Corrosion-indicating materials and methods of making and using the same

A corrosion-indicating material that indicates corrosion of a metal substrate underlying the corrosion-indicating material, the corrosion-indicating material comprising a cured product of reacting a bisphenol A diglycidyl ether (DGEBA) epoxy resin with a curing agent, the curing agent comprising a 1,10-phenanthroline derivative having formula (I):

• where:
• R1 and R2 are independently selected from —NH2;
• —NH(CH2)aNH2, where a is 1, 2, or 3;
• —OC(═O)(CH2)bNH2, where b is 1, 2, or 3;
• and —H;
• R3 and R4 are either:
• non-joined monovalent radicals each independently chosen from —H, —NH2, and (C1-C20)heterohydrocarbyls comprising at least one primary amine or at least one secondary amine;
• or
• joined as a single divalent radical, the single divalent radical being a (C1-C40)heterohydrocarbylene comprising at least one primary amine or at least one secondary amine;
• at least one of R1, R2, R3, and R4 is not —H;
• and
• provided at least one of (i), (ii), (iii), (iv), (v), or (vi) is true:
• (i) R1 and R2 are independently selected from the group consisting of —NH2 and —H and:
• both R1 and R2 are —H, or
• both R1 and R2 are —NH2;
• or
• (ii) R1, R2, R3, and R4 are independently —NH2 or —H, provided at least one of R1, R2, R3, and R4 is —NH2 and:
• R1 and R2 are —H and R3 and R4 are —NH2, or
• R1 and R2 are —NH2 and R3 and R4 are —H;
• or
• (iii) both R3 and R4 are —NH2;
• or
• (iv) R3 and R4 are identical non-joined monovalent radicals selected from the group consisting of —CH2NH2, —CH2N(CH2CH2NH2)2, —CH2N(H)(cyclohexyl), —CH2N(H)[(CH2)dCH3] where d is 1, 2, or 3, —CH2N(H)[CH2)2N(H)(phenyl)], and —CH2N(H)[CH2)(2-pyridyl)];
• or
• (v) R3 and R4 are joined as a single divalent radical having the formula —CH2—NH—[(CH2)xN(H)—]nCH2—, where x is 2 or 3 and n is 2, 3, 4, or 5;
• or
• (vi) R3 and R4 are joined as a single divalent radical having the formula —CH═N—(CH2)2{—N[CH2)2NH2]—(CH2)2}y—N═CH—, where y is 1 or 2.