Defoaming agent and lubricating oil composition

1. A defoaming agent comprising:

a polymer comprising a repeating unit represented by the following general formula (1):

wherein in the general formula (1), X 1 is a repeating unit obtainable by polymerization of a first ethylenic unsaturated group; Y 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 1 is a linking group linking the repeating unit X 1 and the side chain Y 1 ;

wherein in the general formula (2), R 1 and R 2 are each independently an organic group having a carbon number of 1 to 18;

the polymer further comprising a repeating unit represented by the following general formula (3):

wherein in the general formula (3), X 2 is a repeating unit obtainable by polymerization of a second ethylenic unsaturated group; Y 2 is a side chain comprising no less than 3 fluorine atoms; and Z 2 is a linking group linking the repeating unit X 2 and the side chain Y 2 .

2. The defoaming agent according to claim 1 ,

wherein X 2 is a repeating unit obtainable by polymerization of a second (meth)acryloyl group.

3. The defoaming agent according to claim 1 ,

wherein X 1 is a repeating unit obtainable by polymerization of a first (meth)acryloyl group.

4. The defoaming agent according to claim 1 ,

wherein the polymer comprises the repeating unit represented by the general formula (1) in an amount of no less than 10 mass % on the basis of the total mass of all repeating units in the polymer.

5. The defoaming agent according to claim 1 ,

wherein the polymer has a weight average molecular weight of 10,000 to 1,000,000.

6. A defoaming agent comprising:

a polymer comprising a repeating unit represented by the following general formula (1):

wherein in the general formula (1), X 1 is a repeating unit obtainable by polymerization of a first ethylenic unsaturated group; Y 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 1 is a linking group linking the repeating unit X 1 and the side chain Y 1 ;

wherein in the general formula (2), R 1 and R 2 are each independently an organic group having a carbon number of 1 to 18;

wherein the polymer is a star-shaped polymer.

7. A lubricating oil composition comprising:

(A) a lubricant base oil; and

(B) the defoaming agent as in claim 1 , in an amount of 1 to 100 mass ppm in terms of silicon on the basis of the total mass of the composition.

8. A method for lubricating an automobile engine, an automobile transmission, or an automobile transaxle unit, comprising

supplying the lubricating oil composition according to claim 7 to an automobile engine, an automobile transmission, or an automobile transaxle unit.

9. The defoaming agent according to claim 6 ,

wherein X 1 is a repeating unit obtainable by polymerization of a first (meth)acryloyl group.

10. The defoaming agent according to claim 6 ,

wherein the polymer comprises the repeating unit represented by the general formula (1) in an amount of no less than 10 mass % on the basis of the total mass of all repeating units in the polymer.

11. The defoaming agent according to claim 6 ,

wherein the polymer has a weight average molecular weight of 10,000 to 1,000,000.

12. A lubricating oil composition comprising:

(A) a lubricant base oil; and

(B) the defoaming agent as in claim 6 , in an amount of 1 to 100 mass ppm in terms of silicon on the basis of the total mass of the composition.

13. A method for lubricating an automobile engine, an automobile transmission, or an automobile transaxle unit, comprising:

supplying the lubricating oil composition of claim 12 to an automobile engine, an automobile transmission, or an automobile transaxle unit.

14. A lubricating oil composition comprising:

(A) a lubricant base oil; and

(B) a defoaming agent in an amount of 1 to 100 mass ppm in terms of silicon on the basis of the total mass of the composition, the defoaming agent comprising a polymer, the polymer comprising a repeating unit represented by the following general formula (1):

wherein in the general formula (1), X 1 is a repeating unit obtainable by polymerization of a first ethylenic unsaturated group; Y 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 1 is a linking group linking the repeating unit X 1 and the side chain Y 1 ;

wherein in the general formula (2), R 1 and R 2 are each independently an organic group having a carbon number of 1 to 18,

wherein X 1 is a repeating unit obtainable by polymerization of a first (meth)acryloyl group.

15. The defoaming agent according to claim 14 ,

wherein the polymer comprises the repeating unit represented by the general formula (1) in an amount of no less than 10 mass % on the basis of the total mass of all repeating units in the polymer.

16. The defoaming agent according to claim 14 ,

wherein the polymer has a weight average molecular weight of 10,000 to 1,000,000.

17. A method for lubricating an automobile engine, an automobile transmission, or an automobile transaxle unit, the method comprising:

supplying the lubricating oil composition as in claim 14 to an automobile engine, an automobile transmission, or an automobile transaxle unit.