WO2017198522A1

WO2017198522A1 - Next generation polyolefins for lubricant application

Info

Publication number: WO2017198522A1
Application number: PCT/EP2017/061253
Authority: WO
Inventors: Stefan Maier; Michael Neusius; Klaus Schimossek; Stephan Fengler
Original assignee: Evonik Oil Additives Gmbh
Priority date: 2016-05-19
Filing date: 2017-05-11
Publication date: 2017-11-23

Abstract

The present invention relates to lubricant compositions comprising polyolefin polymers, and to the use of these lubricant compositions as an automatic transmission fluid, a continuously variable transmission fluid, an engine oil, a gear oil, or a hydraulic oil.

Description

Next generation polyolefins for lubricant application

FIELD OF THE INVENTION

STATE OF THE ART

Lubricants are compositions that reduce friction between surfaces. In addition to allowing freedom of motion between two surfaces and reducing mechanical wear of the surfaces, a lubricant also may inhibit corrosion of the surfaces and/or may inhibit damage to the surfaces due to heat or oxidation. Examples of lubricant compositions include, but are not limited to, engine oils, transmission fluids, gear oils, industrial lubricating oils, and metalworking oils.

A typical lubricant composition includes a base fluid and optionally one or more additives. Conventional base fluids are hydrocarbons, such as mineral oils. The terminology base oil and base fluid is commonly used interchangeably. Here, base fluid will be used as a general term. The term base oil is used to describe base fluids originating from crude oil.

A wide variety of additives may be combined with the base fluid, depending on the intended use of the lubricant. Examples of lubricant additives include, but are not limited to, oxidation inhibitors, corrosion inhibitors, dispersing agents, high pressure additives, anti-foaming agents and metal deactivators.

The physical and chemical properties of a lubricant are affected by the chemical structures of the various components of the lubricant, the relative amounts of the components in the lubricant, and the processing techniques used to form the lubricant. For example, the chemical structure of the base fluid may determine overall ranges of physical and chemical properties of the lubricant, with the specific properties being affected by the other components of the lubricant composition and/or the manner in which the lubricant composition is prepared. Alteration of the chemical structure of the base fluid can allow for modification of the overall range of properties of a lubricant containing the base fluid.

High viscosity base fluids are used as thickeners for lubricants with very high shear stability requirements. Typically, polyalphaolefins (PAO) with a kinematic viscosity at 100 °C (KV100) of 40 cSt and higher are used in these applications. In the last years the performance of PAOs was improved by the use of metallocene catalysts which gives better control over the molecular structure. As stated by Harrington in Tribologie + Schmierstofftechnik 2014, 14, these metallocene catalyzed PAOs (mPAO) provide improved viscosity index (VI) and low temperature properties such as pour point (PP) at the expense of inferior thickening properties. In contrast, very good thickening properties are an intrinsic feature of low molecular weight ethylene-propylene copolymers which are slightly worse in VI and PP than the mPAOs.

The present invention aims at providing high viscosity base fluids that can be used as thickeners for lubricant compositions with very high shear stability requirements. Further, the present invention aims at providing high viscosity base fluids in lubricant compositions that have improved VI and PP.

SUMMARY OF THE INVENTION

These objects, and also further objects which are not stated explicitly but which can be derived or discerned directly from the connections discussed by way of introduction herein are achieved by a lubricant composition comprising a polymer consisting of units derived from one or more compounds of formula (I)

(I), wherein 5 < x < 10

and 5 < y < 10.

ADVANTAGES OF THE INVENTION

It was surprisingly found that lubricant compositions comprising polymers according to the present invention have viscosity index (VI) and low temperature properties such as pour point (PP) superior to the current state of the art. The polymers as defined in the present invention are accessible via metathesis polymerizations, either ring opening metathesis polymerization (ROMP) or acyclic diene metathesis (ADMET). By these polymerization techniques, the polymer structure can be precisely controlled. The polymers obtained by metathesis polymerizations contain double bonds which have to be hydrogenated for use in lubricant compositions due to oxidative stability requirements.

BRIEF DESCRIPTION OF FIGURES

Figure 1 and Figure 2 show bulk properties of different polyolefin base fluids in comparison to the polymer of the present invention.

In particular, Figure 1 shows the viscosity Index (VI) of different base fluids compared with the ROMP polymer of the invention in correlation with their respective kinematic viscosity at 100 °C (KV100). Figure 2 shows the Pour Point (PP) of different base fluids compared with the ROMP polymer of the invention in correlation with their kinematic viscosity at 100 °C (KV100).

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to lubricant compositions comprising polymers that consists of units derived from one or more compounds of formula (I),

(I), wherein 5 < x < 10

and 5 < y < 10.

Similar polymers have been described by Hillmyer and Kobayashi in J. Am. Chem. Soc. 2011 , 5794, and in Organometallics 2013, 4843.

In a preferred aspect of the present invention, in the units of formula (I) x = 7 and y = 7. This appears to be the best compromise between VI performance that requires long unbranched segments and low temperature performance that requires short distances between the branches. In a preferred aspect of the present invention, the weight average molecular weight (M_w) of the polymer is in the range of from 8 000 to 25 000 g/mol, more preferably 10 000 to 20 000 g/mol, wherein the weight average molecular weight is determined by gel permeation chromatography (GPC) against poly(methyl methacrylate) standards. Tetrahydrofuran (THF) is used as eluent.

In a further preferred aspect of the present invention, the polydispersity index (PDI = M_w / M_n) of the polymer is in the range of 1 to 1 .8, more preferably in the range of 1 to 1 .6, most preferably in the range of 1 to 1 .4.

The polymers as described herein are prepared according to a process comprising the steps of ring-opening metathesis polymerization of a 3-alkyl substituted cycloalkene, the cycloalkene comprising x+1 ring carbon atoms and the alkyl substituent comprising y+1 carbon atoms, and subsequent hydrogenation.

This method is highly selective regarding head to tail coupling of the monomer units, which is expected due to the steric hindrance of the alkyl substituent in the 3-alkyl substituted cycloalkene.

Polymerization reaction can be catalyzed by commercially available Grubbs II catalysts. Molecular weight of the polymer can be controlled by the amount of catalyst and chain transfer agent that may be added to the reaction, such as e.g. 4-octene.

Hydrogenation reaction can be catalyzed by commercially available Wilkinson's catalyst Rh(PPh₃)₃CI.

In a preferred aspect of the present invention, the 3-alkyl substituted cycloalkene is prepared by reaction of a 3-bromo cycloalkene with Alkyl-MgBr.

In a further preferred aspect of the present invention, the 3-bromo cycloalkene is prepared by reaction of a cycloalkene with N-bromosuccinimide. Preferably, bromination is carried out according to Langlois Adv. Synth. Catal. 2010, 447, in order to avoid CCU as a solvent.

The amount of the polymer in the lubricant composition is not particularly limited. In a preferred aspect of the present invention, the lubricant composition as described herein comprises 10 to 60 wt.-% of the polymer, more preferably 15 to 50 wt.-%, most preferably 20 to 40 wt.-%.

According to a preferred aspect of the invention, the lubricating oil composition at least one polymer of the present invention and a base oil.

The base oils correspond to lubricant base oils, mineral, synthetic or natural, animal or vegetable oils suited to their use/chosen depending on the intended use. The base oils used in formulating the lubricating oil compositions according to the present invention include, for example, conventional base stocks selected from API (American Petroleum Institute) base stock categories known as Group I, Group II, Group III, Group IV and Group V. The Group I and II base stocks are mineral oil materials (such as paraffinic and naphthenic oils) having a viscosity index (or VI) of less than 120. Group I is further differentiated from Group II in that the latter contains greater than 90% saturated materials and the former contains less than 90% saturated material (that is more than 10% unsaturated material). Group III is considered the highest level of mineral base oil with a VI of greater than or equal to 120 and a saturates level 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 lubricant composition comprises an API Group III base oil. Group IV base oils are polyalphaolefins (PAO). Group V base oils are esters and any other base oils not included in Group I to IV base oils. These base oils can be used individually or as a mixture. In a preferred embodiment of the invention, the lubricating oil composition comprises from 40 to 90 % by weight of at least one base oil and from 10 to 60 % by weight of at least one polymer 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 comprise any other additional additives suitable for use in the lubricant oil formulations. These additives include viscosity index improvers, pour point depressants, dispersants, demulsifiers, defoamers, lubricity additives, friction modifiers, antioxidants, detergents, dyes, corrosion inhibitors and/or odorants.

Preferably, the lubricant composition matches the requirements of ISO VG classes 220 or 320 or 460, most preferably the class ISO VG 320 (Industrial oils - ISO 3448).

Preferably, the lubricant composition has a viscosity index (VI) calculated according to ASTM D 2270 in the range of from 150 to 220, more preferably 160 to 200, most preferably 170 to 190. Pursuant to ASTM D 2270, VI is calculated from the kinematic viscosity at 40 °C (KV40) and the kinematic viscosity at 100 °C (KV100), both being measured according to ASTM D 445.

Preferably, the lubricant composition has a pour point (PP) measured according to ASTM D 97 of - 39 °C or less, more preferably -45 °C or less, most preferably -51 °C or less. Preferably, the lubricant composition has a Brookfield viscosity (BF) measured at -30 °C according to ASTM D2983 of 100 000 mPas or less, more preferably of 80 000 mPas or less, most preferably of 70 000 mPas or less.

The present invention further relates to the use of the lubricant composition as described herein as an automatic transmission fluid, a continuously variable transmission fluid, an engine oil, a gear oil, or a hydraulic oil. The lubricating oil compositions comprising at least one polymer according to the present invention are favorably used for driving system lubricating oils (such as manual transmission fluids, differential gear oils, automatic transmission fluids and belt-continuously variable transmission fluids, axle fluid formulations, dual clutch transmission fluids, and dedicated hybrid transmission fluids), hydraulic oils (such as hydraulic oils for machinery, power steering oils, shock absorber oils), engine oils (for gasoline engines and for diesel engines) and industrial oil formulations (such as wind turbine).

From the standpoint of the kinetic viscosity of the polymer according to the present invention, the weight content of the polymer in the lubricating oil composition is preferably comprised in the range between 10 wt% and 60 wt%, based on the total weight of the lubricating oil composition.

The present invention is further illustrated by the following non-limiting examples. Example 1 : Ring-opening metathesis polymerization (ROMP) Bromination of Cyclooctene

137.0 g NBS were added to 1 10.2 g cyclooctene in 400 g cyclohexane under vigorous stirring. 0.50 g 2,2'-Azobis-(2,4 dimethylvaleronitril) were added and the reaction was heated under reflux for 3 hours. After cooling the precipitate was removed by filtration. After vacuum distillation 92.7 g of a clear colorless liquid were obtained.

Grignard reaction

300 mL of octylmagnesiumbromide solution (2 M in diethylether) were slowly added at 0 °C under nitrogen to a solution of 84.3 g 3-bromo cyclooctene and 1 .0 g copper(l)iodide in 450 mL of dry THF. After stirring for 2 hours the reaction was quenched with water and the organic layer was separated. The water phase was extracted 3 times with heptane. The combined organic layers were dried over sodium sulfate and after vacuum distillation 74.1 g of a clear colorless liquid were obtained.

Polymerization

0.099 g of 2^nd generation Grubbs catalyst in 33 mL MTBE were added to a solution of 74.1 g 3-octyl cyclooctene and 0.99 g trans-4-octene in 198 mL dry heptane under nitrogen. The reaction mixture was heated to 35 °C 24 hours. After this time 1 mL butylvinylether was added and the reaction mixture was filtered over a basic alumina column. After removal of solvent by distillation at 40 °C and 1 mbar the product was not further purified. The reaction yield is 87%. The obtained polymer has a weight average molecular weight (M_w) of 14 900 g/mol and a PDI of 1 .52 (determined by GPC against PMMA standards with THF as eluent).

Hydrogenation

92 g of poly(3-octylcyclooctene) polymer mixture and 1 g Wilkinson's catalyst Rh(PPh3)3CI were dissolved in 100 mL of Heptane. The mixture was heated for 24 hours to 120 °C at 200 bar hydrogen pressure. The reaction mixture was subsequently filtered over silica gel to remove the catalyst. Low boiling components were removed by vacuum filtration to yield 68 g of a colorless, clear viscous liquid. NMR analysis shows that the product is fully hydrogenated. The final ROMP polymer has a weight average molecular weight (M_w) of 17 000 g/mol and a PDI of 1 .4 (determined by GPC against PMMA standards with THF as eluent). Comparison of the bulk properties of the ROMP polymer (Example 1) according to the invention to commercially available polvolefin base fluids

As shown in Table 1 , the bulk properties of the polymer prepared in Example 1 were measured: the ROMP polymer has a KV100 of 548 cSt, a VI of 264 and a PP of -27 °C.

Table 1

The bulk properties of the polymer claimed in the present invention were compared to commercially available polyolefin base fluids.

To this effect, data for the commercially available polymers were taken from technical datasheets (see Table 2 below). Table 2

The above data are also represented in Figure 1 (Viscosity Index (VI) of different base fluids compared with the ROMP polymer of the invention in correlation with their respective kinematic viscosity at 100 °C (KV100) and in Figure 2 (Pour Point (PP) of the base fluids of Table 2 compared with the ROMP polymer of the invention (Table 1 ) in correlation with their kinematic viscosity at 100 °C (KV100)). Comparison of the bulk properties of a gear oil formulation comprising a polymer according to the invention to gear oil formulations comprising commerciallv available polvolefin base fluids

Table 3 summarizes the comparison of different ISO 320 formulations.

Table 3

While treat rate is on the excellent level for the Lucant^® polymer, a gear oil formulation comprising the polymer of the invention (ROMP polymer) performs better in terms of VI and low temperature viscosity. The Brookfield viscosity of the gear oil composition comprising the inventive polymer is also drastically improved compared to the gear oil compositions comprising commercially available polymers.

Footnotes for Tables 2 and 3:

Lucant^® HC -40, 100, -600, -1100, -2000 from Mitsui Chemicals correspond to hydrocarbon- based synthetic oils having no polar groups and being copolymers of ethylene and propylene (OCP series in Table 2 and Lucant^® HC-600 in Table 3) mPAO series (Table 2) are copolymers prepared by metallocene catalyzed polymerization of different alpha olefins.

SpectraSyn Elite^® 150 from ExxonMobil (Table 3): Copolymer prepared by metallocene catalysis of different alpha olefins with a KV100 of 150 cSt.

Additin^® RC 9420 from RheinChemie: Performance package comprising antiwear additives based on phosphorus-sulfur compounds, antioxidants and corrosion inhibitors PAO series (Table 2) are copolymers of different alpha olefins (polyalphaolefins).

PAO 8 from Chevron (Table 3) : Copolymer of different alpha olefins with a KV100 of 8 cSt. KRL 100h loss @100 °C: Viscosity loss after 100 hours in the tapered roller bearing test (DIN 51350 T6). Viscosity loss is calculated as 1 -KV100after/KV1 OObefore

Claims

A lubricant composition comprising a polymer consisting of units derived from one or more compounds of formula (I)

(I), wherein 5 < x < 10

and 5 < y < 10.

2. The lubricant composition according to claim 1 , wherein the lubricant composition

comprises a polymer wherein in the units of formula (I) x = 7 and y = 7.

3. The lubricant composition according to claim 1 or claim 2, wherein the polymer has a weight average molecular weight (M_w) in the range of from 8 000 to 25 000 g/mol.

4. The lubricant composition according to any one of claims 1 to 3, wherein the polymer has a polydispersity index (PDI = M_w / M_n) in the range of 1 to 1 .8.

5. The lubricant composition according to any one of claims 1 to 4, wherein the lubricant composition comprises 10 to 60 wt.-% of the polymer, based on the total weight of the lubricant composition.

6. The lubricant composition according to any one of claims 1 to 5, wherein the lubricant composition has an International Standards Organization Viscosity Grade 220 or 320 or 460 (ISO VG - IS03428).

7. The lubricant composition according to any one of claims 1 to 6, wherein the lubricant composition has a viscosity index (VI) calculated according to ASTM D 2270 in the range of from 170 to 190.

8. The lubricant composition according to any one of claims 1 to 7, wherein the lubricant composition has a pour point (PP) measured according to ASTM D 97 of -45°C or less.

9. The lubricant composition according to any one of claims 1 to 8, wherein the lubricant composition has a Brookfield viscosity (BF) measured at -30°C according to ASTM D2983 of 70 000 mPas or less.

10. Use of the lubricant composition according to any one of claims 1 to 9 as a gear oil.

11 . Use of the lubricant composition according to any one of claims 1 to 9 as an automatic transmission fluid, a continuously variable transmission fluid, an engine oil, or a hydraulic oil.