bluuebunny/crossref_metadata_2025_split huggingface dataset:
Le mécanisme du gonflement de la cellulose régenerée
Authors: Nowakowski Aleksander 
Published: April 2003

Abstract(1) En se referrant à la littérature et ses propres expériences l'auteur arrive à la conclusion que, si l'on veut améliorer les qualités physicochimiques des fibres de cellulose par des résines polycondensées, il faut s'en tenir à trois principes; notamment: il faut empêcher la formation d'un polycondensé sur la surface des fibres, incorporer les matières plastiques aux pores et à l'interieur des fibres et adapter à chaque cas particulier la qualité de la résine au type des fibres données. (2) Pour approfondir l'étude des lois fondamentales de nature physico‐chimique qui régissent le domaine de la cellulose, le degré de gonflement des hydro‐, aero‐ et organogels isotropiques de la cellulose régenerée a été mesuré ainsi que la dialyse des macromolecules à travers des membranes. (3) Les degrès de gonflement (v) des fils isotropiques de la cellulose régénerée ont été determinés dans l'eau et dans 7 solvants organiques (anhydriques et dilués a l'eau à de differentes concentrations). A la suite de ces résultats les conclusions suivantes peuvent êntre tirées: (a) Le dioxane, la pyridine et le formamide constituent des moyens ideaux pour extruder l'eau liée dans les hydrogels (v = 6,6 à 7,6). Ils se prêtent donc parfaitement à l'impregnation des soies artificielles et à des expériences sur la dialyse. Ce qui est pourtant frappant, c'est la faible aptitude de gonflement de la cellulose sèche dans les solvants mentionnés. (b) L'acide formique occupe une place intermédaire, ayant un degré de gonflement v = 5,8, event. 5,4 pour la filature humide ainsi que pour la matière sèche. (c) Certains solvants (acétone, tétrahydrofurane) donnent des degrés moyens de gonflement (v = 5,3, event. 5,0), si l'extrusion de l'eau du hydrogel par des solvants organiques dont la concentration s'élève graduellement.
Reversible heat coagulation of some water‐soluble amino acid copolymers
Authors: Noguchi Junzo , Hayakawa Tadao , Ebata Mituo 
Published: April 2003

AbstractPoly‐ε‐aminocaproyl‐DL‐alanine, [HN(CH2)5COHNCH(CH3)CO]n, was prepared by the polymerization of N‐carbothiophenyl‐ε‐aminocaproyl‐DL‐alanine. The copolymer synthesized precipitates from an aqueous saturated solution on heating (40 to 60°). The precipitate formed goes back into solution on cooling. Repeated precipitation and dissolution by change of temperature show that the heat coagulation is reversible. The coagulation phenomenon discussed is pH‐dependent, but practically independent of ionic strength or the presence of denaturing agents such as urea. The ability of the following polymers to coagulate from an aqueous solution on heating was investigated: H[HN(CH2)mCOHNCH(CH3)CO]nOH (I), m = 1,2,3,4,5; and H[HN(CH2)mCO]nOH (II), m = 1.2,3,4,5. None of the polymers investigated, except poly‐ε‐aminocaproyl‐DL‐alanine (I, m = 5) showed reversible heat coagulation. The polymers of group I dissolve in water more readily than those of group II. The aqueous solutions of I, m = 1; I, m = 3; and II, m = 1, give a distinct positive biuret reaction. In a series of copolymers of α‐amino acids with ε‐aminocaproic acid it was observed that reversible heat coagulation in water occurs in copolymers containing L‐proline or α‐aminoisobutyric acid, but not in copolymers containing glycine, L‐leucine, or L‐phenylalanine. Reversible heat coagulation was also observed in the case of poly‐L‐proline.
Effect of long‐chain branching on some solution properties of polyethylene
Authors: Trementozzi Q. A. 
Published: April 2003

AbstractTwo polyethylene samples polymerized by the standard high‐pressure technique employing oxygen as the initiator were resolved into a total of 19 fractions. Also, a Zieglertype polyethylene was separated into 12 fractions. A comparison of the intrinsic viscosities and the number‐average molecular weights of the polyethylene fractions prepared at high pressure over a broad molecular weight range shows that the spatial requirements of the polymer molecules increase anomalously with molecular weight. It is shown that this behavior is not due to increasing frequency of over‐all chain branching. Rather, it is due to the increasing degree of long‐chain branching with molecular weight. A comparison of the intrinsic viscosities of unbranched with branched polyethylene at a number‐average molecular weight of 200,000 indicates there are approximately 4 tetrafunctional branch points per molecule. It is demonstrated that polyethylene solutions can be passed through ultrafine filters without loss of soluble polymer under the proper conditions. Angular light scattering intensity measurements of clarified polyethylene solutions in Tetralin show that unbranched polyethylene has a normal M̄w/M̄n ratio, whereas branched polyethylenes have M̄w/M̄n ratios from 7 to more than 100. For the more highly branched polyethylenes it is shown that the dissymmetry method seriously undercorrects the weight‐average molecular weight because of nonconformity to a randomly coiled molecule. The M̄w values of fractions of high‐pressure polyethylene show increasing polydispersity with increasing molecular weight, which is attributed to the influence of long‐chain branching. The magnitude of the polydispersity of these fractions and the parent polymers (high‐pressure) suggests that the degree of long‐chain branching is much greater than previously assumed.
Polymers and group interaction. IV. Hofmann reaction on polyvinylamides
Authors: Mullier M. , Smets G. 
Published: April 2003

AbstractThe Hofmann degradation reaction has been applied to polyvinylamides in order to obtain aminocarboxylic polyampholytes. When the reaction is effected in aqueous solution, interactions occur between isocyanate and neighboring chloroimide ions, with the formation of butyrolactam ring units incorporated in the polymeric chain. The structural composition of the polymers has been determined on the basis of the following analytical results: total and volatile nitrogen, total and ionic chlorine, and conductometric and potentiometric titrations. In the case of polymethacrylamide the end product consists of about 57% lactam rings, 28% free amine chlorohydrate, and 8% methacrylic acid units, while about 5 to 6% amide groups remain unreacted. In the case of polyacrylamide the degree of conversion is usually lower; this difference in behavior has been interpreted as being due to the high substitution in the methacrylic derivative. When the reaction is effected in water‐methanol (50/50) solution, any ring formation is absent; contrariwise, the isocyanate functions are transformed into carbamate units. In alcoholic medium it is possible to obtain polymers containing about 50% carbamic functions, as well as small amounts of free amines (3%); the residual percentages are acid or unreacted amide groups. On alkaline hydrolysis of these carbamic functions, free amine functions are produced; however, the rate of hydrolysis is very low if compared to that of usual amides. This effect has been attributed to the nitrogen substitution in the carbamate units
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and to the electrostatic repulsion effect of the carboxylate functions toward the hydroxyl ion. For verification, the alkaline hydrolysis rate constants of N‐isopropyl methylcarbamate have been compared with those of methylcarbamate; they were found to be about ten times slower. Moreover, the corresponding activation energy of alkaline hydrolysis was 18.7 kcal./mole instead of 14.1 in the case of the unsubstituted methylcarbamate. The products obtained by Hofmann degradation on polymethacrylamide have been compared to those obtained by Lossen rearrangement reaction on polymethacroyl chloride; the structural units were found to be identical in both cases.
Poly‐2‐ and poly‐4‐vinylpiperidine
Authors: Katchalsky A. , Rosenheck K. , Altmann B. 
Published: April 2003

AbstractPoly‐2‐vinylpiperidine and poly‐4‐vinylpiperidine were prepared from poly‐2‐vinylpyridine and poly‐4‐vinylpyridine, respectively, by catalytic hydrogenation at a hydrogen pressure of 3500 p.s.i. and a temperature of 220–250°C., using a palladium catalyst. The hydrochlorides, acetyl derivatives, and phenyl thioureates of the new polymers could also be obtained. The molecular weights of the polymers were estimated by light scattering and viscosity in chloroform and methanol solution and were found to lie in the range of 10,000 to 35,000. The electrochemical properties were investigated by potentiometric titration and electrophoresis. From the character of the titration curves it was concluded that no appreciable nearest neighbor interaction exists in polyvinylpiperidine. By an analysis of the combined potentiometric‐electrophoretic data an intrinsic acid dissociation constant pK0 = 10.08 ± 0.07 was calculated. The discrepancy between this value and the value of the dissociation constants of monomeric piperidines, pK ≈ 11, has been further investigated by thermochemical measurements.
Viscometric properties of salicyloxymethyldimethyl end‐blocked dimethylpolysiloxanes
Authors: Merker Robert L. , Scott Mary Jane 
Published: April 2003

AbstractViscometric data obtained over a temperature range of 0–150°C. for a series of salicyloxymethyldimethyl end‐blocked dimethylpolysiloxane fluids have shown that the molecular weight at which a minimum viscosity is exhibited is temperature‐dependent. Thus, with decreasing temperature, minimum viscosities were manifested at higher molecular weights. With increasing molecular weight, i.e., increasing siloxane character, the energy of activation of viscous flor (Evisc) not only decreases, but also is less temperature dependent. An empirical expression relating Evisc and temperature for such fluids is presented.
Acrylonitrile polymerization in aqueous suspension
Authors: Thomas W. M. , Gleason E. H. , Mino G. 
Published: April 2003

AbstractPolymerization of acrylonitrile in dilute aqueous solution initiated by the chloratesulfite redox was studied kinetically and with the aid of the electron microscope. Polymerization rate depended on the [ClO] [H2SO3] product, the monomer content and the sodium lauryl sulfate concentration. The rate was depressed by agitation and by salts; it was accelerated by Fe++ and by Cu++ and was only moderately dependent on temperature. Particles of polymer separated from the start as spheroids less than 200 A. across and grew rather uniformly to 2000 to 3000 A. After a short time no new particles formed unless more initiator was added. Rate of polymerization per particle was reasonably constant. Salts and agitation led to aggregation of particles and polymerization rate was reduced. Sodium lauryl sulfate and Methocel had the opposite effect. The system bears a general resemblance to typical emulsion polymerization, and thus treatments based on homogeneous kinetics appear to be inadequate.
The system cellulose—methanol
Authors: Lauer K. , Ayer J. E. , A. Seoud Abdel Latif 
Published: April 2003

AbstractThe determination of nonsolvent methanol by a drying technique on cotton and mercerized cotton fibers and a comparison with corresponding values of nonsolvent water showed that methanol forms solvates only with half the number of hydroxyl groups available for hydrate formation in the amorphous part of the fibers. It showed, furthermore, that methanol does not form solvates with hydroxyl groups in semicrystalline regions of mercerized fibers. The method also permits determination of nonsolvent methanol with fibers which reach equilibrium from the wet side. A schematic approach to fiber structure gives good agreement between the quantities of nonsolvent water and methanol and molar integral heats of wetting, respectively. Both characteristics permit an estimation of fiber composition of natural cellulose fibers.
New polymerization catalysts for methyl methacrylate
Authors: Lal Joginder , Green Richard , Ellis Sylvia 
Published: April 2003

AbstractNew free radical catalysts for the polymerization of methyl methacrylate and other acrylic monomers have been reported. They comprise mixtures or salts of N,N‐dialkyl aryl amines and o‐benzoic sulfimide (saccharin). A p‐substituent on N,N‐dimethylaniline or N,N‐diethylaniline had a significant influence upon polymerization. Electron‐donating groups such as methyl or methoxy increased the total yield of the polymer, while electron‐withdrawing groups, namely, chlorine, bromine, or aldehyde, reduced the yield of the polymer. When electron‐withdrawing groups, namely, nitro, nitroso, or phenylazo, were present in the para position of dimethylaniline, no polymer was obtained. Presence of a methyl group in the meta position in dimethylaniline enhanced the yield of the polymer. However, when a methyl group was present in the ortho position, the yield of the polymer was significantly reduced, probably due to a steric factor. Binary mixtures containing equimolar proportions of saccharin and the amine were better initiators for methyl methacrylate polymerization than the corresponding salts of saccharin and amine. A number of organic acids in admixture with dimethylaniline also polymerized methyl methacrylate. The stronger the acid, the greater was the yield of the polymer. However, the yields were considerably lower than in case of dimethaniline‐saccharin mixture as catalyst.
Anomalous behavior of vinylidene cyanide in copolymerization
Authors: Ham George E. 
Published: April 2003

AbstractCopolymerization data involving a wide variety of monomers containing methylenic double bonds led to the conclusion that only acrylonitrile exhibited repulsive effects between adding monomer and copolymer containing higher proportions of the same monomer. Employing a modified procedure based on the Barb equation r1 and r1′ values were determined for the following systems: methyl α‐chloroacrylate‐vinylidene cyanide, methyl methacrylate‐vinylidene cyanide, acrylic acid‐vinylidene cyanide, 2,5‐dichlorostyrene‐vinylidene cyanide, vinylidene chloride‐vinylidene cyanide, and 2‐chlorobutadiene‐vinylidene cyanide. These results confirm the predicted diversions from normal copolymerization behavior of vinylidene cyanide as well.
A comparison of different membranes for osmotic determination of the molecular weight of nitrocellulose
Authors: Alvång Folke , Samuelson Olof 
Published: April 2003

AbstractOsmotic determinations of the degree of polymerization of cellulose nitrate have been performed using different types of cellulosic membranes. For unfractionated samples the results were dependent upon the type of membrane, whereas for fractionated samples good agreement was obtained for different membranes. The leakage of nitrocellulose through the membrane has been determined. In separate experiments the solution used for measurements in osmometers with coarse membranes were transferred to osmometers with tighter membranes. A considerable increase in osmotic pressure was observed in the latter case; this shows that the lower osmotic pressure obtained in osmometers with nonselective membranes cannot be ascribed solely to a lowering in the molar concentration because of leakage. The results are in agreement with the theory postulated by Staverman. Plots of osmotic pressure against time as well as direct determinations of the leakage give insufficient information about the error obtained when using nonselective membranes.
Preparation of graft copolymers by the reaction of primary amine‐terminated polystyrene with copolymers containing β‐isocyanatoethyl methacrylate
Authors: Graham Roger K. 
Published: April 2003

AbstractA variety of polymers containing pendant isocyanate groups was prepared by the copolymerization of small amounts of β‐isocyanatoethyl methacrylate. Polystyrenes prepared by sodium amide initiation in liquid ammonia at −33°C. were characterized and shown to contain one terminal primary amine group per polymer chain. Approximately equivalent amounts (by functional group) were reacted in a dry inert solvent, generally at room temperature for one to two days. Graft copolymers were formed in high efficiency; this was conclusively shown for graft copolymers of poly(methyl methacrylate)‐polystyrene by disappearance of titratable amine groups, extraction of the graft copolymer with diethyl ether, ultraviolet analysis of the product, and agreement between calculated and actual number‐average molecular weight. The preparative method allows control of the length of the backbone and number of attached polystyrene side chains; the complete structure of the graft copolymer is known, including the number and length of side chains.
The rate of particle growth in persulfate initiated emulsion polymerization
Authors: Roe Charles P. , Brass P. D. 
Published: April 2003

AbstractThe initial growth rate of a particle in a polymerizing emulsion is constant with respect to time and also with respect to the aqueous concentration of the initiator. However, as a particle becomes larger, a size is reached where positive deviations from this constant rate are observed. It is shown that the kinetic analysis of Ewart and Smith qualitatively implies this type of behavior. In order to obtain quantitative agreement between theory and experiment, It is necessary to assume that free radicals entering a particle are generated at the particle‐water interface. When this restriction is imposed on the kinetic analysis, the latter gives a highly satisfactory account of the experimental results throughout the region in which the approximation employed in the analysis is valid. The results of the analysis indicate specifically a nontrivial dependence of the kinetics of emulsion polymerization on particle size and initiator concentration.
A study of the creep of nitrocellulose
Authors: van Holde Kensal 
Published: April 2003

AbstractThe creep of a highly nitrated cellulose under constant tensile load has been investigated. Over a wide time range, the strain–time curves were found to obey an equation frequently used to describe the creep of metals. This analysis separates the creep into two components, a rapid elastic deformation and a deformation increasing with the 1/3 power of the time. The first of these components was found to be directly proportional to the applied stress, while the second increased very rapidly with increasing stress, again in accord with observations on metallic creep. The recovery following short creep experiments was found to be complete and accurately predictable from the creep curves and a modified form of the Boltzmann superposition principle. This was not true of the recovery following a very long creep experiment. The superposition principle was also used to calculate a “stress–strain” curve from creep data. This curve was found to be qualitatively similar to curves which have been reported for nitrocellulose.
Viscometric evidence of critical concentration in dilute polymer solution
Authors: Cragg L. H. , Bigelow C. C. 
Published: April 2003

AbstractTwo viscometric methods have been developed for detecting the “critical concentration” (the concentration at which individual polymer molecules interfere with each other) of a dilute solution of a high polymer, B. In the first of these, the intrinsic viscosity, [η], of another polymer, A, is measured in a series of mixed solvents, each consisting of a solution of Polymer B in the solvent S, and each differing from the others only in the concentration of B (CB). For a number of polymer‐polymer‐solvent systems, data are presented which show that [η] is essentially independent of CB, except over a small range where its value changes fairly abruptly. This change marks the critical concentration. The second method is much faster but probably less reliable than the first. Nevertheless, the two gave values in good agreement. A method of calculating the critical concentration, based on the Flory‐Fox theory of intrinsic viscosity, is described. Critical concentrations calculated for the several systems investigated agreed well with those obtained experimentally. The critical concentration was shown to be inversely proportional to the intrinsic viscosity of the Polymer B in experiments in which [η]B was varied by changing the molecular weight of the polymer and by changing the solvent. The effects observed are explained as resulting from interactions of the two polymer species in the solutions.
Some aspects of the direct and cyclohexanone‐sensitized photopolymerization of vinyl chloride
Authors: Valentine L. 
Published: April 2003

AbstractIt is shown that the direct photopolymerization of pure vinyl chloride in bulk shows a “gel effect,” i.e., a long period of accelerating rate at the beginning of the reaction. Cyclohexanone acts as both a solvent for the polymer and a photosensitizer for the polymerization. The mechanism of initiation by cyclohexanone is discussed; it is by no means certain that diradicals are formed.
Mastication. V. Separation and structural investigation of natural rubber‐polymethyl methacrylate interpolymers formed by mastication
Authors: Angier D. J. , Watson W. F. 
Published: April 2003

AbstractPolymerization of methyl methacrylate admixed with natural rubber occurs on rupture of rubber molecules to free radicals by applied shearing forces. The polymeric products after different conditions and extents of reaction have been separated into uncombined rubber, two interpolymer fractions, and uncombined polymethyl methacrylate by fractional precipitation and extraction methods. The structure of the interpolymers has been investigated by measurement of composition and osmotic molecular weight, ozonolysis to degrade the rubber segments and isolation of the polymethyl methacrylate fragments, autoxidation of the rubber segments, and viscosity measurements on the uncombined rubber. The interpolymer is a linear block polymer containing one polymethyl methacrylate segment and of the order of one or two rubber segments per molecule. The Trommsdorff gel effect has a profound influence on the rate of formation, composition, and structure of the interpolymer.
Molecular weight heterogeneity in starch amylopectins
Authors: Stacy Carl J. , Foster Joseph F. 
Published: April 2003

AbstractThe number‐average molecular weight of a corn amylopectin sample is concluded to be approximately 300,000 on basis of both osmotic pressure and reducing group determination. The weight‐average molecular weight of this preparation was previously shown to be approximately 80 × 106. The ratio of Mw/Mn is in accord with that expected on the basis of an essentially random synthesis of the branched polymer. Further evidence for an extreme heterogeneity in amylopectins in provided by light scattering studies on subfractions prepared by fractional centrifugation. Conclusive evidence for this broad heterogeneity is obtained by ultracentrifugal analysis. The distribution of sedimentation coefficients is shown to be extreme, significant percentages of the polymer having sedimentation constants ranging from almost zero to above 400 Svedberg units. Some observations on the sedimentation behavior of other amylopectins, their β amylase limit dextrins, and corn amylose are given.