bluuebunny/crossref_metadata_2025_split huggingface dataset:
Degradation of wood pulp during acetylation
Authors: Neal J. L. 
Published: June 2010

AbstractA comparison of the DP distributions of wood pulps and the cellulose acetates prepared from them shows that the DP distributions of the acetates are essentially exponential and virtually independent of the DP distribution of the original pulp. The DP of a number of acetates prepared under identical conditions from different pulps were unrelated to the DP to the starting pulps. Although the pulp DP is thus not a factor which determines the acetate DP, there are other intrinsic properties of the pulp which do affect the final DP of the cellulose acetate. The nature of these properties is not understood, but it can be shown that they are altered by changes in wood pulp processing. The ratio of hemicellulose in pulp to hemicellulose in the acetate made from it varies from one pulp to another. The acetate solution properties of the cellulose are more closely related to the composition of the acetate flake than to the composition of the original pulp. The viscosity of the concentrated acetate dope can be accounted for almost entirely in terms of flake DP and flake mannan content. Pulp manufacturers and acetate producers should strive toward conditions which increase the rate of degradation of the he mi celluloses and decrease the rate of cellulose degradation during acetylation.
Mechanism of multiple dielectric loss peaks in dilute solution
Authors: Stockmayer W. H. 
Published: June 2010

AbstractIt has long been recognized that the detailed selection rules describing the dielectric loss spectrum of a macromolecule in solution depend on the manner in which the individual polar groups are attached to the structure. As many as three distinct loss peaks may appear, due to contributions respectively from (1) long‐range dipoles whose magnitude and direction are proportional to the overall dimensions of the molecule; (2) dipoles rigidly attached to the chain but without long‐range correlation; and (3) dipoles on flexible side chains. In addition, there is the Kirkwood‐Shumaker mechanism of “proton polarizahility.” Theoretical and experimental examples of the above generalities are discussed.
Specific heat studies of transition and relaxation behavior in polymers
Authors: O'Reilly J. M. , Karasz F. E. 
Published: June 2010

AbstractSpecific heat studies of polymers are reviewed within the framework of Buyer's classification: (a) melting transition (Tm); (b) glass transition (Tg); (c) subglass relaxation (T < Tg); and (d) intermediate relaxation (Tg < T < Tm). The melting transition is readily apparent in specific heat measurements because of the heat of fusion resulting from the transition. Thermodynamic parameters obtained from calorimetric measurements confirm that melting is a first‐order transition and, in general, the phenomena are well understood. The change in Cp at Tg probably provides the least ambiguous assignment of Tg by precision calorimetric measurements. Specific heat studies focus sharply on the thermodynamic aspects of glass formation but still show the relaxational properties. Although complicated, the specific heat behavior of semi crystal line polymers is less complex than other techniques. There are no abrupt changes in Cp from near 0°K. to Tt similar to the mechanical or dielectric relaxations observed below Tg. Although the molecular processes responsible for the low temperature relaxations contribute to Cp, the processes are not sufficiently cooperative to occur over a narrow temperature range. Some examples of molecular processes such as methyl or other group rotation and con‐formational isomerism, which contribute to Cp, are discussed. The intermediate relaxations (Tg < T < Tm) which occur in semi crystalline polymers are complex, and many mechanisms, such as premelting, crystal‐crystal transitions, defects and crystal‐amorphous interactions have been proposed. The few specific heat results available are not conclusive and considerable work is needed in this area.
A survey of multiple transitions by dynamic mechanical methods
Authors: Turley S. G. , Keskkula Henno 
Published: June 2010

AbstractIn the last several years, studies of the dynamic behavior of polymers have shown that many, if not all, polymers exhibit more than one transition region when the investigation covers a sufficiently wide temperature or frequency range. The purpose of this paper is to discuss, for a few selected polymers, those multiple transitions which have been found by using dynamic mechanical methods, with particular emphasis on those exhibited by certain olefinic polymers and copolymers. In addition to work published in the literature, this paper also covers some unpublished results based on measurements made in our laboratory. Although attempts have been made to relate secondary transitions with such types of motion as the rotation and/or oscillation of short side chains, subgroups, and short segments of the main polymer chain, there are few polymers for which secondary transitions have been definitely assigned to a particular motion of a specific group. For the most part, the results to be discussed in this paper are based on measurements made with a torsion pendulum, vibrating reed, or transverse vibration apparatus.
Molecular motion in high molecular weight siloxane polymers
Authors: Haberland Gerald G. , Carmichael Jack B. 
Published: June 2010

AbstractMolecular motions in a series of siloxane polymers and copolymers were studied over the temperature range of 77–296°K. using broadline NMR techniques. From data of second moment versus temperature it is concluded that phenyl groups on silicon are rigid at 77°K. and exhibit only limited motion at 296°K. In contrast, methyl groups exhibit free C3 rotation at 77°K. regardless of the other groups attached to silicon. It is concluded that segmental motion is sterically controlled in siloxane polymers with only phenyl, methyl, and hydrogen groups attached to silicon. It is apparent from the similarity of the broadline NMR data of poly(vinylmethyl)siloxamer, poly(3,3,3‐trinuoropropylmethyl)siloxamer, and poly(dimethyl)siloxamer that other factors, not well understood, also play a significant role in molecular motion.
The viscoelastic relaxation mechanism of inorganic polymers. IV. Simultaneous multiple mechanisms
Authors: Eisenberg A. , Saito S. , Teter L. A. 
Published: June 2010

AbstractThe viscoelastic properties of two polymers have been studied in which both molecular (diffusional) motions and bond interchange were present in the glass transition region. The materials were a lanthanum‐doped (La3+) sodium polyphosphate and an arsenic‐doped sulfur polymer. It is shown that (just as in the case of the acrylate polymers studied by Ferry) the two mechanisms have two different compliance curves associated with them which move with temperature at different rates along the time axis. One of these is due to bond interchange and the other to the diffusional motion of the chains. On the basis of activation energy arguments the compliance curves are matched with the mechanisms, and the relative contributions to the total viscosity due to each mechanism are given as a function of temperature.
Unperturbed chain dimensions of polyethylene in theta solvents
Authors: Nakajima Akio , Hamada Fumiyuki , Hayashi Seiichi 
Published: June 2010

AbstractThe theta temperatures for linear polyethylene in diphenyl, diphenyl methane, and diphenyl ether were determined by the precipitation temperature measurements. The unperturbed mean‐square end‐to‐end distance (R02) and its temperature variationdIn (R02)/dT were estimated from direct intrinsic viscosity measurements in these three theta solvents: <R02/nl2(wherenis the Dumber of bonds, andlis the bond length) in diphenyl, diphenyl methane, and diphenyl ether was 7.10 at 127.5°C, 6.99 at 142.2°C, and 6.80 at 163.9°C., respectively. These numerical values gavedIn <R02/dT = −1.21 × 10−3deg.−1. The results obtained here were in good agreement with those reported by Flory1,2and Chiang,3and in support of the theoretical calculation by Hoeve4and Nagai5.
A semi‐empirical method for estimating unperturbed dimensions of chain polymers from the intrinsic viscosity‐molecular weight relationship
Authors: Inagaki Hiroshi , Suzuki Hidematsu , Kurata Michio 
Published: June 2010

AbstractA semi‐empirical method for estimating unperturbed chain dimensions from relationships between intrinsic viscosity M and molecular weight M is proposed. This method is based on combining the Ptitsyn equation of the excluded volume effect with a semi‐empirical relation between two expansion factors αη and α for the hydrodynamic radius and the end‐to‐end distance, respectively, i.e., αη3 = α5/2, which has been suggested by Yamakawa and Kurata. This combination gives ([η]/M1/2)4/5 = 0.786K4/5 + 0.950‐K4/5*2/3M1/3 for large α, presumably for a larger than 1.4, Experimental tests are made with viscosity data obtained for polystyrene fractions in trans‐decalin, benzene, and butanone and also with those obtained for poly(methyl methacrylate) in various solvents. Light‐scattering data by Berry are discussed in the light of present results. The parameter B describing long‐range interactions is found to be nonlinearly related to the reciprocal of temperature 1/T, that is, the quantity B0 as defined by B/[(1 ‐ (η)/T)] is a decreasing function of T. On (he basis of experimental result, disagreement between two B values deduced from intra‐ and inter‐chain interactions is pointed out.
Streaming Birefringence. VI. Polar Diagrams
Authors: Munk P. 
Published: June 2010

AbstractThe polar plots of streaming birefringence data are sensitive to the types of particles. The effect of deformability of particles is very strong; in contrast, polydispersity affects the plots only little. The method is rewarding, too, if several different types of particles are present in the system. We have devised a nomograph for rapid construction of the polar plots and for the correction of data for streaming birefringence of solvent and of the possibly present microgels.
Aqueous Polymerization Initiated by Hydrazine Hydrate. Part I
Authors: Das Rajat K. , Palit Santi R. 
Published: June 2010

AbstractIt has been shown that hydrazine hydrate initiates aqueous polymerization of methyl methacrylate in the presence of oxygen in alkaline pH. During the induction period oxygen is fixed as monomer peroxide, which at the end of induction period sets up a redox system with an unreacted hydrazine generating N2H3 radical. N2H3 radical is partly captured by monomer and partly oxidized by peroxide, depending upon the relative ratio of peroxide and monomer. This partitioning of the initiating N2H3 radical brings about interesting kinetic features to the study of which a detailed investigation has been devoted in this paper.
Thermal Flow Method for Kinetic Investigation of Fast Reactions
Authors: Bekhli E. Yu , Nesterov O. V. , Entelis S. G. 
Published: June 2010

AbstractReactions of mono‐ and bifunctional acid chlorides with amines have been studied with the help of a flow thermal method both in homogeneous (heptane) and heterogeneous (heptane‐water) media. The multistage character of the reactions may be explained by two coexisting reaction paths with different intermediate products.
Hydrodynamical and Optical Properties of Styrene—Methyl Methacrylate and Styrene—Butyl Methacrylate Graft Copolymers
Authors: Tsvetkov V. N. , Andreeva G. A. , Baranovskaya I. A. , Eskin V. E. , Klenin S. I. , Magarik S. Ya. 
Published: June 2010

AbstractThe hydrodynamical (viscosity, diffusion, sedimentation) and optical (light scattering and flow birefringence) properties of solutions of polymers obtained by the grafting of styrene chains on poly(methyl methacrylate) and poly(butyl methacrylate) chains have been investigated. The graft copolymers have a positive optical anisotropy, despite the negative optical anisotropy of the main component (polystyrene). This is explained by the specific features of the graft structure. It is shown that the rigidity of such macromolecules considerably exceeds that of linear chains.
Relaxation Behavior of Poly(methacrylic Acid) Esters Swollen by Low Molecular Weight Substances at Temperatures Below the Glass Transition Point
Authors: Janáček J. , Kolařik J. 
Published: June 2010

AbstractChanges in temperature of the secondary β loss maximum of poly(ethylene glycol monomethacrylate) and poly(n‐propyl methacrylate) swollen by means of various low molecular weight substances over a wide concentration range were measured. Correlations were found among the temperature Tβ, concentration of the low molecular weight substances, and their molecular weights. Differences were established in the mechanism of function of monofunctional and difunctional low molecular weight substances. It has been found that the temperature Tβ of the swollen poly(ethylene glycol monomethacry–late) depends upon the molecular weight of a complex consisting of a molecule of the low molecular weight substance and one or two kinetic units partaking in the γ process of the dry polymer according to the mechanism of interaction suggested. The rise of the β process and changes in its temperature position were explained on the basis of change occurring in intermolecular interactions polymer–polymer and polymer–low molecular weight substance. Evidence was presented for a correlation between the γ process of dry and the β process of swollen polymers.
Infrared Study on the Distribution of Propylene Units in Ethylene—Propylene Copolymers
Authors: Ciampelli F. , Valvassori A. 
Published: June 2010

AbstractAn accurate comparison of the infrared spectra of ethylene‐propylene copolymers, the infrared spectrum of alternate ethylene‐propylene copolymer obtained by complete hydrogenation of natural rubber, and the infrared spectra of various branched hydrocarbons made it possible to find a method for determining the distribution of the propylene sequences in ethylene‐propylene copolymers. This method is based on the measurement of the ratio of absorbancies at 10.3 and 10.675μ, which are proportional to the number of propylene units in sequences of two or more units and to isolated propylene units, respectively. A distribution index φ is also defined as a ratio between the number of isolated propylene units and the number of units present in sequences of two or more propylene units. This index is compared with that obtained from the calculation for an ideal copolymerization. The comparison suggests that some catalysts give rise to copolymers for which the plot of φ versus propylene units content is very similar to the plot predicted for an ideal copolymerization. Some other catalysts yield copolymers for which the plot of φ is somehow different. However, these copolymers contain considerable amounts of (CH2)2 groups (which are not foreseen in the calculations performed for the ideal copolymerization) that might be responsible for the anomalous behavior of the φ values.
Der Bewitterungsabbau von Polypropylen
Authors: Veselý R. 
Published: June 2010

AbstractThe natural and accelerated weathering of many unstrained samples of isotactic poly‐propylene has been investigated. Changes in some basic properties of the samples during outdoor exposure as well as during treatment in a weatherometer have been compared. As a result of the study two fundamental processes of aging were established: photoinitiated oxidative chain degradation and secondary crystallization accompanied by a volume shrinkage. Mechanisms of these processes are distinct, mainly in the first stages of aging.
Polymerization of Propylene Catalyzed by TiCl3 with Large Specific Surface
Authors: Ambrož J. , Osecký P. , MejzlíK J. , Hamřík O. 
Published: June 2010

AbstractThe kinetics of polymerization of propylene with the use of highly dispersed TiCl3 and triethylaluminum as catalysts have been studied. The overall rate of polymerization decreases with time as a consequence of the deactivation of active centers with time. The interaction of TiCl3 with triethylaluminum yields Al(C2H5)2Cl; the solid phase is depleted in Cl− and contains fragments of the organometallic compound. This reaction, which is in essence the reduction of TiCl3, takes place also in the course of polymerization and brings about the decomposition of active centers. Rate constants in the equation characterizing the course of the overall rate of polymerization with the number of active centers changing with time have been calculated.
Thermodynamic properties of extended chain polymethylene single crystals
Authors: Arakawa Tamio , Wunderlich Bernhard 
Published: June 2010

AbstractDensity, morphology, and melting data on linear polyethylene and high molecular weight polymethylene crystallized from the melt under elevated pressure are presented. For approximately constant supercooling a sharp density increase is noted above 2300 atm. crystallization pressure. Above 4000 atm. densities above 0.99 are achieved. The high molecular weight polymethylene has larger lamellar thickness than polyethylene, but does not reach full chain extension. The melting of polymethylene is extremely sharp with no evidence of premelting up to at least 136°C. Equilibrium maximum melting points of 138.7 and 141.4°C. have been measured for polyethylene of 105 weight‐average molecular weight and polymethylene of 107 molecular weight.
Structure and properties of rubber networks. Part II
Authors: Meissner B. , Klier I. , Kuchařìk S. 
Published: June 2010

AbstractBy the method described in Part I, experimental data have been obtained on cis‐polybutadiene and natural rubber which further elucidate the dependence of the concentration of elastically effective network chains on the network parameters. The results have been interpreted in terms of the equation proposed in Part I. The dependence of the elastic constant C2, defined by the Mooney‐Rivlin equation, upon the network parameters, type of polymer, and presence of diluent has been investigated. The constant C2 has been related to the network parameters by means of a simple equation on the assumption that the magnitude of the C2 effect is proportional to the fraction of elastically effective network.
Chemical transformations of polymers. IV. Chemical reactions of glycol methacrylate gels
Authors: Ševčík S. , Štamberg J. , Schmidt P. 
Published: June 2010

AbstractOne step as well as multisteps of polymeranalogous reactions of hydrophilic gels based on poly(glycol methacrylate) were studied. The reaction medium for these transformations was chosen with respect to the result of linear swelling capacity measurements to reach a satisfactory rate. Attention was devoted to the determination of the region where the gels are chemically stable as well as to the preparation of the new, practically useful, gel system.
Structural investigations of crosslinked cellulose derivatives
Authors: Nikonovich G. V. , Leontyeva S. A. , Usmanov Kh. U. 
Published: June 2010

AbstractElectron microscopy methods are used for investigation of the structure of cellulose fibers modified by some bifunctional reagents (dimethylolurea, formaldehyde, acrolein, epichlorohydrin, and propylene oxide). For sample preparation, mechanical and ultrasonic dispersion, ultrathin sectioning, and treatment by some reagents were used. Some data were obtained indicating extensive changes of the fiber supermolecular structure as a result of crosslinking between the structural elements. These changes are expressed in redistribution of the effective dimensions of structural elements toward their increasing (increase in layer thickness and diameters of fibrillar bundles) and even in the alteration of mutual arrangement of structural elements under very high degrees of substitution, as compared with the untreated fibers. Modification may proceed not only in the most accessible regions of the fiber, between the microfibrils as well as between the secondary wall layers, but also inside the microfibrils themselves, and in some cases affects the most dense fiber regions—crystallites. All these changes of the supermolecular structure after modification leads to essential alterations in the mechanical properties of the fibers.
Dissymmetric der lichtstreuung in polyvinylchlorid‐lösungen
Authors: Hloušek Miroslav , Lánková Jiřina 
Published: June 2010

AbstractThe dependence of the dissymmetry of light scattering on the molecular weight and on the degree of conversion of poly(vinyl chloride) in cyclohexanone solutions was studied. The dissymmetry of unfractionated samples increases with increasing molecular weight Mw. Fractions have a lower dissymmetry than unfractionated polymer of the same Mw. During the polymerization, the dissymmetry of the polymer increases with the conversion, especially at conversions of 90% and above, i.e., in circumstances when other properties of poly(vinyl chloride) (i.e., solubility, filterbility of solutions, thermal stability) also deteriorate, and when increasing branching or crosslinking of macromolecules is believed to occur. The dissymmetry is found to be caused by the presence of microgel particles in the solution. Analysis of the angular dependence of the scattered light has shown that with increasing conversion the concentration of microgel particles increases while their dimensions remain practically unchanged. The molecular weight Mw (determined by light scattering) increases slowly throughout the polymerization, while the intrinsic viscosity [M] decreases slightly at high conversions. This is believed to be caused by the presence of branched macromolecules in the solution. Both the microgel particles and the branched macromolecules can adversely affect the thermal stability of the polymer.
Effect of solvent on the optical behavior of macromolecules in a laminar flow
Authors: Frisman E. V. , Dadivanian A. K. 
Published: June 2010

AbstractThe segmental anisotropy of a series of macromolecules in different solvents was measured by means of streaming birefringence and viscosity. It is shown that the measured segmental anisotropy (α1 — α2) substantially depends on properties of the solvent applied. Analysis of experimental data leads to an assumption that in the vicinity of polymer chains an ordered disposition of solvent molecules (short‐range order) occurs, contributing a value (α1 — α2)s to the measured anisotropy. The magnitude of this contribution depends on the optical anisotropy of solvent molecules and their orientation relative to the macromolecule. Thus the actual segmental optical anisotropy (α1 — α2)K can be evaluated in an isotropic solvent only. Comparison of (α1 — α2)K with the value of (α1 — α2) obtained for the macromolecule in an anisotropic solvent gives (α1 — α2)s. It follows from the estimation that in spite of a strong solvent effect on the measured segmental anisotropy, the actual mutual orientation of solvent‐solute molecules is rather low. It is also shown that the short‐range order is particularly pronounced in systems where polymer‐solvent interactions are favored in comparison to polymer‐polymer and solvent‐solvent interactions.