Solution-processable poly(ether imide)s (PEIs) with ureidopyrimidinone (UPy) end groups were prepared by incorporating monoisocyanato-6-methylisocytosine into amineterminated PEI oligomers. After functionalization with UPy end groups, PEI with a molecular weight as low as 8 kDa (8k-PEI-UPy) can be solution-cast to form films. Tensile tests revealed that 8k-PEI-UPy had an outstanding Young's modulus higher than those of state-of-the-art high-molecular-weight commercial PEIs. The tensile strength, maximum elongation, and Young's modulus of 8k-PEI-UPy were 87.2 ± 10.8 MPa, 3.10 ± 0.39%, and (3.20 ± 0.14) × 10 3 MPa, respectively. The discovery herein significantly advances the chemistry of high-temperature PEI resins. UPybased supramolecular chemistry is an effective and general strategy to achieve outstanding mechanical properties for PEI oligomers.
High mechanical strength, thermal stability, and flame retardancy are three crucial criteria for highperformance polymers to be suitable for aerospace applications. Most polymers, however, cannot meet the three criteria simultaneously. Herein, phosphonium bromide-terminated poly(ether imide)s (PEI-PhPPh 3 Br) simultaneously possessing high mechanical strength, thermal stability, and flame retardancy were synthesized by functionalizing dianhydrideterminated poly(ether imide)s (PEI-DA) with triphenyl-4aminophenylphosphonium bromide. With the judiciously designed end group, PEI-PhPPh 3 Br exhibited excellent tensile properties, thermal stability, and flame retardancy. Importantly, PEI-PhPPh 3 Br with a molecular weight of 12 kDa [PEI-PhPPh 3 Br (12k)] showed a tensile strength of 109 ± 4 MPa and a Young's modulus of 2.75 ± 0.12 GPa, much higher than those of the noncharged PEI analogue. Additionally, PEI-PhPPh 3 Br (12k) showed outstanding flame retardancy, better than the state-of-the-art commercial PEIs, as evidenced by the high limiting oxygen index of 51% and high char yield of 60% at 980 °C. The study herein provides a highly effective strategy to simultaneously improve mechanical strength, thermal stability, and flame retardancy, which are three important properties rarely possessed by most polymers.
Block copolymer-based porous carbon fibers (PCFs) exhibit hierarchical porous structures, high surface areas, and exceptional electrochemical properties. However, the design of block copolymers for PCFs remains a challenge in advancing this type of fibrous material for energy storage applications. Herein, we have systematically synthesized a series of poly(methyl methacrylate-block-acrylonitrile) (PMMA-b-PAN) with well-controlled molecular weights and compositions to study the physical and electrochemical properties of PCFs. PCFs are synthesized via electrospinning, selfassembly, oxidation, and pyrolysis with no additives or chemical activation. By adjusting the molecular weights of polyacrylonitrile (PAN) and poly(methyl methacrylate) blocks, we have achieved tunable mesopore sizes ranging from 10.9 to 18.6 nm and specific capacitances varied from 144 to 345 F g −1 at 10 mV s −1 . Interestingly, regardless of the volume fraction of PAN, all the block copolymers produce hierarchical porous structures because of the self-assembly and cross-linking of PAN. Block copolymers with a PAN volume fraction of near 50% show the highest surface areas and gravimetric capacitances. The PCFs represent a new platform material with tunable specific surface areas, pore sizes, and electrochemical properties. This work has an immediate impact on designing block copolymers to create PCFs for applications in energy conversion and storage.
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.
The glass transition temperature, thermal degradation temperature, and complex viscosity of metal sulfonated polyetherimides decrease with an increase in metal cation size.
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