Polyelectrolyte-in-Ionic-Liquid Electrolytes Churat Tiyapiboonchaiya,* 1 Jennifer M. Pringle, 1 Douglas R. MacFarlane, 1 Maria Forsyth, 2 Jiazeng Sun 2 1 School of Chemistry, Monash University, Wellington Road, Clayton, Victoria 3800, Australia Fax: 0061 399054597; E-mail: Churat.Tiyapiboonchaiya@sci.monash.edu.au 2 School of Physics and Materials Engineering, Monash University, Wellington Road, Clayton, Victoria 3800, Australia Received: June 13, 2003; Revised: August 16, 2003; Accepted: September 3, 2003; DOI: 10.1002/macp.200350073 Keywords: conductivity; diffusion; 1-ethyl-3-methylimidazolium dicyanamide; gels; polyelectrolytes Introduction Solvent free, single-phase polymer electrolytes may be classified into two major types: polymer-salt complexes and polyelectrolytes. [1–2] In polyelectrolytes, covalent bonds bind one type of ion to the polymer backbone whereas in polymer-salt complexes both anion and cation are inde- pendent of the polymer chain. [2] Polyelectrolytes can be de- signed with specific negative groups bound to the polymer chains, and the counter-cation will then be the sole charge carrier, as is desirable in a number of applications. Poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPS) has been widely used as a water-soluble poly- mer, [3] and as a proton-conducting polyelectrolyte [4–5] as well as a lithium ion electrolyte when mixed with a lithium salt. [6] In recent research, [7] a polyelectrolyte gel based on a copolymer of a neutral co-monomer, N,N 0 -dimethylacryl- amide (DMAA) and a charged co-monomer, lithium 2-acrylamido-2-methyl-1-propanesulfonate (AMPSLi), chemically crosslinked with tetraethylene-glycol diacry- late (TEGDA) was prepared. The gel was polymerised in a solvent mixture of N,N-dimethylacetamide/ethylene car- bonate (DMA/EC), but the disadvantage to this procedure is the introduction of a volatile component into the electrolyte. Ionic liquids, also known as room temperature molten salts, have previously been used in polymer electrolyte systems, primarily because of their high ionic conductivity, wide electrochemical window, low volatility, thermal stability and non-flammability. [8–11] In the polymer elec- trolyte systems, [12–14] the ionic liquid plays the role as both a charge carrier and as a non-volatile plasticiser. Imidazolium-based ionic liquids have a favorable electro- chemical window compared to conventional solvents, [10] and we have recently described a new series of imidazolium salts based on the dicyanamide (DCA) anion. [15] DCA is a Full Paper: Novel polymer electrolyte materials based on a polyelectrolyte-in-ionic-liquid principle are described. A combination of a lithium 2-acrylamido-2-methyl-1-propa- nesulfonic acid (AMPSLi) and N,N 0 -dimethylacrylamide (DMMA) are miscible with the ionic liquid, 1-ethyl-3- methylimidazolium dicyanamide (EMIDCA). EMIDCA has remarkably high conductivity ( 2  10 2 S  cm 1 ) at room temperature and acts as a good solvating medium for the polyelectrolyte. At compositions of AMPSLi less than or equal to 75 mol-% in the copolymer (P(AMPSLi-co- DMAA)), the polyelectrolytes in EMIDCA are homoge- neous, flexible elastomeric gel materials at 10  15 wt.-% of total polyelectrolyte. Conductivities higher than 8  10 3 S  cm 1 at 30 8C have been achieved. The effects of the mono- mer composition, polyelectrolyte concentration, temperature and lithium concentration on the ionic conductivity have been studied using thermal and conductivity analysis, and pulsed field gradient nuclear magnetic resonance techniques. Comparison of the measured and calculated lithium con- ductivity at 30 8C. Macromol. Chem. Phys. 2003, 204, 2147–2154 2147 Macromol. Chem. Phys. 2003, 204, No. 17 DOI: 10.1002/macp.200350073 ß 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim