Multitechnique surface spectroscopic studies of plasma modified polymers III. H2O and O2/H2O plasma modified poly(methyl methacrylate)s

The surfaces of poly(methyl methacrylate) (PMMA) films modified by O₂H₂O and H₂O radio-frequency glow discharge plasmas were studied using electron spectroscopy for chemical analysis (ESCA or XPS), low energy ion scattering (LEISS or ISS), Fourier transform IR spectroscopy (FTIR) with attenuated total reflectance (ATR) sampling, and critical surface energy from contact angle measurements. The extent and nature of modification with respect to promotion of a hydrophilic surface compared to the hydrophobic surface of the unmodified PMMA has been probed. Results show drastic decreases in C/O ratio at the near surface, which increases to that of the unmodified PMMA as deeper cross sections are analyzed. In addition peak fitting of ESCA data correlated with FTIR functional group information allows for the qualitative and quantitative analysis of the resulting bonding and structure of the modified layer. From these results combined with the polarity and surface energy differences obtained from contact angle measurements, the structural changes are discussed with respect to plasma reaction mechanisms and differences in the structure of the modified polymer films.     

Infrared studies of chromones—II Isotopically substituted 5-hydroxychromones

By deuteration of the OH group, it has been shown that two bands, at 1665 and 1630 cm⁻¹ (CCl₄), in the IR spectra of 5-hydroxychromones are associated with the H-bonded CO stretching vibration. Nuclear deuteration of 5-hydroxy-2-methylchromone (1) under acidic conditions gave a tri- and a hexadeutero derivative; the latter, isotopically substituted at C-3, shows a single CO band at 1649 cm⁻¹. Hydrolysis of 3-acetyl-5-hydroxy-2-methylchromone with sodium carbonate in deuterium oxide furnished 5-hydroxy-2-trideuteromethylchromone-3-d which also exhibits a single CO absorption. Partial incorporation of O¹⁸ into the CO group of 1 results in a single ν_C=O¹⁸ at 1593 cm⁻¹. It is suggested that the doublet CO absorption of 5-hydroxychromones arises from a Fermi resonance involving a low-energy vibrational mode of the vinyl proton on the nuclear C-3 position.     

A multitechnique surface analytical study of a segmented block copolymer poly(ether-urethane) modified through an H2O radio frequency glow discharge

Recent work in our laboratories has fully characterized the surface region of a segmented poly(ether-urethane) (PEU) extending from the air/polymer interfacial region through bulk depths in the micron range. This characterization utilized energy and angle dependent Electron Spectroscopy for Chemical Analysis (ESCA), Attenuated Total Reflectance–Fourier Transform Infrared Spectroscopy (ATR–FTIR), and Comprehensive Wettability Profiling (contact angle using a homologous series of liquids) as defined by Zisman. In this study this same multi-analytical-technique approach is used to elucidate changes in these PEU surfaces induced through an H₂O Radio Frequency Glow Discharge (RFGD) plasma. This investigation reports both qualitative and quantitative changes due to the modification treatments as well as the permanency of the changes effected on these surfaces through the plasma treatment. From our analyses, the amount of surface residing polyurethane (hard segment) is observed to increase due to a proposed plasma etching mechanism. Further, the addition of oxygen containing functionality is detected at the modified surfaces unique with respect to the unmodified PEU. These surface modifications which show large increases in wettability, are finally observed to be semi-permanent over a time period of 6 months.     

Regioselective synthesis of 3,3‐diethyl‐4‐(methylene)‐1‐quinol‐2‐ones by an intramolecular microwave assisted heck reaction

A protocol for the intramolecular Heck cyclization to afford 3,3‐diethyl‐4‐(methylene)‐1‐quinol‐2‐ones is described. We observed that the use of microwave irradiation increased the efficiency of the reaction. Several examples are presented which show the versatility of the reaction.     

Salting-in of alcohols in aqueous solutions by tetraalkylammonium bromides at the freezing temperature

The freezing-point depression of the ternary systems tetraalkylammonium bromides-t-butanol-water for the first five homologs of R₄NBr was measured. In the case of Bu₄NBr, the effect of size of the alcohol (methahol ton-butanol) was also investigated. From the corresponding freezing-point data for the binary systems the apparent salting constants were calculated. The true salting constantsk _s were obtained by extrapolation to infinite dilution. These are all very close to zero at the freezing temperature. From the corresponding thermochemical data the temperature dependence ofk _s was calculated, and above 5°C all the R₄NBr salts int-butanol; the salting-in increases with temperature and with the size of the hydrophobic cations. The scaled-particle theory is at present the only one which can account semiquantitatively for the temperature dependence of the salting-in effect. On leave of absence from Chemistry Department, The University, Sheffield S3 7HF, England To whom correspondence should be addressed.     

Clays as selective catalysts in organic synthesis

Suitably modified smectite clays can be very selective catalysts for a wide range of organic reactions. While it has long been known that such materials can act as Bronsted and Lewis acids, it has been shown recently that they are also effective Diels-Alder catalysts. A selection of illustrative reactions is given which emphasises their wide range of use, their selectivity, and the ease of work-up after reaction. In each case, mechanistic information is presented, e.g., on the site of reaction (whether interlayer or surface), rate determining steps, etc. The regiochemical consequences of the restricted reaction space are stressed.Based on material presented at the Fourth International Symposium on Inclusion Phenomena and the Third International Symposium on Cyclodextrins, Lancaster, U.K., 20–25 July 1986.     

Operator splitting algorithm for isokinetic SLLOD molecular dynamics

We apply an operator splitting method to develop a simulation algorithm that has complete analytical solutions for the Gaussian thermostated SLLOD equations of motion [D. J. Evans and G. P. Morriss, Phys. Rev. A 30, 1528 (1984)] for a system under shear. This leads to a homogeneous algorithm for performing both equilibrium and nonequilibrium isokinetic molecular dynamics simulation. The resulting algorithm is computationally efficient. In particular, larger integration time steps can be used compared to simulations with regular Gaussian thermostated SLLOD equations of motion. The utility and accuracy of the algorithm are demonstrated through application to the Weeks-Chandler-Anderson fluid. Although strict conservation of the kinetic energy suppresses thermal fluctuations in the system, this algorithm does not allow simulations at lower shear rates than those normally afforded by older nonequilibrium molecular dynamics simulations.     

Infrared studies of chromones—I Carbonyl and hydroxyl regions

Quantitative IR solution data in carbon tetrachloride and chloroform are recorded for the CO and OH regions of 31 chromones. In the 1580–1700 cm⁻¹ region, 5-hydroxychromones show three main maxima, the two of highest frequency, at 1663 ± 3 cm⁻¹ and 1630 ± 5 cm⁻¹ in CCl₄ (1661 ± 2 cm⁻¹ and 1627 ± 5 cm⁻¹ in CHCl₃), being sufficiently intense as to possess high CO character. Typically, 5-alkoxychromones exhibit two intense maxima in this region, 1663 ± 3 cm⁻¹ and 1613 ± 7 cm⁻¹ in CCl₄ (1657 ± 2 cm⁻¹ and 1608 ± 12 cm⁻¹ in CHCl₃). Diagnostically useful changes in contour and principal peak positions can be seen for substituted and annellated 5-hydroxychromones. In the 2500–3650 cm⁻¹ region, the stretching frequencies of OH groups at the most commonly encountered positions (C-5, C-7, and 2-CH₂OH) in natural chromones, are identified.     

Reduction of the pertechnetate anion with bidentate phosphine ligands

The reduction of ammonium pertechnetate with bis(diphenylphosphino)methane (dppm), and with diphenyl-2-pyridyl phosphine (Ph(2)Ppy), has been investigated. The neutral Tc(II) complex, trans-TcCl(2)(dppm)(2) (1), has been isolated from the reaction of (NH(4))[TcO(4)] with excess dppm in refluxing EtOH/HCl. Chemical oxidation with ferricinium hexafluorophosphate results in formation of the cationic Tc(III) analogue, trans-[TcCl(2)(dppm)(2)](PF(6)) (2). The dppm ligands adopt the chelating bonding mode in both complexes, resulting in strained four member metallocycles. With excess PhPpy, the reduction of (NH(4))[TcO(4)] in refluxing EtOH/HCl yields a complex with one chelating Ph(2)Ppy ligand and one unidentate Ph(2)Ppy ligand, mer-TcCl(3)(Ph(2)Ppy-P,N)(Ph(2)Ppy-P) (3). The cationic Tc(III) complexes, trans-[TcCl(2)(Ph(2)P(O)py-N,O)(2)](PF(6)) (4) and trans-[TcCl(2)(dppmO-P,O)(2)](PF(6)) (5) (Ph(2)P(O)py = diphenyl-2-pyridyl phosphine monoxide and dppmO = bis(diphenylphosphino)methane monoxide), have been isolated as byproducts from the reactions of (NH(4))[TcO(4)] with the corresponding phosphine. The products have been characterized in the solid state and in solution via a combination of single-crystal X-ray crystallography and spectroscopic techniques. The solution state spectroscopic results are consistent with the retention of the bonding modes revealed in the crystal structures.