03 Fakultät Chemie
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/4
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Item Open Access Melt-spinning of an intrinsically flame-retardant polyacrylonitrile copolymer(2020) König, Simon; Kreis, Philipp; Herbert, Christian; Wego, Andreas; Steinmann, Mark; Wang, Dongren; Frank, Erik; Buchmeiser, Michael R.Poly(acrylonitrile) (PAN) fibers have two essential drawbacks: they are usually processed by solution-spinning, which is inferior to melt spinning in terms of productivity and costs, and they are flammable in air. Here, we report on the synthesis and melt-spinning of an intrinsically flame-retardant PAN-copolymer with phosphorus-containing dimethylphosphonomethyl acrylate (DPA) as primary comonomer. Furthermore, the copolymerization parameters of the aqueous suspension polymerization of acrylonitrile (AN) and DPA were determined applying both the Fineman and Ross and Kelen and Tüdõs methods. For flame retardancy and melt-spinning tests, multiple PAN copolymers with different amounts of DPA and, in some cases, methyl acrylate (MA) have been synthesized. One of the synthesized PAN-copolymers has been melt-spun with propylene carbonate (PC) as plasticizer; the resulting PAN-fibers had a tenacity of 195 ± 40 MPa and a Young’s modulus of 5.2 ± 0.7 GPa. The flame-retardant properties have been determined by Limiting Oxygen Index (LOI) flame tests. The LOI value of the melt-spinnable PAN was 25.1; it therefore meets the flame retardancy criteria for many applications. In short, the reported method shows that the disadvantage of high comonomer content necessary for flame retardation can be turned into an advantage by enabling melt spinning.Item Open Access Olefin ring‐closing metathesis under spatial confinement and continuous flow(2021) Ziegler, Felix; Roider, Thomas; Pyschik, Markus; Haas, Christian P.; Wang, Dongren; Tallarek, Ulrich; Buchmeiser, Michael R.We report on the use of a 2nd‐generation Hoveyda-Grubbs‐type catalyst immobilized inside mesoporous silica for the application in selective macro(mono)cyclization (MMC) of an α,ω‐diene under spatially confined and continuous‐flow conditions. Reactions carried out with different flow rates allow for variations in residence time; conversion and MMC selectivity can be determined for well‐defined reaction times. Analysis of the reaction mixtures obtained for different reaction times and temperatures in a single flow experiment by NMR and MALDI‐TOF‐MS allows to address confinement effects and to determine olefin metathesis pathways. These investigations revealed that ring‐chain equilibria are quickly established but substantially affected by residence time and flow, allowing for the determination of conditions under which MMC selectivity reaches a maximum. In contrast to reactions carried out in solution, in which oligomers up to the hexamer were observed, MMC under confinement predominantly proceeds via ring‐closing metathesis of the monomer and backbiting from the dimer and trimer, but not from higher oligomers as their formation is suppressed. This leads to the observed high MMC selectivity, reaching 60 % at a 25 mM substrate concentration.Item Open Access Synthesis of dihydroxy telechelic oligomers of β‐butyrolactone catalyzed by titanium(IV)‐alkoxides and their use as macrodiols in polyurethane chemistry(2021) Altmann, Hagen J.; Machat, Martin R.; Wolf, Aurel; Gürtler, Christoph; Wang, Dongren; Buchmeiser, Michael R.We report on a solvent‐free approach for the synthesis of low molecular weight, α,ω‐dihydroxy telechelic poly(β‐butyrolactone). In the presence of Ti(IV) alkoxides, mixtures of β‐butyrolactone and diols, like di‐ or triethylene glycol, were reacted in ratios between 4:1 and 10:1. The oligomerization proceeds at elevated temperatures (80-100°C). Different alkoxide substituents (R = Me, iPr, tBu) of the Ti(IV)(OR)4 catalyst were investigated. The resulting oligomers were characterized by nuclear magnetic resonance (NMR), infra‐red (IR), gel‐permeation chromatography (GPC), titration, and matrix‐assisted laser desorption‐time‐of‐flight mass spectrometry (MALDI‐ToF‐MS) analysis. Aside from low molecular weight products, special effort was devoted to achieve high O‐acyl cleavage selectivity and to circumvent the formation of unsaturated end‐groups in order to form exclusively dihydroxy‐telechelic oligomers. Optimized results in terms of selectivity and reaction rates were achieved at 100°C using catalyst loadings of 0.2 mol% with respect to the monomer. The molecular weights determined by GPC were in good accordance with the ratio of monomer to diol used, confirming successful oligomer formation. Polyurethanes prepared from crude macrodiols without any additional catalyst feature molecular weights up to 50,000 g/mol. The reported work serves as concept to utilize β‐lactones for tailored polyol synthesis; the resulting products are suitable for polyurethane chemistry.