POLY(DIMETHYLSILYLENE-CO-DIPHENYLSILYLENE)

In this work several polyorganosilylenes were synthesized including homo- and copolymers containing SiMe2 and SiPh2 units. A Wurtz-type coupling reaction of the respective dichlorodiorganosilanes with sodium metal, varying the Ph2SiCl2/Me2SiCl2 ratio was the chosen synthesis method. Products with different characteristics for solubility, structure (cyclic or linear), composition, and molecular weight distribution could be obtained depending on the comonomer ratios employed. The polysilane derivatives were characterized by infrared spectroscopy (IR), proton nuclear magnetic resonance (H-1-NMR), and gel permeation chromatography (GPC). Valuable information related to the comonomers' reactivities was obtained, such as molecular weight distribution, composition, and relationships between yields of soluble, insoluble, and cyclic materials of each polycondensation reaction.30112333234

RAMAN AND INFRARED-SPECTRA OF 6LI2C2O4 AND 7LI2C2O4

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INFRARED ACTIVE FREQUENCIES FOR LITHIUM HYDROXIDE

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Photooxidation studies on branched polysilanes

The photooxidation of films of the branched [(SiEt)(m)(SiPh(2))(n)], (SiPh)(n), [(SiPh)(m)(SiMe(2))], [(Sic-hex)(m)(SiPh(2))(n)], and of the linear (SiPhMe)(n) polymers, by UV irradiation (lambda = 337 nm) was studied by IR and UV-vis spectroscopic measurements. The main chemical changes were the formation of siloxane and silanol groups, with a ratio that varied from 1.4 to 3.0, indicating partial degradation of the branched structures. At the saturation dose, the degree of oxidation of the polymer films was approximately the same (35-41%), but the total amount of oxygen incorporation was greater for the more branched ones, due to the higher density of Si-Si bonds in those polymer films. Copyright (C) 1996 Elsevier Science Ltd331818

Synthesis and structure of crosslinked poly[(methylsiloxane)-co-(oxymethylene)] copolymers

A series of new crosslinked copolymers was obtained by cationic ring-opening copolymerization of 1,3,5,7-tetramethylcpclotetrasiloxane and 1,3,5-trioxane. Theqoly[(methylsiloxane)-co-(oxyme thylene)] copolymers are white crystals or glassy. Crosslinking reactions take place in the reaction medium. The degree of crosslinking increases with a higher concentration of the methylsiloxane units in the copolymers. The combination of solid-state magic-angle spinning nuclear magnetic resonance of Si-29 and C-13 and Fourier-transform infrared spectroscopy provided a quantitative description of the copolymer microstructure.18874775

SYNTHESIS AND CHARACTERIZATION OF SOME POLY-P-SILPHENYLENES

The syntheses of some representative low molecular weight poly-p-silphenylenes containing SiMe2 or SiPh2 groups in the main chain are presented. These polymers were obtained from di-Grignard intermediates using either THF or Et2O as solvent. The insertion of the butylenoxy units in the main chains of the polymers was observed when THF was used as a solvent. The polymers were characterized by a combination of IR, H-1 and C-13 - NMR spectra and vapour pressure osmometric analysis. The thermal behaviour of the poly-p-silphenylenes was analysed by thermogravimetry.2941671354

Ceramic matrix composites derived from CrSi2-filled silicone polycyclic network

Ceramic matrix composites (CMC) were prepared by the active-filler-controlled polymer pyrolysis, using a siloxane polycyclic network filled with CrSi2. The starting CrSi2-filled polysiloxane was pyrolyzed in both nitrogen and argon atmospheres, up to 1450degreesC. During the pyrolysis in nitrogen atmosphere, the CrSi2 particles reacted with N-2, and also with carbon from the preceramic polymer binder, still complete consumption of the filler particles. Such reactions led to a dramatic change in the composition and microstructure of the resulting ceramic monoliths, which displayed linear expansion of 1.7%. In argon atmosphere, the CrSi2 particles acted as inert filler during the pyrolysis process. The final CMC compositions obtained in N-2 and Ar atmospheres were Cr0.62C0.25N0.03-Si3N4-Cr3C2 and SiOxCy-SiC-CrSi2, respectively. (C) 2004 Kluwer Academic Publishers.39144507451

Structural evolution of a poly(methylsilane)/tetra-allylsilane mixture into silicon carbide

A polymeric precursor to SiC based on the mixture between poly(methylsilane) and tetra-allylsilane was prepared. The structural evolution by which this precursor system undergoes until its conversion to SiC was monitored by IR, Raman, C-13 and Si-29 MAS NMR spectroscopies, and by XRD techniques. Thermal and density measurements were also run. The role of the hydrosilylation reaction between Si-H and C=C moities on the ceramic conversion was also investigated. (C) 1997 Elsevier Science Ltd.3381301130

Synthesis, characterization, and permeability evaluation of hybrid organic-inorganic films

The preparation and characterization of hybrid organic-inorganic films based on poly(dimethylsiloxane), PDMS, crosslinked with nanoclusters obtained from pentaerythrithol triacrylate (PETA) and 2-aminoethyl-3-aminopropyltrimethoxysilane (AS), are reported. The introduction of silica nanoclusters, obtained from tetraethoxysilane as an additional crosslinker, improved the mechanical stability of the films and also produced a noticeable decrease in the solvent sorption and in the distance between the nodes of the polymeric networks. The performance of these films as membranes for gas separation processes was similar to those reported for commercial PDMS, although they presented polar organic PETA/AS crosslinker nuclei. (C) 2004 Wiley Periodicals, Inc.42234281429

Effect of natural and organically modified montmorillonite clays on the properties of polydimethylsiloxane rubber

The effects of natural (MT) and organically modified (O-MT) montmorillonite clays on the properties of polydimethylsiloxane (PDMS) rubber were evaluated. Rubber composites with different clay contents were prepared by a compounding procedure in in open two-roll mill, which was followed by a compression-molding step in which the PDMS matrix was peroxide crosslinked. The clay rubber composites were characterized by swelling measurements in toluene, thermogravimetric analyses, X-ray diffraction, scanning electron microscopy, and tensile tests. The introduction of NIT restricted the solvent swelling and increased the crosslinking density of the rubber, which indicated the formation of a covalent filler-matrix interface. The enhanced interaction between NIT and PDMS reduced the aggregation size of MT particles in the MT composites and promoted an increase in the separation of the clay layers. When the rubber was filled with O-MT, a higher solvent amount was incorporated in the material, and this trend increased with the clay content. Moreover, the low interaction between O-MT and the PDMS chains resulted in larger clay aggregates in the O-MT composites compared to those with MT. Despite the different interface natures, both clays enhanced thermal stability and acted as reinforcing fillers in relation to Young's modulus and tensile strength. (C) 2008 Wiley Periodicals, Inc.10842587259