Synthesis and Characterization of Sulfonated Polybenzoxazole for High Temperature Proton Exchange Membranes

摘要

Sulfonated Polybenzoxazoles(sPBO) with sulfonation degree ranging from 10% to 30% were synthesized from 4,6-diaminoresorcinol dihydrochloride(DAR), terephthalic acid(TPA), 5-sulfoisophthalic acid monosodium salt (SIPA) by direct polycondensation in polyphosphoric acid (PPA). The structures of sPBOs were verified by FTIR and elemental analysis. The values of inherent viscosity ranged from 2.56 to 1.12 dL/g and decreased with the increasing of sulfonation degree. TGA analysis showed sPBOs were thermal stable up to nearly 250°C. sPBO/PPA polymerization solution were hot pressed directly to form PPA doped sPBO membranes since sPBO was insouble in common solvents. The PPA doping level was about 340% (wt) per gram of sPBOs by theoretical calculations. The tensile strength of PPA doped sPBOs membrances ranged from 9.1 to 3.2 Mpa. At high temperature, sPBO membranes showed excellent proton conductivity. For instance, sPBO membrane with a sulfonation degree of 10% exhibited a proton conductivity of 0.123 S/cm at 170°C. The experimental results indicated sPBO are promising for proton exchange membranes for high temperature proton exchange membranes.