Synthesis and characterization of novel sulfonated polyimides containing triptycene and xanthene moieties

Polymer electrolyte fuel cells (PEFCs) have been identified as promising power sources for vehicular transportation and for other applications requiring cleaning, quiet, and portable power [1]. The most important component of a PEFC is polymer electrolyte membrane itself. At present, sulfonated perfluoropolymers such as Nafion have been almost the only advanced membranes that are used in practical systems due to their high proton conductivity, good mechanical strength, and high thermal and chemical stability. Unfortunately, however, there are some demerits which seriously limit their application. These include high cost, low conductivity at low humidity or high temperatures, and high methanol permeability. Thus, the development of alternative materials overcoming these problems is strongly desired. Up to now, a large number of sulfonated polymers such as poly(styrene sulfonic acid) and the analogous polymers, sulfonated polysulfone, sulfonated poly(ether ether ketone), and sulfonated poly(phenylene sulfide) have been developed, and very recently sulfonated polyimides have been reported to be promising materials for PEFC [2,3]. In this paper, a series of novel sulfonated homo- and copolyimides were synthesized from 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTDA), sulfonated diamine, 4,4′-diaminodiphenyl ether-2,2′-disulfonic acid (ODADS) and nonsulfonated diamines containing triptycene and xanthene groups. The sulfonated polymers were obtained in quantitative yields with inherent viscosities of 0.27-0.74 dL g-1. The resulting polymers dissolved in N-methyl-2-pyrrolidinone, N,N-dimethylacetamide, N,Ndimethylformamide, dimethyl sulfoxide, and pyridine. These polymers were fairly stable up to a temperature > 450 °C and lost 10% weight in the range of 477 °C and 575 °C in nitrogen. The UV-V is absorption spectra revealed that most of the polymers had absorption maxima around 310 and 341 nm.