Synthesis of Sulfonation Poly( N -propylsulfonicacid isatin biphenylene) for Polymer Electrolyte Membrane Fuel Cell Containing SiO₂ Nanocomposite Membrane.

Polymer containing isatin was synthesized by super acid-catalyzed carbon-carbon coupling reaction. Propylsulfonic acid was grafted on isatin unit by substitution reaction with potassium salt of 3-bromo-1-propanesulfonic acid. The sulfonic acid composition was regulated at 25~80 mol% of propylsulfonic acid in order to achieve expected ion exchange capacity of maximum 2.0 meq/g. The copolymers were of high molecular weight (inherent viscosity, η inh = 1.2 dL/g) to afford a tough membrane by solution casting. Composite membranes were prepared by sulfonated polymer and SiO₂ nanoparticles (20 nm, 4~10% wt). All these composite membranes were casted from the solution of sulfonated polymer in dimethylsulfoxide (DMSO) to afford 25 μ m. The structural properties of the synthesized polymers were investigated by 1 H NMR spectroscopy. The membranes were studied by ion exchange capacity (IEC), water uptake, dimensional stability and proton conductivity assessment by comparing with Nafion® . As increasing the IEC values, the small hydrophobic components induced high proton conductivities and proton diffusion coefficients. These kinds of membranes without ether linkages showed low water swelling as well.