Based on patented Wacker technology, elastomeric and highly crosslinked silicone and silicone-organopolymer core-shell materials can be synthesized and manufactured on a large scale. These novel tailor-made materials consist of monodisperse primary particles which can be homogeneously dispersed in thermosetting and thermoplastic resins to improve mechanical properties, e. g., impact resistance, leading to a variety of possibilities for polymer and coating applications. Mechanical studies in several systems exhibited significant effects even with very low particle loading levels.

reactive resins or thermosets, particularly those with high degrees of crosslinking, generally have the disadvantage of excessive brittleness. Over the past twenty or thirty years, there have therefore been many efforts to increase the fracture toughness of highly crosslinked reactive resins. At present, thermoplastic toughening is the solution that offers the most advantageous property combinations. However, the hightemperature-resistant thermoplastic modifiers that influence the toughness of the material are difficult to process. They considerably increase the viscosity of the resin and are only sparingly soluble in it, which is the reason that their use has essentially remained restricted to CRP structural applications in aircraft manufacture. The oldest method of increasing the fracture toughness of reactive resins is modification with liquid reactive rubbers. These dissolve without any problem in the resin and bring about only a moderate increase in viscosity as compared with high-Tg thermoplastics. Because of their relatively favourable price and ease of processing, these reactive rubbers are now widely used as toughening agents. However, they have a number of disadvantages, such as reduced elastic modulus, low glass transition temperatures and high water absorption. Resistance to thermooxidative degradation is also lowered. Unlike with thermoplastic toughening agents, the effectiveness of rubber toughening modifiers is dependent on the network density of the resin matrix: the toughening effect decreases with increasing crosslink density. In toughening thermosets, both with thermoplastic toughening agents and reactive rubbers, the achievable effect is dependent on the thermodynamically and kinetically controlled process of phase separation during curing. Consequently, the resulting properties are also dependent on many factors that influence the thermodynamics and kinetics of phase separation (e. g. fillers and other modifiers, curing regime). If phase separation is prevented by, for example, over-rapid curing, the toughening effect is only minimal. Soft Core, “Hard” Shell

Up to 50 % dye relative to the dead weight may be loaded into poly(organosiloxane) nanoparticles that contain quaternary ammonium groups (vessels 1–3 with hydrophilic thymol blue as a model substance), whereas nanoparticles without quaternary ammonium groups take up no dye (vessels 4, 5). The loading depends inter alia on the construction of the nanoparticles (core–shell, hollow spheres), on the amphiphilicity, which is adjustable by synthesis, and on the method of the phase transfer.

Bis zu 50 % Farbstoff bezogen auf das Eigengewicht nehmen Poly(organosiloxan)-Nanopartikel mit quartären Ammonium-Gruppen (Glas 1–3 mit hydrophilem Thymolblau als Modellsubstanz) im Unterschied zu ammoniumfreien Partikeln (Glas 4, 5) auf. Einfluss auf die Beladung haben unter anderem der Aufbau der Nanopartikel (Kern-Schale, Hohlkugel), die durch die Synthese einstellbare Amphiphilie und die Art des Phasentransfers.

Microgels are monodisperse poly(organosiloxane) microparticles that can be functionalized at their surface. These materials were tested as supports for heterogeneous cocatalysts of the methylaluminoxane type and were used for the polymerizations of olefins with transition-metal catalysts. The cocatalysts were synthesized directly on the surfaces of the microgel particles by the partial hydrolysis of trimethylaluminum and were then used for the activation of homogeneous catalyst precursors. Complexes of various chemical natures were successfully activated and optimized through variations in the Al/H2O ratio used for the synthesis. Metallocene dichloride complexes and coordination compounds of iron and nickel were tested as catalysts for ethylene polymerization, and the results were compared with the results for the homogeneous systems and heterogeneous systems supported on silica gel (SiO2). (C) 2002 Wiley Periodicals, Inc.

Core-shell and core- shell-shell nanospheres with different amphiphilicities were synthesized by sequential condensation of trimethoxymethylsilane (T), diethoxydimethylsilane (D), and the functional monomer (chloromethylphenyl)trimethoxysilane (CIBz-T) and mixtures thereof The condensation was performed in aqueous dispersion in the presence of surfactant. Saturation of reactive surface SiOH groups with monofunctional trimethylsilane monomers prevents interparticle condensation and leads to nanoparticles, which are redispersable in organic solvents. The diameters of the particles range between 20 and 40 nm, depending on the composition. The thickness of the outer, nonfunctionalized shell is determined by asymmetrical flow field-flow fractionation (AF-FFF) and dynamic light scattering (DLS) of the core and core-shell particles, respectively. It varies between 1.5 and 3 nm and is proportional to the volume of added monomer. Incorporating (chloromethylphenyl)siloxane groups in the core and performing a subsequent quaternization reaction of dimethylaminoethanol yield amphiphilic nanospheres with an ionic, hydrophilic core and a hydrophobic outer shell. The amount of ionic moieties is found to be proportional to the amount of functional (chloromethylphenyl)siloxane groups incorporated in the spheres. Additionally, multiple shell topologies were successfully prepared, i.e., particles with a poly(dimethylsiloxane) (PDMS) core, an ionic inner and a hydrophobic outer shell. If linear PDMS chains forming the core are prevented to chemically bind to the inner shell, they may be removed by ultrafiltration, resulting in the formation of hollow spheres.

Zirconocene dichloride and bis(n-butylcyclopentadienyl)zirconium dichloride are used as catalyst precursors for the heterogeneous polymerization of ethene. A methyl-substituted microgel as support material for heterogeneous cocatalysts on the basis of MAO is compared with different commercially available silica-supported cocatalysts. The catalyst performances and the properties of the obtained polyethenes show considerable differences. (C) 2001 John Wiley & Sons, Inc.

Twenty-five different functionalized and nonfunctionalized polyorganosiloxane microgels were applied as support materials for methylalumoxane (MAO)-type compounds to give various heterogeneous cocatalysts which are able to activate metallocene complexes like Cp2ZrCl2 for ethene polymerization. The functionalization of the microgels has a strong influence on the properties of the catalysts and the produced polyethenes. (C) 2001 John Wiley & Sons, Inc.

Advanced MaterialsVolume 11, Issue 9 p. 761-766 Communication Design and Synthesis of Molecular Reactors for the Preparation of Topologically Trapped Gold Cluster Christopher Roos, Christopher Roos Institut für Physikalische Chemie, Johannes Gutenberg-Universität Mainz, Jakob Welder Weg 11, D-55128 Mainz (Germany)Search for more papers by this authorManfred Schmidt, Manfred SchmidtSearch for more papers by this authorJochen Ebenhoch, Jochen Ebenhoch Wacker-Chemie GmbH, D-84480 Burghausen (Germany)Search for more papers by this authorFrank Baumann, Frank Baumann Wacker-Chemie GmbH, D-84480 Burghausen (Germany)Search for more papers by this authorBernward Deubzer, Bernward Deubzer Wacker-Chemie GmbH, D-84480 Burghausen (Germany)Search for more papers by this authorJohann Weis, Johann Weis Wacker-Chemie GmbH, D-84480 Burghausen (Germany)Search for more papers by this author Christopher Roos, Christopher Roos Institut für Physikalische Chemie, Johannes Gutenberg-Universität Mainz, Jakob Welder Weg 11, D-55128 Mainz (Germany)Search for more papers by this authorManfred Schmidt, Manfred SchmidtSearch for more papers by this authorJochen Ebenhoch, Jochen Ebenhoch Wacker-Chemie GmbH, D-84480 Burghausen (Germany)Search for more papers by this authorFrank Baumann, Frank Baumann Wacker-Chemie GmbH, D-84480 Burghausen (Germany)Search for more papers by this authorBernward Deubzer, Bernward Deubzer Wacker-Chemie GmbH, D-84480 Burghausen (Germany)Search for more papers by this authorJohann Weis, Johann Weis Wacker-Chemie GmbH, D-84480 Burghausen (Germany)Search for more papers by this author First published: 08 July 1999 https://doi.org/10.1002/(SICI)1521-4095(199906)11:9<761::AID-ADMA761>3.0.CO;2-DCitations: 37AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Abstract Functionalized core/shell organosilicon micronetworks with siliconhydride groups bound to the core are utilized as active molecular reactors for colloid formation. The Figure shows the various kinetic processes (diffusion in and out, reduction, and nucleation) controlling gold colloid formation. Since reduction is strictly located in the core of the microgels the formation of topologically trapped gold clusters can be observed. Citing Literature Volume11, Issue9June, 1999Pages 761-766 RelatedInformation

Communication: Confined-reaction vessels, drug carriers, and dye dispersants are some of the potential applications of molecular boxes or containers. The synthesis, characterization, and properties of molecular boxes based on hollow organosilicon micronetworks are presented here. The Figure is a scanning force microscopy image of the micronetworks filled with linear poly(dimethylsiloxane) chains.

AbstractNichtkatalysierte Transferhydrierungen sind H2‐Übertragungsreaktionen von Donoren mit schwach gebundenen Wasserstoffatomen auf ungesättigte Acceptoren mit z. B. C‐C‐, C‐O‐, C‐N‐, N‐N‐oder N‐O‐Doppelbindungen, die durch H‐Atom‐Übertragung (Retrodisproportionierung) eingeleitet werden. Transferhydrogenolysen sind Reaktionen, bei denen σ‐Bindungen unter H2‐Addition gespalten werden. Die Hydrierungen werden durch eine H‐Übertragung abgeschlossen und folgen keinem Kettenmechanismus. Die einleitenden H‐Atom‐Übertragungsschritte beider Reaktionen ergänzen die bimolekularen Radikalbildungsreaktionen (Molecule Induced Radical Formation, MIRF) wie die Bildung von 1,4‐Diradikalen aus Alkenen oder Heteroalkenen. Transferhydrierung und ‐hydrogenolyse sind bei der Kohleverflüssigung ebenso von Bedeutung wie bei Aromatisierungen mit Nitroarenen oder Chinonen und möglicherweise sogar bei der biochemischen Dehydrierung. Wir berichten hier über Studien zum Mechanismus, über Struktur‐Reaktivitäts‐Beziehungen und die derzeitige Anwendungsbreite dieser Reaktionen.

AbstractThe uncatalyzed transfer hydrogenation of substituted α‐methylstyrenes with 9,10‐dihydroanthracene (DHA), xanthene (XAN), or 9,10‐dihydroacridine (DHAC) was studied mechanistically. The three hydrogen donors react at very similar rates and with similar activation parameters and with little discrimination between the various substituted styrenes. The kinetic isotope effects are also similar and the solvent effect is small. A hydrogen atom transfer mechanism (retrodisproportionation) is, therefore, preferred to a hydride transfer mechanism. This is supported by the very similar reactivity of the hydrogen transfer reaction of DHA and XAN with 9‐methylenefluorene. The product yields in all reactions investigated in this project were >90%.

Eine effiziente und einfache Methode zur Synthese von zwei einheitlichen Buckminsterfulleren‐Hydrierungsprodukten, C60H18 und C60H36, bietet die Titelreaktion. Das Bild rechts zeigt eine wahrscheinliche, mit MM2‐Rechnungen energieminimierte Struktur von C60H36. Die Ergebnisse sind ein wichtiger Schritt zu einer präparativen Organischen Chemie von C60.magnified image