Preparation and characterization of block copolymers containing multi-sulfonated unit for proton exchange membrane fuel cell

Multi-sulfonated block copolymers (MSBPs) with sulfonated units of 5, 9, 10, and 14 mol% were successfully synthesized for proton exchange membrane. The hydrophobic block oligomer was prepared by 4,4′-dihydroxydiphenylsulfone and 4,4′-difluorodiphenylsulfone. And also hydrophilic block oligomer was prepared by multiphenyl structured monomers of 1,2-bis(4-fluorobenzoyl)-3,4,5,6-tetraphenylbenzene and 1,2-bis(4-hydroxyphenyl)-3,4,5,6-tetraphenylbenzene by varying the different mole ratio to control the degree of sulfonation. The two steps of sulfonation was carried out under chlorosulfonic acid, and then concentrated sulfuric acid separately. The sulfonation was performed selectively on hydrophilic block segment and para position of the side chain phenyl groups. MSBPs were studied by FT-IR, 1H NMR spectroscopy, and thermo gravimetric analysis (TGA). Sorption experiments were conducted to observe the interaction of MSBPs with water. The wateruptakes were 9.6–42.5% at 25 °C and 14.7–90.8% at 80 °C. The resulted ion exchange capacities (IEC) were 0.79–1.87 (mmol g−1) and proton conductivities were evaluated as increasing IEC.