Polymerization initiation of pure 2-hydroxyethylmethacrylate under shock wave compression

Abstract

The ability to initiate chemical reactions without the need for potentially hazardous solvents, catalysts and radical initiators is of key importance for modern biotechnologies and medicine. In this study, laser-driven shock wave compression was performed on pure 2-hydroxyethylmethacrylate (HEMA) free of any additives in order to trigger the polymerization process. We showed that the generated peak shock-wave pressure in the range between 2 and 5.5 GPa permitted initiation of radical polymerization and the formation of poly-HEMA oligomers. The reaction begins with diradicals HEMA₂˙˙ appearing at the peak pressure and, by reactions with HEMA monomers, forming HEMA₃˙˙ diradicals on the 15 ns timescale. The chain propagation further occurs on the sub-μs timescale by associations of the trimer diradicals, which, because of a smaller reactivity, do not react with HEMA monomers. The proposed method can be considered for scale-up of the polymerization process of ultrapure organics.