RU2832346C2 - Copolymers of acrylates and olefins as high-viscosity base fluids - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: present invention relates to copolymers of acrylates and olefins, a method of producing said copolymers and use of copolymers as additives for lubricating materials, as well as a lubricating composition of a lubricating material. Copolymer contains a) from 65% to 90% by weight of monomer units obtained from at least one acrylate of formula , where R₁ is a linear or branched alkyl group containing from 6 to 12 carbon atoms, b) from 10 % to 35 % by weight of monomer units obtained from at least one non-functionalised alpha-olefin of formula , where R₂ is a linear alkyl group containing from 6 to 16 carbon atoms, and c) from 0% to 10% by weight of monomer units obtained from at least one monomer selected from methacrylamide, fumarate, maleate or a mixture thereof, and from 0% to 22% by weight of monomer units obtained from monomers with a linear alkyl group containing more than 8 carbon atoms. Copolymer is characterized by kinematic viscosity from 80 to 600 cSt at 100 °C, as well as COC flash point above 250 °C.

EFFECT: obtained copolymer is characterized by a higher viscosity index than its methacrylate counterparts, as well as a high flash point and good thermal-oxidative stability.

15 cl, 12 tbl, 61 ex

Description

FIELD OF TECHNICAL INVENTION

The present invention relates to copolymers of acrylates and olefins and to a method for producing these polymers. The present invention is also directed to lubricating compositions containing these copolymers, as well as to the use of these copolymers as an additive for lubricants or a synthetic base fluid in a lubricating oil composition, preferably in a gear oil composition, a transmission oil composition, a hydraulic oil composition, a motor oil composition, a marine oil composition, an industrial lubricating oil composition, or in a grease.

BACKGROUND OF THE INVENTION

The present invention relates to the field of lubrication. Lubricants are compositions that reduce friction between surfaces. In addition to providing freedom of movement between two surfaces and reducing mechanical wear of surfaces, a lubricant can also slow down corrosion of surfaces and/or can slow down damage to surfaces caused by heat or oxidation. Examples of lubricating compositions include, but are not limited to, motor oil, transmission fluids, gearbox oils, industrial lubricating oils, greases, and metalworking oils.

Lubricants typically contain a base fluid and varying amounts of additives. Traditional base fluids are hydrocarbons such as mineral oils. The terms "base oil" or "base fluid" are used interchangeably in most cases. In this document, "base fluid" is used as a generic term.

A wide variety of additives can be combined with the base fluid, depending on the intended application of the lubricant. Examples of lubricant additives include, but are not limited to, viscosity index improvers, thickeners, oxidation inhibitors, corrosion inhibitors, dispersants, high-pressure additives, antifoams, and metal deactivators.

Typical non-polymer base fluids are less effective as lubricants because of their low viscosity and further decreasing viscosity at higher operating temperatures. Therefore, polymer additives are used to thicken the base oil and reduce the change in viscosity with temperature. The term viscosity index (VI) is used to describe this change in viscosity with temperature. The lower the VI, the greater the change in viscosity with temperature and vice versa. Thus, a high VI is required for lubricant formulations. Polymer additives or viscosity index improvers (VII) can be added to the lubricant formulation to improve VI.

It is well known in the art that alkyl acrylates are not recommended for use in VI improvers and commercial VI improvers are based on methacrylates. In addition to the literature (Rashad et al. J. of Petr. Sci. and Engineering 2012, 173-177; Evin et al. J. of Sol. Chem 1994, 325-338) and patents (WO 96/17517), it is well known that the performance of polyacrylates as VI improvers is inferior to that of polymethacrylates. In particular, WO 96/17517 mentions that it was surprisingly found that poly(alkyl acrylate) esters generally do not reduce the effect of temperature on viscosity sufficiently when used in hydraulic fluids.

The disadvantage of adding polymer additives to a lubricant is that they will be subject to shear stress and will mechanically break down over time. High molecular weight polymers are better thickeners, but they will be more susceptible to shear stress causing polymer breakdown. To reduce the amount of polymer breakdown, the molecular weight of the polymer can be reduced, thereby producing a more shear stable polymer. These low molecular weight shear stable polymers are no longer very effective thickeners and must be used in higher concentrations in the lubricant to achieve the required viscosity. These low molecular weight polymers are typically characterized by a molecular weight below 20,000 g/mol and are also called synthetic high viscosity base fluids. High viscosity base fluids are used to raise the VI and to thicken lubricant formulations with high shear strength requirements. A typical application is the use of gear oils, which are subject to very high demands due to high mechanical loads and a wide range of operating temperatures.

Typical products in this market are high viscosity polyalphaolefins (PAO) and metallocene polyalphaolefins (mPAO), usually sold with viscosities ranging from 40 to 300 cSt at 100°C (Choudary et al. Lubr. Sci. 2012, 23-44), the main feature of which is good processing properties in terms of viscosity, since these base fluids are polymeric in nature and provide an improved viscosity index. However, their disadvantage is their low polarity. Due to the apolar nature of PAO base oils, DI packages and aging products are poorly soluble in the oil, which causes various problems.

It has already been described that higher polarity is achieved by copolymers of alpha-olefins with maleates (DE 3223694), copolymers of alpha-olefins and acrylates (DE 2243064), copolymers of alpha-olefins and methacrylates (EP 0471266) or terpolymers based on the above-mentioned monomers (WO 2020078770). Alternatively, oil-compatible polyesters (WO 0146350), polyalkyl (meth) acrylates (DE 102010028195) or polyvinyl ethers (US 20130165360) can be used. A major advantage when using polar high-viscosity base fluids is that the use of polar low-viscosity fluids such as esters as compatibility improvers for polar lubricant additives is not required. Polar low viscosity fluids are known to cause problems with coatings and seals, which is less of a problem with high viscosity fluids.

Existing products such as polyolefins (PAO) do not have the required performance characteristics for some applications. There is also a need to provide alternative solutions for industrial equipment oils, not just industrial lubricants. In particular, it would be desirable to replace existing high-viscosity polyalphaolefins, as these products are expensive and do not provide sufficient solubility for critical formulation components.

Therefore, the object of the present invention is to provide highly shear-stable synthetic base fluids or additives for lubricating oil, which in lubricating oil compositions are characterized by a positive effect on the solubility in oil and the solubility of the components, as well as on the performance at low temperatures. In addition, these new polymers should be able to thicken the oil to the required viscosity. These highly shear-stable polymers should also be characterized by a high viscosity index, a high flash point and good thermal-oxidative stability.

BRIEF DESCRIPTION OF THE INVENTION

The inventors of the present invention have surprisingly found that the acrylates and olefins copolymers as defined in claim 1 are suitable as highly shear stable additives for lubricating oils or synthetic base fluids, depending on their dosage in the lubricating composition. The acrylates and olefins copolymers according to the present invention are characterized by a higher viscosity index than their methacrylate analogs, as illustrated in the experimental part of the present invention, which was unexpected. The inventors of the present invention have found that the side chains of the resulting polymer, which are derived from the acrylate monomer as well as from the alpha-olefin, are important for achieving a combination of high VI and good low-temperature properties.

The first aspect of the present invention is a copolymer of acrylates and olefins as defined in claim 1.

The second aspect of the present invention is a process for producing these copolymers as defined in claim 13.

The third aspect of the present invention is a lubricating composition comprising at least one base oil and at least one copolymer according to the present invention, as defined in claim 14.

A fourth aspect of the present invention is the use of these copolymers as a lubricant additive or synthetic base fluid in a lubricating oil composition, preferably in a gear oil composition, a transmission oil composition, a hydraulic oil composition, a motor oil composition, a marine oil composition, an industrial lubricating oil composition or in a grease.

DETAILED DESCRIPTION OF THE INVENTION

Copolymer according to the present invention

The present invention relates to a copolymer comprising:

a) from 65 to 90% by weight, based on the total weight of the copolymer, of monomer units obtained from at least one acrylate of formula (I),

(I),

where R ₁ is a linear or branched alkyl group containing from 6 to 12 carbon atoms,

b) from 10 to 35% by weight, based on the total weight of the copolymer, of monomer units derived from at least one non-functionalized alpha-olefin of formula (II),

(II),

where R ₂ is a linear alkyl group containing from 6 to 16 carbon atoms,

c) from 0 to 10% by weight of monomer units derived from at least one monomer selected from the list consisting of methacrylamides, fumarates, maleates or a mixture thereof, based on the total weight of the copolymer, and

wherein the copolymer is characterized by a kinematic viscosity at 100°C of 80 to 600 cSt according to ASTM D 445, and

wherein the copolymer contains from 0 to 22% by weight of monomer units obtained from monomers with a linear alkyl group containing more than 8 carbon atoms, based on the total weight of the copolymer.

According to one aspect of the present invention, it is preferred that the copolymer contain from 0 to 20% by weight, more preferably from 0 to 18% by weight, of monomer units derived from monomers with a linear alkyl group containing more than 8 carbon atoms, based on the total weight of the copolymer.

According to another aspect of the present invention, it is preferred that the copolymer has a kinematic viscosity at 100°C of from 100 to 500 cSt according to ASTM D 445, more preferably from 150 to 400 cSt according to ASTM D 445, more preferably from 150 to 350 cSt according to ASTM D 445.

According to another preferred aspect of the present invention, the total content of monomer units derived from monomers a) and b) in the copolymer according to the present invention in total is not more than 90% by weight, more preferably in total is not more than 95% by weight, even more preferably in total is not more than 98% by weight, most preferably in total is not more than 100% by weight, based on the total weight of the copolymer.

According to another preferred aspect of the present invention, the total content of monomer units derived from monomers a), b) and c) in the copolymer according to the present invention in total is not more than 90% by weight, more preferably in total is not more than 95% by weight, even more preferably in total is not more than 98% by weight, most preferably in total is not more than 100% by weight, based on the total weight of the copolymer.

Acrylate a) of formula (I) refers to esters of acrylic acid with a straight chain or with branched alcohols containing from 6 to 12 carbon atoms, preferably from 6 to 10 carbon atoms, more preferably from 8 to 10 carbon atoms. The term covers individual acrylic esters with an alcohol of a certain chain length, as well as mixtures of acrylic esters with alcohols of different chain lengths.

According to one aspect of the present invention, it is preferred that R ¹ in the acrylate monomer of formula (I) is a linear or branched alkyl group containing from 6 to 10 carbon atoms, more preferably a linear or branched alkyl group containing from 8 to 10 carbon atoms. Particularly preferred acrylates a) of formula (I) are 2-ethylhexyl acrylate, 2-propylheptyl acrylate, n-octyl acrylate or a mixture thereof.

According to the present invention, it is preferred that the copolymer of the present invention contains from 70 to 90% by weight, more preferably from 75 to 90% by weight, of monomer units derived from the acrylate monomer a) of formula (I), based on the total weight of the copolymer.

According to the present invention, it is preferred that the copolymer of the present invention contains from 10 to 30% by weight, more preferably from 10 to 25% by weight of monomer units derived from the non-functionalized alpha-olefin b) of formula (II), based on the total weight of the copolymer. Particularly preferably, the non-functionalized alpha-olefins b) of formula (II) are selected from the group consisting of decene, dodecene, tetradecene, hexadecene or a mixture thereof.

According to a preferred aspect of the present invention, the copolymer has a weight average molecular weight of 5000 to 30000 g/mol, preferably 7000 to 25000 g/mol, even more preferably 8000 to 20000 g/mol according to DIN 55672-1.

In the present invention, the weight average molecular weights (Mw) or number average molecular weights ( _Mn ) of the copolymers were determined by gel permeation chromatography (GPC) using calibration standards consisting of PMMA according to DIN 55672-1 using the following measurement conditions:

eluent: tetrahydrofuran (THF);

operating temperature: 35°C;

columns: the column setup consists of four columns: two SDV 106 Å columns, one SDV 104 Å column and one SDV 103 Å column (PSS Standards Service GmbH, Mainz, Germany), all with dimensions 300×8 mm and an average particle size of 10 µm;

flow rate: 1 ml/min;

injection volume: 100 µl;

instrument: Agilent 1100 series, consisting of an automatic sampler, pump and column thermostat;

Detection device: Agilent 1100 series refractometric detector.

Preferably, the copolymers of the present invention are characterized by a very low degree of crosslinking and a narrow molecular weight distribution, which also contributes to their shear resistance. The low degree of crosslinking and the narrow molecular weight distribution are reflected in the polydispersity index of the copolymers. Preferably, the polydispersity index (PDI) of the copolymers according to the present invention is in the range of 1.0 to 4.0, more preferably from 1.5 to 3.5. A polydispersity index in the range of 1.0 to 3.5 is considered to be optimal in terms of shear resistance of the copolymers for most industrial applications. The polydispersity index is defined as the ratio of the weight average molecular weight to the number average molecular weight (Mw/Mn).

According to a preferred aspect of the present invention, the copolymer of the present invention is characterized by a COC flash point above 250°C according to ASTM D92.

The copolymers of the present invention optionally comprise monomer units derived from a monomer c) selected from the list consisting of methacrylamides, fumarates, maleates or a mixture thereof. Preferably, the amount of monomer units derived from monomer c) in the resulting copolymer according to the present invention is from 0 to 10% by weight, preferably from 0 to 7% by weight, more preferably from 0 to 5% by weight, even more preferably from 0 to 3% by weight, based on the total weight of the copolymer. Particularly preferred monomers c) are di-2-ethylhexyl maleate, N-3-dimethylaminopropyl methacrylamide, di-2-ethylhexyl fumarate or a mixture thereof.

Surprisingly, it was observed that the incorporation of monomer units c) into the copolymer ensures complete conversion of non-functionalized alpha-olefins b) and, accordingly, no final distillation step is required at the end of the copolymerization.

According to a preferred aspect of the present invention, in addition to the monomer units derived from monomers a), b) and optionally c), the acrylates-olefins copolymer of the present invention also comprises from 0 to 10% by weight, more preferably from 0 to 6% by weight, based on the total weight of the copolymer, of monomer units derived from at least one monomer d) selected from alkyl (meth) acrylates, vinyl esters or a mixture thereof. Particularly preferred monomers d) are lauryl methacrylate (LMA), stearyl methacrylate (SMA) or vinyl laurate (VLA).

According to another preferred aspect of the present invention, the total content of monomer units of monomers a), b) c) and d) in total is not more than 95% by weight, more preferably 98% by weight, even more preferably 100% by weight,

According to another preferred aspect of the present invention, if the copolymer consists of monomer units derived from monomers a), b), optionally c) and optionally d), the copolymer contains from 0 to 22% by weight, more preferably from 0 to 20% by weight, even more preferably from 0 to 18% by weight of monomer units derived from monomers a), b), c) and d) with a linear alkyl group containing more than 8 carbon atoms, based on the total weight of the copolymer.

According to the present invention, the copolymer is a random copolymer with a sequential distribution of monomer units obtained from monomers a) and b) and optionally monomers c) and d).

Preferred Copolymers of the Present Invention

According to a preferred aspect of the present invention, the copolymer comprises:

a) from 65 to 90% by weight, more preferably from 70 to 90% by weight, even more preferably from 75 to 90% by weight, based on the total weight of the copolymer, of monomer units derived from at least one acrylate of formula (I),

(I),

where R ₁ is a linear or branched alkyl group containing from 8 to 10 carbon atoms,

b) from 10 to 35% by weight, more preferably from 10 to 30% by weight, even more preferably from 10 to 25% by weight, based on the total weight of the copolymer, of monomer units derived from at least one non-functionalized alpha-olefin of formula (II),

(II),

where R ₂ is a linear alkyl group containing from 8 to 12 carbon atoms,

c) from 0 to 10% by weight, more preferably from 0 to 5% by weight, even more preferably from 0 to 3% by weight of monomer units derived from at least one monomer selected from the list consisting of methacrylamides, fumarates, maleates or a mixture thereof, based on the total weight of the copolymer, and

wherein the copolymer is characterized by a kinematic viscosity at 100°C of 80 to 600 cSt according to ASTM D 445, and

wherein the copolymer contains from 0 to 22% by weight, preferably from 0 to 18% by weight, of monomer units derived from monomers with a linear alkyl group containing more than 8 carbon atoms, based on the total weight of the copolymer.

According to a preferred embodiment, the total content of monomer units of monomers a), b) and c) in total is no more than 95% by weight, more preferably 98% by weight, even more preferably 100% by weight, based on the total weight of the copolymer.

According to a preferred embodiment, the copolymer also contains from 0 to 10% by weight, more preferably from 0 to 6% by weight, based on the total weight of the copolymer, of monomer units derived from at least one monomer d) selected from alkyl (meth) acrylates, vinyl ester or a mixture thereof. Particularly preferred monomers d) are lauryl methacrylate (LMA), stearyl methacrylate (SMA) or vinyl laurate (VLA).

According to a preferred embodiment, the total content of monomer units of monomers a), b), c) and d) in total is no more than 95% by weight, more preferably 98% by weight, even more preferably 100% by weight.

Method for producing a copolymer according to the present invention

According to the present invention, the above polymers are obtained by a process comprising the steps of:

i) providing the monomer composition described above, and

ii) initiation of radical polymerization in the monomer composition.

Standard free radical polymerization is described in detail, for example, in Ullmann's Encyclopedia of Industrial Chemistry, sixth edition. As a rule, a polymerization initiator and, optionally, a polymerization degree regulator are used for this purpose.

Polymerization can be carried out at standard pressure, reduced pressure or elevated pressure.

For the radical copolymerization of olefins with acrylates, the polymerization temperature is important. Generally, the copolymerization temperature is in the range of 140 to 180°C, preferably 150 to 170°C.

The polymerization step ii) can be carried out with or without dilution in oil. Preferably, the polymerization step (ii) is carried out without dilution in oil or any solvent.

Preferably, step (ii) comprises adding a radical initiator. Preferably, the radical initiator is selected from di-tert-butyl peroxide or dicumyl peroxide. Preferably, the total amount of radical initiator relative to the total weight of the monomer mixture is from 0.01 to 5% by weight, more preferably from 0.1 to 1% by weight. Preferably, the total amount of radical initiator is added continuously during the copolymerization reaction (ii).

Preferably, the copolymerization step (ii) is carried out by feeding the acrylate monomers a) and optionally the monomers c) or any other comonomers together with the initiator into the non-functionalized alpha-olefin monomers b). Preferably, the total reaction time of the radical polymerization is from 2 to 5 hours, more preferably 3 hours.

In another preferred aspect of the present invention, a third step iii) corresponding to a distillation step is optionally carried out to remove unreacted alpha-olefin monomer b). Preferably, the residual unreacted alpha-olefin monomer b) is removed by distillation at 150°C and a pressure of not more than 5 mbar using a rotary evaporator. Preferably, the distillation step iii) is not required if the copolymer of the present invention contains monomer units derived from monomer c). Surprisingly, it has been observed that small amounts of monomers c) (less than 10% by weight, more preferably less than 5% by weight based on the total weight of the copolymer) increase the conversion of olefins in the copolymerization (less than 1% by weight of residual unreacted alpha-olefin b)), so that the distillation step iii) is not required.

Lubricating oil compositions

As noted above, the present invention also relates to a lubricating oil composition comprising at least one base oil and at least one copolymer as defined in the present invention.

Base oils are the base oils of lubricants, mineral, synthetic or natural oils, animal or vegetable oils, selected depending on their application/selected depending on the intended application.

The base oils used in formulating the lubricating oil compositions of the present invention include, for example, conventional base stocks selected from the API (American Petroleum Institute) base stock categories known as Group I, Group II, Group III, Group IV and Group V. The base stocks of Group I and II are mineral oil based materials (such as paraffinic and naphthenic oils) with a viscosity index (or VI) of less than 120. Group I is further distinguished from Group II in that the latter comprises materials with a saturation level of greater than 90%, while the former comprises a material with a saturation level of less than 90% (i.e., a material containing more than 10% unsaturation). Group III is considered to be a high-quality mineral base oil with a VI of greater than or equal to 120 and a saturation level of greater than or equal to 90%. Preferably, the base oil included in the lubricating oil composition of the present invention is selected from the group consisting of API Group II and III base oils. Most preferably, the lubricating composition comprises a base oil of API Group III. Base oils of Group IV are polyalphaolefins (PAO). Base oils of Group V are esters and any other base oils that do not belong to base oils of Groups I-IV. These base oils can be used separately or as a mixture.

In a preferred embodiment of the present invention, the lubricating oil composition comprises from 0.1 to 99.9% by weight, preferably from 1 to 95% by weight, of at least one base oil and from 0.1 to 99.9% by weight, preferably from 5% to 99% by weight, of at least one copolymer according to the present invention, based on the total weight of the lubricating composition.

The lubricating oil compositions according to the present invention may also contain any other additional additives suitable for use in the formulations. These additives include additional viscosity index improvers, pour point depressants, dispersants, demulsifiers, antifoams, lubricity improvers, friction modifiers, antioxidants, detergents, colorants, corrosion inhibitors and/or odorants.

Applications for the copolymer of the present invention

The present invention also relates to the use of the copolymer according to the present invention as an additive for lubricants or a synthetic base fluid in a lubricating oil composition, preferably in a gear oil composition, a transmission oil composition, a hydraulic oil composition, a motor oil composition, a marine oil composition, an industrial lubricating oil composition or in a grease.

EXPERIMENTAL PART

The present invention is further illustrated herein below with reference to examples and comparative examples, without any intention to limit the scope of the present invention. All percentages for monomers or base fluids indicated in the tables below are weight percentages (wt.%).

Abbreviations

BF-26 Brookfield viscosity measured at -26°C

BF-30 Brookfield viscosity measured at -26°C

BV bulk viscosity

BV40 bulk viscosity at 40°C according to ASTM D445

BV100 bulk viscosity at 100°C according to ASTM D445

cSt centistokes

cP centipoise

DBPO di-tert-butyl peroxide

DCP dicumyl peroxide

Dec Dec

DEHF di-2-ethylhexyl fumarate

DEHM di-2-ethylhexyl maleate

DMAPMAM N-3-dimethylaminopropyl methacrylamide

DoDec dodecene

EHA 2-ethylhexyl acrylate

EHMA 2-ethylhexyl methacrylate

HA hexyl acrylate

HexDec hexadecene

^Hitec® 2030 antifoam, commercially available from Afton

^Hitec® 307 DI package, commercially available from Afton

^Hitec® 3250 DI package, commercially available from Afton

IDA isodecyl acrylate

IDMA isodecyl methacrylate

Ini initiator

ITDA isotridecyl acrylate, commercially available from Aldrich

KV kinematic viscosity measured according to ASTM D445

KV ₄₀ kinematic viscosity measured at 40°C according to ASTM D445

KV ₁₀₀ kinematic viscosity measured at 100°C according to ASTM D445

LA lauryl acrylate, dodecyl acrylate

LMA Lauryl Methacrylate, 73% C12, 27% C14, All Linear

Mn number average molecular weight

MO methyl oleate

Mw average molecular weight

n.i. not measured

nOA n-octyl acrylate

NB3080 Nexbase® 3080; Group III base oil from Neste with a KV100 of 7.9 cSt

PAO100 Polyalphaolefin Base Oil with KV100 100 cSt from Chevron Phillips

PAO4 polyalphaolefin base oil with KV100 4 cSt

PAO6 polyalphaolefin base oil with KV100 6 cSt

PAO8 polyalphaolefin base oil INEOS Durasyn 168 with KV ₁₀₀ 7.8 cSt

PAO8 I polyalphaolefin base oil INEOS Durasyn 128 with KV ₁₀₀ 7.8 cSt

PDI polydispersity index

PHA 2-propylheptyl acrylate

PP pour point

Priolube 3970 ester base fluid available from Croda

RC9420 DI package, commercially available from Rheinchemie

ReMo residual monomer content

SMA Stearyl Methacrylate, 35% C16, 65% C18, All Linear

SL KRL20 shear loss after 20 hours measured using KRL determined at 100°C

SL KRL100 shear loss after 100 hours measured using KRL determined at 100°C

TetDec tetradecene

VI viscosity index

VLA vinyl laurate

VPL 1-180 Evonik VISCOPLEX ^® 1-180, depressant

VPL 1-300 Evonik VISCOPLEX ^® 1-300, depressant

Yubase 4 Group III base oil from SK Lubricants with KV ₁₀₀ 4 cSt

Test methods

KV ASTM D445

VI ASTM D2270

PP ASTM D5950

Corrosion on Copper Strip ASTM D130

Corrosion on a steel plate DIN ISO 7120

TOST ASTM D2893

RPVOT ASTM D2272

Foaming ASTM D892

KRL CEC L-45-A-99

BF ASTM D2983

COC ASTM D92

In the present invention, the bulk viscosity (BV) of the product (the product obtained as a result of the polymerization reaction) corresponds to the kinematic viscosity (KV) of the obtained polymerization product measured according to ASTM D 445. Thus, the bulk viscosity of the polymers, BV40 and BV100, as shown in Tables 1, 2, 3 and 4 below, were measured as the kinematic viscosity at 40°C and 100°C, respectively, according to ASTM D445.

Examples

Synthesis 1. Pure acrylate (note 39*)

1.62 g DBPO (0.6 wt.% based on the amount of acrylate) dissolved in 270.0 g EHA was slowly added to 30.0 g PAO8 under nitrogen atmosphere at 160°C over 3 h. After stirring for another hour, the resulting clear and colorless polymer solution was cooled and used in further experiments without further purification.

Synthesis 2. Copolymer of (meth)acrylate and olefin using a distillation step (Note 8)

3.6 g DBPO (0.3 wt.% relative to monomer in the feed) dissolved in 1200 g EHA were slowly fed into 300 g (0.33 molar equivalent relative to (meth)acrylate) 1-decene under nitrogen at 160°C over 3 hours. After stirring for another hour, the resulting transparent and colourless polymer was cooled. The residual decene was then removed by distillation at 150°C and under pressures not exceeding 5 mbar using a rotary evaporator.

Synthesis 3. Acrylate-olefin copolymer without distillation step (note 54)

0.77 g DBPO (0.3 wt.% relative to monomer in the feed) dissolved in 249.3 g EHA and 5.7 g DEHF was slowly fed into 45.0 g 1-tetradecene under nitrogen at 160°C over 3 hours. After stirring for another hour, the resulting transparent and colorless polymer was cooled and used without further purification.

Examples 1-28 were prepared in the same manner as in Synthesis 2, except that the amounts of reactants or other reaction conditions were varied as shown in Table 1. The alpha-olefin monomers were always charged into the reactor first and the (meth)acrylate monomers and initiator were fed over a specified period of time.

Examples 38-43 were prepared in the same manner as in Synthesis 1, except that the amounts of reagents or other reaction conditions were changed as shown in Table 3.

Examples 44-61 were prepared in the same manner as Synthesis 3, except that the amounts of reagents or other reaction conditions were changed as shown in Table 4.

Since the molar ratio in the reaction is not indicative of the final composition, the final ratio of olefin in the polymer after distillation is given in wt.% (olefin incl.). This ratio was determined gravimetrically with the assumption that the conversion of (meth)acrylate is either complete or its boiling point is too high to be removed by distillation. For example, Example 8 has a residual EHA content of less than 0.01 wt.% before the distillation step.

For some examples, up to 3 polymers with similar viscosity values were blended. For the blending process, the products were stirred together at 80°C for one hour. The blends are listed in Table 2 (see examples 29-37). The amount of olefin incorporated was calculated from the values determined for the individual components. Other values such as molecular weight or viscosity were measured for the blend.

A good high viscosity base fluid must combine several properties. An important criterion for high-performance gear oils is the low temperature performance. In addition to the small temperature dependence of viscosity, which is also reflected in the VI, it is important that the polymers do not exhibit strong intermolecular interactions that lead to poor low temperature performance.

The polymers according to the present invention are characterized by a suitable combination of viscosity, viscosity index and shear resistance, as illustrated in Examples 5, 6 or 8. In contrast, it can be observed that Comparative Example 7* of a copolymer of acrylates and olefins, which contains 22.6% by weight of linear side chains containing more than 8 carbon atoms, is characterized by a good VI (236), but, as shown in its lubricant composition (Example F-21*), does not exhibit good low temperature properties (BF -26 = 192,000 cP). In contrast, Example 50 of the acrylates-olefin copolymer of the present invention, containing only 15% by weight of linear side chains containing more than 8 carbon atoms, combines both a high VI (220) and, as shown in its lubricant composition (Example F-28), exhibits very good performance even under more severe low temperature conditions (BF-30 = 102,000 cP) (BF-30 instead of BF-26 for Comparative Example F-21*).

Surprisingly, even longer side chains, such as in Examples 48 (C12 side chain) or 51 (C14 side chain) according to the present invention, exhibit the same level of performance as Example 50 (C10 side chain), since the total amount of monomer units derived from monomers with a linear alkyl group containing in total more than 8 carbon atoms in the copolymer is less than 22% by weight based on the total weight of the copolymer. Long linear side chains (more than 8 carbon atoms) can be any monomer units of the copolymers (any monomers a), b), c), d) or other comonomers), as shown in Comparative Example 13*, which contains 81% by weight of linear side chains containing more than 8 carbon atoms, due to the high content of lauryl acrylate. As shown in the comparative composition of F-38*, the high content of long linear side chains containing more than 8 carbon atoms in the acrylate monomer units provides very poor low temperature performance (PP -18°C) despite the high VI (195), so a good combination of high VI and good low temperature performance is not achieved. The amount of these side chains is presented as ">C8 SC" in Tables 1-4.

Although polymethacrylates are known to be excellent VI improvers, they are surprisingly outperformed in the low molecular weight range by their acrylate counterparts. This is illustrated in Table 5, where F-2 and F-3* are based on very similar polymers (EHA-based for Inventive Example 29 and EHMA for Comparative Example 20*), but the much higher VI of the EHA-based polymer (Inventive Example 29) provides a higher VI of the final formulation and better low temperature viscosity.

F-2 exhibits performance levels similar to those of the base PAO100 F-1* formulation. Compared to neat polyolefins, the polar ester functionalities in the acrylates-olefin copolymer of the present invention are beneficial in providing overall compatibility between the various components of the formulation (for direct comparison with PAO100, the formulations in Table 4 were prepared without additional additives). Unlike PAOs, which must be prepared by cationic or coordination polymerization methods, the radical polymerization process used to prepare the acrylates-olefin copolymers of the present invention provides easy access to high viscosity products with good shear stability in a commercially attractive manner.

Table 5. Lubricant compositions with high-viscosity base fluids characterized by 100 cSt

(*) indicates comparative examples

Examples of formulations with EHA homopolymers can be found in Tables 6 and 7. For processing reasons, the pure acrylates shown in Table 3 were prepared as solutions in oil, so that bulk properties for these polymers are not available. In order not to influence the comparison of the copolymers, the oil used for the polymerization was the same as that later used in the formulations. As can be seen, the mentioned EHA homopolymers (Comparative Examples 38* and 39*) provide lower VIs in the formulation and exhibit poorer low-temperature properties. As shown in Table 8, Comparative Examples of polyacrylates with longer side chains than the EHA homopolymers also do not exhibit properties as good as the acrylates and olefins copolymers of the present invention.

Table 6. Lubricant compositions with high-viscosity base fluids characterized by 150 cSt

(*) indicates comparative examples

Table 7. Lubricant compositions with high-viscosity base fluids characterized by 450 cSt

(*) indicates comparative examples

Table 8. Lubricant compositions with pure polyacrylate high-viscosity base fluids

(*) indicates comparative examples

Table 9. Residual monomers of the polymers (all amounts in wt.%) described in Table 4

High-performance lubricants must also meet a variety of requirements. In particular, excellent low-temperature properties, high flash points and good aging behavior are directly dependent on the selection of high-viscosity base fluids.

Table 10 below shows that the acrylates and olefins copolymers of the present invention are characterized by high flash points, which meet the requirements of gear oil applications.

The effect of the different PAO viscosity grades is shown in Table 11 below (PAO4, PAO 6, PAO8). Lower grades such as PAO4 allow the use of higher amounts of the acrylates-olefin copolymer of the present invention, which further improves the VI and low temperature performance of the resulting formulations. The F-23 formulation of the present invention provides additional performance parameters that are important for industrial gear oil formulations. High values in the TOST and RPVOT tests indicate good stability against severe oxidative stress at temperature. The low foaming tendency and low corrosivity of the formulation highlight the suitability of the acrylates-olefin copolymers of the present invention in gear oil formulations.

Table 10. Flash point of some high viscosity base fluids

Table 11. Lubricant compositions characterized by 320 cSt, with base oils of different viscosities

(*) means comparative example

(**) added on top

The performance of the polymers without the distillation step is shown in Tables 12 and 13 below and is at the same level as the distilled samples (Table 1). Caution must be exercised in comparing the different formulations in PAO8 since two different samples were used. While “PAO8” has excellent low temperature properties, “PAO8 I” showed slightly worse low temperature properties with an improved VI level.

Table 12. Lubricant compositions characterized by 320 cSt with various high-viscosity base fluids

"k" means thousands (10 ³ ), e.g. BF -30 [cP] 89k cP = 89000 cP

Table 13. Lubricant compositions characterized by 320 cSt with various high-viscosity base fluids

Claims (28)

1. A copolymer containing: a) from 65 to 90% by weight, based on the total weight of the copolymer, of monomer units obtained from at least one acrylate of formula (I), (I), where R ₁ is a linear or branched alkyl group containing from 6 to 12 carbon atoms, b) from 10 to 35% by weight, based on the total weight of the copolymer, of monomer units derived from at least one non-functionalized alpha-olefin of formula (II), (II), where R ₂ is a linear alkyl group containing from 6 to 16 carbon atoms, And c) from 0 to 10% by weight of monomer units derived from at least one monomer selected from the list consisting of methacrylamides, fumarates, maleates or a mixture thereof, based on the total weight of the copolymer, and wherein the copolymer is characterized by a kinematic viscosity of 80 to 600 cSt at 100°C according to ASTM D 445, and wherein the copolymer is characterized by a flash point according to the COC method above 250°C according to ASTM D92, and wherein the copolymer contains from 0 to 22% by weight of monomer units obtained from monomers with a linear alkyl group containing more than 8 carbon atoms, based on the total weight of the copolymer. 2. The copolymer of claim 1, wherein the copolymer contains from 0 to 20% by weight, preferably from 0 to 18% by weight, of monomer units derived from monomers with a linear alkyl group containing more than 8 carbon atoms, based on the total weight of the copolymer. 3. The copolymer according to claim 1 or 2, wherein the copolymer is characterized by a kinematic viscosity of from 100 to 500 cSt at 100°C according to ASTM D 445, preferably from 150 to 400 cSt according to ASTM D 445, more preferably from 150 to 350 cSt according to ASTM D 445. 4. The copolymer according to claim 1 or 2, wherein the copolymer contains from 10 to 30% by weight, preferably from 10 to 25% by weight, of monomer units b) obtained from a non-functionalized alpha-olefin of formula (II), based on the total weight of the copolymer. 5. The copolymer according to claim 1 or 2, wherein the non-functionalized alpha-olefin b) of formula (II) is selected from the group consisting of decene, dodecene, tetradecene, hexadecene or a mixture thereof. 6. The copolymer according to claim 1 or 2, wherein R ₁ in the acrylate of formula (I) is a linear or branched alkyl group containing from 6 to 10 carbon atoms, preferably from 8 to 10 carbon atoms, even more preferably the acrylate of formula (I) is selected from 2-ethylhexyl acrylate, 2-propylheptyl acrylate, n-octyl acrylate or a mixture thereof. 7. The copolymer according to claim 1 or 2, wherein the copolymer contains from 0 to 7% by weight, preferably from 0 to 5% by weight, more preferably from 0 to 3% by weight of monomer units derived from monomer c), based on the total weight of the copolymer. 8. The copolymer according to claim 1 or 2, wherein the total amount of monomer units obtained from monomers a) and b) in the copolymer in total is not more than 90% by weight, preferably in total is not more than 95% by weight, even more preferably in total is not more than 98% by weight based on the total weight of the copolymer. 9. The copolymer according to claim 1 or 2, wherein the total amount of monomer units obtained from monomers a), b) and c) in the copolymer in total is not more than 90% by weight, preferably in total is not more than 95% by weight, more preferably in total is not more than 98% by weight, most preferably in total is not more than 100% by weight based on the total weight of the copolymer. 10. The copolymer according to claim 1 or 2, wherein the copolymer has a weight average molecular weight of 5000 to 30000 g/mol, preferably 7000 to 25000 g/mol, even more preferably 8000 to 20000 g/mol according to DIN 55672-1. 11. The copolymer according to claim 1 or 2, wherein the copolymer is characterized by a PDI of 1 to 4, preferably 1.5 to 3.5. 12. A method for producing a copolymer according to any one of paragraphs 1-11, wherein the copolymer is characterized by a COC flash point above 250°C according to ASTM D92 and wherein the method includes the steps of: i) providing a monomer composition, ii) initiating radical polymerization in the monomer composition to produce a copolymer. 13. A lubricating composition of a lubricant containing one or more base oils and at least one copolymer according to any one of claims 1-11. 14. Use of a copolymer according to any one of claims 1 to 11 as an additive for lubricants or a synthetic base fluid in a lubricating oil composition. 15. The use according to claim 14, wherein the lubricating oil composition is a gear oil composition, a transmission oil composition, a hydraulic oil composition, a motor oil composition, a marine oil composition, an industrial lubricating oil composition, or a grease.