Polymer Synthesis in Ionic Liquids: Free Radical Polymerization in Water-Soluble Systems

During the last years, ionic liquids (ILs) have appeared as serious candidates for the replacement of volatile organic compounds (VOCs) in several chemical processes. Due to the fact that solution polymerization is still one of the most frequently used processes in polymer industry, the replacement of the corresponding solvents with ILs as reaction media seems to be a promising alternative. One of the main problems to be solved before ILs may become real substitutes for organic solvents in this kind of processes is the recovery of the synthesized polymers from the respective reaction media: Since ILs are non-volatile substances, the separation of the polymer from the reaction media turns out to be the bottleneck and therefore secondary substances must be utilized in order to achieve an effective separation by extraction and/or precipitation. The choice of this secondary substance is one of the most important issues from the ecological point of view, since it will determine whether the process is really environmentally friendly (green chemistry). Taking advantage of the miscibility of some ILs with water and the insolubility of several important commercial polymers in this natural solvent, an alternative for the separation process is addressed. Preliminary results show the feasibility to use water-soluble ILs efficiently as reaction media, which can be explored in a pilot and/or industrial scale for some important industrial polymerization processes. Among the advantages of this alternative approach are: the saving of resources (since ILs can be reused and the polymerization reactions can be performed at lower temperatures than those normally required) and the minimum emission of VOCs into the environment.