Crosslinked organosiloxane hybrid materials prepared by condensation of silanol and modified silica: Synthesis and characterization

Hybrid materials based on polymethylphenylsiloxane (PMPS) and organic functionalized silica were synthesized via condensation reaction between silanol and alkoxysilyl groups in the presence of quaternary ammonium hydroxide. The structure of prepared materials was investigated by FTIR and NMR, which indicate that the products have incorporated modified silica into the polymer matrix. The prepared hybrid materials show a satisfactory thermal resistance because the initial decomposition of typical product occurred at nearly 100 K higher than that of the pure polymer according to the thermogravimetric analysis (TGA) results. Differential thermogravimetric analysis (DTGA) data confirm that the thermal degradation of prepared hybrid materials comprises of two steps, of which the first one could be controlled by adjusting the content of silica particles and the ratio of surface groups on the particles. The coating films obtained from hybrid products exhibit good thermal mechanical properties. Therefore, the materials are hoped to be used for the application in thermal resistant coating.     

Preparation and properties of biocompatible polymer-grafted silica nanoparticle

Grafting of biocompatible polymer onto the surface of silica nanoparticles was achieved by radical graft polymerization of 2-methacryloyloxyethyl phosphorylcholine (MPC), initiated by azo groups previously introduced onto the surface or by a system consisting of Mo(CO)₆ and trichloroacetyl groups on the silica surface. Both of these systems have the ability to initiate graft polymerization of MPC, resulting in the formation of poly(MPC)-grafted silica, but the percentage of poly(MPC) grafting for the latter initiating system was much higher than that of the former. The amount of moisture that could be adsorbed onto the silica surface was found to increase with increasing poly(MPC) grafting. This indicates that grafting of poly(MPC) onto the silica surface markedly increases the hydrophilic nature of the surface. The contact angle of water in composites prepared from poly(vinyl alcohol) and poly(MPC)-grafted silica was found to decrease with increasing poly(MPC)-grafted silica content. When poly(MPC)-grafted silica was added to water containing a small amount of chloroform, it was found to act as stabilizer for droplets of chloroform. In addition, according to tests by the Lee-White method, poly(MPC)-grafted silica shows non-thrombogenic characteristics.     

Radiation-induced polymerization and grafting of β(−)pinene on silica surface

Poly-β-pinene (pBp) was obtained on silica surface by γ radiation-induced polymerization of β(−)pinene in presence of silica gel with a specific surface area of 300 m²/g. Different radiation doses were employed in the range 50–332 kGy. The pBp–silica hybrid samples obtained have been characterized by FT-IR spectroscopy and the amount of pBp on silica surface has been determined both by gravimetric and TGA measurements. The fraction of pBp chemically grafted on silica surface has been determined by the extraction of the pBp–silica hybrid with boiling toluene and was found to be 10–20% of the total pBp formed on silica surface. The optical activity of pBp extracted from the hybrid was studied by polarimetric measurements and found slightly lower than the typical specific optical rotation of pBp polymerized in bulk with radiation. The thermal stability of the pBp–silica hybrid materials was studied by thermogravimetric and differential thermal analysis. The results show lower thermal stability for the pBp–silica hybrid in comparison to pure pBp. Evidently, silica catalyzes the thermal decomposition of pBp at lower temperatures. Use of the pBp–silica hybrid as stationary phase for liquid chromatography for chiral separations has been proposed.     

Synthesis of novel fluoroalkyl end‐capped oligomers/silica gel polymer hybrids possessing antibacterial activity

New fluoroalkyl end‐capped oligomers/silica gel polymer hybrids‐low‐molecular weight biocide (hibitane) composites were prepared by the reactions of tetraethoxysilane (TEOS) with fluoroalkyl end‐capped N‐(1,1‐dimethyl‐3‐oxobutyl)acrylamide oligomer, N,N‐dimethylacrylamide oligomers, and acrylic acid oligomers in methanol under acidic conditions at room temperature. The presence of hibitane in the composites was clarified by the use of elementary analyses of nitrogen in fluorinated acrylic acid oligomer composite and thermogravimetric analysis (TGA) of these fluorinated composites. Thermal stability of fluorinated composites thus obtained were found to increase significantly compared to those of the parent fluorinated oligomers. Thermal stability of fluorinated N,N‐dimethylacrylamide oligomer, acrylic acid oligomer/silica gel polymers hybrid‐hibitane composites decreased compared to those of the corresponding fluorinated oligomers/silica gel polymer hybrids; however, the thermal stability of fluorinated N‐(1,1‐dimethyl‐3‐oxobutylacryl)amide oligomer/silica gel polymer hybrid‐hibitane composite increased significantly compared to that of the corresponding fluorinated oligomer hybrid. The sol methanol solutions of these fluorinated composites were applied to the surface modification of glass to exhibit not only a strong oleophobicity imparted by end‐capped fluoroalkyl groups in oligomers but also a good hydrophilicity on the glass surface. Fluorinated oligomers/silica gel polymer hybrids‐hibitane composites were found to exhibit high anti‐bacterial activity against Pseudomonas aeruginosa and Staphylococcus aureus. Therefore, these fluorinated hibitane composites are suggested to have high potential for new attractive functional materials through not only their excellent surface active property imparted by fluorine and their thermal stability but also through their anti‐bacterial activity. Copyright © 2005 John Wiley & Sons, Ltd.     

Acrylic polymer/silica organic–inorganic hybrid emulsions for coating materials: Role of the silane coupling agent

Acrylic polymer/silica organic–inorganic hybrid emulsions were synthesized by a simple method, that is, a conventional emulsion polymerization and subsequent sol–gel process, to provide water‐based coating materials. The acrylic polymer emulsions contained a silane coupling agent monomer, such as methacryloxypropyltriethoxysilane, to form highly solvent‐resistant hybrid films. On the other hand, the hybrid films from the surface‐modified polymer emulsions, in which the silane coupling agent was located only on the surface of the polymer particles and the particle core was not crosslinked, did not exhibit high solvent resistance. A honeycomblike array structure, which was derived from the polymer particles (diameter ≈ 50 nm) and the silica domain, on the hybrid film surfaces was observed by atomic force microscopy. The crosslinked core part and silane coupling agent containing the shell part of the polymer particles played important roles in attaining high solvent resistance. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4736–4742, 2006     

Dispersion of silica nano-particles in sol-gel hybrid resins for fabrication of multi-scale hybrid nanocomposite

Multi-scale hybrid nanocomposites containing both ∼15 nm silica colloids and ∼2 nm oligosiloxanes in a methacryl polymer matrix were newly designed and fabricated. Colloidal silica sols were dispersed in methacryl oligosiloxanes nano-hybrid resins synthesized by sol-gel reaction of methacryloxypropylmethoxysilane and diphenylsilanediol. On the basis of TEM and SANS analyses, it was confirmed that the silica colloids were compatibly dispersed and different sizes of colloidal silica and oligosiloxanes co-exist in the solutions. Multi-scale hybrid nanocomposites fabricated by UV and thermal curing with incorporation of silica colloids in the nano-hybrid materials show enhanced mechanical and thermal characteristics.     

Thermal stability of poly(methyl methacrylate)/silica nano- and microcomposites as investigated by dynamic-mechanical experiments

The thermal stability of poly(methyl methacrylate) (PMMA) filled with silicon dioxide particles was investigated by means of rheological tests. The change in the storage modulus G′ was measured, which is a very sensitive method to detect molecular changes in polymers. The long-term thermal stability of the composites was found to depend on the temperature of the melt, the size of the silica particles, which ranged from nano- to micrometers, and the volume fraction of the filler. For high temperatures and a large surface area of the silica particles the behaviour of the composites differs significantly from that of the pure polymer. Pure PMMA degrades at high temperatures, which correlates with a decrease of G′. In contrast an increase in G′ with increasing temperature and filler surface was measured for the composite materials. This behaviour is explained by chemical reactions of the PMMA molecules with the silica particles. Effects of that kind were not found for SiO₂ filled polystyrene.     

Polycaprolactone membranes reinforced by toughened sol–gel produced silica networks

The aim of this work is to develop polycaprolactone based porous materials with improved mechanical performance to be used in bone repair. The hybrid membranes consist in a polymeric porous material in which the pore walls are coated by a silica thin layer. Silica coating increases membrane stiffness with respect to pure polymer but in addition filling the pores of the polymer with a silica phase improves bioactivity due to the delivery of silica ions in the neighborhood of the material in vivo. Nevertheless silica network, even that produced by sol–gel, might be too stiff and brittle what is not desirable for its performance as a coating. In this work we produced a toughened silica coating adding chitosan and 3-glycidoxypropyltrimethoxysilane (GPTMS) to the precursor solution looking for having polymer chains linked by covalent bonding to the silica network. Hybrid polymer–silica coating was produced by in situ sol–gel reaction using Tetraethyl orthosilicate (TEOS), GPTMS and chitosan. Chemical reaction between amine groups of chitosan chains and epoxy groups of GPTMS allowed covalent bonding of polymer chains to the silica network. Physical properties of the hybrid membranes were characterized and cell attachment of MC3T3-E1 pre-osteoblastic cells on the surface of these supports was assessed.     

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.     

Synthesis of fullerene-silica hybrid materials

Fullerene/silica hybrid materials were obtained by radiation grafting on silica surface of toluene or decalin solutions of C₆₀. As determined by thermogravimetric analysis, the amount of C₆₀ grafted on silica surface was dependent from the radiation dose administered and independent from the C₆₀ concentration and the nature of the organic solvent. In absence of air, a dose of 48 kGy was sufficient to ensure a grafting level of 30% by weight of C₆₀ in the hybrid material. The fullerene/silica hybrid material shows a remarkable thermal stability, since the early decomposition starts above 300 °C as measured by DTG and DTA. The chemical structure of the fullerene/silica hybrid material was determined by FT-IR spectroscopy and with solid state ¹³C CP-MAS NMR. The potential application of such materials has been outlined.     

Interaction and Microstructure of Polyurethane/Silica Hybrid Films Prepared by Sol-Gel Process

The polyester/silica hybrid resins and their hybrid polyurethanes were prepared via in situ (IS) or blending (BL) method using different silica sols. The effects of preparation methods, silica type and content on the interaction and microstructure of polymer/silica hybrid materials were investigated by FTIR, viscosity measurement, TGA, DMA and SAXS, respectively. It was found that both IS and BL methods formed agglomerates of silica-rich phases and primary silica-rich phases in the hybrid films, but the former caused stronger interaction between silica and polymer than the latter, resulting in much bigger agglomerates and compacter structure. The ethoxy group at silica was favorable for enhancing the interaction between silica phase and polymer, even between silica phases as well. The interaction between silica phase and polymer caused increasing viscosity, modulus and Tg, while the interaction between silica phases themselves increased the extent of micro-phase separation, especially for the hybrid films prepared by IS method.     

Oil-in-water emulsions stabilized by highly charged polyelectrolyte-grafted silica nanoparticles

Fully sulfonated poly(styrenesulfonate) brushes were grown from the surface of colloidal silica particles and used to prepare stable trichloroethylene-in-water and heptane-in-water Pickering emulsions. These particles were highly charged and colloidally stable in water but could not be dispersed in trichloroethylene or heptane. Both two-phase (emulsion plus neat water) and three-phase (emulsion separating neat oil and water phases) systems were observed, with water-continuous emulsion phases in all cases. Emulsion phases containing as much as 83% (v/v) oil were stable for over six months. Poly(styrenesulfonate)-grafted particles were very efficient emulsifiers; stable emulsion phases were prepared when using as little as 0.04 wt% particles. The emulsifying effectiveness of the poly(styrenesulfonate)-grafted silica particles can be attributed to the hydrophobicity of the vinylic polymer backbone that makes this highly charged polyelectrolyte unusually surface active at the oil/water interface.     

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.     

Synthesis of polymeric organic-inorganic hybrid materials. Partially deacetylated chitin-silica hybrid

This work reports the synthesis of a novel polymeric organic-inorganic hybrid. The inorganic component is a silica network obtained by controlled hydrolysis of tetraethyl orthosilicate via sol-gel process and the organic counterpart is partially deacetylated chitin (CHI). The resulting polymer hybrids were homogeneous transparent film forming glassy materials being compatible through a wide composition range. Simultaneous thermal analysis of a CHI/silica 1:1 mixture confirms the intermolecular complex formation between organic and inorganic polymers.     

Influence of Graft Density of Poly (N-Isopropylacrylamide)-Grafted Silica on Separation Performance

Poly (N-isopropylacrylamide) (PNIPAAm)-grafted silica beads with variable graft densities were prepared by atom transfer radical polymerization (ATRP). The ATRP initiator on the surface of silica was prepared through the aminopropyl silica and 2-bromoisobutyryl bromide. Acetyl chloride was used to control the graft density. The content of carbon, hydrogen, and nitrogen were measured by elemental analyzer. The graft ratio was characterized by thermogravimetric analysis and the molecular weight of the polymer was determined by GPC analysis. The retention behavior of five steroids under different temperature was studied. Furthermore, the influence of temperature and graft densities to the separation of steroid compounds was investigated. The results indicated that graft density had a significant influence on the separation efficiency. Thinner PNIPAAm chains on hydrophilic silica surface can achieve the stationary phase with enhanced temperature sensitivity and better separation property.

     

Colloidal crystallization of colloidal silica modified with ferrocenyl group-contained polymers in organic solvents

Surface modification of colloidal silica with ferrocenyl-grafted polymer and colloidal crystallization of the particles in organic solvent were studied. Poly(methyl methacrylate-co-vinylferrocene)-grafted silica never formed colloidal crystals in polar solvent, such as acetone, acetonitrile, ethanol and N,N-dimethylformamide (DMF), while poly(methyl methacrylate-co-ferrocenyl acrylate)-grafted silica gave colloidal crystallization in DMF. The particles prepared by grafting of poly(N,N-dimethylacrylamide-co-vinylferrocene), with vinylferrocene (Vfc) mole fraction of 1/13 and 1/23, were observed to give the crystallization in ethanol and DMF over particle volume fraction of 0.058. Further, silica modified with copolymer of Vfc and N-vinyl-2-pyrrolidone, N-vinylcarbazole or N-isopropylacrylamide formed colloidal crystals in ethanol and DMF. Especially, poly(N-isopropylacrylamide-co-Vfc)-grafted silica, which was composed of the highest mole fraction of vinylferrocene, 1/3, afforded colloidal crystallization in ethanol over particle volume fraction of 0.053. Relatively high polar vinylferrocene copolymer grafting of silica resulted in colloidal polymerization in organic solvents.     

Preparation of silica microspheres with a broad pore size distribution and their use as the support for a coated cellulose derivative chiral stationary phase

A templating strategy using crosslinked and functionalized polymeric beads to synthesize silica microspheres with a broad pore size distribution has been developed. The polymer/silica hybrid microspheres were prepared by utilizing the combination of a templating weak cation exchange resin, a structure‐directing agent N‐trimethoxysilylpropyl‐N,N,N‐trimethylammonium chloride, and a silica precursor tetraethyl orthosilicate. The silica microspheres were then obtained after calcinating the hybrid microspheres. The as‐prepared materials were characterized by scanning electron microscopy, mercury intrusion porosimeter, and thermal gravimetric analysis. The results showed that the starting templating beads were about 5 μm in diameter and the formed silica microspheres were less than 3 μm with a pore size range of 10–150 nm, some pores were even extended to beyond 250 nm. It was demonstrated that cellulose tris(3,5‐dimethylphenylcarbamate) was readily coated onto the surface of the as‐synthesized silica microspheres without any additional surface pretreatment. The coated silica microspheres were uniformly dispersed even with high loading of the chiral stationary phase, which exhibited high resolution chiral separations in high‐performance liquid chromatography.     

A molecularly imprinted polymer-coated nanocomposite of magnetic nanoparticles for estrone recognition

In this study, we synthesized Fe₃O₄ magnetic nanoparticles coated estrone-imprinted polymer with controlled size using a semi-covalent imprinting strategy. In this protocol, the estrone-silica monomer complex (EstSi) was synthesized by the reaction 3-(triethoxysilyl)propyl isocyanate with estrone, where the template was linked to the silica coating on the iron oxide core via a thermally reversible bond. The removal of the template by a simple thermal reaction produced specific estrone recognition sites on the surface of silica shell.The resulting estrone-imprinted polymer coating Fe₃O₄ magnetic hybrid nanoparticles exhibit a much higher specific recognition and saturation magnetization. The hybrid nanoparticles have been used for biochemical separation of estrone.     

Flame retardancy of carbon nanofibre/intumescent hybrid paper based fibre reinforced polymer composites

A hybrid nanopaper consisting of carbon nanofibre (CNF) and/or clay, polyhedral oligomeric silsesquioxane (POSS), ammonium polyphosphate (APP), has been fabricated through the papermaking process. The as-prepared hybrid nanopaper was then incorporated onto the surface of glass fibre (GF) reinforced polymer matrix composites through injection moulding. The morphologies of hybrid nanopapers with and without the polymer resin were characterized with scanning electron microscopy (SEM). The polymer resin penetrated the entire nanopaper under a high-pressure compressed air system. The thermal decomposition behaviour of hybrid nanopapers infused with resin was studied with real-time thermogravimetric analysis/Fourier transform infrared spectrometry (TGA/FTIR). The test results indicate that the addition of clay in the hybrid paper increased the char residues of the nanocomposites. The fire retardant performance of composite laminates incorporating hybrid nanopaper was evaluated by cone calorimeter testing using a radiant heat flux of 50 kW/m². The cone test results indicated that the peak heat release rate (PHRR) decreased dramatically in the case of laminate composites incorporating CNF/clay/APP hybrid paper. However, the extent of reduction of PHRR of the composite laminates incorporated with CNF/POSS/APP hybrid paper was lower. The formation of compact char materials was observed on the surface of the residues and analyzed by SEM and X-ray photoelectron spectroscopy (XPS). The flame retardant mechanisms of hybrid nanopapers in composite laminates are discussed.     

Sol-gel reaction in acrylic polymer emulsions: the effect of particle surface charge

Acrylic polymer-silica hybrid emulsions were synthesized from both anionic and cationic polymer emulsions by simple post-addition of tetraethoxysilane as a silica precursor. Solvent resistance of the films from the hybrid emulsions and the zeta-potential of the hybrid emulsions suggested the different forms of silica components in each hybrid emulsion. Thermal gravimetric analysis, 29Si NMR measurements, and transmission electron microscope observations revealed that the hybrid emulsion from the anionic polymer emulsion was a mixture of anionic polymer particles and homogeneously dissolved silicate oligomer-polymer. On the contrary, the hybrid emulsion from cationic polymer emulsion consisted of polymer core-silica shell particles. The electrostatic interaction between the cationic polymer particle surface and the silicate would be responsible for the accumulation of the silicate onto the particle surface, leading to the silica shell layer formation. The sol-gel condensation reaction of silicate in the acidic emulsion phase was revealed to be controllable by the surface charge of the coexisting particles.