at least 10 minutes of operating time is preferably at most 3%, measured at a load of 90% of the maximum load or more of a unit providing mechanical energy. The improvements mentioned above can be used to increase the performance of a hydraulic system in an astonishing manner. By providing a system having a low and postponed drop of the power output, the system can be used at the power limits of the unit creating mechanical energy. Therefore, a defined work can be done within a shorter time without the need of constructional changes of the system. Preferably, the engine speed of a unit providing mechanical energy is maintained at a constant rate and the system delivers an increased level of hydraulic power.

According to a preferred embodiment of the present invention, the hydraulic system can be designed to operate at a lower pressure, such that the output power is equivalent to that delivered by a reference system using a hydraulic fluid with a VI of 100. The person skilled in the art can easily perform such design changes. E.g., in an excavator the shovel can be changed. By using a lower pressure, the lifetime and the service intervals of the hydraulic system can be improved in an astonishing manner. According to a preferred embodiment of the present invention, the hydraulic system can demonstrate an improvement in the ratio of hydraulic power output to power input, such that the ratio of power output/power input is preferably improved by at least 3%, more preferably at least 5 % compared to that delivered by a reference system using a hydraulic fluid with a VI of 100.

Preferably, the hydraulic system includes the following components:

1. A unit creating mechanical energy, e.g. a combustion engine or an electrical motor.

2. A fluid flow or force-generating unit that converts mechanical energy into

hydraulic power, such as a pump. 3. Piping for transmitting fluid under pressure.

4. A unit that converts the hydraulic power of the fluid into mechanical work or motion, such as an actuator or fluid motor. There are two types of motors, cylindrical and rotary.

5. A control circuit with valves that regulate flow, pressure, direction of movement, and applied forces.

6. A fluid reservoir that allows for separation of water, foam, entrained air, or debris before the clean fluid is returned to the system through a filter.

7. A liquid with low compressibility capable of operating without degradation under the conditions of the application (temperature, pressure, radiation).

Most complex systems will make use of multiple pumps, rotary motors, cylinders, electronically controlled with valves and regulators. According to a preferred embodiment of the present invention, a vane pump or a piston pump can be used in order to create hydraulic power.

The unit creating mechanical energy, e.g. a motor can be operated at a speed of 500 to 5000 rpm, preferably 1000 to 3000 rpm and more preferably 1400 to 2000 rpm.

According to a special embodiment of the present invention, the hydraulic fluid is used at a low temperature and/or a low pressure. Surprising effects may be achieved at a pressure of at most 300 bars, preferably at most 250 bars and more preferably at most 210 bars. The temperature may preferably be at most 120 °C, especially at most 100°C, more preferably at most 90°C.

The invention will be illustrated in detail hereinafter with reference to examples, without any intention that this should impose a restriction. All amounts are displayed in weight percent unless otherwise stated. Examples

Synthesis Example - Copolymer 1 (13% MMA, ATRP)

A round-bottom flask equipped with a glass stir rod, nitrogen inlet, reflux condenser and thermometer was charged with 150.0 g of Group II oil supplied by Petro-Canada, 537.54 g C12-C13 methacrylate, 211.49 g C14-C15 methacrylate, 130.20 g Ci

methacrylate, 2.10 g CuBr, 2.50 g pentamethyldiethylenetriamine. The mixture was heated up to 80°C while stirring and nitrogen bubbling for inertion. Then polymerization was initiated with 5.61 g Ethyl-2-bromoisobutyrate. Reaction temperature was increased to 95 °C and stirred for 8 hours. After the end of the polymerization the product was diluted with 235.0 g Group II oil supplied by Petro-Canada. Copolymers 3, 5, 7, 9 and 11 were prepared by a similar method wherein the components were adjusted as described in Table 1

Synthesis Example - Copolymer 2 (13% MMA, free radical) A round-bottom flask equipped with a glass stir rod, nitrogen inlet, reflux condenser and thermometer was charged with 78.7 g of Group II oil supplied by Petro-Canada, 537.54 g C12-C13 methacrylate, 211.49 g Ci₄-Ci₅ methacrylate, 130.20 g Ci methacrylate. The mixture was heated up to 1 10°C while stirring and nitrogen bubbling for inertion. Then 3-stage feed for 3 hours feed of a mixture consisting of 8.33 g tert-butyl peroctoate (tBPO) and 125.0 g Group II oil supplied by Petro-Canada was started. After the feed end the mixture was stirred for an addition 30 minutes. After the end of the

polymerization the product was diluted with 170.0 g Petro-Canada Group II Oil.

Copolymers 4, 6, 8, 10 and 12 were prepared by a similar method wherein the components were adjusted as described in Table 1.

Table 1 highlight that the chemical composition of the different polymeric samples, is completely identical belonging to the percentage of the different chain lengths of the alkyl residue of the repeating units in the respective polymer, as well as their solubility parameter chi. Herein, the polarity of the samples is based on said solubility parameter chi and calculated according to the Hildebrand solubility parameters being determined as stated above.

However, each pair of polymeric samples differ largely in molecular weight and 5 molecular weight distribution wherein the preferred samples Copolymers 1 , 3, 5, 7, 9 and 1 1 astonishingly provide much lower values in polydispersity caused by the chosen controlled polymerization mechanism.

The detailed values for all samples can be directly taken from the content of Table 1 0 below:

Table 1 : Composition of VI improvers

Table 1 : omposition of VI improvers (continuation)

When evaluating the viscosity index of a polymeric sample, a comparison between polymers of equivalent shear stability is critical since shear stability can largely influence the viscosity index. Therefore, it has been paid attention to prepare all sample pairs in such a careful way that they exhibit more or less nearly identical shear stability values in order to be comparable for the desired viscosity index measurements. Once the shear stability was achieved, each VI improver was blended in a Group III base stock to a constant kinematic viscosity at either 40 °C or 100 °C, after which the viscosity index was determined. The Shear Stability Index (SSI) was determined according to ASTM D5621 (40 minutes sonic treatment). The viscosimetric determined values of the different VI improvers have been listed in Table 2 below:

Table 2: Viscometrics of VI improvers with varying shear stabilities and polarities blended to constant viscosity in Yubase 4 to KV40 = 46cSt, and using a Group II 100N dilution oil.

Table 2 (continuation)

As can be easily seen in Table 2 the preferred Copolymers 1 , 3, 5, 7, 9 and 1 1 as VI improvers exhibit a clear VI benefit (≥ 3pts) over the Copolymers 2, 4, 6, 8, 10 and 12 prepared by conventional radical polymerization processes. Since the Copolymers 2, 4, 6, 8, 10 and 12 are polymers of similar shear stability and composition compared to preferred samples, it has been successfully demonstrated that when the VI improvers were blended with the same base stock in form of a reference oil to constant viscosity, the improvements in viscosity index of the fluid has to be attributed to the molecular weight distribution of the VI improver.

5 Thus, it can be further derived from Table 2 that the marked improvement in viscosity index with respect to small differences in PDI.

In a second series of experiments of the present invention further samples have been prepared in an analogous manner as described above for the first series of

10 experiments. Copolymers 13, 15 and 17 were prepared by a similar method as

Copolymer 1 and Copolymers 14, 16 and 18 were prepared by a similar method as Copolymer 2, respectively, wherein the components were adjusted as described in Table 3.

15 In this second series viscosity index benefits were also observed for VI improvers of equivalent shear stability over a broad range of polarities.

The composition of the VI improvers of the second series is listed below in Table 3:

20 As can be easily seen the molecular weight distribution, also called the polydispersity of the preferred Copolymers 13, 15 and 17 are much lower than the PD values of the conventional prepared Copolymers 14, 16 and 18. All other compositional features as chain length of the alkyl residue in the repeating unit as well as the solubility parameter chi have been again kept constant for each pair of samples.

25

Table 4 below gives an overview over the viscometric data of these Copolymers, especially over the measured viscosity index values showing the same effect as in the first series of experiments, namely that a tremendous increase in the viscosity index could be achieved (at least an increase of 4 units in VI) after the polymers have been blended to a constant viscosity. The Shear Stability Index (SSI) was determined according to ASTM D5621 (40 minutes sonic treatment).

Table 4: Viscometrics of VI improvers with varying polarity blended to constant viscosity in RMF5 to KV40 = 46cSt, and using a Group II 100N dilution oil.

The data clearly show that higher polarity of the polymers may lead to a smaller inventive effect. Consequently, the improvement in viscosity index by narrowing the molecular weight distribution depends on the polarity. Therefore, the most impressive improvement can be found in the medium range polarity. Higher polarities may lead to a lower difference between the preferred Copolymers and the conventional prepared Copolymers. That effect may depend on the amount of polymer used in the base oil, the amount of Ci to C₄ (meth)acrylates, especially the amount of methyl (meth)acrylate and the amount of (meth)acrylates having at least 16 carbon atoms in the alkyl residue.

Furthermore Examples and Comparative Examples regarding hydraulic efficiency have been performed.

Further compositions have been prepared comprising a group I oil mixture and the Copolymers 3 and 4 as shown in Table 1. Details including the viscosity after shear test according CEC-L-A-99 are provided in Table 5. Hitec 521 is a detergent-inhibitor package and VPL 1-330 is a pour point depressant. Table 5: Hydraulic fluids comprising a group I oil mixture blended to constant viscosity to KV40 = 46cSt.

The efficiency of the compositions has been evaluated in a Denison T6C mobile vane pump. A Denison T6C mobile vane pump is operated under the following controlled conditions:

Speed = 1500 rpm, Pressure = 200 bars, Fluid Temperature = 80° C. The data are compared to a mono grade ISO 46 hydraulic fluid being evaluated under the same conditions. The overall efficiency and energy savings are evaluated as mentioned in documents WO 2008/148586 A1 and WO 2007/096011 A1 which are enclosed herein by reference. The results obtained are also provided in Table 6.

Table 6: Efficiency of the hydraulic fluids as mentioned in Table 5 at 200 bars and 80°C.

The efficiency of the composition has been evaluated in a Denison T6C mobile vane pump. A Denison T6C mobile vane pump is operated under the following controlled conditions:

Speed = 1500 rpm, Pressure = 225 bars, Fluid Temperature = 80° C. The data are compared to a mono grade ISO 46 hydraulic fluid being evaluated under the same conditions. The results obtained are also provided in Table 7. Table 7: Efficiency of the hydraulic fluids as mentioned in Table 5 at 225 bars and

Speed = 1500 rpm, Pressure = 200 bars, Fluid Temperature = 100° C. The data are compared to a mono grade ISO 46 hydraulic fluid being evaluated under the same conditions. The results obtained are also provided in Table 8.

Table 8: Efficiency of the hydraulic fluids as mentioned in Table 5 at 200 bars and 100°C.

Speed = 1500 rpm, Pressure = 225 bars, Fluid Temperature = 100° C. The data are compared to a mono grade ISO 46 hydraulic fluid being evaluated under the same conditions. The results obtained are also provided in Table 9.

Table 9: Efficiency of the hydraulic fluids as mentioned in Table 5 at 250 bars and 100°C.

The data obtained clearly show a surprising improvement in overall efficiency and in energy savings. Astonishingly, the improvement is more significant at low temperature and low pressure. As shown in Table 6, the ratio of the improvement of Copolymer 3 to Copolymer 4 is about 3.6/2.2 = 1.64. That is, the relative improvement is about 64% based on the improvement achieved with a multi grade hydraulic fluid having a high polydispersity. At higher temperatures and higher pressures, the improvement is less significant but noticeable. E.g. at 100°C and 250 bars, the ratio of the improvement of Copolymer 3 to Copolymer 4 is about 24.3/22.3 = 1.09. That is, the relative improvement is about 9% based on the improvement achieved with a multi grade hydraulic fluid having a high polydispersity.

Therefore, the use of a polymer having a low polydispersity index as claimed provides an unexpected improvement in energy savings at low temperature and low pressure. This is especially important based on the fact that working at low temperature and pressure needs usually less energy.

Claims

Patent claims

1. A viscosity index improver comprising a polyalkyl(meth)acrylate polymer

characterized in that the polyalkyl(meth)acrylate polymer comprises a

polydispersity Mw/Mn in the range of 1.05 to 2.0.

2. The viscosity index improver according to claim 1 , wherein said

polyalkyl(meth)acrylate polymer comprises at least 40 % by weight of repeating units being derived from alkyl (meth)acrylates having 10 to 15 carbon atoms in the alkyl residue.

3. The viscosity index improver according to claim 1 or 2, wherein said

polyalkyl(meth)acrylate polymer comprises a weight average molecular weight Mw in the range of 20000 to 1000000 g/mol.

4. The viscosity index improver according to at least one of the preceding claims, wherein said polyalkyl(meth)acrylate polymer comprises at least 10 % by weight of repeating units being derived from alkyl (meth)acrylates having 1 to 4 carbon atoms in the alkyl residue.

5. The viscosity index improver according to at least one of the preceding claims wherein said polyalkyl(meth)acrylate polymer comprises at most 22 % by weight of repeating units being derived from alkyl (meth)acrylates having 1 to 4 carbon atoms in the alkyl residue.

6. The viscosity index improver according to at least one of the preceding claims wherein said polyalkyl(meth)acrylate polymer comprises at least 5 % by weight of repeating units being derived from alkyl (meth)acrylates having 16 to 4000 carbon atoms in the alkyl residue.

7. The viscosity index improver according to at least one of the preceding claims wherein said polyalkyl(meth)acrylate polymer comprises at most 25 % by weight of repeating units being derived from alkyl (meth)acrylates having 16 to 4000 carbon atoms in the alkyl residue.

8. The viscosity index improver according to at least one of the preceding claims wherein said polyalkyl(meth)acrylate polymer comprises a weight average molecular weight Mw in the range of 20000 to 1000000 g/mol.

The viscosity index improver according to at least one of the preceding claims wherein said polyalkyl(meth)acrylate polymer comprises a shear stability index of at most 35 according to ASTM D5621 (40 minutes sonic treatment).

The viscosity index improver according to at least one of the preceding claims wherein the polyalkyl(meth)acrylate polymer comprises a Chi parameter in the range of 0.2 to 0.6.

1 1. The viscosity index improver according to at least one of the preceding claims

wherein the polyalkyl(meth)acrylate polymer comprises a polydispersity in the range of 1.10 to 1.65.

The viscosity index improver according to at least one of the preceding claims wherein the polyalkyl(meth)acrylate polymer is not a polymer comprising about 25 % by weight methyl methacrylate and about 73 % by weight alkyl

methacrylates having 12 to 15 carbon atoms in the alkyl residue and a weight average molecular weight of about 37900 g/mol or a polymer comprising about 13.2 % by weight methyl methacrylate and about 84.6 % by weight alkyl methacrylates having 12 to 15 carbon atoms in the alkyl residue and a weight average molecular weight of about 36900 g/mol

A lubricant comprising the viscosity index improver as claimed in at least one of the claims 1 to 12.

14. The lubricant according to claim 13, comprising a hydrocarbon oil.

15. The lubricant according to claim 13 or 14, wherein said hydrocarbon oil is a mineral oil of Group I, II or III or a poly-alpha-olefin of Group IV, or a mixture of these oils.

16. The lubricant according to one or more of the claims 13 to 15, wherein said lubricant comprises 0.5 to 40 % by weight of said polyalkyl(meth)acrylate polymer based on the total weight of said lubricant.

The lubricant according to one or more of the claims 13 to 16, wherein said lubricant comprises no essential amounts of ester oils.

The lubricant according to one or more of the claims 13 to 17, wherein said lubricant comprises 2 to 13 % by weight of said polyalkyl(meth)acrylate poly based on the total weight of said lubricant.

19. The lubricant according to one or more of the claims 13 to 18, wherein said

lubricant comprises a polyalkyl(meth)acrylate polymer having repeating units being derived from alkyl (meth)acrylates having 1 to 4 carbon atoms in the alkyl residue and the amount of polyalkyl(meth)acrylate polymer in the lubricant and the amount of repeating units being derived from alkyl (meth)acrylates having 1 to 4 carbon atoms in the alkyl residue in the polyalkyl(meth)acrylate polymer is selected such that the lubricant comprises 0.5 to 3 % by weight of repeating units being derived from alkyl (meth)acrylates having 1 to 4 carbon atoms in the alkyl residue based on the total weight of said lubricant.

The lubricant according to one or more of the claims 13 to 19, wherein lubricant oil composition have a viscosity, measured at 40°C to ASTM D 445, in the range of 10 to 120 mm²/s, and a kinematic viscosity KV₁₀o measured at 100°C of at least 3.5 mm²/s.

A use of a polyalkyl(meth)acrylate polymer comprising a polydispersity Mw/Mn the range of 1.05 to 2.0 for improving the viscosity index of a lubricant.

A use of a polyalkyl(meth)acrylate polymer comprising a polydispersity Mw/Mn the range of 1.05 to 2.0 for improving the power output of a hydraulic system.

A use of a polyalkyl(meth)acrylate polymer comprising a polydispersity Mw/Mn in the range of 1.05 to 2.0 for improving the energy efficiency of a hydraulic system.

24. A use of a polyalkyl(meth)acrylate polymer comprising a polydispersity Mw/Mn in the range of 1.05 to 2.0 for reducing a noise of a hydraulic system.

25. A use of a polyalkyl(meth)acrylate polymer comprising a polydispersity Mw/Mn in the range of 1.05 to 2.0 for reducing torque ripple in a hydraulic system.

26. A use of a polyalkyl(meth)acrylate polymer comprising a polydispersity Mw/Mn in the range of 1.05 to 2.0 for improving the air release of a lubricant.

27. A use of a polyalkyl(meth)acrylate polymer comprising a polydispersity Mw/Mn in the range of 1.05 to 2.0 for reducing fuel consumption of a vehicle.

28. The use according to at least one or more of the claims 21 to 27 wherein the polyalkyl(meth)acrylate polymer comprising a polydispersity Mw/Mn in the range of 1.05 to 2.0 have at least 40 % by weight of repeating units being derived from alkyl (meth)acrylates having 10 to 15 carbon atoms in the alkyl residue.