bluuebunny/crossref_metadata_2025_split huggingface dataset:
Theory and application of two supplementary methods of constructing density gradient columns
Authors: Fortuin J. M. H. 
Published: April 2003

AbstractTwo supplementary methods of constructing density gradient columns are described. Formulas are derived for calculating the composition and mass of each of the two liquids used for the construction of a column with a given volume and a desired measuring range. The density of each layer of a column consisting of ideal or nonideal liquids can be accurately predicted. The persistance of a column is dependent on its length and diffusion coefficient, and can be approximately calculated by means of a formula derived from Fick's second law.
Organophosphorus polymers. I. Peroxide‐initiated polymerization of diethyl and diisopropyl vinylphosphonate
Authors: Pike Ronald M. , Cohen Ronald A. 
Published: April 2003

AbstractIt was shown that diethyl vinylphosphonate and diisopropyl vinylphosphonate are polymerized by peroxide initiators to clear, light‐yellow, viscous liquid polymers of low molecular weight. It was found that the yield of the isolated polymers varied directly, while the molecular weight varied inversely, with the concentration of the initiator. Infrared spectra of the monomers used and the polymers obtained established that polymerization occurs through the vinyl group. It is postulated that the low molecular weight is due to the result of chain transfer with polymer and/or monomer through the alkoxy groups attached to the phosphorus atom.
Studies on polyoxypropylene glycols. Part I. Vapor pressures and heats of mixing in the systems: Polyglycols–methanol
Authors: Lakhanpal M. L. , Conway B. E. 
Published: April 2003

AbstractThermodynamic studies have been made on various fractions of polyoxypropylene glycols of molecular weights from 150 to 3350 in methanol. Vapor pressures of the solvent and the relative lowering of vapor pressure of the solvent by the polymer have been determined in a special differential manometer over the temperature range −30°C. to 28°C. Heats of mixing for the systems have been determined in an isothermal phase‐change calorimeter empolying diphenyl ether as the dilatometric fluid. The relative partial molar free energies are derived for the solvent and solute.
Inhibition and retardation of polymerization of methyl methacrylate
Authors: Funt B. Lionel , Williams Fredrick D. 
Published: April 2003

AbstractThe kinetics of the polymerization of methyl methacrylate in the presence of p‐benzoquinone were investigated. The course of the reaction was followed by dilatometry and with tracer methods. Alternate experiments were performed C14‐tagged azobisisobutyronitrile initiator and inactive p‐benzoquinone and, alternatively, radioactive initiator and inactive retarder being used. These data, coupled with number average molecular weights determined by osmometry, served to determine the number of fragments of initiator and retarder incorporated per polymer molecule. It was found that the reaction was retarded at low concentrations of p‐benzoquinone but showed a definite transition to inhibition at higher concentrations. Analysis of the data showed that the number of initiator fragments incorporated per polymer molecule was independent of retarder concentration, but that the number of retarder molecules per polymer molecule increased. The results indicate that the rate of chain initiation decreases with retarder concentration until inhibition is observed. The data are interpreted on the basis of interaction of benzoquinone with primary radicals generated by the initiator. The results also furnish distinct evidence against the acceptance of copolymerization or chain transfer as significant steps in the reaction mechanism.
The viscosity of concentrated polymer solutions
Authors: Gillespie Thomas 
Published: April 2003

AbstractThe general equation for pseudoplasticity previously derived by an extension of Goodeve's impulse theory of viscosity is derived specifically for polymer solutions by a consideration of the rate of energy dissipation in a sheared solution. Its general application to polymer solutions is discussed with particular reference to the fact that unlike other theories it is capable of explaining the linear relation between fluidity and shear stress at very low shear stress, frequently observed, as well as the dependence on the square of the shear stress predicted by other theories. The application to data obtained with aqueous methyl cellulose solutions at moderate shear rates is outlined. The onset of structural viscosity at a more or less critical concentration is explained by a definite type of mechanical interlocking which does not occur in dilute solutions. The average binding energy of an effective molecular entanglement was estimated at about 7kT units and was independent of concentration. The rate constants for shear induced link formation and rupture appeared to be independent of concentration. The corresponding rate constants in the absence of shear appeared to decrease with increased concentration, presumably due to a decreased rate of diffusion as suggested by the theories of Smoluchowski and Kramers.
Polyaddition reaction of polymethylene bis‐N,N‐ethyleneurethane and polymethylene dimercaptan
Authors: Iwakura Yoshio , Sakamoto Munenori 
Published: April 2003

AbstractPolyaddition reactions between polymethylene bis‐N,N‐ethyleneurethanes and polymethylene dimercaptans were investigated. The most successful polyaddition was carried out in dimethylformamide at 75°C. in the presence of triethylamine as catalyst; a fiber‐forming polyurethane sulfide having an intrinsic viscosity of 1.05 was obtained in about 90% yield. Arguments for the linear structure of the product are given.
X‐Ray determination of the crystallite orientation distributions of polyethylene terephthalate films
Authors: Heffelfinger C. J. , Burton R. L. 
Published: April 2003

AbstractA set of definitions is proposed to describe uniquely the six types of orientation possible in semicrystalline polymeric films. Oriented polymer films were studied by a new x‐ray diffraction technique which permits rotation of a sample about a number of independent axes yielding orientation distributions of the crystalline regions. The definitions and the method of measuring the crystallite‐orientation distributions have been applied to polyethylene terephthalate films.
Light scattering and small angle x‐ray scattering by macromolecular coils with finite persistence length
Authors: Peterlin Anton 
Published: April 2003

AbstractThe angular distribution of scattering intensity depends on all intramolecular distances through terms of the form 〈sin ksrmn/ksrmn〉. In the case of statistically coiled linear macromolecules with finite valency angle, exact calculation of these averages is possible by numerical calculation (Monte Carlo method). In the range of light‐scattering experiments, the results agree with previous approximate calculations by Peterlin and, in the range of small‐angle x‐ray scattering, with those by Porod, with the slight modification that with rather short chains the plateau in the plot of Ps2 versus s has a finite slope. At nearly 20 statistically independent chain elements, however, the plateau is virtually horizontal, and the flection at ksa = 2, used for determination of the persistence length a, is well developed. As by‐products of the calculation, the average end‐to‐end distance 〈r 〉and its inverse 〈1/r〉, were obtained. The product 〈r〉〈1/r〉 rather slowly approaches the limit π/4 corresponding to Gaussian distance distribution.
Grundlinien der Chemie hochmolekularer anorganischer Verbindungen
Authors: Thilo Erich 
Published: April 2003

AbstractAls hochmolekulare anorganische Verbindungen sind nur solche zu bezeichnen, deren Bausteine durch kovalente Bindungen untereinander verbunden sind. Um die Gesetzmässigkeiten ihrer Bildung und ihres Abbaues zu erkennen, wurden zunächst die linearpolymerenn Verbindungen untersucht. Drei Typen lassen sich phänomenologisch unterscheiden. Typ 1—z.B. die Polyarsenate—sind in wässeriger Lösung unbeständig und werden zu den monomeren hydrolysiert. Beim Typ 2—z.B. AsOCl—stellen sich in AsCl3—Lösungen Gleichgewichte zwischen Molekülen verschiedenen Polymerisationsgrades ein. Typ 3—z.B. die Polyphosphatc—sind in wässeriger Lösung unter normalen Bedingungen praktisch beliebig lange metastabil. Der Unterschied awischen diesen Typen ist nicht prinzipieller Natur, sondern nur graduell. Der mittlere Polymerisationsgrad P, der sich in Lösungen oder Schmelzen dieser Substanzen einstellt, gehorcht, dem allgemeinen Gesetz:

Bei konstanter Konzentration cL des die Endgruppen der Polymeren liefernden Lösungsmittels vereinfacht sich die Gleichung zu P̄ = 2c/[(4ck + k2)1/2 − k], bei konstanter Konzentration c an Grundmolekülen der Polymeren zu P̄ = (k′/cL)1/2. Am Beispiel des NaH3SiO4 und AsOCl einerseits, und am Beispiel der Polyphosphate andererseits wird die Gültigkeit dieser Beziehungen erwiesen.
Anionic polymerization of styrene by sodium naphthalene
Authors: Allen G. , Gee Geoffrey , Stretch C. 
Published: April 2003

AbstractPolymerization of styrene in dioxane solution by sodium naphthalene proceeds in accordance with the anionic mechanism proposed by Szwarc. Values of Eact = 9 ± 3 kcal and A = 5 × 107 l./mole−1 sec.−1 have been obtained for the anionic propagation reaction.
Sur la structure des polyéthylènes greffes par la technique de préirradiation
Authors: Sella Claude 
Published: April 2003

AbstractOn étudie par diffraction des rayons X aux grands angles et aux petits angles, ainsique par microscopic électronique, la structure et la morphologie des copolymères préparés par greffage sur des polyéthylènes preirradiés aux rayons γ, de différents monomères tels que le styrène, l'acétate de vinyle, l'acrylonitrile, le méthacrylate de méthyle. L'anslyse des diagrammes de rayons X aux grands angles permet de suivre les variations de cristillinité du polymère soumis à la rèaction de greffage ainsi quc les déformations de la maille cristallographique du polyéthylène en fonction de la nature, de la fréquence et de la longueur des séquences greffées sur les chaînes polyéthyléniques. La diffusion centrale des rayons X donne des renseignements importants sur la distribution des dimensions des cristaux et permet de montrer, comme d'ailleurs la diffraction aux grands angles, que les réactions de greffage sont souvent héterogénes et conduisent à la coexistence de trois phases, l'une constituée par du polyéthylène non greffé, la seconde par le copolymère greffé, et la troisième par un homopolymère. On peut déduire de l'analyse aux rayons X une méthode quantitative de dosage de ces trois phases. La microscopie électronique confirme ces conclusions et permet de voir en part,iculier la forme ct la distribution des précipités d'homopolymère en fonction d'une part des conditions dans lesquelles s'est effectué le greffage (conditions de préirradiation, de températnre de greffage, etc.) et d'nutre part de l'histoire thermique (recuit, trempe, etc.…) du copolymère grcffé. Ces différcntes techniques permettent d'aborder les problèmes importants tels quc cclui de l'isomorphisme entre le polyéthylène non greffé et les copolymères dérivés, celni de la comptabilité entre polyéthylène, copolymère greffé et homopolymère et celni de l'influence des traitements thermiques du polymère greffé sur sa structure fine et ses propriétés physiques et mécaniqnes.
Some chemical effects of ionizing radiations on nucleic acids and related compounds
Authors: Scholes G. , Ward J. F. , Weiss J. J. 
Published: April 2003

AbstractThe degradation of deoxyribonucleic acid (DNA) by irradiation of its aqueous solutions with ionizing radiations in the presence of oxygen has been discussed in terms of the reactions of free radicals (produced by the radiolytic decomposition of the water) with the different molecular entities of the macromolecule. It has been found that attack of the radicals on the purine and pyrimidine bases is a major effect of the irradiation, and it has been estimated that about 80% of the OH radicals attack the base components. In the presence of oxygen an important radiation‐induced reaction is the formation of peroxidic compounds from the pyrimidines. Breakage of the strands in the DNA helix is apparently due mainly to an attack of the radiation‐produced radicals on the sugar moieties which leads to a splitting of the phosphate ester linkages along the chains. The extent of attack which leads to breakage of internucleotide bonds, leading to the production of phosphomonoester groups, has been determined directly: the number of endgroups formed on irradiation with 200 k.v. x‐rays corresponds to a yield of G ⋍ 0.5 (endgroups/100 e.v.). Rupture of hydrogen bonds within the helix is a consequence of chemical changes in the polynucleotide chains; several hydrogen bonds can be broken following a single chemical event. The hyperchromic effect which is observed in the action of the radiations on nucleic acids in solutions has been investigated in some detail. It has been concluded that this effect is caused, in general, by environmental changes of the chromophoric groups of the purine and pyrimidine bases of the DNA, and is due to the change of the nature of the hydrogen bonding of the bases within the intact helix, where the bases of one strand are bonded to the bases of the complementary strand, to hydrogen bonding with water molecules when the latter have penetrated between the strands of the helix.
Recherches sur les combinaisons d'insertion de macromolécules
Authors: Parrod J. , Kohler A. 
Published: April 2003

AbstractCet artirle présente certains résultats concernant l'absorption du polyoxyéthylèneglycol (POEG) par l'urBe, la thiourée et l'argile (bentonite Wyoming), en particulier l'extraction du POEG aux dépens de ses solutions benzéniques par ces trois absorbants, et la variations de viscosité de ces solutions par suite de l'absorption du soluté. Les résultats de l'absorption du POEG par l'uriée et la bentonite correspondent aux résultats classiques concernant l'absorption de petites molécules dans des cavités‐canaux de l'urée, en entre les couches de la bentonite; par contre dans le cas de la thiourée, la quantité de POEG absorbée est plus grande que la capacité d'absorption des cavités laisse prévoir. Nous avons observé dans ces trois cas qu'une solution polydispersée dans le benzène de POEG (préparée en mélangeant deux échantillons de POEG de poids moléculaire très différent) en contact avec de l'urée, la thiourée ou la bentonite, présente une viscosité intrinsèque qui décroît rapidement en cours d'absorption du soluté. Ce fait pourrait être le résultat d'un “ancrage” de la molécule absorbée, qui dépendrait de la longueur de la chaîne, les plus courtes chaînes restant en solution; un tel phénombne s'accorderait avec les résultats connus pour l'absorption de molècules parafiniques de petite taille par l'urée, à savoir que les parafines plus longues sont le plus fortementretenues. Si ce phénomène est confirmé et généralisé, une telle propriété de l'urhe, de la thiourée, de la bentonite et peut‐être d'autres absorbants, rendrait possible un test rapide et facile de la polydispersité d'un polymère, au moins d'un échantillon de POEG.
Polymer molecules involving coordination links in the crystals of cupric oxalate and related compounds
Authors: Kubo M. , Kishita M. , Kuroda Y. 
Published: April 2003

AbstractCopper salts of α,ω‐dibasic acids, HOOC(CH2)n−2COOH, in which n = 2–10, show (cupric malonate excepted) abnormal magnetic moments, which are lower than the theoretical spin value (1.73 B.M.) for one free electron. (Therefore structures may be expected containing two copper atoms, as there are in cupric acetate monohydrate crystals) in cristalline cupric salts of α‐ω‐dicarboxylates which show subnormal magnetic moments. A nonplanar structure of oxalic radicals is confirmed experimentally as well by radiostructural analysis as by electron diffraction. These data indicate that cupric oxalate crystals have a dimeric structural network or polymeric molecules containing coordination links and do not behave as isolated molecules with one copper atom or as dimeric molecules, as do the crystals of cupric acetate monohydrate. Analogous network structures are possible for cupric salts of α‐ω‐dicarboxylic acids having an even number of carbon atoms, although the carbon chains may be bent more or less from their normal configurations; the Cu‐Cu links could also be simultaneously changed. Indeed, the magnetic moment of the copper salts of the even series increases with increasing length of carbon chains. For the malonate, the rotation of chains within the central carboxylic groups forbids the formation of such network structures. For the other acids of the odd series the flexibility of the carboxylic groups must take part in bringing two copper atoms together. Indeed, cupric malonate shows a normal magnetic moment as observed for most cupric derivatives, and the effective moment per copper atom in the cupric salts of the odd series decreases with increasing length of carbon chains of the acids until the curve of the magnetic moments of the dibasic acids of the even series practically coalesces with that of the odd series (above pimelic acid). These conclusions, which are based on the magnetic moment data of the polymeric structures of cupric salt crystals of α‐ω‐dicarboxylic acids, are also confirmed by infrared spectral data, especially by the variations of the CO stretching and the CH2 rotation bands. Analogous structures are also proposed for the abnormal magnetic moments observed for the cupric salts of rubeanic acid, thioxamide, and similar derivates.
High polymers and their intermediates in the phosphonitrilic halide system
Authors: Shaw R. A. 
Published: April 2003

AbstractPolymers in the phosphonitrilic halide system are classified into addition and condensation polymers. Recent results bearing on the structure and mechanism of formation of “inorganic rubber” are discussed. Views on the structure of condensation polymers of a ceramic type are put forward, and the first phosphams with different but reproducible physical properties are reported. The stereochemistry of one of the most important intermediates, the cyclic trimer, is discussed in some detail.
Effect of heterogeneity on the second virial coefficient
Authors: Varadaiah V. V. , Rao V. S. R. 
Published: April 2003

AbstractThe values of the second virial coefficient A2, were determined by a light‐scattering method for polymethyl methacrylate mixed fractions in methyl ethyl ketone and ethyl acetate systems. It is shown that in a mixture of two components A2 is sensitive to the presence of the higher molecular weight component in a sample of a lower molecular weight, but not to the presence of a lower molecular weight component in a sample of higher molecular weight. This effect is found to be predominant in the good solvent (methyl ethyl ketone). The results obtained are in general agreement with those of Chien et al. but are in contrast with those of Elias.
Effect of intrachain and interchain interactions on the structures of crystalline regions in linear polymers
Authors: Huggins Maurice L. 
Published: April 2003

AbstractIn order to explain (1) the chain folding observed in single crystals of linear polyethylene and some other polymeric substances and in isolated molecules obtained from dilute solutions, (2) the twisted ribbon structure in polyethylene spherulites, (3) long x‐ray diffraction spacings in various polymers, and (4) the rotation of polarized light by single crystals of n‐paraffins, it is proposed that (1) intrachain forces produce slight departures from a planar zigzag structure of the carbon chain (or from a helical structure of simple multiplicity), (2) intrachain and interchain forces make these departures approximately uniform within each chain, and (3) when the total departure from the simpler structure reaches a limiting value, a sudden alteration in structure occurs.
On wave propagation in viscoelastic media
Authors: Davis J. L. 
Published: April 2003

AbstractA mathematical analysis is made of the problem of wave propagation in a one‐dimensional bounded viscoelastic medium under prescribed boundary conditions. Closed form expressions are obtained for viscoelastic waves for the case of a relaxation function involving a single relaxation time. An expression for the phase velocity as a function of ratio of relaxation frequency to frequency of applied periodic displacement is obtained for the steady state part of the solution. The generalization to a relaxation function involving a finite number of relaxation times is discussed, and a method is sketched out for solving the more general integropartial differential equation of motion. Comments are made on the molecular interpretation of viscoelastic models.
A study of the ionic species present in ionic polymerizations. I. Styrene polymerization initiated by stannic chlorides
Authors: Metz Donald J. 
Published: April 2003

AbstractThe polymerization of styrene initiated by stannic chloride in the mixed solvent carbon tetrachloride‐ethylene dichloride was carried out between co‐axially mounted cylindrical electrodes. The dielectric loss of the polymerizing solution was measured in the frequency range of 104 to 107 cycles per second. The observed dependence of dissipation factor on frequency is interpreted as being indicative of conducting ions in the solution during the reaction. These ions are found only when both monomer and catalyst are present in the solution and not when one or the other is missing. The data also indicate that the concentration of the ions which contribute to the measured dielectric loss is not reduced to zero after completion of the reaction.