TY - JOUR A1 - Zehm, Daniel A1 - Laschewsky, André A1 - Heunemann, Peggy A1 - Gradzielski, Michael A1 - Prevost, Sylvain A1 - Liang, Hua A1 - Rabe, Jürgen P. A1 - Lutz, Jean-Francois T1 - Synthesis and self-assembly of amphiphilic semi-brush and dual brush block copolymers in solution and on surfaces JF - Polymer Chemistry N2 - The combination of two techniques of controlled free radical polymerization, namely the reversible addition fragmentation chain transfer (RAFT) and the atom transfer radical polymerization (ATRP) techniques, together with the use of a macromonomer allowed the synthesis of symmetrical triblock copolymers, designed as amphiphilic dual brushes. One type of brush was made of poly(n-butyl acrylate) as soft hydrophobic block, i.e. characterized by a low glass transition temperature, while the other one was made of hydrophilic poly(ethylene glycol) (PEG). The new triblock polymers represent "giant surfactants" according to their molecular architecture. The hydrophobic and hydrophilic blocks microphase separate in the bulk. In aqueous solution, they aggregate into globular micellar aggregates, their size being determined by the length of the stretched polymer molecules. As determined by the combination of various scattering techniques for the dual brush copolymer, a rather compact structure is formed, which is dominated by the large hydrophobic poly(n-butyl acrylate) block. The aggregation number for the dual brush is about 10 times larger than for the "semi-brush" precursor copolymer, due to the packing requirements for the much bulkier hydrophobic core. On mica surfaces the triblock copolymers adsorb with worm-like backbones and stretched out side chains. Y1 - 2011 U6 - https://doi.org/10.1039/c0py00200c SN - 1759-9954 VL - 2 IS - 1 SP - 137 EP - 147 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Zehm, Daniel A1 - Laschewsky, André A1 - Liang, Hua A1 - Rabe, Jürgen P. T1 - Straightforward access to amphiphilic dual bottle brushes by combining RAFT, ATRP, and NMP polymerization in one sequence JF - Macromolecules : a publication of the American Chemical Society N2 - Molecular brush diblock copolymers were synthesized by the orthogonal overlay of the RAFT (reversible addition-fragmentation chain transfer), the ATRP (atom transfer radical polymerization), and the NMP (nitroxide-mediated polymerization) techniques. This unique combination enabled the synthesis of the complex amphiphilic polymers without the need of postpolymerization modifications, using a diblock copolymer intermediate made from two selectively addressable inimers and applying a sequence of four controlled free radical polymerization steps in total. The resulting polymers are composed of a thermosensitive poly(N-isopropylacrylamide) brush as hydrophilic block and a polystyrene brush as hydrophobic block, thus translating the structure of the established amphiphilic diblock copolymers known as macro surfactants to the higher size level of "giant surfactants". The dual molecular brushes and the aggregates formed on ultra flat solid substrates were visualized by scanning force microscopy (SFM). Y1 - 2011 U6 - https://doi.org/10.1021/ma2015613 SN - 0024-9297 VL - 44 IS - 24 SP - 9635 EP - 9641 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Hildebrand, Viet A1 - Laschewsky, André A1 - Zehm, Daniel T1 - On the hydrophilicity of polyzwitterion poly (N, N-dimethyl-N(3-(methacrylamido)propyl)ammoniopropane sulfonate) in water, deuterated water, and aqueous salt solutions JF - Journal of biomaterials science : Polymer edition KW - polyzwitterion KW - sulfobetaine KW - synthesis KW - fluorescence label KW - upper critical solution temperature KW - isotope effect KW - anti-polyelectrolyte effect Y1 - 2014 U6 - https://doi.org/10.1080/09205063.2014.939918 SN - 0920-5063 SN - 1568-5624 VL - 25 IS - 14-15 SP - 1602 EP - 1618 PB - Routledge, Taylor & Francis Group CY - Abingdon ER - TY - CHAP A1 - Laschewsky, André A1 - Liang, Hua A1 - Rabe, Jürgen P. A1 - Skrabania, Katja A1 - Stahlhut, Frank A1 - Weiss, Jan A1 - Zehm, Daniel T1 - Molecularly designed polymer colloids From giant surfactants to multicompartment micelles T2 - Abstracts of papers : joint conference / The Chemical Institute of Cananda, CIC, American Chemical Society, ACS Y1 - 2012 SN - 0065-7727 VL - 244 IS - 32 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Skrabania, Katja A1 - Miasnikova, Anna A1 - Bivigou Koumba, Achille Mayelle A1 - Zehm, Daniel A1 - Laschewsky, André T1 - Examining the UV-vis absorption of RAFT chain transfer agents and their use for polymer analysis JF - Polymer Chemistry N2 - The absorption characteristics of a large set of thiocarbonyl based chain transfer agents (CTAs) were studied by UV-vis spectroscopy in order to identify appropriate conditions for exploiting their absorbance bands in end-group analysis of polymers prepared by reversible addition-fragmentation chain transfer (RAFT) polymerisation. Substitution pattern and solvent polarity were found to affect notably the wavelengths and intensities of the pi-pi*- and n-pi*-transition of the thiocarbonyl bond of dithioester and trithiocarbonate RAFT agents. Therefore, it is advisable to refer in end group analysis to the spectral parameters of low molar mass analogues of the active polymer chain ends, rather than to rely on the specific RAFT agent engaged in the polymerisation. When using appropriate conditions, the quantification of the thiocarbonyl end-groups via the pi-pi* band of the thiocarbonyl moiety around 300-310 nm allows a facile, sensitive and surprisingly precise estimation of the number average molar mass of the polymers produced, without the need of particular end group labels. Moreover, when additional methods for absolute molar mass determination can be applied, the quantification of the thiocarbonyl end-groups by UV-spectroscopy provides a good estimate of the degree of active end group for a given polymer sample. Y1 - 2011 U6 - https://doi.org/10.1039/c1py00173f SN - 1759-9954 VL - 2 IS - 9 SP - 2074 EP - 2083 PB - Royal Society of Chemistry CY - Cambridge 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 - TY - THES A1 - Zehm, Daniel T1 - Amphiphile Block-Bürstenpolymere : ihre Synthese durch sequentielle Anwendung von CRP-Methoden und ihre Selbstorganisation in ausgewählten Lösungsmitteln Y1 - 2010 CY - Potsdam ER - TY - JOUR A1 - Zehm, Daniel A1 - Fudickar, Werner A1 - Hans, Melanie A1 - Schilde, Uwe A1 - Kelling, Alexandra A1 - Linker, Torsten T1 - 9,10-Diarylanthracenes as molecular switches : syntheses, properties, isomerisations and their reactions with singlet oxygen N2 - A series of 9,10-diarylanthracenes with various substituents at the ortho positions have been synthesised by palladium-catalysed cross-coupling reactions. Such compounds exhibit interesting physical properties and can be applied as molecular switches. Despite the high steric demand of the substituents, products were formed in moderate-to-good yields. In some cases, microwave conditions further improved yields. Bis-coupling afforded two isomers (syn and anti) that do not interconvert at room temperature. These products were easily separated and their relative stereochemistries were unequivocally assigned by NMR spectroscopy and X-ray analysis. The syn and anti isomers exhibit different physical properties (e.g., melting points and solubilities) and interconversion by rotation around the aryl-aryl axis commences at <100 °C for fluoro-substituted diarylanthracenes and at >300 °C for alkyl- or alkoxy-substituted diarylanthracenes. The reactions with singlet oxygen were studied separately and revealed different reactivities and reaction pathways. The yields and reactivities depend on the size and electronic nature of the substituents. The anti isomers form the same 9,10-endoperoxides as the syn species, occasionally accompanied by unexpected 1,4-endoperoxides as byproducts. Thermolysis of the endoperoxides exclusively yielded the syn isomers. The interesting rotation around the aryl-aryl axis allows the application of 9,10-diarylanthracenes as molecular switches, which are triggered by light and air under mild conditions. Finally, the oxygenation and thermolysis sequence provides a simple, synthetic access to a single stereoisomer (syn) from an unselective coupling step. Y1 - 2008 SN - 0947-6539 ER -