Lubricating oil composition, viscosity modifier for lubricating oil, and additive composition for lubricating oil

A lubricating oil composition comprising a polymer (A) and a base oil (B), the lubricating oil composition comprising a viscosity modifier for lubricating oils containing the polymer (A),

• wherein the polymer (A) contains:
• from 65 to 99% by mole of a structural unit derived from 4-methyl-1-pentene;
• and from 1 to 35% by mole of a structural unit derived from at least one selected from ethylene and a-olefins having from 3 to 20 carbon atoms other than 4-methyl-1-pentene;
• wherein the polymer (A) satisfies the following requirements (I) to (III):
• (I) the polymer (A) has an isotactic dyad fraction as measured by 3C-NMR of within the range of from 40 to 95%;
• (II) the polymer (A) has a weight average molecular weight (Mw) as measured by gel permeation chromatography (GPC) of within the range of from 50,000 to 500,000;
• and
• (III) the polymer (A) has a ratio (Mw/Mn) of the weight average molecular weight to the number average molecular weight as measured by gel permeation chromatography (GPC) of within the range of from 2.0 to 20.0;
• and
• wherein the content ratio of the polymer (A) and the base oil (B) is such that the ratio of a resin (A) is within the range of from 0.1 to 50 parts by mass with respect to 100 parts by mass of the total amount of the polymer (A) and the base oil (B).

A viscosity modifier for lubricating oils, comprising a polymer (A) satisfying the following requirements (A-1) to (A-4):

• (A-1) the polymer (A) contains a structural unit derived from 4-methyl-1-pentene in an amount within the range of from 30 to 90% by mole with respect to the total structural units and a structural unit derived from propylene or ethylene in an amount within the range of from 10 to 70% by mole with respect to the total structural units;
• (A-2) the polymer (A) has an intrinsic viscosity [η]as measured in decalin at 135° C. of within the range of from 0.01 to 5.0 dl/g;
• (A-3) the polymer (A) has a melting point (Tm) as measured by differential scanning calorimetry (DSC) of less than 110° C., or is not detected;
• and
• (A-4) the polymer (A) has a glass transition temperature (Tg) as measured by differential scanning calorimetry (DSC) of within the range of from 1 to 50° C.

A viscosity modifier for lubricating oils comprising a polymer (A), wherein the polymer (A) contains:

• from 65 to 99% by mole of a structural unit derived from 4-methyl-1-pentene;
• and from 1 to 35% by mole of a structural unit derived from at least one selected from ethylene and a-olefins having from 3 to 20 carbon atoms other than 4-methyl-1-pentene;
• and
• wherein the polymer (A) satisfies the following requirements (I) to (III):
• (I) the polymer (A) has an isotactic dyad fraction as measured by 13C-NMR of within the range of from 40 to 95%;
• (II) the polymer (A) has a weight average molecular weight (Mw) as measured by gel permeation chromatography (GPC) of within the range of from 50,000 to 500,000;
• and
• (III) the polymer (A) has a ratio (Mw/Mn) of the weight average molecular weight to the number average molecular weight as measured by gel permeation chromatography (GPC) of within the range of from 2.0 to 20.0.