We have succeeded in developing a new methodology for proton exchange membrane (PEM) of direct methanol fuel cell (DMFC), which stemmed formation of a crosslinking structure by UV irradiation to sulfonated poly (aryl ether ketone) (PAEK) copolymer. A new class of the aromatic PAEKs with pendant sulfonate groups and methyl groups have been prepared by a direct aromatic nucleophilic substitution polycondensation reaction of 3,3 0 -disulfonated-4,4 0 -difluorobenzophenone (DSDFBP), 4,4 0 -difluorobenzophenone (DFBP) and the biphenols that have methyl groups. The polymerization quantitatively proceeded to form a high intrinsic viscosity of copolymer. Membranes having high mechanical strength were successfully obtained from the copolymers of DSDFBP, DFBP and the biphenols that have methyl groups including tetramethyl bisphenol A (TMBPA), tetramethyl bisphenol F (TMBPF) and tetramethyl biphenol (TMBP). The ketone of benzophenone group and the methyl group in the repeating structure unit of these PAEKs were easily crosslinked by UV irradiation and induced a crosslinked structure that improved their methanol blocking properties drastically. The membrane of crosslinking copolymer, DSDFBP/DFBP/TMBPF = 5/5/10 mole ratio (F1), was stable at 240 C in air and showed the high proton conductivity at 90 C of 0.23 S/cm and the low methanol permeation rate at 25 C of 5.5 mmol/cm 2 /min. This proton conductivity and methanol permeability are comparable to and half of the values of fluorinated copolymer Nafion112 Ò that is known as the representative material of a PEM of DMFC respectively. These new copolymers, which have proton conductive sites and crosslinking structures, are candidates as new polymeric electrolyte materials for proton exchange membrane fuel cells, especially for DMFCs. The large interest in using polymer electrolyte membrane fuel cells (PEMFCs) as power sources of vehicles or portable applications has been greatly promoted these years. Among many kinds of PEMFCs, direct methanol fuel cells (DMFCs) are promising candidates for portable power sources and transport applications because they don't require fuel process equipment (such as reformers or catalytic burners) and can be operated at room temperature.A DMFC consists of a proton exchange membrane (PEM) sandwiched between an anode and a cathode. The PEM for DMFC requires three major functions, as a proton conductor, as a fuel barrier and as a mechanical separator between the two electrodes. Nafion Ò that is known as a superior membrane for PEMFC has high proton conductivity and suitable mechanical strength. However, methanol goes through the Nafion Ò membrane, so that a large amount of methanol is lost in the DMFC. This is so-called ''methanol crossover.'' To improve DMFC performance, the high methanol blocking property is required while the proton conductivity, the thermo oxidation stability and the mechanical strength are maintained. Methanol permeates through the ionic channels of membranes and the size of these channels increases as swelling of the membrane ...
