Consultation de médecins généralistes sur l'euthanasie (approches éthique et législative en France et en Europe)

AIX-MARSEILLE2-BU Méd/Odontol. (130552103) / SudocPARIS-BIUM (751062103) / SudocSudocFranceF

A Comparative Study of Dibenzylideneacetone Palladium Complexes in Catalysis

Commercial Pdx(dba)y from various suppliers was found to vary considerably in appearance, homogeneity, purity, and catalytic activity. The Buchwald–Hartwig amination of 4-bromoanisole (5) with aniline (6) was established as a sensitive test reaction to probe the efficiency of Pdx(dba)y batches in catalytic transformations. The yields obtained with 17 different Pdx(dba)y batches ranged from 10% to nearly quantitative and could not be predicted reliably on the basis of any physical or spectroscopic descriptor alone. The best results in the catalytic test reaction were consistently achieved with a self-made slowly crystallized Pd2(dba)3·toluene adduct. A protocol is disclosed that allows batches of Pdx(dba)y with unsatisfactory or inconsistent performance to be converted into this reliable precatalyst

Viscosity of ring polymer melts

We have measured the linear rheology of critically purified ring polyisoprenes, polystyrenes, and polyethyleneoxides of different molar masses. The ratio of the zero-shear viscosities of linear polymer melts η0,linear to their ring counterparts η0,ring at isofrictional conditions is discussed as a function of the number of entanglements Z. In the unentangled regime η0,linear/η 0,ring is virtually constant, consistent with the earlier data, atomistic simulations, and the theoretical expectation η0,linear/ η0,ring = 2. In the entanglement regime, the Z-dependence of ring viscosity is much weaker than that of linear polymers, in qualitative agreement with predictions from scaling theory and simulations. The power-law extracted from the available experimental data in the rather limited range 1 < Z < 20, η0,linear/η0,ring ∼ Z 1.2±0.3, is weaker than the scaling prediction (η0,linear/η0,ring ∼ Z 1.6±0.3) and the simulations (η0,linear/ η0,ring ∼ Z2.0±0.3). Nevertheless, the present collection of state-of-the-art experimental data unambiguously demonstrates that rings exhibit a universal trend clearly departing from that of their linear counterparts, and hence it represents a major step toward resolving a 30-year-old problem. © 2013 American Chemical Society