Ionic Polyimides: Hybrid Polymer Architectures and Composites with Ionic Liquids for Advanced Gas Separation Membranes
Ionic Polyimides: Hybrid Polymer Architectures and Composites with Ionic Liquids for Advanced Gas Separation Membranes
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DOI：
10.1021/acs.iecr.7b00462
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发表时间：
2017-05-03
影响因子：
4.2
通讯作者：
Daly, Daniel T.
中科院分区：
文献类型：
--
作者：
Mittenthal, Max S.;Flowers, Brian S.;Daly, Daniel T.
聚酰亚胺和离子液体（IL）是作为气体分离膜被广泛研究的两类材料，每种材料都表现出各自的优点和局限性。聚酰亚胺和离子液体都可以根据所需前体的选择进行改性/功能化。然而，只有少数报告考虑如何整合聚酰亚胺和离子液体以获得具有协同性能的全新材料。在这份手稿中，我们展示了一种新的多功能方法来合成聚酰亚胺，咪唑鎓阳离子直接位于聚合物主链内，形成聚酰亚胺杂化物或离子聚酰亚胺。我们合成离子聚酰亚胺的策略不需要使用氨基功能化的离子液体。相反，酰亚胺化反应在形成咪唑官能化二酰亚胺单体的聚合之前发生。然后，该单体通过逐步增长（缩合）聚合与对二氯二甲苯通过 Menshutkin 反应进行反应，同时连接单体并产生离子组分。所得离子聚酰亚胺适合热处理（例如挤出、熔压）并且能够形成薄膜。将离子型聚酰亚胺薄膜浸泡在广泛使用的 IL 1-丁基-3-甲基咪唑鎓双三氟甲酰亚胺 ([C4mim][Tf2N]) 中后，观察到 IL 化学计量吸收到离子型聚酰亚胺中，形成离子型聚酰亚胺 + IL 复合材料。研究了离子型聚酰亚胺和离子型聚酰亚胺+IL复合膜对CO2、N-2、CH4和H-2的气体分离性能。纯离子聚酰亚胺对 CO2 和 H2 表现出低渗透性（分别接近 0.9 巴和 1.6 巴），对 N2 和 CH4 表现出非常低的渗透性（两者都接近 0.03 巴）。对于离子型聚酰亚胺+IL复合材料，CO2、N-2和CH4的渗透率增加了18002700%，而H-2渗透率仅增加了大约200%。 CO2、N-2 和 CH4 渗透性的大幅增加是由于气体在材料中的扩散率大大增加，而气体溶解度在离子液体存在时基本没有变化。使用多种技术对离子聚酰亚胺和离子聚酰亚胺 + IL 复合材料进行了表征。最有趣的是，薄膜的 X 射线衍射 (XRD) 显示离子聚酰亚胺 + IL 复合材料显示出尖锐的峰，表明离子聚酰亚胺可能在 IL 周围发生超分子组装。尽管这些首个离子聚酰亚胺和离子聚酰亚胺+IL复合膜的性能未达到Robesons上限，但这项工作提供了坚实的基础，在此基础上可以开发具有更复杂结构元素的离子聚酰亚胺材料，以了解离子聚酰亚胺平台背后的结构性能关系，并最终生产高性能气体分离膜。
Polyimides and ionic liquids (ILs) are two classes of materials that have been widely studied as gas separation membranes, each demonstrating respective advantages and limitations. Both polyimides and ILs are amenable to modification/functionalization based on selection of the requisite precursors. However, there have been but a handful of reports considering how polyimides and ILs could be integrated to obtain fundamentally new materials with synergistic properties. In this manuscript, we demonstrate a new and versatile way to synthesize polyimides with imidazolium cations directly located within the polymer backbone to form polyimideionene hybrids, or ionic polyimides. Our strategy for synthesizing ionic polyimides does not require the use of amino-functionalized ILs. Instead, the imidization reaction occurs prior to polymerization in the formation of an imidazole-functionalized diimide monomer. This monomer is then reacted via step-growth (condensation) polymerization with p-dichloroxylene via Menshutkin reactions, simultaneously linking the monomers and creating the ionic components. The resultant ionic polyimide is amenable to thermal processing (e.g., extrusion, melt-pressing) and capable of forming thin films. Upon soaking thin films of the ionic polyimide in a widely used IL, 1-butyl-3-methylimidazolium bistriflimide ([C4mim][Tf2N]), a stoichiometric absorption of the IL into the ionic polyimide was observed, forming an ionic polyimide + IL composite. The gas separation performances of ionic polyimide and ionic polyimide + IL composite membranes were studied with respect to CO2, N-2, CH4, and H-2. The neat ionic polyimide exhibits low permeability to CO2 and H2 (similar to 0.9 and similar to 1.6 barrers, respectively) and very low permeability to N2 and CH4 (similar to 0.03 barrers for both). For the ionic polyimide + IL composite, the permeabilities of CO2, N-2, and CH4 increase by 18002700%, while H-2 permeability only increased by similar to 200%. The large increases in permeability for CO2, N-2, and CH4 are due to greatly increased gas diffusivity through the material, with gas solubility essentially unchanged with the IL present. The ionic polyimide and ionic polyimide + IL composite were characterized using a number of techniques. Most interestingly, X-ray diffractometry (XRD) of the films reveals that the ionic polyimide + IL composite displays a sharp peak, indicating that the ionic polyimide may experience supramolecular assembly around the IL. Although the performances of these first ionic polyimide and ionic polyimide + IL composite membranes fall short of Robesons Upper Bounds, this work provides a strong foundation on which ionic polyimide materials with more sophisticated structural elements can be developed to understand the structureproperty relationships underlying the ionic polyimide platform and ultimately produce high-performance gas separation membranes.