The numerical integration of relative equilibrium solutions. The nonlinear Schrodinger equation

We analyse different error propagation mechanisms for conservativeand nonconservative time-integrators of nonlinear Schrödingerequations. We use a geometric approach based on interpretingwaves as relative equilibria.     

A Single Bioinspired Hexameric Nickel Catechol–Alloxazine Catalyst Combines Metal and Radical Mechanisms for Alkene Hydrosilylation

Mechanisms combining organic radicals and metallic intermediates hold strong potential in homogeneous catalysis. Such activation modes require careful optimization of two interconnected processes: one for the generation of radicals and one for their productive integration towards the final product. We report that a bioinspired polymetallic nickel complex can combine ligand- and metal-centered reactivities to perform fast hydrosilylation of alkenes under mild conditions through an unusual dual radical- and metal-based mechanism. This earth-abundant polymetallic complex incorporating a catechol-alloxazine motif as redox-active ligand operates at low catalyst loading (0.25 mol%) and generates silyl radicals and a nickel-hydride intermediate through a hydrogen atom transfer (HAT) step. Evidence of an isomerization sequence enabling terminal hydrosilylation of internal alkenes points towards the involvement of the nickel-hydride species in chain walking. This single catalyst promotes a hybrid pathway by combining synergistically ligand and metal participation in both inner- and outer- sphere processes.     

The concentration dependence of the compression modulus of iostactic polystyrene/cis-decalin gels

New results for isotactic polystyrene/cis-decalin gels are presented that suggest that a simple fringed micellar model of the gel may not be appropriate. In measuring the room temperature compressive modulus of gels formed at ?20°C, it was found that, not only do the gels exhibit significant stress relaxation but also that the isochronal modulus-concentration diagrams exhibit abrupt changes in modulus (reduced stress) over narrow ranges in concentration rather than the smooth curves (straight lines) typical of swollen rubber and fringed micellar gels.     

Role of the polymer microstructure in the thermoreversible gelation of poly(vinyl chloride)

Gels of polyvinylchloride (PVC) and PVC copolymers of different microstructure and molar composition, were prepared in a series of diester-like solvents. The viscoelastic properties of these gels were evaluated as a function of temperature and the molecular structure was studied by small-angle neutron scattering. The degrees of proton association in the polymer solutions were determined by ¹H NMR spectroscopy by measuring the intensity of proton bands of CH₂ monomeric units. The body of experimental data shows clearly that there is a straight relation between molecular structure, viscoelastic properties of the gel, degree of polymer-solvent interaction and polymer microstructure.     

Complex formation in poly(vinyl chloride) thermoreversible gels

The molecular structure of gels formed by poly(vinyl chloride) with different solvents is analyzed by neutron diffraction and neutron scattering techniques. Structure parameters are determined from the scattering functions and discussed in the light of the fibrillar model. Arguments are given in favour of the formation of PVC-solvent complexes.     

Properties of poly(vinyl alcohol)-graft-polyacrylamide copolymers depending on the graft length. 2. Thermal properties in the bulk state

Thermal behavior of poly(vinyl alcohol)-graft-polyacrylamide copolymers (PVA-g-PAA), so-called intramolecular polymer-polymer complexes (intraPC), with variable M̄ _vPAA and constant average number N of grafts is considered in this report. Complete compatibility of PVA and PAA through hydrogen bonding is realized in the range of the graft lengths not exceeding some critical value. The content of adsorbed and trapped water in graft copolymers reflects some features of PVA-g-PAA_N structure depending on the graft lengths. The first thermal decomposition region in air for copolymers begins at higher temperatures with growing M̄ _vPAA, but the total destruction interval reduces. Formal kinetic decomposition parameters of the first decomposition stage appear to be the largest for the PVA-g-PAA with the largest quantity of H-bonds between the main and graft chains. Chemical transformations in graft copolymers, PVA and PAA during thermal decomposition are discussed.     

Sheathing Polymer Gels Fibrils with Nanotubules

The aim of this preliminary study is to master the making of nanocomposites by physical processes. In particular, the sheathing of polymer fibrils by self-assembled nanotubules is examined. Nanotubules recently prepared from 3,5-Bis-(5-hexylcarbamoyl-pentyloxy)-benzoic acid decyl ester have been used for sheathing fibrils obtained by thermoreversible gelation of isotactic polystyrene. Investigations have been carried out by means of atomic force microscopy (AFM).     

Effect of Stereoregular Polyelectrolyte on Protein Thermal Stability

Myoglobin was used as a model protein to study the effect of polyelectrolyte on protein thermal stability for solutions. Stereoregular polystyrene sulfonate was used to investigate the effect of chain properties on protein polyion binding affinity. Turbidity measurement indicate stronger binding to protein of atactic polystyrene sulfonate than isotactic polystyrene sulfonate, an effect that might be due to the higher chain flexibility of the atactic form. Differential scanning calorimetry (DSC) and small angle x-ray (SAXS) scattering indicate the presence of the polyelectrolyte has a destabilizing effect on the protein. The results showed that, although the presence of polyelectrolytes has no effect on myoglobin structure at room temperature at pH 7.4, myoglobin stability is reduced as the temperature is elevated. This effect is linked to the binding of the protein to the polylectrolyte. This binding is probably driven by a combination of electrostatic and hydrophobic interactions, the latter of which are enhanced at higher temperatures.     

Temperature-Concentration Phase Diagram of PEO-Urea

The present paper reports on the phase diagram of the system PEO/Urea as established by differential scanning calorimetry. From this phase diagram one PEO/Urea compound is indentified with a stoichiometry 1/2. This value is in agreement with results derived from X-ray diffraction.