bluuebunny/crossref_metadata_2025_split huggingface dataset:
Degradation of addition polymers by ultrasonic waves. VI. Effect of frequency
Authors: Mostafa M. A. K. 
Published: April 2003

AbstractThe effect of frequency (megacycle range) on the degradation of addition polymers (polystyrene) is studied. Results give evidence of occurrence of resonance. Optimum frequency for degradation is found to be 1 Mcycle/sec. Cavitation is suppressed at 2 Mcycle/sec. or more, or by irradiation in vacuo. Results show that degradation can be produced by ultrasonic waves in the absence of cavitation.
Copolymerization of vinyl acetate–vinyl n‐butyl ether
Authors: Tichy Jerome R. 
Published: April 2003

AbstractData on the yields and composition of copolymers of vinyl acetate and vinyl n‐butyl ether formed at 170°C. are recorded. The yield of the copolymer is directly proportional to the amount of vinyl acetate in the monomer mixture. A copolymer which is relatively stable at elevated temperatures can be prepared by using a monomer mixture containing about 0.2 M of vinyl acetate. Above this limit of vinyl acetate, the copolymers are less heat stable. The change in composition of these copolymers has been interpreted as a chain degradation process.
The rheology of aqueous solutions of amylose and amylopectin with reference to molecular configuration and intermolecular association
Authors: Storey Bayard Thayer , Merrill Edward Wilson 
Published: April 2003

AbstractMathematical expressions relating shear stress, shear rate and time of shear for aqueous solutions of amylose and amylopectin, respectively, are developed from models based on the concept of the single‐point network association link, similar to that of C. F. Goodeve. The model for amylose solutions is as follows. (a) Molecules are joined by association links in a loose network in solutions at rest; (b) the network, though resisting shear, is disrupted by shear; (c) the linear amylose molecules of helical, rod‐like configuration becomes parallel‐oriented under shear, this orientation being less favorable for reformation of the links. The shear stress on the solution at constant shear rate is predicted to decrease with time, the ultimate relation between shear stress and shear rate being pseudoplastic. For solutions of amylopectin, the following model is suggested. (a) Network association links exist between the highly‐branched, roughly spherical molecules in solutions at rest; (b) disruption of these links occurs under shear, but since the molecules are spherical, orientation unfavorable to reformation of links cannot occur; (c) it is assumed that the rates of destruction and reformation are about equal, but that as shear rates increase, the number of links existing at any time decreases. Thus, the shear stress‐shear rate relation is predicted to be pseudoplastic but independent of time of shear. These conclusions and the mathematical expressions derived from the models are supported by experimental data obtained with a coaxial‐eylinder viscometer so designed that shear stress is recorded versus time of shear over a wide range of shear rates. Temperature was closely controlled at 49°C. to avoid gelation.
Ultrafein filters as osmotic membranes
Authors: Vaughan M. F. 
Published: April 2003

AbstractThe use of ultrafein filters as osmotic membranes has been investigated in various solvents. It has been found that, at 30°C., measurements can be made in benzene, toluene, ethanol, water, and, with difficulty, methyl ethyl ketone, but not in chloroform or dimethylformamide. In benzene it has been found that all grades of the membranes are more selective than the corresponding ultracella filters and that, with the allerfeinst grade, molecular weights of the order of 2000 can be determined. With solutions of pentaerythritol tetrastearate (M.W. 1200), tristearin (M.W. 891), and sucrose octaacetate (M.W. 679), the osmotic pressures developed were less than the theoretical values. The ratios of observed to theoretical osmotic pressure decreased with molecular weight, and these ratios appear to be examples of the reflection coefficients predicted by Staverman.
The initiator efficiency of 2, 2′‐azobisisobutyronitrile in the polymerization of styrene and methyl methacrylate, and dicumyl peroxide as a polymerization initiator
Authors: van Hook J. P. , Tobolsky A. V. 
Published: April 2003

AbstractThe polymerization of styrene with 2,2′‐azobisisobutyronitrile (Azo I) as initiator has been studied at eight temperatures from 30° to 85°C. and methyl methacrylate at six temperatures from 30° to 67°C. With the use of the expression for the thermal rate of decomposition of Azo I given in a previous paper, the maximum scavenger efficiencies of styrene and methyl methacrylate have been calculated to be 60 and 80%, respectively. The efficiency is shown to be almost independent of initiator concentration except in styrene at very low concentrations of Azo I, where f, increases rapidly. If the true efficiency in methyl methacrylate is the same as in styrene, then the ratio of termination by disproportionation to overall termination is equal to about 0.3 for methyl methacrylate. The dicumyl peroxide‐initiated polymerization of styrene and methyl methacrylate has been studied from 60° to 100°C. The rate laws expressing the decomposition of initiator are: (for methyl methacrylate) kdf′ = 1.26 × 1016 exp { −36.4 kcal./RT} and (for styrene) kdf′ = 1.00 × 1016 exp { −36.4 kcal./RT}. Evidence is given to suggest that the initiator efficiency of DCP in styrene and methyl methacrylate is equal to unity.
Kinetic studies of α‐olefin polymerization
Authors: Natta G. 
Published: April 2003

AbstractThe kinetics of chain growth and chain transfer processes in the stereospecific polymerization of propylene, using catalytic systems such as TiCl3Al(C2H5)3 and TiCl3AlCl(C2H5)2, has been examined. The number of active centers present on the catalyst surface has been determined radiochemically by kinetic and adsorption measurements, using aluminum labeled with C14. The mean life of macromolecules was determined by radiochemical determination of terminal groups, and the relationships between intrinsic viscosity and number‐average molecular weight were found. Kinetic research into ethylene‐propylene copolymerization enableld us to determine the different reactivity ratios of the monomers.
Polymerization of methacrylonitrile with lithium in ammonia
Authors: Overberger C. G. , Pearce Eli M. , Mayes N. 
Published: April 2003

AbstractThe molecular weight of polymethacrylonitrile obtained in the system lithiumammonia‐methacrylonitrile at −75° increased with decreasing concentrations of lithium and increasing concentrations of methacrylonitrile, and in addition was found to be proportional to [methacrylonitrile]/[lithium]. On the basis of this and additional evidence, a one‐electron transfer from lithium to methacrylonitrile to give an anion radical is postulated. In addition, the structure of the colored polymer obtained is discussed on the basis of the infrared spectra.
High polymers obtained using organometallic complexes containing lithium and titanium
Authors: Kocheshkov K. A. , Kargin V. A. , Paljev O. A. , Talalajeva T. V. , Sogolova T. I. 
Published: April 2003

AbstractHigh polymers with a regular chain structure have been produced by polymerization of ethylene with complexes containing crystalline organolithium compounds and titanium tetrachloride in organic solvents. For this purpose RLi compounds have been prepared, R being methyl, ethyl, butryl, dodeeyl, tolyl, mesityl, naphthyl, benzyl, and other aliphatic and aromatic groups. The investigation of the polymerization has led to the elucidation of the influence of the nature of the organic radical bound with lithium on the properties of polythene formed. Thermomechanical data, infrared and X‐ray spectra, as well as viscometric molecular weight determination, have shown all specimens of polyethylene to be highly crystalline and of a regular chain structure. The polymers obtained have mechanical properties characteristic of polyethylenes of this type but with elongations that strongly differ in polymers produced using organolithium complexes with different radicals at the lithium. With some specimen, elongation has been found to reach extremely high values. Some suggestions have been made as to the causes of influence of different organic radicals in RLi on the properties of polymers.
On the question of applying chromium oxide and molybdenum oxide catalysts to obtain crystalline poly‐α‐olefins
Authors: Topchiev A. V. , Krentsel B. A. , Perelman A. I. , Miesserov K. G. 
Published: April 2003

AbstractThis article gives experimental data concerning the dependence of polymerization efficiency of chromium oxide catalyst upon the methods of preparation and reports on the character of the polymerization efficiency. The polyethylene and polypropylene obtained in this process of polymerization is characterized by high quality. Besides chromium oxide catalyst, molybdenum oxide catalyst with added lithium hydride was studied.
Polyethers. V. New catalysts for the preparation of isotactic polypropylene oxide
Authors: Osgan Mahesh , Price Charles C. 
Published: April 2003

AbstractAn exploration of a number of metal halides and metal alkoxides has revealed that a considerable number of these compounds are useful catalysts for conversion of propylene oxide to high molecular weight isotactic polymer. All contain metal ions capable of acting as Lewis acids. Mixtures of metal alkoxide and halide seem to be superior catalysts.
Trapped radicals in heterogeneous vinyl polymerization
Authors: Bamford C. H. , Jenkins A. D. , Symons M. C. R. , Townsend M. G. 
Published: April 2003

AbstractThe existence of trapped radicals in polymers prepared heterogeneously from vinyl monomers was first deduced from kinetic observations and subsequently confirmed by electron resonance spectroscopy. We have used this latter technique to determine the concentration of trapped polyacrylonitrile radicals obtained as a function of the experimental variables including the degree of swelling of the polymer, the rate of photo‐initiation and the temperature of polymerization. In the bulk polymerization of acrylonitrile at 25°C. the fraction of radicals which become trapped is approximately 12% for a conversion of 17%. The concentration of trapped radicals obtained in the presence of N,N‐dimethylformamide increases for low concentrations of the swelling agent, passes through a maximum, and subsequently decreases to zero. Qualitatively similar behavior is obtained if the swelling of the polymer is increased by the incorporation of methyl acrylate as commonomer. Addition of a swelling agent to the active photopolymer leads to destruction of the radicals. An increase in the concentration of trapped radicals with increasing light intensity (for a given conversion) is observed initially; at very high intensities the concentration decreases to zero. There is a marked decrease in the concentration of radical as the temperatur of polymerization increase; it is doubtful if trapping occurs significantly at 60°C. There observations are discussed in terms of previous kinetic studies and shown to be in general accord with the occlusion theory of heterogeneous polymerization. The effect of oxygen on the electron‐resonance absorption is characterized by a rapid initial decrease followed by a slow decay. The results are tentatively interpreted in terms of the formation of peroxy and/or HO2 radicals. It is surprising that the absorption line obtained with polyacrylonitrile radicals does not show the fine structure which would be expected to arise from interaction of the unpaired electrons with hydrogen and nitrogen nuclei. A possible reason for this is discussed.
Heterophase radiation polymerization of isobutene and methyl methacrylate
Authors: Worrall R. , Pinnar S. H. 
Published: April 2003

AbstractThe rate of the ionic polymerization of isobutene, induced at low temperatures by high energy radiation, is considerably increased when the reaction is carried out in the presence of certain inorganic compounds, notably metal oxides, of high surface area. The acceleration is not accompanied by a corresponding increase in the molecular weight of the polymer. The rate of polymerization of methyl methacrylate when exposed at room temperature to electrons at high intensity is increased by the presence of polyethylene powder. A consideration of the mechanisms of acceleration under heterogeneous conditions leads us to believe that the increase in rate in the first case is due to an increase in the rate of initiation and in the second case to a decrease in the bimolecular termination rate constant.
Some observaions on the effect of the physical nature of the separating phase on the rate of heterogeneous polymerization
Authors: Palit Santi R. , Guha Tilak 
Published: April 2003

AbstractStudy of the polymerization of methyl methacrylate and acrylonitrile in aqueous solution in a redox‐initiated system consisting in Na2S2O4–K2S2O8 reveals the fact that the initial rate of polymerization increases with increase in concentration of the catalyst or activator, and this is followed by a fall in rate with a further increase in concentration of either of the two, and finally the rate is found to increase again with higher concentration of the catalyst or activator. This peculiarity in the kinetics of the above heterogeneous polymerization seems to be connected with the physical state of the separating phase. In the region where the rate is increasing with increasing catalyst concentration, the insoluble phase is in the form of a fine sol. In the region where the rate falls with increased catalyst or activator concentration, the separating phase is in the form of a coarser, less stable sol (milky sol or latex). In the region where the rate again increases, the insoluble phase is in the form of a coarse precipitate or coagulum. The D.P. is observed to run more or less parallel with the rate. The above observations may have bearing on the kinetics of the emulsion polymerization and “explosive” polymerization.
The kinetics of block and graft copolymerization of acrylonitrile
Authors: Bamford C. H. , Jenkins A. D. , White E. F. T. 
Published: April 2003

AbstractThe polymerization of a monomer in the presence of a preformed polymer with suitable structural features gives rise to block or graft copolymers, which, in favorable circumstances, may be isolated as well‐characterized materials. For preparing block copolymers a primary polymer with amine endgroups can be used as a macromolecular transfer agent. Graft copolymers may be prepared by using a primary polymer with terminal double bonds which copolymerize with the second monomer. We have studied the kinetics of block and graft copolymerization based on these methods with particular references to the systems in which the second monomer is acrylonitrile. All transfer agents reduce the rate of heterogeneous polymerization of acrylonitrile since the reduction in molecular weight leads to a diminution in the mean degree of occlusion of the propagating radicals and a consequent increase in the effective termination coefficient. We have found the effect of macromolecular transfer agents on the rate to be greater than that of simple amines. This behavior is attributed to the fact that the radicals produced by transfer are attached to primary polymer chains which are present in solution; as propagation proceeds the growing radicals remain in solution until a comparatively late stage in their growth on account of the solubilizing action of the primary polymer chains. The termination coefficient for these radicals is therefore relatively high and the rate of polymerization correspondingly low. The solubilization of polymer radicals in graft polymerization is less marked than in block copolymerization; this is shown to be consistant with the mechanism of solubilization suggested.
Intermolecular forces and chain flexibility in linear polymers
Authors: Allen Geoffrey , Gee Geoffrey , Lanceley H. A. , Mangaraj D. 
Published: April 2003

AbstractIntermolecular forces in a fluid can be measured by the internal pressure, obtained most directly from the coefficient (∂P/∂T)v. Results are reported for a fluid polyisobutene over the temperature range −20.9°C. to +38.9°C. (Pi = 76 to 71.7 cal./cc.). Flexibility is assessed by comparing the activation volume for viscous flow (ΔV) with the molar volume (Vm). ΔV is obtained from measurements of the pressure coefficient of viscosity and for polyisobutene of Vm = 500 is ca. 100 cc./mole at low tmperatures. Above 20°C., ΔV begins to fall sharply; this is ascribed to the onset of flexibility, permitting segmental flow.
Sur certaince propriétes des polymères greffés en solution
Authors: Danon J. , Jobard M. , Lautout M. , Magat M. , Michel M. , Riou M. , Wippler C. 
Published: April 2003

AbstractAfin d'établir des régles générales de solubilité des copolymères greffés, nous proposons une ébauche de théorie et nous essayons de dégager, à partir de nos résultats et des données bibliographiques existantes, une base expérimentale pour une théorie plus perfectionnée. Les deux cas limités suivants sont envisagés:(a) Les polymeères sont parfaitement miscibles; (b) les deux polymères sont complètement incompatibles.Dans le cas (a), le coefficient de solubilité des copolymères greffés est une moyenne arithmétique de ceux des homopolyméres correspondants. Dans le cas (b), il est impossible d'attribuer au copolymère greffé un coefficient de solubilité et dans certaines conditions, les copolymères de taux de greffage intermédiaire devraient ětre insolubles. La séparation des copolymères greffés PVC–PAN, PVC–PMMA, PVC–PAN et PI–PS des homopolymères est étudiée et les résultats discutés à la lumière de la théorie cidessus. Dans le cas du copolymère greffé PI–PS, bien que les deux polymères constituants soient incompatibles, l'écart entre les coefficients de solubilité est suffisamment petit pour que son comportement se rapproche du cas (a) et il est possible d'évaluer le taux de greffage à partit des limites de précipitation. Les résultats expérimentaux de différents auteurs, relatifs à la solubilité des copolymères greffé sont également discutés.
Entanglement and other steric effects in crosslinked polymers
Authors: Blanchard A. F. , Wootton P. M. 
Published: April 2003

AbstractIt is well known that the modulus and equilibrium swellling of long‐chain polymers are both related to degree of crosslinking. Modulus theory normally assumes that chain segments are completely free at all points except the junctions of chains (crosslinks). In practice, however, there are trapped entanglements and other steric restrictions on the freedom of chains in highly crosslinked polymers. In addition, real polymers may not conform entirely with the Gaussian distributions assumed by elasticity theory. The present paper discusses these effects, including a steric effect whose contribution to modulus is dependent on chain flexibility and on linkage concentration. Similar but smaller modifications appear necessary in the case of equilibrium swelling in solvent. The molecular weight of the polymer is taken into account by an adaption of Flory's theory, and a simple correction is proposed to take account of entanglements. The relation between modulus and equilibrium swelling is considered for natural rubber when vulcanized by peroxides or by sulfur, and an assessment is made of the relative effects of steric hindrance on modulus and equilibrium swelling. This is converted to an absolute estimate of steric effects by calculations based on Moore and Watson's chemical determinatios of crosslinking. The equations derived have a convenient form in which there is a parameter ω to take account of steric effects. The contribution which this makes to the modlulus is not constant because it is determined by the magnitude of ω relative to the molecular weight Mc between crosslinks. The reciprocal of ω is taken to be a measure of chain flexibility. By measurements of modulus and equilibrium swelling over a wide range of crosslinking a measure of the molecular flexibility can be obtained, together with an estimate of the solubility parameter μ for the polymer and solvent. For peroxide cures it is found thatd that μ is roughly constant when toluene is the solvent, but for sulfor vulcanizates this appears to be true only at low states of cure. The evidence suggests that μ changes from 0.42 to 0.45 when a high proportion of sulfur is combined with the rubber. Therefore peroxide cures should be used for comparing the chain flexibility of polymers. For sulfur vulcanizates these changes in μ make swollen modulus the most reliable methode of measuring crosslinking. It is estimated that eight atoms of sulfur are combined for every crosslink that is formed in the early stages of vulcanization. The work described should assist studies of curative agents and of the difference between polymers.
The orientation of polyethylene
Authors: Stein R. S. 
Published: April 2003

AbstractThe orientation of the crystals and the amorphouse regions of polyethylene occurring during stretching has been studied using the combined techniques of x‐ray diffraction, infrared dichroism, and birefringence. The state of orientation is expressed in terms of the position of a point on a triangular “orientation diagram.” It is found that the a and b crystallographic axes orient differently. The degree of crystalline orientation is greater at a given elongation for a sample oflower degree of crystallinity than higher. An appreciable amount of amorphous orientation occurs, and appears greater in the more crystalline samples. Orientation oflarger crystalline aggregates has been studied using the light scattering technique and is found to parrallel that of the crystallites. A model consistent with these various types of experimental studies is proposed.
Strain‐induced crystallization in polyethylene terephthalate
Authors: Thompson A. B. 
Published: April 2003

AbstractAlthough crystallization under stress occurs in nearly all synthetic fiber making, giving fine fibrillar fiber structures, it has been relatively little studied; and the literature, centered mainly round coarser spherulitic crystallization, does not take us very far in understanding it. However, a simple experiment shows that it is very important. If a filament of amorphous polyethylene terephthalate is stretched over a hot plate between two roller moving at different speeds, stretching can take place either without crystalization at low tension, or with considerable crystallization at high tension, at the same temperature and speed, simply according to the method of starting the machine. A model visco‐elastic theory based on Maxwell's equation is, therefore, developed to describe this behaviour using the simplest possible assumptions. Further experiments then show that this simple and partly empirical theory fits the observed behaviour of polyethylene terephthalate reasonably well, and the simple assumptions made, therefore, seem to give a first approximation to the course of strain induced crystallization. They correspond with the idea of exremely rapid crystallization from a nucleus to a small structural unit, the density of nucleation being dependent on the stress. Parallel work on the streching of spherulitic structures is then mentioned, and it is finally suggested that stress induction and rapid growth to a small structural unit may be common to both spherulitic crystallization under internal stresses, and fibrillar crystallization under an externally applied stress.