Photocrosslinking of functionalized rubber. II. Photoinitiated cationic polymerization of epoxidized liquid natural rubber

Low molecular weight epoxidized natural rubber has been crosslinked within seconds by UV irradiation in the presence of a triarylsulfonium salt. The photoinitiated cationic ring-opening polymerization was studied quantitatively by infrared spectroscopy and shown to proceed with surprisingly long kinetic chains in such solid medium. The high conversion (60%) needed for complete insolubilization, together with the presence of tetrahydrofuran structures, argue in favor of an intramolecular polymerization process involving neighboring epoxy groups. The photoinitiator concentration has a strong influence on the rate and extent of the reaction, as well as on the depth of cure profile. Because of an efficient dark process, close to 100% conversion was reached upon storage of the irradiated elastomer at ambient, with a concomitant increase of the gel fraction and the polymer hardness. The grafting of pendent acrylate groups onto the polymer chain leads to a three-fold decrease of the initial rate of polymerization of the epoxide. The photocuring of natural rubber bearing both epoxy and acrylate groups generates a dual polymer network which combines the properties of the two moieties. © 1995 John Wiley & Sons, Inc.     

The absolute stereochemistry of several cis-dihydrodiols microbially produced from substituted benzenes

The absolute stereochemistry of a series of 3-substituted cis-dihydrodiols obtained by microbial oxidation of toluene, ethylbenzene, chlorobenzene, and biphenyl has been assigned from chemical and spectrophotometric studies. ?-Halogenated toluenes also have been investigated as substrates in these oxidations, and the corresponding cis-dihydrodiols isolated. Implications from the observation that some of the cis-dihydrodiols are racemic are discussed. Oxidation of an olefin, (±)-3-methylcyclohexene, by these microorganisms leads only to cis-diols whose absolute stereochemistry about the hydroxyl-bearing carbons is the same as that found for the cis-dihydrodiols formed from the aromatic substrates.     

Ab initio calculation of the effective valence shell hamiltonian of carbon: Simultaneous treatment of neutral and ion states

The n = 2 effective valence shell hamiltonian, $\text{H}$^v, of carbon is evaluated through second order using ³P Hartree—Fock orbitals (5s4p) with added d functions to provide results within a few percent of the spd convergence limits. The calculated $\text{H}$^v is employed to evaluate the n = 2 valence states of C, C^?, C⁺, C²⁺ and C³⁺ with an average deviation of the 21 excitation energies, ionization potentials and electron affinity from experimental values of 0.32 eV. Three-electron parts of $\text{H}$^v contribute substantially to a number of these excitation energies.     

Synthesis and elaboration of functionalised carbohydrate-derived spiroketals

The scope of a stereoselective three-step approach for the synthesis of sugar derived spiroketals is presented. The methodology consists of Grignard addition of vinyl- or allylmagnesium bromide to a carbohydrate lactone, followed by K-10 clay mediated glycosidation with a terminal alkenol and subsequent ring-closing metathesis of the resulting diene. The generality of this procedure is demonstrated by the synthesis of various pyranose- and furanose-derived spiroketals, as well as more advanced tricyclic spiroketal derivatives. It is shown that functionalisation of the double bond in the resulting spiroketals leads to fused polycyclic ethers.     

Highly selective tritium-from-deuterium isotope separation by pulsed NH3 laser multiple-photon dissociation of chloroform

Infrared multiple-photon dissociation of CTCl₃ was investigated using a pulsed CO₂ laser-pumped NH₃ laser at 12.08 μm. No evidence of any CDCl₃ depletion or decomposition product was observed in photolyzed CTCl₃/CDCl₃ mixtures. A lower limit of the single-step T/D enrichment factor, β, was found to be ≈ 165, based on the sensitivity in measuring CDCl₃ depletion. The low-fluene CTCl₃/CDCl₃ optical selectivity in absorptions is > 9000 at the 835 cm^?1 CTCl₃ ν₄ peak.     

The vibrational analysis of methylarsonic acid,trideuteromethylarsonic acid and their anions

Raman and IR spectra of methylarsonic acid, CH₃AsO₃H₂, trideuteromethylarsonic acid, CD₃AsO₃H₂ and their anions in aqueous solution and the solid state are discussed. Some results of a general valence force field and a Urey-Bradley force field are reported.     

Vibrational analysis of chlorinated methylphosphonic acids: Part 2. Vibrational analysis of CHCl2PO3H2 and its anions

The vibrational spectra (IR and Raman) of CHCl₂PO₃H₂ and its anions in H₂O and D₂O solutions are reported. The IR spectra of the solid dibasic sodium and potassium salts, the solid normal and O-deuterated monobasic sodium and potassium salt and the solid normal and O-deuterated acid are discussed. The principal results of the normal coordinate analysis of the compounds are tabulated.     

Metal speciation dynamics in colloidal ligand dispersions

In this work we propose a dynamic metal speciation theory for colloidal systems in which the complexing ligands are localized on the surface of the particles; i.e., there is spatial heterogeneity of binding sites within the sample volume. The differences between the complex formation and dissociation rate constants of complexes in colloidal dispersions and those in homogeneous solutions originate from the differences in kinetic and mass transport conditions. In colloidal systems, when the effective rate of dissociation of the surface complexes becomes fully diffusion controlled, its value is defined via the geometrical parameters of the particle. We assess the extent to which the conventional approach of assuming a homogeneously smeared-out ligand distribution overestimates the lability of surface complexes in colloidal ligand dispersions. The validity of the theory is illustrated by application to binding of lead and cadmium by carboxyl modified latex particles: our approach correctly predicts the formation/dissociation rate constants, which differ by several orders of magnitude from their homogeneous solution counterparts.