Composition comprising thermoassociative and exchangeable copolymers

Abstract

Compositions resulting from the mixing of at least: a comb polydiol copolymer A1 and a compound A2 including at least two boronic ester functional groups, the comb polydiol copolymer A1 including a main chain and side chains, at least a portion of the side chains of the copolymer A1 being composed of oligomers. They exhibit very varied rheological properties depending on the proportion of the compounds A1 and A2 used. Composition resulting from the mixing of at least one lubricating oil with such a composition of associative and exchangeable polymers and use of this composition for lubricating a mechanical part.

Claims

1. A composition resulting from the mixing of at least: a comb polydiol copolymer A1 and a compound A2 comprising at least two boronic ester functional groups, the comb polydiol copolymer A1 comprising a main chain and side chains, at least a portion of the side chains of the copolymer A1 being composed of oligomers comprising more than 30 carbon atoms.

2. The composition as claimed in claim 1, in which at least a portion of the side chains of the copolymer A1 are composed of oligomers comprising at least 50 carbon atoms.

3. The composition as claimed in claim 1, in which at least a portion of the side chains of the copolymer A1 are composed of oligomers which exhibit a degree of polymerization ranging from 5 to 1000.

4. The composition as claimed in claim 1, in which the side chains composed of oligomers represent from 3% to 95% by weight, with respect to the total weight of the copolymer A1.

5. The composition as claimed in claim 1, in which at least a portion of the side chains of the copolymer A1 are composed of oligomers 01 comprising a polyolefin fragment.

6. The composition as claimed in claim 5, in which the side chains of the copolymer A1 composed of oligomers O1 comprise a polyolefin fragment having from 30 to 500 carbon atoms.

7. The composition as claimed in claim 5, in which the side chains comprising a polyolefin fragment represent from 3% to 85% by weight, with respect to the total weight of the copolymer A1.

8. The composition as claimed in claim 5, in which the oligomers O1 are present in the copolymer A1 in the form of repeat units corresponding to one or more monomers M6 of general formula (IX): ##STR00063## in which: Q.sub.1 is chosen from the group consisting of —H, —CH.sub.3 and —CH.sub.2—CH.sub.3; Q.sub.2 is chosen from the group consisting of -Q′, —O-Q′, —C(O)—O-Q′, —O—C(O)-Q′, —S—(CH.sub.2).sub.2—C(O)—O-Q′, —S-Q′, —N(H)—C(O)-Q′ and —C(O)—N(H)-Q′ group, with Q′ is a polyolefin, n represents an integer chosen from 0 and 1, A represents a divalent group chosen from the group consisting of -A.sub.1-, —O-(-A.sub.2-O—).sub.n-A.sub.1-, —C(O)—O-(-A.sub.2-O—).sub.n-A.sub.1-, —O—C(O)-(-A.sub.2-O—).sub.n′-A.sub.1-, —S—(-A.sub.2-O—).sub.n-A.sub.1-, —N(H)—C(O)-(-A.sub.2-O—).sub.n-A.sub.1- and —C(O)—N(H)-(-A.sub.2-O—).sub.n-A.sub.1- with: A.sub.1 is a divalent radical chosen from the group consisting of a C.sub.1-C.sub.30 alkyl, a C.sub.6-C.sub.30 aryl and a C.sub.6-C.sub.30 aralkyl, A.sub.2 is a divalent radical chosen from C.sub.2-C.sub.4 alkyls, n′ is an integer, n′ represents 0 or 1.

9. The composition as claimed in claim 1, in which at least a portion of the side chains of the copolymer A1 are composed of oligomers O2 comprising repeat units corresponding to monomers M2 of general formula (II): ##STR00064## in which: R.sub.2 is chosen from the group consisting of —H, —CH.sub.3 and —CH.sub.2—CH.sub.3, R.sub.3 is chosen from the group consisting of —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 is a C.sub.1-C.sub.30 alkyl group.

10. The composition as claimed in claim 9, in which at least a portion of the oligomers O2 comprise repeat units corresponding to monomers M1 of general formula (I): ##STR00065## in which: R.sub.1 is chosen from the group consisting of —H, —CH.sub.3 and —CH.sub.2—CH.sub.3; y is an integer equal to 0 or 1; Y represents a divalent linking group chosen from C.sub.1-C.sub.20 alkyl chains, optionally comprising one or more ether —O— bridges; X.sub.1 and X.sub.2, which are identical or different, are chosen from the group consisting of hydrogen, tetrahydropyranyl, methyloxymethyl, tert-butyl, benzyl, trimethylsilyl and t-butyldimethylsilyl; or else X.sub.1 and X.sub.2 form, with the oxygen atoms, a bridge of formula: ##STR00066## in which: the stars (*) symbolize the bonds to the oxygen atoms, R′.sub.2 and R″.sub.2, which are identical or different, are chosen from the group consisting of hydrogen and a C.sub.1-C.sub.11 alkyl; or else X.sub.1 and X.sub.2 form, with the oxygen atoms, a boronic ester of formula: ##STR00067## in which: the stars (*) symbolize the bonds to the oxygen atoms, R″′.sub.2 is chosen from the group consisting of 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.

11. The composition as claimed in claim 1, in which the copolymer A1 comprises repeat units corresponding to at least one monomer M3 of general formula (X): ##STR00068## in which: Z.sub.1, Z.sub.2 and Z.sub.3, which are identical or different, represent groups chosen from the group consisting of a hydrogen atom, a C.sub.1-C.sub.12 alkyl or a —OZ′ or —C(O)—O—Z′ group, with Z′ a C.sub.1-C.sub.12 alkyl.

12. The composition as claimed in claim 11, in which the monomer M3 is styrene.

13. The composition as claimed in claim 11, in which the repeat units corresponding to monomers of formula (X) represent from 2 mol % to 50 mol %, with respect to the total number of moles of the repeat units of which the copolymer A1 is composed.

14. The composition as claimed in claim 1, in which the copolymer A1 exhibits a degree of branching ranging from 0.1 mol % to 10 mol %.

15. The composition as claimed in claim 1, in which the comb copolymer A1 comprises nonoligomeric pendant chains which have a mean length ranging from 1 to 10 carbon atoms.

16. The composition as claimed in claim 1, in which the main chain of the comb copolymer A1 has a number-average degree of polymerization ranging from 40 to 2000.

17. The composition as claimed in claim 1, in which the oligomeric pendant chains of the comb copolymer A1 have a number-average degree of polymerization ranging from 8 to 1000.

18. The composition as claimed in claim 1, in which the compound A2 is chosen from: a compound of formula (III): ##STR00069## in which: w.sub.1 and w.sub.2, which are identical or different, are integers chosen between 0 and 1; R.sub.4, R.sub.5, R.sub.6 and R.sub.7, which are identical or different, represent a group chosen from the group consisting of a hydrogen atom and a hydrocarbon group comprising from 1 to 30 carbon atoms, optionally substituted by one or more groups chosen from the group consisting of a hydroxyl and an —OJ or —C(O)—O-J group, with J a hydrocarbon group comprising from 1 to 24 carbon atoms; L is a divalent linking group chosen from the group consisting of a C.sub.6-C.sub.18 aryl, a C.sub.6-C.sub.15 aralkyl and a C.sub.2-C.sub.24 hydrocarbon chain; a copolymer comprising at least repeat units corresponding to monomers M4 of formula (IV): ##STR00070## in which: t is an integer equal to 0 or 1; u is an integer equal to 0 or 1; M and R.sub.s are divalent linking groups, which are identical or different, chosen from the group consisting of 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 functional group chosen from the group consisting of —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 a hydrocarbon chain comprising from 1 to 15 carbon atoms; R.sub.9 is chosen from the group consisting of —H, —CH.sub.3 and —CH.sub.2—CH.sub.3; R.sub.10 and R.sub.11, which are identical or different, represent a group chosen from the group consisting of a hydrogen atom and a hydrocarbon group comprising from 1 to 30 carbon atoms, optionally substituted by one or more groups chosen from: a hydroxyl or an —OJ or —C(O)—O-J group, with J a hydrocarbon group comprising from 1 to 24 carbon atoms; repeat units corresponding to monomers M5 of general formula (V): ##STR00071## in which: R.sub.12 is chosen from the group consisting of —H, —CH.sub.3 and —CH.sub.2—CH.sub.3, R.sub.13 is chosen from the group consisting of a C.sub.6-C.sub.18 aryl and a C.sub.6-C.sub.15 aryl substituted by a R′.sub.13, —C(O)—O—R′.sub.13, —O—R′.sub.13, —S—R′.sub.13 and —C(O)—N(H)—R′.sub.13 group, with R′.sub.13 is a C.sub.1-C.sub.30 alkyl group.

19. The composition as claimed in claim 18, in which the compound A2 is a copolymer, and A2 is a comb copolymer comprising a main chain and side chains, at least a portion of the side chains of the copolymer A2 being composed of oligomers.

20. A lubricating composition resulting from the mixing of at least: a lubricating oil; and a composition as claimed in claim 1.

Description

FIGURES

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

(2) FIG. 2 diagrammatically represents a comb copolymer.

(3) FIG. 3 diagrammatically illustrates the reactions for exchanges of boronic ester bonds between two polydiol polymers (A1-1 and A1-2) and two boronic ester polymers (A2-1 and A2-2) in the presence of diols.

(4) FIG. 4 diagrammatically illustrates and represents the crosslinking of the composition according to the invention in tetrahydrofuran (THF).

(5) FIG. 5 diagrammatically represents the behavior of the composition of the invention as a function of the temperature. A copolymer (2) having diol functional groups (functional group A) can associate in a thermoreversible way with a copolymer (1) having boronic ester functional groups (functional group B) via a transesterification reaction. The organic group of the boronic ester functional groups (functional group B) which is exchanged during the transesterification reaction is a diol symbolized by a black crescent. A chemical bond (3) of boronic ester type is formed, with release of a diol compound.

(6) FIGS. 6A, 6B and 6C represent different comb copolymers A1.

(7) FIG. 7 represents a scheme for the synthesis of comb copolymers A1.

(8) FIG. 8 represents a scheme for the synthesis of comb copolymers A1.

(9) FIG. 9 represents a graph which reports the relative viscosity of the compositions B, C and D (ordinate) as a function of the temperature (abscissa) from 10° C. to 90° C.

(10) FIG. 10 represents a graph which reports the relative viscosity of the compositions F and G (ordinate) as a function of the temperature (abscissa) from 10° C. to 90° C. over three cycles.

(11) FIG. 11 represents a graph which reports the relative viscosity of the compositions H, I and J (ordinate) as a function of the temperature (abscissa) from 10° C. to 150° C.

(12) FIG. 12 represents a graph which reports the relative viscosity (ordinate) of the compositions I and Id (obtained from the composition I by dilution of the composition I down to 2.10% by weight of copolymer) as a function of the temperature (abscissa) from 10 to 150° C.

(13) FIG. 13 represents a graph which reports the relative viscosity (ordinate) as a function of the temperature (abscissa) of the composition Id during three successive heating-cooling cycles between 10° C. and 150° C. (Id-1, Id-2 and Id-3).

(14) FIG. 14 represents a graph which reports the relative viscosity (ordinate) as a function of the temperature (abscissa) of the composition J during five successive heating-cooling cycles between 10° C. and 150° C. (J-1, J-2, J-3, J-4 and J-5).

EXPERIMENTAL SECTION

(15) The following examples illustrate the invention without limiting it.

(16) 1 Synthesis of Comb Copolymers A1 Carrying Diol Functional Group

(17) 1.1: Synthesis of the Monomers

(18) 1.1.1 Synthesis of the Monomer M1 Carrying a Diol Functional Group

(19) The synthesis of a methacrylate monomer carrying a diol functional group is carried out in three stages (stages 1, 2 and 3) according to the protocol below:

(20) 1.sup.st stage:

(21) 42.1 g (314 mmol) of 1,2,6-hexanetriol (1,2,6-HexTri) are introduced into a 1 liter round-bottomed flask. 5.88 g of molecular sieve (4 Å) are added, followed by 570 ml of acetone. 5.01 g (26.3 mmol) of para-toluenesulfonic acid (pTSA) are subsequently added slowly. The reaction medium is left stirring at ambient temperature for 24 hours. 4.48 g (53.3 mmol) of NaHCO.sub.3 are then added. The reaction medium is left stirring at ambient temperature for 3 hours before being filtered. The filtrate is then concentrated under vacuum using a rotary evaporator until a suspension of white crystals is obtained. 500 ml of water are then added to this suspension. The solution thus obtained is extracted with 4×300 ml of dichloromethane. The organic phases are combined and dried over MgSO.sub.4. The solvent is subsequently completely evaporated under vacuum at 25° C. using a rotary evaporator.

(22) 2.sup.Nd Stage:

(23) 5.01 g (28.8 mmol) of the product thus obtained are introduced into a 1 liter round-bottomed flask. 4.13 g (31.9 mmol) of DIPEA and 37.9 mg (0.31 mmol) of DMAP are subsequently introduced into the round-bottomed flask, followed by 5.34 g (34.6 mmol) of methacrylic anhydride. The round-bottomed flask is then stirred at ambient temperature for 24 hours. 0.95 g of methanol (29.7 mmol) is subsequently added to this solution and the round-bottomed flask was left stirring for an additional 1 hour. The product is then dissolved in 40 ml of hexane. The organic phase is subsequently successively washed with 25 ml of water, 3×25 ml of a 0.5M aqueous hydrochloric acid solution, 3×25 ml of a 0.5M aqueous NaOH solution and again with 25 ml of water. The organic phase is dried over MgSO.sub.4, filtered and then concentrated under vacuum using a rotary evaporator to give a light yellow liquid.

(24) 3.sup.rd Stage:

(25) 17.23 g (71.2 mmol) of the product thus obtained are introduced into a 1 liter round-bottomed flask. 90 ml of water and 90 ml of acetonitrile are subsequently introduced into the round-bottomed flask, followed by 59.1 ml (159 mmol) of acetic acid. The round-bottomed flask is then stirred at 30° C. for 24 hours while allowing a gentle stream of nitrogen to bubble through in order to drive the removal of the acetone. The solution thus obtained is extracted with 6×30 ml of ethyl acetate. The organic phase is subsequently successively washed with 5×30 ml of a 0.5M aqueous NaOH solution and then 3×30 ml of water. The organic phase is subsequently dried over MgSO.sub.4, filtered and then concentrated under vacuum using a rotary evaporator to give a light yellow liquid, the characteristics of which are as follows:

(26) .sup.1H NMR (400 MHz, CDCl.sub.3) δ: 6.02 (singlet, 1H), 5.49 (singlet, 1H), 4.08 (triplet, J=6.4 Hz, 1H), 3.65-3.58 (multiplet, 1H), 3.57-3.50 (multiplet, 3H), 3.35 (split doublet, J=7.6 Hz and J=11.2 Hz, 1H), 1.86 (split doublet, J=1.2 Hz and J=1.6 Hz, 3H), 1.69-1.31 (multiplet, 6H).

(27) 1.1.2 Synthesis of the Brominated Monomer (Branching Monomer):

(28) ##STR00052##

(29) 7 ml of hydroxyethyl methacrylate (58 mmol), 5.4 ml of pyridine (66 mmol) and 75 ml of dichloromethane are introduced into a 250 ml round-bottomed flask. The round-bottomed flask is then closed using a septum, degassed by bubbling with N.sub.2 for 30 min and then placed in a bath of ice-cold water. 7.7 ml of 2-bromo-2-methyl propionyl bromide (64 mmol) are subsequently added dropwise to the reaction mixture over approximately 15 minutes. The round-bottomed flask is kept stirred for 6 hours. A white precipitate is formed during the reaction. The solution is subsequently filtered in order to remove the solid. The solid is rinsed with dichloromethane (2×10 ml). The organic phase is subsequently washed 2 times with 100 ml of distilled water, 2 times with 100 ml of a 10% NaHCO.sub.3 solution and then 2 times with 100 ml of a saturated NaC solution. The organic phase is then dried over MgSO.sub.4 and the solvent removed using a rotary evaporator. 11.6 g of a bright yellow liquid are obtained (yield=72%).

(30) .sup.1H NMR (CDCl.sub.3): δ: 6.05 ppm (m, 1H), 5.52 ppm (m, 1H), 4.35 ppm (m, 4H), 1.87 ppm (m, 3H), 1.85 ppm (s, 6H).

(31) 1.1.3 Synthesis of the Methacrylic Olefinic Macromonomer (Monomer M6-A):

(32) ##STR00053##

(33) 58.8 g (11.6 mmol) of Krasol HLBH 5000M (product supplied by Cray Valley) are dissolved in 150 g of dichloromethane (DCM). 11.9 g of methacrylic anhydride (77.3 mmol), 56.2 mg of 4-dimethylaminopyridine (0.47 mmol) and 7.37 g of trimethylamine (76 mmol) are subsequently added. The solution is left stirring at ambient temperature for 24 h. The solution is subsequently washed 2 times with a 0.5M aqueous sodium hydroxide solution, then 2 times with a 0.5M aqueous hydrochloric acid solution and finally 2 times with distilled water. The organic phase is dried over MgSO.sub.4 and then the solvent is evaporated using a rotary evaporator. The product is subsequently dissolved in tetrahydrofuran (THF) before being precipitated 3 times consecutively from acetone (redissolved in THF before each precipitation). The product is dried under vacuum at 50° C. for 18 hours. A colorless and translucent viscous liquid is thus obtained. The quantitative functionalization of the Krasol (of the alcohol to give methacrylate) is confirmed by .sup.1H NMR by the complete disappearance of the peak between 3.8 and 4.1 ppm, characteristic of the protons in the a position with respect to the alcohol functional group of the Krasol.

(34) .sup.1H NMR (CDCl.sub.3): δ:6.05 ppm (m, 1H), 5.52 ppm (m, 1H), 5.1-4.9 ppm (m, 1H), 1.94 ppm (s, 3H), 2.05-0.48 ppm (1020H), traces of DCM (5.29 ppm), THF (3.75 ppm; 1.84 ppm) and acetone (2.17 ppm).

(35) 1.1.4 Synthesis of the Olefin Macromonomer Carrying a Terminal Styrene Functional Group (Monomer M6-B -OLF1500-St)

(36) The synthesis of the olefin macromonomer carrying a terminal styrene functional group (OLF1500-St) is carried out in two stages (Schemes 13 and 14) according to the following protocol:

(37) 1.sup.st stage

(38) 4.0 g (27 mmol) of 4-vinylbenzoic acid (4-VBA) are dissolved in 110 ml of anhydrous dichloromethane (DCM) with a catalytic amount (15 drops) of anhydrous dimethylformamide (DMF). 5.8 ml (67 mmol) of oxalyl chloride is subsequently added to the solution. The reaction mixture is left stirring at ambient temperature for 2 hours. After evaporation of the solvent under reduced pressure, the yellow liquid obtained is dried under vacuum for 2 h.

(39) 2.sup.nd Stage:

(40) 2.64 g (1.76 mmol) of the olefin copolymer OLF1500-OH exhibiting a number-average molar mass, M.sub.n, of 1500 g/mol and carrying a terminal primary alcohol functional group and 3.8 ml (27.5 mmol) of NEt.sub.3 are dissolved in 50 ml of anhydrous DCM and the mixture is brought to approximately 0° C. using an ice bath. A solution of 4-vinylbenzoyl chloride obtained during the 1.sup.st stage (27 mmol) in 30 ml of DCM is subsequently added dropwise to the reaction mixture over approximately 25 min. The mixture is stirred in the ice bath for 1 hour and then at ambient temperature for 24 hours. The excess 4-vinylbenzoyl chloride is neutralized by addition of 10 ml of water and by leaving the reaction mixture stirring for 1 hour. The reaction mixture is subsequently successively washed with 3×100 ml of a 1M HCl solution, 2×100 ml of a 1M NaOH solution and 1×100 ml of aqueous sodium chloride solution. After drying the organic phase over MgSO.sub.4, the clear yellow solution obtained is filtered through a basic alumina column. The evaporation of the DCM and the drying under vacuum give 2.80 g (97.6%) of a light yellow oil, the characteristics of which are as follows:

(41) .sup.1H NMR (400 MHz, CDCl.sub.3) δ: 8.00 (multiplet, 2H), 7.46 (split doublet, J=1.5 Hz and J=8.3 Hz, 2H), 6.75 (split doublet, J=12.0 Hz and J=17.5 Hz, 1H), 5.86 (split doublet, J=0.8 Hz and J=17.7 Hz, 1H), 5.38 (doublet, J=11.0 Hz, 1H), 4.41-4.28 (multiplet, 2H), 1.83-0.52 (multiplet, 961H).

(42) 1.1.5. Synthesis of the Boronic Ester Condensed with 1,2-Dodecanediol Monomer (mEB-C.sub.12)

(43) This monomer is obtained according to the protocol described in the application WO2016/113229 (Experimental part § 2.1)

(44) 1.2: Synthesis of the Copolymers—Methods

(45) The comb copolymers A1 of the invention are obtained by resorting to the synthesis methods described in the applications W2015/110642, W2015/110643 and WO2016/113229, if appropriate supplemented by the methods described in the present patent application.

(46) The number-average molar mass and the dispersity are obtained by size exclusion chromatography using poly(methyl methacrylate) calibration and THF as eluent.

(47) 1.2.1 Synthesis of a brominated main chain (brominated backbone 1):

(48) ##STR00054##

(49) 0.50 g (1.8 mmol) of brominated monomer obtained according to the protocol described above in point 1.1.2 (Scheme 11), 8.52 g (59.9 mmol) of butyl methacrylate, 1.14 g (11.0 mmol) of styrene, 35.8 mg (0.13 mmol) of cumyl dithiobenzoate, 6.3 mg (0.04 mmol) of azobisisobutyronitrile (AIBN) and 5 g of anisole are introduced into a 50 ml Schlenk tube. The reaction medium is stirred and degassed for 30 minutes by bubbling nitrogen through, before being brought to 65° C. for a period of 16 hours. The polymer is subsequently isolated by 3 successive precipitations from methanol and then dried under vacuum at 50° C. for 16 hours. A copolymer exhibiting a number-average molar mass (M.sub.n) of 38 000 g/mol, a dispersity (Ð) of 1.2 and a number-average degree of polymerization (DP.sub.n) of approximately 300 is obtained. The polymer thus obtained contains approximately 2.3 mol % (approximately 5% by weight) of brominated methacrylate monomer. These values are respectively obtained by size exclusion chromatography, using THF as eluent and poly(methyl methacrylate) (PMMA) calibration, and by monitoring the conversion of monomers during the copolymerization.

(50) 1.2.2 Synthesis of a Brominated Main Chain (Brominated Backbone 2):

(51) ##STR00055##

(52) 0.50 g (1.8 mmol) of brominated monomer obtained according to the protocol described above in point 1.1.2 (Scheme 11), 7.45 g (52.4 mmol) of butyl methacrylate, 1.46 g (7.2 mmol) of 5,6-dihydroxyhexyl methacrylate obtained according to the protocol described in section 1.1.1 above, 1.13 g (10.8 mmol) of styrene, 35.8 mg (0.13 mmol) of cumyl dithiobenzoate, 6.3 mg (0.04 mmol) of AIBN and 5 g of anisole are introduced into a 50 ml Schlenk tube. The reaction medium is stirred and degassed for 30 minutes by bubbling nitrogen through, before being brought to 65° C. for a period of 16 hours. The polymer is subsequently isolated by 3 successive precipitations from methanol and then dried under vacuum at 50° C. for 16 hours. A copolymer exhibiting an M.sub.n of 46 000 g/mol, a dispersity (Ð) of 1.2 and a number-average degree of polymerization (DP.sub.n) of approximately 300 is obtained. The polymer thus obtained contains approximately 2.3 mol % (approximately 5% by weight) of brominated methacrylate monomer. These values are respectively obtained by size exclusion chromatography, using THF as eluent and PMMA calibration, and by monitoring the conversion of monomers during the copolymerization.

(53) 1.2.3 Synthesis by ATRP of the Comb Polydiol Copolymer CPDiol-1

(54) ##STR00056##

(55) 520 mg (87 μmol of brominated monomer and approximately 12 μmol of dithiobenzoate) of brominated backbone 1 obtained according to the protocol described above, 13.4 g (39.5 mmol) of stearyl methacrylate, 0.91 g (4.5 mmol) of 5,6-dihydroxyhexyl methacrylate obtained according to the protocol described above in § 1.1.1, 3 g of N,N-dimethylformamide (DMF) and 10 g of anisole are introduced into a 50 ml Schlenk round-bottomed flask. In parallel, 52 mg (333 μmol) of 2,2′-bipyridine, 5 mg (20 μmol) of copper (II) dibromide (CuBr.sub.2) and 21 mg (147 μmol) of CuBr are dissolved in 2 g of DMF in a sample tube before sealing it using a septum. The flask and the sample tube are degassed by bubbling nitrogen through the solutions for 30 minutes. The solution contained in the sample tube is subsequently withdrawn and then injected into the round-bottomed flask using a syringe. The round-bottomed flask is then placed in an oil bath thermostatically controlled at 60° C. for 7 hours. The solution is subsequently filtered through a basic alumina column in order to remove the copper. Finally, the polymer is isolated by 3 successive precipitations from methanol and then dried under vacuum at 50° C. for 20 hours. A copolymer exhibiting a number-average molar mass M.sub.n of 105 000 g/mol and a dispersity Ð of 1.5 is obtained. These values are obtained by size exclusion chromatography using THF as eluent and PMMA calibration. According to the conversion of monomers determined by .sup.1H NMR, the pendant chains have a number-average degree of polymerization DP.sub.n of approximately 40.

(56) 1.2.4 Synthesis by ATRP of the Comb Polydiol BB:

(57) ##STR00057##

(58) 522 mg (84 μmol of brominated monomer approximately 12 μmol of dithiobenzoate) of brominated backbone 2 obtained according to the protocol described above, 9.22 g (27.2 mmol) of stearyl methacrylate, 0.80 g (3.1 mmol) of lauryl methacrylate and 6.8 g of anisole are introduced into a 50 ml Schlenk round-bottomed flask. In parallel, 48 mg (308 μmol) of 2,2′-bipyridine, 4 mg (18 μmol) of CuBr.sub.2 and 19 mg (133 μmol) of CuBr are dissolved in 3.3 g of DMF in a sample tube before sealing it using a septum. The flask and the sample tube are degassed by bubbling nitrogen through the solutions for 30 minutes. The solution contained in the sample tube is subsequently withdrawn and then injected into the round-bottomed flask using a syringe. The round-bottomed flask is then placed in an oil bath thermostatically controlled at 60° C. for 6.3 hours. The solution is subsequently filtered through a basic alumina column in order to remove the copper. Finally, the polymer is isolated by 3 successive precipitations from methanol and then dried under vacuum at 50° C. for 20 hours. A copolymer exhibiting a number-average molar mass M.sub.n of 210 000 g/mol and a dispersity Ð of 1.6 is obtained. These values are obtained by size exclusion chromatography using THF as eluent and PMMA calibration. According to the conversion of monomers determined by .sup.1H NMR, the pendant chains have a number-average degree of polymerization DP.sub.n of approximately 30 units.

(59) 1.2.5 Synthesis of a comb copolymer of butyl methacrylate, of methacrylate carrying a diol functional group and of the olefin macromonomer OLF1500-St (CPDiol-2)

(60) ##STR00058##

(61) The synthesis of the comb copolymer carrying diol functional groups in the main chain CPDiol-2 is carried out according to the following protocol (Scheme 13 above).

(62) 2.50 g (17.5 mmol) of butyl methacrylate (BMA), 0.18 g (0.89 mmol) of methacrylate monomer carrying a diol functional group, 0.89 g (0.93 mmol) of the olefin macromonomer M6-B-OLF1500-St obtained according to the protocol described in section 1.1.4 above, 9.3 mg (0.04 mmol) of RAFT transfer agent 2-cyano-2-propyl benzodithioate (CPBD), 2.8 mg (0.02 mmol) of azobisisobutyronitrile (AIBN) and 3.6 ml of anisole are introduced into a 25 ml Schlenk tube. The reaction medium is stirred and degassed for 30 min by bubbling nitrogen through, before being brought to 65° C. for a period of 19 hours.

(63) After 19 h of polymerization, the Schlenk tube is placed in an ice bath in order to halt the polymerization. The polymer is subsequently isolated by 2 successive precipitations from methanol cooled using an ice bath, filtration and drying under vacuum at 50° C. overnight. The copolymer thus obtained exhibits a number-average molar mass (M.sub.n) of 65 500 g/mol, a dispersity (Ð) of 1.25 and a number-average degree of polymerization (DP.sub.n) of 350. The first two values are obtained by size exclusion chromatography using THF as eluent and poly(methyl methacrylate) calibration, while the DP.sub.n is obtained by .sup.1H NMR monitoring of the conversion of monomers during polymerization.

(64) A poly(butyl methacrylate-co-alkyldiol methacrylate-co-M6-B-OLF1500-St) copolymer CPDiol-2 containing 4.5 mol % of diol repeat units (4.6% by weight) and 6.8 mol % of pendant OLF1500-OCP chains (32% by weight) is obtained. The mean length of the side chains is 10.9 carbon atoms.

(65) 1.2.6 Synthesis of a Comb Copolymer of Butyl Methacrylate, of Olefin Macromonomer M6-B-OLF1500-St and of Pendant Polydiol Polymeric Chains (CPDiol-3)

(66) The synthesis of the comb copolymer containing the olefin macromonomer M6-B-OLF1500-St and pendant polydiol polymeric chains (CPDiol-3) is carried out according to the following protocol (Scheme 14 below):

(67) ##STR00059## ##STR00060## ##STR00061##

Scheme 14

(68) 1.2.6.1 Synthesis of a main chain containing olefin macromonomer M6-B-OLF1500-St and 2-xanthate ethyl methacrylate (M6-B-OLF1500-St-co-xanthate backbone)

(69) 4.00 g (28.1 mmol) of butyl methacrylate, 1.30 g (1.36 mmol) of the olefin macromonomer M6-B-OLF1500-St, 1.06 g (4.52 mmol) of 2-xanthate ethyl methacrylate (XEMA; synthesized according to the protocol described in the paper “Synthesis of Well-Defined Polythiol Copolymers by RAFT Polymerization”, R. Nicola, Macromolecules, 2012, 45, 821-827), 16.4 mg (0.074 mmol) of RAFT transfer agent 2-cyano-2-propyl benzodithioate (CPBD), 4.8 mg (0.030 mmol) of azobisisobutyronitrile (AIBN) and 6.4 ml of anisole are introduced into a 50 ml Schlenk tube. The reaction medium is stirred and degassed for 30 min by bubbling nitrogen through, before being brought to 65° C. for a period of 20.5 hours.

(70) After 20.5 h of polymerization, the Schlenk tube is placed in an ice bath in order to halt the polymerization. The polymer is subsequently isolated by 2 successive precipitations from methanol cooled using an ice bath, filtration and drying under vacuum at 50° C. overnight. The copolymer thus obtained exhibits a number-average molar mass (M.sub.n) of 80 600 g/mol, a dispersity (Ð) of 1.61 and a number-average degree of polymerization (DP.sub.n) of 350. The first two values are obtained by size exclusion chromatography using THF as eluent and poly(methyl methacrylate) calibration, while the DP.sub.n is obtained by .sup.1H NMR monitoring of the conversion of monomers during polymerization.

(71) A poly(butyl methacrylate-co-2-xanthate ethyl methacrylate-co-M6-B-OLF1500-St) copolymer, “M6-B-OLF1500-St-co-xanthate backbone”, containing 7.9 mol % of 2-xanthate ethyl methacrylate repeat units (9.5% by weight) and 5.6 mol % of pendant OLF1500-OCP chains (27% by weight), is obtained.

(72) 1.2.6.2 Synthesis of a Main Chain Containing Olefin Macromonomer M6-B-OLF1500-St and Pendant Acrylate Functional Groups (M6-B-OLF1500-St-Co-Acrylate backbone)

(73) The xanthate functional groups of the “M6-B-OLF1500-St-co-xanthate backbone” copolymer are subsequently converted into acrylates by Michael addition with 1,6-hexanediol diacrylate according to the following protocol:

(74) 3.70 g (1.50 mmol of XEMA functional groups) of “M6-B-OLF1500-St-co-xanthate backbone” are introduced into a 250 ml Schlenk tube and dissolved in 35 ml of a THF:DMF=1:1 by volume mixture. 0.44 g (6.00 mmol) of n-butylamine and three drops of tributylphosphine are introduced into the Schlenk tube. The reaction medium is degassed for 10 min by bubbling nitrogen through, then stirred at ambient temperature for 2 hours. Subsequently, a solution of 6.79 g (30.0 mmol) of 1,6-hexanediol diacrylate in 3 ml of THF is introduced and the reaction medium is left stirring at ambient temperature for a period of 48 hours.

(75) The reaction medium is subsequently concentrated under vacuum and the polymer is isolated by 3 successive precipitations from methanol cooled using an ice bath, filtration and drying under vacuum at 50° C. overnight. The copolymer thus obtained exhibits a number-average molar mass (M.sub.n) of 60 100 g/mol and a dispersity (Ð) of 1.65, as obtained by size exclusion chromatography using THF as eluent and poly(methyl methacrylate) calibration.

(76) The “M6-B-OLF1500-St-co-acrylate backbone” copolymer, containing 5.1 mol % of repeat units carrying a pendant acrylate functional group (9.4% by weight) and 5.6 mol % of pendant OLF1500-OCP chains (27% by weight), as measured by .sup.1H NMR, is obtained.

(77) 1.2.6.3 Synthesis of a Precursor of Side Chains by Copolymerization of Lauryl Methacrylate, of Styrene and of Methacrylate Carrying a Diol Functional Group (Polydiol Side Chain)

(78) The pendant polydiol polymeric chains of the comb copolymer containing the olefin macromonomer M6-B-OLF1500-St and pendant polydiol polymeric chains (CPDiol-3) are prepared according to the following protocol (Scheme 14 above).

(79) 8.00 g (31.4 mmol) of lauryl methacrylate (LMA), 0.54 g (5.24 mmol) of styrene, 1.86 g (9.17 mmol) of methacrylate monomer carrying a diol functional group, 290 mg (1.31 mmol) of RAFT transfer agent PPBD, 10.8 mg (0.066 mmol) of AIBN and 3.6 ml of anisole are introduced into a 50 ml Schlenk tube. The reaction medium is stirred and degassed for 30 min by bubbling nitrogen through, before being brought to 65° C. for a period of 24 hours.

(80) After 24 h of polymerization, the Schlenk tube is placed in an ice bath in order to halt the polymerization. The polymer is subsequently isolated by precipitation from methanol cooled using an ice bath, separation by settling of the supernatant and drying under vacuum at 50° C. overnight. The copolymer thus obtained exhibits a number-average molar mass (M.sub.n) of 9850 g/mol, a dispersity (Ð) of 1.27 and a number-average degree of polymerization (DP.sub.n) of 27. The first two values are obtained by size exclusion chromatography using THF as eluent and poly(methyl methacrylate) calibration, while the DP.sub.n is obtained by .sup.1H NMR monitoring of the conversion of monomers during polymerization.

(81) A poly(lauryl methacrylate-methacrylate comonomer carrying a diol functional group-co-styrene), “polydiol side chain”, copolymer containing 20 mol % of diol repeat units (18% by weight), 67 mol % of lauryl methacrylate repeat units (76% by weight) and 13 mol % of styrene repeat units (6.0% by weight), is thus obtained.

(82) 1.2.6.4 Synthesis of the Comb Copolymer Containing the Olefin Macromonomer M6-B-OLF1500-St and Pendant Polydiol Polymeric Chains (CPDiol-3)

(83) 1.07 g (0.12 mmol) of “polydiol side chain” copolymer prepared according to the protocol described in 1.2.6.3 are introduced into a 100 ml Schlenk tube and dissolved in 10 ml of a THF:DMF=2:1 by volume mixture. 65 mg (0.88 mmol) of n-butylamine and three drops of tributylphosphine are added to the solution. The reaction medium is degassed for 5 min by bubbling nitrogen through and stirred at ambient temperature for 2 hours. Subsequently, a solution of 1.70 g (0.43 mmol of acrylate functional groups) of “M6-B-OLF1500-St-co-acrylate backbone” copolymer prepared according to the protocol described in 1.2.6.2 in 20 ml of a THF:DMF=2:1 by volume mixture is added to the reaction mixture under a nitrogen atmosphere. The reaction mixture is subsequently brought to 40° C. for a period of 40 hours.

(84) After 40 h of reaction, 125 mg (2.03 mmol) of ethanethiol are added to the reaction medium, which is kept stirred at ambient temperature for 4 hours.

(85) The comb copolymer containing the olefin macromonomer M6-B-OLF1500-St and pendant polydiol polymeric chains (CPDiol-3) is subsequently isolated by 2 successive precipitations from methanol cooled using an ice bath, separation by settling of the supernatant and drying under vacuum at 50° C. overnight.

(86) 1.3: Synthesis of the Comparative Copolymers—Methods

(87) 1.3.1 Linear Polydiol-1 (Comparative LPDiol-1):

(88) The linear polydiol-1 was synthesized according to the protocol described in the application FR 1 661 400 or WO2018096252A1 (Experimental part § 1.2). This polydiol contains approximately 10 mol % of monomer carrying a diol functional group (8.6% by weight), 37 mol % of lauryl methacrylate (39.8% by weight), 28 mol % of stearyl methacrylate (40.1% by weight) and 26 mol % of styrene (11.5% by weight). The copolymer exhibits an M.sub.n of 53 000 g/mol, a Ð of 1.3 and a DP.sub.n of 250. These values are respectively obtained by size exclusion chromatography, using THF as eluent and PMMA calibration, and by monitoring the conversion of monomers during the copolymerization.

(89) 1.3.2 Linear Polydiol-2 (Comparative LPDiol-2):

(90) The linear polydiol-2 was synthesized according to the protocol described in the application FR 1 661 400 or W2018096252A1 (Experimental part § 1.2). This copolymer comprises 7.0 mol % of monomer carrying a diol functional group (6.0% by weight). The mean side chain length is 10.3 carbon atoms. Its number-average molar mass is 40 000 g/mol. Its dispersity is 1.46. Its number-average degree of polymerization (DP.sub.n) is 170. The number-average molar mass and the dispersity are obtained by size exclusion chromatography using poly(methyl methacrylate) calibration.

(91) 1.4: Synthesis of the Boronic Copolymers—Methods

(92) 1.4.1 Linear poly(boronic ester)-1 (LPB1):

(93) A linear poly(boronic ester) was synthesized according to the protocol described in the application WO2016/113229 (Experimental part § 2). This poly(boronic ester) contains approximately 4 mol % of monomer carrying a boronic ester functional group (8.1% by weight), 61 mol % of lauryl methacrylate (69.6% by weight) and 35 mol % of butyl methacrylate (22.3% by weight). The copolymer exhibits an M.sub.n of 41 000 g/mol, a Ð of 1.3 and a DP.sub.n of 210. These values are respectively obtained by size exclusion chromatography, using THF as eluent and PMMA calibration, and by monitoring the conversion of monomers during the copolymerization.

(94) 1.4.2 Random Linear Poly(Boronic Ester) Copolymer (LPB2)

(95) This copolymer comprises 6.0 mol % of B-C.sub.12E repeat units (10% by weight). The mean side chain length is 12 carbon atoms. Its number-average molar mass is 45 700 g/mol. Its dispersity is 1.39. Its number-average degree of polymerization (DP.sub.n) is 175. The number-average molar mass and the dispersity are obtained by size exclusion chromatography using poly(methyl methacrylate) calibration and THE as eluent. This copolymer is obtained according to the protocol described in section 2 of the Experimental part of the application WO2016/113229.

(96) 1.4.3 Synthesis of a comb copolymer of butyl methacrylate, of styrene carrying a boronic-C.sub.12 ester functional group and of the olefin macromonomer M6-B-OLF1500-St (PBB2)

(97) ##STR00062##

(98) The synthesis of the comb copolymer carrying boronic ester functional groups in the main chain PBB2 is carried out according to the following protocol:

(99) 2.50 g (17.5 mmol) of butyl methacrylate (BMA), 0.39 g (0.87 mmol) of the boronic ester condensed with 1,2-dodecanediol monomer (B-C.sub.12Em) obtained according to the protocol described in the application WO2016/113229 (Experimental part § 2.1), 0.89 g (0.93 mmol) of the olefin macromonomer M6-B-OLF1500-St obtained according to the protocol described in section 1.1.4 above, 9.3 mg (0.04 mmol) of RAFT transfer agent 2-cyano-2-propyl benzodithioate (CPBD), 2.8 mg (0.02 mmol) of AIBN and 3.8 ml of anisole are introduced into a 25 ml Schlenk tube. The reaction medium is stirred and degassed for 30 min by bubbling nitrogen through, before being brought to 65° C. for a period of 19 hours.

(100) After 19 h of polymerization, the Schlenk tube is placed in an ice bath in order to halt the polymerization. The polymer is subsequently isolated by precipitation from acetone cooled using an ice bath, separation by settling of the supernatant and drying the pasty polymer phase under vacuum at 50° C. overnight. The copolymer thus obtained exhibits a number-average molar mass (M.sub.n) of 54 800 g/mol, a dispersity (Ð) of 1.23 and a number-average degree of polymerization (DP.sub.n) of 280. The first two values are obtained by size exclusion chromatography using THF as eluent and poly(methyl methacrylate) calibration, while the DP.sub.n is obtained by .sup.1H NMR monitoring of the conversion of monomers during polymerization.

(101) A poly(butyl methacrylate-co-B-C.sub.12Em-co-M6-B-OLF1500-St) copolymer PBB2 containing 5.7 mol % of B-C.sub.12Em repeat units (12% by weight) and 6.8 mol % of M6-B-OLF1500-St repeat units (30% by weight) is obtained.

(102) 2. Preparation of the Compositions

(103) Each polymer is dissolved in a Group III base oil in order to obtain a 10% by weight polymer solution. After complete dissolution of the polymer in the oil, these solutions serve as mother solutions for the preparation of the formulations to be studied in rheology.

(104) 2.1 Ingredients for the Formulation of Compositions

(105) Lubricating Base Oil

(106) The lubricating base oil used in the compositions to be tested is an oil from Group III of the API classification, sold by SK under the name Yubase 4. It exhibits the following characteristics: its kinematic viscosity at 40° C., measured according to the standard ASTM D445, is 19.57 cSt; its kinematic viscosity measured at 100° C. according to the standard ASTM D445 is 4.23 cSt; its viscosity index, measured according to the standard ASTM D2270, is 122; its Noack volatility as percentage by weight, measured according to the standard DIN 51581, is 15; its flash point in degrees Celsius, measured according to the standard ASTM D92, is 230° C.; its pour point in degrees Celsius, measured according to the standard ASTM D97, is −15° C.

(107) 2.2 Formulation of Compositions

(108) Preparation of Composition B

(109) 1.60 g of Group III base oil and 0.40 g of the 10% by weight mother solution of comb polydiol CPDiol-1 are introduced into a sample tube and vigorously mixed using a vortex mixer for 30 seconds. This formulation thus contains 2% by weight of comb polydiol CPDiol-1.

(110) Preparation of Composition C

(111) 1.60 g of Group III base oil and 0.40 g of the 10% by weight mother solution of comb polydiol BB are introduced into a sample tube and vigorously mixed using a vortex mixer for 30 seconds. This formulation thus contains 2% by weight of comb polydiol BB.

(112) Preparation of the composition D (Comparative)

(113) 1.60 g of Group III base oil and 0.40 g of the 10% by weight mother solution of linear polydiol-1 (LPDiol-1) are introduced into a sample tube and vigorously mixed using a vortex mixer for 30 seconds. This formulation thus contains 2% by weight of linear polydiol-1 (LPDiol-1).

(114) Preparation of the Composition F (According to the Invention)

(115) 1.20 g of Group III base oil, 0.40 g of the 10% by weight mother solution of comb polydiol CPDiol-1 and 0.40 g of the 10% by weight mother solution of linear poly(boronic ester)-1 (LPB1) are introduced into a sample tube and vigorously mixed using a vortex mixer for 30 seconds. This formulation thus contains 2% by weight of comb polydiol CPDiol-1, TD 4-37, and 2% by weight of linear poly(boronic ester)-1 (LPB1).

(116) Preparation of the Composition G (According to the Invention)

(117) 1.20 g of Group III base oil, 0.40 g of the 10% by weight mother solution of comb polydiol BB and 0.40 g of the 10% by weight mother solution of linear poly(boronic ester)-1 (LPB1) are introduced into a sample tube and vigorously mixed using a vortex mixer for 30 seconds. This formulation thus contains 2% by weight of comb polydiol BB and 2% by weight of linear poly(boronic ester)-1 (LPB1).

(118) Preparation of the Composition H (Comparative)

(119) 0.53 g of the 39.2% by weight solution of LPB2 in the Group III base oil are mixed with 6.76 g of this same base oil. This mixture is kept stirred in a vortex mixer at ambient temperature for 1 minute. The solution thus obtained of LPB2 is subsequently mixed with 0.71 g of the 25.4% by weight solution of LPDiol-2 in the Group III base oil. The mixture thus obtained is kept stirred in a vortex mixer at ambient temperature for 2 minutes. A solution comprising 2.60% by weight of linear copolymer LPB2 and 2.25% by weight of linear copolymer LPDiol-2 is obtained.

(120) Preparation of the Composition I (According to the Invention)

(121) 0.60 g of comb polydiol copolymer CPDiol-2 and 5.40 g of Group III base oil are introduced into a flask. The mixture thus obtained is kept stirred at 100° C. until the comb polydiol copolymer CPDiol-2 has completely dissolved. A 10% by weight solution of comb polydiol copolymer CPDiol-2 is thus obtained.

(122) 0.60 g of comb poly(boronic ester) copolymer PBB2 and 5.40 g of Group III base oil are introduced into a flask. The mixture thus obtained is kept stirred at 100° C. until the poly(boronic ester) PBB2 has completely dissolved. A 10% by weight solution of comb poly(boronic ester) copolymer PBB2 is thus obtained.

(123) 1.47 g of the 10% by weight solution of polydiol CPDiol-2 in the Group III base oil are mixed with 2.94 g of this same base oil. This mixture is kept stirred in a vortex mixer at ambient temperature for 1 minute. The solution thus obtained of CPDiol-2 is subsequently mixed with 1.47 g of the 10% by weight solution of poly(boronic ester) PBB2 in the Group III base oil and kept stirred in a vortex mixer at ambient temperature for 2 minutes. Composition I, containing 2.50% by weight of comb polydiol copolymer CPDiol-2 and 2.50% by weight of comb poly(boronic ester) copolymer PBB2, is thus obtained.

(124) Preparation of the Composition J (According to the Invention)

(125) 1.47 g of the 10% by weight solution of comb polydiol CPDiol-2 prepared above are mixed with 4.03 g of Group III base oil. This mixture is kept stirred in a vortex mixer at ambient temperature for 1 minute. The solution thus obtained of CPDiol-2 is subsequently mixed with 0.38 g of the 39.2% by weight solution of LPB2 in the Group III base oil and kept stirred in a vortex mixer at ambient temperature for 2 minutes. A solution comprising 2.50% by weight of comb polydiol copolymer CPDiol-2 and 2.50% by weight of linear poly(boronic ester) copolymer LPB2 is thus obtained.

(126) 3. Rheology of the Solutions of Polymers

(127) The relative viscosity, calculated according to the following formula

(128) $\left({\eta }_{\mathrm{relative}}=\frac{{\eta }_{\mathrm{solution}}}{{\eta }_{\mathrm{huile}\mathrm{de}\mathrm{base}}}\right)$

(129) was chosen to represent the change in the viscosity of the system as a function of the temperature because this quantity directly reflects the compensation for the loss of natural viscosity of a Group III base oil of the polymer systems studied.

(130) 3.1 Appliances and Protocols for Measuring the Viscosity (Compositions Q to G)

(131) The rheological studies were carried out using a Lovis 2000 rolling ball viscometer from Anton Paar.

(132) In the case of the formulations of polymers which do not form gels in a base oil of Group III over the temperature range of the study, the rheology measurements were carried out using a reference cylindrical geometry DG 26.7. The viscosity was measured as a function of the shear rate for a temperature range varying from 10° C. to 90° C. For each temperature, the viscosity of the system was measured as a function of the shear rate from 1 to 100 s.sup.−1. The measurements of viscosity as a function of the shear rate at T=10° C., 50° C. and 90° C. were carried out. A mean viscosity was then calculated for each temperature using the measurement points located on the same plate.

(133) 3.2 Results Obtained in Rheology

(134) The relative viscosity of the compositions B, C and D was measured at 90° C., 50° C. and then 10° C. (FIG. 9). All the compositions contain 2% by weight of polymer. Although the two comb polydiols exhibit similar architectures, the relative viscosity of the composition B (diol functional groups on the pendant chains) is significantly lower than the relative viscosity of the composition C (functional groups on the backbone). The composition D is formed of a polydiol exhibiting a mean degree of polymerization of approximately 250 monomer units. This polymer is thus significantly shorter than the polymer of the composition B (backbone having a mean degree of polymerization of approximately 300). Nevertheless, the relative viscosity of the composition D is significantly greater than the relative viscosity of the composition B over the entire range of temperatures. This means that brush diol polymers have a lower impact on the viscosity of the oil than linear diol polymers, notably when the pendant chains of the brushes contain the diol functional groups. In addition, the composition B exhibits a greater increase in its relative viscosity with the temperature than the compositions C and D.

(135) The relative viscosity of the compositions F and G was measured at 90° C., 50° C. and then 10° C. (FIG. 10). These two compositions were studied over 3 cycles of cooling and then heating from 90° C. to 10° C. Whatever the composition, the relative viscosities are very close at each temperature from one cycle to another. This means that the rheological behavior of the formulation is reproducible over at least 3 cycles. These two compositions show a strong increase in their relative viscosity when the temperature increases. The compositions F and G exhibit approximately the same relative viscosity at 50° C. On the other hand, the composition F is less viscous at 10° C. and more viscous at 90° C. This means that the formulation notably formed of the comb polydiol CPDiol-1 makes it possible to obtain a stronger viscosification of nonpolar oils than the formulation notably formed of the comb polydiol BB.

(136) 3.3 Appliances and Protocols for Measuring the Viscosity (Compositions H, I and

(137) The rheological studies were carried out using a rheometer of the stress-controlled Couette MCR 501 type from Anton Paar.

(138) The rheology measurements were carried out using a cylindrical geometry of DG 26.7 reference. The viscosity was measured as a function of the shear rate for a temperature range varying from 10° C. to 150° C. For each temperature, the viscosity of the system was measured as a function of the shear rate from 1 to 100 s.sup.−1. The measurements of viscosity as a function of the shear rate at T=10° C., 40° C., 70° C., 100° C., 130° C. and 150° C. were carried out (ranging from 10° C. to 150° C.). A mean viscosity was then calculated for each temperature using the measurement points located on the same plate (from 15 to 100.sup.s−1).

(139) Table 1 below shows the change in the absolute viscosities of the compositions H to J as a function of temperature.

(140) 3.4 Results Obtained in Rheology (Compositions H, I and J)

(141) The relative viscosities of the compositions I and J were studied over a range of temperatures extending from 10° C. to 150° C. and compared with that of the composition H. The viscosity of the solution was calculated by taking the mean of the absolute viscosities obtained for the shear rates between 15 and 100 s.sup.−1. The relative viscosity of these compositions is shown in FIG. 11.

(142) TABLE-US-00002 TABLE 1 η [mPa .Math. s] η [mPa .Math. s] η [mPa .Math. s] Temperature η [mPa .Math. s] Composition Composition Composition [° C.] Yubase 4 H I J 10 63.4 99.9 82.1 89.7 40 16.4 27.2 21.8 24.2 70 6.61 11.4 8.84 10.2 100 3.45 6.18 4.80 5.87 130 2.10 3.89 3.14 3.92 150 1.60 2.98 2.53 3.18

(143) When the linear polydiol LPDiol-2 and the linear poly(boronic ester) LPB2 are present together in the same lubricating composition (composition H), a significant compensation for the loss of natural viscosity of the Group III base oil over the entire range of the temperatures studied is observed. This is reflected by a virtually linear increase in the relative viscosity between 10° C. and 150° C. (FIG. 11, dashed line-hollow squares). However, the composition H also impacts the cold viscosity of the formulation, with a relative viscosity at 10° C. of 1.58.

(144) The presence of the comb polydiol copolymer CPDiol-2 and of the brush poly(boronic ester) copolymer PBB2 in the same lubricating composition (composition I) makes possible a significant reduction in the relative viscosity at low temperature, down to η.sub.rel=1.30 at 10° C. At the same time, a lower compensation of this formulation for the loss of natural viscosity of the Group III base oil at high temperatures is observed, compared to the formulation H (FIG. 11, dashed/continuous line-stars).

(145) The dilution of the composition I down to 2.10% by weight of brush polydiol copolymer CPDiol-2 and 2.10% by weight of brush poly(boronic ester) copolymer PBB2 makes it possible to further reduce the relative viscosity at 10° C. down to η.sub.rel=1.21 (FIG. 12-Id, dotted line-stars). However, unlike the compositions containing linear copolymers, even having this low relative viscosity under cold conditions, the composition Id preserves its viscosifying behavior at high temperatures (η.sub.rel=1.43 at 150° C.). The relative viscosity values are represented for three successive heating-cooling cycles between 10° C. and 150° C. (Id-1, Id-2 and Id-3). These change in a negligible way during the 3 cycles and always give an increase in the relative viscosity between 10° C. and 150° C. (FIG. 13).

(146) When the comb polydiol copolymer CPDiol-2 and the linear poly(boronic ester) copolymer LPB2 are present together in the same lubricating composition (composition J), the advantages of the two systems are combined. On this intersecting of the types of structure of associative copolymers, a strong compensation for the loss of natural viscosity of the base oil over the temperature range from 100° C. to 150° C. is observed (FIG. 11, continuous line-solid circles), which occurs in combination with a significant decrease in the relative viscosity at low temperature, in comparison with the formulation containing only linear copolymers.

(147) The relative viscosity values are also represented for five successive heating-cooling cycles between 10° C. and 150° C. (J-1, J-2, J-3, J-4 and J-5). They change very slightly during the 5 cycles and always give an increase in the relative viscosity of approximately 0.65 between 10° C. and 150° C., reflecting the good compensation for the natural loss of viscosity of the Group III base oil over this range of temperatures (FIG. 14).