GB1568951A

GB1568951A - Starshaped dispersant viscosity index improver

Info

Publication number: GB1568951A
Application number: GB18463/78A
Authority: GB
Original assignee: Shell Internationale Research Maatschappij BV
Current assignee: Shell Internationale Research Maatschappij BV
Priority date: 1977-05-11
Filing date: 1978-05-09
Publication date: 1980-06-11
Also published as: FR2390496A1; FR2390496B1; DE2820211C2; JPS53139694A; NL184275B; CA1108792A; JPS6134724B2; NL184275C; NL7804898A; DE2820211A1

Description

(54) STAR-SHAPED DISPERSANT VISCOSITY INDEX IMPROVER (71) We, SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ B.V., a company organised under the laws of The Netherlands, of 30 Carel van Bylandtlaan, The Hague, The Netherlands, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The newer engines place increased demands on the lubricants to be employed. In the past a number of different additives have been added to lubricating oils to improve such properties as viscosity index and dispersancy. One such additive added to lubricating oils to improve viscosity index is a two-block copolymer having the general configuration A-B where A is styrene and B is hydrogenated isoprene. See generally U.S. Patent Nos.

3,763,044 and 3,772,196. A VI improver having greatly improved mechanical shear stability is the selectively hydrogenated star-shaped polymer disclosed in Netherlands Patent Application 7700168. Significant reductions in cost can be made by employing a single additive that improves a number of lubricant properties. However, in attempting to improve more than a single lubricant property, care must be taken in not causing the deterioration of other properties. For example, by employing an oxidation step to attach polar groups to the polymer backbone in U.S. 3,864,268, the patentees have reduced lubricant stability by introducing cites for oxidative attack.

Ashless, oil-soluble additives having both dispersant and viscosity-index (VI) improving properties are prepared by the process comprising: (a) reacting a selectively hydrogenated star-shaped polymer with an alpha-beta unsaturated carboxylic acid, anhydride or ester preferably at a temperature of between 1500C and 300"C, for between 1 hour and 24 hours wherein said star-shaped polymer comprises a poly (polyalkenyl coupling agent) nucleus, and at least 4 polymeric arms e.g. 4-25 arms, which arms each can have a number average molecular weight of e.g. 5,000 to 150,000 and which are linked to said nucleus wherein said polymeric arms are selected from the group consist ingof: (i) hydrogenated homopolymers and hydrogenated copolymers of conjugated dienes; (ii) hydrogenated copolymers of conjugated dienes and monoalkenyl arenes; and (iii) mixtures thereof; and wherein at least 80%, preferably 90 to 98So, of the alphatic unsaturation of the starshaped polymer has been reduced by hydrogenation while less than 20% of the aromatic unsaturation has been reduced; and (b) reacting the product of step (a) with a C1 to C18 amine containing 1 to 8 nitrogen atoms and/or with an alkane polyol having at least two hydroxy groups preferably at a temperature of between 1 50 C and 250"C.

In an alternative embodiment, the reaction between the star-shaped polymer and the carboxylic acid or derivative takes place after the chlorination of the polymer or in the presence of chlorine, as more fully explained below.

The dispersant VI improvers of the present invention possess excellent viscosity improving properties, oxidative stability, mechanical shear stability, and dispersancy. In particular, the lubricating oils containing the instant VI improver/ dispersants possess excellent thickening efficiency at high temperature while also possessing very good low temperature viscosity characteristics. Importantly, by employing the instant VI improver/ dispersants, as opposed to the prior art VI improvers, a lower amount of polymer is required in order to obtain the required thickening performance. Further, the instant polymers not only possess much superior oxidative shear stability and permanent shear stability, they also possess significantly improved "tempo,- - hear loss". Temporary shear loss refers to the tempor- ary viscosity loss at high shear stress conditions resulting from the non-Newtonian character of the polymeric VI improvers. Still further, the dispersing power of the instant polymeric additive is excellent. This combination of desirable properties has never before been obtainable in a single additive.

1) Preparation of the Base Polymer - The base polymer employed in making the present dispersant VI improvers is a star polymer. These polymers are generally produced by the process comprising the following reaction steps: (a) polymerizing one or more conjugated dienes and, optionally, one or more monoalkenyl arene compounds, in solution, in the presence of an ionic initiator to form a living polymer; (b) reacting the living polymer with a polyalkenyl coupling agent such as a polyvinyl aromatic compound, preferably divinyl benzene to form a star-shaped polymer; and (c) hydrogenating the star-shaped polymer to form a hydrogenated star-shaped polymer.

The living polymers produced in reaction step (a) of the present process are the precursors of the hydrogenated polymer chains which extend outwardly from the poly(polyalkenyl coupling agent) nucleus.

This preparation is described in detail in Netherlands patent application 7700168. Preferably each polymeric arm is a hydrogenated polyisoprene homopolymer.

The molecular weights of the star-shaped polymer to be hydrogenated in reaction step (c) may vary between relatively wide limits. However, an important aspect of the present invention is that polymers possessing good shear stability may be produced even though the polymers have very high molecular weights. It is possible to produce star polymers having peak molecular weights between 25,000 and 1,250,000. Preferred molecular weights are 100,000 to 500,000. These peak molecular weights are determined by gel permeation chromatography (GPC) on a polystyrene scale.

In step (c), the star-shaped polymers are hydrogenated by any suitable technique. At least 80%, preferably 90 to 98% of the original olefinic unsaturation is hydrogenated. If the star-shaped polymer is partly derived from a monoalkenyl arene compound, then the amount of aromatic unsaturation which is hydrogenated, if any, will depend on the hydrogenation conditions used. However, less than 20%, preferably less than 5% of such aromatic unsaturation is hydrogenated. If the poly(polyalkenyl coupling agent) nucleus is a poly(polyalkenyl aromatic coupling agent) nucleus, then the aromatic unsaturation of the nucleus may or may not be hydrogenated again depending upon the hydrogenation conditions used. The molecular weights of the hydrogenated star-shaped polymers correspond to those of the unhydrogenated star-shaped polymers.

The hydrogenation can be carried out as described in Netherlands patent application 7700168.

A much preferred hydrogenation process is the seIective hydrogenation process shown in U.S. 3,595,942. In that process hydrogenation is conducted, preferably in the same solvent in which the polymer was prepared, utilizing a catalyst comprising the reaction product of an aluminium alkyl and a nickel or cobalt carboxylate or alkoxide. A favoured catalyst is the reaction product formed from triethyl aluminium and nickel octoate.

The hydrogenated star-shaped polymer is then recovered in solid form from the solvent in which it is hydrogenated by any convenient technique such as by evaporation of the solvent. Alternatively, an oil, e.g. a lubricating oil, may be added to the solution and the solvent stripped off from the mixture so formed to produce concentrates. Easily handleable concentrates are produced even when the amount of hydrogenated star-shaped polymer therein exceeds 10%w. Suitable concentrates contain from 10 to 25%w of the hydrogenated star-shaped polymer.

2) Introduction of Sites for Dispersant Activity - The selectively hydrogenated star polymers as prepared above do not have adequate dispersancy characteristics by themselves. Therefore, the base polymer must be derivatized as explained below.

The star polymer is first reacted with the unsaturated carboxylic acid, anhydride or ester.

Suitable unsaturated acids and derivates include maleic acid, maleic anhydride, itaconic acid, dimethyl itaconate, acrylic acid, ethyl acrylate, methyl methacrylate, oleic acid, linoleic acid, etc. Maleic anhydride is especially preferred.

The carboxylic compound and the star polymer are reacted together e.g. at a temperature of between 1500C and 300"C, preferably between 1800C and 250"C. The contacting time is e.g. between 1 hour and 24 hours, preferably between 4 hours and 12 hours. The carboxylic compound reacts with the residual olefinic bonds available on the diene portion of the polymer. When the carboxylic compound employed is maleic anhydride, usually 10% to 100%, preferably 50% to 95 % of the residual double bonds in the polymer are converted to flpccinic anhydride groups.

Various solvents may be employed in the carboxylic acid derivative addition step including generally olefin-free petroleum hydrocarbons, aromatics and halogenated hydrocarbons. A preferred solvent is a lubricating oil basestock. A much-preferred solvent is trichlorobenzene. Preferably, a concentration in the range of 1% to 10% by weight of the copolymer in solvent may conveniently be used for this conversion.

An excess of carboxylic compound over that stoichiometrically necessary to react with all the residual double bonds remaining in the diene portion of the selectively hydrogenated star polymer is typically employed. Preferably, at least one mole of carboxylic compound is used for each olefinic unsaturation present in the selectively hydrogenated star polymer, with equivalent ratios of carboxylic compound to olefinic double bonds of between 1:1 and 2:1 being particularly suitable. However, less than stoichiometric amounts of carboxylic compound may also be used.

The above reaction may occur with or without the use of catalyst or radical initiators such as tertiary butyl hydroperoxide. Any excess carboxylic compound is typically removed by either vacuum distillation or through the use of a stripping gas stream.

In a preferred embodiment, the reaction of the carboxylic compound and star polymer takes place in the presence of chlorine. Chlorination has been disclosed with polymers of isobutene in U.K. Patent 949,981. The molar amount of chlorine used is preferably such that the mixture of polymer and carboxylic compound is contacted with from 0.3 to 1.5, more preferably from 0.5 to 1.2 moles of chlorine for each mole of carboxylic compound.

Insofar as the conversion of the polymer is concerned, threre appears to be no lower limit on the amount of chlorine which may be used. In practice, however, it is preferred to remain within the aforesaid ranges.

Suitably the mixture of polymer and carboxylic compound is heated to the reaction temperature before it is contacted with the chlorine. The mixture is contacted with a molar deficiency of chlorine before any substantial amount, e.g. less than half of the carboxylic compound has reacted. Suitably, substantially none of the carboxylic compound has reacted. The rate of introduction of chlorine into the mixture may vary between wide limits but is preferably such that it equals the rate of chlorine uptake. Usually the chlorine is introduced over a period of from 0.5 to 10 hours, preferably from 3 to 7 hours.

After the chlorination treatment, it is advantageous to subject the resultant product mixture to a post-reaction or thermal treatment. This thermal treatment is suitably carried out at a temperature in the range of from 140"C to 220"C, preferably from 1600C to 210 C. The conditions are usually such, e.g. reflux conditions, that substantially no part of the product mixture is removed during this thermal treatment. The thermal treatment may be for 0.1 to 20 hours, but is preferably from 0.5 to 10 hours. Longer periods tend to increase the formation of tarry by-products.

The star polymer may also be chlorinated before reaction with the alpha, betaunsaturated carboxylic compound. In this case, the hydrogenated polymer is treated with 0.5 to 3 moles of chlorine (Cl2) per 100 carbon atoms of the polymer, i.e. between about 2%w and 12%w Cl2, in a suitable chlorination solvent. After a reaction period of from 0.5 to 2 hours at between 0 and 100"C, unreacted chlorine and hydrogen chlorine are removed by gas stripping. The chlorination solvent may be exchanged by distillation with a second solvent such as a lube oil base stock or other solvent suitable for the subsequent steps as described herein.

The modified polymer is then reacted with the amines and/or polyols to form the oilsoluble product of the instant invention. The resulting imides, esters and the like provide the dispersant function of the additive.

The C1 to C18 amines employed in the instant invention can be branched or unbranched, saturated, aliphatic, primary or secondary amines, containing 1 to 8 nitrogens, preferably mono or diamines, such as ethylamine, butylamine, sec. butylamine, diethylamine, etc., but including higher polyamines such as alkylene polyamines, wherein pairs of nitrogen atoms are joined by alkylene groups of 2 to 4 carbon atoms. Thus, polyamines of the formula: NH2(CH2)n [NH(CH2)n]m NH2 are included where n is 2 to 4 and m is 0 to 6. Examples of such polyamines include tetraethylene pentamine, tripropylene tetramine, N-aminoalkyl piperazines, e.g., N (2-aminoethyl) piperazine, N,N'-di(2-aminoethyl) piperazine, etc. Preferred is tetraethylene pentamine, as well as corresponding commercial mixtures such as "Polyamine H", and "Polyamine 500 ".

The alkane polyols useful in making the esters are alkane polyols having at least two and preferably at least four hydroxy groups such as the trihydroxyalkanes, e.g. ethylene glycol, propylene glycol, polymethylene glycols, trihydroxybutanes, pentanes, hexanes, heptanes, octanes, nonanes, dodecanes, etc., as well as tetrahydroxy alkanes, pentahydroxy alkanes, hexahydroxy alkanes, as well as the sugar alcohols such as erythritol, pentaerythritol, tet ritols, pentitols, hexitols, mannitol, sorbitol, glucose and the like. Particularly preferred alcohols are pentaerythritol and mannitol. Especially preferred is pentaerythritol.

The molar ratio of amine or polyol to carboxylic compound is typically between 0.1:1 and 2:1, preferably between 0.5:1 and 2:1, most preferably about 1:1. The conditions during amidization or esterification are typically 1500C to 250"C for between 1 hour and 20 hours.

In both reaction steps it is much preferred that the reactions take place in the absence of oxygen. A nitrogen blanket is often used to accomplish this result. The reason for performing the reaction in the absence of oxygen is that the resulting additive may be more oxidatively unstable if any oxygen is present during the formation of the additive.

If excess amine or polyol is employed, then it may be desirable to remove the excess. One means of doing this is to first exchange the tri-chlorobenzene solvent for a lube base stock by vacuum distillation, and then add a volume of heptane equal to the volume of oil solution. Then an equal volume of methanol is added and mixed. Two separate layers are therein formed upon settling; one layer comprising predominantly wash solvent and the unreacted amine or polyol, and a second layer comprising predominantly oil, heptane, and the additive product. After separating the wash layer, the volatiles present in the product layer can then be removed by a distillation technique. Alternatively, the excess amine or polyol may be removed under a vacuum or with a stripping gas stream.

The reaction product of this invention can be incorporated in lubricating oil compositions, e.g. automotive crankcase oils, in concentrations e.g. within the range of 0.1 to 15, preferably 0.1 to 3, weight percent based on the weight of the total compositions. The lubricating oils to which the additives of the invention can be added include not only mineral lubricating oils, but synthetic oils also. Synthetic hydrocarbon lubricating oils may also be employed, as well as non-hydrocarbon synthetic oils including dibasic acid esters such as di-2-ethyl hexyl sebacate, carbonate esters, phosphate esters, halogenated hydrocarbons, polysilicones, polygIycols, glycol esters such as C13 OXO acid diesters of tetraethylene glycol, etc. When used in gasoine or fuel oil, e.g. diesel fuel, No. 2 fuel oil, etc., then usually 0.001 to 0.5 weight percent, based on the weight of the total composition of the reaction product will be used. Concentrations comprising a minor proportion, e.g. 15 to 45 weight percent, of said reaction product in a major amount of hydrocarbon diluent, e.g. 85 to 55 weight percent mineral lubricating oil, with or without other additives present, can also be prepared for ease of handling.

In the above compositions or concentrates, other conventional additives may also be present, including dyes, pour point depressants, antiwear agents, e.g. tricresyl phosphate, zinc dialkyl dithiophosphates of 3 to 8 carbon atoms, antioxidants such as phenyl-alpha- naphthylamine, tert-octylphenol sulphide, bisphenols such as 4,4'-methylene bis(3,6-ditert-butylphenol), viscosity index improvers such as the ethylene-higher olefin copolymer, polymethylacrylates, polyisobutylene, alkyl fumaratevinyl acetate copolymers, and the like as well as other ashless dispersants or detergents such as overbased sulphonates.

The invention is further illustrated by means of the following Examples, which are given for the purpose of illustration alone, and is not meant to limit the invention to the particular reactants and amounts disclosed.

Example 1 A hydrogenated star-shaped polymer made from isoprene and a divinyl benzene coupling agent was reacted with maleic anhydride and tetraethylenepentamine to form a dispersant/VI improver according to the present invention.

The star-shaped polymer was prepared by first polymerizing isoprene in a cyclohexane solvent with a secondary butyl lithium initiator. The polymer branch A-Li had a molecular weight of about 45,700. The living polymer was then coupled with commercial divinyl benzene (55 % weight from Dow Chemical) in a molar ratio of divinyl benzene to lithium of 3:1. The coupled polymer had a total molecular weight of 577,000 on a polystyrene equivalent basis. Then the polymer was hydrogenated with an aluminium triethyl/nickel octoate catalyst. The final molecular weight was 609,000, the coupling yield was 96So, the saturation index was 10%, and residual unsaturation by ozone titration was 0.11 milliequivalents per gram.

Then 10 g of the hydrogenated star-shaped polymer prepared above were dissolved in 190 g of a lube base stock. To the polymer solution was added maleic anhydride (0.80 g, 7.0 millimoles) and the mixture heated to 225"C for 8 hours. Excess maleic anhydride was removed by distillation under vacuum. A small part of the solvent also came over. A nitrogen atmosphere was maintained up until vacuum was applied.

Tetraethylenepentamine was added to the maleated polymer solution and the mixture heated to 160"C for 1 1/2 hours and 1900C for 1 i hours under nitrogen.

The oil solution was then cooled, diluted with heptane, filtered, washed with methanol and stripped of volatiles. The product contained about 1 % nitrogen on an active material basis.

The The dispersancy of the product was assessed by a Spot Dispersancy Test. In the Spot Dispersancy Test, one part of a 2% weight solution of the additive to be tested in 100 parts neutral oil is mixed with two parts used, sludge-containing oil and heated overnight at 1500C. Blotter spots are then made on filter paper and the ratio of a sludge spot diameter to oil spot diameter is measured after 24 hours. A poor value is under about 50%. The additive prepared above yielded a value of 68%. Unmodified star polymer gave a value of about 27%.

A 2% by weight concentration of the above-prepared additive in a common mineral lubricating oil base stock increased the 99"C kinematic viscosity from 4 centistokes for the lube stock alone to 21 centistokes for the lube oil plus additive. This viscosity increase demonstrates the usefulness of the present additive as a VI improver.

Example 2 10 g of the hydrogenated star-shaped polymer prepared above were dissolved in 190 g 1,2,4-trichlorobenzene. To the polymer solution was added maleic anydride (0.80 g, 7.0 millimoles) and the mixture heated to 2050C for 4 hours. Excess maleic anydride was removed by distillation under vacuum. A small part of the solvent also came over. A nitrogen atmosphere was maintained up until vacuum was applied.

Pentaerythritol (0.95 g, 7.0 millimoles) was added to the maleated polymer solution and the mixture heated to 2050C for 4 hours under nitrogen. Unreacted pentaerythritol was removed by distillation under vacuum.

An amount of a lube base stock was added which was equal in volume to the reaction mixture and the trichlorobenzene solvent distilled under vacuum. The oil solution was then diluted with heptane, filtered, washed with methanol and stripped of volatiles.

Dispersant power of the oil-soluble product was readily apparent from the formation of a stable emulsion during the washing step. In addition, the dispersancy of the product was assessed by the Spot Dispersancy Test. The additive prepared above yielded a value of 56%. Unmodified star polymer gave a value of about 27%.

A 2% by weight concentration of the above-prepared additive in a common mineral lubricating oil base stock increased the 99"C kinematic viscosity from 4 centistokes for the lube stock alone to 15 centistokes for the lube oil plus additive. This viscosity increase demonstrates the usefulness of the present additive as a VI Improver.

WHAT WE CLAIM IS: 1. An oil-soluble product prepared by the process comprising: a) reacting a selectively hydrogenated star-shaped polymer with an alpha-beta unsatu rated carboxylic acid, anhydride or ester wherein said star-shaped polymer comprises a poly (polyalkenyl coupling agent) nucleus and at least 4 polymeric arms linked to said nucleus wherein said polymeric arms are selected from the group consisting of: i) hydrogenated homopolymers and hydrogenated copolymers of conjugated dienes; ii) hydrogenated copolymers of conjugated dienes and monoalkenyl arenes; and ii) mixtures thereof; and wherein at least 80% of the aliphatic unsaturation of the star-shaped polymer has been reduced by hydrogenation while less than 20% of the aromatic unsaturation has been reduced; and b) reacting the product of step (a) with a C, to C18 amine containing 1 to 8 nitrogen atoms and/or an alkane polyol having at least two hydroxy groups.

2. The product of claim 1, wherein in step (a) the temperature is between 1500C and 300"C and in step (b) between 1500C and 250"C.

3. A product according to claim 1 or 2, wherein the number of polymeric arms is between 4 and 25.

4. A product according to any one of claims 1-3, wherein the polyalkenyl coupling agent is a polyvinyl aromatic compound.

5. A product according to any one of claims 1-4, wherein the polyalkenyl coupling agent is divinyl benzene.

6. A product according to any one of claims 1-5, wherein the number average molecular weight of each polymeric arm is between 5,000 and 150,000.

7. A product according to any one of claims 1-6, wherein the peak molecular weight of the hydrogenated star-shaped polymer is between 25,000 and 1,250,000.

8. A product according to any one of claims 1-7, wherein between 90 and 98% of the aliphatic unsaturation has been reduced by hydrogenation.

9. A product according to any one of claims 1-8, wherein each polymeric arm is a hydrogenated polyisoprene homopolymer.

10. A product according to any one of claims 1-9, wherein said star-shaped copolymer and said carboxylic acid, anhydride or ester are reacted in a ratio of moles of carboxylic acid, anhydride or ester to olefinic double bonds remaining in the selectively hydrogenated star-shaped polymer of between 1:1 and 2:1.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

The The dispersancy of the product was assessed by a Spot Dispersancy Test. In the Spot Dispersancy Test, one part of a 2% weight solution of the additive to be tested in 100 parts neutral oil is mixed with two parts used, sludge-containing oil and heated overnight at 1500C. Blotter spots are then made on filter paper and the ratio of a sludge spot diameter to oil spot diameter is measured after 24 hours. A poor value is under about 50%. The additive prepared above yielded a value of 68%. Unmodified star polymer gave a value of about 27%.

A 2% by weight concentration of the above-prepared additive in a common mineral lubricating oil base stock increased the 99"C kinematic viscosity from 4 centistokes for the lube stock alone to 21 centistokes for the lube oil plus additive. This viscosity increase demonstrates the usefulness of the present additive as a VI improver.

Example 2

10 g of the hydrogenated star-shaped polymer prepared above were dissolved in 190 g 1,2,4-trichlorobenzene. To the polymer solution was added maleic anydride (0.80 g, 7.0 millimoles) and the mixture heated to 2050C for 4 hours. Excess maleic anydride was removed by distillation under vacuum. A small part of the solvent also came over. A nitrogen atmosphere was maintained up until vacuum was applied.

Pentaerythritol (0.95 g, 7.0 millimoles) was added to the maleated polymer solution and the mixture heated to 2050C for 4 hours under nitrogen. Unreacted pentaerythritol was removed by distillation under vacuum.

An amount of a lube base stock was added which was equal in volume to the reaction mixture and the trichlorobenzene solvent distilled under vacuum. The oil solution was then diluted with heptane, filtered, washed with methanol and stripped of volatiles.

Dispersant power of the oil-soluble product was readily apparent from the formation of a stable emulsion during the washing step. In addition, the dispersancy of the product was assessed by the Spot Dispersancy Test. The additive prepared above yielded a value of 56%. Unmodified star polymer gave a value of about 27%.

A 2% by weight concentration of the above-prepared additive in a common mineral lubricating oil base stock increased the 99"C kinematic viscosity from 4 centistokes for the lube stock alone to 15 centistokes for the lube oil plus additive. This viscosity increase demonstrates the usefulness of the present additive as a VI Improver.

WHAT WE CLAIM IS: 1. An oil-soluble product prepared by the process comprising: a) reacting a selectively hydrogenated star-shaped polymer with an alpha-beta unsatu rated carboxylic acid, anhydride or ester wherein said star-shaped polymer comprises a poly (polyalkenyl coupling agent) nucleus and at least 4 polymeric arms linked to said nucleus wherein said polymeric arms are selected from the group consisting of: i) hydrogenated homopolymers and hydrogenated copolymers of conjugated dienes; ii) hydrogenated copolymers of conjugated dienes and monoalkenyl arenes; and ii) mixtures thereof; and wherein at least 80% of the aliphatic unsaturation of the star-shaped polymer has been reduced by hydrogenation while less than 20% of the aromatic unsaturation has been reduced; and b) reacting the product of step (a) with a C, to C18 amine containing 1 to 8 nitrogen atoms and/or an alkane polyol having at least two hydroxy groups.
2. The product of claim 1, wherein in step (a) the temperature is between 1500C and 300"C and in step (b) between 1500C and 250"C.
3. A product according to claim 1 or 2, wherein the number of polymeric arms is between 4 and 25.
4. A product according to any one of claims 1-3, wherein the polyalkenyl coupling agent is a polyvinyl aromatic compound.
5. A product according to any one of claims 1-4, wherein the polyalkenyl coupling agent is divinyl benzene.
6. A product according to any one of claims 1-5, wherein the number average molecular weight of each polymeric arm is between 5,000 and 150,000.
7. A product according to any one of claims 1-6, wherein the peak molecular weight of the hydrogenated star-shaped polymer is between 25,000 and 1,250,000.
8. A product according to any one of claims 1-7, wherein between 90 and 98% of the aliphatic unsaturation has been reduced by hydrogenation.
9. A product according to any one of claims 1-8, wherein each polymeric arm is a hydrogenated polyisoprene homopolymer.
10. A product according to any one of claims 1-9, wherein said star-shaped copolymer and said carboxylic acid, anhydride or ester are reacted in a ratio of moles of carboxylic acid, anhydride or ester to olefinic double bonds remaining in the selectively hydrogenated star-shaped polymer of between 1:1 and 2:1.
11. A product according to any one of claims 1-10, wherein the amine has the formula:

NH2(CH2)st [NH(CH2)n].11 NH2 wherenis2to4andmis0to 6.
12. A product according to claim 11, wherein the amine is tetraethylenepentamine.
13. A product according to any one of claims 1-10, wherein the alkane polyol is pentaerythritol.
14. A product according to any one of claims 1-13, wherein the molar ratio of amine or polyol to carboxylic compound is between 0.5:1 and 2:1.
15. A product according to any one of claims 1-14, wherein in step (a) the polymer is reacted with chlorine prior to or at the same time of the reaction with the carboxylic compound.
16. A product according to claim 15, wherein in step (a) the polymer is reacted with between 0.5 and 3.0 moles of chlorine per 100 carbon atoms of the polymer prior to reaction with the carboxylic compound.
17. A product according to claim 1, substantially as hereinbefore described with special reference to Examples 1 and 2.
18. A lubricating composition comprising a major amount of a lubricating oil and a minor amount of the product of any one of claims 1-17.