IMPEDANCE SPECTROSCOPY OF REACTIVE POLYMERS .2. MULTIFUNCTIONAL EPOXY-AMINE FORMULATIONS

Dielectric measurements were utilized to follow the advancement of cur e in a bifunctional and a tetrafunctional epoxy/amine formulation. In deferance to earlier dielectric studies of cure, complex impedance was measured and used to calculate ionic resistivity. By using complex im pedance we were able to separate, according to their frequency depende nce, the contributions to overall polarization from electrode blocking layers, mobile charge carriers, and dipole relaxations. At any stage of cure, there is a unique frequency at which ionic resistivity can be singularly measured. Our approach does not involve trial-and-error fr equency search, it measures dielectric response in real time, and is c onducive to the development of phenomenological models based on equiva lent circuits. Values of ionic resistivity measured at different cure time and temperature were used to quantify the progress of cure. Excel lent agreement was reported between the calculated Values of normalize d degree of cure obtained by dielectric and calorimetric measurements. It was suggested that apart from the extrinsic conductivity by ionic impurities, an intrinsic mechanism which involves the reactive molecul es contributes to the overall ionic conductivity. (C) 1995 John Wiley & Sons, Inc.