Effect of substituents in aromatic amines on the activation energy of epoxy-amine reaction.

Differential scanning calorimetry has been used to study the kinetics of epoxy-amine curing reaction between diglycidyl ether of 4,4'-bisphenol and aromatic amines with different electron-withdrawing/-donating substituents. The substituents include -NO2, -CN, -OCH3, -OH, and -CH3 groups. An advanced isoconversional method has been employed to determine the effective activation energy of the respective processes. An attempt has been made to link the experimental values with the results of quantum chemistry calculations. It has been found that regardless of the electron-withdrawing/-donating properties the presence of a substituent of a large negative charge in the ortho position causes an increase in the activation energy to approximately 100 kJ mol-1 from the normally observed values of 50-60 kJ mol-1.