EP1446466A1

EP1446466A1 - Viscosity growth inhibition in oil additive concentrates

Info

Publication number: EP1446466A1
Application number: EP02776150A
Authority: EP
Inventors: Karl Duyck; Theodore E. Nalesnik
Original assignee: Crompton Corp
Current assignee: Lanxess Solutions US Inc
Priority date: 2001-11-29
Filing date: 2002-10-04
Publication date: 2004-08-18
Anticipated expiration: 2022-10-04
Also published as: JP2005511818A; JP4393871B2; CN1261550C; DE60212685D1; AU2002341988A1; WO2003048281A1; ATE331016T1; BR0214540A; DE60212685T2; EP1446466B1; CN1596296A

Abstract

A method is disclosed for inhibiting the rate of viscosity growth in an oil concentrate of a VI-dispersant prepared form a copolymer of ethylene and at least one C3-C16 alpha olefin, wherein said copolymer has been grafted with at least one unsaturated carboxylic acid-containing material, further reacted with an amount of a polyamine sufficient to neutralize said acid containing material, or at least one unsaturated nitrogen-containing material, comprising blending a primary antioxidant into said concentrate as a top treatment or as a displacement for an equal amount of diluting oil.

Description

VISCOSITY GROWTH INHIBITION IN OL ADDITIVE CONCENTRATES BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to polymeric viscosity index improver/dispersant additive concentrates for lubricating oils. More particularly, the present invention relates to processes for inhibiting the rate of viscosity growth in grafted and amine-functionalized, hydrocarbon polymer concentrates used in oil compositions.

2. Description of Related Art

High molecular weight hydrocarbon polymers, such as ethylene copolymers, particularly ethylene-propylene copolymers are known as viscosity index (V.I.) improving additives for oil compositions, particularly lubricating oil compositions. These V.I. improvers can be further reacted to form multi-functional V.I. improvers. A multifunctional

V.I. improver is a material that improves not only the V.I. properties of the oil, but also imparts dispersancy so as to suspend sludge that may form during the operation or use of the lubricant and to inhibit varnish deposition in engines. Over time, when stored as an oil concentrate, the viscosity of these concentrates may increase dramatically.

U.S. Patent No. 3,928,497 discloses a process for preparing a graft-modified ethylene polymer or copolymer which comprises reacting an ethylene polymer or copolymer with a dicarboxylic acid graft-copolymerizable therewith, or its graft-copolymerizable derivative in an alkyl-substituted aromatic hydrocarbon solvent in the presence of a radical initiator, characterized in that the reaction is performed while adding the dicarboxylic acid or its derivative gradually to the solvent in which the starting ethylene polymer or copolymer is present. U.S. Patent No. 4,089,794 discloses ethylene copolymers derived from about 2 to 98 wt. % ethylene, and one or more C₃ to C₂₈ alpha olefins, e.g. ethylene-propylene, that are solution-grafted under an inert atmosphere and at elevated temperatures with an ethylenically-unsaturated carboxylic acid material in the presence of a high-temperature decomposable free-radical initiator and thereafter reacted with a polyfunctional material reactive with carboxy groups; such as (a) a polyamine, or (b) a polyol, or (c) a hydroxyamine, or mixtures thereof, to form carboxyl-grafted polymeric derivatives, which have good engine sludge and varnish control behavior in fuels and lubricating oils. If the molecular weight is above 10,000, then these polymers are also useful as multifunctional viscosity index improvers.

U.S. Patent No. 4,219,432 discloses oil-soluble, derivatized ethylene copolymers derived from about 2 to 98 wt. % ethylene, and one or more C₃ to C₂₈ alpha-olefins, e.g. propylene, which are grafted, preferably solution-grafted under an inert atmosphere and at elevated temperatures and in the presence of a high-temperature decomposable free-radical initiator, with an ethylenically-unsaturated dicarboxylic acid material and thereafter firstly reacted with from 0.1 to 0.9 molar equivalents of a t-amino-amine compound containing only one primary amino group to form imido groups and then secondly reacted with from 0.1 to 0.9 molar equivalents of a ,ω primary diamine having at least two primary amine groups,

e.g. a poly(alkylene amine) such as diethylene triamine, to form carboxyl-grafted polymeric imide, usually succinimide, intermediate and thirdly reacted with an anhydride of a C1-C₃₀ hydrocarbon substituted acid, preferably acetic anhydride, to yield an oil-soluble stable amide derivative of said polyamine whereby oil solutions of said amide derivative are characterized by minimal viscosity change over an extended period of time. Useful number average molecular weight of said copolymers range from about 700 to 500,000; however, if the molecular weight is from 10,000 to 500,000 then these copolymers are disclosed to be multifunctional viscosity index improvers of enhanced sludge dispersant activity. If these derivatized copolymers are treated with oil-soluble hydrocarbyl substituted acids, preferably with long chain alkylaryl sulfonic acids with an average side chain carbon number of about 20-40, they are said to yield haze-free hydrocarbon concentrate useful as an additive solution for lubricating oils.

U.S. Patent No. 4,517,104 discloses oil soluble viscosity index improving ethylene copolymers, such as copolymers of ethylene and propylene; and ethylene, propylene and diolefin; etc., that are reacted or grafted with ethylenically unsaturated carboxylic acid moieties, preferably maleic anhydride moieties, and reacted with polyamines having two or more primary amine groups and a carboxylic acid component, preferably alkylene polyamine and alkenyl succinic anhydride, such as polyisobutenyl succinic anhydride. Or the grafted ethylene copolymer can be reacted with already formed salts, amides, imides, etc. of said polyamine and acid component, preferably imides of alkylene polyamine and alkenyl succinic anhydride. These reactions are said to permit the incorporation of varnish inhibition and dispersancy into the ethylene copolymer while inhibiting cross-linking with resulting viscosity increase, haze or gelling. The aforesaid grafting reaction may be carried out thermally, or more preferably with a free radical initiator, such as a peroxide, in a mineral lubricating oil, in which case the acid component, preferably also acts to solubilize insoluble compounds formed by side reactions, such as maleic anhydride grafted oil molecules reacted with amine, to thereby inhibit haze formation, particularly when preparing oil concentrates of the V.I. -dispersant additive for later addition to lubricating oils. U.S. Patent No. 4,693,838 discloses hydrocarbon polymers, such as ethylene copolymers, that may be reacted with unsaturated nitrogen-containing monomers or unsaturated carboxylic acids in a synthetic hydrocarbon lubricating oil in the presence of a free radical initiator such as a peroxide. The copolymer grafted directly with the nitrogen- containing monomers may be utilized as an additive for oil compositions, particularly lubricating oil compositions as a V.I. -dispersant additive. The polymer reacted with carboxylic acid may be further reacted with amines or amino-alcohols to also form a multifunctional V.I. -dispersant additive.

U.S. Patent No. 4,735,736 discloses oil soluble hydrocarbon polymers, said to be useful as V.I. improvers, such as ethylene copolymer, preferably ethylene-propylene copolymer, grafted with an unsaturated acid material, such as maleic anhydride, preferably by solid state grafting followed by reaction with a polyamine, preferably a tertiary-primary amine, and treatment and/or reaction with monoamine. The resulting material is used in oil compositions, such as lubricating oil, as a Viscosity Index improver having sludge dispersancy properties. The monoamine treatment is said to inhibit viscosity growth of the additive upon storage.

U.S. Patent No. 4,808,325 discloses a dispersant and Vl-improving Mannich composition said to have reduced susceptibility to viscosity increase during storage, which composition comprises a physical blend prepared by admixing a phenolic compound with a Mannich condensation product obtained from the Mannich reaction of an oxidized polymer, an amine and a formaldehyde-yielding reagent. U.S. Patent Nos. 5,211,865 and 5,273,671 disclose oleaginous compositions, particularly lubricating oil compositions, said to exhibit improved antioxidant properties containing a viscosity index improving amount of a viscosity index improver-dispersant comprised of the reaction products of: (a) an oil soluble ethylene copolymer comprising from about 15 to 90 wt. % ethylene and from about 10 to 85 wt. % of at least one C₃ to C_2g alpha- olefin, having a number average molecular weight of from about 5,000 to 500,000, grafted with an ethylenically unsaturated carboxylic acid material having 1 or 2 acid or anhydride moieties; (b) an organic polyamine having at least two primary amino groups; (c) an aldehyde; (d) a heterocyclic nitrogen reactant having at least one — N(H)~ group in the heterocyclic ring; and, optionally, (e) an amount effective to provide a V.I. improver- dispersant exhibiting improved low temperature viscometric properties of high functionality long chain hydrocarbyl substituted dicarboxylic acid material having a functionality of at least 1.2.

Mishra, M.K. et al., in Specialty Olefin Copolymers in Oil Additives in Polymer Science (Symp. Proc. Polym. 1991); Vol. 2, pp. 694-699 (published by Tata McGraw-Hill, New Delhi, India) studied the viscosity characteristics of the solutions of ethylene-propylene copolymers with 58-80 mol % ethylene. They reported that for amorphous copolymers intrinsic viscosities and equivalent hydrodynamic volumes showed little variation in the temperature range from -10 to 50° C. By contrast, they decrease precipitously at low temperature for a partially crystalline copolymer with 80 mol % ethylene. They also discussed the use of certain multifunctional olefin copolymers (OCP) based on ethylene- propylene as viscosity index improvers that impart dispersant and antioxidant properties to motor oils. They reported that engine test performance of motor oils containing these multifunctional polymers was superior to oils containing commercial OCP VI improvers.

See, also, Kuczkowski, J.A. et al., Polymer-Bound Antioxidants in Rubber Chemistry and Technology, 57:621-651 (1984). The disclosures of the foregoing are incorporated herein by reference in their entirety.

SUMMARY OF THE INVENTION In accordance with the present invention, hydrocarbon polymers, such as ethylene- alpha olefin copolymers and terpolymers, are reacted with unsaturated carboxylic acids, preferably dissolved in a suitable solvent, such as an alkyl benzene, mineral oil, synthetic oil, and/or an aromatic ester, in the presence of a free radical initiator, such as a peroxide. The polymer, after having been reacted with the carboxylic acid, is further reacted with amines or amino-alcohols to form a multifunctional V.I.-dispersant additive. Hydrocarbon polymers, such as ethylene-alpha olefin copolymers and terpolymers, may also be similarly reacted with unsaturated nitrogen-containing monomers. The grafted copolymers, mixed with an amount of diluting oil and referred to as concentrates, are then used as additives-for oil compositions, particularly lubricating oil compositions, as V.I.-dispersant additives. These concentrates are then combined with a primary antioxidant to significantly inhibit the rate of their viscosity growth. The primary antioxidant is preferably aminic or phenolic in nature and is soluble in the additive concentrate. A preferred phenolic antioxidant is 2,6-di-?-butyl-4-methylphenol (BHT); preferred aminic antioxidants include alkylated diphenylamine and alkylated phenyl- alpha-napthylamines. Even a small percentage of antioxidant, for example, about 0.1% by weight, based on the weight of the concentrate, preferably from about 0.25% up to 5% or more, blended into the dispersant concentrate provides a significant advantage in long term viscosity stability of the dispersant additive concentrate as indicated by the results of oven aging.

More particularly, the present invention is directed to a method for inhibiting the rate of viscosity growth in an oil concentrate of a Vl-dispersant prepared from a copolymer of ethylene and at least one C₃-C₁₆ alpha olefin, wherein said copolymer has been grafted with at least one unsaturated carboxylic acid-containing material further reacted with a polyamine containing at least one primary amine, comprising blending a primary antioxidant into said concentrate as a top treatment or as a displacement for an equal amount of diluting oil.

In another aspect, the present invention is directed to a method for inhibiting the rate of viscosity growth in an oil concentrate of a Vl-dispersant prepared from a copolymer of ethylene and at least one C₃-C₁₆ alpha olefin, wherein said copolymer has been grafted with at least one unsaturated nitrogen-containing material, comprising blending a primary antioxidant into said concentrate as a top treatment or as a displacement for an equal amount of diluting oil. DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides a dispersant-viscosity index improver by solution grafting an unsaturated acid onto a high molecular weight hydrocarbon polymer in an oil diluent in the presence of a free radical initiator and then further reacting the product with an amine or polyol. The high molecular weight hydrocarbon polymer is of high viscosity even at grafting temperatures, so that dilution is required for processing. Mineral (or synthetic) lubricating oil can be added to form a finished additive concentrate after grafting with the unsaturated acid or, if the product is to be further reacted, such as to form a functionalized derivative, the mineral (or synthetic) oil can be used as another diluent to carry out the additional reaction and to form a useful additive concentrate. To this a top treat of primary antioxidant is added to minimize the rate of viscosity increase of the concentrate during storage.

Where the grafting is carried out in a mineral lubricating oil, the oil need not be removed after the grafting step, but can be used as the solvent in the subsequent reaction of the graft polymer with the amine material and as a solvent for the end product to form the lubricating additive concentrate.

Suitable hydrocarbon diluents include polymers of olefins and alkyl benzenes. Suitable polyolefins include liquid polyalkenes of number average molecular weight (M„) of 200 to 10,000, e.g. 300 to 3000, most preferably 350 to 1300 mol. wt. derived from monoethylenically unsaturated olefinic, preferably alkene-1 monomers, of 3 to 18, e.g. 3 to 12 carbon atoms. Suitable polyolefins include poly C₃ -C₄ polymer of olefins, especially polyisobutylene of 200 to about 2000, e.g. 400 to 1300, such as about 500 to 900 molecular weight, polydecene, polymers of mixtures of C₆ to Cι₈ alpha olefins, and the like. Suitable liquid alkyl benzenes are mono and poly alkyl benzenes, including those mono and polyalkylated benzenes where the alkyl groups may have 1 to 300, e.g. 10 to 30 carbon atoms each, with dialkyl benzenes of molecular weight 200 to 800 being preferred.

Polymers used in the practice of the present invention typically have a number average molecular weight of from about 5000 to about 500,000, preferably 10,000 to 200,000, more preferably from about 20,000 to 100,000 and will generally have a narrow range of molecular weight. Examples of suitable hydrocarbon polymers include homopolymers and copolymers of two or more monomers of C₂ to C₁₆, preferably C₂ to C₈ olefins, including both alpha olefins and internal olefins, which may be straight or branched, aliphatic, aromatic, alkylaromatic, cycloaliphatic, and the like. Preferably, they will be copolymers of ethylene with C₃ to C₁₆ olefins, more preferably copolymers of ethylene and propylene. Other hydrocarbons that can be used include styrene, butene, isobutylene, C₆ and higher alpha olefins, atactic isoprene, butadiene, and the like.

The preferred polymers are prepared from ethylene and ethylenically unsaturated hydrocarbons including cyclic, alicyclic and acyclic materials containing from 3 to 16 carbon atoms, preferably 3 to 8 carbons. These ethylene copolymers may contain from 15 to 90 wt. % ethylene, preferably 30 to 80 wt. % of ethylene and 10 to 85 wt. %, preferably 20 to 70 wt. % of one or more C₃ to C₁₆, preferably C₃ to C₈ alpha olefins. Copolymers of ethylene and propylene are most preferred. Other alpha-olefins suitable in place of propylene to form the copolymer, or to be used in combination with ethylene and propylene, to form a terpolymer, tetrapolymer, etc., include 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1- decene, etc.; also branched chain alpha olefins, such as 4-methyl- 1-pentene, 4-methyl-l- hexene, 5-methylpentene-l, 4,4-dimethyl- 1-pentene, and 6-methylheptene-l, etc., and mixtures thereof.

The polymers, which term is intended to include copolymers, terpolymers, tetrapolymers, and the like, used in the practice of the present invention can include one or more non-conjugated diolefins. The amount of non-conjugated diolefin will generally range from about 0.5 to 20 mole percent, preferably about 1 to about 7 mole percent, based on the total amount of hydrocarbon, e.g., ethylene and alpha-olefin present. Representative examples of non-conjugated dienes that can be used include 1,4- hexadiene; 1,5-heptadiene; 1,6-octadiene; 5-methyl-l,4-hexadiene; 3,7-dimethyl 1,6- octadiene; 3,7-dimethyl 1,7-octadiene; mixed isomers of dihydro-myrcene and dihydro- cymene; 1,4-cyclohexadiene; 1,5-cyclooctadiene; 1,5-cyclo-dodecadiene; 4- vinylcyclohexene; 1-allyl, 4-isopropylidene cyclohexane; 3-allyl-cyclopentene; 4-allyl cyclohexene; l-isopropenyl-4-(4-butenyl) cyclohexane; 4,4'-dicyclopentenyl diene; 4,4'- dicyclohexenyl diene; tetrahydroindene; methyl tetrahydroindene; dicyclopentadiene; bicyclo (2.2.1) hepta-2,5-diene; ethyl norbornene; 5-methylene-6-methyl-2-norbornene; 5-methylene- 6, 6-dimethyl-2-norbornene; 5-propenyl-2- norbornene; 5-(3-cyclopentenyl)-2-norbornene; 5- cyclohexylidene-2-norbornene; norbornadiene; and the like.

The compounds that can be grafted onto the hydrocarbon polymer preferably contain from 3 to 10 carbon atoms, ethylenic unsaturation, and at least one, preferably two, carboxylic acid groups, or an anhydride group, or a polar group convertible into such carboxyl groups as by oxidation or hydrolysis. Maleic anhydride or a derivative thereof is preferred as it does not homopolymerize appreciably, but attaches to the polymer to provide two carboxylic acid functionalities. Alternative examples include chloromaleic anhydride, itaconic anhydride, hemic anhydride, maleic acid, fumaric acid, monoesters of the foregoing, and the like.

As taught by U.S. Patent Nos. 4,160,739 and 4,161,452, various other unsaturated comonomers can be grafted on the hydrocarbon polymer together with the unsaturated acid component. One or a mixture of such comonomers that are different from the unsaturated acid component and contain a copolymerizable double bond and are copolymerizable with the unsaturated acid component can be used. Such comonomers normally do not contain free carboxylic acid groups, but can be esters containing α,β-ethylenic unsaturation in the acid or

alcohol portion; hydrocarbons, both aliphatic and aromatic, containing α,β-ethylenic unsaturation, such as the C₄ -C₁₂ alpha olefins, for example, isobutylene, hexene, nonene, dodecene, and the like; styrenes, for example, styrene, α-methyl styrene, -methyl styrene, p- sec-butyl styrene, and the like; and vinyl monomers, for example, vinyl acetate, vinyl chloride, methyl vinyl ketone, ethyl vinyl ketone, and the like.

Nitrogen-containing unsaturated compounds are well known for forming polymers useful as oil additives. These monomers can be grafted onto the hydrocarbon polymer and include, among others, those having from 6 to 30 carbon atoms and from 1 to 4 nitrogen atoms.

Examples of such nitrogen-containing monomers include dimethylaminoethyl methacrylate; dimethylaminoethyl acrylate; N-(l,l-dimethyl-3-oxobutyl)acrylamide; N-(l,2- dimethyl-l-ethyl-3-oxobutyl) acrylamide; N-(l,3-diphenyl-l-methyl-3-oxoproyl) acrylamide; N-(l -methyl- lphenyl-3-oxobutyl)methacrylamide; N,N-diethylaminoethyl acrylamide; 2- hydroxyethyl acrylamide; acrylamide; N-dimethylaminopropyl methacrylamide; N- vinylcaprolactams; N-vinylpyrrolidone, N-vinylthiopyrrolidone, 3 -methyl- 1- vinylpyrrolidone, 4-methyl-l-vinylpyrrolidone, 5-methyl-l-vinylpyrrolidone, 3-ethyl-l- vinylpyrrolidone, 3-butyl-l-vinylpyrrolidone, 3,3-dimethyl-l-vinylpyrrolidone, 4,5-dimethyl- 1-vinylpyrrolidone; 2-vinylpyridine, 4-vinylpyridine; 2-methyl-5-vinylpyridine; 2-methyl-4- vinylpyridine; 2-vinyl-5-ethyl pyridine; 2-vinyl-6-methylpyridine; and the like.

The grafting is carried out using one or more free radical initiators, such as azoisobutyronitrile; 2,5-dimethyl-hex-3-yne-2, 5 bis(t-butyl peroxide) or its hexane analogue, di-t-butyl peroxide, dicumyl peroxide, and the like. The initiator is preferably a peroxide and is generally used at a level of between about 0.005% and about 1%, based on the total weight of the polymer solution, and temperatures of about 25° to 250° C, preferably about 100° to 250° C.

The ethylenically unsaturated carboxylic acid material, which is preferably maleic anhydride, will generally be used in an amount ranging from about 0.05 % to about 10 %, preferably 0.1 to 4.0 %, based on weight of the initial solution. The carboxylic acid material and free radical initiator are generally used in a weight percent ratio range of about 3:1 to about 30:1, preferably about 1 :1 to about 6: 1.

The initiator grafting is preferably carried out in an inert atmosphere, such as that obtained by nitrogen blanketing. While the grafting can be carried out in the presence of air, the yield of the desired graft polymer is generally thereby decreased as compared to grafting under an inert atmosphere substantially free of oxygen. The grafting time will usually range from about 0.1 to 12 hours, preferably from about 0.5 to 10 hours, more preferably 0.5 to 3 hours. The grafted polymer can be reacted with a suitable amine in a conventional manner using reactants and conditions known in the art. Useful amine compounds include mono- and polyamines having from about 2 to about 60, preferably from about 3 to about 20, total carbon atoms and from about 1 to about 12, preferably from about 2 to about 7 nitrogen atoms in the molecule. These amines can be hydrocarbyl amines or hydrocarbyl amines having additional groups, such as alkoxy groups, amide groups, imidazoline groups, and the like. Useful amines include 1,2-diaminoethane; 1,3-diaminopropane; 1,4-diamonobutane; 1,6-diaminohexane; diethylene triamine; triethylene tetramine; tetraethylene pentamine; 1,2- propylene diamine; di-(l,2-propylene) diamine; di-(l,2-propylene)triamine; di-(l,3- propylene) triamine; N,N-dimethyl- 1,3-diaminopropane; N,N-di(2-aminoethyl) ethylene diamine; N,N-di(2-hydroxy ethyl) 1,3 -propylene diamine; 3-dodecyloxy-propylamine; N- dodecyl-l,3-propane diamine; tris hydroxymethylaminomethane; diisopropanol amine; diethanol amine; triethanol amine; mono-, di-, and tri-tallow amines; N-(3- aminopropyl)morpholine; 3-dodecyloxypropylamine; N-(2-aminoethyl) morpholine; 2-amino pyridine, 2-methylamino pyridine; 3-methylamino pyridine; 2-aminothiazoIe; 2-amino- 2thiazoline; 2-amino pyrimidine; 2-amino benzothiazole; methyl- 1-phenyl hydrazine; para- morpholino aniline; N-aminopropyl imidazole and variants; N-aminopropyl pyrrolidone and variants; N-aminopropyl piperidine and variants; phenothiazine and variants; and the like.

Especially preferred are amines having a single primary amine group, with any other amine groups present being tertiary amine groups. This inhibits cross-linking which is particularly important when the polymer has a relatively high degree of acidity, e.g. above 0.1 meq./g. of polymer. Mixtures comprising about 70 wt. % or more of amines having only a single primary or secondary group can be used with small amounts of amines having two or more primary or secondary amine groups. Acidities below 0.1 meq./g. polymer are less sensitive to cross-linking and amines with 2 or more reactive groups, i.e. either primary or secondary amine groups, or both primary and secondary amine groups, or a primary amine group and an alcohol group, can be used. The amines will generally be used in the range of from about 0.1 to about 10 wt. %, preferably from about 0.5 to about 5 wt. %, based on the weight of the hydrocarbon polymer. The amine is preferably used in an amount that neutralizes the acid moieties by formation of amides, imides, or salts. Preferably, the amount of amine used is such that there is 1 to 2 moles of polyamine reacted per equivalent mole of dicarboxylic acid. For example, with an ethylene-propylene copolymer of 40,000 number average molecular weight, grafted with an average of 4 maleic anhydride groups per molecule, preferably about 4 to 8 molecules of amine are used per molecule of grafted ethylene-propylene copolymer. The polymer, grafted with acidic moieties, preferably in solution generally equal to about 5 up to 50 wt. %, preferably 10 to 30 wt. % polymer, can be readily reacted with amines by heating at a temperature of from about 100° C to 250° C, preferably from about

120° to 230° C, for from about 0.5 to about 10 hours, preferably from about 1 to about 6 hours. The heating is preferably carried out to favor formation of imides and amides. Reaction ratios can vary considerably, depending upon the reactants, amounts of excess, type of bonds formed, and the like.

In a preferred embodiment, about 5 to 95 % of the copolymer is dissolved in 95 to 5 wt. % of the solvent to form a solution along with about 0.05 to 10 wt. % of the unsaturated material and about 0.005 to 10 wt. % of the initiator based on the weight of the solution. Then, after the grafting step, about 40 to 500 wt. %, based upon the weight of the solution, of a mineral or synthetic lubricating oil is added, followed by the addition of an amine sufficient to neutralize the acid and heating at 100^° C to 250^° C for 0.5 to 10 hours. The antioxidants employed in the practice of the present invention are primary antioxidants, such as, amine antioxidants and hindered phenols.

The amine antioxidants can be hydrocarbon substituted diarylamines, such as, aryl, alkyl, alkaryl, and aralkyl substituted diphenylamine antioxidant materials. A nonlimiting list of commercially available hydrocarbon substituted diphenylamines includes substituted octylated, nonylated, and heptylated diphenylamines and para-substituted styrenated or α-

methyl styrenated diphenylamines. The sulfur-containing hydrocarbon substituted diphenylamines, such as p-(p-toluenesulfonylamido)-diphenylamine, are also considered as part of this class. Hydrocarbon-substituted diarylamines that are useful in the practice of this invention can be represented by the general formula

AT— H— AT* wherein Ar and Ar' are independently selected aryl radicals, at least one of which is preferably substituted with at least one alkyl radical. The aryl radicals can be, for example, phenyl, biphenyl, terphenyl, naphthyl, anthryl, phenanthryl, and the like. The alkyl substituent(s) can be, for example, methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, isomers thereof, and the like.

Preferred hydrocarbon-substituted diarylamines are those disclosed in U.S. Patent Numbers 3,452,056 and 3,505,225, the disclosures of which are incorporated by reference herein. The preferred hydrocarbon-substituted diarylamines can be represented by the following general formulas:

(I) where

Ri is selected from the group consisting of phenyl and p-tolyl radicals;

R₂ and R₃ are independently selected from the group consisting of methyl, phenyl, and p-tolyl radicals;

R₄ is selected from the group consisting of methyl, phenyl, p-tolyl, and neopentyl radicals;

R₅ is selected from the group consisting of methyl, phenyl, p-tolyl, and 2- phenylisobutyl radicals; and,

Rg is a methyl radical.

(II) where

R_x through R₅ are independently selected from the radicals shown in Formula I and R₇ is selected from the group consisting of methyl, phenyl, and p-tolyl radicals; X is a radical selected from the group consisting of methyl, ethyl, C₃-C₁₀ sec-alkyl, α,α-dimethylbenzyl, α-methylbenzyl, chlorine, bromine, carboxyl, and metal salts of the carboxylic acids where the metal is selected from the group consisting of zinc, cadmium, nickel, lead, tin, magnesium, and copper; and,

Y is a radical selected from the group consisting of hydrogen, methyl, ethyl, C₃-C₁₀ sec-alkyl, chlorine, and bromine.

(III) where

R_x is selected from the group consisting of phenyl or p-tolyl radicals; R₂ and R₃ are independently selected from the group consisting of methyl, phenyl, and p-tolyl radicals;

R₄ is a radical selected from the group consisting of hydrogen, C₃-C₁₀ primary, secondary, and tertiary alkyl, and C₃-C₁₀ alkoxyl, which may be straight chain or branched; and X and Y are radicals independently selected from the group consisting hydrogen, methyl, ethyl, C₃-C₁₀ sec-alkyl, chlorine, and bromine.

(IV) where g is selected from the group consisting of phenyl and p-tolyl radicals; R₁₀ is a radical selected from the group consisting of methyl, phenyl, p-tolyl and 2- phenyl isobutyl; and

R_n is a radical selected from the group consisting methyl, phenyl, and p-tolyl.

(V) where R₁₂ is selected from the group consisting of phenyl or p-tolyl radicals;

R₁₃ is selected from the group consisting of methyl, phenyl, and p-tolyl radicals; R₁₄ is selected from the group consisting of methyl, phenyl, p-tolyl, and 2- phenylisobutyl radicals; and R₁₅ is selected from the group consisting of hydrogen, α,α-dimethylbenzyl, α-

methylbenzhydryl, triphenylmethyl, and α,α p-trimethylbenzyl radicals. Typical chemicals

useful in the invention are as follows:

TYPE I

TYPE III

TYPE IV Rg is phenyl and R₁₀ and R-- are methyl.

Of the foregoing preferred hydrocarbon-substituted diphenylamines, the substituted diphenylamines of the formula:

where R₁₆ and R₁₇ are methyl or phenyl are especially preferred. The compound wherein R₁₆ and R₁₇ are both methyl is 4,4'-bis(α,α-dimethylbenzyl)diphenylamine) and the compound wherein R₁₆ and R17 are both phenyl is 4,4'-bis(c.-methylbenzyl)diphenylamine. A second class of amine antioxidants comprises the reaction products of a diarylamine and an aliphatic ketone. The diarylamine aliphatic ketone reaction products that are useful herein are disclosed in U.S. Patent Nos. 1,906,935; 1,975,167; 2,002,642; and 2,562,802. Briefly described, these products are obtained by reacting a diarylamine, preferably a diphenylamine, which may, if desired, possess one or more substituents on either aryl group, with an aliphatic ketone, preferably acetone, in the presence of a suitable catalyst.

In addition to diphenylamine, other suitable diarylamine reactants include dinaphthyl amines; p-nitrodiphenylamine; 2,4-dinitrodiphenylamine; p-aminodiphenylamine; p- hydroxydiphenylamine; and the like. In addition to acetone, other useful ketone reactants include methylethylketone, diethylketone, monochloroacetone, dichloroacetone, and the like. A preferred diarylamine-aliphatic ketone reaction product is obtained from the condensation reaction of diphenylamine and acetone (NAUGARD A, Uniroyal Chemical), for example, in accordance with the conditions described in U.S. Patent Number 2,562,802. The commercial product is supplied as a light tan-green powder or as greenish brown flakes and has a melting range of85° to 95°C.

A third class of suitable amines comprises the N,N' hydrocarbon substituted p- phenylene diamines. The hydrocarbon substituent may be alkyl or aryl groups, which can be substituted or unsubstituted. As used herein, the term "alkyl," unless specifically described otherwise, is intended to include cycloalkyl. Representative materials are:

N-phenyl-N'-cyclohexyl-p-phenylenediamine;

N-phenyl-N'-sec.-butyl-p-phenylenediamine;

N-phenyl-N'-isopropyl-p-phenylenediamine;

N-phenyl-N'-(l,3-dimethylbutyl)-p-phenylenediamine; N,N'-bis-(l ,4-dimethylpentyl)-p-phenylenediamine;

N,N'-diphenyl-p-phenylenediamine; mixed diaryl-p-N,N'-bis-(l-ethyl-3-methylpentyl)-p-phenylenediamine; and

N,N'-bis-( 1 methylheptyl)-p-phenylenediamine. A final class of amine antioxidants comprises materials based on quinoline, especially, polymerized l,2-dihydro-2,2,4-trimethylquinoline. Representative materials include polymerized 2,2,4-trimethyl-l,2-dihydroquinoline; 6-dodecyl-2,2,4-trimethyl-l,2- dihydroquinoline; 6-ethoxy-2,2,4-trimethyl-l-2-dihydroquinoline, and the like. The hindered phenols that are particularly useful in the practice of the present invention preferably are oil soluble.

Examples of useful hindered phenols include 2,4-dimethyl-6-octyl-phenol; 2,6-di-t- butyl-4-methyl phenol (i.e., butylated hydroxy toluene); 2,6-di-t-butyl-4-ethyl phenol; 2,6-di- t-butyl-4-n-butyl phenol; 2,2'-methylenebis(4-methyl-6-t-butyl phenol); 2,2'-methylenebis(4- ethyl-6-t-butyl-phenol); 2,4-dimethyl-6-t-butyl phenol; 4-hydroxymethyl-2,6-di-t-butyl phenol; n-octadecyl-beta(3,5-di-t-butyl-4-hydroxyphenyl)propionate; 2,6-dioctadecyl-4- methyl phenol; 2,4,6-trimethyl phenol; 2,4,6-triisopropyl phenol; 2,4,6-tri-t-butyl phenol; 2-t- butyl-4,6-dimethyl phenol; 2,6-methyl-4-didodecyl phenol; tris(3,5-di-t-butyl-4-hydroxy isocyanurate, and tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane. Other useful antioxidants include 3,5-di-t-butyl-4-hydroxy hydrocinnamate; octadecyl-3,5-di-t-butyl-4-hydroxy hydrocinnamate (NAUGARD 76, Uniroyal Chemical; IRGANOX 1076, Ciba-Geigy); tetrakis{methylene(3,5-di-t-butyl-4-hydroxy- hydrocinnamate)} methane (IRGANOX 1010, Ciba-Geigy); l,2-bis(3,5-di-t-butyl-4- hydroxyhydrocinnamoyl)hydrazine (IRGANOX MD 1024,Ciba-Geigy); l,3,5-tris(3,5-di-t- butyl-4-hydroxybenzyl)-s-triazine-2,4,6 (lH,3H,5H)trione (IRGANOX 3114,Ciba-Geigy); 2,2'-oxamido bis-{ethyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)}propionate (NAUGARD XL-1, Uniroyal Chemical); 1 ,3,5-tris(4-t-butyl-3 -hydroxy-2,6-dimethylbenzyl)-s-triazine-2,4,6-

(lH,3H,5H)trione (CYANOX 1790, American Cyanamid Co.); l,3,5-trimethyl-2,4,6-tris(3,5- di-t-butyl-4-hydroxybenzyl)benzene (ETHANOX 330, Ethyl Corp.); 3,5-di-t-butyl-4- hydroxyhydrocinnamic acid triester with l,3,5-tris(2-hydroxyethyl)-5-triazine-

2,4,6(lH,3H,5H)-trione, and bis(3,3-bis(4-hydroxy-3-t-butylphenyl)butanoic acid)glycolester. Still other hindered phenols that are useful in the practice of the present invention are polyphenols that contain three or more substituted phenol groups, such as tetrakis{methylene

(3, 5-di-t-butyl-4-hydroxy-hydrocinnamate)}methane (IRGANOX 1010, Ciba-Geigy) and l,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene (ETHANOX 330, Ethyl

Corp.). The advantages and the important features of the present invention will be more apparent from the following examples.

EXAMPLES

The grafted copolymers employed in the practice of the present invention can be prepared in a similar fashion to those disclosed in U.S. Patent Nos. 4,693,838; 4,517,104; or 3,928,497.

After the grafting reaction is completed, there is added a sufficient amount of solvent neutral 100 (SN100), a paraffinic mineral oil, to bring the polymer content to 50 % to facilitate handling.

In a second step, the maleated polymer in oil is stirred with an equal amount of SN100 oil and heated to 160° C under a nitrogen blanket. Neutralization is then carried out with an equimolar amount of amine based on the charged maleic anhydride, followed by a nitrogen sparge for three hours to strip out water produced by the reaction. Each product is then cooled and filtered through a 100 mesh screen. Preparation Examples

Two series of samples were prepared as detailed in Examples 1 through 7 and 8 through 14. The procedure was the same for preparing both series of samples although the antioxidant was blended in at different levels. The antioxidants utilized were 2,6-di-t-butyl- 4-methylphenol (BHT) and alkylated diphenylamine (Naugalube 438L), both supplied by Uniroyal Chemical Company.

Series A Example 1 A quantity of 125 grams of a maleic anhydride graft polymer (rubber), in which the polymer substrate comprised about 57 mole percent ethylene and 43 mole percent propylene having a number average molecular weight of about 27,000, on which had been grafted 2.9 weight percent of maleic anhydride in 375 grams of lubricant diluent oil was heated to 160° C with mechanical stirring while the mixture was maintained under a nitrogen blanket. Once temperature was reached, mixing was continued for an additional hour at 160° C. N-3-aminopropyl morpholine (5.33 grams) was added to the oil solution of the polymer and a reaction was effected over 4 hours at 160° C under mechanical stirring with a nitrogen sparge. The reaction mixture containing the derivatized graft polymer was then cooled and filtered. A sample was placed in a glass jar, the kinematic viscosity of the sample at 210^° F (about 99° C) was measured and then the remainder was sealed and placed into a 65° C oven for stability testing. Example 2

A sample of the product of Example 1 was blended with 0.5 weight percent of 2,6-di- t-butyl-4-methylphenol (BHT). The sample was placed in a glass jar, the kinematic viscosity of the sample at 210° F was measured and then the remainder was sealed and placed into a 65° C oven for stability testing.

Example 3 A sample of the product of Example 1 was blended with 1.0 weight percent of BHT. The sample was placed in a glass jar, the kinematic viscosity of the sample at 210° F was measured and then the remainder was sealed and placed into a 65° C oven for stability testing.

Example 4 A sample of the product of Example 1 was blended with 3.0 weight percent of BHT. The sample was placed in a glass jar, the kinematic viscosity of the sample at 210° F was measured and then the remainder was sealed and placed into a 65° C oven for stability testing.

Example 5 A sample of the product of Example 1 was blended with 0.5 weight percent of alkylated diphenylamine. The sample was placed in a glass jar, the kinematic viscosity of the sample at 210° F was measured and then the remainder was sealed and placed into a 65^° C oven for stability testing. 0074-UP

Example 6

A sample of the product of Example 1 was blended with 1.0 weight percent of alkylated diphenylamine. The sample was placed in a glass jar, the kinematic viscosity of the sample at 210° F was measured and then the remainder was sealed and placed into a 65° C oven for stability testing.

Example 7

A sample of the product of Example 1 was blended with 3.0 weight percent of alkylated diphenylamine. The sample was placed in a glass jar, the kinematic viscosity of the sample at 210° F was measured and then the remainder was sealed and placed into a 65° C oven for stability testing.

The following Table shows the results of the stability study.

Series B Example 8

A quantity of 125 grams of a maleic anhydride graft polymer (rubber), in which the polymer substrate consisted of about 57 mole percent ethylene and 43 mole percent propylene having a number average molecular weight of about 24,000, on which had been grafted 2.9 weight percent of maleic anhydride in 375 grams of lubricant diluent oil was heated to 160° C with mechanical stirring while the mixture was maintained under a nitrogen blanket. Once temperature was reached, mixing was continued for an additional hour at 160° C. N-3-aminopropyl morpholine (5.33 grams) was added to the oil solution of the polymer and a reaction was effected over 4 hours at 160° C under mechanical stirring with a nitrogen sparge. The reaction mixture containing the derivatized graft polymer was then cooled and filtered. A sample was placed in a glass jar, the kinematic viscosity of the sample at 210^° F was measured and then the remainder was sealed and placed into a 65° C oven for stability testing.

Example 9 A sample of the product of Example 8 was blended with 0.1 weight percent of BHT. The sample was placed in a glass jar, the kinematic viscosity of the sample at 210^° F was measured and then the remainder was sealed and placed into a 65° C oven for stability testing. Example 10

A sample of the product of Example 8 was blended with 0.25 weight percent of BHT. The sample was placed in a glass jar, the kinematic viscosity of the sample at 210° F was measured and then the remainder was sealed and placed into a 65° C oven for stability testing.

Example 11 A sample of the product of Example 8 was blended with 3.0 weight percent of BHT. The sample was placed in a glass jar, the kinematic viscosity of the sample at 210° F was measured and then the remainder was sealed and placed into a 65° C oven for stability testing.

Example 12 A sample of the product of Example 8 was blended with 0.1 weight percent of alkylated diphenylamine. The sample was placed in a glass jar, the kinematic viscosity of the sample at 210° F was measured and then the remainder was sealed and placed into a 65° C oven for stability testing.

Example 13 A sample of the product of Example 8 was blended with 0.25 weight percent of alkylated diphenylamine. The sample was placed in a glass jar, the kinematic viscosity of the sample at 210° F was measured and then the remainder was sealed and placed into a 65° C oven for stability testing. Example 14

A sample of the product of Example 8 was blended with 3.0 weight percent of alkylated diphenylamine. The sample was placed in a glass jar, the kinematic viscosity of the sample at 210° F was measured and then the remainder was sealed and placed into a 65° C oven for stability testing.

Table 2

As can be seen from the above two series of examples, the addition of a primary antioxidant (phenolic or aminic) to the base concentrates (Examples 1 and 8) can significantly limit the growth in viscosity of the additive concentrate upon storage.

In view of the many changes and modifications that can be made without departing from principles underlying the invention, reference should be made to the appended claims for an understanding of the scope of the protection to be afforded the invention.

Claims

CLAIMSWhat is claimed is:

1. A method for inhibiting the rate of viscosity growth in an oil concentrate of a VI- dispersant prepared from a copolymer of ethylene and at least one C₃-C₁₆ alpha olefin, wherein said copolymer has been grafted with at least one unsaturated carboxylic acid- containing material and reacted with an amount of polyamine or amino alcohol sufficient to neutralize the acid, comprising blending a primary antioxidant into said concentrate as a top treatment or as a displacement for an equal amount of diluting oil.

2. The method of claim 1 wherein the antioxidant is present at a level of at least about 0.1% by weight, based on the weight of the concentrate.

3. The method of claim 1 where the primary antioxidant is a phenolic antioxidant.

4. The method of claim 3 where the phenolic antioxidant is added into the concentrate at a level of 0.25 to 5.0 percent based on the weight of the concentrate.

5. The method of claim 1 where the primary antioxidant is an aminic antioxidant.

6. The method of claim 5 where the aminic antioxidant is added into the concentrate at a level of 0.25 to 5.0 percent based on the weight of the concentrate.

7. A method for inhibiting the rate of viscosity growth in an oil concentrate of a VI- dispersant prepared from a copolymer of ethylene and at least one C₃-C₁₆ alpha olefin, wherein said copolymer has been grafted with at least one unsaturated nitrogen-containing material, comprising blending a primary antioxidant into said concentrate as a top treatment or as a displacement for an equal amount of diluting oil.

8. The method of claim 7 wherein the antioxidant is present at a level of at least about 0.1% by weight, based on the weight of the concentrate.

9. The method of claim 7 where the primary antioxidant is a phenolic antioxidant.

10. The method of claim 7 where the primary antioxidant is an aminic antioxidant.