bluuebunny/crossref_metadata_2025 huggingface dataset:
Viscosity of dilute solutions of linear and branched polyvinyl acetate
Authors: Hobbs L. M. , Kothari S. C. , Long V. C. , Sutaria G. C.
Published: April 2003

The dilute solution viscosity properties of fractions of two linear and one branched sample of polyvinyl acetate in benzene and of two linear and one branched fraction in several solvents were measured at 35°C. Values of total slope, b (from plots of ηsp/c vs. c), and intrinsic viscosities were obtained under the requirement that k′ + β = 0.500 ± 0.002. Empirical plots of log b vs. log [η] gave lines which were straight within the limits of accuracy of the data. For the linear fractions in benzene, Huggins' k′ was constant and the slope of the log b vs. log [η] line was 2; for the branched fractions in benzene, k′ increased with [η] and the slope of the log b vs. log [η] line was greater than 2. The log b vs. log [η] plots form the basis for a “one‐point” method for determining [η]. Consideration of these data along with results reported in the literature indicates that k′ is measurably sensitive to branching only for fractions possessing a certain minimum combination of size and complexity. However, in some cases where the variations of k′ are inconclusive, use of the slope of the log b vs. log [η] line may provide a reliable indication of branching. It was found that a comparison between the branched and linear series could also be made at constant values of [η] or b. Two linear fractions in different solvents obeyed a type of Huggins relationship in which k′ did not vary with solvent and the slope of the log b vs. log [η] line was 2. For a higher molecular weight branched fraction, however, k′ varied from solvent to solvent and the slope of the log‐log plot was about 1.7. These data do not support a reference point concept of “true” intrinsic viscosity based on a simple linear relationship between b and [η]. Preliminary results dealing with the effects of the shear rate indicated that the measured viscosity properties of branched fractions may be more seriously affected by changes in shear rate than those of linear fractions.
Degradation of long chain molecules by ultrasonic waves. VII. Effect of viscosity and surface tension on cavitation
Authors: Jellinek H. H. G.
Published: April 2003

The effects of viscosity and surface tension on the boundary velocity of a gas filled cavity, collapsing in a liquid exposed to ultrasonic waves, have been calculated.
Infrared spectra of high polymers. V. Polyvinyl alcohol
Authors: Krimm S. , Liang C. Y. , Sutherland G. B. B. M.
Published: April 2003

The infrared spectrum of polyvinyl alcohol has been investigated between 3600 and 70 cm.−1. Polarization measurements on stretched specimens were made down to about 330 cm.−1. The spectrum of a deuterated specimen (about 90% of the OH having been replaced by OD) has also been obtained. These data confirm and extend the results of previous workers. The spectrum is discussed in detail in relation to three structures for polyvinyl alcohol proposed on the basis of x‐ray diffraction studies. The data definitely rule out the structure proposed by Mooney, and are most consistent with the structure proposed by Bunn. A complete assignment of the bands in the spectrum is proposed. From this analysis it appears that the existence of interaction forces between molecules can be convincingly demonstrated. The proposed assignments suggest a new interpretation of the 1326–1446 cm.−1 doublet, viz., that these bands arise from mixed CH and OH in‐plane bending vibrations. This is shown to be in agreement with the results of studies on simple alcohols. An alternative assignment for the 1144 cm.−1 band is also considered.
Pyrolysis of polyacrylonitrile
Authors: Burlant W. J. , Parsons J. L.
Published: April 2003

Polyacrylonitrile of molecular weight 130,000 has been pyrolyzed under nitrogen, between 200° and 320°. The predominant gaseous products are hydrogen cyanide and ammonia; the rates of formation of these have been measured, and at 270° for example, after 300 minutes, only 10% of the available nitrogen is lost. A liquid distillate containing nitriles, amines, and unsaturated groups was also obtained. Using infrared absorption measurements, it was found that the nitrile groups of the polymer disappear as heating progresses, and CN linkages appear. As heating is continued, evidence for aromatization is found. These experimental facts indicate ring formation to be an important reaction; the heat‐stable residues are considered to be mainly fused pyridine systems.
Studies on heterogeneous polymeric systems
Authors: Merz E. H. , Claver G. C. , Baer M.
Published: April 2003

The physical and morphological properties of heterogeneous mixtures of polystyrene with styrene: butadiene copolymers were determined. A mechanism of ultimate failure is proposed which permits the qualitative rationalization of the effects of copolymer composition, structure, and concentration upon certain physical properties of the mixture.
Un nouveau consistomètre à large gamme de gradients et de température
Authors: Kepes M.
Published: April 2003

On donne la description détaillée d'un appareil destiné à faire des mesures continues de viscosités sur de petites quantités de produits (1 à 4 cm3), dans la gamme de 0,01 à 108 poises. L'échelle des températures s'étend de −70° à +350°C.; sa limite supérieure rend le consistomètre particulièrement apte aux investigations sur les polymères fondus. L'appareil est du type tournant, à cône et plan, avec un anneau de garde. Le gradient de vitesses, constant à moins de 0,5% près dans l'entrefer, peut etre réglé de 10−3 à 103 sec−3, en 24 positions. Il est possible de travailler en atomosphère inerte ou sous vapeur saturante. On cite quelques exemples qui illustrent ses possibilités.
Formation of films from polymer dispersions
Authors: Brown George L.
Published: April 2003

Polymer emulsions will undergo film formation upon loss of water if the driving force provided by capillary pressure is sufficient to overcome the resistance of the polymer particles to deformation. The conditions for film formation are expressible in terms of the surface tension and particle size of the dispersion, the time available for the drying process, the temperature, and the rheological properties of the polymer.
Effect of branching on dynamic mechanical properties of polyethylene
Authors: Kline D. E. , Sauer J. A. , Woodward A. E.
Published: April 2003

The effect of chain branching on the dynamic mechanical properties of polyethylene within the temperature region 80 to 380°K. has been studied using an apparatus which drives rod‐like specimens in their transverse modes. The results for three types of polyethylene having 3.2, 1.6, and less than 0.1 branches per 100 carbon atoms of the main chain are compared and discussed. Experimental results indicate that all of the three main dispersion regions (α, β, γ) characteristic of polyethylene are affected to some extent by branching. The β region, starting near 230°K., decreases with decreased branching, and for polyethylene which has negligible branching it is almost entirely absent. This suggests a direct relation between the number of branch points and the size and shape of this peak. The γ dispersion region near 170°K. appears sharper and shifted to higher temperatures with decreased branching, this being attributed to a narrowing of the relaxation times associated with the movement of a small number of CH2 units. The α dispersion region near 370°K. is also shifted to higher temperatures with decreased branching in accord with the shift of melting temperature with degree of crystallinity.
Linear phenol‐formaldehyde polymers—dehalogenation of p‐chlorophenol‐formaldehyde polymers
Authors: Burke W. J. , Ruetman S. H. , Stephens C. W. , Rosenthal Alex
Published: April 2003

High molecular, linear phenol‐formaldehyde polymers were prepared by the dehalogenation of the corresponding p‐chlorophenol‐formaldehyde polymers with sodium in liquid ammonia. The phenol‐formaldehyde polymers and their acetyl derivatives were soluble in acetone and N,N‐dimethylformamide. Infrared studies were consistent with a structure having methylene bridges between the ortho positions of the phenolic residues.
Electron irradiation of polyacrylates
Authors: Shultz Allan R. , Bovey Frank A.
Published: April 2003

The crosslinking and degradation of seven polyacrylates by 1000 kvp. electrons has been investigated. Gel content‐radiation dose analysis reveals the energy dissipation per main‐chain fracture, Ed, to be the same (530 ± 100 electron volts) for methyl, n‐butyl, sec‐butyl, isobutyl, and tert‐butyl acrylate polymers. The energy dissipation per crosslinked unit formation, Ec, is 80–90 e.v. for methyl, n‐butyl, isobutyl and neopentyl acrylate polymers. Ec may be slightly higher for poly‐sec‐butyl acrylate. Poly‐tert‐butyl acrylate possesses a uniquely high Ec of 300 e.v. The presence of hydrogen atoms alpha to the alcoholic oxygen of the ester group is believed to contribute strongly to the crosslinking reactions of polyacrylates under ionizing radiations. Poly‐1,1‐dihydroperfluorobutyl acrylate exhibits an initial Ec of ∼45 e.v. and an Ed of ∼450 e.v. Beyond 15 megareps the ration of main‐chain fracture to crosslink formation increases.
Viscosités des solutions de molécules à chaîne courte
Authors: Rempp P.
Published: April 2003

Dans le but d'étudier le comportement physicochimique de diverses molécules à chaǐne courte, monodisperses et sans ramifications, nous avons fait une série de mesures viscosimétriques comparatives sur des paraffines normales d'une part, et d'autre part sur des dérivés oxygénés: éthers, dialcoxyalcanes, dialcoxydiéthyléther, etc… Toutes ces mesures ont été effectuées en solution diluée, dans le tétrachlorure de carbone et dans le benzène. Les résultats font apparaǐtre que: (1) Dans le cas des paraffines la viscosité intrinsèque devient négative si la chaǐne comporte moins de dix chaǐnons. Les résultats expérimentaux sont valablement représentés par une loi de la forme [η] = − A + B ln N. (2) Le remplacement d'un CH2 par un atome d'oxygène entraǐne une augmentation de [η]. L'ensemble de nos résultats—paraffines et dérivés oxygénés—peut ětre représenté par une loi de la forme

A et B étant des fonctions du rapport du nombre d'atomes d'oxygène au nombre total de chaǐnons de la chaǐne. (3) Le comportement des deux solvants étudiés à l'égard de tous leurs solutés est rigoureusement comparable.
Etude de la polydispersité au moyen de la diffusion brownienne
Authors: Daune M. , Freund L.
Published: April 2003

On rappelle d'abord les résultats déja obtenus lorsqu'on utilise la méthode interférométrique de Scheibling dans l'étude de la diffusion brownienne de corps polydispersés. On développe ensuite le calcul de trois coefficients de diffusion moyens, qu'on peut relier à des moyens en masses particulières, et qui dans le cas d'une fonction de distribution de forme connue permettent de la déterminer complètement. De plus on peut faire l'analyse complète, a partir de ces trois moyennes d'un mélange de deux espèces différents en proportions quelconques. Quelques exemples expérimentaux montrent les possibilités et la précision de cette méthode. On montre enfin qu'on peut mettre la fonction représentant la courbe expérimentale sous la forme d'un produit de composition, ce qui permet d'obtenir la fonction de distribution par deux transformations de Fourier successives. L'application de ce procédé à une répartition théorique donne un résultat satisfaisant qui justifie une étude expérimentale plus poussée.
Dynamic flow birefringence, optical anisotropy, and shape of macromolecules in solutions
Authors: Tsvetkov Victor N.
Published: April 2003

The experimental study of the dynamic double refraction in polymer solutions in different solvents shows a parabolic dependence of the dynamooptical constant from the refractive index of the solvent. This character of the said dependence can be explained qualitatively in terms of the molecular coil asymmetry; it can be interpreted quantitatively on the basis of the equivalent molecular ellipsoids model. The investigation of the Maxwell effect in a series of polymer fractions with different MW gives the following law: If the refractive indexes, ns and nk of the solvent and polymer are equal, the ratio [n]/[η] is independent of the MW. Here [η] is the dynamooptical constant and [η] is the intrinsic viscosity. If the value of nk − ns is high enough, the ratio [n]/[η] increases as the MW becomes higher and sometimes changes the sign. This law is determined also by the form anisotropy of macromolecules. It agrees well with the theory of equivalent ellipsoids. This theory can be used for the quantitative interpretation of the experimental results. It gives the estimation of the value of the molecular coil asymmetry in agreement with Kuhn's theory. In some cases (e.g., polystyrene in dioxane) the experiment shows change of sign of double refraction as the flow velocity gradient increases. This effect can be explained also by the equivalent molecular ellipsoids theory. As the molecular chains are uncoiling in the field of flow velocity gradient, their intrinsic optical anisotropy increases more than the form anisotropy. The comparative study of photoelasticity in the films of some polymers and of dynamic double refraction in their solutions shows the direct dependence of both effects to be in accordance with Kuhn's statistical theory.
Etude expérimentale de l'effet maxwell présenté par les solutions de macromolécules en chaîne
Authors: Leray Joseph
Published: April 2003

On effectue sur deux types de polymères des expériences de biréfringence d'écoulement analogues à celles de Cerf, c'est‐à‐dire que l'on mesure la pente tg α de la tangente à l'origine de la courbe d'extinction dans des solvants de viscosité η0 variable. (a) Polystyrènes. Les mesures portent sur quatre échantillons de masses 520.000, 1.240.000, 3.530.000 et 10.000.000. Pour chacun d'eux, à une concentration c donnée, tg α est une fonction linéaire de η0. Les droites relatives à diverses concentrations ont měme ordonnée à l'origine B. La quantité B est proportionelle à la masse moléculaire. Ces résultats faciliteront les extrapolations à c = 0 et à η0 = 0 des mesures d'angle d'extinction. (b) Acides désoxyribonucléïques. Les valeurs de tg α obtenues sur un échantillon de masse 6 × 106 se placent au voisinage de deux droites d'ordonnées à l'origine respectivement nulle et positive et dont les pentes sont dans un rapport de l'ordre de 4,5. Des observations analogues sont faites sur les résultats obtenus par d'autres auteurs, à l'aide d'un échantillon de měme masse, préparé par une méthode différente. On effectue une premiére confrontation entre les résultats expérimentaux et une théorie récente, fondée sur le modèle à N sous‐chaǐnes de Gauss et qui tient compte de la viscosité interne de la particule. Une interprétation plus complète nécessitera la connaissance des valeurs de la viscosité intrinsèque des polymères étudiés dans les différents solvants utilisés. D'ores et déjà on peut dire que la plupart des données expérimentales sont en accord avec les conclusions théoriques. En particulier, on confirme la possibilité de déterminer le terme de viscosité interne comme ordonnée à l'roigine de l'asymptote à la courbe tg α en fonction de η0. On corrobore les conclusions de Sadron quant à l'existence de deux catégories d'acides désoxyribonucléïques, les deux échantillons examinés ici présentant une rigidité différente. Toutefois, les variations du terme de viscosité interne avec la masse moléculaire paraissent difficilement compatibles avec la théorie.
Comparaison entre les résultats fournis par la détermination des dimensions et du moment électrique moyen des chaînes macromoléculaires
Authors: Marchal J. , Benoit H.
Published: April 2003

Les auteurs ont mesuré les moments électriques des polyoxyéthylèneglycols et des polyoxyéthylèneglycols diéthoxylés de degré de polymérisation compris entre 2 et 230. Ils ont calculé, en tenant compte des interactions, les valeurs théoriques correspondantes qui sont en accord avec les résultats expérimentaux. Ils montrent ensuite que le carré moyen du moment électrique \documentclass{article}\pagestyle{empty}\begin{document}$ \overline {\mu ^2 } $\end{document} est, dans les cas usuels, proportionnel au degré de polymérisation, ce qui signifie que l'“effet de volume” n'a pas d'influence sur la grandeur de \documentclass{article}\pagestyle{empty}\begin{document}$ \overline {\mu ^2 } $\end{document}. Ils en déduisent une méthode de mesure des interactions à courte distance dans un solvant quelconque. L'étude du polyméthacrylate de méthyle montre que ces interactions sont indépendantes du solvant et de la température, aux erreurs d'expérience près.
Le comportement diélectrique des polymères en solutions diluées
Authors: De Brouckere L. , Buess D. , Van Beek L. K. H.
Published: April 2003

Les propriétés diélectriques et les facteurs de perte ont été mesurés pour des solutions diluées de chlorure de polyvinyle dans le tétrahydrofurane et des mélanges de ce solvant avec l'heptane, pour des solutions de polyméthacrylate de méthyle dans le benzène et le toluène, et pour des solutions d'acétate de polyvinyle dans le toluène. Les concentrations variaient de 0.5 à 8 g./100 ml. Les fréquences allaient de 0.01 à 35 mégacycles/sec. et les température de −35° à +25°C. Un seul échantillon de chlorure de polyvinyle a été utilisé (DP = 1750); par contre quatre fractions de polyméthacrylate de méthyle (DP = 240–12.500) et quatre d'acétate de polyvinyle (DP = 2.550–23.250) ont été utilisées. Les valeurs numériques des trois polymères étaient plutǒt similaires. Les moments dipolaires moyens étaient proportionnels à la carrée du DP. Les temps de rélaxation étaient pratiquement indépendants du DP.
Etude de l'interaction solvant‐macromolécule par la constante diélectrique statique des solutions diluées de hauts polymères
Authors: Mandel M.
Published: April 2003

Il semble possible d'attribuer partiellement les propriétés diélectriques de solutions de hauts polymères à une interaction entre la macromolécule et les molécules du solvant, si ce dernier est polaire. L'étude de la variation de la constante diélectrique statique avec la température peut alors apporter des renseignements intéressants. Appliquant à la solution diluée d'une macromolécule polaire dans un solvant polaire, un modèle analogue à celui proposé par Fröhlich pour les liquides purs, on peut définir un facteur de corrélation (g) si l'on tient compte de la polarisation de déformation d'une façon macroscopique à travers l'indice de réfraction de la solution. Le raisonnement est valable aussi bien pour le cas où l'on considère la macromolécule comme un tout plus ou moins rigide que pour celui où on la décompose en chaǐnons statistiques. L'exemple d'une solution à 2% de polyméthacrylate de butyle dans le toluène montre que l'effet existe. I'étude de ces propriétés, commencée depuis peu au laboratoire, aura e.a. pour but de voir s'il existe une relation entre le facteur g pour différentes solutions de hauts polymères dans différents solvants, notamment par rapport à une éventuelle température de précipitation.
Temperature‐dependence of light scattering and intrinsic viscosity of hydrogen bonding polymers
Authors: Silberberg A. , Eliassaf J. , Katchalsky A.
Published: April 2003

A group of chemically related polymers—polymethacrylic acid polymethacrylamide, polyacrylic acid, and polyacrylamide—having a large number of groups capable of forming hydrogen bonds along the chain, was investigated by studying the temperature dependence of the 90° scattering of light and of the viscosity of dilute aqueous solutions, mineral acid being added in the case of the polyacids in order to suppress ionization. The intercepts of the light scattering plot indicated no dependence of molecular weight on temperature, but the slope B of this plot and the intrinsic viscosity [η] were found to change markedly with temperature. The slope parameter B and the intrinsic viscosity decreased with increase in temperature in the case of polymethacrylic acid, but increased with increase in temperature in the other three cases. The exceptional behavior of polymethacrylic acid is correlated with its known tendency to form gels on heating in concentrated aqueous solution. A discussion of the light scattering plot slope parameter B and its temperature‐dependence is given, based on fluctuation theory and the experimental evidence. It is emphasized that B is a measure of the interactions between the kinetic units as they exist in the solution and that its temperature‐dependence gives information about the entropy and energy changes accompanying changes in concentration. These quantities are calculated and briefly discussed. The correlation between B and the intrinsic viscosity [η] is examined in the light of the Flory‐Fox‐Krigbaum treatment. Relationships involving, respectively, the heat and entropy of dilution are derived and used for comparison. Our results are found to conform well with these theoretical predictions. Calculations of the length of the statistical chain element show that these values in the case of polymethacrylic acid and amide are about half the value for polyacrylic acid under corresponding conditions. This is at variance with the fact that the presence of the methyl group should have a marked stiffening effect on the chain. The discrepancy is attributed to intramolecular hydrogen bonding, the polymethacrylic chain being assumed to be the more strongly bonded. The possibility of intramolecular bonding makes the agreement with Flory's treatment of coil expansion particularly interesting. A possible explanation is suggested.
Sorption and diffusion in ethyl cellulose. Part I. History‐dependence of sorption isotherms and permeation rates
Authors: Barrer R. M. , Barrie J. A. , Slater J.
Published: April 2003

The sorption and permeation of benzene, acetone, and methanol in and through ethyl cellulose has been investigated from the point of view of hysteresis and time‐dependence. The three sorbates are imbibed decreasingly in the order given, at any relative pressure, and so swell the polymer to different extents. The medium is one in which anomalous diffusion is to be expected. The study was made in the lower range of concentrations of penetrant. The initial isotherm of acetone at 50°C. lay below subsequent ones at the same temperature. The higher the temperature the smaller this difference tended to be, while the greater the pressure and so the amount imbibed the greater it became. Eventually “settled” reproducible isotherms were found. If the outgassed polymer, following lower temperature isotherms, was “annealed” at a higher temperature and then cooled again, the initial isotherm at 50°C. was more nearly approached. However, subsequent isotherm determinations at the same temperature again established the “settled” isotherm. Permeation rates were determined as a function of pressure under various treatments. Repeated permeation runs caused the permeability of the polymer to decrease to a “settled” value. This behavior may be ascribed to some orientation of polymer, by mass flow, during permeation. After establishing the settled permeability the polymer was outgassed and “annealed” at a higher temperature, and the permeability at the original temperature then lay below the “settled” value. Benzene, which swelled the membrane more than the other sorbates, showed more pronounced effects of the same kind as acetone. On the other hand methanol, which was least sorbed, showed less pronounced time‐ and history‐dependence. Sorption always occurred more slowly than desorption. The various effects have been discussed in terms of a model of the polymer having rather stiff chains with some semipermanent interchain bonds, but other bonds more easily rearranged. The history‐dependent effects can arise at temperatures well above the glass transition usually quoted for ethyl cellulose.
On the additivity of the configurational and electrostatic properties of polyelectrolytes in solution
Authors: Lifson Shneior
Published: April 2003

The theories of Hermans and Overbeek, of Kimball, Cutler, and Samelson and of Katchalsky and Lifson concerning the dimensions of polyelectrolyte molecules in solution are discussed. The assumption that the configurational forces acting in a polyelectrolyte molecule may be adequately represented by the theory of nonelectrolytic polymers is applied in different ways by each theory, and leads to widely different results. It is found that, when additivity of the configurational and electrostatic contributions to the free energy is assumed, the configurational contribution is underestimated. The contribution is overestimated, on the other hand, when the potentials of the forces acting on each segment are assumed to be additive.
SECTION II: Polybase properties of polyvinylamine
Authors: Katchalsky A. , Mazur J. , Spitnik P.
Published: April 2003

The polybase properties of polyvinylamine hydrobromide were studied by pH‐metric titration at concentrations ranging from 10−4 to 10−1 M, in the presence, as well as in the absence, of neutral monomonovalent salt at high concentrations. The dependence of pH on degree of ionization, in all the range of concentrations studied, diverges from the known behavior of polyacids and polybases. The titration curve could not be characterized by a single dissociation constant, even when the electrostatic potential, determined electrophoretically, was taken into account, or when this potential was suppressed by high concentrations of neutral salt. An attempt is made to explain the unusual behavior of polyvinylamine by taking into account the nearest neighbor interaction. A statistical treatment, based on the unidimensional Ising model, leads to potentiometric equations involving two constants‐the intrinsic dissociation constant pK, and a nearest neighbor interaction constant ΔpK. The experimental titration curve could be satisfactorily described by these theoretical potentiometric equations. The titration constants for polyvinylamine derived by this procedure are pK = 9.4 and ΔpK = 1.20. These values compare favorably with the constants obtained from the microscopic dissociation constants of diethylenetriamine and of triethylenetetramine.
Preparation and titration of amphoteric polyelectrolytes
Authors: Alfrey Turner , Pinner S. H.
Published: April 2003

A series of amphoteric polyelectrolytes have been made by copolymerizingN‐dialkylaminoethyl acrylates and methacrylates with acrylic, methacrylic, or itaconic acids in unbuffered aqueous solutions or in nonaqueous solutions at 70°C. using potassium persulfate or azobisisobutyronitrile as the catalyst. The purified copolymers were titrated electrometrically on a semimicro scale. The composition of the copolymers as obtained by titration agreed with calculations based on the analysis of nitrogen content. Except for itaconic acid copolymers, the titration curves exhibited separate and nonoverlapping ionization regions for the acid and basic components and allowed the assessment of the pKvalues of the acid and amine groups and also the pIvalues of the copolymers. The pKand pIvalues varied with the composition of the copolymers in the expected manner. As the frequency of a given group along the main chain increased, its apparent strength decreased. The pIvalues also shifted to lower pH values as the number fraction of acid groups increased. All these effects could be explained on the basis of the theory of the electrical free energy of ionization. The pIvalues computed graphically agreed within experimental error with those calculated from the equation:where α is the degree of ionization of the group present in excess in the polyelectrolyte. The implication is that the electrical free energy of ionization does not appear to vanish at the iso‐electric point.
L'Influence de l'acide polyméthacrylique sur la réfraction moléculaire des électrolytes forts et concentrés
Authors: Kryszewski M.
Published: April 2003

On a mesuré l'influence de l'acide polyméthacrylique ajouté aux solutions concentrées de NaCl, NaBr, NaI sur la réfraction moléculaire de ces sels. On trouve que la présence d'acide polyméthacrylique cause une diminution de réfraction moléculaire des sels qu'on ne peut pas expliquer seulement par la concentration du polymère.
Influence of pH and ionic strength on size, shape, and electric charge of the deoxyribonucleic acid molecule
Authors: Mathieson A. R. , Matty Sheila
Published: April 2003

The methods of electrometric titration, electrophoresis, streaming birefringence, and viscosity have been used to study the deoxyribonucleic acid (DNA) molecule in solutions of different pH. The dissociation constants of the nitrogen bases have been found at various DNA concentrations and ionic strengths, and the difference between the forward and backward titration curves further studied. The electrophoretic mobility has been measured at various pH values and ionic strengths. Calculations of the electrostatic potential indicate why there is little spreading of the titration curves. Comparison of the titration and electrophoretic data has been made to calculate the charge carried by the DNA ion alone and by the DNA ion together with its associated gegenions, and an estimate of the proportion of bound gegenions has been obtained. Measurements of (tan α)0 and [η] from streaming birefringence and viscosity have been made at various pH's on forward and backward titration, and the molecular length, axial ratio, and molecular weight calculated from these. Between pH 4.5 and 10 the length is unchanged but decreases to half its neutral value between pN 2.5–4.5 and 10–12, due to the breakage of the rigid hydrogen‐bonded structure by titration. On backward titration the length remains below half its undenatured value. The molecular weight is unchanged by treatment with acid or alkali between pH 2.5 and 12.
The structure and properties of levan, a polymer of D‐fructose produced by cultures and cell‐free extracts of aerobacter levanicum
Authors: Feingold D. S. , Gehatia M.
Published: April 2003

Living cultures of Aerobacter levanicum, or cell‐free extracts on sucrose, elaborate levan, a polymer of D‐fructose. Exhaustive methylation of the fructosan‐culture levan, and the levan produced in vitro with dimethyl sulfate and sodium hydroxide yielded fully methylated trimethyllevan, which afforded on hydrolyses 1,3,4,6‐tetra‐,1,3,4‐tri‐, and 3,4‐di‐O‐methyl‐D‐fructose in the molar ratio 1 : 7 : 1, respectively. These results indicate that the levan polymers are branched: main linkage C‐2,6; branch linkage C‐2,1; average basal chain length 9. The structural similarity of culture and “enzyme” levan was confirmed by infrared analysis. Partial hydrolyzates of levan examined chromatographically were found to contain more than one oligosaccharide at each level of DP above three. This observation is further evidence for branching in the native molecule. Oligosaccharides of DP 2–10 prepared by mild (2.5%) and extensive (66%) hydrolyses of the native polymer were all totally hydrolyzed to fructose by yeast invertase. This suggests that all the linkages in the levan molecule‐both those at the chain terminals and those within the chains‐are of the β‐fructofuranosyl type. Diffusion and sedimentation measurements on levan provided values from which average molecular weights were calculated. Studies of the use of degraded levan preparations as plasma volume expanders are in progress.
Physical chemistry of native cellulose
Authors: Usmanov H. U.
Published: April 2003

The knowledge of the physical chemical properties of cellulose and the laws of their alteration during the growth of natural filaments is very important for scientifically increasing the production of natural cellulose filaments. While dealing with cotton growing we have been continuously performing the physical chemical investigation of natural cellulose. The results obtained may be summarized as follows. Cellulose appears in the cotton tissue together with the flower and pod and not several days after blossoming, as is the general opinion to be encountered in the literature. The synthesis of cellulose in cotton is at first very slow, showing an acceleration by the 15th day after bloom with a subsequent slow‐down again and complete cessation approximately on the 40th day after bloom. Thus the characteristic curve of cellulose accumulation in cotton has an S‐shaped form. The natural cellulose of an early age has a very low degree of polymerization which later, by the 25th to 30th day after bloom, shows an abrupt increase and remains almost stable. The filament then almost completely consists of α‐cellulose. The kinetics of the polymerization and accumulation of cellulose is connected with the ripening period of cotton under investigation and makes it possible to predict the time of the ripening of pods. Early cellulose is very porous, it easily hydrolyzes, and has a higher sorption capacity and heat of solution than the cellulose of a mature age. However, the tightness of packing of the natural cellulose evaluated in terms of water sorption and heat of solution in water, reaches its maximum in the vegetation period, i.e., approximately on the 40th day of the maturation of filaments. The gradual increase in tightness of cellulose packing and its drop after 40 days can be accounted for if we consider the possibility of synthesis in all layers of the secondary wall of the filament, i. e., throughout the tissue of cellulose and not only in the channel of the filament. The main physicochemical and technological properties of cellulose bodies are the functions of the tightness of molecular packing of cellulose. The tightness of packing may vaccilate within a very broad range depending on the conditions of biosynthesis or processing.
Polypeptides. VIII. Molecular configurations of poly‐L‐glutamic acid in water‐dioxane solution
Authors: Doty Paul , Wada A. , Yang Jen Tsi , Blout E. R.
Published: April 2003

The configuration of a poly‐L‐glutamic acid sample of 34,000 molecular weight has been studied in 0.2 M NaCl‐dioxane (2:1) as a function of pH and temperature by intrinsic viscosity, optical rotation, optical rotatory dispersion and infrared spectroscopy. The intrinsic viscosity and specific rotation fall sharply in the pH range of 5.4–6.4 reaching values that remain constant at higher pH. The indications that these changes correspond to a reversible helix‐random coil transition are substantiated by the demonstration that the optical rotatory dispersion shifts from the type characteristic of helices to the normal type as the pH is increased through the same region. Further evidence of the transition is found in infrared spectroscopic studies in solutions in which D2O has replaced H2O. The temperature dependence of the specific rotation and infrared spectra shows that within the pH region of 5.4 to 6.4 the equilibrium is shifted toward the coiled configuration by an increase in temperature. The analogy of this behavior with protein denaturation is obvious. It is noted that the transition from the helix to the coil does not begin until about 40% of the residues have become charged. The implications of the ability of the helical configuration to withstand this degree of electrostatic repulsion within its side groups is discussed in relation to the configuration of proteins.
Studies on graft copolymers derived by ionizing radiation
Authors: Chen W. K. W. , Mesrobian R. B. , Ballantine D. S. , Metz D. J. , Glines A.
Published: April 2003

Studies are presented on the preparation of graft copolymers by the gamma‐ray irradiation of various polymer‐monomer combinations. The following graft copolymers have been prepared and evaluated for specific applications: (1) vinylcarbazole grafted to polyethylene to produce a higher temperature dielectric material; (2) styrene grafted to polyethylene and sulfonated to produce a cation exchange membrane of high mechanical strength, low resistivity, and high permeaselectivity; (3) surface grafting of styrene to polytetrafluoroethylene for modification of adhesive properties; (4) acrylonitrile grafted to polydimethylsiloxane to increase solvent resistance of the latter.
Alkaline and acid hydrolysis of polyvinylamides
Authors: Moens J. , Smets G.
Published: April 2003

The alkaline and acid hydrolyses of polyvinylamides and their N‐substitution derivatives have been studied and compared to the alkaline and acid hydrolyses of simple homologous substances. The rates of reaction have been followed conductometrically, and the rate constants evaluated at different temperatures in order to determine the energies of activation and the log PZ of the Arrhenius equation. The influence of the polymeric structure on the course of the reactions has been shown. In alkaline medium the increasing negative charges on the polymeric chain exert an electrostatic repulsion effect toward the hydroxyl ion, and, as a consequence, cause a progressive decrease of the rate of reaction. In the case of polyacrylamide (PAA), hydrolysis enhances an uncoiling of the polymeric chain when the degree of conversion reaches about 40%. Therefore the reaction is characterized by two different steps, a first, rapid step analogous to the reaction of aliphatic monoamides (Ea = 13.7 kcal.), and a second, slow step related to the increasing electrostatic effect. This interpretation has been confirmed by hydrolysis measurements on copolymers of acrylamide‐vinylpyrrolidone (42/58) and acrylamide‐acrylic acid (64/36). In the case of polymethacrylamide (PMA), N‐methyl‐PAA, and N,N′‐diethyl‐PAA steric hindrance along the chains confers a stretched configuration on the macromolecules, and reinforces the electrostatic effects; therefore, the rate constants, can be determined only at low degree of conversion. Moreover, the maximum degree of hydrolysis becomes limited and is 72, 55, and 35 for PMA (Ea = 16 kcal.), N‐methyl‐PAA (Ea = 18.3), and N,N′‐diethyl‐PAA (Ea = 22 kcal.), respectively. N,N′‐Diethylpolymethacryamide is completely alkali‐resistant. In acidic medium the hydrolysis of PAA and PMA is characterized by a secondary intramolecular cyclization due to imide formation between amide and acid functional groups. This secondary reaction, which becomes appreciable at 85°C., causes an increase in the overall energy of activation of the hydrolysis, which is consequently 3 to 4 kcal. higher than those of aliphatic low molecular weight compounds. On the other hand, this imidization is absent in the case of the N‐substituted polymers, of which the energies of activation are equal to those of the aliphatic homologous substances (N‐methyl‐PAA = 21.7; N,N′‐diethyl‐PAA = 24.6 kcal.).
Relationships among variously weighted average properties including molecular weights
Authors: Ward Wilfred H.
Published: April 2003

A number‐average property such as a number‐average diffusion constant Dn cannot be defined in terms of weight‐related weighting factors (such as concentrations in weight per unit volume) without postulating a functional relationship between the molecular weight and that property. Conversely, an analogous statement holds concerning any weight‐average property and number‐related weighting factors such as mole fractions. Ordinarily the molecular weight distribution is not known initially for a given sample under study, so that assignment of any such a relationship under these circumstances would be quite arbitrary. It is proposed that the number average analog [Σci/(Σci/Qi)], which is equal to the true number average Qn only when Qi is directly proportional to the molecular weight Mi within the sample considered, be designated the number‐analogous average Qx to distinguish it from Qn. (In this, ci is a weighting factor proportional to the polymer weight fraction having the value Qi of the intensive physical or chemical property under discussion.) Mn is of course necessarily equal to Mx. However, designation of Dx as the number‐average diffusion constant is particularly unreasonable because it implies direct proportionality between the molecular weight and the diffusion constant. Although such a relation may hold for a specific case, in general, other factors being usual, the diffusion constant is inversely related to molecular weight. Discussion of a specific illustration shows the following: Qx may be the same for heterogeneous systems having different values of Qn. Qn cannot in general be found by analyzing a material distribution by means of a property such as the refractive index that is proportional to the mass concentration rather than to the number of molecules in a given volume. Qx sometimes can be found from such data. Although the sedimentation and diffusion constants, with the partial specific volume, define the molecular weight of a homogeneous sample, the average sedimentation and diffusion constants of a mixture do not uniquely determine its average molecular weights. Values found from weight‐, number‐, or number‐analogous average sedimentation and diffusion constants may be either higher or lower than the weight‐ and number‐average molecular weights, even though these latter have been deduced to be limiting values for certain postulated molecular weight distributions. In a given instance, heterogeneity indexes calculated from true weight‐ and number‐averages of sedimentation and diffusion constants more closely approximate the ratio of the weight‐average to number‐average molecular weights than if the more readily determined number‐analogous averages are used.
Determination of average molecular weight of cellulose acetate by dielectric dispersion in solution
Authors: Scherer Philip C. , Levi David W. , Hawkins Miller C.
Published: April 2003

The capacity of cells containing solutions of 5% cellulose acetate in dioxane was measured from 50 cycles to as high as 5 megacycles by a bridge method. A dispersion region was found between zero and approximately 40 kc. The frequency where the dielectric dispersion was 0.50 was taken as the critical frequency which was found to be related to the viscosity determined degree of polymerization. An empirical correlation enabled the calculation of degrees of polymerization from dielectric dispersion which could be readily duplicated and which agreed reasonably well with those found by the viscosity method. It is suggested that this procedure may develop into a very convenient and rapid method for molecular weights pending the accumulation of further experimental evidence.
Condensation polymers containing fluorine. I. Synthesis of linear polyesters from fluorine‐containing diols
Authors: Schweiker George C. , Robitschek Paul
Published: April 2003

Methods of synthesizing linear polyesters from fluorine‐containing diols have been investigated. The most suitable method consists of reacting the fluorine‐containing diols with dicarboxylic acid chlorides. Number‐average molecular weights in excess of 15,000 have been obtained. The polymers are rubberlike gums or waxy solids, depending on the reactants used. Increasing amounts of fluorine, contained either in a pendent group or on the backbone chain of the polymers, decreases their solubilities in common solvents, and raises their brittle temperatures.
Ionic grafting
Authors: Haas Howard C. , Kamath Pandurang M. , Schuler Norman W.
Published: April 2003

Cation initiated polymerizations of various monomers were carried out in the presence of several polystyrene derivatives in an effort to obtain graft copolymers. No success was achieved in grafting with vinyl butyl ether, vinyl ethyl ether, isobutylene, N‐vinylpyrrolidone, or pinene under the particular experimental conditions employed. In the experiments involving vinyl n‐butyl ether, the presence of the various polystyrenes appeared to have no effect on the polymerization of this monomer or on the DP of the polyvinylbutyl ethers obtained. However, when styrene was polymerized in the presence of poly‐p‐methoxystyrene (PPMS), graft copolymer was readily obtained. The success of this reaction demonstrates the feasibility of preparing graft copolymers by an ionic mechanism and yields additional proof of an ionic chain transfer reaction with aromatic species in which the latter are incorporated into the chain. Data obtained on the styrene‐PPMS system are discussed in terms of a simple kinetic scheme. The molecular termination constant of PPMS was found to be only 1/67th of that of p‐methylanisole, a low molecular weight analogue. The low chain transfer effectiveness of PPMS is believed to be due to constraints placed on the availability of the transfer sites which are linked in a polymeric chain.
Infrared determination of orientation, orientation distribution, and crystallinity in polyethylene films
Authors: Tobin Marvin C. , Carrano Matthew J.
Published: April 2003

The problem of determining orientation distribution in polymer films from the measurement of infrared dichroism is treated from the theoretical point of view. It is shown that the distribution function cannot be determined from such measurements. However, if an elliptical distribution function is assumed, the axial ratio of the ellipse of planar components may be calculated. The curve for axial ratio as a function of measured dichroic ratio is given. The dichroisms of the 1300, 730, and 719 cm.−1 bands in polyethylene are discussed and interpreted. It is shown that, in extruded films, chain axes in the amorphous areas lie roughly in the extrusion direction. Chain axes in the crystalline areas lie roughly perpendicular to the extrusion direction. In stretched films, all chain axes line up in the stretch direction. The axial ratios calculated from the 730 and 719 cm.−1 bands are given for a cold‐stretched polyethylene film at different degrees of stretch. Axial ratios of over 100:1 may be attained for the crystalline regions of the film. Specific extinction coefficients for the crystalline band at 730 cm.−1 and the amorphous band at 1300 cm.−1 are determined from measurements on polyethylene films of different crystallinities. The latter values is compared with values measured in molten polyethylenes and normal hydrocarbons. The hydrocarbon values do not agree with the polyethylene values. The amorphous contents of a number of polyethylenes as measured by infrared, density, and x‐ray methods are given. Possible reasons for the disagreement between the results are briefly discussed.
Use of the fluorescence technique as an absolute method for obtaining mean relaxation times of globular proteins
Authors: Steiner R. F. , McAlister A. J.
Published: April 2003

Measurements of excited lifetime and of degree of polarization have been combined to yield values for the mean relaxation time of fluorescent conjugates of bovine serum albumin, egg albumin, and lysozyme. Evidence has been presented for the validity of relaxation times thus computed and for the absence of contributions from nonrandomness of fluorescent residue orientation and from internal degrees of rotational freedom.
Viscosity of dilute solutions of polyvinyl alcohol
Authors: Matsumoto Masakazu , Imai Kiyokazu
Published: April 2003

The viscosity of dilute solutions of polyvinyl alcohol was measured in aqueous and aqueous phenol systems. In the aqueous solution, Huggins' relation does not hold and a2 = 2.01 × 10−1 [η]2.28 was obtained. In the aqueous phenol solution, Huggins' relation holds very well. The relation between a2 and [η] in both systems is independent of the polymerization conversion of the original polyvinyl acetate. The exponent α of [η] = KMα is greater in the aqueous phenol system than in aqueous solution, showing that the aqueous phenol is a better solvent than water.