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What are the most significant results of this study? This work revealed that tuning cross-link chemistry and densities can significantly improveC O 2 permeability and CO 2 /N 2 se-lectivity of polydimethylsiloxane (PDMS)m embranes.I nsitu ring-opening metathesis polymerization of PDMS macromono-mers allowed preparation of lightly cross-linked PDMS-norbor-nene membranes, which showed excellent CO 2 permeability and CO 2 /N 2 selectivity,r oughly af actor of two improvement over the well-studied conventional cross-linked PDMS. This finding can open an ew approach to enhance performance for gas separation and could elucidate additional factorsf or the gas separation mechanismsi nr ubbery polymers. Moreover, our highest performing membrane (if thickness of 1 mmo rl ess is achieved)s hould meet CO 2 capturec ost targets, potentially used in industrial CO 2 separation.

One of the key design components of nature is the utilization of hierarchical arrangements to fabricate materials with outstanding mechanical properties. Employing the concept of hierarchy, a new class of segmented polyurethane/ureas (PUUs) was synthesized containing either a peptidic, triblock soft segment, or an amorphous, nonpeptidic homoblock block soft segment with either an amorphous or a crystalline hard segment to investigate the effects of bioinspired, multiple levels of organization on thermal and mechanical properties. The peptidic soft segment was composed of poly(benzyl-l-glutamate)-block-poly(dimethylsiloxane)-block-poly(benzyl-l-glutamate) (PBLG-b-PDMS-b-PBLG), restricted to the β-sheet conformation by limiting the peptide segment length to <10 residues, whereas the amorphous soft segment was poly(dimethylsiloxane) (PDMS). The hard segment consisted of either 1,6-hexamethylene diisocyanate (crystalline) or isophorone diisocyanate (amorphous) and chain extended with 1,4-butanediol. Thermal and morphological characterization indicated microphase separation in these hierarchically assembled PUUs; furthermore, inclusion of the peptidic segment significantly increased the average long spacing between domains, whereas the peptide domain retained its β-sheet conformation regardless of the hard segment chemistry. Mechanical analysis revealed an enhanced dynamic modulus for the peptidic polymers over a broader temperature range as compared with the nonpeptidic PUUs as well as an over three-fold increase in tensile modulus. However, the elongation-at-break was dramatically reduced, which was attributed to a shift from a flexible, continuous domain morphology to a rigid, continuous matrix in which the peptide, in conjunction with the hard segment, acts as a stiff reinforcing element.

Poly(acrylamidoxime)-based fibers bearing random mixtures of carboxylate and amidoxime groups are the most widely utilized materials for extracting uranium from seawater. However, the competition between uranyl (UO2(2+)) and vanadium ions poses a significant challenge to the industrial mining of uranium from seawater using the current generation of adsorbents. To design more selective adsorbents, a detailed understanding of how major competing ions interact with carboxylate and amidoxime ligands is required. In this work, we employ density functional theory (DFT) and wave-function methods to investigate potential binding motifs of the dioxovanadium ion, VO2(+), with water, formate, and formamidoximate ligands. Employing higher level of theory calculations (CCSD(T)) resolve the existing controversy between the experimental results and previous DFT calculations for the structure of the hydrated VO2(+) ion. Consistent with the EXAFS data, CCSD(T) calculations predict higher stability of the distorted octahedral geometry of VO2(+)(H2O)4 compared to the five-coordinate complex with a single water molecule in the second hydration shell, while all seven tested DFT methods yield the reverse stability of the two conformations. Analysis of the relative stabilities of formate-VO2(+) complexes indicates that both monodentate and bidentate forms may coexist in thermodynamic equilibrium in solution. Investigations of VO2(+) coordination with the formamidoximate anion has revealed the existence of seven possible binding motifs, four of which are within ∼4.0 kcal mol(-1) of each other. Calculations establish that the most stable binding motif entails the coordination of oxime oxygen and amide nitrogen atoms via a tautomeric rearrangement of amidoxime to imino hydroxylamine. The difference in the most stable VO2(+) and UO2(2+) binding conformation has important implications for the design of more selective UO2(2+) ligands.

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A novel ligand-functionalized adsorbent material was prepared using a combination of radiation-induced graft polymerization (RIGP) and click chemistry (1,3 cycloaddition reaction). The design of the ligand-containing amidoxime functionality is based on its chelating efficiency with uranium. In this process, RIGP is used to graft polymer chains on fiber substrates, where the fibers are prepared by irradiating and treating polyethylene (PE) with different bulk ratios of vinyl benzyl chloride and acrylic acid or itaconic acid. Furthermore, chemical modifications of these fibers are performed using a two-step process, where novel bisimidoxime ligands are incorporated into fibers. These ligands contain imidedioxime, which is known to be a uranophile. Also, the core structure of the ligand containing three donor atoms facilitates the formation of chelate with uranyl ion in media such as seawater. Density functional theory calculations were performed to quantify the binding strength with the uranyl ion. When tested with simulated seawater with a uranium concentration of 6 ppm at pH 8.0−8.3, the developed materials showed moderate to high uranium (∼35−50 g U/kg adsorbent) adsorption capacity.

The morphology and chain packing structures in block copolymers strongly impact their mechanical response; therefore, to design and develop high performance materials that utilize block copolymers, it is imperative to have an understanding of their self-assembly behavior. In this research, we utilize coarse-grained (CG) molecular dynamics to study the effects of peptidic volume fraction and secondary structure on the morphological development and chain assembly of the triblocks poly(γ-benzyl-L-glutamate)-b-poly(dimethylsiloxane)-b-poly(γ-benzyl-L-glutamate) (GSG) and poly(dimethylsiloxane)-b-poly(γ-benzyl-L-glutamate)-b-poly(dimethylsiloxane) (SGS). This necessitated developing a complete coarse-grained parameter set for poly(dimethylsiloxane) that closely captures the radial pair distribution of a united atom model and the experimental density at 300 K. These parameters are combined with the MARTINI amino acid CG force field and validated against prior reported values of domain spacing and peptide chain packing for GSG. The combined CG parameter set is then used to model SGS, a triblock currently in development for nature-inspired mechanically enhanced hybrid materials. The results reveal that the peptide side chain strongly influences the final morphology. For instance, lamellar or hexagonally packed cylindrical domain formation can result from the variation in side-chain interactions, namely, side-chain sterics preventing curved interface formation by increasing interfacial free volume. Ultimately, this research lays the foundation for future studies involving systems with dispersity, mixtures of secondary structures, and larger multiblock copolymers, such as polyurethanes and polyureas.

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