Siloxane Compounds Research Articles

Vanadium and tellurium siloxane compounds as precursors of vanadium oxide and tellurium oxide silica materials

The twelve-membred vanadium containing siloxane ring [t-Bu2SiOV(O)ClO]3 (compound 1) and t-Bu2Si(OTeCl3)2 (compound 2) are efficient single-source precursors to vanadium and tellurium–silica materials. The ceramic conversions which occur pyrolytically at about 460 and 300°C for compounds 1 and 2, respectively lead to materials having the V2O5–SiO2 and TeO2–SiO2 compositions, respectively. Thermogravimetric and differential thermal analysis (TG–DTA), X-ray diffraction, 29Si, 51V and 125Te solid NMR as well as vibrational spectroscopy were used to characterise the materials. The molecular route to oxide materials, described here, could represent an alternative way to the sol–gel process.

Determination of ultratrace metallic impurities in polysilane and siloxane polymers for microelectronic devices

Ultratrace metallic elements in polysilane, siloxane and other such organic silicon compounds used in the fabrication of semiconductor devices are determined so as to understand their effects on the devices. Separating organic silicon by means of hydrolysis to SiO2 is a high sensitivity analysis. The established procedures involve dissolution of organic silicon compounds and the hydrolyzed products of organic silicon samples in hydrofluoric acid-containing reagents followed by evaporation of the silicon matrix as H2SiF6. The residual metallic elements in the treated sample solution were then determined by electrothermal atomic absorption spectrometry (ETAAS). The results indicated that a small amount of sulfuric acid was helpful in yielding SiO2 from organic silicon compounds, and that proper controls of the evaporation process are effective in preventing chemical interferences of some metallic elements during recovery and reproducible analysis. The methods developed were applied to the determination of metallic elements such as sodium, iron, and copper in various kinds of organic silicon compounds used for microelectronic devices. The limit of detection for seven metallic elements was as low as 0.1 ng g−1 levels.

Physicochemical Modification of Siloxane Compounds for Electrical Engineering in the Course of Mixing

The effect of silica fillers, used separately or in combination, on the rheological properties of siloxane compounds based on low- and high-molecular-weight rubbers was studied. A model was suggested for formation of the structure of filled compounds during mixing under conditions of shear stresses, and a procedure was proposed for preparing compounds for shells of high-voltage insulators produced by pressure casting.

Determination of low molecular weight silicones in plasma and blood of women after exposure to silicone breast implants by GC/MS.

A sensitive, one-step sample preparation method for detection of volatile, low molecular weight (LMW) cyclic silicones hexamethylcyclotrisiloxane (D3), octamethyl-cyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5), and dodecamethylcyclohexasiloxane (D6) in plasma and blood using gas chromatography coupled with mass spectrometry (GC/MS, SIM mode) is presented. In spiked experiments, extraction efficiencies for these siloxanes (100-20 000 ng/mL) were approximately 90% for plasma and approximately 80% for blood; only in the case of D3 was the recovery very low. Plasma and blood of women who are or were exposed to silicone gel-filled implants and of control subjects were analyzed for low molecular weight silicones. D3-D6 were not detectable in control plasma or blood. Although the investigated numbers of patients samples are very limited, and thus, no statistical analysis is possible, our data clearly show a general increase in the amount of LMW cyclic siloxanes in the bodies of women with silicone implants. In particular, several years after ruptured silicone implants were removed, siloxanes could still be found in blood samples from several women. Siloxane compound D3 varied between 6 and 12 ng/mL (plasma) and between 20 and 28 ng/mL (blood), whereas the concentration range of D4 was 14-50 ng/mL (plasma) and 79-92 ng/mL (blood). D5 and D6, with one exception, could not be detected.

SFC/FTIR, SFC/APCI–MS and MALDI–TOF-MS for the analysis of siloxane–ethylene oxide copolymers

Polydimethylsiloxanes (PDMSs) modified by introducing ethylene oxide units with the aim of forming sufficiently water-soluble siloxane compounds were characterized using supercritical fluid chromatography (SFC) coupled with Fourier transform infrared (FTIR) spectroscopy and atmospheric pressure chemical ionization mass spectrometry (APCI–MS), and matrix-assisted laser desorption–ionization time-of-flight mass spectrometry (MALDI–TOF-MS). SFC has a domain in analyzing oligomers. Hyphenated techniques enable elucidation of the components. Remarkable is the resolution and short analysis time of MALDI–TOF-MS. SFC also allows quantification of the basic and reaction products.

シロキサン・シラノールの有機化学

This article reviews organic chemistry of siloxane and silanol involving the preparative method as well as applications towards organic synthesis. Chapter 1 deals with the formation of siloxane bond and reactions of thus prepared siloxane compounds. Chapter 2 covers recent preparative methods for silanols and new synthetic reaction using silanol involving 1) utilization of silanol oxygen that serves as a base or a nucleophile, 2) transformation of neighboring functionality on the silicon substituent based on the interaction of silanol oxygen with an organometallic reagent, and 3) transformation of a carbon silicon bond of silanols directed to novel carbon-carbon bond forming reactions.

Pilot plant study to assess the fate of two volatile methyl siloxane compounds during municipal wastewater treatment

AbstractThe environmental fate ofoctamethylcyclotetrasiloxane(D4) and decamethylcyclopentasiloxane (D5) during municipal wastewater treatment has been investigated in an activated sludge pilot plant by continuously dosing the influent with exagerated amounts of the compounds and measuring their emissions in the off‐gas, effluent, and sludge streams. The total removal was found to be 86.4 ± 3.9% for D4 and 95.8 ± 1.5% for D5 (±1 SD statistical uncertainty). However, low overall mass balances were found for both compounds in the pilot system. In order to elucidate the detailed removal mechanisms for these two compounds, the model TOXCHEM was used to simulate their removal and analyze their mass balances in the pilot system. Experimental and model results indicated that the low mass balances were caused by the significant underestimation of the primary sludge removal by the grab sampling method used for sludge analyses. This underestimation may be due to the high variability of the primary influent suspended solids concentration and hence inhomogeneity in the primary sludge underflow. When this underestimation was taken into account, primary sludge removal and volatilization in the aeration basin were found to contribute approximately equally to the removal of D4 and D5 in the pilot plant system. The present results are useful for the environmental risk assessment of these two siloxane compounds in the unlikely event of their point source discharge into municipal wastewater systems.

Synthesis and Structure of Octamethylcyclo-di(meta-silphenylenesiloxane)

Octamethylcyclo-di(meta-silphenylenesiloxane) 1 (cyclic meta-dimer) was synthesized from 1,3-bis(dimethylhydroxysilyl)benzene 7 in a dilute THF solution, in the presence of a catalytic amount of 4-dimethylaminopyridine (DMAP). In contrast, only small amounts of the cyclic meta-dimer 1, cyclic meta-trimer 2, cyclic meta-tetramer, etc. were obtained when the condensation reaction was carried out with the catalyst n-hexylamine 2-ethylhexoate or sodium hydroxide. The major product in these reactions is polymer 8. The structure of compound 1 was confirmed by X-ray crystallography. This cyclic molecule is most likely unstrained since the X-ray structure reveals that the Si–O–Si bond angle is 142.1(1)° which is similar to that in most unstrained siloxane compounds.

Adsorption of pentamethylcyclopentasiloxane on the Pd(100) surface studied by high resolution X-ray photoemission spectroscopy

Adsorption and reaction of pentamethylcyclopentasiloxane (PMPS) on a clean Pd(100) surface were investigated with the goal to determine whether anchoring of siloxane compounds on this metal occurs via strong dissociative chemisorption and whether siloxane monolayers can be formed. The room temperature exposure resulted in disordered, partially dissociated PMPS while retaining the Si–O backbone bonds, as indicated by high resolution X-ray photoemission spectroscopy (HRXPS). The quantitative HRXPS analysis showed that the surface Si coverage corresponded to 0.74 ML and that the PMPS adsorbed “flat” with partially broken Si–CH 3 bonds serving as anchoring points. Subsequent exposure of the PMPS-covered Pd surface to CO and O 2 showed no adsorption of these molecules, demonstrating that the adsorbed PMPS completely blocked the metal surface. However, exposure to Cl 2 gave rise to two distinct Cl 2p peaks in the HRXPS spectrum: a main component at 199.73 eV and a much smaller peak shifted from the main peak by ΔBE=−2.11 eV, corresponding to Cl atoms covalently bonded to PMPS and atomic Cl bonded to the Pd metal respectively. Thus, Cl 2 reacts with PMPS and the Cl atoms gain access to the Pd surface by rearranging the Cl/PMPS overlayer.

Structural characterization of thermotropic liquid crystalline dihydroxydicarbosilane mesophase

Molecular mechanics (MM) calculations of the structure formed by bis(hydroxydimethylsilyl)methane [(CH3)2(HO)Si]2CH2(MDCS) molecules have been performed. The calculations lead us to conclude that MDCS can form a columnar liquid crystalline phase which consists of supramolecular H-bonded associates similar to those found earlier for siloxane compounds of the same type. Synthesis of MDCS was performed. IR, NMR, DSC and XRD (powder and single crystal) investigations have shown the existence of a LC phase in a narrow temperature range. The computational and experimental results suggest the existence of similar columnar LC phases in a wider temperature range for Et-, Pr-, and Bu-substituted bis(hydroxydialkylsilyl)methane.

Tetravinyl-tetramethylcyclo-tetrasiloxane (tetravinyl D4) is a mutagen in Rat2lambda lacI fibroblasts.

Small fragments of silicone gels injected intraperitoneally have been used to induce plasmacytomas in genetically susceptible mice. Silicone oils, in contrast to silicone gels, are apparently not tumorigenic in the mouse plasmacytoma system. The reason for this difference as well as the mechanism of silicone gel-induced plasmacytoma development is poorly understood. We chose to examine the possibility that low molecular wt silicone compounds such as siloxanes, leaking from the complex silicone gel matrix into the surrounding tissue, may be mutagenic. We postulate that this mutagenicity may be a critical determinant of the plasmacytoma inducing potency of silicone gels. Six siloxane compounds, either linear or cyclic di-, tri-, or tetrasiloxanes substituted with methyl or vinyl moieties, were selected as model compounds to study mutagenicity in Rat2lambda lacI fibroblasts in vitro. Using phage lambda-derived lacI/lacZ genes as target/reporter genes to quantitate mutagenesis, and gamma-cyclodextrin as vehicle to effectively deliver siloxanes, we found that exposure to 50 microM of tetravinyl-tetramethylcyclo-tetrasiloxane (tetravinyl D4) resulted in a modest 1.7-fold increase of mutant frequencies over controls in Rat2lambda lacI cells. In related toxicity experiments, tetravinyl D4 was shown to perturb lipid membranes leading to a loss of cytosolic glutathione (GSH), which by itself resulted in a 1.5-fold increased mutant rate in Rat2lambda lacI cells. We conclude that certain siloxanes may act as direct mutagens in mammalian cells. In addition, siloxane-induced mutagenicity may be enhanced by the depletion of intracellular GSH caused by the interaction of lipophilic siloxanes with cell membranes.

Characterization of bis-(phenoxy)phosphazene Polymers Using Static Secondary Ion Mass Spectrometry

Phosphazene polymers are a class of materials that are finding applications in membrane separations. A series of substituted bis(pbenoxy)phosphazene polymers were characterized using static secondary ion mass spectrometry. The anion spectra contained ions which originate from the phosphazene backbone, as well as from the pendant aromatic moieties. The cation spectra also contained ions derived from the pendant moieties, but consisted primarily of ions which arise from adventitious surface contaminants, such as siloxane compounds and hydrocarbons. The backbone-derived ions could be distinguished from the pendant-derived ions on the basis of their response to prolonged primary ion bombardment : the pendant ions decay at rates that are generally two to four times the rates observed for the backbone ions. This observation is interpreted in terms of the pendant moieties being more easily removed during ablation than the backbone ions.

Cytotoxicity and membrane damage in vitro by inclusion complexes between gamma-cyclodextrin and siloxanes.

Inclusion complexes of gamma-cyclodextrin and octamethylcyclotetrasiloxane (D4), decamethyltetrasiloxane (M10TS), and 1,3,5,7-tetramethyltetravinylcyclotetra - siloxane (TMTV-D4) were prepared to compare the cytotoxic effects of siloxanes in vitro. In these preparations, the hydrophobic siloxanes are surrounded by a hydrophilic shell of eight circularly linked D-glucose molecules (gamma-cyclodextrin), and upon contact with plasma membranes the siloxane molecule can intercalate into the lipid bilayer of the cell membrane. XRPC24, 2-11 plasmacytoma, CH12.LX lymphoma and P388D1 macrophage-like cells were used as indicator cells in toxicity assays. Using an MTT tetrazolium reduction to formazan test, a colorimetric method to determine the number of viable cells, the 50% minimal lethal doses (CD50) for the siloxane compounds were found to range from 30 to 50 microM. Sublethal doses (e.g., 15 microM and lower) resulted in the loss of lactate dehydrogenase (LDH) and glutathione (GSH) from the cytosolic compartment of the target cells and thus indicated cytotoxicity. Treatment of macrophages with siloxanes resulted in a higher production of interleukin-6 (IL-6) than was exhibited by untreated macrophages. The B9 cell bioassay of these treated cells showed as much as a 10 fold higher production (500 U/ml) of IL-6 than did the untreated cells. The degree of increase was dependent on the compound and concentration used. The results of this study show that low molecular weight siloxanes produce lethal effects on B-lymphocyte derived target cells in vitro and permeabilize the plasma membranes at lower sublethal concentrations.

Dynamic Mechanical Relaxation Behavior of Low Molecular Weight Side-Chain Cyclic Liquid Crystalline Compounds near the Glass Transition Temperature

In this paper, we report the mechanical relaxation behavior of low molecular weight glass-forming side-chain liquid crystalline compounds with cyclic cores and their linear polymeric analogues near the glass transition temperature. We examined two systems : one based on cyclic and linear siloxane backbones and one based on cyclic (cyclohexane) and linear aliphatic backbones. Dynamic mechanical spectroscopy is used to measure the dynamic shear moduli and the complex viscosity near but above T g . The temperature dependence of the zero-shear viscosity of the cyclic compounds is well described by the Vogel-Tammann-Fulcher (VTF) equation. The strong temperature dependence of the viscosity along with the values of the fitted parameters of the VTF equation shows that the cyclic LC compounds are fragile liquids. All cyclic LC compounds, regardless of chemical structure, show identical relaxation behavior when viscosity is plotted versus normalized temperature (T g /T), where T g is the temperature obtained calorimetrically at a heating rate of 10 K/min. All cyclic compounds show lower viscosity than their linear analogues when plotted versus T g /T. The difference in viscosity between the cyclic and linear siloxane compounds is much more pronounced than the difference observed in the aliphatic compounds. For the cyclic compounds, master curves of G' and G can be described by a single Maxwell mode. The linear compounds exhibit much broader mechanical spectra, suggesting a more complex relaxation phenomenon is taking place. Our results show that, while there is little difference in relaxation behavior among low molecular weight cyclic liquid crystalline compounds, the behavior of the linear polymeric systems is quite different.

Investigation of primers reducing the pink‐ring formation in multilayer printed circuit boards

AbstractA rapid and easy screening test was applied to assess the capability of various formulated primers to reduce the defect of pink rings in multilayer printed circuit boards. The mixtures of silanes with multifunctional silanol groups (crosslinkers) and 3‐glycidoxypropyl‐trimethoxysilaneSystematic name: 3‐(2,3‐Epoxypropoxy)propyl‐trimethoxysilane. (referred to as silane C) or N‐(2‐aminoethyl)‐3‐aminopropyl‐trimethoxysilaneSystematic name: 3‐[N‐2‐aminoethyl]aminopropyl‐trimethoxysilane. (silane B) were proved to be effective in reducing the pink rings. The performance of the mixed silanes using silane A and crosslinkers with aromatic groups were better than other formulated primers which was partly attributed to less amounts of hydrophilic groups and better integrity in the primer films. A developed primer consisting of siloxane compounds had the best performance. The online test confirmed the results from the screening test and demonstrated the feasibility of the designed screening test in assessing the performance of primers. The results of FTIR spectroscopy and thermogravimetric analyses confirmed that the effective primers coated on the copper oxides could improve the curing reaction and the thermal oxidative stability of the epoxy/CuO system.

Porous polydimethylsiloxane membranes treated with aminopropyltrimethoxysilane

AbstractPolydimethylsiloxane (PDMS) membranes were made by catalytic hydrosilylation of a siloxane compound having a vinyl group and an SiH group in the presence of 1,4‐dioxane. By washing it with water many pores were formed in the membrane. Then, the pore size of the membrane was controlled by treatment of aminopropyltrimethoxysilane (APTMS) solution. When increasing the APTMS concentration, the pore size of the membrane was reduced by the formation of APTMS oligomer on the surface of the membrane. The characteristics of the membrane was examined by IR, ATR‐IR, and SEM techniques. Also, the permeation properties of dextrans and polystyrene latexes through the treated membrane were examined by the ultrafiltration method. © 1994 John Wiley & Sons, Inc.

Formation of carbon films by ion-beam-assisted deposition

A variety of hard adhesive carbon-rich films can be formed at low temperatures by ion-beam-assisted deposition (IBAD) processing of organic materials, i.e. by vapor deposition of organic materials combined with simultaneous high energy ion irradiation. These films are hydrogenated amorphous carbon (diamond-like carbon) contaminated with other elements such as Si or O, depending on the organic precursors used. They generally exhibit good solid lubrication. In particular, films produced from siloxane compounds ( i-silicone films) exhibit a coefficient μ of friction as low as 0.05 in a humid atmosphere as well as in moisture-free environments. The moisture-insensitive low friction of i-silicone films results from the fact that they contain silicon. Use of a chemically active ion such as Ti + in the IBAD process contributes to enhanced adhesion. The i-silicone films produced by IBAD processing using a low energy ion beam of 30 keV N 2 + contain a significant amount of nitrogen and exhibit values for μ of less than 0.1 in humid air.

Regioselective hydrosilations. IV. The synthesis and polymerization of monomers containing epoxy and alkoxysilane groups

AbstractUsing rhodium and platinum catalyzed regioselective hydrosilation, a series of α‐hydrogen‐ω‐epoxy silane and siloxane compounds have been prepared in good yields. These intermediates have been further condensed with vinyltrimethoxysilane in subsequent hydrosilation reactions to prepare an interesting new class of ambifunctional monomers containing both epoxy and trimethoxysilane groups. It was further shown that these same compounds could be synthesized by a simplified “one‐pot” two‐step procedure. An investigation of the simultaneous cationic ring‐opening polymerization of the epoxy groups and the acid‐catalyzed condensation of the trimethoxysilyl groups was carried out. © 1993 John Wiley & Sons, Inc.

Relaxation processes in the excited state of phenylsiloxanes

The relaxation processes in the excited state of phenylsiloxanes and related compounds have been studied by measurements of fluorescence decay, quantum yields, time-resolved fluorescence spectra and intersystem-crossing yields. The absorption and emission spectra of the phenylsiloxanes used correspond to the π,π* transition (1B2u–1A1g) in benzene. The local (1Lb) emissions for the silicon compounds used are very weak: the quantum yields are less than 0.033. For the compounds 2–4 with phenyl groups, very weak intramolecular excimer emissions (ΦfE < 0.017) are observed together with weak local (1Lb) emissions (ΦfM < 0.025) at 298 K. The intersystem-crossing quantum yields of the siloxane compounds obtained by the thermal lensing method are very small (ΦISC < 0.1) at 298 K. The fluorescence decay kinetics of the compounds 1–4, and 6 and 7 with an Si—O bond give double-exponential decay functions. The decay rates of the siloxane compounds are significantly faster than those of the carbon analogues. The siloxane compounds are photochemically stable (the reaction quantum yields at 254 nm are less than 1 × 10–3). On the basis of these results, it can be said that the main channel of the deactivation processes in the excited singlet states (local and excimer states) at room temperature is internal conversion to the ground state. The fast decay rate (i.e. the rate of internal conversion) of the siloxane compounds may be due to the perturbation of a pseudo-π system of the Si—O bond to the S1(1Lb) state.

イオンビームアシスト蒸着カーボン膜のトライボロジー特性

By combining vapor deposition of organic compounds and simultaneous energetic Ar+ion irradiation, carbonaceous films were deposited onto substrates of a bearing steel (SUJ2). The organic compounds were benzene, pentaphenylether, poly-(dimethylsiloxane) and pentaphenyl-trimethyl-trisiloxane.All the carbonaceous films produced were amorphous and showed low coefficient of friction less than 0.2 in ambient atmosphere. In particular, the films produced from the siloxane compounds (ion-irradiated silicone films) showed extremely low coefficient of friction less than 0.05. Furthermore, the friction coefficient of the ion-irradiated silicone films was much less sensitive to moisture compared to diamond-like carbon films prepared by plasma-enhanced chemical vapor deposition.Scanning electron microscopy and electron-probe micro-analysis for the pins of SUJ2 revealed that the ion-irradiated silicone films are easily transferred to the surface of the pin during sliding. This fact may be related with the very low friction coefficient for the ion-irradiated silicone films.