The present invention is directed to lubricant compositions and additive compositions comprising boronic ester-modified polyalkyl(meth)acrylate copolymers. A simple, cost-effective method for their preparation is also disclosed.

Global government vehicle regulations demand ever better fuel economy to reduce greenhouse gas emissions and conserve fossil fuels. There is an increasing demand for more fuel-efficient vehicles to meet the targets regarding CO2 emissions. Therefore, any incremental improvement in fuel economy (FE) is of great importance in the automotive sector.

Lubricants are playing an important role in reducing a vehicle's fuel consumption and there is a continuing need for improvements in fuel economy performance.

Lubricant properties are typically improved by the addition of additives to lubricating oils. Viscosity index (VI) improvers are generally added to a lubricant to improve its thickening efficiency and to protect the engine as they are applied between the surfaces of moving parts, notably metal surfaces.

The thickening efficiency of a VI improver is specified by its KV100 (kinematic viscosity at 100°C) at a given treat rate. The thickening effect of a polymer increases as its hydrodynamic volume in the oil increases. Increasing temperature increases the solvency of the oil, which, in turn, promotes the uncoiling of the polymer and results in a larger hydrodynamic volume.

The hydrodynamic volume of a polymer in solution depends on many parameters, such as for example the polymer chain length and composition. The longer a polymer chain, the higher is usually the weight-average molecular weight M _w .

The drawback of using VI improvers with a high molecular weight is that they undergo significant and irreversible degradation under mechanical stress. Such degraded polymers then experience a decline in its thickening properties that goes along with an irreversible drop in the viscosity of the lubricant.

One way to overcome this disadvantage is to prepare polymers of lower molecular weight that can associate under higher temperatures by exchanging chemical bonds in a thermo-reversible way.

State of the Art

Patent applications US 2017/008989, US 2017/009176 and US 2018/0023028 disclose a composition resulting from the mixing of at least one copolymer A1 resulting from the copolymerization of at least one monomer functionalized by diol functional groups and of at least one compound A2 comprising at least two boronic ester functional groups. These compounds can associate and exchange chemical bonds in a thermo-reversible way. The polymers according to the present invention are not described.

WO 2019/171006 is directed to a composition resulting from the mixing of at least one comb polymer polydiol A1 and at least one compound A2 comprising at least two boronic ester functions. The polymers according to the present invention are not described. WO 2019/171007 is directed to a composition resulting from the mixing of at least one polydiol compound A1 and at least one comb polymer A2 comprising at least two boronic ester functions. The polymers according to the present invention are not described.

WO 2019/224491 , WO 2019/224492, WO 2019/224493 and WO 2019/224494 are directed to a composition resulting from the mixing of at least one oligomer A1 , functionalized with diols and optionally comprising repeat units from at least one styrene monomer, and at least one compound A2 comprising at least two boronic ester functions. The polymers according to the present invention are not described.

US2019/382679 discloses a composition resulting from the mixing of a polydiol random copolymer A1 , a compound A2 comprising at least two boronic ester functions, and an exogenous compound A5. The polymers according to the present invention are not described.

It was now an object of the present invention to provide thermo-associative polymers that can be used as viscosity index improvers in lubricating oil compositions and that are stable over a broad temperature range. Such polymers should be usable at low treat rates.

Additionally, the synthesis of such polymers should be simple and easy to upscale, and the starting materials should be commercially available.

The Applicant set itself the objective of preparing lubricant compositions based on novel thermoassociative copolymer mixtures which have improved properties when compared with the copolymer mixtures of the prior art. The Applicant also set itself the objective of preparing lubricant compositions based on novel thermoassociative copolymer mixtures which are easy to prepare and are not too costly.

This objective is achieved by means of novel rheological additives which can associate, optionally to form a gel, and which can be exchanged. The additives of the present invention have the advantage of thickening the medium in which they are dispersed, and they maintain this advantage at high temperatures, for instance up to 150°C. These additives show resistance to chemical degradation during a temperature increase when compared with the additives of the prior art. Lubricant compositions comprising them show better stability of their cycling performance and better reproducibility of the lubricant properties over time.

This characteristic results from the combined use of two particular compounds, a copolymer bearing diol functions and a copolymer comprising boronic ester functions.

It is possible, by means of the compositions of the invention, to provide lubricant compositions which have good lubricant properties during the start-up phases of an engine (cold phase) and good lubricant properties when the engine is running at its service temperature (hot phase). These lubricant compositions make it possible to reduce the fuel consumption of a vehicle in which they are used. They allow better resistance to mechanical degradation than the compositions of the prior art.

Summary of the invention

The invention is directed to a lubricating oil composition, comprising at least: - more than 60% by weight, based on the total weight of the lubricating composition, of a base oil,

- a boronic ester-modified polyalkyl (meth)acrylate copolymer 1, comprising at least a vinylboronic acid ester of general formula (I)

- a diol functionalized polyalkyl (meth)acrylate copolymer 2 comprising from 90% to 98% by weight of C1-30 alkyl (meth)acrylates, and from 2% to 10% by weight of a C2-30 a,p-di-hydroxyalkyl (meth)acrylate.

According to a favorite embodiment, the lubricating oil composition comprises at least:

- from more than 60% to 99,8 % by weight of a base oil;

- from 0.1% to 10% by weight of the boronic ester-modified polyalkyl (meth)acrylate copolymer 1, and

- from 0.1% to 10% by weight of the diol functionalized polyalkyl (meth)acrylate copolymer 2

The invention further relates to an additive composition which can be used for the preparation of the lubricating oil composition, comprising at least:

(A) 0.1% to 25% by weight of a boronic ester-modified polyalkyl (meth)acrylate copolymer 1,

(B) 0.1% to 25% by weight of a diol functionalized polyalkyl (meth)acrylate copolymer 2,

(C) 40% to 60% by weight of a base oil; and

(D) 0.1% to 30% by weight of at least one additive selected from the group consisting of conventional VI improvers, dispersants, defoamers, detergents, antioxidants, pour point depressants, antiwear additives, extreme pressure additives, friction modifiers, anticorrosion additives, dyes and mixtures thereof.

Another object of the invention is a method of thickening a lubricating oil composition, comprising the steps of:

(i) preparing a boronic ester-modified polyalkyl (meth)acrylate copolymer 1;

(ii) mixing the boronic ester-modified polyalkyl (meth)acrylate copolymer 1 of step (i) with a diol functionalized polyalkyl (meth)acrylate copolymer 2 to form a thermo-associative polymer mixture; and

(iii) introducing the polymer mixture of step (ii) into a lubricating oil composition, Wherein the boronic ester-modified polyalkyl (meth)acrylate copolymer 1, the diol functionalized polyalkyl (meth)acrylate copolymer 2 and the lubricating oil composition are as defined above and in details here-under.

The invention also relates to the use of the lubricating oil composition or the additive composition, for reducing the fuel consumption of vehicles.

The invention further relates to a process for reducing the energy losses by mechanical part friction, comprising at least one step of placing a mechanical part in contact with the lubricating oil composition.

The invention also relates to a process for reducing the fuel consumption of a vehicle, comprising at least one step of placing a mechanical part of the vehicle engine in contact with the lubricating oil composition.

Description of the invention

The expression “consists essentially of” followed by one or more features means that, besides the components or steps explicitly listed, components or steps which do not significantly modify the properties and features of the invention may be included in the process or the material of the invention.

The expression “between X and Y” includes the limits, unless explicitly mentioned otherwise. This expression thus means that the targeted range comprises the values X and Y and all the values ranging from X to Y.

The term “copolymer” means a linear or branched oligomer or macromolecule having a sequence formed from several repeating units (or monomer units), of which at least two units have a different chemical structure.

The term “monomer unit” or “monomer” means a molecule that is capable of being converted into an oligomer or a macromolecule by combination with itself or with other molecules of the same type. A monomer denotes the smallest constituent unit whose repetition leads to an oligomer or a macromolecule.

In the context of this invention, the expression: ”a copolymer comprising monomer X“ (for example a copolymer comprising a vinylboronic acid ester) means a copolymer comprising repeating units resulting from the copolymerization of monomers X with other monomers. The same applies to each and every monomer and copolymer cited in this application.

The invention is based on the introduction into a base oil, of a thermoassociative copolymer mixture comprising at least a boronic ester-modified polyalkyl (meth)acrylate copolymer 1 and a diol functionalized polyalkyl (meth)acrylate copolymer 2. The boronic ester-modified polyalkyl (meth)acrylate copolymer 1

The first copolymer of the thermoassociative copolymer mixture is a boronic ester-modified polyalkyl (meth)acrylate copolymer 1, comprising the following monomers:

(a1) 0.5% to 30% by weight of C1-4 alkyl (meth)acrylates, preferably methyl methacrylate or butyl methacrylate, more preferably butyl methacrylate;

(a2) 40% to 70% by weight of C12-15 alkyl (meth)acrylates, preferably C12-14 alkyl

(meth)acrylates;

(a3) 15% to 25% by weight of C16-30 alkyl (meth)acrylates, preferably C16-20 alkyl

(meth)acrylates; and

(a4) 5% to 17% by weight of a vinylboronic acid ester of general formula (I)

The content of each component (a1), (a2), (a3) and (a4) is based on the total composition of the boronic ester-modified polyalkyl (meth)acrylate copolymer 1.

According to a more favorite embodiment of the present invention components (a1), (a2), (a3) and (a4) represent from 95% to 100% by weight of the monomers composing copolymer 1 , preferably from 98% to 100% by weight.

In a particular embodiment, the proportions of components (a1), (a2), (a3) and (a4) add up to 100% by weight.

The weight-average molecular weight of the boronic ester-modified polyalkyl (meth)acrylate copolymers 1 used in the lubricating composition according to the present invention is preferably in the range of 50,000 g/mol to 200,000 g/mol, more preferably in the range of 70,000 g/mol to 170,000 g/mol. The number-average molecular weight of the polyalkyl(meth)acrylate polymers according to the present invention is preferably in the range of 10,000 to 100,000 g/mol, more preferably in the range of 20,000 to 60,000 g/mol, more preferably in the range of 20,000 g/mol to 50,000 g/mol.

Preferably, the polyalkyl(meth)acrylate copolymers 1 used in the lubricating composition according to the present invention have a polydispersity index (PDI) M _w /M _n in the range of 1 to 10, more preferably in the range of 2 to 4.

Mw and M _n are determined by size exclusion chromatography (SEC) using commercially available polymethylmethacrylate standards. The determination was done by gel permeation chromatography with THF as eluent. The term "(meth)acrylates" refers to both, esters of acrylic acid and esters of methacrylic acid. Esters of methacrylic acids are preferred.

The C1-4 alkyl (meth)acrylates for use in accordance with the invention are esters of (meth)acrylic acid and straight chain or branched alcohols having 1 to 4 carbon atoms. The term "C1-4 alkyl (meth)acrylates" encompasses individual (meth)acrylic esters with an alcohol of a particular length, and likewise mixtures of (meth)acrylic esters with alcohols of different lengths.

Suitable C1-4 alkyl (meth)acrylates include, for example, methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate), /so-propyl (meth)acrylate, n-butyl (meth)acrylate, /so-butyl (meth)acrylate and tert-butyl (meth)acrylate. Particularly preferred C1-4 alkyl (meth)acrylates are methyl (meth)acrylate and n-butyl (meth)acrylate; methyl methacrylate and n-butyl methacrylate are especially preferred.

The C16-30 alkyl (meth)acrylates for use in accordance with the invention are esters of (meth)acrylic acid and straight chain or branched alcohols having 16 to 30 carbon atoms. The term "C16-30 alkyl methacrylates" encompasses individual (meth)acrylic esters with an alcohol of a particular length, and likewise mixtures of (meth)acrylic esters with alcohols of different lengths. Suitable C16-30 alkyl (meth)acrylates include, for example, 2-hexyldecyl (meth)acrylate, 2- octyldecyl (meth)acrylate, undecyl (meth)acrylate, 5-methylundecyl (meth)acrylate, 2-hexyldodecyl (meth)acrylate, 2-octyldodecyl (meth)acrylate, 2-decyltetradecyl (meth)acrylate, hexadecyl (meth)acrylate, 2-methylhexadecyl (meth)acrylate, 2-dodecylhexadecyl (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, 2- decyloctadecyl (meth)acrylate, 2-tetradecyloctadecyl (meth)acrylate, nonadecyl (meth)acrylate, eicosyl (meth)acrylate, cetyleicosyl (meth)acrylate, stearyleicosyl (meth)acrylate, docosyl (meth)acrylate and/or eicosyltetratriacontyl (meth)acrylate. 2-decyl-tetradecyl (meth)acrylate, 2- decyloctadecyl (meth)acrylate, 2-dodecyl-1 -hexadecyl (meth)acrylate, 1 ,2-octyl-1 -dodecyl (meth)acrylate, 2-tetradecylocadecyl (meth)acrylate, 1 ,2-tetradecyl-octadecyl (meth)acrylate and 2- hexadecyl-eicosyl (meth)acrylate.

The C12-15 alkyl (meth)acrylates for use in accordance with the invention are esters of (meth)acrylic acid and alcohols having 10 to 15 carbon atoms. The term "C12-15 alkyl (meth)acrylates" encompasses individual (meth)acrylic esters with an alcohol of a particular length, and likewise mixtures of (meth)acrylic esters with alcohols of different lengths.

Suitable C12-15 alkyl (meth)acrylates include, for example, decyl (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 and/or pentadecyl (meth)acrylate.

Particularly preferred C12-15 alkyl (meth)acrylates are methacrylic esters of a linear C12-14 alcohol mixture (C12-14 alkyl (meth)acrylate).

The C16-20 alkyl (meth)acrylates for use in accordance with the invention are esters of (meth)acrylic acid and alcohols having 16 to 20 carbon atoms. The term "C16-20 alkyl (meth)acrylates" encompasses individual methacrylic esters with an alcohol of a particular length, and likewise mixtures of (meth)acrylic esters with alcohols of different lengths.

Suitable C16-20 alkyl (meth)acrylates include, for example, 2-hexyldecyl (meth)acrylate, 2- octyldecyl (meth)acrylate, undecyl (meth)acrylate, 5-methylundecyl (meth)acrylate and dodecyl (meth)acrylate.

Particularly preferred C16-20 alkyl (meth)acrylates are (meth)acrylic esters of a linear C16-18 alcohol mixture (C16-18 alkyl (meth)acrylate).

The boronic ester-modified polyalkyl (meth)acrylate copolymers 1 according to the present invention may comprise further comonomers selected from the group consisting of styrene monomers having from 8 to 17 carbon atoms, vinyl esters having from 1 to 11 carbon atoms in the acyl group, vinyl ethers having from 1 to 10 carbon atoms in the alcohol group, (di)alkyl fumarates having from 1 to 10 carbon atoms in the alcohol group, (di)alkyl maleates having from 1 to 10 carbon atoms in the alcohol group, dispersing nitrogen-functionalized monomers, and mixtures of these monomers.

Examples of styrene monomers having from 8 to 17 carbon atoms are styrene, substituted styrenes having an alkyl substituent in the side chain, for example alpha-methylstyrene and alphaethylstyrene, substituted styrenes having an alkyl substituent on the ring, such as vinyltoluene and para-methylstyrene, halogenated styrenes, for example monochlorostyrenes, dichlorostyrenes, tribromostyrenes and tetrabromostyrenes; preferred is styrene.

Examples of vinyl esters having from 1 to 11 carbon atoms in the acyl group include vinyl formiate, vinyl acetate, vinyl propionate, vinyl butyrate. Preferred vinyl esters include from 2 to 9, more preferably from 2 to 5 carbon atoms in the acyl group. The acyl group here may be linear or branched.

Examples of vinyl ethers having from 1 to 10 carbon atoms in the alcohol group include vinyl methyl ether, vinyl ethyl ether, vinyl propyl ether, vinyl butyl ether. Preferred vinyl ethers include from 1 to 8, more preferably from 1 to 4 carbon atoms in the alcohol group. The alcohol group here may be linear or branched.

The notation "(di)ester" means that monoesters, diesters and mixtures of esters, especially of fumaric acid and/or of maleic acid, may be used. The (di)alkyl fumarates having from 1 to 10 carbon atoms in the alcohol group include monomethyl fumarate, dimethyl fumarate, monoethyl fumarate, diethyl fumarate, methyl ethyl fumarate, monobutyl fumarate, dibutyl fumarate, dipentyl fumarate and dihexyl fumarate. Preferred (di)alkyl fumarates comprise from 1 to 8, more preferably from 1 to 4 carbon atoms in the alcohol group. The alcohol group here may be linear or branched. The (di)alkyl maleates having from 1 to 10 carbon atoms in the alcohol group include monomethyl maleate, dimethyl maleate, monoethyl maleate, diethyl maleate, methyl ethyl maleate, monobutyl maleate, dibutyl maleate. Preferred (di)alkyl maleates comprise from 1 to 8, more preferably from 1 to 4 carbon atoms in the alcohol group. The alcohol group here may be linear or branched.

Examples of dispersing nitrogen-functionalized monomers are aminoalkyl (meth)acrylates, such as N,N-dimethylaminoethyl (meth)acrylate, N,N-dimethylaminopropyl (meth)acrylate, N,N- diethylaminopentyl (meth)acrylate, N,N-dibutylaminohexadecyl (meth)acrylate; aminoalkyl(meth)acrylamides, such as N,N-dimethylaminopropyl(meth)acrylamide; heterocyclic (meth)acrylates, such as 2-(1-imidazolyl)ethyl (meth)acrylate, 2-(4-morpholinyl)ethyl (meth)acrylate, 1-(2-methacryloyloxyethyl)-2-pyrrolidone, N-methacryloylmorpholine, N- methacryloyl-2-pyrrolidinone, N-(2-methacryloyloxyethyl)-2-pyrrolidinone, N-(3- methacryloyloxypropyl)-2-pyrrolidinone; heterocyclic vinyl compounds, such as 2-vinylpyridine, 4- vinylpyridine, 2-methyl-5-vinylpyridine, 3-ethyl-4-vinylpyridine, 2,3-dimethyl-5-vinylpyridine, vinylpyrimidine, vinylpiperidine, 9-vinylcarbazole, 3-vinylcarbazole, 4-vinylcarbazole, 1- vinylimidazole, 2-methyl-1-vinylimidazole, N-vinylpyrrolidone, N-vinylpyrrolidine, 3-vinylpyrrolidine, N-vinylcaprolactam, N-vinylbutyrolactam, vinyloxolane, vinylfuran, vinyloxazoles and hydrogenated vinyloxazoles.

The N-dispersant monomer may specifically be at least one monomer selected from the group consisting of N-vinyl pyrrolidinone, N,N-dimethylaminoethyl methacrylate, and N,N- dimethylaminopropyl methacrylamide.

The polymers used in the lubricating oil composition according to the present invention are characterized by their ability to form association-related thickeners.

The diol-functionalized polyalkyl (meth)acrylate copolymer 2

The diol functionalized polyalkyl (meth)acrylate copolymer 2 comprises at least one diol selected from C2-30 a,p-di-hydroxyalkyl (meth)acrylate, preferably from C2-10 a,p-dihydroxyalkyl (meth)acrylates, preferably selected from the group consisting of 2,3-dihydroxypropyl methacrylate and 5,6-dihydroxyhexyl methacrylate, preferably 2,3-dihydroxypropyl methacrylate.

According to a first favorite embodiment, the thermoassociative mixture of copolymers comprises at least a diol functionalized polyalkyl (meth)acrylate copolymer 2 comprising from 90% to 98% by weight of C1-30 alkyl (meth)acrylates, and from 2% to 10% by weight of a C2-30 a,p-di- hydroxyalkyl (meth)acrylate.

According to a favorite embodiment, the diol selected from C2-30 a,p-dihydroxyalkyl (meth)acrylates and the C1-30 alkyl (meth)acrylates represent from 95 to 99 % by weight of monomers composing copolymer 2, preferably from 98% to 100% by weight, even more preferably they represent 100% by weight of the monomers composing copolymer 2.

Advantageously, the polyalkyl (meth)acrylate copolymer 2 comprises the following monomers: (b1 ) 5% to 40% by weight of C1-4 alkyl (meth)acrylates;

(b2) 40% to 65% by weight of C12-15 alkyl (meth)acrylates, preferably C12-14 alkyl

(meth)acrylates;

(b3) 10% to 30% by weight of C16-30 alkyl (meth)acrylates, preferably C16-18 alkyl

(meth)acrylates; and

(b4) 2% to 10% by weight of a diol selected from C2-30 a,p-di-hydroxyalkyl (meth)acrylates preferably C2-10 a,p-dihydroxyalkyl (meth)acrylates, even more preferably selected from the group consisting of 2,3-dihydroxypropyl methacrylate and 5,6-dihydroxyhexyl methacrylate. The content of each component (b1), (b2), (b3) and (b4) is based on the total composition of the diol functionalized polyalkyl (meth)acrylate copolymer 2. In a particular embodiment, the proportions of components (b1), (b2), (b3), (b4) and (e) add up to 100% by weight.

The weight-average molecular weight of the diol functionalized polyalkyl (meth)acrylate copolymers 2 used in the present invention is preferably in the range of 50,000 g/mol to 400,000 g/mol, more preferably in the range of 70,000 g/mol to 200,000 g/mol. The number-average molecular weight of the diol functionalized polyalkyl(meth)acrylate copolymers 2 used in the present invention is preferably in the range of 10,000 g/mol to 150,000 g/mol, more preferably in the range of 20,000 g/mol to 50,000 g/mol.

Preferably, the diol functionalized polyalkyl(meth)acrylate copolymers 2 used in the present invention have a polydipersity index (PDI) M _w /M _n in the range of 1 to 10, more preferably in the range of 2 to 6, more preferably in the range of 3 to 5.

Mw and M _n are determined by size exclusion chromatography (SEC) using commercially available polymethylmethacrylate standards. The determination was done by gel permeation chromatography with THF as eluent.

The proportions of copolymer 1 and copolymer 2 in the compositions comprising them

The favorite proportions of copolymer 1 and copolymer 2 apply to the lubricant composition and also to the stock solutions (or concentrated solutions) comprising them.

According to a favorite embodiment, the lubricant composition of the present invention comprises

(A) the boronic ester-modified polyalkyl (meth)acrylate copolymer 1, and

(B) the diol functionalized polyalkyl (meth)acrylate copolymer 2, in amounts such that the weight ratio (copolymer 1) (copolymer 2) is 1 :2 to 2 :1 , preferably 1 : 1 ,5 to 1 ,5 : 1 , even more preferably 1 :1.

According to a favorite embodiment, the component vinylboronic acid ester of general formula (I) of the boronic ester-modified polyalkyl (meth)acrylate copolymer 1 and the component C2-30 a,p-di- hydroxyalkyl (meth)acrylate of the diol functionalized polyalkyl (meth)acrylate copolymer 2 are present in a molar ratio of 1 :2 to 2 : 1 , preferably from 1 : 1 ,5 to 1 ,5 : 1 , even more preferably of 1 : 1. According to a favorite embodiment, the lubricant oil composition of the present invention comprises a mixture of:

(A) a boronic ester-modified polyalkyl (meth)acrylate copolymer 1 comprising the following monomers:

(a1) 0.5% to 30% by weight of C1-4 alkyl (meth)acrylates, preferably methyl methacrylate or butyl methacrylate, more preferably butyl methacrylate;

(a2) 40% to 70% by weight of C12-15 alkyl (meth)acrylates, preferably C12-14 alkyl

(meth)acrylates;

(a3) 15% to 25% by weight of C16-30 alkyl (meth)acrylates, preferably C16-18 alkyl

(meth)acrylates; and

(a4) 5% to 17% by weight of a vinylboronic acid ester of general formula (I)

(i); and

(B) a polyalkyl (meth)acrylate copolymer 2 comprising the following monomers:

(b1 ) 5% to 40% by weight of C1-4 alkyl (meth)acrylates;

(b2) 40% to 65% by weight of C12-15 alkyl (meth)acrylates, preferably C12-14 alkyl

(meth)acrylates;

(b3) 10% to 30% by weight of C16-30 alkyl (meth)acrylates, preferably C16-18 alkyl

(meth)acrylates; and

(b4) 2% to 10% by weight of a diol selected from the group consisting of 2,3- dihydroxypropyl methacrylate and 5,6-dihydroxyhexyl methacrylate, in amounts such that the weight ratio (copolymer 1) (copolymer 2) is 1 :2 to 2 :1 , preferably 1 : 1 ,5 to 1 ,5 :1 , even more preferably 1:1.

The content of each component (a1), (a2), (a3) and (a4) is based on the total composition of the boronic ester-modified polyalkyl (meth)acrylate copolymer 1. In a particular embodiment, the proportions of components (a1), (a2), (a3) and (a4) add up to 100% by weight.

The content of each component (b1), (b2), (b3) and (b4) is based on the total composition of the diol functionalized polyalkyl (meth)acrylate copolymer 2. In a particular embodiment, the proportions of components (b1), (b2), (b3) and (b4) add up to 100% by weight.

According to a favorite embodiment, the component (a4) vinylboronic acid ester of general formula (I) of the boronic ester-modified polyalkyl (meth)acrylate copolymer 1 and the component (b4) C2- 30 a,p-di-hydroxyalkyl (meth)acrylate of the diol functionalized polyalkyl (meth)acrylate copolymer 2 are present in a molar ratio (a4) : (b4) of 1 :2 to 2 : 1 , preferably from 1 : 1 ,5 to 1 ,5 : 1 , even more preferably of 1 :1.

Advantageously, component (a4) of the boronic ester-modified polyalkyl (meth)acrylate copolymer 1 and component (b4) of the polyalkyl (meth)acrylate copolymer 2 are present in equal amounts of 6 mol% to 8 mol%.

The mixture comprising the above recited amounts of a boronic ester-modified polyalkyl (meth)acrylate copolymer 1 and a diol functionalized polyalkyl (meth)acrylate copolymer 2 can be used to thicken a lubricating oil composition. The base oil

The term “oil” means a fatty substance that is liquid at room temperature (25°C) and atmospheric pressure (760 mmHg i.e. 10 ⁵ Pa).

The term “base oil” or “lubricant oil” means an oil which attenuates the friction between two moving parts in order to facilitate the functioning of these parts. The lubricant oils may be of natural, mineral or synthetic origin.

The lubricant oils of natural origin may be oils of plant or animal origin, preferably oils of plant origin such as rapeseed oil, sunflower oil, palm oil, coconut kernel oil, etc.

The lubricant oils of mineral origin are of petroleum origin and are extracted from petroleum fractions originating from the atmospheric and vacuum distillation of crude oil. The distillation may be followed by refining operations such as solvent extraction, deasphalting, deparaffinning with solvent, hydrotreatment, hydrocracking, hydroisomerization, hydrofinishing, etc. By way of illustration, mention may be made of paraffinic mineral base oils such as the oil Bright Stock Solvent (BSS), naphthenic mineral base oils, aromatic mineral oils, hydrorefined mineral bases whose viscosity index is about 100, hydrocracked mineral bases whose viscosity index is between 120 and 130, or hydroisomerized mineral bases whose viscosity index is between 140 and 150. The lubricant oils of synthetic origin (or synthetic bases) originate, as their name indicates, from chemical synthesis, such as the addition of a product to itself or polymerization, or the addition of one product to another product such as esterification, alkylation, fluorination, etc., of components originating from petrochemistry, carbon chemistry and mineral chemistry such as: olefins, aromatics, alcohols, acids, halogen-based, phosphorus-based, silicon-based compounds, etc. By way of illustration, mention may be made of: synthetic oils based on synthetic hydrocarbons such as poly-alpha-olefins (PAO), internal polyolefins (IPO), polybutenes and polyisobutenes (PIB), alkylbenzenes and alkylated polyphenyls; synthetic oils based on esters such as diacid esters or neopolyol esters; synthetic oils based on polyglycols, such as monoalkylene glycols, polyalkylene glycols and polyalkylene glycol monoethers; synthetic oils based on phosphate esters; synthetic oils based on silicon derivatives such as silicone oils or polysiloxanes.

The base oil may also be defined as specified by the American Petroleum Institute (API) (see April 2008 version of "Appendix E-API Base Oil Interchangeability Guidelines for Passenger Car Motor Oils and Diesel Engine Oils", section 1.3 Sub-heading 1.3. "Base Stock Categories").

The API currently defines five groups of lubricant base stocks (API 1509, Annex E - API Base Oil Interchangeability Guidelines for Passenger Car Motor Oils and Diesel Engine Oils, September 2011). Groups I, II and III are mineral oils which are classified by the amount of saturates and sulphur they contain and by their viscosity indices; Group IV are polyalphaolefins; and Group V are all others, including e.g. ester oils. The table below illustrates these API classifications.

* measured according to the standard ASTM D2007

** measured according to the standards ASTM D2622, ASTM D4294, ASTM D4927 and ASTM D3120

*** measured according to the standard ASTM D2270

The kinematic viscosity at 100°C (KV100) of appropriate apolar base oils used to prepare a lubricating composition in accordance with the present invention is preferably in the range of 1,5 mm ² /s to 150 mm ² /s, more preferably in the range of 1 ,5 mm ² /s to 15 mm ² /s, according to ASTM D445.

Further base oils which can be used in accordance with the present invention are Group Il-Ill Fischer-Tropsch derived base oils.

Fischer-Tropsch derived base oils are known in the art. By the term "Fischer-Tropsch derived" is meant that a base oil is, or is derived from, a synthesis product of a Fischer-Tropsch process. A Fischer-Tropsch derived base oil may also be referred to as a GTL (Gas-To-Liquids) base oil. Suitable Fischer-Tropsch derived base oils that may be conveniently used as the base oil in the lubricating composition of the present invention are those as for example disclosed in EP 0 776 959, EP 0 668 342, WO 97/21788, WO 00/15736, WO 00/14188, WO 00/14187, WO 00/14183, WO 00/14179, WO 00/08115, WO 99/41332, EP 1 029029, WO 01/18156, WO 01/57166 and WO 2013/189951.

Especially for engine oil formulations are used base oils of API Group II to V.

Method of thickening a lubricating oil composition

A further embodiment of the present invention is directed to a method of thickening a lubricating oil composition, comprising the steps of:

(i) preparing a boronic ester-modified polyalkyl (meth)acrylate copolymer 1;

(ii) mixing the boronic ester-modified polyalkyl (meth)acrylate copolymer 1 of step (i) with a diol functionalized polyalkyl (meth)acrylate copolymer 2 to receive a thermo-associative copolymer mixture; and

(iii) introducing the thermo-associative copolymer mixture of step (ii) into a lubricating oil composition.

The favorite embodiments recited for the copolymers 1 and 2 and their proportions apply to the method of thickening a lubricating oil composition. Lubricating oil composition

Another embodiment of the present invention is directed to a lubricating oil composition, comprising:

(A) 0.1% to 10% by weight of a boronic ester-modified polyalkyl (meth)acrylate copolymer 1,

(B) 0.1 % to 10% by weight of a diol functionalized polyalkyl (meth)acrylate copolymer 2,

(C) more than 60% to 99.8 % by weight of a base oil,

(D) 0% to 15% of one or more further additives.

The favorite embodiments recited above for the copolymers 1 and 2 and their proportions apply to the lubricating oil composition. The content of each component (A), (B), (C) and (D) is based on the total composition of the lubricating oil composition. In a particular embodiment, the proportions of components (A), (B), (C) and (D) add up to 100% by weight.

The content of each component (b1), (b2), (b3) and (b4) is based on the total composition of the boronic ester-modified polyalkyl (meth)acrylate copolymer 1. In a particular embodiment, the proportions of components (b1), (b2), (b3), (b4) and (e) add up to 100% by weight.

The content of each component (c1), (c2), (c3) and (c4) is based on the total composition of the polyalkyl (meth)acrylate copolymer 2. In a particular embodiment, the proportions of components (c1), (c2), (c3) and (c4) add up to 100% by weight.

The lubricating oil composition according to the invention may also contain, as component (D), further additives selected from the group consisting of conventional VI improvers, dispersants, defoamers, detergents, antioxidants, pour point depressants, antiwear additives, extreme pressure additives, friction modifiers, anticorrosion additives, dyes and mixtures thereof.

Conventional VI improvers include hydrogenated styrene-diene copolymers (HSDs, US4116 917, US3772196 and US4788316), especially based on butadiene and isoprene, and also olefin copolymers (OCPs, K. Marsden: "Literature Review of OOP Viscosity Modifiers", Lubrication Science 1 (1988), 265), especially of the poly(ethylene-co-propylene) type, which may often also be present in N/O-functional form with dispersing action, or PAMAs, which are usually present in N-functional form with advantageous additive properties (boosters') as dispersants, wear protection additives and/or friction modifiers (DE 1 520 696 to Rohm and Haas, WO 2006/007934 to RohMax Additives).

Compilations of VI improvers and pour point improvers for lubricant oils, especially motor oils, are detailed, for example, in T. Mang, W. Dresel (eds.): "Lubricants and Lubrication", Wiley-VCH, Weinheim 2001 : R. M. Mortier, S. T. Orszulik (eds.): "Chemistry and Technology of Lubricants", Blackie Academic & Professional, London 1992; or J. Bartz: "Additive fur Schmierstoffe", Expert- Verlag, Renningen-Malmsheim 1994.

Appropriate dispersants include poly(isobutylene) derivatives, for example poly(isobutylene)succinimides (PIBSIs), including borated PIBSIs; and ethylene-propylene oligomers having N/O functionalities. Dispersants (including borated dispersants) are preferably used in an amount of 0 to 5% by weight, based on the total amount of the lubricating oil composition.

Suitable defoamers are silicone oils, fluorosilicone oils, fluoroalkyl ethers, etc..

The defoaming agent is preferably used in an amount of 0.005 to 0.1% by weight, based on the total amount of the lubricating oil composition.

The preferred detergents include metal-containing compounds, for example phenoxides; salicylates; thiophosphonates, especially thiopyrophosphonates, thiophosphonates and phosphonates; sulfonates and carbonates. As metal, these compounds may contain especially calcium, magnesium and barium. These compounds may preferably be used in neutral or overbased form.

Detergents are preferably used in an amount of 0.2 to 1% by weight, based on the total amount of the lubricating oil composition.

The suitable antioxidants include, for example, phenol-based antioxidants and amine-based antioxidants.

Phenol-based antioxidants include, for example, octadecyl-3-(3,5-di-tert-butyl-4- hydroxyphenyl)propionate; 4,4' -methylenebis(2,6-di-tert-butylphenol); 4,4' -bis(2,6-di-t- butylphenol); 4,4' -b is(2-methyl-6-t-butylphenol); 2,2' -methylenebis(4-ethyl-6-t-butylphenol); 2,2' - methylenebis( 4-methyl-6-t-butyl phenol); 4,4' -butyl idenebis(3-methyl-6-t-butylphenol); 4,4'- isopropylidenebis(2,6-di-t-butylphenol); 2,2'-methylenebis(4-methyl-6-nonylphenol); 2,2'- isobutylidenebis(4,6-dimethylphenol); 2,2'-methylenebis(4-methyl-6-cyclohexylphenol); 2,6-di-t- butyl-4-methylphenol; 2,6-di-t-butyl-4-ethyl-phenol; 2,4-dimethyl-6-t-butylphenol; 2,6-di-t-amyl-p- cresol; 2,6-di-t-butyi-4-(N,N'-dimethylaminomethylphenol); 4,4'thiobis(2-methyl-6-t-butylphenol); 4,4'-thiobis(3-methyl-6-t-butylphenol); 2,2'-thiobis(4-methyl-6-t-butylphenol); bis(3-methyl-4- hydroxy-5-t-butyl benzyl) sulfide; bis(3,5-di-t-butyl-4-hydroxybenzyl) sulfide; n-octyl-3-(4-hydroxy- 3,5-di-t-butylphenyl)propionate; n-octadecyl-3-(4-hydroxy-3,5-di-t-butylphenyl)propionate; 2,2'- thio[diethyl-bis-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionat e], etc. Of those, especially preferred are bis-phenol-based antioxidants and ester group containing phenol-based antioxidants.

The amine-based antioxidants include, for example, monoalkyldiphenylamines such as monooctyldiphenylamine, monononyldiphenylamine, etc.; dialkyldiphenylamines such as 4,4' - dibutyldiphenylamine, 4,4'-dipentyldiphe nylamine, 4,4'- dihexyldiphenylamine, 4,4'- diheptyldiphenylamine, 4,4'-dioctyldiphenylamine, 4,4'-dinonyldiphenylamine, etc.; polyalkyldiphenylamines such as tetrabutyldiphenylamine, tetrahexyldiphenylamine, tetraoctyldiphenylamine, tetranonyldiphenylamine, etc.; naphthylamines, concretely alphanaphthylamine, phenyl-alpha-naphthylamine and further alkyl-substituted phenyl-alpha- naphthylamines such as butylphenyl-alpha-naphthylamine, pentylphenyl-alpha-naphthylamine, hexylphenyl-alpha-naphthylamine, heptylphenyl-alpha-naphthylamine, octylphenyl-alpha- naphthylamine, nonylphenyl-alpha-naphthylamine, etc. Of those, diphenylamines are preferred to naphthylamines, from the viewpoint of the antioxidation effect thereof. Suitable antioxidants may further be selected from the group consisting of compounds containing sulfur and phosphorus, for example metal dithiophosphates, for example zinc dithiophosphates (ZnDTPs), "OOS triesters" = reaction products of dithiophosphoric acid with activated double bonds from olefins, cyclopentadiene, norbornadiene, a-pinene, polybutene, acrylic esters, maleic esters (ashless on combustion); organosulfur compounds, for example dialkyl sulfides, diaryl sulfides, polysulfides, modified thiols, thiophene derivatives, xanthates, thioglycols, thioaldehydes, sulfur- containing carboxylic acids; heterocyclic sulfur/nitrogen compounds, especially dialkyldimercaptothiadiazoles, 2-mercaptobenzimidazoles; zinc bis(dialkyldithiocarbamate) and methylene bis(dialkyldithiocarbamate); organophosphorus compounds, for example triaryl and trialkyl phosphites; organocopper compounds and overbased calcium- and magnesium-based phenoxides and salicylates.

Antioxidants are used in an amount of 0 to 15% by weight, preferably 0.1 to 10% by weight, more preferably 0.5 to 5% by weight, based on the total amount of the lubricating oil composition.

The pour-point depressants include ethylene-vinyl acetate copolymers, chlorinated paraffinnaphthalene condensates, chlorinated paraffin-phenol condensates, polymethacrylates, polyalkylstyrenes, etc. Preferred are polymethacrylates having a mass-average molecular weight of from 5.000 to 50.000 g/mol.

The amount of the pour point depressant is preferably from 0.1 to 5% by weight, based on the total amount of the lubricating oil composition.

The preferred antiwear and extreme pressure additives include sulfur-containing compounds such as zinc dithiophosphate, zinc di-C3-i2-alkyldithiophosphates (ZnDTPs), zinc phosphate, zinc dithiocarbamate, molybdenum dithiocarbamate, molybdenum dithiophosphate, disulfides, sulfurized olefins, sulfurized oils and fats, sulfurized esters, thiocarbonates, thiocarbamates, polysulfides, etc.; phosphorus-containing compounds such as phosphites, phosphates, for example trialkyl phosphates, triaryl phosphates, e.g. tricresyl phosphate, amine-neutralized mono- and dialkyl phosphates, ethoxylated mono- and dialkyl phosphates, phosphonates, phosphines, amine salts or metal salts of those compounds, etc.; sulfur and phosphorus-containing anti-wear agents such as thiophosphites, thiophosphates, thiophosphonates, amine salts or metal salts of those compounds, etc.

The antiwear agent may be present in an amount of 0 to 3% by weight, preferably 0.1 to 1.5% by weight, more preferably 0.5 to 0.9% by weight, based on the total amount of the lubricating oil composition.

Friction modifiers used may include mechanically active compounds, for example molybdenum disulfide, graphite (including fluorinated graphite), poly(trifluoroethylene), polyamide, polyimide; compounds that form adsorption layers, for example long-chain carboxylic acids, fatty acid esters, ethers, alcohols, amines, amides, imides; compounds which form layers through tribochemical reactions, for example saturated fatty acids, phosphoric acid and thiophosphoric esters, xanthogenates, sulfurized fatty acids; compounds that form polymer-like layers, for example ethoxylated dicarboxylic partial esters, dialkyl phthalates, methacrylates, unsaturated fatty acids, sulfurized olefins or organometallic compounds, for example molybdenum compounds (molybdenum dithiophosphates and molybdenum dithiocarbamates MoDTCs) and combinations thereof with ZnDTPs, copper-containing organic compounds.

Friction modifiers may be used in an amount of 0 to 6% by weight, preferably 0.05 to 4% by weight, more preferably 0.1 to 2% by weight, based on the total amount of the lubricating oil composition. Some of the compounds listed above may fulfil multiple functions. ZnDTP, for example, is primarily an antiwear additive and extreme pressure additive, but also has the character of an antioxidant and corrosion inhibitor (here: metal passivator/deactivator).

The above-detailed additives are described in detail, inter alia, in T. Mang, W. Dresel (eds.): "Lubricants and Lubrication", Wiley-VCH, Weinheim 2001 ; R. M. Mortier, S. T. Orszulik (eds.): "Chemistry and Technology of Lubricants".

Preferably, the total concentration of the one or more additives (D) is 0.05% to 15% by weight, more preferably 3% to 10% by weight, based on the total weight of the lubricating oil composition.

Additive composition

Another embodiment of the present invention is directed to an additive composition, comprising: and

(A) 0.1% to 25% by weight of a boronic ester-modified polyalkyl (meth)acrylate copolymer 1,

(B) 0.1% to 25% by weight of a diol functionalized polyalkyl (meth)acrylate copolymer 2,

(C) 40% to 60% by weight of a base oil;

(D) 0.1% to 30% by weight of at least one additive selected from the group consisting of conventional VI improvers, dispersants, defoamers, detergents, antioxidants, pour point depressants, antiwear additives, extreme pressure additives, friction modifiers, anticorrosion additives, dyes and mixtures thereof.

The additive composition, also known as stock solution, or concentrated solution, or mother solution, is used to prepare a lubricating composition, by dilution with a base oil which can be identical to or different from the base oil of the additive composition.

The favorite embodiments recited above for the copolymers 1 and 2 and their proportions apply to the additive composition.

The content of each component (A), (B), (C) and (D) is based on the total composition of additive. In a particular embodiment, the proportions of components (A), (B), (C) and (D) add up to 100% by weight.

Process for preparing the lubricant and additive compositions of the invention

The lubricant compositions and the additive compositions of the invention are prepared by means that are well known to those skilled in the art. For example, it notably suffices for a person skilled in the art: to take a desired amount of a solution comprising the boronic ester-modified polyalkyl (meth)acrylate copolymer 1 as defined above; to take a desired amount of a solution comprising the diol functionalized polyalkyl (meth)acrylate copolymer 2 as defined previously; optionally to take a desired amount of a solution comprising additives D as defined above; to mix, either simultaneously or sequentially, the solutions in a lubricant base oil, to obtain the lubricant composition of the invention.

The order of addition of the compounds has no influence in the implementation of the process for preparing the lubricant composition.

Alternately, the lubricating oil composition can be prepared by dilution of a concentrated solution of additives.

Process for improving the thickening efficiency of a lubricating oil composition

A further embodiment of the present invention is directed to a process for improving the thickening efficiency of a lubricating oil composition by adding a boronic ester-modified polyalkyl (meth)acrylate copolymer 1 and a diol functionalized polyalkyl (meth)acrylate copolymer 2, comprising the monomers as outlined further above.

Properties of the lubricating compositions according to the invention

The lubricant compositions of the invention result from the mixing of associative copolymers which have the property of increasing the viscosity of the lubricant oil via associations. The lubricant compositions according to the invention have the advantage in that these associations or crosslinking are reversible.

The boronic ester functionalized copolymers 1 and the diol functionalized copolymers 2 as defined above have the advantage of being associative and of exchanging chemical bonds, notably in a hydrophobic medium, notably an apolar hydrophobic medium.

Under certain conditions, the boronic ester functionalized copolymers 1 and the diol functionalized copolymers 2 as defined above may be crosslinked.

The boronic ester functionalized copolymers 1 and the diol functionalized copolymers 2 also have the advantage of being exchangeable.

The term “associative” means that covalent chemical bonds of boronic ester type are established between the boronic ester functionalized copolymers 1 and the diol functionalized copolymers 2. Depending on the functionality of the boronic ester functionalized copolymers 1 and the diol functionalized copolymers 2 and depending on the composition of the mixtures, the formation of covalent bonds between boronic ester functionalized copolymers 1 and the diol functionalized copolymers 2 will optionally be able to lead to the formation of a three-dimensional polymer network. The term “chemical bond” means a covalent chemical bond of boronic ester type.

The term “exchangeable” means that the compounds are capable of exchanging chemical bonds between themselves by transesterification without the total number or nature of the chemical functions being modified.

The lubricant compositions according to the invention have improved thermal stability, an improved viscosity index, improved stability to oxidation, better cycling performance, and better reproducibility of the performance qualities over time, and also better resistance to mechanical degradation.

A person skilled in the art knows how to adjust the various parameters of the various constituents of the composition to obtain a lubricant composition whose viscosity is suitable for use.

The amount of boronic ester bonds that can be established between the diol functionalized copolymers 2 and the boronic ester functionalized copolymers 1 is adjusted by a person skilled in the art by means of an appropriate selection of the diol functionalized copolymers 2, of the boronic ester functionalized copolymers 1, and of their amounts.

Method for obtaining the copolymers used in the lubricating oil composition

The boronic ester-modified polyalkyl (meth)acrylate copolymers 1 and the diol functionalized polyalkyl (meth)acrylate copolymers 2 as disclosed above can be prepared by free-radical polymerization and by related methods of controlled free-radical polymerization, for example ATRP (= atom transfer radical polymerization) or RAFT (= reversible addition fragmentation chain transfer).

Standard free-radical polymerization is detailed, inter alia, in Ullmann's Encyclopedia of Industrial Chemistry, Sixth Edition. In general, a polymerization initiator and optionally a chain transfer agent are used for this purpose.

The usable initiators include 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 perbenzoate, 2,2-bis(tert-butylperoxy)butane, 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 unspecified compounds which can likewise form free radicals. Preferably used in accordance with the present invention are tert-butyl perbenzoate and 2,2- bis(tert-butylperoxy)butane. Suitable chain transfer agents are especially 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 method is known per se. It is assumed that this is a "living" free-radical polymerization, but no restriction is intended by the description of the mechanism. In these processes, a transition metal compound is reacted with a compound having a transferable atom group. This involves transfer of the transferable atom group to the transition metal compound, as a result of which the metal is oxidized. This reaction forms a free radical which adds onto ethylenic groups. However, the transfer of the atom group to the transition metal compound is reversible, and so the atom group is transferred back to the growing polymer chain, which results in formation of a controlled polymerization system. It is accordingly possible to control the formation of the polymer, the molecular weight and the molecular weight distribution.

This reaction regime is described, for example, by J.-S. Wang, et al., J. Am. Chem. Soc, vol. 117, p. 5614-5615 (1995), by Matyjaszewski, Macromolecules, vol. 28, p. 7901-7910 (1995). In addition, patent applications WO 96/30421 , WO 97/47661 , WO 97/18247, WO 98/40415 and WO 99/10387 disclose variants of the above-elucidated ATRP. In addition, the polymers of the invention can also be obtained via RAFT methods, for example. This method is described in detail, for example, in WO 98/01478 and WO 2004/083169.

The polymerization can be conducted under standard pressure, reduced pressure or elevated pressure. The polymerization temperature is also uncritical. In general, however, it is in the range from -20°C to 200°C, preferably 50°C to 150°C and more preferably 80°C to 130°C.

The polymerization can be conducted with or without solvent. The term "solvent" should be understood here in a broad sense. The solvent is selected according to the polarity of the monomers used, it being possible with preference to use 100N oil, comparatively light gas oil and/or aromatic hydrocarbons, for example toluene or xylene, as well as other organic solvents, for example butyl acetate.

Figures

The following figures illustrate the results retrieved for the viscosity indices when using the polymers in the compositions of the present invention:

Figure 1 : Viscosity indices of polymer mixtures A to F (1 :1 polymer mixture in Yubase 4+ as base oil) versus solutions of the single polymers (equal parts of copolymer 1 or copolymer 2 in Yubase 4+ as base oil).

Figure 2: KV100 values of polymer mixtures A to F (1 :1 polymer mixture in Yubase 4+ as base oil) versus solutions of the single polymers (equal parts of copolymer 1 or copolymer 2 in Yubase 4+ as base oil).

The invention is illustrated by the following non-limiting examples.

Experimental Part

Abbreviations

AMA alkyl methacrylate

BAE boronic acid ester 2 = 4-(4-decyl-1 ,3,2-dioxaborolan-2-yl)-benzoic acid (4- ethenylphenyl)methyl ester

BMA C4-alkyl methacrylate = n-butyl methacrylate Diol 1 2,3-dihydroxypropyl methacrylate (2,3-DHMA)

Diol 2 5,6-dihydroxyhexyl methacrylate (5,6-DHMA)

GPC gel permeation chromatography

KV kinematic viscosity measured according to ASTM D445

KV40 kinematic viscosity @40°C, measured according to ASTM D7042

KV100 kinematic viscosity @100°C, measured according to ASTM D7042 LMA lauryl methacrylate, 73% C12, 27% C14, all linear

MMA Ci-alkyl methacrylate = methyl methacrylate

M _n number-average molecular weight

Mw weight-average molecular weight

NB3043 Nexbase® 3043, Group III base oil from Neste with a KV100 of 4.3 cSt

PDI polydispersity index

SMA stearyl methacrylate, 6% C14, 30% C16, 64% C18, all linear tBPO tert-butyl-peroxy-2-ethyl-hexanoate

VI viscosity index, measured according to ISO 2909

Yubase 4+ Group III base oil from SK Lubricants with a KV100 of 4.2 cSt

Test methods

The boronic ester-modified polyalkyl (meth)acrylate copolymers 1 and the polyalkyl (meth)acrylate diol functionalized copolymers 2 were characterized with respect to their molecular weight and PDI.

The weight-average molecular weights (M _w ) of the boronic ester-modified polyalkyl (meth)acrylate copolymers 1 and the diol functionalized polyalkyl (meth)acrylate copolymers 2 were determined by gel permeation chromatography (GPC) using polymethyl methacrylate calibration standards according to DIN 55672-1 using the following measurement conditions: Eluent: tetrahydrofuran (THF)

Operation temperature: 35°C

Column: column set consisting of six columns: SDV (50 x 8 mm), SDV LXL, SDV

LinL, SDV 100 A, SDV 1040 A and KF-800D (100 x 8 mm) (PSS Standards Service GmbH, Mainz, Germany), all with the size of 300 x 8 mm, if not noted differently, and an average particle size of10 pm

Flow rate: 1 mL/min

Injected volume: 100 pL

Instrument: Agilent 1100 series consisting of an autosampler (1260 series), pump, I nline-degaser, control module and column oven

Detection device: A refractive index detector from Agilent 1100 series and a UV detector from Agilent 1260 series.

The additive compositions including the boronic ester-modified polyalkyl (meth)acrylate copolymers 1 and the diol functionalized polyalkyl (meth)acrylate copolymers 2 were characterized with respect to their viscosity index (VI) to ASTM D 2270, kinematic viscosity at 40°C (KV40) and 100°C (KV100) to ASTM D445.

The lubricating oil compositions including the boronic ester-modified polyalkyl (meth)acrylate copolymers 1 and the diol functionalized polyalkyl (meth)acrylate copolymers 2 were characterized with respect to their kinematic viscosity at 40°C (KV40) and 100°C (KV100) to ASTM D445, and their the viscosity index (VI) to ASTM D 2270.

In the experimental, unless stated otherwise, the % are expressed by weight of monomers with regards to the total weight of the copolymers.

(1) Synthesis of the boronic ester-modified polyalkyl (meth)acrylate copolymers 1 (Example 1)

75.00 g of NB3043 were placed in a 4-necked glass flask equipped with a stirrer, temperature sensor and nitrogen pipe and heated to 106°C.

In a beaker, 3.85 g of a vinyl boronic acid ester were dissolved and homogenized in a mixture of 12.28 g of butyl methacrylate, 43.55 g of LMA and 14.14 g of SMA, and 0.44 g (0.6%, based on the total amount of monomers used) of tert-butylperoxy-2-ethylhexanoate were added.

This mixture was metered in with a metering pump over a period of 2 hours at 106°C while passing nitrogen over it.

After the end of the metering, the internal temperature was reduced to 95°C.

Subsequently, another 0.74 g (1.0%, based on the total amount of monomers used) of tert- butylperoxy-2-ethylhexanoate were added. The mixture was stirred for 150 minutes at 95°C and the reaction mixture was then cooled and filled. A 50% solution of the polymer in oil was obtained.

(2) Synthesis of the diol-containing polyalkyl (meth)acrylate copolymers 2 (Example 9) 60.0 g of butyl acetate were placed in a 4-neck glass flask equipped with a stirrer, temperature sensor and nitrogen pipe and heated to 106°C.

A mixture of 19.53 g of butyl methacrylate, 4.44 g of Diol (50% in ethyl acetate), 47.58 g of LMA and 19.43 g of SMA was homogenized and mixed with 0.36 g (0.4%, based on the total amount of monomers used) tert-butylperoxy-2-ethylhexanoate.

The resulting mixture was metered in with a metering pump over a period of 2 hours at 106°C while passing nitrogen over it.

After the end of the metering, the internal temperature was reduced to 95°C.

Subsequently, another 0.91 g (1.0%, based on the total amount of monomers used) of tert- butylperoxy-2-ethylhexanoate was added.

The mixture was then stirred for 150 minutes at 95°C and the reaction mixture is then cooled and filled.

The mixture obtained was mixed with 90 g of NB3043 and the butyl acetate was drawn off on a rotary evaporator at 100°C under vacuum. A 50% solution of the polymer in oil was obtained. The following Table 1 shows the monomers used to prepare copolymers 1 and copolymers 2. Copolymers 1 were prepared according to synthesis (1) described further above for the preparation of Example 1 ; copolymers 2 were prepared according to synthesis (2) described further above for the preparation of Example 3.

Table 1 : Monomer mixtures used to prepare copolymers 1 and copolymers 2.

*) diol 2 was added as a 50% solution in ethyl acetate

Table 2: Preparation details of copolymers 1 and copolymers 2.

Examples 1-8 are boronic ester-modified polyalkyl (meth)acrylate copolymers 1, examples 9-18 are diol-functionalized polyalkyl (meth)acrylate copolymers 2. Diol 1 was used as pure substance in the synthesis of the polymers, diol 2 was used as a 50% solution in ethyl acetate.

Table 3 shows the net compositions of the boronic ester-modified polyalkyl (meth)acrylate copolymers 1 and the diol-functionalized polyalkyl (meth)acrylate copolymers 2. The monomer components will add up to 100%. As the residual monomer content in the retrieved polymers is significantly below 1%, the net compositions of the polymers correspond to used monomer compositions.

Table 3: Net composition of copolymers 1 and copolymers 2.

The resulting polymers were characterized by their molecular weight and PDI. The results are shown in the following Table 4.

Table 4: Physical properties of copolymers 1 and copolymers 2.

The thickening efficiency of a VI improver is specified by its KV100 (kinematic viscosity at 100°C) at a given treat rate.

The single polymers were dissolved in a base oil and the retrieved solutions were characterized by their KV40, KV100 and VI. The results are shown in the following Tables 5 and 6.

Table 5: Viscometric data of solutions of copolymer 1 (boron ester) in Yubase 4+ as base oil.

Table 6: Viscometric data of solutions of copolymer 2 (diol) in Yubase 4+ as base oil.

To show the associative effect of the polymers, mixtures comprising equal parts of a copolymer 1 and a copolymer 2 in a base oil were prepared and, subsequently, KV40, KV100 and viscosity indices were measured.

The corresponding values are outlined in the following Table 7. Table 7: Viscometric data of solutions of 1 :1 mixtures of equal parts of copolymer 1 (boron ester) and copolymer 2 (diol) in Yubase 4+ as base oil.

Table 7 shows that synergistic effects were found for increasing the KV100 and VI of the polymer solutions containing the 1 :1 mixture of copolymer 1 and copolymer 2. The KV100 and VI of the 1 : 1 mixture of the polymers was increased versus the VI of the single polymer solutions (see Figures 1 and 2). The overall polymer concentration was the same in all solutions.

A higher KV100 at the same treat rate is considered to be beneficial for net treat cost and performance criteria.