EP3898907A1

EP3898907A1 - Use of associative triblockcopolymers as viscosity index improvers

Info

Publication number: EP3898907A1
Application number: EP19809873.3A
Authority: EP
Inventors: Stefan Karl Maier; Nicolai KOLB; Michael Neusius; Denise BINGEL; Carmen ZAMPONI; Stefan Hilf; Katrin Schöller
Original assignee: Evonik Operations GmbH
Current assignee: Evonik Operations GmbH
Priority date: 2018-12-19
Filing date: 2019-12-04
Publication date: 2021-10-27
Anticipated expiration: 2039-12-04
Also published as: WO2020126494A1; EP3898907B1

Abstract

The present invention is directed to a process for improving the viscosity index of a lubricating oil composition by adding a triblock copolymer.

Description

Use of Associative Triblockcopolymers as Viscosity Index Improvers

Viscosity index (VI) is a commonly used method of measuring a fluid's change of viscosity in relation to temperature. The higher the VI, the smaller the relative change in viscosity with temperature. VI improvers (also known as viscosity modifiers) are additives that increase the viscosity of the fluid throughout its useful temperature range.

Viscosity modifiers are polymeric molecules that are sensitive to temperature. At elevated temperatures, the polymeric chain is better solvated by the solvent that leads to an increase in hydrodynamic radius of the polymer in solution. Higher hydrodynamic radius equals an increase in thickening power and therefore an increase in VI.

When linear polymers are dissolved in a solvent such as oil, each individual polymer strand is separated from its neighbours and in solution exists in isolation. The polymer is fully solvated by the oil, but still retains a coiled structured, with oil solvent molecules filling the empty spaces within the loosened coil. The polymer then adopts an ellipsoid or spherical form and occupies a discrete volume known as the hydrodynamic volume of the polymer coil (see Scheme 1 below).

Dissolving polymer in a solvent such as oil is accompanied by a large increase viscosity, and this is due to the presence of these larger scale hydrodynamic spheres. The size of the hydrodynamic sphere volume determines the magnitude of the viscosity increase. Polymers yielding a high hydrodynamic volume, either due to a high molecular weight or strong associating with the oil solvent, give a relatively higher increases in the viscosity of the solution.

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. At low temperatures, the long-chained fiberlike polymers are more tightly coiled and contribute relatively little to viscosity. The polymers uncoil at higher temperatures, occupying a larger hydrodynamic volume and increasingly boosting viscosity as shown in the following Scheme 1.

Scheme 1 : Polymer deformation and decomposition under stress Main disadvantage of the coiling/uncoiling mechanism is that the VI effect is strongly dependent on the molecular weight of the polymer. In addition, shear stability and thickening effect are linked to the molecular weight. Shear stability limits have always been a challenge for high VI formulations, but requirements are getting constantly more demanding. A more recent challenge are low viscosity formulations that do not leave much space for thickening polymer species. Therefore, a decoupling of VI effect, shear stability and thickening would be highly desirable. The use of a viscosity index improver in an oil of lubricating viscosity to impart desired low and high temperature viscometrics and other viscosity properties is well known. Some of the most commonly used polymers in lubricating oils include olefin copolymers (OCP), polyalkyl(meth)acrylates (PAMAs) and hydrogenated poly-(styrene-co-conjugated dienes).

The widely reported mechanism of how polymers improve VI is that polymers raise the viscosity of the fluid proportionately more at higher temperatures than at lower temperatures due to expansion of the polymer coil with increasing temperature. Not much is known in the art about other mechanisms that could be used to provide a VI effect.

Armes et al. (Angew. Chem. Int. Ed. 2017, 56, 1746-1750) describes a transition of specific diblock PAMA polymer aggregates from vesicles to worms. This transition occurs around 120°C and drastically increases the viscosity of the solutions which are conducted in dodecane as a lubricant model system. Armes does not disclose the use of triblock copolymers according to the present invention with a weight-average molecular weight of 3,000 to 30,000 g/mol for improving the viscosity index of lubricating oil compositions.

WO 2005/056739 describes the use of (meth)acrylate block copolymers as VI improvers. The block copolymers consist of oil soluble and insoluble blocks and mainly diblock and triblock structures are reported. In case of triblock copolymers, the oil-insoluble part is in the middle and the outer parts are oil-soluble. The working examples comprise at least 90 mol% of acrylic monomers and show number-average molecular weight between 20,000 and 80,000 g/mol. The use of triblock copolymers according to the present invention with a weight-average molecular weight of 3,000 to 30,000 g/mol for improving the viscosity index of lubricating oil compositions is not disclosed. Diblock polymers consisting of a hydrogenated diene and a styrene block (also described as HSDs) are commonly used in the lubricant field (Rudnick; Lubricant Additives: Chemistry and Applications, 3rd Edition, p.263-276). These polymers form micelles in solution which provide a huge thickening effect even at very low treat rates. These aggregates are known to lose their thickening power under shear which is used to reach low HTHS values with rather thick oils. Their permanent shear loss is quite low relative to their thickening power (see US4036910); if temperature is raised too much the aggregates break down and the thickening effect is lost. No exceptional VI effect is provided by these polymers (see US 5,209,862). The oil soluble part can also be polyisobutylene (see US 9,428,709). The use of triblock copolymers according to the present invention with a weight-average molecular weight of 3,000 to 30,000 g/mol for improving the viscosity index of lubricating oil compositions is not disclosed.

EP431706 and EP0298578 describe methacrylate blocks which are used to replace the insoluble styrene block or the oil soluble hydrogenated diene block.

WO 2014/105290 describes diblock polymers including PAMA blocks which are prepared in combination with polypropylene and micelle formation in PA04 of these polymers was investigated. The use of triblock copolymers according to the present invention with a weight-average molecular weight of 3,000 to 30,000 g/mol for improving the viscosity index of lubricating oil compositions is not disclosed.

Pure PAMA diblocks with a dispersant block are described in WO2010/053890 and the use of these polymers as emulsifiers in engine oils was investigated. The use of triblock copolymers according to the present invention with a weight-average molecular weight of 3,000 to 30,000 g/mol for improving the viscosity index of lubricating oil compositions is not disclosed.

It was now surprisingly found that triblock copolymers comprising at least one oil-soluble part and at least one oil-insoluble part and having a relatively low molecular weight show an associative mechanism at higher temperatures and can be used as viscosity index improvers in lubricating oil compositions.

Associative mechanism in this connection means that relatively small molecules self-organize at elevated temperature in order to form bigger structures with an increased hydrodynamic radius. In this way, thickening contribution at low temperatures can be minimized. As the small molecules are too small to be destroyed by mechanical shear, the bigger assemblies could reform after destruction by shear forces.

One embodiment of the present invention is therefore directed to a process for improving the viscosity index of lubricating oil compositions by adding a triblock copolymer of general formula (I) A-B-A (I), wherein each A denotes an oil-insoluble residue and B denotes an oil-soluble residue, characterized in that the weight-average molecular weight of the triblock copolymer is in the range of 3,000 to 30,000 g/mol, preferably 3,500 to 25,000 g/mol, more preferably 4,000 to 20,000 g/mol. The weight-average molecular weight is determined by gel permeation chromatography against polymeric standards. Depending on the nature and composition of the copolymer, either styrene or polyalkylmethacrylates (PMMA) are used as corresponding standard. The triblock copolymers can be derived from different polymer classes as long as the outer segments A are polar and oil-insoluble and the inner segment B is apolar and oil-soluble.

Each segment A can be selected from the group consisting of polyesters, polyalkylene glycols, polystyrenes, polyalkyl(meth)acrylates or mixtures thereof. Preferred segments A are selected from the group consisting of polyesters, polyalkylene glycols, polyalkyl(meth)acrylates or mixtures thereof.

Suitable polyalkylene glycols are selected from the group consisting of polyethylene glycol (also known as polyethylene oxide), polypropylene glycol and mixtures thereof. They are derived from ethylene oxide or propylene oxide.

Polyethylene glycol is produced by the interaction of ethylene oxide with ethylene glycol or ethylene glycol oligomers. The reaction is catalyzed by acidic or basic catalysts. Usually, the mechanism is a ring-opening polymerization which is catalyzed by an alcoholate. Polymer chain length depends on the ratio of reactants. Depending on the catalyst type, the mechanism of polymerization can be cationic or anionic. The anionic mechanism is preferable because PEG with a low polydispersity can be obtained. Polyethylene oxide, or high-molecular weight polyethylene glycol, is synthesized by suspension polymerization. It is necessary to hold the growing polymer chain in solution in the course of the polycondensation process. The reaction is catalyzed by magnesium-, aluminium-, or calcium-organoelement compounds. To prevent coagulation of polymer chains from solution, chelating additives such as dimethylglyoxime are used.

Alkaline catalysts such as sodium hydroxide (NaOH), potassium hydroxide (KOH), or sodium carbonate (Na₂CC>3) are used to prepare low-molecular-weight polyethylene glycol.

Polypropylene glycol is produced by ring-opening polymerization of propylene oxide. The initiator is an alcohol and the catalyst a base, usually potassium hydroxide. When the initiator is ethylene glycol or water the polymer is linear. With a multifunctional initiator like glycerine, pentaerythritol or sorbitol the polymer branches out. Polystyrene is prepared by the polymerization of styrene monomers. Suitable styrene monomers can be selected from the group consisting of styrene and substituted styrenes having an alkyl substituent in the side chain, such as, for example, alpha-methylstyrene and alpha-ethylstyrene, or substituted styrenes having an alkyl substituent on the ring, such as vinyltoluene and p- methylstyrene. In accordance with the present invention, unsubstituted styrene is preferred.

Suitable polyalkyl(meth)acrylates to be used as segments A have to be oil-insoluble. They can be prepared from monomer mixtures, comprising:

(A1 ) 80 to 100% by weight, preferably 85 to 100% by weight, more preferably 90 to 100% by weight, of monomers being selected from the group consisting of Ci-₄-alkyl

(meth)acrylates, styrene, benzyl (meth)acrylate and mixtures thereof, preferred Ci-₄-alkyl (meth)acrylates; and

(A2) 0 to 20% by weight, preferably 0 to 15% by weight, more preferably 0 to 10% by weight, of

C5-3₂-alkyl (meth)acrylates, preferably Cio-i6-alkyl (meth)acrylates.

The content of each component (A1 ) and (A2) is based on the total composition of segments A.

In a particular embodiment, the proportions of components (A1 ) and (A2) add up to 100% by weight.

The term "(meth)acrylate" refers to both, esters of acrylic acid and esters of methacrylic acid. Methacrylates are preferably used in accordance with the present invention.

The Ci-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 "C-i-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 Ci-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 Ci-₄-alkyl (meth)acrylates are methyl (meth)acrylate and n-butyl (meth)acrylate; methyl methacrylate and n-butyl methacrylate are especially preferred.

The C5-3₂-alkyl (meth)acrylates for use in accordance with the invention are esters of (meth)acrylic acid and straight chain or branched alcohols having 5 to 32 carbon atoms. The term "Cs-3₂-alkyl (meth)acrylates" encompasses individual (meth)acrylic esters with an alcohol of a particular length, and likewise mixtures of methacrylic esters with alcohols of different lengths.

Suitable Cs-3₂-alkyl (meth)acrylates include, for example, pentyl (meth)acrylate, hexyl

(meth)acrylate, heptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, 2 tert-butylheptyl (meth)acrylate, octyl (meth)acrylate, 3-isopropylheptyl (meth)acrylate, nonyl (meth)acrylate, 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, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, 2-methylhexadecyl (meth)acrylate, 2- dodecylhexadecyl (meth)acrylate, heptadecyl (meth)acrylate, 5-isopropylheptadecyl (meth)acrylate, 4-ferf-butyloctadecyl (meth)acrylate, 5-ethyloctadecyl (meth)acrylate, 3-isopropyloctadecyl (meth)acrylate, octadecyl (meth)acrylate, 2-decyloctadecyl (meth)acrylate, 2-tetrad ecyloctadecy I (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-tetradecyl-octadecyl (meth)acrylate, 1 ,2- tetrad ecyl-octadecy I (meth)acrylate and 2-hexadecyl-eicosyl (meth)acrylate.

The Cio-16-alkyl (meth)acrylates for use in accordance with the invention are esters of (meth)acrylic acid and straight chain or branched alcohols having 10 to 16 carbon atoms. The term "Cio-i6-alkyl (meth)acrylates" encompasses individual (meth)acrylic esters with an alcohol of a particular length, and likewise mixtures of methacrylic esters with alcohols of different lengths.

Suitable Cio-i6-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, pentadecyl (meth)acrylate and hexadecyl (meth)acrylate.

Amongst these, particularly preferred are methacrylic esters of a linear Ci₂-i₄-alcohol mixture (Ci₂-i₄-alkyl-methacrylate).

Segment B can be selected from the group consisting of polyolefins, polyalkyl(meth)acrylates or mixtures thereof.

In the context of the present invention, polyolefins are understood to mean polymers which are based on alkenes and/or polyenes as monomers. The repeating units of the polyolefins consist exclusively of the elements carbon and hydrogen and do not include any aromatic structures. The polyolefins may contain any desired proportion of double bonds, but they are preferably mainly hydrogenated.

The polyolefin residue of segment B can be selected from the group consisting of polyethylene, polypropylene, polyisobutylene, poly-n-butene, polybutadiene, polyisoprene, polyfarnesene and mixtures thereof. One preferred olefin is derived from hydrogenated polybutadiene (hPBD). In order to initiate the polyester polymerization on both sides, the hPBD needs to be OH-terminated at both ends of the molecule. The hydrogenated polybutadiene is preferably characterized by a number-average molecular weight M_n in the range of 1 ,000 to 4,000 g/mol, preferably in the range of 1 ,500 to 3,500 g/mol, more preferably in the range of 1 ,500 to 2,500, determined by gel permeation chromatography to DIN 55672-1 in tetrahydrofuran as eluent and polystyrene for calibration.

Suitable polyalkyl(meth)acrylates to be used as segment B have to be oil-soluble. They can be prepared from monomer mixtures, comprising:

(B1 ) 80 to 100% by weight of, preferably 85 to 100% by weight, more preferably 90 to 100% by weight, monomers being selected from the group consisting of Cs-3₂-alkyl (meth)acrylates, preferably Cio-i6-alkyl (meth)acrylates; and

(B2) 0 to 20% by weight, preferably 0 to 15% by weight, more preferably 0 to 10% by weight, of monomers being selected from the group consisting of Ci-₄-alkyl (meth)acrylates, styrene, benzyl (meth)acrylate and mixtures thereof, preferably Ci-₄-alkyl (meth)acrylates.

The content of each component (B1 ) and (B2) is based on the total composition of segments B.

In a particular embodiment, the proportions of components (B1 ) and (B2) add up to 100% by weight.

The C5-3₂-alkyl (meth)acrylates, Cio-i6-alkyl (meth)acrylates, Ci-₄-alkyl (meth)acrylates and styrenes for use in accordance with the invention are as defined further above.

The triblock copolymers of general formula (I) consist preferably of:

(a) 30 to 85% by weight, preferably 45 to 85% by weight, of segments A and

(b) 15 to 70% by weight, preferably 15 to 55% by weight, of segment B.

The content of each component (a) and (b) is based on the total composition of the triblock copolymer.

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

The amount of the oil-soluble segment B is dependent on the nature of B. Polyolefins, for example, have different solubilities in oil than polyalkyl(meth)acrylates. This leads to different ratios of A:B as outlined further below.

The triblock copolymers of general formula (I) consist preferably of:

(a) 55 to 85% by weight of segments A and

(b) 15 to 45% by weight of segment B which is a polyolefin,

based on the total composition of the triblock copolymer. The triblock copolymers of general formula (I) consist preferably of:

(a) 45 to 70% by weight of segments A and

(b) 30 to 55% by weight of segment B which is a polyalkyl(meth)acrylate,

based on the total composition of the triblock copolymer.

Another embodiment of the present invention is directed to a process for improving the viscosity index of lubricating oil compositions by adding a triblock copolymer of general formula (la)

A-B-A (la),

wherein each segment A denotes a polyester residue prepared from at least two different monomers 1 and 2, where monomer 1 is selected from a lactone and monomer 2 is selected from the group consisting of lactide and glycolide, and the two monomers are block-wise or randomly distributed over each polyester residue A, and the segment B is derived from a polyolefin residue.

Examples of suitable lactones are especially C3 lactones such as beta-propiolactone, C4 lactones such as beta-butyrolactone or gamma-butyrolactone, Cs lactones such as 4-hydroxy-3-pentenoic acid-gamma-lactone, alpha-methylene-gamma-butyrolactone, gamma-methylene-gamma- butyrolactone, 3-methyl-2(5H)-furanone, gamma-valerolactone, delta-valerolactone, C6 lactones such as delta-hexalactone, epsilon-caprolactone or gamma-hexalactone, or further lactones such as 5-butyl-4-methyldihydro-2(3H)-furanone, delta-octanolactone, gamma-phenyl-epsilon-capro- lactone, oxacyclododecan-2-one, oxacyclotridecan-2-one, pentadecanolide, 16-hexadecanolide, gamma-undecalactone, delta-undecalactone, gamma-methylene-gamma-butyrolactone and mixtures thereof.

Lactides in the context of the present invention are understood to mean cyclic esters of lactic acid which can occur in three isomers: (S,S)-3,6-dimethyl-1 ,4-dioxane-2,5-dione (CAS No. 451 1-42-6), (R,R)-3,6-dimethyl-1 ,4-dioxane-2,5-dione (CAS No. 25038-75-9) and (meso)-3,6-dimethyl-1 ,4- dioxane-2,5-dione (CAS No. 13076-19-2). No isomeric form is particularly preferred here.

Preferably, each polyester residue A is prepared from epsilon-caprolactone as monomer 1 and lactide as monomer 2 and monomers 1 and 2 are randomly distributed over each polyester residue

A.

The ratio of epsilon-caprolactone to lactide is in the range of 12: 1 to 1 :3, preferably in the range of 6: 1 to 1 :2. The resulting triblock copolymers of general formula (la) are characterized in that the polyester residue A can be the same or different and has the general formula (II)

wherein

R¹ is hydrogen or Ch , preferably Ch ,

a is an integer of 3 to 50,

b is an integer of 5 to 60, and

n is an integer of 3 or 4, preferably 4, and

the a and b moieties may be randomly bonded or block-bonded and are preferably randomly bonded.

Examples of suitable polyolefin residues are selected from the group consisting of polyethylene, polypropylene, polyisobutylene, poly-n-butene, polybutadiene, polyisoprene, polyfarnesene and mixtures thereof and is preferably derived from hydrogenated polybutadiene (hPBD).

The hydrogenated polybutadiene residue of segment B consists preferably of:

(a) 60 to 100% by weight, preferably 65 to 100%, more preferably 85 to 100% of monomer units (

(b) 0 to 40% by weight, preferably 0 to 35% by weight, more preferably 0 to 15% by weight of monomer units (IVb) based on the total weight of the segment B and with the proviso that the monomer units (IVa) and (IVb) may be arranged in blocks or in random distribution.

The degree of hydrogenation of the hydrogenated polybutadiene residue of segment B is at least 80%, preferably at least 90%. In order to obtain such a block copolymer, monomer 1 and monomer 2 are mixed with the polyolefin of segment B as starter and the ring-opening polymerization is conducted at elevated temperatures in pure substance using small amounts of a catalyst.

The catalyst to be used in the present invention can be selected from the group consisting of tin(ll)- ethylhexanoate, dibutyltin dilaurate, 1 , 8-diazabicyclo [5.4.0] undec-7-ene, 1 , 5-diazabicyclo [4.3.0] non-5- ene, 1 , 4-diazabicyclo [2.2.2] octane, 1 , 5,7-triazabicyclo [4.4.0] dec-5-ene, titanium tetramethanolate, titanium tetraethanloate, titanium tetrapropylate, titanium tetraisopropylate, titanium tetra-n-butylate, titanium tetra-ferf-butylate, titanium tetraphenylate, titanium

oxidacetylacetonate and titanium acetylacetonate. Preferred catalysts are selected from the group consisting of titanium tetramethanolate, titanium tetraethanolate, titanium tetrapropylate, titanium tetra-/so-propylate, titanium tetra-n-butylate, titanium tetra-ferf-butylate, titanium tetraphenylate, titanium oxidacetylacetonate and titanium acetylacetonate.

Preferred triblock copolymers of general formula (la) to be used in accordance with the present invention comprise:

(a) 55 to 85% by weight, of polyester residues A; and

(b) 15 to 45% by weight, of hydrogenated polybutadiene residues B.

The content of each component (a) and (b) is based on the total composition of the block copolymer.

They are further characterized by a weight-average molecular weight M_w is in the range of 3,000 to 30,000 g/mol, determined by gel permeation chromatography to DIN 55672-1 in tetrahydrofuran as eluent and polystyrene for calibration.

The polydispersity index PDI of the block polymers according to the present invention is in the range of 1 to 5.

The hydrogenated polybutadienes usable with preference in the context of the present invention are commercially available.

Another embodiment of the present invention is directed to a process for improving the viscosity index of lubricating oil compositions by adding a triblock copolymer of general formula (lb),

A-B-A (lb),

wherein each segment A is prepared from a monomer mixture comprising:

(A1 ) 80 to 100% by weight, preferably 85 to 100% by weight, more preferably 90 to 100% by weight, of monomers being selected from the group consisting of Ci-₄-alkyl (meth)acrylates, styrene, benzyl (meth)acrylate and mixtures thereof, preferably C-i-₄-alkyl (meth)acrylates; and

C5-3₂-alkyl (meth)acrylates, preferably Cio-i6-alkyl (meth)acrylates; and segment B is prepared from a monomer mixture comprising:

(B1 ) 80 to 100% by weight, preferably 85 to 100% by weight, more preferably 90 to 100% by weight, of monomers being selected from the group consisting of Cs-3₂-alkyl

(meth)acrylates, preferably Cio-i6-alkyl (meth)acrylates; and

Preferred triblock copolymers of general formula (lb) to be used in accordance with the present invention comprise:

(a) 45 to 70% by weight, of PAMA residues A; and

(b) 30 to 55% by weight, of PAMA residues B.

The resulting polymers are characterized by a number-average molecular weight M_n in the range of 2,000 to 8,000 g/mol, determined by gel permeation chromatography to DIN 55672-1 in tetrahydrofuran as eluent and PMMA for calibration.

They are further characterized by a weight-average molecular weight M_w is in the range of 3,000 to 30,000 g/mol, determined by gel permeation chromatography to DIN 55672-1 in tetrahydrofuran as eluent and PMMA for calibration.

Triblock polymers of general formula (lb) can be generally prepared by any living or controlled polymerization technique. To synthesize copolymers with segments of different polarity, the block copolymers of the present invention are preferably prepared by controlled radical polymerization. These processes generally combine a typical free-radical initiator with a free radical stabilizing compound to control the polymerization process and produce polymers of a specific composition, and having a controlled molecular weight and narrow molecular weight range. The free-radical initiators used may be those known in the art, including, but not limited to peroxy compounds, peroxides, hydroperoxides and azo compounds which decompose thermally to provide free radicals.

Examples of controlled radical polymerization techniques are generally known the person skilled in the art and include, but are not limited to, atom transfer radical polymerization (ATRP), reversible addition fragmentation chain transfer polymerization (RAFT), nitroxide-mediated polymerization (NMP), boron-mediated polymerization, and catalytic chain transfer polymerization (CCT).

Descriptions and comparisons of these types of polymerizations are described in the ACS

Symposium Series 768, entitled "Controlled/Living Radical Polymerization: Process in ATRP, NMP, and RAFT", edited by Krystof Matyjaszewski, American Chemical Society, Washington D.C., 2000.

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

(A) 2 to 20% by weight, preferably 5 to 15% by weight, of a triblock copolymer of general formula (I)

A-B-A (I),

wherein each A denotes an oil-insoluble residue and B denotes an oil-soluble residue, characterized in that the weight-average molecular weight of the triblock copolymer is in the range of 3,000 to 30,000 g/mol, determined by gel permeation chromatography; and

(B) 80 to 98% by weight, preferably 85 to 95% by weight, of a base oil.

The content of each component (A) and (B) is based on the total weight of the additive

composition.

The lubricating oil composition is characterized by a VI of at least 300, preferably at least 400, determined to ASTM D2270, and a kinematic viscosity at 40°C of 4 to 30 mm²/s, preferably 5 to 25 mm²/s, determined to ASTM D445.

The base oil to be used in the additive composition comprises an oil of lubricating viscosity. Such base oils are 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 201 1 ). 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 40°C (KV40) of appropriate apolar base oils used to prepare an additive composition or lubricating composition in accordance with the present invention is preferably in the range of 1 mm²/s to 25 mm²/s, more preferably in the range of 2 mm²/s to 20 mm²/s, according to ASTM D445.

Further base oils which can be used in accordance with the present invention are Group ll-lll 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 00/081 15, WO 99/41332, EP 1 029 029, WO 01/18156, WO 01/57166 and WO 2013/189951.

A-B-A (I),

wherein each A denotes an oil-insoluble residue and B denotes an oil-soluble residue, characterized in that the weight-average molecular weight of the triblock copolymer is in the range of 3,000 to 30,000 g/mol, determined by gel permeation chromatography; (B) 90 to 98% by weight of a base oil selected from the group consisting of API Group II, II, III,

IV, V and mixtures thereof.

The content of each component (A) and (B) is based on the total weight of the lubricating oil composition.

The lubricating oil composition is further characterized in that the base oil (B) comprises:

(B1 ) 0 to 100% by weight, preferably 50 to 100% by weight, of a Group V base oil; and

(B2) 0 to 100 % by weight, preferably 0 to 50% by weight, of a base oil selected from the group consisting of API Group I, II, III, IV oils and mixtures thereof.

The content of each component (B1 ) and (B2) is based on the total weight of the base oil (B).

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

Triblock polymers with insoluble outer parts are known in the art for their ability to aggregate in special micelles. These micelles are described as flower-like as both ends of the polymer are shielded from the solvent in the inner part of the micelle. This is illustrated by the following Scheme 2.

A special feature of these micelles is that the polymer ends can also be part of two different micelles, which is called bridging. The thermodynamic balance in between bridging and nonbridging polymer chains is very complex.

Scheme 2: Schematic illustration of the expected association pattern of the investigated

triblock polymers in solution. oil insoluble ₀il soluble

very polar apolar

When dissolved in apolar fluids such as mineral oils, the triblock polymers according to the present invention show a very pronounced thickening behavior which is not typical for polymers of such low molecular weight indicating an associative thickening mechanism. Another indicator for this hypothesis is that thickening power increases strongly with higher polymer concentration.

Surprisingly, this thickening effect becomes even stronger at elevated temperatures, completely opposite to what was expected. Using this effect oils with very exceptional temperature/viscosity behavior can be formulated. Formulations with extremely high Vis can be formulated in this way. Even behavior that cannot be described by the VI anymore due to lack of definition can be generated in this way. For example, it is possible to generate oil formulations with a higher viscosity at 100°C than at 40°C.

As the effect is based on self-organization of low-molecular weight polymers the system is less susceptible to destruction by mechanical shear. In fact no permanent shear loss was observed in standard industry tests.

The described polymer solutions are usually clear and flowable over the whole relevant temperature range. Neither precipitation at low temperatures nor at high temperatures is observed. For a few polymer compositions precipitation at elevated temperatures can be observed dependent on the solvent. This may be an indicator that the general mechanism is based on reduced miscibility at elevated temperatures which can result in a miscibility gap for some solvent/polymer combinations. By application of the triblock copolymers of the present invention in lubricating oil compositions, formulations with exceptional Vis can be generated.

Another embodiment of the present invention is directed to the use of block copolymers as outlined further above to provide a positive VI effect in lubricating oil compositions, characterized in that the lubricating oil compositions have a VI of 300 or greater, preferably of 400 or greater, determined to ASTM D2270.

Another embodiment of the present invention is directed to a method for improving the viscosity index (VI) of a lubricating oil composition, the method comprising the step of adding a block copolymer of general formula (I) to a lubricating oil composition.

A further object of the present invention is directed to the use of the above-described lubricating oil composition as hydraulic fluid, transmission fluid, gear oil or motor oil.

The invention has been further illustrated by the following non-limiting examples.

Experimental Part Abbreviations

BnMA benzyl methacrylate

Chevron 100R Group II base oil from Chevron with a KV100 of 4.1 cSt

CP cloud point

DDM 1-dodecyl mercaptane

EBIB ethyl alpha-bromoisobutyrate (monofunctional)

e-CL epsilon-caprolactone

2fBiB ethylene bis(2-bromoisobutyrate) (bifunctional)

HITEC521^® hydraulic Dl package from Afton

hPBD hydrogenated polybutadiene

IR8080 lrgalube^®8080, ashless hydraulic Dl package from BASF

KRL Kegelrollenlager (tapered roller bearing)

KV kinematic viscosity measured according to ASTM D445

KV-20 kinematic viscosity @-20°C, measured according to ASTM D445

KV40 kinematic viscosity @40°C, measured according to ASTM D445

KV100 kinematic viscosity @100°C, measured according to ASTM D445

LCST lower critical solution temperature

LMA lauryl methacrylate, 73% C12, 27% C14, all linear

MMA methyl methacrylate

Mn number-average molecular weight

Mw weight-average molecular weight

NB3020 Nexbase^® 3020, Group III base oil from Neste with a KV100 of 2.2 cSt

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

NB3060 Nexbase^® 3060, Group III base oil from Neste with a KV100 of 5.9 cSt NS3^® naphthenic base oil from Nynas with a KV100 of 1.1 cSt

NS8^® naphthenic base oil from Nynas with a KV100 of 2.1 cSt

PDI polydispersity index

PMDETA pentamethyldiethylenetriamine

PP pour point

RC9300^® ashless hydraulic Dl package from Rheinchemie

Tg glass transition temperature

Tm melting point

VI viscosity index

Test methods

The triblock copolymers according to the present invention and the comparative examples were characterized with respect to their molecular weight, PDI and thermal properties (differential scanning calorimetry - DSC).

The number-average molecular weights M_n and the weight-average molecular weights M_w were determined by gel permeation chromatography (GPC) to DIN 55672-1 in tetrahydrofuran as eluent and polymeric standards like polystyrene or polymethylmethacrylate (PMMA) for calibration.

Determining the thermal properties (T_g and T_m) of the block copolymers employed in the present invention was carried out by differential scanning calorimetry (DSC) according to DSC method DIN 1 1357-1.

The block copolymers and the statistical polyester-copolymer prepared have hydroxyl groups as end groups. The concentration of OH groups is determined titrimetrically in mg KOH/g polymer according to DIN 53240-2.

The additive compositions including the block copolymers according to the present invention and comparative examples were characterized with respect to their viscosity index (VI) to ASTM D2270 and their kinematic viscosity at 40°C (KV40) and 100°C (KV100) to ASTM D445.

The lubricating oil compositions including the block copolymers according to the present invention and comparative examples were characterized with respect to kinematic viscosity at -20°C (KV-20), 40°C (KV₄o) and 100°C (KV100) to ASTM D445, their viscosity index (VI) to ASTM D2270, their cloud point to ASTM D5771 and their pour point to ASTM D5950.

KRL measurements to determine the shear loss were also done to CEC L-45-A-99 (20 hours, 60°C and 5kN).

In connection with the evaluation of hydraulic formulations, foam tests to ASTM D892 were run, air release was determined to DIN ISO 9120.

The Brookfield viscosity was determined to DIN 51398. OH-functionalized polyolefins

The following Table 1 lists the polyolefins which were used in accordance with the present invention to produce the working examples and comparative examples.

Table 1 : Dihydroxyl-functionalized polybutadienes used according to the present invention.

As shown in Table 1 , the degree of branching is higher in the material from Nippon Soda. Synthesis 1: General synthesis of the polyolefin-based block copolymers

The in Table 2 mentioned amounts of OH-functional polyolefin, epsilon-caprolactone and lactide were mixed in a 1 L multi-neck flask with reflux condenser and continuous nitrogen flow.

Afterwards, 0.75 g (0.1 % by weight based on the total amount of 750 g starting materials) titanium tetra-n-butanolate (TYTAN TNBT^®, commercially available from Borica Company, Ltd.) were added and the resulting mixture heated to 160°C until complete monomer conversion was determined by GPC. After a polymerization degree of 99.5% or higher was achieved, the melt was transferred to a steel drum and stored under a nitrogen atmosphere at room temperature.

Synthesis 2: Synthesis of a block copolymer based on polyalkyl methacrylates by ATRP

polymerization

1.36 g of pentamethyldiethylenetriamine (PMDETA), 0.56 g CuBr and 55.0 g of lauryl methacrylate (LMA) were dissolved in 98.8 g of Chevron 100R oil. The solution was purged with nitrogen for 30 minutes and heated to 65°C. After addition of 2.83 g of ethylene bis(2-bromoisobutyrate) the reaction mixture was heated to 95°C. 45.0 g of methyl methacrylate were added after 3 h and another 3 h later 0.80 g DDM were added. The mixture was stirred for 2 h, cooled to room temperature and purified by pressure filtration. After filtration, a clear and slightly yellow colored highly viscous liquid was obtained which was applied without further purification.

Synthesis 3: Synthesis of a random polymer based on polyalkyl methacrylates by RAFT

polymerization

27.5 g methyl methacrylate and 3.13 g 2-cyanobutanyl-2-yl 3,5-dimethyl-1 H-pyrazole-1- carbodithioate were dissolved in 98.8 g of toluene and purged with nitrogen for 30 minutes. The mixture was heated to 80°C and 0.48 g 2,2'-azobis(2-methylbutyronitrile) was added. After 2 h,

0.48 g 2,2'-azobis(2-methylbutyronitrile) dissolved in 45.0 g lauryl methacrylate was added and after stirring for another 2 h 0.48 g 2,2'-azobis(2-methylbutyronitrile) dissolved in 27.5 g methyl methacrylate was added. The mixture was stirred overnight. The toluene was removed by vacuum distillation and replaced by 98.8 g of Nexbase 3020. The highly viscous yellow liquid was used without further purification.

Synthesis 4: Synthesis of a random polymer based on polyalkyl methacrylate

(comparative example)

A round-bottom flask equipped with a glass stir rod, nitrogen inlet, reflux condenser and thermometer was charged with 94.3 g of Chevron 100R oil, 50.4 g lauryl methacrylate, 49.6 g methyl methacrylate and 3.75 g DDM. The mixture was heated up to 1 10°C while stirring and nitrogen bubbling for inertion. Then 3-stage feed for 3 hours feed of a mixture consisting of 0.25 g tert-butyl-perhexanoate and 5.7 g Chevron 100R oil was started. After the feed end the mixture was stirred for an additional 60 minutes. The colorless viscous liquid was used without further purification.

Synthesis 5: Synthesis of a random polymer based on hPBD and Polyester

(comparative example)

512 g of NISSO GI 1000 (0.29 mol) were melted together with 122 g neopentyl glycol (1.17 mol) and 194 g adipic acid (1 .32 mol) in a 1 L flask with a distillation attachment under nitrogen. At a temperature of 240°C, the majority of the water of the reaction was formed and distilled off within about four to six hours. Subsequently, 1 g (0.1 wt%) of TYTAN TNBT^® was added and the pressure in the apparatus was lowered stepwise down to 10 mbar. The reaction was ended when no acid end groups are present any longer (acid number < 1 mgKOH/g Polymer) and a concentration of hydroxyl end groups of 10 mg KOH/g Polymer had been attained. The co-polyester had a glass transition temperature of -47°C and an average molecular weight of 8.6 kDa with a PDI of 3.3.

Table 2 shows the reaction mixtures used to prepare examples 1-14 by following the protocol as described in Synthesis 1. The monomer components do in each case add up to 750 g. As initiator was always used titanium tetra-n-butanolate (TYTAN TNBT^®, commercially available by Borica Company, Ltd.) in an amount of 0.75 g (0.1 % by weight, based on the total amount of the monomers used).

Comparative example 15 is a random copolymer based on hPBD and polyester and was prepared by following the protocol as described in Synthesis 5.

Table 2: Reaction mixtures used to prepare examples 1-15.

comparative example

The net compositions of the resulting block copolymers 1-15 are shown in the following Table 3a whereas the characteristic weight-average molecular weights M_w, number-average molecular weights M_n as well as polydispersity indices (PDI), glass transition temperatures and melting points are summarized in Table 3b.

Table 3a: Net compositions of the block copolymers 1-15 prepared according to the present invention.

** comparative example Table 3b: Characteristics of block copolymers 1-15 prepared according to the present invention.

** comparative example

Examples 1-12 are polyolefin-based triblock copolymers A-B-A according to general formula (la). These block copolymers are all non-crystalline and show glass transition temperatures of below 0°C. It can be seen that their weight-average molecular weights are within the claimed range of 3,000 to 30,000 g/mol.

Examples 13 and 14 are comparative examples as their polyolefin content is outside the claimed range.

Example 15 is a comparative example as the polymer has a random distribution and is therefore not an A-B-A triblock copolymer. Table 4 shows the reaction mixtures used to prepare examples 16-20 which are PAMA-based triblock copolymers A-B-A according to general formula (lb) and comparative examples. The reaction was carried out by using Chevron 100R as base oil.

Table 4. Reaction mixtures used to prepare examples 18-22.

comparative example

*** toluene was used for the synthesis instead of 100R oil

Example 16 is a comparative example because the content of segments A (MMA) is lower than the ranges described in the present invention.

Examples 17 and 18 are in accordance with the present invention and were prepared by following the protocol as described in Synthesis 2.

Example 19 is a comparative example as it is an A-B diblock copolymer. As monofunctional initiator was used ethyl-alpha-bromoisobutyrate.

Example 20 is a comparative example as it is an inverse triblock copolymer B-A-B; i.e. the oil- soluble segment B forms the outer parts and the oil-insoluble segment A forms the inner part. As the inner block A was synthesized first, the synthesis was performed in toluene because the A- block alone was insoluble in oil. After polymerization, the whole amount of toluene was exchanged by the same amount of Chevron 100R oil.

The net compositions of the resulting block copolymers 16-20 are shown in the following Table 5 together with their characteristic weight-average molecular weights M_w, number-average molecular weights M_n as well as polydispersity indices. Table 5: Net compositions and characteristics of block copolymers 16-20 prepared

according to the present invention.

It can be seen that their weight-average molecular weights are within the claimed range of 3,000 to 30,000 g/mol.

Table 6 shows the reaction mixtures used to prepare examples 21-24 which are PAMA-based block copolymers A-B-A according to general formula (lb). They were prepared by following the protocol of Synthesis 3. Table 6: Reaction mixtures used to prepare examples 21-24.

Examples 21-24 are all in accordance with the present invention. The synthesis was performed in toluene as solvent. After polymerization, the whole amount of toluene was exchanged by the same amount of NB3020.

As Examples 21-24 are all prepared by RAFT polymerization, the different blocks A and B are built up consecutively. That means that for each block A half of the corresponding monomer mixture is added to the reaction mixture. Regarding the initiator, for each block A and B is added one third of the whole amount.

The net compositions of the resulting block copolymers 21-24 are shown in the following Table 7 together with their characteristic weight-average molecular weights M_w, number-average molecular weights M_n as well as polydispersity indices.

Table 7: Net compositions and characteristics of block copolymers 21-24 prepared

according to the present invention.

Evaluation of the properties of solutions comprising inventive triblock copolymers

To demonstrate the thickening effect of triblock copolymers according to the present invention on the viscosity of base oils, solutions with different polymer content were prepared and corresponding KV40 and KV100 values as well as viscosity indices were measured. The results are shown in the following Table 8. Table 8: Thickening effect of triblock copolymers.

** comparative example

*** not soluble

n.d. = not defined

Table 8 shows that the triblock polymers according to the present invention provide a very strong VI lift in lubricating oil compositions. This origin of the effect is the high thickening power at elevated temperatures. Contrary to standard VI improver technology, this effect can be achieved at comparably low viscosities at 40°C which is highly desirable for modern low viscosity lubricants. Another important factor compared to the existing VI improver technology is that the effect is achieved with low molecular weight polymers which are known to be more resistant to mechanical shear forces. Adjustment of the polymer parameters allows fine-tuning of the desired thickening power at 40°C.

Such an effect is not known for previously reported triblock systems in the patent literature as they do not match the requirements for geometry and polarity of the claimed polymers, which is required for aggregates that show this unusual effect.

Comparative example 16 demonstrates how the effect vanishes when the apolar A segments become too short.

Also, different block structures such as A-B (comparative example 19), B-A-B (comparative example 20) or a multiblock structure (comparative example 15) do not provide the effect.

The size of the aggregates was investigated by dynamic light scattering (DLS). The data were determined to DIN ISO 13321 by using a Zetasizer^® Nano ZS (Malvern Instruments GmbH). The pore size of the nozzle filter was 0.45 pm.

The samples were first measured at 40°C, then heated to 80°C and finally cooled down to 40°C again. The samples were kept at the temperature for 30 minutes prior to the measurement.

The values determined for the polymers in accordance with the present invention are summarized in Table 9.

Table 9: DLS measurements of polymer solutions in NS8.

All samples were filtered prior to the measurements to remove dust and impurities. Polymer concentrations are given in % by weight.

What can be concluded is that rather big polymer aggregates exist in solution and that the aggregation process is reversible which is in line with the viscometric results. Further investigation of the particles was done by transmission electron microscopy, similar as reported in Angew. Chem. Int. Ed. 2017, 56, 1746-1750. The investigation indicates a spherical shape of the particles, but the polymer distribution in the particles is inhomogeneous. No further conclusion can be drawn due to the limitations of the available methods, but a complex mechanism seems to be at work to generate this inverse temperature effect.

Lubricating Compositions

Lubricating compositions will contain a range of other polar additives, which may influence the performance of an associative VI improver. Data for a hydraulic fluid formulation are shown in Table 10.

Table 10: Formulation data of Example 2 with Dl Package (composition HF-2) and without Dl package (composition HF-1 ).

It can be seen that the used package has a detrimental effect on the VI performance of the polymer in this formulation.

It is further shown that the pour point (PP) stays almost the same for both formulations, with and without Dl package. That means that neither turbidity nor separation of the block copolymer is observed and the formulation remains stable even at low temperatures.

The data presented in Table 10 further show the shear stability performance. The polymer is too small to be impacted by KRL; i.e. no permanent shear loss is observed. This is a significant advantage compared to common VI improvers in the market for which a high VI lift is always coupled to a significant loss in performance after severe mechanical shear. Further application tests were run on formulations comprising Example 12 without Dl package and with different Dl packages as presented in following Table 1 1.

Table 1 1 : Formulation data of Example 12.

n.d. = not defined

Further application tests were run on the formulations as presented in following Table 12.

Table 12: Advanced performance testing of a formulation based on Example 3.

Due to the high polarity of some of the polymer blocks an impact on performance tests involving interfaces was expected. For the air release and foam tests no strong effect was observed. Filtration of the fluid is no problem at all which confirms the visual observation that the polymer is completely dissolved in the oil phase.

Claims

1. Process for improving the viscosity index of lubricating oil compositions by adding a triblock copolymer of general formula (I)

A-B-A (I), wherein each A denotes an oil-insoluble residue selected from the group consisting of polyesters, polyalkylene glycols, polystyrenes, polyalkyl(meth)acrylates or mixtures thereof, and B denotes an oil-soluble residue selected from the group consisting of polyolefins,

polyalkyl(meth)acrylates or mixtures thereof,

characterized in that the weight-average molecular weight of the triblock copolymer is in the range of 3,000 to 30,000 g/mol, preferably 3,500 to 25,000 g/mol, more preferably 4,000 to 20,000 g/mol, determined by gel permeation chromatography against polymeric standards (polystyrene or PMMA).

2. The process according to any one of claim 1 , characterized in that each segment A is a polyester residue derived from at least two different monomers 1 and 2, where monomer 1 is selected from a lactone and monomer 2 is selected from the group consisting of lactide and glycolide.

3. The process according to claim 1 , characterized in that the polyalkylene glycols are selected from the group consisting of polyethylene glycol (also known as polyethylene oxide), polypropylene glycol and mixtures thereof.

4. The process according to claim 1 , characterized in that the polystyrenes are selected from the group consisting of styrene, alpha-methylstyrene, alpha-ethylstyrene, vinyltoluene, p- methylstyrene and mixtures thereof; preferably styrene.

5. The process according to claim 1 , characterized in that the polyalkyl(meth)acrylates to be used as segments A are prepared from monomer mixtures, comprising:

(A1 ) 80 to 100% by weight, preferably 85 to 100% by weight, more preferably 90 to 100% by weight, of monomers being selected from the group consisting of C-i-₄-alkyl

C5-3₂-alkyl (meth)acrylates, preferably Cio-i6-alkyl (meth)acrylates,

based on the total composition of segments A.

6. The process according to claim 1 , characterized in that the polyolefin can be selected from the group consisting of polyethylene, polypropylene, polyisobutylene, poly-n-butene, polybutadiene, polyisoprene, polyfarnesene and mixtures thereof.

7. The process according to claim 1 , characterized in that the polyalkyl(meth)acrylates to be used as segment B are prepared from monomer mixtures, comprising:

(B2) 0 to 20% by weight, preferably 0 to 15% by weight, more preferably 0 to 10% by weight, of monomers being selected from the group consisting of C-i-₄-alkyl (meth)acrylates, styrene, benzyl (meth)acrylate and mixtures thereof, preferably Ci-₄-alkyl (meth)acrylates, based on the total composition of segments B.

8. The process according to any one of claims 1 to 7, characterized in that the triblock copolymer of general formula (I) consists of:

(a) 45 to 85% by weight of segments A and

(b) 15 to 55% by weight of segment B,

based on the total composition of the triblock copolymer.

9. The process according to any one of claims 1 to 7, characterized in that the triblock copolymer of general formula (I) consists of:

(a) 45 to 85% by weight of segments A and

(b) 15 to 45% by weight of segment B which is a polyolefin,

based on the total composition of the triblock copolymer.

10. The process according to any one of claims 1 to 7, characterized in that the triblock copolymer of general formula (I) consists of:

(a) 45 to 70% by weight of segments A and

(b) 30 to 55% by weight of segment B which is a polyalkyl(meth)acrylate,

based on the total composition of the triblock copolymer.

1 1. The process according to claim 1 , characterized in that the triblock copolymer is of general formula (la)

A-B-A (lb),

wherein each segment A is prepared from a monomer mixture comprising:

(A1 ) 80 to 100% by weight, preferably 85 to 100% by weight, more preferably 90 to

100% by weight, of monomers being selected from the group consisting of C-i-₄-alkyl (meth)acrylates, styrene, benzyl (meth)acrylate and mixtures thereof, preferably Ci-₄-alkyl (meth)acrylates; and

(A2) 0 to 20% by weight, preferably 0 to 15% by weight, more preferably 0 to 10% by weight, of Cs-3₂-alkyl (meth)acrylates, preferably Cio-i6-alkyl (meth)acrylates, based on the total weight of segments A, and segment B is prepared from a monomer mixture comprising:

(B1 ) 80 to 100% by weight, preferably 85 to 100% by weight, more preferably 90 to

100% by weight, of monomers being selected from the group consisting of C5-3₂-alkyl (meth)acrylates, preferably Cio-i6-alkyl (meth)acrylates; and

(B2) 0 to 20% by weight, preferably 0 to 15% by weight, more preferably 0 to 10% by weight, of monomers being selected from the group consisting of Ci-₄-alkyl (meth)acrylates, styrene, benzyl (meth)acrylate and mixtures thereof, preferably Ci-₄-alkyl (meth)acrylates,

based on the total weight of segments B.

12. The process according to any one of the preceding claims, characterized in that the lubricating oil composition has a VI of 300 or greater, determined to ASTM D2270.

13. Lubricating oil composition, comprising:

(A) 2 to 20% by weight of a triblock copolymer of general formula (I)

A-B-A (I),

wherein each A denotes an oil-insoluble residue selected from the group consisting of polyesters, polyalkylene glycols, polystyrenes,

polyalkyl(meth)acrylates or mixtures thereof, and B denotes an oil-soluble residue selected from the group consisting of polyolefins, polyalkyl(meth)acrylates or mixtures thereof, characterized in that the weight-average molecular weight of the triblock copolymer is in the range of 3,000 to 30,000 g/mol, determined by gel permeation chromatography; and

(B) 80 to 98% by weight of a base oil,

characterized in that the lubricating oil compositions has a VI of at least 300, determined to ASTM

D2270.

14. Lubricating oil composition according to claim 13, characterized in that the triblock copolymer (A) consists of:

(a) 45 to 85% by weight of segments A and

(b) 15 to 55% by weight of segment B,

based on the total composition of the triblock copolymer.

15. Lubricating oil composition according to claim 13 or 14, characterized in that it has a VI of 300 or greater, determined to ASTM D2270.