Curing behavior and properties of epoxy resins cured with the diamine having the quinoxaline or triazine structure

2,3‐Bis(4‐aminophenyl)quinoxaline (1a), 2,3‐bis(4‐aminophenyl)‐6‐methylquinoxaline (1b), and 5,6‐bis(4‐aminophenyl)‐3‐(2‐pyridyl)‐1,2,4‐triazine (2) were studied as curing agents of epoxy resins. The exotherms on differential scanning calorimetry thermograms of the mixtures of diglycidyl ether of bisphenol A (DGEBA) with 1a, 1b, and 2 were observed at higher temperatures than that of the mixture of DGEBA with a commercially used diamine, for example, 4,4′‐diaminodiphenylsulfone (DDS). However, the epoxy resin cured with 1a (EP‐1a) showed higher tensile strength to stainless steel at 20°C than that cured with DDS, and the high tensile strength of EP‐1a was maintained even at 180°C. The epoxy resin cured with 1b or 2 also possessed higher tensile strength at 20°C than that cured with DDS, but the high tensile strength lowered somewhat at 120°C. Using diamines 1a, 1b, and 2 as a curing agent improved heat distortion temperatures of the cured epoxy resins. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 69: 1737–1741, 1998