Resin composition for forming phase-separated structure, method for producing structure including phase-separated structure, and block copolymer

A resin composition for forming a phase-separated structure, comprising:

• a block copolymer having a first block and a second block,
• wherein the first block includes a polymer having a repeating structure of a constituent unit represented by General Formula (b1),
• the second block includes a random copolymer having a structure in which a constituent unit represented by General Formula (b2m) and a constituent unit represented by General Formula (b2g) are arranged in a disorderly manner, and
• a ratio of a volume of the first block to a total volume of the first block and the second block is 20% to 80% by volume,
• wherein, in Formula (b1), R1 is a hydrogen atom or an alkyl group, and Rb1 is a hydrogen atom or a methyl group,
• in Formula (b2g), R2 is an alkyl group which may have a silicon atom, a fluorine atom, a carboxy group, an amino group, a hydroxy group, or a phosphoric acid group, and
• R3 is a linear or branched alkylene group having 1 to 10 carbon atoms, which may have a hydroxy group, and
• in Formula (b2g) and Formula (b2m), Rb2 is a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, or a halogenated alkyl group having 1 to 5 carbon atoms, a plurality of Rb2s may be the same or different from each other, and
• x and 1-x represent a molar ratio, and x is 0.1 or more and 0.9 or less.