Lithium-Ion Conductive Polymers as Prospective Membranes for Lithium−Seawater Batteries

Novel amphiphilic single-ion conductive polynorbornenes with pendent cyclotriphosphazenes have been studied as candidates for lithium-ion conductive membranes for lithium−seawater batteries. The cyclotriphosphazene components were linked to a 5-norbornene-2-methoxy substituent to provide a polymerizable unit. 2-(2-Phenoxyethoxy)ethoxy cosubstituents on the cyclotriphosphazene unit of the first comonomer were utilized to simultaneously facilitate lithium cation transport and introduce hydrophobicity into the polymer electrolyte. 4-(Lithiumcarboxalato)phenoxy side groups were linked to the rings of a second comonomer to provide tethered anions with mobile lithium cations and to increase the dimensional stability of the final polymers. The synthesis of norbornenemethoxy-based cyclotriphosphazene monomers, their ring-opening metathesis polymerization, deprotection and lithiation of the 4-(propylcarboxalato)phenoxy side groups, and the characterization of the polymers are discussed to illustrate the dependence of ion transport and hydrophobic properties on the polymer composition.