The present invention is directed to boronic ester-modified polyalkyl(meth)acrylate polymers, their use to prepare thermo-associative polymers and a method fortheir preparation.

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 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 on 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.

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.

Description of the invention

A first embodiment of the present invention is directed to boronic ester-modified polyalkyl (meth)acrylate copolymers 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 copolymers 1.

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 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 numberaverage 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 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 acid 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 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 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 te/Y-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-te/Y-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 methacrylate).

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 (meth)acrylic 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 methacrylic esters of a linear C16-18 alcohol mixture (C16-18 alkyl methacrylate).

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 according to the present invention are characterized by their ability to form association-related thickeners.

A further embodiment of the present invention is therefore directed to the use of the boronic ester- modified polyalkyl (meth)acrylate copolymers 1 as outlined further above to prepare association- related thickeners.

A second embodiment of the present invention is directed to an additive composition, comprising:

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

(B) 40% to 60% by weight of 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)

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

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 base oil to be used in the additive composition comprises an oil of lubricating viscosity. Such oils include natural and synthetic oils, oil derived from hydrocracking, hydrogenation, and hydrofinishing, unrefined, refined, re-refined oils or mixtures thereof.

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. The kinematic viscosity at 100°C (KV100) of appropriate apolar base oils used to prepare an additive composition in accordance with the present invention is preferably in the range of 3 mm ² /s to 10 mm ² /s, more preferably in the range of 4 mm ² /s to 8 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 additive 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 1 029 029, WO 01/18156, WO 01/57166 and WO 2013/189951.

Especially for engine oil formulations are used base oils of API Group III.

The additive composition of the present invention comprises preferably 45% to 55% by weight, of the base oil (A) and 45% to 55% by weight, of the boronic ester-modified polyalkyl (meth)acrylate (B), based on the total weight of the additive composition.

A third embodiment of the present invention is directed to a mixture comprising equal amounts 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) (B) a diol-functionalized 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.

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

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.

A further third embodiment of the present invention is directed to the mixture as defined further above, wherein component (a4) of the boronic ester-modified polyalkyl (meth)acrylate copolymer 1 and component (b4) of the diol-functionalized polyalkyl (meth)acrylate copolymer 2 are present in equal amounts of 6 mol% to 8 mol%.

The weight-average molecular weight of the diol-functionalized polyalkyl (meth)acrylate copolymers 2 according to 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 numberaverage molecular weight of the polyalkyl(meth)acrylate polymers according to 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 according to 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 mixtures according to the present invention, comprising equal amounts of a polyalkyl (meth)acrylate copolymer 1 and a polyalkyl (meth)acrylate copolymer 2, are characterized by their ability to form association-related thickeners.

A further embodiment of the present invention is therefore directed to the use of the mixture comprising equal amounts of boronic ester-modified polyalkyl (meth)acrylate copolymers 1 and diol-functionalized polyalkyl (meth)acrylate copolymers 2 according to the present invention to prepare association-related thickeners.

A further embodiment of the present invention is directed to a method for preparing association- related thickeners, comprising the steps of:

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

(ii) preparing a diol-functionalized polyalkyl (meth)acrylate copolymer 2; and

(iii) mixing the boronic ester-modified polyalkyl (meth)acrylate copolymer 1 of step (i) with the diol-functionalized polyalkyl (meth)acrylate copolymer 2 to receive a thermo-associative thickener.

The boronic ester-modified polyalkyl (meth)acrylate copolymers 1 and the diol-functionalized polyalkyl (meth)acrylate copolymers 2 according to the present invention 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.

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

Figure 1 : Viscosity indices of polymer mixtures A to F (1 :1 copolymer 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 copolymer 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 further 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 te/Y-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 diol-functionalized polyalkyl (meth)acrylate copolymers 2 according to the present invention were characterized with respect to their molecular weight and PDI.

The weight-average molecular weights (Mw) of the boronic ester-modified polyalkyl (meth)acrylate copolymers 1 and the diol-functionalized polyalkyl (meth)acrylate copolymers 2 according to the present invention 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 according to the present invention 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.

(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 2 (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 prepared in accordance with the present invention. 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 the 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.