Radiation‐grafted ion‐exchange membranes: Influence of the initial matrix on the synthesis and structure

A series of commercial fluoropolymer films was irradiated with an electron beam, grafted with styrene, and sulfonated. The influence of the initial fluoropolymer on the grafting yields and the properties of the grafted and sulfonated membranes were investigated. The same synthesis procedure can be followed for most fluoropolymers and samples with a similar degree of grafting, and a homogenous polystyrene distribution can be prepared by varying the absorbed dose. The main difference among different fluoropolymer‐based membranes is the water uptake from liquid water that has a roughly linear dependence on the crystallinity of the sample. The more amorphous the initial material, the greater the water uptake. Mechanical properties of the membranes at 50% relative humidity differ less than those of the starting materials and are comparable to those of Nafion® 105. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3008–3017, 2001     

Imprinted diffractive optics for terahertz radiation

Terahertz diffractive optic elements have been fabricated in polypropylene by imprinting with a silicon master. A silicon master is created with eight phase levels for high diffraction efficiency and etched using inductively coupled plasma reactive ion etching. This technique enables the rapid replication of complex optical structures in a high transmission material. Excellent replication of multilevel high efficiency Fresnel lenses is shown. The resulting lenses were tested with a 2 THz quantum cascade laser. The signal strength at the focus was 70 times the base signal strength.     

New polymer electrolyte membranes for low temperature fuel cells

Partially fluorinated proton exchange materials were synthesised by pre-irradiation grafting of styrene into poly(vinylidene fluoride) films with subsequent sulfonation. The grafted and sulfonated membranes, PVDF-g-PSSA membranes, have been studied with respect to water uptake, ion and water clustering, ion conductivity and water diffusion coefficients. Water associates with the membranes in three different ways: bound non-freezable water, freezable bound water and freezable free water. The proton conductivity of the membrane is strongly dependent on the hydration, it decreases more rapidly than the water self diffusion with decreasing water content. Ion clusters with a Bragg distance of 25 Å form the conducting channels in the membranes.     

A mild Pummerer-like reaction of carbohydrate-based selenoethers and thioethers involving linear ozonide acetates as putative intermediates

Pummerer-like rearrangements of carbohydrate-based heterocycles containing selenium and sulfur were investigated. To the best of our knowledge, this is the first report on the Pummerer rearrangement in selenoheterocycles. Ozonization of 1,4-anhydro-D-galactitol or 1,5-anhydroxylitol derivatives containing sulfur or selenium as the ring heteroatom gave unstable intermediates that were attributed to ozonides. These intermediates decomposed upon warming to give selenoxides or sulfoxides. Significantly, addition of acetic anhydride at low temperature to the ozonization reaction mixtures gave Pummerer-rearrangement products after warming to ambient temperature. However, when the isolated selenoxides or sulfoxides were treated with acetic anhydride, Pummerer rearrangement occurred but the sulfoxides required much higher reaction temperatures. The latter results are at variance with the former and are interpreted in terms of the rearrangement of the ozonide acetate intermediates in the former cases. To probe whether the rearrangement proceeded heterolytically via extrusion of singlet oxygen or homolytically via the generation of radical species, trapping experiments with rubrene and electron paramagnetic resonance (EPR) studies with the radical trap DMPO were performed. The results of these experiments are consistent with the intermediacy of radical species and suggest a new and milder synthetic method to generate Pummerer-type products.