Method for producing block copolymer

A fine particle, comprising:

• a block copolymer represented by the following Formula (2).
• wherein
• R1 represents an alkanediyl group having 1 to 5 carbon atoms,
• R2 represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms,
• R3 represents —C(R5)(R6)—CN, —C(R7)(R8)—X1, —C(R9)(R10)(R11), —C(R12)(R13)—(CH2)a—COOR14, —C(R15)(X2)—(CH2)b—COOR16, —C(R17)(CN)—(CH2)c—COOR18, —C(R19)(CN)—(CH2)d—OH, —C(R20)(R21)—CON(R22)H, or —C(R23)(R24)—CON(R25)(R26)(R5 to R21, R23, and R24 each independently represent a hydrogen atom or a substituted or unsubstituted alkyl group having 1 to 12 carbon atoms, R22, R25, and R26 each independently represent a substituted or unsubstituted alkyl group having 1 to 12 carbon atoms, X1 and X2 each independently represent a substituted or unsubstituted phenyl group, a substituted or unsubstituted naphthyl group, a substituted or unsubstituted anthracenyl group, a substituted or unsubstituted pyrenyl group, or a substituted or unsubstituted pyridyl group, and a to d each independently represent an integer from 0 to 8),
• R4 represents —S—R27, —S—X3, —S—R28—X4, —N(R29)(R30), —N(R31)(X5), —N(X6)(X7), —N(R32X8)(R33X9), or —N(X10)(R34X11)(R27 and R29 to R31 each independently represent a substituted or unsubstituted alkyl group having 1 to 12 carbon atoms, R28 and R32 to R34 each independently represent a substituted or unsubstituted alkanediyl group having 1 to 12 carbon atoms, and X3 to X11 each independently represent a substituted or unsubstituted phenyl group, a substituted or unsubstituted naphthyl group, a substituted or unsubstituted anthracenyl group, a substituted or unsubstituted pyrenyl group, or a substituted or unsubstituted pyridyl group, provided that R29 and R30 may form a heterocyclic ring with an adjacent nitrogen atom),
• n represents an integer from 1 to 10,
• p represents the number of repetitions of a repeating unit,
• Z represents a repeating unit derived from the hydrophobic monomer, and
• q represents the number of repetitions of the repeating unit derived from the hydrophobic monomer.

A photopolymerization initiator comprising a vinyl ether-based polymer represented by the following Formula (1).

• wherein
• R1 represents an alkanediyl group having 1 to 5 carbon atoms,
• R2 represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms,
• R3 represents —C(R5)(R6)—CN, —C(R7)(R8)—X1, —C(R9)(R10)(R11), —C(R12)(R13)—(CH2)a—COOR14, —C(R15)(X2)—(CH2)b—COOR16, —C(R17)(CN)—(CH2)c—COOR18, —C(R19)(CN)—(CH2)d—OH, —C(R20)(R21)—CON(R22)H, or —C(R23)(R24)—CON(R25)(R26)(R5 to R21, R23, and R24 each independently represent a hydrogen atom or a substituted or unsubstituted alkyl group having 1 to 12 carbon atoms, R22, R25, and R26 each independently represent a substituted or unsubstituted alkyl group having 1 to 12 carbon atoms, X1 and X2 each independently represent a substituted or unsubstituted phenyl group, a substituted or unsubstituted naphthyl group, a substituted or unsubstituted anthracenyl group, a substituted or unsubstituted pyrenyl group, or a substituted or unsubstituted pyridyl group, and a to d each independently represent an integer from 0 to 8),
• R4 represents —S—R27, —S—X3, —S—R28—X4, —N(R29)(R30), —N(R31)(X5), —N(X6)(X7), —N(R32X8)(R33X9), or —N(X10)(R34X11)(R27 and R29 to R31 each independently represent a substituted or unsubstituted alkyl group having 1 to 12 carbon atoms, R28 and R32 to R34 each independently represent a substituted or unsubstituted alkanediyl group having 1 to 12 carbon atoms, and X3 to X11 each independently represent a substituted or unsubstituted phenyl group, a substituted or unsubstituted naphthyl group, a substituted or unsubstituted anthracenyl group, a substituted or unsubstituted pyrenyl group, or a substituted or unsubstituted pyridyl group, provided that R29 and R30 may form a heterocyclic ring with an adjacent nitrogen atom),
• n represents an integer from 1 to 10, and
• p represents the number of repetitions of a repeating unit.