Crosslinking of an epoxy with a mixed amine as a function of stoichiometry. II. Final properties via dynamic mechanical spectroscopy

Variation of the epoxy/curing agent ratio for a system containing a diglycidyl ether of bisphenol‐A (DGEBA) and a mixed aromatic amine was found to have a significant effect on the cure kinetics and final dynamic mechanical properties of both the neat resin and glass reinforced epoxy. For a partial B‐stage cure to an ultimate C‐stage cure, optimum cure temperatures were obtained as a function of stoichiometry. For the ultimately cured (C‐stage) resin, the molecular weight between crosslinks ( M c ) passed through a minimum, and both the glass transition temperature ( T g ) and a secondary (sub‐ T g ) transition passed through a maximum at the stoichiometric ratio. In addition, the activation energy of the ultimately cured resin passed through a maximum at or near the stoichiometric ratio for both the T g and sub‐ T g transitions.