Main-chain viologen polymers with triflimide counterion exhibiting lyotropic liquid-crystalline properties in polar organic solvents

The solution-phase behavior of three main-chain viologen polymers, which are composed of isomeric xylyl units and triflimide as a counterion, was studied in methanol, dimethylformamide, acetonitrile, and dimethyl sulfoxide as solvents microscopically under crossed polarizers. Each of them exhibited a lyotropic lamellar phase in both polar protic and aprotic solvents. Their C* for the formation of biphasic solutions (1-5 wt%) and concentrations (20-30 wt%) for the lyotropic solutions in methanol was much lower than those in polar aprotic solvents (20-71 and 60-81 wt%, respectively). Their high solubility, high C* for the formation of biphasic solutions, and high concentrations for the formation of lyotropic solutions in polar aprotic solvents were related to the significant reduction of strong ionic interactions between triflimide and 4,4'-bipyridinium ions in each of these viologen polymers. They were the first examples of viologen polymers that exhibited a lyotropic phase in polar aprotic solvents. (C) 2002 Wiley Periodicals, Inc.