A series of new high‐performance materials based on poly[4′‐fluorophenyl‐bis(4‐phenyl)phosphine oxide]

A new series of high‐performance poly(arylene phosphine oxide) (PAPO) materials were synthesized postpolymerization from fluorinated poly(arylene phosphine oxide) (f‐PAPO). The new materials had increased solubility and film‐forming ability over the parent f‐PAPO. With the careful choice of the nucleophile, the thermal stability was also increased. The parent polymer f‐PAPO was synthesized via Ni(0) coupling from aromatic chloride and mesylate monomers. Both monomers were polymerized successfully to create polymers with intrinsic viscosities of 0.235 and 0.123 dL/g, respectively. The higher molecular weight f‐PAPO gave a glass transition of 320 °C and a char yield of 54% at 650 °C in air. The substitution of f‐PAPO via nucleophilic aromatic substitution produced PAPO thermoplastics with significant changes in the properties. The largest increase in the thermal stability relative to f‐PAPO was from 563 to 600 °C 10% weight‐loss values in nitrogen after the displacement of fluoride by 4‐aminophenol, which yielded poly[4‐(4‐aminopheonxyphenyl)bis(4′‐phenyl)phosphine oxide]. Additionally, the char yield increased from 54 to 71% in air at 650 °C. The solubility of the parent polymer was improved after substitution with 3‐tert‐butylphenol, n‐nonylamine, and poly(ethylene glycol)monomethyl ether. All of these became soluble in chloroform, N,N‐dimethylacetamide, and dimethyl sulfoxide. Copolymers were synthesized with 2,5‐dichloro‐4′‐fluorobenzophenone to improve the solubility of f‐PAPO without the loss of thermal stability. These copolymers also underwent nucleophilic aromatic substitution to create an epoxy cure agent that was used with the DEN 431 resin. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2277–2287, 2003     

A note on comparison theorems for nonnegative matrices

Summary In a recent paper, [4], Csordas and Varga have unified and extended earlier theorems, of Varga in [10] and Wonicki in [11], on the comparison of the asymptotic rates of convergence of two iteration matrices induced by two regular splittings. The main purpose of this note is to show a connection between the Csordas-Varga paper and a paper by Beauwens, [1], in which a comparison theorem is developed for the asymptotic rate of convergence of two nonnegative iteration matrices induced by two splittings which are not necessarily regular. Monotonic norms already used in [1] play an important role in our work here.Research supported in part by NSF grant number DMS-8400879     

Air-sampling of aldehydes—Application to chromatographic determination of formaldehyde and acetaldehyde

Summary After a brief review of several methods described in the literature this paper discusses air-sampling on 2,4-dinitrophenylhydrazine-coated silica gel and identification requirements for aldehydes and ketones most commonly found in industrial pollution.Quantitative analysis of formaldehyde and acetaldehyde either by GC or by HPLC techniques is established using a dynamic system producing test atmospheres and compared with the usual colorimetric determinations.     

FTIR spectrum of benzene in a supersonic expansion

The 700 and 3050 cm^?1 region of benzene seeded in argon is studied using Fourier-transform infrared absorption spectroscopy. Analysis of the sequence band structure in the 700 cm^?1 region gave new anharmonic constants and values of T_rot (79 ± 15 K) and T_vib (/2~160 K) which indicate a disequilibrium between the rotational and vibrational degrees of freedom. A band contour analysis of the 3050 cm^?1 Fermi triad is used to obtain new values of the Coriolis coupling constants and band origins.     

Advances in Electron Backscatter Diffraction for the Characterisation of Interfaces

This aper describes state-of-the-art analysis of grain boundary populations by EBSD, with particular attention paid to advanced, non-standard analysis. The capability and versatility of EBSD for the characterisation of interfaces is emphasised. The discussion is focussed on boundaries in face-centred cubic metals, since the majority of work has been carried out on this subset of materials. Data processing based both on misorientation alone and customised additions which include the boundary planes are described. Although commercial EBSD packages offer data processing options for interfaces, it is clear that there is a wealth of more in-depth data that can be gleaned from further analysis. In particular, determination of all five degrees of freedom of the boundary population provides an exciting opportunity to study grain boundaries by EBSD in a depth that was hitherto impossible.     

Activation of carbon disulphide by metal carbonyl anions: Formation of trithiocarbonate complexes

Trithiocarbonate complexes are formed when metal carbonyl anions are treated consecutively with carbon disulphide and a neutralising agent such as methyl iodide or Re(CO)₅ Br.     

Importance of spin-orbit coupling for the assignment of the photodetachment spectra of AuX2- (X=Cl, Br, and I).

Recently, photodetachment spectra of AuX2-, X=Cl, Br, and I, have been reported [D. Schr?der et al., Angew. Chem. Int. Ed. 2003, 42, 311] followed by a scalar-relativistic theoretical study of the assignment of these spectra [B. Dai, J. Yang, Chem. Phys. Lett. 2003, 379, 512]. Herein, the photodetachment spectra of the title molecules are reassigned, taking spin-orbit coupling into account and employing relativistic-effective core potentials for gold and the halogen atoms. The composition of the AuX2 electronic states are further analyzed in terms of scalar-relativistic electronic states. The relevance of spin-orbit coupling in the spectroscopy of heavy elements is emphasized by comparing the results of this work with experiment and with other scalar-relativistic theoretical studies.     

A versatile method for tuning the chemistry and size of nanoscopic features by living free radical polymerization

A novel approach is presented for manipulating the size and chemistry of nanoscopic features using a combination of contact molding and living free radical polymerization. In this approach a highly cross-linked photopolymer, based on a methacrylate/acrylate mixture, was patterned into submicrometer-sized features on a silicon wafer using a contact-molding technique. A critical component of the monomer mixture was the incorporation of an initiator containing monomer into the network structure, which provides sites for functional group amplification. Features ranging in size from 5 microm to <60 nm were accurately replicated by this process and living free radical polymerizations, both atom transfer radical and nitroxide-mediated polymerization (NMP), could be conducted from these initiating sites to yield polymer brushes which represent a grafted layer of linear chains attached to the original network polymer. Grafts consisting of polystyrene, poly(methyl methacrylate), and poly(2-hydroxyethyl)methacrylate were grown with controlled thicknesses ranging from 10 to 143 nm and graft molecular weights of between 18 000 to 290 000 amu. As a result of this secondary graft process, feature sizes could be tuned from the original 100 nm down to 20 nm, and the surface chemistry varied from hydrophilic to hydrophobic starting from the same initial master pattern. The thin films and patterned features were characterized by contact angle, ellipsometry, optical, and atomic force microscopies.     

Comparison of conformational analysis techniques to generate pharmacophore hypotheses using catalyst

Generation of reliable pharmacophore models is a key strategy in drug design. The quality of a pharmacophore model is known to depend on several factors, with the quality of the conformer sets used perhaps being one of the most important. The goal of this study was to compare different conformational analysis methods to determine if one was superior to the others for pharmacophore generation using Catalyst/HypoGen. The five methods selected were Catalyst/Fast, Catalyst/Best, Omega, Chem-X and MacroModel. Data sets for which Catalysts models had previously been published were selected using defined quality measures. Hypotheses were generated for each of the data sets and the performance of the different conformational analysis methods was compared using both quantitative (cost and correlation coefficients) and qualitative measures (by comparing the hypotheses in terms of the features present and their spatial relationships). Two main conclusions emerged from the study. First, it was not always possible to replicate the literature results. The reasons for these failures are explored in detail, and a template for use in publications that apply the Catalyst methodology is proposed. Second, the faster rule-based methods for conformational analysis give pharmacophore models that are just as good as, and in some cases better than, the models generated using the slower, more rigorous approaches.     

Proton transfer to nickel-thiolate complexes. 2. Rate-limiting intramolecular proton transfer in the reactions of [Ni(SC(6)H(4)R-4)(PhP[CH(2)CH(2)PPh(2)](2))](+) (R = NO(2), Cl, H, Me, or MeO)

The protonation of [Ni(SC(6)H(4)R-4)(triphos)](+) (triphos = PhP[CH(2)CH(2)PPh(2)](2); R = NO(2), Cl, H, Me, or MeO) by [lutH](+) (lut = 2,6-dimethylpyridine) to form [Ni(S(H)C(6)H(4)R-4)(triphos)](2+) is an equilibrium reaction in MeCN. Kinetic studies, using stopped-flow spectrophotometry, reveal that the reactions occur by a two-step mechanism. Initially, [lutH](+) rapidly binds to the complex (K(2)(R)) in an interaction which probably involves hydrogen-bonding of the acid to the sulfur. Subsequent intramolecular proton transfer from [lutH](+) to sulfur (k(3)(R)) is slow because of both electronic and steric factors. The X-ray crystal structures of [Ni(SC(6)H(4)R-4)(triphos)](+) (R = NO(2), H, Me, or MeO) show that all are best described as square-planar complexes, with the phenyl substituents of the triphos ligand presenting an appreciable barrier to the approach of the sterically demanding [lutH](+) to the sulfur. The kinetic characteristics of the intramolecular proton transfer from [lutH](+) to sulfur have been investigated. The rate of intramolecular proton transfer exhibits a nonlinear dependence on Hammett sigma(+), with both electron-releasing and electron-withdrawing 4-R-substituents on the coordinated thiolate facilitating the rate of proton transfer (NO(2) > Cl > H > Me < MeO). The rate constants for intramolecular proton transfer correlate well with the calculated electron density of the sulfur. The temperature dependence of the rate of the intramolecular proton transfer reactions shows that deltaH() is small but increases as the 4-R-substituent becomes more electron-withdrawing [deltaH = 4.1 (MeO), 6.9 (Me), 11.4 kcal mol(-)(1) (NO(2))], while DeltaS() becomes progressively less negative [deltaS = -50.1 (MeO), -41.2 (Me), -16.4 (NO(2)) cal K(-)(1) mol(-)(1)]. Studies with [lutD](+) show that the rate of intramolecular proton transfer varies with the 4-R-substituent [(k(3)(NO)2)(H)/(k(3)(NO)2)(D) = 0.39; (k(3)(Cl))(H)/(k(3)(Cl))(D) = 0.88; (k(3)(Me))(H)/(k(3)(Me))(D) = 1.3; (k(3)(MeO))(H)/(k(3)(MeO))(D) = 1.2].