bluuebunny/crossref_metadata_2025_split huggingface dataset:
The reaction of cellulose acetate with acetic acid and water
Authors: Hiller L. A. 
Published: April 2003

AbstractReaction curves for the simplest of cellulose acetylation systems; namely, the homogeneous reaction of secondary cellulose acetates with acetic acid and water, were studied. These reactions were found to be slow and complex, consisting of two interdependent simultaneous reversible second‐order processes. The faster process represented the reaction of primary hydroxyl and acetyl groups, while the slower process represented the reaction of the two secondary hydroxyl and acetyl groups. Equilibrium and rate constants and initial and final concentrations of hydroxyl and acetyl groups were calculated for the two simultaneous reactions. Equilibrium constants for the primary groups favored acetylation, while equilibrium constants for the secondary groups favored deacetylation. Final equilibrium was not affected by the presence of sulfuric acid. On the other hand, rate of reaction was increased in the presence of sulfuric acid, indicating catalysis by this reagent. The reaction mechnanism outlined above was confirmed by comparing primary hydroxyl group contents calculated from acetylation results with primary hydroxyl group contents measured by means of the tritylation reaction. Energies of reaction and energies of activation were calculated. Energies of reaction were low, indicating that equilibrium for this process is very nearly temperature independent. Energies of activation were in agreement with energies of activation for esterifications of simple alcohols, from which it was concluded that the acetylation and deacetylation of secondary cellulose acetates in homogeneous solution is but another example of general acid catalyzed esterification with carboxylic acids and general acid catalyzed hydrolysis of fatty acid esters. Degradation of the cellulose chain molecule was followed throughout these studies and energies of activation for this reaction were calculated. These energies of activation were higher than those for the acetylation reactions. It was concluded that degradation is more severe at higher temperatures for a given change in acetyl group substitution. Initial determination of equilibrium and rate constants for acetic acid acetylation of cellulose acetate has been carried out. It is suggested that through use of such procedures as tritylation analysis, which isolates the reaction of the primary groups from the secondary groups, improved values for these constants may be achieved.
Influence of concentration on the viscosity of sodium thymonucleate solutions
Authors: Callanan M. Joan , Carroll William R. 
Published: April 2003

Abstract
A viscometer to which variable pressures may be applied is shown to be convenient for measuring viscosities of sodium thymonucleate (NaTN).
The viscosities of solutions of NaTN investigated vary with velocity gradient. All of the solutions obey the empirical equation:

where p is the average pressure on the solutions during the outflow time, t. A is used to calculate what are believed to be characteristic relative viscosities.
The viscosity of solutions of alcohol precipitable NaTN is found to depend on the concentration according to the equation:

Our preparation of NaTN gives values of 11.1 dl./g. and 0.24 for [η] and k″, respectively.
The viscosity of NaTN solutions not easily precipitable depends on the concentration according to the equation:

Our values for [η] and k′ are 21.8 dl./g. and 0.26, respectively.
The viscous behavior of NaTN is discussed in the light of modernP polymer theory.
An experimental study of the influence of various factors on the time dependent nature of diffusion in polymers
Authors: Park G. S. 
Published: April 2003

AbstractThe kinetics of the sorption and desorption of methylene chloride by cellulose acetate and polystyrene have been studied by following the increase in mass of a polymer sheet suspended from a quartz spring in an atmosphere of the vapor. A tenfold change in the molecular weight of polystyrene does not alter the sorption rate, but a slight increase in rate is obtained when the molecules of this polymer are given a large unidirectional orientation in the plane of the polymer sheet. In agreement with other work, a considerable increase in both sorption and desorption rate is obtained by increasing the pressure of the solvent vapor. Previously it had been shown that a plot of the mass of sorbed vapor against the square root of the time has a slope that increases with time. It was shown that this peculiar characteristic of the sorption kinetics could not be accounted for by a purely concentration dependent diffusion coefficient, and it was suggested that it might be due either to a slow response of the diffusion coefficient to change in solvent concentrationor to the stresses set up between the swollen and unswollen parts of the polymer. Here it is shown that neither hypothesis alone will account for all the observed effects of the thickness of the polystyrene or cellulose acetate sheet upon the sorption and desorption kinetics. Sorption experiments on polymer sheet already containing some dissolved solvent do not show this peculiar characteristic of increasing slope when the concentration difference between the start and the end of the experiment is small, but when this is large very peculiar curves are obtained. The effects can be reconciled with either of the proposed mechanisms. Measurements of the changes in area during sorption and desorption have been measured on polystyrene sheet and these lend support to the strain hypothesis but also indicate that some plastic, as well as elastic, deformation of the polymer takes place during sorption.
A theoretical investigation of the influence of molecular relaxation and internal stress on diffusion in polymers
Authors: Crank J. 
Published: April 2003

AbstractRecent experiments have indicated that the diffusion properties of a penetrant‐polymer system may change with time as diffusion proceeds. It is thought that two possible explanations of these time effects are slow changes of polymer structure accompanying diffusion and internal stresses exerted by one part of the polymer sheet on another as it swells. Two theoretical models are set up in order to express these effects quantitatively. The first model is essentially that in terms of which mechanical and other properties of polymers are commonly discussed, involving the concept of an instantaneous change of diffusion coefficient when the concentration changes, followed by a slow drift toward an equilibrium value. The second model expresses the effect of stresses set up between the outer swollen layers and the unattacked center of a polymer sheet during sorption. These stresses are slowly relieved as the diffusion proceeds, leading to a time‐dependent diffusion coefficient. The main features of diffusion behavior are established by calculation and the models are shown to account for the various types of sorption and desorption curves observed experimentally under different conditions, e.g., for sheets of different thicknesses and for different ranges of penetrant concentration. As examples, sorption and desorption curves calculated from the first model are shown to agree reasonably well with experimental curves for the methylene chloride‐polystyrene system. The rate of sorption and of the associated change in area of the sheet are accounted for by the second model. The presence of internal stresses also provides an explanation for the observation that there may be an appreciable interval of time during which a thin sheet takes up more penetrant than a thicker one under corresponding conditions. On the other hand, it is the slow structural changes which cause the rate of sorption to be not always inversely proportional to the square of the thickness of the sheet. It is concluded that both polymer relaxation and internal stresses play a part in determining diffusion behavior. The particular experimental results examined can be accounted for if the half‐life of the slow structural changes is comparable with that of the sorption experiment itself, and if the internal stresses change the diffusion coefficient by a factor of two or three.
Studies on hydroxyethylpolyvinyl alcohol
Authors: Cohen Saul G. , Haas Howard C. , Slotnick Herbert 
Published: April 2003

AbstractHydroxyethylated polyvinyl alcohols (HEPVA's) containing 12, 19, and 35% combined ethylene oxide were prepared by a heterogeneous reaction between dry polyvinyl alcohol (PVA) and liquid ethylene oxide. Another sample containing 18% was prepared by a more nearly homogeneous reaction in the presence of water. These derivatives may be analyzed satisfactorily by the modified zeisel method of Morgan. The properties of the HEPVA's are briefly described. Reaction of HEPVA with p‐toluenesulfonyl chloride showed that secondary hydroxyls were tosylated along with the primary and that the two reactions cannot be separated kinetically. This method, useful in estimating the primary hydroxyl content of hydroxyethylcellulose, cannot be applied to HEPVA. The stability of the tosylates indicated, however, that in derivatives containing up to 35% combined C2H4O2 ca. 1/2 ethylene oxide per vinyl alcohol unit, no polyethylene glycol chains were present and all combined ethylene oxide existed as individual hydroxyethyl groups distributed along the PVA backbone. Introduction of ethylene oxide into PVA increased the reactivity of residual secondary hydroxyls toward chemical reagents by destroying the normal high degree of hydrogen bonding and making adjacent domains more accessible for reaction. Very noticeable differences in properties were observed between HEPVA's prepared under differing conditions of heterogeneity. Two such polymers of similar ethylene oxide content showed quite different extents of reactions, susceptibility toward swelling agents, and x‐ray diffraction diagrams. These differences are attributed to a more random distribution of hydroxyethyl groups along the PVA backbone in the product of the more homogeneous reaction which leads to a more disordered system.
A color reaction involving vinyl chloride containing polymers and pyridine
Authors: Wechsler Harry 
Published: April 2003

AbstractWhen a dilute pyridine solution of vinyl chloride polymers or copolymers is heated and a few drops of alcoholic hydroxide are added to the hot solution, a dark brown color develops. The response of vinyl chloride polymers in this reaction is much more intense than that of most other organic compounds, probably due to the conjugated double bonds produced in the main chain through the loss of hydrogen chloride. In addition to straight degradation of the polymer, the formation of an isocyanine dye is suggested by a mechanism which, besides pyridine and the polymer, involves the alkali alkoxide as a reactant.
Polymerization of methyl methacrylate by its polymer
Authors: Melville H. W. , Watson W. F. 
Published: April 2003

AbstractAddition of its polymer causes methyl methacrylate to polymerize. The extent of polymerization is linear with time of reaction to at last 5% conversion at 60–90°C. The rate of polymerization is proportional to the first power of the concentration of added polymer and independent of its molecular weight. The molecular weight of the polymer formed increases with increase in reaction temperature. No polymerization caused by polymer occurred with the other polymer/monomer systems tested. The rate and nature of the initiating reaction are discussed.
Adsorption of high polymers from solution on to solids. I. Adsorption of polystyrene on charcoal
Authors: Hobden Joan F. , Jellinek H. H. G. 
Published: April 2003

AbstractRates of adsorption from solution on to charcoal and adsorption isotherms have been determined for unfractionated and fractionated polystyrene samples. The rates and extent of adsorption increase with decreasing solvent power and decreasing molecular weight. The rate curves of the fractionated samples show two distinct steps. Langmuir's adsorption equation is obeyed. Mechanisms of adsorption are discussed.
Mechanism of the crystallization of high polymers
Authors: Schuur G. 
Published: April 2003

AbstractIn this article a conception of the mechanism of crystallization is given, on the basis of which, it is suggested the origin of spherulites might be explained. A tentative explanation of several related phenomena is based on the new concept. Crystallites are conceived to be small collections of strongly oriented polymer which, on fusing, exhibit marked shrinking in the direction of orientation. Particles of amorphous material therefore stretch out in a certain direction during crystallization, as the result of which there is substantial contraction in the other directions. This is termed “auto‐orientation.” As the growing crystallite has to be fed from surrounding material, an orienation is initiated in the latter at right angles to the first crystallite. As a result of this orientation, crystallites are formed there which are oriented Perpendicular to the first crystallite. In their turn, these crystallites induce orientation in the surroundings and in this way crystallization becomes autocatalytic in character. Spherulites owe their origin to the fact that the various sectors in a symmetrical spherical order mutually cancel out their stretching and shrinking tendencies. In highly crystalline polymers with rapid nuclear formation there first comes into existence numerous radomly oriented nuclei which proliferate to small crystallites. Wherever these small crystallites come to be arranged in a suitable position, their relative tensions will be cancelled out and they will grow into a spherulite. Simultaneously small crystallites which are in an unfavorable position will be consumed by the growing spherulite, or else oriented in the correct direction and incorporated. As spherulites commonly measure from 10 to 50 microns, compensation between the tensions of the various sectors has to take place at long distance. At higher temperatures, compensation is as a rule found at short distances, i.e., crystallites which are at right angles to each other are in close proximity. Therefore “spherulites” varying individually come into existence as the crystallites are subject to other influences in addition to auto‐orientation. At very low temperatures the primary small crystallites are too stable to develop into spherulites. The mechanism of crystallization as thus conceived implies that the melting point of a polymer depends not only upon the dimensions and perfection of the crystallites, but also upon the specific arrangement of the crystallites, i. e., the degree in which they stabilize each other by a mutual compensation of tensions. It also helps to explain the following facts which have been noted in experiments performed with natural rubber: (1) The typical S‐shape of the crystallization curve and the constancy of the product of induction period and maximum rate of crystallization. (2) The fact that natural rubber always crystallizes under nonequilibrium conditions. (3) The failure of rubber in latex to crystallize and the fact that the rate of crystallization in films produced from latex is poorly reproducible.
The electrostatic free energy of polyelectrolyte solutions. I. Randomly kinked macromolecules
Authors: Katchalsky A. , Lifson S. , Mazur J. 
Published: April 2003

Abstract(1) The electrostatic free energy of randomly kinked, ionized, macromolecules was calculated for polyelectrolyte solutions of finite ionic strenght. A detailed analysis of the charging process and the reference state of the free energy is given. The mutual electrostatic repulsion of the fixed charges on the macromolecule is the main part of the electrostatic free energy. Its calculation is based on two main assumptions: the validity of Kuhn's statistics and of Debye's approximation. (2) The electrostatic contribution per macromolecule to the free energy of the solution is found to be Fe = (v2ϵ2/Dh)ln {1 + (6h/κh)}, where v is the number of charged groups per polymolecule, ϵ the unit of charge, D the dielectric constant, κ Debye's inverse radius, based on the number of free ions in solution, h the end‐to‐end distance of the charged molecule, and h0 the corresponding end‐to‐end distance in and uncharged reference state. (3) Activity coefficients of free ions in polyelectrolyte solutions have been derived from the theory. The calculated values compare favorably with the activity coefficients from measurements on Donnan distribution of salt.
Peroxides from autoxidized methyl oleate and linoleate as initiators in the preparation of butadiene‐styrene synthetic rubber
Authors: Swern Daniel , Coleman Joseph E. , Knight H. B. , Zilch K. T. , Dutton H. J. , Cowan J. C. , Gyenge J. M. 
Published: April 2003

AbstractIn the dextrose‐free recipe at 41°F. for the copolymerization of butadiene and styrene, using 6 × 10−4 mole of initiator per one hundred grams of monomers, methyl oleate peroxide (MOP) and methyl linoleate peroxide (MLP) gave higher polymerization rates and conversions than cumene hydroperoxide (CHP), and they gave as high rates of conversion as p‐menthane hydroperoxide (PMHP). In the peroxide‐dextrose recipe at 122°F., at both low and high dextrose levels, only about one‐half as much MOP (1.5 × 10−4 mole) as CHP or PMHP was employed on a molar basis to achieve the same conversion and polymerization rate. In the low dextrose‐redox recipe at 41°F., using 6 × 10−4 mole of initiator per one hundred grams of monomers, MLP gave slightly higher conversions than CHP or PMHP, but in the amine recipe at 41°F., MLP gave lower conversions.
Polymeric chain transfer reactions. Polymerization of some vinyl monomers in the presence of vinyl polymers
Authors: Hayes Robert A. 
Published: April 2003

AbstractThe polymerization of certain vinyl monomers in the presence of some vinyl polymers leads to the formation of a chemical bond between the resulting two polymers. A study of the efficiency of this graft copolymerization process under various conditions in emulsion has been made and the following conclusions drawn. An increase in the catalyst concentration and temperature of polymerization increases the efficiency, while the addition of dodecyl mercaptan decreases it. The list of the monomers used in the order of decreasing activity toward graft copolymerization is vinyl chloride, vinyl acetate,and styrene. A list of polymers in order of decreasing susceptibility to graft copolymerization is polyvinyl chloride, polyacrylonitrile, polyvinyl a cetate, and polystyrene.
Orientation processes in synthetic crystalline polymers in terms of morphology
Authors: Keller A. 
Published: April 2003

AbstractA new approach to orientation processes is proposed in terms of the morphology of crystalline polymers. Our present knowledge of the morphology of unoriented crystalline polymers is summarized, and the process of orientation is visualized as an alignment and pulling out of the submicroscopic and microscopic structural units. The various stages of this process are discussed and it is found that in this way several anomalous and hitherto unexplained orientation effects frequently described in the literature can be accounted for. The phenomenon of preferential tilt of the chains with respect to the fiber axis can now be explained in general terms. Peculiarities in the drawing‐relaxation process, and the special case of perpendicular orientation, also substantiated by recent experiments, follow naturally from the new model.
Etat de nos connaissances sur la biréfringence d'écoulement des solutions de macromolécules
Authors: Cerf Roger 
Published: April 2003

AbstractLes résultats classiques concernant les solutions de particules rigides sont brièvement rappelés (théorie de l'orientation). L'éxpérience a montré que la théorie avait une valeur quantitative. On examine ensuite en détail le cas où la particule est déformable. Cette question s'est considérablement clarifiée au cours des dix dernières années. La nature de l'effet présenté est déterminée essentiellement (1) par l'intensité des fluctuations de forme de la molécule et (2) par la durée de vie d'une configuration donnée. Il en résulte que le phénomène peut ětre dans certains cas extrěmes (1) un effet d'orientation analogue à celui que présentent les solutions de particules rigides, (2) un effet de déformation pure complètement différent du précédent. Dans le cas général il y a superposition des deux effets. Pour une molécule donnée il peut y avoir passage continu de l'effet (1) à l'effet (2) lorsqu'on modifie la valeur de la viscosité du solvant. On considère en particulier le cas des solutions de hauts polymères. Les théories pour les deux effets (1) et (2) mentionnés ci‐dessus, ainsi que pour le cas intermédiaire, permettent de comprendre dans une large mesure les phénomènes présentés par ces solutions. Il existe un critère expérimental permettant de déceler si l'effet présenté par une solution donnée est principalement un effet d'orientation ou un effet de déformation. Il est possible de relier les grandeurs observées à des coefficients moléculaires, au moins dans les deux cas extrěmes mentionnés ci‐dessus. Du point de vue expérimental il est intéressant de coupler les mesures de biréfringence d'écoulement avec des mesures de viscosité spécifique, viscosité statique et dispersion de la viscosité (ondes de cisaillement de fréquence ultra‐sonique). On indique finalement sur quelles bases générales une théorie pour les molécules en chaǐnes pourrait ětre développée.
Flow birefringence in solutions of macromolecules: Effect of fluctuations of the shape of the molecule
Authors: Cerf Roger 
Published: April 2003

AbstractA treatment is given for the Brownian deformation of an elastic sphere which permits extension of the theory of the Maxwell effect of solutions of elastic spheres to arbitrary values of the ratio of the time of establishment θ′, of a preferential orientation to the deformation relaxation time θ of the sphere. For large values of η0/ηi the (ratio of solvent viscosity to internal viscosity) the effect reduces to the simple deformation effect described in previous papers. For decreasing values of η0/ηi the deformation effect is gradually replaced by the orientation effect (orientation of elongated configurations). The influence of the intensity of the fluctuations as measured by the mean square value δ02 of the deformation coefficient is discussed. Values of δ0 are given for a series of polystyrene samples of increasing molecular weight. The theory is in qualitative agreement with experimental results on solutions of chain molecules and leads in particular to a new interpretation of the data for thymonucleic acid. The incompatibility of the Kuhn and Kuhn dumbbell theory with experimental results is discussed in more detail than in previous papers.
Les lois de la diffusion de la lumière du point de vue de leur application à l'études des macromolécules en solution étendue
Authors: Sadron Ch. 
Published: April 2003

AbstractDans cet exposé qui constitue simplement une brève revue critique l'auteur résume rapidement les résultats classiques de la théorie de la diffusion de la lumière par les solutions macromoléculaires étendues et souligne les hypothèses simplificatrices qui ont permis les calculs. Il examine en particulier le cas où les dipǒles élémentaires ne sont plus isotropes et montre les conséquences importantes des nouveaux résultats obtenus.Il s'attache en particulier à l'examen du cas important où la solution contient des macromolécules en chaǐne linéaire et résume les plus récentes tentatives qui tendent à traiter les configurations réelles de la molécule et non plus celles d'un “random flight” fictif.