| Abstract: | The dielectric permittivity and loss of diglycidyl ether of bisphenol-A (DGEBA) cured with greater than and less than the stoichiometric amounts of diaminodiphenyl methane (DDM) have been measured over a temperature range 77–350 K prior to curing and gelation, after curing at about 340 K and further aging for a predetermined period. The height of the γ-relaxation peak monotonically decreases during the post-cure period and becomes masked by the contributions from the β-relaxation peak, whose height, in turn, first increases on postcuring to a same maximum value for both nonstoichiometric thermosets and then decreases. This decrease is attributed to physical aging effects. The β-relaxation peak shifts towards higher temperature on postcuring. Comparison between the changes in the dielectric properties of the saturated and starved thermosets show that while the γ-relaxation process may be attributed to the motion of the epoxide dipolar groups of the unreacted DGEBA, the β-relaxation process is not attributable entirely to the motion of ? OH groups and of the unreacted amines in the thermoset. Explanations involving the chain and network packing in the structure of a thermoset are necessary for the observed behavior of the β-relaxation process in amine saturated and starved thermosets. |
