GB2055852A

GB2055852A - Modified Ethylene Copolymers

Info

Publication number: GB2055852A
Application number: GB8021733A
Authority: GB
Original assignee: Exxon Research and Engineering Co
Current assignee: ExxonMobil Technology and Engineering Co
Priority date: 1979-07-03
Filing date: 1980-07-02
Publication date: 1981-03-11
Also published as: IT1131890B; DE3025274A1; GB2055852B; FR2460993A1; IT8023199A0

Abstract

Oil-soluble derivatized ethylene copolymers produced from about 2 to 98 wt.% ethylene and one or more C3 to C28 alpha-olefin, e.g. propylene, and having a number average molecular weight (Mn) of from about 700 to 500,000, are grafted, preferably solution-grafted, under an inert atmosphere and in the presence of a free-radical initiator, with an ethylenically-unsaturated dicarboxylic material and thereafter reacted with a C8-C20 aliphatic heterosubstituted alkylene primary amine to form an aminated carboxyl-grafted polymeric material. The product is a mineral oil sludge dispersant and viscosity index improver which when dissolved in mineral oil provides a haze-free solution.

Description

SPECIFICATION Stable Aminated Graft of Ethylene Copolymeric Additives for Lubricants This invention relates to stable polymeric dispersant additives for lubricating oils which may also be useful as viscosity-index improvers for lubricating oils. More particularly, this invention relates to viscosity-stable and haze-free solutions of substantially saturated polymers comprising ethylene and one or more C3 to C28 alpha-olefins, preferably propylene, which have been grafted in the presence of a free radical initiator with an ethylenically-unsaturated dicarboxylic acid material, preferably at an elevated temperature and in an inert atmosphere, and thereafter reacted with an alkyl heterosubstituted alkylene primary amine to form multifunctional polymeric reaction products characterized by viscosity-stabilizing activity in mineral oil solutions.

Ashless dispersants for lubricating oil compositions are well known to enhance the sludge dispersing ability of said compositions.

One type of dispersant is generally derived from a hydrocarbon-substituted dicarboxylic acid material, such as an alkenyl succinic acid or anhydride, reacted with a nitrogen-containing material, such as an alkylene polyamine.

It is also well known that the introduction of carboxylic acid groups onto ethylene copolymers, as by reaction of an oxidized degraded copolymer with maleic anhydride, provides a means for derivatizing with an alkylene polyamine and thereby providing sludge-dispersant activity to said copolymers which have viscosity index (V.l.) improving activity when dissolved in mineral oils (see U.S.

3,316,177). One means af introducing the carboxylic groups is by grafting of maleic anhydride onto said polymer as by a free radical mechanism. U.S. Patent 4,089,794 discloses the production of oilsoluble, sludge-dispersing additives for hydrocarbon fuels and lubricating oils by the free-radical induced grafting in solution of an ethylenicallyunsaturated dicarboxylic acid material, such as maleic anhydride, onto a substantially saturated copolymer comprising ethylene and at least one other alphaolefin at an elevated temperature to provide, without substantial polymer degradation, a useful precursor copolymer which can be subsequently reacted with a carboxylic acid reacting polyfunctional material, such as a polyamine or a hydroxyamine or mixtures of these, to form multifunctional polymeric imidated derivatives having particular utility as engine sludge and varnish control additives for lubricating oils.

It is an object of this invention to provide a grafted ethylene copolymeric dispersant, generally useful as a mineral oil viscosity index improver of useful sludge performance and enhanced viscosity stabilizing activity, which when dissolved in mineral oil provides a haze-free solution.

U.S. Patent 4,137,185 teaches that the reaction of the organic acid anhydrides, e.g. acetic anhydride, provides amide derivatization of any primary amino groups of the imidated ethylene copolymer whereby viscosity stabilizing activity is provided to said copolymers. The aforesaid reaction can be considered a process for improving the viscosity stabilization of an oil additive concentrate comprising a hydrocarbon solvent, from .1 to 50 wt.%, based on the total weight of said concentrate, of an imidated grafted ethylene C2-C28 alpha-olefin copolymeric viscosity index improver having a molecular weight (Mn) of 700 to 500,000 comprising the step of reacting said concentrate with a hydrocarbon substituted acid anhydride wherein the hydrocarbon constituent has from about 1 to 30 carbons by adding said acid anhydride in about 0.5-2.5 moles per primary amino group of said concentrate and maintaining said concentrate at a temperature ranging from about Soc to about 2500C., preferably 100 to 2000 C., and for a period of 0.25 to 8, preferably 0.5 to 3 hours.The reaction appears to be an acylation of pendant free primary amino group to provide an amide structure which limits the multifunctional copolymers property of solution chain extension thereby inhibiting viscosity increase of oil solutions containing the additives.

It has now been discovered that viscosity stabilization can be enhanced in the multifunctionalized grafted copolymers disclosed in said U.S. Patent 4,137,185 when from 0.5 to 1.5 molar equivalent (based on grafted dicarboxylic acid groups) of a C8-C20 aliphatic preferably alkyl hetero-substituted alkylene primary amine, e.g. amino propyl tridecyl alcohol ether, is reacted with said grafted copolymer with the surprising result of enhanced dispersant activity and the property of providing haze-free solutions when dissolved in mineral oil.

In accordance with this invention, there is provided a composition comprising a lubricating oil having dissolved therein at least a viscosity index improving amount of an oil-soluble C8 to C20 alkyl heterosubstituted alkylene aminated derivative of a carboxyl grafted ethylene polymeric viscosity index improver containing from 0.001 to 8 wt.% of nitrogen, said grafted carboxyl groups ranging from 2 to 20, preferred 4 to 16, average per ethylene copolymer molecule.

This invention results in an additive oil composition of improved viscosity stability and no visually perceptible haze.

Thus, this invention also relates to the novel graft ethylene copolymeric aminated compositions of the amido-imido, preferably succinimido, type as well as lubricants containing these copolymers prepared as described herein.

The Ethylene Copolymers The ethylene copolymers to be grafted contain from about 2 to about 98, preferably 30 to 80 wt% of ethylene, and about 2 to 98, preferably 20 to 70, wt% of one or more C3 to C28, preferably C3 to C18, more preferably C3 to C8, alpha-olefins, e.g. propylene. Such copolymers preferably have a degree of crystallinity of less than 25 wt.%, as determined by X-ray and differential scanning calorimetry, and a number average molecular weight (n) in the range of about 700 to about 500,000, preferably 10,000 to 250,000, as determined by vapor phase osmometry (VPO) or membrane osmometry. 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 include 1-butene, 1-pentene, 1-hexene, 1-octene; also branched chain alpha-olefins, such as 5methylpentene-1 and 6-methylheptene- 1 and mixtures thereof.

Terpolymers of ethylene, said alpha-olefin and a nonconjugated diolefin or mixtures of such diolefins may also be used. The amount of the nonconjugated diolefin ranges from about 0.5 to 20 mole percent, preferably about 1 to about 7 mole percent, based on the total amount of ethylene and alpha-olefin present. Representative diolefins include cyclopentadiene, 2-methylene-5-norbornene, non-conjugated hexadiene, or any other alicyclic or aliphatic nonconjugated diolefin having from 6 to 15 carbon atoms per molecule, such as 2-methyl or ethyl norbornadiene, 2,4-dimethyl-2-octadiene, 3- (2-methyl-1 -propane) cyclopentene, ethylidene norbornene, etc.

These ethylene copolymers, this term including terpolymers, may be prepared using the wellknown Ziegler-Natta catalyst compositions.

Such polymerization may be effected to produce the ethylene copolymers by passing 0.1 to 15, for example, 5 parts of ethylene; 0.05 to 1 0,.for example, 2.5 parts of said higher alpha-olefin, typicaily propylene; and from 10 to 10,000 parts of hydrogen per million parts of ethylene; into 100 parts of an inert liquid solvent containing (a) from about 0.0017 to 0.017, for example, 0.0086 parts of a transition metal principal catalyst, for example, VOCI3; and (b) from about 0.0084 to 0.084, for example, 0.042 parts of cocatalyst, e.g. (C2Hs)3AI2CI3; at a temperature of about 25 C. and a pressure of 60 psig for a period of time sufficient to effect optimum conversion, for example, 15 minutes to onehalf hour; all parts being parts by weight.

Ethylenically Unsaturated Carboxylic Acid Materials These materials which are grafted (attached) onto the copolymer contain at least one ethylenic bond and at least one, preferably two, carboxylic acid or its anhydride groups or a polar group which is convertible into said carboxyl groups by oxidation or hydrolysis Maleic anhydride or a derivative thereof is preferred as it does not appear to homopolymerize appreciably but grafts onto the ethylene copolymer or terpolymer to give two carboxylic acid functionalities. Such preferred materials have the generic formula:

wherein R1 and R2 are hydrogen or a halogen and 0 is oxygen.Suitable examples additionally include chloromaleic anhydride, itaconic anhydride, or the corresponding dicarboxylic acids, such as maleic acid orfumaric acid or their monoesters.

Grafting of the Polymer The free-radical induced grafting of ethylenically unsaturated carboxylic acid materials in solvents, such as benzene is known in the art. The grafting is carried out at an elevated temperature in the range of about 1000C. to 2500C., preferably 150 to 1 800C., e.g. above 1 6OcC., in a solvent, preferably a mineral lubricating oil solution containing, e.g. 1 to 50, preferably 5 to 30 wt.%, based on the initial total oil solution, of the ethylene polymer and preferably under an inert environment. The grafting is usefully carried out in the presence of a high-temperature decomposable compound capable of supplying free radicals at said elevated temperature.

The free-radical initiators which may be used are peroxides, hydroperoxides, and azo compounds and preferably those which have a boiling point greater than about 1000C. and decompose thermally within the grafting temperature range to provide said free radicals. Representative of these free-radical initiators are azobutyro-nitrile, 2,5-dimethyl-hex-3-yne-2,5 bis-tertiary-butyl peroxide (sold as Lupersol 1 wO) or its hexane analogue, di-tertiary butyl peroxide and dicumyl peroxide. The initiator is used at a level of between about 0.005% and about 1%, based on the total weight of the polymer solution.

The ethylenically unsaturated carboxylic acid material, e.g. maleic anhydride, is used in an amount ranging from about 0.01% to about 10%, preferably 0.1 to 2.0%, based on weight of the initial total oil solution. The aforesaid carboxylic acid material and free radical initiator are used in a weight percent ratio range of 1.0:1 to 30:1, preferably 3.0:1 to 6:1.

The grafting is preferably carried out in an inert atmosphere, such as by nitrogen blanketing.

While the grafting can be carried out in the presence of air, the yield of the desired graft polymer is decreased as compared to grafting under an inert atmosphere. The inert environment should be substantially free of oxygen. The grafting time ranges from about 0.1 to 12 hours, preferably from about 0.5 to 6 hours, more preferably 0.5 to 3 hours. The graft reaction is carried out to at least approximately 4 times, preferably at least about 6 times the half-life of the free-radical initiator at the reaction temperature employed, e.g. with 2,5-dimethyl hex-3-yne-2,5-bis(t-butyl peroxide) 2 hours at 1 600C. and one hour at 1 700C.

In the grafting princess, the copolymer solution is first heated to grafting temperature and thereafter said carboxylic acid material and initiator are added with agitation although they could have been added prior to heating. When the reaction is complete, the excess acid material is eliminated by an inert gas purge, e.g. nitrogen sparging.

In the grafting step, the maleic anhydride or other carboxylic acid material used is grafted onto both the polymer and the solvent for the reaction. The wt.% grafted onto the polymer is normally greater than the amount grafted onto the oil due to greater reactivity of the polymer to grafting.

However, the exact split between the two materials depends upon the polymer and its reactivity, the reactivity and type of oil, and also the concentration of the polymer in the oil. The split can be measured empirically from the infrared analyses of product dialyzed into oil and polymer fractions and measuring the anhydride peak absorbance in each.

The grafting is preferably carried out in a mineral lubricating oil which 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 polyfunctional material and as a solvent for the end product to form the concentrate.

The oil having attached, grafted carboxyl, e.g. maleic anhydride, groups will when reacted with the hetero-substituted primary amine also be converted to the corresponding derivatives. If desired, the split between the imidated graft polymer and the imidated graft oil can be determined by dialysis into polymer and oil fractions and infrared or nitrogen analysis of the fractions. Unfortunately the grafted oil appears to be a source of haze should it become excessively polar as by derivatization.

The solution grafting step when carried out in the presence of a high temperature decomposable peroxide is accomplished without degradation of the chain length (molecular weight) of the ethylenecontaining polymer. Measurement of molecular weights and degradation can be evaluated by determination of the thickening efficiency of the polymer.

Thickening efficiency (T.E.) is defined as the ratio of the weight percent of a polyisobutylene (sold as an oil solution by Exxon Chemical Co. as- Paratone N), having a Staudinger Molecular Weight of 20,000, required to thicken a solvent-extracted neutral mineral lubricating oil, having a viscosity of 1 50 SUS at 37.80C., a viscosity index of 105 and an ASTM pour point of OOF., (Solvent 1 50 Neutral) to a viscosity of 1 2.4 centistokes at 98.90C., to the weight percent of a test copolymer required to thicken the same oil to the same viscosity at the same temperature. T.E. is related to rMn) and is a convenient, useful measurement for formulation of lubricating oils of various grades.

Alkyl Heterosubstituted Alkylene Primary Amines Useful alkyl heterosubstituted alkylene primary amines are characterized by an alkyl group having from eight to twenty carbons with 10 to 70 total carbons and from 1 to 11 nitrogens and preferably are of the general formula: H Y[(CH2)sNlt(CH2)sNH2 wherein s is an integer of from two to six, t is an integer of from zero to ten and Y is a substituent of the class consisting of::

(amino group), -S-R (thiol group), -O-R (ether group),

(keto group),

(imidazoline group), and

(glycol ester group) wherein N represents nitrogen, S represents sulfur, 0 represents oxygen, R represents a C8-C20 alkyl group and R' represents hydrogen or Ct to C8 lower alkyl.

The following are illustrative of the useful amines of the invention which for ease of presentation will be categorized according to the above indicated meanings of Y of the general formula.

1. y is an amino group, i.e.

resulting in a product such as amino propyl oleyl amine of the formula C18H38NH-(CH2)3NH2. This type of reactant is readily produced by the cyanoethylation and subsequent reduction of oleyl amine. This means the use of starting materials of from C8H,7NH2 (octyl amine) through C20H41 NH2 (eicosyl amine) through the cyanoethylation step with acrylonitrile and subsequent reduction can provide useful amines such as amino propyl octyl amine, amino propyl nonyl amine, etc. Repeating the cyanoethylation plus reduction step one type with for example the amino propyl oelyl amine gives an amine of the formula C18H38[NH-(CH2)3j2NH2 and further cyanoethylation plus reduction steps increases the t of the general formula one integer for each step.

The cyanoethylation followed by reduction procedure has application to each of the succeeding categories.

2. Y is a thiol group, i.e. -S-R. The primary amine compounds useful with this group are obtained from the cyanoethylation followed by reduction stage of an alkyl mercaptan, e.g. C8H,7SH to C20H41SH, as illustrated by lauryl mercaptan to yield amino propyl lauryl sulfide or stearyl mercaptan to yield (after two stages) amino propyl amino propyl stearyl sulfide.

3. Y is an ether group, i.e. --OO-R. In this instance cyanoethylation and reduction is of an alcohol e.g. tridecyl alcohol and covers those alcohols within the range of 8 to 20 carbons. One such primary amine is amino propyl tridecyl ether C13H27O(CH2)3NH2 sold as Armeen EA-13 by Armak Company of Chicago, Illinois. All of the C8 to C20 alcohols can be cyanoethylated and reduced in as many stages as desired to produce the [C8-C20j-0-[(CH2)3-NH]010(C H2)3NH2 primary amines useful for this invention.

4. Y is a keto group, i.e.

e.g. where R' is a C8H17 group and R is a CgH19 group to provide 9-amino propyl-10-nonadecanone of the formula

obtained from the addition of acrylonitrile under basic conditions to 10-nonadecanone (Michael addition) followed by reduction of the cyano group.

5. Y is an imidazoline group, i.e. -NH-(CH2)2-

which in actuality is related to

when R' is hydrogen and R is the reaction product of oleic acid and diethylene triamine which condenses to provide the imidazoline ring. Subsequent cyanoethylation with acrylonitrile and then reduction using the above reaction product for illustrative pruposes yields amino propyl amino ethyl oleyl imidazoline having the formula

The diversity of primary amines is apparent when the imidazoline condensation features the C7 to C18 acid and the appropriate alkylene polyamine.

6. Y is a glycol ester group, i.e.

which primary amino derivative is available as a Kessco$ glycol ester from Armak Company of Chicago, Illinois. When R is C18H37 the primary amine can be readily produced by the cyanoethylation and reduction of diethylene glycol monostearate to yield amino propyl diethylene glycol monostearate.

Other glycol esters available from Armak Company are ethylene glycol monostearate and propylene glcyol monostearate any of which can be cyanoethylated and reduced to yield the useful amines of the invention.

Multifunctionalization (Imidization) Process The grafted polymer, preferably in solution, can be readily reacted with said alkyl heterosubstituted alkylene primary amine and mixtures thereof by admixture together with said grafted polymer and heating at a temperature of from about 1000C. to 2500C. for from 10 minutes to 30 hours, preferably 10 minutes to 10 hours, usually about 1 5 minutes to about 3 hours. Removal of water assures completion of the imidation reaction. From 0.5 to 1.5 preferably 1 molar equivalent of said primary amine based on the grafted dicarboxylic acid moiety content, e.g. grafted maleic ~~ anhydride content, is used.For example, with an ethylene-propylene copolymer of about 40,000 (M,), i.e. a thickening efficiency of about 2.1, and averaging 4 maleic anhydride groups, from about 2 to 4 moles of the primary amine is preferably used per mole of grafted copolymer. It has been found that at least about 0.5 molar equivalent per mole of grafted maleic anhydride provides a solution in oil of improved clarity although 1 molar equivalent is optimal for clarity (haze free).

A wide range, e.g. 0.001 to 50 wt.%, preferably 0.005 to 20%, of the oil-soluble nitrogencontaining graft polymers produced in accordance with this invention can be incorporated into about a major amount of an oleaginous material, such as a lubricating oil or hydrocarbon fuel. When used in lubricating oil compositions, e.g., automotive or diesel crankcase lubricating oil, the treated polymer concentrations are within the range of about 0.01 to 20 wt.%, e.g. 0.1 to 15.0 wit%, preferably 0.25 to 10.0 wt.%, of the total composition.The lubricating oils to which the products of this invention can be added include not only hydrocarbon oil derived from petroleum, but also include synthetic lubricating oils such as esters of dibasic acids and complex esters made by esterification of monobasic acids, polyglycols, dibasic acids and alcohols.

The imidated graft polymers of the invention may be commercialized and/or utilized in a concentrate form, e.g., from about 10 wt.% to about 50 wt.%, preferably 1 5 to 49 wt.%, in oil, e.g.

mineral lubricating oil, for ease of handling.

The above concentrates and lubricating oil compositions may contain other conventional additives, such as dyes, pour point depressants, antiwear agents, antioxidants, other viscosity-index improvers, dispersants and the like.

The following examples illustrate more clearly the process of the present invention. However, these illustrations are not to be interpreted as specific limitations of this invention.

Practice of this invention may be illustrated by the following examples which show how the invention may be utilized. In these examples, as elsewhere in this specification, all parts are by weight unless specifically indicated otherwise all nitrogen were determined by Kjeldahl analysis.

Example 1 Preparation of ethylenepropylene Succinic Anhydride Copolymer An oil concentrate (220 Ibs.) of about 1 5% ethylene-propylene copolymer (2.1 TE) was charged into a 50 gal. reactor, heated to 121 OC. under nitrogen and sparged (nitrogen) for 1 hr. Maleic an hydride (3.795 Ibs.) was added to the stirred reactor and the temperature raised to 171 0C. At 171 0C., Lupersol 130 (0.95 Ibs.) was added and stirring continued for 1.5 hr. Finally, the reaction was sparged with nitrogen for 1.5 hrs. to remove any unreacted maleic anhydride. The product was diluted with mineral oil to about 15% copolymer.

Example 2 An oil concentrate (300 g) of about 15% ethylenepropylene succinic anhydride copolymer (0.04749 moles grafted maleic anhydride) prepared as above was placed into a 4-necked one liter flask, heated to 1 700C. under a nitrogen blanket and then sparged heaviiy for one hour. The solution was reacted with Armeen EA-13 from Armak Company which is aminopropyl tridecyl ether, C13H27-O- (CH2)3NH2 (12.2 g; 0.04749 moles) and stirred for another 2 hours. Finally the solution was diluted with S100N oil (128 g) to a final active ingredient of 10.5 wt.%.

Example 3 This reaction was identical to that of Example 2 except that the amino propyl tridecyl ether was rep!aced with N-aminopropylmorpholine (NAPM) (15.0 g; 0.04749 moles).

Example 4 This reaction was identical to that of Example 2 except that the Armeen EA-13 replaced with Duomeen EA-13 from Armak Company which is aminopropyl aminopropyl tridecyl ether C13H27-O- (CH2)3-NH-(CH2)3-NH2 (15.0 g; 0.04749 moles).

Example 5 This reaction was identical to that of Example 2 except that the reaction was aminated with a 1:1 mixture of NAPM (3.40 g; 0.023 moles) and amino propyl tridecyl ether (6.10 g; 0.023 moles).

Example 6 This reaction was identical to that of Example 2 except that the reaction was aminated with a 1:1 mixture of NAPM (3.40 g; 0.023 moles) and bis-(aminopropyl) tridecyl ether (7.5 g; 0.023 moles).

Example 7 This reaction was identical to that of Example 5 except that the amino propyl tridecyl ether was added first and the reaction stirred for 30 minutes before NAPM was added. After the NAPM addition the reaction was stirred for 45 minutes before final dilution to said 10.5 wt.% active ingredient.

Example 8 This reaction was identical to that of Example 6 except that the bis-(aminopropyl) tridecyl ether was added first and the reaction stirred for 30 minutes before NAPM was added. After the NAPM addition, the reaction was stirred for another 30 minutes before final dilution to said 10.5 wt.% active ingredient.

Example 9 The products of Examples 2-8 were subjected to a measurement of the clarity, i.e. lack of haze of each sample using an instrument named Nephocolorimeter Model 9 sold by the Coleman Instrument Corporation of Maywood, Illinois. The results are set forth in Table I with the lower the number representing a lower amount of haze (greater clarity).

Table I Example Haze (Nephelos) 2 33 3 230 4 52 5 230 6 205 7 101 8 156 The results in Table I indicate that the products of this invention (Examples 2 and 4) lead to bright, clear stable multifunctional viscosity index improvers concentrate whereas that product from a conventional polyamine such as NAPM (Example 3) leads to a haze containing multifunctional viscosity index improver.

Moreover, the proper addition of polyamine reactants, i.e. a sequential addition of first the haze clearing and then the non-haze-clearing polyamine leads to multifunctional viscosity index improver (MFVl) mineral oil solutions of improved clarity, i.e. less haze (compare Ex. 5 with Ex. 7 and Ex. 6 with Ex. 8). This indicates that the polyamine preferentially reacts first with the haze products i.e. the grafted oil molecules and then with the grafted polymer. This is probably due to differences in solubility of the grafted oil to the grafted copolymer in the mineral oil.

Example 10 Varnish Inhibition Bench (VIB) Test The product from Example 4 was tested in a varnish inhibition bench test (VIB) and compared with the results obtained when using a commercially available MFVI sold as LZ 3702 by Lubrizol Corp.

of Cleveland, Ohio which is believed to be a styrene maleic anhydride copolymer esterified with short chain alcohols and aminated with a polyamine.

In a Varnish Inhibition Bench (VIB) Test, each test sample consists of 10 grams of lubricating oil containing 0.07 of a gram of the additive concentrate (50% active) which results in a total of 0.35 wt.% additive present in the test sample. The test oil to which the additive is admixed was 9.93 grams of a commercial lubricating oil obtained from a taxi after 2,000 miles of driving with said lubricating oil.

Each ten gram sample was heat soaked overnight at about 1 400C. and thereafter centrifuged to remove the sludge. The supernatant fluid of each sample was subjected to heat cycling from about 1 500C. to room temperature over a period of 3.5 hours at a frequency of about 2 cycles per minute.

During the heating phase, the gas containing a mixture of about 0.7 volume percent SO2, 1.4 volume percent NO and balance air was bubbled through the test samples and during the cooling phase water vapor was bubbled through the test samples. At the end of the test period, which testing cycle can be repeated as necessary to determine the inhibiting effect of any additive, the wall surfaces of the test flasks in which the samples were contained are visually evaluated. Flasks in which the samples were contained are visually evaluated as to the varnish inhibition. The amount of varnish imposed on the walls is rated at values of from 1 to 7 with the higher number being the greater amount of varnish. It has been found that this test correlates with the varnish results obtained as a consequence of carrying out an MS-VC engine test.The results of the VIB testing of the product of Example 4 and LZ 3702 are recorded in Table II below: Table II VIB Rating Example 4 LZ 3702 5 The VIB results indicate the product from Example 4 is superior in varnish inhibition to the commerically available MFVI, LZ 3702. The products of this invention make it possible to provide bright, clear mineral oil solutions particularly concentrates of MFVl's which are made in a single derivatization step with activity in varnish inhibition apparently superior to a commercial MFVI.

Example 11 Engine Tests Duomeen EA-13 of Example 4 was compared with the NAPM of Example 3 in the 1 H2 Caterpillar single cylinder supercharged diesel engine 240-hour test using the conditions of procedure ASTM STP509A wherein no dispersant was used. The following results were obtained.

Table III NAPM Duomeen Weighted total demerits 1204 294 (WTD) Top groove fill % 38 52 (TGF) The WTD figure is the more significant of the values; the lower the number, the cleaner is the engine. It will be seen that the Duomeen product is greatly superior in that it has a much lower demerit as compared to the NAPM. The TGF figure indicates a slight advantage for the NAPM but this is of minor significance.

The two materials were also compared in the L-38 engine test which is a single cylinder gasoline engine wherein additives are evaluated for their oil oxidation and bearing corrosion performance using Federal Test Method 3405. The piston skirt varnish value for Duomeen EA-13 was 9.7 while the NAPM gave a figure of 7.7. In this test a value of 10 means a clean engine while zero refers to an engine full of lacquer.

Thus, the invention can be described as a composition comprising an oil-soluble imidated ethylene copolymer having a number average molecular weight (Mn) ranging from 700 to 500,000 (preferably 1,000 to 250,000) and from 2 to 20 (preferably 4 to 10) average grafted imido moieties per molecule, from 50 to 100 mole percent of said imido moieties being nitrogen substituted with C8 to C20 alkyl heterosubstituted alkylene primary amine whereby a haze-free cpmposition of improved viscosity stabilization is realized.

Claims

1. A process of preparing an oil solution of a polymeric viscosity index improver having sludge dispersing properties by mineral oil solution grafting of maleic anhydride onto a copolymer comprising about 30 to 80 wt.% ethylene and about 20 to 70 wt.% of at least one C3-C28 alpha-olefin, said copolymer having a number average molecular weight in the range of about 10,000 to 250,000 to provide an average of two to twenty maleic acid anhydride groups per copolymer molecule, said mineral oil solution containing about 1 to 50 wt.%, based on the total oil solution, of said copolymer, wherein a portion of said maleic anhydride is grafted upon said polymer and another portion of maleic anhydride is grafted upon said oil, to thereby produce a grafted product, and then reacting said grafted product with from 0.5 to 1.5 molar equivalent, based on reacted maleic anhydride, of a C8-C20 alkyl heterosubstituted alkylene primary amine having from 11 to 70 total carbons and from 1 to 11 total nitrogens.

2. A process according to claim 1, wherein said grafting is carried out with a free-radical initiator at a temperature of about 100 to 2500C.

3. A process according to claims 1 or 2, wherein said C8-C20 alkyl heterosubstituted alkylene polyamine is of the general formula

wherein s is an integer of from two to six, t is an integer of from zero to ten and Y is a substituent selected from the group consisting of:

and

wherein N represents nitrogen, S represents sulfur, 0 represents oxygen, R represents a C8-C20 alkyl group and R' represents hydrogen or C1 to C9 alkyl.

4. A process according to claim 3, wherein Y is --OO-R.

5. A process according to claims 1---4, wherein said heterosubstituted alkylene polyamine is aminopropyl tridecyl ether or bis(aminopropyl) tridecyl ether.

6. A process according to claims 1-5, wherein said C8-C20 alkyl heterosubstituted alkylene polyamine is reacted in an amount less than one molar equivalent per grafted maleic anhydride moiety, and the remaining maleic anhydride moieties are subsequently reacted with an alkylene polyamine.

7. A process according to claim 6, wherein said alkylene polyamine is N-aminopropylmorpholine.

8. An oil solution of a viscosity index improver prepared by the process of claims 1-7.

9. A lubricating oil composition comprising a major amount of a lubricating oil and a viscosity index improving amount of the oil solution of claim 8.