To provide a viscosity index-improver which is excellent in viscosity reduction effect at a low temperature and also excellent in viscosity index-improvement effect and shear stability.
The viscosity index-improver for a lubricating oil consists of an oil-soluble copolymer (A) which comprises a constituent unit (a) consisting of a (meth)acrylate monomer having a specified branched alkyl group and one or more kinds of constituent units (b) selected from the group consisting of a phosphate group-containing constituent unit (b1), a phosphono group-containing constituent unit (b2), an amino group-containing constituent unit (b3), and a thiol group-containing constituent unit (b4). Based on the weight of the copolymer (A), the content of the constituent unit (a) is 5-90 wt.% and that of the constituent units (b) is 0.5-50 wt.%.
COPYRIGHT: (C)2009,JPO&INPIT
Takeshi Yuki
Satoshi Utsui
Manami Noda
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