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Polystyrene-block-Polybutadiene-block-Polystyrene Triblock Copolymer Meets Silica: From Modification of Copolymer to Formation of Mesoporous Silica
Abstract
In this work, we reported a facile preparation of mesoporous silica materials assisted by a commercial polystyrene-block-polybutadiene-block-polystyrene (PS-b-PB-b-PS) triblock copolymer. For this purpose, the PS-b-PB-b-PS triblock copolymer was first functionalized with (3-mercaptopropyl)triethoxysilane via a thiol-ene radical addition approach, and then the functionalized triblock copolymer with the midblock bearing triethoxysilane moieties was employed to perform intercomponent sol–gel reactions with tetraethoxysilane (TEOS) to obtain the organic–inorganic gels. The organic–inorganic gels with variable compositions were then used as precursors to obtain mesoporous silica via pyrolysis at elevated temperatures. The functionalized triblock copolymer was characterized by means of Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy, and small-angle X-ray scattering (SAXS). The results of SAXS, transmission electron microscopy, and Brunauer–Emmett–Teller measurements indicate that the mesoporous silica materials were successfully obtained and the porosity of the materials can be modulated with the mass ratios of the functionalized triblock copolymer to the precursor of silica (viz. TEOS).
... Polymer nano composite materials have been found to exhibit exceptional electrical, mechanical and thermal properties when compared to traditional polymer materials [1,2]. In 1994, T. J. Lewis put forward the concept of nano composites [3]. ...
... As far as we know, the interface structures of composite polymer systems have not been observed clearly. The interface concept in nano composites has been proposed and used in composite models and theories [1,20], and that thickness of the interfaces in nano composites ranges from nm to mm. Unfortunately, the observation of interfaces in such systems has been missing in public literatures. ...
The interface plays a decisive role on the performance of nano dielectric composite films, and researchers have made tremendous efforts to confirm the existence of the interface in nano dielectric composite films. However, establishing quantitative determining interface information of nano composites is very difficult. In this paper, a typical nano dielectric, PI/SiO 2 composite film with content of 10% SiO 2 was prepared by an in-situ method and the microstructures of PI/SiO 2 and pure PI were obtained by the small-angle X-ray scattering (SAXS), which is a non-destructive testing method. The TEM results show that the average grain diameter of SiO 2 particles and the thicknesses of the interfaces are about 7.5 nm and 2.2 nm, respectively. The SAXS results are confirmed by direct TEM imaging method, in which SiO 2 particles adsorb the surrounding PI molecular chains, and form the interfaces. The average grain diameters of SiO 2 (not including the absorbed PI) particles and the thicknesses of interfaces are about 6.8 nm and 2.6 nm respectively. From this paper, we have proved that SAXS is a new effective means for the quantitative determining of interface information of nano composites.
... The PACMO-b-PAEFC copolymer is microphase-separated, and the PAEFC or PACMO microdomains are arranged in a lamellar lattice, forming a disordered nanostructure because of only a scattering peak. 42 Meanwhile, it is noticed that the peak intensity increases with increasing the amount of PAEFC moieties, suggesting that the copolymer with high PAEFC contents is well-organized in solid state and the crystallinity is enhanced due to more and stronger π−π stacking or crystal packing of PAEFC chain segments. The peak values or full width at halfmaximum of one-dimensional scattering intensity curves can be used as a parameter representing particle size and spacing regularity, which corresponds to the size of the orderly stacked lamellas, i.e., long spacing (L), and is evaluated based on Bragg's equation (2L sin θ max = λ): ...
Novel well-defined redox-responsive ferrocene-containing amphiphilic block copolymers (PACMO-b-PAEFC) were synthesized by ATRP, with poly(N-acryloylmorpholine) (PACMO) as hydrophilic blocks and poly(2-acryloyloxyethyl ferrocenecarboxylate) (PAEFC) as hydrophobic blocks. The copolymers were characterized by FTIR, 1H NMR, and gel permeation chromatography, and the crystalline behavior was determined by X-ray diffraction and small-angle X-ray scattering. The results showed that the size of the lamellar crystals and crystallinity vary with the systematic compositions while the periodic structure of the lamellar stacks has no obvious change. These block copolymers could self-assemble and form globular nanoscaled core-shell micellar aggregates in aqueous solution. The reductive ferrocene groups could be changed into hydrophilic ferrocenium via mild oxidation, whereas the polymer micelles at oxidation state could reversibly recover from their original states upon reduction by vitamin C. The tunable redox response was investigated and verified by transmission electron microscopy, ultraviolet-visible spectroscopy, cyclic voltammetry and dynamic light scattering measurements. The copolymer micelles were used to entrap anticancer drug paclitaxel (PTX), with high drug encapsulation efficiency of 61.4%, whilst the PTX-loaded drug formulation exhibited oxidation-controlled drug release, and the release rate could be mediated by the kinds and concentrations of oxidants. MTT assay was performed to disclose the biocompatibility and security of the copolymer micelles and to assess anticancer efficiency of the PTX-loaded nanomicelles. The developed copolymer nanomicelles with reversible redox response are anticipated to have potential in targeted drug delivery systems for cancer therapy.
The functionalization of poly(styrene-b-isoprene-b-styrene) block copolymer by full epoxidation of polyisoprene block and its subsequent epoxy rings opening with thiolated nucleophiles was studied. The optimal ring-opening conditions were microwave heating at 110 °C for 3 h in tetrahydrofuran as a solvent, using sodium benzylthiolate as a model system. Afterwards, this methodology was successfully extended to thiolated nucleophiles with aliphatic and heterocyclic substituents. The new derivatives were characterized by size exclusion chromatography, spectroscopic techniques (FTIR-ATR, ¹H and ¹³C NMR), thermal methods (TGA and DSC), and scanning electron microscopy to study morphology. The antioxidant activity of new block copolymers was examined by 1,1-diphenyl-2-picrylhydrazyl test. The polymer films showed an efficient DPPH radical inhibition activity.
A biphasic solvent system consisting of ionic liquids (IL) and petroleum ethers was applied in the extraction of Eucommia ulmoides gum (EUG) from pericarp. Effects of IL and extraction parameters on the yield and purity of EUG were investigated. The results showed that the addition of IL could enhance the yield and purity of EUG extracted from pericarp comparing with the traditional alike pretreatment method. FTIR, XRD and ¹H NMR characterization conformed the chemical structure of EUG. DSC analysis reviewed the partial destruction of crystal structure and the disappearance of β-crystal phase of EUG extracted by biphasic solvent system, resulting in the decrease of the melting point and increase of glass transition temperature. Moreover, the extracted EUG exhibited high tensile strength of 27.68 MPa, excellent elongation at break of 1069%, and thus high toughness of 181.45 MJ∙m⁻³. Additionally, the excellent reusability of IL and petroleum ethers showed the extraction method of the biphasic solvent system promise as a feasible method to replace the traditional alkali pretreatment.
In this contribution, we reported to utilize polystyrene‐block‐polybutadiene‐block‐polystyrene (PS‐b‐PB‐b‐PS), a commercial triblock copolymer to toughen epoxy thermosets. First, a PS‐b‐PB‐b‐PS triblock copolymer was chemically modified with hydroboration‐oxidation reaction, with which the midblock was hydroxylated whereas the endblocks remained unaffected. It was found that the degree of hydroxylation was well controlled. One of the hydroxylated PS‐b‐PB‐b‐PS samples was then used as the macromolecular initiator to synthesize a poly(ε‐caprolactone)‐grafted PS‐b‐PB‐b‐PS via the ring‐opening polymerization. It was found that the PS‐b‐PB‐b‐PS with poly(ε‐caprolactone) grafts can be successfully employed to nanostructure epoxy thermosets; the “core‐shell” microdomains composed of PB and PS were generated in the nanostructured thermosets. The nanostructured thermosets displayed improved fracture toughness. POLYM. ENG. SCI., 59:2387–2396, 2019. © 2019 Society of Plastics Engineers
Eucommia ulmoides gum (EUG) was applied in blend rubber with a heavily limited amount because of its duality of rubber and plastic, and an efficient way of triazolinedione (TAD)‐based Alder‐ene reaction was used to improve the elastic properties of EUG. Binary modification of EUG with two TADs containing hexyl and polyhedral oligomeric silsesquioxane (POSS) groups were conducted to generate the modified EUG elastomers with tunable mechanical properties and good compatibility by varying TAD contents. When the low hexyl (1%) and POSS (0.2%) TADs incorporated, the modified EUGs displayed high tensile strength of 36.57 MPa with the elongation at break of 876%, and thus high toughness of 152.14 MJ m⁻³. If high contents of hexyl (20%) and POSS (0.2%) TADs employed, the modified EUGs exhibited excellent elongation at break of 1165% and recovery rate of 60%, and especially its loss factor reached up to 0.83‑0.65 at 20‑70°C. Therefore, the modified EUGs containing the polar urazole and POSS groups should be a novel elastomer with good compatibility, wear resistance, and damping properties. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019
As an intermediate state between liquid and solid materials, hydrogels display unique properties, opening a wide scope of applications, especially in the biomedical field. Organic hydrogels are composed of an organic network cross-linked via chemical or physical reticulation nodes. In contrast, hybrid hydrogels are defined by the coexistence of organic and inorganic moieties in water. Inorganic polymerization, i.e. sol-gel process, is one of the main techniques leading to hybrid hydrogels. The chemoselectivity of this method proceeds through hydrolysis and condensation reactions of metal oxide moieties. In addition, the mild reaction conditions make this process very promising for the preparation of water-containing materials and their bio-applications
The homogeneous polycarbonate/poly(acrylonitrile-butadiene-styrene) (PC/ABS) nanocomposite thin films were prepared by a facile solvent casting method using phenylene modified-mesoporous silica materials as additives and dichloromethane as a solvent. The physicochemical analyses using small-angle X-ray scattering, nitrogen adsorption–desorption, solid-state 13C and 29Si nuclear magnetic resonance, and scanning electron microscope were investigated to provide clear physical and chemical properties for modified-mesoporous materials and nanocomposite films. Tensile tests were performed at room temperature according to ASTM D638. Rheological properties were also analyzed to observe any variance of solid–liquid property. As a compatibilizer and a reinforcing filler, mesoporous (organo-)silicas showed enhanced features in rheological and mechanical properties. The sound absorption coefficient was measured by the impedance tube up to 6400 Hz according to ISO 10534-2. It was found that the PC/ABS nanocomposites containing mesoporous materials can be used as a sound-proofing support material depending on fabrication process. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 135, 45777.
Poly(styrene-b-butadiene-b-styrene) (SBS) block copolymer has been recently demonstrated to be a polymer membrane material with high selectivity for CH4/N2 gas separation. In this study, two effective approaches of grafting and crosslinking have been explored to improve the gas permeability of SBS polymer by introducing polysiloxane (silicone) polymers to SBS backbone via hydrosilylation reaction. First, a series of novel poly(styrene-b-butadiene-b-styrene)-g-poly(dimethylsiloxane) (SBS-g-PDMS) graft copolymers were synthesized via the hydrosilylation reaction of SBS carbon double bonds and silanes (Si-H) from monohydride terminated PDMS. We found that CH4 permeability was increased 40% by grafting only 1.24% PDMS in SBS. Second, to supplement additional silicone to SBS, the hydrosilylation reaction of SBS carbon double bonds and silanes from poly(methylhydrosiloxane) was used to prepare novel SBS-silicone cross-linked polymer membranes. It was demonstrated that CH4 permeability could be improved by 214%, achieving 118 Barrer when 45 wt% silicone was incorporated in SBS. This successful example of improving gas permeation by molecular design could open up new avenues for researchers to develop future polymer membranes with both high selectivity and permeability for industrial applications including methane enrichment from coalbed gases.
Based on the thiol-ene radical addition reaction, the branched hydroxyl functionalized modified styrene-butadiene-styrene triblock copolymer (SBS-g-OH) was prepared using a commercially available SBS with high molecular weight and low content of 1,2-vinyls as substrate polymer, 2-mercaptoethanol (MCH) as modifying agent, 2,2-azodiisobutyronitrile (AIBN) as initiator, and 1,4-dioxane (DOA) as solvent. By the characterization of Fourier transform-infrared spectroscopy (FT-IR), and 1H nuclear magnetic resonance spectroscopy (1H NMR), the order of reactivity was proved that 1,2-vinyls had a priority to react with MCH at low functionalization degree of SBS-g-OH. A novel reaction kinetics model was set up to only describe the addition reaction between MCH and 1,2-vinyls, but not 1,4-units of PB segments, with this reaction kinetics model, the effect of reaction time, temperature, and initial concentration ratio of MCH to 1,2-vinyls on functionalization degree of SBS-g-OH were investigated, besides the desired operating conditions which were suitable for the preparation of elastic branched hydroxyl functionalized SBS were also established. Subsequently the performances of modified asphalt were investigated, where the softening point, ductility, and needle penetration of SBS-g-OH modified asphalt were almost equal to that of SBS modified asphalt, while the dispersibility of polymer in asphalt and storage stability of modified asphalt had been improved obviously using SBS-g-OH with an appropriate functionalization degree.
(Figure Presented). The nanostructured phenolic thermosets were prepared from the ternary mixtures composed of novolac resin, poly(styrene-alt-maleic anhydride)-block-polystyrene [P(S-alt-MAH)-b-PS] diblock copolymer, and hexamethylenetetramine, which were cured at elevated temperature. The P(S-alt-MAH)-b-PS diblock copolymer was synthesized via a one-pot RAFT polymerization approach. The morphologies of the nanostructured thermosets were modulated by changing the content of the diblock copolymer. The as-obtained nanostructured phenolic thermosets were further used as the precursors to obtain the mesoporous carbons via pyrolysis under highly pure nitrogen atmosphere. The mesoporous carbons were successfully obtained with adjustable porosity. The mesoporous carbons had specific surface areas of 398.9-491.4 m² g⁻¹ and pore volumes of 0.22-0.31 cm³ g⁻¹.
In this work, we explored the preparation of mesoporous silica materials by using polystyrene (PS) homopolymers as the porogens. First, a series of polystyrene (PS) homopolymers with various molecular weights were synthesized via atom transfer radical polymerization (ATRP). The single ends of these PS homopolymers were then functionalized with hydroxyl groups via copper(i)-catalyzed cycloaddition reaction, and these can then react with 3-isocyanatopropyltriethoxysilane to afford the triethoxysilane-terminated PS homopolymers. In the presence of the triethoxysilane-terminated PS homopolymers, the sol-gel process of tetraethoxysilane (TEOS) was carried out to afford a series of organic-inorganic silica gels. These silica gels were then used as precursors to obtain the mesoporous silica materials via the removal of PS microdomains with pyrolysis at elevated temperatures. Transmission electron microscopy (TEM) showed that all the silica materials displayed spherical or cylindrical nanopores with the size of the nanopores being 10-30 nm. The mesoporous structure was further evidenced by the measurement of specific surface areas with nitrogen sorption experiments. It was found that the specific surface areas can be adjusted in terms of the contents and molecular weights of the PS homopolymers. The generation of nanopores in the silica materials is ascribed to the formation of the PS microdomains in the organic-inorganic silica gels as revealed by small angle X-ray scattering (SAXS). It is proposed that the functionalization of the PS chain ends confined the reaction-induced phase separation of the PS homopolymers on the nanometer scale in the organic-inorganic silica gels. The approach reported in this work was in marked contrast to the utilization of amphiphiles as the porogens of the mesoporous silica.
Low-cost, easily fabricated dry cells were constructed by gluing epoxidized styrene-butadiene-cupric oxide conducting copolymer on magnesium or aluminium foils, using a solid electrolyte made from polyvinyl-alcohol (PVA) and polyethylene-oxide (PEO). The e.m.f. values of the cells ranged from 0.45 to 1.24 V and their efficiencies from 1.6 to 8.1 mW h cm−3, or 1.8 to 9.2 W h kg−1.
Indirect Fourier transformation is a well established method for the evaluation of small-angle scattering data. This technique, however, is restricted to dilute solutions, as for higher concentrations particle interactions can no longer be neglected. As the scattering intensity contains intra- and interparticle scattering contributions, the evaluation of scattering data is no longer just the solution of a linear weighted least-squares problem because the scattering intensity can, under certain conditions, be written as the product of the particle form factor and the so-called structure factor, which leads to a highly non-linear problem. In this paper a global evaluation technique including the structure factor is presented so that it is possible to determine the form factor and the structure factor simultaneously. This technique can be understood as a generalized version of the indirect Fourier transformation method. Like in the indirect Fourier transformation, there are no models or no analytical restrictions used for the form factor, and the structure factor is parameterized with up to four parameters for a given interaction model. A simultaneous determination of these two functions is possible due to the different analytical behavior of these functions, which also leads in most cases to the existence of a global minimum in the parameter surface. An algorithm to solve this nonlinear least-squares problem has been developed and applied to simulated data for a variety of different uncharged systems.
Resistivity measurements versus temperature between 80 and 300 K are presented for a new compound consisting of epoxidized styrene-butadiene copolymer with star configuration and cupric oxide (CuO). For a certain concentration, 80 wt.% CuO, for which the CuO molecules are in ‘contact’, the polymer becomes conductive. For a lower concentration in CuO, the material becomes insulating, though, for a concentration higher than 80 wt.% CuO, the polymer disintegrates. The addition of CuS to the epoxidized styrene-butadiene matrix leads to a material less conductive than CuS, though IrO2 and TiO2, which contain oxygen but not Cu, form insulating materials. In addition, styrene-butadiene copolymer with configuration different than the ‘star’ one does not become conductive with the addition of any of the oxides or CuS mentioned above. From these properties the crucial role of the polymer structure, oxygen and copper in the electrical conduction of the styrene-butadiene-CuO polymer becomes apparent. Moreover, the conductivity of the epoxidized styrene-butadiene-CuO polymer is not thermally activated and its temperature dependence resembles a metal.
The 'wishbone' of birds comprises two clavicles fused into a structure1 known as a furcula. In an influential 1926 book on bird origins by Heilmann2, the furcula's supposed absence in dinosaurs was considered powerful evidence barring them from bird ancestry. A furcula has now been found in several theropod dinosaurs3,4, but its absence in other theropods, and the uncertainty of whether this absence is real or an artefact of preservation, obscures the evolutionary history of this structure5. Here we report the discovery of a furcula in Dromaeosauridae, a group posited to be the closest relative of birds6,7.
Mesoporous silica films with large spherical mesopores are synthesized using new laboratory-made polystyrene-block-polybutadiene-block-polystyrene based triblock copolymers in which the polystyrene block is functionalized with hydrophilic sulfonic groups. When the relative weight of the copolymer to silica source is in the range from 10 to 70 mass%, spherical mesopores with uniform sizes can be formed in the films. In addition, when the ratio is lower than 20 mass%, spherical mesopores are separated by thick silica walls in the films. Nevertheless, owing to the presence of small-sized mesopores in the silica walls, all the spherical mesopores are accessible from the outside. With the gradual increase of the chosen copolymer/silica ratios, the distance between neighboring mesopores is reduced without a significant change of the original mesopore size, which has not been observed in previous reports using other block copolymers as templates.
Phase transitions at fluid interfaces and in fluids confined in pores have been investigated by means of a density functional approach that treats attractive forces between fluid molecules in mean-field approximation and models repulsive forces by hard-spheres. Two types of approximation were employed for the hard-sphere free energy functional: ( a ) the well-known local density approximation (LDA) that omits short-ranged correlations and ( b ) a non-local smoothed density approximation (SDA) that includes such correlations and therefore accounts for the oscillations of the density profile near walls. Three different kinds of phase transition were considered: (i) wetting transition . The transition from partial to complete wetting at a single adsorbing wall is shifted to lower temperatures and tends to become first-order when the more-realistic SDA is employed. Comparison of the results suggests that the LDA overestimates the contact angle in a partial wetting situation. (ii) capillary evaporation of a fluid confined between two parallel hard walls. This transition, from dense ‘liquid' to dilute ‘gas', occurs in a supersaturated fluid ( p > p sat ). The lines of capillary coexistence calculated in the LDA and SDA are rather close, suggesting that non-local effects are not especially important in this case. (iii) capillary condensation of fluids confined between two adsorbing walls or in a single cylindrical pore. For a partial wetting situation the condensation pressures p (
Macroporous metals with strong diffractive properties at visible wavelengths can be synthesized from colloidal crystal templates. The synthesis, characterization, and potential applications of macroporous metals created in this manner are summarized in this article. The Figure shows a macroporous copper film, illustrating the long-range order of the porous structure (see also cover).
The formation of nanostructured materials by using colloidal crystals as templates is a relatively new but rapidly growing area of materials science. Colloid crystalline templates are three-dimensional close-packed crystals of submicrometer spheres, whose long-ranged ordered structure is replicated in a solid matrix, to yield materials with ordered pores. These materials hold promise for use as photonic crystals, advanced catalysts, and in a variety of other applications. Here we review the wide range of materials that have been made following the original synthesis of structured porous silica. This method has been recently modified to produce porous metals.
This chemistry and technology of hydrogenation of diene elastomers have substantially grown during the past decade. New applications of hydrogenated elastomers have emerged. Homogeneous hydrogenation has several advantages over heterogeneous hydrogenation because of its higher selectivity, faster rate and cleaner end products. However, separation of catalysts and recycle/reuse of expensive metals still poses problems. The preferred alternative for the hydrogenation of elastomers in solution is the use of Zeigler type catalyst which are less expensive than the noble metal catalysts like Rh, Pd etc. However, such catalysts are not effective when strongly coordinating groups are present in the elastomer. One approach would be to use transition metals, which have less tendency to coordinate with polar monomers in the elastomer. Research is also warranted in the use of less expensive metals for elastomer hydrogenation (Ni, Co, Ru). Use of large quantities of solvent (to keep the solution viscosity low) is another significant cost center in elastomer hydrogenation. Novel agitator systems/reactor configuration to handle higher concentration of rubber in solution, yet provide adequate heat and mass transfer in gas-liquid hydrogenation reaction, needs to be explored. Hydrogenation of diene elastomers in the latex form using water soluble catalyst appear to be hold great promise at the present time since many diene elastomers (like SBR, CR and NBR etc.) are commercially produced directly in the form of latex. Creative exploitation of biphasic catalysts for hydrogenation is expected to gain momentum since early results look promising. This would require greater fundamental understanding of the aqueous-organic interphase in a latex process and the mechanism of transport of catalytic reagent across this interphase. More studies are needed to achieve homogeneous chemical reaction inside of each individual latex particles.
Degradation of hydrogenated styrene-butadiene rubber (HSBR) having different levels of unsaturation has been studied over a wide range of temperatures under anaerobic and aerobic conditions using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), IR and NMR spectroscopy. TGA data indicate higher thermal stability and hydrogenated rubber as compared to SBR in nitrogen, although an anomalous behaviour is observed in air due to crosslinking and oxidation of styrene-butadiene rubber (SBR). Isothermal data confirm the above observations. IR and NMR results reveal thermal isomerization, cyclization, oxidation, depolymerization, and chain scission processes. The nature and amount of products formed depend on the time and temperature of degradation and also on the level of hydrogenation of SBR.
Surfactants have been shown to organize silica into a variety of mesoporous forms, through the mediation of electrostatic, hydrogen-bonding, covalent and van der Waals interactions(1-8). This approach to mesostructured materials has been extended, with sporadic success, to non-silica oxides(5-17), which might promise applications involving electron transfer or magnetic interactions. Here we report a simple and versatile procedure for the synthesis of thermally stable, ordered, large-pore (up to 140 Angstrom) mesoporous metal oxides, including TiO2, ZrO2, Al2O3, Nb2O5, Ta2O5, WO3, HfO2, SnO2, and mixed oxides SiAlO3.5, SiTiO4, ZrTiO4, Al2TiO5 and ZrW2O8. We used amphiphilic poly(alkylene oxide) block copolymers as structure-directing agents in non-aqueous solutions for organizing the network-forming metal-oxide species, for which inorganic salts serve as precursors. Whereas the pore walls of surfactant-templated mesoporous silica(1) are amorphous, our mesoporous oxides contain nanocrystalline domains wi
A commercially important synthetic approach to highly ordered
mesoporous silica materials (SBA-family) with 2-D hexagonal
(P6mm), 3-D hexagonal
(P63/mmc) and cubic (Im3m
and Pm3m) structures, using sodium silicate as the silica
source and amphiphilic block copolymers as the structure-directing agents
is demonstrated.
In order to improve their adhesion to polyurethane adhesives, three unvulcanized block styrene-butadiene-styrene (SBS) rubbers with styrene contents between 33% and 55% were surface-treated with solutions of 2 wt% trichloro-isocyanuric acid (TCI) in ethyl acetate. The joint strength was estimated using T-peel tests and the failed surfaces were analyzed to assess the locus of failure. The failed surfaces were analyzed using ATR-IR spectroscopy, contact angle measurements, XPS, and SEM. An unexpected trend in the joint strength was obtained because the locus of failure depended on both the styrene content and the mechanical properties of each SBS rubber. A mixed mode of failure was obtained in joints produced with S 1 rubber (33 wt% styrene content), whereas failure in the chlorinated layer was observed with S3 rubber (55 wt% styrene content); cohesive failure in the adhesive was found for the joints produced with S2 rubber (44 wt% styrene content).
The formation of nanostructured materials by using colloidal crystals as templates is a relatively new but rapidly growing area of materials science. Colloid crystalline templates are three-dimensional close-packed crystals of submicrometer spheres, whose long-ranged ordered structure is replicated in a solid matrix, to yield materials with ordered pores. These materials hold promise for use as photonic crystals, advanced catalysts, and in a variety of other applications. Here we review the wide range of materials that have been made following the original synthesis of structured porous silica. This method has been recently modified to produce porous metals.
Macroporous metals are monolithic samples composed of around 70% empty space which can be prepared into thick films by various routes. Their porous network is defined by an interconnected set of spherical voids whose diameters replicate those of the colloidal templates used to make them. The air voids are arranged very regularly due to the high crystallinity of the starting templates, resulting in strong diffractive properties at visible wavelengths. Such behavior may find use in several optical applications. Also, the accessible in the internal surface areas and nanocrystalline nature of the metallic films suggest porous metals may prove useful in technologies requiring high electrochemical and catalytic activity.
Highly ordered, hydrothermally stable, caged cubic mesoporous
silica structures (Imm) with unusually large
pore size (120 Å) have been synthesized by using hydrophobic
poly(butylene oxide) containing triblock PEO–PBO–PEO copolymer
as a structure-directing agent.
A silica−poly(methyl methacrylate) (PMMA) composite was prepared by condensation polymerization of a 2 nm shell of the silane coupling agent 3-(trimethoxysilyl)propyl methacrylate (TPM) on the surface of 10.5 nm diameter sol−gel colloidal silica particles followed by free-radical polymerization of a 50 wt % dispersion of the TPM−silica in methyl methacrylate. Cross-polarization combined with magic angle spinning and high-power decoupling (CP/MAS) and single-pulse 29Si NMR spectra together with quasi-adiabatic cross-polarization (QACP) 13C NMR spectra provided quantitative analyses of the structural components of the parent silica, the TPM−silica, and the composite. The parent silica contained one ethoxy group and eleven hydroxy groups per ten silicon atoms. The TPM−silica contained one residual methoxy group per TPM group and no residual hydroxy groups. Polymerization with MMA consumed 85% of the methacrylate groups of the TPM. Time constants T1ρH for proton spin−lattice relaxation in the rotating frame detected via 13C and 29Si CPMAS spectra showed rapid spin diffusion between all CH protons in the samples, but not between the CH protons and the OH protons that cross-polarize 29Si atoms in the parent silica. Time constants T1ρC for carbon spin−lattice relaxation in the rotating frame showed that the TPM−silica has substantial motion at kilohertz frequencies leading to fast relaxation, whereas the PMMA composite is more rigid and the ethoxy groups in the parent silica are more mobile. Measurements of 1H−1H dipolar transverse relaxation times via 13C and 29Si detection showed decreasing strengths of homonuclear dipolar interactions due to increasing molecular motion in the order composite > TPM−silica > OH groups in parent silica.
A styrene–butadiene–styrene triblock copolymer (SBS) was functionalized with glycidyl methacrylate (GMA). Grafting reactions were carried out in an internal mixer at 170°C, using dicumyl peroxide (DCP) as an initiator. The effect of three variables, % GMA, % DCP, and reaction time, on grafting were studied using a factorial design to analyze the experimental data. GMA was grafted onto SBS and its incorporation increased with the % GMA added. The factors levels studied indicated that was an optimum % DCP point about 0.1% w/w to achieve the best incorporation and conversion values. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 2074–2079, 2003
Linear styrene-butadiene block copolymers of polyA-block-polyB-block-polyA type (SBS) were synthesized in the presence of varying amounts of THF functioning as the polar structure modifier. The efficiency of this modifier was studied by analyzing the microstructure of synthesized polymers using 13C-NMR, and the effect of THF on polymerization kinetics was determined by progressive buildup of the molecular weight measured by GPC. Polymerization at 4000 ppm THF concentration resulted in the highest styrene polymerization rate while a 1 wt % concentration gave the highest butadiene polymerization rate. The vinyl content increased from 20 to 64% with an increase in the amount of THF from 200 ppm to 1 wt % while the content of trans-1,4 and cis-1,4 units decreased. For SBS polymer synthesized via a sequential process, the use of THF as the structure modifier enhanced the crossover efficiency that would otherwise result in a skewed molecular weight distribution with a higher polydispersity. For SBS polymer made via a coupling process, the coupling efficiency decreased when the amount of THF exceeded a certain limit. The temperature dependence of the coupling efficiency was also investigated. © 1996 John Wiley & Sons, Inc.
Surfactants have been shown to organize silica into a variety of mesoporous forms, through the mediation of electrostatic, hydrogen-bonding, covalent and van der Waals interactions. This approach to mesostructured materials has been extended, with sporadic success, to non-silica oxides, which might promise applications involving electron transfer or magnetic interactions. Here we report a simple and versatile procedure for the synthesis of thermally stable, ordered, large-pore (up to 140Å) mesoporous metal oxides, including TiO2, ZrO2, Al2O3, Nb2O5, Ta2O5, WO3, HfO2, SnO2, and mixed oxides SiAlO3.5, SiTiO4, ZrTiO4, Al2TiO5 and ZrW2O8. We used amphiphilic poly(alkylene oxide) block copolymers as structure-directing agents in non-aqueous solutions for organizing the network-forming metal-oxide species, for which inorganic salts serve as precursors. Whereas the pore walls of surfactant-templated mesoporous silica are amorphous, our mesoporous oxides contain nanocrystalline domains within relatively thick amorphous walls. We believe that these materials are formed through a mechanism that combines block copolymer self-assembly with complexation of the inorganic species.
Triethoxysilyl functionalized poly(styrene-b-butadiene-b-styrene) (TS-SBS) was prepared by the hydrosilation of carbon-carbon double bonds in a four-arm star SBS and was obtained
by coupling the growing styrene-butadiene block copolymer with SiCl4 and with triethoxysilane in toluene at 70 C using cis-bis(diethyl sulfide) platinum (II) dichloride (CPD) as a catalyst. The reactivity, in increasing order of hydrosilation,
for these three kinds of double bonds was trans-1,4-cis-1,4-< vinyl-. The molecular weight of TS-SBS decreased with time when it was heated with CPD in toluene at 70 C. The gelation
time of the sol-gel solution, TS-SBS/TEOS, was influenced significantly both by the molecular weight of and the attaching
of the triethoxysilyl groups on the TS-SBS. After undergoing an in-situ sol-gel process, the TS-SBS/TEOS became an organic-inorganic
hybrid material, TS-SBS/SiO2. The dynamic mechanical property and elongation of hybrids of the different molecular weights of TS-SBS and silica contents
were studied in detail.
a b s t r a c t Ordered mesoporous carbons (OMCs) with possible face-centered cubic (space group Fm3m) and 2-D hexagonal (p6mm) symmetries have been successfully synthesized by using lab-made poly(ethylene oxide)-block-poly(methyl methacrylate) diblock polymers (PEO-b-PMMA) with different PEO/PMMA ratios as a template. The synthesis process undergoes an evaporation induced self-assembly (EISA) at 100 C by using low-molecular weight phenolic resol as a carbon source and tetrahydrofuran (THF) as the solvent. The atom transfer radical polymerization (ATRP) method was used to prepare the diblock copolymers with different molecular weight and compositions of PEO and PMMA segments by simply changing the PEO initiator and polymerization time. For the first time, we have obtained OMCs with hexagonal p6mm symmetry and large pore size (8.6e12.1 nm) by using PEO-b-PMMA with long PMMA segment as the templates. Notably, the pore size of the ordered mesoporous carbons can be tuned in the range of 8.6e22.0 nm by slightly adjusting the hydrophobic PMMA length of the template or adding desired amount of PMMA homopolymer as a pore expander. Additionally, it is found that the pore wall thickness of OMCs with possible face-centered cubic symmetry can be adjusted from 8.1 to 10.4 nm by simply increasing the weight ratio of resol to the template (R w).
We report an approach for the design of nanostructured thermoplastic elastomeric materials consisting of poly(styrene-b-butadiene-b-styrene) and epoxy. This approach consists in the epoxidation of PB block and further mixing with low contents of the DGEBA:MCDEA system. Morphological behavior as well as thermal and mechanical properties have been investigated. The modification of epoxidized SBS with 10, 20, and 30 wt % epoxy system induces microphase separation at nanoscale from a poorly to well-ordered self-assembled morphology where the shape of these structures depends greatly on the mixture compositions, showing a transition from worm-like to lamellae. The generated nanostructures are accessible owing to the miscibility between the epoxidized PB block and the epoxy system that have been confirmed by an increment on the Tg (before and after curing) of this block in the mixture. The mixing produces a significant increase on strength and stiffness being more relevant in the system with 30 wt % epoxy and well-ordered lamellar morphology.
Microstructured porous silicas have potential applications in catalysis,
separations, coatings, microelectronics and electro-optics, but methods
for producing materials with uniform submicrometre pores have not been
available. We have now developed a method in which modified colloidal
crystals are used as templates for silica polymerization. This method
yields products with highly uniform and structured pores of tuneable
size in the submicrometre region.
The three-dimensional classical many-body system is approximated by the use of collective coordinates, through the assumed knowledge of two-body correlation functions. The resulting approximate statistical state is used to obtain the two-body correlation function. Thus, a self-consistent formulation is available for determining the correlation function. Then, the self-consistent integral equation is solved in virial expansion, and the thermodynamic quantities of the system thereby ascertained. The first three virial coefficients are exactly reproduced, while the fourth is nearly correct, as evidenced by numerical results for the case of hard spheres.
The gradient on block copolymer concentration through film thickness as well as the effects of casting solvents used on the nanostructuring of a thermosetting epoxy coating modified with an epoxidized poly(styrene-b-butadiene-b-styrene) (SBS) triblock copolymer was studied by means of atomic force microscopy and attenuated total reflectance infrared spectroscopy. Thin coating films based on a commercial epoxy amine formulation consisting of diglycidyl ether of bisphenol A and a low-temperature fast curing amine were modified with several amounts of epoxidized SBS triblock copolymer. Toluene and a mixture of tetrahydrofuran and N,N-dimethylformamide were used as casting solvents. With epoxidation degrees higher than 45 mol % of polybutadiene block nanostructuring was achieved. Fast curing rate of the epoxy/amine system and the comparatively slow evaporation rate of the casting solvent led to a gradient of morphologies through the film cross section owing to the coalescence of small micelles into larger micellar domains in the case of low block copolymer content. For these reasons, different morphologies were also obtained in the midtransverse section of a film with variable thickness. Finally, pseudolamellar nanostructure at high copolymer contents was achieved as confirmed by parallel and perpendicular cuttings to the air/polymer interface.
Poly(hydroxymethylsiloxane) (PHMS) has been synthesized by selective oxidation of poly(methylhydrosiloxane) (PMHS) with a dimethyldioxirane solution in acetone. PHMS synthesized in situ showed no tendency for self-condensation to siloxane in solution when the concentration of PHMS was less than 1% (g/mL). PHMS gave ceramic materials at 79% yield at 700 degrees C in a nitrogen atmosphere. Miscibility studies of PHMS with a variety of organic polymers by solution-cast films showed that organic-inorganic polymeric hybrids were formed for poly(N-vinylpyrrolidone) (PVPr), poly(ethyloxazoline) (PEOx), and poly(4-vinylpyridine) (PVPy). The hydrogen-bonding interactions in these hybrids were investigated by FT-IR spectroscopy.
Silica/diblock films with various mesostructures of large characteristic length scales were synthesized through evaporation-induced self-assembly (EISA). The structure-directing agents used were amphiphilic polystyrene-block-poly(ethylene oxide) (PS-b-PEO) diblock copolymers of high molecular weights. The synthesis process began with a dilute homogeneous solution of a silica precursor and the diblock copolymer in a mixture of tetrahydrofuran (THF) and water. After this dilute solution was cast, THF preferentially evaporated; accordingly, the species in the depositing film increasingly concentrated and the solvent quality for the diblock progressively decreased. At some critical point, cooperative self-assembly of both the PS-b-PEO diblock and the silicate started. Subsequently, liquid-crystalline mesophases were obtained. The present study indicates that silica/diblock films with different mesostructures can be synthesized by using one identical diblock; as the volume ratio of the diblock to silica increases, mesostructures change progressively from regular to inverted (reverse) via lamellar. For the silica/diblock films with regular mesophases, copolymer removal produces mesopores; highly ordered mesoporous silica films with different pore sizes result from using diblocks with different molecular weights. Particularly noteworthy is the ready formation of the silica/diblock multi-bilayer vesicular mesostructures. The present system is believed to be the first to use high glass transition temperature (Tg ≈ 373 K), PS-based amphiphilic diblock copolymers to prepare silica/diblock films with regular and reverse mesophases, as well as multi-bilayer vesicular mesostructures, through solvent evaporation-induced self-assembly.
The synthesis and precise structural characterization of highly ordered three-dimensional close-packed cage-type mesoporous silica is reported. The siliceous mesoporous material is proven to be commensurate with the face-centered-cubic Fm3m symmetry in high purity by a combination of experimental and simulated powder X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses. The cage-type calcined samples were additionally characterized by nitrogen physisorption. The aqueous synthesis method to prepare large cage mesoporous silica with cubic Fm3m structure is based on the use of EO106PO70EO106 triblock copolymer (F127) at low HCl concentrations, with no additional salts or organic additives. Here, emphasis is put on the low HCl concentration regime, allowing the facile thermodynamic control of the silica−triblock copolymer mesophase self-assembly. Further, simple application of hydrothermal treatments at various temperatures ranging from 45 to 150 °C enables the tailoring of the mesopore diameters and apertures. The combination of experimental and simulated XRD patterns and TEM images is confirmed to be a very powerful means for the accurate elucidation of the structure of new mesoporous materials.
A method based on nonlocal density functional theory (NLDFT) has been used to interpret the data for the adsorption of nitrogen at 77 K within the pores of three different commercial fluid cracking catalysts (FCCs) before and after their use in a refinery catalytic cracking unit. The integral equation of adsorption was inverted by a regularization method to yield the micropore and mesopore size distribution over a wide range of pore widths. The results obtained are compared with the results of more traditional data treatments and indicate that the NLDFT model can provide a realistic pore volume and surface area estimation in commercial FCCs irrespective of their chemical composition and pore width distribution. Both BET and Langmuir methods grossly underestimate the FCCs surface area, and only the NLDFT method yields reliable surface area and pore volume measurements over the entire micro−meso porosity range present in the cataysts under study. Adsorption microcalorimetry results using ammonia as a probe molecule reveal that as long as Lewis acid sites with strength greater than 100 kJ/mol are present and as long as these sites are available to gas oil, FCCs can retain their useful cracking activity and selectivity properties.
A family of highly ordered mesoporous (20−300 Å) silica structures have been synthesized by the use of commercially available nonionic alkyl poly(ethylene oxide) (PEO) oligomeric surfactants and poly(alkylene oxide) block copolymers in acid media. Periodic arrangements of mescoscopically ordered pores with cubic Im3̄m, cubic Pm3̄m (or others), 3-d hexagonal (P63/mmc), 2-d hexagonal (p6mm), and lamellar (Lα) symmetries have been prepared. Under acidic conditions at room temperature, the nonionic oligomeric surfactants frequently form cubic or 3-d hexagonal mesoporous silica structures, while the nonionic triblock copolymers tend to form hexagonal (p6mm) mesoporous silica structures. A cubic mesoporous silica structure (SBA-11) with Pm3̄m diffraction symmetry has been synthesized in the presence of C16H33(OCH2CH2)10OH (C16EO10) surfactant species, while a 3-d hexagonal (P63/mmc) mesoporous silica structure (SBA-12) results when C18EO10 is used. Surfactants with short EO segments tend to form lamellar mesostructured silica at room temperature. Hexagonal mesoporous silica structures with d(100) spacings of 64−77 Å can be synthesized at 100 °C by using oligomeric nonionic surfactants. Highly ordered hexagonal mesoporous silica structures (SBA-15) with unusually large d(100) spacings of 104−320 Å have been synthesized in the presence of triblock poly(ethylene oxide)−poly(propylene oxide)−poly(ethylene oxide) (PEO−PPO−PEO) copolymers. SBA-15 mesoporous structures have been prepared with BET surface areas of 690−1040 m2/g, pore sizes of 46−300 Å, silica wall thicknesses of 31−64 Å, and pore volumes as large as 2.5 cm3/g. A novel cubic (Im3̄m) cage-structured mesoporous silica structure (SBA-16) with a large cell parameter (a = 176 Å) has been synthesized using triblock copolymers with large PEO segments. The EO/PO ratio of the copolymers can be used to control the formation of the silica mesophase: lowering this ratio of the triblock copolymer moieties promotes the formation of lamellar mesostructured silica, while higher ratios favor cubic mesostructured silica. Cubic mesoporous structures are also obtained when star diblock copolymers are used as structure-directing agents. The calcined ordered mesoporous silicas reported in this paper are thermally stable in boiling water for at least 48 h. The assembly of the inorganic and organic periodic composite materials appears to take place by a hydrogen bonding (S0 H+)(X-I+) pathway. The assembly rate r increases with increasing concentration of [H+] and [Cl-], according to the kinetic expression r = k[H+]0.31[Cl-]0.31.
As part of ongoing research efforts to discover alternative support materials to polymer beads for use in polymer-supported synthesis, particularly under flow-through conditions, this work involves the synthesis of PolyHIPE (High Internal Phase Emulsion) polymer monoliths. PolyHIPEs containing high loadings of chloromethyl groups were efficiently prepared by the direct copolymerization of 4-vinylbenzyl chloride and divinylbenzene monomers. The ‘Merrifield' PolyHIPE proved to be an excellent support for batch and flow-through Suzuki cross-coupling reactions. A remarkably high yield of pure biaryl product was obtained using the PolyHIPE support in cubic form and utilizing an electron-rich boronic acid. In comparison to polymer beads, this material was found to be a much more efficient support in both batch and continuous flow modes. PolyHIPE converted a greater amount of chloromethyl groups into biaryl product under identical reaction conditions. It is suggested that the absence of channelling with PolyHIPE monoliths gives better performance under flow-through conditions than permanently porous beads.
Argon adsorption isotherms were measured at 87 K for two macroporous silicas and a series of high-quality MCM-41 silicas with approximately cylindrical pores of average diameters from 2 to 6.5 nm. The pore sizes of the MCM-41 samples were accurately determined in earlier studies on the basis of powder X-ray diffraction and nitrogen adsorption using a geometrical relation between the pore volume, pore−center distance, and pore size in the honeycomb structure. Thus acquired model argon adsorption data for cylindrical mesopores were used to determine the statistical film thickness in the pores and the relation between the pore core radius and the capillary condensation/evaporation pressure. The statistical film thickness curve (t-curve) was extrapolated over the entire pressure range by using data for suitable macroporous silicas. The t-curve is reported in forms of a simple empirical equation and tabulated data. The relation between the pore core radius and the capillary condensation pressure was interpolated and extrapolated over the range from about 2 to at least 50 nm using a suitable empirical equation, which is approximately equivalent to the Kelvin equation for large mesopore sizes. These relations were used in a standard procedure to calculate mesopore size distributions (PSDs). The obtained pore sizes were in excellent agreement with those evaluated on the basis of the geometrical method using X-ray diffraction (XRD) and primary mesopore volume data. Moreover, positions, heights, and widths of the PSD peaks in the primary mesopore range calculated from argon data were in remarkable agreement with those of the PSD data calculated from nitrogen adsorption data at 77 K using a properly calibrated method reported recently. The agreement extended also on the secondary mesopore range (above about 10 nm). The method also correctly reproduced MCM-41 total pore volumes obtained using a single-point method. Thus, an accurate and self-consistent method for calculating PSDs for silicas with cylindrical pores from argon adsorption data measured at 87 K was successfully developed. Moreover, the reported data for macroporous silicas can be used in comparative plot analysis to determine the external surface areas, primary mesopore volumes, and micropore volumes of microporous and mesoporous silicas.
In this paper, we demonstrate a successful synthesis of highly ordered mesoporous carbons with large pores and tunable pore walls by using a home-designed ABC amphiphilic triblock copolymer poly(ethylene oxide)-block-poly(methyl methacrylate)-block-polystyrene (PEO-b-PMMA-b-PS) with gradient hydrophilicity as a template and resol as a carbon source via the solvent evaporation induced self-assembly (EISA) strategy. SAXS, TEM, HRSEM, and N2 sorption characterizations show that the obtained carbon products possess ordered face-centered cubic (fcc) close-packed (Fm3̅m) mesostructure with large pores of about 20.0 nm. By simply adjusting the resol/template ratios, the wall thickness of products can easily be tuned in the range of 10−19 nm. For the first time, we observed numerous large micro/mesopores in the carbon pore walls, originating from the removal of PMMA segment during the pyrolysis. The obtained mesoporous carbons have an extra-large lattice constant of up to 55.0 nm, high surface areas of 900 m2/g, and pore volume of 0.6 cm3/g, as well as high stability even in concentrated KOH solution. The gradient hydrophilicity of the ABC triblock copolymer template facilitates the continuous invasion of resol precursor molecules along the PEO to PMMA segments of the spherical PEO-PMMA-PS micelles, tuning the pore wall thickness. The rationally designed ABC-type triblock copolymers make it possible to synthesize ordered mesoporous carbons with ultrathick pore walls as well as excellent chemical and thermal stability.
Ordered macroporous particles of silica and titania were fabricated by colloidal templating. The colloidal templates were assembled through colloidal crystallization of suspended polystyrene latex sphere particles in aqueous droplets straddling an air−oil interface. The procedures involve first preparing spherical colloidal crystalline particles of polystyrene latex spheres and then infusing them with metal precursor solutions that form silica or titania in the interstices. Finally, calcination decomposes the polystyrene latex spheres, leaving macropores at their sites. The shape of the template was controlled by the presence of additive surfactant or by the action of an applied electric field. Specifically, spherical, concaved disklike, and ellipsoidal colloidal crystals were prepared successfully and used as templates for the fabrication of ordered macroporous particles. The SEM images of the prepared macroporous particles showed that the pores were interconnected and ordered into a hexagonal arrangement.
In this paper, we report on the assembly of a highly ordered three-dimensional porous structure with nanosized crystalline TiO2 particles by a cooperative assembly method in which the fabrication of the template and the infiltration of the voids of the template are carried out at the same time and the related experimental parameters for the assembly, including temperature, humidity, and concentrations and concentration ratio of the colloid mixture. SEM (scanning electron microscope) images and transmission spectra of these samples demonstrate that these films have a highly ordered three-dimensional structure. The Bragg law was used to calculate the diameter of the spheres of air in the porous TiO2 structure. A good agreement between the calculated results for the diameter of the spheres of air and those measured by SEM further confirms the high quality of the films fabricated using this simple method. Additionally, based on these experimental results, a detailed mechanism of the simple method is also discussed.
A new method for fabricating macroporous inorganic and inorganic composite materials with tailored pore morphologies (i.e., pore wall thickness and open or closed pore structure) is described. Polystyrene (PS) colloidal spheres coated with polyelectrolyte (PE) multilayers (PS−PE) or silica nanoparticle (SiO2)/PE hybrid multilayers (PS−SiO2/PE) have been used as templates to produce macroporous structures. By infiltration of a titanium dioxide (TiO2) precursor, titanium (IV) isopropoxide, into templates of close-packed coated colloidal spheres, followed by removal of the organic material (PS core and PE layers) by calcination, macroporous TiO2 and inorganic composite structures were produced. The pore morphology of the resulting macroporous structures depends on the nature of the multilayers deposited on the colloidal spheres. Open pore structures were obtained by templating close-packed assemblies of PS−PE colloidal spheres, while a closed pore structure was achieved by templating PS−SiO2/PE particle assemblies. The wall thickness of the resulting pores can also be tuned by altering the number of multilayers deposited on the colloidal spheres. Increasing the number of multilayers on the spheres causes an increase in the wall thickness of the macroporous structures.
The organization of cationic or anionic organic and inorganic molecular species to produce three-dimensional periodic biphase arrays is described. The approach uses cooperative nucleation of molecular inorganic solution species with surfactant molecules and their assembly at low temperatures into liquid-crystal-like arrays. The organic/inorganic interface chemistry makes use of four synthesis routes with (S+I-), (S-I+), (S+X-I+), and (S-M+I-) direct and mediated combinations of surfactant (cationic S+, anionic S-) and soluble inorganic (cationic I+, anionic I-) molecular species. The concepts can be widely applied to generate inorganic oxide, phosphate or sulfide framework compositions. Distinct lamellar, cubic silica mesophases were synthesized in a concentrated acidic medium (S+X-I+), with the hexagonal and the cubic phases showing good thermal stability. For the hexagonal mesostructured silica materials high BET surface areas (>1000 m2/g) are found. Hexagonal tungsten(VI) oxide materials were prepared in the presence of quaternary ammonium surfactants in the pH range 4-8. Cubic (Ia3d) and hexagonal antimony(V) oxides were obtained by acidifying (pH = 6-7) homogeneous solutions of soluble Sb(V) anions and quaternary ammonium surfactants at room temperature (S+I-). Using an ionic surfactants, hexagonal and lamellar lead oxide mesostructures were found (S-I+). Crystalline zinc phosphate lamellar phases were obtained at low synthesis temperatures (4-degrees-C) and lamellar sulfide phases could be also readily generated at room temperature. The synthesis procedure presented is relevant to the coorganization of organic and inorganic phases in biomineralization processes, and some of the biomimetic implications are discussed.
Novel epoxy-based blends containing 30 wt % star styrene-b-butadiene block copolymers epoxidized at several degrees (SepB) have been investigated in order to analyze the effect of epoxidation degree on the ability of these copolymers to produce nanostructures inside the epoxy matrix as well as their effect on the network structure of the matrix. For neat styrene-butadiene (SB) and SepB15-modified systems, macroscopic phase separation was observed. The SepB epoxidized at 40-76 mol %, however, yielded hexagonally ordered nanostructures formed by PS cylinders arranged in the matrix containing also the epoxidized and nonepoxidized butadiene units. DSC analysis indicates that the slight differences observed in self-assembling of the mixture containing the 40 wt % epoxidized block copolymer with respect to those for the blends with higher epoxidation degrees could be related with reactivity differences of the epoxidized copolymers with the curing agent. It is envisaged that these novel nanostructured blends may lead to novel materials with excellent optical properties and enhanced fracture toughness.
The functionalisation of a low molecular weight, liquid 1,2‐polybutadiene (PBL) was performed by the addition of either N ‐acetyl‐ L ‐cysteine or its methyl ester through the thiol‐ene radical reaction. The functionalisation runs were carried out in 1,4‐dioxane solution and in the presence of a free radical initiator (2,2′‐azobisisobutyrronitrile, AIBN). The initial feed ratio polymer / cysteine derivative / initiator was varied, in order to highlight the occurrence of side reactions and to understand their possible influence on the process. The ¹ H NMR determination of the functionalisation degree brought out high addition degrees of thiols, regardless of the initial thiol/double bonds ratio. This caused a drastic change in the macroscopic properties of the PBL with improved solubility in hydrophilic solvents (for instance in alkaline aqueous solutions) and impressive increase of the glass transition temperature. The propagation of chiral properties from the functionalising agents to the modified polymers was evaluated by polarimetry and circular dichroism in solution.
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Phase separation which occurs in parallel to the hydrolysis and gelation of alkoxysilane solution containing poly(sodium styrenesulfonate) (NaPSS) has been investigated. Depending on the reaction conditions, gel morphologies such as isolated pores, particle aggregates, and interconnected continuous pores from 0.1 to 100 μm long have been observed. Time-resolved light scattering of gelling solution suggested the occurrence of spinodal phase separation through the polymerization of silica and the subsequent freezing of the developing structure by sol-gel transition. The effects of reaction parameters on the periodic size are explained mainly in terms of their influence on the “chemical cooling” rate which is determined by the polymerizatica rate of silica and the solubility of NaPSS in the reacting solution.
This report highlights developments in the fields of microporous and mesoporous materials that were published mostly during the year 2002. Selected examples are provided to illustrate new zeolite structures, porous coordination materials, mesoporous solids with new compositions, controlled morphologies, and increased hydrothermal and thermal stabilities, as well as porous solids with tunable pore openings or other structural features that can be dynamically modified. A number of applications are discussed, including stabilization of reactive guests, separations, electronic materials, and sensors.
A novel scheme for using modified colloidal crystals as templates for silica polymerization is reported. 3D close-packed crystals of submicrometer latex spheres are assembled on a membrane surface by filtration. To induce silica polymerization, the particles are modified by adsorption of the surfactant hexadecyltrimethylammonium bromide. The colloidal crystals are then infused with a silica solution, which polymerizes in the cavities. In the final stage, the latex particles are removed by calcination, leaving behind porous silica of very low density. Scanning electron microscopy images demonstrate that the product has highly uniform and structured pores, representing a negative replica of the original colloidal crystal. The size of the pores can be controlled by changing the size of the latex used, and we were able to obtain samples with pores ranging from 150 to 1000 nm. Thus the method allows one to obtain structured silica materials of which the pore size, shape, and ordering can be controlled in a wide region that has previously been unattainable.
Siliceous mesostructured cellular foams (MCFs) with well-defined ultralarge mesopores and hydrothermally robust frameworks are described. The MCFs are templated by oil-in-water microemulsions and are characterized by small-angle X-ray scattering, nitrogen sorption, transmission electron microscopy, scanning electron microscopy, thermogravimetry, and differential thermal analysis. The MCFs consist of uniform spherical cells measuring 24-42 nm in diameter, possess BET surface areas up to 1000 m 2 /g and porosities of 80-84%, and give, because of their pores with small size distributions, higher-order scattering peaks even in the absence of long-range order. Windows with diameters of 9-22 nm and narrow size distribution interconnect the cells. The pore size can be controlled by adjusting the amount of the organic swelling agent that is added and by varying the aging temperature. Adding ammonium fluoride selectively enlarges the windows by 50-80%. In addition, the windows can be enlarged by postsynthesis treatment in hot water. The MCF materials resemble aerogels, but offer the benefits of a facilitated synthesis in combination with well-defined pore and wall structure, thick walls, and high hydrothermal stability. The open system of large pores give MCFs unique advantages as catalyst supports and separation media for processes involving large molecules, and the high porosities make them of interest for electrical and thermal insulation applications.
We report the self-assembly and characterization of mesoporous silica thin films with a 3D ordered arrangement of isolated spherical pores. The preparation method was based on solvent-evaporation induced self-assembly (EISA), with MTES (CH3–Si(OCH2CH3)3) as the silica precursor and a polystyrene-block-poly(ethylene oxide) (PS-b-PEO) diblock copolymer as the structure-directing agent. The synthetic approach was designed to suppress the siloxane condensation rate of the siloxane network, allowing co-self-assembly of the silica and the amphiphile, followed by retraction of the PEO chains from the silica matrix and matrix consolidation, to occur unimpeded. The calcined films retained the methyl ligands and exhibited no measurable microporosity, thereby indicating that the 3D-ordered spherical mesopores are not interconnected. A solvent-mediated formation mechanism is proposed for the absence of microporosity. Due to their closed porosity and hydrophobicity, the MTES-based films and MTES-TEOS (Si(OCH2CH3)4)-based hybrid films we describe should be promising for applications such as low-k dielectrics.
Microcrystalline silicalite-1 was formed on the inner surface of macroporus silica glasses prepared by the sol-gel process. By heating a homogeneous precursor solution at 100C under a hydrothermal condition, 2–5 m of plate-like particles of silicalite-1 were deposited. With an increase of mixing time of the precursor solution, the number of silicalite-1 particles increased, accompanied by the relative decrease of the particle size. Depending on the temperature and the duration of the heat-treatment of the macroporous silica, the amount of deposited silicalite-1 varied. Below 1000C, the amount increased with the heat-treatment temperature, as a result of the competition between the precipitation of silicalite-1 and the dissolution of silica from the macroporous silica glass under a strongly basic condition. On the other hand, above 1000C the amount of deposited silicalite-1 decreased in accordance with the decrease of the macropore diameter by the heat-treatment, because of the limited transport of the dissolved silicate species through the smaller macropores.
The thermoplastic elastomers have been widely used in polymer blends to improve their mechanical properties. This work is
about the study of chemical modification of styrene-butadiene-styrene (SBS) with maleic anhydride (MA) by radical reaction.
The functionalization reaction was carried out in a mixer Haake Rheomix 600 and the torque variation was monitored during
the process. The products were characterized by Infrared Spectroscopy (FTIR) and crosslinking was evaluated by extraction.
A calibration curve was plotted to determine the functionality. The results showed that it is possible to accomplish the functionalization
reaction avoiding the crosslinking.
Phase separations of gelling solutions have been investigated for acid-catalyzed, alkoxysilane-based systems containing polyacrylic acid (HPAA). Gels with micrometer-range interconnected porous morphologies were obtained in a composition range broader than that reported for the systems containing sodium polystyrene sulfonate. It is suggested that the data of a light-scattering experiment can be explained by the occurrence of spinodal phase separation which forms an interconnected morphology. The analogy between a chemical crosslinking reaction and a finite-rate cooling of a network-forming liquid is introduced, on which basis the effects of compositional parameters on the resultant gel morphology are explained.
Effects of molecular weight of coexisting polyacrylic acid (HPAA) and reaction temperature on phase separation and gelation behaviors were studied for acid-catalyzed, alkoxy-derived silica systems. The range of concentrations of HPAA which resulted in interconnected porous morphologies decreased and shifted toward lower concentrations as the molecular weight increased. The concentration range became larger with increasing reaction temperature. In addition to the relation between rates of phase separation and polymerization, viscosities of gelling silica network and pore-filling liquid during the domain formation process were responsible for the size and connectivity of resultant domains.