MOLECULAR-DYNAMICS DURING LINEAR-CHAIN POLYMERIZATION FROM REAL-TIME DIELECTRIC SPECTROMETRY AND CALORIMETRY

To obtain physical insight into the slowing of the molecular dynamics when a macromolecule grows as a result of polymerization, (i) the diel ectric relaxation spectra, and (ii) the heat evolved during the growth of a linear chain structure by means of the reaction of diepoxide wit h a monoamine have been measured simultaneously and continuously over time, at a fixed temperature of 314.2 K, during fixed-rate heating to 341.5 K and thereafter cooling from this temperature. An instrument wa s designed for the purpose. The studies yield information, almost simu ltaneously, on the changes in the dc conductivity, on the static and d ynamic behaviours of the dipolar relaxation, and on the number of cova lent bonds, n, in the states of the structures formed by irreversible polymerization. The dc conductivity decreases with increase in n, but this decrease cannot be attributed entirely to the increase in viscosi ty. The decrease in the ion population has a significant effect on the change in dc conductivity. Both the equilibrium permittivity and the limiting high-frequency permittivity decrease on polymerization. This decrease is attributed mainly to a decrease in the dipolar orientation al correlation factor in the former case, and to a predominant increas e in the phonon frequencies in the latter case. It is found that the s lowing of the molecular dynamics that occurs here on increase in n is more than compensated by the acceleration of the dynamics on increase in the thermal energy. This effect is interpreted in terms of the chan ges in the configurational entropy, S-conf, which leads to relations e xpressing the dependence of S-conf on n, as well as on the temperature . A faster molecular dynamics of the Johari-Goldstein relaxation evolv es as n increases. This dynamics does not depend on the decrease in S- conf with decrease in n, but depends only on the change in S-conf with temperature. The dielectric behaviour of the completely polymerized s tate obtained after repeated thermal cycling of the initially molecula r liquid has been studied, and the results are related to the molecula r dynamics observed during the growth of the macromolecules.