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Freiburg University





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Publications - Dr. Yi Thomann 1987-2004
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29: Process for coating metal apparatuses and parts thereof.
Keller, Harald; Jahns, Ekkehard; Lach, Christian; Huffer, Stephan; Krebs, Thilo; Thomann, Yi; Frechen, Thomas.
U.S. Pat. Appl. Publ. (2004), 7 pp.

Abstract: A process for coating surfaces in apparatuses or app. parts for plant construction, preferably for chem. plant construction, involves optionally first hydrophobicizing a polymer film having a microstructure and optionally addnl. macrostructured surface and then fixing it on the app. or app. part to be coated, and also apparatuses and app. parts thus coated.

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28: 3D plotting of scaffolds derived from bio degradable polymer materials and tailored for applications in tissue engineering
R. Landers, Y. Thomann, R. Mülhaupt
European Cells and Material, Vol.6, Supl. 1, 2003, p. 114

Abstract: Scaffolds are of great importance for tissue engineering because they enable the production of functional living implants out of cells obtained from cell culture. A new rapid prototyping (RP) technology was developed at the Freiburg Materials Research Center to meet the demands for desktop fabrication of scaffolds, in which liquids and pastes could be plotted and dispensed in liquid media in three-dimensional (3D). This technique can apply a much larger variety of synthetic as well as natural materials, either as aqueous solutions or pastes, to fabricate 3D scaffolds for application in tissue engineering. Soft tissue scaffolds such as out of hydrogel material and polyelectrolyte complexes was, for the first time, manufactured for cell engineering. Surface coating in the pore formation were achieved to get better biofunctionality and cell compatibility, as well as for a better cell adhesion and cell growth. The versatile applications of this new type of 3D scaffolds will be discussed, especially its potential for tissue engineering.

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27: Biofunctional Processing: Scaffold design, fabrication and surface modification
R.Mülhaupt, R.Landers, Y.Thomann
European Cells and Material, Vol.6, Supl. 1, 2003, p. 12

Abstract: Combination of modern processing technologies for biomaterials and suitable surface modification reactions provides scaffolds highly desirable for TE applications.

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26: Morphology of stereoblock polypropylene.
Thomann, Ralf; Thomann, Yi; Mülhaupt, R.; Kressler, Jörg; Busse, Karsten; Lilge, Dieter; Chien, James C. W.
Macromolecular Science, Physics (2002), B41 (4-6), 1079-1090.

Abstract: The microstructure and morphol. of stereo-block polypropylenes contg. sequences of isotactic (i) and syndiotactic (s) polypropylene (PP) were studied by 13C NMR spectroscopy, wide angle x-ray scattering (WAXS), size exclusion chromatog. (SEC) combined with FT-IR anal. of the fractions, and at. force microscopy. The 13C NMR spectra show the presence of long stereoregular sequences in the resp. stereo-block polypropylene which are able to form the crystal modification known from the resp. stereoregular homopolymers as revealed by WAXS measurements. A bimodal molar-mass distribution is detected by SEC. All SEC fractions contain i-PP and s-PP sequences, proven by FT-IR spectroscopy. It is shown by atomic-force microscopy that the stereo-block polypropylene, synthesized by homopolymn. of propylene using iso- and syndiotactic catalysts, form a microphase-sepd. morphol. The microphase sepn. is preserved also after treatment with hot toluene. A parallel investigation was conducted on a blend of i-PP and s-PP; it exhibits macrophase sepn. Treatment of the blend with hot toluene results in the dissoln. of the s-PP phase.

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25: Method for rendering surfaces resistant to soiling for glass, ceramic, wood, textile, and paper applications.
Keller, Harald; Jahns, Ekkehard; Lach, Christian; Hueffer, Stephan; Stoeckelmann, Elmar; Thomann, Yi; Frechen, Thomas.
Patent DE 2001-10101162 20010112. CAN 137:82526 AN 2002:539616

Abstract: The method is characterized in that the surfaces are coated with particles, which have an av. diam. ranging from 3 nm to 5 μm and which are comprised of a material that has a surface energy of at least 20 mN/m. The particles are manufd. from polymers (e.g., Lugalvan DC), inorg. oxides (e.g., hydrophobic silica pigment), carbonates (e.g., Printex V), phosphates, silicates, or sulfates of 3-14 Groups of periodic table. The surface to be protected is coated with an adhesive and polymer dispersion contg. said particles and heated to evap. solvents to obtain the desired coating. The method is suitable for protecting ceramic tiles, filter membranes, sanitary ware, wood surfaces, fabrics, paper, and cardboard surfaces.

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24: Coating parts of apparatus with microstructured films.
Keller, Harald; Jahns, Ekkehard; Lach, Christian; Hueffer, Stephan; Krebs, Thilo; Thomann, Yi; Frechen, Thomas.
Patent EP 2001-124648 20011016.

Abstract: In the title process, giving antiblocking surfaces and esp. useful on chem. app., polymer films with microstructured surfaces are optionally waterproofed and then attached to the app. surface. A polycarbonate film was cast with a microstructured surface (width .apprx.2 μm, height 4 μm, standoff 6 μm), waterproofed with Dynasylan F, and bonded to stainless steel with an aq. adhesive to give a coating which resisted H2O, coffee, honey, and aq. polymer dispersions.

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23: Composition for producing surfaces which are difficult to wet, their production and their use.
Keller, Harald; Jahns, Ekkehard; Lach, Christian; Hueffer, Stephan; Krebs, Thilo; Thomann, Yi; Frechen, Thomas.
Patent DE 2000-10050788 20001013

Abstract: The invention relates to a compn. comprising at least one hydrophilic, inorg. powder (P) having av. particle size 15-500 μm, and at least one hydrophobic, thermoplastic substance (T) which is characterized by surface tension 20-50 mN/m. The P/T wt. ratio is between 50:1 and 1:2. The compns. may be used to produce coatings or moldings with a self-cleaning effect or reduce resistance to flow over objects coated with or formed from them. Examples were given for coatings contg. poly(octadecyl vinyl ether) as component T and quartz microparticles as component P.

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22: Comparative study of a block copolymer morphology by transmission electron microscopy and scanning force microscopy.
Ott H; Abetz V; Altstadt V; Thomann Y; Pfau A
JOURNAL OF MICROSCOPY (2002 Jan), 205(Pt 1), 106-8.

Abstract: Using transmission electron microscopy (TEM) and scanning force microscopy (SFM) together, it was possible to verify important structural features of a nanostructured bulk material such as the kp-morphology in an ABC triblock copolymer. By applying suitable imaging techniques during the SFM measurements it was possible to determine the morphology without additional manipulation steps in between. In comparison, TEM investigations on this type of material usually require selective staining procedures prior to the measurement. Also electron beam damage is often encountered during TEM measurements especially if components such as poly(methacrylates) are present. In contrast, SFM measurements can be assumed not to significantly change the phase dimensions of the components.

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21: Coating compositions for producing difficultly-wettable surfaces.
Keller, Harald; Kuehn, Ingolf; Jahns, Ekkehard; Lach, Christian; Hueffer, Stephan; Krebs, Thilo; Thomann, Yi; Frechen, Thomas.
Eur. Pat. Appl. (2001), EP 2001-110983 20010507

Abstract: The title compns., giving coatings easily and reproducibly, contain fine powders with hydrophobic surfaces, porous structures, and sp. surface ≥ 1 m2/g, and film-forming binders with surface tension <50 mN/m in powder-binder ratio ≥ 1:4. Dispersing 10.73 g hydrophobized pyrogenic SiO2 (sp. surface 220 m2/g) in a soln. of 10.73 g poly(octadecyl vinyl ether) (mol. wt. 3000, surface tension 27.7 mN/m) in 96.6 g petroleum ether (b.p. 60-80) and coating this mixt. (100 μ m) on PET film gave a surface with repellent power for 10% aq. EtOH 358 mN-1 (droplet wt. 5.44 mg).

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20: Miscibility of Branched Ethene Homopolymers with Iso- and Syndiotactic Polypropenes.
Marquardt, Jürgen; Thomann, Ralf; Thomann, Yi; Heinemann, Johannes; Mülhaupt, Rolf.
Macromolecules (2001), 34(25, k), 8669-8674.

Abstract: The melt miscibility of stereoregular polypropene with branched ethene homopolymers, prepd. by Ni- and Pd-based catalysts, was studied by TEM, at. force microscopy, and differential scanning calorimetry. The no. of branched C atoms per 1000 C atoms, referred to as degree of branching (DB), was varied from 6 to 112. Miscibility increases with increasing DB. Blends of branched ethene homopolymers and poly(ethene-co-1-octene) with isotactic (i-PP) and syndiotactic polypropylene (s-PP) were compared and show slightly improved miscibility for s-PP. For DBs of 98 and 112 partial miscibility with polypropene was found. The miscibility of polyethenes with longer branches resemble that of polyethene/1-octene copolymers, whereas short branched polyethenes behave more like polyethene/1-butene copolymers.

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19: A Temperature- and Molar Mass-Dependent Change in the Crystallization Mechanism of Poly(1-butene): Transition from Chain-Folded to Chain-Extended Crystallization?
Fu, Qiang; Heck, B.; Strobl, G.; Thomann, Y..
Macromolecules (2001), 34(8), 2502-2511.

Abstract: The crystn. behavior of poly(1-butene) (I) was investigated by polarized light microscopy (PLM), at. force microscopy (AFM), wide-angle X-ray scattering (WAXS), dilatometry, and also by time- and temp.-resolved small-angle X-ray scattering expts. (SAXS). Observations in the PLM indicate a temp.-dependent change in the mechanism of crystn. When crossing a certain crit. crystn. temp., the morphol. changes from spherulites to quadratic, platelike single crystals. Investigations of samples with different molar mass show that the transition temp. is molar mass-dependent; on decreasing the molar mass the transition shifts to lower temps. As proved by WAXS, both the spherulites and the single crystals are of the metastable form II. The morphol. change is also obsd. in AFM images obtained after a rapid cooling of the samples to room temp.; the difference in the morphol. appearance is preserved through the transformation from form II to form I. According to dilatometric measurements, the change in the crystn. mechanism leads to variations in the temp. dependence of the crystn. rate and also to a steplike increase in the crystallinity. The results of SAXS expts. show that the formation of I crystallites is governed by the same general laws as for other polymers studied before. Both the crystn. temp., Tc, and the melting temp., Tf, are linearly dependent on the reciprocal cryst. layer thickness, dc-1, but with different slopes and different limiting temps. for dc-1 ® 0. The observations are again indicative for a crystal development in two steps: First an initial form appears which then transforms into the final lamellar crystallites. As a new feature, in direct correspondence to the two different crystn. mechanisms obsd. microscopically, two different crystn. lines (dc-1 vs Tc) show up, indicating the occurrence of two different initial states. On the other hand, only one common melting line (Tf vs. dc-1) is found, which means that the two crystn. mechanisms produce crystallites with similar surface free energies. We discuss the peculiar crystn. properties of I by comparing the radius of gyration Rg of the chains in the melt with the crystal thickness dc and propose that the change in the crystn. mechanism could be due to a change from folded-chain to chain-extended crystn., taking place when dc gets larger than Rg.

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18: Influence of stereoirregularities on the formation of the g-phase in isotactic polypropene.
Thomann, R.; Semke, H.; Maier, R.-D.; Thomann, Y.; Scherble, J.; Mülhaupt, R.; Kressler, J.
Polymer (2001), 42(10), 4597-4603.

Abstract: The mechanism of crystn. of medium to high mol. wt. isotactic polypropenes (i-PP) with different amts. of stereo-irregularities was studied and compared to that of a random copolymer of ethene and propene with 5.8% ethene. The influence of stereoregularity and crystn. temp. on the gamma-content of the crystd. samples was studied by wide angle x-ray scattering, at. force microscopy, and light microscopy. The temp. gradient elution fractionation of i-PP with large amts. of stereoirregularities and the effect of bis(p-ethylbenzylidene)sorbitol, NC-4 nucleation agent on the gamma-content was detd. Effects which render chain folding in lamellae more difficult, enhance formation of the gamma-phase. The necessity of chain folding in isotactic polypropene is described via a model that is based on the no. of chains that emerge from the lamellar surfaces of the alpha- and the gamma-phases.

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17: Morphologies and miscibilities of polypropene with random poly(ethene-co-1-butene).
Thomann, Yi; Suhm, Jurgen; Thomann, Ralf; Maier, Ralf-Dieter; Mülhaupt, Rolf; Bar, Georg.
Polymer (2001), 42(10), 4597-4603.

Abstract: We investigated the miscibilities and morphologies of isotactic and syndiotactic polypropenes (i-PP/s-PP) with random poly(ethene-co-1-butene) (PEB) as a function of 1-butene content in PEB. The blend samples were studied by means of phase imaging at. force microscopy, transmission electron microscopy, differential scanning calorimetry, dynamic mech. anal. and X-ray scattering. It was found that i-PP is melt-miscible with PEB for 1-butene contents of 88 wt.-% (miscibility window). Partial miscibility was found for s-PP/PEB blends for 1-butene contents ranging from 50 - 88 wt.-%.

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16: Translucent acrylic nanocomposites containing anisotropic laminated nanoparticles derived from intercalated layered silicates.
Dietsche, Frank; Thomann, Yi; Thomann, Ralf; Mülhaupt, Rolf.
Journal of Applied Polymer Science (2000), 75(3), 396-405.

Abstract: Acrylic nanocomposites consisting of Me methacrylate (MMA)/lauryl methacrylate (LMA) copolymers and intercalated layered silicates were prepd. The silicates are based on bentonite which was rendered organophilic by ion exchange with dimethyldioctadecylammonium ions. The morphol., thermal, mech., and optical properties were examd. as a function of bentonite and LMA content. The LMA improved the compatibility between the layered silicate and the acrylic matrix, thus promoting bentonite intercalation and formation of anisotropic laminated silicate nanoparticles. Addn. of 2-10 wt% intercalated layered silicate gives improved stiffness/toughness balance, higher Tg and enhanced thermal stability of the MMA/LMA copolymer.

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15: Recent progress in atomic force microscopy of elastomers, TPE block copolymers, and blends.
Ganter, Markus; Brandsch, Rainer; Thomann, Yi; Malner, Thomas; Bar, Georg.
Kautschuk Gummi Kunststoffe (1999), 52(11), 717-718,720-723.

Abstract: The film formation study of latex blends based on fluorinated and F-free acrylates demonstrates the ability of at. force microscopy (AFM) to distinguish between the 2 latex components. The film formation and accumulation of the F-contg. component at the surface upon annealing can be monitored. New developments in sample prepn. allow to study the bulk morphol. and nanostructure of cryomicrotomed samples by AFM. This technol. was applied to investigate poly(propene)/poly(1-olefin) blends as well as filler-modified 1,4-BR/SBR blends. In the first case, miscibility and compatibility windows were found for poly(propene)/poly(ethene-co-1-butene) blends depending on the 1-butene content. In the second case it is demonstrated that systematic AFM measurements can provide information about the local distribution of the filler particles as well as about the morphol. of the immiscible rubber components.

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14: Combined ultramicrotomy for AFM and TEM using a novel sample holder
Thomann Y; Thomann R; Bar G; Ganter M; Machutta B; Mülhaupt R
JOURNAL OF MICROSCOPY (1999 Aug), 195 ( Pt 2) 161-3.

Abstract: A new sample holder that allows combined microtomy for atomic force microscopy (AFM) and transmission electron microscopy (TEM) is described. The main feature of this sample holder is a small central part holding the sample. This central part fits into the head of an atomic force microscope. AFM measurements can be performed with a sample mounted in this central part of the sample holder. This makes the alignment of a microtomed bulk sample unnecessary, and offers the opportunity of an easy and fast combined sample preparation for AFM and TEM.

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13: Influence of comonomer incorporation on morphology and thermal and mechanical properties of blends based upon isotactic metallocene-polypropene and random ethene/1-butene copolymers.
Mader, Dietmar; Thomann, Yi; Suhm, Jurgen; Mülhaupt, Rolf.
Journal of Applied Polymer Science (1999), 74(4), 838-848.

Abstract: Blends of isotactic polypropene (i-PP) with random ethene/1-butene (EB) copolymers contg. 10, 24, 48, 58, 62, 82, and 90 wt. % 1-butene were prepd. in order to examine the influence of the EB mol. architecture on the morphol. development as well as on the thermal and mech. properties. Compatibility between i-PP and EB increased with increasing 1-butene content in EB to afford single-phase blends at a 1-butene content exceeding 82 wt. %. The morphol. was investigated using AFM and TEM. Improved compatibility accounted for enhanced EB dispersion and interfacial adhesion. Highly flexible as well as stiff blends with improved toughness were obtained.

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12: Investigation of morphologies and nanostructures of polymer blends by tapping mode phase imaging.
Thomann, Y.; Cantow, H.-J.; Bar, G.; Whangbo, M.-H.
Applied Physics A: Materials Science & Processing (1998), A66(Suppl., Pt. 2, Scanning Tunneling Microscopy/Spectroscopy and Related Techniques), S1233-S1236.

Abstract: Tapping mode at. force microscopy (TMAFM) measurements were carried out for blends of a triblock copolymer, poly(styrene)-block-poly(ethene-co-1-butene)-block-poly(styrene) (SEBS), with isotactic polypropylene (iPP). The TMAFM work on SEBS/iPP blends show that phase imaging is an important and competitive tool for studying the microphase sepn. of polymers, and that the use of the film-glass interface is relevant in learning about the bulk morphol. of polyolefinic samples by TMAFM

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11: Investigation of Morphologies of One- and Two-Phase Blends of Isotactic Poly(propene) with Random Poly(ethene-co-1-butene).
Thomann, Y.; Suhm, J.; Thomann, R.; Bar, G.; Maier, R.-D.; Mülhaupt, R.
Macromolecules (1998), 31(16), 5441-5449.

Abstract: 50/50 wt % blends of isotactic polypropene (i-PP) with metallocene-based random poly(ethene-co-1-butene) (PEB) were prepd. with 1-butene content varied from 52 to 100 wt %. The melt miscibility of the i-PP/PEB blends as a function of 1-butene content was studied by investigating the morphologies of the blends in the solid state by phase-imaging tapping mode at. force microscopy (AFM) and transmission electron microscopy (TEM). It was found that i-PP is melt miscible with PEB for 1-butene contents of 88 wt % (miscibility window). Differential scanning calorimetry (DSC) anal. showed a slower and hindered i-PP crystn. in the miscible or partially miscible blends. Intensive investigations on the apparently one-phase blend were performed by optical microscopy, small-angle X-ray scattering and dynamic mech. anal.

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10: Influence of rubber particle size on mechanical properties of polypropylene-SEBS blends.
Stricker, F.; Thomann, Y.; Mülhaupt, R.
Journal of Applied Polymer Science (1998), 68(12), 1891-1901.

Abstract: Isotactic polypropylene blends with 0-20 vol.% Kraton G thermoplastic elastomer (Kraton G) were prepd. to study the influence of elastomer particle size on mech. properties. The thermoplastic elastomer had the structure of polystyrene-block-poly(ethene-co-but-1-ene)-block-polystyrene (SEBS). SEBS particle size, detd. by means of transmission electron and at. force microscopy, was varied by using polypropylene and SEBS of different mol. wt. With increasing polypropylene mol. wt. and, consequently, melt viscosity and decreasing SEBS mol. wt., SEBS particle size decreases. Impact strength of pure polypropylene is almost independent of mol. wt., whereas impact strength of polypropylene blends increases strongly with increasing polypropylene mol. wt. The obsd. sharp brittle-tough transition is caused by micromech. processes, mostly shear yielding, esp. occurring below a crit. interparticle distance. The interparticle distance is decreasing with decreasing SEBS particle size and increasing vol. fraction. If the polypropylene matrix ligament between the SEBS particles is thinner than 0.27 mm, the blends become ductile. Stiffness and yield stress of polypropylene and polypropylene blends increase with increasing polypropylene mol. wt. in the same extent, and are consequently only dependent on matrix properties and not on SEBS particle size.

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9: m-PP blends. Processing and properties of blends based on m-PP and ethylene copolymers.
Stricker, Florian; Maier, Ralph Dieter; Thomann, Yi; Mülhaupt, Rolf.
Kunststoffe (1998), 88(4), 527-530.

Abstract: Blends of Ziegler-Natta or metallocene isotactic PP with 0-20% ethylene-1-octene copolymer with a varying 1-octene content were made in a co-rotating twin-screw extruder, and tests of mech. and rheol. properties were carried out, showing improvement in impact strength and flexibility.

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8: New molecular and supermolecular polymer architectures via transition metal catalyzed alkene polymerization.
Suhm, Jurgen; Heinemann, Johannes; Thomann, Yi; Thomann, Ralf; Maier, Ralph-dieter; Schleis, Thomas; Okuda, Jun; Kressler, Jorg; Mülhaupt, Rolf.
Journal of Materials Chemistry (1998), 8(3), 553-563.

Abstract: Superstructure formation during crystn. was examd. as a function of isotactic polypropene and polyethene mol. architectures, tailored by metallocene catalyzed propene polymn., metallocene catalyzed ethene/alk-1-ene copolymn., and Ni-catalyzed migratory insertion polymn. of ethene to afford Me-branched polyethene without using comonomers. The role of steric irregularities in the chain resulting from false insertion in stereoselective polymn. or from short chain branching, resp., was investigated. Randomly distributed regio- and stereo-regularities in isotactic polypropene chains and variation of crystn. temp. were the key to controlled polypropene crystn. and predominant formation of the g-modification. Polypropene melting temp. increased with increasing isotactic segment length between stereo- and regio-irregularities. Superstructures of isotactic g-polypropene were analyzed by light and at. force microscopy. Both types of short-chain branched polyethenes, prepd. by ethene/oct-1-ene copolymn. and migratory insertion homopolymn., showed similar dependence of melting temp. on the degree of branching, calcd. as the no. of branching C atoms per 1000 C atoms. Phase transitions were monitored by wide-angle X-ray scattering and pressure-vol.-temp. measurements. At. force microscopy was applied to image both lamella- and fringed micelle-type superstructures as a function of the degree of branching.

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7: Vapor-induced crystallization of syndiotactic random copolymers of styrene with 4-n-butylstyrene
Thomann, Ralf; Thomann, Yi; Sernetz, Friedrich G.; Mülhaupt, Rolf; Kressler, Joerg.
Polymer Bulletin (Berlin) (1998), 40(2-3), 313-319.

Abstract: The vapor-induced modification of bulk samples of syndiotactic random copolymers of styrene and 4-n-butylstyrene (BS) is studied by wide-angle x-ray scattering and light microscopy. Two samples with BS contents of 4 and 11 mol% are compared. It is shown that treatment with CHCl3 leads to the formation of a clathrate modification similar to that of neat syndiotactic polystyrene. The change of the surface topog. of the copolymers as a result of CHCl3 vapor exposition is studied by tapping-mode/height-mode at. force microscopy.

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6: Characterization of the Morphologies and Nanostructures of Blends of Poly(styrene)-block-poly(ethene-co-but-1-ene)-block-poly(styrene) with Isotactic and Atactic Polypropylenes by Tapping-Mode Atomic Force Microscopy.
Bar, G.; Thomann, Y.; Whangbo, M.-H.
Langmuir (1998), 14(5), 1219-1226.

Abstract: Blends of poly(styrene)-block-poly(ethene-co-but-1-ene)-block-poly(styrene) (SEBS) with isotactic polypropylene (i-PP) and with atactic polypropylene (a-PP) were prepd. under different thermal treatments. The nanostructures and the morphologies of these blends as well as their dependence on blending history were investigated based on the phase imaging of tapping-mode at. force microscopy (TMAFM). The obsd. macrophase sepn. in i-PP/SEBS blends is caused by the incompatibility of the 2 polymer components. The microphase sepn. of the SEBS component depends on the thermal treatment. The morphol. of a-PP/SEBS blends exhibits domains that span a wide range of sizes from 15 mm down to 15 nm. TMAFM phase imaging is shown to be an important and competitive tool for studying the microphase sepn. of polymers.

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5: Characterization of heterogeneous organic surfaces using atomic force microscopy
R. Brandsch, Y. Thomann, HJ Cantow, G. Bar
EUROPEAN JOURNAL OF CELL BIOLOGY, Volume 74, Page 10, Suppl. 45, 1997

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4: Morphology of banded spherulites in poly(e-caprolactone)/poly(styrene-ran-acrylonitrile) blends.
Wang, Chun; Thomann, R.; Kressler, J.; Thomann, Y.; Cramer, K.; Stuhn, B.; Svoboda, P.; Inoue, T.
Acta Polymerica (1997), 48(9), 354-362

Abstract: The occurrence of banded spherulites in blends of poly(e-caprolactone) with poly(styrene-ran-acrylonitrile) is studied by means of optical, scanning electron, environmental scanning electron, and at. force microscopy, as well as small-angle x-ray scattering. The measurements reveal that lamellae are confined in fibrils that bend periodically from the center of spherulites in a radial direction. The fibrils show also a regular spacing in the lateral direction. Single bent lamellae can be obsd. by at. force microscopy after permanganic etching. The enrichment of amorphous material near to the growth front of the spherulites can be directly obsd. by polarized light microscopy after temp. jump expts. The excluded amorphous material on the surface of the growing spherulites has the shape of droplets. This might be the main reason for the initiation of the bending process because the result is a non-uniform stress distribution acting on the growing lamellae at the interface between spherulites and the surrounding melt. The amorphous material of the blends can be found in 3 areas as obsd. by small-angle x-ray scattering expts. and microscopical methods: between the lamellae, excluded from the interlamellar region but within the spherulite, and for high contents of non-crystallizable material, it can be excluded from the spherulite. The banding periodicity of spherulites as a function of the crystn. temp. can be described in terms of 2 models, based either on the inherent twisting of lamellae perpendicular to the axis of a screw dislocation or on the dependence of the diffusion of amorphous material away from the growth front of lamellae and the temp. dependence of the rate of crystn. Both models fail at very low supercoolings near to temps. where the banding disappears completely.

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3: Factors affecting the height and phase images in tapping mode atomic force microscopy. Study of phase-separated polymer blends of poly(ethene-co-styrene) and poly(2,6-dimethyl-1,4-phenylene oxide).
Bar, G.; Thomann, Y.; Brandsch, R.; Cantow, H.-J.; Whangbo, M.-H.
Langmuir (1997), 13(14), 3807-3812.

Abstract: Blends of two polymers, poly(ethene-co-styrene) and poly(2,6-dimethyl-1,4-phenylene oxide), were examd. with tapping mode at. force microscopy using various values of the driving amplitude A0 and set-point amplitude ratio rsp = Asp/A0, where Asp is the set-point amplitude. In height and phase images of the blend samples, the relative contrast of chem. different regions depends sensitively on the rsp and A0 values. As the tip-sample force is increased from small to large, both phase and height images of blend samples can undergo a contrast reversal twice. This makes it difficult to assign the features of height and phase images to different chem. components without performing addnl. expts. Phase and height images were interpreted by analyzing several factors that affect the dependence of phase shift and amplitude damping on rsp and A0.

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2: Temperature rising elution fractionation of a random ethene/styrene copolymer.
Yi Thomann, Friedrich G. Sernetz, Ralf Thomann, Jörg Kressler, Rolf Mülhaupt
Macromolecular Chemistry and Physics (1997), 198(3), 739-748.

Abstract: A random ethene/styrene copolymer contg. 13.8 mol% styrene was prepd. with the metallocene catalyst system Me2Si(Me4Cp)(N-tert-butyl)TiCl2/Me aluminoxane and characterized by preparative temp. rising elution fractionation (TREF) combined with size-exclusion chromatog., NMR spectroscopy, DSC, and wide-angle x-ray scattering anal. of the copolymer fractions. Efforts are made to describe the distribution of the styrene content of the fractions using the Stockmayer-Tacx distribution function. Both comonomer distribution and mol. wt. distribution strongly support the presence of a single type of catalytically active center.

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1: The Advances in Polyurethane Elastomers At Home and Abroad
Yi Xu ( Yi Thomann ), Ding Fang Xiao
China Plastics (1987), Vol. 2, 46-53.

Abstract: This article is a review on the new development of urethane elastomers. It explains with detail about the raw materials,properties, equipments and applications of PUE that developed in recent years.