Preparation Of CO₂-crosslinked Poly （Ionic Liquid） Hydrogels For Ionic Skin Applications

With the rapid development of flexible electronic devices,it has received ever-increasing attention in soft robots,wearable sensors,and biomedical devices.Hydrogels are highly researched in the field of flexible sensors due to their high ionic conductivity,transparency,and flexibility.However,most hydrogels-based sensors surfer from the evaporation of water,frozen at low temperature,poor self-adhesion,and the trade-off between high strain and high sensitivity.Poly（ionic liquid）s are a kind of functional polymer via covalent bond with IL as monomer,which inherit the unique properties of ILs and polymers,including high ionic conductivity,high adhesion,freezing resistance,antibacterial activity,good mechanical property,chemical/thermal stability,and designable structures.CO₂ as an abundant,low-cost,and green C1 feedstock,has been converted into valuable chemicals and polymer materials.The CO₂-sourced cyclic carbonates derived polyurethane possess plentiful carbamates and hydroxyl groups.Meanwhile,these polar oxygen-containing functional groups can improve the ionic transportation and form strong hydrogen bond with water,which can enhance the water retention capacity and inhibit water from freezing in the hydrogel.Moreover,the polyurethane structure exhibit good adhesion towards various substrates.Herein,two CO₂-crosslinked poly（ionic liquid）s were prepared for flexible electronic sensors.The main research of this thesis are summarized as follows:1.Preparation of anti-freezing and antibacterial poly（ionic liquid）hydrogels for flexible sensor application.Amino functionalized ionic liquid monomer was first synthesized from the 1-vinyl imidazole and 3-bromopropylamine hydrobromate.The poly（ionic liquid）hydrogels were prepared via the copolymerization of amino functionalized ionic liquid monomer,acrylamide and CO₂-sourced crosslinker.Notedly,the CO₂-sourced crosslinker was prepared by the cycloaddition of CO₂and polyethylene glycol diglycidyl ether with the Zn Br₂ and 1-butyl-3-methyl imidazolium bromide as catalyst.It was found that the poly（ionic liquid）hydrogels exhibited good water-retaining property,freezing resistance,high ionic conductivity,good adhesion and antibacterial activity,mainly arising from the synergistic effect between poly（ionic liquid）s and CO₂-sourced polyurethane.Meanwhile,the poly（ionic liquid）hydrogels based sensor showed good sensing property with high sensitivity under strain from 50%to 400%.2.The thermal-responsive poly（ionic liquid）hydrogels were prepared by the copolymerization of amino functionalized ionic liquid monomer,acrylamide,isopropyl acrylamide,and the CO₂-sourced cyclic carbonates as the crosslinker with the ammonium persulfate as the initiator.Apparently,the transparency of the thermal responsive poly（ionic liquid）hydrogels can reversibly changed with the variation in the temperature.Meanwhile,the thermal-responsive poly（ionic liquid）s exhibited good antibacterial activity towards S.aureus（100%）and E.coli（92%）.