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Publication numberUS2895915 A
Publication typeGrant
Publication dateJul 21, 1959
Filing dateAug 28, 1956
Priority dateAug 28, 1956
Publication numberUS 2895915 A, US 2895915A, US-A-2895915, US2895915 A, US2895915A
InventorsWilliam A Hewett, Robert C Jones, Lyman E Lorensen
Original AssigneeShell Dev
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Polymeric pour point depressant compositions
US 2895915 A
Abstract  available in
Images(5)
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Claims  available in
Description  (OCR text may contain errors)

United Stats PatentOfiice POLYMERIC POUR POlNT DEPRESSANT COMPOSITIONS No Drawing. Application August 28, 1956 Serial No. 606,536

6 Claims. (Cl. 252-59) This invention relates to the production of lubricating oil compositions having improved, i.e. lower, pour points. More particularly, it relates to mineral lubricating oils containing hydrocarbon polymers of a restricted class which depress the pour point of the lubricating oil.

Lubricating oils and, particularly, hydrocarbon lubricating oils such as petroleum lubricants increase in viscosity and eventually cease to flow as the temperature of the oil is reduced. In many hydrocarbon oils the reason for poor flow properties at low temperatures is due to the freezing or crystallization of certain fractions of the oil, most commonly, paraffin Waxes and the like. However, at sufiiciently low temperatures, other hydrocarbons or components present in the lubricating oil may freeze and prevent the flow of the entire lubricating oil 1 even though said frozen components are not normally ;regarded as waxes.

Numerous materials have been incorporated in lubrircating oils for reducing the temperature at which the s oil ceases to flow; that is, the pour point of the oils has been reduced by means of said additives. and other additives have been employed for improvement These in the viscosity response to the temperature of the oil and for increasing the consistency of the oil, particularly at increasingly high temperatures.

This function is normally referred to as the viscosity index improvernent. The function of viscosity index improvement is not necessarily directly related to the depression in the pour point of the oil, even though the same additive may at times function for both purposes in a given lubricating oil.

One of the most commonly employed and highly effective types of additives for either or both viscosity index improvement and pour point depression comprises the substantially linear polymethacrylate esters. While these are satisfactory for many purposes, they exhibit several shortcomings such as shear instability and thermal instability, two features which indicate that improvement is required.

Among the other materials which have been incorporated in lubricating oils are polyethylene and polyisobutylene which may be useful for the improvement in viscosity index of the lubricating oil, but have little effect upon the pour point characteristics of the composition.

It is an object of the present invention to provide improved lubricating oil compositions. It is another object of the present invention to provide lubricating oil compositions having improved viscosity-temperature characteristics. It is a particular and major object of the present invention to provide lubricating compositions having their pour points reduced to a maximum extent. Other objects will become apparent from the description of the invention.

Now, in accordance with the present invention, it has been found that an unexpectedly great depression in the pour point of lubricating oils can be obtained by incorporating therewith a minor amount, suflicient to depress Patented July 21, 1959 the pour point of said oil, of a polymerized alpha-olefin about 14 carbon atoms (preferably 1113) each. Still more preferably, said alkyl substit-uents should contain no less than about 8 and no more than about 22 carbon atoms each. The greatest pour point depression is obtained from those copolymers of alpha-olefins wherein the alkyl substituents attached to alternate carbon atoms in the linear polymer chain have between 10 and 16 carbon atoms each. Further, the greatest pour point depression is obtained when the average carbon atom content per alkyl radical is between about 11.5 and 12.5, preferably 12.0.

The present invention is especially striking in view of the fact that alpha-olefin polymers having substantially the same molecular weight as the polymers just described, but bearing alkyl substituents outside of the limits set forth hereinabove, show only a minor pour point depressing elfect or no effect whatsoever. Again, the effect is noted with respect to pour point only, and not with respect to viscosity-temperature improvement.

The polymers utilized for the present invention may be prepared by a number of different processes, but the most satisfactory polymerizing process comprises the polymerization of alpha-olefins having from 2 to 22 carbon atoms each, using one of two preferred processes. When alpha-olefins having less than about 6 carbon atoms per molecule are to be polymerized, it is preferred to conduct the initial polymerization in the presenceof an aluminum trialkyl in the substantial absence of any catalyst promoter. Under these conditions, the polymers obtained are dimers of the monomer and varying amounts of higher polymers generally Within the range of 10 to 22 carbon atoms per average polymer molecule. Subsequent to the preparation of this relatively low molecular weight polymerization mixture, the reaction product is subjected to partial distillation or vaporization whereby the fractions of the products boiling below about decene are removed and thereafter adding to the residual portions of the reaction mixture a catalyst promoter such as titanium tetrachloride, thus causing intensive polymerization of the residual portion to occur resulting in extremely high molecular weight polymers.

While a polymer having average C1143 side chains is essential for the maximum pour point depression of mineral oil lubricants, a second aspect of oil properties requiresconsideration, namely, the effect of polymer side chain length on the viscosity-temperature relationship of compositions comprising the lubricating oil and polymer. Maximum improvement (i.e., promoting a more nearly horizontal linear viscosity-temperature slope) is achieved when the polymer contains a restricted proportion of C alkyl side chains, in the order of between about 5 percent and about 15 percent C of all side chains present. Such a polymer, having an average of C1143 side chains but also containing the recited proportion of lower alkyl side chains has an optimum combination of pour point depressing and viscosity-temperature improving efiects. The limitation on the proportion of short side chains is essential, since higher ratios of short chains minimize the pour point depressing eilect, even if the C1143 average is maintained.

The alternate process comprises the polymerization of an alpha-olefin or a mixture of alpha-olefins having between 10 and 22 carbon atoms per molecule by means of the combination of an aluminum trialkyl and a catalyst promoter such as titanium tetrachloride. The prod- 3 uct so obtained, as described in greater detail hereinafter, has the extremely high molecular weight desired and also has alkyl side chains within the critical limits described herein. a

The lubricating oils forming the major component present in the described compositions are normally mineral oil lubricants but may comprise hydrocarbon lubricants from other sources such as olefin polymerization, the hydrogenation of cracked wax olefins, wax isomerization, and may be either waxy lubricating oils or partially or completely dewaxed hydrocarbon oils. While the effect is most striking with hydrocarbon oils containing minor amounts of parafiin waxes, the most practical application of the present invention comprises the addition of the described olefin polymers to lubricating oils from which a major portion of the wax has been removed. Suitable lubricating oils generally have pour points from about +30 F. to about -20 F.

The proportion of olefin polymer added to the lubricating oil will be within the skill of those familiar with this art. The proportion will generally vary from about 0.05% to about 5% by weight of the lubricating oil, but will be present in an amount to effect a substantial reduction in the pour point thereof. The specific proportion required will depend upon a number of factors, namely, the identity of the oil with respect to its composition, the pour point of the oil which is dependent upon its composition, the identity of the polymer with particular respect to the average alkyl chain length, and the alteration in viscosity-temperature relationship which is desired together with the pour point reducing effect. Normally the proportion of polymer will be between about 0.1 and 2.5% by weight of the oil.

The alpha-olefins useful in the production of the subject class of high molecular weight polymers are those having from 2 to 22 carbon atoms per molecule and comprise alpha-olefins (preferably normal) such as ethylene,

propylene, butylene, octene-l, decene-l, dodecene-l, tetradecene-l, hexadecene-l, octadecene-l and eicosene-l. When the single stage polymerization process is to be utilized, namely, when the aluminum trialkyl catalyst is combined in the initial phase with a catalyst promoter such as a variable valence metal compound, e.g. titanium tetrachloride, the alpha-olefins to be utilized should have between about 10 and about 22 carbon atoms per molecule and should be used in such a ratio that the average carbon atom content is between about 13 and about 15 carbon atoms per molecule so that the alkyl substituents as described more fully hereinafter will have in the prodnot an average of between 11 and 13 carbon atoms each.

The metal trihydrocarbyls which may be used in this type of polymerization are preferably aluminum trialkyls containing from 1 to 18 carbon atoms per alkyl radical. However, other hydrocarbon substituents may be utilized, such as aryl or alkaryl radicals as well as aralkyl radicals. These hydrocarbyl radicals should preferably contain minum trihydrocarbyl. Other promoters include titanium subhalide, e.g. titanium diand tri-chloride.

Under the preferred conditions of polymerization, the alpha-olefin is dispersed in a non-polymerizing hydrocarbon diluent, although a diluent is not essential. This may be, for example, normally liquid preferably saturated hydrocarbons other than alpha-olefins, cyclohexane, methylcyclohexane, the dimethylcyclohexanes, pentane, and hexane, as well as aromatics, e.g. benzene, toluene and xylene. The hydrocarbon diluent should preferably have from about 5 to about 10 carbon atoms per mole cule and should be used in an amount from about 0.1 to about 5 volumes for each volume of the olefin monomers. The conditions of polymerization include temperatures from about 0 to about 100 C. for periods of time ranging from about 2 to about 12 hours. A preferred set of conditions comprises the dilution of the alpha-olefin monomer with an approximately equal quantity by volume of dry cyclohexane, the addition of 1% of titanium tetrachloride and 2.5% of triethyl aluminum to the olefin solution, the reaction being maintained at room temperature overnight. The catalyst is destroyed by the addition of an alcohol and water and the solvent removed. The conversion to product after precipitation is about 50 to about 99%.

The above-described conditions are those utilized when alpha-olefin monomers having from 10 to 22 carbon atoms per molecule are to be polymerized, the average carbon atom content being 13 to 15 carbon atoms per molecule. When lower molecular weight alpha-olefins me to be polymerized to obtain the products for use in the present invention, the following conditions are to be observed as a preferred process: The alpha-olefin (or mixtures thereof) having from 2 to 9 carbon atoms per molecule, such as ethylene, is polymerized in the presence of an aluminum trihydrocarbyl but in the initial absence of the catalyst promoter.

about 250 C., temperatures between about 130 and about 170 C. being favored for the production of optimum proportions of olefin products having from 8 to 18 carbon atoms per molecule. from 250 to 2000 pounds per square inch gauge, pre-' ferred pressures being between about 500 and about 1500 pounds per square inch. The higher temperatures favor the production of olefin products having from 8 to 18 carbon atoms per molecule. An excess of ethylene is present and the proportion of ethylene reacted to form higher molecular weight alpha-olefins increases with increasing pressure within the reaction vessel. The time of reaction is normally between about 2 and about 20 hours.

The products obtained under these conditions normally comprise ethylene which has not reacted, dimers and from 1 to 6 carbon atoms each. The lower aluminum trialkyls wherein each alkyl radical contains from 2 to 4 carbon atoms each are preferred. These include aluminum triethyl, aluminum tripropyl, aluminum triisobutyl, aluminum trimethyl, aluminum triphenyl, aluminum tribenzyl, aluminum trixylyl, aluminum diethylmethyl, aluminum diethylisobutyl, aluminum phenyldiethyl, aluminum tricycloalkyls such as aluminum tricyclohexyl, and the like. The proportion of aluminum trihydrocarbyl to alpha-olefin may vary from about 0.1 to about 0.01 mole per mole of olefin. In place of aluminum, other metals such as zinc or magnesium, beryllium, indium or gallium may be used. Aluminum dialkylchlorides may be used in place of aluminum trialkyls.

Catalyst promoters are typified by titanium tetrachloride, and are to be used in a proportion of about 0.05- 0.005 mole of titanium tetrachloride per mole of alutrimers, and higher molecular weight alpha-olefin polymers. For use in the present invention it is preferred that the maximum possible amount of the product be obtained in the form of C C alpha-olefins, since this is the preferred molecular weight range of alpha-olefins to be further polymerized for the production of the extremely high molecular weight products useful in the compositions of this invention.

Having obtained the initial polymerization product as described above, it is then necessary to remove the lower molecular weight products, namely, monomer, dimer and trimer, and preferably, all hydrocarbons having less than about 6 carbon atoms per molecule. This is easily done by vaporization either at room temperature and pressure or under reduced pressure. The product so obtained as a residue is free of hydrocarbons having less than 6 carbon atoms per molecule and can be used directly in the production of the high molecular Weight polymers desired by addition thereto of titanium tetrachloride and proceeding under the conditions of polymerization as described previously. The products so obtained have been found to be unexpectedly effective, especially when The temperatures to be employed under these conditions vary from about to The pressure is preferably.

seem

mer chain is within the range from about 11.5 to about 12.5.

Another process for the production of polymers for the present purpose comprises the socalled block polymer formation, wherein a homopolymer or copolymer is first formed and then is utilized as one component in the further polymerization of additional monomeric material so as to obtain a final product having the desired high molecular weight and an average alkyl side chain of 11-13 carbon atoms. For example, dodecene can be polymerized in the presence of an aluminum trialkyl, such as aluminum triethyl and titanium tetrachloride to obtain a high molecular weight polymer which is then combined with octadecene. The polymerization is continued to produce a copolymer wherein a large block consisting of dodecene units is combined with a second large block consisting of octadecene units, the ratio of the two being such that the alkyl substituents from alternate carbon atoms in the linear chain have an average of to 14 carbon atoms.

The products obtained by the various processes just described have the general formula radicals that the average molecular weight of the olefin polymer is between about 100,000 and about 1,000,000.

In general it is believed that the polymers may be designated as l, 3, 5, 7 (2n-1)-polyalkyl-C ,,-normal alkanes (or C -2n-normal alkenes), where n is the number of carbon atoms in the backbone chain portion of the polymer, corresponding to 2m in the foregoing genmodified lubricating oil is of a minor degree and is normally unsatisfactory. It will, of course, be apparent that an economically small amount of the polymer must give a highly effective pour point reduction in order to be economically satisfactory as well as technically etficient. The examples which follow illustrate the nature of the present invention and differentiate the products being claimed in conjunction with the lubricating oils for pour point depression as compared to other polymers having alkyl substituents not meeting the requirements ofthis invention.

A number of homopolymers and copolymers as set out in Table I were prepared as described hereinafter and incorporated in a medium viscosity dewaxed East Texas lubricating oil having a pour point of +20 F. 0.5% by weight of the polymer was used in each composition. Reference to Table I will show that a critical relationship exists between the average alkyl substituent and the effect of the polymer upon the depression of the pour point of the lubricating oil. A C side chain had relatively no effect upon pour point depression and likewise a C alkyl substituent was equally ineifective. When the alkyl side chain was 14 carbon atoms in length on the average, it will be seen that only a moderate depression in pour point occurred. The same is true when an average alkyl side chain had 11 carbon atoms. However, within the range of 12 and 13 carbon atoms for the average alkyl radical, maximum depression in pour point was experienced. The data in Table I show the greatest elfect occurred when the average alkyl radical contained 12 carbon atoms.

It will be noted that the block polymer having an average of 12 carbon atoms was an effective pour point depressant but not as effective as a hetero-copolymer hav- .ing the same average alkyl side chain. It is important to note that a mixture of two homopolymers, namely, octadecene and dodecene homopolymers (therefore having alkyl side chains of 16 and 10 carbon atoms respectively),

was completely ineffective as a pour point depressant, even though the two polymers were mixed in proportions to yield a C average side chain.

TABLE I Polymeric a-olefins as pour point depressants CH2CH Ratio of R F. Type Monomer Monomers Pour Point Average Depression Length of R Homopolymar Lootadpr-ene 1 5 Do r. LDodecene 10 5 DO l-Tetrarlpnonn 12 30 M(lix/t1)1re of Homopolymers l-Octadecene l-Dodecene 12 0 l-octadecene l-Dodecene 1/5 11 20 dn 1/2 12 do 0. 9/1 12. 9 35 -do 1/1 13 25 do 2/1 14 15 l-Octadecene/l-Octene 3/2 12 10 Terpolymer 1-0ctadecene/l-Dodecene/l-Decene- 3/2/2 12 40 Block Poly-mer" l-Octadecene/l-Dodecene 1/2 12 30 a Standard East Texas 250 Neutral, pour point +20 F. b Concentration of polymer, 0.5% by weight.

eral formula. For an average alkyl R of 12 carbon atoms and an average polymer molecular weight of from 100,000 to 1,000,000, n in the foregoing is from about 500 to about 5000.

The products so obtained and described are to be dispersed in the lubricating oil within the proportions pre viously set out to produce lubricating oil compositions having surprisingly reduced pour points. By pour point is meant the pour point as determined by ASTM Method D97-47. When utilizing polymers having alkyl substituents shorter than about an average of 11 or greater than an average of about 13, the pour point reduction of the The polymers just described were incorporated in 2% concentration in a lubricating oil comprising of a low viscosity dewaxed neutral lubricating oil and 20% of a medium viscosity East Texas neutral. Table II given below shows the effect upon viscosity, viscosity index and SAE grade caused by the addition of the various polymers. It is noteworthy that the side chain alkyl group does not appear to have a major effect upon the degree of improvement in viscosity index. In fact, all of the polymers given in Table II indicate the relatively large effect which improves to a certain extent with increasing molecular weight.

TABLE II 2% w. of u-olefin polymer m an SAE 5 W base 011 CH -OH Ratio of Viscosity, l Viscosity, SAE Type Monomer (all straight chain) Monomers Cks. at R Cks. at VI Grade Mol wt.

100 F. 210 F. Aver. Length of R Standard Base O 27.21 4. 70 98 Homopolymer l-o d e 59. 6 16 10. 4 144 10W-30 530,000 Do do 43. 96 16 7. 45 134 10W-20 200,000 l-Dodecene 41. 92 10 7. 11 133 10W-20 160, 000 l-octadeeenell-Dodecene 0. 9/1 32. 21 12. 9 5. 46 116 5W-20 0.9/1 41. 58 12.9 7. 00 132 10W-20 160,000 dn 1/1 43.05 13 7. 27 133 10W-20 180, 000

do 2/1 48. 59 14 8. 26 138 10W-20 270, 1/2 42. 67 12 7. 42 135 10W20 175,000

dn 1/2 49. 65 12 8. 36 137 10W-20 300,

do 1/2 60. 9 12 10. 17 140 10W-30 B 560, 000 rin 1/5 49. 30 11 8. 31 137 10W-20 290, 000 Do Octadecene/l-O ctene 3/2 68. 3 12 11. 55 142 10W-30 790, 000 Terpolyiner 1-0ctadecene/l-Dodecenel1-Decene. 3/2/2 57. 6 12 9. 93 142 10W-30 430, 000 Block Polymer. l-Octadecene/l-Dodecene 1/2 39. 22 12 6. 66 130 10W-20 l 80% 100 Neutral, 250 Neutral.

b Light scattering.

e Viscosity average molecular weight, vs. log molecular weight at 2% polymer concentration.

Norm-100,250 and 380 oils refer to SUS at 100 F.

In order to determine whether the optimum average alkyl length of 12 carbon atoms was peculiar to a particular lubricating oil, polymers described in Tables I and II were tested in several other high viscosity lubricating oils. Table III presents the comparative data obtained. The oils involved, namely, West Texas Ellenburger-Oklahoma City (WTEOC) and high viscosity index Oklahoma City (OCHVI) lube oils, were dewaxed to a greater extent than the East Texas neutral utilized in the compositions described in Table I. This is indicated by the lower pour points as shown in the footnotes of Table III. Examination of the data given in Table III will show that the same critical relationship appears to exist substantially irrespective of the specific lubricating oil being modified. Thus, it will be seen that the alkyl substituent dependent from alternate carbon atoms in the substantially linear chain should be maintained between 11 and 13, and preferably about 12.

interpreted from the straight line relationship of log [visc., 100 F. base 011 polymer visc., 100 F. base oil] overnight at room temperature in order to complete the desired polymerization. Isopropyl alcohol and water were added to destroy the catalyst, after which the mixture was water washed to remove undesired by-products and solvent and unreacted monomer were removed by evaporation. The polymer was purified by reprecipitation with methanol from benzene solution.

The block polymer was obtained by forming an initial octadecene homopolymer having an average molecular weight of about 100,000, and then dispersing this polymer together with dodecene and proceeding as just described.

Surprisingly effective results were obtained by a preferred variation in the preparation of the desired polymers. Ethylene was polymerized in the presence of triethyl aluminum but in the absence of titanium tetrachloride. A temperature of 150 C. was employed, using a total pressure of 1000 p.s.i.g. with a residence time of 5 hours, the polymerization being carried out in benzene solution.

TABLE III Pour point activity of a-olefin polymers m various oils 0.5% w. 0.25% W. 0.5% w 0.25% W. Ratio of Av. Side Polymer Polymer Polymer Polymer Type Monomers Mono- Chain in ET 25 inWTEOO in OOHVI in OCHVI mers Length ON F 38ON 'F. 38ON F 38ON F Depres- Depres- Depres- Depression sion sion sion Homopolymer I-O 16 +5 0 D l-Tetr ri n 12 +30 +30 l-Dodecene -10 +5 +5 1 Octadecene/l-Dodeceu '1/5 11 +20 +40 rin l/2 12 +45 (10 0.9/1 12. 9 +35 +30 do 1/1 13 +25 +40 d0 2/1 14 +15 +15 l-Octadeoene/l-Octene 3/2 12 +10 +20 Terpolymer 1-Octadccene/l-Dodecene/l-Deceue- 3/2/2 12 +40 0 Block Polymer-.. l-Octadecene/l-Dodecene 1/2 12 +30 +25 Pour Point, +20 F. Pour Point, 0 F. *Pour Point, +5 F.

The polymers described in Tables I, II and III were each prepared by the following processes: 20 parts by weight of the alpha-olefin or indicated mixture thereof was dissolved in an equal amount of dry cyclohexane. This was placed in a reaction vessel blanketed with dry nitrogen. Into this a mixture of 1% titanium tetrachloride and 2.5% triethyl aluminum, based on the olefin weight, was injected and the reaction mixture was stirred The unreacted ethylene and lower molecular weight dimers and trimers were removed from this reaction mixture by means of evaporation at a temperature of about 100 C. and atmospheric pressure. Analysis of the residue indicated the following constituents to be present: 55% of material was in the C to C range, 31% from C to C and the remainder longer than C material *with a free olefin content of about 70%, of which was alpha-olefin. In order to obtain a reaction mixture having the correct ratio of alpha-olefins to give a high molecular weight polymer having the optimum alkyl side chain length of 12, equal amounts by weight of octadecene and dodecene were added, after which titanium tetrachloride was injected into the reaction mixture and polymerization was conducted under the conditions previously described. The polymer so obtained had a molecular weight of about 550,000 and when dispersed in East Texas medium viscosity lubricating oil identical with that described in Table I gave a pour point depression of 55 F.

We claim as our invention:

1. A lubricating composition consisting essentially of mineral oil and 0.1-2.5 by weight, sufiicient to reduce the pour point thereof, of a linear alpha-olefin polymer of at least two alpha-olefins having -22 carbon atoms permolecule having an average molecular weight between about 100,000 and about 1,000,000, substantially each alternate carbon atom in the linear polymer chain having dependent therefrom a C alkyl radical, the average number of carbon atoms of said alkyl radicals being between about 11 and about 13.

2. A lubricating composition consisting essentially of mineral oil and 0.1-2.5 by weight, sufficient to reduce the pour point thereof, of a linear alpha-olefin polymer having an average molecular weight between about 100,000 and about 1,000,000, substantially each alternate carbon atom in the linear polymer chain having dependent therefrom a C alkyl radical, the average number of carbon atoms per alkyl radical being between about 11.5 and about 12.5.

3. A lubricating composition consisting essentially of mineral oil and 0.12.5% by weight, suflicient to reduce the pour point thereof, of a linear alpha-olefin polymer having an average molecular weight between about 100,000 and about 1,000,000, substantially each alternate carbon atom in the linear polymer chain having dependent therefrom decyl and hexadecyl radicals, the average number of carbon atoms in said radicals being between about 11.5 and about 12.5.

4. A lubricating composition consisting essentially of mineral oil and 0.1-2.5% by weight, suflicient to reduce the pour point thereof, of a substantially linear copolymer of a polymerized alpha-octadecene having an average molecular weight between about 100,000 and about 500,000 and alpha-dodecene, said copolymer having an average molecular weight between about 100,000 and about 500,000, the alkyl substituents dependent from alternate carbon atoms in the linear copolyrner chain having an average number of carbon atoms between about 11.5 and about 12.5.

5. A lubricating composition consisting essentially of mineral oil and 0.1-2.5% by weight, sufiicient to reduce the pour point thereof, of a substantially linear polymer of tetradecene, having an average molecular weight be-- tween about 100,000 and about 1,000,000, said polymer being characterized by the dodecyl radicals attached to each alternate carbon atom in the linear polymer chain.

6. A lubricating composition consisting essentially of mineral oil and 0.1-2.5 by weight, sufiicient to reduce the pour point thereof, of a substantially linear alphaolefin polymer having an average molecular weight between about 100,000 and about 1,000,000 and having alkyl radicals dependent from substantially each alternate carbon atom in the linear polymer chain, said alkyl radicals having an average of 12 carbon atoms each.

ReferencesCited in the file of this patent UNITED STATES PATENTS 2,085,525 De Simo et a1 June 29, 1937 2,410,885 Lieber Nov. 12, 1946 2,525,788 Fontana et al. Oct. 17, 1950 2,534,095 Young Dec. 12, 1950 2,746,925 Garber et a1. May 22, 1956 FOREIGN PATENTS 676,516 Great Britain July 30, 1952

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US2999120 *Nov 12, 1958Sep 5, 1961Donovan R WilgusViscosity index improving agents
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