Hydrolysis Of Silane Research Articles

Study of the vapor-assisted method for bonding PDMS and glass: effect of the vapor source

Different chemicals were tested in order to check their effectiveness as the vapor source for the vapor-assisted method to bond PDMS and glass, bringing clarification to the mechanism of the bonding. While no increase in the adhesion strength of PDMS–glass samples was observed when silanes without chloro functional groups were used, increase in the bonding strength of PDMS–glass was obtained with all alkyl chlorosilanes tested in this study, including tri-, di- and monochlorosilanes, as well as with hydrochloric acid solution. These results experimentally demonstrate that the hydrogen chloride gas obtained from the hydrolysis and polymerization of silanes or simply from the evaporation of hydrochloric acid solution assist with the formation of PDMS–glass bonding, making the vapor-assisted method a very simple and reliable method to bond PDMS and glass with multiple applications in both small-scale laboratory research and large-scale manufacturing processes.

A simple method for healing nonzeolitic pores of MFI membranes by hydrolysis of silanes

In this paper, we proposed a simple method with hydrolysis of silanes to heal nonzeolitic pores of pure silica MFI (silicalite) zeolite membranes. Three silane precursors, tetraethoxysilane (TEOS), tetramethoxysilane (TMOS) and dimethoxydimethylsilane (DMDS) were used for membrane modification at room temperature. The modified membranes were evaluated by the separation of p-/o-xylene mixture. It was found that the hydrolysis of silanes in nonzeolitic pores could obviously improve separation performance of the MFI zeolite membranes. The modification results of nonzeolitic pores were related to the silane precursors with different physical–chemical properties and molecular kinetic diameter. Compared with TEOS and TMOS, DMDS was more suitable as a precursor for healing nonzeolitic pores. For a zeolite membrane after DMDS modification, p-/o-xylene separation factor could be increased from 2.34 to 10.84 while p-xylene flux decreased only about 12.6%.

Resin Bonding to Silicatized Zirconia with Two Isocyanatosilanes and a Cross-linking Silane. Part II: Mechanistic Approach

In this paper we discuss and interpret the results of shear bond strengths achieved after the use of two silane coupling agents with isocyanato functionality, viz. 3-isocyanatopropyltrimethoxysilane and 3-isocyanatopropyltriethoxysilane. The silanes were used alone and also blended with a non-functional cross-linking silane on silicatized zirconia before light-curing of resin stubs on the surface, as described elsewhere in the first part of our study (see “Part I: Experimental”). A series of reaction mechanisms and conceptual diagrams are also presented. The reaction mechanisms illustrating the effect of adding a cross-linking silane into a silane blend, the silane hydrolysis and the behavior of two organofunctional groups (isocyanate and alkene) of silanes upon reaction with Rely X Unicem Aplicap resin-composite cement are discussed in detail.

Preparation of Microsized Monodisperse Silica Spheres by Hydrolysis of Tetraethoxy Silane

Monodispersed silica spheres have attracted much attention because of their widely applications in the areas of catalysis, adsorption, chromatography packing materials and advanced ceramics. This paper focused on its application as a packing material of function coatings for space applications. Nanosized monodispersed silica spheres can be fabricated by Stöber method. However, microsized monodispersed silica spheres are not easy obtained. In this paper monodispersed silica spheres with the size between 200nm to 2000nm were fabricated by hydrolysis of tetraethoxy silane (TEOS) in isopropyl alcohol solvent and using ammonia as catalyst through multi-step growth method. The influence of silica seed number density and TEOS concentration on monodispersity and size of silica sphere were studied. The result shows that monodispersed silica spheres could be obtained through control the concentration of TEOS and the silica seed number density during every growth step. The diameter of monodispersed silica spheres increased with the steps of growth.

An investigation of the effect of silane water‐crosslinking on the properties of poly(L‐lactide)

AbstractA silane‐grafting water‐crosslinking approach was developed to crosslink poly(L‐lactide) (PLLA) by grafting vinylalkoxysilane onto PLLA using dicumyl peroxide, followed by silane hydrolysis to form siloxane linkages between PLLA chains. The degree of silane grafting onto PLLA was qualitatively characterized using Fourier transform infrared spectroscopy and quantitatively determined using inductively coupled plasma mass spectrometry. Crosslinked PLLA films were obtained by curing of silane‐grafted PLLA in hot water. Gel fractions were evaluated in order to calculate the crosslinking reaction kinetics and crosslinking density. Various techniques were used to investigate the effect of silane water‐crosslinking on the thermomechanical properties, hydrolysis resistance and biodegradation of PLLA. In addition to an improvement in thermal stability and mechanical properties, hydrolysis resistance was significantly enhanced as a result of silane water‐crosslinking of PLLA. Moreover, the biodegradation of silane water‐crosslinked PLLA was retarded compared with neat PLLA. Copyright © 2010 Society of Chemical Industry

The Influence of pH on the Hydrolysis Process of γ-Methacryloxypropyltrimethoxysilane, Analyzed by FT-IR, and the Silanization of Electrogalvanized Steel

Silanes are commonly used as coupling agents to enhance the adhesion between polymeric and inorganic materials. Once silane hydrolysis has taken place, the condensation of the silane on the substrate surface should follow. Optimum hydrolysis conditions will depend on the type of silane and the process conditions of the solution. The pH is particularly important as it has a significant effect on the hydrolysis process. This paper deals with the hydrolysis process of 1 vol% γ-methacryloxypropyltrimethoxysilane (MPS) in aqueous solution at different pHs (2, 4, 6, 8 and 10). Because the hydrolysis rate is a function of pH, hydrolysis times, ranging from 2 min to 48 h, were studied. Fourier transform infrared spectroscopy was used to evaluate the chemical modifications produced by changing the hydrolysis time. The disappearance of the infrared band due to the Si–O–C groups and the appearance of the bands due to the Si–OH bonds were studied. It was shown that longer times were necessary for complete hydrolysis, under almost neutral pH conditions. On the other hand, the Zn-electrocoated steel was silanized with MPS under an optimum pH and the hydrolysis time conditions and the resulting surfaces were analysed by Reflection–Absorption Infrared Reflectance Spectroscopy.

Synthesis and Properties of Non-functional Cubic Silsesquioxane Macromonomers

Cubic silsesquioxane macromonomers (R8Si8O12) were prepared by the hydrolysis and polycondensation of trifunctional silane (RSi(OC2H5)3) in the solvents with acid and base acting as catalysts. The effects of reaction conditions, such as monomer concentration, type of solvents, amount of water, reaction temperature, pH value of medium, and catalyst were investigated by calculating the yield of the products. We used the mixture solvents of methyl isobutyl ketone (MIBK) and anhydrous ethanol instead of the single solvent. The high boiling point of MIBK solvent was advantageous of increasing the reaction temperature and the formation of the silsesquioxane (SSQ), and eventually shortening the reaction time and increasing the yield. The results showed that the chose of these reaction parameters determine the properties of trifunctional silane. The microstructures of SSQ macromers were investigated by Fourier transform infrared (FT-IR) spectroscopy, element analysis and 29Si-NMR spectroscopy, and the results showed these synthesized macromonomers having the formula R8Si8O12 and the cage structure. The solubility of SSQs was found to be related to their structure; the longer the corner groups, the higher the solubility. The thermal properties of SSQ macromers were studied by thermogravimetric analysis (TGA) and the data showed that SSQ had a higher decomposition temperature and higher thermal residue.

Influence of coating bath chemistry on the deposition of 3-mercaptopropyl trimethoxysilane films deposited on magnesium alloy

Magnesium alloys have a low specific density and a high strength to weight ratio. This makes them sought after light weight construction materials for automotive and aerospace applications. These materials have also recently become of interest for biomedical applications. Unfortunately, the use of magnesium alloys in many applications has been limited due to its high susceptibility to corrosion. One way to improve the corrosion resistance of magnesium alloys is through the deposition of protective coatings. Many of the current pretreatments/coatings available use toxic chemicals such as chromates and hydrofluoric acid. One possible environmentally friendly alternative is organosilane coatings which have been shown to offer significant corrosion protection to both aluminum alloys and steels. Organosilanes are ambifunctional molecules that are capable of covalent bonding to metal hydroxide surfaces. In order for covalent bonding to occur, the organosilane must undergo hydrolysis in the coating bath followed by a condensation reaction with the surface. There are a number of factors that influence the rates of these reactions such as pH and concentration of reactants. These factors can also influence competing reactions in solution such as oligomerization. The rates of hydrolysis and condensation of 3-mercaptopropyltrimethoxy silane in methanol have been analyzed with 1H NMR and ATR–FTIR. The results indicate that organosilane oligomers begin to form in solution before the molecules are fully hydrolyzed. The organosilane films deposited on magnesium alloy AZ91 at a variety of concentrations and pre-hydrolysis times were characterized with a combination of ATR–FTIR, ellipsometry and SEM/EDS. The results show that both organosilane film thickness and uniformity are affected by the chemistry occurring in the coating bath prior to deposition.

Facile synthesis of mesoporous silica nanoparticles with controlled morphologies using water–acetone media

Mesoporous silica nanoparticles with controlled morphologies including nanococoons, nanorods and nanospheres have been synthesized in water–acetone media at room temperature using cetyltrimethylammonium bromide (CTAB) as the template. The obtained nanoparticles generally show hexagonal-like mesoporous structures with average pore size ranging from 2.7 to 3.3 nm and surface area from 806 to 1055 m 2/g, respectively. It was found that the changes in water-to-acetone molar ratios have a dramatic impact on the morphologies of the mesoporous silica with different surface roughness, probably due to the solvent influence on the rate of the hydrolysis of tetraethoxy silane (TEOS) and the polymerization of inorganic species. Interestingly, the morphology of the mesoporous silica products can be controlled in shape from nanococoons to nanorods to nanospheres just by decreasing the water-to-acetone molar ratio from 75 to 30 to 15, respectively. From transmission electron microscopy (TEM) images, it was observed that mesoporous parallel channels run along the short axis in some areas in the nanorods, whereas the radially arranged mesopore channels are present in the nanospheres. Additionally, hydrothermal treatment leads to rougher surfaces while retaining the morphologies and nanostructures of these mesoporous silicas.

Effect of silane-grafting on water tree resistance of XLPE cable insulation

Water treeing is one of the main deterioration phenomena observed in the polymeric insulation of extruded crosslinked polyethylene (XLPE) cables, which can affect the service life of power cables. In this work, we investigated the effect of grafting of a silane (vinyl trimethoxysilane, VTMS) on the resistance of XLPE to water treeing. A series of water-treeing tests, the mechanical and dielectric measurements indicated that the silane-grafting could significantly improve the water tree resistance of the conventional XLPE cable insulation with little influences on its dielectric properties, e.g., the dielectric breakdown strength, dielectric constant and loss tangent, and its mechanical performance. It was found that there exists an optimum value of VTMS concentration (about 0.6 phr) corresponding to the minimum water tree length. The water tree resistance mechanism of silane-grafted XLPE was proposed on the basis of the process of silane hydrolysis and crosslinking. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Sol–Gel Synthesis and Microstructure Analysis of Amino‐Modified Hybrid Silica Nanoparticles from Aminopropyltriethoxysilane and Tetraethoxysilane

Agglomerated amino‐modified silica nanoparticles were prepared from a novel Stöber‐like precursor system consisting of aminopropyltriethoxysilane (APTES), tetraethoxysilane (TEOS), ethanol, and water where the molar ratio APTES/TEOS was 0, 0.1, 1.0, and 2.0, and the molar ratio H2O/‐SiOC2H5 was about 20 to 60, or great excess amounts of H2O were employed. APTES catalyzed the hydrolysis and condensation of both silanes. 29Si magic angle spinning nuclear magnetic resonance spectra confirmed that the particles consisted of Qn species (Si(OSi)n(OH)4−n; n=2, 3, 4) and Tn species (NH2(CH2)3–Si(OSi)n(OH)3−n; n=2, 3). The APTES content in the precursor solutions controlled the agglomerating spherical particle size and morphology: 0.1 in the ratio APTES/TEOS led to almost independent spheres of 300–400 nm, while the larger ratios 1 and 2 led to ∼250 and ∼150 nm spheres, respectively, that were largely agglomerated and some were fused to look like peanut‐shells. When soaked in Kokubo's simulated body fluid, those amino‐modified particles deposited apatite. The mechanisms of particle formation and apatite deposition were discussed in terms of an intraparticle hydrated layer.

Chemistry of mixtures of bis-[trimethoxysilylpropyl]amine and vinyltriacetoxysilane: an NMR analysis

13C, 29Si, and 1H NMR were used to investigate the interaction of bis-[trimethoxysilylpropyl]amine (silane A) with vinyltriacetoxysilane (silane V). The reaction was found to generate a hydroxylamine, an amide and a silanol. A series of hydrolysis and condensation reactions were found to occur concurrently with the formation of the major reaction products. Upon dilution with acidified water, the amide decomposes, initiating hydrolysis of unreacted silanes. Hydrogen bonding between the N–H and SiOH groups is likely to be responsible for the stability of the dilute solutions.

Catalysis by cationic oxorhenium(v): hydrolysis and alcoholysis of organic silanes

The cationic [2-(2'-hydroxyphenyl)-2-oxazolinato(-2)]oxorhenium(v) complex promotes oxidative dehydrogenation of organosilanes with water and alcohols in a catalytic manner to give excellent yields of silanols and silyl ethers, respectively. The reactions proceed conveniently under ambient and open-flask conditions with low catalyst loading (<or=1 mol%). The scope of the reaction with water is quite broad and includes aliphatic, aromatic, tertiary, secondary and primary silanes. The rate of reaction depends on the catalyst and silane concentrations and kinetic isotope effect measurements demonstrate involvement of the Si-H bond in the activated complex. The most influential factor on the silane affecting reactivity is steric hindrance and a quantitative correlation with the Taft steric parameter (E) is presented. A combination of kinetic data and isotope labelling results are used to discuss plausible mechanisms for the oxidative dehydrogenation reaction pathway.

Characterization of thiol-functionalised silica films deposited on electrode surfaces

Thiol-functionalised silica films were deposited on various electrode surfaces (gold, platinum, glassy carbon) by spin-coating sol-gel mixtures in the presence of a surfactant template. Film formation occurred by evaporation induced self-assembly (EISA) involving the hydrolysis and (co)condensation of silane and organosilane precursors on the electrode surface. The characterization of such material was performed by IR spectroscopy, thermogravimetry (TG), elemental analysis (EA), atomic force microscopy (AFM), scanning electron microscopy (SEM) and cyclic voltammetry (CV).

Non-supercritically dried silica–silica composite aerogel and its possible application for confining simulated nuclear wastes

The simpler non-supercritical drying approach has been used for the first time for the preparation of silica–silica composite aerogels (CA) and the efficiency of the process being demonstrated by testing the use of the aerogels for simulated high level nuclear waste confinement. Compositions of 5, 10, 20, 30, 40 and 50 wt% of silica (aerosil® 380) in silica–aerogel were prepared by introducing pyrogenic silica in to silica sol derived by hydrolysis of Tetraethoxy silane (TEOS). The silica–silica composite aerogels (CA) possessed very high surface area and low bulk densities. The effectiveness of the prepared composite aerogels as precursor for high level nuclear waste immobilized glass is also presented. Neodymium nitrate dissolved in isopropanol is used to simulate +3 valent actinides. The stability of neodymium in the glass matrix has been found to be extremely high. Transmission electron microscopy (TEM) has been used to characterise the aerogels as well as neodymium incorporated sintered gels. X-ray diffraction (XRD) studies of the sintered samples reveal the formation of neodymium silicates.

Adsorption of silane onto cellulose fibers. II. The effect of pH on silane hydrolysis, condensation, and adsorption behavior

AbstractThe hydrolysis of four alkoxysilane agents, γ‐methacryloxypropyl trimethoxysilane (MPS), γ‐mercaptopropyl trimetoxysilane (MRPS), octyl trimethoxysilane OS), and N‐phenyl‐γ‐aminopropyl trimethoxysilane (PAPS), was carried out in an ethanol/water (80/20) solution under both acid and basic conditions. 1H, 13C, and 29Si NMR spectroscopy were used to provide quantitative analyses of the structural components during hydrolysis and condensation reaction. The analysis revealed that the acid‐catalyzed hydrolysis of silane allows the formation of high amount of silanol groups, reduced the selfcondensation reaction among silanol groups and stabilized the proportion of intermediary hydrolyzed species for several days. However, under basic condition, condensation reactions proceed as soon as the hydrolysis reaction started leading to the rapid consumption of silanol groups through selfcondensation and to the growth of three‐dimensional high molecular structures. The interaction of MPS and MRPS with cellulose fibers and the evolution of their surface properties were then investigated using adsorption isotherms and contact angle measurement. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Effect of nanosized ferric oxide on the thermostability of methylsilicone resin

Nanocomposite of methylsilicone resin/Fe2O3 (MSR/Fe2O3, metal oxide nanoparticles with average particle-size of 20 nm) was successfully synthesized by acid-catalyzed hydrolysis and condensation of methyltrimethoxy silane (MTMS). The obtained nanocomposite was characterized by Fourier-transformed infrared (FT-IR) and X-ray photoelectron spectroscopy (XPS). The FTIR and XPS results show that the nanoparticles were well dispersed in the MSR matrix. The thermogravimetric analysis (TGA) results show that Fe2O3 nanoparticles can remarkably improve the thermal stability of MSR. In comparison with methylsilicone resin, the temperature values of the resulting nanocomposite at the onset of degradation and the maximum rate of mass loss were increased 55 and 76 °C, respectively.

Kinetics of hydrolysis and self condensation reactions of silanes by NMR spectroscopy

The hydrolysis of four alkoxy-silane coupling agents, 3-methacryloxypropyl trimethoxy silane (MPMS), 3-mercaptopropyl trimethoxy silane (MRPMS), octyl triethoxy silane (OES) and 3-aminopropyl triethoxy silane (APES) was carried out in an ethanol/water 80/20 (w/w) solution under acidic, alkaline and neutral conditions and followed by 1H, 13C and 29Si NMR spectroscopy. It was found that the kinetic rate of the hydrolysis of the silanes under neutral conditions was very low, except for APES, which displayed the fastest reaction speed. The addition of TEA catalyzed both silane hydrolysis and self condensation reactions. Acidic conditions enhanced the hydrolysis and the ensuing silanol entities were quite stable. In fact, these conditions slowed down the rate of the self condensation reactions, as deduced from in situ 1H and 13C NMR. Thanks to in situ 29Si NMR spectroscopy, the nature of the intermediary species versus reaction time was established.

Mechanism of a one‐step method for preparing silane grafting and cross‐linking polypropylene

AbstractA high‐melt‐strength polypropylene (HMSPP) with partially cross‐linking, modified from a normal isotactic polypropylene (IPP), is prepared by a one‐step silane grafting and cross‐linking method in a twin‐screw reactive extruder. The melt grafting and cross‐linking of IPP is achieved by using vinyl unsaturated silane with long chain as a grafting monomer, benzoyl peroxide (BPO) as an initiator, styrene as a coagent, and a little water as a catalyst for cross‐linking. By analyzing the difference of the Fourier transformed infrared spectra between raw and modified PP, comparing the variety of the melt flow rate (MFR) and gel percentage between cured and uncured PP samples, and investigating the effect of catalyst on the MFR and gel percentage of modified PP, the partially cross‐linked polypropylene in the way of one‐step reactive extrusion has been verified. We put forward the reactive mechanism of one‐step method based on our experimental results. In this mechanism, the hydrolysis and condensation of silane occur first through the catalysis of water and a compound with two or more double‐bond is formed, which then the compound reacts with PP macroradicals to form the partially cross‐linked PP. POLYM. ENG. SCI., 47:1004–1008, 2007. © 2007 Society of Plastics Engineers

Grafting of montmorillonite with different functional silanes via two different reaction systems

Silane grafted montmorillonites were synthesized by using 3-aminopropyltriethoxysilane and trimethylchlorosilane via two different grafting reaction systems: (a) ethanol–water mixture and (b) vapor of silane. The resulting products were investigated using Fourier transform infrared (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA). XRD patterns demonstrate that silane was intercalated into the montmorillonite gallery, as indicated by the increase of the basal spacing. The product prepared by vapor deposition has a larger basal spacing than that obtained from solution, due to the different extent of silane hydrolysis in various grafting systems. TGA curves indicate that the methyl groups penetrate into the siloxane clay are the primary reason for the decrease of the dehydroxylation temperature of the grafted products. 3-Aminopropyltriethoxysilane in the grafted montmorillonite adopts a bilayer arrangement while trimethylchlorosilane adopts a monolayer arrangement within the clay gallery.