Cross-linked Sulfonated Polyether Accidentally Acyl Ketone Of Proton Exchange Membrane Preparation And Performance

Proton exchange membrane (PEM) is a key component of proton exchange membrane fuel cell (PEMFC). Non-fluorinated sulfonated polyaromatic proton exchange membranes have been extensively studied as alternative PEM of expensive perfluoro sulfonate polymer membrane (Nafion) due to their low cost and high proton conductivity. Among the alternative PEM materials, sulfonated poly(arylene ether ketone)(SPAEK) with high ion exchange capacity (IEC) makes them extensive swelling and even soluble in water, in spite of its high proton conductivity. In recent years, to further improve the membrane stability of SPAEK membrane and decrease methanol permeability, covalent crosslinking, acid-base crosslinking, and blend complex have been developed. Herein, the crosslinkable1,2-bis(4-(4-hydroxyphenoxy)phenyl) ethane-1,2-dione (BHPED) and sulfonated poly(arylether benzyl ketone)(SPEBK) were prepared via substitution reaction and polycondensation reaction, respectively. In addition, novel crosslinking method for SPEBK was developed to achieve covalent-ionically crosslinking structure. The effect of crosslinking structure on membrane properties was studied. The work includes the following aspects:(1) The difluoride benzil monomer was synthesized via the benzoin condensation and oxidation reaction using4-fluorobenzaldehyde as raw materials, and diphenolic monomer BHPED was then prepared through etherifition and demethylation reaction with the HPLC purity of99.5%and yields of91.6%. The structures of the monomer and the intermediate were confirmed by H-NMR and IR. The results showed that the condensation and oxidation reaction used for the preparation of the difluorobenzil benzoin could be carried out in a pot.(2) A series of crosslinkable SPEBKs with different ion exchange capacity and quinoxaline capacity were synsthesized by copolymerization of4,4’-biphenol (BP) with BHPED and3,3’-disulfonic acid sodium-4,4’-difluoride dibenzene methyl ketone (CBFBS). Quinoxaline-based crosslinked SPEBKs were prepared via the cyclocondensation of benzil moieties in polymer main-chain with3,3’-diaminobenzidine (DAB) to form quinoxaline groups acting as covalent and acid-base ionic crosslinking. The structures of the crosslinkable polymers were characterized by1H-NMR and IR. The crosslinking structures were confirmed through IR, thermal gravimetric analysis (TGA) and solubility test. The crosslinked membranes had the lower membrane dimensional change, lower methanol permeability and higher oxidative stability than the corresponding precursor membranes, with keeping the slightly low proton conducticity. This indicated that the crosslinking significantly improved the membrane performance and the crosslinked SPEBK membranes have potential for PEFC and DMFCs.