Abstract
ABSTRACT Diamines having heterocyclic ring, 4,5-bis (4-aminophenyl)-2-phenyl-imidazole (BAPI), 4,5-bis(4-aminophenyl)-2-methyloxazole (BAPO) and novel diamine, 2,3-bis(4-aminophenyl)benzo[g]quinoxaline (BABQ) were prepared as curing agents for epoxy resin. Epoxy resins were obtained by curing diglycidyl ether of bisphenol A (DGEBA) with the above diamines. Properties of these DGEBA-diamine systems were studied and compared to that of DGEBA cured with commercially available diamine, 4,4′-diaminodiphenyl sulfone (DDS). On differential scanning calorimetry (DSC), the peaks of exotherms of the mixtures of DGEBA with these diamines having heterocyclic rings were observed at lower temperature and these reactions were completed in shorter time than that of DGEBA with DDS. The epoxy resins cured with these diamines containing heterocyclic ring showed excellent bonding strength even at high temperature and thermal resistance, e.g., DGEBA-BABQ gives greater bonding strengths as 35.1, 30.0, and 26.2 MPa when tested at 20, 120, and 180°C, respectively and residual weight at 600°C was 44% after being cured at 160°C for 2 hours. In the curing of DEGBA-BAPI, the reaction was accelerated and completed in a shorter time, but the bonding strength lowered somewhat, since the tertiary amine in the imidazole ring acts as catalytic curing agent which leads to epoxy homopolymerization.
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