Design of Dual Stimuli-Responsive Copolymerized Ionic Liquid with Flexible Phase Transition Temperature and Its Application in Selective Separation of Artemisitene/Artemisinin

Abstract

Smart materials are a kind of material which can respond to subtle changes in the environmental conditions, and their use in chemical processes is becoming increasingly widespread. In this work, stimuli-responsive copolymerized ionic liquids (ILs) were designed to ease the recycling of IL, and they were prepared by free radical polymerization of isopropylacrylamide and 1-methyl-3-(4-vinylbenzyl)imidazolium chloride. The turbidity point temperature (for phase transition) of the copolymerized IL aqueous solution can be precisely controlled by varying the IL concentration in the copolymerized IL, adding inorganic salt, and changing the salt content. It was demonstrated that the introduction of IL increased the interaction between the copolymerized IL and water, resulting in higher turbidity point temperature of the copolymerized IL than that of polyisopropylacrylamide. The addition of salt weakened the electrostatic shielding and increased the cation−π interaction, resulting in particle agglomeration and precipitation of the copolymerized IL. Moreover, the copolymerized IL aqueous solution exhibited excellent performance for selective separation of artemisitene/artemisinin (ARE/ART), two structural analogues. The separation selectivity of ARE/ART increased with the increase of IL content in the copolymerized IL, reaching 3.62 for the copolymer containing 11.25 mol % IL. Additionally, the copolymerized IL can be easily recycled by the dual stimuli response of heating and addition of salt.