DIELECTRIC-SPECTROSCOPY OF THE POLYMERIZATION PROCESS OF METHYL-METHACRYLATE

The dielectric properties of methyl methacrylate have been studied ove r the frequency range 100 Hz-20 MHz during the process of its polymeri zation at a fixed temperature in the presence of a reaction initiator. The decrease in the permittivity and loss measured for a fixed freque ncy, as the reaction proceeds, is phenomenologically similar to that o bserved on increasing the a.c. frequency for a time-invariant system a nd obeys a stretched exponential function. The relaxation time increas es 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 e xpressed in terms of the stretched exponential function is likely to b e a reflection of the distribution of reaction rates. The negative fee dback between chemical reactions and molecular diffusion affects the r elaxation time in the same manner as the supercooling of an unpolymeri zed liquid.