A sulfonated diamine monomer, 4,4‘-diaminodiphenyl ether-2,2‘-disulfonic acid (ODADS),
was successfully synthesized by direct sulfonation of a commercially available diamine, 4,4‘-diaminodiphenyl ether (ODA), using fuming sulfuric acid as the sulfonating reagent. A series of sulfonated
polyimides were prepared from 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTDA), ODADS, and
common nonsulfonated diamines. The resulting sulfonated polyimides displayed much better stability
toward water than those derived from the widely used sulfonated diamine 2,2‘-benzidinedisulfonic acid
(BDSA). This is because ODADS-based polyimide membranes have a more flexible structure than the
corresponding BDSA-based ones. Fenton's reagent test revealed that ODADS-based polyimide membranes
also had fair good stability to oxidation. Polyimide membranes with good water stability as well as high
proton conductivity were developed. NTDA−ODADS/BAPB(1/1) copolyimide membrane (BAPB refers to
4,4‘-bis(4-aminophenoxy)biphenyl)), for example, did not lose mechanical properties after being soaked
in water at 80 °C for 200 h, while its proton conductivity was still at a high level (comparable to that of
Nafion 117).
A new sulfonated diamine monomer, 9,9-bis(4-aminophenyl)fluorene-2,7-disulfonic acid (BAPFDS), was synthesized by direct sulfonation of the parent diamine, 9,9-bis(4-aminophenyl)fluorene (BAPF), using fuming sulfuric acid as the sulfonating reagent. A series of sulfonated polyimides with different sulfonation degrees were prepared from 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTDA), BAPFDS, and common nonsulfonated diamines. The resulting sulfonated polyimides generally showed good solubility in m-cresol and DMSO. Proton conductivities of these polyimide membranes were measured as the functions of relative humidity and temperature. The resulting homopolyimide, NTDA-BAPFDS, displayed proton conductivities quite similar to those of Nafion 117 in the whole humidity range (RH < 100%). At 100% relative humidity, all the BAPFDS-based polyimide membranes showed proton conductivities similar to or higher than those of Nafion 117. In addition, BAPFDS-based polyimide membranes exhibited much better water stability than those derived from a widely used sulfonated diamine, 2,2′-benzidinedisulfonic acid (BDSA), with similar IEC. This is probably because of the higher basicity of BAPFDS, which is favorable for maintaining the stability of imido rings.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.