The lipase-catalyzed synthesis of furan-comprising polyester oligomer diols (α,ω-telechelic diols) is reported. Oligofuranoate diols with excellent end-group fidelity and a yield of 95% were synthesized using a solvent-free two-stage polycondensation of dimethyl furan-2,5-dicarboxylate (DMFDCA) and 1,4-cyclohexanedimethanol (1,4-CHDM) using immobilized Candida antarctica Lipase B (CalB). Recycling of immobilized CalB to further decrease the production cost is successfully demonstrated. However, it showed limitation in the product yield that decreases ±20% with each additional reuse. The synthetic procedure has been scaled up, easily opening the possibility to use the developed diols in industrial polycondensations utilizing the excellent flame retardancy property and high thermal stability typical for furan-based polymers.
The stability of polycyclic aromatic hydrocarbons (PAHs) upon soft X-ray absorption is of crucial relevance for PAH survival in X-ray dominated regions (XDRs). PAH stability depends on molecular size but also on the degree of hydrogenation that is related to H2 formation in the interstellar medium (ISM). In this project, we intend to reveal the changes of electronic structure caused by hydrogenation and the impact of hydrogenation on the stability of the carbon backbone for cationic pyrene and its hydrogenated derivatives by analysis of near C K-edge soft X-ray photoions. In our experiments, the PAH cations were trapped in a cryogenic radiofrequency (RF) linear ion trap and exposed to monochromatic X-rays with energies from 279 eV to 300 eV. The photo-products were mass-analyzed by means of time-of-flight (TOF) spectroscopy. Partial ion yields (PIYs) were then studied as a function of photon energy. X-ray absorption spectra computed by time-dependent density functional theory (TD-DFT) aided the interpretation of the experimental results. A very good agreement between experimental data and TDDFT with short-range corrected (SRC) functionals for all PAH ions was reached. The near-edge X-ray absorption mass spectra (NEXAMS) exhibit clear peaks due to C 1s transitions to singly occupied molecular orbitals SOMO and to low-lying unoccupied molecular orbitals. In contrast to coronene cations, where hydrogen attachment drastically increases photostability of coronene, the influence of hydrogenation on photostability is substantially weaker for pyrene cations. Here, hydrogen attachment even destabilizes the molecular structure. An astrophysical model describes the half-life of PAH ions in interstellar environments.
Significant improvement in mechanical properties and shape recovery in polyurethanes can be obtained by cross-linking, usually performed in a traditional chemical fashion. Here, we report model studies of enzymatic transamidations of urethane-bondcontaining esters to study the principles of an enzymatic build-up of covalent cross-linked polyurethane networks via amide bond formation. The Lipase-catalyzed transamidation reaction of a urethane-bondcontaining model ester ethyl 2-(hexylcarbamoyloxy)propanoate with various amines is discussed. A side product was formed, that could be successfully identified, and its synthesis reduced to a minimum (<1%). Furthermore, a noncatalyzed transamidation that is performed without CalB as the catalyst could be observed. Both observations are due to the known high reactivity of amines with urethane bonds.
Here we demonstrate the feasibility and successful application of enzymes in polyurethane network synthesis as well as occurring hurdles that have to be addressed when using urethanes synthesis substrates. The enzymatic transesterification of an urethanebond containing monofunctional ester and a model alcohol carbitol using lipases is discussed. The reaction is optimized in terms of transesterification time and temperature, the reaction solvent, the possibility of a cosolvent and the alcohol amount, the used transesterification environment, and the biocatalyst. Enzymatic cross-linking of polyurethanes can open up a pool of new possibilities for cross-linking and related polyurethane network properties due to the enzymes high enantio-, stereo-, and regioselectivity and broad substrate spectrum.
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