Materials Science

In this work MAPO-11 molecular sieve was prepared with several degrees of magnesium substitution. The syntheses were carried by using phosphoric acid, pseudo-boehmite and magnesium acetate as sources of structural elements and diisopropylamine as the structure-directing agent. The samples were characterized by powder X-ray diffraction, thermogravimetry, infrared spectroscopy, solid-state nuclear magnetic resonance, scanning electron microscopy and elemental analysis. The X-ray diffractograms indicate that the AEL structure is obtained free of contaminating phases up to a magnesium molar ratio of 0.3 in the reaction mixture. Higher levels of magnesium cause the formation of other phases. Thermogravimetry, MAS nuclear magnetic resonance of 31P and infrared spectroscopy confirm the magnesium isomorphous substitution for aluminum up to this magnesium content in the reaction mixture.

Proton and sodium-23 spectra are reported on acid and sodium neutralized forms of the perfluorosulfonate ionomer (Nafion), respectively. This local structural view is compared with pulse field gradient diffusion measurements of water, methanol and dimethyl methylphosphonate (DMMP) in several Nafion films. Both the proton and sodium-23 spectra indicate that the counter ions are primarily in clusters or aggregates with no evidence for isolated ions. The proton resonance from the sulfonic acid group reflects hydrogen bonding but these protons rapidly exchange with sorbed water. There is also evidence for small amounts of water not in contact with the ionic clusters. Pulse field gradient diffusion measurements of water show little evidence of tortuous diffusion though a tortuous pathway might be expected for diffusion through domains of ionic clusters. A cast film shows greater evidence of a tortuous pathway than commercially prepared Nafion sheets though the level of tortuosity is still low. Methanol diffusion shows more tortuosity in both commercial films and cast films with the most tortuosity in a cast film containing fumed silica nanoparticles. Even greater tortuosity is observed for DMMP. The greatest tortuoisty is observed for DMMP in cast films with nanoparticles and this is an improvement in terms of potential applications of Nafion in chemical protection. Though the high-resolution proton spectra show only modest differences between commercial film, cast film and nanocomposite film, more significant structural changes on a larger length scale are detected in the pulse field gradient NMR experiments. Cast films may display more tortuous diffusion because of better-organized domains of ionic groups, backbone units and side chains even though this is not clearly indicated by focusing on the structure of the ionic cluster itself.

Fluorine-19 NMR was used to study the structure and mobility of the perfluorosulfonate ionomer Nafion (Dupont trademark) in the presence of dimethyl methylphosphonate (DMMP). Fluorine-19 resonances arising from the ionomeric side chain narrowed rapidly with increasing DMMP content while the resonances arising from the perfluoroethylene backbone units remained broad. The plasticization of the side chains indicates that the DMMP is primarily associated with this structural unit which forms its own nanophase in Nafion. To further characterize the morphological structure, fluorine-19 spin diffusion experiments between the side chain and backbone resonances were performed. At low DMMP content, swelling of the pendant group domain is observed while at higher concentrations an unusual change in the spin diffusion indicates the development of a new morphology consisting of larger domains associated with the pendant group plus DMMP. To augment information on this system, proton pulse field gradient experiments were performed as a function of concentration and temperature to obtain DMMP self-diffusion constants. In the same concentration range where morphological change occurred, there was a rapid rise in translational mobility of the DMMP. This reflects the influence of the new larger domains which allow longer range motion of DMMP with fewer obstructions from the backbone domains which are relatively impermeable to DMMP. A fraction of the smaller domains originally present in dry Nafion remain even at high levels of DMMP, indicating an inability of all of the Nafion to undergo the morphological transition to the larger domains.

Pulse field gradient (PFG) NMR measurements of diffusion in heterogeneous solid polymer systems provide a measure of the structure influencing translational motion. The influence of structure leads to a dependence of the apparent diffusion constant on the time over which diffusion is observed. The effects of structural heterogeneity have been observed for penetrant diffusion in random copolymers, 2-4 polymer blends, 5 nanocomposites, 6,7 and dispersed oil drops in polymers. The structure is not regular or well-defined in these systems so observing diffusion in a strongly segregated block copolymer with a well-defined morphology would be informative. The effect of morphology on diffusion in block copolymers has been considered before, 9 but NMR allows for the diffusion to be viewed directly over a range of length scales. Diffusion in solutions of block copolymers has been examined by PFG NMR; 10,11 however, the case for consideration here is the solid where the morphology of a cast film is retained and only swollen with a selective penetrant. The system selected for study is a SEBS triblock polymer: poly(styrene)block-poly(ethene-co-but-1-ene)-block-poly(styrene) with a molecular weight of 49K and styrene end blocks of 16K. With a styrene content of 66 wt %, a morphology consisting of hexagonally packed rubbery ethylene butylene (EB) rods in a glassy polystyrene (PS) matrix is expected. The penetrant selected for this study is 2,2,4-trimethylpentane (TMP) which has a low solubility in PS and a high solubility in EB rubber. The measured solubility in polystyrene is 2.85 and 227 wt % in the SEBS triblock under study, which implies a solubility of 625 wt % in the EB rubber. The diffusion of TMP is expected to be of the order of 10 -7 cm 2 s -1 in the EB rubber 15 and 10 -14 cm 2 s -1 in glassy PS. The combination of the solubility and diffusion differences ensures that the conductive phase will be the EB rubber and the surrounding PS will act as a barrier. Although cylinders are the expected morphology, similar PFG NMR results are expected for lamella as well. The large solubility and diffusivity difference between the two domains is an ideal circumstance for observing the influence of morphological structure on the translational motion of a penetrant.

Poly(ethylene glycol) distearate (PEGD) complexed with lithium perchlorate has been studied by NMR, SAXS, DSC, and Polarized-Light Optical Microscopy (PLOM). Unlike other polymer electrolytes, highly Lithium-doped PEGD samples exhibit sharp Li-7 NMR quadrupolar powder patterns even at temperatures well above the melting point, indicating that this copolymer is microphase separated and the dynamics in the poly(ethylene glycol) (PEG) phase are anisotropic. Measurements of the Li-7 central transition linewidth in highly doped samples show three distinct line narrowings, due to the PEG glass transition ( 20°C), the stearate melting point of the polymer ( 35°C), and an order-disorder transition ( 72°C). SAXS, DSC, and PLOM confirm the presence of a microphase-separated state up to 72 °C. C-13 and H-1 NMR show that the segmental mobility in the ordered state is reduced compared to the isotropic melt. The results confirm the previously proposed order-disorder model to explain the dependence of the ionic conductivity on the lithium concentration for Lithium-doped PEGD samples.

The aim of this work was to study the hydrothermal synthesis of Si and SiAlMCM-41 performed under both autogenic pressure and refluxing conditions. XRD data showed that the MCM-41 phase may be formed by both processes and that the synthesized material in the presence of Al and/or under reflux presents the hexagonally arrangement of less ordered mesopores. However, as verified by XRD and physisorption data, the order was improved with higher synthesis times. 29 Si and 1 H - 29 Si C/P MAS NMR spectra showed that a great part of the Si atoms exists as silanol groups which originate resonance peaks at -110, -100 and -91 ppm. The presence of Al atoms may generate Si(3Si, Al) and Si(2Si, 2Al) environments which might be contributing to resonance peaks at -100 and -91 ppm. The 27 Al MAS NMR spectrum of the as synthesized AlSiMCM-41 showed a resonance peak of tetrahedral framework aluminum close to 53 ppm and two others, one close to 14 ppm attributed to Al(H2O)6 +3 species and the other a weak signal close to 32 ppm attributed to pentacoordinated Al. 27 Al MAS NMR spectra of the calcined sample showed a peak at 0 ppm corresponding to an hexacoordinated extra-framework aluminum formed during calcination.

A novel porous silica matrix has been prepared from Pyrex glass, using hydrothermal treatment under saturated-steam condition. This process makes it possible to obtain, in one step, a silica support formed of a homogeneously distributed and interconnected macropore microstructure. The new matrix contains silanol groups that can be used in reactions of surface modification to provide a hybrid material and a selective macrofiltration membrane, and also it can improve chemical inertness. The porous matrix is noncrystalline as obtained and, after thermal treatment at temperatures higher than 950°C, exhibits an X-ray pattern characteristic of α-cristobalite and low volume contraction. The present samples were characterized by scanning electron microscopy, mercury intrusion porosimetry, nitrogen adsorption-desorption isotherms, infrared spectroscopy, X-ray powder diffractometry, atomic absorption, and high-resolution solid-state nuclear magnetic resonance. The results present a new way of producing a macroporous silica matrix.

Typically, phenylethynyl (PE) end-capped oligomides require a temperature of 370 C for 1 h to develop a crosslinked system. A published method using poly(ethylene glycol)s (DM-PEG-250 and PEG-400) as cosolvents with NMP was effective in crosslinking the ethynyl end-caps at 250 C/3 h in nonsulfonated oligomides. The application of this novel crosslinked method to PE end-capped sulfonated oligomides was effective but caused a secondary crosslinked network via the sulfonic acid groups and ethylene glycol solvents. The solid-state 13 C NMR spectral data on 13 C-labeled end-caps in the PE-3F-SPI-3 oligomide provide evidence for the ethynyl to ethynyl and ethylene oxide sulfonate ester dual crosslinked structure. Infrared spectroscopy of model compounds also provides evidence for the presence of crosslinked sulfonate ester and appended sulfonate ester side chains. 13 C NMR also provided quantitative data on the extent of the ethynyl to ethynyl crosslinking reaction and sulfonate ester crosslinks and side chains. V C 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 4476-4491, 2011

A relatively low-temperature crosslinking method for phenylethynyl (PE) end-capped oligomides was developed. PE end-capped oligomides are typically cured into crosslinked polyimides at 370 C for about 1 h. The addition of a low viscosity mixed-solvent of N-methylpyrrolidinone (NMP)/dimethyl ether of polyethylene glycol (M ¼ 250 g/mol), NMP/DM-PEG-250, or NMP/polyethylene glycol (M ¼ 400 g/mol), NMP/PEG-400, as film forming medium for PE-end-capped oligomides was investigated. Fourier transform infrared spectroscopy and 13 C NMR showed that the mixed solvent addition was effective for achieving low-temperature crosslinking of the ethynyl endcaps over the temperature range 200-250 C. The low temperature crosslinking process was explained by thermolysis of the PEG molecules over this temperature range forming free radical species such as $CH 2 CH 2 OÁ or $CH 2 CH 2 Á which initiate cure of the ethynyl groups resulting in a cross linked polyimide membrane. The PEG solvents also provide a radical source for the degradation polymerization of the solvents to a water and NMP insoluble polymer, which formed a miscible blend with the crosslinked membrane. Glass transition temperature (differential scanning calorimetry) data and thermo gravimetric analysis data provide evidence for the miscible blend.

Dispersed metal nanoparticles synthesized by functionalization of complex on SBA-15. The growth of Ru, Cu, Zn or Co nanocrystals oxides onto SBA-15 was observed. Solids highly actives for 1-hydroxyacetone production. RuO 2 or Co 3 O 4 on SBA-15 achieved best results due to the sites strengths in limiting their deactivation by sintering.

Edible and non-edible lipid feedstocks A B S T R A C T This study reports the synthesis, physicochemical characterization by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and solid-state MAS NMR (1 H, 23 Na, 29 Si and 119 Sn MAS NMR) of a metallo-stan-nosilicate and its application as a heterogeneous catalyst for biodiesel production via ethanolysis and metha-nolysis routes using edible, non-edible an waste oils as feedstocks. XRD characterization of the metallo-stan-nosilicate has revealed a typical structure of mixed octahedral-pentahedral-tetrahedral material with an orthorhombic unit cell (a = 14.522 Ǻ, b = 12.469 Ǻ, and c = 10.654 Ǻ). 119 Sn single-pulse MAS NMR results presented two resonance lines, at δ 1 =-683.8 ppm and δ 2 =-690.9 ppm, which were assigned to the tin oc-tahedrally coordinated in the metallo-stannosilicate structure. Heterogenous catalytic studies in the transes-terification of refined edible, non-edible, and waste oils have resulted in high yields of FAMEs and FAEEs (fatty acid methyl and ethyl esters), nevertheless the highest FAMES (98.2%) and FAEEs (96.6%) yields were obtained for non-edible microalgae oil extracted from the genetically modified heterotrophic algal strain Prototheca moriformis. Catalytic studies also using non-edible macaw palm oil (Acrocomia aculeata) with a high content of free fatty acids (FFAs) demonstrated that the catalyst could simultaneously perform esterification and transes-terification reactions. These findings indicate the potential application of this novel metallo-stannosilicate in the production of renewable and environmentally clean biofuels, like biodiesel, using different sources of lipids feedstocks, notably those that do not compete with food production.

We have synthesized a catalytically active polymer inspired by the naturally occurring protein silicatein R and have shown it to catalyze the formation of silica from tetraethoxysilane under near-neutral pH and ambient temperatures. We based the composition of the polymer on the functionalities found in silicatein R, specifically those essential components of the catalytically active site for the hydrolysis of silicon alkoxides. Our bioinspired polymer is a block copolymer of poly(2-vinylpyridine-b-1,2-butadiene), functionalized by the addition of hydroxyl groups via hydroboration chemistry. The catalytic action of our polymer on tetraethoxysilane at neutral pH and ambient temperature conditions has been confirmed using a modified molybdic acid assay method, thermogravimetric analysis, and Fourier transform infrared spectroscopy. The structure of the resulting gel is investigated by scanning electron microscopy and solid-state nuclear magnetic resonance. The microscopic features of the material formed resemble that of gels formed by the acid-catalyzed hydrolysis of tetraethoxysilane.

Vanadosilicates with the structures of ETS-10 and AM-6 microporous materials have been hydrothermally synthesized using organic directing structures agent (SDAs) derivatives of decahydroquinoline, 3,5-dimethyl-piperidine, 2,6-dimethyl-piperidine and (S)-Sparteine. Derivatives of these chiral amines have not been explored before in the sol gel chemistry of vanadosilicates. Physicochemical characterization of the obtained vanadosilicate materials with these different chiral templates was carried out by Xray diffraction (XRD), scanning electron microscopy (SEM), Raman and infrared (IR) spectroscopy, solidstate NMR spectroscopy, and differential thermogravimetric analysis (DTA)/thermogravimetric analysis (TGA). The results suggest that the presence of the chiral organic templates have different effects in terms of the final phase of the synthesized materials and their morphology. The products obtained using chiral template derivatives of decahydroquinoline reveal that certain products might be very enriched with chiral polymorph A while others present structures which are similar to other large-porous vanadosilicate such as AM-6 and AM-13. Derivatives of 2,6-dimethyl-piperidine and 3,5-dimethyl-piperidine have not favored any structure that resembles a chiral polymorph A, but only known vanadosilicates such as AM-6, AM-13. Derivatives of (S)-Sparteine, on the other hand, have not only favored the formation of structures enriched with a large amount of chiral polymorph A, but also their use has resulted in other unknown vanadosilicate structures whose physicochemical characterizations are in progress.