Electrochemical comparison of several cross- linked polyethers F. Alloin and J-Y. Sanchez* Laboratoire D'Electrochimie et de Physicochimie, des MateÂriaux et des Interfaces, Domaine Universitaire, BP75, Saint-Martin D'HeÁres, Cedex, France (Received 16 September 1996; accepted 2 May 1997) AbstractÐSeveral unsaturated polyethers have been prepared by a polycondensation route, from a, o dihy- droxy oligoethers, and cross-linked by free-radical initiation. The ionic conductivities and thermal behavior of LiTFSI/network electrolytes have been investigated and show that conductivities depend on the nature of the solvating oligomeric blocks, the maxima corresponding to poly(oxyethylene) based networks. Oligo- meric poly(oxypropylene) and poly(oxytetramethylene) blocks however provide a quite satisfactory conduc- tivity level. # 1998 Published by Elsevier Science Ltd. All rights reserved. Key words: polymer electrolytes, network, lithium salts, poly(oxytetramethylene), poly(oxypropylene). 1. INTRODUCTION Through the ionic conductivities of polymer electro- lytes, one may dierentiate the solvating behaviour of several solvating polyether units. Nevertheless, according to the nature of monomers and to the propagation mechanisms, the long-range regularity, thus the crystallinity and melting points, of the host polymers may be clearly dierent. Thus the sym- metry of ethylene oxide monomer and the absence of polymer branching provides highly regular poly- (oxyethylene). As for propylene oxide, the long- range regularity of poly(oxypropylene) is dependent on the head-to-tail content and on the tacticity and, depending on the temperature and on the catalyst, the synthesis results in semi-crystalline or in fully amorphous polymer [1, 2]. The dierence in crystal- linity and melting points therefore prevents the comparison of ionic conductivities in a wide tem- perature range. This drawback may be overcome, using oligoethers instead of high molecular weight polymers. Thus, due to their lower melting point, the comparison may be performed in a wider tem- perature range. However C. Vincent [3] reported from solid NMR investigation that up to a molecu- lar weight of 3,200, the diusion coecient of oligo- poly(oxyethylene) is close to that of lithium cation indicating that Li moves with the chain. Another way has been explored by Le Nest et al. [4] and Watanabe et al. [5] with amorphous cross-linked polyurethane-ethers. Thus oligopolyethers a,o dihy- droxy poly(oxypropylene) and poly(oxyethylene) were reacted with triisocyanates, but this compara- tive study dealt with LiCIO 4 and was not extended to poly(oxytetramethylene) solvating blocks. Looking for fully aprotic polyethers, we have over- come the crystallinity problems either by perform- ing anionic ring-opening copolymerization of ethylene oxide/allyl glycidyl ether mixtures [6], or by polycondensation reactions [7]. These latter, besides their potential industrial scale-up, would allow polycondensation of any kind of oligomers provided that the end groups are alcohols. This pre- liminary paper therefore reports a comparative study of three solvating units: oxyethylene, oxypro- pylene, oxytetramethylene. 2. EXPERIMENTAL 2.1 Polycondensation reaction The polycondensates were prepared using dier- ent polyethers and the 3-chloro-2-chloromethyl-1- propene from Aldrich used as received. The poly- condensation procedure has been adapted to the starting oligomers, namely oligo(polyoxypropylene) PPG, oligo(polyoxytetramethylene) PTHF and oli- Electrochimica Acta, Vol. 43, Nos 10±11, pp. 1199±1204, 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)10020-2 *Author to whom correspondence should be addressed. 1199