Lade...
Journal Title
Polymer
3 Ergebnisse
Filter
Einstellungen
Gerade angezeigt 1 - 3 von 3
- Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, 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.Wissenschaftlicher ArtikelBand:27641 73 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, 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.Wissenschaftlicher ArtikelBand:22917 20 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, 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.Wissenschaftlicher Artikel189 245