STAR COPOLYMER AND USE THEREOF AS A VISCOSITY IMPROVER

Abstract

Disclosed is a star copolymer (C) including at least 10 wt. % of units derived from styrene monomer and including arms that include a statistical copolymer (EP) including ethylene units and propylene units, and the method for preparing same. Also disclosed is the use thereof in lubricating compositions, in particular for improving the viscosity index, to the lubricating compositions thus obtained and to the uses thereof.

Claims

1-20. (canceled)

21. Star copolymer (C) comprising at least 10% by weight of styrene monomer-derived units and having arms comprising a statistical copolymer (EP) comprising ethylene repeat units and propylene repeat units.

22. The copolymer (C) according to claim 21, having arms comprising a copolymer of general formula S-EP, where: S is a block comprising styrene monomer-derived units; EP is a statistical copolymer comprising ethylene repeat units and propylene repeat units, the star copolymer (C) comprising at least 10% by weight of styrene monomer-derived units.

23. The copolymer (C) according to claim 21 comprising: a cross-linked core comprising styrene monomer-derived units; and arms comprising a statistical copolymer (EP) comprising ethylene repeat units (E) and propylene repeat units (P); the copolymer (C) comprising at least 10% by weight of styrene monomer-derived units.

24. The copolymer (C) according to claim 22, wherein block S of the S-EP copolymer is positioned on the periphery of the core and the EP copolymer at the ends.

25. The star copolymer (C) according to claim 21 comprising from 10 to 60% by weight of styrene monomer-derived units relative to the total weight of the copolymer (C).

26. The star copolymer (C) according to claim 21, having a weight-average molecular weight (Mw) of between 90 000 and 15 000 000 g/mol.

27. The star copolymer (C) according to claim 21, having 3 to 25 arms.

28. The star copolymer (C) according to claim 21, wherein each of the arms, the same or different, has a weight-average molecular weight (Mw) of between 25 000 and 300 000 g/mol.

29. The star copolymer (C) according to claim 21, wherein the arms are all the same or different and the molecular weight average (Mw) of the arms is between 25 000 and 300 000 g/mol.

30. The star copolymer (C) according to claim 21, wherein the EP copolymer in each of the arms is the same or different and comprises from 14 to 90% by weight of ethylene repeat units relative to the total weight of said EP copolymer.

31. The star copolymer (C) according to claim 21, wherein the EP copolymers in each of the arms are all the same or different and on average comprise from 14 to 90% by weight of ethylene repeat units relative to the average weight of the EP copolymer.

32. The star copolymer (C) according to claim 21, further comprising at least one group comprising at least one polar function located on at least one of the arms.

33. The star copolymer (C) according to claim 21 in the form of a dispersion in an anhydrous medium.

34. Lubricating composition comprising at least one base oil and at least one star copolymer (C) according to claim 21.

35. Lubricating composition comprising from 0.1 to 50% by weight of star copolymer (C), according to claim 21, relative to the total weight of the composition.

36. A method for improving the viscosity index of a lubricating composition, comprising a step of addition of a star copolymer (C) according to claim 21 to said lubricating composition.

37. Method according to claim 36, wherein the star copolymer (C) is added to the lubricating composition in a proportion of from 0.1 to 50% by weight relative to the total weight of the composition.

38. A method for reducing the friction coefficient of a lubricating composition, comprising a step of addition of a star copolymer (C) according to claim 21 to said lubricating composition.

39. A method for reducing the fuel consumption of an engine, comprising a step of applying the lubricating composition according to claim 34 to said engine.

40. Method for preparing a star copolymer (C) according to claim 21, comprising: a) a step to synthesize a statistical copolymer (EP) comprising ethylene repeat units, propylene repeat units and residual double bonds; b) a step to functionalise the copolymer (EP) derived from step a) with a nucleophilic addition reactive function; c) a step to polymerize styrene monomers in the presence of a cross-linking agent; d) a step to add the polymer derived from step c) onto the copolymer (EP) derived from step b); e) a step to recover the star copolymer (C) obtained at step d).

41. A method for reducing fuel consumption of an engine lubricated by means of a lubricating composition, comprising a step of addition of a star copolymer (C) according to claim 21 to said lubricating composition.

42. A method for reducing the fuel consumption of a vehicle equipped with a drive axle or gearbox and lubricated by means of a lubricating composition, comprising a step of addition of a star copolymer (C) according to claim 21 to said lubricating composition.

43. A method for reducing the fuel consumption of a vehicle equipped with a transmission and lubricated by means of a lubricating composition, comprising a step of addition of a star copolymer (C) according to claim 21 to said lubricating composition.

44. A method for reducing the traction coefficient of lubricating composition, comprising a step of addition of a star copolymer (C) according to claim 21 to said lubricating composition.

45. A method for improving the Fuel Eco (FE) of a lubricating composition, comprising a step of addition of a star copolymer (C) according to claim 21 to said lubricating composition.

46. A method for reducing the fuel consumption of a vehicle equipped with a drive axle or gearbox, comprising a step of applying the lubricating composition according to claim 34 to said drive axle or gearbox.

47. A method for reducing the fuel consumption of a vehicle equipped with a transmission, comprising a step of applying the lubricating composition according to claim 34 to said transmission.

Description

EXAMPLE 1

Preparation of a Star Copolymer (C) of the Invention

[0224] The entire preparation method is conducted in a controlled nitrogen atmosphere. Also, all the monomers are purified on a neutral, activated aluminium oxide column and stored on a 4A molecular sieve in an inert atmosphere. The solution of sec-BuLi used is 1.4 M in hexane.

[0225] A 2L reactor equipped with mechanical agitator (anchor type) and counter blade is charged with 500 mL anhydrous toluene (purification via azeotropic entrainment), 1.0 mL of Styrene (8.7 mmol) and 1.20 mL of N,N,N,N-tetramethylethylenediamine (4.0 mmol). The solution obtained is degassed with three vacuum/nitrogen cycles and cooled to 20 C. under agitation (200 rpm). The proton impurities are neutralized with the dropwise addition of sec-Butyllithium until a persistent orange/yellow colouring is obtained (amount of sec-BuLi varying between 0.2 and 0.6 mL). The sec-BuLi charge is then rapidly added (2.85 mL, 4 mmol) under 350 rpm agitation, followed by the addition of 1, 12 mL divinylbenzene (8 mmol). The medium quickly takes on a dark red colouring. The medium is left under agitation 30 min at 20 C. (200 rpm). The styrene (15 mL, 130 mmol) is then quickly added at 20 C. The medium is heated to 50 C. for 2h, then lowered to ambient temperature (the medium is of bright orange colour). A solution of statistical ethylene/propylene copolymer comprising maleic anhydride functions (V4021 distributed by FUNCTIONAL PRODUCTS INC and later called OCP/MAH) is added to the medium using a cannula in an inert atmosphere.

[0226] Before addition, the OCP/MAH is purified with the following method: in a round bottom flask equipped with mechanical agitation, 30 g of OCP/MAH are solubilised in 500 mL toluene. The copolymer dissolves in 16h under vigorous agitation at 35 C. The copolymer is then precipitated in 1.5 L of MeOH under vigorous agitation. The solid is washed with 500 mL additional methanol by trituration. The solid is then dried under reduced pressure at 40 C. for 4h.

[0227] The OCP/MAH obtained (28.5 g) is dissolved in 700 mL toluene. The solution obtained is placed under nitrogen reflux in an assembly of Dean-Stark type for 24h with regular draining of the toluene/water binary in the Dean-Stark apparatus. The solution is then cooled to ambient temperature for IR analysis.

[0228] The addition is halted as soon as the orange colour has fully disappeared (pale yellow medium) (75% by volume of solution i.e. 21 g of OCP). 20 mL of methanol are added to quench the reaction. The copolymer obtained is purified by precipitation and washed by trituration in 2L of methanol. The copolymer is vacuum dried overnight at ambient temperature.

[0229] The copolymer (C) obtained is a star copolymer comprising 34% by weight of styrene repeat units (measured by NMR spectroscopy) and arms comprising a statistical ethylene/propylene copolymer.

EXAMPLE 2

Evaluation of the Viscosity Index Improving Properties of a Star Copolymer (C) of the Invention

[0230] The star copolymer of Example 1 was solubilised in the following base oils: [0231] base oil 1: Group I base oil (kinematic viscosity measured at 100 C. as per ISO standard: 3104=5.19 mm.sup.2/s) [0232] base oil 2: Group V base oil of alkylnaphthalene type (Synesstic 5 marketed by Exxonmobil)

[0233] For solubilisation, 1 g of star copolymer of Example 1 was solubilised in 100 g of base oil and subjected to agitation on a magnetic hot plate at 150 C. for 96 h.

[0234] Each mixture was then filtered and centrifuged.

[0235] Mixtures 1 and 2 thus prepared are described in Table I (the values given correspond to weight percentages).

TABLE-US-00002 TABLE I Mixture 1 Mixture 2 Star copolymer of Example 0.9 0.9 1 Base oil 1 99.1 Base oil 2 99.1

[0236] The viscosity index of mixtures 1 and 2, and of the base oils 1 and 2 were measured in accordance with standard ISO 2909; the results are given in Table II.

TABLE-US-00003 TABLE II Base oil 1 Mixture 1 Base oil 2 Mixture 2 Viscosity Index 104 118 79 145 (VI)

[0237] These results show that the star copolymer (C) of the invention allows the viscosity index of a base oil to be improved, irrespective of the type of base oil.

[0238] These results therefore demonstrate that the star copolymer of the invention can be used in a lubricating composition as VI improver.