Deep Eutectic Solvents in The Synthesis of Polymers

Solvent utilization creates the largest volume of auxiliary waste in polymer synthesis. However, increasing awareness of the environmental problems has led to the use of alternative reaction media to reduce or eliminate organic solvent use. Deep eutectic solvents (DESs) are systems formed from a eutectic mixture of Lewis or Bronsted acids and bases which can contain a variety of anionic and/or cationic species [1]. They incorporate a hydrogen bond acceptor (HBA) and a hydrogen bond donor (HBD), which are able to give a eutectic with a melting point much lower than either of the individual components (Figure 1) [2]. One of the most significant deep eutectic phenomenon’s was observed for a mixture of choline chloride and urea in a 1:2 mole ratio respectively. The resulting mixture has a melting point of 12°C, which makes it liquid at room temperature. DESs are obtained by complexion of quaternary ammonium salts with hydrogen bond donors. The charge delocalization occurring through hydrogen bonding between the halide anion and the hydrogen donor moiety is responsible for the decrease in the freezing point of the mixture relative to the melting points of the individual components (Figure 2) [3].