Block copolymers and use thereof

A block copolymer comprising at least one segment having an acid group and at least one segment substantially free from acid groups, wherein the segment substantially free from acid groups contains a repeating structure of the following formula (1):

• wherein m represents an integer of 10 or more;
• Ar1, Ar2, and Ar3 mutually independently represent a divalent aromatic group, wherein the divalent aromatic group may be substituted by an alkyl group having 1 to 10 total carbon atoms, an alkoxy group having 1 to 10 total carbon atoms, an aryl group having 6 to 10 total carbon atoms, or an aryloxy group having 6 to 10 total carbon atoms;
• and Z represents —CO— or —SO2—, each Z in the segments representing independently —CO— or —SO2—;
• wherein the segment having an acid group is the following general formula (6):
• wherein n represents an integer of 10 or more, Y represents —CO— or —SO2—, each Y in the segments representing independently —CO— or —SO2—, r represents 0 or 1, s represents 0 or 1, r+s being 1 or 2, t represents 1 or 2, and u represents 1 or 2.