Single-ion-conducting polymer electrolytes based upon borate-chain step-growth polymers

Abstract

Lithium salts of anionic polymers comprising internal anionic, fully saturated boron atoms are presented as single-ion-conducting polymer electrolytes. The linear linkage of BH₂⁺ units by linear, bidentate p-catecholate, benzene-1,4-bis(thiolate), and 1,4-phenylenedimethanide is achieved by the reaction of the borate precursor BH₂Cl(SMe₂) with the dilithiated substrates. These reactions give linear anionic polymers with the formula Li_n[–X–C₆H₄–X–BH₂–]_nⁿ⁻ (X = O, S, CH₂). A structural model compound is prepared by reaction of the lithium catecholate with triphenylboron to give the monomeric, unlinked model compound Li₂[Ph₃B–O–C₆H₄–O–BPh₃], which is characterized by X-ray crystallography. In the case of the catecholate-based polymer, addition of lithium benzene-1,3,5-tris(olate) as a crosslinking agent provides a means of stiffening the polymer material. Characterization and ionic conductivity properties are described.