EFFECT OF STRUCTURE OF AROMATIC DIAMINES ON CURING CHARACTERISTICS, THERMAL-STABILITY, AND MECHANICAL-PROPERTIES OF EPOXY-RESINS - I

The curing behavior of diglycidyl ether of bisphenol-A (DGEBA) with ar omatic diamines having aryl-ether, aryl-ether-carbonyl, and aryl-ether -sulfone linkages was studied using differential scanning calorimetry (DSC). Aromatic diamines such as 1,3-bis(aminophenoxy)benzene (R), 1,4 -bis( aminophenoxy)benzene (H), 2,2'-bis[4-(4-aminophenoxy)phenyl]prop ane (B), 4,4'-bis(4-aminophenoxy)benzophenone (P), and his [4-(4-amino phenoxy) phenyl] sulfone (S) were synthesized and characterized in the laboratory. Curing of DGEBA was done using both stoichiometric and no nstoichiometric amounts of diamines and the reaction was monitored usi ng DSC. The reactivity of the diamines depended on the structure. The presence of electron withdrawing groups, even though significantly apa rt from the reaction site, reduced the nucleophilicity. No significant change was observed in the activation energy for curing, which was ar ound 56 +/- 2 kJ/mol. The glass transition temperature of the epoxy ne twork depended on the structure and was higher when diamines P and S w ere used in comparison to diamines R, H, and B. The cured resins were stable up to 300 degrees C, and maximum char yield (i.e., 32% at 600 d egrees C) was obtained in DGEBA cured with diamine P. The room tempera ture mechanical properties only changed marginally with the structure of the diamines. (C) 1998 John Wiley & Sons, Inc.