Thermoassociative additive compositions, the association of which is controlled, and lubricating compositions containing same

Abstract

The invention concerns additive compositions obtained by mixing at least two thermoassociative and exchangeable compounds and at least one boronic ester compound that enables the association of these two copolymers to be controlled; a lubricating composition obtained by mixing at least one lubricating base oil, at least two thermoassociative and exchangeable compounds, and at least one boronic ester compound that enables the association of these two copolymers to be controlled; a method for adjusting the viscosity of a lubricating composition obtained by mixing at least one lubricating base oil and at least two thermoassociative and exchangeable compounds; and the use of a boronic ester compound to adjust the viscosity of a lubricating composition.

Claims

1. A composition resulting from the mixing of at least one polydiol random copolymer A1, one compound A2 comprising at least two boronic ester functions, one exogenous compound A5 chosen from those corresponding to formula (XI): ##STR00051## in which: Q represents a group chosen from 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, G.sub.4 and G.sub.5, which may be identical or different, represent groups chosen from a hydrogen atom, a C1-C24 alkyl, a hydroxyl and a group —OJ or —C(O)—O-J with J being a C1-C24 alkyl, g represents 0 or 1, wherein the molar percentage of exogenous compound A5 relative to the diol functions of the random copolymer A1 ranges from 1% to 150% and the mass ratio between copolymer A1 and compound A2 (ratio A1/A2) ranges from 0.05 to 20, wherein the random copolymer A1 results from the copolymerization: of at least one first monomer M1 of general formula (I): ##STR00052## 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 ##STR00053## 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: ##STR00054## 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; with at least one second monomer M2 of general formula (II): ##STR00055## 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 a C.sub.6-C.sub.18 aryl, a C.sub.6-C.sub.18 aryl with a group R′.sub.3, —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 being a C.sub.1-C.sub.30 alkyl group.

2. The composition as claimed in claim 1, in which the exogenous compound A5 is chosen from those corresponding to formula (XIA): ##STR00056## in which: G.sub.1, G.sub.2, G.sub.3, G.sub.4 and G.sub.5, which may be identical or different, represent groups chosen from a hydrogen atom, a C1-C24 alkyl, a hydroxyl and a group —OJ or —C(O)—O-J with J being a C1-C24 alkyl, g represents 0 or 1.

3. The composition as claimed in claim 2, in which the exogenous compound A5 is chosen from those corresponding to formula (XI B): ##STR00057## wherein G4 and G5, which may be identical or different, represent groups chosen from a hydrogen atom, a C1-C24 alkyl, a hydroxyl and a group —OJ or —C(O)—O-J with J being a C1-C24 alkyl.

4. The composition as claimed in claim 3, in which the exogenous compound A5 is chosen from those corresponding to formula (XI B) with g=0, G.sub.4=H and G.sub.5 represents a C1-C24 alkyl.

5. The composition as claimed in claim 1, in which the random copolymer A1 results from the copolymerization of: at least one first monomer M1 of general formula (I), with at least one second monomer M2 of general formula (II): ##STR00058## 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 being a C.sub.1-C.sub.30 alkyl group, and with at least one third monomer M3 of general formula (X): ##STR00059## 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.

6. The composition as claimed in claim 5, in which the third monomer M3 is styrene.

7. The composition as claimed in claim 5, in which the random copolymer A1 results from the copolymerization of at least one monomer M1 with at least two monomers M2 bearing different groups R.sub.3 and at least one monomer M3.

8. The composition as claimed in claim 7, in which the two monomers M2 of the random copolymer A1 have the general formula (II-B): ##STR00060## 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 a C.sub.9-C.sub.30 alkyl group.

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

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

11. The composition as claimed in claim 1, in which compound A2 is a compound of formula (III): ##STR00061## 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, are chosen from the group formed by hydrogen and 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.

12. The composition as claimed in claim 1, in which compound A2 is a random copolymer resulting from the copolymerization of at least one monomer M4 of formula (IV): ##STR00062## 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 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, are chosen from the group formed by hydrogen and a hydrocarbon-based group having 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; with at least one second monomer M5 of general formula (V): ##STR00063## 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 a C.sub.6-C.sub.18 aryl, a C.sub.6-C.sub.18 aryl substituted with a group 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 with R′.sub.13 being a C.sub.1-C.sub.30 alkyl group.

13. The composition as claimed in claim 12 in which at least one of the following three conditions is met: either, in formula (IV): u=1, R.sub.9 is H and R.sub.8 represents a C.sub.6-C.sub.18 aryl or a C.sub.7-C.sub.24 aralkyl and the double bond of the monomer M4 of formula (IV) is directly connected to the aryl group; or, in formula (V): R.sub.12 represents H and R.sub.13 is chosen from the group formed by a C.sub.6-C.sub.18 aryl and a C.sub.6-C.sub.18 aryl substituted with a group R′.sub.13 with R′.sub.13 being a C.sub.1-C.sub.25 alkyl group and the double bond of the monomer M5 of formula (V) is directly connected to the aryl group; or, copolymer A2 comprises at least one third monomer M3 of formula (X) ##STR00064## 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.

14. The composition as claimed in claim 12, 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.

15. The composition as claimed in claim 12, in which copolymer A2 has a number-average degree of polymerization ranging from 50 to 1500.

16. The composition as claimed in claim 12, in which copolymer A2 has a polydispersity index (Ip) ranging from 1.04 to 3.54.

17. The composition as claimed in claim 1, in which the mass ratio between copolymer A1 and compound A2 (ratio A1/A2) ranges from 0.1 to 10.

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

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 represents a comb copolymer.

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

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

(5) FIG. 5 schematically represents the behavior of the composition of the invention as a function of the temperature. A random copolymer (2) bearing diol functions (function A) can thermoreversibly associate with a random copolymer (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.

(6) FIG. 6 represents the change in relative viscosity (unitless, on the y-axis) as a function of the temperature (° C., on the x-axis) of compositions B and C.

(7) FIG. 7 represents the change in relative viscosity (unitless, on the y-axis) as a function of the temperature (° C., on the x-axis) of compositions A, E, F and G.

EXPERIMENTAL SECTION

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

(9) 1. Synthesis of Random Copolymers A1 Bearing a Diol Function

(10) 1.1: Starting with a Monomer Bearing a Diol Function

(11) In one embodiment, the random copolymer A1 of the invention is obtained according to reaction scheme 11 below:

(12) ##STR00050##

(13) The copolymer obtained after removing the RAFT chain end contains, inter alia, styrene as comonomer and the thiocarbonylthio residue was removed, for example by converting it into a thioether.

(14) 1.1.1. Synthesis of the Monomer M1 Bearing a Diol Function

(15) The synthesis of a methacrylate monomer bearing a diol function is performed in three steps (steps 1, 2 and 3 of reaction scheme 11) according to the protocol below:

(16) First Step:

(17) 42.1 g (314 mmol) of 1,2,6-hexanetriol (1,2,6-HexTri) are placed in a 1 L round-bottomed flask. 5.88 g of molecular sieves (4 Å) are added, followed by 570 mL of acetone. 5.01 g (26.3 mmol) of para-toluenesulfonic acid (pTSA) are then slowly added. The reaction medium is stirred for 24 hours at room temperature. 4.48 g (53.3 mmol) of NaHCO.sub.3 are then added. The reaction medium is stirred for 3 hours at room temperature 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 then totally evaporated off under vacuum at 25° C. using a rotary evaporator.

(18) Second Step:

(19) 5.01 g (28.8 mmol) of the product thus obtained is then placed in a 1 L round-bottomed flask. 4.13 g (31.9 mmol) of DIPEA and 37.9 mg (0.31 mmol) of DMAP are then placed in the flask, followed by 5.34 g (34.6 mmol) of methacrylic anhydride. The flask is then stirred at room temperature for 24 hours. 0.95 g of methanol (29.7 mmol) is then added to the solution and the flask is stirred for a further 1 hour. The product is then dissolved in 40 mL of hexane. The organic phase is then washed successively with 25 mL of water, 3×25 mL of aqueous 0.5 M hydrochloric acid solution, 3×25 mL of aqueous 0.5 M 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 pale yellow liquid, the characteristics of which are as follows:

(20) Third Step:

(21) 17.23 g (71.2 mmol) of the product thus obtained is then placed in a 1 L round-bottomed flask. 90 mL of water and 90 mL of acetonitrile are then placed in the flask, followed by 59.1 mL (159 mmol) of acetic acid. The flask is then stirred for 24 hours at 30° C. while a gentle stream of nitrogen is bubbled through to force the removal of the acetone. The solution thus obtained is extracted with 6×30 mL of ethyl acetate. The organic phase is washed successively with 5×30 mL of aqueous 0.5 M NaOH solution and then 3×30 mL of water. The organic phase is then dried over MgSO.sub.4, filtered and then concentrated under vacuum using a rotary evaporator to give a pale yellow liquid, the characteristics of which are as follows:

(22) .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 (doublet of doublets, J=7.6 Hz and J=11.2 Hz, 1H), 1.86 (doublet of doublets, J=1.2 Hz and J=1.6 Hz, 3H), 1.69-1.31 (multiplet, 6H).

(23) 1.1.2. Synthesis of Methacrylate Copolymers Bearing Diol Functions

(24) The synthesis of methacrylate copolymers bearing diol functions is performed in two steps (steps 4 and 5 of reaction scheme 11): Copolymerization of two alkyl methacrylate monomers with a methacrylate monomer bearing a diol function and a styrene monomer; Removal of the RAFT chain end (aminolysis followed by Michael addition of the thiol with an alkyl acrylate).

(25) More specifically, the synthesis of the copolymer A-1a is performed according to the following protocol:

(26) First Step:

(27) 12.56 g (37.1 mmol) of stearyl methacrylate (StMA), 12.59 g (49.5 mmol) of lauryl methacrylate (LMA), 2.57 g (24.7 mmol) of styrene (Sty), 2.54 g (12.4 mmol) of methacrylate bearing a diol function obtained according to the protocol described in section 1.1.1, 82.5 mg (0.30 mmol) of cumyl dithiobenzoate, 15 mg (0.09 mmol) of azobisisobutyronitrile (AIBN) and 30 mL of anisole are placed in a 250 mL Schlenk tube. The reaction medium is stirred and degassed for 30 minutes by bubbling nitrogen through, and is then maintained at 65° C. for a period of 24 hours.

(28) Second Step:

(29) After 24 hours of polymerization, the Schlenk tube is placed in an ice bath to stop the polymerization, and 30 mL of dimethylformamide (DMF) and 0.4 mL of n-butylamine (4 mmol) are added to the solution without degassing the medium, hours later, the polymer was completely discolored and 3 mL (21 mmol) of butyl acrylate are added. 16 hours later, the polymer is isolated by 3 successive precipitations in methanol, filtering and drying under vacuum at 50° C. overnight. A copolymer is thus obtained with a number-average molar mass (M.sub.n) of 53 000 g/mol, a polydispersity index (Ip) of 1.19 and a number-average degree of polymerization (DP) of 253. These values are obtained, respectively, by size exclusion chromatography using tetrahydrofuran as eluent and poly(methyl methacrylate) calibration and by monitoring the monomer conversion during the copolymerization.

(30) A poly(alkyl methacrylate-co-alkyldiol methacrylate-co-styrene) copolymer containing about 10 mol % of diol monomer units M1 is obtained.

(31) 2. Synthesis of the Poly(Alkyl Methacrylate-Co-Boronic Ester Monomer) Copolymer

(32) This synthesis is performed according to the protocol described in patent application WO 2016/113229 (experimental section § 2.).

(33) 3. Synthesis of Compound A5

(34) The synthesis of compound A5 is performed in one step according to the protocol below:

(35) 5000 g of phenylboronic acid (PBA) (41.0 mmol) are introduced into a 500 mL round-bottomed flask followed by 200 mL of THF. The reaction medium is then stirred. 0.5 mL (28 mmol) of water is added dropwise until the phenytboronic acid has fully dissolved. The reaction medium then becomes transparent and homogeneous. 8.286 g of 1,2-dodecanediol (1,2-DDD) (41.0 mmol) are then added slowly, followed by an excess of anhydrous magnesium sulfate so as to trap the water initially introduced and also the water released by the condensation between the PBA and the 1,2-DDD. The reaction medium is stirred for 2 hours at 25° C. and then filtered. The solvent is then removed from the filtrate on a rotary evaporator. The compound obtained is a mixture containing about 93 mol % of the boronic ester and 7 mol % of residual 1,2-dodecanediol.

(36) .sup.1H NMR (400 MHz, CDCl.sub.3) δ: 7.90 (multiplet, 2H), 7.60-7.40 (multiplet, 3H), 4.60 (multiplet, 1H), 4.46 (triplet, J=9.2 Hz, 1H), 3.99 (doublet of doublets, J=7.2 Hz and J=8.8 Hz, 1H), 1.85-1.20 (multiplet, 18H), 0.96 (triplet. J=6.8 Hz, 3.2H).

(37) 4. Rheological Studies

(38) 4.1 Ingredients for the Formulation of Compositions A to G

(39) Lubricant Base Oil

(40) 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. It has 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 a weight percentage, measured according to the standard DIN 51581 is 14.5; 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 097 is −15° C.

(41) Polydiol Random Copolymer A-1

(42) This copolymer comprises 10 mol % of monomers having diol functions and mol % of styrene monomers. The mean side chain length is 13.5 carbon atoms. Its number-average molar mass is 50 500 g/mol. Its polydispersity index is 1.26. Its number-average degree of polymerization (DPn) is 240. The number-average molar mass and the polydispersity index are measured by size exclusion chromatography measurement using poly(methyl methacrylate) calibration. This copolymer is obtained by performing the protocol described in section 1 above.

(43) Boronic Ester Random Copolymer A-2:

(44) This copolymer comprises 5 mol % of monomers bearing boronic ester functions. The mean side chain length is 12 carbon atoms. Its number-average molar mass is 39 000 g/mol. Its polydispersity index is 1.41. Its number-average degree of polymerization (DPn) is 192. Its number-average molar mass and the polydispersity index are measured by size exclusion chromatography measurement using poly(methyl methacrylate) calibration. This copolymer is obtained by performing the protocol described in section 2 above.

(45) Compound A5

(46) This compound consists of 93 mol % of the boronic ester formed by the esterification of the phenylboronic acid and of 1,2-dodecanediol and 7 mol % of an excess of 1,2-dodecanediol. This compound is obtained by performing the protocol described in section 3 above.

(47) 4.2 Formulation of Compositions for the Viscosity Study

(48) Composition a (Comparative) is Obtained in the Following Manner:

(49) It contains a solution containing 4.2% by mass of a polymethacrylate polymer in a lubricant base oil from group III of the API classification. The polymer has a number-average molar mass (Mn) equal to 106 000 g/mol, a polydispersity index (Ip) equal to 3.06, a number-average degree of polymerization of 466 and the mean side chain length is 14 carbon atoms.

(50) This polymethacrylate is used as viscosity-index-enhancing additive. 4.95 g of a formulation with a mass concentration of 42% of this polymethacrylate in a group III base oil and 44.6 g of group III base oil are placed in a flask. The solution thus obtained is stirred at 90° C. until the polymethacrylate has fully dissolved.

(51) A solution containing 4.2% by mass of this polymethacrylate is obtained. This composition is used as reference for the viscosity study. It represents the rheological behavior of commercial lubricant compositions.

(52) Composition B (Comparative) is Obtained in the Following Manner

(53) 6.52 g of polydiol copolymer A-1 and 58.68 g of a group III base oil are placed in a flask. The solution thus obtained is stirred at room temperature until the polydiol A-1 has fully dissolved. A solution containing 10% by mass of polydiol copolymer A-1 is obtained.

(54) 4.2 g of this solution of polydiol A-1 at 10% by mass in the group III base oil are mixed with 2.8 g of this same base oil. The solution thus obtained is stirred at room temperature for 5 minutes. A solution containing 6% by mass of polydiol copolymer A-1 is obtained.

(55) Composition C (Comparative) is Obtained in the Following Manner.

(56) 7.33 g of poly(boronic ester) copolymer A-2 and 65.97 g of a group III base oil are placed in a flask. The solution thus obtained is stirred at room temperature until the poly(boronic ester) A-2 has fully dissolved. A solution containing 10% by mass of poly(boronic ester) copolymer A-2 is obtained.

(57) 4.2 g of this solution of poly(boronic ester) A-2 at 10% by mass in the group III base oil are mixed with 2.8 g of this same base oil. The solution thus obtained is stirred at room temperature for 5 minutes. A solution containing 6% by mass of poly(boronic ester) copolymer A-2 is obtained.

(58) Composition D is Obtained in the Following Manner:

(59) 1.65 g of compound A-5 and 14.85 g of a group III base oil are placed in a flask. The solution thus obtained is stirred at room temperature until the compound A-5 has fully dissolved. A solution containing 10% by mass of compound A-5 is obtained.

(60) Composition E (Comparative) is Obtained in the Following Manner:

(61) 2.80 g of the solution containing 10% by mass of polydiol A-1 prepared previously and 1.40 g of group III base oil are placed in a flask. 2.80 g of the solution containing 10% by mass of poly(boronic ester) A-2 prepared previously are added to this solution. The solution thus obtained is stirred at room temperature for 5 minutes. A solution containing 4% by mass of polydiol copolymer A-1 and 4% by mass of poly(boronic ester) copolymer A-2 is obtained.
Composition F (According to the Invention) is Obtained in the Following Manner:

(62) 2.80 g of the solution containing 10% by mass of polydiol A-1 prepared previously and 1.26 g of group III base oil are placed in a flask. 2.80 g of the solution containing 10% by mass of poly(boronic ester) A-2 prepared previously and 0.14 g of the composition D prepared previously are added to this solution. The solution thus obtained is stirred at room temperature for 5 minutes. A solution is obtained containing 4% by mass of polydiol copolymer A-1, 4% by mass of poly(boronic ester) copolymer A-2 and 48.6 μmol of compound A-5. The solution thus comprises 43 mol % of compound A-5 relative to the diol functions of the polydiol A-1 and 93 mol % of compound A-5 relative to the BE functions of the poly(boronic ester) A-2.

(63) Composition G (According to the Invention) is Obtained in the Following Manner:

(64) 2.80 g of the solution containing 10% by mass of polydiol A-1 prepared previously and 1.12 g of group III base oil are placed in a flask. 2.80 g of the solution containing 10% by mass of poly(boronic ester) A-2 prepared previously and 0.28 g of the composition D prepared previously are added to this solution. The solution thus obtained is stirred at room temperature for 5 minutes. A solution containing 4% by mass of polydiol copolymer A-1 4% by mass of poly(boronic ester) copolymer A-2 and 97.2 μmol of compound A-5 is obtained. The solution thus comprises 86 mol % of compound A-5 relative to the diol functions of the polydiol A-1 and 186 mol % of compound A-5 relative to the BE functions of the poly(boronic ester) A-2.

(65) 4.4 Apparatus and Protocol for Measuring the Viscosity

(66) The rheological studies were performed using a Couette MCR 501 controlled stress rheometer from the company Anton Paar.

(67) In the case of the polymer formulations which do not form gels in a group III base oil over the temperature range of the study (compositions A to G), the rheology measurements were performed using a cylindrical geometry of reference DG 26.7. The viscosity was measured as a function of the shear rate for a temperature range extending from 10° C. to 110° 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 the viscosity as a function of the shear rate at T=10° C., 50° C., 70° C., and 110° C. were performed (going from 10° C. to 110° C.). A mean viscosity was then calculated for each temperature using the measurement points located on the same plateau.

(68) The relative viscosity calculated according to the following formula

(69) $\left({\eta }_{\mathrm{relative}}=\frac{{\eta }_{\mathrm{solution}}}{{\eta }_{\mathrm{base}\mathrm{oil}}}\right)$
was chosen to represent the change in viscosity of the system as a function of the temperature, since this magnitude directly reflects the compensation for the natural viscosity loss of a group III base oil of the polymer systems studied.

(70) 4.5 Rheological Results Obtained

(71) The viscosity of compositions A to F was studied on a temperature range extending from 10° C. to 110° C. The relative viscosity of these compositions is illustrated in FIGS. 6 and 7. Polydiol random copolymer A-1, alone in composition B, does not allow a significant compensation for the natural viscosity loss of the group III base oil (FIG. 6). This is likewise the case for the poly(boronic ester) copolymer A-2 when this copolymer is used alone in composition C (FIG. 6).

(72) When the polydiol random copolymer A-1 and the poly(boronic ester) copolymer A-2 are present together in the same lubricant composition (composition E), compensation for the natural viscosity loss of the group III base oil which is greater than that which results from the addition of the polymethacrylate polymer in the group III base oil (composition A) is observed (FIG. 7).

(73) When the composition (composition F) also comprises 43 mol % of free compound A-5 relative to the diol functions of the polydiol copolymer A-1; a slight decrease in the relative viscosity at low temperatures and also a slight decrease in the compensation for the loss of hot viscosity are observed relative to that of composition E which comprises the polydiol random copolymer A-1 and the poly(boronic ester) copolymer A-2 (FIG. 7). Composition F also makes it possible to obtain better compensation for the loss of hot viscosity of the oil than composition A while at the same time giving a lower viscosity than this same composition A from 10° C. to 70° C.

(74) When the composition (composition G) also comprises 86 mol % of free compound A-5 relative to the diol functions of the polydiol copolymer A-1; a greater decrease in the relative viscosity at low temperatures and also a decrease in the compensation for the loss of hot viscosity are observed relative to that of composition E which comprises the polydiol random copolymer A-1 and the poly(boronic ester) copolymer A-2 (FIG. 7). Compositions F and G still conserve the property of compensating for the loss of viscosity of the group III base oil for high temperatures. Compound A-5 thus makes it possible to modify, as a function of the temperature, the viscosity of a lubricant composition resulting from the mixing of at least one polydiol random copolymer A-1 and of at least one poly(boronic ester) random copolymer A-2 by controlling the degree of association of the chains of these two copolymers.