TY - JOUR A1 - Harms, Stephan A1 - Raetzke, Klaus A1 - Faupel, Franz A1 - Egger, Werner A1 - Ravello, Lori Boyd de A1 - Laschewsky, André A1 - Wang, Weinan A1 - Müller-Buschbaum, Peter T1 - Free volume and swelling in thin films of poly(n-isopropylacrylamide) end-capped with n-butyltrithiocarbonate N2 - The free volume in thin films of poly(N-isopropylacrylamid) end-capped with n-butyltrio-carbonate (nbc-PNIPAM) is probed with positron annihilation lifetime spectroscopy (PALS). The PALS measurements are performed as function of energy to obtain depth profiles of the free volume of nbc-PNIPAM films. The range of nbc-PNIPAM films with thicknesses from 40 to 200 nm is focused. With decreasing film thickness the free volume increases in good agreement with an increase in the maximum swelling capability of the nbc-PNIPAM films. Thus in thin hydrogel films the sorption and swelling behavior is governed by free volume. Y1 - 2010 UR - http://www3.interscience.wiley.com/cgi-bin/jhome/10003270 U6 - https://doi.org/10.1002/marc.201000067 SN - 1022-1336 ER - TY - JOUR A1 - Glatzel, Stefan A1 - Badi, Nezha A1 - Paech, Michael A1 - Laschewsky, André A1 - Lutz, Jean-Francois T1 - Well-defined synthetic polymers with a protein-like gelation behavior in water N2 - Homopolymers of N-acryloyl glycinamide were prepared by reversible addition-fragmentation chain transfer polymerization in water. The formed macromolecules exhibit strong polymer-polymer interactions in aqueous milieu and therefore form thermoreversible physical hydrogels in pure water, physiological buffer or cell medium. Y1 - 2010 UR - http://xlink.rsc.org/jumptojournal.cfm?journal_code=CC U6 - https://doi.org/10.1039/C0cc00038h SN - 1359-7345 ER - TY - JOUR A1 - Fandrich, Nick A1 - Falkenhagen, Jana A1 - Weidner, Steffen M. A1 - Staal, Bastiaan A1 - Thuenemann, Andreas F. A1 - Laschewsky, André T1 - Characterization of new amphiphilic block copolymers of N-vinylpyrrolidone and vinyl acetate, 2-chromatographic separation and analysis by MALDI-TOF and FT-IR coupling N2 - PVP-block-PVAc block copolymers were synthesized by controlled radical polymerization applying a RAFT/MADIX system and were investigated by HPLC and by coupling of chromatography to FT-IR spectroscopy and MALDI-TOF MS. Chromatographic methods (LACCC and gradient techniques) were developed that allowed a separation of block copolymers according to their repeating units. The results of the spectroscopic and spectrometric analysis clearly showed transfer between radicals and process solvent. With the use of hyphenated techniques differences between main and side products were detected. In agreement with previously published results, obtained by NMR, SEC, static light scattering and MALDI- TOF MS, our data proved a non-ideal RAFT polymerization. Y1 - 2010 UR - http://www3.interscience.wiley.com/journal/10003495/home U6 - https://doi.org/10.1002/macp.201000044 SN - 1022-1352 ER - TY - JOUR A1 - Fandrich, Nick A1 - Falkenhagen, Jana A1 - Weidner, Steffen M. A1 - Pfeifer, Dietmar A1 - Staal, Bastiaan A1 - Thuenemann, Andreas F. A1 - Laschewsky, André T1 - Characterization of new amphiphilic block copolymers of N-vinyl pyrrolidone and vinyl acetate, 1-analysis of copolymer composition, end groups, molar masses and molar mass distributions N2 - New amphiphilic block copolymers consisting of N-vinyl pyrrolidone and vinyl acetate were synthesized via controlled radical polymerization using a reversible addition/fragmentation chain transfer (RAFT)/macromolecular design via the interchange of xanthates (MADIX) system. The synthesis was carried out in 1,4-dioxane as process solvent. In order to get conclusions on the mechanism of the polymerization the molecular structure of formed copolymers was analysed by means of different analytical techniques. C-13 NMR spectroscopy was used for the determination of the monomer ratios. End groups were analysed by means of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. This technique was also used to determine possible fragmentations of the RAFT end groups. By means of a combination of size exclusion chromatography, C-13 NMR and static light scattering molar mass distributions and absolute molar masses could be analysed. The results clearly show a non-ideal RAFT mechanism. Y1 - 2010 UR - http://www3.interscience.wiley.com/journal/10003495/home U6 - https://doi.org/10.1002/macp.200900466 SN - 1022-1352 ER - TY - JOUR A1 - Bivigou Koumba, Achille Mayelle A1 - Goernitz, Eckhard A1 - Laschewsky, André A1 - Müller-Buschbaum, Peter A1 - Papadakis, Christine M. T1 - Thermoresponsive amphiphilic symmetrical triblock copolymers with a hydrophilic middle block made of poly(N- isopropylacrylamide) : synthesis, self-organization, and hydrogel formation N2 - Several series of symmetrical triblock copolymers were synthesized by the reversible addition fragmentation chain transfer method. They consist of a long block of poly(N-isopropylacrylamide) as hydrophilic, thermoresponsive middle block, which is end-capped by two small strongly hydrophobic blocks made from five different vinyl polymers. The association of the amphiphilic polymers was studied in dilute and concentrated aqueous solution. The polymer micelles found at low concentrations form hydrogels at high concentrations, typically above 30-35 wt.%. Hydrogel formation and the thermosensitive rheological behavior were studied exemplarily for copolymers with hydrophobic blocks of polystyrene, poly(2-ethylhexyl acrylate), and poly(n-octadecyl acrylate). All systems exhibited a cloud point around 30 A degrees C. Heating beyond the cloud point initially favors hydrogel formation but continued heating results in macroscopic phase separation. The rheological behavior suggests that the copolymers associate into flower-like micelles, with only a small share of polymers that bridge the micelles and act as physical cross-linkers, even at high concentrations. Y1 - 2010 UR - http://www.springerlink.com/content/101551 U6 - https://doi.org/10.1007/s00396-009-2179-9 SN - 0303-402X ER - TY - JOUR A1 - Adelsberger, Joseph A1 - Kulkarni, Amit A1 - Jain, Abhinav A1 - Wang, Weinan A1 - Bivigou Koumba, Achille Mayelle A1 - Busch, Peter A1 - Pipich, Vitaliy A1 - Holderer, Olaf A1 - Hellweg, Thomas A1 - Laschewsky, André A1 - Müller-Buschbaum, Peter A1 - Papadakis, Christine M. T1 - Thermoresponsive PS-b-PNIPAM-b-PS micelles : aggregation behavior, segmental dynamics, and thermal response N2 - We have studied I lie thermal behavior of amphiphilic, symmetric triblock copolymers having short, deuterated polystyrene (PS) end blocks and a large poly(N-isopropylacrylarnicle) (PNIPAM) middle block exhibiting a lower critical solution temperature (LCST) in aqueous solution. A wide range of concentrations (0.1-300 mg/mL) is investigated using it number of analytical methods such as fluorescence correlation spectroscopy (FCS), turbidimetry, dynamic light scattering (DLS), small-angle neutron scattering (SANS), and neutron spin-echo spectroscopy (NSE). The critical micelle concentration is determined using FCS to be 1 mu M or less. The collapse of the micelles at the LCST is investigated using turbidimetry and DLS and shows a weak dependence on the degree of polymerization of the PNIPAM block. SANS with contrast matching allows its to reveal the core-shell Structure of the micelles as well as their correlation as a function of temperature. The segmental dynamics of the PNIPAM shell are studied as a function of temperature and arc found to be faster in the collapsed state than in the swollen state. The mode detected has a linear dispersion in q(2) and is found to be faster in the collapsed state as compared to the swollen state. We attribute this result to the averaging over mobile and immobilized segments. Y1 - 2010 UR - http://pubs.acs.org/journal/mamobx U6 - https://doi.org/10.1021/Ma902714p SN - 0024-9297 ER - TY - JOUR A1 - Wang, Weijia A1 - Kaune, Gunar A1 - Perlich, Jan A1 - Paradakis, Christine M. A1 - Bivigou Koumba, Achille Mayelle A1 - Laschewsky, André A1 - Schlage, K. A1 - Röhlsberger, Ralf A1 - Roth, Stephan V. A1 - Cubitt, Robert A1 - Müller-Buschbaum, Peter T1 - Swelling and switching kinetics of gold coated end-capped poly(N-isopropylacrylamide) thin films N2 - Thin thermoresponsive hydrogel films of poly(N-isopropylacrylamide) end-capped with n-butyltrithiocarbonate(nbc- PNIPAM) oil si I icon supports with a gold layer on top, causing an asymmetric confinement, are investigated. For two different gold layer thicknesses (nominally 0.4 and 5 rim), the swelling and switching kinetics are probed with in situ neutron reflectivity. With a temperature jump from 23 to 40 degrees C the film is switched from a swollen into a collapsed state. For the thin gold layer this switching is faster as compared to the thick gold layer. The switching is a two-step process of water release and a subsequent structural relaxation. fit swelling and deswelling cycles, aging of the films is probed. After five cycles, the film exhibits enhanced water storage capacity. Grazing-incidence small-angle X-ray scattering (GISAXS) shows that these gold coated nbc-PNIPAM films do not age with respect to the inner structure but slightly roughen at the gold surface. As revealed by atomic force microscopy, the morphology of the gold layer is changed by the water uptake and release. Y1 - 2010 UR - http://pubs.acs.org/journal/mamobx U6 - https://doi.org/10.1021/Ma902637a SN - 0024-9297 ER - TY - JOUR A1 - Uhlig, Katja A1 - Wischerhoff, Erik A1 - Lutz, Jean-Francois A1 - Laschewsky, André A1 - Jäger, Magnus S. A1 - Lankenau, Andreas A1 - Duschl, Claus T1 - Monitoring cell detachment on PEG-based thermoresponsive surfaces using TIRF microscopy N2 - Recently, we introduced a thermoresponsive copolymer that consists of oligo(ethylene glycol) methacrylate (OEGMA) and 2-(2- methoxyethoxy) ethyl methacrylate (MEO(2)MA). The polymer exhibited an LCST at 35 degrees C in PBS buffer and was anchored onto gold substrates using disulfide polymerisation initiators. It allows the noninvasive detachment of adherent cells from their substrate. As the mechanisms that determine the interaction of cells with such polymers are not well understood, we employed Total Internal Reflection Fluorescence (TIRF) microscopy in order to monitor the detachment process of cells of two different types. We identified contact area and average cell-substrate distance as crucial parameters for the evaluation of the detachment process. The sensitivity of TIRF microscopy allowed us to correlate the specific adhesion pattern of MCF-7 breast cancer cells with the morphology of cell deposits that may serve as fingerprints for a nondestructive characterisation of live cells. Y1 - 2010 UR - http://www.rsc.org/Publishing/Journals/sm/index.asp U6 - https://doi.org/10.1039/C0sm00010h SN - 1744-683X ER - TY - JOUR A1 - Skrabania, Katja A1 - von Berlepsch, Hans A1 - Böttcher, Christoph A1 - Laschewsky, André T1 - Synthesis of ternary, hydrophilic-lipophilic-fluorophilic block copolymers by consecutive RAFT polymerizations and their self-assembly into multicompartment micelles N2 - Linear amphiphilic diblock and ternary triblock copolymers were synthesized by the RAFT method in three Successive Steps, using oligo(ethylene oxide) monomethyl ether acrylate, butyl or 2-ethylhexyl acrylate, and 1H, 1H, 2H, 2H-perfluorodecyl acrylate. The diblock and the triblock copolymers, which consist of a hydrophilic, a lipophilic, and a fluorophilic block, self-assemble in water into spherical micellar aggregates. Imaging by cryogenic transmission electron microscopy (cryo-TEM) revealed that the cores of the micellar aggregates made from these "triphilic" copolymers undergo local phase separation to form various ultrastructures, which depend sensitivity on the given block sequence. While the sequence hydrophilic-lipophilic-fluorophilic resulted in multicompartment cores with core-shell-corona morphology, the sequence lipophilic-hydrophilic-fluorophilic provided new "patched double micelle" and larger "soccer ball" structures. Y1 - 2010 UR - http://pubs.acs.org/journal/mamobx U6 - https://doi.org/10.1021/Ma901913f SN - 0024-9297 ER - TY - JOUR A1 - Zehm, Daniel A1 - Laschewsky, André A1 - Gradzielski, Michael A1 - Prévost, Sylvain A1 - Liang, Hua A1 - Rabe, Jürgen P. A1 - Schweins, Ralf A1 - Gummel, Jérémie T1 - Amphiphilic dual brush block copolymers as "giant surfactants" and their aqueous self-assembly N2 - Amphiphilic dual brush diblock as well as symmetrical triblock polymers were synthesized by the overlay of the reversible addition-fragmentation chain transfer and the nitroxide mediated polymerization (NMP) techniques. While poly(ethylene glycol) brushes served as hydrophilic block, the hydrophobic block was made of polystyrene brushes. The resulting "giant surfactants" correspond structurally to the established amphiphilic diblock and triblock copolymer known as macrosurfactants. The aggregation behavior of the novel "giant surfactants" in aqueous solution was studied by dynamic light scattering, small-angle neutron scattering (SANS), and small-angle X-ray scattering (SAXS) over a large range in reciprocal space. Further, the self-assembled aggregates Were investigated by scanning force microscopy (SFM) after deposition on differently functionalized ultraflat solid substrates. Despite the high fraction of hydrophobic segments, the polymers form stable mesoscopic, spherical aggregates with hydrodynamic diameters in the range of 150-350 nm. Though prepared from well-defined individual polymers, the aggregates show several similarities to hard core latexes. They are stable enough to he deposited without much changes onto surfaces, where they cluster and show Spontaneous sorting according to their size within the clusters, with the larger aggregates being in the center. Y1 - 2010 UR - http://pubs.acs.org/journal/langd5 U6 - https://doi.org/10.1021/La903087p SN - 0743-7463 ER -