后官能化工艺制备侧链离子结构的部分氟化阴离子交换膜

Preparation of Partly Fluorinated Anion Exchange Membranes with Side Chain Ionic Groups via a Post-functionalization Process

以十氟联苯、双酚A低温聚合制备可高温官能化的聚合物主链,以3,5-二甲基苯酚为功能侧链,采用后官能化工艺制备了系列不同离子交换容量(IEC)值的含侧链苄基季铵基团的部分氟化阴离子交换膜.用GPC、1H-NMR、19F-NMR、IR、SASX等表征了膜的分子结构及聚集态结构,并且测试了膜的各种性能.结果表明,该系列部分氟化阴离子交换膜的分子主链线性好,官能度可控,具有明显的微相分离结构.部分氟化结构和微相分离的侧链离子结构极大的改善了膜的吸水溶胀性、电导率和化学稳定性.QFPAE-95膜具有最高的氢氧根离子电导率和适度吸水溶胀性,80oC时离子电导率和溶胀比分别达到108.6 m S cm-1和42.6%.QFPAE-55具有最大的拉伸强度,达到21.01 MPa.该系列膜还具有出色的碱稳定性,QFPAE-55膜在1 mol/L Na OH溶液中于60oC下浸泡20天后,其电导率和IEC值分别保持为原膜的82.3%和84.2%,有望作为新型阴离子交换膜并应用于碱性膜燃料电池.

Controlled polycondensation of decafluorobiphenyl and bisphenol A at low temperature gave a highly linear polymer with its main chain consisting of octafluoro benzene moiety, which acted as grafting reaction position for post-functionalization at higher temperature. 3,5-dimethylphenol grafted onto the main chain of the mother polymer by partial elimination of the fluorine atoms in the octafluoro benzene moiety to form the ionomers precursor with side chain benzyl groups. The precursor transformed then into a series of partly fluorinated anion exchange membranes containing side chain benzyl quaternary ammonium groups with varying IEC values by bromination and quaternization. The participation of the ortho- and meta-fluorine atoms to the polycondensation, leading to the cross linking gelation, was successfully avoided through this method. Moreover, the method could achieve the controllable degree of functionalization by controlling the feed ratio of NBS to the benzyl groups in the precursor polymer. In addition, two benzyl groups on the side chains could be brominated and quaternized to form local domains of high density ionization, which could form ion clusters of microphase separation to increase the ion conductivity. The molecular structure and aggregation structure of the membranes were characterized by GPC, 1H-NMR, 19F-NMR, IR and SASX. The results confirmed that the precursor polymer of the partly fluorinated anion exchange membranes had a linear skeleton, adjustable functionality and the obtained membranes showed obvious microphase separation aggregation morphology. The results of the property evaluation indicated that the swelling ratio, ion conductivity and alkaline stability were greatly improved by the designed structure of the partly fluorinated main chain and the aromatic side chain ionic group. QFPAE-95 had the highest ion conductivity and appropriate swelling ratio with the values of 108.6 mS cm-1 and 42.6% at 80 ℃ respectively. QFPAE-55 possessed the highest tensile strength of 21.01 MPa. Moreover, the series of membranes also showed excellent alkaline stability. The ion conductivity and IEC value of QFPAE-55 remained 82.3% and 84.2% of the values in the original membrane after being immersed into 1 mol/L NaOH solution at 60 ℃ for 20 days. The membranes are promising anion exchange membranes for alkaline fuel cells.