bluuebunny/crossref_metadata_2025_split huggingface dataset:
Swelling of cellulosic gels
Authors: Chitumbo K. , Brown W. , De Ruvo A. 
Published: June 2010

AbstractThe swelling behavior of a tightly cross‐linked cellulose gel has been studied in various polar solvents as a function of temperature. Pronounced second‐order transitions were observed at about 25 and 60°C, which may correspond to those previously reported in the literature dealing with cellulosic fibers. The transitions are attributed to changes in hydrogen bonding in the system.With the carboxymethyl and dicarboxymethyl derivatives of the cellulose gel, sharp second‐order transitions were found at about 25 and 50°C, characterizing interactions involving carboxyl groups. The solvent dependence of the swelling behavior is pronounced.No temperature dependence of swelling was observed with acetylated, methylated, and trimethylsilylated forms of the gel, in which systems hydrogen bonding has been effectively eliminated.
Complex formation between poly(vinyl alcohol) and metallic ions in aqueous solution
Authors: Hojo Nobumasa , Shirai Hirofusa , Hayashi Sadao 
Published: June 2010

AbstractAs the basic research for the study of complex reactions in polymers, the complex formation of poly(vinyl alcohol) (PVA) with copper and other metals was tried. Spectroscopy, pH titration, and elementary analysis were employed in the reaction of PVA and Cu(II) ions in aqueous solution. The complexing protonation was found in the higher pH region (above 7.0), and the maximum absorptions at 640 and 260 nm were observed. These ϵmax were proportional to the concentrations of Cu(II) ions bound to the hydroxyl groups of PVA. Formation constants of the PVA–Cu(II) complexes were measured by applying a modified Bjerrum's method. The effects of the ratio Tcu2+/THL, the anions in copper salts, and the degree of polymerization on the formation constants were studied. Four hydroxyl groups combined with one Cu(II) ion in the pH range above 7.0. The stability constants for the complexes of PVA with bivalent transition metallic ions were in agreement with the Irving‐William's series. The changes in viscosity, solubility, tacticity, mechanochemical phenomenon, and the other properties based on the complex formation are discussed.
The use of NMR techniques in the study of protein hydration
Authors: Lynch L. J. , Webster D. S. 
Published: June 2010

AbstractAn attempt is made to outline the role of nuclear magnetic resonance (NMR) in the study of the hydration of proteins. NMR techniques are very effective in these studies because of the sensitivity of the magnetic resonance of isotopes of the water molecule (usually 1H, 2H, and 17O) to the changes in the molecular state and environment that are brought about by the water‐protein interaction. The NMR techniques which are effective in characterizing specific properties of the hydration water such as mobility, anisotropy, and heterogeneity are discussed. Methods of interpreting the data so obtained in terms of these molecular properties as applied to particular protein‐water systems are outlined.
Determination of the sequence of peptides using paramagnetic probes with NMR spectroscopy
Authors: Warren Brian , Bradbury J. H. 
Published: June 2010

AbstractThe paramagnetic ion Gd3+ binds to the α‐carboxyl group of a peptide and broadens the resonances from the 13C and 1H nuclei of the backbone sequentially along the chain. The sequential broadening of both carbonyl and Cα nuclei of PheAspAlaSerVal have been observed in 6 M guanidine hydrochloride at pH 4.0. Sequential broadening from the N‐terminus is also possible using Cu2+ at pH ≥ 8.Broadening experiments using triglycine and either Gd3+ or Cu2+ show that it is more difficult to broaden 13C than 1H resonances on the same amino acid residue. The ratio of [Gd3+]CMR/[Gd3+]PMR is 12 ± 5, which agrees reasonably well with the theoretical value of 16. The ratio [Cu2+]CMR/[Cu2+]PMR is 3 ± 2.The relative advantages of proton magnetic resonance (PMR) and carbon‐13 magnetic resonance (CMR) spectroscopy for this application are discussed. It is concluded that sequence determinations of 20 mg samples of peptides, ranging in size up to 7–9 residues, should be possible using CMR spectroscopy. The main advantage of PMR spectroscopy is the much smaller amounts of material required, but other problems preclude its use at this time except for very simple peptides.
Mechanical degradation of gluten proteins during high‐speed mixing of doughs
Authors: Macritchie F. 
Published: June 2010

AbstractBueche's theory of the mechanical degradation of polymers in shear is applied to try to account for the changes in flour proteins following high‐speed mixing of doughs. Because of the high viscosity of dough (∼ 108 poise), shear strain rates on the order of 102 sec−1, which are encountered in standard dough mixers, are sufficient to cause scission of covalent bonds. The limiting amount of protein, extractable after mixing, increased with mixing speed, in agreement with the predicted effect of strain rate on breakdown. Agents which crosslinked protein chains through strong covalent bonds increased the mixing stability of doughs, while those which crosslinked by formation of SS bonds greatly accelerated breakdown, reflecting the more labile nature of the SS bond. Some predictions about the rheclogical effectiveness of different SS bonds follow from the theory. Predicted changes in molecular weight distribution of protein following mixing are in agreement with experimental results obtained by other workers.
The insolubilization of trypsin by attachment to radiation graft copolymers of polypropylene
Authors: Liddy Michael J. , Garnett John L. , Kenyon Robert S. 
Published: June 2010

AbstractNovel methods have been developed for the preparation of polymers suitable for the attachment of enzymes, or other biochemical macromolecules, to render them water insoluble. By a new irradiation process, p‐nitrostyrene has been graft copolymerized to trunk polymers, such as polypropylene. Reduction of the nitro group in the graft copolymer gives the amino derivative, which may be converted to other functional groups (isothiocyanato or diazo) or used in conjunction with bifunctional reagents in order to covalently bind enzymes to produce active, water‐insoluble conjugates. The properties of one such conjugate, in which trypsin was immobilized by covalent attachment to poly(p‐isothiocyanatostyrene‐g‐propylene) are discussed. The advantages of the present radiation grafting technique are compared with conventional methods for insolubilizing enzymes.
Gel permeation chromatography of polymers
Authors: Hammond J. M. , Hooper J. F. , Stutchbury J. E. 
Published: June 2010

AbstractThe literature on gel permeation chromatography (GPC) is surveyed and briefly reviewed to provide a guide to some of the more important references, particularly those dealing with equipment and polymer molecular weight determination. A number of applications of GPC in the authors' laboratories are discussed in order to illustrate use of the GPC technique, with particular regard to its value in estimating low molecular weight substances present in polymers.
Pulse radiolysis of styrene and acrylate monomers
Authors: Sangster David F. , Davison Alan 
Published: June 2010

AbstractPulse radiolysis has been used to investigate the transient species formed in aqueous and methanolic solutions of styrene, α‐methyl styrene, methyl methacrylate, and butyl acrylate. The reaction rate constants for formation and disappearance of these species and their activation energies are reported.In aqueous solutions, the primary radical products of the radiolysis of water react with styrene. About 20% of the ·OH radicals and about 45% of the reducing radicals, eaq and ·H, give the benzyl radicals C6H5CHCH2OH and C6H5CHCH3, respectively. The remaining 80% and 55% give the cyclohexadienyl radicals HOC6H5CHCH2 and C6H6 CHCH2, respectively. In methanol solutions, the cyclohexadienyl radical C6H6 CHCH2 is the only one detected.The kinetic parameters for radical‐radical dimerization of methyl methacrylate and of butyl acrylate are similar, showing that the differences in termination rates observed for the conventional polymerization of these monomers are due not to electronic, but to viscosity‐structural factors.
Electroinitiated ionic polymerization
Authors: Giusti Paolo 
Published: June 2010

AbstractA classification of the electroinitiation processes which takes into account the nature of the electrodic processes undergone by the different substances present in the reaction mixture is proposed.Some of the most recent results obtained in the author's laboratories on both electroinitiated and electroinfluenced polymerizations are briefly described and discussed.An algebraic treatment is also illustrated, which stresses the importance of the diffusion phenomena thus far neglected by most researchers. The theoretical results of this treatment are shown to closely agree with the experimental results.
Copolymérisation Radiochimique Des Mélanges Acide Acrylique‐N‐Vinylcarbazole en Solution
Authors: Chapiro Adolphe , Mankowski Zbigniew 
Published: June 2010

AbstractL'acide acrylique forme avec le vinylcarbazole un complexe moléculaire qui a été caractérisé par une discontinuité sur la courbe des indices de réfraction des mélanges et par l'apparition d'une nouvelle bande d'absorption dans l'infra‐rouge à 1180 cm−1. Ce complexe est d'autant plus stable que la concentration des monomères est plus élevée et que la température est plus basse. La cinétique de la copolymérisation des deux monomères a été étudiée dans différents solvants et à différentes températures. La variation des vitesses en fonction de la composition du mélange des monomères est complexe. En solution dans le chloroforme et dans le méthanol la vitesse est maximale pour le mélange équimoléculaire ce qui indique que la réaction de propagation est favorisée dans le complexe moléculaire; cependant, dans le dioxanne et le n‐hexane la vitesse décroit régulièrement avec la teneur de vinylcarbazole dans le mélange et dans le toluène on observe un maximum des vitesses pour une fraction molaire de vinylcarbazole de 0,30. Les copolyméres formés dans les diffèrents solvants possèdent souvent une composition 50‐50 constante dans un domaine de compositions plus ou moins vaste du mélange initial. Ce résultat suggère que ces copolymères ont une structure régulièrement alternée. La tendance à l'alternance augmente avec la concentration des deux monomères dans la solution et elle diminue lorsque la température de la réaction s'élève. Dans le dioxanne on n'a pas obtenu de copolymère alterné. On discute l'ensemble de ces résultats dans le cadre des associations moléculaires qui existent dans les différents milieux. On a étudié les caractères de solubilité du copolymère alterné et on les a comparés avec celles d'un copolymère de měme composition 50‐50 mais dont la distribution des motifs est plus statistique.
Properties and methods of synthesis of several optically active polyoxiranes and polythiiranes
Authors: Spassky Nicolas , Dumas Philippe , Sepulchre Maurice , Sigwalt Pierre 
Published: June 2010

AbstractOptically active oxiranes and thiiranes are prepared from the corresponding asymmetric 1,2‐diols or by means of stereoelective polymerization.The properties of polymers prepared from chiral monomers by polymerization with anionic, cationic, and stereospecific initiators are compared. In the latter case, the stereospecificity depends not only on the nature of the monomer but also on its enantiomeric distribution. The direction of ring opening could be easily followed when using optically active monomers and there are satisfactory correlations with other methods such as ozonolysis or NMR spectroscopy. In some cases properties of optically active and racemic polymers are different, this enables their separation by physical methods. Chiroptical properties of monomers and polymers having thioether chromophores are given. The stereoregularity of the polymers determined by NMR spectroscopy may be correlated and substantiated by calculations of enantiomeric distribution from optical activity. Optical activity is, therefore, a useful tool for studying the mechanistic aspects of polymerization and the properties of the obtained products.
Crosslinking with s2ci2 of some epdm rubbers and their stress‐strain behaviors
Authors: Penati Amabile , Pegoraro Mario 
Published: June 2010

AbstractCrosslinking of swollen terpolymers of ethylene‐propylene‐diene (EPDM) with S2CI2 dissolved in n‐butylacetate was carried out at room temperature.Small, low thickness EPDM specimens, characterized by different amounts of double bonds (3,5, 4, 6, 10 weight‐% of 5‐ethylidene‐2‐norbornene), were crosslinked; the kinetic reaction was followed by measuring the degree of swelling in benzene, and calculating the elastically effective chain density according to the Flory‐Rehner theory. Using an excess of S2CI2 solution to operate at an almost constant S2CI2 concentration, we observed that the crosslinking rate depends on the double bond percentage only at the beginning of the reaction; after some hours the reaction rate decreases. This demonstrates the importance of the S2CI2 diffusion rate inside the samples.Stress‐strain curves of four different EPDM were obtained before and after crosslinking. Before crosslinking the EPDM behavior depends principally on the ethylene content: the 5‐ethylidene‐2‐norbornene decreases the values of the maximum initial stress, which is attributed to the ethylenic unit distribution in the chains. After crosslinking the EPDM behavior depends, instead, on the crosslinking density.
Effect of steric obstructions in networks on equilibrium properties of crosslinked polymers
Authors: Priss L. S. 
Published: June 2010

AbstractAccording to the statistical theory of polymer chains in Gaussian approximation, their transversal dimensions, characterized by the root‐mean‐square distances between the chain segments and the straight line connecting the ends of the chain (r2 1/2 = r), do not depend on the end‐to‐end distance (h). Therefore, the classical rubber‐like elasticity theory takes into account only the entropy change (δSh) related to the variation of h. Upon instantaneous deformation, all linear dimensions of the chains are changed, and the establishment of equilibrium involves, in particular, the recovery of initial r. In the real network, the chains, having drawn together after deformation, hinder the completion of the process since they cannot pass through each other. Thus, in an equilibrium deformed network, r does not reach its actual equilibrium value, thus causing the additional entropy change (δSr). δSr and δSh depend on elongation ratios λi in different ways, for h and r change at deformation in a dissimilar manner.The theory based on these premises describes well the regularities of various types of deformation. In particular, for the nominal stress f at uniaxial tension one gets the formula which is close to the Mooney‐Rivlin equation for 0.2 < λ−1 < 0.9. Here C1 is expressed through molecular parameters in the usual way, and K is a constant determined by arrangement of steric obstructions. The same ideas allow us to propose a qualitative explanation for a wide range of regularities found for the equilibrium properties of rubbers.
Swelling equilibrium in the system ethyl‐benzene‐1,3 diphenylbutane‐crosslinked polystyrene
Authors: Máša Z. , Pouchlý J. , Přibilová J. , Biroš J. 
Published: June 2010

AbstractThe equations for total and preferential sorptions in a ternary mixture liquid(1)‐liquid(2)‐polymer network(3) were derived for systems obeying the Flory‐Huggins equation with the concentration dependent interaction parameters. The equilibrium degree of swelling of the three styrene‐divinylbenzene copolymers in toluene, ethylbenzene, 2,2′‐ditolyl, 3,3′‐ditolyl, and 1,3‐diphenylbutane was measured along with the total swelling and the preferential sorption in the system of the three members of one homologous series ethylbenzene‐1,3‐diphenylbutane‐crosslinked polystyrene. The difference in molar volumes of components is revealed in two ways: via the combinatorial entropy and the interaction parameters (through the Prigogine‐Patterson structural effect). Both these counteractive influences are more fully compensated in the case of the total swelling than in the preferential sorption. The positive value of χ12 parameter increases the degree of swelling of the polymer in a binary mixture of components 1 and 2, but the increase is lower than that according to the Flory‐Huggins theory; this fact justifies the introduction of a ternary parameter χT as an empirical correction. Similar results were obtained by Bristow in a study of benzene‐cyclohexane‐polymer network systems.
Low‐frequency dynamic mechanical behavior of polyacrylate networks
Authors: Janáček J. , Hrouz J. 
Published: June 2010

AbstractA low‐frequency vibration apparatus was used for measurements of the dynamic mechanical behavior of poly (methyl acrylate), poly (ethyl acrylate), and poly(octyl acrylate) networks in the frequency range of 0.001 to 0.5 Hz, and with temperatures from –40 to 100°C. The polymers were prepared by radical polymerization in the absence of crosslinking agent, and in the presence of 0.1 and 0.2 × 10−4 mole cm−3 ethylene dimethacrylate. The complex dynamic compliance values were determined in the rubber‐like region starting from log J'p = –7.5 and higher; the data obtained were reduced to a reference temperature of 25°C.The contribution of long retardation times of untrapped entanglements to the compliance in the rubber‐like region, according to Ferry (Je – JeN), was compared with the values obtained earlier for networks of poly (butyl methacrylate), poly (butyl acrylate), natural, butadiene‐styrene, and polybutadiene rubber. It was found that this contribution, at the same equilibrium compliance, is highest for rubbers, and higher for methacrylates compared to acrylates. The increasing length of side chains of polyacrylates leads to an increase in the difference (Je – JeN).
Differences in the mechanical and optical behavior of the physical network of amorphous poly(ethylene terephthalate) as a result of annealing
Authors: Vaníček J. , Janáček J. 
Published: June 2010

AbstractThe properties of undrawn amorphous poly(ethylene terephthalate) fibers where the optical anisotropy had a of magnitude of 10−3 were investigated. The fibers behave as a deformed frozen network of entanglements formed in the process of spinning. The shrinking of the fibers is observed when heating them to a temperature above Tg. It was found that the annealing of fibers at a constant length at temperatures near Tg results in a decrease of their birefringence, but that shrinking and the retractive force changed only negligibly. The results obtained can be explained by means of Yeh's model of amorphous polymers. It can be assumed that annealing leads to conformational changes inside the nodules, with a predominantly parallel order of the chains, probably without involving any changes in the network of entanglements. As a consequence, annealing results in a decrease in the stress‐optical coefficient. Annealing does not produce any changes in the natural drawing ratio of the fibers which seems to indicate that its value is not directly related with the birefringence, as has been assumed up to now but that it has a relation to the network of entanglements.
Molecular weight determinations by vapor‐pressure osmometry
Authors: Morris C. E. M. 
Published: June 2010

AbstractSome of the factors which affect the accuracy of number‐average molecular weight determinations by vapor‐pressure osmometry are discussed. It is shown that care is required in the selection of compounds for calibration purposes to ensure that solute volatility effects do not lead to erroneous results. It is also demonstrated that, in certain systems at least, the calibration factor has a small but important dependence on the solute molecular weight over the molecular weight range examined (128–883).
Atmospheric heat aging of carboxyl‐terminated polybutadiene
Authors: Cowan J. R. , Hammond J. M. , Hooper J. F. 
Published: June 2010

AbstractThiokol HC 434 carboxyl‐terminated polybutadiene on hot storage in air increases in viscosity and molecular weight until, finally, gelation occurs. It was found that rate of aging can vary greatly from lot to lot. The difference in aging between lots is thought to be caused by a decrease in the catalytic activity of metal ion impurities due to chelation by varying amounts of glutaric acid remaining in HC 434 after manufacture. Stability of poorer‐aging HC 434 is improved by adding glutaric acid or other chelating agents.
The influence of molecular characteristics of synthetic rubbers on mixing and extrusion behavior
Authors: Giurco Flavio , Mills Wayne 
Published: June 2010

AbstractThis paper presents results which indicate that nonuniformities in the mixing and extrusion behavior of nominally standard grades of emulsion‐ and solution‐polymerized oil‐extended SBR are associated with variations in molecular weight distribution, which are not reflected by Mooney viscosity values.Generally, copolymers with broader molecular weight distribution have higher compound die swell, and lower rates of carbon black dispersion during mixing. Delta Mooney values and torque rheometer t' point tests were found to be of utility in predicting extrusion die swell and carbon black dispersion characteristics of oil‐extended SBR.
Variable‐composition polysulfones by free‐radical copolymerization of vinyl chloride with sulfur dioxide
Authors: Cais R. E. , O'Donnell J. H. 
Published: June 2010

AbstractThe relationship between copolymer composition and comonomer composition for the freeradical copolymerization of vinyl chloride with sulfur dioxide, initiated by γ‐irradiation and by tert‐butyl hydroperoxide/methanol at low temperatures, is compared with the relationships calculated from various possible copolymerization mechanisms using a range of reactivity ratios and equilibrium constants. The copolymerization approaches Lewis‐Mayo behavior at low temperatures (–78°C), but this model is inapplicable at higher temperatures. Copolymerization models involving (i) a 1:1 comonomer complex as a third monomer, or (ii) a penultimate effect of SO2 on SO2 addition to the propagating chain, are satisfactory at – 78°C, when they are indistinguishable from Lewis‐Mayo behavior, and also at 0°C, but not at other temperatures. A depropagation model involving reversibility of three propagation reactions with different temperature dependences will, however, satisfactorily explain the observed behavior at all temperatures.
New composite ion‐exchange resins made from neutral precursors
Authors: Bolto B. A. , Jackson M. B. , Siudak R. V. , Battaerd H. A. J. , Shah P. G. S. 
Published: June 2010

AbstractThe preparation of composite ion‐exchange or “no‐matrix” resins by polymerizing a mixture of basic and acidic monomers is a practical proposition only if some means can be found to minimize interaction between the monomers, so that the sites in the final polymer are not rendered inactive by internal salt formation. This paper reports one method of avoiding the strong interaction between the oppositely charged monomers by employing one or both of the monomers as an electrically neutral precursor. After carrying out the polymerization, the groups may be converted to a usable form by hydrolysis. The effect of solvent, the acid to base ratio, the degree of crosslinking, and the effect of the nature of the initiator on the preparation and properties of no‐matrix resins prepared using neutral acid precursors was studied; it was found that no‐matrix resins may be obtained with thermally regenerable capacities comparable to “plum pudding” resins.