Synthesis and properties of multiblock ionomers containing densely functionalized hydrophilic blocks for anion exchange membranes

Abstract

A series of novel anion conductive multiblock ionomers, quaternized copoly(arylene ether sulfone)s (QPAESs) with sequential hydrophobic/hydrophilic structures and quaternary ammonium groups densely functionalized hydrophilic blocks, were successfully synthesized by chloromethylation, quaternization and alkalization of the parent copolymers. Hydrophilic precursor oligomers containing triphenyl methane moieties underwent block polycondensation with hydrophobic oligomers to provide the parent copolymers. We explored the influences of the block size of the hydrophobic/hydrophilic segments and functionalized degree of hydrophilic blocks on the morphology and properties of the obtained multiblock QPAESs membranes. The multiblock QPAESs membranes showed well-defined phase segregation. The QPAESs membranes demonstrated greatly enhanced hydroxide ion mobility due to the phase segregation and strong field effects of the dense functional clusters in hydrophilic blocks. The QPAESs membranes with higher densities of functional groups exhibited excellent hydroxide ion conductivity, moderate water uptakes and swelling ratios, excellent thermal properties, acceptable mechanical properties and good chemical stability. Especially, the QPAESs membranes with matched hydrophobic/hydrophilic blocks kept their appearances and kept their residual weights higher than 89% of the original values after treatment of 1M NaOH solution at 60°C for 132 days. These properties indicate the multiblock ionomers membranes are promising as anion exchange membranes of alkaline fuel cells.