Showing papers by "ExxonMobil published in 1991"

Ionic metallocene catalyst compositions

Abstract: Ionic catalyst compositions can be prepared by combining two components. The first component is a bis(cyclopentadienyl) Group IV-B metal complex containing at least one ligand which will combine irreversibly with the second component or at least a portion thereof such as a cation portion thereof. The second component comprises a cation which will irreversibly react with at least one ligand on the Group IV-B metal complex and a non-coordinating anion. The combination of the two components produces an ionic catalyst composition comprising a cationic bis(cyclopentadienyl) Group IV-B metal complex which has a formal coordination number of 3 and a 4+ valence charge and the aforementioned non-coordinating anion. The anion is (i) labile and can be displaced by an olefin, diolefin or acetylenically unsaturated monomer; (ii) has a molecular diameter about or greater than 4 angstroms; (iii) forms stable salts with reducible Lewis acids and protonated Lewis bases; (v) has a negative charge delocalized over the framework on the anion or within the core thereof; (v) is not a reducing or oxidizing agent; and (vi) is a relatively poor nucleophile. These ionic catalyst compositions can be used to polymerize α-olefins, diolefins and/or acetylenically unsaturated monomers, either alone or in combination, to polymers and copolymers.

Catalyst system of enhanced productivity

Abstract: This invention relates to catalyst systems, and a method for using such system, for the enhanced production of homo and copolymer products of olefin, diolefin and/or acetylenically unsaturated monomers. This invention catalyst system comprises a Group III-A element compound for improving the productivity of an olefin polymerization catalyst which is the reaction product of a metallocene of a Group IV-B transition metal and an ionic activator compound comprising a cation capable of donating a proton and an anion which is bulky, labile and noncoordinateable with the Group IV transition metal cation produced upon reaction of the metallocene and activator compound to form the catalyst component of the catalyst system.

A general recursion method for calculating diffracted intensities from crystals containing planar faults

Abstract: A general recursion algorithm is described for calculating kinematical diffraction intensities from crystals containing coherent planar faults. The method exploits the self-similar stacking sequences that occur when layers stack non-deterministically. Recursion gives a set of simple relations between average interference terms from a statistical crystal, which can be solved as a set of simultaneous equations. The diffracted intensity for a polycrystalline sample is given by the incoherent sum of scattered intensities over an ensemble of crystallites. The relations between this and previous approaches, namely the Hendricks-Teller matrix formulation, the difference equation method, the summed series formula of Cowley, and Michalski’s recurrence relations between average phase factors, are discussed. Although formally identical to these previous methods, the present recursive description has an intuitive appeal and proves easier to apply to complex crystal structure types. The method is valid for all types of planar faults, can accommodate long-range stacking correlations, and is applicable to crystals that contain only a finite number of layers. A FORTRAN program DIFFaX , based on this recursion algorithm, has been written and used to simulate powder X-ray (and neutron) diffraction patterns and single crystal electron (kinematical) diffraction patterns. Calculations for diamond-lonsdaleite and for several synthetic zeolite systems that contain high densities of stacking faults are presented as examples.

Dipole interactions with random anisotropy in a frozen ferrofluid.

Abstract: Glassy behavior (including hysteresis, irreversibility, a peak in the zero-field-cooled magnetization, and nonexponential relaxation) is observed in a quenched ferrofluid system consisting of 50-angstrom magnetite particles. An Arrott plot, M^2 vs H/M, shows clear features of random anisotropy similar to what is found in amorphous ferromagnets. We discuss the glassy behavior in terms of both the random anisotropy and the dipole interactions, and we contrast the unusual response of our system with canonical spin glasses.

Mono-Cp heteroatom containing Group IVB transition metal complexes with MAO: supported catalysts for olefin polymerization

Abstract: The invention is a supported catalyst system including an inert support material, a Group IV B transition metal component and an alumoxane component which may be employed to polymerize olefins to produce a high molecular weight polymer.

Aluminum-free monocyclopentadienyl metallocene catalysts for olefin polymerization

Abstract: The invention is a catalyst system including a Group IV-B transition metal component and an activator component which may be employed to polymerize olefins to produce a high molecular weight polymer. The Group IV-B transition metal component contains a single cyclopentadienyl ligand and a single heteroatom ligand, which ligands may be bridged one to another; the activator component comprises a cation, which may be a Bronsted acid capable of donating a proton (hereafter denoted as L'-H wherein L' is a neutral Lewis base and H is hydrogen), and a compatible noncoordinating anion.

Internal reflection of diffusive light in random media

Abstract: The consequences of internal reflection of multiply scattered light at the boundaries of disordered media are studied We show that the effect of internal reflection due to index mismatch can be quantitatively accounted for with a single parameter by incorporating a reflection coefficient into the boundary condition for the diffusive light We measure the angular correlation functions in transmission and reflection at different thicknesses for both high- and low-index mismatch By including the effect of internal reflection, we are able to obtain consistent quantitative agreement between experiment and theory Extensions to other experiments including diffusing-wave spectroscopy, coherent backscattering, frequency correlations, and pulse propagation are discussed

Reactivity of organic compounds in hot water: geochemical and technological implications.

Abstract: Understanding of the reactivity of organic molecules in hot water is developing from studies aimed at explaining how organic matter (kerogen) forms in natural environments and then breaks down into energy source materials. In natural systems where kerogens are depolymerized, hot water is ubiquitous and usually contains salt and minerals. Reactions such as ionic condensation, cleavage, and hydrolysis are facilitated by changes in the chemical and physical properties of water as temperature increases. These changes make the solvent properties of water at high temperature similar to those of polar organic solvents at room temperature, thus facilitating reactions with organic compounds. An understanding of aqueous organic chemistry may lead to potential applications in areas as diverse as the recycling of plastics, the synthesis of chemicals, and coal liquefaction.

Electrical devices comprising polymeric insulating or semiconducting members

Abstract: Disclosed are electrically conductive and semiconductive devices utilizing polymers having resistance to water treeing and good dielectric properties. The polymer comprises ethylene polymerized with at least one C 3 to C 20 alpha-olefin and optionally at least one C 3 to C 20 polyene. The polymer utilized has a density in the range of about 0.86 g/cm 3 to about 0.96 g/cm 3 , a melt index in the range of about 0.2 dg/min to about 100 dg/min, a molecular weight distribution in the range of about 1.5 to about 30, and a composition distribution breadth index greater than about 45 percent. For the polymer utilized, the tree rating is generally less than about 40, the power factor is in the range of about 0.0002 to about 0.0005, and the dielectric constant is in the range of about 1.8 to about 2.4.

Multiple Light-Scattering Probes of Foam Structure and Dynamics

Abstract: The structure and dynamics of three-dimensional foams are probed quantitatively by exploiting the strong multiple scattering of light that gives foams their familiar white color. Approximating the propagation of light as a diffusion process, transmission measurements provide a direct probe of the average bubble size. A model for dynamic light scattering is developed that can be used to interpret temporal fluctuations in the intensity of multiply scattered light. The results identify previously unrecognized internal dynamics of the foam bubbles. These light-scattering techniques are direct, noninvasive probes of bulk foams and therefore should find wide use in the study of their properties.

A New Look at Predicting Gas-Well Load-Up

Abstract: This paper discusses results of field tests conducted to verify minimum flow rate (critical rate) required to keep low-pressure gas wells unloaded and compares results to previous work. This paper also covers liquid yield effects, liquid sources, verification that wellhead conditions control onset of load-up, and effects of temperature, gas/liquid gravities, wellbore diameter, and packer/tubing setting depth.

Granular flow: Friction and the dilatancy transition.

Abstract: Molecular-dynamics simulations of noncohesive granular assemblies under shear are described. At low shear rate \ensuremath{\gamma}\ifmmode \dot{}\else \.{}\fi{}, the assembly is unstable to uniform motion and exhibits stick-slip dynamics involving periodic dilatancy transitions and gravitational compactification. Steady-state motion occurs at larger \ensuremath{\gamma}\ifmmode \dot{}\else \.{}\fi{} where 6--12 layers of grains flow over a compact, static assembly. A phase boundary, characterized by a discontinuity in \ensuremath{\gamma}\ifmmode \dot{}\else \.{}\fi{} and an enhanced normal stress, separates the static and flowing regions. In the steady-state regime, dilatancy leads to a shear stress that is independent of \ensuremath{\gamma}\ifmmode \dot{}\else \.{}\fi{}.

Scaling behavior in shaving cream

Abstract: The coarsening of a three-dimensional foam is studied with multiple light-scattering techniques. Scaling behavior is observed with the average bubble diameter growing in time as ${\mathit{t}}^{\mathit{z}}$ where z=0.45\ifmmode\pm\else\textpm\fi{}0.05. Changes in the packing conditions during coarsening give rise to a dynamical process that also exhibits temporal scaling. Neighboring bubbles undergo sudden structural rearrangement events at a rate per unit volume that decays as ${\mathit{t}}^{\mathrm{\ensuremath{-}}\mathit{y}}$ where y=2.0\ifmmode\pm\else\textpm\fi{}0.2.

An amido transition metal compound and a catalyst system for the production of isotactic polypropylene.

Abstract: Bridged and unbridged amido transition metal compounds of the Group IV-B metals are disclosed. They are represented by general formula (I) wherein: 'y' is 1 denoting the presence of a bridging group T between nitrogen atoms; 'Z' is - y; 'M' is zirconium, hafnium or titanium; 'N' is a nitrogen atom having three substituents; each 'X' is, independently, any univalent anionic ligand such as a halide, hydride, substituted or unsubstituted C1-C30 hydrocarbyl, alkoxide, aryloxide, amide, arylamide, phosphide, or arylphosphide; 'T' is a covalent bridging group selected from the group consisting of unsubstituted hydrocarbyl and substituted hydrocarbyls containing a Group IV-A or VI-A element; and each 'R' is, independently, a radical selected from the group consisting of singly branched hydrocarbyl radicals having between 4 and 30 carbon atoms, multiply branched hydrocarbyl radicals having between 4 and 30 carbon atoms, halogen radicals, amido radicals, phosphido radicals, silyl radicals, alkoxy radicals, alkylborido radicals, C1-C30 hydrocarbyl-substituted Group IV-A metalloid radicals; and substituted C1-C30 hydrocarbyl radicals wherein one or more hydrogen atoms is replaced by a halogen radical, an amino radical, a phosphido radical, an alkoxy radical or any other radical containing a Lewis acidic or basic functionality. These compounds may be used in a catalyst system comprising the amido transition metal compound and an alumoxane. Also disclosed is a process using the catalyst system for the production of high molecular weight polyolefins and, particularly, high molecular weight isotactic polypropylene.

Gold clusters: reactions and deuterium uptake

Abstract: We have examined the reactivity and saturation of small gold clusters (cations, neutrals and anions) towards several molecules and find that specific small gold clusters exhibit a pronounced variation in their reactivity towards hydrogen, methane and oxygen. The reactivity not only depends strongly on cluster size but also on the cluster charge state. For example, small (n<15) gold cations react readily with D2, but no evidence of reaction is observed for the anions under our experimental conditions. Similar behavior is seen for methane. With oxygen only even atom (odd electron) anions are reactive, and Au 10 + is the only cation which exhibits evidence of reaction. The global features (small cluster cations reactive towards H2, CH4, but large ones not reactive, odd electron anions reactive towards O2) are qualitatively explained by appealing to a simple frontier orbital picture. The uptake of deuterium and methane on gold clusters also exhibits a pronounced size dependence with D/Au varying from a high of 3 for the dimer to zero for clusters containing more than 15 Au atoms. Comparison of the methane and deuterium saturation behavior leads us to suggest that methane is dissociated and bound as CH3 and H.

Effects of concentration and thermodynamic interaction on the viscoelastic properties of polymer solutions

Abstract: Linear viscoelastic measurements are reported for solutions of a high molecular weight polybutadiene covering the entire range of concentration from pure polymer to pure solvent at 25°C in a nearly θ solvent (dioctyl phtalate) and a good solvent (phenyloctane). Three regimes of concentration are found for the viscosity in each solvent. Elastic response is also identical for the two solvents, with G° N (inferred from G″ m ) ∞1/J° e ∞φ 2.3 for φ>0.02. The results in semidilute solution compare favorably with the predictions of a recent two-parameter scaling theory

Structure of CH3(CH2)17SH Self-Assembled on the Ag(111) Surface: An Incommensurate Monolayer

Abstract: We describe the first experimental study of the molecular structure of the self-assembled monolayer of CH 3 (CH 2 ) 17 SH formed on the Ag(111) surface. Using both low-energy He diffraction and grazing incidence X-ray diffraction, we show that the monolayer formed on Ag is both incommensurate and rotated with respect to the Ag lattice, with a lattice spacing which is very similar to n-alkane chains in bulk hydrocarbon crystals.

Nematic to smectic-A phase transition under shear flow: A nonequilibrium synchrotron x-ray study.

Abstract: We report on x-ray scattering studies of the nematic to smectic-A transition in 4-cyano-4'-octylbiphenyl under nonequilibrium shear-flow conditions. As the transition is approached, the interplay between the viscous frictional and the flow-induced-fluctuation forces on the nematic director leads to a series of regimes whose occurrence results from the divergence in one of the viscosities due to the critical slowing down of the smectic-A order-parameter fluctuations. The experiments demonstrate that, under flow, synchrotron x-ray-diffraction techniques provide a powerful structural probe of steady-state dynamical behavior.

Method of estimating property and/or composition data of a test sample

Abstract: A method of operating a spectrometer to determine property (13) and/or composition data of a sample comprises an on-line spectral measurement (1) of the sample using a computer controlled spectrometer, statistical analysis of the sample data based upon a statistical mode (2, 3, 4) using sample calibration data, and automatically identifying a sample if necessary based upon statistical and expert system (rule-based) criteria. Sample collection based upon statistical criteria consists of performing a statistical or rule-based check against the model to identify measurement data which are indicative of chemical species not in the samples already stored in the model. Samples identified either by a statistical criteria or using an expert system (rule-based decisions) are used preferably to isolate the liquid sample using a computer controlled automatic sampling system. The samples can be saved for subsequent laboratory analysis in removable sample containers. The results of the laboratory analysis together with the on-line spectroscopic measurements are preferably used to update the model being used for the analysis.

Thermodynamics of random copolymer melts.

Abstract: We report on a mean-field thermodynamic analysis of AB random copolymer melts with (backbone) composition correlations that reflect realistic polymerization conditions. Depending on the strength and sign of these correlations, multiple homogeneous phases, periodic mesophases, or disordered mesophases are possible. We identify an isotropic Lifshitz point and the critical lines that emerge from it. Our results should facilitate the design of new copolymeric materials.

Dynamically cured thermoplastic olefin polymers and process for producing the same

Abstract: A dynamically vulcanized thermoplastic composition is provided which comprises a polymer blend of a thermoplastic olefinic resin, and an elastomeric halogen-containing copolymer of a C4 to C7 isomonoolefin and a paraalkylstyrene. A process for preparing the dynamically vulcanized composition is also provided.

Chemical and Biological Microstructures as Probed by Dynamic Processes

Abstract: The dynamic process of electronic energy transfer is shown to be an important tool for probing the microstructure of molecular systems, particularly those in which donors and acceptors occupy specifically labeled sites of spatially confining host matrices. Special attention is given to analyzing the temporal behavior of the direct energy transfer reaction for systems in which the dipolar coupling is between a donor and randomly distributed acceptors. This dynamic process is dependent on two competing lengths when the donor and acceptor distribution is determined by the microstructure of the confining system: Rp, the dominant length characterizing the size of the confinement, and R0, which scales the strength of the dipolar coupling. When energy transfer processes are viewed in the context of these two competing lengths, a picture emerges of the microstructure of the confinement that is consistent with and corroborated by other structural probes.

A copper-thiolate polynuclear cluster in the ACE1 transcription factor.

Abstract: ACE1 is the transcriptional activator of the metallothionein (CUP1 locus) gene in Saccharomyces cerevisiae. Previous data had implicated the N-terminal domain of ACE1 as responsible for the Cu-dependent specific DNA binding. An expression system in Escherichia coli was constructed to enable the isolation of an ACE1 domain containing the DNA and Cu-binding regions. Here we report the purification and characterization of the Cu-ACE1 truncated molecule. Spectroscopic techniques showed that ACE1 contains an unusual type of DNA binding structure that is based on a polynuclear Cu(I)-cysteinyl thiolate cluster. The cluster consists of six or seven Cu(I) ions coordinated to cysteinyl thiolates in a trigonal geometry distorted from planarity. The Cu(I)-cysteine cluster of Cu-ACE1 exhibits structural properties analogous to the Cu(I)-thiolate polynuclear cluster in yeast Cu-metallothionein itself, suggesting an unusual mechanism for the evolution of this regulatory factor. The Cu cluster organizes and stabilizes the conformation of the N-terminal domain of ACE1 for specific DNA binding.

Orientational order, topology, and vesicle shapes.

Abstract: While ideal fluid membranes are characterized solely by curvature elasticity, many structural (``external'') properties of real membranes are strongly influenced by internal degrees of freedom. Here, we consider, within mean-field theory, the effect of in-plane vector order (such as the molecular tilt in surfactant bilayers) on the shapes of closed vesicles with the topology of a sphere. We find that coupling between in-plane order and Gaussian curvature causes continuous shape changes from spherical to cylindrical vesicles as the degree of in-plane order increases.

Ethylene alpha-olefin copolymer substituted mannich base lubricant dispersant additives

Abstract: The present invention is directed to oil-soluble lubricating oil additives comprising Mannich Base condensates of an alkyl substituted hydroxy aromatic compound with formaldehyde and an amine, wherein the alkyl-moiety of the aromatic compounds is derived from at least one ethylene alpha-olefin copolymer of 300 to 20,000 number average molecular weight, wherein at least about 30% of the polymer's chains contain terminal ethenylidene unsaturation. The Mannich Base condensates of this invention are useful as dispersants.