The invention provides a diamine compound polymer having a 1,3-phenylene group selected from structural formulae represented by formulae (I-1) and (I-2): where, in the formulae (I-1) and (I-2), A represents a structure represented by the following formula (II); R represents a hydrogen atom, an alkyl group, a substituted or non-substituted aryl group, or a substituted or non-substituted aralkyl group; Y represents a divalent alcoholic residue; Z represents a divalent carboxylic acid residue; B and B′ independently represent —O—(Y—O)n—R or —O—(Y—O)n—CO—Z—CO—O—R′ (where R, Y and Z have the same meanings as described above, and R′ represents an alkyl group, a substituted or non-substituted aryl group, or a substituted or non-substituted aralkyl group); n represents an integer of 1 to 5; and p represents an integer of 5 to 5000; where, in the formula (II), Ar represents a substituted or non-substituted aromatic group; X represents a substituted or non-substituted divalent 1,3-phenylene group; T represents a divalent linear hydrocarbon group having 1 to 6 carbon atoms or a branched hydrocarbon group having 2 to 10 carbon atoms; and k and m represent an integer of 0 or 1, respectively.