Block copoly(phenylquinoxaline)s as potential ionomers for proton exchange membranes

Poly(phenylquinoxaline)s are a family of aromatic condensation polymers known for their outstanding thermal and chemical stability. Based on this polymer class new sulfonated block copoly(phenylquinoxaline)s with different hydrophobic segments have been developed. The block copolymers were synthesized via polycondensation reactions between 3,3′,4,4′-tetraaminodiphenylether and two different tetraketones: tetrafluorphenylbis-phenylethandion and phenylbisphenylethandion. Block copoly(phenylquinoxaline)s up to a molecular weight Mn of 29.3 kg mol-1 were obtained. The sulfonations of these block copolymers were carried out in a mixture of concentrated sulfuric acid and oleum (4:1) leading to ion exchange capacities of 1.77-2.36 mmol g-1. Flexible films of sulfonated block copoly(phenylquinoxaline)s were realized by doctor blading of solutions in N'N-dimethylacetamide (DMAC) or N-ethyl-2-pyrrolidone (NEP). The resulting membranes achieved proton conductivities in the range of 48–110 mS cm-1. Additionally, water uptake and dimensional stability were determined and presented.