Associative and exchangeable oligomers, and composition comprising same

Abstract

Compositions resulting from the mixing of at least one oligomer A1, resulting from the copolymerization of at least one monomer functionalized by diol functions with at least a second monomer, and at least one compound A2 including at least two boronic ester functions. The compositions exhibit very varied rheological properties, depending on the proportion of the compounds A1 and A2 used. A composition also results from mixing at least one lubricating oil with such a composition of associative and exchangeable polymers, and to the use of this composition to lubricate a mechanical part.

Claims

1. A composition resulting from the mixing of at least a polydiol oligomer A1 with a number-average molar mass of greater than or equal to 600 g/mol and less than 5000 g/mol, comprising repeating units corresponding to: at least two monomers M1, and from 2 mol % to 50 mol % of repeating units corresponding to one or more monomers M3, and optionally at least one monomer M2, and a compound A2 comprising at least two boronic ester functions, the monomer M1 corresponding to the general formula (I): ##STR00038## in which: R.sub.1 is chosen from the group formed by —H, —CH.sub.3 and —CH.sub.2—CH.sub.3; x is an integer ranging from 1 to 18; y is an integer equal to 0 or 1; X.sub.1 and X.sub.2, which may be identical or different, are chosen from the group formed by hydrogen, tetrahydropyranyl, methyloxymethyl, tert-butyl, benzyl, trimethylsilyl and t-butyldimethylsilyl; or X.sub.1 and X.sub.2 form, with the oxygen atoms, a bridge having the following formula ##STR00039## in which: the asterisks (*) symbolize the bonds to oxygen atoms, R′.sub.2 and R″.sub.2, which may be identical or different, are chosen from the group formed by hydrogen and a C.sub.1-C.sub.11 alkyl; or X.sub.1 and X.sub.2 form, with the oxygen atoms, a boronic ester having the following formula: ##STR00040## in which: the asterisks (*) symbolize the bonds to oxygen atoms, R″′.sub.2 is chosen from the group formed by a C.sub.6-C.sub.30 aryl, a C.sub.7-C.sub.30 aralkyl and a C.sub.2-C.sub.30 alkyl; the monomer M2 corresponding to the general formula (II): ##STR00041## in which: R.sub.2 is chosen from the group formed by —H, —CH.sub.3 and —CH.sub.2—CH.sub.3; R.sub.3 is chosen from the group formed by: —C(O)—O—R′.sub.3; —O—R′.sub.3; —S—R′.sub.3 and —C(O)—N(H)—R′.sub.3 with R′.sub.3 a C.sub.1-C.sub.30 alkyl group, the monomer M3 corresponding to the general formula (X): ##STR00042## in which: Z.sub.1, Z.sub.2 and Z.sub.3, which may be identical or different, represent groups chosen from a hydrogen atom, a C.sub.1-C.sub.12 alkyl, and a group —OZ′ or —C(O)—O—Z′ with Z′ being a C.sub.1-C.sub.12 alkyl.

2. The composition as claimed in claim 1, in which the oligomer A1 has a number-average molar mass ranging from 600 g/mol to 4900 g/mol.

3. The composition as claimed in claim 1, in which the monomer M3 is styrene.

4. The composition as claimed in claim 1, in which the side chains of the oligomer A1 have a mean length ranging from 8 to 20 carbon atoms.

5. The composition as claimed in claim 1, in which the oligomer A1 has a molar percentage of repeating units corresponding to the monomer M1 of formula (I) ranging from 2% to 70%.

6. The composition as claimed in claim 1, in which the oligomer A1 has a number-average degree of polymerization ranging from 3 to 100.

7. The composition as claimed in claim 1, in which the oligomer A1 has a polydispersity index (Ip) ranging from 1.05 to 4.0.

8. The composition as claimed in claim 1, in which compound A2 is a compound of formula (III): ##STR00043## in which: w.sub.1 and w.sub.2, which may be identical or different, are integers chosen between 0 and 1; R.sub.4, R.sub.5, R.sub.6 and R.sub.7, which may be identical or different, represent a group chosen from a hydrogen atom, a hydrocarbon-based group comprising from 1 to 30 carbon atoms, optionally substituted with one or more groups chosen from: a hydroxyl, a group —OJ or —C(O)—O-J with J being a hydrocarbon-based group comprising from 1 to 24 carbon atoms; L is a divalent bonding group chosen from the group formed by a C.sub.6-C.sub.18 aryl, a C.sub.6-C.sub.18 aralkyl and a C.sub.2-C.sub.24 hydrocarbon-based chain.

9. The composition as claimed in claim 1, in which compound A2 is an oligomer comprising repeating units which correspond to at least two monomers M4 of formula (IV): ##STR00044## in which: t is an integer equal to 0 or 1; u is an integer equal to 0 or 1; M and R.sub.8 are identical or different divalent bonding groups, chosen from the group formed by a C.sub.6-C.sub.18 aryl, a C.sub.7-C.sub.24 aralkyl and a C.sub.2-C.sub.24 alkyl, X is a function chosen from the group formed by —O—C(O)—, —C(O)—O—, —C(O)—N(H)—, —N(H)—C(O)—, —S—, —N(H)—, —N(R′.sub.4)— and —O— with R′.sub.4 being a hydrocarbon-based chain comprising from 1 to 15 carbon atoms; R.sub.9 is chosen from the group formed by —H, —CH.sub.3 and —CH.sub.2—CH.sub.3; R.sub.10 and R.sub.11, which may be identical or different, represent a group chosen from a hydrogen atom, a hydrocarbon-based group comprising from 1 to 30 carbon atoms, optionally substituted with one or more groups chosen from: a hydroxyl, a group —OJ or —C(O)—O-J with J being a hydrocarbon-based group comprising from 1 to 24 carbon atoms; and optionally at least one monomer M5 of general formula (V): ##STR00045## in which: R.sub.12 is chosen from the group formed by —H, —CH.sub.3 and —CH.sub.2—CH.sub.3, R.sub.13 is chosen from the group formed by —C(O)—O—R′.sub.13; —O—R′.sub.13, —S—R′.sub.13 and —C(O)—N(H)—R′.sub.13, with R′.sub.13 a C.sub.1-C.sub.30 alkyl group, optionally at least one monomer M3 of general formula (X) ##STR00046## in which: Z.sub.1, Z.sub.2 and Z.sub.3, which may be identical or different, represent groups chosen from a hydrogen atom, a C.sub.1-C.sub.12 alkyl, and a group —OZ′ or —C(O)—O—Z′ with Z′ being a C.sub.1-C.sub.12 alkyl.

10. The composition as claimed in claim 9, in which the oligomer A2 has a number-average molar mass ranging from 600 g/mol to less than 10 000 g/mol.

11. The composition as claimed in claim 9, in which the oligomer A2 has a molar percentage of monomer M4 of formula (IV) in said oligomer ranging from 4% to 50%.

12. The composition as claimed in claim 9, in which, the chain formed by the sequence of groups R.sub.10, M, X and (R.sub.8).sub.u with u equal to 0 or 1 of the monomer of formula (IV) has a total number of carbon atoms ranging from 8 to 38.

13. The composition as claimed in claim 9, in which the side chains of the oligomer A2 have a mean length of greater than or equal to 8 carbon atoms.

14. The composition as claimed in claim 9, in which the oligomer A2 has a number-average degree of polymerization ranging from 2 to 100.

15. The composition as claimed in claim 9, in which the oligomer A2 has a polydispersity index (Ip) ranging from 1.04 to 3.54.

16. The composition as claimed in claim 1, in which the content of oligomer A1 ranges from 0.1% to 50% by weight relative to the total weight of the composition.

17. The composition as claimed in claim 1, in which the content of oligomer A2 ranges from 0.1% to 50% by weight relative to the total weight of the composition.

18. The composition as claimed in claim 1, in which the mass ratio between the oligomer A1 and compound A2 (ratio A1/A2) ranges from 0.002 to 500.

19. A lubricant composition resulting from the mixing of at least: a lubricant oil; and a composition as defined in claim 1.

20. A process for reducing the fuel consumption of a vehicle, comprising at least one step of placing a mechanical part of the vehicle engine in contact with a lubricant composition as claimed in claim 19.

Description

FIGURES

(1) FIG. 1 schematically represents a random copolymer (P1), a gradient copolymer (P2) and a block copolymer (P3); each circle represents a monomer unit. The difference in chemical structure between the monomers is symbolized by a different color (light gray/black).

(2) FIG. 2 schematically illustrates the exchange reactions of boronic ester bonds between two polydiol oligomers (A1-1 and A1-2) and two boronic diester oligomers (A2-1 and a 2-2) in the presence of diols.

(3) FIG. 3 schematically illustrates and represents the crosslinking of the composition according to the invention in tetrahydrofuran (THF).

(4) FIG. 4 schematically represents the behavior of the composition of the invention as a function of an external stimulus, in this example the temperature. An oligomer (2) bearing diol functions (function A) can reversibly associate with an oligomer (1) bearing boronic ester functions (function B) via a transesterification reaction. The organic group of the boronic ester functions (function B) which exchanges during the transesterification reaction is a diol symbolized by a black crescent. It forms a chemical bond (3) of boronic ester type with release of a diol compound.

(5) FIG. 5 is a graph showing the curves of variation in dynamic viscosity measured as a function of the shear rate applied to compositions A, B and F at 40° C. The (.circle-solid.) curve corresponds to composition A. The (.square-solid.) curve corresponds to composition F. The x-axis of the graph represents the shear rate values in s.sup.−1, and the y-axis represents the viscosity values measured in mPa.Math.s.

(6) FIG. 6 is a graph showing the curves of variation in dynamic viscosity measured as a function of the shear rate applied to compositions A, B and F at 100° C. The (.circle-solid.) curve corresponds to composition A. The (.square-solid.) curve corresponds to composition F. The x-axis of the graph represents the shear rate values in s.sup.−1, and the y-axis represents the viscosity values measured in mPa.Math.s.

(7) FIG. 7 is a graph showing the curves of variation in dynamic viscosity measured as a function of the shear rate applied to compositions A, B and F at 150° C. The (.circle-solid.) curve corresponds to composition A. The (.square-solid.) curve corresponds to composition F. The x-axis of the graph represents the shear rate values in s.sup.−1, and the y-axis represents the viscosity values measured in mPa.Math.s.

(8) FIG. 8 schematically illustrates and represents a chemical exchange reaction (transesterification) according to an embodiment.

EXPERIMENTAL SECTION

(9) The examples that follow illustrate the invention without limiting it.

1. Syntheses

1.1. Synthesis of the Polydiol Oligomer

1.1.1. Monomers

Monomer M1: Methacrylate Bearing a Diol Function (Mono-Diol

(10) This synthesis is performed according to the protocol described in patent application WO 2018/096253 (experimental section § 1.1.1).

Monomer M2: Stearyl Methacrylate (StMA

(11) The stearyl methacrylate is that sold by Sigma-Aldrich® and TCI®.

Monomer M3: Styrene

(12) The styrene is that sold by Sigma-Aldrich®.

1.1.2. Synthesis of the Oligomer o-Diol-3

(13) The synthesis of the oligomer o-Diol-3 is performed according to the following reaction scheme:

(14) ##STR00033##

(15) For the amounts introduced, refer to Table 1.1 below.

(16) Stearyl methacrylate (StMA), methacrylate bearing a diol function (mono-Diol) and ethyl 2-mercaptopropionate (Solution 1) as well as 300 mL of toluene are placed in a 1 L reactor connected to a condenser, a thermometer and a nitrogen supply. The reaction medium is degassed by sparging with nitrogen, and stirred until the temperature reaches 100° C. Next, 4 mL of a solution of azobisisobutyronitrile (AIBN) in toluene (Solution 2) is added to the reaction medium. Once evolution of gas has appeared, the remainder of Solution 2 and of Solution 3 is added simultaneously over a period of 40 minutes. The reaction progress is monitored by SEC analysis. After 4 hours of polymerization at 100° C., the reaction medium is cooled to room temperature. The polymer is precipitated three times from 300 mL of methanol. The volatile substances are evaporated off under reduced pressure at a temperature below 50° C. The product is then dried under vacuum for 72 hours at 40° C. in order to remove the solvent residues. 101.1 g of a pasty white solid are obtained. Yield: 81%.

(17) TABLE-US-00002 TABLE 1.1 amounts introduced for the synthesis of the oligomer o-Diol-3 Mass/Volume Solution 1: StMA 106.69 g Mono-Diol 9.12 g pure Ethyl 2-mercaptopropionate 7.16 g Solution 2: Styrene 9.39 g Solution 3: AIBN 1.47 g Toluene 35 mL

Characterization

(18) The oligomer obtained comprises 10 mol % of repeating units containing diol functions, 72 mol % of StMA repeating units and 18 mol % of styrene repeating units as determined by .sup.1H NMR (400 MHz, CDCl.sub.3).

(19) The oligomer has a number-average molar mass of approximately 4500 g.Math.mol.sup.−1 and a polydispersity index of 1.34 as determined by SEC in THF using poly(methyl methacrylate) calibration at 40° C.

1.2. Synthesis of the Boronic Ester Oligomer

1.2.1. Monomers

Monomer M4: Monomer Bearing a Boronic Ester Function (Mono-EB

(20) This synthesis is performed according to the protocol described in patent application WO 2016/113229 (experimental section § 2.1).

1.2.2. Synthesis of the Oligomer o-EB-1

(21) The synthesis of the oligomer o-EB-1 is performed according to the following reaction scheme:

(22) ##STR00034##

(23) Stearyl methacrylate, the monomer bearing a boronic ester function (mono-EB), isopropanol, AIBN and toluene (Solution 4) are placed in a 500 mL reactor connected to a condenser, a thermometer and a nitrogen supply. The amounts introduced are presented in Table 1.3 below. The reaction medium is degassed by sparging with nitrogen for 30 minutes, stirred and then brought to 86° C. When the reaction medium is at 75° C. and when evolution of gas is observed, a solution of StMA and of mono-EB in toluene (Solution 5) is introduced dropwise over a period of 80 minutes. The reaction progress is monitored by SEC analysis. After 3 hours of polymerization at 80° C., the reaction medium is cooled to room temperature. The polymer is precipitated three times from 300 mL of methanol. The volatile substances are evaporated off under reduced pressure at a temperature below 50° C. The product is then dried under vacuum for 72 hours at 40° C. in order to remove the solvent residues. 115.6 g of a pasty white solid are obtained. Yield: 87%.

(24) TABLE-US-00003 TABLE 1.3 amounts introduced for the synthesis of the oligomer o-EB-1 Mass/Volume Solution 4: StMA 11.95 g mono-EB 1.87 g AIBN 4.53 g Toluene 50 mL Isopropanol 200 mL Solution 5: StMA 104.19 g mono-EB 15.39 g Toluene 150 mL

Characterization

(25) The oligomer obtained comprises 90 mol % of repeating units containing boronic ester functions and 10 mol % of StMA repeating units as determined by .sup.1H NMR (400 MHz, CDCl.sub.3).

(26) The oligomer has a number-average molar mass of approximately 7100 g.Math.mol.sup.−1 and a polydispersity index of 1.74 as determined by SEC in THF using poly(methyl methacrylate) calibration at 40° C.

1.3. Synthesis of the Boronic Diester Molecule Di-EB

(27) The synthesis of the molecule Di-EB is performed according to the following reaction scheme:

(28) ##STR00035##

(29) The following are introduced into a 500 mL three-necked round-bottomed flask connected to Dean-Stark apparatus, a condenser and a nitrogen supply: 38 mL of distilled water, 200 mL of toluene and 38.2 g of 1-phenylenediboronic acid. The mixture obtained is in the form of a solid in suspension. 93.1 g of 1,2-dodecanediol are then added. 200 mL of the remaining toluene are added so as to facilitate the rinsing of the walls of the three-necked flask. The reaction medium is then heated until the solid has dissolved. The medium is then placed under a nitrogen atmosphere, stirred and refluxed for 16 hours. The temperature of the reaction medium rises from 97° C. (boiling point of the water/toluene azeotrope) to 111° C. (boiling point of toluene). The water evaporated off azeotropically is removed regularly from the Dean-Stark apparatus. The reaction progress is monitored by monitoring the reflux temperature and the amount of water removed from the Dean-Stark apparatus.

(30) After 16 hours, the reaction medium is cooled to room temperature. The volatile substances are evaporated off under reduced pressure below 30° C. The white solid obtained is dried using a rotary evaporator, for 2 hours. 108.1 g of a white solid are obtained. Yield=94%.

Characterization

(31) .sup.1H NMR (400 MHz, Acetone-D6 with TCNB (2,3,4,5-tetrachloronitrobenzene)): Purity>99%.

1.4. Synthesis of the Polydiol Polymer p-Diol (Comparative

(32) The synthesis of the polydiol polymer p-Diol is performed according to the following reaction scheme:

(33) ##STR00036##

(34) The following are introduced into a 4 L reactor connected to a condenser, a nitrogen supply and a 500 mL dropping funnel: 734.4 g of anisole, 36.2 g of cumyl dithiobenzoate solution, 45.3 g of lauryl methacrylate, 45.2 g of stearyl methacrylate, 9.3 g of styrene and 2.7 g of mono-Diol. 181.2 g of lauryl methacrylate, 180.9 g of stearyl methacrylate and 37.1 g of styrene are placed in the dropping funnel.

(35) The reactor, the dropping funnel and the remainder of the mono-Diol (50.3 g) are placed under a nitrogen atmosphere. The reaction medium is heated with stirring to T=80° C. The reaction progress is monitored by SEC analysis. A solution of 0.2660 g of AIBN in 3 mL of anisole is introduced slowly over a period of 15 minutes. The rest of the mono-Diol is then introduced in a syringe pump, and the other monomers are introduced using the dropping funnel, over a period of about 30 hours.

(36) Three solutions containing, respectively, 0.1362 g, 0.1338 g and 0.1450 g of AIBN in 3 mL of anisole are prepared and then introduced, respectively, at t=4 hours, t=25 hours and t=45 hours over a period of about 10 minutes. After 48 hours, the reaction medium is cooled to room temperature, and 150 mL of THF and 25 mL of n-butylamine are added. The reaction medium is maintained at room temperature for 4 hours, and 250 mL of butyl acrylate are then added. Stirring is continued for 18 hours at room temperature.

(37) The product is then precipitated from 2 L of methanol and, after separation of the phases by settling, the supernatant is then discarded. The precipitated polymer is dissolved in THF and then precipitated again from 2 L of methanol. The operation is repeated a third time. The polymer is dissolved in a minimum volume of THF, and 1000 g of group III base oil are then added to the polymer. The residual solvents are removed by entrainment with nitrogen under mechanical stirring of the solution, and 1355.6 g of polydiol p-Diol are obtained. Degree of dilution=25.4% of polymer.

Characterization

(38) The polymer thus obtained and diluted comprises 68 mol % of StMA/lauryl MA repeating units, 25 mol % of styrene repeating units and 7 mol % of hexanediol MA (mono-Diol) repeating units as determined by .sup.13C NMR (100 MHz, CDCl.sub.3).

(39) The polymer has a number-average molar mass of approximately 40 000 g.Math.mol.sup.−1 and a polydispersity index of 1.46 as determined by SEC in THF using poly(methyl methacrylate) calibration at 40° C.

1.5. Synthesis of Poly(Boronic Ester) Polymer p-EB (Comparative

(40) The synthesis of the poly(boronic ester) polymer p-EB is performed according to the following reaction scheme:

(41) ##STR00037##

(42) 1 L of anisole, 3.56 g of a solution of cumyl dithiobenzoate, 900 g of lauryl methacrylate and 76 g of mono-EB are placed in a 2 L reactor connected to a condenser and to a nitrogen supply. The reaction medium is placed under a nitrogen atmosphere, stirred and heated to 90° C. The reaction medium is heated with stirring at T=90° C. The reaction progress is monitored by SEC analysis. After 2 hours 30 minutes of polymerization, the reaction medium is cooled to 0° C. and the product is precipitated from 4 L of acetone, and, after separation of the phases by settling, the supernatant is then removed. The precipitated polymer is dissolved in THF and then precipitated again from 4 L of acetone. The operation is repeated a final time. The polymer is then dissolved in a minimum volume of THF, and 900 g of group III base oil are then added to the polymer. The residual solvents are removed by entrainment with nitrogen under mechanical stirring of the solution, and 1381.0 g of poly(boronic ester) p-EB are obtained. Degree of dilution=39.2% of polymer.

Characterization

(43) The polymer thus obtained and diluted comprises 94 mol % of lauryl MA repeating units and 6 mol % of boronic ester repeating units as determined by .sup.13C NMR (100 MHz, CDCl.sub.3).

(44) The polymer has a number-average molar mass of approximately 45 000 g.Math.mol.sup.−1 and a polydispersity index of 1.39 as determined by SEC in THF using poly(methyl methacrylate) calibration at 40° C.

2. Formulation of the Compositions

(45) Each oligomer/polymer is dissolved in a base oil to obtain a solution containing 10% by mass of pure oligomer/polymer. After dissolution of the oligomer/polymer in the oil with magnetic stirring and heating at 80° C., these solutions are filtered, if need be, through a 0.8 μm Millipore filter. They serve as stock solutions for the preparation of the formulations below.

2.1. Lubricant Base Oil

(46) The lubricant base oil used in the test compositions is an oil from group III of the API classification, sold by SK under the name Yubase 4+.

(47) It has the following characteristics:

(48) its kinematic viscosity at 40° C. measured according to the standard ASTM D445 is 18.51 cSt;

(49) its kinematic viscosity measured at 100° C. according to the standard ASTM D445 is 4.206 cSt;

(50) its viscosity index measured according to the standard ASTM D2270 is 135;

(51) its Noack volatility, as a weight percentage, measured according to the standard CEC L-40-93, is 13.4% by mass;

(52) its flash point in degrees Celsius, measured according to the standard NF EN ISO 2592, is 234° C.;

(53) its pour point in degrees Celsius, measured according to the standard NF T60-105, is −18° C.

2.2. Preparation of Composition A (According to the Invention

(54) 8.00 g of the stock solution containing 10% by mass of boronic ester oligomer o-EB-1 and 8.00 g of the stock solution containing 10% by mass of the oligomer o-Diol-3 are placed in a flask and mixed with a magnetic stirrer for 5 minutes. This formulation thus contains 5% by mass of boronic ester oligomer o-EB-1 and 5% by mass of oligomer o-Diol-3.

2.3. Preparation of Composition B (According to the Invention

(55) The amount of the compounds of the preparation is adjusted so that this formulation contains 5% by mass of the boronic diester molecule Di-EB and 10% by mass of oligomer o-Diol-3.

2.4. Preparation of Composition F (Comparative

(56) 5.2 g of the stock solution containing 10% by mass of the poly(boronic ester) polymer p-EB, 4.5 g of the stock solution containing 10% by mass of the polydiol polymer p-Diol and 10.3 g of group III base oil are placed in a flask and mixed with a magnetic stirrer for 5 minutes. This formulation thus contains 2.6% by mass of poly(boronic ester) p-EB and 2.25% by mass of polydiol p-Diol.

3. Rheological Studies

3.1. Measurement Apparatus and Protocols

Shear Measurements

(57) The low-shear (10, 100, 1000, 5000 and 10000 s.sup.−1) dynamic viscosities were measured at 40° C., 100° C. and 150° C. in a stabilized regime with a DHR-2 rheometer from the company TA Instruments, equipped with cone-plate geometry (0.5°-40 mm).

(58) The high-shear (1, 2, 3, 4.10.sup.6 s.sup.−1 at 40° C. and 1, 4, 7, 10.10.sup.6 s.sup.−1 at 100° C. and 150° C.) dynamic viscosities were measured with a USV high-shear viscometer from the company PCS Instruments.

Mechanical Degradation Test

(59) The KRL mechanical degradation test was performed at 60° C. for 20 hours according to the standard CEC L-45-A-99 and the kinematic viscosities were measured before and after the KRL test. The kinematic viscosity of compositions A, F and of the group III base oil were measured at 40° C. and 100° C. with a capillary viscometer from the company Herzog according to the standard ASTM D445.

Kinematic Viscosity Measurements

(60) The kinematic viscosity of composition B and the group III base oil were measured at 40° C. and 100° C. with a capillary viscometer from the company Herzog according to the standard ASTM D445.

3.2. Results

Shear Measurements

(61) FIGS. 5, 6 and 7 show the curves of variation in dynamic viscosity measured as a function of the shear rate at, respectively, 40, 100 and 150° C. for compositions A according to the invention and composition F.

(62) When the shear rate is low (up to 10 000 s.sup.−1), the rheological behavior of formulations A and F is identical. When a high shear rate is applied, composition F shows a significant drop in dynamic viscosity; this behavior shows poor shear strength of the high molar mass polymers. Composition A, comprising the combination of oligomers according to the invention, shows stability of the viscosity at a high shear rate at 40 and 100° C., and even at high temperature up to 150° C. This illustrates the technical effect of the capacity of the claimed oligomer mixture of thickening the medium in which it is dispersed and of conserving this capacity under shear at high temperatures.

Mechanical Degradation

(63) The kinematic viscosity of compositions A and F was measured at 40 and 100° C. before and after the KRL 20-hour mechanical degradation test. The results obtained are collated in table 2.1.

(64) TABLE-US-00004 TABLE 2.1 Results of kinematic viscosity measurement at 40 and 100° C. before and after the KRL 20-hour mechanical degradation test for composition A according to the invention and composition F. Group III base oil Composition A Composition F Initial kinematic viscosities measured KV40 in mm.sup.2/s 18.51 25.11 31.95 KV100 in mm.sup.2/s 4.206 5.478 8.765 VI 135 164 274 Kinematic viscosities measured after KRL shear test KV40 in mm.sup.2/s 25.02 26.16 KV100 in mm.sup.2/s 5.461 6.135 VI 163 196 PSSI 40 in % 1 43 PSSI 100 in % 1 58

(65) Composition F comprising 2.6% by mass of poly(boronic ester) p-EB and 2.25% by mass of polydiol p-Diol shows an irreversible loss of viscosity after shear for temperatures of 40 and 100° C. When composition A, containing the combination of oligomers o-Diol-3 and o-EB-1 according to the invention is used, no significant loss of viscosity is observed. This composition still conserves its properties for high temperatures. These results show better resistance to mechanical degradation of composition A according to the invention compared with composition F comprising high molar mass polymers.

(66) The shear stability characterized by the PSSI (permanent shear stability index) was calculated from the kinematic viscosities of the compositions in oil after the KRL 20-hour shear process at 40 and at 100° C. C according to the following mathematical formula:
PSSI=[(initial KV−KV after KRL)/(initial KV−KV base oil)]×100

(67) Composition F has a permanent shear stability index of greater than 40%. This indicates that certain high molar mass polymer molecules are destroyed under mechanical shear stress, leading to an irreversible loss of viscosity of the formulation studied. On the other hand, composition A has a PSSI of only 1%. This shows the sparingly shear-sensitive behavior of the formulations according to the invention and their resistance to mechanical degradation.

Kinematic Viscosity Measurements

(68) The kinematic viscosity of composition B and of the group III base oil were measured at 40° C. and 100° C. The results obtained are collated in table 2.2.

(69) TABLE-US-00005 TABLE 2.2 Results of kinematic viscosity measurement at 40 and 100° C. for composition B according to the invention Group III base oil Composition B Kinematic viscosities measured KV40 in mm.sup.2/s 18.51 25.14 KV100 in mm.sup.2/s 4.206 5.479 VI 135 163

(70) Composition B comprising 5% by mass of the boronic diester molecule Di-EB and 10% by mass of the oligomer o-Diol-3 shows an increased kinematic viscosity at 40 and 100° C. The increase in viscosity is more particularly observed when hot: the viscosity index is thus greatly improved.