The effect of side chain architectures on the properties and proton conductivities of poly(styrene sulfonic acid) graft poly(vinylidene fluoride) copolymer membranes for direct methanol fuel cells

The effect of side chain architectures on the properties and proton conductivities of graft copolymer membranes for direct methanol fuel cells (DMFCs) are studied. Poly(vinylidene fluoride)-g-poly(styrene sulfonic acid) (PVDF-g-PSSA) copolymers with either linear or arborescent PSSA side chains are prepared and examined. For the copolymers with similar ion exchange values, both graft copolymers show similar water uptakes and bound water contents. Meanwhile, the arborescent samples exhibit higher proton conductivity, lower methanol permeability, and higher selectivity compared to the linear analogues. Incorporation of highly branched side chains effectively increases the properties of the PVDF-g-PSSA-based PEMs for DMFCs because of formation of agglomerate PSSA domains. The PSSA domains promote proton conduction and depress methanol permeation through the PEMs, consequently significantly increase the selectivities (proton conductivity/methanol permeability) of the PEMs.