2,6-Bis(4-azidobenzylidene)-4-methylcyclohexanone（Cas 5284-79-7 ）Cross-Linked Membranes Fuel Cell Applications

 Novel aromatic polyethers bearing polar pyridine units along the main chain and side cross-linkable propenyl groups have been successfully synthesized. Their properties relating to their ability to be used as polymer electrolyte membranes for high temperature fuel cell applications, were thoroughly investigated. Cross-linked membranes were obtained by thermal curing of the cross-linkable polymers with the use of a bisazide as the cross-linking agent. The glass transition temperatures of the cross-linked membranes were determined by dynamic mechanical analysis and found to be higher compared to the neat polymers proving the successful cross-linked network. The doping ability in phosphoric acid and the proton conductivity of the cross-linked membranes were higher compared to the noncross-linked analogues. Finally, membrane electrode assemblies (MEAs) were constructed and tested in a single cell at temperatures between 180 and 220 ℃. The superior performance of the cross-linkedmembranes in combination with the operating stability at 200 ℃ for 48 h demonstrate the potential use of these materials as electrolytes for high temperature PEM fuel cells。

1、Synthesis of Copolymers P[Py(x)-Prο(y)/SO2]

To a degassed flask equipped with a Dean_Stark trap were added a mixture of bis(4-fluorophenyl) sulfone (1.000 g, 3.93 mmol), 2,5-bis(4-hydroxyphenyl)pyridine (0.8272 g, 3.14 mmol), 2,2’-diallyl bisphenol A (0.2426 g, 0.78 mmol), K2CO3 (0.6269 g, 4.56 mmol), toluene(5.0 mL), and DMSO (15.0 mL). The mixture was degassed under argon and stirred at 140 ℃ for 16 h. After distilling off the azeotropic mixture of the formed water with toluene, the temperature was gradually raised at 180 ℃ for 6 h. The viscous solution was poured into methanol to precipitate out the polymer, filtered off, stirred in water at 60℃ , and dried at 80 ℃ under vacuum for 24 h. The results are summarized in Table 1.

2、Synthesis of Copolymers P[Py(x)-Prο(y)/PO].

The same procedure was followed for the synthesis of copolymers P[Py(x)-

Pro(y)/PO] using bis(4-fluorophenyl)phenylphosphine oxide as the difluoride reagent instead of bis(4-fluorophenyl) sulfone. (Scheme 1). A mixture of bis(4-fluorophenyl)phenylphosphine oxide (1.000 g, 3.18 mmol), 2,5-bis(4-hydroxy-phenyl) pyridine (0.6698 g, 2.54 mmol), 2,2’-diallylbisphenol A (0.1964 g, 0.63 mmol), K2CO3 (0.5098 g, 3.69 mmol),toluene (5.0 mL) and DMSO (15.0 mL) was stirred at 140 ℃ for 16 h and at 180℃  for 8 h. The viscous solution was precipitated in methanol,filtered off, stirred in water at 60 ℃, and dried at 80℃ under vacuum for 24 h. The results are summarized in Table 1.

3、Fabrication of the Cross-Linked Membranes

The dried polymers were dissolved in dimethylacetamide (DMAc) at a 3 wt % concentration, at room temperature. In this solution different amounts of the commercially available bisazide 2,6-bis(4-azidobenzylidene)-4-methylcyclohexanone, which was used as the cross-linking agent, were added as seen in Table 2. The chemical structures of the cross-linked membranes are represented in Scheme 2. The mixture was then filtered and the membranes were obtained using the solution-casting method where the solvent was left to evaporate at 140 ℃ for 24 h and then the temperature was elevated at 200℃ for 5 more hours to complete the cross-linking procedure. The obtained films were then dried under vacuum at 160℃ for 3 days. For comparison, membranes of the neat polymers were fabricated in the same method without the addition of the cross-linking agent.