Reversal in the dielectric relaxation time during polymerization: Thermal energy compensation on macromolecular growth

摘要

The increase in the dielectric relaxation time #tau#_0 and in the number of covalent bonds n formed during polymerization of an equimolar mixture of cyclohexylamine and a diepoxide have been studies in real time, in two experiments: (i) under isothermal conditions when the dielectric spectrum monotonically shifts to the low-frequency side and the configuration entropy decreases and (ii) on heating the polymerizing liquid at a fixed rate when the spectrum initially shifts to the low-frequency side, reverses direction at a certain temperature, and shifts towards the high-frequency side. The reversal in #tau#_0 occurs when an increase in thermal energy begins to dominate the effects of increase in n. Consequences of the two competitive effects on the measured dielectric behavior have been discussed and relations between the change in configurational entropy, and #tau#_0 of the ultimately formed linear chain polymer, are discussed. It is shown mathematically that for a fixed #tau#_0 and a configurational entropy, there are an infinite number of combinations of temperature and n, some of which may be explored by altering the temperature-time profile during the macromolecular growth.