SINGLE-ION AND SALT CONDUCTOR POLYMER ELECTROLYTES BASED ON POLY(4-VINYLPYRIDINE) QUATERNIZED WITH POLY(ETHYLENE OXIDE) SIDE-CHAINS

A new type of single-ion conductor with fixed cation was synthesized b y spontaneous anionic polymerization of 4-vinylpyridine in the presenc e of short polyethylene oxide (PEG) chains as alkylating agents. These comblike polymers have low T(g)s and are amorphous with the shorter P EOs. Their conductivities are unaffected by the nature of the anion (B r-, ClO4-, and tosylate) and are controlled by the free volume and the mobility of the pendant cation. By comparison of the results at const ant free volume, it is shown that the charge density decreases with th e increasing length of pendant PEO demonstrating that PEO acts only as a plasticizing agent. Best conductivity results (sigma = 10(-5) S cm( -1) at 60 degrees C) are obtained with PEO side chains of molecular we ight 350. With this sample, the conductivity in the presence of variou s amounts of added salt (LiTFSI) was studied. A best value of 10(-4) S cm(-1) at 60 degrees 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 sigma(r)/c increases linearly wi th increasing salt concentration showing that the ion mobility increas es continuously. Such behavior is quite unusual since in this concentr ation range a maximum is generally observed with PEO systems. To inter pret this result and by analogy with the behavior of this type of poly mer in solution, it is proposed that the conformation of these polymer s in the solid state is segregated with the P4VP skeleton more or less confined inside the dense coils surrounded by the PEO side chains. Un der the influence of the increasing salt concentration, this microphas e separation vanishes progressively: The LiTFSI salt exchanges with th e tosylate anions and acts as a miscibility improver agent. (C) 1997 J ohn Wiley & Sons, Inc.