Poly(Ionic Liquid)-based Thermosensitive Nanogel Prepared By Raft Cross-linking Copolymerization And Its Property

Stimuli-responsive polymers can undergo reversible changes in physical-chemicalproperties or colloidal properties in response to external stimuli such as temperature, pH, ionicstrength, light, magnetic field, electric field, ultrasound, redox/thiol, etc. These smart polymershave found applications in many scientific areas. Especially, stimuli-responsivepolymers of reversibility and biological compatibility are very appealing andimportant, which have been used in drug controlled release, separation extraction,immobilization of enzymes, tissue engineering, smart materials, biological sensorsand other areas. Therefore, it is very important theoretical significance and applicationvalue to design and prepare novel stimuli-responsive polymer.In our previous study, we found that the introduction of hydrogen bondinteractions into nanogels based on poly (ionic liquid)s can produce novelthermosensitive polymer materials. Based on this founding, we herein prepared poly(ionic liquid)-based thermosensitive nanogel by RAFT cross-linkingcopolymerization. Due to the introduction of carboxyl-containing chain transferagents, the novel PIL-based nanogel presented reversible temperature-responsive andpH-responsive. The formation mechanism of PIL-based thermosensitive nanogelprepared by RAFT cross-linking copolymerization and the relationship between thedifferent polymerization conditions with thermosensitive nanogel were investigated.The responsive behaviors and properties were detailedly characterized, and thenanogel was employed in the cycloaddition of CO2to epoxides. The main contentsinclude the following:1. Preparation of the ionic liquid monomer and chain transfer agent havedifferent composition and structure, including:(4-vinylbenzyl-triphenyl phosphorouschloride ionic liquids (PILPh),4-vinylbenzyl-tributylphosphorous chloride ionicliquids (PILBu), imidazole ionic liquid monomer3-(4-vinylbenzyl)-1-vinylimidazolium chloride (VBEIm),3-(4-vinyl benzyl)-1-methylimidazolium chloride (VBMIm), S,S’-bis(α,α’-dimethyl-α"-acetic acid)-trithiocarbonate (CTA1), S-1-dodecyl-S’-(α, α’-dimethyl-α"-acetic acid)trithiocarbonate (CTA2) and benzyl9H-carbazole-9-carbodithioate (CTA3), and these were characterized using1H and13C NMR, IR, MS and melting point.2. Preparation of poly (quaternary phosphonium salt ionic liquid)-basedstimuli-responsive nanogels, using trithiocarbonate containing carboxy group as chaintransfer agent, via one-step synthesis poly (quaternary phosphonium salt ionicliquid)-based nanogel by RAFT cross-linking copolymerization. The resultsillustrated that the nanogel can form stable macrogel in the lower temperature, and thechange is a reversible process, while using the free carboxyl group of dithioest chaintransfer agent, the nanogel has no thermosensitivity. Therefore, It is an effective waythat poly (ionic liquid)-based thermosensitive nanogel was prepared by introducedcarboxyl chain transfer agent RAFT cross-linking copolymerization. It was alsofound that the thermosensitive nanogel has pH-responsive because of the introductionof carboxyl group. The nanogels were characterized using FTIR, dynamic rheological,TGA, SEM, TEM, XRD, elemental analysis and the responsive mechanism ofnanogels was discussed. In addition, grafting thermosensitive PNIPAAm via surfacereversible addition-fragmentation chain transfer polymerization, the results illustratedthat the grafted nanogel also has reversible sol-gel transition behavior, and can becontrolled via molecular weight of PNIPAAm to change gel transition temperature,the thermosensitive, structure, properties and morphology be detailed measured.3. The preparation of poly(imidazolium salt ionic liquid)-based stimuli-responsive nanogel, using trithiocarbonate containing carboxy group as chain transferagent, via one-step synthsis poly(imidazolium salt ionic liquid)-based nanogel byRAFT cross-linking copolymerization. The results illustrated that the polyimidazolium salt ionic liquids nanogels and the poly quaternary phosphonium ionicliquids nanogels are similar in all aspects, such as thermosensitive and pH-responsive,the nanogels of morphology, performance and characterization were using the abovemeans. Besides, grafted PNIPAAm to the nanogel, also has a reversible sol-geltransition behavior. In addition, the nanogel can be exploited as highly active andselective catalysts for the cycloaddition of CO2to epoxides, its applications in theCO2fixation, conversion and other areas.