Patent ID: 8436103

Claim:
A star polymer comprising a core portion and an arm portion, wherein the arm portion includes a first generation composed of a polymer chain and a second generation composed of a polymer chain formed at the outer shell of the first generation, the number of arms of the second generation is larger than the number of arms of the first generation, the first generation composed of the polymer chain is a polymer chain derived from a monomer having a polymerizable double bond, and a ratio of a weight average molecular weight (Mw) to a number average molecular weight (Mn), (Mw/Mn), of the star polymer is within a range from 1.001 to 2.50, the second generation is a polymer chain which includes a repeating unit containing a structure represented by formula (II): wherein R 501a and R 501b each independently represents a hydrogen atom or a C1-C10 hydrocarbon group, m21 represents an integer of 2 or more, each R 501a may be the same as or different from one another and R 501b , may be the same as or different from one another, and m11 represents an integer of 1 or more, or a repeating unit represented by formula (III): wherein R 101 to R 301 each independently represents a hydrogen atom or a C1-C10 hydrocarbon group, and R 101 and R 301 may be bonded to form a ring, R 401a and R 401b each independently represents a hydrogen atom or a methyl group, R 501 represents a hydrogen atom, a hydrocarbon group, an acyl group or a silyl group, and s11 represents any integer from 1 to 100 and when s11 is 2 or more, groups represented by the formula —CH(R 401a )CH(R 401b )O— may be the same or different.