Electron depletion in mesic atoms

Assuming there is no serious electron depletion in mesic atoms, most previously calculated Auger electron spectra for nuclear emulsion have ignored a large low energy (18–25 keV) contribution. A method for investigating electron depletion in mesic atoms is suggested.     

Pressure–Volume–Temperature properties of polyolefin liquids and their melt miscibility

The pressure–volume–temperature (P–V–T) properties of a number of metallocene-produced polyolefins were measured experimentally at 10 MPa ≤ P ≤ 200 MPa and 30°C ≤ T ≤ 220°C in a dilatometer-type P–V–T apparatus. These included ethylene copolymers typical of linear low density polyethylene, with several α-olefins as comonomers and a wide range of comonomer content. The experimental P–V–T data were correlated with the equations of state from the Sanchez–Lacombe and Flory–Orwoll–Vrij theories. The solubility parameter map of the polyolefins, at atmospheric pressure, was established on the basis of the thermodynamic data. As the temperature increases, the solubility parameter of the polyolefin decreases. The solubility parameters of copolymers of ethylene with propylene, butene, hexene, and octene under constant temperature are all more or less the same at equal weight percent of comonomer. As the incorporation of branches increases, the solubility parameter decreases. The melt miscibility of the polyolefin blends can be predicted to design various blend products for specific applications from this solubility parameter map. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2835–2844, 1999     

Negative muons as solid state probes

Abstract

It is shown that the use of negative muons as solid state probes is complicated by the de-excitation scheme of muonic atoms. A comparison with some recent radiation damage experiments suggest that the μ^? atom (at least in silicon) is displaced to an interstitial position.     

In situ measurement of the glass transition temperature of polymers with compressed fluid diluents

In situ measurement of the creep compliance of poly(methyl methacrylate) (PMMA) and poly(ethyl methacrylate) (PEMA), equilibrated with a pressurized CO₂ phase, is used to determine the glass transition temperature. Corrections due to dilation of the polymer by CO₂ as well as the buoyancy are assessed. Both polymer systems exhibit a recently discovered phenomenon, retrograde vitrification, in which a liquid polymer becomes a glass with an increase in temperature. The experimental results are predicted semi-quantitatively in terms of the temperature and pressure effects on the solubility of the compressed fluid in the polymer. © 1994 John Wiley & Sons, Inc.     

Reaction of ketones with lithium hexamethyldisilazide: competitive enolizations and 1,2-additions

Reaction of 2-methylcyclohexanone with lithium hexamethyldisilazide (LiHMDS, TMS(2)NLi) displays highly solvent-dependent chemoselectivity. LiHMDS in THF/toluene effect enolization. Rate studies using in situ IR spectroscopy are consistent with a THF concentration-dependent monomer-based pathway. LiHMDS in pyrrolidine/toluene affords exclusively 1,2-addition of the pyrrolidine fragment to form an alpha-amino alkoxide-LiHMDS mixed dimer shown to be a pair of conformers by using (6)Li, (15)N, and (13)C NMR spectroscopies. Rate studies are consistent with a monomer-based transition structure [(TMS(2)NLi)(ketone)(pyrrolidine)(3)](). The partitioning between enolization and 1,2-addition is kinetically controlled.