US2522155A

US2522155A - Lubricating compositions

Info

Publication number: US2522155A
Application number: US704283A
Authority: US
Inventors: Seaver A Ballard; Rupert C Morris; John L Van Winkle
Original assignee: Shell Development Co
Current assignee: Shell Development Co
Priority date: 1946-10-18
Filing date: 1946-10-18
Publication date: 1950-09-12
Anticipated expiration: 1967-09-12

Description

Patented Sept. 12, 1950 2,522,155 LUBRICATING coMrosrTions Seaver A. Ballard, Orincia, Rnpeit C. 'ltlorria,

Berkeley, and John L. Van

Winkle, San Lorenzo,

Callf., assignors to Shell DevelopmentCompany, San Francisco, Calif., a corporation of Delaware No Drawing. ltpplication october is, 1946, Serial No. 704,2 3

This invention relates to superior lubricating materials, and more particularly to improved non-hydrocarbon lubricants.

Mineral oil lubricants, such as those made from paraiiin base petroleum oils or naphthenic base petroleum oils, are useful for most lubricating purposes when the conditions to which said lubricants are subjected are relatively mild. However, lubricants of petroleum origin are limited in'their utility by certain inherent characteristics. For example, especially when employed for aviation purposes, a lubricant is often subjected to wide temperature variations, such as hot ground temperatures and the extremely ,cold temperatures encountered at high altitudes, for instance at about 10,000 to 20,000 feet elevation. Under these conditions, the ordinary mineral oil base lubricants fail to function properly, either being too fluid when warm, or too stifi when cold.

The tendency of mineral oils to oxidize rapidly, especially in the presence of certain metallic substances such as copper, iron oxide, etc., is wellknown. While the addition of anti-oxidants corrects this adverse feature to a limited extent, in many instances mineral oil lubricants are unsatisfactory, due to sludge. and gum formation, both of which are results of oxidation reactions:

Certain non-hydrocarbon substances of syn: thetic origin have been used for specialized lubrication purposes. For example, polymeric alkylene oxides, such as polymerized propylene oxide, have been used for lubricating purposes. Other similar polymers have found restricted use as substitutes for mineral oil lubricants. Many of these have hydroxyl or alkoxyl end-groups on one or both ends of the polymeric chain. These various liquid polymeric lubricants have one or more properties which make their substitution for mineral oil advantageous for certain lubrication purposes. For example, the viscosity indices of many of them are relatively high, in comparison with those of mineral oils, and for this reason operate over a comparatively wide temperature range. However, due to, the free hydroxyls or loosely bound terminal alkoxyl groups, the synthetic lubricants are usually unsatisfactory for many purposes, since they are unstable towards oxidizing influences, change their characteristics relatively rapidly during engine use, volatilize at relatively low temperatures, absorb water from the surrounding atmosphere, etc.

It is an object of this invention to provide improved non-mineral oil lubricants. It is another object of this invention to provide a non-petroleum base lubricant having improved resistance 3 Claims. (01. 25.2-51.5)

' to oxidation- It is a third object of this invention to provide a process for preparing non-hydrocarbon lubricants having substantially no ability to absorb water. It is still another object of a this invention to provide new lubricants which are thermally stable. Other objects will be obvious from the following description of the present invention.

Now, in accordance wth this invention, it has been found that liquid polymers having repeating structural units of the general configuration wherein R is any organic radical (especially a hydrocarbon radical) form unexpectedly superior lubricating compositions when at least one of the end-groups of each polymer chain is an amino radical. Thus, the general formula of the lubricants of the present invention is wherein R is'an organic radical (preferably a hydrocarbon radical), n is an integenand at least one of the Xs is an amino (including substituted amino) group and the other is a group such as a hydroxyl, ether or ester group. Lubricants having the above configuration have unexpectedly highresistance to oxidation, respond to a much greater extent to inhibitors than if the amino group is absent, and exhibit superior characteristics when used as engine lubricants.

Lubricants having the above configuration are derived, for example, from the polymers and copolymers of alkylene oxides and alkylene glycols which have the general formula 1 wherein the Rs are hydrogens or organic radi= cals, particularly hydrocarbon radicals.

Alkylene oxides-which form such polymers include ethylene oxide, propylene oxide, 1,2-butylene oxide, 2,3-butylene oxide, isobutylene oxide, tetramethylethylene oxide, n-hexylethylene oxide, methylphenylethylene oxide, cyclohexene oxide, methylcyclohexene oxide, 1,2-cetene oxide; and other substances containing the. epoxide, linkage such as epichlorohydrin epibromohydrine, and glycides such as glycidol and 1,2-epoxybutanol- 2, and glycidyl ethers such as glycidyl isopropyL;

ether, as well as derivatives and polymerizable homologs and analogs of the abovesubstances'.

Copolymers of the alkylene oxides include. the copolymers of ethylene oxide and propylene oxide; the copolymers of ethyleneqoxide and isobutylene oxide; the copolym'ersof propylene oxide. and epichlorohydrin; the copolymers of propylene oxide and l,2-buty1ene oxide; the copolymers of propylene oxide and glycidol and the co polymers of propylene oxide and isobutylene oxide.

Glycols forming polyiiiers which may .be improved according to the present invention includethose derived from ethylene glycol; and having the general formula. .1

, \v I ll. where in s is an integer. and the free carbon valences'are satisfied with hydrogens or organicv radicals. Preferably s is a whole number from 1 to 10, and still.more preferably from 1 to 4.

While. the carbon constituents. may be hydrogen or any organic radical, it is preferred that each group have at least 2 hydrogen substituents the balance being hydrocarbon, preferably alkyl radicals. When a is 1-, such glycols.- include ethylene glycol, propylene glycol, butylene glycol, etc. When s is more than 1,.the. glycols include diethylene glycol, triethylene glycol, tetraethylene glycol, pentaethylene glycol, and the corresponding propylene, butylene, etc. glycols. When 3 is more than 1, mixed glycols useful. in the present invention include ethylene propylene glycol, diethylene propylene glycol, diethylene dipropylene glycol, etc. as well as their: substituted derivatives, andzpolymerizable homologs andanalogs. l. 'I-he glycols having the' general configuration.

H--O- --.OH

l I]. wherein t is an integer and the unsatisfied. carbon valences carry hydrfogen atoms or organic: substituents, are all derived; theoretically from tri-' methylene glycoh. Hence, glycols of: the above configuration will be referred to herein as the trimethylene glycols. When t is 1, the trimethylene glycols have the general formula @(ita methylene glycols, including 1-methyl-1,3-propanediol; 2-methy1-1,3-propanediol; 1,1-dimethyl-l,3 propanediol; 1,2-dimethyl-1,3-propanediol; 1,3-dimethy1propane-l,B-diol; 2,2-dimethylpropan 1,3-diol; 1,1,2-trimethylpropane-1,3- diolj 1,1,3 trimethylpiopane-lfi-diol; 1,2,2-trlznethylpropane-1,3-diol; 1,2,3-trimethylpropanel., 3 diol; 1,1,2,2 tetramethylpropane-1,3-diol;

methylpropane-LB-diol;

'tetramethylpropane 1,3-diol;

'etc'.,, radicals, as well as their isomers.

1,l,3,3 tetramethylpropane 1,3-diol; 1,2,13,3- 1,l,2,2,3-pental,l,2,3,3-pentamethylpropane-l,3-diol; and hexamethylpropane-1,3- diol.

In place of the. methyl groups other alkyl groups may be utilized, such as ethyl, propyl, butyl, amyl, hexyl, heptyl, octyl, nonyl, decyl,

Preferably, when alkyl groups are the substituents R1 and/or'Rz, they have from 1 to 10 carbon atoms,

and still more preferably from 1 to 5. It will be understood that R1 and R2 may be similar or dissimilarsgroups. Thus, when expanding the general formula given hereinbefore to its indicated number of carbon atoms, it then becomes R! R; R5 HO(JJ(|J-4}-OH i B; '7 8:

wherein R3 through Rs are either hydrogen atoms or similar or dissimilarorganic (especially hydrocarbon) radicals; Those derivatives of trimethylene glycol, other than trimethylene glycol itself, which: give the most satisfactory polymers for general: use have either one Or two of the Rs as lower alkyl groups. Thus, 2-methy1-l-,3- propanediol and ZLZ -di'methyl-LB-propanediol, form excellent polymers when treated according to the method of the present invention.

Other lower alkyl substituted trimethylene glycols which'pol-ymerize readily are l-methyl-Z- ethyl-l,3.-propanediol; 2-methyl-2-ethylpropanel',3-d.iol; 1-methyl-3-ethyl-l,3propanediol; 2- methyl 2'-butytl-I,3-propanediol; 2-methyI-3- butyl-1*,3-propanediol; and the homologs, analogs and derivatives of the same.

Cycloali'phatic radicals may be one or more of thesubstitu'entsrepresented by R3 to RB in the above general formula. Thus, R3 through Rs may besucl' r radicals as cyclohexyl, methylcyclohexyl, dimethylcyclohexyl, ethylcyclohexyl, etc. However, open-chain alkl substituents give polymers having preferred properties.

The polymers have somewhat different properties if the trimethylene glycol derivative contains other activegroups, such as additional hydroxyls, or carboxyls, carbonyls, or elements such as halogens, sulfur, nitrogen, phosphorus, selenium, tellurium, etc. I

While the polymers formed may be prepared fronrtrlmeth ylene glycol alone, or from a single trimethylene glycol derivative", copol'ymers also may be prepared in order to varyto a certain degree the properties of the polymeric lubricant for a particular purpose. Thus, trimethylene glycol-1 maybe copolymerized with trimethylene glycol derivatives, ortwo-or more trimethylene glycol derivatives may be cop'ol'ymerized. While: any proportions of the monomersmay be employed in preparing the copolymeric materials, copolymers having greater than about 10 parts of one monomer to 1 part of the: other (or others) show no substantial dilference in properties from a polymer prepared. from the first. monomer alone. There-fore, it is a preferred; practice, when prey paring copolymers to use proportions of monomers. .frpr abqu :1

1an laboutl:1.2 .Cosummer v n mono enratios; on5;1 andof 6:4 as well as 1:1 showhwellrdefined diiferencesin properties from polymers ,;prepared from any single monomer. i When t in the general formula l ;E-; ;LL;5L LYQ is more than 1, itpreferably is from "2 to 5, but may be from 2to 10 or even'higher. Such glycols are the dimers,-tr1mers, et'ci, of the monomeric trimethylene glycols. They include the lower polymers or single trimethylene glycols, r the lower copolymers of mixed trim'ethylene glycols. Other glycols from which polymers of' the present invention may be prepared have the gen eral formula R i r H I O( i )Y i- I OH I wherein z is an integer, y is an integer. greater than 5 and the R substituents attachedto yearbons are hydrogens or organic. radicals, :particu-. larly hydrocarbon radicals. Preferably a is an integer less than 10, and :more .preferablyds an integer from 1 to 4. :Actually, when z:is more than 1, the glycol is a dimer, trimer, etc, of the corresponding monomeric I glycol. The polymethylene glycols polymerizing. most readily are those in which U is an integer from 6' to 20. l

. Monomeric, unsubstituted glycols falling:within the above formula 1 include. h-exanediol-LG; heptanediol-1,7 octanedio1-1,8; nOnanediol-LQ; decanediol-1,10; dodecanedio1-L12; and polymerizable homologs, analogs and derivatlves'of thesame.

The above glycols are those in which all of the R substituents attached to the y carbons are hydrogens. When R's other than hydrogensare present, they may be hydrocarbon radicals, such as aliphatic, aromatic, or alicyclic hydrocarbon radicals, or radicals containing non-hydrocarbon members, such as -hydroxyl,-carboxyl, or carbonyl groups, or sulfur, selenium, itellurium, phosphorus or nitrogen atoms. Preferably, however, any organic radicals attached to the glycol are hydrocarbon radicals.""' of these, the aliphatic hydrocarbonsare' preferred, "and the saturated lower aliphatic' radicals 'givethe most versatile polymeric lubricants. Hence, the preferred Rs, other than hydrogen, are the lower alkyl groups, such as methyl, ethyl, propyl, isopropyl, butyl, sec butyl, tert b'utyl', amyljis'oamyl, hexyl, etc., groups, Again, even when Rs other than hydrogen arepresent, it is preferred that the monomeric glycolcontain a preponderance of hydrogen substituent Rs. The most reactive glycols are those in which less than 4 Rs are other than hydrogen, and the greatest reactivity is possessed by those having 2 or less Rs which are organic radicals.

Glycols which fall Within the above classification include 1,6-heptanediol; 1,6-octanediol; 1,( inonanediol; 1,7-dodecanedio1; 1,8-n'onanedio1; 1,8-decanedi ol; 1,8-dodecai1ediol;v 1,9-,decanedio1 1,9 dodecanediol; 1,10 'dodecanediol; 2,7 oc-. tanediol; 2,7-nonanediol; 2,7-decanedio1; 2,7- dodecanediol; 2,8 nonanediol; 2,8 decanediol; 2,8 dodecanediol; 2,9 decahediol; 2,9 dodecanediol; 2,3 dimethyl-1,6 hexanediol; 2,4 dimethyl-1,6-hexanediol; 2,5 dimethyl-l,6 hexanediol; 2,2 dimethyl-1,6 hexanediol; 3,3 di-- methyl -1,6-hexanediol;v 4,4 dimethyl-:1,6 hexanediol; 5,5-dimethyl-1,6-hexanedio1; .2.-methy1 B-ethyl-LT-heptanediol; 2-ethyl-3-methyl: 1,7-1 heptanediol; 3,3 diethyl-1,7 heptanediol; 3,4-r diisopropyl-1,8-octanedio1; etc.,v and their polymerizable homologs, analogs I and derivatives;

The lubricants ofythe. present invention may be derived from polymers ofone ormore glycols of theabove type, or are copolymers-nfi'oneor more glycols of the above .type .withalkylene glycols wherein theglycollic hydroxyls are-separated by either 2or 3 carbon atoms. These two latter classesof glycols have the general formula I l H I I I 11". I 1 1.. i.,,, wherein m is an integer and r is an integeriless than 3. Thus, when a: and m are 1, thegeneral formula becomes that of an ethylene glycolderivativez. a. w

tem

wherein the remaining valences are satisfied with hydrogens and/ or organic radicals. When m is 1 and a: is 2 the general formula becomes that of a trimethyl'ene glycol derivative: "1

| o-on wherein m andnare integers, ails an integer less than 3, and y is an integer greater than 5,

the free valences being either hydrogens or organic substitutes. In accordance with one phase of'th'e present invention, the stable lubricants of the present invention may be prepared by reaction'of the end groups of said polymers, either during or subsequent to polymerization with ammonia or] an amine.

The amines useful forthe preparation of stable polymers of the present invention are pri mary or secondary aminesof aliphatic, aromatic or aliphatic-aromatic configurations.

, Primary aliphatic. amines are one of the re; ferred classes useful in forming the stable lubricants of the present invention. These have the general formula R'i-NHz V H V wherein R1 is an alkyl group. While R1 maybe an alkyl group having any number of carbon atoms, those having thegreatest stabilizing action on the subjectlubricants have from 3 to;1 5 carbon atoms, and optimum results are obtained when R1 is an alkylgroup containing from 3150.3:

7. carbon atoms. Thus, this latter optimum group is represented by propylamine, isopropylamine, butylamine, sec-butylamine, tert-butylamine', amylamine, isoamylamine, hexylamines, heptylamines and octylamines.

Other members of the preferred group include higher primary aliphatic amines include decylamine, dodecylamine, etc. The primary aliphatic amines may be regarded as hydrocarbons having a NH2 group replacing one of the hydrogens attached to a carbon atom. Thus, the preferred group of amines also includes, among others, 2-aminobutane, 2- or 3-aminopentane, 2-, 3-, or l-aminoheptane, 2-, 3-, 4-, or 5-aminoctane, etc. Other branched primary amines include 2-ethylhexylamine, 3-ethylhexylamine, 4-ethy1hexylamine, z-methylheptylamine, and their analogs and homologs.

Another preferred grou of amines useful for the preparation of the stable lubricants of the present invention are the secondary aliphatic amines. These include amines having similar or dissimilar alkyl groups, and have the general formula n M N-11? wherein R1 and R2 are alkyl groups. It is preferred that R1 and R2 be similar alkyl groups, each having from 3 to 15 carbon atoms, and optimum results are obtained when the alkyl groups each have from 3 to 8 carbon atoms. Thus, the optimum group includes dipropylamine, diisopropylamine, dibutylamine, di-secbutylamine, di-tert-butylamine, diamylamines, dihexylamines, diheptylamines and dioctylamines.

Mixed secondary aliphatic amines include methylaminoethane, 1- or, Z-methylaminopropane, 1- or 2-ethylaminobutane, 1-, 2- or 3- isopropylaminopentane, etc.

Aromatic amines of either primary or secondary configuration may be employed in the production of the stable lubricants described herein. Thus aniline and naphthylamine, as well as derivatives thereof, react with the subject polymers to form stable lubricants. The amines described above may contain other groups or elements other than hydrocarbons. Other substituents which may be present include acyl and hydroxyl groups, as well as sulfur, selenium, or tellurium. Thus, asninophenols and aliphatic hydroxylamines may be employed according to the present invention:

When alkylene oxides are the monomers from which the stable lubricants of present invention are prepared, it is a preferred practice to add an amine to the polymerization reaction mixture, thus allowing the amine to form end-groups of the polymer chains substantially as they are formed.

Alkylene oxides may be polymerized by heat ing the monomer at temperatures from about 25 C. to about 175 C. (preferably 35 C. to 150" C.) in the presence of catalysts such as alkali metal hydroxides, aluminum chloride, boron trifiuoride, or salts such as stannic chloride. Inert diluents, such as hydrocarbons or chlorinated hydrocarbons are preferably present to promote uniformity of reaction, and provide temperature control.

The various amines described hereinbefore may be added to the above reaction mixture con taining a monomeric alkylene oxide, a catalyst and, optionally, a diluent. Depending upon the constituents and the reaction conditions the reaction may be conducted in liquid, emulsion or gaseous phases or in more than one of such phases. Ammonia and the more volatile amines, such as inethylami'ne, etc., may be used especially when polymerization is conducted in the gas phase. The higher boiling amines are more properly used when the polymerization is car ried out in an emulsion or solution state. However, especially when the polymerization is carried out in an autoclave or other closed system the gaseous or low boiling amines likewise may be used in an emulsion or solution polymerization.

The alkylene glycols are polymerized under somewhat difierent conditions. The monomeric (or dimer, trimer, etc.,) glycol is heated at a temperature from about -250 C. (preferably -225 C.) in the presence of a dehydration catalyst, such as sulfuric acid, phosphoric acid, iodine, hydrogen iodide, etc., under conditions whereby the water formed during the reaction is substantially continuously removed from the polymerization zone. Preferably, a diluent is used during the polymerization, since it can aid in the control of the reaction and form an azectrope with the water of polymerization, thus facilitating the removal thereof.

While an amine may be added to the alkylene glycol polymerization system, preferably the endgroup conversion is effected subsequent to polymerization. Likewise, polymers of alkylene oxides may be treated with an amine subsequent to (instead of during) polymerization. In carrying out the reaction, the amine and polymer are heated in the presence of a dehydration catalyst, preferably in the presence 'of a solvent.

In carrying out the end-group conversion either during or subsequent to polymerization, enough of the amine is added to replaceone or more of the end-groups of each polymer chain. While one or both end group hydroxyls of some chains may be completely replaced by an amino (including substituted amino) group, as little as 2% conversion of the end-group hydroxyls to amines in any single product has been found to provide lubricants having excellent stability and superior lubricating properties. These lower proportions of amino groups may be formed by diluting the amino-substituted product with non-substituted material or by other methods.

The lubricants of the present invention contain polymers which have the general formula ll-- -12 X wherein R is any organic radical, n is an integer and at least one of the Xs is an amino (including substituted amino) end-group, the remainder being a hydroxyl, ester or ether group. Thus, when both end-groups have been completely converted, the polymer has the general formula partial conversionto ether .drieste'r end-groups. Euthermorepsubsequent to theintroduction of amino end-groups, the polymers may be treated with acids to form amine salts. I

The lubricants comprising polymers of the alkylene oxides or alkylene-glycols containing amino end-groups are highly resistant to 'oxida-'- tion andhavea superior response to oxidation inhibitors, as compared with lubricating polymers. having no amino end-groups; Thesubject lubri cants may containadditives further modifying their properties, including anticorrosion agents such as organic acid materials which form water EXAMPLE I One hundred parts glycidyl isopropyl ether was mixed with 315 parts isopentane and 5.4 parts di-isopropylamine. Sixteen and one-half parts borontrifiuoride-ether complex was added slowly under reflux (30 C.). After one hour the mixture was washed with water and heated at 100 C. under reduced pressure. An 87% yield of a polymer was recovered having the following properties:

Molecular weight 7'73 Centipoises viscosity at 100 F 100.5 Centipoises viscosity at 212 F. 10.34 Viscosity index 91 Nitrogen content per cent 0.15

For comparison, a similar polymer was prepared, omitting the di-isopropylamine. The latter polymer had the following properties:

Molecular weight 785 Centipoises viscosity at 100 F 103.5

Centipoises viscosity at 212 F 10.?

Viscosity index 94 EXAMPLE II The polymerization of glycidyl isopropyl ether was carried out as described in Example I, except that phenyl-alpha-naphthylamine was added to the polymerization reaction mixture instead of di-isopropylamine. Seventy-five grams of the resulting polymer, containing phenylalpha-naphthylamine end-groups, was subjected to oxidation by bubbling oxygen therethrough at 1 140 C. It required 19 hours for the polymer to absorb 1800 cc. oxygen.

EXAMPLE HI .165 addition of borontrifluoride. v The products had th frollowing properties:

Table I Di-isopropylamino End- Groups Hydroxyl Polymer End- Groups Time for pressure to drop 10 p. s. i 29 Time for pressure to drop 20 p. s. i 32% 55 Induction period 28 EXAlVIPLE V 35 The two polymers prepared as described in Example I were subjected to the oxidation test described in Example IV. 1.5% phenyl-alphanaphthylamine being added to each polymer prior to the test. The results are given in Table II, below:

TABLE II Hydroxyl Di-isopropyl- Endamino Endgroups groups Hours to absorb 250 cc. oxygen 2 30 Hours to absorb 500 cc. oxygen- 2. 5 35 Hours to absorb 1,000 cc. oxygen" 3 37 Hours to absorb 1,800 cc. oxygen 4 38 We claim as our invention:

1. A lubricating composition comprising as the major lubricating constituent thereof a mixture of linear polymers of glycidyl isopropyl ether having a molecular weight of about '773 and a nitrogen content of about 0.15%, said nitrogen content being contained in di-isopropylamino end groups attached to polymeric members of said mixture, and a minor amount, sufiicient to stabilize said mixture against oxidation, of

phenyl-alpha-naphthylamine.

2. A lubricating composition comprising as the major lubricating constituent thereof a mixture of linear polymers of glycidyl isopropyl ether having a molecular weight of about 7'73, a minor proportion of said polymers having phenylalpha-naphthylamino end groups, the amount of said amino end groups being at least 2% of the end groups of all of the polymers, and in addition thereto a minor amount, sufficient to stabilize said mixture against oxidation, of phenylalpha-naphthylamine.

A lubricating composition comprising as the major lubricating constituent thereof a mixture of linear polymers of glycidyl isopropyl ether 2,522,155 11- 12 having a molecular weightoi about 273, a minor REFERENCES CITED proportion of said polymers havingamino end groups selected from the class consisting of diisopropyl amino end groups and phenyl-alpha- The following references are of record in the file of this patent:

naphthyl amino end groups, the amount of said 5 UNITED STATES PATENTS amino end groups being at least about 2% of the Number Name Date end groups of all of the polymers, and in addi- 1,970,578 Schoeller Q. Aug. 21, 1934 tion thereto a minor amount, sufficient to sta- 2,089,569 Orthner Aug. 10, 1937 bilize said mixture against oxidation, of phenyl- 10 2,434,978 Zisman Jan. 27, 1948 alpha-naphthylamine, 2,435,655 Rhodes Feb. 10, 1948 7 FOREIGN PATENTS SEAVER A. BALLARD. N t t RUPERT c. MORRIS. umber Cmm ry Da 8 JOHN L. VAN wmxm. 15 406,443 Great Britain Mar. 1, 1934

Claims

1. A LUBRICATING COMPOSITION COMPRISING AS THE MAJOR LUBRICATING CONSTITUENT THEREOF A MIXTURE OF LINEAR POLYMERS OF GLYCIDYL ISOPROPYL ETHER HAVING A MOLECULAR WEIGHT OF ABOUT 773 AND A NITROGEN CONTENT OF ABOUT 0.15%, SAID NITROGEN CONTENT BEING CONTAINED IN DI-ISOPROPYLAMINO END GROUPS ATTACHED TO POLYMERIC MEMBERS OF SAID MIXTURE, AND A MINOR AMOUNT, SUFFICIENT TO STABILIZE SAID MIXTURE AGAINST OXIDATION, OF PHENYL-ALPHA-NAPHTHYLAMINE.