Effect of Block Length on the Properties of Multiblock Polysulfone-Poly(diallylpiperidinium hydroxide) Anion Exchange Membranes

Research in anion exchange membranes(AEM)s has continued withthe development of materials bearing base stable cations. DesigningAEMs that microphase separate into hydroxide conductive, hydrophilicdomains within a hydrophobic and mechanically robust matrix has beenshown to be successful for improving AEM performance. A series ofmultiblock polysulfone-poly(diallylpiperidinium hydroxide) copolymers(PSf-PDApipOH) of similar hydrophobic/hydrophilic composition wasprepared in which the molecular weight of the hydroxide conductingPDApipOH segments was varied. The variable hydrophilic segment molecularweight was designed to assess the impact on microphase separation,hydroxide conductivity, and water management. The multiblock copolymersinvestigated were prepared by condensation polymerization of preformed4-fluorophenyl sulfone terminated poly(diallylpiperidinium hexafluorophosphate)(PDApipPF6) oligomers with polysulfone monomers. The structure-propertyrelationship between the molecular weight of the conductive PDApipOHsegments and AEM performance was demonstrated by evaluation of themicrophase separation, water uptake, and hydroxide conductivity. Membranesfabricated from the polysulfone-poly(diallylpiperidinium hexafluorophosphate)(PSf-PDApipPF6) multiblock copolymers were shown to form well-connectedconductive domains by SAXS and atomic force microscopy experiments.The PSf-PDApipOH membranes were highly conductive with the maximumhydroxide conductivity reaching 62.9 mS & BULL;cm(-1) at 60 & DEG;C and 95% relative humidity. Furthermore, it was demonstratedthat the conductivity increased with increasing PDApipOH segment molecularweight.