Membranes have emerged as a critical component in solving vital energy and environmental problems and are intensively explored for gas separations, water purifications, and fuel cell and battery applications. These applications demand the membranes with the capability of controlling the transport of small molecules (such as gas and water) or ions. Polymeric materials play a leading role in membrane development because of their excellent processability, low cost, and abundance, and they will remain at the core of membrane technology, as manifested through the chemistry‐processing‐structure‐performance paradigm. New polymer chemistry provides opportunities to tune polymer‐penetrant interactions to improve the separation of molecules and ions. A better understanding of control over the structure formation during self‐assembly and phase separation can lead to membranes with desired free volumes or pores. Innovation in polymer processing is critical for realizing the potentials of promising polymer chemistry and structures. This special issue highlights the role of polymer science in membrane technology applications.

Polymeric membranes are attractive for industrial gas separations due to their inherently high energy‐efficiency. However, there exists a trade‐off, i.e., polymers with high gas permeability often exhibit low gas selectivity.1, 2 A variety of strategies have been developed to molecularly engineer polymers to enhance gas separation properties to cross the upper bound. Young Moo Lee and colleagues review two approaches to effectively manipulate polymer microporosity (resulting in polymers re‐defining the permeability/selectivity trade‐off), i.e., incorporating intrinsically microporous units to form polymers with intrinsic microporosity (PIMs) and increasing chain rigidity by thermal rearrangement (TR) to enhance microporosity. Jianyong Jin and colleagues demonstrate that PIMs can be post‐modified with metalation (such as Na⁺) to improve CO₂/CH₄ and CO₂/N₂ selectivity due to the pore blocking by Na⁺ ions. Jason Bara and colleagues introduce cations in the backbones of conventional 6FDA‐based polyimides and show that the doping with ionic liquids (ILs) improves CO₂/CH₄ and CO₂/N₂ separation properties. Liyuang Deng and colleagues synthesize cross‐linked poly(ethylene glycol) (PEG) via thiol‐ene/epoxy reaction and show that the doping with ILs can improve CO₂ solubility and diffusivity and CO₂/N₂ separation properties. Chulsung Bae and colleagues graft a block copolymer of polystyrene‐b‐polybutadiene‐b‐polystyrene (SBS) using CO₂‐philic triethylene oxide (TEO) and demonstrate that increasing the TEO content improves the CO₂/gas separation properties while retaining excellent mechanical properties from the SBS.

Polymer‐based mixed matrix materials (MMMs) have been widely studied for gas separations, as they combine the unique molecular sieving ability of the fillers and excellent processability of the polymers. Bin Mu and colleagues provide an exhaustive overview of the MMMs based on metal‐organic frameworks (MOFs) for gas separations, including modeling, challenges (such as interfacial incompatibility), strategies to address them, and future outlook. Ruilan Guo and colleagues report surface modification of ZIF‐90 nanoparticles with triptycene to effectively improve their interfacial compatibility with a triptycene‐based polyimide and thus gas separation properties.

The evolvement of the polymeric gas separation membranes benefits tremendously from the urgent need of CO₂ capture, utilization, and sequestration (CCUS) from fossil fuel‐derived power plants to mitigate the CO₂ emissions to the atmosphere. With the inherently high energy‐efficiency, membrane technology is essential for CO₂/N₂ and CO₂/H₂ separations to enable economically viable CCUS.3 Yang Han and Winston Ho comprehensively review facilitated transport membranes based on amine‐containing polymers, which exhibit extremely high CO₂/N₂ and CO₂/H₂ selectivity in the presence of water vapor. Brian Long and colleagues conduct systematic studies of the effect of CO₂‐philic functional groups (such as amidoxime and ethereal side chains) on polynorbornene backbones on CO₂/N₂ separation properties. The aforementioned cross‐linked PEG doped with the ILs by Deng's group and SEBS grafted with TEO by Bae's group also shed some light on designing CO₂‐philic polymers for CO₂/N₂ separation. Haiqing Lin and colleagues examine the state‐of‐the‐art of molecularly engineered polymers for high‐temperature H₂/CO₂ separation, including chemical functionalization, cross‐linking, polymer blending, thermal treatment, and mixing with porous fillers and H₂‐sorptive nanoparticles.

Polymeric membranes have been widely used for water purification (such as desalination and wastewater treatment), but the trade‐off issue between water permeance and selectivity still remains. Janina Gaalken and Mathias Ulbricht synthesize amphiphilic poly(ethylene oxide)‐b‐poly(isopropyl methacrylate) diblock copolymers (BCPs) to produce isoporous ultrafiltration (UF) membranes using a self‐assembling nonsolvent induced phase separation (SNIPS) process. The obtained UF membranes display promising performance in overcoming permeance/selectivity trade‐off.

Putting positive charges onto UF membranes can improve their performance in treating wastewaters containing cationic dyes and heavy metal ions from the textile and printing industries. However, a direct coating of polyelectrolyte on the membrane surface can form a dense layer that reduces surface porosity. Jianxin Li and colleagues report a novel way of incorporating positively charged polyelectrolyte into UF membranes through blending charge‐functionalized polysulfone with polyethersulfone that is used for the phase inversion process. The membranes display superior separation performance in terms of rejecting cationic dyes and robustness against fouling.

Polymeric membranes have also been explored for hydrocarbon liquid separations, which are currently performed using energy‐intensive distillation processes. Chen Zhang and colleagues provide a comprehensive review of hydrocarbon separations using glassy polymers. The review compares different separation processes (including vapor separation, pervaporation, and the emerging organic solvent reverse osmosis process), surveys performances of different glassy polymers for several hydrocarbon mixtures, and highlights the significant plasticization challenges and aging for the membranes as well as the fabrication of defect‐free membranes. Finally, the review provides an outlook into the future commercialization of the membrane technology for hydrocarbon separations and formulates several specific areas of research needs.

MMMs are also evaluated for hydrocarbon liquid separations. Gongping Liu and colleagues incorporate polyhedral oligomeric silsesquioxanes (POSS) particles into polydimethylsiloxane (PDMS) membranes via cross‐linking between POSS‐containing monomer and PDMS precursors. At low loadings, the POSS can be molecularly dispersed in the PDMS. The incorporation of POSS shifts the free volume distribution of the MMMs and leads to superior pervaporation performance surpassing the upper bound for butanol/water separation.

The incorporation of molecular fillers into MMMs often leads to complex adsorption behaviors that need to be understood. Kazukiyo Nagai and colleagues develop POSS‐containing methacrylate polymers with varying POSS substituents and spacer lengths. The sorption of methanol and ethanol is dictated by the POSS moieties with a solid adsorption mechanism, unlike the conventional dissolution diffusion mechanism. As a result, the chemical nature of the substituents on the POSS has a profound impact on the sorption. For example, the polymer containing isobutyl‐substituted POSS displays endothermic mixing, which is unusual for glassy polymers.

Plasticization of polymers by penetrants is a significant challenge for organic solvent nanofiltration (OSN). Michele Galizia and colleagues report the use of in situ FTIR measurements to monitor the sorption of methanol in polybenzimidazole (PBI). Methanol forms hydrogen bonding with PBI, disrupting the hydrogen bonding network of PBI and enhancing its chain mobility. Both findings and new methodology can be valuable for the design of solvent‐resistant OSN membranes.

Last but not least, polymer‐based proton exchange membranes (PEMs) with a combination of high proton conductivity and excellent stability are critical to fuel cell applications. Jun Lin and colleagues design novel MMMs using amino‐modified halloysite nanotubes to stabilize phosphotungstic acid within the sulfonated poly(ether ether ketone). The functionalized halloysite nanotubes form strong acid‐based pairs with both the acid and the polymer matrix and improve both proton conductivity and long‐term stability.

We would like to conclude by thanking all the authors, reviewers, and editorial staff at the Journal of Polymer Science for contributing to this special issue. We hope this issue can further stimulate the interests and efforts of polymer scientists to address significant challenges in the field of membrane technology.

膜已成为解决重要的能源和环境问题的重要组成部分，并在气体分离，水净化以及燃料电池和电池应用方面进行了深入研究。这些应用要求膜具有控制小分子（例如气体和水）或离子的传输的能力。高分子材料由于其优异的可加工性，低成本和丰富性而在膜的开发中起着主导作用，并且通过化学，加工，结构，性能范式可以证明，它们仍将是膜技术的核心。新的聚合物化学为调节聚合物与渗透剂之间的相互作用提供了机会，以改善分子和离子的分离。在自组装和相分离过程中对结构形成的控制有更好的了解，可以使膜具有所需的自由体积或孔。聚合物加工方面的创新对于实现有前途的聚合物化学和结构潜力至关重要。本期专刊着重介绍了聚合物科学在膜技术应用中的作用。

聚合物膜固有的高能源效率，因此对工业气体分离具有吸引力。但是，需要权衡取舍，即具有高透气性的聚合物通常表现出较低的气体选择性。1，2已开发出各种策略来对聚合物进行分子工程处理，以增强气体分离性能，使其越过上限。Young Moo Lee及其同事回顾了有效控制聚合物微孔性的两种方法（导致聚合物重新定义了渗透率/选择性的折衷方案），即，合并固有的微孔单元以形成具有固有微孔性（PIM）的聚合物并通过增加链刚性来热重排（TR）以增强微孔性。Jianyong Jin及其同事证明了PIM可以通过金属化（例如Na ⁺）进行后修饰，以改善Na ²⁺离子对孔的阻塞，从而提高CO ₂ / CH ₄和CO ₂ / N _2的选择性。Jason Bara及其同事在传统的基于6FDA的聚酰亚胺的骨架中引入了阳离子，并证明了用离子液体（ILs）进行掺杂可以改善CO ₂ / CH ₄和CO ₂ / N _2的分离性能。邓丽媛和他的同事们通过硫醇/环氧反应合成了交联的聚乙二醇（PEG），并表明用IL掺杂可以提高CO _2的溶解度和扩散性以及CO ₂ / N _2的分离性能。Chulsung Bae及其同事使用CO _2-亲油三环氧乙烷（TEO）接枝了聚苯乙烯b-聚丁二烯b-聚苯乙烯（SBS）的嵌段共聚物，并证明增加TEO含量可改善CO ₂ /气体分离性能，同时保留出色的机械性能SBS的属性。

基于聚合物的混合基质材料（MMM）已针对气体分离进行了广泛研究，因为它们结合了填料独特的分子筛分能力和聚合物的出色加工性能。Bin Mu及其同事对用于气体分离的金属有机框架（MOF）进行了详尽的MMM概述，包括建模，挑战（例如界面不相容性），解决它们的策略以及未来前景。Guo Ruilan Guo及其同事报告了用三萜烯对ZIF-90纳米颗粒进行表面改性，以有效改善其与基于三萜烯的聚酰亚胺的界面相容性，从而改善了气体分离性能。

聚合气体分离膜的发展极大地受益于来自化石燃料发电厂的CO ₂捕获，利用和封存（CCUS）的迫切需求，以减轻向大气中的CO ₂排放。由于固有的高能效，膜技术对于实现CO ₂ / N ₂和CO ₂ / H ₂分离以实现经济可行的CCUS至关重要。3 Yang Han和Ho Winston全面回顾了基于含胺聚合物的便利运输膜，该膜具有极高的CO ₂ / N ₂和CO ₂ / H ₂在水蒸气存在下的选择性。Brian Long及其同事对聚降冰片烯主链上的CO _2-亲电官能团（如a胺肟和醚侧链）的影响对CO ₂ / N ₂分离性能进行了系统研究。前面提到的Deng's组掺杂有ILs的交联PEG和Bae's组掺杂了TEO的SEBS接枝的SEBS也为设计用于CO ₂ / N ₂分离的CO ₂亲电聚合物提供了一些启示。林海青及其同事研究了用于高温H ₂ / CO ₂的分子工程聚合物的最新技术分离，包括化学官能化，交联，聚合物共混，热处理以及与多孔填料和对H ₂吸附的纳米颗粒的混合。

聚合物膜已被广泛用于水净化（例如脱盐和废水处理），但是在水渗透率和选择性之间仍然需要权衡取舍。Janina Gaalken和Mathias Ulbricht使用自组装非溶剂诱导相分离（SNIPS）工艺合成两亲性聚环氧乙烷b聚甲基丙烯酸异丙酯二嵌段共聚物（BCP），以生产等孔超滤（UF）膜。获得的超滤膜在克服渗透率/选择性的折衷方面显示出有希望的性能。

在超滤膜上带正电荷可改善其在处理纺织和印刷行业中含有阳离子染料和重金属离子的废水中的性能。但是，在膜表面上直接涂覆聚电解质会形成致密层，从而降低表面孔隙率。李建新及其同事报告了一种通过将电荷官能化的聚砜与用于相转化过程的聚醚砜混合，将带正电荷的聚电解质掺入超滤膜的新方法。该膜在排斥阳离子染料和抗结垢方面表现出优异的分离性能。

还探索了用于碳氢化合物液体分离的聚合物膜，目前使用能量密集型蒸馏工艺进行分离。陈章和他的同事对使用玻璃状聚合物的烃分离进行了全面的综述。这篇综述比较了不同的分离工艺（包括蒸汽分离，全蒸发和新兴的有机溶剂反渗透工艺），调查了几种玻璃状聚合物对几种烃混合物的性能，并着重指出了膜的显着增塑挑战和老化以及制造工艺。无缺陷的膜。最后，该综述提供了用于烃分离的膜技术的未来商业化前景，并提出了研究需求的几个特定领域。

还对MMM进行了烃类液体分离评估。Gongping Liu及其同事通过含POSS的单体与PDMS前体之间的交联将多面体低聚倍半硅氧烷（POSS）颗粒掺入聚二甲基硅氧烷（PDMS）膜中。在低负载下，POSS可以分子分散在PDMS中。POSS的加入改变了MMM的自由体积分布，并导致优异的渗透蒸发性能，超过了丁醇/水分离的上限。

将分子填料掺入MMM中通常会导致需要理解的复杂吸附行为。Kazukiyo Nagai及其同事开发了具有不同POSS取代基和间隔长度的POSS甲基丙烯酸酯聚合物。与常规的溶解扩散机制不同，甲醇和乙醇的吸附是由具有固体吸附机制的POSS部分决定的。结果，POSS上取代基的化学性质对吸附有深远的影响。例如，含有异丁基取代的POSS的聚合物表现出吸热混合，这对于玻璃状聚合物是不常见的。

渗透剂对聚合物的增塑是有机溶剂纳米过滤（OSN）的重大挑战。Michele Galizia及其同事报告了使用原位FTIR测量来监测聚苯并咪唑（PBI）中甲醇的吸附。甲醇与PBI形成氢键，破坏PBI的氢键网络并增强其链迁移性。研究结果和新方法学对于耐溶剂OSN膜的设计都是有价值的。

最后但并非最不重要的是，具有高质子传导性和出色稳定性的聚合物基质子交换膜（PEM）对于燃料电池应用至关重要。Jun Lin及其同事使用氨基修饰的埃洛石纳米管设计了新型的MMM，以稳定磺化聚醚醚酮中的磷钨酸。功能化的埃洛石纳米管与酸和聚合物基体形成基于酸的强对，并提高了质子传导性和长期稳定性。

最后，我们要感谢《高分子科学杂志》的所有作者，审稿人和编辑人员为这一特殊问题做出的贡献。我们希望这个问题能够进一步激发聚合物科学家的兴趣和努力，以应对膜技术领域的重大挑战。