基于辐射法的聚乙烯苄基磺酸接枝氟膜的制备及研究

Direct methanol fuel cells (DMFC) were attracting a lot of attention as the ideal power source for potable electronics such as mobile phones, digital cameras, and laptops. The polymer electrolyte membrane (PEM) was a very important part of the DMFC, which separates methanol and oxygen, while transferring protons from the cathode to the anode.Among the many polymer electrolyte membranes, Nafion® membranes with good proton conductivity, mechanical property as well as good chemical stability were widely applied to the proton exchange membrane (PEM). However, well-known problems, such as high production cost, high methanol crossover, and low operating temperature were limited the wide application of DMFC.Therefore, extensive efforts were devoted to the development of the new polymer electrolyte membranes including the modification of the Nafion® membranes, as well as some of the sulfonated hydrocarbon membranes, hybride membranes, and radiation-grafted membranes..The radiation grafting technique was known to be a very convenient and effective way in the preparation of polymer electrolyte membranes for fuel cell applications. The desired properties of membranes was readily achieved by choosing the proper grafting substrate film and monomer, and adjusting irradiation conditions, including dose, dose rate, and monomer concentration. Fluorinated polymer films including poly(tetrafluoroethylene-co-hexafluropropylene) (FEP), poly(tetrafluoroethylene-co-perfluorovinyl ether) (PFA), poly(vinylidene fluoride) (PVDF) and poly(ethylene-co-tetrafluoro-ethylene) (ETFE) with excellent thermal, chemical, and mechanical properties were commonly used as the substrate polymer films. Substituted styrene monomers including styrene and methyl substituted styrene were widely used as grafting monomers for fuel cell membrane preparation..In this study, a new polymer electrolyte, poly(vinylbenzyl sulfonic acid)-grafted poly(tetrafluoroethylene-co-hexafluoropropylene)(FEP-g-PVBSA) membrane would be prepared by simultaneous irradiation grafting of a vinylbenzyl chloride (VBC) monomer onto FEP film using γ-ray irradiation, and subsequent chemical conversion processes for the introduction of a sulfonic acid group. The sulfonic acid group of the membrane was designed to indirectly connect the benzene ring with a methylene spacer group, and this new structural change of the substitute showed a more enhanced chemical stability than the polystyrene sulfonic acid grafted FEP (FEP-g-PSSA) membranes. The physio-chemical properties, including IEC value, water and methanol uptake, methanol permeability, chemical stability, and proton conductivity of the FEP-g-PVBSA membranes for direct methanol fuel cell application would be evaluated..

直接甲醇燃料电池(DMFC)作为一种新能源，近年来倍受关注。其中的核心部件质子交换膜为质子的迁移和输送提供通道，其性能的好坏直接影响到DMFC的性能及其使用寿命。当今应用最广泛的DuPont公司开发的Nafion系列全氟型磺酸膜，由于其价格昂贵，甲醇透过率高等缺点，限制了它在DMFC领域的应用。本课题拟利用共辐射法将选取的各类共聚体、交联剂和单体乙烯基苄基氯接枝到含氟基体上，制备出交联网络结构均匀的阳离子交换膜，研究其内部结构及性能的影响。设计不同支链长度、不同支化度的分子链结构，研究不同链结构对膜性能的影响。通过对膜结构与性能的研究，阐明质子交换膜性能与其内部高分子链结构的关系；建立高阻醇、高质子导电性与化学稳定性俱佳的分子链及交联网络结构设计与性能调控的方法。本研究结果将对探索设计与制备特殊结构的高性能质子交换膜具有重要的理论意义

乙烯基苄基氯(vinylbenzyl chloride）( VBC）单体并非新型单体材料，被用做聚乙烯基苄基氯（PVBC）接枝氟膜被作为阴离子交换膜广泛应用于碱性燃料电池上。此类PVBC接枝膜具有较高的玻璃化转变温度、良好的机械性能和化学稳定性等性能。PVBC拥有反应性较强的氯基，不仅可以与碱性反应物生成已经广泛应用的碱性燃料电池用膜外，还应该可以通过磺化反应生成磺酸基，或者磷酸反应生成磷酸基，应用与燃料电池用阳离子交换膜中，然而从未有利用VBC单体制备阳离子交换膜在直接甲醇燃料电池中使用过的相关报道。因为PSSA接枝膜的化学稳定性能差，主要是因为磺酸基的对苯位置的C-H键，易受到氧攻击脱落。如果使用PVBC再经磺化处理后，得到的聚乙烯基苄基磺酸（PVBSA）中，对苯位置由苄基相连而未直接连接磺酸根，应该其抗氧化性能会高于PSSA接枝膜。有望在保持PSSA接枝膜各项性能优点的同时，提高其抗氧化性能。. 研究采用同步辐照方法，研究并讨论了制备交联聚氯乙烯/ DVB接枝薄膜的最佳接枝条件。采用适当的同步辐射诱导接枝条件，制备交联聚乙烯基苄基氯/ DVB接枝膜，最高可达12% DVB，剂量率为1 kGy/ h, VBC浓度为30%。在VBC和DVB的接枝中，发现二氯甲烷是一种较好的溶剂。辐照时间不得超过20小时，以避免凝胶和薄膜的脆性。IR和TGA 结果表明，由VBC和DVB同步辐射诱导的PVBC / DVB接枝ETFE薄膜在ETFE膜上成功制备。DVB交联剂的加入对热稳定性的影响不大。力学性能试验表明，随着DVB含量的增加，PVBC / DVB接枝膜断裂伸长率降低。本研究预计将为进一步制备交联PVBSA接枝膜及其在DMFC系统中的聚合物电解质膜的适用性作出贡献。. 研究发现，辐照剂量、剂量率、单体浓度、DVB含量等因素对接枝的程度和聚合物的性能都有明显的影响。