Synthesis and characterization of poly(vinylidene fluoride)-g-sulfonated polystyrene graft copolymers for proton exchange membrane

A series of poly(vinylidene fluoride)-g-sulfonated polystyrene (PVDF-g-SPS) graft copolymers were synthesized and examined with the focus of understanding how the polymer microstructure (backbone molecular weight, graft density, graft length, sulfonic acid concentration, ion exchange capacity, etc.) affects their morphology, water uptake and proton conductivity under various environmental conditions. The PVDF-g-SPS graft copolymer with a combination of a high PVDF backbone, low SPS graft density, and high graft length self-assembles into a microphase-separated morphology with randomly oriented ionic channels imbedded in the hydrophobic PVDF matrix, offers a high ion exchange capacity (IEC=2.75 mmol/g) and resistance to excessive water swelling, which yields notable higher proton conductivity than Nafion under 30-120°C and high humidity conditions.