bluuebunny/crossref_metadata_2025_split huggingface dataset:
Determination of molecular weight distribution from osmolically measured “permeation”
Authors: Hoffmann M. , Uxbehend M. 
Published: June 2010

AbstractWith a quick‐acting osmometer it can be shown that in an osmotic experiment the diffusion of dissolved molecules through the membrane follows the well‐known diffusion equations. On paper intended for probability curves the dependence of the osmotic pressure on time can be represented by a straight line whose inclination, when the degree of swelling and thickness of the membrane are known, supplies the diffusion constant of the dissolved molecules in the membrane. These diffusion coefficients depend exponentially on the amount of swelling undergone by the membrane and the molecular weight of the dissolved substance. If the dissolved material is not unimolecular, a straight line is no longer obtained on paper intended for probability curves. A tangent is placed on the curve at a low time value and shifted until it has a definite ordinate value at t = ∞. The inclination of the tangent supplies the diffusion constant, whereas the quotient of the ordinates of the shifted and unshifted tangents at the point of contact is equivalent to the quotient of the total pressure and the partial pressure of the fraction. The time‐dependent partial pressure is then subtracted from the total pressure and the diffusion constant and partial pressure of the next fraction are calculated from the dependence of the residual pressure on time. Calibration measurements are carried out to find the dependence of the diffusion constants on molecular weight and in this way the molecular weights of the fractions and‐with their partial pressures‐their concentrations are determined. The partial pressures of rapidly diffusing molecules must be corrected by means of the Staverman coefficients, which can be calculated from the diffusion constants and molecular weights of the fractions and of the solvent. The method is particularly suitable for determining the low‐molecular portion of the molecular weight distribution and is insensitive to differences in the chemical nature of the dissolved molecules.
Über die anionische polymerisation α,β‐ungesältigler aldehyde. 33. Mill, über polymere acroleine
Authors: Schulz Rolf C. , Wegner Gerhard , Kern Werner 
Published: June 2010

AbstractAcrolein was polymerized by anionic catalysts in bulk and in solution in the temperature range from −78 to +20°C. Effective catalysts were aliphatic and aromatic tert‐phosphines, triethylamine, alkali borohydrides, naphthyllithium, sodium naphthalene, alkali cyanides, and alkali thiocyanates. The structure of the polymers was investigated by means of physical and chemical methods. It was shown that the polyacroleins obtained with sodium cyanide in tetrahydrofuran or toluene have a uniform structure, containing only the repeating unit…—CH—O—…—CH=CH2 They are easily soluble in many organic solvents and reveal high thermal stability. In addition to acrolein the following α,β‐unsaturated aldehydes have been polymerized: methacrolein, crotonaldehyde, and propionaldehyde. With the above‐mentioned initiators they form polymers composed of several different structural units. Substitution in a‐positiou is of minor importance than substitution in α‐position with respect to the arrangement of the structural units. The polymerization activity decreases in the order acrolein > methacrolein > crotonaldehyde > propiolaldehyde.
Grafting efficiency of atactic polypropylene
Authors: Pavlinec J. , Lazár M. , Maňásek Z. 
Published: June 2010

AbstractThe changes of grafting efficiency of atactic polypropylene in grafting with methyl methaerylate and styrene, initiated by low molecular weight peroxides and peroxides of polypropylene, have been investigated. The assumption that the grafting efficiency of atactic polypropylene increases with an increase in temperature, monomer concentration in the initial mixture, and with the increase of molecular weight of the initial polymer was confirmed. It was also found that to reach high grafting efficiency of the basic polymer, it is necessary to select a reaction medium with maximum compatibility of the components of the system. The average number of grafted branches was determined by means of grafting efficiency of the polymer and by using Poisson's equation of distribution probability of this phenomenon.
The role of oxygen in solid‐state polymerization. I. Acrylamide and its solid solutions
Authors: Adler George 
Published: June 2010

AbstractIt has been shown that the presence of oxygen has little effect on the ESR spectrum of acrylamide. On the other hand, the spectrum of propionamide is markedly changed and shows sharply increased decay rates with oxygen. The behavior of solid solutions of the two is intermediate and depends on the relative concentrations of the two materials. The polymerization is markedly decreased in the solid solutions when oxygen is present. The polymerization data are thus consistent with those derived from the ESR spectra. These effects are interpreted in terms of the crystal structure of the materials and the polymerization mechanism.
A physicochemical study of poly(vinyl chloride) in solution
Authors: Kratochvíl P. , Petrus V. , Munk P. , Bohdanecký M. , Šolc K. 
Published: June 2010

AbstractThis paper summarizes results obtained by studying solutions of poly (vinyl chloride) in various solvents by light‐scattering, sedimentation analysis, streaming birefringence, viscometry, and osmometry. Determination of certain molecular parameters (molecular weight, dimensions of maeromolecules, and optical anisotropy of segments) is described and attention is paid to the complications which arise from the presence of supermolecular structures occurring in the solutions of poly(vinyl) chloride even in good solvents. Some conditions are given for the occurrence of the sepermolecular structures in thermodynamically good, as well as poor solvents (both single and mixed), and the structures are partially characterized. The presence of supermolecular structures makes it impossible to determine directly certain parameters, in particular, molecular dimensions.
Study of the activity of some sulfur compounds in the modification of vulcanizates by vinyl monomers
Authors: Beniska J. , Štaudner E. 
Published: June 2010

AbstractThe kinetics of the bulk polymerization of styrene in the presence of tetramethylthiu‐ramdisulfide ([TMTD]; 2.11 × 10−4‐1.67 × 10−1 mole/1., and some other sulfur compounds at 80, 95, 115, 130, and 140°C, were studied. The rate of polymerization has been measured as a function of the concentration of the studied compound. The formal order of reaction (n) was determined with respect to the concentration of TMTD, which varies with the increase of the concentration of TMTD and temperature of polymerization in the range 0 < n < 0.5 and it is possible to express by the relation: n = d In Rp/d In [I] = n0(1 − C[I]2)/(1 + B[I] + C[I]2). The decrease of the polymerization rate compared with the rate arising from the simple reaction scheme is caused by the participation of radicals on the termination reactions: (P' + RS', RS' + RS'), which permits us to solve this type of polymerization as a retardation polymerization: Rp − A[I]1/2 /(I + B[I] + C[I]2)1/2. (A, B, and C are complex constants dependent on temperature.) The calculated values of the fraction of primary radicals taking part in the termination reaction (assuming the neglect of the reaction (RS' + RS') grow with the increase of the concentration TMTD and temperature. The relatively high values of complex transfer constants Ci'‐(0.57–0.98) and the observed decrease of values of effective activation energies with an increasing concentration of TMTD are in accordance with the given reaction scheme. The observation of other sulfur compounds (zincdiethyldithiocarbamate, dibenzothiazolyldisulfide, dipentamethylenthiuramtetrasulfide, and N‐cyclohexyl‐2‐benz‐thiazylsulfenamide) showed that they had a considerably smaller influence on the polymerization of styrene than did TMTD.
Über Vernetzte Makromolekulare Stoffe mit Inhomogener Netzwerkdichte
Authors: Funke Werner 
Published: June 2010

AbstractVisual swelling characteristics of crosslinked polyester resins in good swelling agents lead one to suppose that in these resins the crosslinks are not equally distributed. When polyester resins are cured by heat without added peroxide, the maximum conversion and therefore also the maximum crosslink density have been shown to depend on the initial radical concentration in the reaction medium. After the gelling point the conversion could not be enhanced by increasing the polymerization temperature. Obviously the primary network, which arises at the gelling point, predetermines the structure of the fully cured resin. Because of the relatively high functionality of the polyester molecules, the large degree of polymerization of the arising copolymer chains and their predominantly alternating structure, growing chain radicals are rapidly attached to the network. It must be assumed that after the gelling point the polymerization proceeds mainly at certain centers, the final number and extent of which depend on the special conditions of the polymerization reaction. The change of the reactivity ratios of the monomers, normally to be observed at high conversions, is explained by the restricted mobility of the still‐unsaturated polyester chains. The conversion at which this restriction appears depends on the structure of the primary network. Under special conditions popcorn formation takes place during polymerization of polyester resins. These popcorn polymers may be considered as an extreme case of a network with an unequal distribution of crosslinks. The composition of these popcorn‐containing polyester resins indicates that their existence is due to the reduction of the mobility and reactivity of the polyester chains at a very low conversion.
New class of film‐forming electrically conducting polymers
Authors: Lupinski J. H. , Kopple K. D. , Hertz J. J. 
Published: June 2010

AbstractConducting polymers consisting of a polycation, 7,7,8,8‐tetracyanoquinodimethan anions (TCNQ−) and neutral TCNQ are described. Polycations employed were derived from poly‐4‐vinylpyridine, atactic and isotactic poly‐2‐vinylpyridine, poly‐N‐vinyl‐imidazole, polyethyleneimine, poly‐4‐dimethylaminostyrene, and a copolymer of 4‐vinyl‐pyridine and styrene. These materials have an unusual combination of properties, not reported before for organic semiconductors, in that they are of high molecular weight, are soluble in organic solvents, and have conductivity controllable over several orders of magnitude by varying their content of neutral TCNQ. The highest conductivity observed so far for these materials is 10−3 Ω−1 cm.−1. In the solid‐state conduction proceeds through an electronic mechanism.
Determination of critical points in multicomponent polymer solutions
Authors: Koningsveld R. , Staverman A. J. 
Published: June 2010

AbstractAs a rule, critical temperatures of liquid‐liquid phase separations in polymer solutions do not coincide with the maximum separation temperatures. It can be shown that the critical point is situated on the right‐hand branch of the cloud‐point curve, which is a quasibinary section of the multidimensional temperature–composition diagram. Determination of the exact position of the critical point is possible by measuring phase–volume ratios as a function of concentration at temperatures close to the cloud‐point. This is demonstrated by measurements on the systems polyethylene‐diphenyl ether and polystyrene‐cyclohexane. Determination of the critical circumstances appears to be a sensitive means of testing the relation for the free enthalpy of mixing.
The role of the homogenous and heterogeneous components of ziegler catalysts in the development of polymerization activity
Authors: Váradi J. , Czájlik I. , Baán A. , Chirkov N. M. , Tsvetkova V. I. 
Published: June 2010

AbstractThe eomposition and polymerization activity of a given catalyst system (TiCI4‐Et2AlCl) were determined. The solid particles formed by the reaction of the catalyst components were separated at two given times, which were characteristic of the polymerization kinetics. The polymerization activities of the catalyst precipitates were determined in the presence of Et2AlCl and other cocatalysts. It was established that the measured polymerization activities of the catalyst precipitates are higher in the initial system than in the presence of other cocatalysts. The composition of the liquid phase of the catalyst was studied and it was found to contain certain dissolved Ti compounds, the titanium content of which could be determined after hydrolysis as trivalent Ti. The concentration of this titanium compound depends on the solvent used. The polymerization kinetic studies provided evidence that the maximum polymerization rate, i.e., the process of polymerization as a whole, depends on the kind of the solvent used and thus on the quantity of dissolved titanium compounds in the liquid phase.
Intermolecular forces in the process of heat aggregation of globular proteins and the problem of correlation between aggregation and denaturation phenomena
Authors: Jaenicke R. 
Published: June 2010

AbstractThe heat aggregation of globular proteins depends on a coupled coagulation and exchange reaction which may be differentiated with respect to its relative proportions by specific inhibition of aggregation and by degradation analysis. In general, the coagulation by weak intermolecular forces exceeds the covalent exchange reaction (disulfide and lanthionine bonds). Decreasing net charge further diminishes the covalent aggregation and at the same time the rate of denaturation, so that under isoelectric conditions as the limiting case, the particles agglomerate with conservation of their native state. At high electrostatic potential denaturation is the precursor of aggregation. Inhibition of aggregation is produced by formaldehyde, weak protic solvents, ionic detergents, and urea, etc.; only formaldehyde seems to react without denaturation, leading to the conclusion that hydrogen bonds cause the coagulation of the native particles while aggregation by hydrophobic interactions presupposes (partial) denaturation. Ion‐pair bonds may participate in the aggregation at extreme pH values. As regards the tertiary and quaternary structure, one may conclude that in the native state polar groups must be situated in the periphery of the molecule while the nonpolar side chains cluster together in the center of the globular molecule. This result verifies Kendrew's principle of tertiary structure formation derived from solid‐state x‐ray analysis for the molecule in solution and is also compatible with the specific dissociation‐association phenomena observed in the case of the quaternary structure.
A review of the electrical properties of monomeric and polymeric charge‐transfer complexes
Authors: Labes M. M. 
Published: June 2010

AbstractThe electrical properties of a large number of monomeric charge‐transfer (CT) complexes have been studied; a range of 20 decades is observed in their conductivity. We have learned that there is a structurally related anisotropy of the conductivity, that powder measurements can be very misleading, and that the conductivity is high in CT complexes having a large radical‐ion component in the ground state. Further progress requires learning how to achieve purity and measure carrier mobility in single crystals, and attempts made thus far in these directions are reviewed. A major problem in achieving high conductivity in polymers is to increase chain‐chain interaction; CT complexing is an effective way of accomplishing this and a number of donor polymer‐monomeric acceptor systems have been examined. There has been very little work on carrier mobility. The emphasis in the future must be to achieve and study pure, well‐understood structures.
Crystal nucleation in polyethylene: The droplet experiment
Authors: Gornick F. , Ross G. S. , Frolen L. J. 
Published: June 2010

AbstractThe droplet technique was utilized to obtain estimates of the isothermal rate of homogeneous crystal nucleation in highly supercooled melts of unfractionated linear polyethylene. In a typical experiment a cell containing a suspension of several hundred micron‐size spherical droplets of the polymer was placed on a microscope hot stage and quenched from a temperature well above the melting point of polyethylene to the desired crystallization temperature. When viewed between crossed polarizers, the droplets were initially invisible but, upon freezing, they appeared as visible birefringent spheres. The time dependence of the process was followed by time‐lapse photography. Half times (T1/2) for the freezing of those droplets remaining unfrozen by the time the crystallization temperature was attained were thus obtained at a series of undercoolings and related to the desired nucleation rate constant I (nuclei cm.−1 sec.−1) by the equation I = In 2/T1/2/v, where v is the droplet volume. The temperature dependence of I, as obtained by the above procedure, was analyzed in accord with current theories of homogeneous nucleation of chain‐folded polymer crystals. From this analysis, an estimate, 14,960 ergs3 cm.−6 was made of the quantity (%sG2%sGe), where %sG and %sGe are, respectively, the lateral and end‐surface free energies of the crystal.
The effects of structural modifications on the critical properties of PBI fiber
Authors: Singleton R. W. , Noether H. D. , Tracy J. F. 
Published: June 2010

AbstractThe only improvement seen in increasing the molecular orientation of PBI fiber over that exhibited by presently defined target property material is the improvement seen in the strength and stiffness of the material at high strain rates. This improvement, however, cannot be extrapolated to a good impact performance. No advantage of fiber crystallization was detected in the properties measured in this evaluation conducted in accordance with the current state of the art of testing of high temperature fibers. However, as the testing of high temperature performance fibers becomes more sophisticated, advantages of crystallization undetectable in this investigation may appear. Should this occur, it would then be advisable to explore the crystallization of PBI further in an attempt to induce a higher degree of crystallinity than accomplished in this work while maintaining adequate tensile properties.
High‐strength, high‐modulus glass fibers
Authors: Lewis Albert , Robbins David L. 
Published: June 2010

AbstractThis paper describes work that was conducted to develop high‐strength, high‐modulus glass fibers. Statistical experimental design and data analysis were used to determine some of the sampling, testing, and fiberizing variables that affect the dispersion of mechanical property data of glass fiber specimens. The simplex lattice experimental design was used in glass compounding studies. The experimental method is described. Three glass compositions with high mechanical properties are described. One of these glasses is composed of MgOAl2O3SiO2. The other two are 4‐component glasses and contain MgOAl2O3SiO2 and BeO, or La2O3.
Translation of fiber properties into composites
Authors: Schwartz H. S. 
Published: June 2010

AbstractThe strength and modulus of elasticity of fiber‐reinforced plastic composites are a function of the strength, modulus, volume content, and directional orientation of the fibers used in the composites. Continuous fibers are generally preferable to noncontinuous fibers because the continuous types are easier to align, impregnate with resin, and fabricate into large structures by filament‐winding techniques. The principal function of the matrix in a composite is the transfer of loads between and among fibers. For plastic matrices both chemical adhesion of the matrix to the fibers and shrinkage of the matrix around the fibers are important factors in this load transfer. The structural efficiency of fibers in composites is usually determined by measuring mechanical properties of simple composite specimens containing known volume per cents of the fibers, and comparing the measured mechanical properties of the composites with those predicted analytically.
The relationship of fibers structure to diffusion of dyes
Authors: Sprague B. Sheldon 
Published: June 2010

AbstractA series of cellulose acetate yarns representing wide ranges of orientation and molecular aggregation were dyed with several disperse (non‐ionic) dyes at various temperatures, and the average diffusion coefficient of dye in fiber was determined. The activation energy for diffusion is determined, and the transition phenomena noted with cellulose acetate are discussed. The role of water and temperature in modifying fiber structure, as related to dye diffusion, is discussed, and dye diffusion is shown to be a most sensitive tool for the examination of small structural differences in fibers.
Fractionation of linear polyethylene with gel permeation chromatography. Part II
Authors: Nakajima Nobuyuki 
Published: June 2010

AbstractSeveral commercial samples of linear polyethylene were fractionated by gel permeation chromatorgraphy (GPC); they had four columns of maximum nominal capacity of 107 A. The molecular weight distribution thus obtained revealed delicate variations: none of the results could be perfectly represented by a log‐normal distribution. With selected samples the performances were compared among four GPC units, all having four columns. With columns of similar capacity satisfactory reproducibility could be achieved from different units, if sufficient care were taken in calibration and operation. The results with the two‐column unit were significantly different from those with the four‐column units. The difference in concentration of sample solutions appeared to be a part of the cause. The different elution times of two columns and four columns seemed also to have contributed. Among the four‐column units slightly variant results were obtained in the high molecular weight tail, when the maximum capacity of the column was different. Two solvents, o‐dichlorobenzene and 1,2,4‐trichlorobenzene, were used for this work. Solvent effects were found in neither GPC nor dilute‐solution viscosity.
Über synthetische Matrizenreaktionen
Authors: Kämmerer H. , Shukla J. , Oender N. , Scheuermann G. 
Published: June 2010

AbstractMolecularly homogeneous, polynuclear phenolic compounds were esterified with acrylic acid and methacrylic acid chlorides. The pcresyl esters of acrylic and methacrylic acid react in high dilution in boiling benzene with a large excess of radicals derived from AIBN in such manner that the growth step of the free‐radical polymerization is prevented; this may be denoted a “suppressed” polymerization. The application of these conditions to the previously mentioned poly‐nuclear esters results in the formation of molecularly homogeneous cyclooligomers (ladder oligomers). Alkaline hydrolysis of these oligomers permits recovery of the polynuclear phenols and yields molecularly homogeneous oligoacrylic acid and oligomethacrylic acid, the structures of which were proved by the preparation of a variety of ester derivatives. The presented reaction path seems to be a very simple model of the biosynthesis of proteins. Finally, evidence is presented for the consideration of this reaction sequence as a synthetic matrix reaction.