Synthesis by RAFT and Ionic Responsiveness of Double Hydrophilic Block Copolymers Based on Ionic Liquid Monomer Units

Three imidazolium-based ionic liquid (IL) monomers, namely, 3-(1-ethyl imidazolium-3-yl)propylmethacrylamido bromide (IL- 1 ), 2-(1-methylimidazolium-3-yl)ethyl methacrylate bromide (IL- 2 ), and 2-(1-ethylimidazolium-3-yl)ethyl methacrylate bromide (IL- 3 ), and methacrylic acid (MAA) were polymerized by the reversible addition fragmentation chain transfer (RAFT) process in methanolic solutions at 70 °C, using either 2-cyanopropyl dithiobenzoate (CTA- 1 ) or (4-cyanopentanoic acid)-4-dithiobenzoate (CTA- 2 ) as chain transfer agents (CTAs). Under these conditions, polymers exhibited molar masses predetermined by the initial molar ratio of the monomers to the dithioester precursor, as evidenced by 1 H NMR spectroscopy from chain ends analysis. These hydrophilic polymers were subsequently used as macro-CTAs in chain extension experiments in aqueous or in alcoholic solutions, affording IL-based double hydrophilic block copolymers (DHBCs) of the type PIL- 1 - b -PAm, PMAA- b -PIL- 2 and PMAA- b -PIL- 3, where PAm and PIL stand for polyacrylamide and polymeric ionic liquid. These DHBCs could be further manipulated and made to self-assemble in micelle-like structures in water by exchanging the bromide (Br − ) counteranion of IL blocks for − N(SO 2 CF 3 ) 2 . This anion exchange indeed turned the solution properties of the PIL blocks from hydrophilic to hydrophobic, as verified on the corresponding IL-based homopolymers which were immiscible with water after the anion switch. Investigations by 1 H NMR evidenced that the diblock copolymers exhibited salt-responsive behavior in aqueous solutions: anion exchange induced the formation of water-soluble micellar aggregates consisting of hydrophobic − N(SO 2 CF 3 ) 2 -based IL blocks at the core stabilized by water-soluble PAm or PMAA at the shell.