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Universität Freiburg





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Veröffentlichungen - Dr. Yi Thomann 2010-....
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69: Nanophasic morphologies as a function of the composition and molecular weight of the macromolecular cross-linker in poly(N-vinylimidazole)-l-poly(tetrahydrofuran) amphiphilic conetworks: bicontinuous domain structure in broad composition ranges
Csaba Fodor, Gergely Kali, Ralf Thomann, Yi Thomann, Bela Ivan, Rolf Mulhaupt
RSC Advances (2017), 7(12), 6827-6834

Abstract: Macroscopically homogeneous poly(N-vinylimidazole)-linked by-poly(tetrahydrofuran) (PVIm-l-PTHF) amphiphilic conetworks (APCNs) were investigated to reveal the effect of conetwork compn. in a broad compn. range between 25-91 wt% PTHF content and the mol. wt. of the components on phase sepn. and the formation of different morphol. features. No macroscopic phase sepn. was found in these conetworks with semicryst. PTHF phase, but the segregation of the various covalently connected phases occurs in the nanoscale. The nanophase sepd. APCNs possess compositionally asym. morphol. with spherical and elongated domains together with a bicontinuous (cocontinuous) domain structure having 7-19 nm av. domain sizes. The mol. wt. of the PTHFDMA cross-?linker, varying between 2170 and 10 030 g mol-1, also influences the size and distance between the phases. Moreover, morphol. dependent interactions with polar and non-?polar solvents, as well as amphiphilic swelling behavior were found. These nanostructured materials, due to their unique nanophasic morphol. and swelling properties possess significant importance and have numerous potential applications in various fields from medicine to material science and engineering.

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68: Nanostructured Polyethylene Reactor Blends with Tailored Trimodal Molar Mass Distributions as Melt-Processable All-Polymer Composites
Markus Stuerzel, Timo Hees, Markus Enders, Yi Thomann, Hannes Blattmann, Rolf Muelhaupt
Macromolecules (Washington, DC, United States) (2016), 49(21), 8048-8060.

Abstract: Tailoring trimodal polyethylene (PE) molar mass distributions by means of ethylene polymn. on three-site catalysts, supported on functionalized graphene (FG), enables nanophase sepn. during polymn. and melt processing, paralleled by PE self-?reinforcement. Typically, FG/MAO-supported three-site catalysts combine bis(iminopyridyl)?chromium trichloride (CrBIP), producing PE wax having high crystn. rate, and quinolylcyclopentadienylchromium dichloride (CrQCp), forming in situ ultrahigh mol. wt. PE (UHMWPE) nanostructures, with bis(iminopyridyl)iron dichloride (FeBIP) or bis(tert-Bu cyclopentadienyl)zirconium (ZrCp), resp., producing HDPE with variable intermediate molar mass. During injection molding, the formation of shish-kebab fiber-like extended-?chain UHMWPE structures, as verified by SEM, AFM, and DSC, account for effective self-reinforcement. Only in the presence of high UHMWPE content, PE wax, usually an unwanted byproduct in HDPE synthesis, functions as a built-in processing aid and enables the incorporation of much higher UHMWPE contents (30 wt. %) than previously thought to be tolerable in injection molding. Whereas the incorporation of UHMWPE/PE wax blends improves stiffness and strength, the simultaneous FG dispersion accounts for substantially higher impact strength.

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67: Multisite catalyst mediated polymer nanostructure formation and self-reinforced polyethylene reactor blends with improved toughness/stiffness balance
Markus Stuerzel, Alexander Kurek, Timo Hees, Yi Thomann, Hannes Blattmann, Rolf Muelhaupt
Polymer (2016), 102, 112-118

Abstract: The design of supported two- and three-site catalysts for ethylene polymn. and tailoring nanophase-?sepd. polyethylene reactor blends represents the key to the development of advanced all-polyethylene nanocomposite materials exhibiting substantially improved performance and high resource-, eco- and energy efficiency. Two or three different single-site catalysts independently produce high d. polyethylene (HDPE), ultrahigh mol. wt. polyethylene (UHMWPE) and PE wax on the same catalyst support. Since this catalyst-?mediated nanophase sepn. prevents UHMWPE entanglement, typical for conventional homogeneous reactor blends, much higher UHMWPE content up to 30 wt% is incorporated in the presence of PE wax without impairing injection molding. During melt processing the shear-induced oriented UHMWPE crystn. affords shish-kebab-fiber-like nanostructures. This accounts for effective PE self-reinforcement paralleled by simultaneous improvement of stiffness, strength and toughness. Hence, this strategy holds great promise for converting commodity PE into high performance plastics and single component PE composites, entering the performance range currently claimed by glass fiber reinforced PE.

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66: Poly(N-vinylimidazole)-l-poly(propylene glycol) amphiphilic conetworks and gels: molecularly forced blends of incompatible polymers with single glass transition temperatures of unusual dependence on the composition
Csaba Fodor, Timea Stumphauser, Ralf Thomann, Yi Thomann, Bela Ivan
Polymer Chemistry (2016), 7(34), 5375-5385

Abstract: A series of macroscopically homogeneous poly(N-vinylimidazole)-l-poly(propylene glycol) (PVIm-l-PPG) ("l" stands for "linked by") amphiphilic conetworks (APCNs) composed of otherwise incompatible polymers were successfully synthesized in a broad compn. range (34-88 wt% PPG) by free radical copolymn. of hydrophilic N-vinylimidazole (VIm) and hydrophobic poly(propylene glycol) dimethacrylate (PPGDMA) macromol. cross-linkers. Strikingly, while PVIm and PPGDMA homopolymers are immiscible and their blends have two distinct glass transition temps. (Tg), the PVIm-l-PPG conetworks possess only one Tg indicating the absence of considerable phase sepn. in the conetworks, which was also confirmed by AFM measurements. This is in sharp contrast to the two Tgs of APCNs reported so far in the literature, on the one hand. On the other hand, the Tg values do not follow known correlations between Tg and compn., like the Fox equation or additive rule, widely applied for compatible polymers. These results indicate a strong interpolymer interaction on the mol. level between the PVIm and PPG chains in these new APCNs resulting in single Tg. Thermogravimetric anal. (TGA) shows that degrdn. of the conetworks occurs at high temps. in two stages without sharp changes, but with a transition period in between. The DTG curves indicate that the components retain their chem. integrity to certain extent in these APCNs. The amphiphilic nature of the PVIm-l-PPG conetworks was confirmed by their compn. dependent swelling in both polar (water, ethanol) and nonpolar (THF) solvents, that is in spite of the lack of phase sepn., these new materials behave as either hydrogels or hydrophobic gels (organogels) depending on the swelling medium in a broad compn. range.

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65: Graphene-Supported Dual-Site Catalysts for Preparing Self-Reinforcing Polyethylene Reactor Blends Containing UHMWPE Nanoplatelets and in Situ UHMWPE Shish-Kebab Nanofibers
Markus Stürzel, Yi Thomann, Markus Enders, and Rolf Mülhaupt
Macromolecules, 2014, Volume47, Issue15, Pages 4979-4986

Abstract: The catalytic ethylene polymerization on dual-site catalysts, supported on functionalized graphene, enables nanostructure formation in polyethylene reactor blends by in situ formation of uniformly dispersed ultrahigh molecular weight polyethylene (UHMWPE) nanoplatelets and in situ formed aligned UHMWPE shish-kebab nanofibers. For tailoring bimodal molar mass distributions, the quinolylsilylcyclopentadienylchromium(III) complex (Cr-1), producing UHMWPE with Mw > 3 x 106 g mol-1, is blended together with bisiminopyridine complexes of either chromium(III) (CrBIP), producing polyethylene (PE) wax (2 x 103 g mol-1), or iron(II) (FeBIP), producing PE with Mw = 2.0 x 105 g mol-1. Hence, the FeBIP/Cr-1 and CrBIP/Cr-1 molar ratios govern the PE/UHMWPE weight ratio without affecting the average molar mass of the individual PE fractions. In sharp contrast to conventional UHMWPE/PE reactor blends, the UHMWPE content is substantially increased up to 17 wt % without impairing melt processing. In the case of graphene-supported FeBIP/Cr-1, SEM and TEM analysis reveal that UHMWPE nanoplatelets are formed during polymerization. This is attributed to graphene-mediated mesoscopic shape replication. During injection molding, the UHMWPE nanoplatelets are transformed into aligned UHMWPE shish-kebab nanofibers, thus enabling efficient polyethylene matrix reinforcement.

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64: Gas phase mineralized graphene as core/shell nanosheet supports for single-site olefin polymerization catalysts and in-situ formation of graphene/polyolefin nanocomposites
Felix Kirschvink, Markus Stürzel, Yi Thomann, Rolf Mülhaupt
Polymer (2014), 55(18), 4547-4550.

Abstract: A versatile gas phase mineralization process affords nanosheets containing a functionalized graphene (FG) core and a thin silica shell. The number of cycles, exposing FG to sequenced tetrachlorosilane and water vapors, controls the silica content and the silica shell thickness. The resulting high surface area core/shell nanosheets, containing 22 to 34 wt.-% silica, are used to immobilize single-site catalysts. During polymerization, the FG/silica nanosheets are uniformly dispersed in ultrahigh molecular weight polyethylene. This catalytic polymerization filling process, exploiting the encapsulation of graphene in a silica shell, is of interest to prepare electrically insulating carbon/polyolefin composite materials with high thermal conductivity useful in lightweight engineering.

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63: Improving Melt Flow of Polyoxymethylene ("High-Speed POM"): Additive Design, Melt Rheology, and In Situ Composition Gradient Formation
Karlheinz Gamp, Yi Thomann, Christian Friedrich, André Hebel, Kirsten Markgraf, Hanno Hückstädt, Klaus Kurz and Rolf Mülhaupt
Macromolecular Materials and Engineering (2014), 299(1), 51264.

Abstract: Variation of isocyanurate substitution patterns and functionalities is the key to novel additives for "high-speed POM". In injection molding only 3wt% isocyanurate urethane (I3O) are sufficient for increasing the POM melt flow path by 60%. Such additives can reduce processing temperature by 40?K. Lubrication mechanisms and the role of in situ composition gradient formation, resulting from additive surface migration, are studied.

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62: Novel Graphene UHMWPE Nanocomposites Prepared by Polymerization Filling Using Single-Site Catalysts Supported on Functionalized Graphene Nanosheet Dispersions
Markus Stürzel, Fabian Kempe, Yi Thomann, Stefan Mark, Markus Enders, and Rolf Mülhaupt
Macromolecules, (2012), 45(17), 6878-6887.

Abstract: Novel families of ultrahigh-molecular-weight polyethylene (UHMWPE) nanocomposites, containing uniformly dispersed, functionalized graphene (FG) nanosheets, were prepared by means of the polymerization filling technique (PFT). Unparalleled by any other carbon and boehmite nanocomposites, FG/UHMWPE exhibited an unusual simultaneous improvement in stiffness, elongation at break, and effective nucleation of polyethylene crystallization at only 1 wt % FG content. FG nanosheets are ultrathin-with a thickness of only one carbon atom and lateral dimensions of several micrometers. Owing to the presence of surface hydroxyl groups on the FG, single FG/methylaluminoxane (MAO) nanosheets can be effectively dispersed in n-heptane, thus enabling immobilization of an MAO-activated chromium (Cr1) single-site catalyst on FG. In contrast to nanometer-scale carbon black (CB), multiwall carbon nanotubes (CNT), graphite, and nanoboehmite, which failed to form stable dispersions, FG/MAO/Cr1 afforded the highest catalyst activities and excellent morphological control. In polymerization filling, the integration of a nanoparticle dispersion into the polymerization process eliminated the need for special safety and handling precautions typically required by conventional compounding of nanoparticles with ultralow bulk densities.

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61: Turning Teflon-coated magnetic stirring bars to catalyst systems with metal nanoparticle trace deposits - a caveat and a chance
Christian Vollmer, Marcel Schröder, Yi Thomann, Ralf Thomann, Christoph Janiak
Applied Catalysis A: General, 425-426, p.178-183, May 2012

Abstract: It could be an unintentional effect to deposit metal nanoparticles on a simple Teflon-coated magnetic stirring bar. Rhodium nanoparticles, as an example, were reproducibly deposited onto a standard, commercial Teflon-coated magnetic stirring bar by easy and rapid microwave-assisted decomposition of the metal carbonyl precursor Rh6(CO)16 in the ionic liquid 1-n-butyl-3-methyl-imidazolium-tetrafluoroborate. Such metal nanoparticle deposits are not easy to remove from the Teflon surface by simple washing procedures and present active catalysts which one is not necessarily aware of. Barely visible metal-nanoparticle deposits on a stirring bar can act as trace metal impurities in catalytic reactions. As a proof-of-principle the rhodium-nanoparticle deposits of 32 µg or less Rh metal on a 20 × 6 mm magnetic stirring bar were shown to catalyze the hydrogenation reaction of neat cyclohexene or benzene to cyclohexane with quantitative conversion. Rhodium-nanoparticle-coated stirring bars were easily handable, separable and re-usable catalyst system for the heterogeneous hydrogenation with quantitative conversion and very high turnover frequencies of up to 32800 mol cyclohexene × (mol Rh)-1 × h-1 under organic-solvent-free conditions.

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60: Self-Healing Rubbers Based on NBR Blends with Hyperbranched Polyethylenimines
Andreas C. Schüssele, Fritz Nübling, Yi Thomann, Oliver Carstensen, Georg Bauer, Thomas Speck, Rolf Mülhaupt
Macromolecular Materials and Engineering, Volume 297, Issue 5, May 2012, Pages: 411-419

Abstract: Hyperbranched PEI and urea-functionalized PEI amphiphiles are employed as additives in NBR compounding. Polarity design governing phase separation, PEI migration and PEI-mediated self-healing of NBR is demonstrated. The compatibility of PEI and NBR decreases with increasing molecular weight of PEI and with decreasing degree of substitution. Microphase-separated NBR/PEI blends are prepared with varying PEI molecular architectures. Thermal self-healing of NBR/PEI is monitored by applying tests combining crack initiation with annealing under compression. All PEI additives show complete crack-healing upon annealing at 100°C for 12h. In contrast to neat NBR, the NBR/PEI-2 blend afforded a self-healing efficiency of 44% after cutting and re-joining by compression and annealing.

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59: Comparison of bacterial adhesion and cellular proliferation on newly developed three-dimensional scaffolds manufactured by rapid prototyping technology
A. Al-Ahmad, C. Schubert, C. Carvalho, Y. Thomann, A. Wittmer, M. Metzger, E. Hellwig, W. Swieszkowski, M. Wiedmann-Al-Ahmad
Journal of Biomedical Materials Research, Part A (2011), 98(2), 303-311.

Abstract: Scaffolds used in the field of tissue engineering should facilitate the adherence, spreading, and ingrowth of cells as well as prevent microbial adherence. For the first time, this study simultaneously deals with microbial and tissue cell adhesion to rapid prototyping-produced 3D-scaffolds. The cell growth of human osteosarcoma cells (CAL-72) over a time period of 3-11 days were examined on three scaffolds (PLGA, PLLA, PLLA-TCP) and compared to the adhesion of salivary microorganisms and representative germs of the oral flora (Porphyromonas gingivalis, Prevotella nigrescens, Candida albicans, Enterococcus faecalis, Streptococcus mutans, and Streptococcus sanguinis). Scanning electron microscopy (SEM), cell proliferation measurements, and determination of the colony forming units (CFU) were performed. The cell proliferation rates on PLLA and PLLA-TCP after 3, 7, and 11 days of cultivation were higher than on PLGA. On day 3 the proliferation rates on PLLA and PLLA-TCP, and on day 5 on PLLA-TCP, proved to be significantly higher compared to that of the control (culture plate). The strain which showed the most CFUs on all of the investigated scaffolds was P. gingivalis, followed by E. faecalis. No significant CFU differences were determined examining P. gingivalis among the biomaterials. In contrast, E. faecalis was significantly more adherent to PLGA and PLLA compared to PLLA-TCP. The lowest CFU values were seen with C. albicans and P. nigrescens. Salivary born aerobic and anaerobic microorganisms adhered significantly more to PLGA compared to PLLA-TCP. These results supported by SEM point out the high potential of PLLA-TCP in the field of tissue engineering.

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58: The Effect of additive on performance and shelf-stability of HSX-1/PCBM photovoltaic devices
Weiwei Li, Yi Zhou, B. Viktor Andersson, L. Mattias Andersson, Yi Thomann, Clemens Veit, Kristofer Tvingstedt, Ruiping Qin, Zhishan Bo, Olle Inganäs, Uli Würfel and Fengling Zhang
Organic Electronics, (2011), 12(9), 1544-1551

Abstract: How 1,8-diiodooctane (DIO) enhances performance of polymer solar cells based on polymer HXS-1 and fullerene [6,6]-phenyl C71-butyric acid methyl ester (PC71BM) from 3.6% to 5.4% is scrutinized with several techniques by comparing devices or blend films spin-coated from dichlorobenzene (DCB) to those from DCB/DIO (97.5:2.5 v/v). Morphology of blend films is examined with atomic force microscopy (AFM), transmission electron microscopy (TEM) and electron tomography (3-D TEM), respectively. Charge generation and recombination is studied with photoluminescence, and charge transport with field effect transistors. The morphology with domain size in 10-20 nm and vertical elongated clusters formed in DIO system is supposed to facilitate charge transport and minimize charge carrier recombination, which are the main reasons for enhancing power conversion efficiency (PCE) from 3.6% (without DIO) to 5.4% (with DIO). Furthermore, a two year inspection shows no significant impact of DIO on the shelf-stability of the solar cells. No visible degradation in the second year indicates that the morphology of the active layers in the devices is relatively stable after initial relaxation in the first year.

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57: Protein yoctowell nanoarchitectures: assembly of donut shaped protein containers and nanofibres.
Andreas Schreiber, Ekaterina Zaitseva, Yi Thomann,Ralf Thomann, Joern Dengjel, Ralf Hanselmann, Stefan M. Schiller
Soft Matter (2011), 7(6), 2875-2878.

Abstract: Proteins able to form "donut shaped" assemblies have been expressed in Escherichia coli and used for reversible in vitro assembly of cylindrical yoctowells (yoctolitre: 1 yL = 10-24 L). Their assembly and disassembly were studied spectroscopically and fibers ranging from mol. to multibundle structures have been assembled.

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56: Amphiphilic polymer conetworks as chiral separation membranes
Jan Tobis, Lisa Boch, Yi Thomann and Jörg C. Tiller
Journal of Membrane Science, Volume 372, Issues 1-2, 15 April 2011, Pages 219-227

Abstract: There is an urgent need for enantiopure chemicals, e.g., as basic compounds for pharmaceuticals. Although great progress has been made to obtain these compound using chiral catalysts, enzymes or even whole cells, it is often not possible or at least not economic to obtain enantiopure compounds. Thus enantioseparation is still required. Besides the elaborate and expensive chromatography and crystallization techniques, chiral membranes have been found to be effective in enantioseparation. Generally such membranes have to be developed specifically for a certain compound in a suited solvent. This is an elaborate development, because little is known about the complex transport process through a chiral membrane. In order to get better insights in the function of such membranes, we have designed a new class of chiral separating membranes that are applicable for nearly every solvent and therefore potentially many substrates. The conetworks are based on nanophasic, amphiphilic polymer conetworks (APCN) featuring a chiral phase of poly((R),(S)-N-(1-hydroxy-butan-2-yl)acrylamide( (P-(R),(S)-HBA) and a non-chiral polydimethylsiloxane (PDMS) phase. This APCN allows to directly exploring interactions between a chiral membrane and an enantiopure compound in dependence on a broad range of solvents varying from n(heptane to water by simply measuring the permeabilities of the compounds. Besides the numerous insights in the solvent-dependent interactions between membrane and five model substrates, we demonstrate that the APCNs are excellent chiral separation membranes. Further, it could be shown that the superior selectivity of these materials is based on the structure of their nanophases.

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55: Contact-Active Antimicrobial and Potentially Self-Polishing Coatings Based on Cellulose
Arno M. Bieser, Yi Thomann, Jörg C. Tiller
Macromolecular Bioscience, 2011, 11, 111-121

Abstract: A contact-active antimicrobial coating is described that is only degraded in the presence of cellulase, which is an extracellular enzyme of numerous microbial strains. Antimicrobial DDA was grafted to a cellulose backbone via a polymeric spacer. The antimicrobial activity of the coatings, their biodegradability and their self-polishing potential were investigated. It was found that all coatings were antimicrobially active against Staphylococcus aureus. Coatings with high DS and long polymeric spacers degraded in water, while coatings with low DS and short spacers were not hydrolyzed even in the presence of cellulase. One coating was found to be selectively degradable by cellulase and recovered most of its antimicrobial activity after overloading and subsequent treatment with cellulase.

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54: Novel acrylic nanocomposites containing in-situ formed calcium phosphate/layered silicate hybrid nanoparticles for photochemical rapid prototyping, rapid tooling and rapid manufacturing processes
Matthias Gurr, Yi Thomann, Michael Nedelcu, Rainer Kübler, Laszlo Könczöl, Rolf Mülhaupt
Polymer (2010), 51(22), 5058-5070

Abstract: Novel acrylic nanocomposites containing calcium phosphate/layered silicate hybrid nanoparticles have been developed for use in photochemical Rapid Prototyping processes like Structural Light Modulation (SLM) and Stereolithography (SL). When tertiary alkyl amines, protonated with phosphoric acid, were added to an acrylic suspension of calcium bentonite, the cation exchange of Ca2+ rendered bentonite organophilic, caused swelling, intercalation and dispersion of silicate nanoplatelets in the monomer. The simultaneous precipitation of calcium phosphate onto the silicate nanoplatelets accounted for the in-situ formation of hybrid nanoparticles. The uniform dispersions of such hybrid nanoparticles afforded a high degree of shear thinning, reflecting the presence of anisotropic filler particles, and increased photosensitivity in SLM with respect to the unfilled resin. Young's modulus of green and postcured parts increased by 30% at a filler content of 15 wt.% with respect to that of the unfilled benchmark material. This enhanced stiffness was paralleled by 30% increased fracture toughness. As evidenced by fracture surface analysis using Environmental Electron Microscopy (ESEM) and optical microscopy, the improved energy dissipation at the crack tip correlated with roughness of the fracture surfaces, increasing with increasing filler content. Moreover, the examination of the volumetric polymerization shrinkage and the fabrication of H-shaped diagnostic specimens revealed that the nanocomposites were processed with high accuracy, increasing with increasing filler content. Nanocomposite morphologies, examined by means of Transmission Electron Microscopy (TEM), demonstrated that the large primary bentonite particles with average diameters >10 Ám fragmented into much smaller particles with average diameters in the range of 1 µm. According to TEM and Wide Angle X-Ray Scattering (WAXS), such in-situ formed nanoparticles were composed of both stacks of organoclay nanoplatelets and also isolated nanoplatelets typical for fully exfoliated organoclays.

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53: Synthesis and characterization of chiral and thermo responsive amphiphilic conetworks
Jan Tobis, Yi Thomann, Jörg C. Tiller
Polymer (2010), 51(1), 35-45

Abstract: Amphiphilic polymer conetworks (APCN) combine the properties of different polymers on the nanoscale affording advanced materials with unique properties. Here, we present the first APCN with a chiral hydrophilic phase. The conetworks were prepared by copolymerizing the tailored chiral monomer (R)-N-(1-hydroxybutan-2-yl)acrylamide (R-HBA) with two different crosslinkers that consist of bitelechelic methacrylate-terminated poly(dimethylsiloxane) (PDMS) of a molecular weight of 1100 g/mol and 5620 g/mol, respectively. The resulting polymer conetworks P-R-HBA-l-PDMS exhibited both two different Tg values, indicating nanophase separation. However, the conetwork with PDMS1.1 did not show nanophases in the AFM and did not swell the phases separately in orthogonal solvents. On the other hand the materials with PDMS5.6 acted like a typical APCN. The APCN P-R-HBA-l-PDMS5.6 was found to be temperature sensitive in water, decreasing its degree of swelling linearly with increasing temperature. Additionally, the conetwork is increasing its degree of swelling in n-heptane in the region of the Tg of the P-R-HBA phase. The impact of the chiral polymer on the release of cinchona alkaloids was examined. For example, (-)-cinchonine diffuses four times faster off the P-R-HBA-l-PDMS networks than off the P-S-HBA-l-PDMS conetworks.