Showing papers on "Methacrylic acid published in 2000"
TL;DR: In this paper, a sequential UV polymerization method was used to construct an interpenetrating polymeric network (IPN) composed of the temperature-sensitive poly(N-isopropylacrylamide) (PNIPAAm) and the pH sensitive poly(methacrylic acid) (PMAA), which exhibited a combined pH and temperature-sensitivity at a temperature range of 31−32 °C and a pH value of approximately 5.5.
Abstract: Hydrogels of an interpenetrating polymeric network (IPN) composed of the temperature-sensitive poly(N-isopropylacrylamide) (PNIPAAm) and the pH-sensitive poly(methacrylic acid) (PMAA) were prepared by a sequential UV polymerization method. The IPN hydrogels were characterized for their temperature- and pH-responsive behavior by equilibrium swelling studies, oscillatory swelling studies, and differential scanning calorimetry. The permeability of these IPNs has been investigated under various pH and temperature conditions. The results showed that these hydrogels exhibited a combined pH- and temperature-sensitivity at a temperature range of 31−32 °C and a pH value of approximately 5.5. Permeation study results indicate a significant size exclusion behavior while model drugs with different sizes permeate through the IPN membranes. The permeability of the IPN membrane can be significantly affected by varying the pH and temperature conditions.
478 citations
TL;DR: PH-responsive polymeric micelles loaded with AlClPc were found to exhibit higher cytotoxicity against EMT-6 mouse mammary cells in vitro than control Cremophor EL formulation, showing the potential of poly(NIPA-co-MAA- co-ODA) for in vivo administration of water-insoluble, photosensitizing anticancer drugs.
149 citations
TL;DR: In this paper, a series of organic-inorganic hybrid materials have been prepared by copolymerizing styrene and alkoxysilane-methacrylate via the sol-gel process.
148 citations
TL;DR: In this paper, high-linked network polymers prepared by molecular imprinting catalyzed enantioselectively the hydrolysis of N-tert-butoxycarbonyl phenylalanine-p-nitrophenyl ester (BOCPheONP) were designed to allow incorporation of the key catalytic elements, found in the proteolytic enzyme chymotrypsin, into the polymer active sites.
Abstract: Highly cross-linked network polymers prepared by molecular imprinting catalyzed enantioselectively the hydrolysis of N-tert-butoxycarbonyl phenylalanine-p-nitrophenyl ester (BOCPheONP). The templates were designed to allow incorporation of the key catalytic elements, found in the proteolytic enzyme chymotrypsin, into the polymer active sites. Three model systems were evaluated. These were constructed from a chiral phosphonate analogue of phenylalanine (series A, C) or L-phenylalanine (series B) attached by a labile ester linkage to an imidazole-containing vinyl monomer. Free radical copolymerization of the template with methacrylic acid (MAA) and ethylene glycol dimethacrylate (EDMA) gave a highly cross-linked network polymer. The templates could be liberated from the polymers by hydrolysis, giving catalytically active sites envisaged to contain an enantioselective binding site, a site complementary to a transition state like structure (series A, C), and a hydroxyl, imidazole, and carboxylic acid group at hydrogen bond distance. As predicted, the enantiomer of BOCPheONP complementary to the configuration of the template was preferentially hydrolyzed with D-selectivity for the series A polymers (kD/kL = 1.9) and L-selectivity for the series B polymers (kL/kD = 1.2). The maximum rate enhancement, when compared with a control polymer, prepared using a benzoyl-substituted imidazole monomer as template, was 2.5, and comparing with the imidazole monomer in solution, a maximum rate enhancement of 10 was observed. The catalytic activity was higher for polymers subjected to the nucleophilic treatment. This was explained by a higher site density and flexibility of the polymer matrix caused by this treatment. In a comparison of template rebinding to polymers imprinted with a template containing either a carboxylate (planar ground state structure) or a phosphonate (tetrahedral transition state like structure) functionality, it was observed that imprinted polymers are able to discriminate between a transition state like and a ground state structure for transesterification. However the influence of transition state stabilization on the observed rate enhancements remains obscure. Only at acidic pH's was catalysis observed, whereas at basic pH's the polymers inhibit the reaction. At a later stage, the catalytic activity of the polymers for nonactivated D- and L-phenylalanine ethyl esters was investigated. A rate enhancement of up to 3 was observed when compared to the blank. Most important, however, the polymers imprinted with a D template preferentially hydrolyzed the D-ethyl ester and exhibited saturation kinetics.
123 citations
TL;DR: Pulsed laser-induced polymerization in combination with analysis of formed polymer by size exclusion chromatography (SEC) has been successfully applied in determining propagation rate coefficient, kp, of acrylic and methacrylic acid in organic solvents and water as discussed by the authors.
Abstract: Pulsed laser-induced polymerization (PLP) in combination with analysis of formed polymer by size exclusion chromatography (SEC) has been successfully applied in determining propagation rate coefficient, kp, of acrylic and methacrylic acid in organic solvents and water. For methacrylic acid solution polymerization in methanol and in dimethyl sulfoxide (DMSO), minor but not negligible variations of kp with solvent have been observed. In contrast, kp values for polymerizations in water are significantly influenced by the solvent and furthermore by monomer concentration. The kp values obtained from polymerization experiments in water are significantly larger than the corresponding values obtained in methanol or DMSO. Weighted nonlinear least-squares fitting (NLLS) has been applied to calculate frequency factors, A, and activation energies, Ea, from the temperature dependence of kp for methacrylic acid in methanol, DMSO, and water in order to underline the reliability of the data. For acrylic acid it turns out...
121 citations
Journal Article•
TL;DR: It appears that the monomer constituents, such as MAA or NVP, control protein adsorption, and interactions of the surface lactam groups of NVP with proteins may be attributable to the attraction of proteins to NVP.
Abstract: PURPOSE. To examine the effect of hydrogel lens monomer constituents on protein sorption.METHODS. A series of hydroxyethylmethacrylate (HEMA)-based hydrogels with various amounts of methacrylic acid (MAA) or N-vinyl pyrrolidone (NVP) were synthesized. A radiolabel tracer technique was used to measure the amount of protein adsorbed on or penetrating into the hydrogels. Penetration of fluorescence-labeled proteins in the hydrogels was studied by laser scanning confocal microscopy. Single-protein solutions of human serum albumin (HSA) and hen egg lysozyme were studied.RESULTS. Inclusion of the comonomers MAA or NVP in hydrogels resulted in an increase, in water content and also had a strong impact on protein sorption. An increase in the amount of MAA in the poly(HEMA-co-MAA) hydrogels increased lysozyme adsorption and penetration but reduced HSA adsorption. However, the amount of protein adsorbed for both HSA and lysozyme increased with the amount of NVP in the poly(HEMA-co-NVP) hydrogels. In contrast to the marked effect of MAA on protein sorption, in particular, on lysozyme sorption, NVP had little influence on protein sorption. When a hydrogel contains both MAA and NVP, MAA has the dominant effect on protein sorption - in particular, on lysozyme sorption. Furthermore, a large difference was observed in the amount of lysozyme adsorbed on the hydrogels that had similar water contents but little variation in adsorption of HSA.CONCLUSIONS. Negatively charged carboxyl groups of the IL MAA constituent may influence lysozyme sorption in two ways: by electrostatic attraction and by increasing the possibility for the small lysozyme molecule to penetrate the hydrogels. Interactions of the surface lactam groups of NVP with proteins may be attributable to the attraction of proteins to NVP. Water content is not a primary factor in determining protein adsorption. It appears that the monomer constituents, such as MAA or NVP, control protein adsorption.
119 citations
TL;DR: Forster et al. as mentioned in this paper used fluorescence correlation spectroscopy (FCS), static and dynamic light scattering (SLS, DLS), analytical ultracentrifuge (AUC), and by transmission electron microscopy (TEM) with freeze-fracturing and staining techniques.
Abstract: Four amphiphilic block copolymers polyisobutylene-block-poly(methacrylic acid) (IBm-MAAn; m = 70−134, n = 52−228) were synthesized and transferred into aqueous medium at pH 10−12. Their structure in solution was characterized by fluorescence correlation spectroscopy (FCS), static and dynamic light scattering (SLS, DLS), analytical ultracentrifuge (AUC), and by transmission electron microscopy (TEM) with freeze-fracturing and staining techniques. DLS data, AUC sedimentation traces, and TEM images indicate at least two different kinds of particles. TEM shows spherical micelles; however, especially for polymers with larger hydrophobic blocks, additional particles are observed. FCS shows extremely low critical micelle concentrations (cmc < 0.3 mg/L). The main part of the particles consists of micelles with diameters from 15 to 50 nm, built by 130−200 block copolymer molecules. Aggregation numbers and diameters are consistent with a model recently proposed by Forster et al. (J. Chem. Phys. 1996, 104, 9956−9970...
114 citations
TL;DR: Weakly cross-linked heteropolymer gels that memorize molecular pairs have been designed and synthesized as mentioned in this paper, which consists of a main monomer component responsible for volume phase transition, methacrylic acid that adsorbs one divalent ion as a pair, and cross links.
Abstract: Weakly cross-linked heteropolymer gels that memorize molecular pairs have been designed and synthesized. The polymer consists of a main monomer component responsible for volume phase transition, methacrylic acid that adsorbs one divalent ion as a pair, and cross-links. The memory of pairing of methacrylic acids within the gels was encoded in the primary sequence of main monomers, methacrylic acids and cross-links within the gels, which was achieved by “imprinting”, namely, by synthesizing gels while methacrylic monomers were paired prior to polymerization. The control gels, where methacrylic monomers were randomly distributed, showed frustration in forming pairs, whereas such frustration was completely diminished in the imprinted gels allowing the memory of pair formation.
111 citations
TL;DR: In this paper, a new kind of monolithic capillary electrochromatography column with poly(styrene-co-divinylbenzene, co-methacrylic acid) as the stationary phase has been developed.
Abstract: A new kind of monolithic capillary electrochromatography column with poly(styrene-co-divinylbenzene-co-methacrylic acid) as the stationary phase has been developed. The stationary phase was found to be porous by scanning electron microscopy and the composition of the continuous bed was proved by IR spectroscopy to be the ternary polymer of styrene, divinylbenzene, and methacrylic acid. The effects of operating parameters, such as voltage, electrolyte, and organic modifier concentration in the mobile phase on electroosmotic flow were studied systematically. The retention mechanism of neutral solutes on such a column proved to be similar to that of reversed-phase high performance liquid chromatography. In addition, fast analyses of phenols, chlorobenzenes, anilines, isomeric compounds of phenylenediamine and alkylbenzenes within 4.5 min were achieved.
106 citations
TL;DR: In this paper, a cografting of methacrylic acid (MAA) with acrylonitrile (AN) onto polypropylene fibers and subsequent conversion of the produced cyano group to an amidoxime group by reaction with hydroxylamine was performed.
102 citations
15 Jan 2000
TL;DR: Overall, the production of temperature- and/or pH-sensitive polymers by inverse suspension polymerization results in particles with swelling characteristics similar to those produced by emulsion polymerization, albeit with differing particle sizes.
Abstract: The characterization of temperature- and pH-sensitive poly- N -isopropylacrylamide (poly-NIPAM) microgel particles, produced by surfactant-free emulsion polymerization, has been extensively reported. In the work described here poly(NIPAM) gel particles, cross-linked with N - N ′-methylenebisacrylamide (BA), have been produced using inverse suspension polymerization. These particles have been termed “minigels” here since they are somewhat larger than conventional microgels. Results suggest that minigel particles are formed as a dilute suspension, within the aqueous dispersed (droplet) phase. The hydrodynamic diameter of the minigel particles produced in this work is ≤2.5 μm, at 25°C. The effects of temperature and pH changes, variation in cross-linker concentration, and incorporation of a charged comonomer (methacrylic acid, MAA) have been investigated. Both poly(NIPAM-BA) and poly(NIPAM-BA-MAA) minigel particles are temperature sensitive with swelling behavior consistent with comparable microgels. Variations in pH were found to effect the size of minigels containing ionizable groups (such as a carboxylate) by a mechanism of increased electrostatic repulsion of charged groups with increasing pH. Overall, the production of temperature- and/or pH-sensitive polymers by inverse suspension polymerization results in particles with swelling characteristics similar to those produced by emulsion polymerization, albeit with differing particle sizes.
TL;DR: The optimum value of the weight ratio of AN/MAA = 60/40 in the monomer mixture was observed both in a submerged mode at an ocean site and in a flow-through mode in the laboratory to enhance the uranium adsorption from seawater.
Abstract: Methacrylic acid (MAA) and 2-hydroxyethyl methacrylate (HEMA) were cografted with acrylonitrile (AN) onto polyethylene fiber by radiation-induced graft polymerization The cyano groups produced were converted to amidoxime groups (−C(NOH)NH2) by reaction with hydroxylamine (NH2OH) to recover uranium in seawater Various weight ratios of AN/MAA or AN/HEMA in the monomer mixture for cografting generated MAA- and HEMA-cografted amidoxime (AO) fibers with various hydrophilicities The amidoxime group density and water content were balanced to enhance the uranium adsorption from seawater MAA-cografted AO fibers exhibited a higher adsorption rate than HEMA-cografted AO fibers The optimum value of the weight ratio of AN/MAA = 60/40 in the monomer mixture was observed both in a submerged mode at an ocean site and in a flow-through mode in the laboratory The amount of uranium adsorbed was 090 g/kg of the MAA-cografted AO fiber at 293−298 K after 20 days of contact at the ocean site
TL;DR: In this paper, it was shown that the methacrylic acid units subsequently formed anhydride links, which probably impede depolymerization of the remaining MMA sequences, resulting in evolution of less MMA.
TL;DR: In this paper, the modification of polymeric substrates bisphenol A poly(carbonate) (PC), polyvinyl chloride (PVC) and poly(tetrafluoro ethylene) (PTFE) by the vinylic monomers styrene (S), methyl methacrylate (MMA) and methacrylic acid (MAA) under supercritical conditions was investigated systematically.
Abstract: The modification of the polymeric substrates bisphenol A poly(carbonate) (PC), poly(vinyl chloride) (PVC) and poly(tetrafluoro ethylene) (PTFE) by the vinylic monomers styrene (S), methyl methacrylate (MMA) and methacrylic acid (MAA) under supercritical conditions was investigated systematically. In a first step, the polymers were impregnated with the monomers and a radicalic initiator, followed by a polymerization inside the swollen substrates to generate a polymer within a polymer. The process parameters were controlled by the radicalic initiator and by the solubility of the monomers in scCO2. As a result, PTFE shows the least ability to be modified due to its limited swelling capability. With the generation of the water-soluble poly(methacrylic acid) (PMAA) inside the hydrophobic PVC- or PMMA substrates, it was possible to obtain polymer mixtures inaccessible by common techniques such as melt mixing. The modification of PVC with PMAA was characterized in detail and the limits of the modification process evaluated. The comparison with impregnation under common conditions showed the significance of the presence of CO2 during both impregnation and polymerization. Carbon dioxide acts as a low-molecular-weight plasticizing agent, which enhances the mobility of the monomer inside the swollen substrate, but does not change the compatibility of the polymers with the monomers. Another peculiarity was the observation of a mixing gradient. There was a linear decrease in the PMAA content from the surface to the inner bulk of the polymer mixtures. The maximal penetration depth found for PMAA during 4 h of impregnation was 180 μm. This means, that polymer blends can readily be obtained with thin films and fibers, but is limited with bulkier substrates. In short, scCO2 enables the smooth refinement of polymer surfaces and, moreover, has the potential to generate new polymer mixtures.
TL;DR: For Days 1-7, methacrylic acid released in water at 37 degrees C by Ariston was significantly greater than that of the other composites and generally decreased with time.
TL;DR: Polymers of this type may have great potential in controlling, via means of formulation, the release of drug eutomer whilst enhancing retention of distomer in the dosage form.
TL;DR: The selectivity of the imprinted polymers was investigated and an imprinted polymer-based competitive binding assay for B-Me was demonstrated using biotin p-nitrophenyl ester as a nonisotopic-labeled ligand.
Abstract: Synthetic biotin-binding polymers were prepared by molecular imprinting. Methacrylic acid (MAA) was copolymerized with ethylene glycol dimethacrylate in the presence of biotin methyl ester (B-Me) in chloroform. Hydrogen-bonding-based complexation of B-Me with MAA generates the binding sites complementary to B-Me after extracting B-Me from the resulting copolymers. Data from NMR titration suggest a one-to-one prepolymerization complex formation of B-Me with MAA in chloroform. A possible complex structure was estimated by docking of the most stable conformers by intermolecular Monte Carlo conformational search under the assumption of a one-to-one association. The selectivity of the imprinted polymers was investigated and an imprinted polymer-based competitive binding assay for B-Me was demonstrated using biotin p-nitrophenyl ester as a nonisotopic-labeled ligand.
TL;DR: In this article, the degree of interpolymer complexation in poly(methacrylic acid-g-ethylene glycol) graft copolymer networks was determined as a function of copolymers composition, PEG graft chain molecular weight and environmental pH.
TL;DR: In this paper, the stability of water-in-CO2 (W/C) emulsions with poly(dimethylsiloxane)-b-poly(methacrylic acid) (PDMS-b-PMA) and PDMS b-polypoly(acrylic acids) (PAA) ionomer surfactants is reported as a function of surfactant architecture, pH, temperature, pressure, and droplet flocculation.
Abstract: The stability of water-in-CO2 (W/C) emulsions stabilized with poly(dimethylsiloxane)-b-poly(methacrylic acid) (PDMS-b-PMA) and PDMS-b-poly(acrylic acid) (PDMS-b-PAA) ionomer surfactants is reported as a function of surfactant architecture, pH, temperature, pressure, and droplet flocculation. For a given PDMS block length, the stability of the emulsion is correlated with the distance from the balanced state where the surfactant prefers the water and CO2 phases equally. When the pH starting at 3 is raised up to 5−6, the hydrophilic/CO2-philic balance of the surfactant increases, because of ionization of COOH, and the emulsion becomes more stable. At the pH of maximum stability, the emulsion becomes more stable with a decrease in the PDMS length, for a given ratio of block lengths, because of gelation of the flocculated 2−5 μm primary droplets. W/C emulsions are stable with respect to sedimentation for >24 h and are resistant to coalescence for more than 7 days. Because of gelation, the W/C emulsions are mor...
TL;DR: In this paper, the effect of anionic polyelectrolytes on the electrokinetic and rheological properties of concentrated Si 3 N 4 suspensions was investigated experimentally.
Abstract: The effect of anionic polyelectrolytes on the electrokinetic and rheological properties of concentrated Si 3 N 4 suspensions was investigated experimentally. We found that polyelectrolyte adsorption and, thus, colloidal stability at pH>pH Si 3 N 4 iep is mainly governed by the surface charge density of the solid phase. Comparing anionic methacrylic acid comb copolymer modifications with grafted poly(ethylene oxide) chains (PMMA-PEO), with poly(acrylic acid) (PAA) showed that the grafted PEO chains have a minor influence on the colloidal stability. The common viscosity minimum for all the anionic polyelectrolytes around pH 7 suggests that the suspensions are electrosterically stabilized. The polyacrylic backbone attains an extended conformation perpendicular to the surface. The effect of excess addition of polyelectrolyte was also discussed; we attribute the significant increase in suspension viscosity to the increased ionic strength caused by the release of associated counterions of the polymer functional groups.
TL;DR: In this paper, the behavior of poly(methacrylic acid) chains is investigated in aqueous micellar systems. But the authors focus on the shell of a polysoap-like polyelectrolyte.
Abstract: Block polyelectrolyte samples containing long hydrophobic blocks, e.g., polystyrene, and long polyelectrolyte blocks, e.g., poly(methacrylic acid), do not dissolve in aqueous media. However, multimolecular micelles consisting of compact polystyrene cores and polyelectrolyte shells may be prepared by dialysis from organic solvent−water mixtures into aqueous buffers. Polystyrene cores are kinetically frozen in water and the behavior of the micellar systems is determined by the polyelectrolyte behavior of the shell. Poly(methacrylic acid) does not represent a typical polyelectrolyte. Due to the presence of a strongly hydrophobic methyl group in each repeating unit, its behavior more resembles that of a polysoap. In aqueous micellar systems, poly(methacrylic acid) chains form a fairly compact hydrophobic layer close to the core/shell interface. In our recent works, we have found that the state of the inner part of the shell responds rather slowly to shock changes in the bulk pH and the ionic strength of the s...
TL;DR: In this article, a molecularly imprinted polymer (MIP) was ground and packed into a micro-column for selective solid phase extraction (SPE) of 2-aminopyridine from 20μl of sample solution.
TL;DR: In this paper, the authors performed free radical copolymerisation of NIPA with acrylic acid (AA), methacrylic acid (MAA), and 2-methyl-2-acrylamidopropane sulphonic acid (AMPS) in ethanol, ethanol and water respectively.
TL;DR: In this paper, the crosslinking structure of peroxide-cured NBR vulcanizates was studied and the results showed that ZnO/MAA had a great reinforcing effect for NBR, and their amounts and ratio played important roles in influencing the mechanical properties.
Abstract: Through the neutralization reaction of zinc oxide (ZnO) and methacrylic acid (MAA) or acrylic acid (AA), zinc methacrylate (ZMA) or zinc acrylate (ZA) was in situ prepared in nitrile rubber (NBR). The mechanical properties and crosslinking structure of the resulting peroxide-cured NBR vulcanizates were studied. The results showed that ZnO/MAA (AA) had a great reinforcing effect for NBR, and their amounts and ratio played important roles in influencing the mechanical properties. Such vulcanizate contains both covalent crosslinks and salt crosslinks, and the change in the tensile strength of the vulcanizate was related to the variation of the salt crosslink density. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2740–2748, 2000
TL;DR: In this article, a stepwise assembly of isotactic poly(methyl methacrylate) and syndiotactic poly (methacrylic acid) from acetonitrile/water solutions onto a gold substrate was studied.
Abstract: Stepwise assembly of isotactic poly(methyl methacrylate) and syndiotactic poly(methacrylic acid) from acetonitrile and mixed acetonitrile/water solutions, respectively, onto a gold substrate was studied. Quantitative quartz crystal microbalance analysis of the molar ratio (monomer unit) between assembled polymers suggested stepwise stereocomplex formation. The assembled amount and the assembly ratio between PMAA and PMAA were dependent on the acetonitrile content of the poly(methacrylic acid) solution. Infrared spectra of the assembly and cast films of each polymer also showed stereocomplex formation in the assembly. Atomic force microscopic observation showed the assembled polymer to have a molecularly smooth surface. The solvent species used was an important factor in stereocomplex formation at the liquid−polymer film interface.
TL;DR: In this article, the graft copolymerization of acrylonitrile (AN)/acrylic acid (AA), acrylanitrile(AN)/methacric acid (MA), and acrylinkitrile-(AN)/glycidyl methacrylate (GMA) onto pre-irradiated polyethylene (PE) films were studied.
TL;DR: In this article, the properties of poly(N-isopropylacrylamide) with poly(acrylic acid) and poly(methacrylic acid) partially neutralized have been isolated, for degrees of neutralization up to 15%.
TL;DR: In this paper, a physical model describing the microstructure of a model HASE polymer in aqueous salt solution is proposed, which contains a copolymer backbone of equal moles of methacrylic acid (MAA) and ethyl acrylate (EA).
Abstract: The microstructure of a model HASE associative polymer in aqueous salt solution is complex and has not been defined until now. On the basis of the results from static and dynamic light scattering studies, a physical model describing the microstructure of a model HASE polymer in aqueous salt solution is proposed. The model HASE polymer contains a copolymer backbone of equal moles of methacrylic acid (MAA) and ethyl acrylate (EA) with 1 mol % of C16H33 hydrophobic modified macromonomer distributed randomly along the backbone. In very dilute aqueous solutions (0.005−0.1 wt %), two decay modes are observed in the relaxation time distribution function. The fast and the slow modes correspond to the translational diffusion of the unimers and the polymer aggregates (consisting of about five polymer chains), respectively. The polymer aggregate is formed by association of the hydrophobic macromonomer via a closed association mechanism. When the polymer concentration increases, the polymer aggregates grow in size. T...
TL;DR: In this article, a novel comb water-soluble associative polymer (HASE) consisting of a random copolymer of methacrylic acid (MAA), ethyl acrylate (EA), and 1 mol % of hydrophobically modified macromonomers was studied using laser light scattering and rheological techniques.
Abstract: A novel comb water-soluble associative polymer (hydrophobically modified alkali-soluble emulsion (HASE)), comprising of a random copolymer of methacrylic acid (MAA), ethyl acrylate (EA), and 1 mol % of hydrophobically modified macromonomers, was studied using laser light scattering and rheological techniques. The hydrophobic substituents are separated from the backbone by a poly(ethylene glycol) (PEG or PEO) spacer chain. The hydrophobicity of the hydrophobic substituents and the length of PEO spacers control the microstructure of the aggregates or clusters. In dilute solution regime, the relaxation times of both unimers and aggregates are almost independent of hydrophobic groups and PEO spacer length. The aggregates are formed via the closed-association mechanism, and the balance of electrostatic and hydrophobic interactions controls their microstructures. However, by varying the hydrophobicity and the length of the PEO spacer chains, the internal conformation of the aggregates changes. Results from stat...
TL;DR: In this article, the effect of iron on the redox and catalytic properties for the oxidation of isobutane into methacrylic acid (MAA) has also been studied.
Abstract: Keggin-type molybdophosphoric heteropolyacid with protons partially substituted by iron cations in a bulk form (Fe0.85H0.45PMo12O40) or supported on the cesium salt (Cs2Fe0.2H0.4PMo12O40) have been synthesized and characterized by different techniques like the Mossbauer spectroscopy and the electron spin resonance (ESR). The effect of iron on the redox and catalytic properties for the oxidation of isobutane into methacrylic acid (MAA) has also been studied. Iron has been shown to have a different effect whether acts as a counter-cation in the bulk acid or in the acid supported on the cesium salt. In the first case, it increases both the selectivity in methacrylic acid and methacrolein (MA) and the activity of the acid phase whereas in the second case, it increases only the selectivity. This difference has been explained by the existence of an electron transfer between iron and molybdenum occurring only in the bulk acid. This electron transfer was related to a combined hydration-oxidation mechanism which promotes the reducibility of the solid and consequently its catalytic activity.