Polymerization-Induced Vitrification and Kinetic Heterogenization at the Onset of the Trommsdorff Effect

The reaction kinetics during bulk free radical polymerization is still not fully understood. As the reaction proceeds, many parameters, including monomer/polymer fraction, radical concentration, viscosity, and temperature, change in a non-equilibrium manner. In this study, we investigate the bulk polymerization of methyl methacrylate, focusing on a sudden acceleration in reaction kinetics known as the Trommsdorff effect. Dielectric spectroscopy shows that a temperature increase occurs at the vicinity of polymerization-induced vitrification. At the same timing as the temperature increase, the polymerization solution becomes heterogeneous. This heterogenization causes a decrease in transmittance at a wavelength of 400 nm. We discuss phenomena related to the Trommsdorff effect, including the kinetic heterogenization, vitrification, change in the amorphous structure, and the formation of discontinuously high-molecular-weight polymers.