Polymerizable eutectics : a new method towards the synthesis of polymeric materials

Deep eutectic solvents have attracted significant research interest due to their high solvation capacity, low flammability, ease of recovery and environmentally friendly preparation, amongst other appealing properties. In the context of polymerization, eutectic solvents known as ‘polymerizable eutectics’ can play multiple roles in a reaction system: as a solvent, monomer, and templating agent, making them unique in comparison to traditional methods of solution-phase polymerization. The overall aim of this work was to explore the potential of polymerizable eutectics in various aspects of materials synthesis, such as the preparation of polymer hydrogels, porous monoliths and photopolymerization. In all instances, polymerization via a eutectic was benchmarked relative to polymerization under ‘standard’ conditions, either aqueous-phase or organic phase solution polymerization. This comparative study enabled the benefit of polymerizable eutectics to be clearly demonstrated: significant rate enhancement and improved mechanical and physical properties of the material were observed relative to conventional methods of preparation
Different types of polymerizable eutectics were prepared in this work based on the specific application. Firstly, mixtures of monomers (as hydrogen bond donors) and various choline salts (as hydrogen bond acceptors) were used to prepare polymerizable eutectics for hydrogel synthesis. The eutectics were extensively characterized by 1D and 2D NMR spectroscopy, viscometry, differential scanning calorimetry and thermogravimetric analysis to understand the supramolecular nature of these systems. Upon the addition of initiator and crosslinker, cross-linked hydrogels were prepared that possessed thermoresponsive swelling behaviour in water. Eutectic-based gels showed a reduced swelling capacity and increased mechanical strength due to their high cross-linking density compared to the gels prepared in water. Secondly, non-ionic polymerizable eutectics, based on various mixtures of amide-containing monomers, were then used as the continuous phase for the preparation of polymerizable high internal phase emulsions (HIPE) to yield highly porous monolithic materials via RAFT polymerization; the eutectic based polyHIPEs had vastly different mechanical and morphological properties to those prepared from traditional emulsions. Thirdly, polymerizable eutectics were shown to be unique systems for bulk photopolymerization to generate optically transparent polymeric materials in the complete absence of solvent. Lastly, polymerizable eutectics were used for block copolymer synthesis by utilizing photoinduced one pot PET-RAFT and ring opening polymerization approach.