Flash chemistry is a field of chemical synthesis where extremely fast reactions are conducted in a highly controlled manner. A key element of flash chemistry is the control of extremely fast reactions to obtain the desired products selectively. For extremely fast reactions, kinetics often cannot be used because of the lack of homogeneity of the reaction environment when they are conducted in conventional reactors such as flasks. Fast micromixing by virtue of short diffusion path solves such problems. Fast reactions are usually highly exothermic, and heat removal is an important factor in controlling such reactions. Heat transfer occurs very rapidly in micro flow systems by virtue of a large surface area per unit volume, making precise temperature control possible. Another important point is that fast reactions often involve highly unstable intermediates, which decompose very quickly, making reaction control difficult. The residence time can be greatly reduced in micro flow systems, and this feature is quite effective in controlling such reactions. The concept of flash chemistry has been successfully applied to various organic reactions for synthesis including (a) reactions in which undesired byproducts are produced in the subsequent reactions in conventional reactors, (b) highly exothermic reactions that are difficult to control in conventional reactors, and (c) reactions in which a reactive intermediate easily decomposes in conventional reactors. The concept of flash chemistry can be also applied to polymer synthesis. Cationic polymerization can be conducted with an excellent level of molecular-weight control and molecular-weight distribution control. Radical polymerization in micro flow systems leads to better molecular weight distribution control than macro batch systems. Anionic polymerization can also be carried out micro flow systems at higher temperatures than macro batch systems with high degree of molecular weight distribution control.

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