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 hydrocarbyl group; and Z.sup.1 is a linking group linking X.sup.1 and Y.sup.1.

A composition comprising a sheared antifoam solution/mixture with a mean particle size from about 0.01 microns to about 0.5 microns and a maximum particle size of less than about 1 micron. In this composition the sheared antifoam solution/mixture comprises antifoam solution/mixture comprising an antifoam and a base stock.

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 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.

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 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.2 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 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.

The present disclosure relates to comb or brush polymers and, in some approaches, comb or brush polymers suitable for use as viscosity index improvers in lubricating oil compositions. The present disclosure further relates to oil compositions comprising such polymers. The disclosure also relates to brush polymer compositions derived from sulfur functionalized polydialkylsiloxane backbones and various (meth)acrylate monomers.

A composition comprising a sheared antifoam solution/mixture with a mean particle size from about 0.01 microns to about 0.5 microns and a maximum particle size of less than about 1 micron. In this composition the sheared antifoam solution/mixture comprises antifoam solution/mixture comprising an antifoam and a base stock.