A resin composition contains: (a) a resin which constitutes a polymer having a structure represented by any one of the following general formulae (1) to (3) below and/or a copolymer having the structure; and (b) a basic compound, wherein R1 is a C4-C30 organic group, R2 is a divalent C4-C30 organic group, X is a sulfonic group, hydroxy group, or carboxy group, p is 1 to 4, and n is 2 to 100,000; wherein R3 is a C4-C30 organic group, R4 is a divalent C4-C30 organic group, Y is a sulfonic group, hydroxy group, or carboxy group, q is 1 to 4, and m is 2 to 100,000; wherein R5 represents a C4-C30 organic group, R6 is a divalent C4-C30 organic group, Z is a sulfonic group, hydroxy group, or carboxy group, r is 1 to 4, and l is 2 to 100,000.