Cation Ordering and Exsolution in Copper-Containing Forms of the Flexible Zeolite Rho (Cu,M-Rho; M=H,Na) and Their Consequences for CO2 Adsorption

The flexibility of the zeolite Rho framework offers great potential for tunable molecular sieving. The fully copper-exchanged form of Rho and mixed Cu,H- and Cu,Na-forms have been prepared. EPR spectroscopy reveals that Cu²⁺ ions are present in the dehydrated forms and Rietveld refinement shows these prefer S6R sites, away from the d8r windows that control diffusion. Fully exchanged Cu-Rho remains in an open form upon dehydration, the d8r windows remain nearly circular and the occupancy of window sites is low, so that it adsorbs CO₂ rapidly at room temperature. Breakthrough tests with 10 % CO₂/40 % CH₄ mixtures show that Cu_4.9-Rho is able to produce pure methane, albeit with a relatively low capacity at this p_CO2 due to the weak interaction of CO₂ with Cu cations. This is in strong contrast to Na-Rho, where cations in narrow elliptical window sites enable CO₂ to be adsorbed with high selectivity and uptake but too slowly to enable the production of pure methane in similar breakthrough experiments. A series of Cu,Na-Rho materials was prepared to improve uptake and selectivity compared to Cu-Rho, and kinetics compared to Na-Rho. Remarkably, Cu,Na-Rho with >2 Cu cations per unit cell exhibited exsolution, due to the preference of Na cations for narrow S8R sites in distorted Rho and of Cu cations for S6R sites in the centric, open form of Rho. The exsolved Cu,Na-Rho showed improved performance in CO₂/CH₄ breakthrough tests, producing pure CH₄ with improved uptake and CO₂/CH₄ selectivity compared to that of Cu_4.9-Rho.     

Fluorescent dendritic polymers and nanostructured coatings for the detection of chemical warfare agents and other analytes

Polyamidoamine (PAMAM) dendrimers of generations zero (G0) to four (G4), and a hyperbranched polyurea (HB‐PU), were functionalized with 1,5‐dansyl (1,5‐D), 2,5‐dansyl (2,5‐D), 2,6‐dansyl (2,6‐D) and nitrobenzofurazan (NBD) fluorophores that change their fluorescence emission wavelength in response to chemical environment, and the resulting dendritic polymers were characterized by MALDI‐TOF mass spectrometry, ¹H NMR, ¹³C NMR, and fluorescence spectroscopy. Fluorophore‐functionalized dendritic polymers were then reacted further with 3‐acryloxypropyldimethoxymethylsilane (AOP‐DMOMS) at various fluorophore to DMOMS substitution ratios. The resulting materials were cast onto glass slides, and cured into robust nanostructured coatings. Coatings with 50% fluorophore–50% DMOMS substitution showed the strongest fluorescence and the best physical properties. Coated coupons were tested against a wide range of analytes including the chemical warfare agent simulants dimethyl methylphosphonate (DMMP) and chloroethylethylsulfide (CEES), and the water‐methanol‐ethanol series. It was found that the ability of the coatings to distinguish between analytes decreased with increasing cross‐link density for both dendrimer and hyperbranched polymer‐based coatings. It was also found that the percent fluorophore substitution and the type of dendritic polymer carrying the fluorophore had no significant effect upon fluorescence emission wavelength, but fluorescence emission wavelength became less dependent upon solvent with increasing dendrimer generation and molecular mass. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5101–5115, 2009     

Liquid crystal and solution phases of sodium dodecyl-p-benzene sulphonate (NaLAS) and octa-oxyethylene glycol hexadecyl ether (C16E8): 1:1 mixtures in water

The liquid crystals and other phases formed when the mixed surfactant system sodium dodecyl-p-benzene sulphonate (NaLAS) and octa-oxyethylene glycol hexadecyl ether (C₁₆E₈, 1:1 by weight) is dispersed in water have been investigated using optical microscopy, X-ray diffraction and differential scanning calorimetry. Despite the fact that neat LAS is a multi-phase solid and C₁₆E₈ is a crystalline solid, when the two are mixed at temperatures above the melting temperature of the C₁₆E₈ with no water present, what appears to be a metastable gel phase formed containing only a small volume fraction of un-dissolved LAS (ca. 5%). Moreover, when water is added to the system, the phase behaviour of the mixture considerably differs to that of either of the individual components. We report a detailed phase study on this mixture here particularly focussing on the ‘neat’ mixture. The phase behaviour when water is added is also discussed. Particularly interesting is the presence of a micellar phase between the hexagonal and lamellar phases thought to be due to weak interactions between micelles during the transition from rods to discs. In addition, the presence of a low temperature intermediate phase is discussed.     

An efficient process for synthesizing and hydrolyzing a phosphonated methacrylate: Investigation of the adhesive and anticorrosive properties

A new phosphonated methacrylate, namely dimethyl(methacryloyloxy)methyl phosphonate (MAPC₁), has been synthesized using paraformaldehyde and potassium carbonate according to the Pudovik reaction. The quantitative synthesis of MAPC₁ was followed by selective hydrolysis of the ester group with sodium bromide to replace NaI (imparting non‐negligible ecological impact). Pure MAPC₁(OH) was obtained in high yield and efficiently copolymerized with MMA. The r₁ for MAPC₁(OH)) and r₂ (for MMA) values are 0.99 and 1.02, respectively, which indicates that the monophosphonic groups are statistically linked to the methacrylate backbone. When blended with PVDF, MMA/MAPC₁(OH) copolymers show very good adhesion promoters in both dry and wet conditions and subsequently provide good anticorrosive properties. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4794–4803, 2008     

Etude de L'oxydation de Polyethylenes Par Analyse Thermique Identification des produits de dégradation par infra-rouge

The oxidation of pure and recycled polyethylene samples was studied by thermal analysis (DTA-TG-DSC): presence of two exothermic peaks and mass loss. The thermo-oxidation products, containing C-O and C=O links, were identified by IR spectrometry and GC-MS spectrometry. The oxidation is easier from low to high density polyethylene. This revised version was published online in July 2006 with corrections to the Cover Date.     

[bmim][OTf]: a versatile room temperature glycosylation promoter

[bmim][OTf] is a versatile, ionic liquid promoter for the room temperature glycosylation of both thiophenyl and trichloroacetimidate glycoside donors; the conditions are mild, with no requirement for molecular sieves, and are compatible with a wide range of donors and protecting groups.     

Green–Lazarsfeld's conjecture for generic curves of large gonality

We use Green's canonical syzygy conjecture for generic curves to prove that the Green–Lazarsfeld gonality conjecture holds for generic curves of genus g, and gonality d, if g/3<d<[g/2]+2. To cite this article: M. Aprodu, C. Voisin, C. R. Acad. Sci. Paris, Ser. I 336 (2003).