bluuebunny/crossref_metadata_2025_split huggingface dataset:
A kinetic investigation of the emulsion polymerization of vinyl chloride
Authors: Ugelstad J. , Mork P. C. , Dahl P. , Rangnes P. 
Published: June 2010

AbstractAn investigation of the kinetics of the emulsion polymerization of vinyl chloride has been performed. The effect on the rate of reaction of such variables as concentration of initiator (K2S2O8), amount and type of emulsifier and number of latex particles has been investigated at 50°C. The order of reaction with respect to initiator was found to be 0.5. The rate of reaction was found to increase with increasing conversion. The number of latex particles was found to be constant during the polymerization, between 10 and 90% conversion, and also found to be independent of the concentration of initiator. The order of reaction with respect to the number of particles was found to increase from 0.05 to 0.15 in the range investigated (Nw = 1016‐1019 per liter H2O). The order decreases slightly with increasing conversion. A mechanism involving a rapid desorption and reabsorption of radicals in the latex particles is proposed. A marked increase in rate was observed at about 70–80% conversion. A closer investigation of this phenomenon was performed by a continuous addition of vinyl chloride at a pressure below the saturation pressure of vinyl chloride corresponding to the reaction temperature. It appeared that under such conditions reaction rates of about twice those of the ordinary runs might be obtained. No change in the number of particles was observed, either during the polymerization or compared to the ordinary run at the same concentrations of emulsifier and initiator. The effect of the degree of reduction in the pressure of vinyl chloride was also investigated. It was found that the rate of reaction passed through a maximum at a pressure of about 6.75 atm, as compared to 7.75 atm in an ordinary run (Saturation pressure of vinyl chloride at 50°C).
The application of continuously uniform latices to kinetic studies of “ideal” emulsion polymerization
Authors: Williams D. J. , Grancio M. R. 
Published: June 2010

AbstractIn kinetic studies of emulsion polymerization, the use of latices which are completely uniform through all stages of growth offer a marked improvement in analytic accessibility over their polydispersed counterparts. This paper first reports recent developments in the technique of generating such model systems and their utility in studying the “ideal” period in emulsion polymerization. Special precautions are necessary in the use of the slow soap addition techniques since soap starvation can sometimes lead to agitation‐controlled reaction rate, and/or latex instability. A convenient‐to‐use, single‐charge formulation for styrene was developed, based on a combination of anionic and nonionic surfactants; this formulation eliminated the mixing problem and produced stable, continuously uniform latices suitable for generalized kinetic studies. Also, data on the development of both Mv and Mv in these systems give some insight into the nature of the reaction. Current steady‐state theories and the rationale associated with them predict for the “ideal” period the generation of polymer with constant molecular weight, but a substantial increase in both Mv and Mv is observed. These results suggest that either an unsteady‐state mechanism prevails or that our knowledge of the mechanism of initiation is inadequate.
Determination of latex particle size by light scattering. VIII. Forward angle ratio method
Authors: Maron Samuel H. , Pierce Percy E. 
Published: June 2010

AbstractAlthough dissymmetry of light scattering is a simple and attractive method for determination of latex particle size, it is limited in application to values of D/γm below 0.60 for monodisperse systems, and practically inapplicable to polydisperse ones. Further, its use requires Fresnel corrections, and a knowledge of the refractive index ratios of the systems investigated. To obviate some of these difficulties, a method is described which utilizes the intensity ratios for two forward angles differing by 10°, such as 45°/35°. With such forward angle ratios Mie calculations show, and experiment confirms, that particle diameters up to D/γm = 2.00 or higher can be measured for monodisperse systems. Again, no Fresnel corrections are required, and the results are practically independent of refractive index ratio between 1.15 and 1.20. However, like the dissymmetry method, the forward angle ratio method is very sensitive to polydispersity, and results are obtained here which vary with the distribution of the systems, the angle ratio, and the wavelength of light used.
Particle size and molecular weight distributions of various polystyrene emulsions
Authors: Krackeler J. J. , Naidus H. 
Published: June 2010

AbstractThree different emulsion polymerization techniques, the batch (B), monomer addition (M Add), and emulsion addition (E Add) procedures were studied. Rates of polymerization indicated that the B reacted more rapidly than either the M Add or E Add. This was related to the lower monomer concentration present in the M Add and E Add systems. This is described as monomer starvation. MW and MW distributions were compared for these polymers. The B polymer had a significantly higher MW than either the M Add or E Add polymer. This could also be related to monomer starvation in the latter systems. However, the MW distribution of these polymers gave comparable values of Mw/Mn = 3.1. This indicates a similar molecular growth phenomena which appears to result from polymerization occurring near the particle surface for the addition systems. Particle size distribution measurements showed the B latex to have the narrowest distribution while the E Add latex had the widest. Also, the M Add had a particle diameter distribution which was approximated by a normal distribution. This is explained by use of the monomer starvation concept. Additional polymerizations were carried out called “hybrids” which were variations of the polymerizations discussed above. Significant differences result from the various techniques of emulsion polymerization. These differences manifest themselves not only in average particle size and MW, but also in particle size distribution. No significant differences were obtained in MW distributions.
Packing efficiency in sediments of monodisperse latexes and bimodal latex mixtures
Authors: Hiemenz Paul C. 
Published: June 2010

AbstractThe packing efficiency of monodisperse polystyrene latexes stabilized by the sodium salt of 2‐sulfoethylmethacrylate was studied by centrifuging the dialyzed latexes. The solids level of the sediments were examined for 0.6 and 3.4 μ particles alone and in mixtures of various proportions. Monodisperse latexes produced sediment densities in the range of 54 to 64 vol‐%, and binary mixtures ultimately produced residues showing maximum sediment densities of about 80 vol‐% at some optimum mixture composition. Both the uniform and bimodal samples thus showed packing efficiencies somewhat less than the theoretical maxima, about 74 and 86 vol‐%, respectively. Colloidal instability and particle solvation are discussed as explanations for the deviations from maximum packing efficiency.
Investigation of the disposition of surfactant in a latex by the “rate of dialysis method.” Mechanism of detergent dialysis
Authors: Edelhauser Helmut A. 
Published: June 2010

AbstractThe initial rate of dialysis across a cellophane membrane for sodium dodecylsulfate and dodecylbenzenesulfonate proved to be dependent on surfactant concentration without a break at the critical micelle concentration (cmc) and could, therefore, be used to determine free surfactant concentration in latices over a wide range. Equilibrium dialysis is not a suitable tool, because, if the cmc is exceeded in the dialyzate, diffusion comes practically to a dead stop long before equilibration, at least with ordinary detergents. (Dialysis is, however, resumed at a substantial rate if dialyzate and dialyzed solution are replaced by newly prepared solutions of the same concentration.) An explanation for these phenomena is suggested. Free surfactant concentrations measured by rate of dialysis were far below the cmc in a polystyrene latex and far above the cmc in a comparable poly(vinyl acetate) (PVA) latex. When increasing the surfactant‐polymer ratio in a PVA dispersion by post‐addition complete solubilization of the polymer is observed eventually. Concentrations of free surfactant and of solubilized polymer were measured for the intermediate stages. The experimental data indicate a twofold mechanism for the solubilization process: Surfactant penetrates into the interior of PVA particles taking water with it and causing swelling to the point of disintegration, parallel to which single chains from the outer parts of the particles are already disentangled and solubilized. It is concluded that in a PVA latex only a comparatively small portion of the anionic surfactant will be at the particle surface, a relatively large part being in the aqueous phase and in the particle interior, which may account for this surfactant being a poor stabilizer in vinyl acetate emulsion polymerization at high total solids content.
Chitin and its association with other molecules
Authors: Rudall K. M. 
Published: June 2010

AbstractChitin or poly‐N‐acetyl‐D‐glucosamine occurs in three crystallographic forms α, β and γ. The α form is the most stable and consists of antiparallel chains. The β form (parallel chains – one chain per unit cell) and the γ form (probably two chains up and one down per unit cell) are both converted to the antiparallel arrangement (α form) on treatment in strong HCl. Chitin in the cuticles, apodemes and chaetae of animals occurs together with a considerable quantity of protein. X‐ray diffraction diagrams of the intact structures show repetition along the fiber axis corresponding to six NAG residues, or (more rarely observed) to eight NAG residues. The structural studies of Phillips and his colleagues on the reaction of lysozyme with NAG oligomers are taken as a relevant model for those chitin/protein complexes showing a repetition of six NAG residues/protein unit. In the case of locust tibia cuticles, evidence is presented for the existence of corpuscular protein units along chitin microfibrils and these repeat at 31 Å i.e. every six NAG residues. It is suggested that these protein units are basically a chitin synthetase but serving also as a “plasticiser” to modify the mechanical and water‐holding properties of the chitin.
The wetting of cellulose and wood hemicelluloses
Authors: Luner P. , Sandell M. 
Published: June 2010

AbstractThe wetting properties of wood polysaccharides were characterized by Zisman's empirical parameter, the critical surface tension of wetting, γc. Cellulose was tested in the form of cellulose films regenerated from viscose and cellulose acetate. It was found that the source of cellulose (cotton, wood and hydrolyzed cellulose), the method of film preparation (single‐bath, two‐bath, dry‐cast, orientation), and consequently the physical state of the cellulose surface, influenced the wettability of the samples. Contact angles were also measured on hemicellulose films derived from hardwoods and softwoods. The critical surface tension γc ranged from 35.5 to 49.0 erg cm−2 for cellulose and from 33 to 36.5 erg cm−2 for hemicellulose films. The hemicellulose samples showed the smallest hysteresis effects which may be related to its energetically more uniform surface or lower porosity. The effect of moisture on contact angle measurements is discussed. Finally, the wetting of cellulose is evaluated in terms of recent theories relating surface energies and intermolecular forces.
Conformational analysis of polysaccharides. III. The relation between stereochemistry and properties of some natural polysaccharide sulfates (1)
Authors: Rees D. A. , Steele I. W. , Williamson F. B. 
Published: June 2010

AbstractThe sol → gel → sol transformation of aqueous K‐carrageenan occurs with complex changes in optical rotation which may be explained qualitatively in terms of the double helix model for junction zones. Evidence is given that the double helices in the gel are normally aggregated but can be kept separate within a narrow temperature range, and that gelation is a kinetic rather than an equilibrium process. An attempt has been made to predict the preferred conformations of irregular carrageenans by joining segments of simpler polysaccharides; the effect of certain structural variations on gel properties may then be explained. Model building in the computer does not exclude the possibility of double helices for the following polysaccharides which are structurally related to K‐ and i‐carrageenan: hyaluronic acid, chondroitin, chondroitin 4‐sulfate, chondroitin 6‐sulfate, dermatan sulfate, keratan sulfate, agarose, porphyran, μ‐carrageenan and furcellaran.
A short history of superconductivity
Authors: Bloch Felix 
Published: June 2010

AbstractShortly after its discovery the electron was recognized as the carrier of electricity in metals. The difficulties encountered in treating the conduction electrons as a classical ideal gas was removed upon the advent of quantum mechanics and led to a satisfactory explanation of normal metallic conductivity. Although superconductivity was discovered more than fifty years ago, however, the first phenomenological theory did not come until the middle thirties and it took another twenty years before the first microscopic theory was presented. It was based upon the assumption that the conduction electrons formed a degenerate Bose gas but was soon replaced through the recognition that the pairing of electrons in a Fermi gas furnished a more realistic and quantitative explanation of superconductivity. The striking manifestation of superconductivity as a quantum phenomenon on macroscopic scale was demonstrated in the early sixties through the discovery of flux‐quantization in a closed superconductive ring and led shortly afterwards to the interesting related effects which arise from the introduction of a dividing barrier.
The exciton mechanism: Studies in model compounds
Authors: Schneider Richard S. 
Published: June 2010

AbstractThe “Little” model for a macromolecular high temperature superconductor can be discussed in terms of its component parts. Studies on molecules designed to serve as the polyene and the polyene spine indicate that polymeric metallocenes, in which planar aromatic hydrocarbon rings and meatal atmos alternate, may be suitable. Toward this end the hydrocarbon dicyclopentanaphthalene, and various substituted derivatives were synthesized, and the polymerization of the corresponding dianions with ferrous chloride were investigated.
Electron delocalization in anion‐radicals of permethylcyclopolysilanes
Authors: West Robert 
Published: June 2010

AbstractThe family of cyclic permethylpolysilanes, [(CH3)2Si]n, has been synthesized. Compounds in which n = 5, 6 and 7 undergo reduction at low temperatures to form anion‐radicals. The five‐ and six‐membered rings give the parent anion‐radicals [(CH3)2Si]5− and [(CH3)2Si]6− when reduced electrolytically, but all three compounds give [(CH3)2Si]5− when reduced with alkali metals. The ESR spectra of the anion‐radicals show that the unpaired electron contacts all of the methyl protons equally, and so is fully delocalized over all the silicon atoms in the ring. The permethylpolysilanes have electron affinities similar to that of benzene; the ease of reduction is in the order [(CH3)2Si]5 > benzene > [(CH3)2Si]6. These findings suggest that electron mobility and delocalization is not limited to “conjugated” molecules but can also be observed in systems not normally considered as “unsaturated.” Implications for the design of organic conducting elements will be mentioned.
Inelastic electron scattering from organic compounds
Authors: Gerber Sheldon H. 
Published: June 2010

AbstractIn calculations of possible superconductivity in a system, knowledge of certain matrix elements determines whether or not bound electron pairs can exist and thus lead to superconductivity. These matrix elements involve ground and excited state wave functions. We are presently attempting to experimentally determine such matrix elements in certain organic compounds by measuring differential cross sections for inelastic electron scattering. Such cross sections involve the square of the matrix elements of interest. To do this we are using a crossed beam technique with an electrostatic electron spectrometer for the production of the incident electron beam and analysis of the scattered beam. The apparatus is described, as well as the present status of the experiment.
The effect of molecular weight on frictional coefficients of poly‐α‐methylstyrene
Authors: Cowie J. M. G. , Bywater S. 
Published: June 2010

AbstractThe frictional coefficients. [f] of a wide range of poly‐α‐methylstyrene samples ranging in molecular weight from dimer to polymers of M ∼ 106 have been measured in a good solvent (toluene) and under θ conditions (cyclohexane, 37°C). All products were prepared anionically, and the very low molecular weight samples were initiated with phenyl‐isopropyl potassium to ensure that the end‐groups were not significantly different from the polymer chain. [f] was measured using both diffusion and sedimentation techniques. At molecular weights below ∼ 104, [f] is independent of solvent and proportional to M0.5 to quite low molecular weight. Divergences only occur at the very lowest part of the range. Above M∼ 104, [f] continues to be proportional to M0.5 in cyclohexane as expected, but the values in toluene become greater because of greater chain expansion in the better solvent. The results are discussed in terms of current theories of conformations of polymers in solution and its effect on flow properties.
A comment on non‐uniform expansion of a coiled polymer
Authors: Chikahisa Yoshiaki , Tanaka Tsuruyo 
Published: June 2010

AbstractIn many approximate theories of the excluded volume effect a coiled polymer chain is assumed to expand uniformly as the solvent power is increased. The failure of this assumption is demonstrated explicitly for the first‐order (single contact) perturbation; i.e., for ∣z∣>>1, where z is the usual excluded‐volume parameter. It is shown that parts of a chain near the ends suffer less expansion than the regions near the middle.
Reinforcement in rubber‐modified polystyrene
Authors: Schmitt J. A. 
Published: June 2010

AbstractIt has been proposed recently that polystrene is reinforced by rubber because the energy of an impact is dissipated by separation of rubber particles from polystyrene with the formation of many associated micro‐cracks and/or crazes in the polystyrene, starting at the separations. A necessary condition is that the rubber is in a state of triaxial tension which result from its higher rate of contraction compared to that of polystyrene. Further evidence is presented to support this mechanism. The higher rate of contraction of rubber compared to other polymers is demonstrated visually by embedding pieces of rubber in epoxy resin and curing at various temperatures. Holes develop in the rubber on coolling. Triaxial tension can develop only when the rubber is sufficiently cross‐linked and when there is good adhesion to the matrix polymer, otherwise, the rubber particle will either separate at the interface or develop a hole. This is demonstrated by embedding radiation cross‐linked rubber in epoxy and also by milling such rubbers into polystyrene. This mechanism explains the failure of other types of fillers to reinforce polystyrene. The optimum rubber particle size is also closely related. A polystyrene‐rubber system is described to which fillers were added to modify the triaxial tension and thus affect the impact strength.
Molecular motions in some polycarbonates
Authors: Garfield Lawrence J. 
Published: June 2010

AbstractMolecular motions in the bulk polycarbonates of bis(4‐hydroxyphenyl)‐2,2‐propane, bis(4‐hydroxyphenyl)hexafluoro‐2,2‐propane, and bis(4‐hydroxyphenyl)1,3‐dichloro, tetrafluoro‐2,2‐propane have been studied by wide‐line nuclear magnetic resonance techniques. Magnetic resonance information obtained over a broad temperature range from both H1 and F19 nuclei has been used to assign various mobility phenomena to specific segments of the macromolecules. Furthermore, because of the close similarity in size of the fluorine and hydrogen atoms, F19 resonance information yields some further insights on molecular motions in BPA polycarbonate. The rotation of ‐CF3 groups, which begins at 283°K, is apparently cooperative with the motion of the adjacent phenyl groups. The effect of the ‐CF3 groups on the restricted motion of the adjacent phenyl groups is the same as that of ‐CH3 groups. Furthermore, it is inferred that in BPA polycarbonates the restricted motion of the phenyl groups occurs cooperatively with the carbonyl group and that this mode of motion is the principal contributor to the dielectric and mechanical loss peaks observed near 170°K. The glass transition temperature of the dichlorotetrafluoro compound is only 5°C higher than the hexafluoro compound. Nevertheless, the reorientation of the ‐CF2CL groups and the phenyl groups in the dichlorotetrafluoro compound occurs 100°C higher than the corresponding motions in the hexafluoro compound.
Hemical and spectral sensitization of the photoconductivity and the photo‐E.M.F. In polymeric acetylenides
Authors: Mylnikov V. 
Published: June 2010

AbstractThe marked change of the conductivity, the photoconductivity and the photo‐e.m.f. is revealed when the poly‐copperphenyl acetylenide (PAC) is treated by DNA, RNA and adenine. The spectral characteristics of the photoeffect, the sign of the charge carrier and kinetics of the photoconductivity are studied. The data obtained is explained by the creation of the new recombination centers after treatment of the PAC. The treatment of the polymer by amino acids leads to creating the complex copper (II) compounds and aminoacid residue. It is shown that the inner photoeffect in PAC can be spectrally sensitized up to the near infra‐red region after the dye adsorption on the polymer surface. The energy transfer mechanism is preferred for the explanation of the I.R. sensitization.
Thermodynamics and the equilibrium state of a binary copolymer that is determined by next‐nearest neighbor intrachain effects
Authors: Theil Michael H. 
Published: June 2010

AbstractThe equilibrium state of an infinite molecular weight, binary copolymer which is determined by next‐nearest neighbor placements of its counits is defined in terms of the conditional probabilities describing such placements and the standard state free energies governing them. The combinatorial method is used to derive the entropy of sequence length distribution, ΔSD. When ΔSD is combined with an expression for the energy of reaction which employs the standard‐state free energies of triad formation an expression for the copolymer's free energy is obtained. Since enumeration of the interrelationships among the possible triplets reveal three independent conditional probabilities, separate differentiations with respect to each of three conditional probabilities are equated to zero in defining the equilibrium state. These equations reduce to the more special case previously derived when only nearest‐neighbor effects are considered.