Preparation and Characterization of the Hybrids Containing Silica Nanoparticles by Sol-Gel Crosslinking Process

The organic/inorganic hybrid nanomaterials containing silica nanoparticles are synthesized by sol-gel crosslinking process. The tetraethoxysilane (TEOS) and γ-aminopropyltriethoxylsilane as coupling agents are used as a precursor. The 2,4,6-tri [(2-epihydrin-3-bimethyl-ammonium)propyl]-1,3,5-triazine chloride (Tri-EBAC) as crosslinking agent is used to form covalent bonds among the inorganic nanoparticles. The chemical and morphological structures of the organic/inorganic hybrid are characterized with FTIR spectra, ²⁹Si-NMR, x-ray diffraction (XRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and atomic force microscope (AFM). The results show that the organic/inorganic hybrid forms covalent bond between the inorganic nanoparticle and Tri-EBAC. The network organic/inorganic hybrid can form good film with even nanometer particles. The network organic/inorganic hybrids nanomaterial not only exhibits the thermal properties of inorganic compounds, but also exhibits the thermal properties of organic polymer.     

Organic–inorganic tandem route to polymer nanocomposites: kinetic products versus thermodynamic products

We report a facile single-step photochemical methodology to afford alkylsiloxane-polymer hybrid films which relies on the tandem photoacid-catalyzed polymerization of n-alkyltrimethoxysilane precursors and a diglycidyl ether organic monomer. Photoacids liberated by the UV decomposition of iodonium salt triggers simultaneously the sol–gel process and epoxy cationic polymerization. Such conditions are intended to favour the formation of kinetic products trapped by cross-linking reactions instead of the thermodynamically most stable structures, whose preference would be for macrophase segregation. Organosilane precursor exhibiting different structures and chain lengths (n-butyl, n-octyl, n-dodecyl, n-hexadecyl, isobutyl and isooctyl) were systematically investigated to afford a range of transparent alkylsiloxane-polyether hybrids. The competitive organic–inorganic reaction kinetics were investigated using in situ real-time Fourier transform infrared spectroscopy. A main emphasis has been on discussing the effect of the alkyl substituent structure on the photoinduced polymerization kinetics and the silicate networks characterized by ²⁹Si solid-state NMR. To avoid phase separation, the rate of formation of the two phases was tailored to favour concomitancy upon modulating several experimental parameters: film thickness, alkyl structure, photoacid generator concentration. Finally, the viscoelastic and surface properties were also assessed by dynamic mechanical analysis and water contact angle measurements, respectively.     

Synthesis and characterization of UV‐curable phosphorus containing hybrid materials prepared by sol–gel technique

In this study, a series of ultraviolet (UV)‐curable organic–inorganic hybrid coating materials containing phosphorus were prepared by sol–gel approach from acrylate end‐capped urethane resin, acrylated phenyl phosphine oxide oligomer (APPO), and inorganic precursors. TEOS and MAPTMS were used to obtain the silica network and Ti:acac complex was employed for the formation of the titania network in the hybrid coating systems. Coating performance of the hybrid coating materials applied on aluminum substrates was determined by the analysis techniques, such as hardness, gloss, impact strength, cross‐cut adhesion, taber abrasion resistance, which were accepted by international organization. Also, stress–strain test of the hybrids was carried out on the free films. These measurements showed that all the properties of the hybrids were enhanced effectively by gradual increase in sol–gel precursors and APPO oligomer content. The thermal behavior of the hybrid coatings was investigated by thermogravimetric analysis (TGA) analysis. The flame retardancy of the hybrid materials was examined by the limiting oxygen index (LOI); the LOI values of pure organic coating (BF) increased from 31 to 44 for the hybrid materials containing phosphorus (BF‐P:40/Si:10). The data from thermal analysis and LOI showed that the hybrid coating materials containing phosphorus have higher thermal stability and flame resistance properties than the organic polymer. Besides that, it was found that the double bond conversion values for the hybrid mixtures were adequate in order to form an organic matrix. The polycondensation reactions of TEOS and MAPTMS compounds were also investigated by ²⁹Si‐NMR spectroscopy. SEM studies of the hybrid coatings showed that silica/titania particles were homogenously dispersed through the organic matrix. In addition, it was determined that the hybrid material containing phosphorus and silica showed fibrillar structure. Copyright © 2009 John Wiley & Sons, Ltd.     

Fabrication and properties of thermosensitive organic/inorganic hybrid hydrogel thin films

We report on a facile method for fabricating thermosensitive organic/inorganic hybrid hydrogel thin films from a cross-linkable organic/inorganic hydrid copolymer, poly[ N-isopropylacrylamide- co-3-(trimethoxysilyl)propylmethacrylate] [P(NIPAm- co-TMSPMA)]. Fourier transform infrared (FT-IR) spectra confirmed the formation of hybrid hydrogel thin films after hydrolysis of the methoxysilyl groups (Si-O-CH 3) and subsequent condensation of the silanol groups (Si-OH). Atomic force microscopy (AFM) images revealed that the surface morphology of the hydrogel thin films depended on the supporting substrates. Microdomains were observed for the hydrogel thin films on a gold surface, which can be attributed to inhomogeneous network structures. The thermoresponsive swelling-deswelling behavior and the viscoelastic properties of the hydrogel thin films were investigated as a function of temperature (25-45 degrees C) by using a quartz crystal microbalance (QCM) operated in water. The high frequency shear modulus of the P(NIPAm- co-TMPSMA) hydrogel thin films was several hundred kilopascals.     

Polysaccharides/silica hybrid materials: New perspectives for sustainable raw materials

Polysaccharides/silica hybrids prepared through sol-gel reaction have been studied as a model for new generation of hybrid materials for a virtually unlimited number of applications. Numerous studies have therefore attempted to increase the homogeneity between the organic and inorganic moieties using a wide variety of silica precursors and crosslinking reagents. The current review summarizes and discusses the attempts for using polysaccharides for producing hybrid materials with collective properties from the two counterparts. It discusses several issues and strategies to tune the homogeneity of polysaccharide/silica hybrids and the potential applicability of these hybrid materials in biomedical and industrial fields.     

Structural and mechanical properties of Laponite-PEG hybrid films

Inorganic/organic hybrids were obtained by the sol-gel type organic modification reaction of Laponite sidewalls with poly(ethylene glycol) (PEG) bearing alkoxysiloxy terminal functionality. By casting an aqueous dispersion of the hybrid, the flexible and transparent hybrid films were obtained. Regardless of the inorganic/organic component ratio, the hybrid film had the ordered structure of Laponite in-plane flat arrays. The mechanical strength of hybrid films was drastically improved by the presence of cross-linking among alkoxysilyl functionalities of PEG terminals and the absence of PEG crystallines. Hybrid films, especially those that consisted of PEG with short chain, showed good mechanical properties that originate from quasi-homogeneous dispersion of components due to anchoring of PEG terminal to Laponite sidewall and interaction of PEG to Laponite surface.     

溶胶-凝胶法制备丙烯酸树脂/TiO2有机-无机杂化材料及其结构表征

通过预水解的二氧化钛(TiO2 )溶胶与丙烯酸树脂共混或原位聚合的方法制备了均匀透明的丙烯酸树脂 TiO2 有机 无机杂化材料.考察了TiO2 溶胶制备方法、聚合物中—COOH官能团含量和杂化材料制备方法对杂化材料结构的影响.索氏抽提实验表明聚合物中的羧酸官能团和无机TiO2 相间发生了交联反应,且随着—COOH官能团含量的增加,交联程度增大.小角X射线散射(SAXS)结果发现,杂化材料中TiO2 为疏松的三维网状结构,且在纳米尺度范围内,但这种三维网状结构随着TiO2 溶胶制备中水或酸的用量增加,其致密度增加,尺寸增大.同原位聚合法相比,共混法可制备出更均匀的杂化体系,且TiO2 为单分散.     

Acrylic polymer/silica hybrids prepared by emulsifier‐free emulsion polymerization and the sol–gel process

Acrylic polymer/silica hybrids were prepared by emulsifier‐free emulsion polymerization and the sol–gel process. Acrylic polymer emulsions containing triethoxysilyl groups were synthesized by emulsifier‐free batch emulsion polymerization. The acrylic polymer/silica hybrid films prepared from the acrylic polymer emulsions and tetraethoxysilane (TEOS) were transparent and solvent‐resistant. Atomic force microscopy studies of the hybrid film surface suggested that the hybrid films did not contain large (e.g., micrometer‐size) silica particles, which could be formed because of the organic–inorganic phase separation. The Si? O? Si bond formed by the cocondensation of TEOS and the triethoxysilyl groups on the acrylic polymer increased the miscibility between the acrylic polymer component and the silica component in the hybrid films, in which the nanometer‐size silica domains (particles) were dispersed homogeneously in the acrylic polymer component. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 273–280, 2006     

Skewered reactions in free‐radical crosslinking (co)polymerizations of liquid polybutadiene as internal olefinic multivinyl crosslinker

As an extension of our continuing studies concerned with the mechanistic discussion of network formation in the free‐radical crosslinking (co)polymerization of multivinyl monomers, this work refers to the skewered reactions in the crosslinking (co)polymerizations of liquid polybutadiene rubber (LBR) as an internal olefinic multivinyl monomer or crosslinker, especially focused on the competitive occurrence of both addition or skewered reaction to internal carbon–carbon (CC) double bonds and abstraction reaction of allylic hydrogens in LBR by growing polymer radical. Thus, LBR is regarded as an internal olefinic multiallyl monomer‐linked allyl groups (? CH?CH? CH₂? ) with methylene units (? CH₂? ). First, gelation in the polymerization of LBR was explored in detail, especially at elevated temperatures. The occurrence of intermolecular crosslinking was easier in the order LBR > LBR containing 20 mol % of 1,2‐structural units > liquid polyisoprene rubber. Then, we pursued the polymerization of LBR using dicumyl peroxide (DCPO) as typical organic peroxide used at elevated temperatures. The primary cumyloxy radical generated by the thermal decomposition of DCPO may add to CC double bond or abstract allylic hydrogen or undergo β‐scission to generate a secondary methyl radical. The initiation by the cumyloxy radical was omitted. The ratio of allylic hydrogen abstraction to β‐scission reaction was estimated; thus, only 39% of cumyloxy radical was used for the allylic hydrogen abstraction reaction. The addition of methyl radical to CC double bond was clearly observed. Finally, we pursued the intermolecular and intramolecular skewered reactions in free‐radical crosslinking LBR/vinyl pivalate copolymerizations. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Nanostructured oligo(p-phenylene vinylene)/silicate hybrid films: one-step fabrication and energy transfer studies

Novel hybrid materials containing silicate and charged oligo(p-phenylene vinylene) (OPV) amphiphiles were fabricated in one step by spin casting using evaporation-induced self assembly. The conjugated segments were substituted with trimethylammonium bromide groups at both termini, and tetraethyl orthosilicate served as the silicate precursor. X-ray diffraction scans of the hybrid films revealed Bragg diffraction peaks with d-spacings of 2.76 and 1.37 nm, indicating the presence of order in the hybrid structure. Optical properties of the hybrid films were characterized by UV-vis absorption and fluorescence spectra, and molecular orientation was characterized by IR spectroscopy. A rhodamine B derivative containing a triethoxysilane group was covalently incorporated into the silicate network of the films during the sol-gel reaction. Relative to disordered polymer films with identical organic composition, the ordered hybrid films revealed significantly enhanced emission from rhodamine B and also fluorescence quenching from OPV segments. These results indicate that the ordered and nanostructured environment leads to highly efficient energy transfer among organic components in these hybrid films.     

Control of the Morphology of Organic-Inorganic Hybrid Materials Elaborated by Reactive Processing Without Solvent

We study the synthesis of organic-inorganic hybrids in the molten state of the polymer without solvent, by reactive processing. The synthesis is based in a first step upon the crosslinking of ethylene vinyl acetate copolymer (EVA) through an exchange reaction between the pendant ester groups of EVA and tetrapropoxysilane (TPOS) in presence of dibutyltin oxide (DBTO) as an indispensable catalyst. Then in a second step the hydrolysis-condensation reactions of residual alkoxide groups results in silica network formation, which is covalently bonded with the organic network. An original approach was developed to correlate the evolution of the hydrolysis-condensation reactions through the assessment of propanol by gas chromatography and the evolution of the morphology through SAXS and TEM analysis. Silica-rich domains with a diameter close to 5 nm are obtained.     

Preparation and characters of hyperbranched polyester‐based organic‐inorganic hybrid material compared with linear polyester

To compare the properties of hyperbranched polymers with linear oligomers for preparing organic‐inorganic hybrids, hyperbranched aliphatic polyester (Boltorn^TM H20) and linear polyester hexa‐acrylate (EB830) were selected as organic components for preparing UV‐curable transparent hybrid materials using 3‐(trimethoxysilyl) propylmethacrylate as a coupling agent via a sol‐gel process. The prehydrolyzed product of tetraethoxysilane was used as an inorganic component. The effects of inorganic content on the morphologies, thermal behaviors, photopolymerizaiton kinetics and mechanical properties of the hybrids were investigated. The results show that for hyperbranched polyester‐based hybrids, the organic phase shows much better compatibility with inorganic phase even at high inorganic component content due to its special spheral shape and plenty of functional end groups, compared with linear EB830‐based hybrids. Copyright © 2004 John Wiley & Sons, Ltd.     

ESR study on chemical crosslinking reaction mechanisms of polyethylene using a chemical agent

The reaction mechanisms of thermal crosslinking of polyethylene with dicumyl peroxide (DCP) at high temperatures were investigated by electron spin resonance (ESR). The crosslinking reactions were induced by the alkyl radicals formed by the thermal decomposition of DCP above 120°C. The kinetics of the free radical reaction were followed during crosslinking reactions at temperatures between 145 and 180°C. © 1997 John Wiley & Sons, Inc.     

Effect of preparation conditions on the optical and physical properties of an epoxy-functional inorganic-organic hybrid material system

A hybrid material system consisting of (3-glycidyloxypropyl)trimethoxysilane, dimethyldimethoxysilane and zirconium(IV) n-propoxide was prepared. The influence of processing parameters including Zr content, UV irradiation and sol ageing on the properties of the resultant thin films was discussed. Refractive index, at 633 nm, and reflectance measurements were performed and near-field waveguide images of the samples were taken. Optical propagation loss measurements, at 633 nm, were studied. Film thickness and cross-sectional scanning electron microscopy images were obtained as a function of process conditions. FT-IR spectroscopy was used to monitor chemical reaction pathways in the system during processing. It was demonstrated that the crosslinking of epoxy groups in the structure, along with inorganic network formation as a result of sol-gel reactions, was the primary reason for the changes in the optical and physical properties of the system. As Zr containing species and/or UV irradiation may be employed to crosslink the epoxy groups in the structure, the optical and physical properties of the system can be tuned by optimal combination of these two crosslinking methods, as well as sol ageing process.     

In Situ Fabrication of ZnS Semiconductor Nanoparticles in Layered Organic-inorganic Solid Template

Ordered ZnS semiconductor nanoparticles were in situ synthesized in metal halide perovskite organic/inorganic layered hybrids (CnH2n 1NH3)2ZnCl4 (n=10 and 12) by reaction of their spin-casting films with H2S gas. Transmission electron microscopy, UV-vis spectroscopy and small-angle X-ray diffraction were used to characterize the morphology and the structure of formed nanoparticles. Obtained results indicate an effective way to incorporate functional inorganic nanoparticles into structured organic matrices.     

Photopatternable hybrid sol–gel films: A liquid Si NMR investigation of the inorganic network formation

Methacryloxypropyltrimethoxysilane precursor has been involved in the realization of optical elements in crack free thick films (ranging from 15 to 100 μm), through spatially controlled photopolymerization. First, alkoxysilane functions were partially hydrolyzed and condensed. Then, using a photoinitiator, free radical photopolymerization was proceeded by irradiating the sample under UV or visible light. Since an organic network is formed in the matrix of the primarily formed inorganic network, understanding the formation of the silicate backbone was of first importance to ensure the creation of crack free thick films through efficient polymerization.

Liquid ²⁹Si NMR spectroscopy was used to investigate the inorganic network formation. Material preparation required evaporation of the volatile solvents released by the sol–gel process and limitation of the condensation degree. Both conditions were achieved by a drying process at room temperature. The structure and the composition of the dried sols were investigated and compared to non-dried sols. NMR peak fitting pointed out to the presence of a large variety of cyclic and linear oligomers in the sol. The structure of the dried sol appeared to depend both on the aging time and on the storage temperature. All these results have to be taken into account when the condensation degree has to be limited for specific optical applications.     

Synthesis of raspberry-like monodisperse magnetic hollow hybrid nanospheres by coating polystyrene template with Fe(3)O(4)@SiO(2) particles

A new inorganic/organic hybrid material containing silsesquioxane was prepared by the reaction of caged octa (aminopropyl silsesquioxane) (POSS-NH(2)) with n-butyl glycidyl ether (nBGE) and 1,4-butanediol diglycidyl ether (BDGE). The copolymers of POSS, nBGE, and BDGE could be obtained with varied feed ratio of POSS-NH(2), nBGE, and BDGE in the preparation. The hybrid material was added into an epoxy resin (E51) for enhancing the toughening and thermal properties of the epoxy resin. The results showed that the toughening and the thermal properties of the cured epoxy resin were greatly improved by the addition of the hybrid. The enhancement was ascribed to nano-scale effect of the POSS structure and the formation of anchor structure in the cured network. The investigation of kinetics for the curing process of the hybrid-modified epoxy resin revealed that two kinds of curing reactions occurred in different temperature ranges. They were attributed to the reactions between amino groups of the curing agent with epoxy groups of E51 and with residue epoxy groups in the hybrid. The reacting activation energies were calculated based on Kissinger's and Flynn-Wall-Ozawa's methods, respectively.     

含硅氧烷结构聚酰亚胺树脂的耐热稳定性及高温结构演变

基于含硅芳香二胺双(4-氨基苯氧基)二甲基硅烷(APDS)设计制备了系列苯乙炔基封端的含硅氧烷结构聚酰亚胺树脂预聚物(PEPA-PIS), 考察了硅氧烷含量对树脂固化物耐热稳定性的影响规律. 利用非反应性苯酐基团封端的模型预聚物(PA-PIS)证明了温度对于硅氧烷结构演变的影响. 通过对树脂固化物高温固化处理后耐热稳定性与微观结构和表面形貌的关系进行深入研究, 发现在高温下硅氧烷结构发生氧化交联反应, 并在树脂表面形成具有无机特性的二氧化硅结构, 这种有机/无机杂化特性可显著提高聚酰亚胺树脂的耐热稳定性.     

Poly(γ‐glutamic acid)/Silica Hybrids with Calcium Incorporated in the Silica Network by Use of a Calcium Alkoxide Precursor

Current materials used for bone regeneration are usually bioactive ceramics or glasses. Although they bond to bone, they are brittle. There is a need for new materials that can combine bioactivity with toughness and controlled biodegradation. Sol‐gel hybrids have the potential to do this through their nanoscale interpenetrating networks (IPN) of inorganic and organic components. Poly(γ‐glutamic acid) (γ‐PGA) was introduced into the sol‐gel process to produce a hybrid of γ‐PGA and bioactive silica. Calcium is an important element for bone regeneration but calcium sources that are used traditionally in the sol‐gel process, such as Ca salts, do not allow Ca incorporation into the silicate network during low‐temperature processing. The hypothesis for this study was that using calcium methoxyethoxide (CME) as the Ca source would allow Ca incorporation into the silicate component of the hybrid at room temperature. The produced hybrids would have improved mechanical properties and controlled degradation compared with hybrids of calcium chloride (CaCl₂), in which the Ca is not incorporated into the silicate network. Class II hybrids, with covalent bonds between the inorganic and organic species, were synthesised by using organosilane. Calcium incorporation in both the organic and inorganic IPNs of the hybrid was improved when CME was used. This was clearly observed by using FTIR and solid‐state NMR spectroscopy, which showed ionic cross‐linking of γ‐PGA by Ca and a lower degree of condensation of the Si species compared with the hybrids made with CaCl₂ as the Ca source. The ionic cross‐linking of γ‐PGA by Ca resulted in excellent compressive strength and reduced elastic modulus as measured by compressive testing and nanoindentation, respectively. All hybrids showed bioactivity as hydroxyapatite (HA) was formed after immersion in simulated body fluid (SBF).