Synthesis and Characterization of Branched Sulfonated Poly(ether sulfone ketone) as Proton Exchange Membrane

Branched sulfonated poly(ether sulfone ketone)s (Br-SPESK) were prepared with bisphenol A, 4,4′-difluorobenzophenone, 3,3′-disodiumsulfonyl-4,4′-difluorophenylsulfone, and THPE (1,1,1-tris-p-hydroxyphenylethane), respectively, at 160 °C using potassium carbonate in DMAC (Dimethylacetamide). THPE, as a branching agent, was used with 0.4 mol % of bisphenol A to synthesize branched copolymers. Copolymers containing 10–50 mol % disulfonated units were cast from dimethylsulfoxide solutions to form films. Linear sulfonated poly(ether sulfone ketone)s (SPESK) were also synthesized without THPE. The films were converted from the salt to acid forms with dilute hydrochloric acid. A series of copolymers were studied by FT-IR, 1H NMR spectroscopy, differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). Sorption experiments were conducted to observe the interaction of sulfonated polymers with water and methanol. The ion exchange capacity (IEC), a measure of proton conductivity, was evaluated. The synthesized Br-SPESK and SPESK membranes exhibit conductivities (25 °C) from 1.02×10−3 to 4.53×10−3 S/cm, water swell from 22.25 to 61.50%, IEC from 0.35 to 0.81 meq/g and methanol diffusion coefficients from 3.10×10−7 to 4.90×10−7 cm2/S at 25 °C.