Electrical properties of epoxy resins during polymerization

Variations in electrical properties of epoxies during polymerization permit interpretation of molecular changes occuring. Three liquid epoxy resins selected for test were of different molecular weights, varying from 6,400 to 26,800 cycles/sec. Curing agents selected included triethylene tetramine, m‐phenylenediamine, and phthalic anhydride. Test specimens were cast between glass plates containing thin foil electrodes which permitted observations of electrical properties during cure. Test results disclose that for each of the resin systems, dissipation factors fell sharply as cure commenced and then at the onset of gelation, values rose again to a peak value, falling with continued cure and hardening of the product. These measurements were conducted over a range of frequencies, the higher the frequency the higher the peak value of dissipation factor and the sooner it occurs. The disclosures of peak values of dissipation factor during cure are unique and appeared to be correlated to the mechanical changes occuring in the polymer. Measurements of other electrical parameters were made during polymerization, such as dielectric constant and volume resistivity, and while data were carefully noted and plotted in the charts, the most revealing was dissipation factor. The influence of heat and other factors upon results is explored.