Synthesis and Properties of Anion Conductive Ionomers Containing Tetraphenyl Methane Moieties

Abstract

A series of anion conductive aromatic ionomers, poly(arylene ether)s containing various polymer backbones and quaternary ammonium basic group functioned tetraphenyl methane moieties, were synthesized via nucleophilic substitution polycondensation, chloromethylation, quaternization, and the subsequent alkalization reactions. The structures of poly(arylene ether)s (PAEs), chloromethylated poly(arylene ether)s (CMPAEs), and quaternizated poly(arylene ether)s (QPAEs) ionomers were confirmed by (1)H NMR technique. Their thermal stabilities were evaluated by thermo gravimetric analysis (TGA). The water uptakes, ion exchange capacities (IEC), hydroxide ion conductivities, mechanical properties, and chemical stabilities of the membranes derived from the synthesized ionomers were assessed as anion exchange membranes. The QPAEs membranes were tough and thermally stable up to 170 °C. The IEC of the ionomers varied from 0.21 to 2.38 meq g(-1) which can be controlled by chloromethylation reaction conditions. The ion conductivities of QPAEs membranes increase dramatically with increasing temperature. The hydroxide ion transport activation energy, Ea, of the QPAEs membranes varied from 13.18 to 42.30 kJ mol(-1). The QPAE-d membrane with lower IEC value of 1.04 meq g(-1), derived from copolymer CMPAE-d bearing sulfone/ketone structure, displayed the highest hydroxide ion conductivity of 75 mS cm(-1) at 80 °C and showed strong tensile strength (29.2 MPa) at 25 °C. The QPAE-e membrane with IEC value of 1.09 meq g(-1), derived from copolymer CMPAE-e bearing sulfone/ketone-ketone structure, demonstrated 68 mS cm(-1) at 80 °C. The QPAE-d membrane kept 90% of mechanical properties and 82% of hydroxide ion conductivity after being conditioned with 1 M NaOH at 60 °C for 170 h. These properties of the ionomers membranes show their potential as an anion exchange membrane of alkaline fuel cells.