bluuebunny/crossref_metadata_2025_split huggingface dataset:
Preparation and water absorptive capacity of sodium cellulose carboxylate
Authors: Godsay M. P. , Gupta V. N. , Lafond R. L. , Macdonald D. M. 
Published: June 2010

AbstractSodium cellulose carboxylate was prepared by oxidation of cellulose with gaseous nitrogen dioxide followed by treatment with buffer at pH 7.0. The oxidation reaction rate increased with higher initial gas flow rates, higher total weights of nitrogen dioxide and with nitrogen dioxide pressures higher than 1 atmosphere. Moisture acts as a weak catalyst but is also responsible for loss of nitrogen dioxide by formation of nitrogen acids. Sodium cellulose carboxylate absorbs much more water than cellulose. It is formed without loss of fibrous character or gel formation and with high water absorptivity only if an efficient buffer is used at pH 6.5 to 7.0. Higher pH levels lead to gel formation; lower pH levels lead to impaired absorptivity. Salt formation rate appears to be a diffusion controlled process which is highly sensitive to localized depletion of buffer solution. Use of NaOH in place of buffer does not give the highly absorbent salt. Gelation occurs instead. The diameter of 6‐carboxy cellulose fibers prepared from softwood pulp increases about 90% during the pH 7.0 buffer treatment.
A proposed new mechanism for catalyzed and uncatalyzed graft polymerization onto cellulose
Authors: Gaylord Norman 
Published: June 2010

AbstractGraft copolymerization of polar vinyl monomers onto cellulose in the presence of oxidizing agents, ceric ion, and radiation has been presumed to be solely the result of propagation from radical sites generated on the cellulose. The uncatalyzed polymerization and graft copolymerization of methyl methacrylate in the presence of cellulose and water has been presumed to involve the formation of a cellulose‐water‐monomer complex with the resultant generation of a covalently bonded monomer radical which then propagates in the usual manner. The formation of grafted alternating copolymer from the radiation induced polymerization of styrene‐acrylonitrile and butadiene‐acrylonitrile, the radical catalyzed polymerization of styrene‐methyl methacrylate and styrene‐acrylonitrile‐ZnCl2 as well as the uncatalyzed polymerization of butadiene‐methyl methacrylate in the presence of cellulose and water indicates the participation of comonomer charge transfer complexes in the graft copolymerization. It is proposed that cellulose acts as a complexing agent for the activation of acceptor monomers and as a matrix for the alignment of acceptor monomer complexes (A*−A‐cellulose‐water) and donor‐acceptor comonomer complexes (D+−A‐cellulose‐water). Polymerization of the complexes is initiated spontaneously or by radicals generated on the cellulose although the latter do not become incorporated into the polymer chain. Graft copolymerization results from termination of the growing polymer chains on cellulose by insertion into aldehyde groups.
Graft copolymerization to cellulose by mutual irradiation
Authors: Guthrie J. T. , Huglin M. B. , Phillips G. O. 
Published: June 2010

AbstractThe mutual irradiation technique in vacuo has been used to study the grafting (G) of styrene to regenerated cellulose film in a dioxan/water medium and the simultaneous homopolymerization (H). The initial rates RG and RH are both found to be directly proportional to the concentration of styrene, but the ratio of the rate constants kP2/kt is ca. 105 times greater in grafting than in homopolymerization (58 cf. 3.3 × 10−4 1. mole−1 sec−1). Bimolecular termination is indicated in both cases by the observed dependences of RG and RH on (intensity)0.5. The degrees of grafting utilized to determine RG were shown to be apparent values only, since extraction of ungrafted cellulose yielded products in which the true degrees of grafting were all some ten times greater.From ESR spectra of cellulose irradiated in air a value of 1.6 was derived for G (radical) and there was some evidence of scission. Corresponding spectra of cellulose irradiated in vacuo gave G(radical) = 2.9, but no evidence of scission. The radical, formed by hydrogen abstraction, was shown to be located at the C1 atom. However, evidence for scission in cellulose irradiated (in the presence of dioxan/water) in vacuo and in air was provided by measurements of intrinsic viscosity, values of 13.5 and 24.6, respectively being derived for G(scission).
Morphology and kinetics of growth of supermolecular structures in molten polyoxymethylene and mixtures with other substances
Authors: Mihajlov M. , Nedkov E. 
Published: June 2010

AbstractThe results of an investigation of the morphological changes and kinetics of supermolecular structure growth in a thin film of supercooled melt of polyoxymethylene diacetate under the influence of small amounts of organic low molecular, oligomeric, and polymeric compounds and their mixtures have been summarized. A relationship has been found between morphology and kinetics of the supermolecular structure growth and their dependence on the crystallization temperature, chemical structure, and admixture concentration. A possible model of the formation and growth of the supermolecular structures and the influence of the admixtures is presented.
Formation of supermolecular structures of semicrystalline polymers under molecular orientation
Authors: Baranov V. G. , Frenkel' S. Ya. , Gromov V. I. , Volkov T. I. , Zurabian R. S. 
Published: June 2010

AbstractThe effect of stretching on the process of structure formation in fiber spinning and film extrusion and in isothermal crystallization of crosslinked polyethylene has been investigated. It has been shown that the stretching forces (jet stretching) in these systems cause the formation of spherulites flattened with respect to the stretching direction. As a rule, the spherulite radius decreases while the degree of flattening increases with the jet stretching. Thermodynamic analysis of the kinetics and morphology of the spherulite growth during stretching enabled us to interpret these effects and to establish relationships connecting the degree of flattening of the spherulites with the characteristics of molecular orientation in the melt. Taking into account the changes in the conformational entropy of the deformed macromolecule (or the network) in the course of nucleation and crystal the deformed macromolecule (or the network) in the course of nucleation and crystal growth it is possible to explain not only the effect of the spherulite flattening but also the formation of tilted crystals and other peculiarities of crystallization taking place with the occurrence of molecular orientation. A general picture is given of the effect of a mechanical field on the morphology of the crystallizing polymers at various degrees of stretching.
Pore size distribution in swollen macroporous cation exchangers determined from electrolyte uptake and by electron microscopy
Authors: Krska F. , Dusek K. 
Published: June 2010

AbstractThe dependence of the equilibrium electrolyte uptake by macroporous styrene‐divinylbenzene cation exchangers on the external concentration of electrolyte has been studied and distribution functions for the concentration of counterions (exchange groups) in the resin have been calculated using deviations from the Donnan law. The distribution functions for macroporous resins have two maxima: a narrow maximum at higher concentrations of the exchange groups is characteristic of the gel phase, and its position is the same for different cation exchangers; the maximum at low concentrations of the exchange groups corresponds to the macropores, and its position and shape depend on the manner of preparation of the resin. On the assumption of alamellar shape of the pores, the distribution of the macropore sizes has been calculated and compared with the distribution obtained by electron microscopy in dry and swollen states. For cation exchangers with pores not too large, the agreement was quite good; however, the exclusion of the electrolyte in large pores is already negligible, so that the uptake method cannot detect pores of large sizes (> 2000 Å).
Change of spherulitic structure in melt‐crystallized polymer fibers and films during uniaxial stretching
Authors: Bezruk L. I. , Lipatov Yu. S. 
Published: June 2010

AbstractAs revealed by electron‐microscopic studies, the morphology of melt‐crystallized polymer films and fibers subjected to the ultimate degree of orientation, is characterized by layer‐like organization of lamellar crystals (paracrystalline structure). If the direction of the long axes of the macromolecules in crystallites coincides with the texture axis, the morphological orientation of paracrystalline layers is orthogonal to the stretching direction. Partial transformation of a spherulite into a “microneck” can lead to flattening of spherulites.
The influence of morphology on submicrocrack formation in oriented crystalline polymers
Authors: Kuksenko V. S. , Gezalov M. A. , Slutsker A. I. , Yastrebinsky A. A. , Zakrevsky V. A. 
Published: June 2010

AbstractThe supermolecular structure of oriented crystalline polymers and the submicrocracks created in them under mechanical loading were studied by small‐angle x‐ray diffraction.Most of these polymers consist of fibril‐like formations disposed along the polymer orientation axis, and ranging in thickness from tens to hundreds of angstroms. Crystalline and amorphous regions alternate along the fibrils with periods of hundreds of angstroms. Amorphous regions are mechanically weak. The weakest amorphous regions are torn under loading along the axis of orientation, and submicrocracks are formed. Interlayer rupture occurs by a chain mechanism of successive decomposition of stressed molecules. This process is initiated by free radicals formed at primary thermofluctuation ruptures of macromolecules and is terminated on the amorphous interlayer boundaries. Submicrocracks have the form of disks with transverse dimensions which practically coincide with the fibril thickness. Thus the specific morphology of an oriented crystalline polymer determines the course of development of the fracture from the initial stage.
Chemical potential of KCI and its ion constituents in concentrated protein salt solutions
Authors: Pfister H. , Pauly H. 
Published: June 2010

AbstractIn order to obtain information about the thermodynamic state of simple salts in living cells we measured the mean activity coefficients of KCl and the “apparent” single ion activity coefficients of K+ and Cl‐ in concentrated bovine serum albumin‐KCl solutions and bovine hemoglobin‐KCl solutions and in water soluble fractions of the cytoplasm of calf liver cells, using the EMF method with ion‐exchange membrane electrodes. The protein concentration range extended up to 45% by weight with neutral salt concentration of about 0.1 mole/kg H2O. The pH value varied from 3.5 to 9.8.Allowing for the effect of site binding and for nonsolvent water, the results show that the “electrostatic” mean activity coefficient of KCl decreases linearly with the equivalent concentration of the polyions. The effect is small, since, in a 0.1 M KCl solution with 20% protein, the activity coefficient of KCl is only 10 to 20% lower than in the pure 0.1M KCl solution.The meaning of the measured “apparent” single ion activity coefficients is discussed briefly. The results are compared with the predictions of the Marcus‐Katchalsky‐Alexandrowicz theory and of the Oosawa theory.
Solution behavior of homopolymers and random copolymers of l‐methionine and s‐ethyl‐l‐cysteine
Authors: Fougnot Christine , Jozefonvicz Jacqueline 
Published: June 2010

AbstractSynthesis and conformational studies of polypeptide homopolymers and random copolymers of L‐methionine and S‐ethyl‐L‐cysteine are reported. Syntheses were carried out by sodium methoxide initiation of the N‐carboxyanhydrides of the α‐amino‐acids dissolved in nitrobenzene. The polymers were studied in solution by classical techniques: optical rotatory dispersion, viscometry, light scattering, and spectrophotometry. The effect of the solvent composition on the helix‐random coil transition for poly (L‐methionine) indicates that this polypeptide is still about 60% helical in pure dichloroacetic acid (DCA). Similar behavior of random copolymers containing 60% or more of L‐methionine is observed. The infrared spectra indicate the “β‐structure” of poly (S‐ethyl‐L‐cysteine) and random copolymers rich in S‐ethyl‐L‐cysteine. The influence of solvent composition on the conformational behavior of these polymers is slight. Weight‐average molecular weight and radius of gyration have been determined in pure DCA. In the case of poly (L‐methionine) the experimental observations agree with the interrupted‐helix model.
Fluorimetric investigations of interactions with macromolecules in solution
Authors: Killmann Erwin , Bittler Rolf 
Published: June 2010

AbstractBlancophor dyes show a considerable increase in fluorescence yield upon adsorption onto poly(vinyl pyrrolidone). A fluorometric method was used for the quantitative determination of adsorption in polymer‐dye solutions. The adsorption isotherms differ from Langmuir adsorption behavior, and an adsorption isotherm is derived by taking into account the electrostatic repulsion potential of the adsorbed Blancophor ions. Adding foreign electrolytes causes a decrease in the electrostatic potential, which is independent of the species of salt, and is characterized by the Debye‐Hückel shielding parameter. The macromolecule with adsorbed ions represents a good model for a polyelectrolyte having the capability of altering or readjusting its charge density. Macromolecular sizes measured by various methods are related to the effective potential on the surface of the macromolecule. The expansion of the poly(vinyl pyrrolidone) molecule caused by the electrostatic repulsion of the adsorbed Blancophor ions was investigated by viscosity and light‐scattering measurements. Relationships among charge on the macromolecule and screening by added salt ions, on the one hand, and the molecular weight, the end‐to‐end distance, and the second virial coefficient, on the other hand were found and interpreted.
NMR relaxation and solvation equilibrium in the ternary system CCl4‐polymethylmethacrylate‐benzene
Authors: Lütje Hans 
Published: June 2010

AbstractIn the ternary system CCl4‐PMMA‐benzene, benzene is preferentially adsorbed in the solvation shell of the polymer. One solvation equilibrium constant allows a satisfactory description of the preferential solvation for a large range of solvent compositions. The nuclear magnetic relaxation time T1 of benzene protons was measured for different values of the polymer concentration. The measurements are compared with analogous measurements in the system C6D6‐PMMA‐C6H6 where no preferential solvation is to be expected. For the system CCl4‐PMMA‐benzene the resulting dimensionless solvation equilibrium constant is K = c32c10/c12c30 = 2.5 ± 0.5 where c10 is the CCl4 concentration in the “free” solvent; c30 is the benzene concentration in the free solvent; c12 and c32 are the concentrations of CCl4 and benzene in contact with the polymer chain, respectively.
Composite protostructures: An exercise in model building
Authors: Hahn C. W. 
Published: June 2010

AbstractOne of the most evident characteristics of life, at the subcellular, macroscopic level, is the phenomenon of structure, i.e., the anisotropic organization of matter and processes in space and in time. However, if we know a good deal about the (macroscopically isotropic aspects of the) chemistry of life, our understanding of structure (as defined above) does not go very far beyond what is known about the configuration and conformation of single (macro)molecules, or of finite or infinite symmetrical assemblies of (macro)molecules, and about changes in configuration, conformation, or spatial arrangement of these units – changes to which stereospecific intramolecular and intermolecular interactions can be assigned as causes. As to other macroscopic structures (on a scale comprised between the dimensions of single macromolecules and those of cells), the belief seems to prevail that the principles governing these are of the same kind as the principles governing the former: that “stereospecific intrinsic molecular determinisms” unambiguously determine every kind of biological structure.In this article, attention is drawn to other macroscopic mechanisms for the organization of matter and processes, mechanisms which are known in classical polymer chemistry under the topics of microphase separation and phase inversion, which are phenomena proper to the macroscopic level of size, not necessarily predictable from, or reducible to, stereospecific molecular determinisms. An attempt is made, at the level of hypothesis and speculative model building, to investigate the possible significance of these phenomena for biological organization.
EPR‐untersuchungen des radikal‐ und molekularzerfalls von hydroperoxyden unter einfluss von zink dialkyl dithiophosphatinhibitoren
Authors: Kateva J. , Ivanov S. 
Published: June 2010

AbstractThe decomposition of the cumene, tetralin, and t‐butylhydroperoxides in the presence of zinc diisopropyl dithiophosphate and of radical‐type inhibitors has been studied. A poisoning of the catalyst and a further change into an inactive form has been found. This leads to an inhibition of the overall decomposition rate of the hydroperoxides. It is suggested that the accumulation of RO* radicals arising from the thermal decomposition of the hydroperoxides reactivates the inactive catalyst. Based on the consumption of phenyl‐β‐naphtylamine and the stable 2,2,6,6‐tetrametylpiperidinoxyl radical, a homolytic decomposition of the hydroperoxides has been shown to take place. The rate of decomposition of the hydroperoxides to free radicals is 103 times slower than that leading to molecular products.
Inhibition of cumene oxidation by polyarylenes
Authors: Ivanov A. A. , Berlin A. A. 
Published: June 2010

AbstractThe kinetics of the initiated cumene oxidation at 60°C in the presence of polyarylenes (polyanthracene (PA), polynaphthalene (PN), copolymers of benzene with anthracene (AB), and naphthalene (NB) has been investigated. The initial oxidation rate dependence upon the initial concentration of inhibitor has been described by the equation obtained for inhibition mechanism which defines the radical attaching to a molecule of inhibitor as the rate limiting step of the reaction, rather than the reversible complex formation. Radical reactivity of polyarylenes increases in the order NB < PN < PA < AB, that is, it is consistent with the increase of reactivity of repeating units of polymer molecules. Reactivity of PA (calculated per repeating unit) is unaffected by the increase of molecular weight. The total quantity of radicals consumed by one molecule of inhibitor is calculated to be equal to 0.29; 1.4; 7.6 and 11 for NB, PN, PA, and AB, respectively. The most active centers in the reaction of inhibition are shown to be paramagnetic centers. Conjugation degree in polyarylene molecules diminishes during the course of the reaction. The main products of PA transformation are PA molecules having 1,4‐anthraquinone units.
The reactivity of antioxidants with peroxy and alkoxy radicals in the presence of transition metals. II. Radical processes in multicomponent antioxidant systems
Authors: Tkáč A. , Omelka L. 
Published: June 2010

AbstractIn nonpolar solvents the mechanism of bimolecular substitution reactions between t‐butyl‐peroxy and t‐butoxy radicals with different phenols and diarylamines was quantitatively studied by means of electron paramagnetic resonance (EPR) spectroscopy in the temperature range of +70 to −140°C. The selective reactivity, in the ligand field, of cobalt complex‐bonded radicals [Co] BuO2, [Co] BuO., and the free continuously generated noncomplex‐bonded BuO2 and BuO radicals to antioxidants are compared. The antioxidant ArH forms with cobalt (II)‐acetylacetonate a complex [Co(acac)2]2 [Arh]n = 1‐4 and prevents the subsequent reactions of the primarily generated RO. radicals with the transition metal (RO. + Co(II) → RO′ + Co(III)) and with the excess of hydroperoxides (RO. + ROOH → ROH + RO2). The concentration and the ratio of RO. and RO.2 radicals in a chain oxidation process in the presence of phenyl β‐ or α‐napthylamine (Ar1HNAr2) can be determined from the different EPR spectra of fixed [Co] [Ar1 NAr2]. and free stable nitroxy (Ar1HNAr2) radicals.
Antioxidants and stabilizers. XXXIX. GPC analyses of the additives for polyolefins and pvc used as food wrappings
Authors: Protivová J. , Pospíšil J. , Zikmund L. 
Published: June 2010

AbstractGel permeation chromatography (GPC) method, either alone or in combination with thin‐layer chromatography (TLC) or PC, has been used for determining the number of mononuclear and binuclear phenolic antioxidants used for the stabilization of polyethylene, and of some organophosphites and organotin compounds suitable for the stabilization of poly(vinyl chloride) (PVC). A differential flow refractometer and a UV detector were used for the detection of the compounds by GPC. Qualitative determination of the components of more complex mixtures is facilitated by the use of a curve resolver. Particular attention has been devoted to the types of stabilizer approved by the food codex. The data on PVC stabilizers have been complemented by the Ve values of the plasticizers, and their interference with the stabilizing components has been investigated. The control analyses have been carried out on mixtures of stabilizers and polymer extracts.
Antioxidants and stabilizers. XLVI. Transformations of antioxidants during inhibited oxidative degradation: Dihydric phenols in tetralin and polypropylene
Authors: Pospíšil J. , Taimr L. , Horák J. 
Published: June 2010

AbstractAn investigation was made of reactions of 2‐tert‐butylhydroquinone and 4‐tert‐butyl‐pyrocatechol with tert‐butylhydroperoxide and tetralylhydroperoxide in the presence and absence of a cobalt catalyst, modeling the transformations of these antioxidants during inhibited oxidation. The reaction product was a benzoquinone derivative in the first case and a mixture of benzoquinone and hydroxybenzoquinone, in the second. The formation of products also corresponded to the transformations of both isomeric tert‐butylated benzoquinones caused by tert‐butyl hydroperoxide. In agreement with the investigated model the same products of the oxidative transformation of dihydric phenols during inhibited oxidation of tetralin and atactic polypropylene were detected. Under the conditions for oxidative degradation of polyolefins at temperatures above 150°C, deactivation due to direct oxidation with oxygen must also be taken into account. The extent and rate of the formation of transformational products is one of the reasons for different antioxidative activity of isomeric dihydric phenols.
Sorption of water vapor in partially hydrolyzed poly(vinyl acetate)
Authors: Spencer H. Garth , Honeycutt S. C. 
Published: June 2010

AbstractThe diffusion and sorption properties of water vapor‐polymer systems are of considerable interest because these properties are uniquely influenced by certain structural features of the polymer, i.e., the presence of hydrophilic groups, and because many uses of polymer membranes and films depend on their water permenation characteristics. The concentration dependence of the diffusion coefficient D varies from a conconstant or slightly decreasing function in hydrophobic polymers [1] to a strongly increasing function in hydrophilic polymers [2].The sorption kinetics of H2O and D2O in copolymers of partially hydrolyzed poly(vinyl acetate) (PVAc) is the subject of this study. The value of D and its lack of dependence on concentration in PVAc is well known [3,4], and a strong dependence of D on concentration in poly(vinyl alcohol) (PVOH) has been reported [3, 5]. Emphasis in this work is placed on the comparison of the sorption kinetics within the sequence: PVAc, VAc‐VOH copolymers, and PVOH.Transient‐state sorption studies in water vapor‐polymer systems present special measurement problems [5, 6]. These problems and their limitations on the results are discussed.