bluuebunny/crossref_metadata_2025_split huggingface dataset:
Sur le greffage du polyméthacrylate de méthyle sur le caoutchouc d'Hévéa
Authors: Kobryner W. , Banderet A. 
Published: April 2003

AbstractLa polymérisation de méthacrylate de méthyle par un catalyseur convenable en présence de caoutchouc naturel conduit à la formation d'un mélange composé de polyméthacrylate de méthyle libre, de caoutchoue n'ayant pas réagi et de polymère greffé. Après avoir mis au point la séparation du P.M.M. libre, les auteurs ont élaboré une méthode permettant de détacher les chaǐnes latérales polyméthacryliques greffées sur le tronc polyisoprénique en le détruisant à l'ozone. On a étudié, et on tient compte de la faible degradation que subit le P.M.M. par ce traitement. Les masses moléculaires du P.M.M. libre et du P.M.M. libre et du P.M.M. greffé a permis d'étabir les deux courbes de distribution. Une série de polymères greffés a été préparée en faisant varier les proportions de caoutchouc, de monomère et de catalyseur. On a examiné l'influence de chacun de ces facteurs sur le nombre et la masse des greffons, ainsi que sur le rendement en P.M.M. greffé. On constate que si l'on peut effectivement obtenir des longueurs de greffons très variables, il ne semble pas possible de fixer plus qu'un nombre assez limité de greffons par gramme de caoutchouc. Il apparaǐt que les chaǐnes de P.M.M. libre sont systématiquement plus longues que les chaǐnes greffées. Sur la base de cet ensemble de résultats, les auteurs proposent un mécanisme, selon lequel le greffage se produit uniquement par une réaction de terminaison par combinaison entre le macroradical polyisopréne et les chaǐnes du P.M.M. en croissance.
Irradiation grafting of styrene to high pressure and low pressure polyethylene films
Authors: Hoffman Allan S. , Gilliland E. R. , Merrill E. W. , Stockmayer W. H. 
Published: April 2003

AbstractThe cobalt‐60 gamma irradiation of high pressure and low pressure (Marlex‐50) polyethylene films immersed in styrene monomer to produce graft Polymers was studied as a function of dose, temperature, and film thickness. It was found that grafting generally increased with dose, but reached a level for all films at 10–20°C. and an average dose rate of 228,000 rad/hr., where the grafting was higher for the thinnest films (1.5–2 mils) than the thicker films (up to 20 mils). At 40 and 70°C. and an average dose rate of 93,500 rad/hr., the grafting increased approximately linearly with dose for all films. The post‐effects were also studied and found to be more significant for higher film thickness, higher Polymer crystallinities, and lower temperatures. Observations of the hetergeneity found in the grafted films were described, photos were shown, and these effects were discussed. It was concluded that for the dose rates employed, grafting was probably diffusion‐controlled for all films at 10–20°C. and perhaps for the thicker films at 40°C. The effects of changes in the various independent and dependent variables on the grafting mechanism were discussed and a qualitative picture of this mechanism was described. It was then concluded that the different polycrystalline natures and different thicknesses of the films (as they affected the monomer diffusion rate), and the dose rate or rate of initiation of free radicals were among the most important factors in determining the mechanism and resultant efficiency of grafting.
Graft copolymers from natural rubber latex using visible, ultraviolet, and γ‐ray initiation
Authors: Cooper W. , Vaughan G. , Miller S. , Fielden M. 
Published: April 2003

AbstractGraft copolymers have been prepared from natural rubber latex and methyl methacrylate using visible, ultraviolet, and γ‐radiation. The influence of monomer concentration, temperature, radiation intensity, and, in the case of photoinitiation, photosensitizer concentration, on polymerization rates and molecular weights have been studied. The proportion of graft polymer is very high initially but falls with conversion and with increase in monomer concentration. Photoinitiated grafting depends on the photosensitizer and on temperature, but with γ‐initiation the fraction grafted is independent of temperature. In the latter case the high proportion of graft cannot be explained in terms ofthe relative G values and concentrations of monomer and rubber. The fall‐off in proportion of graft with conversion is thought to result from microscopic heterogeneous regions formed during polymerization, which are believed to increase in size as polymerization proceeds, thereby reducing further the possibility of grafting. Degradation of previously grafted polymer by prolonged irradiation is not of consequence in this case. Molecular weights of grafted and ungrafted polymers are very similar, except at low monomer concentrations, and a marked feature of this system is their constancy with change in all reaction conditions other than monomer concentration. Estimates of the utilization of radiation energy have been made and it is concluded that on an energy basis γ and photoinitiated reactions are of comparable efficiency.
The production of graft copolymers from poly‐α‐olefin hydroperoxides
Authors: Natta G. , Beati E. , Severini F. 
Published: April 2003

AbstractThe catalytic and autocatalytic hydroperoxidations of the surface of filaments and laminae of isotactic and stereoblock poly‐α‐olefins have been studied. The peroxidation of atactic and stereoblock polymers in solution has also been examined. Peroxidized polymers have been used as radical initiators in the polymerization of vinyl monomers to achieve their grafting on poly‐α‐olefin chains. Some properties of these graft polymers, e.g., antishock properties of polystyrenes grafted on poly‐α‐butene, have been reported.
Morphologische strukturen in polyäthylenen, polyamiden und anderen kristallisierenden hochpolymeren
Authors: Eppe R. , Fischer E. W. , Stuart H. A. 
Published: April 2003

AbstractBei der Kristallisation von Niederdruckpolyäthylen aus Lösung in dünnsten Filmenerhält man lamellen‐bzw.fibrillenartige Einkristalle, in denen nach Elektronenbeugungsmessungen die Molekülketten senkrecht zur Lamellenbene bzw. zur Längsrichtung der Fibrillen stehen. Die Moleküle müssen also gefaltet sein. Bei sehr verschidener Wachstumsgeschwindigkeit der kristallographischen Ebenen entarted die Lamellen zu stäbchenartigen Fibrillen. Auch bei der Kristallisation von Lösungs‐ und Schmelzfilmen (bulk‐material) kann die Lamellenstruktur nachgewiesen werden. Lamellen bzw. Fibrillien stellen also eine unter sehr verschiedenen Kristallisationsbedingungen entstehende morphologische Grundform dar. Elektronenoptisch und genetisch sind sie Einkristalle. Zur Erklärung der Molekülfaltung sowie der Entstehung von Lamellen konstanter Dicke wird ein bestimmter Keimbildungsmechanismus diskutiert. Bei der Kristallisation von Polyurethan aus dem Glaszustande zeigen die elektronenmikroskopischen Versuche, dass auch hier morphologische Grundformen entstehen. Ihre Ausbildung kann auch im Röntgenkleinwinkeldiagramm verfolgt werden. Amorphes, glasklares Terylen zeigt schon beim Tempern bei 110° Sphärolithe, deren Wachstum lichtmikroskopisch beobachtbar ist. Die Molekülketten müssen also bereits weits unterhalb des Schmelzbereiches eine viel grössere Kettenbeweglichkeit besitzen, als bisher angenommen. Genügend teif abgeschrecktes Polyurethan ist im Elektronenmikroskop strukturlos und zeight auch keinerlei Kleinwinkelstreuung. Auch hier zeight sich zwischen der Ausbildung morphologischer Strukturen und den scharfen Röntgenkleinwinkelinterferenzen ein enger Zusammenhang. Das alte Bild des Kristallin‐amorphen Gefüges vermag die hier geschilderten Erscheinungen nicht zu erklären.
Solution properites of dialdehyde starch
Authors: Levine Samuel , Griffin H. L. , Senti F. R. 
Published: April 2003

AbstractLow levels of periodate oxidation increased the dispersibility of cornstarch in water at 98°C. Above the 10% level of oxidation, cornstarch became more resistant, and longer heating times were generally required to form stable solutions. Light‐scattering, sedimentation, and viscosity measurements showed that the average particle weight in solutions of periodate‐oxidized starches generally decreased with increased level of oxidation and time of heating. Introduction of dialdehyde groups into the anhydroglucose residues of the starch molecules thus made the structure labile toward degradation on heating in water. The experimental results showed, however, that an aggregation reaction also occurred in solutions of oxidized starches. This reaction was most evident at 10% oxidation level, but it was found to occur simultaneously with degradation over a range of oxidation levels. Aggregation probably results from the reaction of aldehyde groups of one molecule with hydroxyl groups of neighboring molecules. The observation that aggregation could be prevented by additon of glucose was explained by competition of hydroxyl groups of glucose with hydroxyl groups of starch in their reaction with aldehyde groups. The angular dependence of the light‐scattering measurements indicated that formation of dumbbell‐shaped particles by crosslinking of near‐spherical particles was probably quite important to the aggregation reaction. Preliminary investigation of periodate‐oxidized waxy maize starch showed that this starch had a much lower average molecular weight in solution than ordinary cornstarch at a comparable level of oxidation. This value may result from the contribution of amylose to the aggregation of ordinary oxystarch.
Studies in the changes in fine structure of cellulosic fibers during mild acid hydrolysis
Authors: Achwal W. B. , Daruwalla E. H. , Nabar G. M. , Subramaniam P. 
Published: April 2003

AbstractChanges in the accessibility of the fine structure of cellulose as a result of mild acid action on standard cellulose, cellulose mercerized with and without the application of tension, viscose rayon, and cuprammonium rayon have been studied with respect to changes in DP, fiber density, fiber crystallinity, moisture regain, oxidative susceptibility, and equilibrium adsorption of Chrysophenine G, Chlorazol Sky Blue FF, and Procion Brilliant Red 2Bs. Results indicate that the mild acid action on all the cellulosic fibers studied, appears to proceed in three different stages. In the initial stages the acid action is rapid and results in a sudden decrease in DP, moisture region, oxidative susceptibility, and adsorption of dyes with a simultaneous increase in fiber crystallinity and fiber density. The subsequent acid action is slower than that in the initial stages during which the extent of lowering in the values of fiber characteristis is much less, and during the final stages of acid action there is a tendency for the leveling‐off of all the fiber characteristics. The extent of reduction in the values of the fiber properties and the stages during hydrolysis at which the changes take place in different cellulosic fibers depend mainly on the rate of removal of hydrolyzable fraction and the extent of crystallization of cellulose chains taking place during the acid action.
Wandering of crosslinks in rubber at high temperatures
Authors: Voorn M. J. , Hermans J. J. 
Published: April 2003

AbstractBy crosslinking natural rubber in benzene, networks are prepared in which the degree of coiling is higher than normal (“supercoiled” networks). On heating, these networsk are converted to normal ones with the same number of crosslinks but a lower degree of equilibrium swelling. The results of the swelling experiments are in quantitative agreement with theoretical predictions. Results of strees relaxation experiments at elevated temperatures support the conclusion reached on the basis of swelling. It follows that great caution is needed when calculating changes in the density of the crosslinks from changes in stress alone as is sometimes done in kinetic studies.
Enzymatic polymerization. II. Branching by rearrangement and its application to the dextran system
Authors: Bovey F. A. 
Published: April 2003

AbstractIt is shown that increases in molecular weight and branching during the formation of dextran can be qualitatively accounted for by a random rearrangement of initially linear chains. Very large increases of molecular weight can result from the formation of branches at less than 1% of the glucose units of the original chains. The expressions presented do not account rigorously for the actual behavior of the dextran system, probably chiefly because the rearrangement process is no longer random when the molecules have become very large and highly branched.
Enzymatic polymerization. III. The influence of a glucosyl accepto, methyl α‐D‐glucoside, on the molecular weight and kinetics of formation of dextran
Authors: Bovey F. A. 
Published: April 2003

AbstractThe presence of the glucosyl acceptor, methyl α‐D‐glucoside increases the rate of formation of dextran from sucrose, and partially diverts the reaction from production of polymer of very high molecular weight to production of polymer of very low molecular weight. A mechanism to explain this behavior is proposed. It is suggested that, in the absence of an acceptor, high molecular weight polymer is produced by an enzymatic chain reaction. In the presence of acceptor, a nonchain reaction, producing low molecular weight polymer, competes with the chain reaction. This proposal is formulated in detail, and it is shwon that its predictions are in agreement with the observed behavior of the system.
Light scattering of isotactic polystyrene
Authors: Trossarelli Luigi , Campi Ennio , Saini Guido 
Published: April 2003

AbstractResults of light scattering as well as viscosity measurements on a series of isotactic polystyrene fractions, and on a sample of unfractionated isotactic polymer in toluene at 30°C. are reported. The results are in agreement with the conclusion of Natta, Danusso, and Moraglio that no difference exists between the viscometric behavior of atactic and isotactic polystyrene; the same seems to hold also for the molecular dimensions. The ratio A2M/[η] for isotactic polystyrene is lower than for atactic fractions, and according to the results of Danusso and Moraglio, the second virial coefficient, A2, is probably responsible for the observed difference. The data obtained with the unfractionated sample can be explained in terms of an unusually high M̄w/M̄n ratio.
Copolymerization of N‐vinylurethane
Authors: Ghosez L. , Smets G. 
Published: April 2003

AbstractN‐Vinylurethane (M1), prepared by the method of Hart, has been copolymerized with vinylacetate vinylpyrrolidone, acrylic acid, and maleic anhydride. From the copolymerization reactivity ratios with vinyl acetate (r1 = 0.33; r2 = 0.33) and with vinylpyrrolidone (r1 = 0.42; r2 = 2) Q and e values were evaluated, in agreement with the Alfrey‐Price equation, to 0.12 and −1.91, respectively. These results are compared to those of other N‐vinyl‐substituted monomers.
Studies in inorganic polyelectrolytes. I. Graham's salt: Dependence of molecular weight on the conditions of formation
Authors: Chatterji A. C. , Bhargava Harihar Nath 
Published: April 2003

AbstractNearly 70 samples of Graham's salt were prepared by heating sodium dihydrogen phosphate under varying conditions and then chilling the melt. The molecular weights of the samples, determined according to Strauss by measuring intrinsic viscosity in 0.035 N sodium bromide solution, were found to depend on the conditions of formation, e.g., the nature of the surface of the vessel in which the melt was prepared and the temperature of the melt. Endgroup molecular weights of many samples were also calculated, and an attempt has been made to correlate these calculations with the weight‐average molecular weights. A modification of an empirical formula of Strauss giving molecular weights by a single determination of specific viscosity in water has also been suggested.
A recording sorption kinetics apparatus
Authors: Rosen Bernard 
Published: April 2003

AbstractAutomatic recordings of the rates of sorption and desorption of gases are obtained by measurement of the volume of the ambient gas under conditions of constant pressure and temperature. The apparatus, which approaches microgram sensitivity, is applicable in the field of diffusion of vapors in polymeric solids (and in obtaining the permeability coefficient). It is especially suited for rapid detection of rate changes and provides operational conveniences for extended measurements. Although exhibiting an over‐sensitivity at low pressures, the apparatus does not share the load‐sensitivity limitations of quartz spiral techniques. As a detector of the kinetics of gas evolution or consumption, the apparatus shows promise of application in other fields of research as well.
A convenient laboratory preparation of isotactic polystyrene
Authors: Overberger C. G. , Angj F. , Mark H. 
Published: April 2003

AbstractReaction conditions for improving the yield of the crystalline fraction of the product obtained on polymerization of styrene with a heterogeneous catalyst system were determined for the purpose of determining the best conditions for copolymerization studies. The best reaction temperature at atmospheric pressure was found to be about 70°C. The initial ratio of triisobutylaluminum to titanium tetrachloride, if above 3: 1, did not influence the yield of isotactic product appreciably. The addition of lithium aluminum hydride to the catalyst resulted in a slight improvement of vield of isotactic polymer. In the titanium trichloride‐triisobutylaluminum catalyst system, preheating the two catalyst components prior to the addition of solvent and monomer led to improved Activity. Polymerization carried out under conditions of minimum swelling resulted in a lesser amount of amorphous product and improved yield of crystalline fraction. This was accomplished by the use of a nonswelling solvent and the controlled addition of monomer. Maintaining triisobutylaluminum concentration above a given level by stepwise addition during the polymerization greatly increased the activity of the catalyst. In the trichloride system, preheating, together with the use of Nujol as a solvent, controlled monomer addition, and stepwise addition of triisobutylaluminum improved the yield from in average of 0.4 to 6.0 g. of polymer per gram of titanium salt.
Occurrence of globular formations in thermosetting resins
Authors: Erath Edward H. , Spurr Robert A. 
Published: April 2003

AbstractElectron‐microscopic examination discloses the existence of globular formations, or micelles, in thermosetting resins, varying in apparent diameter from 400–900 A. These micelles are seen in thin sections, in preshadowed carbon replicas, in shadowed plastic strips revealed in profile, and as shadowed individuals. Micelles are abundant in phenolic, diallyl phthalate, and epoxy resins, and comparatively rare in silicones. The existence of micelles is in accordance with the theories of Houwink and Stäger, who consider that polymerization proceeds most rapidly at specific points in the resin; and explains the discrepancies between theoretical and observed tensile strengths. At least in the case of phenolics, micelles appear to arise in filaments formed in the polymerization process. The occurrence of linear arrays is in accordance with this mechanism of micelle formation.
A remark on an equation of state for linear polymers in monolayers
Authors: Kawai Tōtru 
Published: April 2003

AbstractA few years ago, Singer, following Huggins' method of treatment of high polymer in bulk phase, derived an equation of state for monolayers of large, threadlike molecules. Davies and his co‐worker defined a quantity ω as a measure of flexibility of a polymer chain in the interface, where ω =z– 2 (zis the coordination number of the unit in the postulated two‐dimensional quasi‐lattice in the interface), assuming that each segment in a chain has exactly two positions in which its two neighbors in the chain must fit whenz= 2. Using this definition, they have developed their discussion as to flexibility of polymer chains at the interface. It is one of the purposes of this note to point out that their definition of ω is lacking in its theoretical background. Nevertheless, the values ofzobtained from the observed force‐area relations seem to afford a reasonable order of magnitudes for various types of polymer molecules, in accordance with other data on the flexibility of the polymer chains. Another purpose of this note lies in clarifying the origin of the just‐mentioned contradiction. The reason why the values ofzappear, at first sight, to give a good representation of the degree of flexibility of polymer chains, lies in the remarkable difference in molecular configurations between the “condensed” and “expanded” states at the interface. In conclusion,zor ω resembles the empirical parameter μ often used in the discussion on thermodynamic properties of polymer solutions. Careful analysis of this value is necessary before conclusions can be drawn about the structural characteristics of polymer molecules and the intra‐ and intermolecular cohesions acting on them.
Ultrasonic velocity and adiabatic compressibility in polyelectrolyte solutions
Authors: Sohma Junkichi 
Published: April 2003

AbstractUltrasonic velocities in poly(potassium methyl acrylate) solutions were measured at various concentrations. The ultrasonic frequency was (453.8 ± 0.1) kcycles/sec. The ultrasonic interferometer method was used to measure the sound velocity, the relative error of the measurement being kept within 0.1%. Moreover, the temperature variation of the sound velocity in these solutions in the dilute state was measured. While measuring the density, the adiabatic compressibilities at various conditions were estimated. It was found that both the increment of the ultrasonic velocity per unit concentration and the decrement of the adiabatic compressibility per unit concentration showed sharp maxima, at some very dilute concentration, in the case of a pure water solvent, and that these maxima disappeared when the solvent was changed from water to KCI solution. A plot of the ratio of the compressibility for solutions with pure water as solvent, to that for additions with KCI solution as solvent vs. temperature showed an inflection at a given temperature and thereafter leveled off at higher temperatures. The concentration change and temperature variation of the ultrasonic velocity and of the adiabatic conpressibility are qualitatively explained on the basis of Oosawa's theory of polyelectrolyte, solutions.
Influence of the velocity gradient on the viscosity of polystyrene solutions
Authors: Guzmán G. M. , Fatou J. M. G. 
Published: April 2003

AbstractThe purpose of this study has been to study the flow behavior of several polystyrene samples ranging in molecular weight between 1 × 105 and 2 × 101 in several solvents. Intrinsic viscosities corrected for shear effects have been obtained according to several treatments already described in the literature. The results obtained show considerable divergences. The flow behavior of the samples was then studied from a rheological point of view; it is shown that the solutions are more and more Newtonian, the nearer they approach to zero shear stress. Interpretations of the viscosity plots are given. As a consequence, extrapolation of the viscosity curves obtained at very low shear stresses with the use of a special capillary viscometef to zero shear is considered to be the most convenient way of obtaining intrinsic viscosities corrected for shear; such a method is described. The results, in some cases, may be up to 60%, larger than the highest value obtained by the classical methods. The influence of solvent and molecular weight on this shear effect is also considered, and the whole situation is considered, taking into account the possible “structure” of the solutions and the nature of the polymers.