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  1. Abstract

    Rechargeable aqueous Zn−MnO2batteries are promising for stationary energy storage because of their high energy density, safety, environmental benignity, and low cost. Conventional gravel MnO2cathodes have low electrical conductivity, slow ion (de‐)insertion, and poor cycle stability, resulting in poor recharging performance and severe capacity fading. To improve the rechargeability of MnO2, strategies have been devised such as depositing micrometer‐thick MnO2on carbon cloth and blending nanostructured MnO2with additives and binders. The low electrical conductivity of binders and sluggish ion (de‐)insertion in micrometer‐thick MnO2, however, still limit the fast‐charging performance. Herein, we have prepared porous carbon fiber (PCF) supported MnO2cathodes (PCF@MnO2), comprised of nanometer‐thick MnO2uniformly deposited on electrospun block copolymer‐derived PCF that have abundant uniform mesopores. The high electrical conductivity of PCF, fast electrochemical reactions in nanometer‐thick MnO2,and fast ion transport through porous nonwoven fibers contribute to a high rate capability at high loadings. PCF@MnO2, at a MnO2loading of 59.1 wt %, achieves a MnO2‐based specific capacity of 326 and 184 mAh g−1at a current density of 0.1 and 1.0 A g−1, respectively. Our approach of block copolymer‐based PCF as a support for zinc‐ion cathode inspires future designs of fast‐charging electrodes with other active materials.

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  2. Abstract

    High‐performance polymers have been concomitant with advanced technology for half a century. With the advancement of synthetic chemistry, the recent development of high‐performance polymers has provided superior properties and enabled wide applications. This article reviews recent research progress in aromatic high‐performance polymers. Particularly, we focus on the synthesis and processing of polyimides, as well as the application in gas separation membranes. We begin with a brief introduction to highlight important history and physiochemical characteristics of polyimides. Then, we review the various synthesis methods, followed by recent advances for improving processability. Finally, we evaluate the use of high‐performance polymers in gas separation membranes with focus given to the key issues of plasticization and aging. Overall, the information presented herein provides an up‐to‐date overview of high‐performance polymers, polyimides particularly, and serves as a guide for further research involving the applications in membrane technologies.

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  3. Abstract

    Poly(ether imide) (PEI) from polycondensation of 2,2‐bis[4‐(3,4‐dicarboxyphenoxy) phenyl] propane dianhydride (BPADA) andm‐phenylenediamine (mPD) is a type of high‐temperature engineering thermoplastics that have high glass transition temperature and outstanding mechanical properties. Owing to its wide use in many fields including automotive, aircraft, and electronics, the research of PEI has surged in the last few decades. As science and technology continue to progress rapidly, there is a growing demand for PEIs with better properties. Although a few approaches have successfully improved the properties of PEI, it is recognized that these approaches require complex procedures and are uneconomical. Contrastingly, end‐group modification of PEI is highly effective, simple, and economical. Over the last few years, our group has extensively studied the methods for improving the properties of PEI through end‐group modification. The end‐group moieties and polymer blocks introduce multiple hydrogen bonding, electrostatics, and microphase separation to PEI. In this article, we first classify the end groups based on their characteristics. Then, we compare their effects on the properties of PEIs, including thermal, rheological, mechanical, optical, flame‐retardant, and morphological, and discuss the roots of these effects. The in‐depth comparisons and discussion generate principles to guide the synthesis of PEIs with tailored properties by modifying the end groups. This timely article will provide insights into the synthesis of other novel high‐temperature polymers and entice endeavors to develop novel end groups.

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  4. Abstract

    Graphene holds promise for thin, ultralightweight, and high‐performance nanoelectromechanical transducers. However, graphene‐only devices are limited in size due to fatigue and fracture of suspended graphene membranes. Here, a lightweight, flexible, transparent, and conductive bilayer composite of polyetherimide and single‐layer graphene is prepared and suspended on the centimeter scale with an unprecedentedly high aspect ratio of 105. The coupling of the two components leads to mutual reinforcement and creates an ultrastrong membrane that supports 30 000 times its own weight. Upon electromechanical actuation, the membrane pushes a massive amount of air and generates high‐quality acoustic sound. The energy efficiency is10–100 times better than state‐of‐the‐art electrodynamic speakers. The bilayer membrane's combined properties of electrical conductivity, mechanical strength, optical transparency, thermal stability, and chemical resistance will promote applications in electronics, mechanics, and optics.

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    Ternary block copolymer (BCP)‐homopolymer (HP) blends offer a simple method for tuning nanostructure sizes to meet application‐specific demands. Comprehensive dissipative particle dynamic (DPD) simulations were performed to study the impact of polymer interactions, molecular weight, and HP volume fraction (φHP) on symmetric ternary blend morphological stability and domain spacing. DPD reproduces key features of the experimental phase diagram, including lamellar domain swelling with increasingφHP, the formation of an asymmetric bicontinuous microemulsion at a critical HP concentration , and macrophase separation with further HP addition. Simulation results matched experimental values for and lamellar swelling as a function of HP to BCP chain length ratio,α = NHP/NBCP. Structural analysis of blends with fixedφHPbut varyingαconfirmed that ternary blends follow the wet/dry brush model of domain swelling with the miscibility of HPs and BCPs depending onα. Longer HPs concentrate in the center of domains, boosting their swelling efficiencies compared to shorter chains. These results advance our understanding of BCP‐HP blend phase behavior and demonstrate the value of DPD for studying polymeric blends. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys.2019,57, 794–803

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  6. Plastic waste represents one of the most urgent environmental challenges facing humankind. Upcycling has been proposed to solve the low profitability and high market sensitivity of known recycling methods. Existing upcycling methods operate under energy-intense conditions and use precious-metal catalysts, but produce low-value oligomers, monomers, and common aromatics. Herein, we report a tandem degradation-upcycling strategy to exploit high-value chemicals from polystyrene (PS) waste with high selectivity. We first degrade PS waste to aromatics using ultraviolet (UV) light and then valorize the intermediate to diphenylmethane. Low-cost AlCl 3 catalyzes both the reactions of degradation and upcycling at ambient temperatures under atmospheric pressure. The degraded intermediates can advantageously serve as solvents for processing the solid plastic wastes, forming a self-sustainable circuitry. The low-value-input and high-value-output approach is thus substantially more sustainable and economically viable than conventional thermal processes, which operate at high-temperature, high-pressure conditions and use precious-metal catalysts, but produce low-value oligomers, monomers, and common aromatics. The cascade strategy is resilient to impurities from plastic waste streams and is generalizable to other high-value chemicals (e.g., benzophenone, 1,2-diphenylethane, and 4-phenyl-4-oxo butyric acid). The upcycling to diphenylmethane was tested at 1-kg laboratory scale and attested by industrial-scale techno-economic analysis, demonstrating sustainability and economic viability without government subsidies or tax credits. 
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