Polymer electrolytes derived from chitosan/ polyether networks Patricia Velazquez-Morales, Jean-Franc ° ois Le Nest* and Alessandro Gandini MateÂriaux PolymeÁres, Ecole Franc ° aise de Papeterie et des Industries Graphiques (INPG), BP 65, 38402 Saint Martin d'HeÁres, France (Received 16 September 1996; accepted 21 March 1997) AbstractÐPolysaccharides like cellulose and chitosan are well known for their aptitude to generate thin ®lms. This paper reports the synthesis and characterization of oxipropylated chitosan and their reaction with oligoether-based mono and di-isocyanate. The resulting networks, containing LiN (CF 3 SO 2 ) 2 , were investigated by dierential scanning calorimetry and complex impedance measurements # 1998 Published by Elsevier Science Ltd. All rights reserved Key words: polymer electrodes, oxipropylated chitosan, polyether networks, glass transition temperature, ionic conductivity. INTRODUCTION Among the various structures based on polyethers which have been put forward in the last couple of decades in order to prepare polymer electrolytes with a good overall performance [1, 2], we have chosen to study crosslinked topologies [3]. This deliberate strategy is justi®ed because creep pro- blems are eliminated and, if the length of the poly- ether chains in the network is kept reasonably low, crystallization is minimized. Within this general approach, a very wide selec- tion of cross-linked architectures was elaborated in which the type of ether unit and the DP of the cor- responding oligomers, as well as the cross-link agent and its functionality, were varied. The ionic moieties were also changed, not only in terms of the salt introduced, but also with respect to the fact that either both anion and cation were free to dif- fuse in the polymer or the anion was attached cova- lently to the network. All these materials were used to establish general criteria about ionic mobility by carrying out a very comprehensive investigation of their physico-chemical properties. This systematic study called upon the establishment of structure/ properties relationships in which such fundamental parameters as T g , dynamic mechanical behaviour, swelling in dierent liquids, nuclear magnetic relax- ation, ionic conductivity and electrochemical stab- ility were thoroughly inspected [3, 4]. The understanding of the fundamental features of these electrolytes, which clearly showed that free- volume considerations adequately explained all the experimental observations, led to the optimization of the conductivity with PEO-based networks in which a maximum degree of structural disorder was purposely introduced [5]. Having reached what we consider as a good achievement in terms of stable and highly conduc- tive polymer electrolytes, it became interesting to move onto a more applied problem, namely the possibility of improving the ®lm-forming properties of these networks in order to optimize the elabor- ation of thin devices (battery, electrochromic win- dows, ... ). The idea was of course to keep the good overall performance already attained and add the new capability of processing the material into ®lms as thin as possible. Some polysaccharides and their synthetic derivatives are well known for their ®lm-forming aptitude and we moved therefore in that direction. The ®rst investigation was conducted with cellulosic ethers which were branched and cross-linked with PEO or PPO chains using conden- sation reactions based on urethane chemistry [3, 6±8]. Results were satisfactory because we were able to conserve the good mechanical and electrical Electrochimica Acta, Vol. 43, Nos 10±11, pp. 1275±1279, 1998 # 1998 Published by Elsevier Science Ltd. All rights reserved Printed in Great Britain 0013±4686/98 $19.00 + 0.00 PII: S0013-4686(97)10030-5 *Author to whom correspondence should be addressed. 1275