Synthesis and characterization of novel sulfonated naphthalenic polyimides as proton conductive membrane for DMFC applications

To prepare proton conductive membrane for direct methanol fuel cells (DMFC), a novel sulfortated aromatic diamine monomer, 1,4-bis(4-amino-2-sulfonic acid-phenoxy)-benzene (DSBAPB) was synthesized and characterized by H-1 NMR and FT-IR. Then a series of sulfonated polyimides (SPIs) were prepared from DSBAPB with 1,4,5,8-naphthalene tetracarboxylic dianhydride (NTDA) and a non-sulfonated diamine, 4,4'-oxydianiline (ODA) via one-step high-temperature polymerization method. The sulfonation degree of the SPIs can be controlled by changing the mole ratio of sulfortated monomer to non-sulfonated monomer. The obtained SPI membranes exhibit desirable proton conductivity ranged from 7.9 x 10(-3) to 7.2 x 10(-2) S cm(-1) and low methanol permeability of less than 2.85 x 10(-7) cm(2) s(-1). Furthermore, the hydrolysis stability of the obtained SPIs is better than the BDSA based SPIs caused by the flexible structure. (c) 2006 Elsevier Ltd. All rights reserved.