The temperature and polymerization effects on the relaxation time and conductivity, and the evolution of the localized motions

To examine the manner in which molecular dynamics of a polymerizing liquid (stoichiometric amounts of 4,4'-diaminodicyclohexylamine and diglycidyl eth er of bisphenol-A) evolves during thermal cycling from its (molecular) vitr eous state to its fully polymerized vitreous state, calorimetry, and dielec tric spectrometry were performed simultaneously in real time. The half-widt h of the relaxation spectrum of the liquid was relatively narrow and became narrower on heating. This was followed by an increase in the characteristi c relaxation time and the spectrum became broader as polymerization occurre d and reached completion. The dc conductivity initially increased and then decreased. The faster dynamics of the Johari-Goldstein relaxation in the fu lly polymerized state evolved as polymerization reached completion and the temperature increased. The dielectric polarization associated with this rel axation had a broad spectrum, whose half-width increased with decrease in t he temperature. Its relaxation rate followed the Arrhenius equation with an activation energy of 63.4 kJ/mol. The temperature dependence of the faster relaxation did not change with the change in the overall configurational e ntropy of the liquid, a feature that substantiates the dynamic heterogeneit y theories for the structure of the liquid and for the origin of the relaxa tion. (C) 2000 American Institute of Physics. [S0021-9606(00)50840-X].