PHENOMENOLOGICAL ASPECTS OF RELAXATIONS IN CHEMICALLY CONTROLLED DIPOLAR DIFFUSION IN POLYMERS

The phenomenology of chemically controlled dipolar diffusion, or negative feedback process, has been described for a thermoset made from diglycidyl ether of bisphenol-A and diamino diphenylmethane at different temperatures. The dielectric spectroscopy shows an approach of dc conductivity towards a singularity at the gel point according to a power law sigma-0 is-proportional-to (t(g)-t)x and to a new equation, sigma-0 is-proportional-to exp - [B/(t0 - t)], where t(g), x, B and t0 are empirical constants that are temperature dependent. The evolution of the dielectric features of a thermoset during its curing and after a time when its dc conductivity has reached a negligibly small value is phenomenologically similar to that of the dielectric features of physically and chemically stable dipolar liquids and solids observed with increasing frequency or decreasing temperature. The stretched exponential relaxation function satisfactorily describes the dielectric results. The value of its parameter, which is named gamma, lies between 0.26 and 0.31, and monotonically decreases with increasing temperature of the cure. The curing time dependence of the dipolar relaxation time, tau, has been determined and found to have the shape of an elongated S, with a point of inflexion.