Single-ion and salt conductor polymer electrolytes based on poly(4-vinylpyridine) quaternized with poly(ethylene oxide) side chains

Abstract

A new type of single-ion conductor with fixed cation was synthesized by spontaneous anionic polymerization of 4-vinylpyridine in the presence of short polyethylene oxide (PEO) chains as alkylating agents. These comblike polymers have low Tgs and are amorphous with the shorter PEOs. Their conductivities are unaffected by the nature of the anion (Br−, ClO4−, and tosylate) and are controlled by the free volume and the mobility of the pendant cation. By comparison of the results at constant free volume, it is shown that the charge density decreases with the increasing length of pendant PEO demonstrating that PEO acts only as a plasticizing agent. Best conductivity results (σ = 10−5 S cm−1 at 60°C) are obtained with PEO side chains of molecular weight 350. With this sample, the conductivity in the presence of various amounts of added salt (LiTFSI) was studied. A best value of 10−4 S cm−1 at 60°C is obtained with a molar ratio EO/Li of 10. It is shown that, over the range of examined concentrations (0.2–1.3 mol Li kg−1), the reduced conductivity σr/c increases linearly with increasing salt concentration showing that the ion mobility increases continuously. Such behavior is quite unusual since in this concentration range a maximum is generally observed with PEO systems. To interpret this result and by analogy with the behavior of this type of polymer in solution, it is proposed that the conformation of these polymers in the solid state is segregated with the P4VP skeleton more or less confined inside the dense coils surrounded by the PEO side chains. Under the influence of the increasing salt concentration, this microphase separation vanishes progressively: The LiTFSI salt exchanges with the tosylate anions and acts as a miscibility improver agent. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 2719–2728, 1997