Synthesis and properties of anion conductive multiblock copolymers containing tetraphenyl methane moieties for fuel cell application

Novel anion conductive multiblock copolymers containing quaternary ammonium basic groups functionalized tetraphenyl methane moieties with sequential hydrophobic/hydrophilic structure were synthesized via prepolycondensation, block copolycondensation, chloromethylation, quaternization, and alkalization. The quaternary ammonium groups were selectively introduced onto the tetraphenyl methane moieties in hydrophilic blocks. The multiblock QPAEs membranes showed well-defined phase segregations. At similar IEC values, hydroxide ion conductivities and mechanical properties strongly depended on the oligomer lengths of hydrophobic blocks and hydrophilic blocks. Hydroxide ion conductivities increased with increasing oligomer length of hydrophilic blocks. Mechanical properties of the QPAE membranes were strengthened by the increase of block length of the hydrophobic segments. The multiblock QPAEs membranes with the IEC values lower than 1.91 meq g−1 showed high stabilities under strong basic conditions even with the concentration of NaOH up to 8 M, and retained high conductivities and acceptable mechanical properties after being conditioned with 1 M NaOH at 60 °C for 336 h. The obtained QPAE-X15Y15 membranes with matched hydrophobic/hydrophilic block structure demonstrated the best comprehensive properties. These properties of the multiblock copolymer membranes show their potential as an anion exchange membrane of alkaline fuel cells.