Addition Of Silane Research Articles

Intramolecular anion effect in polyoxometalate-based organocatalysts: reactivity enhancement and chirality transfer by a metal oxide-organic cation interaction.

An α1 -Dawson polyanion bearing a lateral side chain with a 4-aminopyridine end group was synthesized. This organopolyoxometalate catalyzes the addition of indenyl allyl silanes to cinnamoyl fluorides. The polyanionic framework influences the organocatalyst activity and selectivity. A moderate but nonzero chirality transfer from the chiral inorganic framework to the organic substrate was observed.

Ligand-controlled reactivity, selectivity, and mechanism of cationic ruthenium-catalyzed hydrosilylations of alkynes, ketones, and nitriles: a theoretical study.

Density functional theory calculations with the M06 functional have been performed on the reactivity, selectivity, and mechanism of hydrosilylations of alkynes, ketones, and nitriles catalyzed by cationic ruthenium complexes [CpRu(L)(MeCN)2](+), with L = P(i)Pr3 or MeCN. The hydrosilylation of alkynes with L = P(i)Pr3 involves an initial silyl migration mechanism to generate the anti-Markovnikov product, in contrast to the Markovnikov product obtained with L = MeCN. The bulky phosphine ligand directs the silyl group to migrate to Cβ of the alkyne. This explains the anti-Markovnikov selectivity of the catalyst with L = P(i)Pr3. By contrast, the silane additions to either ketone or nitrile proceed through an ionic SN2-Si outer-sphere mechanism, in which the substrate attacks the Si center. The P(i)Pr3 ligand facilitates the activation of the Si-H bond to furnish a η(2)-silane complex, whereas a η(1)-silane complex is formed for the MeCN ligand. This property of the phosphine ligand enables the catalytic hydrosilylation of ketones and nitriles in addition to that of alkynes.

Effect of matrix modification on durability of cementitious composites in an acid rain environment

The durability of silane-modified mortar, a cementitious composite, in acid rain environment was investigated given its extensive usage as a structural material. The results indicated that the addition of silane decreased the compressive strength of the cementitious composite. Wetting angle was increased by incorporating silane into the matrix. Decrease in both water absorption ability and coefficient of capillary suction confirmed hydrophobicity as induced by silane addition. Results of mechanical testing, scanning electron microscopy and X-ray diffraction showed that the sulfuric acid resistance of mortar was enhanced by silane. Based on these results, it is revealed that silane addition inhibits the diffusion of water, and consequently, sulfate ion diffusion rate decreases, thereby resulting in reduction in the rate of corrosion of cementitious composites by sulfuric acid.

Serendipitous Metal‐Catalyzed H–H/Si–H Exchange

AbstractVarious metal complexes catalyze exchange between H2 and hydrosilanes. Catalyst screening suggests that the electron deficiency of the metal center is necessary for exchange, but silane and/or hydrogen addition or σ‐bond metathesis with the M–Si and M–H bonds are not required. Kinetic measurements for the system [(ArN=)Mo(PMe3)3(H)(SiH2Ph)/H2/H3SiPh] (Ar = 2,6‐iPr2C6H3) suggest that the reaction proceeds through activation of the silane.

Impact strength and flexural properties enhancement of methacrylate silane treated oil palm mesocarp fiber reinforced biodegradable hybrid composites.

Natural fiber as reinforcement filler in polymer composites is an attractive approach due to being fully biodegradable and cheap. However, incompatibility between hydrophilic natural fiber and hydrophobic polymer matrix restricts the application. The current studies focus on the effects of incorporation of silane treated OPMF into polylactic acid (PLA)/polycaprolactone (PCL)/nanoclay/OPMF hybrid composites. The composites were prepared by melt blending technique and characterize the composites with Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). FTIR spectra indicated that peak shifting occurs when silane treated OPMF was incorporated into hybrid composites. Based on mechanical properties results, incorporation of silane treated OPMF enhances the mechanical properties of unmodified OPMF hybrid composites with the enhancement of flexural and impact strength being 17.60% and 48.43%, respectively, at 10% fiber loading. TGA thermogram shows that incorporation of silane treated OPMF did not show increment in thermal properties of hybrid composites. SEM micrographs revealed that silane treated OPMF hybrid composites show good fiber/matrix adhesion as fiber is still embedded in the matrix and no cavity is present on the surface. Water absorption test shows that addition of less hydrophilic silane treated OPMF successfully reduces the water uptake of hybrid composites.

Multiple coupling of silanes with imido complexes of Mo.

The bis(imido) complexes ((t)BuN[double bond, length as m-dash])2Mo(PMe3)(L) (L = PMe3, C2H4) react with up to three equivalents of silane PhSiH3 to give the imido-bridged disilyl silyl Mo(vi) complex ((t)BuN){μ-(t)BuN(SiHPh)2}Mo(H)(SiH2Ph)(PMe3)2 (3) studied by NMR, IR and X-ray diffraction. NMR data supported by DFT calculations show that complex 3 is an unusual example of a silyl hydride of Mo(VI), without significant SiH interaction. Mechanistic NMR studies revealed that silane addition proceeds in a stepwise manner via a series of Si-H∙∙∙M agostic and silanimine complexes whose structures were further elucidated by DFT calculations.

Effect of Silane Treated and Untreated Talc on the Properties of Thermoplastic Polyurethane/Polypropylene Blends

The effect of the silane treated talc on the mechanical and thermal properties of talc filled thermoplastic polyurethane/polypropylene blends (TPU/PP blends) was investigated. Thermoplastic polyurethane and polypropylene are partially miscible due to the lack of interfacial interaction between the nonpolar crystalline PP and polar TPU. Blends of TPU and PP with silane treated and untreated-talc were prepared using melt blending in a laboratory twin-screw extruder. Organosilane (3-glycidoxypropyl-trimetoxy silane coupling agent) was used to treat talc in order to improve the affinity between the filler and the TPU/PP blends. Dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC) and mechanical (tensile test) measurements were used to characterize the talc filled and silane treated talc filled composites and TPU/PP/talc blends. The addition of silane treated and untreated talc in TPU/PP blends improved miscibility in all investigated TPU/PP/talc blends. The silane treatment increases the storage modulus in all investigated TPU/PP/talc blends in comparison with that of the untreated TPU/PP/talc blends. The obtained DSC results show that the addition of silane treated talc increases the degree of crystallinity (χc) of TPU/PP/talc blends because of the improved adhesion between the polymer and the treated talc. Addition of silane treated talc improved the mechanical properties as compared to TPU/PP/talc blends without chemical modification of talc. The results of strength correlate to the values of the storage modulus and crystallinity of the investigated TPU/PP/talc blends.

Morphology and performances of the anodic oxide films on Ti6Al4V alloy formed in alkaline-silicate electrolyte with aminopropyl silane addition under low potential

Oxide films on Ti6Al4V alloy are prepared using sodium hydroxide–sodium silicate as the base electrolyte with addition of aminopropyl trimethoxysilane (APS) as additive by potentiostatic anodizing under 10V. APS is incorporated into the films during anodizing and the surface morphology of the oxide films is changed from particle stacked to honeycomb-like porous surfaces as shown by scanning electron microscopy (SEM) with Energy Disperse Spectroscopy (EDX). The surface roughness and aminopropyl existence on the oxide films result in their differences in wettability as tested by the surface profile topography and contact angle measurements. The anti-abrasive ability of the anodic films is improved with the addition of APS due to its toughening effects and serving as lubricants in the ceramic oxide films as measured by ball-on-disk friction test. Also, potentiodynamic corrosion test proves that their anticorrosive ability in 3.5wt.% NaCl is greatly improved as reflected by their much lower corrosion current (Icorr) and higher corrosion potential (Ecorr) than those of the substrate.

Effect of low dosages of waste GRP dust on fresh and hardened properties of mortars: Part 2

Part 1 of the work reported that by replacing 5–10% of sand volume with GRP dust, workability, autogeneous shrinkage, deformability and total porosity, though with a smaller average radius, of mortars increased, thereby reducing significantly the mechanical performance, when wet curing conditions are adopted. However, the risk of cracking induced by restrained shrinkage and the capillary water absorption is lower in the presence of GRP dust, leading to enhanced durability of GRP mortars when used as supporting role. Therefore, in the present work, plaster mortars manufactured by replacing 0–2.5–5% of sand volume with GRP dust were characterized. For comparison, the addition of an hydrophobic admixture at different dosages was also considered. Permeability is not significantly reduced by the low addition of GRP dust, but it is slightly increased by silane addition. Thermal insulation properties, capillary water absorption and resistance to efflorescence are better with waste GRP dust addition, especially when combined with silane.

Mechanical and anti‐stabbing properties of modified thermoplastic polymers impregnated multiaxial p‐aramid fabrics

New forms of hybrid multiaxial nanocomposites with enhanced mechanical and stab resisting properties are presented. This study is motivated by the lack of knowledge in the study of the multiaxial fabric nanocomposites with two modified thermoplastic matrices for antiballistic protection. Introduction of 5 wt.% silica nanoparticles in the composite of polyurethane/p‐aramid/poly (vinyl butyral) leads to significant improvement in mechanical properties, and the addition of silane as a coupling agents and glutaraldehyde as a crosslinking agents yielded maximal values of storage modulus, tensile modulus and anti‐stabbing properties for hybrid nanocomposites. Ballistic resistance testing and penetration depth of the hybrid nanocomposites were visualized using image analysis. Copyright © 2013 John Wiley & Sons, Ltd.

Stoichiometric C═O Bond Oxidative Addition of Benzophenone by a Discrete Radical Intermediate To Form a Cobalt(I) Carbene

Single electron transfer from the Zr(III)Co(0) heterobimetallic complex (THF)Zr(MesNP(i)Pr2)3Co-N2 (1) to benzophenone was previously shown to result in the isobenzopinacol product [(Ph2CO)Zr(MesNP(i)Pr2)3Co-N2]2 (2) via coupling of two ketyl radicals. In this work, thermolysis of 2 in an attempt to favor a monomeric ketyl radical species unexpectedly led to cleavage of the C-O bond to generate a Zr/Co μ-oxo species featuring an unusual terminal Co═CPh2 carbene linkage, (η(2)-MesNP(i)Pr2)Zr(μ-O)(MesNP(i)Pr2)2Co═CPh2 (3). This complex was characterized structurally and spectroscopically, and its electronic structure is discussed in the context of density functional theory calculations. Complex 3 was also shown to be active toward carbene group transfer (cyclopropanation), and silane addition to 3 leads to PhSiH2O-Zr(MesNP(i)Pr2)3Co-N2 (5) via a proposed Co-alkyl bond homolysis route.

Impact of Silane and Siloxane Based Hydrophobic Powder on Cement-Based Mortar

Impact of the addition of silane and siloxane based hydrophobic powders on cement based mortar was studied. Effect of powder addition on mechanical properties and water absorption of cement based mortar is described. Impact of accelerated ageing, including UV radiation, and rain-sun cycles on hydrophobic performance was assessed, demonstrating excellent durability of silane-based hydrophobic performance.

UV-Induced Frontal Polymerization of a Pt-Catalyzed Hydrosilation Reaction

The bis(acetylacetonato)platinum(II) is a common thermal catalyst for the hydrosilation reaction, and it is reported to serve also as a photoactivated catalyst for hydrosilation addition of silanes to alkenes and alkynes. In this paper, it is demonstrated that the UV-activation of hydrosilation reaction proceeds via a thermal-frontal mechanism. UV light activates the polymerization on the surface of the sample and, subsequently, the heat released by hydrosilation generates a thermal front, converting the UV-generated homogeneous catalyst to a Pt0 heterogeneous catalyst. The UV-induced frontal polymerization mechanism can exhaustively explain the dark-curing process observed in the UV-activated hydrosilation reaction.

Investigation of the effect of different silane coupling agents on mechanical performance of basalt fiber composite laminates with biobased epoxy matrices

AbstractIn recent years, it has been detected an increased interest in the development of materials from renewable resources. This trend has been intensified in the industrial sector where significant efforts have been made in this field in order to adapt these natural fibers to conventional industrial processes and applications. As a result, research has been done into developing new thermoplastic matrices which are compatible with this type of reinforcing fibers. This study evaluates the influence of different coupling agents based on silanes, on the mechanical properties of composite laminates made from a biobased epoxy resin matrix and basalt fabric by using vacuum assisted resin transfer moulding. The curing behavior of the biobased epoxy resin was evaluated by differential scanning calorimetry (DSC), gel point determination, and ionic conductivity. The evaluation of mechanical properties was done by tensile, flexural, impact, and hardness tests. Compatibility between basalt fibers and epoxy resin generally has managed to increase through the addition of silanes, after the addition of these, their mechanical properties are substantially improved compared to the sample without silane treatment, obtaining this way an easily processable material, with good properties and capable of competing with materials with petroleum‐based epoxy resins. POLYM. COMPOS., 2013. © 2013 Society of Plastics Engineers

Total synthesis of (±)-leuconolam: intramolecular allylic silane addition to a maleimide carbonyl group.

A concise total synthesis of the plant alkaloid (±)-leuconolam (1) has been achieved. A regio- and diastereoselective Lewis-acid mediated allylative cyclization was used to establish, simultaneously, two adjacent tetrasubstituted carbon centers. Furthermore, an essential arene cross-coupling to a hindered haloalkene was enabled by the use of a novel 2-anilinostannane.

Thermal and chemical treatments of montmorillonite clay

Abstract Montmorillonite clay from a natural deposit was processed to remove impurities and later submitted for thermal and chemical treatments. The sample was first subjected to a thermal treatment at 400 °C, for 1 h, to remove organic components. The chemical treatment was conducted first by using an acid attack with nitric acid and sulfuric acid, then, adding sodium acetate in ethylene glycol clay dispersion, and finally the clay was dispersed in xylene with subsequent addition of silane, N-(b-aminoethyl)-g-aminopropyiltrimethylsilane. The combined thermal and chemical treatment was found to have a significant effect on the final chemical composition of the nanoclay. X-ray diffraction patterns suggested that the combined thermal and chemical treatment resulted in increased interplanar distances, thus favoring exfoliation of the clay lamellae, which was also confirmed by SEM images. Fourier transform infrared (FTIR) spectroscopy analysis suggested that the combined thermal and chemical treatment resulted in removal of water from the montmorillonite, without any modification or destruction of the clay structure. Thus, the combination of thermal and chemical treatments proposed in this work may be a promising approach to process montmorillonite intended for the production of advanced materials.

Effect of addition of surface modified nanosilica into silica–zirconia hybrid sol–gel matrix

An organic–inorganic hybrid sol (MZ) comprising a methacrylate functionalized silane matrix (M) and zirconium-n-propoxide (Z) was prepared using sol–gel technique. Two methodologies were adopted to modify the hybrid sol for generating nanocomposite coatings viz., (a) addition of acrylic surface modified silica nanoparticles (N) of diameter ∼20 nm to the sol to enhance their compatibility with the hybrid sol–gel matrix and (b) in-situ formation of a three dimensional silica network by addition of tetraethoxy silane (T) to the sol MZ. In the first methodology, the sols were prepared with six different weight ratios of the nanoparticles to the sol, i.e. 0, 0.01, 0.05, 0.1, 0.25 and 1 which were labelled as MZ+N x where x =0, 1, 2, 3, 4 and 5 respectively. The prepared sols were dip coated on 100 mm×100 mm polycarbonate substrates followed by thermal curing at 130 °C. The coatings were characterized for their mechanical properties like pencil scratch hardness, scratch resistance using scratch tester, nanoindentation hardness, and abrasion resistance as well as visible light transmittance. FT-IR studies were also carried out on heat-treated gels derived from the sols. A maximum pencil scratch hardness of 3H was obtained for the MZ+T coatings and these coatings withstood a critical load of 4.3±0.7 N before failure during scratch test. The maximum nanoindentation hardness of 3.8±0.01 GPa was obtained for the MZ+N5 coatings. The abrasion resistance of MZ+T coatings was higher when compared to MZ+N0 and MZ+N5 coatings. The scratch and nanoindentation hardness were seen to be better for an in-situ formed –Si–O–Si– network in the hybrid sol when compared to those obtained from coatings generated by external addition of acrylic surface modified silica nanoparticles. The difference in properties was attributed to the level of interaction between the nanoparticles and hybrid sol–gel matrix.

Wear of Carbon Nanofiber Reinforced HDPE Nanocomposites Under Dry Sliding Condition

High density polyethylene (HDPE) is widely used as a bearing material in industrial application because of its low friction and high wear resistance properties. Carbon nanofiber (CNF) reinforced HDPE nanocomposites are promising materials for biomedical applications as well, such as being the bearing materials in total joint replacements. The main objective of the present study is to investigate how the wear of HDPE can be altered by the addition of either pristine or silane treated CNFs at different loading levels (0.5 wt. % and 3 wt. %). Two types of silane coating thicknesses, 2.8 nm and 46 nm, were applied on the surfaces of oxidized CNFs to improve the interfacial bonding strength between the CNFs and the matrix. The CNF/HDPE nanocomposites were prepared through melt mixing and hot-pressing. The coefficients of friction (COFs) and wear rates of the neat HDPE and CNF/HDPE nanocomposites were determined using a pin-on-disc tribometer under dry sliding conditions. The microstructures of the worn surfaces of the nanocomposites were characterized using both scanning electron microscope (SEM) and optical microscope to analyze their wear mechanisms. Compared with the neat HDPE, the COF of the nanocomposites were reduced. The nanocomposite reinforced with CNFs coated with the thicker silane coating (46 nm) at 0.5 wt. % loading level was found to yield the highest wear resistance with a wear rate reduction of nearly 68% compared to the neat HDPE.

ChemInform Abstract: Bifunctional Homoallylic Carbamates from Chiral Silane Addition to in situ Generated N‐Acyl Iminium Ions.

AbstractThree‐component aminocrotylation reaction of the novel silanes (I) and (XIII) leads to homoallylic carbamates bearing an unsaturated ester or allylic carbonate in good syn‐selectivity.

Morphological structures and tribological performance of unsaturated polyester based untreated/silane-treated halloysite nanotubes

In this study, pristine halloysite nanotubes (HNT) and silane-treated halloysite (s-HNT) particles were incorporated into highly crosslink unsaturated polyester (UPE) to explore the morphological structure and tribological performance of UPE-HNT nanocomposite. Wear resistance of cured UPE/HNT and UPE/s-HNT nanocomposites were systematically evaluated using block-on-ring (BOR) configuration against stainless steel counterpart under a certain dry sliding conditions. TEM micrographs revealed a uniform morphological dispersion of halloysite particles in the UPE matrix. Both pristine and silane-treated HNT particles induced a modest decrease in a specific wear rate and coefficient of friction of nanocomposites. There was a pronounce reduction in the specific wear rate of the polyester composites at more than 5wt.% of halloysite. However, the addition of silane exhibited insignificant results especially at higher percentages of HNT. The investigation of worn surface morphology and wear mechanism of materials by using SEM is also discussed.