Dielectric analysis of the linear polymerization of an epoxy resin

The dielectric properties of a diglycidyl ether of bisphenol A (DGEBA) epox y resin and n-butylamine have been studied in the frequency range 100 Hz to 3 GHz at 25 degreesC. The unreacted mixture showed a single relaxation whi ch gradually split in two relaxations, the separation of which increased as the reaction progressed. The low and high frequency relaxations are attrib uted to the structural dynamics of the growing macromolecules and to the mo tions of the dipoles associated with the monomers, respectively. The increa se of the structural relaxation time is described by a phenomenological rel ationship, similar to the Williams-Landel-Ferry equation, that allows estim ation of the conversion at vitrification. A marked decrease of the electric al conductivity has also been observed, as a result of the increasing visco sity of the system. The conductivity and the structural relaxation time are correlated by means of a generalized Debye-Stokes-Einstein model. It has a lso been found that both components of the complex dielectric permittivity, measured at microwave frequencies, yield information on the advancement of the polymerization process. (C) 2001 Society of Chemical Industry.