Koschek, Katharina
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Item type:Publication, Multifunctional hyperbranched prepolymers with tailored degree of methylation and methacrylation(Elsevier, 2023-05-16); ; ; ; A synthesis approach for multifunctional crosslinkable hyperbranched prepolymers with tailored degree of methylation and methacrylation with full conversion of all hydroxyl groups was investigated. Prepared by catalyzed esterification various methacrylate substitution degrees could be adjusted using predefined partially methylated polyglycerol-based precursors. The combination of methacrylic anhydride, triethylamine and 4-dimethylaminopyridine was proven to be beneficial for the esterification and full conversion of the remaining primary as well as secondary hydroxyl groups. NMR, IR and Raman spectroscopy were used to prove the insertion of methacrylic crosslinking groups in the polymeric backbone. The obtained prepolymers can be photopolymerized in bulk, while a higher methacrylate content leads to a higher crosslink density after UV curing resulting in higher stiffness and higher glass transition temperature. Atomistic model simulation clarified spatial structure of the crosslinked macromolecules and allowed Tg predictions. Viscoelastic to ideal-viscous behaviour dominates in the obtained polymeric products with low network density.journal articleBand:27641 73 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Synthesis and characterization of hyperbranched polyglycerols with various degree of methylation employing phase-transfer conditionsA simple method for partial methylation of the hyperbranched polyglycerol hydroxyl groups was achieved by a combination of phase-transfer catalysis approach with dimethyl sulfate and tetrabutylammonium bromide and the use of a mixed-bed ion exchanger for purification. Various degrees of methylation between 0 and 98% could be adjusted in a controlled manner via the added amount of alkylating agent resulting in modified polymers with moderate polydispersities. NMR spectroscopy was used to determine the methylation progress and the resulting molecular structure. The methylation degree affected associative intra- and intermolecular interactions, such as hydrogen bonds, entailing reduced glass transition temperature and viscosities with increasing hydroxyl group conversion. In addition, the attenuation of hydrogen bonds upon methylation proved to facilitate a straightforward estimation of methylation degree by infrared spectroscopy.journal articleBand:22917 20 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, The effects of manufacturing processes on the physical and mechanical properties of basalt fibre reinforced polybenzoxazine(Elsevier Science, 2021-01-23); ; ; ; The present work provides a comparative investigation between different methods of manufacturing basalt fibre reinforced polybenzoxazines (BFRP), including vacuum infusion, hand laminating, dynamic fluid compression moulding and autoclave curing processes. In comparison to the high pressure based autoclave-cured and compression-moulded BFRPs, vacuum-infused BFRPs showed similar or even higher mechanical properties. Despite the low pressure curing, vacuum infusion yielded BFRPs with a 10% higher tensile strength and a 24% higher strain at failure compared to its autoclave-cured counterparts. Thus, it is possible to gain BFRPs with near-zero porosity and high mechanical properties without the need of high pressure curing methods.journal article146 270 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, How solvent-free crosslinking conditions alter the chemistry and topology of hemiketal based polymer networks(Elsevier Science, 2021-06-30); ; ; ; A solvent free reaction of PCL based polyester polyols with a crosslinking molecule based on a vicinal tricarbonyl results covalent adaptable polymer networks that differ in their thermal behavior, swelling, and solubility properties. Mild processing results polymer networks based on hemiketal/ketone equilibrium with properties typical for dissociative networks including dissolution in presence of water or elevated temperature and self-healing properties. Further thermal treatment of the polymer entails changes in swelling, and solubility properties. Constant glass transition temperatures of the differently treated polymers indicate a steady overall network density, but changes in the nature of the network structure. By varying the number of OH-groups, molar mass and stoichiometric ratio of the polyester polyol and the crosslinking molecule, respectively, material properties can be adjusted. This approach gives access to reversibly crosslinked polymers varying in their responsivness and overall mechanical properties.journal article189 246 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Disclosing the complex crystallization of PBAT/PLA/Babassu biocompounds through MDSC analysis(Springer, 2021-09-18)39 24 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Surface-initiated ring-opening polymerization of ɛ-caprolactone as a feasible approach to modify flax yarn(Elsevier, 2022-01); ; ; Surface-initiated ring-opening (SI-ROP) polymerization of ɛ-caprolactone is known as possible modification method to increase the hydrophobicity of cellulosic substrates. In this study SI-ROP of ɛ-caprolactone is applied on native and mercerized flax yarn. By use of triazabicyclodecene as catalyst, SI-ROP at room temperature was possible and poly-ɛ-caprolactone (PCL) was linked with a weight content of 4–10% to flax yarns. Besides a lower hydrophilicity an increased surface energy was achieved for PCL modified flax yarn. Furthermore, the positive effect of PCL linkage on the fibers surface regarding adhesion potential to an epoxy matrix was shown via conducting fiber-pull-out tests. After SI-ROP of ɛ-caprolactone on flax fiber surface a reduction of fiber pull-out up to 33% was achieved, evoked by physical improvement e.g. better wettability of fiber with epoxy matrix as well as enhanced crosslinking between the hydroxyl groups of the surface grafted PCL and the epoxy resin.journal articleBand:15261 36 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Biodegradation and thermal-oxidative degradation of propanediol based poly (lactic acid) oligomers(Springer, 2023-05-25); 38 42 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Synthesis of bio-polyurethanes with isosorbide and propanediol based poly(lactic acid) diol(Wiley, 2023-01-17); 54 34 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Approaches on the Complex Crystallization in PLA/Babassu Based on Modulated Differential Scanning Calorimetry Analyses(Springer, 2022-05-24)26 19 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Solid-State NMR Revealing the Impact of Polymer Additives on Li-Ion Motions in Plastic-Crystalline Succinonitrile Electrolytes(American Chemical Society, 2023-01-10); ; ; To enhance the safety of lithium-ion batteries (LIBs), alternatives to liquid electrolytes are widely studied. One of them is the plastic-crystal succinonitrile (SN) which is able to solvate various Li salts. This system can be further extended by inserting polymers, bringing additional advantages such as higher melting points and the possibility of adjusting thermo-mechanical and electrochemical properties. The plastic-crystalline electrolyte consisting of the Li salt lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) dissolved in SN was extended by adding various thermoplastic polymers, namely, polyacrylonitrile (PAN), poly(ethylene oxide) (PEO), polyethylene carbonate (PEC), and polyvinylpyrrolidone (PVP). Even small amounts (10 wt %) of added polymer to the SN-base were found to impact the Li-ion mobility. Variable temperature investigations on structure and ion dynamics were performed using static and magic angle spinning (MAS) solid-state NMR and various relaxometry measurements. Influence of the Li concentration and the polymers’ functional groups on the structure of SN and the resulting Li-ion mobility was elaborated. Activation energies and jump rates of the Li ions were determined. As a result, the PAN-containing system stands out to be a promising candidate for application in future LIBs as it shows high ion mobility, low activation energy, and a high potential for further modifications. Solid-state NMR turned out to be a reliable method and a good alternative to impedance spectroscopy measurements for investigating ion mobility behavior providing even more information.journal articleBand:127Heft:338 44