Molecular dynamics and reaction kinetics during the network structure formation of a diepoxide and diamine mixture under high pressures using dielectric measurements

Abstract

The dielectric relaxation behaviour of a stoichiometric mixture of ethylene diamine and a diepoxide in which addition reactions produce a polymeric network structure has been studied at isobaric conditions of pressure from 1 to 206 bar and several temperatures from 296 to 314 K. The changes occur faster at high pressure, and the curves of the relative permittivity and loss against the polymerization time, which resemble the corresponding dielectric spectra, shift to a shorter time. This effect is due to an increase in the rate of reaction, and attributed to the mass-controlled reaction kinetics in the region of the polymerization, because the rate of reaction is expected to be slowed by application of pressure when the reaction is in the diffusion-controlled region. The rapid increase in the relaxation time with the polymerization time at high pressures is a consequence of: (a) the acceleration of the reaction kinetics, (b) an increase in the equilibrium constant of the polymerization according to Le Chatelier's principle and (c) a decrease in the configurational entropy. An attempt is made to resolve the magnitude of these effects. A formalism for the changes in the relaxation time and dc conductivity, which includes the change in the chemical as well as physical states of the polymerizing liquid, is given, and the decrease in the configurational entropy formulated in terms of the pressure's effect on the relaxation time. The rate of decrease in the static permittivity on polymerization is increased by the pressure. The polymerization characteristics of this network polymer under hydrostatic pressure are compared with those of the linear-chain polymerization of a stoichiometric mixture of a diepoxide with a monoamine.