bluuebunny/crossref_metadata_2025_split huggingface dataset:
Sedimentation analysis and some related problems
Authors: Williams J. W. 
Published: April 2003

AbstractWith the development of the ultracentrifuge by Svedberg there was provided a group of methods for the determination of solute molecular weight and of distribution of molecular weights in proper solutions. In addition to the sedimentation equilibrium and the sedimentation velocity experiments, there are other closely related molecular kinetic phenomena which, when taken together, form a collection of very useful tools in an area of macromolecular chemistry.The principal past use of the ultracentrifuge has been in the determination of the molecular weight and the homogeneity of proteins. In this report the attempt has been made to point the way for concerted action in the return to the original problem–that of investigating the dispersity of macromolecular and other colloidal solutions. Among other things, there is proposed in outline a combination of the sedimentation velocity and sedimentation equilibrium experiments to provide mass distribution data in macromolecular systems. While the main emphasis is devoted to the theory of the sedimentation methods and their unique usefulness to this end, there have been presented shorter discussions of diffusion and osmotic pressure as such and in their relationships to the sedimentation problems.Recognition is also made of the fact that the optical systems for the study of the redistribution of the components in the diffusion and sedimentation cells are now in a state of change, with a rapid adaptation of several interference methods to take the place of the more classical refractometric schemes. The change is being made in the interest of a greatly enhanced accuracy, even to the point that diffusion behavior in systems which contain two solutes can properly be observed.
Synthetische Kohlenhydrat‐Eiweissverbindungen
Authors: Micheel Fritz 
Published: April 2003

AbstractDie besten Methoden zur Synthese von Kohlenhydrat‐Eiweissverbindungen, in denen beide Komponenten in biologisch möglicher Art kovalent miteinander verbunden sind: (1) Mono‐saccharid‐ oder Poly‐saccharid‐carbonsäuren werden über ihre Azide peptidartig an die ε‐Aminogruppen der Lysinreste in Proteinen gebunden. (2) 1‐Cyanamidoverbindungen von Monosacchariden kondensieren sich mit den freien Aminogruppen (siehe 1) der Proteine zu Zucker‐guanyl‐proteinen. (3) 1‐Alkyl‐iso‐thioharnstoffderivate von Mono‐sacchariden geben (wie bei 2) mit Proteinen Zucker‐guanyl‐proteine. Es reagieren nach Verfahren (2) und (3) weniger als 50% der ε‐Aminogruppen der Lysinreste in den Proteinen. Dies dürfte auf eine Blockierung der Aminogruppen durch Carboxyl‐ u.a. Gruppen zurückzuführen sein. Durch Umsetzung von Poly‐saccharidproteinverbindungen (nach Methode 1 erhalten) mit Ölsäurechlorid werden Kohlenhydrat‐oleyl‐proteine synthetisiert, in denen die Oleyl‐reste an die Protein‐reste, nicht an die Kohlenhydratreste, gebunden sind. Sie enthalten die Bausteine von Lipoiden in kovalenter Bindung. Salzartige Kohlenhydrat‐Eiweissverbindungen werden aus D‐Glucose‐6‐schwefelsäure und Xylan‐schwefelsäure mit Proteinen erhalten. Die Zusammensetzung der Salze entspricht dem Äquivalenzverhältnis zwischen den Schwefelsäure‐resten der Kohlenhydrate und den basischen Aminosäuren der betreffenden Proteine. Die sich daraus errechnenden Äquivalentgewichte der Proteine sind von der gleichen Grösse wie die nach anderen Methoden gefundenen.
Preparation, properties and structure of polyhydrocarbons derived from p‐xylene and related compounds
Authors: Kaufman Martin H. , Mark Herman F. , Mesrobian Robert B. 
Published: April 2003

AbstractA pyrolytic dehydrogenation technique originally proposed by Szwarc has been employed for the preparation of polyhydrocarbons from p‐xylylene, pseudocumene, and durene. With particular emphasis on poly‐p‐xylylene, the structure and physical properties of the polymers were investigated. Poly‐p‐xylylene may be obtained in two modifications: a transparent form and opaque form. The transparent form of poly‐p‐xylylene exhibits uniaxial, negative birefringence. The opaque form on purification by chloroform extraction melts at 412°C. Heat treatment of either modification appears to result in an irreversible, polymorphic transition. Poly‐p‐xylylene may be stretched at temeratures above 150°C. to reveal a well‐defined x‐ray fiber diagram, having an identity period of one. Sulfonation of poly‐p‐xylylene yields a product having one sulfonic acid group per benzene ring. The product swells anisotropically but does not dissolve in water. This observation, as well as the observation that the rate of dissolution of poly‐p‐xylylene in high boiling solvents is dependent upon the presence of oxygen, suggest that the polymer is crosslinked to a small but finite extent. The polymer derived from pseudocumene is also crosslinked but contains up to ca. 21% of a chloroform‐extractable component. The number‐average molecular weight of the chloroform soluble component is 23,900.
The half‐life of the styrene free radical. I. Photopolymerization in a free falling stream
Authors: Goldfinger George , Heffelfinger Carl 
Published: April 2003

AbstractThe principle of the method of Paneth and Hofeditz of studying gaseous free radicals has been employed for chain reactions in liquid monomers. The half‐life of a photochemically initiated polystyrene free radical has been found to be 0.088 ± 0.015 second. A simple extension of the technique should also give absolute values of the propagation rate constant and the chain transfer constant.
The absolute turbidities of some pure liquids
Authors: Maron Samuel H. , Lou Richard L. H. 
Published: April 2003

AbstractTurbidities and Rayleigh ratios have been measured at 25°C. and at wave lengths of 4358 and 5461 A. for benzene, carbon tetrachloride, toluene, and methyl ethyl ketone. The results obtained are in agreement with the theoretical Einstein equation for the scattering of light by pure liquids, the data yielding for Avogadro's number a value of 5.98 × 1023 ± 4.7%, as against the accepted value of 6.02 × 1023. Further, the Rayleigh ratios are in accord with the published measurements of Doty, Zimm, Brice, and their co‐workers, but not with the older literature or the values of Stamm and Button.
Infrared analysis of some chlorinated natural rubbers
Authors: Salomon G. , Van Der Schee A. Chr. 
Published: April 2003

AbstractChanges in the infrared spectra due to the introduction of 1 to 4 chlorine atoms per isoprene unit in the natural rubber molecule have been studied. Four prototypes are discussed in greater detail: hydrochlorides, rubber dichlorides, chlorinated hydrochlorides, and products obtained by the direct chlorination of rubber and of cyclized rubber. Within certain limits it is possible to follow double bond shifts which occur during the process of hydrochlorination or of chlorination. Chlorinated rubber differs from other chlorinated polymers with a similar composition by a large reduction of the intensity of the CH3 frequency. Absorptions due to the presence of chlorine atoms are observed in the 13–18 μ region, but these bands show little individual differences. Small quantities of oxygen in the form of CO or OH groups are readily detected.
Relative reactivities of polymer radicals in vinyl polymerizations
Authors: Herbst Ralph L. , Martin Robert E. 
Published: April 2003

AbstractThe relative reactivities of polymer radicals in vinyl polymerization have been correlated semiquantitatively according to the Alfrey‐Price Q′ and e scheme. Polystyrene radicals are arbitrarily assigned a Q′r value of unity. The relative reactivities of other polymer radicals are then characterized by the Q′ and e values of the parent monomers. This is shown by data concerned with copolymerization, homopolymerization, and chain transfer. It is proposed that the dispersion forces of London are the predominant influence in chain transfer reactions of polymer radicals with solvents.
Precision rotation viscometer with electrostatic restoring torque for the centipoise range
Authors: Eisenberg H. , Frei E. H. 
Published: April 2003

AbstractA concentric cylinder rotation viscometer with conical ends was constructed for the measurement of shearing stresses from about 2 × 10−3 to 1.6 dyne‐cm.−2 with a precision of 0.3% at rates of shear from 0.2 to 40 sec.−1. The instrument is intended for the study of dilute high polymer and polyelectrolyte solutions. A stable “suspension” having a negligible frictional torque was obtained by freely floating the inner stationary cylinder in the sheared liquid under investigation. The restoring torque was applied by means of an electrostatic system. Preliminary measurements showed that aqueous solutions of polyvinyl alcohol (du Pont Elvanol 72–60) showed Newtonian behavior at concentrations from 10−2 to 2 × 10−3 g./ml.; aqueous solutions of methylcellulose (Dow Methocel 4000 cps.) of concentration ranging from 10−3 to 4 × 10−5 g./ml. exhibited structural viscosity below rates of shear of 5 sec.−1.
The birefringence of polyisobutylene
Authors: Stein Richard S. , Holmes Frank H. , Tobolsky Arthur V. 
Published: April 2003

AbstractThe variation of stress and birefringence occurring during the relaxation of elongated samples of polyisobutylene at constant length was observed at temperatures between −40° and +50°C. It is found that stress and birefringence relax in the same way throughout this region, and that the quantity (stress/birefringence × temperature) is a constant. This indicates that this material behaves in a manner consistent with the kinetic theories of elasticity and birefringence for an ideal rubber, and that the statistical segment size is fairly independent of temperature in this range. A value of 3.5 × 10−24 cm.3 is obtained for the difference between the principal polarizabilities of the statistical segment.
The significance of some parameters in formulas of polymerization kinetics
Authors: Murphy I. , Wassermann A. 
Published: April 2003

AbstractA treatment of polymerization reactions is described that involves the assumptions that: (a) intermediates of short lifetime play a role and (b) the velocity coefficients of propagation, (kp)r, and of termination, (kt)r, vary with the chain length, r, of the growing polymers. General formulas are derived and it is shown that they reduce to the previously deduced formulas if the ratio kt/kp is independent of r. Identical formulas can also be deduced, however, if the ratio (kt)r/(kp)r depends on r in a specified manner. Agreement between the previously deduced formulas and the results of experiments does not prove, therefore, that the ratio (kt)r/(kp)r is actually independent of the chain length.
Application of the cell model to the statistical thermodynamics of r‐mers solutions. II
Authors: Bellemans A. , Colin‐Naar C. 
Published: April 2003

AbstractThe cell model for r‐mers and r‐mer solutions developed by Prigogine, Trappeniers, and Mathot is applied to pure diphenyl, diphenylmethane, dibenzyl, and tolan (diphenylacetylene) and to their solutions in benzene. This model introduces new contributions for the excess functions arising from volume changes and modification of the curvature of intermolecular potential with change in composition. The excess functions are written in an explicit form and contain only molecular quantities without any arbitrary parameter. The agreement for the different excess functions (excess free energy, entropy, and excess volume) is satisfactory. The existence of a negative excess specific heat can also be understood on the basis of the cell model and is related to the negative excess volume.
The random chain model for polyelectrolytes
Authors: Harris Frank E. , Rice Stuart A. 
Published: April 2003

AbstractThe random chain model for polyelectrolytes proposed by Kuhn, Kunzle, and Katchalsky is considered. The thermodynamic and configurational properties calculated by Katchalsky and Lifson are shown to be somewhat in error because they have used an incomplete expression for the stretching free energy of the polymer. The agreement of the theory with experiment is not substantially affected in most regions of interest.
Crosslinking in isoprene polymerization
Authors: Morton Maurice , Cala J. A. , Piirma Irja 
Published: April 2003

AbstractA study has been carried out on the emulsion polymerization of isoprene in an attempt to evaluate the relative rate of the crosslinking reaction and its variation with temperature. From the relation between primary chain length and gel formation during polymerization, the following values were obtained for the relative crosslinking rate constant, i.e., ratio of the velocity constants of the crosslinking and propagation reactions.

Temperature,

°C.
K = kx/kp

60
3.4 × 10−5

70
4.3 × 10−5

80
5.2 × 10−5

The above data lead to a calculated value for the difference in the activation energy between the crosslinking and the propagation reaction (Ex − Ep) of 5.0 kcal. From these data and the known value of the propagation rate constant, it is possible to calculate the following absolute rate expression for the crosslinking reaction itself:

It is noteworthy that the relative crosslinking rate in isoprene polymerization is only about one‐sixth that found for butadiene (K = 2 × 10−4 at 60°C.) apparently owing largely to a higher steric factor. Hence longer chains are possible for polyisoprene before network formation leads to gelation. In the Mutual Recipe, the rate per particle for isoprene polymerization is about three times as fast as for butadiene, although it is still short of the rate found in the ideal low temperature systems.
Some copolymerizations of cis‐ and trans‐Dibenzoylethylene
Authors: Marvel C. S. , Galun Arjeh B. 
Published: April 2003

Abstracttrans‐Dibenzoylethylene has been copolymerized in emulsion with butadiene, 2,3‐dimethylbutadiene, and isoprene. It was found to be of advantage to use low temperatures for the copolymerization with diene monomers, to avoid interference of the Diels‐Alder reaction. trans‐Dibenzoylethylene retarded the polymerization of styrene, but it was incorporated into the copolymer after an induction period. It inhibited the polymerization of vinyl acetate and acrylonitrile which could not be polymerized in emulsions in its presence. cis‐Dibenzoylethylene has been copolymerized with styrene. The incorporation was low (about three per cent), but the viscosities were twice as high as those of polystyrene prepared under the same conditions. cis‐Dibenzoylethylene did not inhibit the polymerization of either butadiene or acrylonitrile and no incorporation of the disketone into the polymer could be proved in either case.
Reduced viscosities of polyelectrolytes in the presence of added salts
Authors: Terayama Hiroshi , Wall F. T. 
Published: April 2003

AbstractTwo different techniques for diluting polyelectrolyte solutions with salt solutions are discussed. The first is the so‐called isoionic dilution and the second is a method using salt solutions of concentrations so chosen as to make the reduced viscosity a linear function of polymer concentration.For isoionic dilutions, in which the total counterion concentration is kept constant, the reduced viscosity curves are not linear over the whole range but are rather sharply curved at the early stages of dilution. However, it is observed that the viscosity of solutions subject to such dilutions can be expressed by an empirical equation similar in form to that of Fuoss and Strauss.The second method is carried out by diluting the polymer solution with a simple salt solution whose concentration, c1, is selected by trial and error to make the reduced viscosity a linear function of concentration. The ratio r = c1/c0 where c0 is the concentration of counterions from the original polymer solution, increases as the charge density of the polyelectrolyte decreases and is rather insensitive to c0. The values of 1 − r obtained for the partially neutralized polyacrylate were compared with the degrees of counterion fixation obtained by electrolytic methods, and good agreement was found between the two.
Etude de la polydispersité par diffusion brownienne
Authors: Daune M. , Benoit H. , Sadron Ch. 
Published: April 2003

AbstractLes auteurs présentent une méthode de mesure des coefficients de diffusion de translation qui permet, dans le cas d'un milieu polydispersé, de définir deux valeurs moyennes D1 et D2. Leur rapport est un critère de polydispersité et, en prenant pour exemple la distribution de Zimm, on discute de la sensibilité de la méthode qui peut en principe mettre en évidence une polydispersité de forme.
Freezing point depression of gels produced by high polymer network
Authors: Kuhn W. , Peterli E. , Majer H. 
Published: April 2003

AbstractWeakly vulcanized rubber swollen in benzene for one or several days forms a gel whose freezing point is about 5°C. lower than the freezing point of the solvent with which the gel is in equilibrium. This anomaly of the freezing point depression is to be explained by the three‐dimensional network present in the gel, which mechanically prevents the formation of macroscopic crystals. The phenomena observed in the benzene system are compared with similar observations made recently in the case of aqueous gels of polyvinyl alcohol and polyacrylic acid. The benzene system differs from the aqueous system in that an undercooling is observed in the benzene system as well for the formation of crystals outside at the surface of the gel as for the formation of crystals inside the gel. Furthermore, in the case of the benzene system at temperatures below the freezing point of pure benzene a transport of solvent from the inside to the outside of the gel takes place, i.e. a freeze‐drying of the gel is observed. These differences in the behavior of the aqueous and benzene systems are understood as being due to the volume dilation connected with the crystallization of water and the volume contraction occurring in the case of crystallization of benzene. The anomaly of the freezing point depression is a means of characterizing the width of ultramicroscopic structures present in high polymer, essentially also in biological systems.
Gelation of concentrated polyacrylonitrile solutions. II
Authors: Bisschops J. 
Published: April 2003

AbstractThe rate of gelation of concentrated polyacrylonitrile solutions is measured by the increase of the elasticity modulus of the gels with time at constant temperature. The influence of the following factors has been determined : temperature, concentration, molecular weight of the polymer, and water content of the solutions. The rate of gelation increases when the temperature decreases and becomes rapid enough to be measured between 0 and −10°C. The rate of gelation increases further by a factor 150 when the concentration varies from 18 to 23% and by a factor of approximately 3, for a 20% solution, when the molecular weight changes from 100,000 to 150,000. The influence of the water content is such that gelation already takes place at room temperature when the solution contains more than 2% water. The gelation has been ascribed to the formation of crystalline nuclei in the supersaturated solutions and the influence of the factors mentioned above is in agreement with the prediction of the nucleation theory.
A new viscodilatometer with applications to the trommsdorf effect in unsaturated polyester resins
Authors: Gordon Manfred , Grieveson Brian M. 
Published: April 2003

AbstractA new combined viscometer‐dilatometer is described which requires only small quantities of liquid. The polymerization of unsaturated polyester “contact” resins has been studied, and the “Trommsdorf effect” is shown to be compressed into a sharp kink in the rate curve. This is compared with the form which the Trommsdorf effect takes in a simple methyl methacrylate polymerization, and an explanation for the difference is offered. The breakdown of polymers by mechanical means, and its effect on a system in the vicinity of its gel point, are discussed.
Infrared studies on natural rubber and aged natural rubber
Authors: Dasgupta Sharda , Pande J. B. , Ramakrishnan C. S. 
Published: April 2003

AbstractIn the infrared absorption spectra of solutions of natural rubber in carbon tetrachloride, two new absorptions are observed, one at 6.52 μ and another at 8.2 μ. These bands disappear when films from the solution are examined. Possible origins of these bands are discussed and it is suggested that the absorption at 6.52 μ may be due to a perturbed double bond in a loose complex formed between rubber and carbon tetrachloride. The infrared absorption spectrum of rubber aged in solution also shows these absorptions. However, in the film from aged rubber the 8.2 μ absorption is found to persist. Chemical evidence for the loss in unsaturation is advanced.
Relation between the structure of polymers and their dynamic mechanical and electrical properties. Part II. Glassy state mechanical dispersions in acrylic polymers
Authors: Hoff E. A. W. , Robinson D. W. , Willbourn A. H. 
Published: April 2003

AbstractSome dynamic mechanical properties of a series of polymethacrylic and polychloroacrylic esters have been measured over a wide temperature range at about 200 c.p.s. using a cantilever vibration method. The sharp changes in dynamic modulus, and the associated mechanical loss maxima, which occur at various temperatures are discussed in relation to the chemical structures of the polymers and in particular to the ester group in their side chains. The main softening region is shown to be influenced by the presence of polar atoms in both the main and the side chains and by the spatial size and flexibility of the side chains. The data further support the recently postulated view that a secondary dispersion occurring just below the main softening region is associated with rearrangements of the CO.Ogroup in the side chains. Some new low temperature transitions are reported, one of which at −30°C. is characteristic only of polycyclohexyl methacrylate and polycyclohexyl chloroacrylate; it is suggested that this is associated with intramolecular flexibility within the cyclohexyl ring. Another process occurring at about −150°C. is found for those polymers whose linear side chain alkyl components possess sufficient flexibility to enable them to take up more than one unique spatial configuration; such flexibility is characteristic of the n‐propyl, n‐butyl, and sec‐butyl esters in both series and of the β‐chloroethyl, neopentyl carbinyl, and stearyl esters in the polymethacrylic series. Finally, the strengths of the low temperature relaxation processes, defined in terms of the percentage modulus change, are compared and discussed.
Temperature dependence of mechanical shear degradation
Authors: Goodman P. , Bestul A. B. 
Published: April 2003

AbstractThe rate of mechanical shear degradation of a 10% solution of Vistanex B‐100 polyisobutene (viscosity‐average molecular weight 1,740,000) in cetane has been studied at 60 and 80°C. at high rates of shear. The rate constants for the reaction at a given rate of shear energy application are found to decrease with temperature in this range. This result is interpreted as arising from a decreased efficiency at higher temperatures in the process of temporarily concentrating mechanical energy by means of intermolecular entanglements. The energy input requirements for degradation are found to increase with temperature.