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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.

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.

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.

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.