Patent ID: 8211576

Claim:
A block copolymer comprising at least one segment having an acid group which is represented by the following formula (4) and at least one segment substantially free from acid groups which comprises repeating units represented by the following formula (2): (wherein, m represents an integer of 10 or more, Y represents —CO— or —SO 2 —, each Y in the segment being independently —CO— or —SO 2 —, r and s each represent 1, u represents 1 or 2, and t represents 1 or 2) (wherein, n represents an integer of 10 or more, Ar 4 and Ar 5 represent each independently a divalent aromatic group which is optionally substituted by an alkyl group having 1 to 10 carbon atoms, alkoxy group having 1 to 10 carbon atoms, aryl group having 6 to 10 carbon atoms, aryloxy group having 6 to 10 carbon atoms or fluoro group. Z represents —CO— or —SO2—, and each 2 in the segment being independently —CO— or —SO 2 —), wherein the weight composition ratio of a segment having an acid group to a segment substantially free from acid groups is from 27:73 to 33:67.