bluuebunny/crossref_metadata_2025_split huggingface dataset:
Thermogravimetric analysis of cellulose
Authors: Chatterjee Pronoy K. , Conrad Carl M. 
Published: April 2003

AbstractAn application of TGA technique to elucidate the chain reaction mechanism of cellulose pyrolysis is discussed. The mathematical expressions for isothermal kinetics are modified for use with temperature‐programmed kinetics. It is shown that in temperature‐programmed kinetics, the initial reaction should theoretically be a pseudo zero‐order type, whereas the latter part should be a pseudo first‐order type. Experimental data from the present study and from the literature are in good agreement with the theory. Energies of activation for the initiation and the propagation steps of cellulose pyrolytic reactions are analyzed from TG data. Various cellulose samples, such as adsorbent cotton, vibratory ball‐milled absorbent cotton, mercerized commercial yarn, mercerized and treated commercial yarn, dewaxed‐kiered cotton, and microcrystalline cellulose are included in this study. A basic problem which is associated with all thermogravimetric kinetic expressions is also discussed.
Polyhydrazides. II. N‐methylated polyhydrazides by direct solution polycondensations of methylated hydrazines and dicarboxylic acid components
Authors: Iwakura Yoshio , Uno Keikichi , Hara Shigeyoshi , Kurosawa Shigeru 
Published: April 2003

AbstractN‐Methylated polyhydrazides were prepared from methylated hydrazines and terephthalic acid or dimethyl terephthalate, and from terephthalic acid, hydrazine sulfate, and dimethyl sulfate by the solution polycondensation method in fuming sulfuric acid or polyphosphoric acid.
Some studies of the crystallization of polychlorotrifluoroethylene copolymer films
Authors: Adams G. C. , Stein R. S. 
Published: April 2003

AbstractA fluorocarbon copolymer of chlorotrifluoroethylene (96%) and vinylidene fluoride has been isothermally crystallized and the quenched films analyzed by the light microscope, photographic light‐scattering, and density measurements. Above a supercooling of 79°C., homogeneous nucleation dominates, giving a morphology that appears to be that of a twisted ribbon. At supercoolings below 79°C., heterogeneous nucleation dominates and leads to spherulitic morphology. Sheaf or rodlike morphology occurs at very low supercoolings. Crystallization rates determined from density measurements at room temperature indicate maximum rate due to heterogeneous nucleation occurring at a supercooling greater than 79°C., but the temperature for maximum rate cannot be identified because of the transition to homogeneous nucleation which causes a discontinuity in the rate versus temperature curve. Superposability of crystallization isotherms constructed from density values are inconsistent with the large melting point lowering from that of polychlorotrifluoroethylene for this copolymer. However, this may be explained by the presence of a different crystal system for each monomer in the copolymer.
Molecular weights and molecular weight distribution of polymers by equilibrium ultracentrifugation. Part I. Average molecular weights
Authors: Scholte Th. G. 
Published: April 2003

AbstractFrom the sedimentation‐diffusion equilibria of some polymer solutions the average molecular weights M̄n, M̄w, M̄z, and M̄z+1 have been determined in different ways. In particular, the applicability of Fujita's method, which utilizes concentration gradient values at the midpoint of the solution column at a number of rotor speeds, was examined. It appears that if the gradients at some other places in the column are also used, a smaller range of rotor speeds suffices. This method is generally applicable for determining the average molecular weights specified above.
Viscoelasticity of a butadiene–styrene block copolymer
Authors: Canter Nathan H. 
Published: April 2003

AbstractA commercial elastomeric block copolymer of butadiene (B) with styrene (A) is studied. A single chain of the material has the formula A‐B‐A. Differential thermal analysis studies show the presence of two transitions. The lower transformation temperature corresponds to the Tg of the butadiene chain segments, and the upper transformation temperature corresponds to the Tg of the styrene chain segments. The upper transition of the material is also studied by following the variation of the torsional modulus with temperature. This transition is found to be quite unusual. Our experiments show that the upper transformation of unstressed block copolymer samples is broad. The transition sharpens for samples which, prior to the modulus–temperature experiments, are stress‐relaxed at high elongations. These observations (and those of the literature) suggest that the styrene and butadiene chain segments in the block copolymer aggregate in the solid state and give rise to two distinct transition phenomena. Our studies of the upper transformation suggest that stretching of the bulk material enhances the aggregation of the styrene chain segments. Pure polystyrene (A) blocks of the material are recovered by selective cleavage and fractionation experiments. The Tg of the pure polystyrene blocks is found to be similar to the value of the upper transition temperature of the copolymer. The ABA blocks copolymer is found also to undergo a stress‐softening phenomenon analogous to that of reinforced rubber.
Temperature dependence of the growth rate of spherulites
Authors: Mandelkern L. , Jain N. L. , Kim H. 
Published: April 2003

AbstractThe spherulitic growth data that exist in the literature for a wide diversity of polymers have been analyzed according to various possible nucleation mechanisms. It is demonstrated that, if allowed a reasonable choice for the equilibrium melting temperature, no unbiased selection of a unique nucleation process can be made. Moreover, a set of universal parameters exists for each of the allowable nucleation processes which enables the data to be represented by a single straight line which encompasses all the polymers. The only quantities specific to a given polymer are the equilibrium melting temperature and the activation energy for transport. The magnitude of the latter quantity is shown to be dependent on the glass temperature of the polymer.
NMR studies of chlorinated poly(vinyl chloride) and polybutadiene
Authors: Sobajima Shigenobu , Takagi Norio , Watase Hideo 
Published: April 2003

AbstractMolecular structures of chlorinated poly(vinyl chloride) and polybutadiene have been studied by high resolution NMR. The spectra of the chlorinated polymers give broad signals. New peaks appear in the lower fields of the CH2 and CHCl groups with increasing chlorine content. The chlorination of poly(vinyl chloride) takes place predominantly on CH2 rather than on CHCl, e.g., a 70% chlorinated polymer has about 10 mole‐% of CCl2 groups. Polybutadiene reacts first with chlorine by addition to give a head‐to‐head poly(vinyl chloride), and then the substitution of the hydrogen atom takes place. Chlorinated polybutadiene with 70% Cl has about 18 mole‐% of CCl2. The multiplets characteristic of spin‐spin couplings in the spectrum of the original poly(vinyl chloride) are still observed in that of the highly chlorinated product. This fact shows that a considerable number of poly(vinyl chloride) sequences of certain lengths persist in the highly chlorinated polymer.
Kinetic interpretation of the glass transition: Glass temperatures of n‐alkane liquids and polyethylene
Authors: Miller A. A. 
Published: April 2003

AbstractOn the basis of an isoviscosity criterion for the glass transition (ηg ⋍ 1013 poise) in liquids of low molecular weight, theoretical Tg values were calculated for the n‐alkane series by the equation log η = log A + B/(T − T0), with the use of values reported by Lewis for the parameters. The Tg/T0 ratio reaches a limiting value of 1.25 and ϕg = (Tg − T0)/2.3B = 0.027, a constant. Extrapolation to (CH2)∞ gives Tg = 200°K., T0 = 160°K., and B = 640°K. This Tg is consistent with other estimates for poly‐ethylene, and T0 coincides with the temperature at which the “excess” liquid entropy for (CH2)∞ becomes zero from thermodynamic data. For polymer liquids it is proposed that E0 = 2.3RB is determined by the internal barriers to rotation for the “isolated” polymer chains. Thus, E0 = 2.9 kcal./mole for polyethylene, 3.0 kcal./mole for polystyrene, 5.7 kcal./mole for polyisobutylene, and 1.9 kcal./mole for polydimethylsiloxane.
Change with temperature of the ESR spectra of peroxy radicals trapped in irradiated polytetrafluoroethylene
Authors: Iwasaki Machio , Sakai Yoshiro 
Published: April 2003

AbstractThe ESR spectra of peroxy radicals in irradiated powders and oriented samples of polytetrafluoroethylene (PTEE) have been measured with a K‐band spectrometer, and the principal values and directions of the g tensor were determined both at room temperature and at 77°K. In contrast to the spectra of the usual peroxy radicals, those trapped in γ‐irradiated PTFE exhibited an ESR spectrum apparently having a larger principal value for g⊥ than for g∥ when measured at room temperature, although the normal principal values were observed at 77°K. As for the directions of the principal axes, g∥ was directed along the chain axis at room temperature and was perpendicular to the chain axis at 77°K. From the temperature change of the g tensor and the line shapes in the oriented samples, it is shown that the observed temperature change of the spectra is due to rapid rotation at room temperature around the chain axis rather than around the CO bond axis. Assuming this, the apparent principal values of the g tensor at room temperature were calculated from the g tensor obtained at 77°K. for the rigid state, and the results are in good agreement with observations at room temperature. A structure for the peroxy radicals is also proposed. In addition, the spectral line shape function for the uniaxially oriented samples has been derived.
Liquid–liquid phase separation in multicomponent polymer solutions. I. Statement of the problem and description of methods of calculation
Authors: Koningsveld R. , Staverman A. J. 
Published: April 2003

AbstractPolymers are complex mixtures that may have widely different compositions even if they contain only components having the same chemical constitution. The effect of the chain length distribution on the phase behavior of polymer solutions in a single solvent is described qualitatively. To obtain a quantitative understanding of these phenomena a numerical calculation method is developed which is based on the Flory‐Huggins relation for the free energy of mixing. Some examples are presented, and the accuracy and the reliability of the results are discussed.
Liquid–liquid phase separation in multicomponent polymer solutions. II. The critical state
Authors: Koningsveld R. , Staverman A. J. 
Published: April 2003

AbstractTheoretical and experimental evidence is put forward to prove that the determination of the phase‐volume ratio as a function of temperature and concentration is a sensitive and simple means of determining the liquid–liquid critical state. Knowledge of the critical conditions permits very accurate calculations of the interaction parameter g in the free‐energy function. In experiments with polystyrene–cyclohexane, g was found to depend on the concentration. The value of g and its concentration dependence agree very well with the results of osmotic measurements by Rehage and Palmen. In experiments with polyethylene–diphenyl ether, g proved to be independent of concentration in the range of measurement. The temperature function was found to be: g = −0.6086 + 482.2/T (at 137–148°C.). Gibbs' expressions for the critical conditions were worked out for a free‐energy relation in the form of an extended Flory‐Huggins function.
Electrical conduction in olefin oxide polymers
Authors: Binks A. E. , Sharples A. 
Published: April 2003

AbstractThe electrical conductivities in vacuo of poly(ethylene oxide) and two higher olefin oxide polymers have been found to be ∼9 orders higher than for other saturated organic polymers. The possibility of ionic transport resulting from the presence of impurities (including water) has been eliminated, and it is proposed that an inherent ionic process is operative, involving the generation of protons and then subsequent transport by a handing‐on process. The two general requirements are the presence of proton‐accepting atoms (in this case oxygen) in the polymer chains; and proximity to the melting point to ensure adequate chain‐mobility. These requirements are met by poly(ethylene oxide), poly(trimethylene oxide), and poly(tetramethylene oxide), which are all close to their melting points at room temperature. poly(methylene oxide), with a melting point of ∼180°C., on the other hand, has the low conductivity of a typical insulator.
Electric properties of macromolecules. XIII. Transient electric birefringence of sodium polyethylenesulfonate solutions
Authors: Yoshioka Koshiro , O'Konski Chester T. 
Published: April 2003

AbstractThe electric birefringence of sodium polyethylenesulfonate in water has been studied. For a low molecular weight fraction, the electric field dependence followed the Kerr law quite closely. For a higher molecular weight fraction, the specific Kerr constant was much larger, and pronounced saturation of the electric birefringence was observed in fields of 15 kv./cm. The specific Kerr constant increased with decreasing polyelectrolyte concentration in pure water. On the other hand, it decreased on isoionic dilution. The saturation effect was the more marked, the lower the polyelectrolyte concentration. The saturation behavior resembled that of permanent dipole orientation, but this mechanism was not supported by the build‐up of the birefringence. The magnitudes of specific Kerr constants of various types of macromolecules in solution are tabulated and discussed.
Nuclear magnetic resonance of poly‐β‐alanine
Authors: Tsutsumi Akihiro , Hikichi Kunio , Kaneko Motozo , Furuichi Jiro 
Published: April 2003

AbstractNuclear magnetic resonance of poly‐β‐alanine samples differing in solubility in water was studied over a wide temperature range as part of an investigation of their physical properties. Water‐soluble poly‐β‐alanine has more branches and a lower degree of crystallinity than water‐insoluble poly‐β‐alanine. NMR spectra of poly‐β‐alanine show one component at 77°K. which splits into two components, broad and narrow, at room temperature. Two transition regions were observed in curves for line width and second moment versus temperature. The higher transition temperature, corresponding to the glass transition of the polymer, appears to decrease with increasing water content. The second moment for the water‐soluble polymer differs from that of the water‐insoluble polymer at 77°K. This is interpreted in terms of the difference in the degree of crystallinity of the polymers.
Stochastic model for gel permeation separation of polymers
Authors: Carmichael Jack B. 
Published: April 2003

AbstractThe stochastic theory of chromatography developed by Giddings and Eyring and by McQuarrie is applied to gel permeation chromatography (GPC) by first recasting their assumptions to fit the GPC process and secondly by making specific assumptions about the molecular size dependence of the rate constants λ1 and λ2 for entrapment and elution of a polymer molecule, respectively. The model assumes that: (1) a monodisperse sample is injected; (2) molecules behave independently within the column; (3) no molecular diffusion occurs; (4) the polymer molecules are unperturbed random coils; (5) entrapment sites in the bed are identical; (6) λ1 is proportional to the probability Pe that the square of the polymer end‐to‐end distance is less than the square of the average pore radius in the bed; (7) λ2 is constant. The calculated difference in retention times, tR‐to (where tR is the retention time for a molecule of arbitrary molecular size and to is the retention time for a molecule whose size totally precludes entrance into the pores of the bed), is shown to be proportional to Pe. The model as thus applied is based on only one parameter. The theory is tested by examining the ratio Pe/(tR − to)exp, predicted to be constant, for narrow polystyrene fractions in the molecular weight range 1.1 × 104 – 8.9 × 105. Chromatographs were obtained by Moore and Arrington by using a θ solvent and a single column packed with a porous glass bed having a sharp distribution of pore sizes. Ratio values ranged from 0.046 to 0.073 with an average value of 0.058 ± 0.009. This relative constancy demonstrates semiquantitative utility of the model for gaining insight into the GPC process.
Structure of a novel polyimide
Authors: Reimschuessel H. K. , Roldan L. G. , Sibilia J. P. 
Published: April 2003

AbstractThe product of the thermal polymerization of ß‐carboxymethyl caprolactam has been identified as a poly[(2,6‐dioxo‐1,4‐piperidinediyl)trimethylene]. An indication of various chain conformations has been explained by the possible existence of two different conformations of the dioxopiperidine moiety. One conformation pertains to an equatorial position of the trimethylene moiety with respect to the plane of the imide group. The other is derived from a structural unit in which the trimethylene group is positioned axially to the plane of the ring. While the former conformation has been ascribed to the crystalline modification the latter appears to be the predominant structure of the polymer in formic acid solution as indicated by NMR analysis. In the glassy state the macromolecule is assumed to be composed of segments of either conformation. The unoriented linear polymer crystallizes upon annealing in positively birefringent spherulites. A triclinic unit cell with the following parameters: a = 9.64 A., b = 11.32 A., c = 15.80 A., α = 98°, β = 96°, γ = 114° has been found to contain eight structural units. The calculated density, 1.30 g./cm.3, agrees with experimental data. A crystal structure is proposed on the basis of the x‐ray data.
Fuming nitric acid treatment of polyethylene. IV. Morphology of drawn polyethylene
Authors: Meinel G. , Peterlin A. 
Published: April 2003

AbstractDrawn PE of different draw ratios (ranging from 1 to 25) and thermal treatment (annealing temperature 80, 100, 110, 120, 127°C.) was treated with fuming nitric acid at 80°C. Weight loss, molecular weight, elastic modulus, and thermograms were measured for annealed and unannealed samples as a function of the treatment time and draw ratio. As a consequence of the preferential oxidation of the noncrystalline portions, there occurs initially a high rate of weight loss and a steep drop in molecular weight, followed by a lower rate of weight loss at nearly constant molecular weight. The elastic modulus stays practically constant up to the moment where the brittleness of the sample prevents further measurement. During the later period the thermograms exhibit one melting peak during the first melting. The remelt of the same sample, however, has two melting peaks with a relative intensity independent of the treatment time. That the two melting peaks are caused by two components of different molecular weights present in the sample is substantiated by fractionation. At very high annealing temperature (127°C.), two peaks appear, not only in the first melting curve of the etched sample, but also in the melting curve of the unetched material. Such an effect is the consequence of partial melting during annealing followed by new crystallization during cooling the sample to room temperature. The findings are related to the morphology of the drawn material under the assumption of preferential scission of chain loops in the amorphous‐crystalline sandwich layer model.
Diffusion in atactic polystyrene above the glass transition point
Authors: Duda J. L. , Vrentas J. S. 
Published: April 2003

AbstractDiffusivities and solubilities in the system n‐pentane‐polystyrene were measured for low penetrant concentrations at several temperatures above the glass transition temperature. The relatively sharp changes in the activation energy of diffusion and the heat of solution near 150°C. are interpreted tentatively as indicating that a second‐order transition exists in atactic polystyrene above the glass transition temperature. Evidence indicating the existence of this transition has been obtained by other techniques and the effects observed in this study should also be present in the diffusion of other penetrants in polystyrene. Correlation of these and other available data for diffusion in polystyrene as a function of the molecular size of the penetrant indicates that specific thermodynamic interactions between polymer and penetrant have little influence on the diffusion process.
Isochronal temperature–concentration diagram for a polymer–diluent system
Authors: Yannas Ioannis 
Published: April 2003

AbstractThe results of an investigation of the viscoelastic and thermal properties of the gelatin–glycerol system are presented in the form of a complete temperature–composition diagram. This diagram shows the isochronal (10‐sec.) mechanical behavior of the system along lines of constant modulus and thereby affords a convenient assessment of variation in viscoelastic behavior along any isotherm or isopleth of interest. Comparison of the results with previously obtained limited sets of data on a number of other polymer–dilent systems indicates the applicability and utility of such a presentation.
Ductile behavior of single crystal mats of an ethylene–propylene copolymer
Authors: Holdsworth P. J. , Keller A. 
Published: April 2003

AbstractIt is reported that mats formed by the sedimentation of single crystals of methyl‐ and ethyl‐branched polyethylene exhibit strength and ductility comparable with that of melt‐crystallized films. In fact, in the case of methyl‐branched polymers, extensions of up to 50× were obtained on cold drawing. Observations on separate crystals suggest that this extension is due to the pulling out of individual lamellae. In view of the magnitude of the extension, this implies unfolding of the molecules. That considerable coherence can be obtained without original molecular ties between crystals is of significance as regards the molecular interpretation of the strength and ductility of crystalline polymers.