Dielectric spectroscopy of the polymerization process of methyl methacrylate

Abstract

The dielectric properties of methyl methacrylate have been studied over the frequency range 100 Hz–20 MHz during the process of its polymerization at a fixed temperature in the presence of a reaction initiator. The decrease in the permittivity and loss measured for a fixed frequency, as the reaction proceeds, is phenomenologically similar to that observed on increasing the a.c. frequency for a time-invariant system and obeys a stretched exponential function. The relaxation time increases irreversibly with the reaction time according to a sigmoidal curve, which resembles the corresponding plot for the extent of reaction in other polymerization processes. The distribution of relaxation times expressed in terms of the stretched exponential function is likely to be a reflection of the distribution of reaction rates. The negative feedback between chemical reactions and molecular diffusion affects the relaxation time in the same manner as the supercooling of an unpolymerized liquid.