Anion conductive aromatic polymers containing fluorenyl groups: Effect of the position and number of ammonium groups

Synthesis and properties of anion conductive aromatic block copolymers, QPE-bl-3, QPE-bl-3 M2, and M4, containing fluorenylidene biphenylene groups as scaffold for ammonium groups are described. These copolymers share the same main chain structure, but the position and the number of ammonium groups on a fluorenyl group differ. High molecular weight quaternized block copolymers were obtained via typical chloromethylation reaction or using preaminated monomers, and were well-characterized by ¹H NMR spectra. Self-standing bendable membranes were obtained by solution casting. QPE-bl-3 M4 membranes containing four ammonium groups per hydrophilic repeat unit (highest ammonium density) in the hydrophilic block exhibited well developed phase-separated morphology, while QPE-bl-3 membranes containing two ammonium groups per hydrophilic repeat unit exhibited high anion conductivity. The highest anion conductivity (104 mS/cm) was obtained with QPE-bl-3 membrane (IEC = 2.1 meq/g) at 80 C in water. An H₂/O₂ alkaline fuel cell was operable with the membrane to achieve 62 mW/cm² of the maximum power density at 161 mA/cm² of the current density.