Fully aromatic polyimides are amenable to efficient carbonization in thin two-dimensional (2D) films due to a complement of aromaticity and planarity of backbone repeating units. However, repeating unit rigidity traditionally imposes processing limitations, restricting many fully aromatic polyimides, e.g., pyromellitic dianhydride with 4,4′-oxidianiline (PMDA-ODA) polyimides, to a 2D form factor. Recently, research efforts in our laboratories enabled additive manufacturing of micron-scale resolution PMDA-ODA polyimide objects using vat photopolymerization (VP) and ultraviolet-assisted direct ink write (UV-DIW) following careful thermal postprocessing of the three-dimensional (3D) organogel precursors to 400 °C. Further thermal postprocessing of printed objects to 1000 °C induced pyrolysis of the PMDA-ODA objects to disordered carbon. The pyrolyzed objects retained excellent geometric resolution, and Raman spectroscopy displayed characteristic disordered (D) and graphitic (G) carbon bands. Scanning electron microscopy probed the cross-sectional homogeneity of the carbonized samples, revealing an absence of pore formation during carbonization. Likewise, impedance analysis of carbonized specimens indicated only a moderate decrease in conductivity compared to thin films that were pyrolyzed using an identical carbonization process. Facile pyrolysis of PMDA-ODA objects now enables the production of carbonaceous monoliths with complex and predictable three-dimensional geometries using commercially available starting materials.
Water‐soluble polymers (WSPs) represent a diverse class of macromolecules, and this diversity arises from the breadth of functionality derived from both natural and synthetic sources. Nature provides abundant WSPs through biosynthetic pathways in plants, animals, and fungi, and biological processes yield precisely controlled and well‐defined structures. Polymer chemists strive to develop synthetic methods that mimic the precision of natural processes. Monomers that are derived from petroleum feedstocks together with naturally sourced monomers provide a rich catalog of WSP precursors. Monomer structure, reactivity, concentration, sequence control, and reaction conditions influence polymeric microstructures, solubility, and aqueous solution structure. This article provides an overview of WSP fundamentals and highlights recent advancements in natural, nonionic, ionic, associative, and high‐performance WSPs. Recent advances in the design and performance of WSPs have critically improved the technological impact of filtration processes, water purification, drilling efficiency, and pharmaceutical applications. From modulating the rheological and filtration properties to establishing novel drug delivery systems through controllable self‐assembly, WSPs represent a critical enabling field for many emerging and diverse applications. WSPs will help to address many of the emerging challenges of our times, from energy generation and storage to water availability and next‐generation life‐saving medical technologies. This article will point to the potential impacts based on fundamental structure‐property‐processing relationships.
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