bluuebunny/crossref_metadata_2025_split huggingface dataset:
Solubility of gases in polyethylene
Authors: Michaels Alan S. , Bixler Harris J. 
Published: April 2003

AbstractThe solubility constants for thirteen permanent gases were measured within the temperature range 5–55°C. in a linear and a branched polyethylene, hydrogenated polybutadiene, and natural rubber. Equilibrium and time lag solubility determinations were made, the latter being indirectly obtained as the ratio of the permeability to the diffusion constants. Within experimental precision, equilibrium and time lag measurements were in agreement. The solubility of each gas in polyethylene was found to be proportional to the volume fraction of amorphous material when the polymer was treated as a simple, two‐phase mixture of crystalline and amorphous polymer, each with a characteristic specific volume. Even the small helium molecule exhibited no detectible solubility in the crystallites according to this model. Therefore, a solubility constant in completely amorphous polyethylene could be determined for each gas which, with the density of an arbitrary sample, would enable calculation of the solubility of each gas in that particular sample. A correlation of the solubility constants in completely amorphous polyethylene was obtained from a thermodynamic model of the disolution process. Comparison of this correlation with a similar one for normal hydrocarbon liquids emphasized the analogy between the amorphous phase in polyethylene and these low molecular weight substances. The solubility constants in natural rubber, a completely amorphous polymer under the experimental conditions, were approximately 50% higher than those in amorphous polyethylene. Higher intermolecular forces due to the unsaturation in natural rubber may account for this result. The apparent heats of solution of all gases in branched polyethylene were approximately 1.0 kcal./g. mole more positive than those in linear polyethylene. This behavior was shown quantitatively, by comparison with dilatometric data, to be simply the result of crystalline melt‐out in branched polyethylene. In linear polyethylene the experimental solubility data yielded essentially true heats of solution, since negligible crystalline melt‐out occurred between 5 and 55°C. These were correlated quite satisfactorily by further application of the thermodynamic model for the dissolution process. Available evidence, therefore, indicates that the crystallites in polyethylene are impenetrable, and are randomly distributed on a macroscopic scale with respect to the diffusion and dissolution processes. The amorphous phase behaves as a homogeneous liquid whose thermodynamic properties are independent of the mode of polymer preparation, thermal history of the sample, and level of crystallinity.
Thermal conductivity studies of polymers
Authors: Kline Donald E. 
Published: April 2003

AbstractA study of the thermal conductivity of some amorphous and partially crystalline polymers as a function of temperature (0–100°C.) is described. Experiments have been carried out, with the use of a thermal conductivity cell with cylindrical geometry, on polyethylene, polytetrafluoroethylene, polystyrene, polyhexamethylene adipamide, and polymerized epoxy resin. Results indicate that the conductivity of amorphous polymers increases with temperature and that the conductivity is significantly higher in crystalline regions than in the amorphous regions. Data concerning the change of thermal conductivity of polymerized epoxy with the addition of powdered aluminum filler are given. The results presented in the paper are discussed and compared with those reported by other investigators.
Internal friction in stereoregular polymethyl methacrylate
Authors: Gall W. G. , McCrum N. G. 
Published: April 2003

AbstractNew stereospecific polymerization systems for methyl methacrylate are reported. The temperature dependence of the internal friction of the stereoregular forms of polymethyl methacrylate (PMMA) has been determined at frequencies of ca. 1 cycle/sec. Isotactic PMMA does not exhibit a side chain relaxation and its main chain relaxation is 66°C. lower than that of conventional PMMA. Syndiotactic PMMA exhibits exactly the same relaxations as conventional PMMA. Since the density and infrared absorption spectra of syndiotactic and conventional PMMA are also comparable and differ from the isotactic form, it is concluded that conventional radical‐initiated polymer is not truly atactic but has considerable syndiotactic character.
The chemical composition of carbohydrates of wood cells
Authors: Perilä Olavi 
Published: April 2003

AbstractWood cell fractions were quantitatively prepared from pine wood and holocellulose, from spruce holocellulose, and from birch holocellulose. The vertical tracheids were separated from ray cells of pine wood by micromanipulation under a microscope. The total hydrolysate of the tracheids contains more mannose and less xylose than the hydrolysate of the ray cells. The vertical tracheids and ray cells were fractionated from pine holocellulose by being first passed through a 40 mesh laboratory screen and then through a 180 mesh screen. The tracheids amounted to 97.8% and the ray cells 1.8% by weight of the holocellulose. The total hydrolysate of the tracheids was found to be richer in mannose and poorer in xylose than the hydrolysate of the ray cells. Both cell fractions were found to contain nearly equal amounts, about 20%, of hemicellulose soluble in an alkaline borate solution (17.5% NaOH + 4% H3BO3). Mannose was the predominant (nearly 70% of neutral monosaccharides) monosaccharide in the hydrolysate of the hemicellulose of the tracheids; xylose (nearly 50%), in the hydrolysate of the hemicellulose of the ray cells. The latter contained more glucose, arabinose, and galactose than the tracheids. The spruce holocellulose was found to contain 98.9% vertical tracheids and 1.1% ray cells by weight in microscopical fractionation. The total hydrolysate of the tracheids prepared via screening of holocellulose was found to be richer in mannose and glucose and poorer in xylose and arabinose than the hydrolysate of the ray cells. The hemicellulose amounted to 17.8% of the tracheids and to 30.3y0 of the ray cells. The total hydrolysate of the hemicellulose of the tracheids was found to be richer in mannose and poorer in xylose, arabinose, and galactose than the hydrolysate of the hemicellulose of the ray cells. Mannose was the predominant (50% of neutral monosaccharides) monosaccharide in the hydrolysate of the hemicellulose of the tracheids and xylose (50%) in the hydrolysate of the hemicellulose of the ray cells. The prosenchyma and parenchyma cells were fractionated from birch holo‐cellulose by scretmirig. The vessels have been separated from the fibers by manual fractionation of the prosenchyma cell fraction under a microscope. The holocellulose was found to contain 86.1% fibers, 9.3% vessels and 4.6% parenchyma cells, by weight. The ratio of xylose/glucose in the total hydrolysates of the fibers and of the vessels was about 0.6: 1.0, but xylose was the predominant (77% of neutral monosaccharides) mono‐saccharide in the total hydrolysate of the parenchyma cells. The hemicellulose was 21.5% of the prosenchyma cells and 39% of the parenchyma cells. The hydrolysate of the hemicellulose of the prosenchyma cells was found to be richer in mannose and poorer in xglose than the hydrolysate of the hemicellulose of the parenchyma cells. The former was found to contain xylose 86% of neutral monosaccharide; the latter 93%.
Preparation and characterization of sodium cellulosates
Authors: Schwenker Robert F. , Kinoshita Tetsuo , Beurling Karin , Pacsu Eugene 
Published: April 2003

AbstractA method of preparing sodium cellulosates by an exchange reaction between cellulose and sodium alkoxide in alcohol medium is proposed. Anhydrous systems of sodium methoxide in methanol and sodium n‐butoxide in n‐butanol were used to treat cotton and viscose rayon celluloses to form sodium alcoholates of cellulose. It is shown that alcohols used as extraction solvents in the purification of the reaction products must be of low acidity, such as branched chain alcohols, since straight chain alcohols of relatively high acidity are shown to cause destruction of the sodio derivatives. The distribution of sodium in the products was found indirectly by methylating the sodio derivatives in pure methyl iodide and determining the distribution of methoxyl groups by paper chromatographic techniques. It was indicated that the sodium substituent was distributed in the various sodium cellulosates in a somewhat random arrangement. Glucose, mono‐O‐methyl glucose, di‐O‐methyl glucose, and tri‐O‐methyl glucose constituted the distribution products. The mono‐O‐methyl glucose fractions were further separated, to disclose the presence of the 2,3, and 6 isomers. The degree of substitution (DS) found for the sodium cellulosates ranged from 0.52 to 1.72.
Preparation, characterization, and properties of a deoxycellulose
Authors: Carter Mary E. 
Published: April 2003

AbstractIt has been shown that reduction of a cyanoethyl cellulose gives a deoxy cellulose. The deoxy cellulose averaged one deoxy group per anhydroglucose in one third of the monomer units in the polymer chain. This was determined by elemental analysis and acetyl content. Further study showed that the 2‐deoxy‐β‐anhydroglucopyranose was the predominant deoxy sugar. Weight loss upon acid hydrolysis, alkaline degradation, and periodate oxidation studies were made. The behavior of the cellulose toward cellulosic solvents indicates the presence of a few crosslinks.
The application of nuclear magnetic resonance to structural studies of carbohydrates in aqueous solution
Authors: Lenz Robert W. , Heeschen Jerry P. 
Published: April 2003

AbstractHigh‐resolution nuclear magnetic resonance spectroscopy was applied to the study of the structure of carbohydrates in deuterium oxide solution. The structural problems considered were the configuration of anomeric protons, the conformation of pyranoside rings, the preferred ring form, the existence and form of complexes, and the mutarotation of carbohydrates in solution. A modification of the Karplus equation was applied to the calculation of the dihedral angles between the C1 and C2 carbon–hydrogen bonds for a number of carbohydrates. A harmonic oscillation of ±15° about the equilibrium dihedral angle was assumed in these calculations. The preferred conformations of several carbohydrates were deduced from the dihedral angles, and an analysis of the diamagnetic susceptibility anisotropy was applied to the predicted conformations in two cases. Observed and calculated shielding differences were determined for each of the ring protons in β‐glucose and β‐mannose. The good agreement obtained from this treatment appears to support the proposed distorted chair and half‐chair conformations for β‐glucose and β‐mannose respectively. Conclusions reached from consideration of NMR spectra were applied to discussions of the stability and structure of several borate complexes and of the preferred ring size of xylose in solution.
Highly stereospecific catalytic systems for the polymerization of α‐olefins to isotactic polymers
Authors: Natta G. , Pasquon I. , Zambelli A. , Gatti G. 
Published: April 2003

AbstractThe highly stereospecific catalytic systems for the polymerization of α‐olefins have been compared. These are obtained starting either from the α, γ, or δ modifications of violet TiCl3 with or without AlCl3 present in solid solution, and from aluminum diethyl monohalides, or from metalloorganic products obtained by reacting two molecules of aluminum monoalkyl dihalide with one molecule of particular electron donor compounds. The catalytic systems considered polymerize propylene, giving rise to crude polymers containing 90 to 100% isotatic propylene (nonextractable in boiling n‐heptane) for a wide range of polymerization temperatures. By fractionation of crude polymers prepared with the use of these catalytic systems, highly isotactic polypropylenes, having a melting temperature up to 177°C., have been separated. The results, correlated with those obtained in x‐ray determinations of the structure of the modification of TiCl3 used, demonstrate that the stereospecificity of all the catalytic systems examined is independent of the particular type of violet modification (α, γ, or δ), whether or not these contain aluminum as AlCl3 in solid solution. This proves that the single active centers are substantially of the same type; a variation in their number causes only a variation of the overall polymerization rate.
Changes in orientation of crystallites during stretching and relaxation of polyethylene films
Authors: Aggarwal Sundar L. , Tilley George P. , Sweeting Orville J. 
Published: April 2003

AbstractA microbeam camera has been used in x‐ray diffraction studies of the changes which occur in orientation of crystallites in polyethylene film when the film is stretched and later relaxed. The collimator of the microbeam camera, 100 μ in diameter, allows one to follow the orientation changes very closely in the necked‐down region of a stretched sample. The stretching of polyethylene proceeds by alignment of the a‐axes of the crystallites perpendicular to the stretching direction with the planes containing b‐ and c‐axes perpendicular to the a‐axis but randomly oriented, followed by a gradual change to a state in which the c‐axes become more nearly aligned in the stretching direction although perfect alignment is not achieved. On relaxation, either the orientation of the c‐axis parallel to the original stretching direction becomes less perfect, or folding of the oriented crystallites about the b‐axis takes place. In the latter case the preferred crystallographic directions parallel to the stretching direction have indices such as [u0w]. These orientation changes during stretching and relaxation of the stretched samples suggest that crystallites in polyethylene films consist of parallel arrangements of platelets containing b‐ and c‐axes. The distinction between directions in the reciprocal lattice and the crystal lattice is clarified. A number of x‐ray diffraction patterns and charts of dimensional changes illustrate the paper.
Méthodes de synthèse de polymères greffés et de polymères à blocs
Authors: Smets Georges 
Published: April 2003

AbstractTrois méthodes synthétiques principales de préparation de polymères greffés et séquencés ont été discutées. Dans la première méthode, basée sur des réactions de transfert de chaîne sur polymère, on envisage l'influence de la nature de l'initiateur (Bz2O2, azobisisobutyronitrile, et le peroxyde de di‐tert‐butyle) et des radieaux primaires, de même que l'influence de la présence de sites réactionnels dans le polymère. Dans la seconde méthode, ou l'initiation est réalisée par activation, on considère plus spécialement l'utilisation de radicaux piégés à la préparation de polymères séquencés; certains résultats nouveaux sont discutés et interprêtés. Finalement dans le cas de la méthode par initiation chimique, on a étudié la cinétique du greffage en utilisant des polymères contenant des groupes peroxy‐tert‐butyliques, soit comme groupes peresters latéraux, soit comme groupes peroxydiques terminaux. Les efficacités relatives des macroradicaux par rapport aux radicaux habituels ont été évaluées et comparées entr'elles; elles sont également fonction de la nature de monomère. Les autres méthodes de préparation de polymères greffés et séquencés ne sont que brièvement mentionnées.
Polymerisation et copolymérisation cationiques de l'indéne
Authors: Sigwalt P. 
Published: April 2003

AbstractEn général on considère que des monomères éthyléniques substitués en 1,2, tels que l'indène et la coumarone, ne peuvent pas donner de polymères de très haut poids moléculaire. On a obtenu les plus hauts poids moleculaires moyens par la polymerisation cationique de lindirne et leur valeur etait de quelques milliers. Une etude systematique des differents facteurs influenqant la polymbrisation cationique de lindbne nous a permis de prkparer des hauts polymbres dont la viscositt? intrinsirque peut re aussi blevee que 2 ou 4 pour des polyindhes ou polycoumarones. Laccroissement des poids mole‐ culaires de polymkres obtenus en utilisant des catalyseurs de Friedel‐Crafts a conduit & une classification de ces catalyseurs qui est analogue ii celle connue pour la polymerisation de lisobuthne. La viscosite intrinshque des polymirres croit regulibrement lorsque la temperature de polymerisation dhcroit La roncentration en monomere doit re limitee en vue dobtenir de hauts poids molkculaires, parce que la reaction est trirs rapide et exothermique, et parce clue la constante diklectrique du milieu est abaissee par la presence du monomere. La nature du solvant est trks importante: les halogenures dalcoyles qui sont de bons solvnnts pour le polymh‐e la temperature de polj mhrisation, et qui ont une constante diklectrique suffisamnient Clevee, donnent des polymkres avec les poids moleculaires les plus élevées. La copolymerisation dindhne avec la coumarone et une serie de monombres vinyliques fut egalement etudide. En general, les viscosites intrinsitques des copolymirres sont infhrieures & celles des honiopolymirres correspondants. Les plus hauts poids mol6culaires sont obtenus avec des comonomeres qui polymerisent aisCment avec des initiateurs cationiques (coumarone, ryrlopentadihe, a‐methyl‐ styrene, p‐m6thoxvstyrkne, isobuthe).
Polymerization inhibition by aromatic compounds
Authors: Bagdasar'Ian Kh. S. , Sinitsina Z. A. 
Published: April 2003

AbstractA quantiative study of chain transfer and inhibition reactions makes it possible to determine the ratios kx/Kp where Kp and kx are the rate coefficients for propagation and for chain tranfer, respectively. Since the absolute values of the constants Kp are known for a number of monomers it is possible to determine the absolute values of the constants kx. We have investigated the inhibiting action of some types of aromatic compounds in the polymerization of vinyl acetate, methyl acrylate, acrylonitrile, and methyl methacrylate. In the polymerization of vinyl acetate the inhibiting effect of the aromatic hydrocarbons increases in the order: toluene, diphenyl, naphthalene, phenanthrene, anthracene. The logarithm of kx is linearly related to the logarithm of the methyl affinity. The inhibiting effect increases on incorporating substituents, both electrondonating and electron‐accepting, in the benzene ring. There is no relation, however, between the value of kx and Hammet's σ‐constant. An outstanding position is assumed by nitrobenzene, for which kx is higher by 3–4 orders of magnitude than that of the other substituted benzenes. The incorporation of substitutents in the meta and para positions of the benzene ring follows the Hammet rule, the electron‐donating substituents causing a decrease in the kx values. Similar relations are observed in the polymerization of methyl acrylate, but the absolute values of kx are lower by 3–4 orders of magnitude than in the polymerization of vinyl acetate. Because of this, under the experimental conditions the interaction of the polymethyl acrylate radical with molecules of the transier agent was not revealed (kx < 0.21 1./mole‐sec. at 50°) in the case of many of the substances investigated, for instance of all mono‐substituted benzenes except nitrobenzene. A comparison of the kx values for polyvinyl acetate, polymethyl acrylate, polymethyl methacrylate, and acrylonitrile radicals permits a number of conclusions to be made concerning the influence of the polar factor on radical reactions. The data obtained lead to definite conclusions as to the inhibiting mechanism of aromatic compounds. The primary act is the addition of the polymer radical to the aromatic ring with the formation of a nonreactive radical. In the case of nitro compounds, the polymer radical reacts with the nitro group, probably by transferring to it a β‐hydrogen atom. It has been found that in the polymerization of vinyl acetate in the presence of the inhibitors in question each molecule of the latter terminates two kinetic chains; regeneration of the chains does not take place, and the polymer molecules form as the result of disproportionation between the polymer radical and the radical formed during interaction of the former with the inhibitor molecule.
The mechanism of formation of stereoregular polymers
Authors: Mihail R. , Herscovici J. 
Published: April 2003

AbstractAt present various polymerization reactions are known which yield approximately identical types of eutactic polymers. This has been confirmed experimentally for a sufficient number of monomers (α‐olefins, conjugated diolefins, vinyl esters, alkylene oxides, etc.) to lead to the conclusion that stereoregularity is based on a single or a few general acts. The mechanisms proposed for the formation of stereoregular polymers, i.e., radical, through alkyltitanium compounds (Nenitescu), semiconductor surface (Topchiev), or ionic (Natta, Furukawa), do not give a sufficiently general solution to the problem. Whereas some authors do not take into account the ionic character of some types of polymerization reactions and the possibility of free rotation of the macroradical around the CC axis, others neglect the fact that radical reactions are known which leading to the formation of stereoregular units. Particularly useful is a generalization of the remarks concerning the steric control of unsymmetric induction (Cram). Stereospecific polymerization, or, to be more exact, the act or elementary acts leading to stereo‐regularity of the molecules formed, should proceed just in the same manner as other stereospecific reactions. The authors of the present report attempted to find common elements between the different reaction mechanism leading to the formation of eutactic polymers.
Rate of polymerization of a single particle in emulsion polymerization
Authors: Ryšáanek A. , Hloušek M. 
Published: April 2003

AbstractThe rate of polymerization for a single particle in emulsion polymerization in the region of constant reaction velocities has previously been expressed in the form of an equation which can be modified to the form:

where K = k2[M]/NA, and vpol (1) is the rate of polymerization of single particle (mole/sec.); n is the concentration of all particles in emulsion (mole/l.); v′i is the rate of incorporation of radical initiator into particles; [X] is active inhibitor concentration about the growing radical (mole/l.); k3 is the kinetic inhibitor chain scission constant (l./molesec.); k2 is the kinetic chain propagation constant (l./mole‐sec.); [M] is the active monomer concentration about the growing radical (mole/l.); and NA is Avogadro's number. With the aid of this equation one may experimentally determine the dependence of the rate of polymerization of a single particle upon the total number and upon the rate of initiation. For a given monomer K and k3[X] are constants and the expression 1/vpol(1) depends only upon the value of n/v′i. Extrapolating graphically the dependence of 1/vpol(1) upon n/v′i we obtain an intercept on the ordinate axis, the value of which is the reciprocal of the maximum rate of polymerization for a single particle in the given system. Maintaining v′i constant, from a series of experiments in which the number of particles is varied we obtain the dependence of the polymerization rate upon the particle number. In another series of experiments with constant particle number and changing rate of initiation (for instance, by varying the initiator concentration) we obtain the dependence of the rate of polymerization of a single particle upon 1/v′i. Changing both parameters simultaneously we obtain the dependence of the rate for a single particle upon the value of n/v′i. These relations were confirmed in experiments on the polymerization of vinyl acetate, styrene, and chloroprene.