The synthesis and characterization of new thermoplastic poly(thiourethane‐urethane)s

New thermoplastic segmented poly(thiourethane‐urethane)s (SPTUUs) were prepared by a one‐step melt polymerization from 20 to 80 mol % poly(tetramethylene oxide) of = 1000 or poly(hexamethylene carbonate) diol (PHCD) of = 860 as soft segments, hexamethylene diisocyanate (HDI) and bis[4‐(mercaptomethyl)phenyl]methanone (BMMPM) as a new dithiol chain extender at the NCO/(OH + SH) molar ratio of 1 in the presence of dibutyltin dilaurate as a catalyst. The structures of the SPTUUs were examined by FTIR, X‐ray diffraction analysis, and scanning electron microscopy. The SPTUUs were also characterized by physicochemical, thermal, and tensile properties as well as Shore A/D hardness. The SPTUUs with the PHCD soft segments showed better tensile properties than those with the PTMO soft segments. A nonsegmented polythiourethane based on BMMPM and HDI is also described. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1770–1782, 2008     

Functionalized SBA-15 organosilicas as sorbents of zinc(II) ions

SBA-15 nanoporous silicas functionalized with amine-, thiol-, vinyl-, phenyl- and cyano surface groups were synthesized by using the amphiphilic block copolymer P123 as the structure-directing agent. The obtained materials have a well-developed porous structure - the values of specific surface area are in the range 800-950 m²/g and the sizes of cylindrical mesopores are in the range 7.4-8.6 nm. It was established that the size of the mesopores strongly depends even on small amounts of co-monomers co-condensing with TEOS. Adsorption of Zn(II) ions at the SBA-15/NaCl interface was investigated by means of the radioactive isotope tracer technique over the pH range of 3-11. Surface charge density, adsorption density, pH_50% and ΔpH_10-90% parameters for different concentrations of the carrying electrolyte were evaluated and discussed.     

Characterization of uranium(VI) sorption by organobentonite

The U(VI) sorption on the bentonite modified by hexadecyltrimethylammonium bromide (HDTMA) was studied in the concentration range: 0.0001-0.001 mol/dm³ in the aqueous phase and in the pH range: 3-10. The experiments concerning the pH influence on the molar absorption coefficient c_b of U(VI) in the bentonite phase showed that the species: UO₂²⁺, UO₂(OH)⁺, UO₂(OH)₂ UO₂(OH)₃⁻, UO₂(OH)₄²⁻, (UO₂)₃(OH)₅⁺, (UO₂)₃(OH)₇⁻, present in the aqueous phase, are responsible for uranium sorption. Their sorption parameters K were determined and it is evident that for higher concentrations of HDTMA⁺ cations in the bentonite phase, i.e. for b96-b157 bentonite, the presence of anionic species: UO₂(OH)₃⁻, UO₂(OH)₄²⁻, and (UO₂)₃(OH)₇⁻ in the aqueous phase results in the increase of U(VI) molar absorption coefficient c_b in the sorbent phase.     

Thermal properties of lanthanide(III) complexes with 5-amino-1,3-benzenedicarboxylic acid

The complexes of yttrium(III) and lanthanides(III) with 5-amino-1,3-benzenedicarboxylic acid form two isostructural series of compounds and have the general formula Ln₂(C₈H₅O₄N)₃·nH₂O, where n = 13 for Y, La-Er and n=9 for Tm, Yb, Lu. They are insoluble in water and stable at room temperature. On heating in air or inert gas atmosphere they lose all water molecules in several steps. The anhydrous compounds are stable to about 400°C and next decompose to oxides.     

Synthesis of FDU-1 silica with narrow pore size distribution and tailorable pore entrance size in the presence of sodium chloride

Ordered silicas with large (9-15 nm), uniform, cagelike mesopores were synthesized under acidic aqueous conditions from tetraethyl orthosilicate in the presence of sodium chloride using poly(ethylene oxide)-poly(butylene oxide)-poly(ethylene oxide) triblock copolymer B50-6600 (EO39BO47EO39, Dow Chemicals) as a supramolecular template. Except for the use of NaCl in our case, the synthesis mixture composition was the same as that originally reported by Zhao et al. for the synthesis of FDU-1 silica, which was later shown to exhibit a cubic close-packed (Fm3m) structure with stacking faults related to the occurrence of hexagonal close-packed stacking sequences. The copolymer-templated silicas were formed at room temperature and in most cases were subjected to the hydrothermal treatment at 373 or 393 K. The calcined materials were characterized using small-angle X-ray scattering (SAXS) and nitrogen and argon adsorption at 77 K. SAXS patterns were generally similar to those reported for FDU-1 silica, indicating the cubic close-packed (Fm3m) structure, but the presence of stacking faults characteristic of a hexagonal close-packed structure cannot be precluded. The addition of the salt was found to significantly narrow the pore size distributions and to improve the uniformity of entrances to the cagelike mesopores, whereas the pore diameter, specific surface area, and pore volume were similar (in most cases slightly lower) to those for FDU-1 silicas obtained in the absence of NaCl. The materials synthesized in the presence of NaCl also appeared to have better resolved SAXS patterns. The feasibility of tailoring the pore cage diameter (from approximately 9.5 to 14.5 nm) and pore entrance diameter (from below 4 to approximately 8 nm) simply by adjusting the hydrothermal treatment temperature and time was demonstrated, indicating that these simple and convenient ways of structural design of cagelike mesopores are operative in the case of syntheses in the presence of inorganic salts.     

Anharmonic V–V pumping and asymmetric electron-elementary excitation interaction in emission and absorption of O2(Δg) in the crystalline phases of oxygen

Three luminescence bands in the yellow and red spectral region, which are related to the ¹Δ_g¹Δ_g→³Σ_g^{− 3}Σ_g⁻ double electronic transition of O₂, have been investigated in the , β, and γ phase of solid oxygen. The temperature dependence of the intensity of the yellow band is strongly influenced by emission from higher vibrational levels of O₂(¹Δ_g), which are populated by anharmonic V–V pumping. The broken mirror symmetry of the luminescence and absorption bands in the phase of solid O₂ points to an interaction between the electrons and the elementary excitations of the crystal, which is different in the ground and excited electronic states, e.g., a quadratic electron–phonon interaction.     

Weak localization in semiconductor structures with strong spin-orbit coupling

A theory of weak localization is constructed for p-type semiconductor structures with a complex Γ₈ valence band. An equation for the Cooperon is obtained and solved in the case when spin relaxation cannot be treated as a perturbation. The anomalous magnetoresistance is calculated in bulk samples as a function of the external deformation and in quantum wells as a function of the doping level. The results of the theory are represented in a form that allows direct comparison with experiment. Zh. éksp. Teor. Fiz. 113, 1429–1445 (April 1998)     

Comparative studies of p6m siliceous mesostructures by powder X-ray diffraction and nitrogen adsorption

Two-dimensional mesostructures with p6m symmetry such as MCM-41 and SBA-15 are the subject of intensive studies by using nitrogen and argon adsorption, transmission electron microscopy, and powder X-ray diffraction/scattering techniques. The latter may involve the X-ray diffraction (XRD) or small angle X-ray scattering (SAXS) measurements. The XRD/SAXS patterns for the aforementioned ordered mesostructures often exhibit four or more reflections, the most intensive one, 1 0 0 peak, and three less intensive peaks, 1 1 0, 2 0 0, 2 1 0. So far, analysis of these patterns was usually limited for the evaluation of the unit cell parameter and the identification of the observed peaks. In this work we present an attempt to analyze the XRD/SAXS patterns by including not only the position of observed peaks but also their intensity. It is shown that the intensity of these peaks, especially 1 1 0 peak, depends on the ratio of the pore diameter to the unit cell parameter. In particular, this dependence was studied for the intensity ratio of 1 1 0 and 2 0 0 peaks assuming 2 0 0 peak as a reference reflection because of its nearness to 1 1 0 peak (which minimizes the influence of other factors than the structural ones on the 1 1 0/2 0 0 intensity ratio analysis) and similar intensity to that of 1 1 0 peak. The values of the 1 1 0/2 0 0 intensity ratio were determined for many MCM-41 and SBA-15 samples and analyzed in relation to the pore width/unit cell ratio, where the pore width was estimated on the basis of nitrogen adsorption data or by the XRD/SAXS structure modeling. Comparative analysis of this intensity ratio for numerous MCM-41 and SBA-15 samples allows for a quick estimation of the pore width and provides some information about hexagonality of mesopores in these materials.     

Tetrad effect in the adsorption of the lanthanides on zeolite Y

The adsorption of the lanthanides (except for Pm) on the zeolite Y was investigated under various solution conditions of nitrate ion concentration ([NO(-)(3)]: 0.001-2 mol/dm(3)) and total lanthanide concentration (from 0.0001 to 0.001 mol/dm(3)). The solutions of the lanthanide nitrates were equilibrated with the zeolite samples at 296 K. The concentrations of lanthanides in the initial and equilibrium solutions were determined by means of spectrophotometrical method with Arsenazo III reagent and distribution constants K(d) of the lanthanides between aqueous and zeolite phases were calculated. The evident concave tetrad effect in the change of logK(d) values (nitrate concentrations 0.4-2 mol/dm(3)) within the lanthanide series was noticed and an attempt at its explanation through the comparison of covalence in LnO bonds existing in triple bond AlO(1/3Ln)Si triple bond species in the zeolite phase and in Ln(NO(3))(2+) complexes forming in the aqueous phase was presented. The weak convex tetrad effect for equilibrium nitrate concentrations 0.001-0.32 mol/dm(3), manifesting in the change of logK(d) values and in the alteration of logK (adsorption constants), is evidence of the complexation of the tripositive lanthanide ions by the oxygens originating both from water molecules and from the zeolite framework.     

Nanostructured polymer–titanium composites and titanium oxide through polymer swelling in titania precursor

Polymer (XAD7HP)/Ti⁴⁺ nanocomposites were prepared through the swelling of polymer in titanium (IV) ethoxide as a titanium dioxide precursor. The nanocomposite beads exhibit relatively high porosity different than the porosity of the initial polymer. Thermal treatment of composite particles up to 200 °C in vacuum causes the change of their internal structure. At higher temperature, the components of composite become more tightly packed. Calcination at 600 °C and total removal of polymer produce spherically shaped TiO₂ condensed phase as determined by XRD. Thermally treated composites show the substantial change of pore dimensions within micro- and mesopores. The presence of micropores and their transformation during thermal processing was studied successfully by positron annihilation lifetime spectroscopy (PALS). The results derived from PALS experiment were compared with those obtaining from low-temperature nitrogen adsorption data.