3 research outputs found

    Synthesis and Thermorheological Analysis of Biobased Lignin-<i>graft</i>-poly(lactide) Copolymers and Their Blends

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    Despite numerous accounts of biobased composite materials through blending and copolymerization of lignin and other polymers, there are no systematic studies connecting the synthetic methodology, molecular structure, and polymer topology with the rheological properties of these materials. In this report lignin-<i>graft</i>-poly­(lactide) copolymers are synthesized via three routes (indium and organocatalyzed “graft-from” methods as well as a “graft-to” method) and the resulting reaction products (shown to include linear PLAs, cyclic PLAs, and star-shaped lignin-<i>graft</i>-PLA copolymers) are investigated using chemical and rheological methods. The topology of the products of the graft-from methods is affected by the initial lignin concentration; polymerizations with low lignin loading generate cyclic PLAs, which can be identified by 10-fold lower viscosities compared to linear PLAs of the same molecular weight. Under higher lignin loadings, star-shaped lignin-<i>graft</i>-PLA copolymers are formed which show viscosities 2 orders of magnitude lower than those of comparable linear PLAs. Rheological studies show that cyclic PLAs lack a well-defined rubber plateau, whereas star-shaped lignin-<i>graft</i>-PLAs lack a significant <i>G</i>′ to <i>G</i>′′ cross-over. The rheological results coupled with thermogravimetric analysis give an indication to the structure of star-shaped lignin-<i>graft</i>-PLA copolymers, which are estimated to contain a small lignin core surrounded by PLA segments with molecular weights from 2.0 to 20 kg mol<sup>–1</sup>

    Free Volume Manipulation and <i>In Situ</i> Oxidative Crosslinking of Amine-Functionalized Microporous Polymer Membranes

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    Membranes for gas separations are limited by the trade-off relationship between permeability and selectivity. In this study, we demonstrate an in situ thermal oxidative crosslinking strategy for amine-functionalized polymers using tert-butoxycarbonyl (tBOC) groups to improve separation performance. The use of labile tBOC groups offers two major benefits for inducing thermal oxidative crosslinks: (1) they trigger free radical chain reactions at more moderate temperatures, preventing polymer backbone degradation pathways that otherwise occur at elevated temperatures, and (2) they enable free volume manipulation (FVM) conditions that yield increased free volume and narrower free volume element size distribution. This thermal oxidative crosslinking strategy is demonstrated using an amine-functionalized polymer of intrinsic microporosity (PIM-NH2). The resulting crosslinked polymer yielded up to a 22-fold increase in H2/CH4 selectivity while retaining 96% of H2 permeability from pristine PIM-NH2 films. By combining thermal oxidative crosslinks and FVM, we demonstrate an effective approach to overcome the traditional permeability–selectivity trade-off and offer a greater resistance to major performance stability issues like plasticization and physical aging, making membranes better suited for industrial applications

    Geometric Transformations Afforded by Rotational Freedom in Aramid Amphiphile Nanostructures

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    Molecular self-assembly in water leads to nanostructure geometries that can be tuned owing to the highly dynamic nature of amphiphiles. There is growing interest in strongly interacting amphiphiles with suppressed dynamics, as they exhibit ultrastability in extreme environments. However, such amphiphiles tend to assume a limited range of geometries upon self-assembly due to the specific spatial packing induced by their strong intermolecular interactions. To overcome this limitation while maintaining structural robustness, we incorporate rotational freedom into the aramid amphiphile molecular design by introducing a diacetylene moiety between two aramid units, resulting in diacetylene aramid amphiphiles (D-AAs). This design strategy enables rotations along the carbon–carbon sp hybridized bonds of an otherwise fixed aramid domain. We show that varying concentrations and equilibration temperatures of D-AA in water lead to self-assembly into four different nanoribbon geometries: short, extended, helical, and twisted nanoribbons, all while maintaining robust structure with thermodynamic stability. We use advanced microscopy, X-ray scattering, spectroscopic techniques, and two-dimensional (2D) NMR to understand the relationship between conformational freedom within strongly interacting amphiphiles and their self-assembly pathways
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