Patent Publication Number: US-2021189280-A1

Title: Lubricant Composition Comprising an Antioxidant Composition

Description:
RELATED APPLICATIONS 
     This application claims filing benefit of U.S. Provisional Patent Application No. 62/951,284 having a filing date of Dec. 20, 2019 and U.S. Provisional Patent Application No. 62/988,061 having a filing date of Mar. 11, 2020, both of which are hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     Lubricant compositions are utilized in a variety of applications. During use and even prior to use, these lubricant compositions are exposed to heat and oxygen which can result in oxidation of the lubricant composition. Such oxidation can result in decreased performance and can also potentially damage the machinery on which the composition is utilized. Accordingly, the lubricant composition has a decreased service life thereby requiring replacement sooner than desired. In order to prevent the oxidation or extend the oxidation induction, various types of antioxidants are employed. However, certain available antioxidants may not perform as well as desired. For instance, they may not prevent oxidation or extend the oxidation induction as desired thereby resulting in oxidation of the lubricant composition earlier than desired. 
     As such, a need continues to exist for a lubricant composition having improved antioxidation performance. 
     SUMMARY OF THE INVENTION 
     In accordance with one embodiment of the present invention, a lubricant composition is disclosed. The lubricant composition comprises an antioxidant composition and a lubricating oil. The antioxidant composition comprises a phenolic antioxidant having the following structure (I) 
     
       
         
         
             
             
         
       
     
     and
 
a phosphite antioxidant having the following structure (II)
 
     
       
         
         
             
             
         
       
     
     wherein, 
     A is a direct bond or an alkylene; 
     X is —C(O)O—, —OC(O)—, —C(O)N(R 7 )—, —N(R 7 )C(O)—, —C(O)—, —N(R 7 )—, —O— or —S—; 
     R 1  and R 2  are each independently a C 1 -C 10  alkyl, a C 2 -C 10  alkenyl, a C 2 -C 10  alkynyl, or a C 3 -C 12  aryl; 
     R 3  includes a C 1 -C 80  alkyl, a C 2 -C 80  alkenyl, a C 2 -C 80  alkynyl, or a C 3 -C 12  aryl; 
     R 4 , R 5 , and R 6  are each independently hydrogen, alkyl, alkenyl, alkynyl, or aryl provided that at least one of R 4 , R 5 , and R 6  is not hydrogen; 
     R 7  is H or an alkyl; and 
     m, n, and o are each independently from 1 to 3. 
     In accordance with another embodiment of the present invention, a method of forming a lubricant composition is disclosed. The method comprises combining a lubricating oil with the aforementioned antioxidant composition. 
     Other features and aspects of the present invention are set forth in greater detail below. 
     Definitions 
     It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of the present invention. 
     “Alkyl” refers to straight chain, branched chain, or cyclic monovalent saturated aliphatic hydrocarbyl groups and “C q -C r  alkyl” refers to alkyl groups having from q to r carbon atoms. This term includes, by way of example, straight chain, branched chain, or cyclic hydrocarbyl groups, such as methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl, icosanyl, henicosanyl, docosanyl, tricosanyl, tetracosanyl, pentacosanyl, hexacosanyl, heptacosanyl, octacosanyl, and the like. Alkyl includes a substituted alkyl or an unsubstituted alkyl. For example, the alkyl may be substituted (e.g., having from 1 to 5 and, in some embodiments, 1 to 3 or 1 to 2 substituents). Alternatively, the alkyl may be unsubstituted. 
     “Alkylene” refers to a straight chain or branched chain divalent hydrocarbyl. For example, “C y -C z  alkylene” refers to an alkylene group having from y to z carbon atoms. This term includes, by way of example, straight chain or branched chain hydrocarbyl groups, such as methylene, ethylene, propylene (e.g., n-propylene), butylene (e.g., n-butylene), and the like. 
     “Alkenyl” refers to a straight chain or branched chain monovalent aliphatic hydrocarbyl group having at least 1 site of vinyl unsaturation (&gt;C═C&lt;). For example, “C s -C t  alkenyl” refers to alkenyl groups having from s to t carbon atoms. This term includes, by way of example, straight chain or branched chain hydrocarbyl groups, such as ethenyl, propenyl, 1,3-butadienyl, and the like. Alkenyl includes a substituted alkenyl or an unsubstituted alkenyl. For example, the alkenyl may be substituted (e.g., having from 1 to 5 and, in some embodiments, 1 to 3 or 1 to 2 substituents). Alternatively, the alkenyl may be unsubstituted. 
     “Alkynyl” refers to a straight chain or branched chain monovalent aliphatic hydrocarbyl group having at least one carbon triple bond. The term “alkynyl” is also meant to include those hydrocarbyl groups having one triple bond and one double bond. For example, “C u -C v  alkynyl” refers to alkynyl groups having from u to v carbon atoms. This term includes, by way of example, straight chain or branched chain hydrocarbyl groups, such as ethynyl, propynyl, and the like. Alkynyl includes a substituted alkynyl or an unsubstituted alkynyl. For example, the alkynyl may be substituted (e.g., having from 1 to 5 and, in some embodiments, 1 to 3 or 1 to 2 substituents). Alternatively, the alkynyl may be unsubstituted. 
     “Aryl” refers to an aromatic hydrocarbyl group. For example, “C w -C x  aryl” refers to aryl groups having from w to x carbon atoms. This term includes, by way of example, linear and branched hydrocarbyl groups, such as phenyl, naphthyl, indenyl, azulenyl, fluorenyl, anthracenyl, phenanthrenyl, tetrahydronaphthyl, indanyl, phenanthridinyl and the like. Aryl includes a substituted aryl or an unsubstituted aryl. For example, the aryl may be substituted (e.g., having from 1 to 5 and, in some embodiments, 1 to 3 or 1 to 2 substituents). Alternatively, the aryl may be unsubstituted. 
     It is understood that the above definitions are not intended to include impermissible substitution patterns (e.g., methyl substituted with 5 fluoro groups). Such impermissible substitution patterns are well known to a person skilled in the art. 
    
    
     DETAILED DESCRIPTION 
     It is to be understood by one of ordinary skill in the art that the present discussion is a description of exemplary embodiments only, and is not intended as limiting the broader aspects of the present invention. 
     Generally speaking, the present invention is directed to a lubricant composition including a lubricating oil and a specific antioxidant composition. In particular, the antioxidant composition comprises at least one phenolic antioxidant and at least one phosphite antioxidant as defined herein. The present inventors have discovered that when such an antioxidant composition is utilized, it can provide a lubricant composition with improved properties. In particular, the present inventors have discovered that the antioxidant composition can be utilized to further stabilize a lubricating oil for a lubricant composition. For instance, the antioxidant composition may extend the lubricant composition&#39;s oxidation induction time, mitigate the viscosity increase of the lubricant composition, and/or abate the lubricant composition&#39;s acid number increase. 
     For example, the lubricant composition may exhibit improved oxidation stability as determined according to a standard rotating pressure vessel oxidation test (RPVOT). In particular, the lubricant composition may exhibit a standard RPVOT oxidation induction time of 150 minutes or more, such as 200 minutes or more, such as 250 minutes or more, such as 275 minutes or more, such as 290 minutes or more, such as 300 minutes or more, such as 325 minutes or more, such as 350 minutes or more. The standard RPVOT oxidation induction time may be 600 minutes or less, such as 500 minutes or less, such as 450 minutes or less, such as 400 minutes or less, such as 375 minutes or less, such as 350 minutes or less, such as 325 minutes or less. In general, the longer the oxidation induction time, the better the oxidation stability of the oil. The standard RPVOT oxidation induction time may be determined according to ASTM D2272-14a and at a temperature of 150° C. In addition, the actual standard RPVOT oxidation induction time may be greater than an expected standard RPVOT oxidation induction time as determined herein. For instance, such actual standard RPVOT oxidation induction time may be at least 20% greater, such as at least 30% greater, such as at least 40% greater, such as at least 50% greater, such as at least 60% greater than an expected standard RPVOT oxidation induction time. Accordingly, by exhibiting a standard RPVOT oxidation induction time greater than an expected standard RPVOT oxidation induction time, the antioxidant composition may demonstrate a synergistic antioxidant activity. While the aforementioned references the standard RPVOT oxidation induction time of the lubricant composition, in another embodiment, such oxidation induction times may be realized for the antioxidant composition when measured utilizing the lubricating oil as described in the test method and examples below. 
     In addition, the lubricant composition may also exhibit improved oxidation stability when determined according to a dry RPVOT without the use of water. For example, the lubricant composition may exhibit a dry RPVOT oxidation induction time of 200 minutes or more, such as 300 minutes or more, such as 400 minutes or more, such as 450 minutes or more, such as 500 minutes or more, such as 550 minutes or more. The dry RPVOT oxidation induction time may be 1,000 minutes or less, such as 900 minutes or less, such as 800 minutes or less, such as 700 minutes or less, such as 650 minutes or less, such as 600 minutes or less, such as 575 minutes or less, such as 550 minutes or less, such as 500 minutes or less. In general, the longer the oxidation induction time, the better the oxidation stability of the oil. The dry RPVOT oxidation induction time may be determined according to a modified ASTM D2272-14a and at a temperature of 150° C. except that the test does not utilize water (e.g., the 5 g of water as required by the test for determining the standard RPVOT oxidation induction time). In addition, the actual dry RPVOT oxidation induction time may be greater than an expected dry RPVOT oxidation induction time as determined herein. For instance, such actual dry RPVOT oxidation induction time may be at least 20% greater, such as at least 30% greater, such as at least 40% greater, such as at least 50% greater, such as at least 60% greater, such as at least 70% greater than an expected dry RPVOT oxidation induction time. Accordingly, by exhibiting a dry RPVOT oxidation induction time greater than an expected dry RPVOT oxidation induction time, the antioxidant composition may demonstrate a synergistic antioxidant activity. While the aforementioned references the dry RPVOT oxidation induction time of the lubricant composition, in another embodiment, such oxidation induction times may be realized for the antioxidant composition when measured utilizing the lubricating oil as described in the test method and examples below. 
     Also, the lubricant composition may demonstrate improved oxidation performance when measured according to pressure differential scanning calorimetry (PDSC). For example, the lubricant composition may exhibit a PDSC oxidation induction time of 20 minutes or more, such as 40 minutes or more, such as 50 minutes or more, such as 70 minutes or more, such as 90 minutes or more, such as 100 minutes or more, such as 120 minutes or more, such as 140 minutes or more, such as 160 minutes or more. The PDSC oxidation induction time may be 350 minutes or less, such as 300 minutes or less, such as 250 minutes or less, such as 200 minutes or less, such as 190 minutes or less, such as 175 minutes or less, such as 150 minutes or less, such as 130 minutes or less, such as 110 minutes or less, such as 100 minutes or less. In general, the longer the oxidation induction time, the better the oxidation stability of the oil. The PDSC oxidation induction time may be determined at a temperature of 160° C. In addition, the actual PDSC oxidation induction time may be greater than an expected PDSC oxidation induction time as determined herein. For instance, such actual PDSC oxidation induction time may be at least 20% greater, such as at least 30% greater, such as at least 50% greater, such as at least 70% greater, such as at least 100% greater, such as at least 150% greater, such as at least 200% greater than an expected PDSC oxidation induction time. Accordingly, by exhibiting a PDSC oxidation induction time greater than an expected PDSC oxidation induction time, the antioxidant composition may demonstrate a synergistic antioxidant activity. While the aforementioned references the PDSC oxidation induction time of the lubricant composition, in another embodiment, such oxidation induction times may be realized for the antioxidant composition when measured utilizing the lubricating oil as described in the test method and examples below. 
     In addition, the lubricant composition may demonstrate a reduced amount of deposits, which can be important in regard to maintaining the performance of machinery on which the lubricant composition is utilized. For example, the lubricant composition may have deposits as demonstrated according to a thermo-oxidation engine oil simulation test (TEOST 33C) in an amount of 50 mg or less, such as 40 mg or less, such as 30 mg or less, such as 25 mg or less, such as 20 mg or less, such as 18 mg or less, such as 15 mg or less, such as 13 mg or less. The TEOST 33C deposit may be more than 0 mg, such as 1 mg or more, such as 2 mg or more, such as 5 mg or more, such as 8 mg or more, such as 10 mg or more. In general, the less the amount of deposits obtained, the better the oxidation stability of the oil. The TEOST 33C deposit may be determined according to ASTM D6335-16 and a temperature change on a depositor rod of from 200° C. to 480° C. While the aforementioned references the TEOST 33C deposit of the lubricant composition, in another embodiment, such TEOST 33C deposit may be realized for the antioxidant composition when measured utilizing the lubricating oil as described in the test method and examples below. 
     Also, with the improvements realized as mentioned above, the lubricant composition may still demonstrate an acceptable antiwear performance. In this regard, the antiwear performance may not be detrimentally affected and in certain instances may even be improved. In general, the antiwear performance as determined according to ASTM D4172-18 may indicate the presence of a generally low wear scar. For instance, the wear scar may be 5 mm or less, such as 3 mm or less, such as 2 mm or less, such as 1.8 mm or less, such as 1.5 mm or less, such as 1.3 mm or less, such as 1 mm or less, such as 0.9 mm or less, such as 0.8 mm or less, such as 0.7 mm or less, such as 0.6 mm or less. The wear scar may be more than 0 mm, such as 0.1 mm or more, such as 0.2 mm or more, such as 0.3 mm or more, such as 0.4 mm or more, such as 0.5 mm or more, such as 0.6 mm or more, such as 0.7 mm or more. In addition, the actual wear scar may be less than an expected wear scar as determined herein. For instance, such wear scar may be at least 2% less, such as at least 5% less, such as at least 10% less, such as at least 15% less, such as at least 20% less, such as at least 25% less, such as at least 30% less, such as at least 40% less than an expected wear scar. Accordingly, by exhibiting a wear scar less than an expected wear scar, the antioxidant composition may demonstrate a synergistic antioxidant activity. While the aforementioned references the wear scar of the lubricant composition, in another embodiment, such wear scar may be realized for the antioxidant composition when measured utilizing the lubricating oil as described in the test method and examples below. 
     A. Antioxidant Composition 
     As indicated above, the antioxidant composition as disclosed herein provides a lubricating oil and resulting lubricant composition with improved oxidation stability. In this regard, the antioxidant composition includes at least one phenolic antioxidant and at least one phosphite antioxidant as defined herein. The present inventors have discovered that utilizing such a composition can improve the performance of the composition and the resulting lubricating composition. In addition, in certain embodiments, the respective antioxidants may be provided in certain amounts to improve such performance. 
     For instance, the weight ratio of the phenolic antioxidant to the phosphite antioxidant may be within a certain range. For instance, the weight ratio may be about 0.1 or more, such as about 0.2 or more, such as about 0.3 or more, such as about 0.33 or more, such as about 0.4 or more, such as about 0.5 or more, such as about 0.6 or more, such as about 0.66 or more. The weight ratio may be about 10 or less, such as about 8 or less, such as about 6 or less, such as about 4 or less, such as about 3 or less, such as about 2 or less, such as about 1.7 or less, such as about 1.5 or less, such as about 1.2 or less, such as about 1 or less, such as about 0.9 or less, such as about 0.75 or less, such as about 0.66 or less, such as about 0.6 or less, such as about 0.55 or less. In one embodiment, the molar ratio of the phenolic antioxidant to the phosphite antioxidant may also be within the aforementioned ranges. 
     The phenolic antioxidant may be present in the antioxidant composition in an amount of more than 0 wt. %, such as about 5 wt. % or more, such as about 10 wt. % or more, such as about 20 wt. % or more, such as about 30 wt. % or more, such as about 40 wt. % or more, such as about 50 wt. % or more, such as about 60 wt. % or more, such as about 70 wt. % or more, such as about 80 wt. % or more. The phenolic antioxidant may be present in the antioxidant composition in an amount of less than 100 wt. %, such as about 95 wt. % or less, such as about 90 wt. % or less, such as about 80 wt. % or less, such as about 70 wt. % or less, such as about 60 wt. % or less, such as about 50 wt. % or less, such as about 40 wt. % or less, such as about 30 wt. % or less, such as about 20 wt. % or less. 
     The phenolic antioxidant may be present in the lubricating composition in an amount of about 0.01 wt. % or more, such as about 0.1 wt. % or more, such as about 0.2 wt. % or more, such as about 0.5 wt. % or more, such as about 1 wt. % or more, such as about 1.5 wt. % or more, such as about 2 wt. % or more. The phenolic antioxidant may be present in the lubricating composition in an amount of about 10 wt. % or less, such as about 8 wt. % or less, such as about 6 wt. % or less, such as about 5 wt. % or less, such as about 4 wt. % or less, such as about 3 wt. % or less, such as about 2.5 wt. % or less, such as about 2 wt. % or less, such as about 1.5 wt. % or less, such as about 1 wt. % or less. 
     The phosphite antioxidant may be present in the antioxidant composition in an amount of more than 0 wt. %, such as about 5 wt. % or more, such as about 10 wt. % or more, such as about 20 wt. % or more, such as about 30 wt. % or more, such as about 40 wt. % or more, such as about 50 wt. % or more, such as about 60 wt. % or more, such as about 70 wt. % or more, such as about 80 wt. % or more. The phosphite antioxidant may be present in the antioxidant composition in an amount of less than 100 wt. %, such as about 95 wt. % or less, such as about 90 wt. % or less, such as about 80 wt. % or less, such as about 70 wt. % or less, such as about 60 wt. % or less, such as about 50 wt. % or less, such as about 40 wt. % or less, such as about 30 wt. % or less, such as about 20 wt. % or less. 
     The phosphite antioxidant may be present in the lubricating composition in an amount of about 0.01 wt. % or more, such as about 0.1 wt. % or more, such as about 0.2 wt. % or more, such as about 0.5 wt. % or more, such as about 1 wt. % or more, such as about 1.5 wt. % or more, such as about 2 wt. % or more. The phosphite antioxidant may be present in the lubricating composition in an amount of about 10 wt. % or less, such as about 8 wt. % or less, such as about 6 wt. % or less, such as about 5 wt. % or less, such as about 4 wt. % or less, such as about 3 wt. % or less, such as about 2.5 wt. % or less, such as about 2 wt. % or less, such as about 1.5 wt. % or less, such as about 1 wt. % or less. 
     In one embodiment, the phenolic antioxidant may be present in an amount greater than the phosphite antioxidant based on weight. In another embodiment, the phenolic antioxidant may be present in an amount less than the phosphite antioxidant based on weight. In a further embodiment, the phenolic antioxidant may be present in an amount the same as the phosphite antioxidant based on weight. 
     Also, in one embodiment, the antioxidant composition may be a liquid at ambient conditions (i.e., at atmospheric pressure and a temperature of 25° C.). By providing such antioxidant composition as a liquid, it may be easily combined with a lubricating oil to form the lubricant composition. 
     i. Phenolic Antioxidant 
     As indicated herein, the antioxidant composition includes at least one phenolic antioxidant. In this regard, the phenolic antioxidant may have the following structure (I): 
     
       
         
         
             
             
         
       
     
     wherein, 
     A is a direct bond or an alkylene; 
     X is —C(O)O—, —OC(O)—, —C(O)N(R 7 )—, —N(R 7 )C(O)—, —C(O)—, —N(R 7 )—, —O— or —S—; 
     R 1  and R 2  are each independently a C 1 -C 10  alkyl, a C 2 -C 10  alkenyl, a C 2 -C 10  alkynyl, or a C 3 -C 12  aryl; 
     R 3  includes a C 1 -C 80  alkyl, a C 2 -C 80  alkenyl, a C 2 -C 80  alkynyl, or a C 3 -C 12  aryl; and 
     R 7  is H or an alkyl. 
     As indicated above, “A” is a direct bond or an alkylene. In one embodiment, “A” is a direct bond such that the carbon in the ring is bonded directly to “X.” In another embodiment, “A” is an alkylene (i.e., an alkylene bridge) bonded to the carbon in the ring and “X.” For instance, the alkylene may be a C 1 -C 8  alkylene, such as a C 1 -C 5  alkylene, such as a C 1 -C 3  alkylene, such as a C 1 -C 2  alkylene or a C 2 -C 3  alkylene. For instance, the alkylene may be a methylene, an ethylene, a propylene, a butylene, etc. In one embodiment, the alkylene may be a methylene. In another embodiment, the alkylene may be an ethylene. In a further embodiment, the alkylene may be a propylene. In an even further embodiment, the alkylene may be a butylene. Also, it should be understood that, in one embodiment, the alkylene may be a substituted alkylene wherein the substitution may comprise a C 1 -C 20  alkyl, such as a C 1 -C 15  alkyl, such as a C 1 -C 10  alkyl, such as a C 1 -C 8  alkyl, such as a C 1 -C 4  alkyl. 
     As indicated above, “X” is —C(O)O—, —OC(O)—, —C(O)N(R 7 )—, —N(R 7 )C(O)—, —C(O)—, —N(R 7 )—, —O—, or —S—. For instance, “X” may be —C(O)O—, —OC(O)—, —C(O)N(R 7 )—, —N(R 7 )C(O)—, or —C(O)—. In particular, “X” may be —C(O)O— or —OC(O)—. In this regard, in one embodiment, “X” is —C(O)O—. In another embodiment, “X” is —OC(O)—. In a further embodiment, “X” is —C(O)N(R 7 )—. In an even further embodiment, “X” is —N(R 7 )C(O)—. In another embodiment, “X” is —C(O)—. In a further embodiment, “X” is —O—. 
     As indicated above, in one embodiment, “X” may be —C(O)N(R 7 )—, —N(R 7 )C(O)—, or —N(R 7 )—. In this regard, as also indicated above, R 7  is H or an alkyl. In one embodiment, R 7  is H. In another embodiment, R 7  is an alkyl. For instance, the R 7  alkyl may be a C 1 -C 30  alkyl, such as a C 1 -C 26  alkyl, such as a C 1 -C 20  alkyl, such as a C 1 -C 14  alkyl, such as a C 1 -C 10  alkyl, such as a C 1 -C 4  alkyl, such as a C 1 -C 3  alkyl, such as a C 1 -C 2  alkyl. For instance, the R 7  alkyl may have 1 or more, such as 2 or more, such as 3 or more, such as 5 or more, such as 10 or more carbon atoms. The R 7  alkyl may have 30 or less, such as 24 or less, such as 20 or less, such as 18 or less, such as 12 or less, such as 8 or less, such as 6 or less, such as 4 or less, such as 3 or less, such as 2 or less carbon atoms. In addition, the R 7  alkyl may be a straight chain, a branched chain, or cyclic. In one embodiment, the R 7  alkyl is a straight chain. In another embodiment, the R alkyl is a branched chain. In a further embodiment, the R alkyl is cyclic. 
     As indicated above, R 1  and R 2  are each independently a C 1 -C 10  alkyl, a C 2 -C 10  alkenyl, a C 2 -C 10  alkynyl, or a C 3 -C 12  aryl. In one embodiment, R 1  and R 2  may be different. For instance, while they may have the same chemical formula, they may be isomers having a different structure or configuration. In another embodiment, however, R 1  and R 2  may be the same. 
     In one embodiment, at least one of R 1  and R 2  may be a C 1 -C 10  alkyl. For instance, in one embodiment, R 1  may be a C 1 -C 10  alkyl. In another embodiment, R 2  may be a C 1 -C 10  alkyl. In a further embodiment, R 1  and R 2  may be a C 1 -C 10  alkyl. In particular, the alkyl may be a C 1 -C 7  alkyl, such as a C 1 -C 6  alkyl, such as a C 1 -C 5  alkyl, such as a C 1 -C 4  alkyl, such as a C 2 -C 4  alkyl, such as a C 3 -C 4  alkyl, such as a C 1 -C 3  alkyl. In this regard, the alkyl may be heptyl, hexyl, pentyl (e.g., n-pentyl, sec-pentyl, iso-pentyl, tert-pentyl, neo-pentyl), butyl (e.g., n-butyl, sec-butyl, iso-butyl, tert-butyl), propyl (e.g., n-propyl, iso-propyl), ethyl, methyl, etc. In one particular embodiment, the alkyl may be butyl, such as tert-butyl. 
     In another embodiment, at least one of R 1  and R 2  may be a C 2 -C 10  alkenyl. For instance, in one embodiment, R 1  may be a C 2 -C 10  alkenyl. In another embodiment, R 2  may be a C 2 -C 10  alkenyl. In a further embodiment, R 1  and R 2  may be a C 2 -C 10  alkenyl. In particular, the alkenyl may be a C 2 -C 7  alkenyl, such as a C 2 -C 6  alkenyl, such as a C 2 -C 5  alkenyl, such as a C 2 -C 4  alkenyl. 
     In a further embodiment, at least one of R 1  and R 2  may be a C 2 -C 10  alkynyl. For instance, in one embodiment, R 1  may be a C 2 -C 10  alkynyl. In another embodiment, R 2  may be a C 2 -C 10  alkynyl. In a further embodiment, R 1  and R 2  may be a C 2 -C 1  alkynyl. In particular, the alkynyl may be a C 2 -C 7  alkynyl, such as a C 2 -C 6  alkynyl, such as a C 2 -C 5  alkynyl, such as a C 2 -C 4  alkynyl. 
     In another further embodiment, at least one of R 1  and R 2  may be a C 3 -C 12  aryl. For instance, in one embodiment, R 1  may be a C 3 -C 12  aryl. In another embodiment, R 2  may be a C 3 -C 12  aryl. In a further embodiment, R 1  and R 2  may be a C 3 -C 12  aryl. In particular, the aryl may be a C 3 -C 8  aryl, such as a C 3 -C 6  aryl, such as a C 4 -C 6  aryl. 
     As indicated above, R 3  includes a C 1 -C 80  alkyl, a C 2 -C 80  alkenyl, a C 2 -C 40  alkynyl, or a C 3 -C 12  aryl. In one embodiment, R 3  includes a C 1 -C 80  alkyl. In another embodiment, R 3  includes a C 2 -C 80  alkenyl. In a further embodiment, R 3  includes a C 2 -C 80  alkynyl. In an even further embodiment, R 3  includes a C 3 -C 12  aryl. 
     As indicated above, in one embodiment, R 3  may include a C 1 -C 80  alkyl. In this regard, the R 3  alkyl may be a C 1 -C 80  alkyl, such as a C 3 -C 80  alkyl, such as a C 4 -C 70  alkyl, such as a C 5 -C 60  alkyl, such as a C 6 -C 50  alkyl, such as a C 8 -C 40  alkyl, such as a C 10 -C 30  alkyl, such as a C 12 -C 26  alkyl, such as a C 12 -C 20  alkyl, such as a C 13 -C 20  alkyl, such as a C 13 -C 15  alkyl. In addition, the R 3  alkyl may be a C 1 -C 80  alkyl, such as a C 10 -C 80  alkyl, such as a C 20 -C 80  alkyl, such as a C 30 -C 80  alkyl. For instance, the R 3  alkyl may have 1 or more, such as 2 or more, such as 3 or more, such as 4 or more, such as 5 or more, such as 6 or more, such as 8 or more, such as 10 or more, such as 11 or more, such as 12 or more, such as 13 or more, such as 14 or more, such as 16 or more, such as 18 or more, such as 20 or more, such as 21 or more, such as 22 or more, such as 24 or more carbon atoms. The R 3  alkyl may have 80 or less, such as 70 or less, such as 60 or less, such as 50 or less, such as 40 or less, such as 30 or less, such as 26 or less, such as 24 or less, such as 20 or less, such as 18 or less, such as 16 or less, such as 15 or less carbon atoms. In addition, the R 3  alkyl may be a straight chain, a branched chain, or cyclic. In one embodiment, the R 3  alkyl is a straight chain. In another embodiment, the R 3  alkyl is a branched chain. In a further embodiment, the R 3  alkyl is cyclic. 
     As indicated above, in one embodiment, R 3  may be a branched chain alkyl. In this regard, the R 3  alkyl may be provided by reacting a Guerbet alcohol with a monomer precursor (i.e., a dialkylphenol or a deprotected dialkylphenol). As generally known in the art, Guerbet alcohols are saturated primary alcohols with branching of the carbon chain. In this regard, such alcohols may be described as 2-alkyl-1-alkanols. Without being limited, these alcohols may yield 2-butyl hexyl, 2-butyl octyl, 2-butyl decyl, 2-butyl dodecyl, 2-butyl tetradecyl, 2-butyl hexadecyl, 2-butyl octadecyl, 2-hexyl octyl, 2-hexyl decyl, 2-hexyl dodecyl, 2-hexyl tetradecyl, 2-hexyl hexadecyl, 2-hexyl octadecyl, 2-octyl hexyl, 2-octyl decyl, 2-octyl dodecyl, 2-octyl tetradecyl, 2-octyl hexadecyl, 2-octyl octadecyl, 2-decyl hexyl, 2-decyl octyl, 2-decyl dodecyl, 2-decyl tetradecyl, 2-decyl hexadecyl, 2-decyl octadecyl, 2-dodecyl hexyl, 2-dodecyl octyl, 2-dodecyl decyl, 2-dodecyl tetradecyl, 2-dodecyl hexadecyl, 2-dodecyl octadecyl, 2-tetradecyl hexyl, 2-tetradecyl octyl, 2-tetradecyl decyl, 2-tetradecyl dodecyl, 2-tetradecyl hexadecyl, and 2-tetradecyl octadecyl. 
     As indicated above, in one embodiment, R 3  may include a C 2 -C 80  alkenyl. In this regard, the R 3  alkenyl may be a C 2 -C 80  alkenyl, such as a C 3 -C 80  alkenyl, such as a C 4 -C 70  alkenyl, such as a C 5 -C 60  alkenyl, such as a C 6 -C 50  alkenyl, such as a C 8 -C 40  alkenyl, such as a C 10 -C 30  alkenyl, such as a C 12 -C 26  alkenyl, such as a C 12 -C 20  alkenyl, such as a C 13 -C 20  alkenyl, such as a C 13 -C 15  alkenyl. In addition, the R 3  alkenyl may be a C 2 -C 80  alkenyl, such as a C 10 -C 80  alkenyl, such as a C 2 -C 80  alkenyl, such as a C 30 -C 80  alkenyl. For instance, the R 3  alkenyl may have 2 or more, such as 3 or more, such as 4 or more, such as 5 or more, such as 6 or more, such as 8 or more, such as 10 or more, such as 11 or more, such as 12 or more, such as 13 or more, such as 14 or more, such as 16 or more, such as 18 or more, such as 20 or more, such as 24 or more carbon atoms. The R 3  alkenyl may have 80 or less, such as 70 or less, such as 60 or less, such as 50 or less, such as 40 or less, such as 30 or less, such as 26 or less, such as 24 or less, such as 20 or less, such as 18 or less, such as 16 or less, such as 15 or less, such as 14 or less, such as 12 or less, such as 10 or less, such as 8 or less, such as 6 or less carbon atoms. In addition, the R 3  alkenyl may be a straight chain or a branched chain. In one embodiment, the R 3  alkenyl is a straight chain. In another embodiment, the R 3  alkenyl is a branched chain. 
     As indicated above, in one embodiment, R 3  may include a C 2 -C 80  alkynyl. In this regard, the R 3  alkynyl may be a C 2 -C 80  alkynyl, such as a C 3 -C 80  alkynyl, such as a C 4 -C 70  alkynyl, such as a C 5 -C 60  alkynyl, such as a C 6 -C 50  alkynyl, such as a C 8 -C 40  alkynyl, such as a C 10 -C 30  alkynyl, such as a C 12 -C 26  alkynyl, such as a C 12 -C 20  alkynyl, such as a C 13 -C 20  alkynyl, such as a C 13 -C 15  alkynyl. In addition, the R 3  alkynyl may be a C 2 -C 80  alkynyl, such as a C 10 -C 80  alkynyl, such as a C 20 -C 80  alkynyl, such as a C 30 -C 80  alkynyl. For instance, the R 3  alkynyl may have 2 or more, such as 3 or more, such as 4 or more, such as 5 or more, such as 6 or more, such as 8 or more, such as 10 or more, such as 11 or more, such as 12 or more, such as 13 or more, such as 14 or more, such as 16 or more, such as 18 or more, such as 20 or more, such as 24 or more carbon atoms. The R 3  alkynyl may have 80 or less, such as 70 or less, such as 60 or less, such as 50 or less, such as 40 or less, such as 30 or less, such as 26 or less, such as 24 or less, such as 20 or less, such as 18 or less, such as 16 or less, such as 15 or less, such as 14 or less, such as 12 or less, such as 10 or less, such as 8 or less, such as 6 or less carbon atoms. In addition, the R 3  alkynyl may be a straight chain or a branched chain. In one embodiment, the R 3  alkynyl is a straight chain. In another embodiment, the R 3  alkynyl is a branched chain. 
     As indicated above, in one embodiment, R 3  may include a C 3 -C 12  aryl. In this regard, the R 3  aryl may be a C 3 -C 12  aryl, such as a C 4 -C 12  aryl, such as a C 6 -C 12  aryl, such as a C 6 -C 10  aryl, such as a C 6 -C 8  aryl. For instance, the R 3  aryl may have 3 or more, such as 4 or more, such as 5 or more, such as 6 or more carbon atoms. The R 3  aryl may have 12 or less, such as 10 or less, such as 8 or less, such as 7 or less, such as 6 or less, such as 5 or less carbon atoms. In addition, in one embodiment, the R 3  aryl may be polycyclic. The polycyclic aryl may include fused, bridged, and spiro rings. 
     Regarding the R 3  alkyl, R 3  alkenyl, and R 3  alkynyl, it should be understood that these may also include a distribution. For instance, if R 3  includes a distribution of alkyls wherein the R 3  alkyl is a C q -C r  alkyl, the R 3  group of the copolymer may include other alkyls outside of this range of q to r; however, the average chain length would be from q to r. For example, if the R 3  alkyl is a C 14 -C 24  alkyl, the R 3  group of the copolymer may include other alkyls outside of the range of 14 to 24 carbon atoms; however, the average chain length would be between 14 and 24 carbon atoms. Although the R 3  alkyl is expressly mentioned in the examples within this paragraph, it should be understood that such also applies to the R 3  alkenyl and the R 3  alkynyl. 
     In one particular embodiment, R 3  may be an alkyl, such as a C 12 -C 15  alkyl, such as a C 13 -C 15  alkyl. For instance, the phenolic antioxidant may be a mixture of phenolic antioxidants wherein each R 3  alkyl is a different C 12 -C 15  alkyl, such as a different C 13 -C 15  alkyl. For instance, the mixture may include phenolic antioxidants each including a linear C 12  alkyl, a branched C 12  alkyl, a linear C 13  alkyl, a branched C 13  alkyl, a linear C 14  alkyl, a branched C 14  alkyl, a linear C 15  alkyl, and/or a branched C 15  alkyl. In one particular embodiment, the mixture may include phenolic antioxidants each including a linear C 13  alkyl, a branched C 13  alkyl, a linear C 14  alkyl, a branched C 14  alkyl, a linear C 15  alkyl, and/or a branched C 15  alkyl. Accordingly, one particular phenolic antioxidant comprises C 13 -C 15  linear and branched alkyl esters of 3-(3′5′-di-t-butyl-4′-hydroxyphenyl) propionic acid. 
     Also, it should be understood that the antioxidant composition may include a mixture of phenolic antioxidants. For instance, the antioxidant composition may include at least one, such as at least two, such as at least three phenolic antioxidants. As an example, each of the phenolic antioxidants may have a different R 3  group as defined above. In combination, the phenolic antioxidants may be present in the lubricant composition in the percentages mentioned above. In addition or alternatively, each individual phenolic antioxidant may be present in the lubricant composition in the percentages mentioned above. 
     Furthermore, in one embodiment, the phenolic antioxidant may be a liquid at ambient conditions (i.e., at atmospheric pressure and a temperature of 25° C.). By providing such phenolic antioxidant as a liquid, it may be easily combined with the phosphite antioxidant to form the antioxidant composition. 
     ii. Phosphite Antioxidant 
     As indicated herein, the antioxidant composition includes at least one phosphite antioxidant. In this regard, the phosphite antioxidant may have the following structure (II): 
     
       
         
         
             
             
         
       
     
     wherein, 
     R 4 , R 5 , and R 6  are each independently hydrogen, alkyl, alkenyl, alkynyl, or aryl provided that at least one of R 4 , R 5 , and R 6  is not hydrogen; and 
     m, n, and o are each independently from 1 to 3. 
     As indicated above, R 4 , R 5 , and R 6  are each independently hydrogen, alkyl, alkenyl, alkynyl, or aryl provided that at least one of R 4 , R 5 , and R 6  is not hydrogen. In this regard, at least one, such as at least two of R 4 , R 5 , and R 6  may be hydrogen provided that at least one of R 4 , R 5 , and R 6  is not hydrogen. Accordingly, in one embodiment, at least one of R 4 , R 5 , and R 6  may be an alkyl. In another embodiment, at least one of R 4 , R 5 , and R 6  may be an alkenyl. In a further embodiment, at least one of R 4 , R 5 , and R 6  may be an alkynyl. In another further embodiment, at least one of R 4 , R 5 , and R 6  may be an aryl. 
     In particular, R 4 , R 5 , and R 6  may each independently be a C 1 -C 20  alkyl, a C 2 -C 20  alkenyl, a C 2 -C 20  alkynyl, or a C 3 -C 12  aryl. In this regard, in one embodiment, at least one of R 4 , R 5 , and R 6  may be a C 1 -C 20  alkyl. In another embodiment, at least one of R 4 , R 5 , and R 6  may be a C 2 -C 20  alkenyl. In a further embodiment, at least one of R 4 , R 5 , and R 6  may be a C 2 -C 20  alkynyl. In another further embodiment, at least one of R 4 , R 5 , and R 6  may be a C 3 -C 12  aryl. 
     As indicated above, in one embodiment, at least one of, such as at least two of, such as all three of R 4 , R 5 , and R 6  may include an alkyl. In particular, it may include a C 1 -C 20  alkyl. In this regard, the alkyl may be a C 1 -C 20  alkyl, such as a C 1 -C 16  alkyl, such as a C 1 -C 12  alkyl, such as a C 1 -C 10  alkyl, such as a C 2 -C 8  alkyl, such as a C 3 -C 6  alkyl, such as a C 4 -C 6  alkyl. For instance, the alkyl may have 1 or more, such as 2 or more, such as 3 or more, such as 4 or more, such as 5 or more, such as 6 or more, such as 8 or more, such as 10 or more carbon atoms. The alkyl may have 20 or less, such as 18 or less, such as 16 or less carbon atoms, such as 14 or less, such as 12 or less, such as 10 or less, such as 8 or less, such as 6 or less carbon atoms. In addition, the alkyl may be a straight chain or a branched chain. In one embodiment, the alkyl is a straight chain. In another embodiment, the alkyl is a branched chain. 
     In one particular embodiment, at least one of R 4 , R 5 , and R 6  may be tert-butyl or tert-pentyl. For instance, at least one of, such as at least two of, such as at least three of R 4 , R 5 , and R 6  may be tert-butyl. In another embodiment, at least one of, such as at least two of, such as at least three of R 4 , R 5 , and R 6  may be tert-pentyl. 
     In one particular embodiment, at least one of R 4 , R 5 , and R 6  may be nonyl. For instance, at least one of, such as at least two of, such as at least three of R 4 , R 5 , and R 6  may be nonyl. In another embodiment, at least one of, such as at least two of, such as at least three of R 4 , R 5 , and R 6  may be nonyl. 
     However, in one embodiment, the phosphite antioxidant may include a very low amount of certain alkyls. For example, such alkyls may be C 8 -C 10 , in particular C 9  alkyls. In this regard, in one embodiment, the alkyl may comprise less than 1,000 ppm, such as less than 500 ppm, such as less than 100 ppm, such as less than 50 ppm, such as less than 25 ppm, such as less than 10 ppm, such as less than 5 ppm, such as less than 1 ppm, such as 0 ppm of such alkyl. 
     As indicated above, in one embodiment, at least one of, such as at least two of, such as all three of R 4 , R 5 , and R 6  may include an alkenyl. In particular, it may include a C 2 -C 20  alkenyl. In this regard, the alkenyl may be a C 2 -C 20  alkenyl, such as a C 2 -C 16  alkenyl, such as a C 2 -C 12  alkenyl, such as a C 2 -C 10  alkenyl, such as a C 2 -C 8  alkenyl, such as a C 3 -C 6  alkenyl, such as a C 4 -C 6  alkenyl. For instance, the alkenyl may have 2 or more, such as 3 or more, such as 4 or more, such as 5 or more, such as 6 or more, such as 8 or more, such as 10 or more, such as 12 or more, such as 14 or more, such as 16 or more carbon atoms. The alkenyl may have 20 or less, such as 18 or less, such as 16 or less carbon atoms, such as 14 or less, such as 12 or less, such as 10 or less, such as 8 or less, such as 6 or less carbon atoms. In addition, the alkenyl may be a straight chain or a branched chain. In one embodiment, the alkenyl is a straight chain. In another embodiment, the alkenyl is a branched chain. 
     As indicated above, in one embodiment, at least one of, such as at least two of, such as all three of R 4 , R 5 , and R 6  may include an alkynyl. In particular, it may include a C 2 -C 20  alkynyl. In this regard, the alkynyl may be a C 2 -C 20  alkynyl, such as a C 2 -C 16  alkynyl, such as a C 2 -C 12  alkynyl, such as a C 2 -C 10  alkynyl, such as a C 2 -C 8  alkynyl, such as a C 3 -C 6  alkynyl, such as a C 4 -C 6  alkynyl. For instance, the alkynyl may have 2 or more, such as 3 or more, such as 4 or more, such as 5 or more, such as 6 or more, such as 8 or more, such as 10 or more, such as 12 or more, such as 14 or more, such as 16 or more carbon atoms. The alkynyl may have 20 or less, such as 18 or less, such as 16 or less carbon atoms, such as 14 or less, such as 12 or less, such as 10 or less, such as 8 or less, such as 6 or less carbon atoms. In addition, the alkynyl may be a straight chain or a branched chain. In one embodiment, the alkynyl is a straight chain. In another embodiment, the alkynyl is a branched chain. 
     As indicated above, in one embodiment, at least one of, such as at least two of, such as all three of R 4 , R 5 , and R 6  may include an aryl. In particular, it may include a C 3 -C 12  aryl. In this regard, the aryl may be a C 3 -C 12  aryl, such as a C 4 -C 12  aryl, such as a C 6 -C 12  aryl, such as a C 6 -C 10  aryl, such as a C 6 -C 8  aryl. For instance, the aryl may have 3 or more, such as 4 or more, such as 5 or more, such as 6 or more carbon atoms. The aryl may have 12 or less, such as 10 or less, such as 8 or less, such as 7 or less, such as 6 or less, such as 5 or less carbon atoms. In addition, in one embodiment, the aryl may be polycyclic. The polycyclic aryl may include fused, bridged, and spiro ring systems. 
     In one embodiment, R 4 , R 5 , and R 6  may all be the same. By same, it should be understood that the substituent is the same substituent group and having the same length. For example, in one embodiment, R 4 , R 5 , and R 6  may all be alkyl, such as a C 5  alkyl. In another embodiment, however, R 4 , R 5 , and R 6  may be different. For instance, in one embodiment, all three R 4 , R 5 , and R 6  may be different. For instance, while they may have the same chemical formula, they may be isomers having a different structure or configuration. In another embodiment, at least two of R 4 , R 5 , and R 6  may be the same while the other is different. By different, it should be understood that the substituent is a different substituent group. For example, one of the groups may be an alkyl while another may be an alkenyl. Alternatively, as another example, at least two of the groups may be an alkyl wherein each alkyl has a different chain length. 
     As indicated above, m, n, and o are each independently from 1 to 3. For instance, m may be from 1 to 3. In this regard, in one embodiment, m may be 1. In another embodiment, m may be 2. In a further embodiment, m may be 3. Similarly, n may be from 1 to 3. In this regard, in one embodiment, n may be 1. In another embodiment, n may be 2. In a further embodiment, n may be 3. Further, o may be from 1 to 3. In this regard, in one embodiment, o may be 1. In another embodiment, o may be 2. In a further embodiment, o may be 3. 
     Furthermore, in one embodiment, R 4 , R 5 , and R 6  may each independently be at the para position. For instance, when m, n, and o are each independently 1, R 4 , R 5 , and R 6  may each independently be at the para position. In another embodiment, R 4 , R 5 , and R 6  may each independently be at the ortho position. For instance, in one embodiment, when m, n, and o are each independently 1, R 4 , R 5 , and R 6  may each independently be at the ortho position. In another embodiment, when m, n, and o are each independently 2, R 4 , R 5 , and R 6  may each independently be at the para position and the ortho position. 
     In this regard, in one embodiment, m, n, and o may each be the same. For instance, in one embodiment, m, n, and o may be 1. Accordingly, in one embodiment, the phosphite antioxidant may have the following structure (III) wherein m, n, and o are each 1: 
     
       
         
         
             
             
         
       
     
     In another embodiment, m, n, and o may be 2. In this regard, the phosphite antioxidant may have the following structure (IV) wherein m, n, and o are each 2: 
     
       
         
         
             
             
         
       
     
     In a further embodiment, m, n, and o may be 3. 
     In addition, it should be understood that in one embodiment, all three of m, n, and o may be different. For instance, at least one of m, n, and o may be 1, while another of m, n, and o may be 2, while another of m, n, and o may be 3. 
     In a further embodiment, at least two of m, n, and o may be the same while the other is different. For instance, at least two of m, n, and o may be 1 while the third may be 2 or 3, such as 2 in one embodiment or 3 in another embodiment. In this regard, the phosphite antioxidant may have the following structure (V) wherein n and o are 1 and m is 2: 
     
       
         
         
             
             
         
       
     
     Alternatively, at least two of m, n, and o may be 2 while the third may be 1 or 3, such as 1 in one embodiment or 3 in another embodiment. In this regard, the phosphite antioxidant may have the following structure (VI) wherein m and n are 2 and o is 1: 
     
       
         
         
             
             
         
       
     
     In a further embodiment, at least two of m, n, and o may be 3 while the third may be 1 or 2, such as 1 in one embodiment or 2 in another embodiment. 
     In addition, it should be understood that any of the aforementioned phosphite antioxidants of structures (III), (IV), (V), or (VI) may be utilized individually or in combination. For instance, at least one, such as at least two, such as at least three, such as at least all four of the aforementioned phosphite antioxidants of structures (III), (IV), (V), or (VI) may be utilized in the antioxidant composition. 
     Also, it should be understood that the antioxidant composition may include a mixture of phosphite antioxidants. For instance, the antioxidant composition may include at least one, such as at least two, such as at least three, such as at least four phosphite antioxidants. As an example, each of the phosphite antioxidants may have a different number of substituent groups and/or different substituent groups as defined above. In combination, the phosphite antioxidants may be present in the lubricant composition in the percentages mentioned above. In addition or alternatively, each individual phosphite antioxidant may be present in the lubricant composition in the percentages mentioned above. 
     Furthermore, when a mixture of phosphite antioxidants are utilized, they may be utilized within certain amounts. For instance, the weight ratio of the tris(monoalkylaryl)phosphites to the combination of bis(monoalkylaryl)dialkylaryl phosphites, bis(dialkylaryl)monoalkylaryl phosphites, and tris(dialkylaryl)phosphites may be within a certain range. Furthermore, the weight ratio of bis(monoalkylaryl)dialkylaryl phosphites to the combination of tris(monoalkylaryl)phosphites, bis(dialkylaryl)monoalkylaryl phosphites, and tris(dialkylaryl)phosphites may be within a certain range. In addition, the weight ratio of bis(dialkylaryl)monoalkylaryl phosphites to the combination of tris(monoalkylaryl)phosphites, bis(monoalkylaryl)dialkylaryl phosphites, and tris(dialkylaryl)phosphites may be within a certain range. Such weight ratios may be about 0.01 or more, such as about 0.033 or more, such as about 0.05 or more, such as about 0.1 or more, such as about 0.15 or more, such as about 0.2 or more, such as about 0.3 or more, such as about 0.33 or more, such as about 0.4 or more, such as about 0.5 or more, such as about 0.6 or more, such as about 0.66 or more. The weight ratios may be about 10 or less, such as about 8 or less, such as about 6 or less, such as about 4 or less, such as about 3 or less, such as about 2 or less, such as about 1.7 or less, such as about 1.5 or less, such as about 1.2 or less, such as about 1.1 or less, such as about 1 or less, such as about 0.9 or less, such as about 0.75 or less, such as about 0.66 or less, such as about 0.6 or less, such as about 0.55 or less, such as about 0.4 or less, such as about 0.2 or less, such as about 0.15 or less, such as about 0.11 or less, such as about 0.1 or less, such as about 0.05 or less, such as about 0.02 or less. In one embodiment, the molar ratio of the phenolic antioxidant to the phosphite antioxidant may also be within the aforementioned ranges. 
     Also, the weight ratio of the tris(dialkylaryl)phosphites to the combination of bis(monoalkylaryl)dialkylaryl phosphites, bis(dialkylaryl)monoalkylaryl phosphites and tris(monoalkylaryl)phosphites may also be within a certain range. For instance, the weight ratio may be about 0.0001 or more, such as about 0.0002 or more, such as about 0.001 or more, such as about 0.01 or more, such as about 0.1 or more, such as about 0.2 or more, such as about 0.5 or more. The weight ratio may be about 5 or less, such as about 3 or less, such as about 2.5 or less, such as about 1.5 or less, such as about 1 or less, such as about 0.5 or less, such as about 0.1 or less, such as about 0.05 or less, such as about 0.02 or less, such as about 0.01 or less, such as about 0.005 or less. 
     For instance, the weight ratio of the phenolic antioxidant to the phosphite antioxidant may be within a certain range. For instance, the weight ratio may about 0.1 or more, such as about 0.2 or more, such as about 0.3 or more, such as about 0.33 or more, such as about 0.4 or more, such as about 0.5 or more, such as about 0.6 or more, such as about 0.66 or more. The weight ratio may be about 10 or less, such as about 8 or less, such as about 6 or less, such as about 4 or less, such as about 3 or less, such as about 2 or less, such as about 1.7 or less, such as about 1.5 or less, such as about 1.2 or less, such as about 1 or less, such as about 0.9 or less, such as about 0.75 or less, such as about 0.66 or less, such as about 0.6 or less, such as about 0.55 or less. In one embodiment, the molar ratio of the phenolic antioxidant to the phosphite antioxidant may also be within the aforementioned ranges. 
     As examples, the phosphite antioxidant may include, but is not limited to, tris-4-tert-butyl phenyl phosphite, tris 2,4-di-tert-butyl phenyl phosphite, bis(4-tert-butylphenyl)-2,4-di-tert-butylphenyl phosphite, bis(2,4-di-tert-butylphenyl)-4-tert-butylphenyl phosphite, tris 4-tert-pentyl phenyl phosphite, tris 2,4-di-tert-pentyl phenyl phosphite, bis(4-tert-pentylphenyl)-2,4-di-tert-pentylphenyl phosphite, bis(2,4-di-tert-pentylphenyl)-4-tert-pentylphenyl phosphite, the like, as well as mixtures thereof. 
     The phosphite antioxidant may have a certain molecular weight. For instance, the molecular weight may be 400 g/mol or more, such as 450 g/mol or more, such as 500 g/mol or more, such as 550 g/mol or more, such as 600 g/mol or more, such as 650 g/mol or more. The molecular weight may be 1,000 g/mol or less, such as 900 g/mol or less, such as 800 g/mol or less, such as 750 g/mol or less, such as 700 g/mol or less, such as 650 g/mol or less, such as 600 g/mol or less. 
     The phosphite antioxidant may also have a certain phosphorus content. For instance, the phosphorus content may be 0.5 wt. % or more, such as 1 wt. % or more, such as 2 wt. % or more, such as 3 wt. % or more, such as 4 wt. % or more, such as 4.5 wt. % or more, such as 4.8 wt. % or more, such as 5 wt. % or more. The phosphorus content may be 10 wt. % or less, such as 8 wt. % or less, such as 6 wt. % or less, such as 5.5 wt. % or less, such as 5.3 wt. % or less. 
     The phosphite antioxidant may also have a certain kinematic viscosity. For instance, the kinematic viscosity may be 11,000 mm 2 /s or less, such as 8,000 mm 2 /s or less, such as 7,500 mm 2 /s or less, such as 6,500 mm 2 /s or less, such as 5,500 mm 2 /s or less, such as 5,000 mm 2 /s or less, such as 3,000 mm 2 /s or less when measured at 30° C. The kinematic viscosity may be 1 mm 2 /s or more, such as 50 mm 2 /s or more, such as 100 mm 2 /s or more, such as 500 mm 2 /s or more, such as 1,000 mm 2 /s or more, such as 2,000 mm 2 /s or more, such as 3,000 mm 2 /s or more, such as 4,000 mm 2 /s or more when measured at 30° C. The viscosity may be determined using a glass capillary viscometer according to ASTM D445-19. 
     Furthermore, in one embodiment, the phosphite antioxidant may be a liquid at ambient conditions (i.e., at atmospheric pressure and a temperature of 25° C.). By providing such phosphite antioxidant as a liquid, it may be easily combined with the phenolic antioxidant to form the antioxidant composition. 
     B. Lubricating Oil 
     In addition to the antioxidant composition, the lubricant composition also comprises a lubricating oil. The lubricating oil is not necessarily limited by the present invention. Regardless, the lubricating oil may be present in the composition in an amount of about 70 wt. % or more, such as 75 wt. % or more, such as 80 wt. % or more, such as 85 wt. % or more, such as 90 wt. % or more. The lubricating oil may be present in the lubricant composition in an amount of less than 100 wt. %, such as 99 wt. % or less, such as 97 wt. % or less, such as 95 wt. % or less, such as 93 wt. % or less, such as 90 wt. % or less. 
     The lubricating oil may include a natural lubricating oil, a synthetic lubricating oil, or a mixture thereof. In one embodiment, the oil may be a natural lubricating oil. In another embodiment, the oil may be a synthetic lubricating oil. In a further embodiment, the oil may be a mixture of a natural lubricating oil and a synthetic lubricating oil. 
     Furthermore, the lubricating oil may have a certain kinematic viscosity. For example, the kinematic viscosity may be 3 mm 2 /s or more, such as 3.5 mm 2 /s or more, such as 4 mm 2 /s or more, such as 4.5 mm 2 /s or more, such as 5 mm 2 /s or more at 100° C. The kinematic viscosity may be 200 mm 2 /s or less, such as 150 mm 2 /s or less, such as 125 mm 2 /s or less, such as 100 mm 2 /s or less, such as 80 mm 2 /s or less, such as 60 mm 2 /s or less, such as 50 mm 2 /s or less, such as 30 mm 2 /s or less, such as 20 mm 2 /s or less, such as 15 mm 2 /s or less, such as 12 mm 2 /s or less, such as 10 mm 2 /s or less, such as 9 mm 2 /s or less, such as 8 mm 2 /s or less at 100° C. The kinematic viscosity can be determined in accordance with ASTM D445-19. 
     The lubricating oil may be one of lubricating viscosity comprising a Group I, Group II, Group III, Group IV, or synthetic ester base stock. In general, the various base stock groups are identified chemically and physically in the American Petroleum Institute (API) publication Engine Oil Licensing and Certification System, Industry Services Department, 14th Ed. (December 1996) Addendum 1 (December 1998), which is hereby incorporated by reference in its entirety for any purpose. 
     In general, the Group I mineral oil base stocks may contain less than 90 wt. % of saturates. Also, the Group I mineral base stocks may contain greater than 0.3 wt. % of sulfur. Furthermore, the Group I mineral base stocks may have a viscosity index of 80 or more, such as 85 or more, such as 90 or more, such as 100 or more to 120 or less, such as 115 or less, such as 110 or less. The viscosity index may be determined in accordance to ASTM D2270-10. 
     In general, the Group II mineral oil base stocks may contain 80 wt. % or more, such as 85 wt. % or more, such as 90 wt. % or more, such as 93 wt. % or more, such as 95 wt. % or more saturates. The Group II mineral base stocks may contain 0.1 wt. % or less, such as 0.05 wt. % or less, such as 0.03 wt. % or less, such as 0.01 wt. % or less of sulfur. Furthermore, the Group II mineral base stocks may have a viscosity index of 70 or more, such as 75 or more, such as 80 or more, such as 85 or more, such as 90 or more, such as 100 or more to 120 or less, such as 115 or less, such as 110 or less. The viscosity index may be determined in accordance to ASTM D2270-10. 
     In general, Group III mineral oil base stocks may contain 80 wt. % or more, such as 85 wt. % or more, such as 90 wt. % or more, such as 93 wt. % or more, such as 95 wt. % or more saturates. The Group III mineral base stocks may contain 0.1 wt. % or less, such as 0.05 wt. % or less, such as 0.03 wt. % or less, such as 0.01 wt. % or less of sulfur. Furthermore, the Group III mineral base stocks may have a viscosity index of 120 or more, such as 125 or more, such as 130 or more. The viscosity index may be determined in accordance to ASTM D2270-10. 
     In general, the Group IV base stocks may include poly-α-olefins. In addition to the poly-α-olefins, the lubricating oil may include silicon-based oils, such as polyalkyl-, polyaryl-, polyalkoxy-, or polyaryloxy-siloxane oils and silicate oils, comprise another useful class of synthetic lubricating oils. 
     In general, the ester base stocks may include esters of dicarboxylic acids (e.g., phthalic acid, succinic acid, alkyl succinic acids, alkenyl succinic acids, maleic acid, azelaic acid, suberic acid, sebacic acid, fumaric acid, adipic acid, linoleic acid dimer, malonic acid, alkyl malonic acids, alkenyl malonic acids, etc.) with a variety of alcohols (e.g., butyl alcohol, hexyl alcohol, dodecyl alcohol, 2-ethylhexyl alcohol, ethylene glycol, diethylene glycol monoether, propylene glycol, etc.). In this regard, specific examples of these esters may include, but are not limited to, dibutyl adipate, bis(2-ethylhexyl) sebacate, di-n-hexyl fumarate, dioctyl sebacate, di-isooctyl azelate, di-isodecyl azelate, dioctyl phthalate, didecyl phthalate, dieicosyl sebacate, 2-ethylhexyl diester of linoleic acid dimer, complex ester formed by reacting one mole of sebacic acid with two moles of tetraethylene glycol and two moles of 2-ethylhexanoic acid, and the like. The esters useful as base stocks may also include those made from C 5 -C 12  monocarboxylic acids and polyols and polyol ethers, such as neopentyl glycol, trimethylol propane, pentaerythritol, dipentaerythritol, tripentaerythritol, etc. 
     In one embodiment, natural lubricating oils may include, but are not limited to, animal oils, such as lard oil, tallow oil, vegetable oils including canola oils, castor oils, and sunflower oils, for example, petroleum oils, mineral oils, and oils derived from coal or shale. 
     In one embodiment, synthetic lubricating oils may include hydrocarbon oils and halo-substituted hydrocarbon oils, such as polymerized and interpolymerized olefins, gas-to-liquids prepared by Fischer-Tropsch technology, alkylbenzenes, polyphenyls, alkylated diphenyl ethers, alkylated diphenyl sulfides, as well as their derivatives, analogs, homologs, and the like. Synthetic lubricating oils may also include alkylene oxide polymers, interpolymers, copolymers, and derivatives thereof, wherein the terminal hydroxyl groups have been modified by esterification, and etherification, for example. 
     In general, the lubricating oil may be derived from unrefined, refined, re-refined oils, or mixtures thereof. For instance, unrefined oils may be obtained directly from a natural source or synthetic source (e.g., coal, shale, or tar and bitumen) without further purification or treatment. Examples of unrefined oils may include, but are not limited to, a shale oil obtained directly from a retorting operation, a petroleum oil obtained directly from distillation, or an ester oil obtained directly from an esterification process, each of which is then used without further treatment. Furthermore, refined oils are similar to unrefined oils, except that refined oils have been treated in one or more purification steps to improve one or more properties. Suitable purification techniques can include, but are not limited to, distillation, hydrotreating, dewaxing, solvent extraction, acid or base extraction, filtration, percolation, and the like, all of which are well-known to those skilled in the art. In addition, re-refined oils are obtained by treating refined oils in processes similar to those used to obtain the refined oils. These re-refined oils are also known as reclaimed or reprocessed oils and often are additionally processed by techniques for removal of spent additives and oil breakdown products. 
     Also, it should be understood that the lubricating oil may include a mixture of lubricating oils. For instance, the lubricating oil may include at least one, such as at least two, such as at least three, such as at least four lubricating oils. 
     C. Lubricant Composition 
     In addition to the antioxidant composition and lubricating oil as mentioned above, the lubricant composition may also include other additives. For instance, in one embodiment, the lubricant composition may further comprise an alkanolamine. As generally understood in the art, alkanolamines contain both a hydroxyl group and an amino group on an alkane backbone. The alkanolamine may include, but is not limited to, a methanolamine, an ethanolamine, a propanolamine, or a mixture thereof. In one embodiment, the alkanolamine may be an ethanolamine, a propanolamine, or a mixture thereof. In a further embodiment, the alkanolamine may include a propanolamine. 
     Furthermore, the alkanolamine may be a monoalkanolamine, a dialkanolamine, a trialkanolamine, or a mixture thereof. In one embodiment, the alkanolamine may be a dialkanolamine, a trialkanolamine, or a mixture thereof. In a further embodiment, the alkanolamine may be a trialkanolamine. Examples of these alkanolamines may specifically include monoethanolamine, diethanolamine, triethanolamine, monoisopropanolamine, diisopropanolamine, triisopropanolamine, or a mixture thereof. In one particular embodiment, the alkanolamine may include triisopropanolamine. Other alkanolamines may include, but are not limited to, octyl-bis(2-ethanol)amine, nonyl-bis(2-ethanol)amine, decyl-bis(2-ethanolamine, undecyl-bis(2-ethanol)amine, dodecyl-bis(2-ethanol)amine, tridecyl-bis(2-ethanol)amine, tetradecyl-bis(2-ethanol)amine, pentadecyl-bis(2-ethanol)amine, hexadecyl-bis(2-ethanol)amine, heptadecyl-bis(2-ethanol)amine, octadecyl-bis(2-ethanol)amine, octyl-bis(2-propanol)amine, nonyl-bis(2-propanol)amine, decyl-bis(2-propanol)amine, undecyl-bis(2-propanol)amine, dodecyl-bis(2-propanol)amine, tridecyl-bis(2-propanol)amine, tetradecyl-bis(2-propanol)amine, pentadecyl-bis(2-propanol)amine, hexadecyl-bis(2-propanol)amine, heptadecyl-bis(2-propanol)amine, octadecyl-bis(2-propanol)amine, and mixtures thereof. 
     When present, the alkanolamine may be in the lubricant composition in an amount of 5 wt. % or less, such as 4 wt. % or less, such as 3 wt. % or less, such as 2 wt. % or less, such as 1.5 wt. % or less, such as 1 wt. % or less, such as 0.5 wt. % or less, such as 0.4 wt. % or less, such as 0.3 wt. % or less, such as 0.2 wt. % or less, such as 0.1 wt. % or less, such as 0.05 wt. % or less, such as 0.01 wt. % or less based on the combined weight of the phosphite antioxidants and the alkanolamine. The alkanolamine may be present in the lubricant composition in an amount of 0.001 wt. % or more, such as 0.01 wt. % or more, such as 0.1 wt. % or more, such as 0.2 wt. % or more based on the combined weight of the phosphite antioxidants and the alkanolamine. In one embodiment, the alkanolamine may be in the lubricant composition in an amount of about 0 wt. %. In another embodiment, the aforementioned weight percentages may apply to the alkanolamine based on the total weight of the lubricant composition. 
     The lubricant composition may also include other additives as generally known in the art. For instance, these may include, but are not limited to, dispersants, detergents, antiwear agents, antioxidants, friction modifiers, seal swell agents, demulsifiers, VI (viscosity index) improvers, pour point depressants, antifoamants, corrosion inhibitors, metal deactivators, etc. Such additives are well known to those skilled in the art and thus are not limited by the present invention. When utilized, they may be present in the lubricant composition in an amount of 10 wt. % or less, such as 7 wt. % or less, such as 5 wt. % or less, such as 4 wt. % or less, such as 3 wt. % or less, such as 2 wt. % or less, such as 1.5 wt. % or less, such as 1 wt. % or less, such as 0.5 wt. % or less, such as 0.3 wt. % or less, such as 0.1 wt. % or less. In one particular embodiment, a respective additive may be present in the lubricant composition in an amount of 0 wt. %. 
     In addition, the present invention is also directed to a method of forming the lubricant composition. The method is not necessarily limited by the present invention. In this regard, the method may comprise a step of combining a lubricating oil with the antioxidant composition as defined herein. For instance, prior to the combining step, the antioxidant composition including the phenolic antioxidant and phosphite antioxidant as disclosed herein may be prepared. Then, the lubricating oil may be combined with the antioxidant composition. Alternatively, the lubricating oil may first be combined with at least one of the phenolic antioxidant and the phosphite antioxidant and then combined with the other of the phenolic antioxidant and the phosphite antioxidant. In this regard, although not directly combined with the antioxidant composition initially, the lubricant composition in the end may contain such antioxidant composition. 
     Regardless of the method in which it is manufactured, the lubricant composition as disclosed herein may be utilized in a variety of applications and thus is not limited by the present invention. For instance, the lubricant composition can be used as an automatic crank case lubricant, an automatic gear lubricant, an industrial gear lubricant, a gas engine lubricant, a steam and gas turbine lubricant, an automatic transmission fluid, a compressor lubricant, a metal-working lubricant, a transmission fluid, a hydraulic fluid, etc. The lubricant composition of the present invention, in one embodiment, may be particularly useful as a passenger vehicle engine oil product. 
     EXAMPLES 
     Test Methods 
     Standard RPVOT Oxidation Induction Time: 
     The standard rotating pressure vessel oxidation test (RPVOT) was conducted according to ASTM D2272-14a. The standard RPVOT test conditions were as follows: copper catalyst coil weight (55.6+/−0.3 g), sample size weight (50+/−0.5 g), distilled water volume (5 mL), temperature (150° C.), oxygen initial pressure at room temperature (90 psi), and pressure drop to end test (25.4 psi). The RPVOT utilized an oxygen-pressured vessel to evaluate the oxidation stability, in the presence of water and a copper catalyst coil at 150° C. The test lubricant composition, water, and a copper catalyst coil, which were separately contained in a covered glass container, were placed in a vessel equipped with a pressure gauge. The vessel was charged with oxygen to a pressure of 90 psi at room temperature. The vessel was rotated axially at 100 rpm at an angle of 30 degrees from the horizontal. The number of minutes required to reach a specific drop of 25.4 psi in gauge pressure indicated the oxidation stability of the test sample. For this test, an average value of two or more samples was obtained. 
     Dry RPVOT Oxidation Induction Time: 
     The dry rotating pressure vessel oxidation test (RPVOT) was conducted according to a modified ASTM D2272-14a by using a TANNAS Quantum™ oxidation tester and the method mentioned above except that water was not charged into the test beaker. For this test, an average value of two or more samples was obtained. 
     PDSC Oxidation Induction Time: 
     The pressurized differential scanning calorimetry (PDSC) measured the oxidation induction time of the lubricant composition. The instrument used was a TA Instruments™ Q20P, Pressure DSC. The PDSC test conditions were as follows: isothermal temperature (160° C.), cell pressure (500+/−25 psi of O 2 ), O 2  gas flow rate through the cell (100 mL/min), sample holder (open aluminum pan), lubricant composition sample size (2.9-3.1 mg, and induction time based on the onset temperature of the exothermic oxidation peak (enthalpy change)). At the beginning of a PDSC run, the DSC cell was heated at a rate of 100° C./minute to the isothermal temperature (160° C.), then held isothermally for 2 minutes. The cell was then pressurized to 500 psi and held isothermally at 160° C. The induction time was measured from the start time of the cell pressurization until the enthalpy change was observed. 
     Expected Standard RPVOT, Dry RPVOT, and PDSC Oxidation Induction Times: 
     Using the aforementioned methods, the oxidation induction times were determined for each antioxidant individually, rather than using both in combination. Then, using a linear extrapolation, the expected value was determined as a function of the weight percentage of each antioxidant in the composition. As an example, if antioxidant A had an actual oxidation induction time of 100 minutes and antioxidant B had an actual oxidation induction time of 200 minutes, an antioxidant composition having antioxidant A in an amount of 25 wt. % and antioxidant B in an amount of 75 wt. % would have an expected oxidation induction time of 175 minutes (e.g., 0.25*100 minutes+0.75*200 minutes). Similarly, an antioxidant composition having antioxidant A in an amount of 40 wt. % and antioxidant B in an amount of 60 wt. % would have an expected oxidation induction time of 160 minutes (e.g., 0.40*100 minutes+0.60*200 minutes). As another example, an antioxidant composition having antioxidant A in an amount of 66.6 wt. % and antioxidant B in an amount of 33.3 wt. % would have an expected oxidation induction time of 133.33 minutes (e.g., 0.66*100 minutes+0.33*200 minutes). 
     TEOST 33C Deposit: 
     The thermo-oxidative engine oil simulation test (TEOST 33C) was performed according to ASTM D6335-16. The TEOST 33C test conditions were as follows. A 116 mL sample of the lubricant composition containing 100 mg/kg of ferric naphthenate was placed into the reaction chamber and heated and stirred at a temperature of 100° C. Nitrous oxide and moist air were injected from a bottom channel opening, each at a flow rate of 3.5 mL/min. The catalyzed oil was pumped past a tared depositor rod that was resistively heated through twelve, 9.5 min temperature cycles that went from 200° C. to 480° C. When the twelve-cycle program was complete, the depositor rod was rinsed of oil residue and dried and the gross rod mass was determined. The remaining test oil sample, including washing from the deposit rod, was flushed from the system and filtered through a tared filter. The mass of deposits on the rod plus the mass of deposits on the filter was determined to be the total deposit. For this test, an average value of two or more samples was obtained. 
     Antiwear: 
     The antiwear performance was determined according to ASTM D4172-18. In particular, a 4-ball wear test was conducted wherein three steel balls are clamped together and covered with the lubricant. A fourth steel ball, referred to as the top ball, is pressed with a normal force of 40 kgf onto three clamped balls for three-point contact. The temperature of the lubricant composition is regulated at 75° C. and then the top ball is rotated at 1200 rpm for 60 min. Lubricants are compared by measuring the average size of the wear scar diameters worn on the three lower clamped balls. In general, higher antiwear values correspond to a greater wear and poorer antiwear performance while lower antiwear values corresponding to better antiwear performance. 
     Expected Antiwear: 
     Using the aforementioned method, the antiwear performance was determined for each antioxidant individually, rather than using both in combination. Then, using a linear extrapolation, the expected value was determined as a function of the weight percentage of each antioxidant in the composition. As an example, if antioxidant A had an actual wear scar of 0.8 mm and antioxidant B had an actual wear scar of 0.4 mm, an antioxidant composition having antioxidant A in an amount of 25 wt. % and antioxidant B in an amount of 75 wt. % would have an expected wear scar of 0.5 mm (e.g., 0.25*0.8 mm+0.75*0.4 mm). Similarly, an antioxidant composition having antioxidant A in an amount of 40 wt. % and antioxidant B in an amount of 60 wt. % would have an expected wear scar of 0.56 mm (e.g., 0.40*0.8 mm+0.60*0.4 mm). As another example, an antioxidant composition having antioxidant A in an amount of 66.6 wt. % and antioxidant B in an amount of 33.3 wt. % would have an expected wear scar of 0.66 mm (e.g., 0.66*0.8 mm+0.33*0.4 mm). 
     Example 1 
     This example demonstrated the efficacy of the antioxidant composition in a particular lubricating oil. In particular, the standard RPVOT oxidation induction time, dry RPVOT oxidation induction time, PDSC oxidation induction time, TEOST 33C deposit, and antiwear performance were determined. 
     The lubricating oil was EHC™ 65 from ExxonMobil. EHC™ 65, which includes severely treated based oils, is a Group 2 base oil. For each sample, the total amount of the antioxidant(s) in each sample was 1 wt. % in the EHC™ 65. 
     The phosphite antioxidant included one or more phosphite antioxidants having the structure as defined herein wherein m, n, and o are each independently 1 or 2 and wherein R 4 , R 5 , and R 6  are each a C 5  alkyl (i.e., tert-pentyl). 
     The phenolic antioxidant included one or more phenolic antioxidants having the structure as defined herein wherein A is a C 2  alkylene, X is —C(O)O—, R 1  and R 2  are a C 4  alkyl (i.e., tert-butyl), and R 3  is a C—C alkyl. 
     The lubricant composition was prepared by mixing the antioxidants with the lubricating oil at 50° C. for 30 minutes. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Effect of Antioxidant Composition on RPVOT, 
               
               
                 PDSC, TEOST 33C, and Antiwear Performance 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Compar- 
                 Sample 
                 Sample 
                 Sample 
                 Compar- 
               
               
                   
                 ative 1 
                 1 
                 2 
                 3 
                 ative 2 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Phosphite 
                 1 
                 0.75 
                 0.5 
                 0.25 
                 0 
               
               
                 Antioxidant 
               
               
                 (wt. %) 
               
               
                 Phenolic 
                 0 
                 0.25 
                 0.5 
                 0.75 
                 1 
               
               
                 Antioxidant 
               
               
                 (wt. %) 
               
               
                 Dry RPVOT 
                 529  
                 572 
                 554 
                 476 
                 188 
               
               
                 (min) 
               
               
                 Expected Dry 
                 — 
                 443 
                 358 
                 273 
                 — 
               
               
                 RPVOT 
               
               
                 (min) 
               
               
                 % Increase 
                 — 
                 29.1 
                 54.7 
                 74.4 
                 — 
               
               
                 Dry RPVOT 
               
               
                 Standard 
                 272  
                 310 
                 364 
                 324 
                 184 
               
               
                 RPVOT 
               
               
                 (min) 
               
               
                 Expected 
                 — 
                 250 
                 228 
                 206 
                 — 
               
               
                 Standard 
               
               
                 RPVOT 
               
               
                 (min) 
               
               
                 % Increase 
                 — 
                 24.0 
                 59.6 
                 57.3 
                 — 
               
               
                 Standard 
               
               
                 RPVOT 
               
               
                 PDSC 
                 43  
                 168 
                 122 
                 96 
                 81 
               
               
                 (min) 
               
               
                 Expected 
                 — 
                 52 
                 62 
                 72 
                 — 
               
               
                 PDSC 
               
               
                 (min) 
               
               
                 % Increase 
                 — 
                 223.1 
                 96.8 
                 33.3 
                 — 
               
               
                 Dry PDSC 
               
               
                 TEOST 33C 
                  11.4 
                 10.8 
                 11.3 
                 12.1 
                 9.7 
               
               
                 (mg) 
               
               
                 Wear Scar 
                   0.86 
                 0.48 
                 0.90 
                 0.77 
                 0.73 
               
               
                 (mm) 
               
               
                 Expected 
                 — 
                 0.83 
                 0.80 
                 0.76 
                 — 
               
               
                 Wear Scar 
               
               
                 (mm) 
               
               
                 % Change 
                 — 
                 −42.2 
                 12.5 
                 −6.6 
                 — 
               
               
                 Wear Scar 
               
               
                   
               
            
           
         
       
     
     As indicated in the table above, compared to an expected oxidation induction time, the inventive samples containing both the phenolic antioxidant and the phosphite antioxidant demonstrate improved antioxidation performance. In particular, compared to the expected oxidation induction time, the actual oxidation induction times were greater thereby demonstrating a synergistic effect when utilizing both antioxidants in combination. Furthermore, the actual oxidation induction time when utilizing the antioxidant composition containing both antioxidants was greater than the oxidation induction time when utilizing each antioxidant individually in certain instances. Also, the amount of deposits when utilizing the antioxidant composition also appeared to be unaffected. For example, the amount of deposits appeared to be substantially similar to the amount of deposits exhibited when utilizing each antioxidant individually. In addition, in certain examples, the antioxidant composition resulted in a lubricant composition that appeared to demonstrate improved antiwear performance. 
     Example 2 
     This example demonstrated the oxidation performance of the phosphite antioxidant and the phenolic antioxidant individually. In addition, in one example, the phosphite antioxidant was combined with triisopropanolamine. In particular, the standard RPVOT oxidation induction time, dry RPVOT oxidation induction time, PDSC oxidation induction time and TEOST 33C deposit were determined. 
     The lubricating oil was EHC™ 65 from ExxonMobil. EHC™ 65, which includes severely treated based oils, is a Group 2 base oil. For each sample, the total amount of the antioxidant in each sample was 0.5 wt. % in the EHC™ 65. 
     The phosphite antioxidant included one or more phosphite antioxidants having the structure as defined herein wherein m, n, and o are each independently 1 or 2 and wherein R 4 , R 5 , and R 6  are each a C 5  alkyl (i.e., tert-pentyl). When present, the amount of triisopropanolamine was from 0.10 wt. % to 0.30 wt. % based on the combined weight of the phosphite antioxidants and the triisopropanolamine. 
     The phenolic antioxidant included one or more phenolic antioxidants having the structure as defined herein wherein A is a C 2  alkylene, X is —C(O)O—, R 1  and R 2  are a C 4  alkyl (i.e., tert-butyl), and R 3  is a C—C alkyl. 
     The lubricant composition was prepared by mixing the antioxidants with the lubricating oil at 50° C. for 30 minutes. 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Effect of Triisopropanolamine on RPVOT and PDSC 
               
            
           
           
               
               
               
               
            
               
                   
                   
                   
                 Phosphite 
               
               
                   
                 Phenolic 
                 Phosphite 
                 Antioxidant at 
               
               
                   
                 Antioxidant at 
                 Antioxidant at 
                 0.5 wt. % (with 
               
               
                   
                 0.5 wt. % 
                 0.5 wt. % 
                 Triisopropanolamine) 
               
               
                   
                   
               
            
           
           
               
               
               
               
            
               
                 Dry 
                 144 
                 516 
                 513 
               
               
                 RPVOT (min) 
               
               
                 Standard 
                 369 
                 976 
                 937 
               
               
                 RPVOT* (min) 
               
               
                 PDSC (min) 
                 76.2 
                 42.2 
                 42.2 
               
               
                   
               
               
                 *EHC ™ 65 was combined with a rust inhibitor and an anti-corrosion agent. 
               
            
           
         
       
     
     Example 3 
     This example demonstrated the efficacy of the antioxidant composition in a particular lubricating oil. In particular, the standard RPVOT oxidation induction time, dry RPVOT oxidation induction time, TEOST 33C deposit, and antiwear performance were determined. 
     The lubricating oil was EHC™ 65 from ExxonMobil. EHC™ 65, which includes severely treated based oils, is a Group 2 base oil. For each sample, the total amount of the antioxidant(s) in each sample was 1 wt. % in the EHC™ 65. 
     The phosphite antioxidant included one or more phosphite antioxidants having the structure as defined herein wherein m, n, and o are each independently 1 or 2 and wherein R 4 , R 5 , and R 6  are each a C 5  alkyl (i.e., tert-pentyl). Triisopropanolamine was also present in an amount of from 0.10 wt. % to 0.30 wt. % based on the combined weight of the phosphite antioxidants and the triisopropanolamine. 
     The phenolic antioxidant included one or more phenolic antioxidants having the structure as defined herein wherein A is a C 2  alkylene, X is —C(O)O—, R 1  and R 2  are a C 4  alkyl (i.e., tert-butyl), and R 3  is a C—C alkyl. 
     The lubricant composition was prepared by mixing the antioxidants with the lubricating oil at 50° C. for 30 minutes. 
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Effect of Antioxidant Composition on RPVOT, 
               
               
                 TEOST 33C, and Antiwear Performance 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Compar- 
                 Sample 
                 Sample 
                 Sample 
                 Compar- 
               
               
                   
                 ative 3 
                 4 
                 5 
                 6 
                 ative 2 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Phosphite 
                 1 
                 0.75 
                 0.5 
                 0.25 
                 0 
               
               
                 Antioxidant 
               
               
                 (wt. %) 
               
               
                 Phenolic 
                 0 
                 0.25 
                 0.5 
                 0.75 
                 1 
               
               
                 Antioxidant 
               
               
                 (wt. %) 
               
               
                 Dry RPVOT 
                 526 
                 587 
                 637 
                 580 
                 188 
               
               
                 (min) 
               
               
                 Expected Dry 
                 — 
                 441 
                 357 
                 272 
                 — 
               
               
                 RPVOT 
               
               
                 (min) 
               
               
                 % Increase 
                 — 
                 33.1 
                 78.4 
                 113.2 
                 — 
               
               
                 Dry RPVOT 
               
               
                 Standard 
                 265 
                 374 
                 324 
                 366 
                 184 
               
               
                 RPVOT 
               
               
                 (min) 
               
               
                 Expected 
                 — 
                 244 
                 224 
                 204 
                 — 
               
               
                 Standard 
               
               
                 RPVOT 
               
               
                 (min) 
               
               
                 % Increase 
                 — 
                 53.2 
                 44.6 
                 79.4 
                 — 
               
               
                 Standard 
               
               
                 RPVOT 
               
               
                 TEOST 33C 
                 11.9 
                 11.8 
                 12.0 
                 7.6 
                 9.7 
               
               
                 (mg) 
               
               
                 Wear Scar 
                 1.44 
                 0.78 
                 0.96 
                 0.78 
                 0.73 
               
               
                 (mm) 
               
               
                 Expected 
                 — 
                 1.26 
                 1.09 
                 0.91 
                 — 
               
               
                 Wear Scar 
               
               
                 (mm) 
               
               
                 % Change 
                 — 
                 −38.1 
                 −11.9 
                 −14.3 
                 — 
               
               
                 Wear Scar 
               
               
                   
               
            
           
         
       
     
     As indicated in the table above, compared to an expected oxidation induction time, the inventive samples containing bath the phenolic antioxidant and the phosphite antioxidant demonstrate improved antioxidation performance. In particular, compared to the expected oxidation induction time, the actual oxidation induction times were greater thereby demonstrating a synergistic effect when utilizing both antioxidants in combination. Furthermore, the actual oxidation induction time when utilizing the antioxidant composition containing both antioxidants was greater than the oxidation induction time when utilizing each antioxidant individually in certain instances. Also, the amount of deposits when utilizing the antioxidant composition also appeared to be unaffected. For example, the amount of deposits appeared to be substantially similar to the amount of deposits exhibited when utilizing each antioxidant individually. In addition, the antioxidant composition resulted in a lubricant composition that appeared to demonstrate improved antiwear performance. 
     Without intending to be limited by theory, phosphite antioxidants may generally provide improvements to antiwear performance. In addition, when combined simply with an alkanolamine, in certain instances, the antiwear performance may be negatively affected. However, as indicated above, when a phosphite antioxidant with an alkanolamine is combined with a phenolic antioxidant, antiwear performance may not be negatively affected. For instance, the adverse antiwear performance generally observed with simply a phosphite antioxidant and an alkanolamine, such as triisopropanolamine, is mitigated and a synergistic antiwear performance is realized when the aforementioned are utilized in combination with a phenolic antioxidant. Without intending to be limited by theory, this may be due to the hydrogen bond(s) between the triisopropanolamine and the phenol moiety and/or the ester group of the phenolic antioxidant. 
     These and other modifications and variations of the present invention may be practiced by those of ordinary skill in the art, without departing from the spirit and scope of the present invention. In addition, it should be understood that aspects of the various embodiments may be interchanged both in whole or in part. Furthermore, those of ordinary skill in the art will appreciate that the foregoing description is by way of example only, and is not intended to limit the invention so further described in such appended claims.