Formation mechanism of Pt particles by photoreduction of Pt ions in polymer solutions

The formation mechanisms of metal particles (platinum (Pt) particles) in an aqueous ethanol solution of poly(N-vinyl-2-pyrrolidone) (PVP) by the photoreduction method have been studied by transmission electron microscopy (TEM) and in situ and ex situ X-ray absorption fine structure (XAFS) analysis. The average diameter of the dilute and concentrated Pt particles in the PVP solution is estimated from TEM to be 2.0 and 2.5 nm, respectively. XAFS analysis was performed for the reduction process of Pt4+ ions to metallic Pt particles for the Pt L3 edge of the colloidal dispersions of the concentrated Pt solutions. The photoreduction process proceeds by the following steps: (1) reduction of PtCl6(2-) to PtCl4(2-), (2) dissociation of Cl from PtCl4(2-), followed by reduction of Pt2+ ionic species to Pt0, (3) formation of a Pt0-Pt0 bond and particle growth by the association of Pt0-Pt0. The reduction of PtCl4(2-) to Pt0 is a slower process, compared with the reduction of PtCl6(2-) to PtCl4(2-). There is a delay between the disappearance of PtCl4(2-) and the formation of Pt0-Pt0 clusters.     

A novel approach to confront electroweak data and theory

A novel approach to study electroweak physics at one-loop level in generic SU(2)_L×U(1)_Y theories is introduced. It separates the 1-loop corrections into two pieces: process specific ones from vertex and box contributions, and universal ones from contributions to the gauge boson propagators. The latter are parametrized in terms of four effective form factors $\bar e^2 (q^2 ), \bar s^2 (q^2 ), \bar g_Z^2 (q^2 )$ and $\bar g_W^2 (q^2 )$ corresponding to the γγ, γZ,ZZ andWW propagators. Under the assumption that only the Standard Model contributes to the process specific corrections, the magnitudes of the four form factors are determined atq ²=0 and atq ²=m _Z ² by fitting to all available precision experiments. These values are then compared systematically with predictions of SU(2)_L×U(1)_Y theories. In all fits α _s (m _Z ) and $\bar \alpha (m_Z^2 )$ are treated as external parameters in order to keep the interpretation as flexible as possible. The treatment of the electroweak data is presented in detail together with the relevant theoretical formulae used to interpret the data. No deviation from the Standard Model has been identified. Ranges of the top quark and Higgs boson masses are derived as functions of α _s (m _Z ) and $\bar \alpha (m_Z^2 )$ . Also discussed are consequences of the recent precision measurement of the left-right asymmetry at SLC as well as the impact of a top quark mass and an improvedW mass measurement.     

Temperature-induced transformations of peroxide radicals formed in polytetrafluoroethylene with γ-ray irradiation

At 200°C, temperature-induced transformations of peroxide radicals from ? CF₂CF(OO·)CF₂? (radical I) to ? CF₂CFCF₂? (radical 1) and ? CF₂CF₂OO· (radical II) to ? CF₂CF₂ (radical 2) in vacuo, and from I to II in oxygen atmosphere were observed. In these thermal transformations, the evolution of CO₂ with a small amount of CO and CF₂O was observed. Further, measurements of the heat of crystallization of the treated polytetrafluoroethylene suggest that a reduction of polymer molecular weight occurs during the transformations from I to 1 and I to II.     

Anionic polymerization of N-substituted maleimide. II. Polymerization of N-ethylmaleimide

Anionic polymerization of N-ethylmaleimide (N-EMI) was carried out with potassium t-butoxide, lithium t-butoxide, n-butyllithium, and ethylmagnesium bromide as initiators in THF and in toluene. An almost quantitative yield of poly(N-EMI) was obtained with potassium t-butoxide as initiator in THF in a wide range of polymerization temperatures. Initiators possessing lithium as counter cation produced poly(N-EMI) in slightly lower yields and ethylmagnesium bromide gave the polymer only in less than 35% yield in THF. As a polymerization reaction solvent, THF was preferable for the polymerization of N-EMI compared with toluene with respect to polymer yields. Poly(N-EMI) obtained with anionic initiators exerted unimodal molecular weight distribution. From ¹H- and ¹³C-NMR spectra of poly(N-EMI) anionic polymerization of N-EMI with potassium t-butoxide was revealed to proceed at carbon–carbon double bond. t-Butoxide system was found to have a “living” polymerization character, i.e., the observed average degree of polymerization was in good agreement with the one calculated from the initial molar ratio of N-EMI/initiator and the yield of polymer.     

Effect of acetylene on the γ-radiation-induced polymerization of ethylene

The effects of acetylene on the γ-radiation-induced polymerization of ethylene were studied from the viewpoint of the gaseous products and polymer structure. The experiments were carried out under a pressure of 400 kg/cm²; the temperature was 30°C; the does rate was 1.1 × 10⁵ rad/hr; and the acetylene content was 0–20%. The solid polymer was obtained in the polymerization of ethylene containing 2.2% acetylene, while the monomer containing 19.7% acetylene gave a yellowish viscous oil. The polymer yield and molecular weight decreased remarkably with acetylene content. The main gaseous product was hydrogen, and trace amounts of butane, butene-1, butadiene-1,3, and benzene and its derivatives were also observed. The rate of formation of hydrogen was almost independent of acetylene content and there was no difference in acetylene contents before and after the irradiation was found. The infrared spectra of the polymers showed the presence of vinylidene, trans-vinylene, and terminal vinyl unsaturations, 1,4-disubstituted benzene, and carbonyl groups. The contents of trans-vinylene, terminal vinyl, and methyl groups increased with acetylene content, and that of vinylidene was independent of acetylene content. The monomer reactivity ratios of ethylene and acetylene were evaluated as 45.5 and 66.0, respectively. On the basis of the results, the effects of acetylene on the γ-radiation-induced polymerization of ethylene were discussed.     

SmI2-induced reductive cyclization of optically active β-alkoxyvinyl sulfoxides with aldehyde

SmI₂-induced reductive cyclization of optically active (E)- and (Z)-β-alkoxyvinyl sulfoxides with aldehyde was developed for the construction of several stereoisomers of tetrahydropyran derivatives.     

Effect of oxygen on the γ-radiation-induced polymerization of ethylene

The effects of oxygen on the γ-radiation-induced polymerization of ethylene were studied at a temperature of 30°C.; the pressure was 400 kg./cm.², the dose rate was 1.9 × 10⁵ rad/hr.; and oxygen content was from 1–2000 ppm. The main product was solid polymer, and no liquid product was found. The gaseous products were hydrogen, acetylene, higher hydrocarbons, carbon dioxide, aldehydes, and acids. Several kinds of carbonyls similar to those formed in γ-ray oxidized polyethylene were observed in the polymer. The polymer yield and the degree of polymerization decreased markedly with increasing oxygen content, while the amount of carbonyls in the polymer increased. The number of moles of polymer chain and the amounts of hydrogen and acetylene were found to be almost independent of the oxygen content. The polymerization of pure ethylene was not affected by carbon dioxide and formic acid. On addition of acetaldehyde, the polymer yield and the degree of polymerization decreased markedly, while the number of moles of polymer chain increased. In the polymerization of ethylene containing oxygen, both the rate of oxygen consumption and the carbonyl content of the polymer increased, while the inhibition period decreased by the addition of acetaldehyde. It was found that the degree of polymerization after the inhibition period is almost independent of the reaction time in the presence of acetaldehyde, while it increases with the time in the absence of acetaldehyde.     

A Complete Frequency-Field Chart for the Antiferromagnetic Resonance in MnF2

Antiferromagnetic resonance (AFMR) measurements on a well characterized single crystal sample of MnF₂ have been performed using various kinds of millimeter and submillimeter sources up to 570 GHz and a superconducting magnet up to 20 T. All the AFMR modes predicted from the theory have been observed. We report a complete frequency-field chart for these AFMR modes.