Search

Tris(pentafluorophenyl)borane (TPFPB) is a unique Lewis acid that catalyzes the condensation between hydrosilanes (Si-H) and alkoxysilanes (Si-OR), leading to the formation of siloxane bonds (Si-OSi) with the release of hydrocarbon (R-H) as a byproduct—the so-called Piers–Rubinsztajn reaction. The analogous reactions of hydrosilanes with silanols (Si-OH), alcohols (R-OH), ethers (R-OR′) or water in the presence of TPFPB leads to the formation of a siloxane bond, alkoxysilane (Si-OR or Si-OR′) or silanol (Si-OH), respectively. The above processes, often referred to as Piers–Rubinsztajn reactions, provide new synthetic tools for the controlled synthesis of siloxane materials under mild conditions with high yields. The common feature of these reactions is the TPFPB-mediated hydride transfer from silicon to carbon or hydrogen. This review presents a summary of 20 years of research efforts related to this field, with a focus on new synthetic methodologies leading to numerous previously difficult to synthesize well-defined siloxane oligomers, polymers and copolymers of a complex structure and potential applications of these new materials. In addition, the mechanistic aspects of the recently discovered reactions involving hydride transfer from silicon to silicon are discussed in more detail. [ABSTRACT FROM AUTHOR]

Conjugates of metal hydroxyl phthalocyanines (М(ОН)nРс; М = Si, Ge, Al, Ga) with 3-aminopropyltriethoxysilane (APTEOS) are synthesized. By means of the sol-gel method, polymeric silicate gel materials doped with the (APTEOS)n-М(ОН)nРс conjugates are prepared: the latter form structural links in the composition of the copolymer with the siloxane fragments of the polymeric chains (in the case of n = 2) or are ″grafted″ to such chains in the form of side substituents (n = 1). It is shown by spectral-luminescent and kinetic spectroscopy methods that the (APTEOS)n-М(ОН)nРс conjugates, on the introduction into a silicate gel material, retain their molecular structure and the photophysical characteristics of MPc in the monomeric form. The obtained macromolecular substances are promising as monomeric dopants in new functional materials for optics and quantum electronics. [ABSTRACT FROM AUTHOR]

Cultural heritage objects and structures are subjected to a range of weathering processes that result in their decay and destruction. To slow weathering rates and/or mitigate their effects, several protective and consolidant materials have been used during conservation interventions. Treatments based on organic polymers and alkoxysilanes, as well as some traditional inorganic treatments such as lime water, are in many cases either incompatible and/or show limited efficacy. In recent years nanolimes, that is, dispersions of Ca(OH)2 nanoparticles in alcohol (as well as alcohol dispersions of other alkaline-earth metal hydroxide nanoparticles), have emerged as an effective and compatible conservation material. Here we review recent advances in the synthesis and application of nanolimes in the field of heritage conservation. First, we present an overview of lime-based conservation materials, with an emphasis on the earliest reports on the use of nanolimes. Subsequently, we present the different methods used to synthesize nanolimes. Afterwards, we describe their carbonation and its consolidation effects. Practical application of nanolimes in heritage conservation are summarized, including consolidation of stone, ceramics, lime mortars and mural painting, as well as deacidification of paper, canvas, and wood. The advantages and limitations of this novel nanotechnology for cultural heritage conservation are outlined. Finally, some conclusions and areas for future research are presented. [ABSTRACT FROM AUTHOR]

Organosilica membranes were fabricated using bridged organoalkoxysilanes (bis(triethoxysilyl)methane (BTESM), bis(triethoxysilyl)ethane (BTESE), bis(triethoxysilyl)propane (BTESP), bis(trimethoxysilyl)hexane (BTMSH), bis(triethoxysilyl)benzene (BTESB), and bis(triethoxysilyl)octane (BTESO)) to produce highly permeable molecular sieving membranes. The effect of the organoalkoxysilanes on network pore size and microporous structure was evaluated by examining the molecular size and temperature dependence of gas permeance across a wide range of temperatures. Organosilica membranes showed H2/N2 and H2/CH4 permeance ratios that ranged from 10 to 150, corresponding to network pore size, and both H2 selectivity decreased with an increase in the carbon number between 2 Si atoms. Organosilica membranes showed activated diffusion for He and H2, and a slope of temperature dependence that increased approximate to the increase in the carbon number between 2 Si atoms. The relationship between activation energy and He/H2 permeance ratio for SiO2 and organosilica membranes suggested that the molecular sieving can dominate He and H2 permeation properties via the rigid microporous structure, which was constructed by BTESM and BTESE. With increased in the carbon concentration in silica, polymer chain vibration in organic bridges, which is a kind of solution/diffusion mechanism, can dominate the permeation properties. © 2017 American Institute of Chemical Engineers AIChE J, 63: 4491-4498, 2017 [ABSTRACT FROM AUTHOR]

In this study, we present new inorganic-organic hybrid particles and their possible application as an adsorbent for simultaneous removal of hydrophobic and hydrophilic pollutants from water. These hybrid particles were prepared using tailor-made alkoxysilane-functionalized amphiphilic polymer precursors (M-APAS), which have amphiphilic polymers and reactive alkoxysilane groups attached to the same backbone. Through a single conventional sol-gel process, the polymerization of M-APAS and the chemical conjugation of M-APAS onto silica nanoparticles was simultaneous, resulting in the formation of hybrid particles (M-APAS-SiO 2 ) comprised of hyperbranch-like amphiphilic polymers bonded onto silica nanoparticles with a relatively high grafting efficiency. A test for the adsorption of water-soluble dye (organe-16) and water insoluble dye (solvent blue-35) onto the hybrid particles was performed to evaluate the possibility of adsorbing hydrophilic and hydrophobic compound within the same particle. The hybrid particle was also evaluated as an adsorbent for the removal of contaminated water containing various pollutants by wastewater treatment test. The hybrid particle could remove phenolic compounds from wastewater and the azo dye reactive orange-16 from aqueous solutions, and it was easily separated from the treated wastewater because of the different densities involved. These results demonstrate that the hybrid particles are a promising sorbent for hydrophilic and/or hydrophobic pollutants in water. [ABSTRACT FROM AUTHOR]

Surface modification of nanoparticles by grafting silane coupling agents has proven to be a significant approach to improve the interfacial compatibility between inorganic filler and polymer matrix. However, the impact of grafted silane molecular structure after the nanoparticle surface modification, induced by the utilized solvents and the silane alkoxy groups, on the electrical properties of the corresponding nanocomposites, has been seldom investigated. Herein, the silanization on the surface of hydroxylated barium titanate (BT-OH) nanoparticles was introduced by using two kinds of trialkoxysilane, 3-aminopropyltriethoxysilane (AMEO) and 3-aminopropyltrimethoxysilane (AMMO), with different solvents (toluene and ethanol), respectively. Solid-state 13 C, 29 Si nuclear magnetic resonance (NMR) spectroscopy and high-resolution X-ray photoelectron spectroscopy (XPS) were employed to validate the structure differences of alkoxysilane attachment to the nanoparticles. The effect of alkoxysilane structure attached to the nanoparticle surface on the dielectric properties of the BT based poly(vinylidene fluoride) (PVDF) nanocomposites were investigated. The results reveal that the solvents used for BT nanoparticle surface modification exhibit a significant effect on the breakdown strength of the nanocomposites. Nevertheless, the alkoxy groups of silane show a marginal influence on the dielectric properties of the nanocomposites. These research results provide important insights into the fabrication of advanced polymer nanocomposites for dielectric applications. [ABSTRACT FROM AUTHOR]

Transmission FTIR was successfully applied to monitor the hydrolysis reaction of an alkoxysilane-terminated polybutadiene model polymer for a selection of catalytic and co-catalytic systems under controlled environmental conditions (23 °C, 50% relative humidity). Monitoring of the condensation reaction of the model polymer via FTIR spectroscopy was limited to qualitative evaluation. The aim of this work was to find a new tin-free alkoxysilane crosslinking catalyst, active at room temperature as an alternative to dibutyltin dilaurate (DBTDL). Hydrolysis rates ( k ), hydrolysis turn overs, and tack free times were determined for the model system with added water and in the presence of different catalysts, such as DBTDL, diisobutoxy bis(ethylacetoacetato) titanate (Tyzor IBAY), 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), boron trifluoride monoethylamine (BF 3 -MEA) and tris(pentafluorophenyl)borane (BCF) in concentrations of 3 mol%. For BCF a high catalytic activity was observed for both, the alkoxysilane hydrolysis and the condensation reaction. The simultaneous use of BCF and Tyzor IBAY was found to increase hydrolysis reaction׳s turn overs significantly. Thereby a highly efficient co-catalytic system was established, which was found to be active at room temperature showing potential as a new, tin-free alkoxysilane crosslinking catalyst. [ABSTRACT FROM AUTHOR]

Siloxane formation reactions of both the nonhydrolytic sol-gel process and Piers-Rubinsztajn reaction can be integrated as Lewis acid promoted siloxane syntheses without involving silanol groups. The former was developed in the field of inorganic materials chemistry and the latter was initiated in polymer chemistry. We have realized both reactions are quite similar, in terms of 1) the nonhydrolytic reaction, 2) the use of alkoxysilanes, 3) the group-exchange reactions competing with the siloxane formation, and 4) the proposed reaction mechanisms. This Minireview focuses on the above two reactions. The evolution of both reactions should realize a more sophisticated molecular design of siloxane compounds, which surely contributes to the development of advanced functional materials. [ABSTRACT FROM AUTHOR]

Abstract: The characterization of nanofiltration (NF) membranes is necessary for predicting their performance under different operating conditions, and for optimizing the membrane-separation process. A thin-film composite (TFC) polymer membrane for nanofiltration, modified with tri- and tetra-alkoxysilanes, was produced using a sol–gel procedure. The surface charges of the modified membranes were determined at different pHs by means of the zeta-potential. The streaming current was measured for a zeta-potential analysis of the flat-sheet membranes. Knowledge of the zeta-potential is essential for designing and operating membrane processes, and its measurement provides the key to understanding the control of charge-related phenomena. The zeta-potential of modified membranes is distinct from that of an untreated membrane. The isoelectric point was found to be at a higher pH after a treatment with any of the alkoxysilanes. The surfaces of the modified membranes showed an amphoteric behaviour. The homogeneity and stability of the treatment were assessed by a repeated zeta-potential analysis of the same and different membrane samples. [Copyright &y& Elsevier]

Abstract: An efficient synthesis of biaryls using a Hiyama reaction between aryl iodides and aryltrialkoxysilanes in the presence of a diphenylphosphinomethylpolystyrene-supported palladium catalyst is described. The cross-coupling proceeds in the presence of only 0.1 mol % of supported palladium. The catalyst can be used at least four times and the palladium leaching is extremely low (ca. 1% of the initial amount). [Copyright &y& Elsevier]

Abstract: Protective coatings containing polymer microcapsules loaded with water displacing alkoxysilanes were studied by means of a new apparatus allowing the study of advancing and receding contact angles during the simultaneous stretch forming of the coated substrate. FE-SEM studies were performed after stretch forming to correlate the defect structure with the process of hydrophobization. It could be shown that the incorporation of alkoxysilane loaded polymer capsules into a coating system led to a pronounced hydrophobization of cracks that were formed during the stretching of the sample. The local hydrophobization is assigned to the conversion of alkoxysilanes to polysiloxanes via hydrolysis and condensation which are initiated by the contact of those alkoxysilanes with the aqueous electrolyte during water attack. [Copyright &y& Elsevier]

The sol-gel process has been frequently employed for preparation of high performance silica/polymer composites. In this paper, novel sol-gel precursor triethoxysilane-terminated poly(urethane-imide) (PUI-Si), combining the advantages of polyurethane (PU) and polyimide, was synthesized and characterized. Then PUI-Si was incorporated into the epoxy resin matrix to prepare a series of EP/PUI-Si organic-inorganic hybrids through an in situ sol-gel process and crosslinking reactions. The thermal stability of EP/PUI-Si hybrids was evaluated by thermogravimetric analysis and the results show that the PUI-Si could significantly improve the thermal properties of epoxy resin. The initial decomposition temperature of composites with 50 wt% PUI-Si reached 347.1 °C, 157.3 °C higher than that of neat epoxy resin. Furthermore, the tensile strength and breaking elongation can also be clearly improved by adding a suitable amount of PUI-Si. Similarly, the water contact angle increased to 97.4° with 70 wt% PUI-Si, showing a hydrophobic surface. The morphology was investigated by transmission electron microscopy and the results reveal that the silica particles are smaller than 20 nm and have a strong interaction with the epoxy resin matrix, resulting in the above-mentioned high performance properties. Copyright © 2011 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

We have developed a new class of proton-conducting organic-inorganic hybrid silicophosphite membranes, produced by ethanol condensation of organically modified alkoxysilanes and anhydrous vinylphosphonic acid under solventless, catalyst-free, low-temperature, one-pot conditions. The membranes synthesized in this study are crack-free, large, and flexible, and they exhibit good thermal stability up to intermediate temperatures (~218 °C). Structural analyses using 29Si and 31P nuclear magnetic resonance spectroscopy and infrared measurements revealed that ethanol condensation produced an inorganic alternating copolymer structure, Si-O-P, with a phosphole group, and successive polymerization between vinyl and/or methacryl groups enabled these structures to connect with each other. In this way, it is possible to achieve structure manufacturing of inorganic-organic networks. The proton conductivities of the hybrids are as high as 5.2 x 10-3 S/cm at 85 °C under 80% relative humidity. [ABSTRACT FROM AUTHOR]

The impressive surface activity of silicones can be enhanced by the incorporation of hydrophilic organic functional groups and polymers. Traditional routes to such compounds, which typically involve platinum-catalyzed hydrosilylation, suffer from incompatibility with certain functional groups. B(C6F5)3-catalyzed condensation of hydrosilanes with alkoxysilanes offers new opportunities to prepare explicit silicone structures. We demonstrate here that conversion of alcohols to silyl ethers competes unproductively with alkoxysilane conversion to disiloxanes. By contrast, a wide range of structurally complex alkyl halide and oligovinyl compounds can be readily made in high yield. Thermal 3+2-cycloadditions and thiol-ene click reactions are used to convert these compounds into surface active materials. [ABSTRACT FROM AUTHOR]

Abstract: In this paper a surface treatment is described for preparation of hydrophobic sol–gel coatings that simultaneously offer antistatic properties for an appropriate finishing of textiles and refinement of polymer foils. Sol–gel based formulations are modified with both hydrophilic and hydrophobic components simultaneously. Hydrophobic components are, e.g., alkoxysilanes modified with alkyl chains while the hydrophilic ones are amino-functionalized alkoxysilanes. The basic idea is that due to an enrichment of hydrophobic groups at the solid/air interface the surface of the as prepared coatings will be hydrophobic while the deeper region will be more hydrophilic. Textiles finished with these coatings exhibit sufficient water repellence and simultaneously absorb sufficient amounts of humidity in the deeper areas of the coating guaranteeing antistatic properties. This concept offers interesting approaches for the preparation of multifunctional surface coatings not only focussing on combining water repellence with antistatic properties for textile materials. [Copyright &y& Elsevier]

One of the key challenges in materials science is to control the size and shape of inorganic nanoparticles with a high degree of precision, as these parameters have a significant influence on the nanoparticles' properties and potential applications. Here, we describe the preparation of highly monodisperse silica nanoparticles smaller than 5 nm in diameter by using self-assembled, hollow, spherical compounds as ‘endo-templates’. These coordination complexes with pendant sugar groups lining their interiors—assembled from 12 metal ions and 24 bis-pyridyl ligands containing glucose substituents—acted as structurally well-defined templates for the sol–gel condensation of alkoxysilanes. The polydispersities of the silica nanoparticles made with this method approached unity, with Mw/Mn < 1.01. The component ligands are modified easily, which enables an accurate expansion of the coordination complex and the subsequent control of the monodisperse silica nanoparticles that span molecular weights of 5,000 to 31,000 Da (corresponding to 2–4 nm in diameter). This method could be applicable to the preparation of other inorganic nanoparticles. [ABSTRACT FROM AUTHOR]

Abstract: Incorporation of metal alkoxides into polymers through sol–gel process is of significant interest for tuning the refractive index of optical materials. In this paper, the organic–inorganic hybrid material with high refractive index (RI) and transparency was studied. Tetrabutoxytitanate (TBOT) and alkoxysilanes including diphenyldimethoxysilane (DPS) and γ-glycidoxypropyl trimethoxysilane (GPTS) were employed as sources of the titania sol and the silica sol, respectively. Two series of titania-based inorganic–organic hybrid materials with and without acetylacetone (AcAc) were prepared using the sol–gel method. Subsequently, crack-free films were fabricated by spin coating. The hybrid films with different Ti content were characterized by various techniques including IR, UV–vis, TG/DSC, SEM and auto-laser ellipsometer. The results indicated that the hybrid films displayed homogeneous morphology and titania was crosslinked with alkoxysilanes. Films without AcAc showed higher optical transparency in the visible region than those containing AcAc. The RI of films without AcAc increased from 1.54 to 1.64 at 633nm with Ti molar fraction varying from 10 to 70%. Whereas, in the films with AcAc, the refractive indices were higher and unorderly. The study has demonstrated great potential to obtain titania hybrid films with high RI and transparency. [Copyright &y& Elsevier]

The article discusses the role of polymers in the conservation and protection of historic monuments or significant cultural structures. It presents the various aspects of monument protection including the mains causes of damages and the importance of contact angle as a factor in choosing polymeric coatings. It introduces a new class of protective materials made of hybrid organic-inorganic coatings such as fluorinated polymers, Paraloids or acrylic-based polymers and alkoxysilanes.

Poly(methyl acrylate) (PMA) + SiO2 composites were synthesized via a sol-gel reaction. The base acrylic copolymers with a content of alkoxysilane groups were prepared by co-polymerization of methylacrylate (MA) with 3-(trimethoxysilyl) propylmethacrylate (3MPS) or vinyltrimethoxysilane (VTMS); the products were cocondensed with tetraethylorthosilicate (TEOS). The PMA + SiO2 hybrids were characterized. Thermal stability of PMA is enhanced by copolymerization with 3-MPS or VTMS and the presence of SiO2; significant weight loss occurs only above 400 °C. Decomposition temperatures are higher by 20 - 25 K as compared to the initial PMA. During the sol-gel process the trimethoxysilyl groups in PMA/3MPS are transformed into a strong silica network. Two different methods of creation of hybrids were used; ESEM shows that only one of them leads to uniform distribution of silica in polymeric matrices. [ABSTRACT FROM AUTHOR]

Summary  A series of moisture curable polyurethane/polysiloxane (PUSR) copolymers with different end-capping agents were prepared based on amine terminated polysiloxane (PDMS), poly-1,4-butylene adipate glycol (PBA), 4,4′-diphenylmethane diisocyanate (MDI). The copolymers were characterized by Fourier transform infrared (FT-IR) spectroscopy, thermogarvimetric (TGA), X-ray diffraction (XRD), dynamic mechanical thermal analysis (DMTA), X-ray photoelectron spectroscopy (XPS), surface contact angle and stress–strain measurement. Compared with conventional moisture curable PU the PUSR copolymer showed the better thermal stability and surface properties due to the forming of Si-O-Si crosslinking network and the enrichment of siloxane chains on the surface of films , and the tensile strength was not obviously damaged. DMTA results suggested that micro-phase separation was formed in the PUSR copolymer. It was found that the PUSR copolymer with mixed alkoxysilanes as end-capping agents showed better compromised properties than that with single alkoxysilane. [ABSTRACT FROM AUTHOR]

Abstract: Hybrid organic–inorganic nanocomposites containing PEO segments linked to an acrylate–methacrylate network were prepared through a dual-curing process, involving photopolymerization and condensation of alkoxysilane groups. A Polyethyleneglycol 600 α,ω diacrylate (PEGDA 600) and a similar oligomer containing a Bisphenol A unit and α,ω methacrylate groups (BEMA 1400) were used. Mixtures of the oligomers together with methacryloyloxypropyltrimethoxysilane (MEMO) and tetraethoxysilane (TEOS) were prepared. The kinetics of the reactions of photopolymerization and condensation was investigated. The conditions suitable for obtaining a complete conversion of both the reactive groups were settled up. The obtained films were perfectly transparent and amorphous. The T g values of the hybrids were found to increase by increasing the TEOS content and the alkoxysilane groups condensation. TEM analyses indicated the formation of silica phases at a nanometric level; TGA curves revealed a higher thermal stability of the hybrid structures. [Copyright &y& Elsevier]

Organic-inorganic polymer hybrids were prepared utilizing the CH/π interactions. The sol-gel reaction of alkoxysilanes such as tetramethoxysilane (TMOS), methyltrimethoxysilane (MeTMOS), and phenyltrimethoxysilane (PhTMOS) was carried out in the presence of the polymer having the activated CH groups such as poly(vinyl chloride) (PVC). It was found that the transparent and homogeneous polymer hybrid was obtained from PVC and the alkoxysilane having aromatic groups such as PhTMOS. The transparent and homogeneous polymer hybrids could be obtained in a wide range of mass ratios (PVC/PhSiO1.5 = 9/1-3/7). In these polymer hybrids, the CH/π interaction was found to act as an important role for the dispersion of PVC in the silica matrix. [ABSTRACT FROM AUTHOR]

The present paper deals with the study of stone consolidants which consist of mixtures of Ethylsiticate 40 and Paraloid B-72. The composition of the mixtures under evaluation was chosen so that the effects on consolidation quality of the addition of Paraloid B-72 and of various catalysts could be assessed. The penetration rate of the consolidating mixtures in stone was studied; compression strength was measured, as well as water absorption under normal pressure and resistivity to crystallizing salts. Porosity of the consolidated surface layer was determined for some samples. When the stone samples were treated with consolidants containing Ethylsilicate 40 and Paraloid B-72, all observed properties of the stone were improved. Although absolute values of these quantities differ considerably--they are affected by the catalysts used--the presence of Paraloid B-72 has a positive effect. Of particular importance is the fact that surface stone porosity and the appearance of the stone are not greatly affected by consolidation. [ABSTRACT FROM AUTHOR]

The development of improved cold-cured resins, to be used as either adhesives or matrices for FRP (fiber reinforced polymer) composites employed in the construction industry, has become the focus of several academic and industrial research projects. It is expected that the use of nano-structured organic–inorganic hybrid materials could represent a realistic alternative to commercial epoxy-based resins due to their superior properties, especially in terms of higher durability against: moisture, temperatures, harsh environments, and fire. In this context, organic–inorganic epoxy hybrids were synthesized by a modified sol–gel method without the addition of water. The experimental formulations were prepared starting from a mixture of a silane-functionalized epoxy resin, alkoxysilane components and a deep eutectic solvent (DES) based on a blend of choline chloride and urea. The latter was added in two different loads in order to analyze in depth its effect as a promoter for an effective dispersion of silica nano-phases, formed through hydrolysis and condensation reactions, into the cross-linked epoxy network. The produced formulations were cold-cured for different time spans in the presence of two hardeners, both suitable for a curing process at ambient temperature. In this first part of a wider experimental program, several analyses were carried out on the liquid (rheological and calorimetric) and cold-cured (calorimetric, thermogravimetric, dynamic-mechanical, flexural mechanical, and morphological) systems to evaluate and quantify the improvement in properties brought about by the presence of two different phases (organic and inorganic) in the same epoxy-based hybrid system. [ABSTRACT FROM AUTHOR]