Simultaneous, real-time calorimetry and dielectric spectrometry were performed to study the manner in which molecular dynamics of a polymerizing liquid (stoichiometric amounts of 4,4'-diaminodicyclohexylamine and diglycidyl ether of bisphenol A) evolves during the thermal cycle which converts its initially (molecular) liquid to a vitrified solid of a cross-linked network structure without extraneous products and a loss of mass. As the extent of polymerization and temperature increase at a fixed heating rate, the dielectric relaxation spectra broadens, the characteristic relaxation time increases, and the equilibrium dielectric permittivity and dc conductivity decrease. An indication of the localized motions of the Johari-Goldstein relaxation was evident at high frequencies during the course of polymerization. The relaxation dynamics further evolves as further polymerization occurs on heating, and a new relaxation process develops in the partially polymerized state. Its spectra is described by a symmetric distribution of relaxation times, whose width increases on cooling and relaxation strength remains constant. Its relaxation rate follows the Arrhenius equation with an activation energy of 64 kj/mol. There is also an indication of a further relaxation at high frequencies. The changes in the molecular dynamics observed as the liquid binary mixture at 298 K gradually became a vitrified solid at 393.2 K are expressed in terms of a decrease in the configurational entropy.
The combined effects of temperature and polymerization rate changes on the real-time conduction and relaxation of a liquid, and the evolution of localized motions
Tombari E;
2001
Abstract
Simultaneous, real-time calorimetry and dielectric spectrometry were performed to study the manner in which molecular dynamics of a polymerizing liquid (stoichiometric amounts of 4,4'-diaminodicyclohexylamine and diglycidyl ether of bisphenol A) evolves during the thermal cycle which converts its initially (molecular) liquid to a vitrified solid of a cross-linked network structure without extraneous products and a loss of mass. As the extent of polymerization and temperature increase at a fixed heating rate, the dielectric relaxation spectra broadens, the characteristic relaxation time increases, and the equilibrium dielectric permittivity and dc conductivity decrease. An indication of the localized motions of the Johari-Goldstein relaxation was evident at high frequencies during the course of polymerization. The relaxation dynamics further evolves as further polymerization occurs on heating, and a new relaxation process develops in the partially polymerized state. Its spectra is described by a symmetric distribution of relaxation times, whose width increases on cooling and relaxation strength remains constant. Its relaxation rate follows the Arrhenius equation with an activation energy of 64 kj/mol. There is also an indication of a further relaxation at high frequencies. The changes in the molecular dynamics observed as the liquid binary mixture at 298 K gradually became a vitrified solid at 393.2 K are expressed in terms of a decrease in the configurational entropy.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
