Physico-chemical aspects of dielectric and thermodynamic changes during high-temperature polymerization and their technical use

When polymerization temperature is high, almost 100% polymerization occurs in a relatively short time. The ultimate product is either a high-viscosity fluid or an elastomer: the former when linear-chains form and the latter w hen a network structure forms. During polymerization at such temperatures, the liquid's configurational entropy still decreases on macromolecular grow th, but most of this decrease is compensated by the high thermal energy. Th e amount of heat released and the change in the dielectric spectra during t he step-addition polymerization of cyclohexylamine-diglycidyl ether of bisp henol-A and hexamethylene-1,6-diamine-diglycidyl ether of 1,4 butanediol ha ve been studied in real time both isothermally and during heating, by means of an equipment designed for the purpose. These show that two competing ef fects determine the molecular dynamics during polymerization: (i) decrease in the configurational entropy on macromolecular growth, and (ii) increase in the configurational entropy on increasing the temperature. It is propose d that a liquid may be polymerized at such a temperature where its chosen d ielectric properties reach a time-invariant value prescribed for the polyme r shaping procedures. Thus a single step of thermal treatment for polymer p roduction and shaping processes may become sufficient. The temperature for polymerization may be determined from the knowledge of the dielectric prope rties of the polymerized state. The chemical physics involved in this proce dure has been described formally in terms of both the molecular dynamics an d configurational entropy.