Ionomers for proton exchange membrane fuel cells by sulfonation of novel dendritic multiblock copoly(ether‐sulfone)s

The synthesis and properties of the first examples of dendritic multiblock co PES s, bearing sulfonated dendritic clusters, that form strong membranes are described. End‐capped dendritic multiblock co PES s with various average block lengths (n = 50–80) were synthesized by two‐step reactions. The synthesis of dendritic blocks consisting of difunctional dendritic block and monofunctional dendritic end‐group was accomplished by an aromatic nucleophilic substitution reaction of hexakis(4‐(4‐fluorophenylsulfonyl)phenyl)benzene with varying amounts of 1‐(4‐hydroxyphenyl)‐2,3,4,5,6‐pentaphenylbenzene, which provides a number of pendant phenyl rings as postsulfonation sites. Polycondensation of a controlled molar ratio between 4,4′‐dihydroxybenzophenone and bis(4‐fluorophenyl)sulfone monomers was carried out in the presence of the difunctional and monofunctional dendritic blocks in sulfolane at 215 °C for 3.5 h. Essentially six sulfonic acid groups were introduced into each hexaphenylbenzene moiety on the dendritic blocks by reaction with a large excess of chlorosulfonic acid, followed by hydrolysis with KOH aqueous solution. The introduction of longer average blocks (n = 60–80) into the dendritic PES s improved the mechanical properties of the resulting sulfonated dendritic PES membranes. At a level of IEC (0.92–1.26 meq/g) similar to Nafion (0.91 meq/g), PES membranes showed proton conductivities (58–67 mS/cm) comparable with that of Nafion (99 mS/cm). © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5461–5473, 2009     

Simple technique for texture function analysis in granular thin film media

In this work a simple technique to extract the texture function in granular thin film media is implemented. The technique is based on previous work in which the distribution function of particles easy axes f(α) is calculated from the measured parallel remanence curve (M_rp(β)). In this simple technique we consider that the measured M_rp(β) curve can be fitted to a series of cos(2β), i.e. M_rp(β)=B₀+B₂ cos(2β)+B₄ cos(4β) where the angle β is the angle by which the film is rotated. This approximation is found to be valid when the texture function has a standard deviation >20°. On this basis, the constants B₀, B₂ and B₄ can be determined by using only three data points for the parallel remanence, M_rp(0), M_rp(45°) and M_rp(90°). The new technique is applied to a textured thin film consisting of cobalt ferrite particles 17 nm in diameter and to a commercial Sony video tape. Using this simple technique, the obtained texture functions are found to be similar to those obtained from the full M_rp(β) curves. This new technique will furnish a simple method with which the texture function in 2D systems can be obtained.     

Stereoselective Synthesis of Methoxy Substituted 2, 3-Dibenzylbutyrolactones Via Organic Phosphonates

A highly convergent, short and stereoselective synthesis of a series of methoxy substituted 2, 3-dibenzylbutyrolactones was achieved using a Horner-Wadsworth-Emmons (HWE) reaction as the key step in overall yields above 32%.     

Structure and Synthesis of a New Library of N,N-Bis-[1,2,4]triazol-1-ylmethyl-amino Compounds

New N,N-bis(triazol-1-ylmethyl)amines have been prepared in one step by condensation of 1-(hydroxymethyl)triazole with a series of primary substituted aromatic amines. These reactions were carried out in refluxed CH₃CN for 4 h. The products were recuperated with excellent and good yields (75–90.5%). The x-ray crystallography structure of one of them has been studied.     

Allgemeine Nephelometrie

Ohne Zusammenfassung     

Membrane distillation operated at high seawater concentration factors: Role of the membrane on CaCO3 scaling in presence of humic acid

This study aims at investigating the kinetics of calcium carbonate precipitation (scaling), that occurs in the form of vaterite, when treating seawater by direct contact membrane distillation (DCMD) operated at high concentration factors (from 4 to 6). Induction time measurements carried out by dynamic light scattering (DLS) allowed to identify the shifting between homogeneous and heterogeneous nucleation mechanisms as a function of supersaturation. CaCO₃ interfacial energy, evaluated for concentrated seawater solutions as 45 mJ/m², increased by 7% as a consequence of the inhibition effect of humic acid, and it was reduced to 32 mJ/m² in correspondence of heterogeneous nucleation occurring on microporous polypropylene membranes. Gibbs free energy barrier to the formation of critical nuclei was predicted with good accuracy as a function of physico-chemical properties of the membrane (porosity: 0.70, contact angle: 115 ± 2°).