Defoaming agent and lubricating oil composition

A defoaming agent obtainable by a process, the process comprising:

• polymerizing (A) at least one polymerizable monomer in a composition, the composition comprising (C) a solvent and (B) at least one non-polymerizable polysiloxane dissolved in the (C) solvent,
• wherein the component (A) comprises at least one Si-atom-containing monomer in an amount of no more than 5 mass % on the basis of the total mass of the component (A), and
• wherein the component (B) comprises at least one polysiloxane represented by the following formula (2):
• wherein in the general formula (2), polysiloxane repeating units may be in any order;
• R1 and R2 are each independently a no-fluorine-atom-containing non-polymerizable C1-18 organic group;
• R3 and R4 are each independently a fluorine-atom-containing non-polymerizable organic group, or a no-fluorine-atom-containing non-polymerizable C1-18 organic group, wherein at least one of R3 and R4 is a non-polymerizable organic group comprising no less than 3 fluorine atoms;
• R5, R6, R7, R8, R9, and R10 are each independently a non-polymerizable C1-18 organic group;
• n and m are each independently an integer of no less than 0;
• n+m is no less than 1;
• and
• a ratio m/(n+m) is 0 to 1.