A method for constructing ordered continua

We present a method for constructing ordered continua. We illustrate our method by constructing (i) a new order-homogeneous non-reversible continuum, and (ii) an ordered continuum with a minimal set of continuous self-maps.     

Chemical effects of (n, γ) nuclear reaction on (Mo6Cl8)Cl4

The chemical effects of⁹⁸Mo(n, )⁹⁹ Mo reaction on molybdenum(II) chloride [(Mo₆Cl₈)Cl₄] have been studied. Retention, thermal and radiolytical annealing were determined. It was found that this molybdenum compound has low retention, a negligible tendency to thermal annealing and a virtual insensitivity to hydrolysis. For practical application in the enrichment of⁹⁹Mo by the Shilard-Chalmers method, molybdenum(II) chloride [(Mo₆Cl₈)Cl₄] appears to offer good prospects.     

Aging and degradation of polyolefins. IV. Thermal and photodecompositions of model peroxides

There appear to be no unusual effects of phase change or near-ultraviolet radiation on the reactions of alkoxy radical models for atactic polypropylene. The oxidation of purified atactic polypropylene by singlet oxygen is not an important process at 50°. Photochemical and thermal cleavages of tert-amyloxy radicals, a model for polypropylene oxy radicals, give nearly the same ratio of k_a/k_d at 50°C. Photochemical cleavage of the model compound 1,1-dinonylethyl hydroperoxide (10-methyl-10-nonadecyl hydropenoxide) gives exclusive cleavage of a nonyl group both in solution and in polypropylene film at 50°C.     

Studies on copolymers of vinyl chloride with diethyl fumarate,isobutylene and vinyl bromide as PVC models with chain irregularities—III The influence of the tacticity and of the copolymer composition on the thermal degradation: The influence of the tacticity and of the copolymer composition on the thermal degradation

The thermal degradation kinetics of pairs of vinyl chloride copolymers with diethyl fumarate, isobutylene and vinyl bromide, having the same composition but different tacticity, were followed by conductivity measurements. From the results for degradation up to 0·3% and up to 10%, it follows that syndiotactic sequences in PVC give rise to high degradation rates in agreement with results of previous work on homopolymers of vinyl chloride. On the basis of kinetic aspects as well as u.v.- visible spectra of degraded samples, the influence of tacticity on the thermal degradation of copolymers is discussed. This effect is compared to that of weak points introduced in the PVC chain by means of copolymerization.     

Universal frames

For a class of frames we define the notion of a universal element and prove that in the class of all frames of weight less than or equal to a fixed infinite cardinal number τ there are such elements.     

Initial Steps in Thermal Degradation of Fractions of PVC with Different Tacticities

PVC samples were prepared in bulk by using AIBN and UV radiation as the initiator system. The polymerization temperatures were 40, 0, -25, and -50oC. The samples were fractionated by means of successive extractions with dioxane, tetrahydro-furan, and cyclohexanone, and two fractions of each sample were characterized in order to study their thermal degradation. This was carried out by conductivity measurements with the use of a differential conductimetry cell for degradations up to 0.1% and a single cell for degradations up to 0.4%. From the UV-visible spectra of equally degraded samples it is concluded that the higher the tacticity of PVC, the higher the proportion of long polyene sequences is; this behavior is independent of the conversion. The degraded samples were ozonized in order to measure the number of scissions per chain. This number was found to be low for syndiotactic samples and high for atactic samples, which is accounted for by the increased clustering of double bonds to form long polyene sequences in the more syndiotactic polymers. Previous results suggesting increased ease of propagation along syndiotactic sequences are therefore confirmed more quantitatively.     

Phase separation of carboxylic acids on graphite surface at submonolayer regime

Mixing behaviour of solid crystalline monolayers adsorbed onto graphite from different mixtures of undecanoic and dodecanoic acids at submonolayer coverage has been investigated. X-ray diffraction measurements have been collected from a variety of compositions as a function of temperature. An extensive phase separation is found for all the compositions – the scattering patterns characteristic of the pure material crystalline structures being preserved across the entire composition range. The temperature dependence of the monolayer melting points and their depression is also clearly indicative of separation of the two surface components, in clear contrast to that expected if the two carboxylic acids mixed ideally in the monolayer.     

Wooden-based materials: Eco-friendly materials for direct mass spectrometric analysis and microextraction

Lignocellulosic materials have arisen as a sustainable alternative in microextraction techniques during the last 10 years. As they are natural materials, their use fits into some of the principles of Green Analytical Chemistry. Their inherent porosity, narrow shape, and rigidity permit their use in ambient ionization mass spectrometry techniques. In particular, the combination of wooden-based materials and direct analysis gives birth to the so-called wooden-tip electrospray ionization mass spectrometry technique. This approach has been used for the direct analysis of complex samples, and as a streamlined tool for fingerprint quality analysis. Also, wooden-based materials can be superficially modified to boost the interaction with target compounds, allowing their isolation from complex samples. This review describes the potential and applicability of direct analysis using lignocellulosic materials, as well as other alternatives related to their use in microextraction.     

Anchoring dyes into multidimensional large-pore zeolites: a prospective use as chromogenic sensing materials

A versatile procedure for anchoring dyes into the pores of multidimensional zeolites by including organic dye precursors in the synthesis gel has been developed. To prove the concept, an aniline-functionalised zeolite Beta was obtained by reaction of triethylorthosilicate (TEOS), tetraethylammonium hydroxide, and N-methyl,N-(propyl-3-trimethoxysilyl)aniline (MPTMSA) in the presence of HF. Further extraction of the structure-directing agents resulted in a highly crystalline, white, functionalised zeolite Beta containing anchored aniline groups. Similar organic functionalised molecular sieves (OFMS) have been explored as novel catalysts, but, as far as we know, OFMS have never been used as precursors for dye-immobilisation or to design new solid-based host systems for selective molecular sensing processes as is reported here. In a second step the solids containing dyes were prepared by reaction of the hybrid material with the appropriate reactives to obtain tricyanovinylbenzene, triphenylpyrylium, azoic, and squaraine derivatives. All these reactions are straightforward and involve electrophilic aromatic substitution or diazotisation reactions at the electron-rich aniline ring. The final dye-functionalised solid materials were isolated by simple filtration and washing procedures and have been characterised by a number of techniques. In all cases the Beta structure of the solid remains unaltered. Among the large number of areas where dye-containing zeolites might be of importance, we were interested in testing their unconventional use as heterosupramolecular hosts in chromogenic protocols. To check their potential use as chemosensors, microporous solids with anchored triphenylpyrilium and squaraine dyes were selected and used as sensors for the chromogenic discrimination of amines. It was found that the response of both solids to amines was basically governed by the three-dimensional (3D) solid architecture that tuned the intrinsic unselective reactivity of the pyrylium dye. By using new solid-state supramolecular chemistry protocols we believe that these, and similar future dye-zeolite hosts, might be promising new sensor materials allowing the visible discrimination of selected target guests by size and/or polarity within families or closely related molecules.