03 Fakultät Chemie

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    Chitin/cellulose blend fibers prepared by wet and dry‐wet spinning
    (2020) Ota, Antje; Beyer, Ronald; Hageroth, Ulrich; Müller, Alexandra; Tomasic, Patricija; Hermanutz, Frank; Buchmeiser, Michael R.
    We describe the wet and dry‐wet spinning of multifilament cellulosic composite fibers, namely chitin/cellulose fibers. The direct solution process for the two biopolymers based on an ionic liquid as solvent represents an environmentally friendly and alternative technology to the industrially applied viscose and lyocell process. Both cellulose and chitin possess good solubility in 1‐ethyl‐3‐methylimidazolium propionate ([C2C1Im][OPr]) and were spun into multifilament composite fibers. Moreover, for the first time, pure chitin multifilament fibers were obtained by dry‐wet spinning. The effect of chitin addition on the filament properties was investigated and evaluated by microscopic, spectroscopic, and mechanical analyses.
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    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.
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    Reversible N‐heterocyclic carbene‐induced α‐H abstraction in Tungsten(VI) imido dialkyl dialkoxide complexes
    (2020) Musso, Janis V.; Benedikter, Mathis J.; Wang, Dongren; Frey, Wolfgang; Altmann, Hagen J.; Buchmeiser, Michael R.
    The first reversible N‐heterocyclic carbene (NHC) induced α‐H abstraction in tungsten(VI) imido‐dialkyl dialkoxide complexes is reported. Treatment of W(NAr)(CH2Ph)2(OtBu)2 (Ar=2,6‐dichlorophenyl, 2,6‐dimethylphenyl, 2,6‐diisopropylphenyl) with different NHCs leads to the formation of complexes of the type W(NAr)(CHPh)(NHC)(CH2Ph)(OtBu) in excellent isolated yields of up to 96 %. The highly unusual release of the tert‐butoxide ligand as tBuOH in the course of the reaction was observed. The formed alkylidene complexes and tBuOH are in an equilibrium with the NHC and the dialkyl complexes. Reaction kinetics were monitored by 1H NMR spectroscopy. A correlation between the steric and electronic properties of the NHC and the reaction rates was observed. Kinetics of a deuterium‐labeled complex in comparison to its non‐deuterated counterpart revealed the presence of a strong primary kinetic isotope effect (KIE) of 4.2, indicating that α‐H abstraction is the rate‐determining step (RDS) of the reaction.
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    Chromium(VI) bisimido dichloro, bisimido alkylidene, and chromium(V) bisimido iodo N‐heterocyclic carbene complexes
    (2020) Panyam, Pradeep K. R.; Stöhr, Laura; Wang, Dongren; Frey, Wolfgang; Buchmeiser, Michael R.
    Reaction of CrCl2(N-tBu)2 with 1,3-dimethylimidazol-2-ylidene (IMe), 1,3-dimethyl-4,5-dichloroimidazol-2-ylidene (IMeCl2), 1,3-di(2-propyl)imidazol-2-ylidene (IPr), 1,3-dimesitylimidazol-2-ylidene (IMes) and 1,3-bis(2,6-(2-Pr)2C6H3)imidazol-2-ylidene (IDipp) yields the corresponding N-heterocyclic carbene (NHC) adducts CrCl2(IMe)(N-tBu)2 (1), CrCl2(IMeCl2)(N-tBu)2 (2), CrCl2(IPr)(N-tBu)2 (3), CrCl2(IMes)(N-tBu)2 (4) and CrCl2(IDipp)(N-tBu)2 (5). Likewise, reaction of CrCl2(N-2,6-(2-Pr)2C6H3)2 and CrCl2(N-adamantyl)2 with IMes yields CrCl2(N-2,6-(2-Pr)2C6H3)2(IMes) (6) and CrCl2(N-adamantyl)2(IMes) (7), respectively. Reaction of CrCl2(N-tBu)2 with the bidentate NHCs 1-R-3-(1-(2-LiO-C6H4))imidazol-2-ylidene yields the corresponding pentacoordinated Cr(VI) complexes CrCl2(1-R-3-(1-(2-O-C6H4))imidazol-2-ylidene)2C6H3)2(IMes) (R = 2,4,6-(CH3)3C6H2, 8), (R = tBu, 9), (R = 2-phenyl-C6H4, 10). Reaction of the chromium(VI) complex Cr(N-2,6-(2-Pr)2-C6H3)2(CH2C(CH3)3)2 with 1,3-dimethylimidazol-2-ylidene·AgI yields the bimetallic silver adduct of the chromium alkylidene complex (11) along with the tetrahedral chromium(V) complex CrI(N-2,6-(2-Pr)2-C6H3)2(1,3-dimethylimidazol-2-ylidene) (12). Compounds 1-4, 7, 9-12 were characterized by single-crystal X-ray analysis. Finally, the chromium(VI) bisimido-amido complexes 13-14 bearing the N-6-(2-(diethylboryl)phenyl)pyridyl-2-yl-motif are reported.
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    High‐performance magnesium‐sulfur batteries based on a sulfurated poly(acrylonitrile) cathode, a borohydride electrolyte, and a high‐surface area magnesium anode
    (2020) Wang, Peiwen; Trück, Janina; Niesen, Stefan; Kappler, Julian; Küster, Kathrin; Starke, Ulrich; Ziegler, Felix; Hintennach, Andreas; Buchmeiser, Michael R.
    Post‐lithium‐ion battery technology is considered a key element of future energy storage and management. Apart from high gravimetric and volumetric energy densities, economic, ecologic and safety issues become increasingly important. In that regards, both the anode and cathode materials must be easily available, recyclable, non‐toxic and safe, which renders magnesium‐sulfur (Mg-S) batteries a promising choice. Herein, we present Mg-S cells based on a sulfurated poly(acrylonitrile) composite cathode (SPAN), together with a halogen‐free electrolyte containing both Mg[BH4]2 and Li[BH4] in diglyme and a high‐specific surface area magnesium anode based on Rieke magnesium powder. These cells deliver discharge capacities of 1400 and 800 mAh/gsulfur with >99 % Coulombic efficiency at 0.1 C and 0.5 C, respectively, and are stable over at least 300 cycles. Energy densities are 470 and 400 Wh/kgsulfur at 0.1 C and 0.5 C, respectively. Rate tests carried out between 0.1 C and 2 C demonstrate good rate capability of the cells. Detailed mechanistic studies based on X‐ray photoelectron spectroscopy and electric impedance spectroscopy are presented.
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    Sulfurized polypropylene as low‐cost cathode material for high‐capacity lithium‐sulfur batteries
    (2022) Du, Qian; Benedikter, Mathis; Küster, Kathrin; Acartürk, Tolga; Starke, Ulrich; Hoslauer, Jean‐Louis; Schleid, Thomas; Buchmeiser, Michael R.
    Among ‘beyond lithium ion’ energy storage, lithium sulfur (Li-S) batteries are one of the most promising technologies, as a result of the potential for high theoretical energy capacity at low cost. A key obstacle in exploiting the vast potential of Li-S batteries is the formation of soluble polysulfide species. Here, we report sulfurized polypropylene (S/PP‐500) synthesized in one‐step by reacting polypropylene (PP) with sulfur as a new polysulfide shuttle‐free cathode material for Li-S batteries. It exhibits a reversible capacity as high as 1000 mAh/gsulfur at 0.1 C and a sulfur loading of up to 68 wt%, which in turn allows for high sulfur loadings up to 47 % in the final cathode. The low‐cost starting materials together with the simple synthetic procedure and the good electrochemical performance in combination with a commercially available eslectrolyte make the S/PP‐500 a very promising cathode material for Li‐S batteries.
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    Method of manufacturing structural, optically transparent glass fiber-reinforced polymers (tGFRP) using infusion techniques with epoxy resin systems and E-glass fabrics
    (2023) Heudorfer, Klaus; Bauer, Johannes; Caydamli, Yavuz; Gompf, Bruno; Take, Jens; Buchmeiser, Michael R.; Middendorf, Peter
    Recently, fiber-reinforced, epoxy-based, optically transparent composites were successfully produced using resin transfer molding (RTM) techniques. Generally, the production of structural, optically transparent composites is challenging since it requires the combination of a very smooth mold surface with a sufficient control of resin flow that leads to no visible voids. Furthermore, it requires a minimum deviation of the refractive indices (RIs) of the matrix polymer and the reinforcement fibers. Here, a new mold design is described and three plates of optically transparent glass fiber-reinforced polymers (tGFRP) with reproducible properties as well as high fiber volume fractions were produced using the RTM process and in situ polymerization of an epoxy resin system enclosing E-glass fiber textiles. Their mechanical (flexural), microstructural (fiber volume fraction, surface roughness, etc.), thermal (DSC, TGA, etc.), and optical (dispersion curves of glass fibers and polymer as well as transmission over visible spectra curves of the tGFRP at varying tempering states) properties were evaluated. The research showed improved surface quality and good transmission data for samples manufactured by a new Optical-RTM setup compared to a standard RTM mold. The maximum transmission was reported to be ≈74%. In addition, no detectable voids were found in these samples. Furthermore, a flexural modulus of 23.49 ± 0.64 GPa was achieved for the Optical-RTM samples having a fiber volume fraction of ≈42%.
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    Dual catalysis with an N‐heterocyclic carbene and a Lewis acid : thermally latent precatalyst for the polymerization of ε‐caprolactam
    (2020) Altmann, Hagen J.; Steinmann, Mark; Elser, Iris; Benedikter, Mathis J.; Naumann, Stefan; Buchmeiser, Michael R.
    So far, the earlier reported strong correlation between basicity of an N‐heterocyclic carbene (NHC) and its reactivity in poly(ε‐caprolactam) (PA6) synthesis resulted in a substantial limitation of applicable carbenes. Here, to overcome this issue, 1,3‐dimethylimidazolium‐2‐carboxylate, an easily accessible, air and moisture‐stable NHC, was applied as thermally latent initiator. In order to compensate for its low basicity, reactivity was enhanced by the addition of both a Lewis acid and an activator to ease the initial polymerization step. The resulting mixtures of ε‐caprolactam, the CO2‐protected NHC, a Lewis acid and N‐acylazepan‐2‐one constitute homogeneous, thermally fully latent “single‐component” blends for the anionic polymerization‐based synthesis of PA6. They can be stored both in the liquid and solid state for days and months, respectively, without any loss in activity. The role of the Lewis acid as well as technical implications of the prolonged pot‐times are discussed.
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    Toward sustainable fiber‐reinforced polymer composites
    (2024) Elser, Iris; Buchmeiser, Michael R.
    Fiber‐reinforced polymer composites (FRPCs) are versatile materials with applications in diverse fields such as transportation, construction, and electronics. With the composites market expected to reach 15.5 Mt by 2026, increasing the sustainability of FRPCs is imperative. The main factors driving the sustainability of FRPCs, namely end‐of‐life management and recyclability, the use of natural, bio‐based, and sustainable materials, as well as biodegradability and product simplification are presented and discussed.
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    Hydrosilylation of alkynes under continuous flow using polyurethane‐based monolithic supports with tailored mesoporosity
    (2022) Acikalin, Hande; Panyam, Pradeep K. R.; Shaikh, Abdul Wasif; Wang, Dongren; Kousik, Shravan R.; Atanasova, Petia; Buchmeiser, Michael R.
    Non‐porous polyurethane‐based monoliths are prepared under solvent‐induced phase separation conditions. They possess low specific surface areas of 0.15 m2 g-1, pore volumes of 1 µL g-1, and a non‐permanent, solvent‐induced microporosity with pore dimensions ≤1 nm. Mesoporosity can be introduced by varying the monomers and solvents. A tuning of the average solubility parameter of the solvent mixture by increasing the macroporogen content results in a decrease in the volume fraction of micropores from 70% to 40% and an increase in the volume fraction of pores in the range of 1.7-9.6 nm from 22% to 41% with only minor changes in the volume fraction of larger mesopores in the range of 9.6–50 nm. The polymeric monoliths are functionalized with quaternary ammonium groups, which allowed for the immobilization of an ionic liquid that contained the ionic Rh‐catalyst [1‐(pyrid‐2‐yl)‐3‐mesityl)‐imidazol‐2‐ylidene))(η4‐1,5‐cyclooctadiene)Rh(I) tetrafluoroborate]. The supported catalyst is used in the hydrosilylation of 1‐alkynes with dimethylphenylsilane under continuous flow using methyl‐tert‐butyl ether as second liquid transport phase. E/Z‐selectivity in hydrosilylation is compared to the one of the analogous biphasic reactions. The strong increase in Z‐selectivity is attributed to a confinement effect provided by the small mesopores.