With the development of fiber reinforced composite and additive manufacturing technologies, thermoplastic resins that can be cured with reactive processings are desired. Although bulk free radical polymerization can be a good candidate for the purpose, it has long been realized that sudden temperature increase occurs during the bulk polymerization. Since the phenomena was first reported by Trommsdorff in 1948, it is called Trommsdorff effect. Qualitatively, the effect is attributed to the sudden drop of the termination rate associated with the increased viscosity during polymerization. However, the detailed mechanism of Trommsdorff effect is still elusive.<br/>In this study, we investigate the bulk polymerization of methyl methacrylate (MMA) at relatively low temperature (i.e. room temperature). Although PMMA and MMA are typically considered as miscible, phase separation during the bulk polymerization was observed. As the reaction proceeds, the ratio of MMA and PMMA changes continuously. Separation into MMA-rich and PMMA-rich phases occurs at the same timing with the onset of Trommsdorff effect. Dielectric spectroscopy measurement revealed that vitrification occurs at the constant temperature as the concentration of PMMA increases. The Flory-Huggins theory predicts phase separation of PMMA and MMA at much lower temperature than the room temperature. Plausible mechanism of the phase separation is viscoelastic phase separation which occurs when dynamic heterogeneity of the mixture is large. We discuss a new aspect of understanding Trommsdorff effect and a possibility of actively control the onset of the effect.

Polymerization induced phase separation of methyl methacrylate and Trommsdorff effect

2019 Fall National Meeting

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