- Thicker is better? Synthesis and evaluation of well-defined polymer brushes with controllable catalytic loadings
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Polymer brushes (PBs) have been used as supports for the immobilization of palladium complexes on silicon surfaces. The polymers were grown by surface-initiated atom-transfer radical polymerization (SI-ATRP) and postdecorated with dipyridylamine (dpa) ligands. The pendant dpa units were in turn complexed with [Pd(OAc)2] to afford hybrid catalytic surfaces. A series of catalytic samples of various thicknesses (ca. 20-160 nm) and associated palladium loadings (ca. 10-45 nmol cm-2) were obtained by adjusting the SI-ATRP reaction time and characterized by ellipsometry, X-ray reflectivity, X-ray photoelectron spectroscopy, and inductively coupled plasma mass spectrometry (ICP-MS). ICP-MS revealed a near-linear relationship between thickness of the polymer brush and palladium content, which confirmed the robustness of the preparation and postmodification sequence presented herein, rendering possible the creation of functional architectures with predefined catalytic potential. The activities of the catalytic PBs were determined by systematically exploring a full range of substrate-to-catalyst ratios in a model palladium(0)-catalyzed reaction. Quantitative transformations were observed for loadings down to 0.03 mol % and a maximum turnover number (TON) of around 3500 was established for the system. Comparison of the catalytic performances evidenced a singular influence of the thickness on conversions and TONs. The limited recyclability of the hairy catalysts has been attributed to palladium leaching.
- Fernandes, Antony E.,Dirani, Ali,D'Haese, Cecile,Deumer, Gladys,Guo, Weiming,Hensenne, Peter,Nahra, Fady,Laloyaux, Xavier,Haufroid, Vincent,Nysten, Bernard,Riant, Olivier,Jonas, Alain M.
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- Liquid crystal mono- and nano-layers covalently bonded to silicon and silica surface for alignment of LC layers
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We synthesized two types of liquid crystalline nano-layers covalently bonded to Si and Si/SiO2 wafers. Monolayers of terminal and lateral low molecular weight mesogens exhibit spontaneous homeotropic orientation, while planar orientation is obtained by means of rubbing process. On the other hand a novel polymer liquid crystal nano-layer, obtained via atom transfer radical polymerization (ATRP) of acrylate monomer from Si/SiO2 surface, exhibits planar orientation of liquid crystalline side chain moieties. Structure of such novel composites was confirmed by optical studies as well as spectroscopic methods, including ellipsometry. The goal was to obtain low molecular weight liquid crystals alignment just from the mentioned above, modified surfaces. Copyright Taylor & Francis Group, LLC.
- Stanczyk, Wodzimierz A.,Szelg, Anna,Kurjata, Jan,Nowinowski-Kruszelnicki, Edward,Walczak, Andrzej
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- Silicon compound
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The present invention provides a novel silicon compound represented by Formula (1) having a living radical polymerization initiating ability for addition-polymerizable monomers and a polymer obtained using the same. The above polymer can provide an organic-inorganic composite material having a distinct structure. wherein R1 is hydrogen, alkyl, aryl or arylalkyl; R2 and R3 are alkyl, phenyl or cyclohexyl; and A is a group having an ability to initiate polymerization of a monomer.
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(2008/06/13)
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