A lubricant composition for application onto a surface of drive elements includes: a base oil; and a silasesquioxane. In an embodiment, the silasesquioxane has the chemical formula [RSiO3/2].sub.n with: n=6, 8, 10, 12; where R independently of one another=alkyl (C1-C20), cycloalkyl (C3-C20), alkenyl (C2-C20), cycloalkenyl (C5-C20), alkynyl (C2-C20), cycloalkynyl (C5-C20), aryl (C6-C18) or heteroaryl group, oxy, hydroxy, alkoxy (C4-C10), oxirane polymer (degree of polymerization with 4 to 20 repeat units), carboxy, silyl, alkylsilyl, alkoxysilyl, siloxy, alkylsiloxy, alkoxysiloxy, silylalkyl, alkoxysilylalkyl, alkylsilylalkyl, halogen, epoxy (C2-C20), ester, aryl ether, fluoroalkyl, blocked isocyanate, acrylate, methacrylate, mercapto, nitrile, amine, and/or phosphine group, each substituted or unsubstituted.

A lubricant composition for application onto a surface of drive elements includes: a base oil; and a silasesquioxane. In an embodiment, the silasesquioxane has the chemical formula [RSiO3/2].sub.n with: n=6, 8, 10, 12; where R independently of one another=alkyl (C1-C20), cycloalkyl (C3-C20), alkenyl (C2-C20), cycloalkenyl (C5-C20), alkynyl (C2-C20), cycloalkynyl (C5-C20), aryl (C6-C18) or heteroaryl group, oxy, hydroxy, alkoxy (C4-C10), oxirane polymer (degree of polymerization with 4 to 20 repeat units), carboxy, silyl, alkylsilyl, alkoxysilyl, siloxy, alkylsiloxy, alkoxysiloxy, silylalkyl, alkoxysilylalkyl, alkylsilylalkyl, halogen, epoxy (C2-C20), ester, aryl ether, fluoroalkyl, blocked isocyanate, acrylate, methacrylate, mercapto, nitrile, amine, and/or phosphine group, each substituted or unsubstituted.

A lubricant composition for application onto a surface of drive elements includes: a base oil; and a silasesquioxane. In an embodiment, the silasesquioxane has the chemical formula [RSiO3/2].sub.n with: n=6, 8, 10, 12; where R independently of one another=alkyl (C1-C20), cycloalkyl (C3-C20), alkenyl (C2-C20), cycloalkenyl (C5-C20), alkynyl (C2-C20), cycloalkynyl (C5-C20), aryl (C6-C18) or heteroaryl group, oxy, hydroxy, alkoxy (C4-C10), oxirane polymer (degree of polymerization with 4 to 20 repeat units), carboxy, silyl, alkylsilyl, alkoxysilyl, siloxy, alkylsiloxy, alkoxysiloxy, silylalkyl, alkoxysilylalkyl, alkylsilylalkyl, halogen, epoxy (C2-C20), ester, aryl ether, fluoroalkyl, blocked isocyanate, acrylate, methacrylate, mercapto, nitrile, amine, and/or phosphine group, each substituted or unsubstituted.

A defoaming agent including a polymer, the polymer including: at least one first polymer chain including a polysiloxane structure represented by the following general formula (1); and at least one second polymer chain including a repeating unit represented by the following general formula (2) and bonded to the first polymer chain: ##STR00001##
wherein in the formula (1), repeating units may be in any order; each of R.sup.1 and R.sup.2 is independently a C.sub.1-18 organic group comprising no fluorine atom; at least one of R.sup.3 and R.sup.4 is the organic group comprising no less than 3 fluorine atoms; m is an integer of no less than 1; and n+m is 5 to 2000, ##STR00002##
wherein in the formula (2), X.sup.1 is a repeating unit obtainable by polymerization of an ethylenic unsaturated group; Y.sup.1 is a substituted or unsubstituted C.sub.1-40 hydrocarbyl group; and Z.sup.1 is a linking group linking X.sup.1 and Y.sup.1.

A defoaming agent obtainable by a process, the process including the step of: (i) polymerizing (B) at least one defoaming agent monomer in (A) a polymerization solvent under coexistence of (C) a polymer soluble in the polymerization solvent.

A lubricating oil composition including: a lubricant base oil; (A) a first defoaming agent obtainable by a process, the process including the step of: polymerizing (b) at least one defoaming agent monomer in (a) a polymerization solvent under coexistence of (c) a polymer soluble in the polymerization solvent; and (B) a second defoaming agent being a silicone defoaming agent.

A lubricant composition for application onto a surface of drive elements includes: a base oil; and a silasesquioxane. In an embodiment, the silasesquioxane has the chemical formula [RSiO3/2].sub.n with: n=6, 8, 10, 12; where R independently of one another=alkyl (C1-C20), cycloalkyl (C3-C20), alkenyl (C2-C20), cycloalkenyl (C5-C20), alkynyl (C2-C20), cycloalkynyl (C5-C20), aryl (C6-C18) or heteroaryl group, oxy, hydroxy, alkoxy (C4-C10), oxirane polymer (degree of polymerization with 4 to 20 repeat units), carboxy, silyl, alkylsilyl, alkoxysilyl, siloxy, alkylsiloxy, alkoxysiloxy, silylalkyl, alkoxysilylalkyl, alkylsilylalkyl, halogen, epoxy (C2-C20), ester, aryl ether, fluoroalkyl, blocked isocyanate, acrylate, methacrylate, mercapto, nitrile, amine, and/or phosphine group, each substituted or unsubstituted.

A defoaming agent including a polymer, the polymer including a repeating unit represented by the following general formula (1); and a repeating unit represented by the following general formula (3): ##STR00001##
wherein in the general formula (1), X.sup.1 is a repeating unit obtainable by polymerization of a first ethylenic unsaturated group; Y.sup.1 is a side chain including a linear or branched polysiloxane structure, the polysiloxane structure having a polymerization degree of 5 to 300; and Z.sup.1 is a linking group linking the repeating unit X.sup.1 and the side chain Y.sup.1; ##STR00002##
wherein in the general formula (3), X.sup.2 is a repeating unit obtainable by polymerization of a second ethylenic unsaturated group, Y.sup.2 is a C.sub.1-30 hydrocarbyl side chain; and Z.sup.2 is a linking group linking the repeating unit X.sup.2 and the side chain Y.sup.2.

A defoaming agent comprising: a polymer comprising a repeating unit represented by the following general formula (1): ##STR00001##
where in the general formula (1), X.sup.1 is a repeating unit obtainable by polymerization of an ethylenic unsaturated group; Y.sup.1 is a side chain comprising a linear or branched polysiloxane structure, the polysiloxane structure comprising a repeating unit represented by the following general formula (2) and having a polymerization degree of 5 to 300; and Z.sup.1 is a linking group linking the repeating unit X.sup.1 and the side chain Y.sup.1; ##STR00002##
wherein in the general formula (2), R.sup.1 and R.sup.2 are each independently an organic group having a carbon number of 1 to 18.

A method for improving filterability, while maintaining or improving antifoaming performance, of a lubricating oil in an engine or other mechanical component lubricated with the lubricating oil by using as the lubricating oil a formulated oil. A method for improving antifoaming performance, while maintaining or improving filterability, of a lubricating oil in an engine or other mechanical component lubricated with the lubricating oil by using as the lubricating oil a formulated oil. The formulated oil has a composition including a lubricating oil base stock as a major component, and at least one antifoam agent, as a minor component. A lubricating oil having a composition including a lubricating oil base stock as a major component, and at least one antifoam agent, as a minor component. The antifoam agent is a silicone composition having a highly branched functionalized silicone backbone. The lubricating oils are useful as automotive gear lubricating compositions.