Sulfonated Polybenzothiazoles Containing Hexafluoroisopropyl Units for Proton Exchange Membrane Fuel Cells

A sulfonated dicarboxylic monomer containing hexafluoroisopropyl,i.e., 3,3 & PRIME;-disulfonate-2,2-bis(4-carboxyphenyl)hexafluoropropane(SCFA), was prepared via sulfonation and oxidation to synthesize novelsulfonated polybenzothiazoles (sPBT-F) through polycondensation of2,2-bis(4-carboxyphenyl)hexafluoropropane (CFA), SCFA, and 2,5-diamino-1,4-benzenedithioldihydrochloride (DABDT). These sPBT-F series polymers exhibited excellentsolubility due to the incorporation of a flexible hexafluoroisopropylgroup. Meanwhile, the sPBT-F series polymers displayed high thermalstability and were used to prepare tough and soft membranes by solutioncasting. Interestingly, sPBT-F series membranes exhibited excellentwater uptake and low swelling ratio, indicating excellent dimensionalstability. AFM images displayed a region of obvious separation oflight/dark phases, indicating high proton conductivity of sPBT-F seriesmembranes. The sPBT-F82.5 membrane with a high degree of sulfonationdemonstrated a conductivity of 0.14 S cm(-1) at 80 & DEG;C and 100% RH, superior to the results of Nafion 117. Furthermore,the sPBT-F82.5 membrane displayed a maximum power density of 344.33mW cm(-2) and superb durability at a current densityof 0.2 A cm(-2) for 20 h. In summary, the sPBT-F polymersare potential matrix materials for PEMs.