Atom transfer radical polymerization of sodium2‐acrylamido‐2‐methylpropanesulfonate

The first example of well‐controlled atom transfer radical polymerization (ATRP) of a permanently charged anionic acrylamide monomer is reported. ATRP of sodium 2‐acrylamido‐2‐methylpropanesulfonate (NaAMPS) was achieved with ethyl 2‐chloropropionate (ECP) as an initiator and the CuCl/CuCl₂/tris(2‐dimethylaminoethyl)amine (Me₆TREN) catalytic system. The polymerizations were carried out in 50:50 (v/v) N,N‐dimethylformamide (DMF)/water mixtures at 20 °C. Linear first‐order kinetic plots up to a 92% conversion for a target degree of polymerization of 50 were obtained with [ECP]/[CuCl]/[CuCl₂]/[Me₆TREN] = 1:1:1:2 and [AMPS] = 1 M. The molecular weight increased linearly with the conversion in good agreement with the theoretical values, and the polydispersities decreased with increasing conversion, reaching a lower limit of 1.11. The living character of the polymerization was confirmed by chain‐extension experiments. Block copolymers with N,N‐dimethylacrylamide and N‐isopropylacrylamide were also prepared. The use of a DMF/water mixed solvent should make possible the synthesis of new amphiphilic ionic block copolymers without the use of protecting group chemistry. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4446–4454, 2005     

Optical study of dye-containing fluorinated polyimide thin films

Thin films of dye-containing fluorinated polyimide have been obtained by adding the dye powder to the polyamic acid resin and by spin coating the resulting solution on silica and silicon substrates. 6FDA (4,4’-hexafluoroisopropylidene diphthalic anhydride) and DAB (diaminobenzophenone) have been used as precursor monomers and rhodamine B as dye. The influence of the rhodamine-B molecule on the completeness of the imidization process has been studied by coupled thermogravimetric and mass-spectrometric analyses (TG-MS) of pure and doped polyamic acid resin and by FT-IR analysis of samples before and after curing. Optical emission, excitation and absorption spectra have been collected in order to study spectroscopic and aggregation characteristics of rhodamine as a function of the deposition parameters. Received: 2 March 2000 / Accepted: 24 July 2000 / Published online: 9 November 2000     

Laser cleaning of gilded wood: A comparative study of colour variations induced by irradiation at different wavelengths

There is a growing interest by art conservators for laser cleaning of wood artworks, since traditional cleaning with chemical solvents can be a source of decay, due to the prolonged action of chemicals after the restoration. In this experiment we used excimer and Nd:YAG lasers, emitting radiation in the ultraviolet (248 nm), visible (532 nm) and near infrared (1064 nm), to investigate the effect of laser interaction on gilded wood samples at different wavelengths. Increasing fluence levels were tested to assess threshold values both for surface damage and colour changes. Detailed colorimetric analyses of the irradiated samples show that cleaning effectiveness is related to the emission wavelength, the fluence and the number of pulses.     

Entanglement of electrons in interacting molecules

We use the concept of quantum entanglement to give a physical meaning to the electron correlation energy in systems of interacting electrons. The electron correlation is not directly observable, being defined as the difference between the exact ground state energy of the many-electron Schrödinger equation and the Hartree-Fock energy. Using the configuration interaction method for the hydrogen molecule, we calculate the correlation energy and compare it with the entanglement as a function of the nucleus-nucleus separation. In the same spirit, we analyze a dimer of ethylene, which represents the simplest organic conjugate system, changing the relative orientation and distance of the molecules to obtain the configuration corresponding to maximum entanglement.     

Synthesis of 4-Substituted-1,2-Dihydroquinolines by Means of Gold-Catalyzed Intramolecular Hydroarylation Reaction of N-Ethoxycarbonyl-N-Propargylanilines

An alternative Au(I)-catalyzed synthetic route to functionalized 1,2-dihydroquinolines is reported. This novel approach is based on the use of N-ethoxycarbonyl protected-N-propargylanilines as building blocks that rapidly undergo the IMHA reaction affording the 6-endo cyclization product in good to high yields. In the presence of N-ethoxycarbonyl-N-propargyl-meta-substituted anilines, the regiodivergent cyclization at the ortho-/para-position is achieved by the means of catalyst fine tuning.     

The Diels-Alder reaction of ethene and 1,3-butadiene: an extended multireference ab initio investigation.

The concerted and stepwise mechanisms of the Diels-Alder reaction between 1,3-butadiene and ethene have been investigated using highly correlated multireference methods (MRAQCC) and extended basis sets. Full MRAQCC geometry optimizations have been performed in all cases. The best estimate for the energy barrier of the Diels-Alder reaction is 22 kcalmol(-1). Anti- and gauche-out minima for the biradical structures and corresponding fragmentation saddle points have been determined. The biradical anti fragmentation saddle point is located 6.5 kcalmol(-1) above the concerted saddle point. The gauche-in structure does not correspond to a local minimum, but leads on geometry optimization directly to cyclohexene.     

Weighted approximation of functions with endpoint or inner singularities by Bernstein operators

We give direct and converse results for the weighted approximation of functions with endpoint or inner singularities by Bernstein operators.     

CMS Status

The European Physical Journal C - The status of the construction and installation of CMS is reviewed. All big mechanical pieces have been assembled in the surface hall SX5 (except the 2 nd hadronic...     

Assessment of damage in old parchments by DSC and SEM</o:p>

Summary Environmental impact on parchment was investigated by differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). Parchments subjected to accelerated ageing and old parchments were compared to evaluate quality and extent of deterioration. Stability of fibrillar collagen within parchment was determined from the changes in thermodynamic parameters associated with thermal denaturation. Parchment surface was characterised, and specific morphological criteria were selected for damage assessment. The thermodynamic and morphological changes of collagen induced by deterioration are discussed, and their correlations are proposed as a means of ranking damage in old parchments.</o:p>