PHYSICAL ASPECTS OF NETWORK POLYMERIZATION FROM CALORIMETRY AND DIELECTRIC-SPECTROSCOPY OF A TRIEPOXIDE REACTING WITH DIFFERENT MONOAMINES

Calorimetry and dielectric relaxation spectroscopy were used to study the evolution of molecular dynamics during the isothermal polymerizati on of two stoichiometric mixtures of a molecule with three epoxide gro ups with (i) aniline and (ii) 3-chloroaniline, whose dipole moments as well as the degrees of steric hindrance to chemical reactions differ. The heat evolved on polymerization was used to calculate the number o f covalent bonds formed at any instant during the polymerization react ion. The approach of the DC conductivity towards a singularity as the reaction progressed agrees with the Flory-Stockmayer theory of connect ivity at gelation and not the percolation theory. It is demonstrated t hat a plot of DC conductivity against the extent of reaction does not have the same shape as the plot against the time of reaction. The perm ittivity and loss spectra obtained for structural states containing a fixed number of covalent bonds could be described by equations analogo us, but not equivalent to, or the same as, the equations used for desc ribing the dielectric properties measured for a fixed frequency during the growth of a macromolecule's network. structure. For a fixed tempe rature, the relaxation time of the structure formed increased as the e xponential of the extent of reaction (raised to the power > I)increase d. Comparative parameter-fits to the spectra showed that the DC conduc tivity and interfacial polarization alter the shape of the dielectric spectra such as to make misleadingly alternative parameter fits possib le. The decrease of the equilibrium dielectric permittivity on polymer ization is attributed to a decrease in the dipolar orientational corre lation as well as the net dipole moment on increase in the number of c ovalent bonds. The configurational entropy decreased with increase in the number of covalent bonds formed in a manner that differs from the decrease on cooling, and a formalism relating the two effects is given . As the network structure grew isothermally, a second, high-frequency relaxation process came into evidence. This relaxation is attributed to the availability and growth of local regions of low density and hig h density in the network structure of the macromolecule. A number of i ssues of a fundamental nature that have risen since our earliest repor t on this subject have been elaborated and analytically clarified. (C) 1997 John Wiley & Sons, Inc.