Fixation of ionic liquids into polyether-based polyurethane films to maintain long-term antistatic properties Takuya Iwata a, b, c , Akiko Tsurumaki a, b , Saori Tajima a, b , Hiroyuki Ohno a, b, * a Department of Biotechnology, Tokyo University of Agriculture and Technology, 2-24-16 Naka-cho, Koganei, Tokyo 184-8588, Japan b Functional Ionic Liquid Laboratories, Graduate School of Engineering, TokyoUniversity of Agriculture and Technology, 2-24-16 Naka-cho, Koganei, Tokyo 184-8588, Japan c Iwata & Co., Ltd., 1-2-11, Nishiki, Naka-ku, Nagoya, Aichi 460-0003 Japan article info Article history: Received 10 January 2014 Received in revised form 13 March 2014 Accepted 17 March 2014 Available online 25 March 2014 Keywords: Ionic liquids Antistatic effect Polyurethanes abstract Ionic liquids (ILs) were fixed into polyether-based polyurethane (PU) films for sustainable antistatic properties. Preliminarily, ILs were screened in terms of efficiency of antistatic effect. Surface resistivity (r s ) for IL-doped PU films changed depending the anion species, and the smallest r s was found for the PU films containing bis(trifluoromethanesulfonyl)imide ([Tf 2 N])-type ILs. Then, [Tf 2 N]-type ILs composed of ammonium cations having hydroxyl groups were fixed into the PUs through urethane bonds. The fixation of 1000 ppm of the ILs reduced the r s of the PU films from 2.1  10 12 to 2.1  10 9 U sq 1 . These IL-fixed PU films were revealed to possess high washing durability confirmed by negligible change of r s before and after ultra-sonication treatment in methanol. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction Polyurethanes have been recognised as important materials whose properties are tuneable between rubber-like elasticity and plastic-like toughness. These can be controlled by changing the ratio of polyisocyanate to polyols as components, plasticising con- ditions, and other factors [1]. Among engineering and electronics fields, there are strong requirements to design elastic and flexible polyurethanes which can be used in a wide range of temperature, and this attempt has been successfully carried out by using poly- ether polyols [2,3]. These polyether-based polyurethanes (PUs) have been applied as films and sheets for packaging and stuffing during production, packing, shipping, and materials for electronics devices. However, these PUs are insulating and they cause elec- trostatic discharge (ESD) damage of electronic devices such as precision instruments and office automation equipment. There is a strong demand to prevent ESD of PUs so that the electronic devices which have contact with PUs may not be suffered from ESD damage. In order to prevent ESD of PUs, resistivity of PUs has to be reduced. Surface resistivity and volume resistivity are frequently used to evaluate ESD protective materials together with charge decay time and triboelectric properties. Materials showing surface resistivity (r s ) greater than 10 12 U sq 1 are generally classified as insulators [4,5], and the r s of 10 10 U sq 1 is practically recognised as a preferable value to keep antistatic effect [6]. In order to reduce r s , antistatic agents, such as carbon black, intrinsically conductive polymers, and surfactants have been added to polymers as ESD protective materials [7e10]. Antistatic effects of these agents are realised by electron or ion conduction mainly occurred through successive conduction paths formed by additives or moisture adsorbed on the polymer surfaces. In the area of polymer electrolytes, polyethers (e.g., poly(ethylene oxide); PEO) have long been recognised as potential matrices for ion conduction due to their low glass transition temperature (T g ) and high polarity. For the case of inorganic salts/PEO composites, ionic conductivity is enhanced with both dissociated ions produced by the large dipole moment on ether oxygens and ion motion accompanied with segmental motion of PEO [11,12]. Recently, ionic liquids (ILs) have been recognised as potential salts due to their low T g [13], and ILs/ PEO composites have been reported to generate large amounts of free ions compared to PEO composites with inorganic salts [14]. Since many ILs are highly dissociable and their T g is quite low as compared with most inorganic salts, these ILs are expected to be excellent additives to prepare ion conductive polymers. * Corresponding author. Department of Biotechnology, Tokyo University of Agriculture and Technology, 2-24-16 Naka-cho, Koganei, Tokyo 184-8588, Japan. Tel./fax: þ81 42 388 7024. E-mail address: ohnoh@cc.tuat.ac.jp (H. Ohno). Contents lists available at ScienceDirect Polymer journal homepage: www.elsevier.com/locate/polymer http://dx.doi.org/10.1016/j.polymer.2014.03.028 0032-3861/Ó 2014 Elsevier Ltd. All rights reserved. Polymer 55 (2014) 2501e2504