Synthesis And Properties Of Photosensitive Sulfonated Poly(Aryl Ether Ketone)s Used As Pronton Exchange Membrane

Proton exchange membrane (PEM) is a key part of the PEMFC system and it directly determines the performance of PEMFC. At present, commercialized PEM are mainly perfluorosulfonie acids PEMs, but it can't be widely used because of some drawbacks, such as the high cost material, low proton conductivity in low humidity and high temperature, high permeability of methanol, etc. Sulfonaed poly (aryl ether ketenes) is a kind of PEM material with the chief advantages of low cost, high thermal stability and high proton conductivity, and it is hopeful to replace perfluorosulfonie acid PEMs used in PEMFC. However, Sulfonaed poly(aryl ether ketone)s with high degree of sulfonation(DS) were restricted in practical application for its poor properties containing dimensional stability, oxidation stability, hydrolysis stability and mechanical property. In order to overcome this problem, preparing the crosslinked Sulfonaed poly(aryl ether ketone)s is a well-proven method.In this article, sulfonated 4,4'-difluirobenzophenone (SDFK) was prepared by sulfonation of 4,4'-difluirobenzophenone using 50% fuming sulfuric acid, and the purity of SDFK was up to 98.8% after 4 times recrystallization. Then, we synthesized the three DS, UV-crosslinkable and photosensitive sulfonaed poly (aryl ether ketenes) (SPAEKs) by using the way of copolycondensation,in which 4,4'-dihydroxylchalcone, SDFK and decafluorobiphenyl (DFBP) were using as monomers. The chemical structures of resulted polymers were characterized by 1H-NMR and FT-IR and the molecular weight was characterized by logarithmic viscosity number. The effects of different water separation in polymers viscosity were also compared, and the result indicated that water separation in low temperature and under vacuum was better than in high temperature and under normal pressure.The SPAEKs proton exchange membranes were produced by solution cast and the crosslinked membranes could be gained by UV light radiating the SPAEKs membrane. The photosensitivity and thermal atability of SPAEKs were tested by UV-Vis spectrum,XPS, and TG,DSC. SPAEKs had good photosensitivity, the photo-reaction rate of >C=C< in chalcone group was fast and the maximum degree of >C=C< photo-cyclization was up to about 70%. In the XPS spectrum, the conjugated structures of chalcone was correspondence to the two small peaks located in high energy extremity of C1s peak, and these peaks will disappear after the membranes were UV light radiation 15minute, which further confirmed the >C=C< in chalcone structure have been photo-crossliked under UV light radiation. SPAEKs also have high thermal stability, the first decomposition temperature of polymer membrane before and after crosslinking in acid form were between 240-259°C, the glass transition temperature (Tg) of polymer films in sodium salt form were 178-183oC.The physical and chemical properties, electrical properties of PEM were tested respectively, including solubility, mechanical property, ion exchange capacity (IEC), water uptake, swelling ratio, oxidation and hydrolysis stability, and proton conductivity and so on. The results show that the proton conductivity of SPAEKs with DS≥0.8 was above 0.097S/cm, which was higher than Nafion?117. Although the proton conductivities of crosslinked PEM decreased in some extent, theσvalue was also higher than Nafion?117. In addition, the comprehensive properties of PEM were improved by crosslnking, especially in dimensional stability, mechanical property, oxidation stability and hydrolysis stability.