USE OF ASSOCIATIVE TRIBLOCK COPOLYMERS AS VISCOSITY INDEX IMPROVERS

Description

[0001] The present invention is directed to a process for improving the viscosity index of a lubricating oil composition by adding a triblock copolymer.

[0002] 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.

[0003] 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.

[0004] 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).

[0005] 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.

[0006] Increasing temperature increases the solvency of the oil, which, in turn, promotes the uncoiling of the polymer and results in a larger hydrodynamic volume.

[0007] 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 fiber-like 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.

[0008] 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.

[0009] 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).

[0010] 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.

[0011] 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.

[0012] 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.

[0013] 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.

[0014] US 6,054,539 discloses a selectively hydrogenated butadiene-isoprene-butadiene triblock copolymer with a weight-average molecular weight of 15150 g / mol (polymer A) and a process for improving viscosity index of lubricating oil compositions.

[0015] EP431706 and EP0298578 describe methacrylate blocks which are used to replace the insoluble styrene block or the oil soluble hydrogenated diene block.

[0016] WO 2014 / 105290 describes diblock polymers including PAMA blocks which are prepared in combination with polypropylene and micelle formation in PAO4 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.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] 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 (Ib)         A-B-A      (Ib), wherein each segment A is prepared from a monomer mixture comprising: (A1) 80 to 100% by weight of monomers being selected from the group consisting of C 1-4 -alkyl (meth)acrylates, styrene, benzyl (meth)acrylate and mixtures thereof, preferably C 1-4 -alkyl (meth)acrylates; and (A2) 0 to 20% by weight of C 5-32 -alkyl (meth)acrylates, preferably C 10-16 -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 of monomers being selected from the group consisting of C 5-32 -alkyl (meth)acrylates, preferably C 10-16 -alkyl (meth)acrylates; and (B2) 0 to 20% by weight of monomers being selected from the group consisting of C 1-4 -alkyl (meth)acrylates, styrene, benzyl (meth)acrylate and mixtures thereof, preferably C 1-4 -alkyl (meth)acrylates, based on the total weight of segments B, 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, characterized in that the triblock copolymer of general formula (Ib) consists of: (a) 45 to 70% by weight of segments A and (b) 30 to 55% by weight of segment B, based on the total composition of the triblock copolymer.

[0021] The weight-average molecular weight is determined by gel permeation chromatography against polymeric standards. Depending on the nature and composition of the copolymer, polyalkylmethacrylates (PMMA) are used as corresponding standard.

[0022] Suitable polyalkyl(meth)acrylates to be used as segments A can be prepared from monomer mixtures, comprising: (A1) 85 to 100% by weight, more preferably 90 to 100% by weight, of monomers being selected from the group consisting of C 1-4 -alkyl (meth)acrylates, styrene, benzyl (meth)acrylate and mixtures thereof, preferred C 1-4 -alkyl (meth)acrylates; and (A2) 0 to 15% by weight, more preferably 0 to 10% by weight, of C 5-32 -alkyl (meth)acrylates, preferably C 10-16 -alkyl (meth)acrylates.

[0023] 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.

[0024] 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.

[0025] The C 1-4 -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 1-4 -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.

[0026] Suitable C 1-4 -alkyl (meth)acrylates include, for example, methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate), iso-propyl (meth)acrylate, n-butyl (meth)acrylate, iso-butyl (meth)acrylate and tert-butyl (meth)acrylate. Particularly preferred C 1-4 -alkyl (meth)acrylates are methyl (meth)acrylate and n-butyl (meth)acrylate; methyl methacrylate and n-butyl methacrylate are especially preferred.

[0027] The C 5-32 -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 "C 5-32 -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.

[0028] Suitable C 5-32 -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-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-tetradecyl-octadecyl (meth)acrylate, 1,2-tetradecyl-octadecyl (meth)acrylate and 2-hexadecyl-eicosyl (meth)acrylate.

[0029] The C 10-16 -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 "C 10-16 -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.

[0030] Suitable C 10-16 -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.

[0031] Amongst these, particularly preferred are methacrylic esters of a linear C 12-14 -alcohol mixture (C 12-14 -alkyl-methacrylate).

[0032] Suitable polyalkyl(meth)acrylates to be used as segment B can be prepared from monomer mixtures, comprising: (B1) 85 to 100% by weight, more preferably 90 to 100% by weight, monomers being selected from the group consisting of C 5-32 -alkyl (meth)acrylates, preferably C 10-16 -alkyl (meth)acrylates; and (B2) 0 to 15% by weight, more preferably 0 to 10% by weight, of monomers being selected from the group consisting of C 1-4 -alkyl (meth)acrylates, styrene, benzyl (meth)acrylate and mixtures thereof, preferably C 1-4 -alkyl (meth)acrylates.

[0033] 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.

[0034] The C 5-32 -alkyl (meth)acrylates, C 10-16 -alkyl (meth)acrylates, C 1-4 -alkyl (meth)acrylates and styrenes for use in accordance with the invention are as defined further above.

[0035] 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.

[0036] They are further characterized by a weight-average molecular weight M w , determined by gel permeation chromatography to DIN 55672-1 in tetrahydrofuran as eluent and PMMA for calibration. The polydispersity index PDI of the block polymers according to the present invention is in the range of 1 to 5.

[0037] Triblock polymers of general formula (Ib) 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.

[0038] 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.

[0039] 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.

[0040] 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 (Ib)         A-B-A      (Ib), wherein each segment A denotes apolyalkyl(meth)acrylate 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 1-4 -alkyl (meth)acrylates, styrene, benzyl (meth)acrylate and mixtures thereof, preferably C 1-4 -alkyl (meth)acrylates; and (A2) 0 to 20% by weight, preferably 0 to 15% by weight, more preferably 0 to 10% by weight, of C 5-32 -alkyl (meth)acrylates, preferably C 10-16 -alkyl (meth)acrylates, based on the total weight of segments A, and segment B denotes a polyalkyl(meth)acrylate 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 C 5-32 -alkyl (meth)acrylates, preferably C 10-16 -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 C 1-4 -alkyl (meth)acrylates, styrene, benzyl (meth)acrylate and mixtures thereof, preferably C 1-4 -alkyl (meth)acrylates, based on the total weight of segments B, 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 against PMMA standards, characterized in that the triblock copolymer of general formula (Ib) consists of: (a) 45 to 70% by weight of segments A and (b) 30 to 55% by weight of segment B, based on the total composition of the triblock copolymer; and (B) 80 to 98% by weight, preferably 85 to 95% by weight, of a base oil, characterized in that the lubricating oil compositions has a VI of at least 300, determined to ASTM D2270.

[0041] The content of each component (A) and (B) is based on the total weight of the lubricating oil composition.

[0042] In a particular embodiment, the proportions of components (A) and (B) add up to 100% by weight.

[0043] 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 mm 2< / s, preferably 5 to 25 mm 2< / s, determined to ASTM D445.

[0044] 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").

[0045] 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. GroupSaturatesSulphur contentViscosity Index (VI)I< 90%> 0.03%80-120IIat least 90%not more than 0.03%80-120IIIat least 90%not more than 0.03%at least 120IVAll polyalphaolefins (PAOs)VAll others not included in Groups I, II, III or IV (e.g. ester oils and naphthenic oils)

[0046] The kinematic viscosity at 40°C (KV 40 ) 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 mm 2< / s to 25 mm 2< / s, more preferably in the range of 2 mm 2< / s to 20 mm 2< / s, according to ASTM D445.

[0047] Further base oils which can be used in accordance with the present invention are Group II-III Fischer-Tropsch derived base oils.

[0048] 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 1 029 029, WO 01 / 18156, WO 01 / 57166 and WO 2013 / 189951.

[0049] 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.

[0050] The content of each component (B1) and (B2) is based on the total weight of the base oil (B).

[0051] In a particular embodiment, the proportions of components (B1) and (B2) add up to 100% by weight.

[0052] 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 mm 2< / s, preferably 5 to 25 mm 2< / s, determined to ASTM D445.

[0053] 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.

[0054] 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.

[0055] 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 non- bridging polymer chains is very complex.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] By application of the triblock copolymers of the present invention in lubricating oil compositions, formulations with exceptional VIs can be generated.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] The invention has been further illustrated by the following non-limiting examples.Experimental Part Abbreviations

[0064] BnMAbenzyl methacrylate Chevron 100RGroup II base oil from Chevron with a KV 100 of 4.1 cSt CPcloud point DDM1-dodecyl mercaptane EBIBethyl alpha-bromoisobutyrate (monofunctional) e-CLepsilon-caprolactone 2fBiBethylene bis(2-bromoisobutyrate) (bifunctional) HITEC521 ®< hydraulic DI package from Afton hPBDhydrogenated polybutadiene IR8080Irgalube ®< 8080, ashless hydraulic DI package from BASF KRLKegelrollenlager (tapered roller bearing) KVkinematic viscosity measured according to ASTM D445 KV -20 kinematic viscosity @-20°C, measured according to ASTM D445 KV 40 kinematic viscosity @40°C, measured according to ASTM D445 KV 100 kinematic viscosity @100°C, measured according to ASTM D445 LCSTlower critical solution temperature LMAlauryl methacrylate, 73% C12, 27% C14, all linear MMAmethyl methacrylate M n number-average molecular weight M w weight-average molecular weight NB3020Nexbase ®< 3020, Group III base oil from Neste with a KV 100 of 2.2 cSt NB3043Nexbase ®< 3043, Group III base oil from Neste with a KV 100 of 4.3 cSt NB3060Nexbase ®< 3060, Group III base oil from Neste with a KV 100 of 5.9 cSt NS3 ®< naphthenic base oil from Nynas with a KV 100 of 1.1 cSt NS8 ®< naphthenic base oil from Nynas with a KV 100 of 2.1 cSt PDIpolydispersity index PMDETApentamethyldiethylenetriamine PPpour point RC9300 ®< ashless hydraulic DI package from Rheinchemie T g glass transition temperature T m melting point VIviscosity index Test methods

[0065] 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).

[0066] 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 11357-1.

[0067] 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.

[0068] 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 (KV 40 ) and 100°C (KV 100 ) to ASTM D445.

[0069] 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 (KV 40 ) and 100°C (KV 100 ) to ASTM D445, their viscosity index (VI) to ASTM D2270, their cloud point to ASTM D5771 and their pour point to ASTM D5950.

[0070] KRL measurements to determine the shear loss were also done to CEC L-45-A-99 (20 hours, 60°C and 5kN).

[0071] In connection with the evaluation of hydraulic formulations, foam tests to ASTM D892 were run, air release was determined to DIN ISO 9120.

[0072] The Brookfield viscosity was determined to DIN 51398.Synthesis 2: Synthesis of a block copolymer based on polyalkyl methacrylates by ATRP polymerization

[0073] 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

[0074] 27.5 g methyl methacrylate and 3.13 g 2-cyanobutanyl-2-yl 3,5-dimethyl-1H-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)

[0075] 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 110°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.

[0076] 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 (Ib) and comparative examples. The reaction was carried out by using Chevron 100R as base oil. Table 4: Reaction mixtures used to prepare examples 16-20.LMA (complete) MMA (complete) 100R oil PMDETA CuBr 2f-BiB DDM EBiB [g] [g] [g] [g] [g] [g] [g] [g] 16*) 6040100.91.30.542.70.76--17 5545100.91.360.562.830.8--18 45551011.490.623.10.87--19* )< 307099.32.531.05--1.482.8520* )< 4555101** )< 1.490.623.10.87--* )< comparative example ** )< toluene was used for the synthesis instead of 100R oil

[0077] Example 16 is a comparative example because the content of segments A (MMA) is lower than the ranges described in the present invention.

[0078] Examples 17 and 18 are in accordance with the present invention and were prepared by following the protocol as described in Synthesis 2.

[0079] Example 19 is a comparative example as it is an A-B diblock copolymer. As monofunctional initiator was used ethyl-alpha-bromoisobutyrate.

[0080] 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.

[0081] 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.Ex. # MMA LMA Mn Mw PDI [wt%] [wt%] [g / mol] [g / mol] 16* )< 406014,50019,2001.317 455514,20018,5001.318 554513,40017,4001.319* )< 70306,52012,8002.020* )< 554513,00017,5001.4

[0082] It can be seen that their weight-average molecular weights are within the claimed range of 3,000 to 30,000 g / mol.

[0083] 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 (Ib). They were prepared by following the protocol of Synthesis 3. Table 6: Reaction mixtures used to prepare examples 21-24.LMA (complete) MMA (complete) BnMA (complete) toluene / N B3020 RAFT initiator (complete) [g] [g] [g] [g] [g] [g] 21 30--7098.82.81.2922 3070--98.83.161.4423 5545--98.44.11.8624 4555--98.83.131.44

[0084] 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.

[0085] 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.

[0086] 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.Ex. MMA LMA BnMA Mn Mw PDI # [wt%] [wt%] [wt%] [g / mol] [g / mol] 21 --30708,49013,4001.622 7030--8,51014,0001.623 4555--7,49011,6001.624 5545--8,57014,5001.7

[0087] It can be seen that their weight-average molecular weights are within the claimed range of 3,000 to 30,000 g / mol.Evaluation of the properties of solutions comprising inventive triblock copolymers

[0088] 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 KV 40 and KV 100 values as well as viscosity indices were measured. The results are shown in the following Table 8. Table 8: Thickening effect of triblock copolymers.Example #base oil amount polymer KV 40 KV 100 VI [wt%] [mm 2< / s] [mm 2< / s] 16*) NB30201327.847.6226516*) NS31320.294.7716517 NB30201323.167.0830117 NS31315.825.2931918 NB30201318.395.6528718 NS31310.814.4341619*) NB30201313.133.7625219*) NS3135.402.0919520*) NB302013** )< ** )< ** )< 20*) NS31311.843.2314721 NS3105.932.4132821 NS31513.824.8132722 NS3106.152.5032922 NS31515.725.1436523 NS3104.482.5782623 NS3157.393.8161224 NS3104.572.7891824 NS3158.774.37575* )< comparative example ** )< not soluble n.d. = not defined

[0089] 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.

[0090] 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.

[0091] Comparative example 16 demonstrates how the effect vanishes when the apolar A segments become too short.

[0092] Also, different block structures such as A-B (comparative example 19), B-A-B (comparative example 20) do not provide the effect.

Claims

1. Process for improving the viscosity index of lubricating oil compositions by adding a triblock copolymer of general formula (Ib)         A-B-A     (Ib), wherein each segment A is prepared from a monomer mixture comprising: (A1) 80 to 100% by weight of monomers being selected from the group consisting of C1-4-alkyl (meth)acrylates, styrene, benzyl (meth)acrylate and mixtures thereof, preferably C1-4-alkyl (meth)acrylates; and (A2) 0 to 20% by weight of C5-32-alkyl (meth)acrylates, preferably C10-16-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 of monomers being selected from the group consisting of C5-32-alkyl (meth)acrylates, preferably C10-16-alkyl (meth)acrylates; and (B2) 0 to 20% by weight of monomers being selected from the group consisting of C1-4-alkyl (meth)acrylates, styrene, benzyl (meth)acrylate and mixtures thereof, preferably C1-4-alkyl (meth)acrylates, based on the total weight of segments B, 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 PMMA standards, characterized in that the triblock copolymer of general formula (Ib) consists of: (a) 45 to 70% by weight of segments A and (b) 30 to 55% by weight of segment B, based on the total composition of the triblock copolymer.

2. The process according to claim 1, wherein each segment A is prepared from a monomer mixture comprising: (A1) 85 to 100% by weight of monomers being selected from the group consisting of C1-4-alkyl (meth)acrylates, styrene, benzyl (meth)acrylate and mixtures thereof, preferably C1-4-alkyl (meth)acrylates; and (A2) 0 to 15% by weight of C5-32-alkyl (meth)acrylates, preferably C10-16-alkyl (meth)acrylates, based on the total weight of segments A, and segment B is prepared from a monomer mixture comprising: (B1) 85 to 100% by weight of monomers being selected from the group consisting of C5-32-alkyl (meth)acrylates, preferably C10-16-alkyl (meth)acrylates; and (B2) 0 to 15% by weight of monomers being selected from the group consisting of C1-4-alkyl (meth)acrylates, styrene, benzyl (meth)acrylate and mixtures thereof, preferably C1-4-alkyl (meth)acrylates, based on the total weight of segments B.

3. The process according to claim 1, wherein each segment A is prepared from a monomer mixture comprising: (A1) 90 to 100% by weight, of monomers being selected from the group consisting of C1-4-alkyl (meth)acrylates, styrene, benzyl (meth)acrylate and mixtures thereof, preferably C1-4-alkyl (meth)acrylates; and (A2) 0 to 10% by weight, of C5-32-alkyl (meth)acrylates, preferably C10-16-alkyl (meth)acrylates, based on the total weight of segments A, and segment B is prepared from a monomer mixture comprising: (B1) 90 to 100% by weight, of monomers being selected from the group consisting of C5-32-alkyl (meth)acrylates, preferably C10-16-alkyl (meth)acrylates; and (B2) 0 to 10% by weight, of monomers being selected from the group consisting of C1-4-alkyl (meth)acrylates, styrene, benzyl (meth)acrylate and mixtures thereof, preferably C1-4-alkyl (meth)acrylates, based on the total weight of segments B.

4. 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.

5. Lubricating oil composition, comprising: (A) 2 to 20% by weight of a triblock copolymer of general formula (Ib)         A-B-A     (Ib), wherein each segment A denotes a polyalkyl(meth)acrylate prepared from a monomer mixture comprising: (A1) 80 to 100% by weight of monomers being selected from the group consisting of C1-4-alkyl (meth)acrylates, styrene, benzyl (meth)acrylate and mixtures thereof, preferably C1-4-alkyl (meth)acrylates; and (A2) 0 to 20% by weight of C5-32-alkyl (meth)acrylates, preferably C10-16-alkyl (meth)acrylates, based on the total weight of segments A, based on the total weight of segments A, and segment B denotes a polyalkyl(meth)acrylate prepared from a monomer mixture comprising: (B1) 80 to 100% by weight of monomers being selected from the group consisting of C5-32-alkyl (meth)acrylates, preferably C10-16-alkyl (meth)acrylates; and (B2) 0 to 20% by weight of monomers being selected from the group consisting of C1-4-alkyl (meth)acrylates, styrene, benzyl (meth)acrylate and mixtures thereof, preferably C1-4-alkyl (meth)acrylates, based on the total weight of segments B, 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 against PMMA standards, characterized in that the triblock copolymer of general formula (Ib) consists of: (a) 45 to 70% by weight of segments A and (b) 30 to 55% by weight of segment B, based on the total composition of the triblock copolymer; 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.

6. The lubricating composition according to claim 5, wherein each segment A is prepared from a monomer mixture comprising: (A1) 85 to 100% by weight of monomers being selected from the group consisting of C1-4-alkyl (meth)acrylates, styrene, benzyl (meth)acrylate and mixtures thereof, preferably C1-4-alkyl (meth)acrylates; and (A2) 0 to 15% by weight of C5-32-alkyl (meth)acrylates, preferably C10-16-alkyl (meth)acrylates, based on the total weight of segments A, and segment B is prepared from a monomer mixture comprising: (B1) 85 to 100% by weight of monomers being selected from the group consisting of C5-32-alkyl (meth)acrylates, preferably C10-16-alkyl (meth)acrylates; and (B2) 0 to 15% by weight of monomers being selected from the group consisting of C1-4-alkyl (meth)acrylates, styrene, benzyl (meth)acrylate and mixtures thereof, preferably C1-4-alkyl (meth)acrylates, based on the total weight of segments B.

7. The lubricating composition according to claim 5, wherein each segment A is prepared from a monomer mixture comprising: (A1) 90 to 100% by weight, of monomers being selected from the group consisting of C1-4-alkyl (meth)acrylates, styrene, benzyl (meth)acrylate and mixtures thereof, preferably C1-4-alkyl (meth)acrylates; and (A2) 0 to 10% by weight, of C5-32-alkyl (meth)acrylates, preferably C10-16-alkyl (meth)acrylates, based on the total weight of segments A, and segment B is prepared from a monomer mixture comprising: (B1) 90 to 100% by weight, of monomers being selected from the group consisting of C5-32-alkyl (meth)acrylates, preferably C10-16-alkyl (meth)acrylates; and (B2) 0 to 10% by weight, of monomers being selected from the group consisting of C1-4-alkyl (meth)acrylates, styrene, benzyl (meth)acrylate and mixtures thereof, preferably C1-4-alkyl (meth)acrylates, based on the total weight of segments B.

8. The lubricating composition according to any one of claims 5 to 7, wherein the base oil (B) is selected from the group consisting of API Group I, II, III, IV, V and mixtures thereof.

9. The lubricating composition according to any one of claims 5 to 7, wherein the base oil (B) comprises: (B1) 50 to 100% by weight, of a Group V base oil; and (B2) 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.

10. The lubricating composition according to any one of claims 5 to 9, characterized by a VI of at least 300, determined to ASTM D2270, and a kinematic viscosity at 40°C of 4 to 30 mm2 / s, determined to ASTM D445.

11. The lubricating composition according to any one of claims 5 to 10, characterized by a VI of at least 400, determined to ASTM D2270, and a kinematic viscosity at 40°C of 5 to 25 mm2 / s, determined to ASTM D445.

12. Use of a lubricating oil composition according to any one of claims 5 to 11 as hydraulic fluid, transmission fluid, gear oil or motor oil.