bluuebunny/crossref_metadata_2025_split huggingface dataset:
Kinetics of the reactions of thiourea with formaldehyde. Reactions in alkaline media
Authors: Dušek Karel 
Published: April 2003

AbstractThe kinetics of formation and dissociation of mono‐ and dimethylolthiourea were studied as well as the equilibria among the constituents in alkaline and neutral solutions. The polarographic determination of free formaldehyde and the determination of the reacting constituents by paper chromatography were used as analytical methods. A generally valid relation for equilibrium with a polyfunctional compound, to which formaldehyde is added, was derived and used to calculate both the equilibrium constants for the case of thiourea. The equilibrium constants found do not depend on pH. It was found from the temperature dependence of the equilibrium constant that the formation of monomethylolthiourea is an exothermal reaction. The possibility of formation of tri‐ and tetramethylolthiourea was discussed. Ways of simplifying the complex kinetic scheme were found which are suitable for calculation of the rate constants. The rate constants of formation and dissociation of mono‐ and dimethylolthiourea are directly proportional to the concentration of hydroxyl ions in the alkaline region and depend only slightly on the concentration of buffer. The reaction of thiourea with formaldehyde was found to be more rapid than the reaction of urea with formaldehyde in this region. By a graphical solution in which the known rate constants were used, the time dependence was found for the concentrations of all the constituents. The polarographic study of the reaction of thiourea with formaldehyde in strongly alkaline media of Chasanov and Lynch was discussed.
Alkaline polymerization of caprolactam. IV. Equilibrium and degradation with alkaline polymers of caprolactam
Authors: Králíček Jar. , Šebenda J. 
Published: April 2003

AbstractThe change in the intrinsic viscosity brought about by heating samples of alkalipolymerized polycaprolactam to 220–250°C. for extended periods has been investigated. The polymer samples were obtained by the catalytic action of the sodium salt of caprolactam. The experimental results shows that the intrinsic viscosity of the polymer decreases over the course of about 50 hours, but remains constant after this time. The equilibrium value of the intrinsic viscosity depends on the concentration of the catalyst and on the temperature. The viscosity drop at the beginning of the period of heating is due to the change of the original very unstable broad molecular weight distribution to the equilibrium distribution. Only basic groups, but no carboxyl groups, were detected. The concentration of basic groups remains constant, within the limits of experimental error, over the period required to reach the final value of the intrinsic viscosity.
Synthesis of some new esters and ethers of cellulose and examination of their properties
Authors: Rogovin Z. A. 
Published: April 2003

AbstractA new method has been devised for the synthesis of normal esters of cellulose and carbonic acid by reaction of cellulose alcoholate and methyl chlorocarbonate:
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A normal ester of cellulose with monothiocarbonic acid has been prepared analogously as follows:
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A disulfide has been prepared by oxidation of the sodium salt of the thioester with iodine:
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A comparison was made of the stabilities toward various reagents of cellulose esters of carbonic, normal thiocarbonic, and dithiocarbonic acid and also of the acid and neutral esters of cellulose and monothiocarbonic acid. It was found that the stabilities of the esters toward acids and bases as well as to light and heat very considerably with the nature of the acid grouping introduced. A method has been worked out for the synthesis of phenyl esters of cellulose by the reaction of sodium phenoxide with p‐toluenesulfonylesters of cellulose:

A phenyl ester of cellulose (γ = 70–80) has been prepared and its properties investigated. It was shown that by this procedure the phenyl group is introduced into position 6.
Über den mechanochemischen abbau von zellstoff durch schwingmahlung
Authors: Grohn H. 
Published: April 2003

Abstract1. Geschwindigkeit und Grad des mechanochemischen Abbaus von wasserhaltigem Sulfitzellstoff sind von den mechanischen Bedingungen der Schwingmahlung abhängig. Nach einer Mahldauer von 900 Stunden wurde ein DP‐Wert von 11 (Viskositätszahl) bzw. 7 (Reduktionsvermögen) erreicht. 2. Der lineare Anstieg der Cu‐Zahlen mit dem viskosimetrisch ermittelten Spaltungsgrad berechtigt zu dem Schluss, dass der mechanische Abbau von wasserhaltigem Zellstoff im wesentlichen als mechanisch aktivierte Hydrolyse verläuft. 3. Die Wasserlöslichkeit der Mahlprodukte steigt mit fallendem DP erst langsam, dann schnell bis auf etwa 90% an. Demnach erfolgt die mechanische Bindungsspaltung nicht von den Ketteneden her, sondern vorzugsweise zwischen mittleren Kettengliedern. 4. Die bisher unbeachtet gebliebene grosse Wasserlöslichkeit mechanisch abgebauter Zellulose erklärt ihre gute Rekristallisierbarkeit. Nur der wasserunlösliche Anteil, der von dem Abbau den höchsten Kristallinitätsgrad besass, wird nach dem Herauslösen aller aus den weniger orientierten Anteilen enstandenen niedermolekularen Abbauprodukte rekristallisiert.
Dielectric studies of the methacrylate series. III. Poly‐n‐hexyl methacrylate. IV. Poly‐n‐octyl methacrylate
Authors: Strella S. , Chinai S. N. 
Published: April 2003

AbstractThe complex dielectric constant of a pure molecular weight fraction of poly‐n‐hexyl methacrylate and of poly‐n‐octyl methacrylate was determined over a frequency range of 30 to 3 × 105 cycles/sec. and a temperature range of −66 to 106°C. and −61 to 81°C., respectively. The data indicate the presence of two transition regions, with the transitions being further apart with increasing side chain length. Examination of the data showed that superposition was not possible using the usual superposition schemes.
On the reversibility of the acid denaturation of sodium desoxyribose nucleate
Authors: Geiduschek E. Peter 
Published: April 2003

AbstractThe current disagreement as to whether the acid denaturation of DNA produces reversible or irreversible changes of macromolecular configuration can be resolved by paying proper attention to the temperature dependence of the denaturation process. Light scattering measurements have been made on a sample of sodium desoxyribosenucleate taken to pH 2.6 and reneutralized at 0 and 25°C. in 0.1 M NaCl. Whereas the material, acid treated at 25°C., is irreversibly collapsed (radius of gyration = 1370 A., molecular weight unchanged), 0°C. titration leaves the size of the DNA molecule unchanged (ρ = 2800 A.). Viscosity measurements at 0°C. and pH 2.6 show that at this pH the DNA is nearly as fully extended as in neutral solution ([η] = 40 dl./g. compared to 63 dl./g. in neutral aqueous salt solution). However, collapse occurs at pH 2.6 between 0 and 25°C., and this thermal denaturation at pH 2.6 is irreversible. The light scattering properties of acid‐denatured DNA are interpreted in terms of a more heterogeneous distribution of macromolecular configurations than in the native material.
Peroxide crosslinked carbon black polyethylene compositions
Authors: Dannenberg Eli M. , Jordan Merrill E. , Cole Harvey M. 
Published: April 2003

AbstractPolyethylene containing large quantities of carbon black can be crosslinked by a chemical free radical mechanism utilizing the thermal decomposition of dicumyl peroxide as the source of free radicals. Crosslinking in the presence of different types of blacks was studied in a liquid paraffin model system. The information obtained from this study provides a logical basis for speculation on the mechanism of crosslinking of carbon‐black‐loaded polyethylene compositions. Evidence is presented that the grade of carbon black is an important factor and that the course of the peroxide decomposition is largely determined by the chemical nature of the carbon surface. Carbon blacks having a highly oxygenated surface cause an ionic decomposition which is not effective for crosslinking, while those of low oxygen content allow the decomposition to follow a free radical mechanism which results in the crosslinking of polyethylene. Marked changes in the physical characteristics of the polymer are brought about as a result of pigmentation and subsequent crosslinking. Such compositions display a surprising degree of flexibility and strength over a wide range of temperatures. Moreover, significant strength is observed at temperatures above the crystalline melting point of the polymer. These improved properties are attributed to the reinforcing ability of the carbon black and the crosslinked network of polymer chains.
Structure and photochemical behavior of nucleic acids and related components
Authors: Shugar D. , Wierzchowski K. L. 
Published: April 2003

AbstractA study has been made of the photochemical behavior at 2537 A. of the following substances: 2′‐, 3′‐, 5′‐, and cyclic 2′:3′‐cytidylic acids and various preparations of apurinic, ribonucleic, and deaminated ribonucleic acids. The behavior of all the cytidylic acids is qualitatively similar, the photoproduct exhibiting a new maximum at 2360 A. The reaction can be reversed completely in the dark by heating, acidification, or addition of alkai. The 5′‐cytidylic acid differs quanlitatively from the other cytidylic acids in that the quantum yield is lower, as is also the extinction of the new maximum. These results are in agreement with previous findings and support the suggestion that there is hydrogen bonding in cytosine nucleosides and nucleotides between the pyrimidine 2‐carbonyl and the 5′‐sugar hydroxyl which influences the photochemical reaction. The results indicate also the possible existence of weaker bonds involving the 2′‐ and 3′‐hydroxyls. The irradiation of apurinic and ribonucleic acids is accompanied by a decrease in extinction of the principal absorption maximum and very little change below 2400 A. If the decrease of the principal absorption maximum does not exceed 50% as a result of photolysis, then it is subsequently possible to restore about 50% of this decrease by heating a few minutes at 70–90°C. The quantum yield for photolysis of apurinic acid is of the same order of magnitude as for 2′‐ and 3′‐cytidine nucleotides; for ribonucleic acid it is lower. For deaminated ribonucleic acid, the reaction is not reversible. The photochemical behavior of nucleic acids is discussed from the point of view of the photochemistry of uracil and cytosine nucleotides, as well as the relation of the results to the phenomenon of photoreactivation.
The orientation of the crystalline and amorphous regions in polyethylene film
Authors: Holmes D. R. , Palmer R. P. 
Published: April 2003

AbstractThe orientation in the crystalline and amorphous regions of a series of polyethylene films prepared by the tubular films extrusion process has been studied by a combination of x‐ray diffraction and optical methods. All of these films show a relaxation orientation differing both from the fully relaxed type of orientation previously proposed by the authors, and from the more complicated type of orientation suggested by Keller. In all films there is cylindrical symmetry about the machine direction and the b‐axes of the crystallites are preferentially oriented in the plane perpendicular to this direction. The preferred directions of the a and c crystallite axes depend both on the extrusion conditions and on the nature of the polymer; at low blow‐up ratios and high haul of speeds the c axes tend to lie more nearly parallel to the machine direction, but as the blow‐up ratios is increased and the haul‐off speed decreased rotation of the crystallites about their b axes occurs, and eventually the a axes tend to lie more nearly parallel to the machine direction. Both the preferred crystallite orientation and its angular distribution have been measured for a large number of films made from various ethylene polymers, and a linear relation between a function of the orientation angle and the optical birefringence has been established. As the c axes tilt away from the machine direction towards the plane perpendicular to this direction the birefringence steadily decreases, and eventually becomes negative. An expression is given for the birefringence of such a cylindrically symmetrical array of crystallites tilted to various angles, and is used to predict the orientation at which the crystallite birefringence contribution will be zero and also the extreme values of the crystalline birefringence contribution in the fully drawn and fully relaxed conditions. By comparing the theoretical and experimental relations between crystallite orientation and birefringence, it has been deduced that in these films the amorphous material appears to provide a nearly constant small positive contribution to the birefringence irrespective of the birefringence contribution of the crystallite regions; this means that in the negatively birefringent films some of the molecules in the amorphous regions are crossed with respect to those in the crystalline regions. When allowance is made for this amorphous contribution, crystallinities calculated from the extrapolated observed and theoretical extreme values of the birefringence are in reasonable agreement with the x‐ray measured crystallinity of 45%. The mechanism resulting in the formation of this unusual orientation is considered in reference to the manufacturing process.
Stabilization of viscose rayon by heat treatment
Authors: Kanamaru Kisou , Tokita Noboru , Noyama Susumu 
Published: April 2003

AbstractViscose fibers preswollen by treatment with very dilute sulfuric acid solutions of various concentrations (pH 2.4–5.1) were heat treated at various temperatures (60–200°C.). The effects of the heat treatment were considered from the measurements of: (1) The transition modulus of elasticity and other constants of a three‐parameter model for viscoelasticity, as well as the dynamic modulus of elasticity. (2) The breaking strength as well as elongation. (3) The percentage crystallinity. (4) The amount of water absorbed. Thus it was concluded that the effects of heat treatments of stabilizing viscose rayon, as exhibited by the above‐mentioned properties of the fibers, make their most prominent appearance in the range of pH optimal for the maximal hydration of regenerated cellulose, that is, pH = 3.0–5.0 of the acid bath, in which the fibers are soaked and swollen, and in the range of the temperature for the heat treatment near, or just above, the glass transition temperature of cellulose hydrate, i.e., at 60–70°C. where the acid‐bath‐treated fibers are heat treated. From the results of these measurements and also from the characteristic features of x‐ray diagrams qualitatively observed, it was considered that the heat treatment affects mainly the more disordered (amorphous) regions so that the more ordered regions are newly developed at the expense of the former.
Electrophoresis of polyelectrolyte in salt solutions
Authors: Nagasawa Mitsuru , Soda Atsuhiko , Kagawa Ikumi 
Published: April 2003

AbstractSome measurements of the electrophoretic velocity were carried out on sodium polyvinyl alcohol sulfates. The intrinsic mobility of the polyion in sodium chloride solutions was obtained by extrapolating the values at various polymer concentrations. The extrapolating value at the zero polymer concentration was the same for both descending and ascending boundaries. The mobility of polyion vs. sodium chloride concentration curve thus obtained showed the following features. (a) At zero NaCl concentration the mobility of polyion quite agrees with the mobility of the monomer acid. (b) In the limit of sufficiently concentrated NaCl solution, the mobility also approaches the mobility of the monomer acid. (c) In the intermediate state between these two limits, measured mobilities of polyion are always larger than the mobility of the monomer acid. Accordingly, there is a maximum of the mobility at a certain NaCl concentration. These experimental results were analyzed in terms of the theory of Hermans and Fujita on the electrophoresis of coiled polyelectrolyte, and it was found that their theory gives a satisfactory (at least qualitatively) explanation of our experimental data.
Fractionation of polyethylene
Authors: Francis P. S. , Cooke R. C. , Elliott J. H. 
Published: April 2003

AbstractThe relatively rapid Desreux technique for polymer fractionation has been modified and applied to both linear and highly branched polyethylenes. The polymer is precipitated from p‐xylene solution onto a sand column by cooling from 127° to room temperature. After removal of solvent, the column temperature is again raised to 127° and fractions are eluted, using p‐xylene‐ethylene glycol monoethyl ether mixtures of increasing solvent power. Approximately 15 fractions are obtained and polymer recovery is essentially quantitative. The reproducibility of the integral distribution curves is within ±2% for a cumulative weight‐% of 85 or higher. In certain cases difficulty has been encountered in resolving the less soluble portion of the sample. The selective nature of the system is indicated by the fact that the reduced specific viscosities of the highest and lowest molecular weight fractions are generally in the ratio of 50 or higher.
Rupture of rubber. V. Cut growth in natural rubber vulcanizates
Authors: Thomas A. G. 
Published: April 2003

AbstractCut growth in natural rubber gum vulcanizates has been studied using both steady and repeated loading. The results have been expressed in terms of the concept of the energy for tearing that has been put forward previously. With cut growth under repeated loading the tip, initially smooth, becomes rough and the rate of growth simultaneously decreases markedly to a final steady value. Some consequences of this roughening have been discussed. Measurements of cut growth under repeated loading have also been made using two different types of test piece. A rupture criterion, which has been previously proposed, predicts a definite relationship between the behavior of the two test pieces, and this has been confirmed experimentally.
Structure of drawn polyethylene terephthalate
Authors: Dulmage W. J. , Geddes A. L. 
Published: April 2003

AbstractMeasurements of birefringence, infrared dichrosim, and x‐ray diffraction have been made on crystallized and uncrystallized polyethylene terephthalate films stretched up to 500%. The results show that, at high elongations, stretching induces high linear orientation of the chain molecules parallel to the direction of stretch. In the uncrystallized samples, a biaxial orientation in which the plane of the molecules tends to be parallel to the plane of the film can be detected in the x‐ray diffraction patterns and from the birefringence measurements. This higher orientation, as well as the usual linear orientation, is enhanced by crystallization, owing to directional crystal growth on oriented crystal nuclei which develop during the stretching operation. At low extension, pronounced tipping of the crystalline regions occurs during crystallization. As a result, the preferred direction for the fiber axis of the crystallites varies from a direction approximately perpendicular to the direction of stretch at low extension, to a direction almost parallel to the direction of stretch at the highest extensions.
Infrared spectra of high polymers. VII. Polyacrylonitrile
Authors: Liang C. Y. , Krimm S. 
Published: April 2003

AbstractThe infrared spectrum of polyacrylonitrile has been obtained in the extended region of 70 to 3200 cm.−1 Polarized measurements were made on stretched and rolled specimens in the range of 350 to 3200 cm.−1. An analysis of the spectrum has been made on the basis of an atactic chain configuration, and has been shown to be in agreement with the observed data. Detailed assignments are proposed for all of the absorption bands in the spectrum, being aided by previous studies of high polymer spectra and by approximate normal frequency calculations for the nitrile group.
Copolymers of vinyl alcohol and vinyl stearate
Authors: Jordan Edmund F. , Palm William E. , Swern Daniel , Witnauer Lee P. , Port William S. 
Published: April 2003

AbstractCopolymers of vinyl formate containing various amounts of vinyl stearate were prepared by mass polymerization at 30°C. in the presence of small amounts of isopropanol. A study of the molecular weights and the viscosity properties of these copolymers indicated that they have high degrees of polymerization and are little branched. A study of the x‐ray diffraction patterns of the copolymers of vinyl alcohol and vinyl stearate indicated that the alcohol and stearate segments crystallize in separate lattices. The tensile strength of vinyl alcohol copolymers decreased as the vinyl stearate content increased and as their water content increased. When the samples were dried or were oriented, their tensile strengths increased. Copolymers of vinyl alcohol containing as little as 1.5 mole‐% of vinyl stearate had greatly improved resistance to water and were insoluble in water at 98°C.
Deformation of networks by detachment and formation of crosslinks
Authors: Oosawa Fumio 
Published: April 2003

AbstractThis paper is concerned with problems relating to dimensional changes in networks of long chain polymers caused by detachment and formation of crosslinks. Particular attention is paid to the dependency of the dimensional change caused by detachment of crosslink on the conditions at which the crosslinks were formed. A network having crosslinks formed under a given tension is elongated by detachment of these crosslinks under a tension higher than that at crosslink formation and is contracted by detachment under a lower tension. Similar results are obtained for the deformation caused by detachment of crosslinks formed under shear stress. The increment of configurational entropy produced by detaching a crosslink depends on both the state of the network at the time of crosslink formation and the state at which the crosslink is detached. In a network having many crosslinks formed in various states of deformation, when the attractive energy between polymers forming linkages is gradually decreased under a constant tension, the crosslinks are detached successively, and it can be expected that the network first contracts and then elongates. In swollen networks, the detachment of crosslinks always brings about the extension of volume, and the critical tension at which the deformation in the direction of tension caused by the detachment is changed from elongation to contraction is increased with decreasing number of crosslinks remaining. While, in networks containing no solvents, the formation of crosslinks does not produce any deformation directly, formation of crosslinks in swollen networks can produce contraction directly. By assuming that polymer chains with a given degree of orientation are distributed densely and uniformly in networks at the moment of crosslink formation, we obtain these results. The validity of this assumption is briefly examined. The theoretical results obtained in this paper are found to be useful for analyzing the behavior of living muscle and muscle models in various stages.