Abstract:
An antioxidant bound VII polymethacrylate lubricant additive composition prepared by: 
     (a) combining an antioxidant monomer (C 1  -C 20 ) alkyl monomers in an oil solvent to provide an intermediate reaction mixture; 
     (b) stirring and purging the reaction mixture by nitrogen ebullotion for about 25-35 minutes at about 200 ml/min; 
     (c) reducing nitrogen ebullotion to 15-25 ml/min and heating the purged mixture to about 70°-85° C.; 
     (d) adding both a mercaptan and a radical polymerization catalyst to the heated mixture and then after about 2.0 hours adding an additional amount of the catalyst to said heated mixture, and then heating said heated mixture for an additional 2.0 hours; 
     (e) increasing the temperature of the heated mixture to about 95°-105° C. and maintaining the mixture at such temperature for a sufficient period of time to remove any excess of the polymerization catalyst; and 
     (f) recovering the product polymethacrylate.

Description:
This invention relates to Viscosity Index Improvers (VII), and more particularly to an antioxidant bound Viscosity Index Improving polymethacrylate lubricant additive. 
     As is well known to those skilled in the art, lubricating oils for internal combustion engines typically contain a multitude of additives which function as detergents, dispersants, viscosity index improvers, pour depressants, etc., to improve the properties of the oil. It is found that it is particularly necessary to improve the resistance of a lubricating oil to oxidation. 
     In developing suitable additives for imparting various properties to lubricating oils, polymethacrylate polymers have been found to be useful for a variety of applications in lubricants. Some of their chief uses are as Viscosity Index (VI) improvers and pour point depressants (PPD&#39;s) for lubricants. The preparation of functionalized PMA&#39;s has increased in recent years. Many functionalized PMA&#39;s contain some amine functionality for the purpose of imparting dispersancy to the polymer. Other functionalized PMA&#39;s are also known, but to a lesser extent. There are, however, only a few examples of antioxidants being incorporated into the polymers. In developing PMA&#39;s which impart multifunctional properties to VII&#39;s and lubricants there has not been proved an adequate process for synthesizing a multifunctional PMA, incorporating an amine type antioxidant. 
     DISCLOSURE STATEMENT 
     U.S. Pat. No. 4,036,766 discloses a complex reaction product of an interpolymer of dialkylamino methacrylate, (C 1  -C 20 ) alkyl methacrylates and a liquid poly (alkene -1) of a molecular weight of 200 to 10,000 which results in a product of good VI improving properties but also a product which has improved dispersant and antioxidant properties when incorporated in automatic transmission and crankcase fluids for a given nitrogen content. 
     U.S. Pat. No. 4,606,834 discloses lubricating oil compositions which contain a VI improving (VII) pour point depressant. The VII consists essentially of a terepolymer where the monomers are selected from various ((C 1  -C 20 ) alcohols and acrylates. 
     U.S. Pat. No. 4,098,700 discloses polymers containing post-reacted hindered phenol antioxidant functionality as viscosity index (VI) improvers for high temperature service, particularly for lubricating oils used in diesel engines. 
     Co-assigned U.S. application Ser. No. 172,664 discloses a reaction product of an ethylene copolymer or terpolymer of a (C 3  -C 10 ) alphamonolefin and optionally a non-conjugated diene or triene on which has been grafted an ethylenically unsaturated carboxylic function which is then further derivatized with an amino-aromatic polyamine compound. 
     SUMMARY OF THE INVENTION 
     The invention provides an antioxidant bound, Viscosity Index-improving polymethacrylate composition having a molecular weight ranging from about 20,000 to about 2,500,000. The composition comprises a base oil and effective amounts of alkyl and antioxidant monomers. The composition being prepared by: 
     (a) combining an antioxidant monomer (C 1  -C 20 ) alkyl monomers in an oil solvent to provide an intermediate reaction mixture; 
     (b) stirring and purging the reaction mixture by nitrogen ebullation for about 25-35 minutes at about 200 ml/min; 
     (c) reducing nitrogen ebullation to 15-25 ml/min and heating the purged mixture to about 70°-85° C.; 
     (d) adding both a mercaptan and a radical polymerization catalyst to the heated mixture and then after about 2.0 hours adding an additional amount of the catalyst to said heated mixture; 
     (e) increasing the temperature of the heated mixture to about 95°-105° C. and maintaining the mixture at such temperature for a sufficient period of time to remove any excess of the polymerization catalyst; and 
     (f) recovering the product polymethacrylate. 
     The antioxidant monomer is selected from the group consisting of an acrylate, a methacrylate, an acrylamide or a methacrylamide derived from acrylic of methacrylic acid or their derivatives, an aromatic alcohol, an amine and a phenol compound. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention resides in a dispersant/antioxidant bound, Viscosity Index Improving (VII) polymethacrylate lubricant additive comprising an antioxidant monomer. 
     The antioxidant monomers that may be used to make the present lubricant additive may be selected from the group consisting of an acrylate, a methacrylate, an acrylamide or a methacrylamide derived from acrylic or methacrylic acid or their derivatives, an aromatic alcohol, an amine and a phenol compound. 
     The aromatic alcohol is a hydroxy diphenylamine represented by the formula: ##STR1## where R is a (C 1  -C 14 ) alkyl radical or aryl group or a hydroxy phenothiazine represented by the formula ##STR2## where R is a (C 1  -C 14 ) alkyl radical or aryl group. 
     The acrylate or methacrylate monomers and alkyl acrylate or methacrylate monomers of the present invention are conveniently prepared from the corresponding acrylic or methacrylic acids or their derivatives. These acids can be synthesized using conventional methods and techniques. For example, acrylic acid is prepared by the acidic hydrolysis and dehydration of ethylene cyanohydrin or by the polymerization of β-propiolactone and the destructive distillation of the polymer to form acrylic acid. 
     Methacrylic acid is readily prepared by the oxidation of methyl α-alkyl vinyl ketone with metal hypochlorites; the dehydration of α-hydroxyisobutyric acid with phosphorus pentoxide; or the hydrolysis of acetone cyanohydrin. 
     The alkyl acrylate or methacrylate monomers of the present invention are conveniently prepared by reacting the desired primary alcohol with the acrylic acid or methacrylic acid in a conventional esterification catalyzed by acid, preferably p-toluene sulfonic acid inhibited from polymerization by MEHQ or hydroquinone. Suitable alkyl acrylates or alkyl methacrylates contain from about to about 30 carbon atoms in the alkyl carbon chain. Typical examples of starting alcohols include methyl alcohol, ethyl alcohol, butyl alcohol, octyl alcohol, iso-octyl alcohol, isodecyl alcohol, undecyl alcohol, dodecyl alcohol, tridecyl alcohol, capryl alcohol, lauryl alcohol, myristyl alcohol, pentadecyl alcohol, palmityl alcohol or stearyl alcohol. It is to be noted that all of the starting alcohols described above can be reacted with acrylic acid or methacrylic acid to form desirable acrylates or methacrylates. 
     The copolymers useful in the practice of this invention can be prepared in a conventional manner by bulk, solution or dispersant polymerization methods using known catalysts. Thus, the copolymers utilized by this invention can be prepared from the corresponding monomers with a diluent such as water in a heterogeneous system, usually referred to as emulsion or suspension polymerization, or in a homogenous system with a solvent such as toluene, benzene, ethylene dichloride, or an oil solvent which is normally referred to as solution polymerization. Solution polymerization in benzene, toluene or an oil solvent having similar chain transfer activity is the preferred method used in forming the copolymers disclosed herein, because this method and solvent produce the preferred copolymers characterized by a relatively high molecular weight. Solvents normally comprise from about 10 to about 50 weight percent based on the weight of the copolymer. 
     The polymerization of the monomers uses suitable catalysts which include peroxide type free radical catalysts such as benzoyl peroxide, lauroyl peroxide, or t-butylhydroperoxide; and free radical catalysts such as 2,2&#39;-azobisisobutyronitrile. The catalysts, when used, are employed in concentrations ranging from a few hundredths of a percent to two percent by weight of the monomers. The preferred concentration is from about 0.2 to about 1.0 percent by weight of the monomers. 
     Copolymerization of the monomers used herein takes place over a wide temperature range depending upon the particular monomers and catalyst utilized in the reaction. For example, copolymerization can take place at temperatures as low as -103° F.(-75° C.) or lower when metallic sodium in liquid ammonia is used as the catalyst. However, the copolymerization reaction is generally carried out at temperatures ranging from about 77° F.(25° C.) to about 302° F.(150° C.&gt;) when a catalyst such as 2,2&#39;azobisisobutyronitrile is used. The copolymerization reaction is preferably carried out in an inert atmosphere, for example, argon or nitrogen to favor the formation of copolymers having relatively high viscosities and molecular weights. 
     Preferably, the copolymerization reaction is carried out to substantial completion so that the finished product is essentially comprised of the ratio of monomers introduced into the vessel. Normally, a reaction time of from about 1 to about 72 hours, preferably from about 1 to about 50 hours, is sufficient to complete the copolymerization process. 
     The copolymers disclosed herein have an average molecular weight of greater than about 20,000, especially a molecular weight range of from about 20,000 to about 300,000, preferably from about 100,000 to about 200,000. The molecular weight of the copolymer can conveniently be determined using conventional techniques. 
     The copolymers of this invention may be formed from ##STR3## wherein R 1  is H or a lower alkyl group; 
     R 2  is a (C 2  -C 20 ) alkyl group; 
     and 
     Y is an aromatic amine or amine residue. 
     In the above formula, R 1  may be H or methyl, most preferably methyl. 
     R 2  may be an alkyl group containing 1-20 carbon atoms typified by decyl, undecyl, lauryl, tridecyl, myristyl, pentadecyl, etc. 
     Illustrative of the first monomers which may be employed are those provided below in Table I, the first listed being preferred. 
     
                       TABLE I______________________________________Neodol 25L          methacrylateAlfol 1620 SP       methacrylateNeodol 25L          acrylateAlfol 1620 SP       acrylatelauryl              methacrylatelauryl              acrylatelauryl              ethacrylatedecyl               methacrylatedecyl               acrylateundecyl             methacrylateundecyl             acrylatetridecyl            methacrylatetridecyl            acrylatemyristyl            methacrylatemyristyl            acrylatepentadecyl          methacrylatepentacecyl          acrylateisodecyl            methacrylateisodecyl            acrylatestearyl             methacrylatestearyl             acrylatecetyl               methacrylatecetyl               acrylate______________________________________ 
    
     The NMA and the AMA monomers described above are respectively derived from Neodol 25L and Alfol 1620 SP which are trade names for technical grade alkanols, respectively, of Shell Chemical Co. and Continental Oil Co. of the following typical analyses. 
     
         ______________________________________           Typical Approx. Homolog           Distribution, wt %______________________________________Neodol 25L(Synthetic Lauryl Alcohol)Lighter than C.sub.12 OH              4C.sub.12 OH       24C.sub.13 OH       24C.sub.14 OH       24C.sub.15 OH       13C.sub.16 OH        2Alfol 1620 SP(Synthetic Stearly Alcohol)C.sub.14 OH and lighter              4C.sub.16 OH       55C.sub.18 OH       28C.sub.20 OH        9______________________________________ 
    
     The second monomer which contains an amine or residue thereof may be any of the following: 
     (a) an amino phenothiazine represented by the formula ##STR4## where R is H or a (C 1  -C 14 ) alkyl radical or a (C 1  -C 14 ) alkaryl group; 
     (b) an N-arylphenylenediamine represented by the formula: ##STR5## in which R 1  is H, aryl-NHaryl, -NHarylalkyl, a branched or straight chain radical having from 4 to 24 carbon atoms that can be alkyl, alkenyl, alkoxyl, aralkyl alkaryl, hydroxyalkyl or aminoalkyl, R 2  is NH 2  CH 2  --(CH 2 ) n  --NH 2  --CH 2  --arylNH 2  in which N has a value from 1 to 10, R 3  is alkyl, alkenyl, alkoxyl, aralkyl, alkaryl, having from 4 to 24 carbon atoms; 
     (c) an aminothiazole from the group consisting of aminothiazole, aminobenzothiazole, aminobenzothiadiazole and aminoalkylthiazole; 
     (d) an aminocarbazole represented by the formula: ##STR6## in which R and R&#39; represent hydrogen or an alkyl or alkenyl, radical having from 1 to 14 carbon atoms; 
     (e) an aminoindole represented by the formula: ##STR7## in which R represents hydrogen or an alkyl radical having from 1 to 14 carbon atoms; 
     (f) an aminopyrrole represented by the formula: ##STR8## in which R is a divalent alkylene radical having 2-6 carbon atoms and R&#39; hydrogen or an alkyl radical having from 1 to 14 carbon atoms; (g) an amino-indazolinone represented by the formula: ##STR9## in which R is hydrogen or an alkyl radical having from 1 to 14 carbon atoms; (h) an aminomercaptotriazole represented by the formula: ##STR10## 
     (i) an aminoperimidine represented by the formula: ##STR11## in which R represents hydrogen or an alkyl radical having from 1 to 14 carbon atom. 
     The first monomer when prepared commercially may in fact be a mixture obtained by use of a crude alcohol mixture during esterification. The carbon number of the monomer is that of the ester which is the predominant ester in the monomer. Commonly, the carbon number may be the weight average carbon number of the alcohol-derived alkyl group making up the esters. 
     The two component copolymers of this invention may be prepared by contacting a mixture consisting essentially of first monomer and the second monomer in the presence of a polymerization initiator-catalyst and chain transfer agent in an inert atmosphere in the presence of a diluent. Typically 75-98 parts, preferably 90-99, say 96 of the first monomer and 1-15 parts, preferably 2-10, say 4 parts of the second monomer may be added to the reaction operation. 
     The polymerization solvent may typically be an inert hydrocarbon, preferably hydrocarbon lubricating oil (typically N 100 pale oil) which is compatible with or identical to the lubricating oil in which the additive is to be employed present in amount of 5-50 parts, preferably 20-50 parts, say 43 parts per 100 parts of total reactants. 
     Polymerization initiator-catalyst may be 2,2&#39;-azobisisobutyronitrile (AIBN), or a peroxide such as benzoyl peroxide, present in amount of 0.05-0.25 parts, preferably 0.1-0.2 parts, say 0.16 parts. Chain terminator may typically be C8-C10 mercaptans, typified by lauryl mercaptan, present in amount of 0.10 parts, preferably 0.02-0.08 parts, say 0.06 parts. 
     Polymerization is carried out with agitation at 25° C.-150° C., preferably 50°-C.-100° C., say 83° C., and 0-100 psig, preferably 0-50 psig, say 0 psig for 1-8 hours, say 3 hours. Reaction may be continued until two identical refractive indices are recorded. 
     The product polymer is characterized by a molecular weight (Mn) of preferably 20,000-250,000, say 80,000. The component weight ratio of first and second monomers may be 85-99: 1-15, say 96:4. 
     The polydispersity index (Mw/Mn) of these oilsoluble polymers may be 1-5, preferably 1.5-4, say 2.3. 
     In a typical reaction, the monomers are charged to the reactor together with polymerization solvent followed by chain terminator. Agitation and inert gas (e.g. nitrogen) flow are initiated. Polymerization initiator is added and the reaction mixture is heated to reaction temperature at which it is maintained until the desired degree of polymerization is attained. Diluent oil (if employed) is added to yield a lube oil concentrate containing about 25-80 wt %, preferably 35-70 wt %, say 40 wt % of the product terpolymer. 
     The terpolymers prepared may be characterized by the formula: ##STR12## 
     In practice of this invention, a hydrocarbon lubricating oil composition may comprise a major effective portion of a hydrocarbon lubricating oil and a minor effective portion of the additive polymer. The minor effective portion may typically be 0.01-10.0 parts. Preferably 0.1-8 parts, say 5.0 parts, per 100 parts of hydrocarbon lubricating oil. The total composition may also contain other additives typified by oxidation inhibitors, corrosion inhibitors, antifoamants, detergents, dispersants, etc. 
     Typical of the supplementary detergent-dispersants which may be present may be alkenylsuccinimides derived from polyisobutylene (Mn of 700-5000) overbased calcium alkyl aromatic sulfonate having a total base number of about 300; sulfurized normal calcium alkylphenolate; alkenyl succinimides; etc. as disclosed U.S. Pat. No. 3,087,956 and U.S. Pat. No. 3,549,534 and U.S. Pat. No. 3,537,966. 
     Typical of the antioxidants which may be present may be zinc or cadmium dialkyl dithiophosphates; alkylated diphenyl amines; sulfurized alkylphenols and phenolates; hindered phenols; etc. 
     Typical of the corrosion inhibitors which may be present may be zinc dialkyldithiophosphates, basic calcium, barium, or magnesium, sulfonates; calcium, barium, and magnesium phenolates, etc. 
     It is a feature of this invention that the novel lubricating oil compositions may be characterized by improved pour point when the novel additives are present in amount of 0.05-5.0 wt %, preferably 0.1-0.7 wt %, say 0.3 wt % of the lubricating oil. 
     Typically it may be possible to treat a base lubricating oil of pour point of -12° C., by addition of only 0.3 wt % of additive to yield a product having a pour point of minus 36° C. The pour point is commonly measured by ASTM D-97. 
     When used as a pour point depressant, it is preferred that the molecular weight (Mn) of the polymer be 20,000-120,000, preferably 20,000-80,000, say 20,000. 
     It is also a feature of this invention that the novel additives may be used as dispersancy improvers when present in lubricating oil compositions in effective amount of 1.0 wt %-10.0 wt %, preferably 2.0 wt %-8.0 wt %, say 5.0 wt %. When dispersancy is primarily desired, the molecular weight (Mn) of the polymer may be 20,000-120,000, say 80,000. 
     The novel additives of this invention may impart viscosity index improvement to lubricating oils when present in amount to of 0.25 wt %-10.0 wt %, preferably 2 wt %-8 wt %, say 5.0 wt %. When they are employed primarily as viscosity index improvers, the molecular weight (Mn) may be 20,000-150,000, preferably 40,000-120,000, say 80,000. The Viscosity Index is measured by ASTM D-2270. 
     It is a feature of the terpolymer additives of this invention (which consist essentially of first, second and third monomer components) that they unexpectedly provide improvements in pour dispersancy, dispersancy, and viscosity index, i.e. they may be used, either in whole or in part, to provide all of these functions. When it is desired to utilize the novel additive to provide all three of these functions, it is preferred that the additive be present in amount of 1.0-5.0 wt %, say 3.8 wt % of the lubricating oil composition. In this instance the molecular weight Mn may be 20,000-120,000, preferably 40,000-90,000, say 80,000. 
     In order to show the advantages of the present invention the following Example is provided as being representative of the best mode of how to practice the invention described herein and not intended to limit the scope thereof. 
    
    
     EXAMPLE I 
     PREPARATION OF AN ANTIOXIDANT POLYMETHACRYLATE (AOPMA) 
     To a 1000 ml resin kettle equipped with a condenser, thermocouple, thermometer, and heavy duty stirrer, was added N-(4-anilinophenyl) methacrylamide (8 g, 4%, dimethylaminopropyl methacrylamide (8 g, 4%), butyl methacrylate (20 g, 10%) neodol 25L methacrylate (152 g, 76%), alfol 1620 SP methacrylate (12 g, 6%) and an oil solvent (N100 Pale Oil, 86 g). The reaction mixture was stirred and purged by nitrogen ebullition for 30 min. at 200 ml/min. The mixture was then heated to 80 C. by means of a heat lamp, and dodecyl mercaptan (0.2 g) and AIBN (0.3 g) were then added. After 2 hrs., an additional amount of AIBN (0.3 g) was added. After 2 hrs., the reaction temperature was increased to 100 C. and maintained for 1 hr. to destroy any excess AIBN. The product was diluted in the reaction vessel with N55 Pale Oil (214  g) to give a final concentration of ˜40% in oil. An analyses of the product is given below in Table III. 
     
                       TABLE III______________________________________Typical Product Analyses______________________________________Kin. Vis. 40C             97.2 cStKin. Vis. 100C            14.09 cStRefractive Index 80% Conc. (48.3° C.)                     1.4667______________________________________ 
    
     In an additional test, the pour point was determined to be -36° C. In the test a 5 wt % blend of polymer was blended in a conventional base oil. In order to measure the antioxidant properties of the polymer product a Bench Oxidation Test (BOT) was used as described below. 
     Evaluation of Antioxidant Properties 
     A Bench Oxidation Test (BOT) was used to measure the antioxidant properties of the polymer. This test measures the relative increase of the carbonyl absorption band of 1710 cm -1  of an oxidized oil, over that of the starting material. 
     BOT TEST PROCEDURE 
     The test is conducted in a 2 L, 4-neck resin kettle equipped with a thermometer, condenser, gas bubbling tube and a mechanical stirrer. The polymer (3.75 wt % of a 40 wt % concentrate) was added along with 1235 g of SNO-7 oil. The reaction mixture was stirred and purged with nitrogen for 30 min. The solution was then heated to 150° C. and initial samples were taken (0 hr. samples). The oxidation is started by switching from a nitrogen purge to one of air at a rate of 500 ml/min. The stirring rate is kept between 675 and 700 rpm&#39;s. Samples are taken periodically using a syringe and evacuated test tubes. They are then quickly stored in a refrigerator to quench the oxidation. BOT DIR values are obtained by using a Differential Infrared technique (DIR) in which the carbonyl absorption band at 1710 cm -1  of the zero hour sample, is subtracted from that of the final product (144 hrs.). 
     The SNO-7 will give a DIR of ˜7 if no antioxidant is used, so values less that 7 are considered indicative of antioxidant properties. In Example 1, a DIR of 1.77 was obtained. 
     In the formation of an oil, a low pour point is important. According to the present invention, the pour point may be lowered from about -25° C. to about -40° C. The procedure for evaluating the pour point depressant properties is provided below. 
     Evaluation of Pour Point Depressant Properties 
     The pour point of an oil is measured by the ASTM D-97 test. Pour point depressants are evaluated at how much they depress the pour point of an oil. A base oil has a pour point of -12° C. The addition of a commercial pour point depressant at 5.0 wt % effectively lowers the pour point of the base oil to at least -30° C. The product of Example 1, accordingly, effectively lowers the pour point of the base oil to about -36° C. when used at 5.0 wt %.