US2613184A

US2613184A - Lubricating oil containing a copolymer of an ester of an unsaturated acid and a n-hydrocarbon amide of an unsaturated acid

Info

Publication number: US2613184A
Application number: US255523A
Authority: US
Inventors: Willard E Catlin
Original assignee: EI Du Pont de Nemours and Co
Current assignee: EIDP Inc
Priority date: 1951-11-08
Filing date: 1951-11-08
Publication date: 1952-10-07
Anticipated expiration: 1969-10-07

Description

viscosity with change in temperature.

Patented Oct. 7, 1952 LUBRICATING OIL CONTAINING A COPOLY- MER OF AN ESTER OF AN UNSATURATED ACID AND A N-HYDROCARBON AMIDE OF AN UNSATURATED ACID Willard E. Catlin, Wilmington, Del., assignor to E. I. du Pont de Nemours and Company, W1].- mington, Del., a corporation of Delaware.

No Drawing. Application November 8, 1951,

Serial No. 255,523

This invention relates to lubricants and, more particularly, to lubricating oil compositions having improved lubricating qualities. This application is a continuation-in-part of applicant's copending application Serial No. 111,349, filed August 19, 1949, now abandoned.

Lubricating oils have the undesirable characteristic of decreasing in viscosity as the temperature of the oil is increased. The rate of change of viscosity with temperature varies with the nature of the particular oil. Oils with a low rate of change of viscosity with temperature are desired for lubrication purposes, especially in applications'where widely varying temperature conditions are encountered. Hence, numerous materials have been proposed as additives to oils to minimize their change in viscosity with temperature.

peraturesare afiorded by the viscosity index and by the slope calculated from the viscosity-temperature characteristics of the oil. The viscosity index is calculated from the measured viscosities of the oil at two temperatures, 100 F. and 210 F., by the standard A. S. T. M. method identified as D567-41.' By this method of calculation oils having the least change in viscosity with a given increase in temperature havethe highest viscosity index. An increase of 5 viscosity index units is a significant improvement. The slope of an oil is calculated as the quotient of the viscosity increase of the oil at 100 F. divided by that at 210 F. In this calculation oils having the lowest values for the slope exhibit the least change in crease of 0.5 in slope is a significant improvement. Many of the additives which hitherto have been proposed for improving lubricating oils increase the. viscosity index ofthe oil to an appreciable extent. However, some of the most effective of these additives, which are polymeric materials,

so tliat at the operating temperature "of the 17 Claims. (Cl. 252-515) A de-' 2 engine there will be only a small decrease in the viscosity of the oil. i

This invention has as an object an improved lubricating oil which possesses the extremely desirable combination of high viscosity index with a minimum thickening of the oil. Further objects reside in methods for obtaining these improved lubricating oils. Other objects will appear hereinafter. r

The above objects are accomplished by incorporating in lubricating oil a small proportion of an oil-soluble copolymer of an alkyl ester of an unsaturated aliphatic acid, which is either acrylic acid or an alpha-alkylacrylic acid, and an N- monohydrocarbon amide or" such an unsaturated aliphatic acid. Inthese esters and amides from which the copolymers are obtained, the ester alkyl group in theester contains from 4 13018 carbon atoms, and the hydrocarbon radical attached to the nitrogen in the N-hydrocarbon amide can be any alkyl, cycloalkyl, or aryl radical containing from to 18 carbon atoms. The sum of the carbon atoms in the alkyl and N-hydrocarbon radicals should be between 14 and 30 to provide the best solubility of the copolymer in mineral oil. As indicated previously the ester and amide components of the copolymer can be derived from either acrylic acid or an alphaalkylacrylic acid, that is from an acid of the formula where R is H in the case of acrylic acid or an alkyl group in the case of an alpha-alkylacrylic acid. The copolymers most useful for the present purpose are obtained when the ester and amide components are derived from acrylic acid or from an alpha-alkylacrylic acid Where R in the above formula is a lower alkyl group, i. e., an alkyl group of oneto three carbon atoms. The preferred copolymers are thus copolymers of where R is hydrogen or an alkyl radical of 1 to 3 carbon atoms, R is an alkyl radical of 4 to 18 carbon atoms, and R is a monovalent hydrocarbon radicalof 4 to 18 carbon atoms. The amide-nitrogen content of the copolymers useful in the practice of this invention is between 0.2% and 7.0% by weight of the copolymer.

Copolymers of N-arylacrylamides, and particularly of N-phenylmethacrylamide, are especially useful as the lubricant additives of the present invention since they are very effective in increasing the viscosity index and decreasing the slope value of a lubricating oil. Copolymers of N- alkylacrylamides in which the alkyl group contains from twelve to eighteen carbon atoms, and particularly N-octadecylmethacrylamide, are also especially effective in lowering the pourpoint of the lubricating oil at the same time they are increasing the viscosity index of the oils. Copolymers in which the alkyl group of the N -alkylacrylamide component is highly branched, e. g., N- l,1,3,3-tetramethylbutyl) methacrylamide. obtained by reaction of diisobutylene and methacrylonitrile in the presence of glacial acetic acid and concentrated sulfuric acid, followed by hydrolysis, are also especially effective additives for lubricating oils, since the branched chain imparts better solubility in hydrocarbon oils. copolymers in which the acrylic ester component is-an ester of technical lauryl alcohol are especially effective in the lubricating oil compositions of this invention, and are, therefore, the preferred modification.

The copolymers defined above are used in lubricating oils in amounts ranging from 0.1% to 10% of the weight of the oil. Usually amounts of from 1% to 5% are preferred, the optimum amount of any particular copolymer being dependent on the particular substituent groups in the ester and amide components of the copolymer, the particular type ofoil being treated, and the degree of increase in viscosity index desired in the oil. Lubricating oils containing the above proportions, i. e., 0.1% to %,of th se copo ymers are useful for hydraulic oils and for torque converter fluids.

The lubricating oils with which the copolymers defined above are effective viscosity index improvers include all types of oils obtained from petroleum, i. e., the paraffin base, naphthenic base and mixed base oils, andalso the ester type of lubricants, e. g., alkyl esters of aliphatic dicarboxylic acid such'as di-2-ethylhexyl sebacate.

The lubricating oils may also contain in solution or suspension conventional lubricating oil modiflers which impart other desirable characteristics to the oil, e. g., antioxidants, etc.

The copolymers may be incorporated in the oils by simply blending with stirring at ordinary temperatures, or, if desired, a mixture of oil and copolymer may beheated to elevated temperature, e. g., 100 to 130 0., wi h agitation, to form the compositions of this inv tion.

The alkyl acrylate/N -hydrocarboacrylamide copolymers employed in accordance with this invention can be prepared by the copolymerization of monomeric alkyl acrylates and N-hydrocarboacrylamides of the above-defined types by customary bulk or solution polymerization methods in the presence of known addition polymerization catalysts. Oxygen-yielding catalysts such as benzoyl peroxide and azo catalysts such "as alpha,alpha' azodiisobutyronitrile are suitable polymerization catalysts. The polymerization is usually carried out in an inert atmosphere, e. g., in an atmosphere of nitrogenor carbon dioxide, at temperatures ranging'from 30 to 150C;,-'depending on the catalyst used, and preferably at "temperatures'between 50 and 70 Ciwhn alpha;-

alp'ha'-azodiisobutyronitrile is used as catalyst. The preparation of polymers suitable for fusein v the lubricating compositions ofthis invention is 4 illustrated further by the following description of the copolymerization of a mixture of lauryl methacrylate and N-phenylmethacrylamide consisting of 15% by weight of the amide ingredient: A mixture of 17 parts of lauryl methacrylate, 3 parts of N-phenylmethacrylamide and 0.15 part of alpha,alpha-azodiisobutyronitrile is polymerized by heating for 2 hours in a flask held at 55 to 60 C. Stirring is efiected and an inert atmosphere is maintained by passing oxygen-free nitrogen through the mixture. The resulting polymer is clear and homogeneous in appearance and is completely soluble in hydrocarbon lubricating oils of both naphthenic and paraflinic types. The copolymers of methacrylanilide, i. e., N-phenylmethacrylamide, with alkyl esters of acrylic and methacrylic acids are more fully disclosed and claimed in applicant's copending application Serial No. 170,271, filed June 24, 1950, 111 e t NO. 1 3 issued February 12,

The N-phe'nylme thacrylamide used in the..polymerization described above is conveniently prepared as follows: To a cooled, preferably below 30 C., and stirred slurry of 186 parts of anil'ir'ie, 184.8 parts of sodium bicarbonate and 0.5 part of m-dinitrobenzene in 1000 parts of water is added, during the course of an hour, 228 parts of 'meth'acrylyl chloride. After standing overnight at roomv temperature the reaction mixture is filte'red. The solid reaction product is recrystallized from a mixture of equal parts by volume of water and methanol. There is obtained, after vacuum drying, 284 parts, 91% of'theory, of white crystalline N -phenylinethacrylamide, melting at 8 C.

Polymers 'of extremely high molecular weight are less desirable than similar copolymers of lower molecular weight because the high molecular weight copolymers cause an undesirable degree of thickening when added to the lubricating oil, and also because extremely high molecular weight copolymers are subject to greater changes in properties when subjected'to mechanical shear than is the case with lower molecular weight copolymers. For these reasons the copolymers best used in the practice of this invention range in molecular weight from about 200,000 to about 1,200,000, these being weight-average molecular weights determined by light scattering of polymer solutions. Intrinsic viscosities, determined in bromobenzene solution, should preferably be between 0.3 and 1.2. A'sa'mple which shows 'excellent properties as a lubricant additive has "a. weight-average molecular weight of 580,000 and an intrinsic viscosity in bromoben'zen "solution at F. of 0.74 and at 210 F. of 0.70. The molecular weight or degree of polymerization of the copolymer-can be controlled by regulating the polymerization procedure or by after-treatment of a high molecular weight polymer. For example, the degree of polymerization of the copolymer is reduced by polymerizing the comon'o- "mers in the prese'nce'of a'neutral white mineral "oil amounting to about 50% of the weight of the comonomers. The molecular Weight of "a "0'0- polymer too high in molecular weight to impart optimum properties to a lubricant can be reducedby milling'the copolymer ona two-roll differential speed-mill at 95 to F. Modifiers such-as antioxidants and/or mercaptans may be added during this'operation. I b

The invention is illustrated further by the 75 ingredients are expressed in parts by weight unless otherwise specified. Inthe'se examplesthe alkyl acrylate/N-hydrocarboacrylamide copolymers are blended with the lubricating oil by stirring theindicated proportionof copolymer with the oil, e. g., one part of .polymer with 49 parts of oil to give a composition containing 2% of copolymer, while warming the mixture to 100 to 130* C. The viscosities of the modified oil compositions are determined by standard methods at temperatures of 100 F. and 210 F. and the results are expressed in centistokes. The viscosity index is calculated by the method identified as A. S. T. M. method D567-41. The slope values for the oil compositions of this invention are calculated from the observed viscosities, in centistokes, of the unmodified base oil and the oil solution of the copolymer by means of the following equation:

Slope 6 from a commercial lauryl'alcohol obtained by reduction of coconut oil fatty acids, and having the following approximate composition:

, 1 Per cent C10H210'H '3,

C'12H25OH 61 C14H290'H 23 C16H33OH 11 CIBHMOH 2 TABLE I Lauryl methacrylate/N-phenylmethacrylamide copolymers (1.5%) in mixed base lubricating oil Viscosityin oopolymer centistokes Example No. 1 Viscosity S10 e Ester: imide Amide at Index p re 10 (by weight) Percent 1000 2100 F 90: 10 0. 87 20. 07 5.33 187 3. 08 85: 15 1. 31 19. 23 5. 40 193 2.66 :20 1. 74 17. 89 4. 99 197 2. 54 75:25 2. 18 16. 63 4. 70 203 2. 25 70:30 2. 61 i3. 3. 54 155 2. 15 1 60:40 3. 15.15 3. 67 149 3. 31 Lauryl methacrylate... 21. 38 4. 96 168 4. 25 N-phenylmethacrylamide (complete y insoluble in oil) Control oil (no modified. 12.53 2. 88 82 1 Incompletely soluble in the oil.

phenylmethacrylamide coploymers containing different proportions of the two components in 3% (by weight) concentration in a solvent extracted paraffin base lubricating oil. Also included in this table for purposes of comparison are the viscosity data for the unmodified oil and for the same oil modified with homopolymers of lauryl methacrylate of different molecular weights.

TABLE II Lauryl 'methacrylate/N phenyltnethacrylamide copolymers (3.0%) in solventewtracted paraf fin base lubricating oil Viscosity in oopolymer centistokes- Example N0. Viscosity Slope Esterzlmide Amide at at Index re. 10 Q o (by weight) Percent 100 210 F 5 97. 7:2. 3 0. 2 106. 7 17. 0 141 5. 89 6 95: 5 0. 43 101 17. 4 145 5. 02 92. 5:7. 5 0. 65 97. 8 18. 3 148 4. 33 8 90: 10 0. 87 99. 8 19. 0 149 4. 24 85: 15 1. 31 96. 2 l9. 3 150 3.91 Lauryl Methacry1ate 0 102 14. 9 136 6. 53 do 0 131 19. 5 138 6. 52

C o n t r 01 oil (11 o m o d i ficr) 46. 5 6. 5 98 The lauryl methaciylate/N-octadecylmethacrylamide copolymers' of Examples l0, l1 and 12 are also effective viscosity index improvers in ester lubricants. Examples of 13, 14 and 15 illustrate the use of these three copolymers in 2%, by weight, concentration in di-Z-ethylhexyl sebacate. The details of the compositions and the viscosity data for these examples are summarized in Table IV. There are also included in Table IV for purposes of comparison the corresponding data for the unmodified di-2-ethyl- TABLE IV Lauryl "m ethacrylate/N-octadecylmethacrylamide copol ym'ers "(2 in di-z-ethylh'exyl sebacate i Viscosity in F Oopolymer "centistokes- Example N o. viscosity 810 e Ester: kmide Amide at at Index p re 10 K (by weight) Percent 80:20 0.83 :56 i s. 52 176 3.45 60:40 1. 66 24. 96 7. 25 183 3. 14 2. 49 19. 06 5. 89 198 2. 49 Control, no modlfler 12. 3. 36 156 Laurylmetbacrylate. 28. 29 7. 60 176 3. 67 N-oetadecylmethactylamide 15. 66 4. 07 184 4. l0

modified with the homopolymers of lauryl methacrylate and N-octadecylmethacrylamide.

TABLE III hexyl sebacate lubricant and compositions containing the same proportions (2%) of homo- Lauryl metbacrzilate/N-octadecylmethacrylamide copolymers (2.0%) in SAE 10 W naphthenic base lubricating oil Viscosity in 'Cwolymer centistokes- Exemple =No. ii ggg Slope EstenAmide Amide at at 100 F 21o" F (by weight) Percent :20 0.83 61. 42 11.05 146. 2 5. 22 60:40 .1. 66 43. 61 8.44 150. 2 .4. 34 v 40560 "2. 49 34. '40 6x85 151. 5 j 3. 59 Laurylmetbacrylate. .55. 50 1 .9. 08 136 I 6.05 N octedecylmethacrylamide 29. I1 -4. 66 74 6. 40 Control oll '(n'o modifier)- '23. 28 13. 75 12 polymers of lauryl methacrylate and 'N-oc'tadecylmethacrylamide.

Examples 16,, '17, '18, 19, 20., '21 and 22 illustrate the use of other copolymers of alkyl esters of an acrylic acid and N-hydrocarbon amides of an acrylic acid of the previously defined types as modifiers for the mixed base lubricating oil used in Examples I to IV. These examples are summarized in Table V.

TABLE V Alkyl methacryZate/N-hydrocarboacrylamide copolymers (1.5 in mixed base lubricating oil Viscosity in Copolymer centistokes :Example N0. lii t e c Slope v 'Ratio Amide N, at 100 at 210 Ingredlents by wt. Percent F. F.

LaurylmethecrylatelN- :16 1.20 20.85 5.85 18 p-tolyl-m'ethacrylamide. 9 2 Lauryl'methacrylate/N- 75:15:10 1. 31 18. 84 4. 92 187. 5 3. l0

pbenyl-methacrylamide/ styrene. .1 InurylacrylatelN-phenyl- 85:15 1.31 19.56 4.85 170. 2 3. 57

.metbacrylamlde.

' TABLE V-Oontinued v Viscosity in Copolymer centistokes Example No. Viscosity Slope Index Ratio, Amide N, at 100 at 210 Ingredients by Wt. Percent F. F.

LsurylacrylatelN-phenyl- 85:15 1.43 18.56 4.35 165.0 4.11

acrylemide. p

Octyl methacryIate/N- 85:15 1.31 25. 44 13.03 184.2 1.27

phenyl-methacrylamide.

n-Hexyl methacrylate/ 50:50 3.55 16.49 4.19 181.0 3.02

N-(l; 1, 3, 3-tetramethylbutyD-methacrylamide.

22. n-Hexyl methacrylate/ 75:25 1.77 18.64 4.87 187.9 3.07

N-(l, 1, 3, S-tetramethylbutyD-metha crylamide. 1

Control, no modifier 12. 53 2.88 82 N-(l, 1, 3, 3-tetramethylbutyb- 7.1 18.63 4.35 164.1 4.15

methacrylamide Q l 1 incompletely soluble in the oil.

and of N-phenylmethacrylamide monomer is copolymerized in the presence of alpha,alpha'- azodiiso'butyronitrile and one part of a low viscosity, highly acid-treated white oil from a Pennsylvania crude stock per two parts of monomering'redient for hours at to C. in an atmosphere of carbon dioxide. The resulting polymer is incorporated in 1.5% concentration in a mixed base lubricating oil of the type used in Examples 1 to 4. The viscosity data for these two modified polymers are tabulated in Table VI together withthe corresponding data for the unmodified copolymer (Example 23). I a

TABLE VI Modified lauryl methacrylate/N-phenylmethacrylamide :15) copolymers (1.5%) in mixed base lubricating oil N-phenylmethacrylamide prepared from a 85 15 ratio of monomers is milled for seven minutes on a two-roll differential speed mill at to F. with 0.25% added dodecyl mercaptan and 0.25% phenyl-beta-naphthylamine. The milled copolymer is incorporated, in 1.5% concentration, in the mixed base oil of the type used in Examples 1 to 4. In Example 25 a The copolymer ofilauryl 'methacrylate and N-phenylmethacrylamide may be used tov convert a base oil to an oil having viscosities and a viscosity index intthe" range acceptable for torque converter'fluids, and, moreover, this can be efiected by using a lower concentration of the given polymer than of commercial viscosity- 1 index improvers. The value of these copolymers for this ur ose is shown h mixture of 85% of lauryl methacrylate monomer 60 p by t e followmg Table TABLE VII Polymer, Viscosity of oil- Oil wt. percent vgggg Slope 210, SUS 210, cs. 100, cs.

Base on (low viscosity Mid-Conc 40.14 4. 24 23.16 93 tinent). Base Oil-I-Commercial viscosityindex lmprover A. 2. 84 55.86 9.02 47.15 5.00 Base Oil+00mmercial viscosity- 4. 30 55. 99 9. 06 47.28 150 5.00

index improver B. a Base OiH-Copolymer of 85 parts 1. 75 54. 28 8. 56 36.32 3. 09 laurylmethacrylate and 15 parts i I I N-phenylmethacrylamide.

1 as solutions of the polymer in oil.

In the above table the heading A. I. of the first column represents the active ingredient. In connection with this column it may be noted that the commercial viscosity improvers are sold In the remaining headings SUS refers to Saybolt. Universal seconds, and cs. to centistokes. Improvers A and B are commercial products and are oil solutions of lauryl methacrylate polymer which differ in the molecular weight of the polymer.

The present requirements for a torque converter fluid for automotive transmissions and the like are a viscosity index of at least 150, with a SUS viscosity at 210 F. of 54-56 seconds. It will be apparent from the data given in the above table that the polymers: used in the practice of this invention are so efficient that only small amounts are needed to arrive at the desired viscosity range, and that the viscosity index so obtained is very high.

In addition to the specificcopolymers mentioned in the examples, other copolymers of alkyl acrylates and N-hydrocarboacrylamides having the composition defined previously are operable in the lubricating oil compositions of this invention. Specific examples'of suitable alkyl radicals in the alkyl acrylate component include butyl, hexyl, octyl, decyl, dodecyl, tetradecyl, hexadecyl and octadecyl radicals. As indicated previously acrylates containing four to eighteen carbon atoms must be employed in the copolymers used in this invention. When the hydrocarbon group of the N-monohydrocarbon acrylamide component of the copolymer is an aryl group or a straight chain alkyl group, the alkyl group of the alkyl acrylate component preferably contains twelve to eighteen carbon atoms since copolymers of this type are more soluble in hydrocarbon oils than copolymers of acrylates having four to ten carbon atoms in the alkyl radical. On the other hand,

when the hydrocarbon group in the acrylamide component of the copolymer is a highly branched alkyl group such as the 1,1,3,3-tetramethy1butyl group, the lower alkyl acrylates, i. e., those in which the alkyl groups contain four to ten carbon atoms are preferred, since the high branching of the alkyl group in the amide component imparts better oil solubility to the copolymer than straight-chain derivatives of the same carbon content. It is not necessary that the alkyl radical in the acrylate component of the copolymer be derived from a pure alcohol. Technical grades 01' alcohols having an average carbon content within the range. specified above are entirely suitable. Alkyl radicals derived from the commercially available alcohols such as the technical lauryl alcohol obtained by reduction of the fatty acids in coconut oil, and the analogous products made by hydrogenation of carbon monoxide, are especially suitable. Specific examples of the hydrocarbon radicals attached to the amide nitrogen of the acrylamide component of the copolymer defined previously include alkyl radicals such as t-butyl, hexyl, octyl, decyl, tetradecyl, octadecyl; cycloalkyl radicals such as cyclohexyl; and aryl radicals such as phenyl,

p-tolyl, o-tolyl, and naphthyl (however, the latter tends to give products of lower monomer and polymer solubility than does the pre- I ferred phenyl radical). More specific illustrations of other copolymers which can be used in the oil compositions of this invention include: octadecyl acrylate/N-phenylacrylamide, isobutyl 12 methacrylate/N-(1,l,3,3-tetramethylbutyl) acrylamide, n-decyl a-(lfi-PIOIJYI) acrylate/N-dodecylacrylamide, lauryl methacrylate/N-cyclohexylacrylamide, lauryl acrylate/N-phenyl-a-(n-propyl) acrylamide, and lauryl methacrylate/N-tbutylmethacrylamide.

As mentioned previously, the proportion of the acrylate ester and the acrylamide components of the copolymers operable in this invention must be such that the amide-nitrogen content of the copolymer is between 0.2 and 7.0% by weight. The particular amide-nitrogen content which is selected for best results depends on the particular type of hydrocarbon group in the acrylamide component of the copolymer. Thus, copolymers of acrylamides in which the Nhydrocarbon substituent is an aryl or straight-chain alkyl group are most effective as additives for lubricants when the amide-nitrogen content is between 02 and 2.2%. On the other hand, when the hydrocarbon substituent on the acrylamide is a highly branched alkyl group higher amide-nitrogen contents are preferred, copolymers of this type containing 1.5 to 3.6% amidemitrogen being very efiective.

Furthermore, the particular monomeric ingredients and their proportions, and the polymerization conditions are selected so that the resulting polymer is homogeneous and is soluble in the lubricating oil. In order to obtain homogeneous copolymers, it is necessary to employ a N- hydrocarboacrylamide which is soluble in the monomeric ester component at the polymerization temperature. If an amide monomer which is not completely soluble in the ester monomer is used, the copolymer obtained contains some amide homopolymer which is insoluble in lubricating oil. For example, N-phenylacrylamide (15%) is not completely soluble in lauryl acrylate or in lauryl methacrylate at 60 C. However, at 90-95 C. solution is complete; and homogeneous, clear, water-white, oil-soluble copolymers are obtained from this particular amide using a catalyst chosen for effectiveness at the higher temperature, e. g., 1,1-azodicyclohexanecarbonitrile. Also, the higher N-arylacrylamides, e. g., N- alpha-naphthylmethacrylamide, have poor solubility in lauryl methacrylate at 60 C.

From the viscosity data obtained with the lubricating oil compositions of the examples, it is evident that the copolymers of alkyl acrylates and N-hydrocarboacrylamides impart an unexpected improvement in viscosity characteristics to lubricating oils containing them in comparison with the same properties possessed by oil compositions containing homopolymers of the alkyl acrylates or of the N-hydrocarboacrylamides. This makes the oil compositions of this invention especially valuable for lubricating purposes and as hydraulic oils and torque converter fluids. Furthermore, lubricating oil compositions containing the copolymers of this invention possess better viscosity characteristics than the same oil containing commercially available modifiers such as the alkyl methacrylates and the alkylated polystyrenes. Thus, oils having higher viscosity indices and lower slopes can be obtained with the aid of preferred copolymers of this invention than can be obtained at an equal degree of thickening a substantial decrease in the slope of an oil composition.

As many apparently widely difierent embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that this invention is not limited to the specific embodiments thereof except as defined in the appended claims.

The invention claimed is:

1. A lubricating oil containing from 0.1% to by Weight of an oil-soluble copolymer of an alkyl ester, in which the alkyl ester group contains from four to eighteen carbon atoms, of an unsaturated aliphatic acid, and a N-hydrocarbon amide of an unsaturated aliphatic acid in which the hydrocarbon radical attached to the nitrogen atom has from four to eighteen carbon atoms, said unsaturated acid in each instance being selected from the group consisting of acrylic acid and alpha-alkylacrylic acids in which the alkyl group contains from 1 to 3 carbon atoms,.the amide-nitrogen content of said copolymer ranging from 0.2% to 7.0% by weight.

2. The lubricating oil defined in claim 1 in which said N-hydrocarbon amide is an N-arylacrylamide, and the amide-nitrogen content of said copolymer is from 0.2% to 2.2% by weight.

3. The lubricating oil defined in claim 1 in which said N-hydrocarbon amide is N-phenylmethacrylamide, and the amide-nitrogen content of said copolymer is from 0.2% to 2.2% by weight.

4. The lubricating oil defined in claim 1 in which said N-hydrocarbon amide is an Nalkylacrylamicle in which the alkyl group contains from four to eighteen carbon atoms.

5. The lubricating oil defined in claim 1 in which said N-hydrocarbon amide is N-(1,1,3,3- tetramethylbutyl) methacrylamide, and the amide-nitrogen content Of said copolymer ranges from 1.5% to 3.6% by weight.

6. The lubricating oil defined in claim 1 in which said alkyl ester is the ester of lauryl alcohol with said unsaturated aliphatic acid.

7. A lubricating oil containing from 0.1% to 10% by weight of the copolymer of N-phenylmethacrylamide and the ester of lauryl alcohol with an acid selected from the group consisting of acrylic acid and alpha-alkylacrylic acids in which the alkyl group contains from 1 to 3 carbon atoms, the amide-nitrogen content of said copolymer ranging from 0.2% to 2.2% by weight.

8. The lubricating oil defined in claim 7 in which said lubricating oil contains said copolymer in amount of from 1% to 5% by weight.

9. A lubricating oil containing from 0.1% to 10% by weight of the copolymer of N-phenylmethacrylamide and lauryl methacrylate, the amide-nitrogen content of said copolymer ranging from 0.2% to 2.2% by weight.

10. The lubricating oil defined in claim 9 in which said lubricating oil contains said copolymer in amount oi from 1% to 5% by weight.

11. A lubricating oil containing from 0.1% to 10% by weight of the copolymer of N-(1,1,3,3- tetramethylbutyl) -methacrylamide and the ester of hexyl alcohol with an acid selected from the group consisting of arcylic acid and alphaalkylacrylic acids in which the alkyl group contains from 1 to 3 carbon atoms, thev amide-nitrogen content of said copolymer ranging from 1.5% to 3.6% by weight.

12. The lubricating oil defined in claim 11 in which said lubricating oil contains said copolymer in amount of from 1% to 5% by weight.

13. A lubricating oil containing from 0.1% to 10% by weight of the copolymer of N-(1,1,3,3- tetramethylbutyl)methacrylamide and hexyl methacrylate, the amide-nitrogen content of said copolymer ranging from 1.5%. to 3.6% by weight.

14. The lubricating oil defined in claim 13 in which said lubricating oil contains said copolymer in amount of from 1% to 5% by weight.

15. A lubricating oil containing from 0.1% to 10% by weight of the copolymer of N-octadecylmethacrylamide and lauryl methacrylate, the amide-nitrogen content of said copolymer ranging from 0.2% to 2.2% by weight.

16. A lubricating oil containing from 0.1% to 10% by weight of the copolymer of N-phenyl methacrylamide and lauryl acrylate, the amidenitrogen content of said copolymer ranging from 0.2% to 2.2% by weight.

17. A lubricating oil containing from 0.1% to 10% by weight of the copolymer of N-phenylmethacrylamide and octyl methacrylate, the amide-nitrogen content of said copolymer ranging from 0.2% to 2.2% by weight.

WILLARD E. CATLIN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,311,548 Jacobson Feb. 16, 1943 2,387,501 Dietrich Oct. 23, 1945 2,584,968 Catlin Feb. 12, 1952

Claims

1. A LUBRICATING OIL CONTAINING FROM 0.1% TO 10% BY WEIGHT OF AN OIL-SOLUBLE COPOLYMER OF AN ALKYL ESTER, IN WHICH THE ALKYL ESTER GROUP CONTAINS FROM FOUR TO EIGHTEEN CARBON ATOMS, OF AN UNSATURATED ALIPHATIC ACID, AND A N-HYDROCARBON AMIDE OF AN UNSATURATED ALIPHATIC ACID IN WHICH THE HYDROCARBON RADICAL ATTACHED TO THE NITROGEN ATOM HAS FROM FOUR TO EIGHTEEN CARBON ATOMS, SAID UNSATURATED ACID IN EACH INSTANCE BEING SELECTED FROM THE GROUP CONSISTING OF ACRYLIC ACID AND ALPHA-ALKYLACRYLIC ACIDS IN WHICH THE ALKYL GROUP CONTAINS FROM 1 TO 3 CARBON ATOMS, THE AMIDE-NITROGEN CONTENT OF SAID COPOLYMER RANGING FROM 0.2% TO 7.0% BY WEIGHT.