Sulfonated poly(ether ether ketone)–silica membranes doped with phosphotungstic acid. Morphology and proton conductivity

Sulfonated poly(ether ether ketone) (SPEEK)–silica membranes doped with phosphotungstic acid (PWA) are presented. The silica is generated in situ via the water free sol–gel process of polyethoxysiloxane (PEOS), a liquid hyperbranched inorganic polymer of low viscosity. At 100 °C and 90% RH the membrane prepared with PEOS (silica content = 20 wt%) shows two times higher conductivity than the pure SPEEK. The addition of small amounts of PWA (2 wt% of the total solid content) introduced in the early stage of membrane preparation brings to a further increase in conductivity (more than three times the pure SPEEK). During membrane formation PWA and the sulfonic acid groups of SPEEK act as catalysts in the conversion of PEOS in silica. Once the membranes are formed, PWA is incorporated in the silica network and acts as proton conductivity enhancer. The correlation between morphology and proton conductivity allows establishing the optimal doping level and preparation procedure. The morphology is studied by transmission electron microscopy (TEM) while the proton conductivity is measured by impedance spectroscopy (IS). The direct methanol fuel cell performance is also investigated.     

β-Substituted cyclopropyl rádicals grafted to silica surface. Methods of preparation,structure, and properties

Cyclopropyl type radicals were identified on a surface of activated silica by ESR. The possibility of their preparation by two methods,i.e., by photocyclization of substituted allyl radicals and by interaction of cyclopropane molecules with particular surface defects, was demonstrated. The effects of -substituents on radiospectroscopic characteristics and thermal stabilities of the radicals were studied. Rate constants and activation energies of decomposition of substituted cyclopropyl radicals were estimated. The experimental data obtained were compared with the results of quantum-chemical calculations of model systems. The mechanism of photocyclization of allyl radicals was discussed. The transition states of decomposition of cyclopropyl and -fluorine-substituted cyclopropyl radicals were calculated. Electronegative substitution was found to result in a considerable decrease in the activation energy of the cyclopropane ring opening.The authors are grateful to E. G. Baskir for calling their attention to this publication.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2409–2421, December, 1995.The work was carried out with financial support of the Russian Foundation for Basic Research (Project code 94-03-09137) and the International Science Foundation (Grant No. MK9000).     

Redox-active silica nanoparticles. Part 6. Synthesis and spectroscopic and electrochemical characterization of viologen-modified Stöber silica particles with diameters of approximately 125 nm

The synthesis of Stöber silica particles and their redox behavior after viologen modification are reported. The particles were synthesized using high reaction temperatures and a postsynthetic calcination step to yield nonporous silica spheres with d of approximately 125 nm and low polydispersity. As the immobilization strategy, the condensation of surface hydroxyl groups with an alkoxysilane-substituted viologen modifier was chosen. The successful attachment was confirmed by ¹³C-CP/MAS-NMR and diffuse reflectance Fourier transform infrared as well as UV/Vis and energy dispersive X-ray spectroscopy. The surface concentration was estimated to be between 48 and 100  $\upmu$ mol/g. The modified material is redox-active. Differential pulse voltammetry and cyclic voltammetry experiments in nonaqueous solvents at Pt and mercaptopropionic acid-modified gold electrodes reveal two separated and pronounced signals of the first and second reduction of the viologen unit. The observed potentials are in good agreement with those of the free modifier. Furthermore, the treatment of the viologen-modified material with Na₂S₂O₄ leads to the formation of a nanoparticulate silica material with stable free radicals located at the particle surface. In addition, such radicals are generated by the in situ electrolysis at Pt net electrodes in acetonitrile or dimethylformamide. The radical formation was confirmed by EPR and UV/Vis spectroscopy. The reduction is reversed by air oxidation.     

Luminescence properties of sol-gel derived silica gels doped and undoped with RE-complexes(RE=Eu,Tb)

The luminescence properties of silica gels and silica gels doped with two rare earth complexes,Eu(TTA)3 and Tb(o-CBA)3 (TTA=thenoyltrifluocetate,o-CBA=o-chlorobenzoic acid) are reported and discussed.Pure silica gels show a blue luminescence,and the maximum excitation and emission wavelengths depend strongly on the solvents used.Both of the studied rare earth complexes exhibit the characteristic emissions of the rare earth ions in silica gels,i.e.,Eu3+5 Do→7 FJ(J=0,1,2,3,4),Tb3+5D4→7FJ(J=3,4,5,6) transitions.Compared with the pure RE-complexes powder,the silica gels doped with RE-complexes show fewer emission lines of the rare earth ions.Furthermore the rare earth ion (Tb3+) presents a longer lifetime (1346μs) in silica gel doped with Tb(o-CBA)3 than in pure Tb(o-CBA)3 powder (744μs).The reasons responsible for these results are discussed in the context.     

Fumed silica – rheological additive for adhesives,resins, and paints

Fumed silica, a synthetic silicon dioxide, is a powerful rheological additive for resins and paints to introduce thixotropy or even a yield point. The rheological effectiveness of fumed silica is based on its ability to form percolating networks which immobilize large volumes of liquid. By a combination of advanced rheological experiments, spectroscopical investigations, and quantum chemical calculations it could be demonstrated that the formation and stability of the silica network is strongly influenced by particle-resin interactions. The results can be used to develop comprehensive models, which explain the rheological performance of different grades of fumed silica in different resins.     

Poly (ether amide) and silica nanocomposites derived from sol–gel process

The sol–gel derived chemically combined organic–inorganic nanocomposites were synthesized from poly(etheramide) and tetraethoxysilane. Reaction of a mixture of 4-aminophenyl ether and 1,3-phenyldiamine with terephthaloyl chloride (TPC) in dimethylacetamide (DMAc) produced the amide chains. These chains were modified with carbonyl chloride end groups using a slight excess of diacid chloride and were then reacted with aminophenyl trimethoxysilane (APTMOS), where the amine group reacted with carbonyl chloride end groups. Hydrolysis/condensation of tetraethoxysilane (TEOS) and alkoxy groups present in APTMOS developed bonding between the polyamide chains and inorganic silica network generated in situ. By changing the relative proportions of the polymer solution and the amount of TEOS, the composition of hybrid films was varied. Thin hybrid films with various concentrations of silica network obtained after evaporation of the solvent were subjected to mechanical, dynamic mechanical thermal and morphological measurements. The results indicate a gradual increase in the modulus (3.84 GPa) and tensile strength (121 MPa) up to 15-wt.% silica relative to the pure polyamide. The elongation at break point and toughness gradually decrease with addition of silica content. These hybrids were found to be thermally stable up to a temperature of 500 °C. The weight retained above 800 °C was roughly proportional to amount of silica in the matrix. The glass transition temperature and the storage moduli increased with increasing silica concentration. The maximum increase in the T _g value (358 °C) was observed with 15-wt.% silica. Scanning electron micrographs indicated the uniform distribution of silica in the composites with an average particle size ranging from 9 to 47 nm.     

Preconcentration and separation of trace Pd(II) and Pt(IV) with silica gel bonded by aminopropyl-benzoylazo-4-(2-pyridyl-azo)-resorcinol

This paper reports a simple and highly selective method for preconcentrating and separating of trace Pd(II) and Pt(IV) with silica gel bonded by aminopropyl-benzoylazo-4-(2-pyridy-lazo)-resorcinol (ABPR-SG). ABPR-SG is stable in solution from 6 mol/L HCl to pH 7.0 and in common organic solvents. The maximum adsorptive capacity of Pd(n) on ABPR-SG is 362 μmol/g. After preconcentration and separation by using ABPR-SG column, Pd(II) and Pt(IV) of μg/L level in artificial water samples can be measured reliably by common spedrophotometry. The maximum concentration factors of Pd(II) and Pt(IV) on ABPR-SG column are 143 and 125 respectively. The chromatographic column packed with ABPR-SG can be reused. The method is simple and efficient.     

3-ethyl-3-phenylazetidinone-2—I. Synthesis of (R)-, (S)- and (RS)-monomer,polymerization and properties of polymers

Synthesis and optical resolution of 3-ethyl-3-phenylazetidinone-2 were improved to obtain (RS)-, (R)- and (S)-monomers having optical purities up to 98%, which could successfully be determined by ¹H-NMR 250 MHz using tris[3-(2,2,2-trifluoro-l-hydroxymethylidene)d-camphorato]europium III as a shift reagent. These monomers were polymerized anionically in HMPT using potassium salt as a catalyst and by the addition of 1-acetyl-4,4-dimethylazetidinone-2 as a chain initiator. Optical purity of the starting monomer seemed to be maintained in the resulting polymers, the thermal properties of which were found to depend on the mean length of the stereoblocks contained in the chain. While the reactivity, in particular the case of polymerization, of monomer increased with the optical purity, no evidence could be obtained for stereoregulation by a preferential incorporation of a monomer enantiomer according to the configuration of the growing chain end unit.     

Structural studies of gel phases—IV. An infrared reflectance and Fourier transform Raman study of silica and silica/titania gel glasses

Infrared reflectance and Fourier transform Raman spectroscopy have been used to study silica and silica/titania monoliths produced by the sol—gel route which had been subjected to a series of heat treatments. With increasing thermal treatment temperature, the gel—glass matrix is strengthed by bond shortening and a reduction in mean SiOSi bond angle and angular distribution for this feature. Results obtained at a range of temperatures were in good agreement to those obtained for vitreous silica. The incorporation of low levels (3% by weight) of titanium led to more disordered glasses which contain titanium in tetrahedral sites only. Evidence was obtained for the formation of SiOTi bonds, principally during the latter stages of densification at temperatures between 615 and 1000°C.     

2-(p -toluidino)-6-naphthalene sulfonate as a fluorescent probe for flocculation studies of cationic potato amylopectin and nanosized silica particles. 2. Flocculation by binding of nanosized silica particles

2-(p-toluidino)-6-naphthalene sulfonate (TNS) is a probe that fluoresces strongly when bound to certain proteins and polymers, but weakly in aqueous solutions. The reversible association of TNS is used to monitor the binding of anionic nanosized silica particles (NSP) to cationic potato amylopectin starch (CApS) through the decreasing fluorescence emission as TNS is competitively released by the particle binding. Steady-state fluorescence measurements at different mixing ratios of CApS and NSP provide data on the equilibrium binding. The isotherm derived is used to establish the fact that the most efficient flocculation between CApS and NSP occurs when the polymer coils are nearly saturated by NSP, but still have positively charged parts left. This supports a patch-flocculation mechanism. Stopped-flow experiments show that NSP binding to CApS occurs within a few milli seconds. This observation allows turbidity changes which occur on longer timescales to be ascribed to particle-decorated polymers undergoing changes in the conformation or aggregation. Received: 14 August 1998 Accepted in revised form: 4 December 1998     

Monoaquabis(2,2′-bipyridine)saccharinatozinc(II) Saccharinate. 1. Structural Study by Single Crystal X-Ray Diffraction, FTIR, and DS Calorimetry

Structural characteristics of monoaquabis(2,2-bipyridine)saccharinatozinc(II) saccharinate (I) were studied by X-ray diffraction, Fourier transform IR spectroscopy, and differential scanning calorimetry (DSC). The X-ray study led to the formula [Zn(H₂O)(bpy)₂(sac)](sac), where bpy = 2,2-bipyridine, and sac = saccharinato ion/ligand. The structure is built from [Zn(H₂O)(bpy)₂(sac)]⁺ cations and [sac]^– anions. There are two crystallographically independent saccharinate anions and 2,2-bipyridine molecules. In the crystal structure, the packing is dominated by the net of hydrogen bonds between the saccharinato ligand ions and the water molecules and within these ions and molecules, and also by C–HO contacts. IR spectra in characteristic regions of H₂O, CO, and SO₂ stretching vibrations have been studied. The geometry of the water molecules is discussed with allowance for the spectroscopic and structural data. The appearance of the CO and SO₂ stretching vibrations in the spectrum of the compound correlates with the number of nonequivalent carbonyl and sulfonyl groups in the structure. Thermal DSC analysis was used to determine the decomposition rate and the stability of the complex.     

Convectional, sedimentation, and drying dissipative patterns of colloidal silica (183 nm in diameter) suspensions in a glass dish and a watch glass

Convectional, sedimentation, and drying dissipative structural patterns formed during the course of drying aqueous colloidal crystals of silica spheres (183 nm in diameter) have been studied in a glass dish and a watch glass. Spoke-like convectional patterns were observed in a watch glass. The broad ring sedimentation patterns formed especially in a glass dish within 30–40 min in suspension state by the convectional flow of water and colloidal spheres. The macroscopic broad ring drying patterns formed both in a glass dish and a watch glass. The ratio of the broad ring size in a glass dish against the initial size of suspension, i.e., inner diameter of the glass dish, d _f/d _i, in this work, were compared with previous work of other silica spheres having sizes of 305 and 560 nm and 1.2 μm in diameter. The d _f/d _i values in a glass dish increased as sphere concentration increased, but were rather insensitive to colloidal size. The d _f/d _i values on a watch glass also increased as sphere concentration increased, and further increased as sphere size decreased. Segregation effect by sphere size in a watch glass takes place by the balancing between the upward convectional flow of spheres in the lower layers of the liquid and the downward sedimentation of spheres. Colorful microscopic drying patterns formed both in a glass dish and a watch glass.