Synthesis of molten salt-type polymer brush and effect of brush structure on the ionic conductivity

Poly(ethylene oxide) (PEO) derivatives having both vinyl group and imidazolium salt structure on their ends were prepared and polymerized. Molten salt-type polymer brushes having different ethylene oxide (EO) unit number and different tethering structure were prepared to analyze the effect of flexible spacer. The ionic conductivity and DSC measurement of molten salt-type polymer brushes were carried out. When the counteranion species of the polymer was TFSI-, molten salt polymer (1) in spite of rubber-like properties showed high ionic conductivity (1.49 x 10(-4) S cm(-1) at 30 degreesC) corresponds to that of monomers reflecting low T-g (- 56 degreesC). The PEO-tethering of molten salt with polymer matrix was effective to suppress the drop of ionic conductivity after polymerization. Three kinds of imidazolium cations, such as n-ethylimidazolium, n-methylimidazolium or 1-benzyl-2-methylimidazolium, were selected, and corresponding monomers were synthesized. These were polymerized to analyze the effect of terminal cationic structure on the ionic conductivity. In spite of different imidazolium cation, the ionic conductivity and T-g of macromonomers and their polymers were equivalent. The ionic conductivity of molten-salt polymers increased with increasing EO or ethylene unit number. It is suggested that the distance between vinyl polymer and terminal imidazolium cation was important factor with respect to high ionic conductivity for molten salt-type polymer brushes. (C) 2001 Elsevier Science Ltd. All rights reserved.