bluuebunny/crossref_metadata_2025_split huggingface dataset:
Characterization of molecular weight distributions in high polymers
Authors: Billmeyer Fred W. 
Published: June 2010

AbstractIn this review paper, these types of molecular weight distribution found in typical polymers are described. It is pointed out that procedures for fractionating polymers usually yield incomplete information on molecular weight distribution unless the fractions are characterized for molecular weight. In addition, measurement of different average molecular weights can itself give limited information on molecular weight distribution breadth. Experimental methods for molecular weight determination are described with emphasis on range of applicability, precision, accuracy, convenience, and cost. For measuring number‐average molecular weight, the thermodynamic methods of cryoscopy, ebulliometry, and osmometry have proven absolute accuracy. The thermoelectric differential vapor pressure technique, while a transport rather than a thermodynamio method, is simple and, in most cases, accurate. Weigh average molecular weight can be measured by light scattering, equilibrium ultracentrifugation, and approach‐to‐equilibrium ultracentrifugation, all thermodynamic methods. Transport properties such as the sedimentation constant, the diffusion constant, the intrinsic viscosity, or the Newtonian melt viscosity, can be empirically correlated with molecular weight. Although in principle these properties can be combined in pairs to yield molecular weights without resort to outside calibration, as in the sedimentation transport method, the results of such treatments must be applied with considerable caution to random coil polymers.
The temperature dependence of the specific refractive index increment of polyethylene in various solvents
Authors: Chiang R. 
Published: June 2010

AbstractThe specific refractive index increment, dn/dc, of polyethylene in α‐chloronaphthalene, tetralin, and n‐decane bas been determined as a function of temperature in the range of 50–80°C. The value of dn/dc was found to be a linear function of the refractive index of the solvent. The temperature coefficient of dn/dc of polyethylene in α‐chloronaphthalene, tetralin, and n‐decane was found to be approximately 0.1 × 10−4, 0.96 × 10−4, and 2.43 × 10−4 cc./g. °C, respectively. There results are interpreted on the basis of the Gladstone‐Dale equation. A simple modification of the Brice‐Phoenix differential refractometer for use at moderately high temperatures is described.
Morphological foundations of fiber properties
Authors: Rebenfeld Ludwig 
Published: June 2010

AbstractStructural theories which have been developed to interpret the chemical, physical, and mechanical properties of fibers are reviewed, with particular emphasis on the natural fibers. It is pointed out that many of the current theories of fiber structure derive from early concepts of the natural cellulosic or vegetable fibers. The micellar, the fringed micellar, and the fringed fibrillar theories, as well ay the concept of lateral order distribution are presented. The growth and development of cotton fibers are discussed and variations in structure are shown to be reflected in their properties. In this connection fibrillar orientation and helical reversals in cotton fibers are particularly important. The complex organochemical and supermolecular structure of keratin fibers is presented and is shown to be related to the chemical and mechanical properties of these fibers. Cortical asymmetry is a unique structural feature of keratin fibers which is responsible for the characteristic three‐dimensional crimp of wool fibers. The well‐known supercontraction of keratin fibers in a variety of chemical systems is discussed in terms of a chemical mechanism involving sulfhydryl‐disulfide interchange.
The permeability of poly(ethyl methacrylate) to gases and water vapor
Authors: Stannett V. , Williams J. L. 
Published: June 2010

AbstractThe permeabilities, diffusivities and solubilities of He, Ne, A, O2, N2, Kr, CO2, H2S, and H2O in poly(ethyl methacrylate) have been measured above and below the glass temperature. Water showed a small increase in solubility when the polymer was heated above the glass temperature. Water also showed anomalous behavior in that the solubilities calculated from the permeability constants and the time‐lag diffusion constants are much less than those measured by direct weighing. The behavior had been found previously with other polymers and has been interpreted in terms of the clustering of water molecules in the polymer. The Arrhenius plots of the permeability and diffusion constants for water showed the change in slope at the glass temperature reported to occur with many gases and vapors through other polymers. The gases, however, showed no change in slope even with large molecular size gases such as silicon tetrafluoride and sulfur hexafluoride. The results found with water are interpreted as due to the plasticizing effect of the penetrant when the polymer is above the glass temperature. In the case of the gases, the lack of a transition effect is interpreted in terms of the relative sizes of the gas molecule and the average hole she of the polymer. The energies of activation for diffusion were found to be proportional to the 1.6 power of the molecular diameter of the; penetrants, i.e., intermediate between that found for rubber and for both poly(vinyl acetate) and poly(ethylene terephthalate).
Polyethylene‐encapsulated cellulose
Authors: Herman D. F. , Kruse U. , Brancato J. J. 
Published: June 2010

AbstractAn encapsulation process is described in which cellulose fibers were enveloped with sheaths of polyethylene by the use of transition‐metal catalysts. Cellulose‐catalyst interactions resulted in a fiber surface completely covered with initiating sites, and growth of polymer occurred from the fiber surface outward to form a shell around each individual fiber. Removal of moisture and in situ catalyst formation were found to be essential for successful encapsulation. Catalyst interactions during different stages of formation were studied by following the absorption of the various catalyst components on cellulose. Active sites on fiber surfaces were postulated to have been formed by interaction with TiCl4 and by reaction of reduced transition metal compounds with electron donor groups in the cellulose. Polymer growth was followed in a series of electron microphotographs and polyp‐like spherical polyethylene particles were observed at an early stage in the polymerization. It was concluded that encapsulation was a chemical means of placing polymer around a fiber core and not a grafting reaction. Fiber properties, uses of encapsulated cellulose, and conversion into web structures by use of paper making techniques were also discussed.
Brightness reversion of birch sulfate pulp
Authors: Croon Ingemar , Dillén Sten , Olsson Jan‐Erik 
Published: June 2010

AbstractThree methods of improving brightness stability have been examined: (1) Avoidance of chlorination of extractive components and the residual resin. (2) Modification of the hemicellulose by high‐temperature treatment of the pulp to remove xylan components of poor brightness stability. (3) Maximum reduction of the residual lignin in the pulp. The results of the three methods have been compared and an examination of their combined effect has thrown light on the main cause of brightness reversion in each case. The chlorinated extractives adversely affect the brightness stability during aging in a dry atmosphere, and the reversion in this case is due to degradation mainly of carbohydrates by the hydrogen chloride liberated from the chlorinated extractives. Different fractions of the extractives have been tested with respect to their ability to promote this effect. It would seem that the brightness stability of the pulp is dependent on its carbohydrate composition. An aqueous treatment of the pulp at a high temperature removes some hemicellulose components sensitive to reversion (particularly xylan, which has a high content of uronic acid). Under moist conditions, the hydrochloric acid released from the extractives is diluted and thus has much less influence on the degradation of the carbohydrates. The extractives then contribute to the reversion mainly through their own discoloration. The transformation of the carboxyl groups in the pulp to the hydrogen form by a sulfur dioxide treatment usually increases the brightness stability in a moist atmosphere and decreases it under dry conditions. Our results also strongly indicate that the brightness reversion is highly dependent on the degree of chlorination of residual lignin.
Analysis of the α, β, and γ relaxations in polychlorotrifluoroethylene and polyethylene: Dielectric and mechanical properties
Authors: Hoffman John D. , Williams G. , Passaglia E. 
Published: June 2010

AbstractTheoretical models for the ac and γe relaxation effects found in chain‐folded polymer crystals (single crystal mats and bulk) are presented and compared with the available dielectric and mechanical loss data for polyethylene and polychlorotrifluoroethylene. Details of morphology and crystal structure that can be varied by crystallization and annealing procedures, e.g., roughness of chain‐folded surfaces, number of intercrystalline links and cilia, number of chain‐end defects and dislocations, and the existence of the extended‐chain phase, are brought into the discussion. The αc process, which consists of two overlapping mechanisms, is a result of motions of chain folds and reorientation (with translation) of chains in the interior. (Chain twisting also occurs for long chains.) The theory connects the data on the n‐paraffins and their polar derivatives (n‐ketones, esters, ethers) with the results on polymers: the common feature is the chain reorientation and twisting process. A new theory of chain twisting is introduced. The β relaxation is a result of reorientation of chains in a “loose” chain‐end induced defect (a vacancy row) in the polymer crystal. When the effect of chain twisting is included, the theory successfully predicts the unusually broad and asymmetric loss curve found in the polymer, and is consistent with the experimental activation energies. The β relaxation arising in the amorphous component of PCTFTC is analyzed, and its upward shift in temperature with increasing crystallinity discussed in terms of the Adam‐Gibbs theory of relaxation in the glassy state. The γa amorphous relaxation, and the δ relaxation which is found at cryogenic temperatures, are also discussed.
Elastic moduli of the crystal lattices of polymers
Authors: Satcurada Ichiro , Ito Taisuke , Nakamae Katsuhiko 
Published: June 2010

AbstractElastic moduli of the crystalline regions in high polymers have been studied. Oriented specimens were used throughout. Lattice strains were measured by an x‐ray technique in the direction of the fiber axis as well as in that perpendicular to the fiber axis. The moduli for both directions were calculated on the basis of the assumption that the stress is homogeneous within a specimen held under a load. Remits obtained for various kinds of polymers were discussed in terms of the crystal structures of the polymers, pan icularly the skeleton conformation and the cross‐sectional bulkiness of the chain molecule in the crystal. It was shown that the moduli in the direction of the fiber axis are widely different depending upon the polymer. They vary from 240 × 104 kg./cm.2 for polyethylene to 4.1 × 104 kg./cm.2 for isotactic poly (vinyl tert‐butyl ether). In the direction perpendicular to the fiber axis, the moduli were shown to take values within a narrow range of magnitude, 3–9 × 104 kg./cm.2. Some of these moduli were compared with the calculated values reported by several authors. To find experimental support for the assumption of the homogeneous stress, measurements were made by using several oriented specimens of different fine textural structures. Inherent values of the lattice moduli were obtained, regardless of the specimens used, which gives a strong support for the assumption.
Mechanical properties of polyethylene crystals. II. Deformation process of spherulite
Authors: Kobayashi Keinosuke , Nagasawa Toshio 
Published: June 2010

AbstractOptical and electron microscopy of the plastic deformation process of polyethylene spherulitic film revealed the variation of the process with the temperature. Even within a single spherulite the mode of deformation differs with the relative position in the overall deformation; hence it is hard to represent with a simple affine model. The morphological change can be classified by dividing a spherulite into a few zones by conical boundaries which incline 45° to the direction of stretching and pass the center of the spherulite. At 20°C, the unfolding of molecules takes place in two sectors; the concentric extinction patterns are disturbed, probably due to rotation or bending of lamellae. At 95°C., the necking or the unfolding of molecules is not detected in any sector but the deformation with the slip between or within lamellae occurs preferentially in two side sectors. The anisotropic parameters corresponding to the tensile and shear compliances of simple lamellar structures are estimated from mechanical properties of tubular extruded film in which lamellae pile up along the machine direction. Applying these values of parameters to the structure model of spherulite, the mechanism of its deformation is analyzed. One of these parameters which relates to shear deformation inducing the “slip” between or within lamellae is most sensitive to temperature and varies widely with the irradiation dose (number of crosslinkings).
Temperature dependence of polymer viscosity. The influence of polymer composition
Authors: Porter Roger S. , Johnson Julian F. 
Published: June 2010

AbstractThe change of viscosity with temperature has been reported in the literature for a variety of linear, amorphous polymers. These data in terms of the flow activation energy, E*, indicate a wide variation among polymers with each exhibiting an essentially constant and characteristic E* at high temperature and high polymer molecular weight. These characteristic values of E* have been evaluated in terms of chemical composition and structure of individual polymer coils. The value of E* increases as a regular function of the molar volume of pendant groups along the polymer chain. More generally, a relation is shown between E* and the steric or conformational factor σ. For polyolefins, E* also increases regularly with the molar volume per monomer unit and with the mean‐square displacement length per chain unit.
Thermomechanical Behavior of Poly(ethylene Glycol Methacrylate) and Poly(diethylene Glycol Methacrylate)
Authors: Ilavský M. , Slonlmskii G. L. , Janáček J. 
Published: June 2010

AbstractThe influence of the length of side groups on the thermomechanical behavior of poly‐(ethylene glycol methacrylate), poly(diethylene glycol methacrylate), and their copolymers was studied. It was found that the hydroxyl endgroups increase the viseosity of these polymers compared to poly(propyl methacrylate) and poly(hexyl methacrylate); the increasing length of the side chains lowers the differences between the mechanical behavior of the poly(alkyl methacrylates) and poly(glycol methacrylates). The thermomechanical curves are sufficiently sensitive to determination of the fundamental mechanical characteristies of network polymers with very small differences of network density. A relation was obtained between the physical degree of crosslinking of poly‐(ethylene glycol methacrylate) and poly(diethylene glycol methacrylate) and the content of the crosslinking agent based on thermomechanical measurements, and the assumption has been expressed, that the physical degree of crosslinking can be partly influenced by the supermolecular structure of the polymers.
Intcractions of Macroradicals in Polyethylene‐Polypropylene Blends
Authors: Bartoň J. , Lazár M. 
Published: June 2010

AbstractTransfer reactions of primary radicals formed by decomposition of dicumyl peroxide in atactic polypropylene–polyethylene blends give rise to the corresponding macroradicals. A mutual recombination of polypropylene and of polyethylene macroradicals leads to the formation of hybrid copolymer. From the values obtained experimentally it follows that the total crosslinking efficiencyE of the blend (defined as a number of total crosslinks formed per mole of dicumyl peroxide decomposed) depends on the concentration of atactic polypropylene in the blend and not on the concentration of dicumyl peroxide. The decrease in the total crosslinking efficiency of the blend is attributed to scission reactions of polypropylene macroradicals. On the basis of kinetic analysis of the crosslinking process, relations expressing the dependence of the total and interpolymer crosslinking efficiencies of the blend (the latter defined as the number of crosslinks between polypropylene and polyethylene macromolecules per mole of dicumyl peroxide decomposed) on the concentration of polypropylene and polyethylene monomer units in the blend were derived. The calculated course of interpolymer crosslinking efficiency of blend is in good agreement with the values of the interpolymer crosslinking efficiency E' for the blends determined from the concentration of polypropylene bound in the crosslinked blends. For the ratio of the rate constants of transfer to polypropylene and polyethylene we obtained a value k3/k2 = 2.3. The influence of the microheterogeneity of blends on the relations derived is discussed briefly.
Anionische Kopolymerisation einiger cyklischer Polysiloxane
Authors: Jelínek M. , Laita Z. , Kučera M. 
Published: June 2010

AbstractThe anionic copolymerization of some cyclic polysiloxanes catalyzed by strong bases was studied. Copolymerizations were carried out with the use of dodecamethylcyclohexasiloxane and tetradecamethylcycloheptasiloxane as M1 and heptamethylvinyl‐cyclotetrasiloxane and tetramethyltetravinylcyclotetrasiloxane as M2. LiOH, NaOH, and KOH were used as catalysts. The Mayo and Lewis method was applied in evaluating the copolymerization experiments. The values of the monomer reactivity ratios r1 and r2 obtained imply that changes in temperature do not practically affect the entry of cyclic polysiloxanes into the copolymer chain. On the other hand, copolymerization is strongly influenced by the activity of the catalyst. The character of the metal gegenion is shown in the reaction of the catalyst with the monomer in the first elementary step where it affects the equilibrium of the formation of the transition complex. It has presumably no effect on the second elementary step, i.e., the transformation and linearization of the cyclic part of the complex. The electronegative effect of the vinyl substitution on the Si atom of the cyclic tetramer results in an increased electropositivity of Si in the siloxane unit of the monomer and a decresaed electron density on oxygen of the silanolate group. As a result of these electron effects tetramethyltetravinylcyclo‐tetrasiloxane and heptamethylvinylcyclotetrasiloxane are more reactive as monomers than octamethylcyclotetrasiloxane.
Changes of Radicals in the Poly(methyl Methacrylate)—Polystyrene Systems
Authors: Lazár M. , Szǒs F. 
Published: June 2010

AbstractThe reactions of macroradicals produced by mechanical destruction in the systems poly (methyl methacrylate)‐polystyrene have been studied by following changes of the ESR spectra. The parent polymers were random copolymers, the mixtures of homopolymers, and graft and block copolymers with various ratios of styrene and methyl methacrylate. The transfer constants as well as the termination constants for the macroradicals have been determined. The mechanism of the transfer reactions and the importance of the chemical nature of the polymeric matrix in the decay of macroradicals are discussed.
Determination of Dispersion Characteristics of Polychloroprene Latices by Electron Microscopy and Soap Sorption Methods
Authors: Pelzbauer Z. , Hynková V. , Bezděk M. , Hrabák F. 
Published: June 2010

AbstractTo estimate the dispersion characteristics of polychloroprene latices, two independent methods, electron microscopy and soap sorption, were used. Within the framework of microscopic determination, agreement was demonstrated between the calculation and bromination methods. From the comparison of electron microscopy with sorption, a new value, 48.7 A.2, was assessed for the active surface of the potassium laurate molecule on the surface of latex particles. The dispersion characteristics of 19 latices were used to calculate the conversion factors between different mean particle sizes dependent on their polydispersities.
Kinelic Study of Thermal Dehydrochlorination of Poly (vinyl Chloride) in the Presence of Oxygen. Part II. Correlations of Derived Equations with Experimental Results
Authors: Valko L. 
Published: June 2010

AbstractA correlation of experimental results with the equation for τ(t) derived in the first part of this study has been carried out. From the results it is evident the equation for η(t) expresses the true course of the thermal dehydrochlorination of PVC in oxygen at any temperature. It has been found that the elimination of HCl and the cleavage of C—C bonds represent a monomolecular stochastic process. The course of the kinetic curves of the first‐order reaction is changed by the influence of the dissipative factors on the asymmetrical “S” curves. From the distribution function of the bonds it appears that the bonds of the same type in the polymer chain are not equivalent in respect to the energy, and they are characterized by a “predissociated state.” From the value of the frequency factor (104 sec.−1) it can be assumed that the elimination of hydrogen chloride represents a first‐order reaction of nonadiabatic character. The rate of elimination of HC1 is not only caused by the interaction of oxygen with the double bonds but also by the number of cleft C—C bonds autocatalytically influenced. From the activation energy of scission the C—C bonds (57 kcal./mole it can be assumed that there is question of predominantly simple C—C bonds.
Photodegradation of cis‐1,4‐polyisoprene in solution sensitized by the addition of nitroso compounds in the presence of visible light
Authors: Rabek Jan F. 
Published: June 2010

AbstractIt was found that apart from chloronitroso compounds bromonitroso and nitronitroso compounds also sensitize the photodegradation by visible light of cis‐1,4‐polyisoprene in solution. The investigation of the kinetics of the relative viscosity decrease in solutions containing chloronitroso compounds and stable free radicals, e.g., α, α‐diphenyl‐β‐picryl hydrazyl (DPPH), di(4‐methoxyphenylo)‐N‐oxide, 2,2,4‐trimethyl‐6‐ethoxy‐1,2‐dihydroquinolin‐N‐oxide, shows that the addition of stable radicals does not prevent the photochemical reaction, but merely slows down its rate. The present investigation of the photodegradation mechanism of cis‐1,4‐polyisoprene in solution, induced by the addition of chloronitroso compounds, excludes the possibility of a direct transfer of light energy over the donor‐acceptor complex, and shows that the degradation reaction is due to free radicals formed by the decomposition of the sensitizing agent.