Novel cation conductors based on rigid-rod poly(p-phenylene)s

One approach to combine sufficient ion conductivity and mechanical strength in solid polymer electrolytes (SPE) involves the construction of supramole cular architectures consisting of a liquid-like phase in intimate contact w ith a rigid phase, both dispersed on a molecular level. Taking advantage of the self-assembling tendencies of poly(p-phenylene)s (PPP) as rigid rods, layered structures as reinforcing elements were formed which were separated by a liquid matrix of ethyleneoxide (EO) side chains, in which Lithium sal ts were dissolved and ion conduction occurs. Single-ion conductors with EO- side chains plus Li-sulfonate groups attached to the PPP backbones exhibit lower conductivities. Although the EO-side chain to Li sulfonate molar rati o was chosen so that O/Li+ approximate to 25, the de conductivity of such a material was found to be approximately two orders of magnitude lower than in a PPP(EO)(5/6)-Lithium-triflate blend with the same O/Li+ ratio. The con ductivity decreases further when the EO-side chain to sulfonate ratio is de creased. Thus, the increase in the molar concentration of the Li-sulfonate moieties does not lead to higher conductivities either because the number o f "free", i.e. mobile, charge carriers is decreased or because the mobility of the ionic species is drastically reduced due to the lack of segmental m otion of the matrix. Consequently, when the matrix is plasticized by the ad dition of large amounts of oligoether, the ionic conductivity increases dra matically and becomes comparable to that of the corresponding multi ion con ducting SPE with the same O/Li+ ratio. (C) 1999 Elsevier Science Ltd. All r ights reserved.