bluuebunny/crossref_metadata_2025_split huggingface dataset:
The critical factors involved in fractionating cellulose acetate by selective adsorption onto carbon
Authors: Miller Bernard , Pacsu Eugene 
Published: April 2003

AbstractCellulose acetate can be fractionated by allowing it to be adsorbed from acetone solution onto activated carbon. Sharpest fractions are obtained when small amounts of adsorbent are used successively to take up increments of the total polymer in solution. Each adsorbate is refractionated during elution with a good solvent, and in one adsorption‐desorption cycle the polymer can be divided into a large number of fractions, suitable with certain limitations, for molecular weight distribution analysis. Smaller molecules are both preferentially adsorbed and are the first eluted. Temperature and concentration have some influence on the sharpness of fractionation, but the most critical factor is the ratio of adsorbent to polymer.
Polymer texture: The arrangement of crystallites
Authors: Statton W. O. 
Published: April 2003

AbstractThis is a study of the structural arrangement in a polymer which is on a size level larger than the crystallite but smaller than the spherulite. It is based on the data from x‐ray diagrams at small angles, combined with crystallite dimensions measured from wide‐angle x‐ray patterns. The earlier interpretations of polymer texture by Hess and Kiessig which describe alternating regions of order and disorder appear to be most probable. However, those earlier interpretations are extended by showing that oriented crystalline polymers can be thought of as having aligned elementary fibrils which consist along their length of a regular alternation of bulky and condensed regions. The width of these elementary fibrils is proportional to the width of the crystallites. The amount of regularity of crystallite positions along an elementary fibril and the length of the repeat period are both variable; they depend on the manner of original nucleation and the thermal treatment after nucleation. The length of the long period is a function of the length of the crystallites. These elementary fibrils can pack closely to form a higher state of ordered texture. The amount of close packing is variable; it is optimal after a relaxation treatment. Elongated voids exist between the elementary fibrils. The difference between the effects of original nucleation and thermal after‐treatment is emphasized. Elementary fibrils are proposed as a basic unit of aggregation in polymer melts, solutions, and fibers.
Diffusion measurements on low molecular weight polystyrenes
Authors: Rossi Corrado , Bianchi Estella 
Published: April 2003

AbstractMeasurements of diffusion, viscosity, and cryoscopic determinations of molecular weight were carried out in benzene on eight fractions of polystyrene with low molecular weight (up to about 3,000). These indicate that there is a linear relation between MD and M1/2. This relationship corresponds to the Einstein‐Stokes equation in which the equivalent radius is replaced by the gyration radius. The value of the rotation hindrance factor A calculated from the results of diffusion measurements on polystyrenes with low molecular weights was found to be equal to that calculated from the viscosity data on polymers of high molecular weight in θ solvents, where the swelling effect is nil. This confirms, therefore, that this factor is constant over a wide range of molecular weights. The viscosity data on low molecular weight polystyrene in benzene at 20°C. are very similar to those for samples of high molecular weight in θ solvents. The molecular dimensions of polystyrenes with low molecular weight are therefore unaffected by the swelling effect. The Flory constant Φ, deduced from cryoscopic, diffusion, and viscosity measurements, for the values of M, (h̄2)1/2, and [η], respectively, assumes a value of 3 × 1021. The results have been briefly discussed, from the point of view of the Kirkwood‐Riseman and Debye‐Bueche theories.
The crystallization of modified cis‐polybutadiene
Authors: Trick G. S. 
Published: April 2003

AbstractFrom a sample of polybutadiene of high cis‐1,4 content, the microstructure is modified by cis‐trans isomerization or by crosslinking. Measurements of rates of crystallization and melting point are made on the modified samples. An increase in trans content or crosslink density markedly decreases the rate of crystallization at a fixed temperature. It is found, however, that this retardation in rate may usually be accounted for by the depressed melting point of the modified samples.
Diffusion of small molecules in semicrystalline polymers. II. The permeability of unoriented polymer films
Authors: Klute C. H. 
Published: April 2003

AbstractIn a previous publication, the diffusion of small molecules through semicrystalline polymers was compared with the flow of electrical current through a heterogeneous conductor. In this way it was possible to solve the diffusion equations numerically, and to apply the results successfully to the description of the permeability of some polyethylene films as a function of their density. In the present paper, the electrical model has been investigated further and in particular, the effect of blind alleys in the diffusion path has been described. The theory has then been applied to the permeability data published recently by Lasoski and Cobbs for three series of unoriented polymer films differing primarily in crystalline content. Although the experimental data do not conform perfectly to the theory, a large area of agreement has been established, and in view of the complexity of the problem this agreement appears to be satisfactory. The theory developed here requires that the activation energy for permeation be substantially independent of the degree of crystallinity. This has been shown to be in harmony with activation energy data determined on polyethylene specimens of different densities, both by permeability measurements and by nuclear magnetic resonance measurements. The abrupt increase in the apparent activation energy for the permeation of natural rubber films by small molecules below the temperature of crystallization has been shown to be due, most probably, to the reduction of the amorphous volume fraction as the temperature is decreased.
Phase separation in mixed polymer solutions
Authors: Sieglaff Charles L. 
Published: April 2003

AbstractA phase separation occurs in the system microgel‐linear polymer‐solvent due to an attractive force between microgel molecules. A theory is proposed that attributes the attractive force to the fact that linear polymer is excluded from a shell surrounding the microgel particle and the overlapping of these shells gives rise to a net decrease in the free energy of the system. This decrease in free energy is a function of the free energy of dilution for the linear polymer and of the shape and size of the microgel and linear polymer. The system styrene‐divinylbenzene microgel‐polystyrene‐toluene has been studied. The findings of these studies substantiate the proposed theory.
Polymers of ketene dialkylacetals
Authors: Lal Joginder 
Published: April 2003

AbstractThe observed insolubility of poly(kentene diethylacetal) in chloroform, carbon tetrachloride, and other organic solvents has been found to be due to its crystallinity. Its solubility in hot o‐dichlorobenzene suggests that the polymer is linear and not crosslinked. Poly(ketene di‐n‐butylacetal), also crystalline, was readily soluble in chloroform and carbon tetrachloride, as were also the copolymers prepared from ketene diethylacetal and ketene dibutylacetal.
The effect of polymer density on the diffusion of ethane in polyethylene
Authors: Brandt W. Wilfried 
Published: April 2003

AbstractDiffusion and solubility coefficient were determined by the time‐lag method for ethane and some other low hydrocarbons in various polyethylenes. The time‐lag method was modified to give significant savings in experimental time and increased precision. Diffusion and solubility coefficients both depend quite strongly on the density and hence on the crystallinity. There is no discernible effect of weight‐average molecular weight, and the effect of polymer chain side branches is found to be small or absent. The thermal and fabrication history of the samples has some effect on the diffusion coefficients. The character of the amorphous regions appears to be independent of the overall density as far as the diffusion process is concerned. The effect of the size of the penetrant molecule is analogous to that found by other authors for rubbers. The findings support the view that small molecule diffusion in polymers requires only short range motions, whereas other mechanisms, such as the dissolution of entanglements, are known to be of importance in melt flow and polymer self‐diffusion.
Small molecule diffusion in cold‐drawn or stretched polymer films
Authors: Brandt W. Wilfried 
Published: April 2003

AbstractDiffusion and solubility coefficients for several gases in undrawn and drawn films of four high polymers (polyvinyl butyral, nylon 66, polyethylene, and polypropylene) are reported as functions of temperature. In general, the diffusion, solubility, and permeability coefficients of the semicrystalline polymers investigated changed on drawing. The magnitude and direction of such changes depended on the penetrant used and on the experimental temperature. The molecular orientation introduced by stretching in one direction had little or no effect on the diffusion properties of the amorphous polyvinyl butyral. With the other polymers, the changes in void content on cold drawing were usually found to be associated with changes of the opposite sign in the activation energy of diffusion, in consequence of the relatively weak temperature dependence of diffusion in the gas phase. The process of solution of low molecular weight gases in high polymers was found to be more exothermic for those samples which had a comparatively low void content (i.e., drawn polyethylene, undrawn nylon 66, and undrawn polypropylene, as compared, respectively, to undrawn polyethylene, drawn nylon 66, and drawn polypropylene). Possible explanations for this result are given.
The sorption and desorption kinetics of water in a regenerated cellulose
Authors: Newns A. C. 
Published: April 2003

AbstractThe sorption and desorption kinetics for different parts of the hysteresis loop of a water–cellulose system have been determined. Tentative explanations of these kinetics are advanced in terms of changes of polymer structure. It is proposed that during sorption the water first clusters in the more accessible regions of the polymer structure, and that this is followed by a dissolution of network bonds. During desorption the reformation of interchain bonds is hindered by the presence of water and the rigidity of the structure. The proposed structural changes which occur during sorption are somewhat similar to those advanced to explain the viscoelastic properties of the polymer.
Caprolactam polymerization
Authors: Reimschuessel Herbert K. 
Published: April 2003

AbstractThe equilibrium resulting from the water initiated polymerization of caprolactam has been investigated for initial water concentrations (w) in the range, 0.01 ≤ w ≤ 1 (moles H2O/mole caprolactam) at temperatures 220, 235, 250, and 265°C. Based upon the postulate that, at a given temperature, the degree of polymerization is directly proportional to that part of caprolactam converted to linear macromolecules and inversely proportional to the initial water concentration, the following formula, which is a combination of functions, has been derived:
Infrared study of oxygenated groups formed in polyethylene during oxidation
Authors: Luongo J. P. 
Published: April 2003

AbstractThe changes in the molecular structure of polyethylene during oxidation are studied. The presently accepted theory involves a free‐radical process and is based largely on measurements of reaction kinetics with model compounds. Infrared spectroscopy afford an alternate method of following the course of the oxidation reaction. By recording the infrared spectra of polyethylene samples during oxidation, it was possible to follow continuously the formation of various oxygen‐containing groups. During the early stages of oxidation, the formation of hydroperoxides was noted, as was their subsequent decomposition into the predominant secondary oxidation products. The alpha carbon was found to be quite susceptible to oxygen attack after autocatalytic oxidation had begun, and a resulting decrease in methylene content was observed. The results provide a description of the oxygenated molecular groups that form during the initial stages of oxidation and support and broaden the presently accepted mechanism for the oxidative degradation in polyethylene.
Crystalline modifications of cellulose. Part VI. Unit cell and molecular symmetry of cellulose I
Authors: Fisher D. G. , Mann J. 
Published: April 2003

AbstractA study of the electron diffraction diagram of Valonia ventricosa cellulose has confirmed the conclusions reached by Honjo and Watanabe concerning the size of its unit cell. The a and c axes of the cell are twice the length of those usually accepted for cellulose I. The symmetry of the cell is P1, but the evidence available at present does not allow a decision to be made concerning the symmetry of the molecular chains. Consideration of x‐ray diffraction and infrared spectroscopic data suggests that bacterial cellulose probably has the same unit cell as Valonia ventricosa, but that other native celluloses may have different cells.
The effect of polymer dilution on acid‐catalyzed gelation of partially N‐methylolcarbamoylethylated polyvinyl alcohol
Authors: Nakamura Y. , Koide T. , Negishi M. 
Published: April 2003

AbstractThe effect of polymer dilution on the acid‐catalyzed gelation of partially N‐methylolcarbamoylethylated polyvinyl alcohol has been studied viscometrically and chemically. The result that the higher the degree of dilution the greater the extent of reaction at gelation, especially in the polymer concentration below 15% by weight, indicates that a certain increase of intramolecular crosslinking with dilution occurs. However, sufficient agreement with Kilb's theory could not be found. Also, even when the extent of reaction at gelation was extrapolated to infinite concentration of polymer, it was far greater than that obtained from Flory's theory. The discrepancy may presumably be attributed to the fact that in addition to the intramolecular crosslinking, all the methylol groups on the polymer chains which are coiled, entangled, and strongly solvated prior to crosslinking are not equally reactive sterically.
Isomorphous replacement in copolyamide systems: Adipic and terephthalic acids
Authors: Yu Arthur J. , Evans Robert D. 
Published: April 2003

AbstractCopolyamides with mixtures of adipic and terephthalic acids in various mole rations and three types of diamine were prepared, and a melting point vs. composition curve for each system was constructed. The three types of diamine were: (1) straight‐chain aliphatic diamines with six to twelve carbon atoms, (2) m‐xylylenediamine, and (3) 4,4‐dimethyl‐1,7‐heptanediamine. These curves for copolyamides containing straight chain aliphatic diamines had no minimum at the intermediate ranges of composition. The curve for m‐xylylene diamine had a minimum at a point corresponding to 77 mole‐% of adipic acid. The copolyamide containing 4,4‐dimethyl‐1,7‐heptanediamine was not crystalline. Evidence suggested that isomorphous replacement of adipic and terephthalic acids in copolyamide systems was greatly influenced by the structure of the diamine, possibly through the bulk effect of its substituents on chain‐packing.
Synthesis kinetics and sequence distribution in synthetic polynucleotides
Authors: Simha Robert , Zimmerman J. M. 
Published: April 2003

AbstractA simple kinetic model for the formation of a nucleotide homopolymer is presented and evaluated. It consists of an initial dinucleotide formation followed by growth through further monomer addition and a competitive phosphorolysis. The molecular weight distribution is narrow up to the first 10–30% conversion and broadens on approach to equilibrium. From the equilibrium amounts of phosphate liberated, the final average molecular weight, and the time pattern of the synthesis, it is possible to obtain estimates of the rate constants. Turning to copolymers, the analysis of experimental data on sequence frequencies in an AU polymer in terms of addition probabilities indicates the existence of a penultimate effect, and a consistent set of four such probability parameters is derived. Finally, we consider a set of rate equations for binary copolymer formation suggested by these results. Their solution will permit a calculation of sequence distributions by utilizing kinetic experimental results exclusively.
Studies of the ethylenediamine‐cellulose complex. II. Stability of the complex
Authors: Segal Leon , Loeb Leopold 
Published: April 2003

AbstractThe ethylenediamine‐cellulose complex in the dry state has a sharp characteristic x‐ray diffraction pattern and usually contains from 17 to 26% diamine when freshly prepared. High vacuum and elevated temperature failed to reduce this below 17%. Rapid decomposition of the complex as evidenced by the x‐ray diffraction patterns was associated, however, with storage at room temperature in a paper envelope. A slow decrease in diamine content accompanied by shifts in the x‐ray pattern resulted from storage under controlled conditions of temperature and humidity. An especially dried sample rapidly gained weight at first when exposed to the open air, then very slowly lost weight. There is an indication from the data that a 2:1 complex is present with two anhydroglucose units per diamine molecule, strongly suggesting a hydrogen‐bonded crosslink. The increase in fiber cross‐sectional area and the distention of the crystal unit cell are of an order of magnitude to suggest that complex formation can account for most of the fiber swelling.
Diisocyanate‐linked polymers. II. Mechanical and swelling properties of some polyurethane elastomers
Authors: Smith Thor L. , Magnusson Alan B. 
Published: April 2003

AbstractA study was made of the mechanical and equilibrium swelling properties of five series of polyurethane elastomers prepared from polyoxypropylene glycol 2025, dipropylene glycol, trimethylol propane, and either toluene diisocyanate (TDI) or hexamethylene diisocyanate (HDI). The study included the dependence of the properties on the ratio of isocyanate to hydroxyl groups, the concentration of urethane groups, [U], and the triol concentration; the triol concentration and [U] were varied independently in four series of elastomers. It was found that the glass transition temperature for both the TDI elastomers and HDI elastomers increased linearly with [U]. For elastomers having a constant [U], the quasi‐equilibrium elongation at a given value of T − Tg increased linearly with the reciprocal of the number of effective chains per unit volume, but the tensile strength depended only slightly on this quantity. For elastomers having the same triol concentration, the ultimate properties over a wide temperature range were compared at equal values of T − Tg and were found to depend on [U], especially for elastomers having the largest [U]‐values. Several factors that might contribute to this behavior are considered. No major differences between TDI and HDI elastomers were observed except in Tg values. The equilibrium swelling ratios in benzene were used along with equilibrium modulus data to calculate the polymer–solvent interaction parameter χ1. This parameter was found to be independent of crosslinking density, but it increased with [U] and was slightly less for the HDI elastomers than for the TDI elastomers.
The initiation of polymerization of methyl methacrylate by the poly(methyl methacrylate) anion
Authors: Graham Roger K. , Dunkelberger David L. , Cohn Elizabeth S. 
Published: April 2003

AbstractAddition of methyl methacrylate monomer to poly(methyl methacrylate) which has been polymerized with fluorenyllithium or sodium‐naphthalene in tetrahydrofuran at −78°C. produces high conversion of monomer to polymer. By a comparison of the number‐average molecular weights before and after the addition of the second monomer, it is demonstrated that no new polymer chains are formed on polymerization of the second monomer, so that the polymerization is initiated by the poly(methyl methacrylate) anion. Styrene is shown to be an inert diluent in these systems. The technique is also applied to additions of styrene and of methyl methacrylate monomer to polystyrene initiated with sodium‐naphthalene; the new polymer is demonstrated to be initiated by the polystyrene anions.
Interaction constants for the system isoprene–cis‐1,4‐polyisoprene (synthetic)
Authors: Cunningham Robert E. 
Published: April 2003

AbstractValues of the interaction parameter χ1 for the system isoprene–(synthetic) cis‐1,4‐polyisoprene have been determined over a range of compositions and temperatures, from results of vapor pressure measurements and the Flory‐Huggins equation. At constant temperature χ1 decreases as V2 increases. At V2 ≈ 0.95, χ1 decreases also with increasing temperature. Densities of the monomer and polymer were also determined.
Organic peroxides. I. Initiation of styrene polymerization
Authors: Lowell A. I. , Price J. R. 
Published: April 2003

AbstractThe relationship between peroxide activity for several aliphatic and aromatic peroxides, as given by the respective decomposition rate constants (kd), and their influence on the polymerization of styrene at 70°C. is reported. Particular emphasis was placed on studying the role of these peroxides in determining rates and degrees of polymerization (DP) and the “efficiency” of these peroxides in the initiation of polymerization. A correlation of peroxide activity could best be made with rates of polymerization. Most of the peroxides studied did not exhibit chain transfer activity, and the DP was a function of the propagation and termination characteristics of the monomer‐polymer radical system. Two chlorinated benzoyl peroxides had considerable chain transfer activity, but this could not be correlated with their decomposition rate constants. Although there was no relationship of peroxide activity to efficiency of initiation, some of these efficiency values appeared to be unreasonably low. The major uncertainty appeared to be the use of published peroxide kd values which were not determined under conditions suitable for use with polymerization data to calculate efficiencies. Where necessary, kd values were redetermined and the final results gave a more suitable basis for comparison of peroxide activities and their influence on polymerization. The use of infrared analysis for determination of peroxide decomposition rate constants is described.