Thermodynamics and dielectric relaxation during the polymerization of a flexible diamine–diepoxide mixture and its glassy-state relaxation

Abstract

To examine the manner in which molecular dynamics of a stoichiometric mixture of 4,4′-diaminodicyclohexylamine and diglycidyl ether of bisphenol-A changes during its polymerization, (i) the dielectric relaxation spectra during the spontaneous growth of the network structure polymer, and (ii) the extent of polymerization, α, were measured simultaneously and continuously by means of an instrument designed for the purpose. Measurements were made both under isothermal conditions and during a fixed-rate heating and cooling and the evolutions of both the slow dynamics associated with vitrification and the fast dynamics associated with the localized motions (or Johari–Goldstein process) in the liquid and glassy state of the polymer were studied. The logarithm of the characteristic time of the slow dynamics increases in proportion to α^1.874. Also the faster relaxation dynamics evolve as α→1. The polarization associated with this dynamics increases with increasing temperature, and its rate changes according to the Arrhenius equation with an activation energy of 63.4 kJ mol^-1. It is argued that the rate of localized modes of motions does not change with decrease in the overall configurational entropy of a liquid or a glass, a feature that substantiates the dynamic heterogeneity theories for the structure of liquids and for the origin of their relaxations.