Bulk polymerization is a polymerization method without a solvent. Relatively high molecular weight polymer can be obtained in high purity. Bulk polymerization is used in several applications, including coatings, dental fillings, and thermal curing processes. Recently, it has been proposed to use bulk polymerization as a resin for fiber-reinforced plastics and additive manufacturing (3D printing). For such applications, precise control of the reaction is required, while thermal management during bulk polymerization is still challenging. During bulk polymerization, reaction acceleration known as Trommsdorff effect may occur. Qualitatively, it has long been attributed to the increased viscosity and hence decreased termination rate. However, quantitative prediction of the effect from the first principles has not been achieved and the molecular mechanism of the reaction acceleration is still elusive.<br/>Here, we investigate the bulk polymerization of methyl methacrylate (MMA) in detail. Starting from a liquid MMA, glassy poly(methyl methacrylate) (PMMA) is eventually obtained. We applied dielectric spectroscopy under isothermal conditions during bulk polymerization of MMA. Polymerization-induced vitrification was successfully detected. We found that the reaction acceleration occurs at the vicinity of polymerization-induced vitrification. At the onset of Trommsdorff effect, the reaction solution becomes heterogeneous in a microscopic scale. Subsequently, apparent phase separation into monomer-rich phase and polymer-rich phase occurs. In other words, our data suggest that Trommsdorff effect occurs discontinuously in conjunction with heterogenization. This discontinuity can be also confirmed by the molecular weight distribution. The molecular weight distribution becomes suddenly bimodal at the onset of Trommsdorff effect. We will also discuss the change in amorphous structure measured by X-ray scattering. Our findings shed new light in the vitrification caused by relative concentration change.

Polymerization-induced vitrification, kinetic heterogenization, and reaction acceleration during bulk polymerization of methyl methacrylate

Where thousands of chemistry professionals meet to share ideas and advance scientific and technical knowledge. Spring 2023 abstracts, posters, and presentations will launch at the end of March.

ACS Spring 2023

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.