US2999067A - Synthetic oil additive - Google Patents

Description

2,999,067 SYNTHETIC OIL ADDITIVE Thomas F. Banigan, Jr., Walnut Creek, Calif., assignor to 'Iidewater Oil Company, San Francisco, Calif., a corporation of Delaware 1 No Drawing. Filed Nov. '27, 1956, Ser. No. 624,493 9 Claims. (Cl. 252F-49.8)

This invention relates to a new family of chemical compounds comprising a group of linear polymeric esters, particularly useful as viscosity-index improvers for certain types of synthetic lubricating oils. The invention also relates to synthetic lubricating oil chosen from the group consisting of the diesters and the phosphate esters having an improved viscosity index as a result of addition of compounds of this invention. The invention further relates to a method for producing the new family of compounds and to a method for improving the viscosity indices of certain synthetic ester lubricating oils.

In recent years synthetic lubricants have been developed in an attempt to meet the stringent requirements of new engines, including jet aircraft engines. These are superior to hydrocarbon oils in their ability to withstand temperatures as high as 450 without breaking down. They also flow at 65 F. and possess numerous other qualities enabling them to perform well under diflicult conditions.

One class of such synthetic lubricating oil is usually referred to as diesters. Examples are the (2-ethylhexyl) diesters, such as dioctyl azelate, dioctyl sebacate, dioctyl glutarate, and dioctyl adipate. In addition there are various sebacates such as di-(methylethyl) sebacate, di-(3-rnethylbutyl) sebacate, di-(Z-ethylbutyl) sebacate, di-(l,3-dimethyl butyl) sebacate, di(undecyl) sebaeate, di- (tetradecyl) sebacate, and di(heptadecyl) sebaoate. There are corresponding adipates, azelates, and glutarates. There are other diesters such as 1,6-hexamet-hylene glycol di-(Z-ethylhexanoate), tri-ethylene glycol di-(Z-ethylhexanoate), and di-[2-(2'-butoxyethoxy)ethyl] adipate. There are also useful phthalate diesters, such as dibutyl phthalate (di-n-butyl orthophthalate). All these compounds may be grouped as diester synthetic lubricating oils, or aliphatic branched-chain diesters that remain liquid in the temperature range from about -30 F. to 300 F.

Another type of synthetic oil to which this invention relates comprises the phosphate esters such as tributyl' phosphate and tricresyl phosphate.

The diester synthetic lubricating oils as a class possess high viscosity indices. However, some of the lowermolecular-weight members such as dioctyl adipate tend to be relatively deficient in this property, thus eliminating them from consideration as jet engine lubricants. It is the lower-molecular-weight diesters which offer the greatest promise for the future development of lubricants which will remain fluid at extremely low temperatures. The phosphate esters have outstanding lubricity characteristics, excelling most other classes of synthetic oils. Low viscosity index is probably the chief obstacle to their wider use as specialty lubricants. It has therefore been a problem to produce an additive which would increase the viscosity index in these two groups of synthetic oils, without causing trouble elsewhere. To do so is one of the objects of this invention, which accomplishes it by means of a new family of chemical compounds.

Another object of the invention is to provide a viscosity index improver such that the improvement takes place when only a small quantity of the improver is added, thereby not interfering with the other qualities of the synthetic lubricant and holding costs down.

2,999,067 Patented Sept. 5, 1961 ice The new compound broadly The new compounds of the present invention comprise a new class of linear polymeric esters, the class being delined by the general formula:

in which G represents a polypropylene glycol group of at least 7 alkylene radicals joined linearly by ether oxygen atoms;

A represents an organic dibasic acid radical;

n is a number lying between 0.875 and 1.111;

x is an integer corresponding to the average degreeorf polymerization; and

R and R each represent an end group either or both of which may the a hydroxy radical, a carboxy radical, or an alkyl or aryl group.

The chemical nature of the end groups R and R with respect to the functioning of these polymers as viscosity index improvers, appears secondary in importance to several other factors, including: (a) the molecular weight of the polypropylene glycol, (b) the dibasic acid used, and (c) the degree of polymerization. However, there have been indications that the introduction of relatively nonpolar end groups helps to protect the polymer from haze and color formation during preparation and is therefore preferable to the hydroxy and carboxy end groups.

The polypropylene glycol group (G) Polymers prepared from polyoxyalkylene .glycols composed of alkylene radicals of less than 3 carbon atoms, such as polyethylene glycols, usually proved to he water soluble and were invariably insoluble in the synthetic lubricating oils disclosed herein.

However, polymers prepared from polypropylene glycols have displayed the requisite solubility in the synthetic lubricating oils when said polypropylene glycols contained 7 or more oxypropylene units. Optimum activity as a viscosity-index improver was noted with a polymer prepared from polypropylene glycol possessing 35 oxypropylene units. Only slightly less effective was the polymer made from a glycol with 17 oxypropyleue Still soluble in synthetic lubricants, but much less effective, was the polymer made using a glycol with 8 oxypropylene units. The use of tripropylene glycol (3 oxypropylene units) gave rise to an insoluble polymer. The tests indicate that there should be at least 7 oxypropylene groups, and there may he as many as 35 or 40.

T he dibasic acid radical (A) Various dibasic organic acids may be used. Excellent results are obtained where A is the oxalyl radical, but carbonyl, succinyl, adipyl, sebacyl, isophthalyl, orthophthalyl, and terephthalyl radicals have also given good compounds.

Polymers prepared by reaction of polypropylene glycols (containing 7 or more oxypropylene units) with dibasic acid chlorides (see the description of the method) ranging from oxalic to sebacic have all been shown to be soluble in the synthetic oils claimed herein. However, the polymers prepared using oxayl chloride have invariably been the most potent viscosity index improvers as well as possessing the least color and haze. The somewhat greater reactivity of oxalyl chloride cornpared to the higher acid chlorides enables the use of lower reaction temperatures, a condition which favors the production of a very high polymer possessing a of color and haze.

The ratio of glycol to dibasic acid (G/A or n) Optimum results are usually obtained where equimolar ratios of glycol and acid halide are used. This favors a high degree of polymerization yielding a polymer with 4 However, the use of non-polar end groups, those in (4) above, does give more clarity and freedom from haze and color formation. Typical compounds are shown in Table I below.

TABLE I Chemical composition of synthetic polyoxypropylene esters Polymer R R: A G I Viscos- G/A ities b #1 hydroxy hydroxy terephthalyln PPG1025 300 1.111 #2 do -do orthophthalyl. PPG1025. 475 1,111 #3 polypropylene glypolypropylene gly- ..do PPG1025 1,500 0.875

col ether 65 4 col ether 65 d #4 hydroxy carboxyoxalyl PPG 1,200 1.000 #5.- I1butyl.. n-butyl d PPG2025 00,000 0.875 #6.- ..do do do TPG 5,000 0.950 #7. do do r1n PPG1025-.-. 20.000 0.875 #8 hydroxv carboxy adipyl PPG2025 4,200 1.000

I PPG=polypropylene glycol, TPG=tripropylene glycol, and the numbers refer to the average molecular weight, from which number of oxylakylenc units can be calculated.

b Viscosities at 210 F. in seconds Saybolt Universal are a function of chain length.

* G/A refers to the ratio of glycol to dibasic acid.

Sold commercially by Carbide and Carbon Chemical Company under the trade-name oi Ucon LB-tlfi, the 65 referring to the Saybolt Universal viscosity at 100 F.

great capacity for improving the viscosity index of certain synthetic oils. Polymers useful for this purpose can be obtained where the glycol to acid halide ratio lies within the range 0.875 to 1.111 and with end groups R and R from any of the four choices enumerated below.

The degree of polymerization (x) It is difiicult to determine x precisely because of the rather high molecular weight of the polymers; moreover, 1: appears to be capable of variation over wide limits depending on the molecular weight of the oxyalkylene glycol used in the polymerization. A smaller x can give a useful polymer when a high molecular weight glycol is used such as polypropylene glycol 2025 (a propylene glycol polymer having an average molecular weight of 2025) whereas a larger x is needed for a lower molecular weight glycol. Viscosity has been found useful as a guide to the required molecular weight. For example, polymers ranging in viscosity (210 F.) from about 250 to 13,000 ccntistokes, and especially those from about 4000 to 13,000 centistokes, have shown activity as viscosity index improves. Polymers of this same type with even higher viscositics should also prove useful if they posses the requisite solubility and shear stability characteristics (extremely high molecular weight polymers are often deficient in such properties).

The end groups R and R R and R will generally be:

1) An hydroxy radical in both cases if excess polyoxyalkylene glycol was used in preparation,

(2) A carboxy radical in both cases if excess dibasic acid was used,

(3) One hydroxy and one carboxy radical, respectively, if equimolar reagent ratios were used, or

(4) An alkyl or aryl group, if excess dibasic acid dihalide is used to produce a polymer possessing terminal acyl halide atoms capable of further condensation reaction as with an alcohol or phenol, such as methanol, ethanol, n-butanol, ethylene glycol monoethyl ether, diethylene glycol mono-n-butyl ether, polypropylene glycol monomethyl ether, tripropylene glycol mono-n-butyl ether, polypropylene glycol 425 mono-n-butyl ether, phenol, paracrcsol, and nonylphenol.

As stated earlier, the end groups R and R are rela tively unimportant, merely a necessary chemical fact.

Some important qualities of each of these compounds are shown in Table II, the number assigned each polymer remaining the same through all tables and examples in this specification.

TABLE II Analytical data of synthetic polymers Polymer Acid Noe Sap. No. Vis. 210 Color 1 Acid N0.as in ASTM-D974-55T.

e Viscosities at 210 in Saybolt; Seconds Universal. 6 Col0r-ASTl\iD-l5545T.

Methods of preparing the polypropylene esters Two preferred methods of preparation may be used: (1) ester exchange and (2) reaction of glycols with dibasic acid dichlorides. The second method is an excellent one for research work, with high yields of high molecular weight polymers with minimum effort, while the first method uses cheaper and less reactive intermediates and is therefore better suited to commercial manufacture. Examples of each type follow.

The two preferred methods are aspects or embodiments of a single broad concept, namely, that of reacting polypropylene glycol with a dibasic acid derivative. The dcrivative is preferably chosen from the group consisting of the dibasic acid diesters and the dibasic acid dichlorides.

FIRST METHOD: ESTER EXCHANGE When the dibasic acid diester is used in the method of preparing these polypropylene glycol esters, the reaction takes place in the presence of a basic catalyst, such as sodium methylate. Preferably, the reaction is conducted in an inert atmosphere, heat being applied so that the temperatures lie in the range between C. and 200 C. Methyl alcohol is formed as a by-product but may easily be removed. Preferably, the reagents are diluted with some suitable solvent, such as xylene, to prevent sublimation of the dibasic acid diester. The following example of the first method (ester exchange) follows.

Example l.--Preparation of poly [polypropylene glycol 1025 (])-terephthalate (9)] (polymer #1) by ester exchange The reaction was conducted in a 1-liter, 3-necked, round-bottomed flask equipped with a stirrer, a thermometer and a condenser with water trap, and provided with a nitrogen atmosphere. The reagents proved to be miscible at about 100 C. but further heat caused the terephthalate to sublime. Therefore, the contents were cooled, diluted with 100 ml. of xylene, mixed with 5 g. of sodium methylate, and heated slowly to 170175 C. After three hours of refluxing 19.5 ml. of methanol was removed azeotropically. Vacuum was then applied and the temperature raised gradually to 200 C. to remove the solvent and force the reaction toward completion. The prodnot was obtained as 317 g. (97% theor.) of a straw colored resin. The crude polymer was purified by dilution with three parts of pentane, followed by charcoal and clay treatment and filtration. On evaporation of the pentane from the filtrate the polymer was obtained as 291 g. of very pale viscous oil.

The polymer exhibited the properties tabulated in Tables I and 11 under polymer #1. Also it had a refractive index 11 of 1.4664 and a specific gravity (sp. gr of 1.04.

SECOND METHOD: REACTION OF GLYCOLS WITH DIBASIC ACID DICHLORIDE Broadly speaking, the second method, that of reaction of glycols with dibasic acid dichlorides, is carried on in the presence of an acid acceptor, such as. pyridine or tributyl amine. Since the dichloride radical is the one to be removed, a still more accurate designation of the acid acceptor would be to say that it is an HCl acceptor. This reaction also forms a by-product, the-hydrochloride of the HCl acceptor, such as pyridine hydrochloride.

This reaction does not require a high temperature, and in fact may take place at low temperatures, around 5 to C. To insure completion of the reaction, the temperature may be gradually increased up to about as high at 85 or 90 C.less than 100 C. It has. been found preferable, though not essential, when using this method, to remove all the water by means of a trap prior to the halide addition, because such removal gives rise to a higher degree of polymerization. The following examples illustrate this second method.

Example 2.Preparation of poly[polypropylene glycol 1025 (7)-orth0phthalate (8).-p0lypr0pylene glycol ether 65 (2)] (polymer #3) by reaction of glycol with dibasic acid dichloride Another way of stating the formula of this composition is O O H CH- O laaaaollt- Jonah H I! where m is about 3 and n is about 17'.

0 \il H'll b The orthophthalyl' chloride diluited with an equal volume of benzene was added dropwise to a stirred solution of the glycol and 47 g. of pyridine dissolved in ml. of dry benzene. The temperature was held at 10 C. by external cooling. Reaction was indicated by copious salt formation (pyridine hydrochloride). The polypropylene glycol ether (Carbon and Carbide Chemical Company Ucon LB .65) was mixed with 18 g. of pyridine and 50 ml. of benzene and was introduced dropwise after the chloride was in. The reaction mixture was diluted with additional benzene and stirred for about three hours at temperatures of 2545 C. The polymer solution was then filtered from the by-product pyridine hydrochloride, decolorized with charcoal and super eel, refiltered, and solvent-evaporated to give 352 g. of yellow viscous resin.

In addition to the properties given in Tables I and II, the following properties were found for polymer #3: Refractive index 11 of 1.4689, viscosity at F. of 6875 Saybolt Universal Seconds, and a viscosity index of 124.

Example 3.Prepararion of Poly[polypropylene glycol 2025 (1)-oxalate(1)] (polymer #4) by reaction of glycol with dibasic acid dichloride The glycol, molecular weight of 2025, and pyridine were mixed together with ml. of dry benzene, placed in a reaction flask and cooled to 5 C. The ox-alyl chloride in an equal volume of benzene was then added dropwi'se during one hour to the stirred reaction mixture held at 5-10 C. An additional 50 ml. of benzene was added, and stirring continued as the temperature was gradually raised to about 85 C. The reaction mixture was refluxed for three hours and allowed to stand overnight. The product was thinned with additional benzene and filtered to remove pyridine hydrochloride. The solvents were removed under vacuum with the aid of a nitrogen bubbler to yield 290 g. (94% theor.) of virtually colorless viscous resin. I

In addition to the properties noted in Tables I and II, the refractive index n was 1.4522.

Example 4'.-Preparation of poly [polypropylene glycol 2025 (7)-oxalate(8)-n-butyl(2)]'(polymer #5) by reaction of the glycol with the dibasic acid dichloride and with n-butyl end groups added 9 Another way of expressing the formula of this composition is wherein n averages about 34.

The glycol, pyridine and 200 ml. of benzene were refluxed until a total of 0.5 ml. of water had been removed by means of a trap. (This exhaustive removel of water gave rise to a higher degree of polymerization than in Example 3.) The oxalyl chloride in benzene was added dropwise to the cooled, stirred solution as before. Extreme viscosity of the reaction mixture necessitated several dilutions with benzene during the reaction period. The temperature was gradually elevated to 85 C. and then cooled to 40 C. At this point a mixture of n-butyl alcohol and pyridine was added dropwise. Stirring was continued and the contents allowed to stand overnight. The mixture was diluted with 750 ml. of n-heptane and filtered. The filtrate was charcoal treated, filtered and solvent-evaporated to yield 301 g. (95% theor.) of extremely viscous pale yellow resin.

Example 5.-Preparati0n of poly[tripr0pylene glycol (I9)-oxalate(20)-n butyl (2)] (polymer #6) by the method of Example #4 This reaction was conducted according to the directions outlined for the preparation of polymer #5. All traces of water were removed by azeotropic distillation as before. The polymer was obtained as 99 g. (97% yield) of a very viscous light amber resin.

Example 6.--Preparation of poly[polypropylene glycol 1025 (7)-0xalate(8)-n-butyl (2)] (polymer #7) by the method of Example #4 3 The reaction was conducted essentially according to directions outlined for the preparation of polymer #5.

Pyridine hydrochloride (by-product) formed copiously at the initial reaction temperature of 10 C. As the solution viscosity remained low compared to earlier preparations of oxalate polyesters, external heat was applied to force the reaction. A reaction temperature of 85 C. was held for about 3.5 hours following addition of the adipyl chloride to the stirred glycol-benzene-pyridine solution. No noticeable increase in solution viscosity occurred after about three hours of refluxing. The product resin was isolated as before to yield 309 g. (98% theor.) of viscous straw'colored polymer. This resin showed a greater tendency toward mineral oil solubility than did corresponding oxalates. However, it is still deficient in this property.

Use of the polymers of this invention as viscosity index improvers Representative polymers of this invention were evaluated as viscosity index improvers in various mineral oil stocks and in four of the principal classes of synthetic lubricating oils including (a) diesters, (b) polyglycol ethers, (c) silicones, and (d) phosphorous compounds. The first thing tested was their solubility in the various oils, shown in Table III.

As Table III shows, these polymers had only limited solubility in the mineral oil stocks including both solvent pale and bright stocks, so they could not be used therein. They appeared to be completely insoluble and hence without efiect on the silicone oils tested. The polymers were entirely miscible with the polyglycol ethers but later research showed that they had no effect on the viscositytemperature characteristics of this class of synthetic oils.

The new polymers were very soluble in the diester oils and exhibited high viscosity index activity, comparable and often better than that observed with the best available commercial VI improvers.

The excellent performances of some of these polymeric esters as viscosity index improvers for diester synthetic Reagents Wt" M0195 oils are shown in the following Table IV.

grams Polypropylene glycol 1025 150 0. 146 Oxalyl chloride 21.2 0.167 TABLE m n-Butyl alcohol 1 0.162 Pyridine 36.5 0. 461 Qualitative solubzhties of synthetzc polymers Mineral Oil S thetl Oils This reaction was earned out according to directions Stocks W e I for polymer #5 with special care again directed to trace P0X ymer water removal. The polymer was obtained as 158 g. 150 Phos- Polyale right Diesters Silicones phato glycol (99.5 ,0 theor.) of very viscous light brown resin. took Esters Esters Example 7.Preparation. of p0ly[polypr0pylene glycol PS 3 I s s 2025 (1)-adipate(1)] (polymer #8) by the method of f g S 5 Example #4 PS 3 I s 5 r S I s s I PS I I PB Reagents Wt., Moles I S I S S grams PS 8 I S S Polypropylene glycol 2025 300 0.148 Examples of synthetic oils used for these solubility determinations or 9 27.1 0.148 include: bis(2-ethylhexyl)sebacate, Dow-Corning silicone fluid 200, 25 0.320 %cresIylBp3l6gsphate, and Carbon and Carbide Chemical Company b S completely soluble, PS =partia1iy soluble, I =insolub1e.

9. TABLE IV Viscosity index (A'STM D567) of polymer blends in diester synthetic oils 10 TABLE V Viscosities and viscosity indices of polymer blends in tricresyl phosphate synthetic oil V Blend Vis. Vis. V.I. Blend V1s. VlsJ V.I. F. 210 F. 100 F. 210 k Dloctyl azelate 1 64.0 36.3 3 T i l h t 1 Pl s 1% Polyme #3--- 67- 2 36. 9 142 r i iii; fi gi rer #5-.-. iii 33.; 33 Plus 2% Polymer #3.- 70. 7 37. 6 153 Plus 1.5% Polymer 185 43. 4 50 Plus 1% Polymer e7. 5 37.0 145 10 Plus 2.0% Polymer #5. 202 41. s 66 Plus 2% Polymer #4. 71. 4 38.0 165 Plus 8.0% Polymer 235 47. 5 83 Ens a? llzolymcr $5- fins 4.0% golymer #5. 275 50. 9 97 us 0 er a. 5.0 1 Plus 3% Polfier #5 96. s 42. 5 17s us met #5 312 53 9 103 Plus 1% Polymer #7- 71. 1 37. 7 I 155 Plus 2% Polymer '79. 1 39. 4 182 l Viscosities are seconds Saybolt Universal. Plus 1% Polymer #8..- 69.1 37.4 154 Plus 2% Polymer #8"; 74. 9 38.9 182 Dioctyl sebacate 1 68. 4 37.3 152 $2: Whether diester oils or phosphate ester oils are used, Plus 1% Polymer 79. 9 39.1 168 it 1s not to be understood that the only materials involved g3? Q2: 8%:3 it; are necessarily the oil and my new polyester as a vis- D bPluls 2 galygmler #7 ggg 12g cosity index unprover. As a mater of fact, other matei 11W P a a e rials not only may be present but may be very desirable Pl 2 P01 er #5 72.9 37.0 111 I us m to prevent oxidation, 1nh1b1t rust, and for other reasons. 1 The dioctyl azelate and diootyl sebacate were the bistZ-ethyl-hexyl) F01: example slilch antioxidants as phenyl alphanphthyl' esttlelrs fifhllille respective acids; the dibutyl phthalate was di-n-butyl ammo, O1 2,6-d1tert-buty1 para cresol, O1 polymerized m- W t a 5 methyl dihydroquinoline (sold under the trade-name Age- 2S dS bltU vesal.

econ S 0 m r R1te Resin D) are suitable antioxldants, and other well known antioxidants may also be used. Similarly, any of the well known rust inhibitors or metal deactivators may be used too. Blending of the viscosity index improver with diester and phosphate ester synthetic lubricants may be accom- A most surprising and unexpected finding Was'the b6- plished by simple mixingi It may be desirable in some havior f these polymers i i h h t t syninstances to prepare a concentrate because the polyester thetic oils, where they were not only soluble but displayed vlscous F therefore be mwnvement to handle th d v in some applicatlons. Thus, a small amount of tricresyl remarkable gfiectweness mlsmg f phosphate synthetic oil or some suitable diester synthetic y Phosphate aster 0115 have excellent lubrlclty and oil may be used as the solvent to carry the viscosity index noninflammability but are notoriously poor in viscosityimprover into more of the same lubricant. This contemperature characteristics, a shortcoming which has 40 t l g i i? *E PF i t 1 O mos o o e v1scos1y-1n ex-nnproving p0 yes er. harflpered' the: moreover are general y me The concentrate also may contam any of the ant1ox1dants Pailble Wlth and hence unresponslve to the commercial mentioned above, or others. It may also contain rust in- ViSCOSiEY indeX impfovefs $11011 as the P y y P 3 hibitors, metal deactivators, and other materials not inisobutylenes and polyvinyl othe The compatability compatible with the lubncant or the polyester. and susceptibility to viscosity index improvement which gicgi 3 522 3 9 and desmbed the Pnnclples of has now been shown to result from the add1t1on of these 1. A lubricant composition consisting essentially of a new polyoxypropyl glycol polyesters to P P' lubricant selected from the group consisting of diester ester oils serves to broaden the field of usefulness of this lubricating oils and phosphate ester lubricating oils, and class of synthetic oils. a sufiicient amount to increase appreciably the viscosity o nds :to act as index of said lubricant of a polymerized polypropylene f m ablhty i these comp V glycol ester of an unsubstltuted, low molecular weight Vlscoslty Index P 13 shown by Ta dibasic organic acid having a glycol-to-acid mol ratio in the range of about 0.875 to 1.111 and having a viscosity of at least 250 centistokes at 210 F. and with at least H (EH; (6

seven oxypropylene units in the polypropylene glycol radical.

2. The composition of claim 1 wherein the ester is wherein n averages about 34.

3. The composition of claim 1 wherein the ester is llafliiiliiaoill iiilwt.

where m is about 3 and n is about 17.

2,999,067 11 12 4. The composition of claim 1 wherein the polymerized has been exhaustively removed, and then reacting the ester has a viscosity between 250 and 13,000 centistokes glycol with a dibasic acid dichloride in a 1 1 at 210 F. th

5. The composition of claim 4 wherein the polymerized mol rang m the range between 0375 and L111 6 presence of an HCI acceptor at a temperature 111 the ester is present in an amount between 1% and of the 5 lubricant range between 0 C. and 100 C. sald'polymer having a 6. Dioctyl azelate containing between 1% and 5% of viscosity of at least 250 centistokes at 210 F.

11111111 00 HCHa 11011300 HHHH L 51 llll ll I III! l lll H I -o- I -0o--o-o--c :-r J0--c 2 0o-c-ol 1143- 0-11 HHH HH /.,HH .IHHHH wherein n averages about 34.

7. Tricresyl phosphate containing an amount sutficient to increase its viscosity index of wherein n averages about 34.

8. A new composition of matter having the property of References Cited in the file of this patent improving the viscosity indices of diester and phosphate U TED STATES PATENTS ester lubricants, and consisting of a concentrate that con 2,465,150 Dickson 22, 1949 sists essentially of up to 95% of a vehicle freely miscible 5 fiuchs g 'f in said lubricant and of more than 5% of a polymer of a 2:485:376 g 1949 polypropylene glycol ester of an unsubstituted low molecu- 2,562,878 Bl i A 7, 1951 lar weight dibasic organic acid having a glycol-to-acid ,6 8,97 Sanderson Feb. 17, 1953 mol ratio in the range of about 0.875 to 1.111, said glycol 2,647,885 Biuica 4, 1953 containing a least oxypmpylene {wits Said Polymer 5:233:32 1 3412 322555;1:211:11: $512. it; 132% having a viscosity of at least 250 centistokes at 210 F. 337 55 Mamszak et a1 June 3, 1958 9. A method of preparing a polymer of a polypropylene 2,929,786 Young et a1 Mar. 22, 1960 glycol ester of an unsubstituted low molecular weight di- OTHER REFERENCES basic acid, comprising: refluxing a polypropylene glycol Experiments in Organic Chemistry, by Fieser, 2nd

having at least seven oxypropylene units until the water Edition, 1941, D. C. Heath & 00., p. 398.

Claims (1)

1. A LUBRICANT COMPOSITION CONSISTING ESSENTIALLY OF A LUBRICANT SELECTED FROM THE GROUP CONSISTING OF DIESTER LUBRICATING OILS AND PHOSPHATE ESTER LUBRICATING OILS, AND A SUFFICIENT AMOUNT TO INCREASE APPRECIABLY THE VISCOSITY INDEX OF SAID LUBRICANT OF A POLYMERIZED POLYPROPYLENE GLYCOL ESTER OF AN UNSUBSTITUTED, LOW MOLECULAR WEIGHT DIBASIC ORGANIC ACID HAVING A GLYCOL-TO-ACID MOL RATIO IN THE RANGE OF ABOUT 0.875 TO 1.111 AND HAVING A VISCOSITY OF AT LEAST 250 CENTISTOKES AT 210*F. AND WITH AT LEAST SEVEN OXYPROPYLENE UNITS IN THE POLYPROPYLENE GLYCOL RADICAL.