Synthesis And Properties Of Sulfonated Naphthalenic Polyimides As Proton Exchange Membranes

Fuel cells have drawn extensive attention in the 21st century as effective, clean and green energy technologies, since the world is facing an ever increasing problem of energy shortages and pollution. Polymer electrolyte membrane fuel cells (PEMFCs) and direct methanol fuel cells (DMFCs) have been recognized as promising energy devices in automotive, stationary and portable electronic applications. The characteristics of polymer electrolyte membranes (PEMs), which are the proton conducting core components of PEMFCs and DMFCs, have a great influence on the performance of fuel cells. Perfluorosulfonic acid type membranes, which possess excellent oxidative and dimensional stabilities and high proton conductivity, are the commercial state-of-the-art PEMs currently utilized in PEMFC and DMFC systems. However, some deficiencies are well-recognized. In this respect, much research effort is being directed to develop new PEMs which have excellent comprehensive performance.Most recently, several sulfonated polyaryletherketones containing rigid and regular phenyl-ketone-phenyl-ketone-phenyl linkages in the polymer backbones (SPEEKKs) have been found to exhibit many attractive properties as PEMs for DMFCs.In the first part, two series of sulfonated naphthalenic polyimides containing ether and ketone linkages (SPI-KK-X and SPI-K-X) were prepared by a one-pot polymerization reaction of sulfonated diamine monomers,1,4-bis[3-sodium sulfonate-4-(4-aminophenoxy)benzoyl]benzene or 4,4-bis[3-sodium sulfonate-4-aminophenoxy]benzophenone, with 4,4-diaminodiphenyl ether and 1,4,5,8-naphthalenetetracarboxylic dianhydride. The membranes cast from the resulting polymers had good thermal and oxidative stability,dimensional stability and mechanical properties. At 80℃, the proton conductivities of several samples, including SPI-KK-1, SPI-K-1 and SPI-K-2 were higher than 0.10 S/cm, which were comparable to that of Nafion. Methanol permeabilities of the obtained polymer electrolyte membranes (PEMs) were in the range of 1.43-2.03×10-7 cm2/s, which were several times lower than that of Nafion 117. It is interesting to note that the SPI-KK-X series, having a more rigid phenyl-ketone-phenyl-ketone-phenyl moiety, had a lower dimensional swelling ratio and lower methanol permeability in comparison with the corresponding SPI-K-X series at the same level of ion exchange capacity (IEC).In the second part, [1,4-bis(2-trifluoromethyl-4-amino) phenoxy -2-potassium sulfonate]benzene and [1,4-bis(4-amino) phenoxy -2- potassium sulfonate]benzene were prepared by nucleophilic substitution reaction, and then two series of sulfonated naphthalenic polyimides(CF3-SPI-X and SPI-X) were synthesized by a one-pot polymerization reaction of sulfonated diamine monomers,4,4-diaminodiphenyl ether and 1,4,5,8-naphthalenetetracarboxylic dianhydride. The membranes cast from the resulting polymers were in comparation, It is worth noting that CF3-SPI-X polymers have better dimensional stability, lower methanol permeability and better Oxidation stability then the other series.