Liquid salts as eco-friendly solvents for atom transfer radical polymerization: a review

Liquid salts, comprising ionic liquids (ILs) and eutectic mixtures (EMs), are organic compounds/mixtures characterized by a low melting point that have been emerging as a very promising eco-friendly alternative to common organic solvents in different areas. Atom transfer radical polymerization (ATRP) of different monomer families using ionic liquids as solvents has been extensively studied, showing promising results in terms of control over the polymerization and the possibility of recycling the catalytic system. However, recent concerns about the toxicity of ILs, along with their expensive synthesis, have shifted the attention to the use of EMs as solvents for ATRP. Despite the attractive features of EMs (inexpensive synthesis from natural compounds, non-toxicity, and similar physicochemical properties to ILs), this is still a recent area of research and thus the number of publications is scarce. Here, the recent advances in the use of liquid salts as solvents for ATRP and their influence on the polymerization features are critically discussed.