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It is shown that Raman spectra and thermal analysis data (TGA and DSC) both discriminate among the hydroxycarbonate precursors that lead to successful Cu Zn - containing catalysts and those that lead to inactive catalysts. For binary Cu/Zn catalysts, the optimum precursor is single-phase three-dimensional aurichalcite, (Cu,Zn)5(OH)6(CO3)2, which is readily distinguished by these techniques from undesirable precursor materials such as copper hydroxynitrate [Cu2(OH)3NO3], rosasite [(Cu,Zn)2(OH)2CO3] and hydrozincite [Zn5(OH)6(CO3)2]. Ternary Cu Zn/Al catalysts are successfully made via a layer-structured hydrotalcite-like precursor, i.e., (Cu,Zn)6Al2(OH)16CO3·4H2O. Thermal decomposition and infrared analyses indicate that the interlayer carbonate anion is retained by the ternary catalyst even to calcination temperatures of 350–450 °C, which has implications for the subsequent aqueous surface doping treatments used to further promote these catalysts

Surface morphology and compositions of multiblock and starblock copolymers of poly(a-methyl styrene) (PMS) and poly(dimethyl siloxane) (PDMS) were investigated by cross-sectional transmission electron microscopy, angle- and energy-dependent ESCA, and infrared spectroscopy. The extent of surface segregation of PDMS was determined for multiblock and starblock copolymers to depth of 210{angstrom}. No surface excess was with high PDMS bulk concentrations (60 wt%) have a highly oriented lamellar morphology in the near air surface region, and the topmost air surface region (27 {angstrom}) is exclusively composed of PDMS. The PMS-PDMS block copolymers with lower PDMS bulk concentrations (40 wt%) have lesser or no domain orientation and the surface region includes detectable PMS.

The surface segregation of poly(dimethylsiloxane) (PDMS) in chloroform solution cast films of styrene and dimethylsiloxane block copolymers in AB diblock and ABA and BAB triblock types was investigated by ESCA and ATR-FTIR spectroscopy. The results show that the PDMS surface segregation is mainly dependent on the architectures of the block copolymers and the PDMS block length. AB-type diblock copolymers exhibit a relatively thicker pure PDMS surface layer and the PDMS surface segregation effects swere detected up to the ATR-FTIR sampling depth

A linear relationship between fractional surface excess of PDMS (Ψ) and PDMS block length (N A ), Ψ=α'-β'N A -1/2 , is found for the PS-PDMS-PS type triblock copolymers from ESCA results over three different sampling depth, ranging from 27 to 103 A. The effect of PDMS surface segregation Ψ is compared within the PS-PDMS diblock, PS-PDMS-PS and PDMS-PS-PDMS triblock copolymer series as N A changes. At similar bulk composition, the PDMS segments in the diblock copolymers are the most apt to segregate in the free surface region, while the PDMS segments of the triblock copolymers are the least probable to segregate.

The ESR spin-probe technique with the use of the nitroxide probe 2, 2, 6, 6-tetramethyl-4-hydroxypiperidin-1-oxyl benzoate (BzONO), has been used to study Tg variation in a series of polystyrenes of varying molecular weight and molecular weight distribution. Glass temperatures, as determined by ESR, for “monodisperse” polystyrenes vary smoothly as a function of molecular weight. From results on polystyrene binary blends it is shown that the technique is responsive to M n rather than M w. Data obtained by ESR are shown to agree with conventional DSC measurements. Some advantages, limitations, and implications of the technique are also presented and discussed. The actual shapes of extrema separation vs. temperature plots are functions of molecular weight (becoming broader as molecular weight increases) and are discussed in terms of free volume effects.

Role d'espaceur inerte des motifs chlorure de vinylidene qui diminuent les associations intramoleculaires entre les dipoles carbonyl des motifs MMA du copolymere. Stabilite thermique minimale des copolymeres lorsque le nombre de motifs MMA et VDC adjacents est maximal; degradation thermique via une cyclisation intramoleculaire et perte de HCl pour donner une lactone a 5 chainons insatures

Copolymers of ethylene with hexene-1 have been prepared by catalytic polymerization. Three types of specimens were studied: (a) as the polymerized material; (b) the same after extraction with heptane; (c) the low molecular weight extract. These specimens were subjected to one or more of the following characterization techniques: Mn by several methods, X-ray diffraction, GPC, DSC, Rheovibron at 110 Hz, and Tg by an ESR spin probe technique. The hexene content of the extracted polymer did not exceed 4 mol%; that in the extract was as high as 89.5%. The characterization data and dynamic mechanical loss results in this paper have been examined in the context of an exhaustive study of ethylene-ethylene-α-olefin copolymers by Shirayama et al. with some additional details by Wilson et al. All Tg data are summarized in the form of a plot of temperature vs log (wt% hexene-1). It is emphasized that increasing hexene content decreases crystallinity, crystallite size and molecular weight, so that caution is required in interpreting results. For high mol wt low hexene-1 whole and extracted polymers, the spin probe method gives Tg for the amorphous phase whereas Rheovibron data reflect Tβ( >Tg) for the composite amorphous-crystallite specimens. The ESR data indicate that Tg for amorphous PE, called Tg(L), is very close to 200 K which is above and distinct from Tγ at c, 150 K. It would still be desirable to investigate a series of ethylene-hexene-1 copolymers over the entire composition range at essentially constant, high molecular weight.

ESR spin-probe values of glass temperatures are reported for a series of di-, tri-, and radial block copolymers. With one exception, in which the hard phase is poly(t-butylstyrene), the hard component is polystyrene (PS); the soft components include polybutadiene (PBD), polyisoprene (PI), hydrogenated PBD, hydrogenated PI, and poly(dimethyl siloxane) (PDMS). Tg's of the soft phase are in general agreement with those of the respective high molecular weight homopolymers; Tg's of the hard phase generally deviate widely from those of corresponding high molecular weight homopolymers. This deviation is interpreted in teens of a number of factors, including, the molecular weight of the hard phase, differences in solubility parameters for the two phases, percent of the hard phase present, and the presence of crystallinity. Comparison of Tg's determined by ESR with Tg's from dynamic mechanical methods on S-B-S triblocks of similar composition demonstrates that the ESR method is measuring the Tg of the interpliase and hence, in principle, its composition.

The conversion of an appropriate terminal alkene to a 1,2-epoxyalkane by Pseudomonas oleovorans introduces students to the techniques used in carrying out chemical conversions employing microorganisms.

The authors have devised an experiment which fulfills a number of pedagogical objectives: it combines organic, biological and quantitative techniques; the capability of completion in 2-3 3-hour per...

This experiment involves carrying out a photochemical irradiation and subsequent determination of the number and types of products produced.

Irradiation of dibenzyl diselenide (l) with 350 nm light in the presence of oxygen afforded benzaldehyde and elemental selenium, whereas irradiation in the absence of oxygen produced dibenzyl monoselenide (ll); irradiation of dibenzyl triselenocarbonate (III) produced dibenzyl diselenide.