| The anion exchange membrane(AEM) is the key component of anion exchange membrane fuel cells(AEMFC), which directly affects the performance of the fuel cells. Poly(arylene ether sulfone) is a kind of anion exchange membrane material with low cost and high thermal stability, however, the practical application of this material is limited because of its low ionic conductivity and poor stability under alkaline condition. It has been proved effective to overcome these two shortcomings through crosslinking or forming block copolymers.In this study, we synthesized 2,2'-Bimethylaminemethylene-4,4'-dihydroxy diphenyl ether(DABPE)and 4,4'-Dihydroxy chalcone ketones(4DHC)monomers by Mannich reaction and ultrasonic technology respectively. By controlling the ratio of the monomers, we synthesized hydrophilic oligomers containing tertiary amino groups with repeat unit number of 8, 11, 15, and hydrophobic oligomers containing chalcone with repeat unit number of 11 respectively. Then the photosensitive poly(arylene ether sulfone) block copolymers(PSTNPSF-x-y, where x and y denotes the number of repeat units in the hydrophilic and hydrophobic blocks, respectively) were synthesized by condensation reaction between the two oligomers. The structures of monomers and polymers were characterized by 1H-NMR and FT-IR.The PSTNPSF-x-y polymers possess excellent photosensitivity. The UV-vis spectra showed an absorption maximum at 324 nm. The [2+2] cyclization reaction occurred between the molecular chains to form a crosslinked structure under UV irradiation at room temperature, and the maximum crosslinking degree reached 73%. The block copolymers showed good solubility in common aprotic solvents such as DMAc, NMP, however, after crosslinking, they were insoluble in all of these solvents. The membrane also demonstrated good thermal performance. The initial decomposition temperature of the crosslinked as well as the non-crosslinked polymers was within the range of 205~210?.After reacting with quaternary ammonium, quaternized membrane was obtained by solution casting; then the PSTNPSF-x-y anion-exchange membrane was obtained through alkalination. The quaternized membrane was exposed to UV irradiation in swollen state for a certain amount of time at room temperature to fabricate the crosslinked block poly(arylene ether sulfone) anion-exchange membrane(c QPSTNPSF-x-y). The surface structure of the membrane was compact and the distribution of quaternary ammonium salt was uniform.The ion exchange capacity(IEC)- the IECW and IECV values- of the QPSTNPSF-x-y membrane were in the range of 1.15~1. 45 mmol g-1 and 1.67~2.36 mmol cm-3 respectively. The water absorption, swelling ratio and hydration coefficient of the membrane were tested, and the results showed that the crosslinked film had good dimensional stability. The c QPSTNPSF-x-y anion-exchange membranes remained intact and the IEC values showed almost no change after being soaked in 2M Na OH solution under 50?for 96 h, exhibiting excellent alkaline stability.The ionic conductivity of the QPSTNPSF-x-y membrane was in the range of 11.04~26.45 m S cm-1 at room temperature. It increased with the increase of temperature, with a maximum of 208.73 m S cm-1 at 100 ?; However, the conductivity of the crosslinked membrane(c QPSTNPSF-x-y) decreased slightly. The QPSTNPSF-x-y membrane showed excellent methanol-resistance performance. The methanol permeability was around 0.6576~3.310×10-7cm-2s-1 at room temperature, much lower than that of the Nafion117 proton exchange membrane. The results demonstrate that this series of QPSTNPSF-x-y anion-exchange membranes have excellent comprehensive performance, and hold great promise for application in anion-exchange membrane fuel cells. |
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