Novel Aqueous Biphasic System Using Poly(Ionic Liquid)s with Controllable Structure for Highly Efficient Extractions

Ionic liquid (IL)-based aqueous biphasic systems (ABSs) provide a sustainable and efficient alternative to conventional liquid-liquid extraction techniques and can be used for the extraction, recovery, and purification of diverse solutes. However, the construction of a high-performance ABS that has both excellent phase separation ability and extraction performance remains challenging. This study concerns the preparation of a family of novel ABSs based on poly(ionic liquid)s (PILs) with customized structure and controllable molecular weight for the extraction of bioactive compounds. Several tailor-made PILs consisting of a hydrophobic backbone, hydrophilic imidazolium pendant groups and strong hydrogen bonding basic counteranions are prepared by reversible addition fragmentation chain-transfer polymerization. The PILs have a perfect balance of hydrophobicity/hydrophilicity and functionality, affording outstanding phase separation, which was better than with either the IL monomer poly(1-butyl-3-vinylimidazolium bromide ([BVIm]Br) or the normal free-radical polymer P[BVIm]Br*. More importantly, PIL-based ABSs exhibited unprecedented high partition coefficients for six bioactive compounds including tryptophan, phenylalanine, and caffeine, as well as high extraction yields. The performance of the PIL-based ABSs could also be tuned by changing the molecular weight and anionic character of the PILs. This work shows that tailor-made PIL-based ABSs are a promising platform for bioactive compound extraction and provides significant clues for the design of new ABSs for various applications.