Structure Of Silane Research Articles

Fe/Thiol Cooperative Hydrogen Atom Transfer Olefin Hydrogenation: Mechanistic Insights That Inform Enantioselective Catalysis.

Asymmetric hydrogenation of activated olefins using transition metal catalysis is a powerful tool for the synthesis of complex molecules, but traditional metal catalysts have difficulty with enantioselective reduction of electron-neutral, electron-rich, and minimally functionalized olefins. Hydrogenation based on radical, metal-catalyzed hydrogen atom transfer (mHAT) mechanisms offers an outstanding opportunity to overcome these difficulties, enabling the mild reduction of these challenging olefins with selectivity that is complementary to traditional hydrogenations with H2. Further, mHAT presents an opportunity for asymmetric induction through cooperative hydrogen atom transfer (cHAT) using chiral thiols. Here, we report insights from a mechanistic study of an iron-catalyzed achiral cHAT reaction and leverage these insights to deliver stereocontrol from chiral thiols. Kinetic analysis and variation of silane structure point to the transfer of hydride from silane to iron as the likely rate-limiting step. The data indicate that the selectivity-determining step is quenching of the alkyl radical by thiol, which becomes a more potent H atom donor when coordinated to iron(II). The resulting iron(III)-thiolate complex is in equilibrium with other iron species, including FeII(acac)2, which is shown to be the predominant off-cycle species. The enantiodetermining nature of the thiol trapping step enables enantioselective net hydrogenation of olefins through cHAT using a commercially available glucose-derived thiol catalyst with up to 80:20 enantiomeric ratio. To the best of our knowledge, this is the first demonstration of asymmetric hydrogenation via iron-catalyzed mHAT. These findings advance our understanding of cooperative radical catalysis and act as a proof of principle for the development of enantioselective iron-catalyzed mHAT reactions.

A tannic acid-based intumescent flame retardant for improving flame retardancy of epoxy composites

A biomass intumescent flame retardant (TA-g-DOPO) was fabricated from tannic acid (TA) and 9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) through the bridge of silane coupling agent (KH560), which showed a low degradation rate at Tmax of 2.71%/min and a high char yield of 55.8%. Then, various EP composites with 4–10% TA-g-DOPO were prepared. Due to the presence of flexible silane structures and rigid phosphaphenanthrene rings as well as the remained phenol groups (tending to form hydrogen bonds with epoxy matrix), EP composite with a high content of 10% TA-g-DOPO exhibited no deterioration on the tensile and impact properties as well as the glass transition temperature (Tg) when compared with pure EP. More importantly, it reached a high LOI value of 30.3% and passed a V-0 rating in the UL-94 burning test. Additionally, its peak heat release rate (PHRR), total heat release (THR) and average mass loss rate (av-MLR) decreased by 23.2%, 15.5% and 30.2% respectively. Analyses from the condensed char and pyrolysis gases indicated that the improved flame retardancy was mainly attributed to the cooperation of the free-radical quenching effect of P-containing radicals and phenoxy radicals working in stages (derived from DOPO and TA respectively) and the physical barrier effect caused by the highly graphited, intumescent and porous char layer (reinforced by P- and Si-containing cross-linked structures). This work provides a sustainable biomass flame retardant with good flame-retarding efficiency based on TA.

Hydrophobic and hygroscopic properties of cellulose treated with silicone agents

The effects of various cellulose treatments on the hydrophobic properties and sorption behavior with respect to liquid water uptake and water vapor sorption were examined within the study. Different hydrophobic agents based on silicon compounds were applied to improve the properties of cellulose-based sheets. The 1H,1H,2H,2H perfluorooctyltriethoxysilane treatment increased hydrophobicity significantly, while N-octyltriethoxysilane and inorganic sodium silicate solution treatments only slightly affected the properties. Silicone-cellulose interaction varied, influencing the fiber saturation and moisture content of the material. The swelling differences between untreated and treated cellulose and, consequently, the uncovering of new active sorption sites during a swelling process and the increase in the content of bound water were confirmed by the T2 relaxation times analysis. The GDW sorption model estimated maximum water content but lacked activation dynamics. The blocking phenomenon of active sorption sites together with silicone improved hydrophobicity had different mechanisms for applied agents. The 1H,1H,2H,2H perfluorooctyltriethoxysilane additionally cross-linked silane structure and restricted cellulose swelling.

Molecular Layer Deposition (MLD) of a Blocked Mercapto Silane on Precipitated Silica

Chemically modified silica is widely used as a reinforcing filler in elastomers. The modification is generally done in situ while preparing the rubber. However, in order to increase the efficiency and facilitate the mixing process, the silica can be pre-treated by a 2-step molecular layer deposition. The precursors for the modification are 3-mercaptopropyl-triethoxysilane (MPTES) and octanoyl chloride (OC) to react with MPTES and form a blocked silane. The precipitated silica nanofiller was successfully treated with MPTES and showed a self-limiting behavior: saturation occurred at 2.7%. Furthermore, DRIFTS (diffuse reflectance infrared Fourier transform spectroscopy) analysis confirmed the successful deposition of MPTES on the silica surface by showing the -SH peak that appeared after the reaction of MPTES and silica. In the second step, OC was introduced to form a thioester on the surface of the MPTES-treated silica, controlling the reactivity of the mercapto group from MPTES by blocking it to prevent a negative influence on the processing behavior of the rubber. Thermogravimetric analysis (TGA), Fourier-transform infrared spectroscopy, and X-ray photoelectron spectroscopy (XPS) analytical results confirmed the deposition of the blocked mercapto silane on the silica. TGA results demonstrated the self-limiting behavior of OC, and DRIFTS and XPS proved the thioester formation. A thioester peak after the 2nd reaction step with OC appeared. At the same time, the disappearance of the -SH signal from the MPTES was observed, indicating the formation of the blocked mercapto silane structure. Transmission electron microscopy results showed that the treated silica has a well-distributed carbon and sulfur deposition after MPTES/OC treatment.

Copper(I)-Catalyzed Regio- and Stereoselective Silaboration of Terminal Allenes.

Organic compounds bearing both silyl and boryl groups are important building blocks in organic synthesis because of the adequate reactivity of the silyl and boryl groups and high stereospecificity in their derivatization reactions. The difference in reactivity between the silyl and boryl groups enables stepwise derivatization of these groups to afford complex molecules. Here, we report the copper(I)-catalyzed silaboration of terminal allenes to produce multisubstituted allylic boronates embedded with an alkenyl silane structure. The reaction can proceed with a variety of allenes and silylboranes. Furthermore, the silyl and boryl groups were successfully converted into other functional groups, while retaining the stereochemistry of the alkene moiety.

A review study on coupling agents used as ceramic fillers modifiers for dental applications

The aim of this study is to provide a review on silanized composite performance when exposed in a complex wet aqueous environment and the role of titanium coupling agent as a more stable and reinforcement material in the construction of dental composites. Silanes are considered as the most dominant materials used for surface modification of the filler added to the polymer material in dental applications. Due to the presence of silica in the silane structure, so, the silane coupling agent were considered to be more effective in modifying materials which are consisting of silica because of the similarity in their ordered structure. Silanes are relatively characterized by dehydration inside the oral aqueous environment. On the other hand, titanate coupling agents are effective in serving at a wet environment, because its ability to react with the positive proton available on the surface of the filler (H+). TCAs are superior in performance in comparison to silane by creating a strong internal bonding between the filler and polymer matrix, and having a significant effect on the dispersion and resolving of particles agglomeration and good hydrolytic stability inside the mouth. This paper presents a comparative study between the effects of silane coupling agents against the TCAs performance in oral environment.

Structure and Photophysical Properties of Silane Bridged Tetraphenylethylene-Oligothiophene Derivatives

Structure and Photophysical Properties of Silane Bridged Tetraphenylethylene-Oligothiophene Derivatives

Effect of Organo-Silanes Structure on the Properties of Silane-Crosslinked Membranes Based on Cardo Polybenzimidazole PBI-O-PhT.

Polybenzimidazoles (PBI) doped with phosphoric acid (PA) are promising electrolytes for medium temperature fuel cells. Their significant disadvantage is a partial or complete loss of mechanical properties and an increase in hydrogen permeability at elevated temperatures. Covalent silanol crosslinking is one possible way to stabilize PBI membranes in the presence of PA. Three organo-substituted silanes, namely (3-Bromopropyl)trimethoxysilane (SiBr), trimethoxy [2-(7-oxabicyclo [4.1.0]hept-3-yl)ethyl]silane (Si-biC) and (3-Glycidyloxypropyl)trimethoxysilane (KH 560), were used as covalent crosslinkers of PBI-O-PhT in order to determine the effect of the silane structure and crosslinking degree on membrane properties. The crosslinking degree was 1-50%. All crosslinked membranes were characterized by impedance and IR-spectroscopy. The mechanical properties, morphology, stability and hydrogen permeability of the membranes were determined. In the case of silanes with linear substituents (SiBr, KH 560), a denser structure is formed, which is characterized by greater oxidative stability and lower hydrogen permeability in comparison to the silane with a bulk group. All the crosslinked membranes have a higher mechanical strength compared with the initial PBI-O-PhT membrane both before and after doping with PA. Despite the hardening of the polymer matrix of the membranes, their proton conductivity changes insignificantly. It was shown that cross-linked membranes can be used in fuel cells.

Effect of type of organic modifier on the clay layered-based nanocomposites flammability and toxic gases emission

Well dispersed polyethylene (PE) nanocomposites were developed. Montmorillonite (MMT) as aluminosilicate clay layers was modified using organic silanes of different side chains. The MMT was grafted using 3-(trimethoxysilyl)propylamine, N-[3-(trimethoxysilyl)propyl]ethylenediamine, and trimethoxyvinylsilane. The modification process of MMT using organic different silanes was elucidated using microscopic, thermogravimetric, spectroscopic, and X-ray diffraction tools. Then, the developed organoclays were dispersed uniformly in PE matrix producing well exfoliated and dispersed polymer nanocomposites. The mass loadings of dispersed organoclay were varied and the impact of organic silane structure was studied. Thermal stability and flammability properties of the developed polymer nanocomposites were evaluated. The peak heat release rate and average heat release rate were reduced by 48% and 61%, respectively compared to virgin polymer. Also, the average mass loss rate was significantly reduced by 50%. This is in addition to reduction in emission of carbon monoxide (CO) and carbon dioxide (CO2) by 45% and 56%, respectively. The effect of side chain of organosilane on the performance of modified clay layers was studied. The toxicity of gases evolved during combustion process of PE and their polymer nanocomposites were evaluated using Fourier transform infrared connected to cone calorimeter. Additionally, the influence of organic silane on the pyrolysis and toxic gases emission was further studied.

Comprehensively improved mechanical properties of silane crosslinked polypropylene/ethylene propylene diene monomer elastomer blends

AbstractThe properties and structure of silane crosslinked polypropylene (PP)/ethylene propylene diene monomer (EPDM) elastomer blends had been carried out. Fourier transform infrared spectroscopy and gel content tests were employed to evaluate the crosslinking reaction of PP/EPDM blends. Crosslinking efficiency of PP/EPDM blends was investigated using thermogravimetric analysis, differential scanning calorimeter, dynamic mechanical analysis, dynamic rheology, and tensile testing. Tanδcurves of silane crosslinked PP/EPDM blends exhibited an obvious “gel point” originated from the formation of dynamic crosslinking network. The blend corresponding to the “gel point” presented comprehensively improved mechanical properties. These results demonstrated that characteristic rheological parameters showed close correlations with key mechanical properties of silane crosslinked PP/EPDM blends. Scanning electron microscopy images illustrated that crosslinking had remarkably changed the morphologies of PP/EPDM blends. The large deformation mechanism of these blends had been suggested.

Dynamic Covalent Chemistry at Interfaces: Development of Tougher, Healable Composites through Stress Relaxation at the Resin-Silica Nanoparticles Interface.

The interfacial region in composites that incorporate filler materials of dramatically different modulus relative to the resin phase acts as a stress concentrator and becomes a primary locus for composite failure. A novel adaptive interface (AI) platform formed by coupling moieties capable of dynamic covalent chemistry (DCC) is introduced to the resin-filler interface to promote stress relaxation. Specifically, silica nanoparticles (SNP) are functionalized with a silane capable of addition fragmentation chain transfer (AFT), a process by which DCC-active bonds are reversibly exchanged upon light exposure and concomitant radical generation, and copolymerized with a thiol-ene resin. At a fixed SNP loading of 25 wt%, the toughness (2.3 MJ m-3) is more than doubled and polymerization shrinkage stress (0.4 MPa) is cut in half in the AI composite relative to otherwise identical composites that possess a passive interface (PI) with similar silane structure, but without the AFT moiety. In situ activation of the AI during mechanical loading results in 70% stress relaxation and three times higher fracture toughness than the PI control. When interfacial DCC was combined with resin-based DCC, the toughness was improved by 10 times relative to the composite without DCC in either the resin or at the resin-filler interface.

Comparison of Wet Deposition and Plasma Deposition of Aluminosilane Coatings

Silane coatings are suitable for various applications of metal surfaces, such as forming a corrosion protection layer or as a primer for subsequent coating. In this work, bis-1,2- (triethoxy) ethane (BTSE) was used as a precursor on a 99.99% aluminum substrate for deposition of the coating, with three diff erent techniques: dipping (water-based solution ), Vacuum plasma and atmospheric plasma. (IRRAS), X-ray photoelectron spectroscopy (XPS) and fi eld emission gun scanning electron microscopy (FE-SEM) were used to characterize the structure, composition and surface morphology of silane coating. The purpose of this study is to compare the surface and body properties of membranes prepared by three different methods to obtain information on how BTSE molecules are modified by deposition techniques. The results show that in addition to the more traditional wet dip coating, the film can also be vacuum and atmospheric plasma deposition. The vacuum plasma deposition layer can be considered as an organic and inorganic mixture, which can be obtained by dipping as well as the silane layer. However, atmospheric plasma treatment leads to the formation of more inorganic fi lms containing Si-O. Photon spectroscopy and infrared spectroscopy showed the presence of Si-O-Si bonds, while IRRAS measurements showed Si-O-Si, Si-O-C, Si-O and Si-CH3 absorption bands.

Vapor-Phase Deposited Chlorosilane-Based Self-Assembled Monolayers on Various Substrates for Thermal Stability Analysis

Chlorosilane-based self-assembled monolayers (SAMs), including octyltrichlorosilane (C8-OTS), (tridecafluoro-1,1,2,2-tetrahydrooctyl) trichlorosilane (FOTS) and dimethyldichlorosilane (DDMS), are applied on various substrates via a vapor-phase coating process for thermal stability analysis. Si(100) wafer dies and commercial vapor-phase-deposited nanoparticle films are utilized as substrates to characterize the thermal stability enhancement. Atomic-force microscopy data prove that the vapor-based deposition technique results in a smooth surface with few aggregates. Contact angle goniometry data show that DDMS-based SAMs function effectively as the final protection layer for various substrates and these results are confirmed by thermogravimetric analysis of SAMs on the fumed silica supports. Quantitative analysis from X-ray photoelectron spectroscopy data shows that polymerized DDMS may exist on various surfaces and can contribute to the stable silane structures for DDMS. These test results yield improved u...

Effects of silane-modified fillers on properties of dental composite resin

The effect of silanization on the mechanical, chemical, and physical properties of dental composites was investigated. Silica fillers were obtained from colloidal silica solution, Ludox® HS-40 and they were silanized by using 3-methacryloxypropyl trimethoxysilane (MPTMS) in an acidic media. Mineralogical and chemical structures of unsilanized and silanized fillers were determined by using XRD and FT-IR analyses. The modification of unsilanized/silanized fillers were investigated by performing XPS and TGA analyses. The morphological evaluations, surface area, and particle size measurements were performed by using SEM, BET, and Zeta-Sizer, respectively. Eventually, pure and amorphous silica fillers were obtained. Furthermore, the weight percentage of the silane in silica/silane structure was compatible with theoretical values. SEM images, surface area, and particle size measurements showed that agglomeration tendencies of silanized fillers were lower compared to silanized fillers because of the MPTMS addition. Experimental composites (5/10/10/5BisGMA/HEMA/UDMA/TEGDMA resin reinforced with 70wt% silanized/unsilanized SiO2) were fabricated into 4mm diameter×6mm thick discs for compressive strength (CS), angular flexural strength (AFS), curing depth (CD), and polymerization shrinkage (PS) on a 25×2×2mm rectangular Teflon mold for flexural strength (FS) and modulus of elasticity (E) tests. The curing depth (CD) and degree of polymerization percentage (DP) of composites were determined. Consequently, results showed that mechanical properties and DP of composite resins can be greatly influenced by silanization as a result of the organic matrix-inorganic filler interface bonding formed by silane structures. Despite of these findings, silanization of the SiO2 was not effected DC and PS values.

Efficiency of sugarcane bagasse-based sorbents for oil removal from engine washing wastewater.

This work evaluates the efficiency of sugarcane bagasse-based sorbents in the sorption of oil from engine washing wastewater. The sorbents were obtained from sugarcane bagasse in the natural form (SB-N) and modified with either acetic anhydride (SB-Acet) or 3-aminopropyltriethoxysilane (SB-APTS). The results showed that the sorption capacity of these materials decreased in the following order: SB-APTS > SB-N > SB-Acet. The superior oil sorption capacity observed for SB-APTS was attributed to the polar amino end groups in the silane structure, which acted to increase the hydrophilic character of the fibers. However, all the sorbents obtained in this study were able to clean a real sample of wastewater from engine washing, leading to significant reductions in suspended matter, sediment, anionic surfactants, and turbidity.

One‐Step Synthesis of Superbright Water‐Soluble Silicon Nanoparticles with Photoluminescence Quantum Yield Exceeding 80%

Fluorescent silicon nanoparticles (SiNPs) have shown potential applications in bioimaging/biolabelling, sensing, and nanomedicine/cancer therapy due to their superior properties such as excellent photostability, low cytotoxicity, and versatile surface modification capability. Here, a simple, high‐yield, and one‐pot method is developed to prepare superbright, water‐soluble, and amine‐functionalized SiNPs with photoluminescence quantum yield (PLQY) comparable to fluorescent II–VI semiconductor quantum dots (QDs) but with much lower cytotoxicity. By introducing a commercially available amine‐containing silane molecule, N‐[3‐(trimethoxysilyl)propyl]ethylenediamine (DAMO), water‐soluble SiNPs are prepared with PLQY of 82.4% via a microwave‐assisted method. To the best of our knowledge, this is the highest PLQY value ever reported for water‐soluble fluorescent SiNPs. The silicon element in our SiNPs is mainly four‐valent silicon and thus these SiNPs may also be termed as oxidized silicon nanospheres or silica nanodots. We have also demonstrated the importance of the silane structure (e.g., a suitable amine content) on the photoluminescence property of the prepared SiNPs. As revealed by the time‐resolved photoluminescence technique, the highest PLQY value of DAMO SiNPs is correlated with their monoexponential decay with a relatively long fluorescence lifetime. In addition, the potential use of these SiNPs has also been demonstrated for fluorescent patterning/printing and ion sensing (including Cu2+ and Hg2+).

Aspects of Interfacial Structure of Silane Coupling Agents in Particulate-Filled Polymer Composites and the Reinforcement Effect: A Critical Review

In order to form an effective interphase in a polymer composite, the preparation and characterization of silane structure on particle surface and in the interfacial layer in the composite are reviewed. The polycondensation of silane is affected by the concentration and pH of silane solution and the pH of inorganic particle. Pulsed 1H nuclear magnetic resonance (pulsed NMR) analysis is useful to characterize the structure of silane layer on the particle surface. It is found that the linear chain structure formed from dialkoxy type silane is flexible, whereas the network structure formed from trialkoxy type silane is rigid. To form an effective interphase, the linear chain structure formed from dialkoxy type is more useful than the network structure formed from trialkoxy type in the silica-filled rubber composites. The pre-treatment method and the integral blend method are compared in the silica-filled rubber composites. As a result, the dialkoxy type is found to be suitable for the pre-treatment method, whereas the trialkoxy type is suitable for the integral blend method. In the pre-treatment method, the linear silane chains form entanglements with the rubber chains in the interfacial region and improve the reinforcement effect. In the integral blend of trialkoxy type, the formation of the silane network and the entanglement proceed simultaneously during the preparation process and a well-entangled interfacial region is formed. Pulsed NMR analysis for the silica-filled unvulcanized rubber composites is useful to analyze the interfacial layer in the composites. The surface treatment of CaCO3 with a mixture of amino and mercapto functional silanes is found to be useful to improve the reinforcement effect in rubber/CaCO3 composites.

High-temperature superconductivity in compressed solid silane.

Crystal structures of silane have been extensively investigated using ab initio evolutionary simulation methods at high pressures. Two metallic structures with P21/c and C2/m symmetries are found stable above 383 GPa. The superconductivities of metallic phases are fully explored under BCS theory, including the reported C2/c one. Perturbative linear-response calculations for C2/m silane at 610 GPa reveal a high superconducting critical temperature that beyond the order of 102 K.

The molecular structure of methylfluoroisocyanato silane: a combined microwave spectral and theoretical study.

The structure of methylfluoroisocyanato silane (Me-SiHF-NCO) has been deduced by a combination of microwave (MW) spectra including data from (12,13)C, (14,15)N, and (28,29,30)Si isotopomers, and ab initio calculations. The rotational constants (RC) for the most abundant isotopes are A = 6301.415(45), B = 1535.078(39), and C = 1310.485(39) MHz. The symmetric quartic centrifugal distortion constants have been identified, using the I(r) representation for C1 symmetry, which includes the 3-fold rotor. The spectra of the isotopomer combinations gave a partial substitution structure where the C2Si3, Si3N4, and N4C9 bond lengths are 1.8427(70), 1.7086(77), and 1.2120(90)Å; although the C2Si3N4 angle is close to tetrahedral (109.71° (52)), the Si3N4C9 angle is wide (157.69° (18)). The rotational constants are only consistent with a trans-orientation for each of the dihedral angles (HC2Si3N4, C2Si3N4C9, and Si3N4C9O10). The structural analysis was completed by calculations of the equilibrium structure, using MP3 in conjunction with an aug-cc-pVTZ basis set (434 Cartesian basis functions). This gave A = 6240.324, B = 1518.489, and C = 1297.819 MHz. The equilibrium structure bond lengths for C2Si3, Si3N4, and N4C9 were 1.8485, 1.7147, and 1.1947 Å, with the C2Si3N4 and Si3N4C9 angles 109.55 and 156.67°, respectively. Although the SiNC polynomial bending surface is complex, the data points can be fit to the simple form V(x) = 50.36(91)x(4) - 7.53(44)x(5), with comparatively little loss of accuracy. The A-rotational constant is strongly influenced by the Si3N4C9 angle, and smaller bases lead to this angle being nearly linear. The theoretical results suggest a very heavily polarized molecule, which is supported by the positions of the local electron density minima within the bonds and electron density calculations.

Influence of silane structure on curing behavior and surface properties of sol–gel based UV-curable organic–inorganic hybrid coatings

In this study, three usual silane precursors, tetraethoxysilane (TEOS), vinyltrimethoxysilane (VTMS), and 3-methacryloxypropyltrimethoxysilane (MPS), and different binary and triplet blends of them were polymerized via a sol–gel method under acidic conditions. 29Si NMR spectroscopy was used to characterize and quantify the degree of condensation of oligomers. The organic phase was based on a three-acrylate monomer trimethylolpropane triacrylate (TMPTA). The effect of prepared oligomers on the curing behavior of hybrid materials and the interaction between organic and inorganic phases were monitored via photo differential scanning calorimetry (Photo-DSC). Atomic force microscopy (AFM) was used to investigate the surface properties of UV-cured hybrid materials. Photo-DSC results showed that the addition of functionalized oligomers can increase both the photopolymerization rate and the final degree of conversion. They also indicated that oligomers containing MPS are more compatible with the organic phase than other oligomers. Topography and phase trace images of AFM showed that oligomers containing VTMS migrate to the surface of films and affect the water contact angle. In contrast to VTMS, the presence of MPS in oligomers causes the formation of covalent bonds between the organic and inorganic phases in the bulk of the film, and so the surface properties of the film remain unchanged.