Ionic liquid-containing non-aqueous Pickering emulsions prepared with sterically-stabilized polymer nanoparticles: A highly efficient platform for Knoevenagel reaction

Abstract

Room temperature ionic liquids (RTILs)-containing Pickering emulsions exhibit promising application potentials because of the integration of the “green” quality and the tunable applications of RTILs with the advantages of Pickering emulsions, such as the high stability and adjustable droplet size. In the present study, sterically-stabilized polymer nanoparticles (SSPNs) were first prepared via the reversible addition-fragmentation chain transfer (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 spherical/worm-like morphologies could be achieved at a target copolymer composition. Subsequently, core cross-linked SSPNs (CSSPNs) were obtained by means of chemical cross-linking of P4VP cores of SSPNs with 1,4-dibromobutane in a diluted solution of SSPNs in toluene (0.4 mg/mL). Stable 1-butyl-3-methylimidazolium tetrafluoroborate-in-toluene ([Bmim][BF4]-in-toluene) non-aqueous Pickering emulsions could be formed at a low emulsifier content of 0.005 wt% adopting CSSPNs with mixed spherical/worm-like morphologies as Pickering emulsifiers. Benefiting from large surface areas of Pickering emulsions and unique chemical/physical properties of RTILs, [Bmim][BF4]-in-toluene Pickering emulsions provided readily available platforms for many organic reactions. As a proof of the concept, proline catalyzed Knoevenagel reaction of 4-nitrobenzaldehyde with malononitrile was chosen as a model here. Both high reaction efficiency and good recyclability were observed.