By changing the ratio of resin to hardener, a series of epoxy resin samples has been
produced with differing network structures and different retained chemical
functionalities. The resulting materials were characterized by thermal analysis, dielectric
spectroscopy, DC conductivity, and DC and AC breakdown strength measurements, to
explore the effect of network structure and chemical composition on molecular dynamics
and electrical properties. Differential scanning calorimetry showed that the glass
transition temperature is primarily determined by the crosslinking density and indicates
that, under the range of conditions employed here, side reactions, such as etherification
or homopolarization, are negligible. Conversely, changes in DC conductivity with resin
stoichiometry appear to occur as a result of changes in the chemical content of the system,
rather than variations in network structure or dynamics. Specifically, we suggest that the
DC conductivity is markedly affected by the residual amine group concentration in the
system. While DC conductivity and DC breakdown appear broadly to be correlated, AC
breakdown results indicated that this parameter does not vary with changing
stoichiometry, which suggests that the AC and DC breakdown strengths are controlled
by different mechanisms.