Non-aqueous Pickering Emulsions Stabilized By Polymer Nanoparticles: Preparation And Application

Pickering emulsions exhibit many advantages,such as high stability,low toxicity,and tunable droplet size,which in turn facilitated their broad applications in material synthesis,oil recovery,interfacial reaction,and so on.To date,studies on Pickering emulsions are mainly centered on the water-oil system,including oil-in-water and water-in-oil.However,the existence of water is unfavorable in some cases in which Pickering emulsions acted as microreactors for water-sensitive reactions or as the carriers for drugs that were liable to hydrolysis.Therefore,a nonaqueous Pickering emulsion is a necessary complement and should enjoy an equal importance as oil-water Pickering emulsions.The main contents of this thesis were centered on the preparation of diblock copolymer nanoparticles and non-aqueous Pickering emulsions.(1)Efficient synthesis of diblock polymer nanoparticles for the preparation of non-aqueous Pickering emulsions.Sterically-stabilized polymer nanoparticles(SSPNs)were first prepared via RAFT-mediated non-aqueous dispersion polymerization,in which poly(lauryl methacrylate)(PLMA)and poly(4-vinyl pyridine)(P4VP)acted as the stabilizer block and the core-forming block,respectively.Kinetically-trapped PLMA-b-P4VP spheres and mixed sphere/worm morphologies could be achieved at a target copolymer composition.The factors influencing the morphologies of PLMA-b-P4VP were studied.Subsequently,core cross-linked SSPNs(CSSPNs)were obtained by means of the chemical cross-linking of P4VP cores of SSPNs with 1,4-dibromobutane at a dilute concentration of SSPNs in toluene.CSSPNs were used as Pickering emulsifiers for the formation of1-butyl-3-methylimidazolium tetrafluoroborate-in-toluene([Bmim][BF₄]-in-toluene)non-aqueous Pickering emulsions,and the emulsifying performances of PLMA-b-P4VP with different morphologies were investigated.[Bmim][BF₄]-in-toluene Pickering emulsions were then acted as a platform for Knoevenagel reaction of 4-nitrobenzaldehyde with malononitrile catalyzed by proline.And the reaction efficiency and recyclability were investigated.(2)Synthesis of worm-like triblock copolymer nanoparticles and their application as non-aqueous Pickering emulsifiers.PS-b-P4VP diblock copolymer nanoparticles were prepared via RAFT-mediated non-aqueous dispersion polymerization in toluene using PS and P4VP as the stabilizer block and core-forming block,respectively.Different morphologies,including spheres,worms,branched worms,sheet-like,vesicles and large compound vesicles,could be achieved under the rational synthesis.The factors affecting the morphologies of PS-b-P4VP nanoparticles were studied.PS-b-P4VP diblock copolymer worms were then further extended with PLMA in toluene,leading to the formation of PS-b-P4VP-b-PLMA triblock copolymer nanoparticles.It was found that whether the cores of PS-b-P4VP worms were cross-linked or not has remarkable effect on the morphologies of PS-b-P4VP-b-PLMA triblock copolymer nanoparticles.For PS-b-P4VP worms with uncross-linked cores,only PS-b-P4VP-b-PLMA spheres were produced after the chain extension.Core cross-linked PS-b-P4VP worms,core cross-linked PS-b-P4VP-b-PLMA spheres and core cross-linked PS-b-P4VP-b-PLMA worms were then applied as Pickering emulsifiers to prepare n-hexane-in-DMF non-aqueous Pickering emulsions.The emulsion performances of polymer nanoparticles with different morphologies were compared.