RAFT Polymerization of N-Vinylimidazolium Salts and Synthesis of Thermoresponsive Ionic Liquid Block Copolymers

The polymerizations of N-vinylimidazolium salts, 1-(3-phenylpropyl)-3-vinylimidazolium bromide (PVI-Br), 1-(6-ethoxycarbonylhexyl)-3-vinylimidazolium bromide (EHVI-Br), and 1-(2-ethoxyethyl)-3-vinylimidazolium bromide (EtOEVI-Br), were performed by reversible addition−fragmentation chain transfer (RAFT)/macromolecular design via interchange of xanthate (MADIX) process. Two xanthate-type chain transfer agents (CTAs), O-ethyl-S-(1-phenylethyl) dithiocarbonate (CTA 1) and O-ethyl-S-(1-ethoxycarbonyl) ethyldithiocarbonate (CTA 2), proved efficient for obtaining poly(PVI-Br)s and (EHVI-Br)s with relatively low polydispersities (M w/M n < 1.4). Poly(EtOEVI-Br)s with moderate molecular weight distributions (M w/M n = 1.5−1.6) were also obtained under the same conditions. Controlled character of the polymerization of PVI-Br was confirmed by the molecular weight controlled by the monomer/CTA molar ratio, a linear increase in the number-average molecular weight (M n) with conversion, and the ability to extend the chain by a second addition of monomer. Polymerizations of the N-vinylimidazolium salts using the dithiocarbonate-terminated poly(N-isopropylacrylamide) as a macro-chain-transfer agent provided well-defined thermoresponsive ionic liquid block copolymers. Thermally induced phase separation behavior and assembled structures of the block copolymers were also studied in aqueous solution.