61 research outputs found

    Synthesis of 1,2,3-triazole functionalized hyperbranched poly(ethyleneimine) and its use as multifunctional anionic macroinitiator for diglycidyl ether of bisphenol A curing

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    Hyperbranched poly(ethyleneimine) (PEI) has been modified by the addition of propargyl acrylate following a Michael addition reaction. On this polymer (PEI-yne) a copper (I)-catalyzed azide alkyne cycloaddition (CuAAC) has been performed to obtain a multifunctional triazole initiator (PEI-TA). After structural and thermal characterization, this polymer has been used in different proportions as anionic multifunctional macroinitiator in diglycidyl ether of bisphenol A (DGEBA) homopolymerization. The curing process has been studied by calorimetry and the thermosets obtained have been thermally characterized and compared with thermosets prepared by using 1-methylimidazole (1-MI) as standard initiator. The electron microscopy inspection of the fracture surfaces of the new materials prepared shows the formation of submicrometer particles that should enhance toughness characteristics, changing smooth fracture surfaces in 1-MI initiated materials to multi-planar surface with tortuous and thicker cracks.Postprint (author's final draft

    Characterization of Zahari Zograph's nave wall paintings in the church "The nativity of the virgin" of Rila Monastery (Bulgaria) by vibrational spectroscopy and SEM-EDX analysis

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    An analytical study on the nave mural paintings of the church “The Nativity of the Virgin” of Rila monastery, Bulgaria, painted by Zahari Zograph was carried out. Vibrational spectroscopy was applied to identify the pigments and organic materials used in the mural paintings. To complement the spectral information, elemental composition of the samples was determined by SEM-EDX. The data showed that smalt with carbohydrate binder was applied for the blue background, green colour was executed by green earths and red-orange colour – by red lead. Azurite is the pigment used to paint the blue colour of the saints’ hoods. The mordant for gilding was prepared of drying oil, resin and siccative metal oxides as evidenced by SEM-EDX, ATR-FTIR and pyrolysis GC-MS analysis. The use of azurite is related to Zahari Zograph’s works as it was not found in any of the previously studied murals in the church painted by other artists

    A mild, efficient and catalyst-free thermoreversible ligation system based on dithiooxalates

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    We demonstrate a novel and ready to prepare thermoreversible hetero Diels–Alder dilinker on the basis of dithiooxalates, enabling the mild, rapid and catalyst-free linkage of diverse diene species under ambient conditions for applications in the fields of, for example, modular ligation, self-healing or recyclable materials and surface modification amongst others. The linker was studied using quantum chemical calculations, and experimentally in small molecular reactions via UV/Vis spectroscopy, mass spectrometry and NMR as well as in step-growth polymerizations with diene-difunctional building blocks – characterized via (temperature dependent) SEC and HT NMR – as an example for efficient polymer ligation

    Amphiphilic block copolymers featuring a reversible hetero Diels-Alder linkage

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    The present article reports the preparation of a novel class of switchable amphiphilic diblock copolymers with a temperature switchable linkage. Reversible addition fragmentation chain transfer (RAFT) polymerization was used to synthesize the individual blocks: for the preparation of the non-polar block{,} i.e. poly(isoprene-co-styrene) (P(I-co-S)) (9200 g mol-1 [less-than-or-equal] Mn [less-than-or-equal] 50 000 g mol-1{,} 1.22 [less-than-or-equal] D [less-than-or-equal] 1.36){,} a chain transfer agent (CTA{,} 3-((2-bromo-2-methylpropanoyl)oxy)propyl 2-(((dodecylthio)carbonothioyl)thio)-2-methylpropanoate) carrying a bromine group was employed{,} ready for subsequent cyclopentadienyl (Cp) transformation. For the preparation of the polar block{,} triethylene glycol methyl ether acrylate (TEGA) was polymerized (6600 g mol-1 [less-than-or-equal] Mn [less-than-or-equal] 35 000 g mol-1{,} 1.12 [less-than-or-equal] D [less-than-or-equal] 1.30) using a RAFT agent carrying a phosphoryl Z-group{,} which is able to undergo hetero Diels-Alder (HDA) ligation with Cp moieties. Both building blocks were conjugated at ambient temperature in the presence of ZnCl2 as catalyst yielding the amphiphilic block copolymer P(I-co-S)-b-PTEGA (16 000 g mol-1 [less-than-or-equal] Mn [less-than-or-equal] 68 000 g mol-1{,} 1.15 [less-than-or-equal] D [less-than-or-equal] 1.32). To investigate the bonding/debonding capability of the HDA linkage{,} high temperature nuclear magnetic resonance (HT-NMR) spectroscopy{,} high temperature dynamic light scattering (HT-DLS) and high temperature size exclusion chromatography (HT-SEC) were carried out{,} evidencing that efficiently switchable amphiphilic block copolymers were generated (>4 cycles)

    Avidin Localizations in pH-Responsive Polymersomes for Probing the Docking of Biotinylated (Macro)molecules in the Membrane and Lumen

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    To mimic organelles and cells and to construct next-generation therapeutics, asymmetric functionalization and location of proteins for artificial vesicles is thoroughly needed to emphasize the complex interplay of biological units and systems through spatially separated and spatiotemporal controlled actions, release, and communications. For the challenge of vesicle (= polymersome) construction, the membrane permeability and the location of the cargo are important key characteristics that determine their potential applications. Herein, an in situ and post loading process of avidin in pH-responsive and photo-cross-linked polymersomes is developed and characterized. First, loading efficiency, main location (inside, lumen, outside), and release of avidin under different conditions have been validated, including the pH-stable presence of avidin in polymersomes’ membrane outside and inside. This advantageous approach allows us to selectively functionalize the outer and inner membranes as well as the lumen with several bio(macro)molecules, generally suited for the construction of asymmetrically functionalized artificial organelles. In addition, a fluorescence resonance energy transfer (FRET) effect was used to study the permeability or uptake of the polymersome membrane against a broad range of biotinylated (macro)molecules (different typology, sizes, and shapes) under different conditions

    Harnessing entropy to direct the bonding/debonding of polymer systems based on reversible chemistry

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    The widely accepted approach for controlling polymer debonding/rebonding properties in responsive materials has been to purposefully engineer the functional end-groups responsible for monomer dynamic bonding. Here, however, we evidence that the debondin
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