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

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 cy clohexylamine and a diepoxide have been studies in real time, in two experi ments: (i) under isothermal conditions when the dielectric spectrum monoton ically shifts to the low-frequency side and the configuration entropy decre ases and (ii) on heating the polymerizing liquid at a fixed rate when the s pectrum initially shifts to the low-frequency side, reverses direction at a certain temperature, and shifts towards the high-frequency side. This reve rsal 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 betwe en the change in configurational entropy, and tau(0) of the ultimately form ed 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 alt ering the temperature-time profile during the macromolecular growth. (C) 19 99 American Institute of Physics. [S0021-9606(99)51919-3].