The Synthesis Of Stimuli-responsive Polymer Materials And Their Applications In Separation

Stimuli-responsive polymers?SRPs?are a new class of materials,which are sensitive to a tiny change in its environment,and respond by changing their physical and/or chemical properties.They have been used in a wide range of fields,such as chemical engineering,pharmaceutical engineering,bioengineering,and many others.Among them,utilization of SRPs in chemical separation area has progressed rapidly in recent years.SRPSs have been mainly used in several separation technologies,including adsorption,aqueous two-phase extraction,membrane separation,aqueous chromatography,and affinity precipitation separation.However,there are still high demands for the development of other SRPs-based separation technologies in response to various practical production processes.We synthesized several novel materials based on different stimuli-responsive properties and explored their application in liquid-liquid extraction,adsorption,and flocculation.Firstly,we designed and developed a series of ionic liquid polymers?PIL?,which were synthesized via reversible addition-fragmentation chain transfer?RAFT?copolymerization of 1-vinyl-3-butylimidazolium bromide and N-isopropylacrylamide,followed by anion exchange of bromide to amino acid D-alanine.The PIL was thermoresponsive in acetonitrile and could be completely precipitated out by lowering the solution temperature.The PIL/acetonitrile solutions were used as the extract phase for the separation of tocopherol homologues in hexane.The resulting separation efficiency of this mixture was found to be much higher than that of pure acetonitrile.In addition,the PILs could be reused for multiple extraction cycles with negligible change in the tocopherol distribution and selectivity coefficients.Secondly,we developed an easy but versatile method for fast collection and re-dispersion of metal organic framework?MOF?particles in water.It is through the simple addition of a small amount of thermoresponsive poly?N-isopropylacrylamide?,that is,PNIPAM,to MOF particle suspension.The PNIPAM improved the stability of MOF particles in water below its LCST and led to the formation of large MOF-PNIPAM aggregates above its LCST,which can then be easily collected.Compared to grafting smart polymers onto MOFs,this method does not involve any chemical reactions,thus imposes little risk to damaging the MOF structures and properties.This novel method can also be applied to various MOF-water systems.Thirdly,a novel thermoresponsive polymer-based adsorbent,?PNIAPM-co-QDMAPMA?-g-MR?PNqD-M?,was synthesized by surface-initiated atom transfer radical polymerization and subsequent alkylation reaction,which can be used as a smart adsorbent in adsorption processes.PNqD-M possessed a large amount of positive charge on its surface and can therefore be used for the removal of phenol from water by electrostatic interaction.Owing to the thermoresponsive properties of PNqD-M,the adsorbed phenol can be subsequently desorbed in 40 ? water,thus simplifying the regeneration process of adsorbents.Finally,we reported a green method to directly graft poly?ionic liquid?onto polydopamine-modified Fe₃O₄ nanoparticles through an organic solvent-free process of self-initiated photografting and photopolymerization,resulting in a magnetic responsive adsorbent,PIL@PDA@Fe₃O₄.PIL@PDA@Fe₃O₄ possessed a large amount of negative charge on its surface and can be used for selective removal of anionic dyes by ion exchange.The equilibrium adsorption time was found to be less than 2 minutes.Moreover,PIL@PDA@Fe₃O₄ can be collected by a magnet and regenerated by washing with a salt solution after the adsorption,thus it can be reused for multiple adsorption cycles.The results showed negligible change in the adsorption and desorption efficiency after 5 cycles.