Changes in amorphous structure and reaction acceleration during bulk polymerization of methacrylates

It has long been known that a sudden reaction acceleration (i.e., the Trommsdorff effect) occurs during bulk polymerization of methacrylates. While this effect has been qualitatively explained by an increased macroscopic viscosity and decreased termination rate, the detailed mechanism is still debated. This is because the effect occurs so suddenly that the change in macroscopic viscosity is not sufficient to explain the effect quantitatively. Less attention has been given to the change in the amorphous structure during bulk polymerization. In this study, we investigate the amorphous structure during bulk polymerization of methyl methacrylate (MMA), ethyl methacrylate (EMA), and butyl methacrylate (BMA) via X-ray scattering. The amorphous structure changes dramatically at some point during bulk polymerization. To obtain detailed microscopic information, we applied pair distribution function (PDF) analysis during the bulk polymerization of MMA. Our results suggest that a change in the amorphous structure influences the reaction kinetics during bulk polymerization. Changes in the amorphous structure during the bulk polymerization of methacrylates were analyzed using X-ray scattering. As the polymerization progresses, the relative concentrations of monomer and polymer change. Traditionally, it has been assumed a priori that the change in the amorphous structure of the polymerization solution is smooth and continuous. In contrast, our results indicate that the amorphous structure undergoes a sudden change in the late stage of bulk polymerization. Furthermore, this sudden change in the amorphous structure coincides with the rapid reaction acceleration known as the Trommsdorff effect.