Anion-Conducting Polymer Electrolyte without Ether Linkages and with Ionic Groups Grafted on Long Side Chains: Poly(Alkylene Biphenyl Butyltrimethyl Ammonium) (ABBA)

Abstract

In this work we report the synthesis of the new ionomer poly(alkylene biphenyl butyltrimethyl ammonium) (ABBA) with a backbone devoid of alkaline-labile C-O-C bonds and with quaternary ammonium groups grafted on long side chains. The ionomer was achieved by metalation reaction with n-butyllithium of 2-bromobiphenyl, followed by the introduction of the long chain with 1,4-dibromobutane. The reaction steps were followed by 1H-NMR spectroscopy showing the characteristic signals of the Br-butyl chain and indicating the complete functionalization of the biphenyl moiety. The precursor was polycondensed with 1,1,1-trifluoroacetone and then quaternized using trimethylamine (TMA). After the acid catalyzed polycondensation, the stoichiometric ratio between the precursors was respected. The quaternization with TMA gave a final degree of amination of 0.83 in agreement with the thermogravimetric analysis and with the ion exchange capacity of 2.5 meq/g determined by acid–base titration. The new ionomer blended with poly(vinylalcohol) (PVA) or poly(vinylidene difluoride) (PVDF) was also characterized by water uptake (WU) and ionic conductivity measurements. The higher water uptake and ionic conductivity observed with the PVDF blend might be related to a better nanophase separation.

Keywords

• anion exchange membrane
• polycondensation
• blend membrane
• ionic conductivity