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Creators/Authors contains: "Gianneschi, Nathan C."

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  1. Abstract

    Here, we study the upper critical solution temperature triggered phase transition of thermally responsive poly(ethylene glycol)-block-poly(ethylene glycol) methyl ether acrylate-co-poly(ethylene glycol) phenyl ether acrylate-block-polystyrene nanoassemblies in isopropanol. To gain mechanistic insight into the organic solution-phase dynamics of the upper critical solution temperature polymer, we leverage variable temperature liquid-cell transmission electron microscopy correlated with variable temperature liquid resonant soft X-ray scattering. Heating above the upper critical solution temperature triggers a reduction in particle size and a morphological transition from a spherical core shell particle with a complex, multiphase core to a micelle with a uniform core and Gaussian polymer chains attached to the surface. These correlated solution phase methods, coupled with mass spectral validation and modeling, provide unique insight into these thermoresponsive materials. Moreover, we detail a generalizable workflow for studying complex, solution-phase nanomaterials via correlative methods.

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  2. Metal–organic nanotubes (MONTs) are 1-dimensional crystalline porous materials that are formed from ligands and metals in a manner identical to more typical 3-dimensional metal–organic frameworks (MOFs). MONTs form anisotropically in one dimension making them excellent candidates for linker engineering for control of chemical composition and spacing. A novel series of MONTs was synthesized utilizing a mixture of 1,2,4-ditriazole ligands containing both a fully protonated aryl moiety and its tetrafluorinated analog in ratios of, 0 : 1, 1 : 4, 1 : 1, 4 : 1, and 1 : 0, respectively. All MONTs were characterized by both bulk and nanoscale measurements, including SCXRD, PXRD, ssNMR and TEM, to determine the resulting co-polymer architecture (alternating, block, or statistical) and the ligand ratios in the solid materials. All characterization methods point towards statistical copolymerization of the materials in a manner analogous to 3D MOFs, all of which notably could be achieved without destructive analytical methods. 
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  3. Abstract

    Herein, phase transitions of a class of thermally-responsive polymers, namely a homopolymer, diblock, and triblock copolymer, were studied to gain mechanistic insight into nanoscale assembly dynamics via variable temperature liquid-cell transmission electron microscopy (VT-LCTEM) correlated with variable temperature small angle X-ray scattering (VT-SAXS). We study thermoresponsive poly(diethylene glycol methyl ether methacrylate) (PDEGMA)-based block copolymers and mitigate sample damage by screening electron flux and solvent conditions during LCTEM and by evaluating polymer survival viapost-mortemmatrix-assisted laser desorption/ionization imaging mass spectrometry (MALDI-IMS). Our multimodal approach, utilizing VT-LCTEM with MS validation and VT-SAXS, is generalizable across polymeric systems and can be used to directly image solvated nanoscale structures and thermally-induced transitions. Our strategy of correlating VT-SAXS with VT-LCTEM provided direct insight into transient nanoscale intermediates formed during the thermally-triggered morphological transformation of a PDEGMA-based triblock. Notably, we observed the temperature-triggered formation and slow relaxation of core-shell particles with complex microphase separation in the core by both VT-SAXS and VT-LCTEM.

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  4. Abstract

    Polymerization‐induced self‐assembly (PISA) is a powerful technique for preparing block copolymer nanostructures. Recently, efforts have been focused on applying photochemistry to promote PISA due to the mild reaction conditions, low cost, and spatiotemporal control that light confers. Despite these advantages, chain‐end degradation and long reaction times can mar the efficacy of this process. Herein, we demonstrate the use of ultrafast photoiniferter PISA to produce polymeric nanostructures. By exploiting the rapid photolysis of xanthates, near‐quantitative monomer conversion can be achieved within five minutes to prepare micelles, worms, and vesicles at various core‐chain lengths, concentrations, or molar compositions.

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