bluuebunny/crossref_metadata_2025 huggingface dataset:
On the theory of polymer adsorption at an interface
Authors: Hoeve C. A. J.
Published: June 2010

Exact results are given for the grand partition function of a single model chain adsorbed at an interface. The model chosen corresponds to a walk on a 5‐choice, instead of a 6‐choice, simple cubic lattice by disallowing step reversals. The flexibility of this model is rendered variable by assigning different weights to consecutive steps made in the same direction. The obtained results are compared to those of a previous model for Gaussian chains. Satisfactory agreement between the models allows the previously undetermined flexibility parameter to be determined. The segment density in the vicinity of the interface is obtained as a function of this parameter. Correspondence with polymer chains is established through this parameter. We conjecture that the volume fraction of segments in the diffuse layer resulting from the loops does not exceed 0.1, even when the volume fraction in the interface is unity.
Some domain‐size effects in polymer transitions
Authors: Couchman P. R. , Karasz F. E.
Published: June 2010

Size‐dependent changes of transition temperatures in polymers are shown to derive from two principal sources: the effect of surface energy (or interfacial tension) and the role of the interface in the mixing of foreign material with the system. The formal elements and physical insight necessary for a description of the influence of domain size on the two main polymer transitions, the glass transition and melting, are discussed in some detail.
Radical ring‐opening polymerization and copolymerization with expansion in volume
Authors: Bailey William J. , Endo Takeshi
Published: June 2010

Although ring‐opening polymerization involving ionic intermediates and Ziegler catalysts are quite extensively used in polymer chemistry, free radical ring‐opening polymerization is extremely rare. We have been able to show that unsaturated spiro ortho carbonates will undergo double ring‐opening polymerization under radical conditions. In addition these monomers will undergo ready copolymerization with common monomers, such as styrene, methyl methacrylate, and diallyl carbonate.

Since this process involves a double ring‐opening, a slight expansion in volume occurs. For a number of industrial applications, such as precision castings, strain‐free composites, binders for solid propellants, high strength adhesives, dental fillings, and rock‐cracking materials, it is highly desirable to have monomers that expand on polymerization. In the formation of composites, such a monomer might minimize poor adhesion between the matrix and the reinforcing agent or eliminate microcracks. Formation of additional polymers usually involves shrinkage since the monomer undergoes a transition from a van der Waals distance to a covalent distance in the polymeric material. Ring‐opening polymerization usually involves somewhat less shrinkage because for every new bond that is formed involving a shift from a van der Waals distance to a covalent distance, another bond is broken involving a shift from a covalent distance to a near van der Waals distance. Thus, if monomers are utilized in which two bonds are broken for every new bond that is formed in the polymerization process, near zero shrinkage or expansion takes place.
Mechanochemical syntheses
Authors: Simionescu Cristofor , Oprea Cleopatra Vasiliu , Negulianu Claudia
Published: June 2010

In the present paper some main directions in mechanochemical synthesis are developed, based on the mechano‐destructive process induced under different conditions in homo‐ and heterochain solid polymers (polyethylene, cellulose and derivatives, polyesters and polyamides). The fact is known that the elastic energy conferred to crystalline amorphous polymers focuses on structural and composition defects distributed statistically, causing molecular ruptures of the homolytic type which generate nascent microcracks propagating and increasing within the solid leading finally to a fracture. The nascent microcrack represents in fact the existence within small volumes of a number of active macroradicals (or of a number of reactive functional groups after the stabilization of the destruction fragments) capable of reacting with appropriate chemical reagents existing in the working medium. On this basis became possible the initiation of graft polymerization, block copolymerization, polycondensation, and complexing reactions. The concentration of the elastic energy not on molecular underlayers but on metallic surfaces, even when these are the reaction vessel walls, leads to the formation of active centers of a particular type, capable of initiating homo‐ or copolymerization reactions.
Some physicochemical aspects regarding the synthesis of polyvinyl alcohol
Authors: Dimonie M. , Cincu C. , Oprescu C. , Hubcǎ Gh.
Published: June 2010

The present paper reports some theoretical aspects related to recent technology for the production of polyvinyl alcohol. The procedure involves the polymerization of vinyl acetate in two stages and the alcoholysis of polyvinyl acetate. A model for the calculation of the polymerization degree and grafting degree of vinyl acetate was developed in view of a quantitative evaluation of various possibilities for conducting the polymerization process. The alcoholysis of polyvinyl acetate was studied by conducting the reaction in a Brabender‐type mixer. The dependence of the reaction rate on the catalyst or polymer concentration or on the temperature evidences the important role played by the diffusion processes and supports the idea of the cocatalytic effect of OH groups in the alcoholysis reaction of the polyvinyl acetate in the basic catalysis.
Copolymerization of vinyl chloride with bis(beta‐chloroethyl) vinylphosphonate
Authors: Gallagher R. , Hwa J. C. H.
Published: June 2010

Bis(beta‐chloroethyl) vinylphosphonate and vinyl chloride were copolymerized free‐radically in water suspension and in toluene solution at 55°C. From compositional analysis of the low‐conversion copolymers, the reactivity ratios of bis(beta‐chloroethyl) vinylphosphonate (r1) and vinyl chloride (r2) were found to be 0.37 ± 0.1 and 0.26 ± 0.05, respectively, indicating that the two monomers have a marked tendency to alternate. From the Q and e values of vinyl chloride, the corresponding Q.e values for the vinylphosphonate are calculated to be 0.23 and 1.73, respectively. Interestingly, the rate of copolymerization is greater than that of homopolymerization, and is also greater when water is present. These copolymerization characteristics are deemed favorable in industrial productions. The copolymers have lower viscosities and glass temperatures than poly (vinyl chloride). From patent literature, the copolymers also show useful flame retardant properties.
Polyquinolines: A class of rigid‐chain polymers
Authors: Beever W. H. , Stille J. K.
Published: June 2010

The reaction product of m‐cresol and phosphorus pentoxide has been shown by 31P‐nmr to consist of an equimolar mixture of mono‐ and di‐m‐cresyl phosphate. A mixture of pure di‐m‐cresyl phosphate and m‐cresol is an excellent polymerization medium for the preparation of polyquinolines via the Friedländer reaction, giving higher‐molecular‐weight polymers than can be obtained from the crude reaction of m‐cresol and phosphorus pentoxide. Spin‐lattice relaxation times T1 have been used to relate the chain mobility of the polymers in solution to the glass transition temperature (Tg) in the solid.
Kinetic aspects of the formation of the ordered phase in stiff‐chain helical polyamino acids
Authors: Miller Wilmer G. , Kou Lee , Tohyama Kohji , Voltaggio Vincent
Published: June 2010

The helical polyamino acids exhibit a two‐component temperature‐composition phase diagram that corresponds well in overall appearance to the Flory prediction for rigid, impenetrable rods. The phase diagram may be characterized as a narrow, typically 1–2%, biphasic region separating the disordered (isotropic) state from the ordered (liquid–crystalline) state, connected to a wide biphasic region in which nearly pure polymer is in equilibrium with nearly pure solvent. Initial studies have been undertaken to deduce the kinetics of formation of the ordered phase, both when the thermodynamically stable state is the ordered state, as well as when it is in an ordered‐disordered biphasic state. The time course of the formation of the ordered phase at different temperatures is reminiscent of analogous studies on polymer crystallization, describable by a nucleation and growth mechanism. Formation of the ordered phase when the final state is the narow biphasic state appears also to follow a nucleation‐growth mechanism. However, when the final state is the wide biphasic region, the morphology of the final state is that of an optically clear, self‐supporting gel, even at very low concentrations (as low as 0.03 wt %). The reasons for and nature of the gel state are believed to be a kinetic phenomenon. The shape of the phase diagram is such that the temperature range of thermodynamic metastability is small and phase separation occurs in the thermodynamically unstable region. In the unstable region the zero activation‐energy spinodal decomposition mechanism dominates the kinetics of phase separation, leading to bicontinuous interconnected phases that have little possibility or driving force to rearrange further. The polymer network structure is proposed to be a bulk thermodynamic phase, characterized by bundles or sheets of polymer between branch points, rather than individual chains as in the usual polymer network. Rheological, electron microscope, and light‐scattering data are presented that support this view. The possibility of other stiff‐chain polymers forming a network structure for similar reasons is discussed.
Properties of the ladder polymer cis‐syndiotactic poly(phenylsilsesquioxane) in solution
Authors: Helminiak T. E. , Berry G. C.
Published: June 2010

Studies on the properties of the double‐chain ladder polymer of cis‐syndiotactic poly(phenylsilsesquioxane) (PPSQ) in dilute and concentrated solutions are reported. Data on the intrinsic viscosity [η], the second virial coefficient A2, and the mean‐square radius of gyration 〈s2〉 as functions of molecular weight M, temperature, and solvent lead to the conclusion that the conformation of PPSQ can be modeled with a wormlike chain model with a persistence length ρ of 74 Å. These data cannot be used to assess the extent of intramolecular inflexibility, e.g., resistance to rotational isomerization, of PPSQ. For concentrated solutions (0.05 ⩽ c ⩽ 0.20 g/ml) the limiting viscosity ⩾0 at zero shear rate is proportional to cM for cM < ⩾2Mc and to (cM)3,4 for cM ⩾ ρ2Mc, where Mc = 9120. The product Xc (〈s20/M) × ρ2Mc/ma is equal to 356 × 10−17 for PPSQ, close to the value 400 × 10−17 typical of single‐chain polymers. The reduced flow curve ηK/ϵ0 versus ηCK for the viscosity ϵK as a function of shear rate K is not far different from that for single‐chain polymers—here, the time constant ηC is equal to η0R0 with R0 the limits of the recovery function RK, at small K(R0 is often denoted Je0). The values of ηc are intermediate to ηc for a flexible single‐chain polymer and the relaxation time ηR for rotatory diffusion of a rigid coil. Plots of RK versus K superpose with plots of the transient recovery R0(ϑ) with ϑ = K−1 over the limited range ηCK < 1 where ϑ is the recovery time (R0(ϑ) goes to R0 for large ϑ), similar to behavior found with solutions of single‐chain polymers.
Properties of an optically anisotropic heterocyclic ladder polymer (BBL) in dilute solution
Authors: Berry G. C.
Published: June 2010

Light scattering, intrinsic viscosity, gel‐permeation chromatography, and fluorescence depolarization measurements are reported on dilute solutions of a heterocyclic polymer (BBL) prepared by polymerization of 1, 4, 5, 8‐naphthalene tetracarboxylic acid with 1, 2, 4, 5‐tetraaminobenzene. The light‐scattering data on fractions of the polymer giving the anisotropy δ and the mean‐square radius of gyration s2 are discussed in terms of equations for the scattering from polydisperse anisotropic polymer. It is concluded from the dependence of δ and 〈s2〉 on the molecular weight that the polymer has a nearly rodlike conformation. The intrinsic viscosity data are analyzed in terms of relations for rods and wormlike chains. The fluorescence emission anisotropy is found to be so sensitive to molecular‐weight distribution that analysis in terms of molecular parameters is prohibited. Association that can occur under certain circumstances is discussed.
Production, characterization, and solution properties of dextran fractions of narrow molecular weight distributions
Authors: Basedow Arno Max , Ebert Klaus Heinrich
Published: June 2010

Fractional solution, fractional precipitation, and fractionation by incompatibility with polyethylene glycol are described for the preparation of dextran fractions in the molecular weight (MW) range from 10,000 to 500,000. Polydispersity (Mw/Mn) was about 1.1 at low MWs, increasing up to 1.3 for high MWs. Dextran fractions of lower polydispersity (<1.05) were obtained with preparative GPC on controlled pore glass columns. For the characterization of the dextran fractions, molecular weight distributions (MWD) were determined by GPC on calibrated columns. By combination of low‐angle laser light scattering and GPC absolute MWDs were obtained. Various studies of the properties of solutions of narrow dextran fractions were performed, such as viscosity measurements, calorimetric investigations (heats of solution and dilution) in several solvents, preferential solvation in mixed solvents, and solubility determinations in aqueous solutions of salts and other substances. The results indicate that dextrans with MWs > 2000 are almost perfect statistical coils in solution and that interactions between dextran molecules in solution are small, so that no association occurs. For MWs < 2000 solution properties give support to the assumption that transition to rodlike conformation occurs.
Cross‐linked copolymers of N,N‐diethylacrylamide with improved mechanical properties
Authors: Ulbrich K. , Kopeček J.
Published: June 2010

By using radical solution copolymerization of N,N‐diethylacrylamide and N‐tert‐butylacrylamide in the presence of a small amount of the cross‐linking agent, gels were prepared swollen to equilibrium in water at 25°C and possessing much better mechanical properties (elongation at break, stress at break) than those of the cross‐linked poly‐(N,N‐diethylacrylamide) alone. This is probably due to an increased possibility of hydrophobic interactions of copolymers. At the same time, the effect of the comonomer structure on the mechanical properties of the resulting gel is considered. The equilibrium degree of swelling of the gels steeply decreases with increasing temperature. Some parameters are compared which characterize the three‐dimensional network prepared both by the cross‐linking polymerization of N,N‐diethylacrylamide and by its copolymerization with N‐tert‐butylacrylamide (moduli of elasticity, X parameters, concentration of elastically effective chains, crosslinking effectivity, etc.), and the effect of these quantities on the gel properties is discussed.
On biological (anticoagulant) activity of heparin the high productive method for fractionation of commercial heparin
Authors: Noreika R. , Stepaniukiene E. , Lashas L.
Published: June 2010

A universal high productive chromatographic system is proposed for fractionation of com‐ mercial preparations of heparin. The system is suitable for the characterization on an analyti‐ cal scale and fractionation on a large scale of different preparations of heparin.
The biologic activity of polyanions: Past history and new prospectives
Authors: Regelson William
Published: June 2010

The toxicology of synthetic polyanions relates to molecular weight. This developed from experience with pyran copolymer (divinyl ether maleic anhydride copolymer), which was tested clinically as an antitumor agent and found to be too toxic for continued clinical trial. Synthetic polyanions of low molecular weight are potent stimuli to macrophage phagocytic function and possess antitumor activity. Increased host resistance to pathogens including bacteria, fungi, viruses, and trypanosomes is seen. In contrast to lower‐molecular‐weight fractions, higher‐molecular‐weight samples inhibit macrophage function, and apparently increased molecular weight > 15,000 is necessary for antiviral and immunologic stimulating capacity. One possible mechanism for the action of polyanions may relate to redistribution of calcium ions within the cell and increasing cyclic GMP activity. This is a redefinition for the role of polyanions in sol–gel alteration in cytoplasm. The killing effect of the polyanion‐activated macrophage on tumor cells resembles that of the polyanion on the nucleus. Polyanions may be potent controllers of the stability of DNA within the nucleus and can act to derepress cells to turn on protein synthesis or, alternatively, inhibit enzymes involved in virus synthesis and control of RNA or DNA polymerase. Thus, they are cogent tools in an understanding of the physiology of nuclear interaction. Biological use for these agents can be developed not only in clinical approaches to inhibition of tumor or viral infection, but to eliminate plutonium, and provide selective enzyme inhibition and protein interaction which allows for isolation, neutralization, and characterization of blood and tissue protein and glycoprotein fractions vital for a wide range of pathophysiology.
Polymerization of acetylene monomers by molybdenum compounds fixed on the macromolecular supports
Authors: Kiyashkina Zh. S. , Pomogailo A. D. , Kuzayev A. I. , Lagodzinskaya G. V. , Dyachkovskii F. S.
Published: June 2010

The techniques of heterogenization of homogeneous catalysts (molybdenum halogenized) for acetylene monomers polymerization on polymer supports have been worked out. The latter were carbon‐chain polymers grafted with functional groups. The properties of homogeneous and heterogenized catalytic systems have been compared. Heterogenized catalysts induce formation of the greatest amount of high‐molecular polyphenylacetylene. Some assumptions (on basis of MMD polymer analysis) about the mechanism of acetylene monomers polymerization by use of such catalysts have been suggested.
Metal‐containing co‐ordination polymers. VII. Studies on the structure of complexes formed in the reaction of a semicrystalline polyester with mgo
Authors: Vancsó‐Szmercsányi I. , Székely‐Pécsi Zs. , Kalló A.
Published: June 2010

Structural changes are detected by x‐ray diffractometry when a semicrystalline polyester of molecular weight of about 1000 having free carboxyl and hydroxyl end groups is reacted with MgO. The ratio of MgO to the COOH end groups alters the diffractograms. Supplementary structural studies were performed by various electron microscopic techniques. Differences were also detected in the supermolecular structure as a function of the MgO to COOH ratio. Furthermore, at the equivalent ratio a fiber‐forming solution can be prepared; while the equimolar ratio results in a gel‐like system. This is in accordance with our previous conclusions about the mechanism of the reaction (association), i.e., at a molar ratio of the COOH group to MgO of 2:1 (equivalent amounts) the forming of aCOO− Mg2+ −OOClinkage is preferred; while in the case of an equimolecular amount of COOH and MgO, the possibility of the association of other groups of the polyester chain (such as CO groups and alcoholic end groups) increases creating associates of greater size.
A new support for whole cell immobilization
Authors: Vijayalakshmi M. A. , Marcipar A. , Cochet N.
Published: June 2010

A new support for whole‐cell immobilization based on crosslinked pectate with iminodiacetate as polydentate spacer and iron is proposed. Microorganisms of the strains Escherichia coli, Staphiloccoccus aureus, Saccharomyces cereviseae, and Candida tropicalis have been immobilized on this matrix. Immobilization capacity of the support, conditions of adsorption, and differences in respiration between free and fixed cells have been evaluated. Using scanning electron microcopy, electron micrographs of the support and of cells fixed on the support were prepared in order to examine fixation in detail. It was found that it is possible to immobilize an important active biomass, with a very strong binding strength, between cells and support, without the inherent diffusional limitations encountered in other methods. Respiration measurements showed increased oxygen demand by immobilized cells.
Investigation of interaction between methemoglobin and polymethacrylates containing imidazole or hydrophobic side chains by means of epr spectroscopy
Authors: Pommerening K. , Ristau O. , Kühn M. , Mohr P. , Štamberg J. , Beneš M.
Published: June 2010

Macroporous polymethacrylates containing imidazole groups as well as hydrophobic side chains adsorb methemoglobin (metHb). The protein‐matrix interaction was investigated by means of an electron paramagnetic resonance (EPR) spectroscopy. The adsorption of metHb to the imidazole containing matrices occurs by complex formation with the iron of the prosthetic group. In case of steric hindrance or long spacers, this complex formation is not primarily responsible for the adsorption. The binding of metHb to hydrophobic side chains clearly demonstrates the presence of a metHb‐H2O‐metHb‐OH mixture. Moreover, the protein‐matrix interaction induces conformational changes in the protein component. In this case, additional signals in the EPR spectra indicate the formation of a cytochrome P450‐like structure.
Molecular aspects of affinity chromatography
Authors: Mohr P. , Pommerening K. , Kühn M.
Published: June 2010

Affinity chromatography is based on the well‐known specific interaction between biomacromolecules and between biomacromolecules and low‐molecular partners. To separate the one component (bioaffine component), the complementary bioaffinant has to be attached chemically to a solid‐phase support. This interaction, however, can be disturbed considerably by the linkage of one partner to the insoluble matrix. Some molecular aspects of this interaction discussed in a summarized presentation of our investigations are: (1) conformational state of immobilized biomacromolecules; (2) nonspecific interaction between matrix and bioaffine component; (3) steric factors; and (4) interaction between spacer and/or carrier and bioaffine components.
Application of macroporous sorbents in antioxidants determination
Authors: Šmejkal František , Popl Milan , Čihová Alena
Published: June 2010

For LC separation of antioxidants with differently sterically shielded polar groups, a selective interactions solute‐mobile phase may be utilized. Improvement of the separation in the reversed‐phase LLC can be achieved by means of utilization of the various interaction profiles of some solvents. In this study, reversed‐phase LLC with a macroporous gel, Separon SE, was applied for characterization of the retention behavior of some antioxidants and for the determination of these compounds in rubber and plastics.
Equilibrium and nonequilibrium dynamics of sorption and chromatography on ion exchangers with polyelectrolyte surface layer
Authors: Samsonov G. V. , Elkin G. E.
Published: June 2010

Dynamic and chromatographic processes of isolation and purification of antibiotics and amino acids on surface‐layer ion exchangers have been investigated. It was shown that the optimum conditions of sorption and desorption on these exchangers can be determined by using a criterion for the regularity of the dynamic process. Theoretical predictions are in agreement with experimental data on the sorption and desorption of slowly diffusing organic ions.
Oxidation of isopropanol catalyzed by polymer‐bound cobalt complexes
Authors: Maternová J. , Setínek K.
Published: June 2010

The oxidation of isopropanol in glacial acetic acid catalyzed by soluble and polymer‐bound cobalt (II) complex ions has been studied. In both cases, the oxidation proceeds as a homolytic reaction and the catalyst acts as an initiator of the decomposition of peroxides to radicals. The oxidation activity of the free‐ and fixed‐cobalt (II) ions increases in the presence of the bromine ion. Heterogenized cobalt (II) ions also catalyze the gas‐phase oxidation of the title alcohol. Their activity is conditioned by the presence of acetic acid in the inner co‐ordination sphere of the metal. The gasand liquid‐phase reactions proceed by the same reaction mechanism.
Stretching calorimetry of some poly(α‐amino acid)s
Authors: Ebert G. , Knispel G. , Müller F. H.
Published: June 2010

Stretching of poly(α‐amino acid) fibers or films as well as natural occurring protein fibers like wool is accompanied by heat effects due to conformation changes of the macromolecules and by orientation changes, sliding processes, etc. Such phenomena were studied by using a stretching calorimeter.
The radiation resistance of nylon‐6
Authors: Wilski H.
Published: June 2010

This article presents a systematic investigation into the influence of dose rate on the results of irradiation of Nylon‐6 in air.
Thermodynamic properties and glass transition of polystyrene
Authors: Chang Shu‐Sing
Published: June 2010

The heat capacity of a narrow molecular weight distribution polystyrene, National Bureau of Standards—Standard Reference Material 1478, has been determined by a fully automated adiabatic calorimeter from 5 to 380 K for the sample subjected to different thermal history. The number‐average molecular weight of this sample is 35,800 and the dispersity in the molecular weights, Mw:Mn, is 1.045. The heat capacities of the glass and of the liquid of this material are found to be within 0.5% of other atactic polystyrenes over most of the temperature range studied. The glass transition temperature Tg of the annealed glass (cooling rate < 1 K/h) at 366 K and that of the quenched glass (cooling rate about 6 K/min) at 366 K are determined by the intersections of enthalpy‐temperature curves of the glasses with the liquid. The glass transition temperature is slightly higher than that calculated from dilatometrically determined Tgs of a series of low‐polydispersity polystyrenes cooled at 0.1 K/h, but is lower than that from thermal analytically determined Tgs.
Stretching calorimetry and thermoelasticity of rubbers at different temperatures
Authors: Kilian H.‐G. , Höhne G. W. H. , Trögele P. , Ambacher H.
Published: June 2010

The data of isothermal stretching calorimetry on rubbers at different temperatures above room temperature are presented. Based upon the van der Waals equation of state for rubbers calculations can be fitted to the experimental data obtained by simple elongation whereby the thermoelastic behavior is related to a constant thermal expansion coefficient in the unstrained state and to an invariant temperature coefficient of the end‐to‐end distance of the equivalent freely jointed chain.
Effects of ph and electrolytes on absorption and luminescence spectra of water‐soluble polydiacetylenes
Authors: Bhattacharjee H. R. , Preziosi A. F. , Patel G. N.
Published: June 2010

Water‐soluble polydiacetylenes, RC—CC—CR, where R is either (CH2)3,4OCONHCH2COOK or (CH2)3,4COOK, undergo visual (yellow ↔ red or purple) reversible conformational (nonplanar ↔ planar) transitions by varying the pH of the solution as well as by the addition of different monovalent electrolytes, such as KCl and LiCl. Polyvalent cations such as Ca2+ cause precipitation of the polymer due to crosslinking. The conformational changes caused by the variations in pHs can be viewed as a gradual ion exchange process, for example, K+ is exchanged with H+ or vice versa. The transition phenomena were studied by visible absorption spectroscopy. The broadest spectral change (465 nm ↔ 575 nm) occurred when the pH of the solution was changed from 9 to 2. The spectral shifts displayed by the additions of electrolytes were rather narrow (465 nm ↔ 515 nm), the corresponding color change being yellow ↔ red only. The luminescence properties (fluorescence only) of these water‐soluble polydiacetylenes were also studied. The fluorescence is pH dependent, being observed only at relatively higher pHs. Both absorption and emission spectra revealed some anomalous phenomena for which explanations are provided through experimental evidence.
Netted or tangled? hydrophobic or hydrophilic? stiff or flexible? a review of some polyelectrolyte chemistry
Authors: Hatch Melvin J.
Published: June 2010

In this talk, highlights and an interconnected thread of ideas will be presented in relation to the following specific areas of polyelectrolyte research: (1) the development of ion retardation resins, which are “snake‐cage” or semi‐interpenetrating polyelectrolyte systems that absorb ionic species reversibly; (2) the synthesis of specially and chelating ion exchange resins, by overcoming barriers to polymer reactivity; (3) reactive sulfonium monomers and polymers, in relation to coatings; (4) the enhancement, by chain stiffening, of the viscosifying effect of high molecular weight polyelectrolytes, in relation to improved water‐flooding of oil wells. In the talk, the qualitative importance of the factors given in the title will be emphasized, and the influence of the work of Turner Alfrey will be illustrated.
Sorption and diffusion in multicomponent polymers
Authors: Rogers C. E.
Published: June 2010

The solution, diffusion, and permeation of low molecular weight substances in polymeric materials are governed by the relative chemical compositions and physical structures of the penetrant molecule and the polymer. Those factors determine the chain segmental mobility, defect structures, and interactions which control the sorption magnitude and penetrant molecular mobility within the polymer. The transport of relatively noninteracting penetrant molecules in a polymer almost always follows the classical behavior predicted by Fick's law relationships with a constant (or nearly so) diffusion coefficient. An increase in generalized interactions (van der Waals, etc.) leads to increased sorption of the penetrant, with consequent increase in plasticization of the polymer, such that the diffusion process often becomes concentration‐dependent. Then, depending upon the relative rates of polymer relaxation processes concurrent with the sorption‐diffusion process, the overall transport process may exhibit Fickian behavior with a simple concentration‐dependent diffusion coefficient or it may deviate significantly from that behavior due to complicating relaxation effects. Systems in which there may be more specific interactions (hydrogen‐bonding, polar, ionic) often show a pronounced dependence of transport behavior on compositional, temporal, and spatial parameters which relate to changes in sorption modes. In these present investigations, we have used copolymer systems, prepared under controlled conditions, to gain some further insight into the dependence of polymer structure on variations in composition and how these variations affect or are reflected by transport and relaxation properties.
Correlations between polymer matrix and composite mechanical properties
Authors: Adams Donald F.
Published: June 2010

During the past decade or more, the composite materials community has restricted itself primarily to the use of only a few structural epoxy matrix materials. Very recently, whole new families of polymer matrices have become of practical interest. In order to select from this wide range of new polymers for each specific structural application, the relation between the various polymer mechanical and physical properties, e.g., modulus, strength, strain to failure, thermal and moisture expansion coefficients, moisture absorption rate, etc., and resulting composite properties must be known. Correlations of finite element analysis predictions with actual experimental data will be presented, using measured mechanical and physical response properties of various toughened epoxy, bismaleimide, polyimide, and thermoplastic matrix systems as inputs to the analyses. Results will include fracture mechanics evaluations, the role of matrix nonlinear response, crack initiation and propagation, thermally induced damage, and the influence of the interface. Matrix properties to be modeled have been generated in the author's own laboratories, as part of several current and ongoing funded research studies for various government and industry groups. Several types of finite element analyses have been used, including 2‐dimensional generalized plane strain with longitudinal shear loading, 2‐dimensional axisymmetric, and fully 3‐dimensional formulations. All of these analyses permit the input of actual matrix nonlinear stress‐strain response, and how it varies as a function of temperature and moisture content. Fibers having anisotropic properties in a composite of arbitrary fiber volume are included. Time‐dependent response, e.g., creep, recovery, and relaxation, and crack propagation are also possible response modes. Results will be presented in the form of composite stress‐strain curves, plots of stress contours in the matrix, and at the fiber‐matrix interface.
Some criteria for the design of polyurethaneurea elastomers
Authors: Spell H. L. , Macdonald C. E. , Turner R. B.
Published: June 2010

Given the numerous variables in composition, reaction conditions, and processing, the design of a polyurethane elastomer with a specified set of properties is indeed a challenging task. The control of characteristics such as heat stability, toughness, fatigue, and other key qualities requires a compendium of theoretical and experimental knowledge. Optimizing a single property, e.g., low temperature resiliency, can necessitate changes in composition that may compromise other important properties. Thus, to balance the entire system in order to meet the specification limits, much more than an empirical approach is needed to achieve the goal in a reasonable time. In this presentation, we will demonstrate that, by use of an array of sophisticated testing methods and carefully designed experiments combined with computer modeling, the tailoring of a segmented elastomer can be placed on a scientific basis. Key methods of characterization are dynamic mechanical spectroscopy, small angle X‐ray scattering, electron microscopy, Fourier transform infrared, and differential scanning calorimetry. Special experiments included the systematic synthesis and testing of a wide range of model compounds. Optimum soft segment properties such as chain length and mobility were defined. Hard segments that are properly segregated and have high thermal and mechanical integrity were synthesized and characterized. These and related experiments have led us to a better understanding of the molecular mechanisms underlying the mechanical and thermal behavior of an elastomer. With this knowledge we can select molecular components and control phase relationships in building elastomers to meet end use requirements that demand maximum static and dynamic polymer properties.
Modern design data for short‐fiber thermoplastic composites
Authors: Turner S.
Published: June 2010

Items fabricated from thermoplastics containing short glass fibers are anisotropic and the anisotropy varies from point to point. Guidance as to how such materials should be evaluated and what data are required for the design of end products molded from them is provided by a combination of the theories of viscoelasticity and anisotropic elasticity, whereby the stiffness and compliance coefficients of the latter are functions of time, temperature, and strain. A methodology then emerges, similar in overall nature to that pertaining to thermosetting resins containing long aligned fibers, but rather more complex because of the variations in fiber alignment. However, an adequately comprehensive evaluation in accordance with the formal rationale tends to be prohibitively expensive and, on the other hand, a curtailed evaluation can yield misleading data. Recent work aimed at resolving that impasse seems promising. The central principle is the use of special test specimens chosen because their flow geometries and possible flow irregularities are similar to those commonly found in commercial end products. The data that can be derived from such specimens can be related quantitatively to those derived from the conventional tests, and therefore the presentation and use of the new class of data entail no interpretation difficulties. Examples of what has been achieved and speculations about what might further be achieved are presented in the paper.
The thinking injection molding machine: A followup to systematic process analyses
Authors: Menges G. , Janke W. , Matzke A.
Published: June 2010

Latest injection molding machines are often equipped with process control computers monitoring and controlling operating sequence, injection speed, holding pressure, clamping motion, clamping force, and all temperatures. This provides for the possibility to overlay process‐related optimization programs for adaptation of the machine to the respective material condition and programs for the machine control. The following pages inform about such optimization programs.
Recent developments in sheet molding compound technology
Authors: Newman Seymour , Fesko Donald G.
Published: June 2010

The molding of fiber‐reinforced thermoset components is a complex process involving a highly exothermic chemical reaction which takes place in the presence of flow and thermal gradients. The flow in turn is complicated by time and temperature‐dependent rheological characteristics. The industry has grown largely on the basis of empirical developments. However, numerous problems do remain which required increased understanding for solution. This report reviews work underway in numerous laboratories to characterize the flow and cure of SMC and phenomena associated with these processes such as orientation, mechanical properties, residual internal stresses, mold fill, and surface defects.
Mean field theory for the rheological properties of moderately concentrated polymer solutions in transversal shear flow
Authors: Hess Walter
Published: June 2010

Moderately concentrated polymer solutions are described as a suspension of interacting harmonic dumbbells. The interaction is treated in a mean field approximation. In the framework of this model the exact conformational distribution function for transversal shear flow is obtained. The shear viscosity and the first normal stress coefficient show the typical non‐Newtonian form with a distinct power law behavior after the onset of shear rate dependence.
Extended Occupational and Positional Disorder in Pavonite Homologous Copper Bismuth Chalcogenide Halogenides
Authors: Heerwig Andreas , Thybaut Cyril Louis Jaques , Ruck Michael
Published: June 2010

Melting reactions of CuBr, BiBr3 and Bi2Q3 (Q = S or Se) resulted in black needles of quaternary chalcogenide bromides. Cu1.5Bi2.64S3.42Br2.58 has a melting point of 708(5) K and crystallizes in the monoclinic space group C2/m with a = 1315.1(3) pm, b = 410.28(5) pm, c = 937.2(2) pm, β = 90.33(2)° at T = 293(2) K. The isostructural selenide Cu1.57Bi2.37Se2.68Br3.32, which melts at 724(5) K, has the lattice parameters a = 1353.9(3) pm, b = 417.54(5) pm, c = 960.4(2) pm, β = 91.13(2)°. Black needles of the selenide iodides Cu1.57Bi4.69Se7.64I0.36 and Cu2.31Bi5Se8.31I0.69 were obtained by chemical vapor transport of CuI and Bi2Se3. They also crystallize in space group type C2/m with a = 1373.9(4) pm, b = 417.4(1) pm, c = 1464.6(4) pm, β = 115.57(2)°, and a = 1369.1(3) pm, b = 416.6(1) pm, c = 1526.4(3) pm, β = 99.81(3)°, respectively. All four compounds belong to pavonite homologous series. Their structures are built up of two alternating types of layered modules parallel (001), denoted A and B. Composition and shape of module A are almost the same in all structures. They consist of paired rods $\rm ^1_\infty[BiQ_{3/3}X_{2/2}Z_{2/2}]$ = Br, I) running along [010] and copper(I) cations that are distributed over various voids between the rods. Modules of type B are composed of [MZ6] octahedra (M = Bi/Cu), which are arranged in NaCl‐type fragments of thickness N = 1, 3 or 4. The Joint Probability Density Function (JPDF) reveals a continuous pathway for copper ion transport along [010] in the case of the sulfide bromide. The pseudo‐potential for hopping of copper ions was calculated as 47 meV only. The electrical and thermal conductivities as well as the Seebeck coefficient were determined to evaluate the thermoelectric properties.
Surgical correction of equinus deformity in children with cerebral palsy: A systematic review
Authors: Shore Benjamin J. , White Nathan , Kerr Graham H.
Published: June 2010

Purpose

Equinus is the most common deformity in cerebral palsy. However, despite the large volume of published studies, there are poor levels of evidence to support surgical intervention. This study was undertaken to examine the current evidence base for the surgical management of equinus deformity in cerebral palsy.

Methods

A systematic review of the literature using “equinus deformity”, “cerebral palsy” and “orthopaedic surgery” generated 49 articles. After applying inclusion and exclusion criteria, 35 articles remained. The Oxford Centre for Evidence-Based Medicine (CEBM) levels of evidence and the Methodological Index for Non-Randomized Studies (MINORS) were used to grade the articles.

Results

Studies ranged in sample size from 9 to 156 subjects, with an average of 38 subjects. The mean age of subjects at index surgery ranged from 5 to 19 years. Nineteen studies used instrumented gait analysis, with an average follow-up of 2.8 years. Seven studies reported that a younger age at index surgery was associated with an increased risk of recurrent equinus. The average rate of calcaneus in hemiplegic children was 1% and it was 15% in those with spastic diplegia. Most studies were level 4 quality of evidence, leading to, at best, only grade C recommendation.

Conclusions

Cerebral palsy subtype (hemiplegia versus diplegia) and age at index surgery were the two most important variables for determining the outcome of surgery for equinus deformity in cerebral palsy. Despite the great emphasis on differences in surgical procedures, there was less evidence to support the type of operation in relation to outcome.
Patterns in rotating Rayleigh–Bénard convection at high rotation rates
Authors: SCHEEL J. D. , MUTYABA P. L. , KIMMEL T.
Published: June 2010

We present the results from numerical and theoretical investigations of rotating Rayleigh–Bénard convection for relatively large dimensionless rotation rates, 170 < Ω < 274, and a Prandtl number of 6.4. Unexpected square patterns were found experimentally by Bajaj et al. (Phys. Rev. Lett., vol. 81, 1998, p. 806) in this parameter regime and near threshold for instability in the bulk. These square patterns have not yet been understood theoretically. Sánchez-Álvarez et al. (Phys. Rev. E, vol. 72, 2005, p. 036307) have found square patterns in numerical simulations for similar parameters when only the Coriolis force is included. We performed detailed numerical studies of rotating Rayleigh–Bénard convection for the same parameters as the experiments and simulations. To better understand these patterns, we compared the effects of the Coriolis force as well as the centrifugal force. We also computed the coefficients of the amplitude equation describing one-, two- and three-mode bulk solutions to rotating Rayleigh–Bénard convection. We find that squares are unstable, but we do find stable limit cycles consisting of three coupled oscillating amplitudes, which can superficially resemble squares, since one of the three amplitudes is rather small.
Internal tide generation by arbitrary two-dimensional topography
Authors: ECHEVERRI PAULA , PEACOCK THOMAS
Published: June 2010

To date, analytical models of internal tide generation by two-dimensional ridges have considered only idealized shapes. Here, we advance the Green function approach to address the generation of internal tides by two-dimensional topography of arbitrary shape, employing the Wentzel-Kramers-Brillouin (WKB) approximation to consider the impact of non-uniform stratifications. This allows for a more accurate analytical estimation of tidal conversion rates. Studies of single and double ridges reveal that the conversion rate and the nature of the radiated internal tide can be sensitive to the topographic shape, particularly around criticality and when there is interference between wave fields generated by neighbouring ridges. The method is then applied to the study of two important internal tide generation sites, the Hawaiian and Luzon Ridges, where it captures key features of the generation process.
The Meaning and Legacy of the Magna Carta
Authors: Worcester Kent
Published: June 2010

The six essays of this symposium address different aspects of the meaning and legacy of the Magna Carta—“the Great Charter” in Latin. Although social scientists and legal scholars routinely describe the Magna Carta as foundational for concepts of justice and liberty, the charter itself is rarely assigned in political science classes or scrutinized by political theorists. The aim of the symposium is twofold: first, to affirm the document's historical rootedness and intellectual richness, and, second, to explore the ways in which the Magna Carta's text and reputation have informed the development of common law and modern politics. The Magna Carta was the product of times very different from our own, yet it continues to be cited by jurists and human rights activists around the globe. This symposium makes the case for why political scientists should take an interest in the Magna Carta, not just as a cultural icon, but as a durable political text.
With a Little Help from a Friend: Habeas Corpus and the Magna Carta after Runnymede
Authors: Wert Justin J.
Published: June 2010

At the beginning of the twentieth century, Charles McIlwain observed that the new histories of the Magna Carta were portraying the charter as a “document of reaction” that could only fulfill its purported greatness “when men [were] no longer able to understand its real meaning” (McIlwain 1914, 46). Characteristic of these early-twentieth-century writers was Edward Jenks, who, in his 1904 article “The Myth of Magna Carta,” came to the conclusion that the real beneficiaries of the document—the liber homo of Article 39—were not “the people” we traditionally imagine, but rather an “aristocratic class … who can no more be ranked amongst the people, than the country gentleman of to-day” (Jenks 1904, 269). Although Jenks's position is often criticized as extreme, it is nevertheless the case that virtually all of the Magna Carta's modern commentators recognize vast historical inaccuracies in the Whiggish accounts of the charter's development up until the late nineteenth century (Radin 1946; Reid 1993; Halliday 2010, 15–16). What these new revisionist histories suggested was that the Magna Carta's great provisions—due process and trial by jury—only became great when, forgetting or ignoring the charter's seemingly lackluster beginnings, generations subsequent to 1215 gave them new meaning.
Tortured Relations: Human Rights Abuses and Counterterrorism Cooperation
Authors: Hafner-Burton Emilie M. , Shapiro Jacob N.
Published: June 2010

Two big assumptions fuel current mobilization against and policy discussions about the U.S. war on terror and its implications for human rights and international cooperation. First, terrorism creates strong pressures on governments—especially democracies—to restrict human rights. Second, these restrictions are not only immoral and illegal, but also counterproductive to curbing terrorism. If these two assumptions are correct, then democracies face a vicious circle: terrorist attacks provoke a reaction that makes it harder to defeat terrorist organizations.