bluuebunny/crossref_metadata_2025_split huggingface dataset:
X‐Ray and light scattering by chain molecules in solution
Authors: Porod G. 
Published: April 2003

AbstractStarting from Debyes theory the problem of x‐ray and visible light scattering of chain molecules in solution is shown to be essentially a problem of distance statistics. The exact calculation of the average \documentclass{article}\pagestyle{empty}\begin{document}$\overline {r^4 }$\end{document} is carried out for a simple model in order to characterize the distance distribution functions as to their width. On that basis a refined approximation of the scattering function is available. By a numerical example the essential features of the preliminary theory are corroborated. It is shown that the scattering function of a coiled chain molecule approaches asymptotically that of the corresponding rigid rod.
The distribution of polymer fractions
Authors: Sayre Edward V. 
Published: April 2003

AbstractSystems which obey the Flory‐Scott equation are discussed, and it is shown that the molecular‐weight distribution of increasingly small fractions taken from a polymer solution of the same initial concentration becomes constant. Means of calculating this limiting distribution of an incipient fraction are presented, and it is shown that, in a practical sense, all fractions smaller than the order of one‐sixth the polymer present have nearly the same distribution. To obtain sharp fractions it is more efficacious to take a small number of cuts per stage and refractionate a number of times.
Viscometric detection of branching in polymers. II. Branching in poly(butadiene‐co‐styrene) as a function of polymerization temperature
Authors: Cragg L. H. , Fern G. R. H. 
Published: April 2003

AbstractSamples of poly(butadiene‐co‐styrene)—all of charge ratio butadiene:styrene 72:28—were prepared in emulsion at 15, 30, 40, and 50°C. Essentially the same redox recipe was used for each, with slight modifications to produce in about the same time polymers of similar intrinsic vistex (1.9 to 2.0) at similar conversions (about 65%) well below the gel point. Each sample was fractionated by precipitation from 1% benzene solution with methanol, special pains being taken to obtain fractions of equal size (each around 5% of the original rubber in the sample fractionated). Careful measurements of the viscosity functions [η], β, and k′ for each fraction were made; with every sample except that prepared at the lowest temperature, the values of β and k′ were observed to deviate in the high molecular weight region from the “base value” common to lower fractions, the deviation starting at a lower molecular weight, and being greater at a given high molecular weight, the higher the temperature of polymerization. It is concluded that branching in a diene polymer of this type is repressed as the temperature of polymerization is decreased: the lower the temperature the higher is the molecular weight at which branching is detectable and the lower is the degree of branching at a given molecular weight. In the 15°C. rubber no branching was detectable at any molecular weight.
Hydratation de diverses formes polymorphes de la cellulose
Authors: Champetier G. , Legrand C. 
Published: April 2003

AbstractX‐ray diffraction experiments confirm the data obtained by the blotting or centrifuging method, concerning the action of water which penetrates at different degrees in the regions of cellulose. Different forms of cellulose are more or less easily accessible. X‐rays only show variations of intensity for native cellulose, but the unit cells are changed for lattices II and IIIα; the transformations are still deeper for cellulose IIIβ. X‐ray diffraction does not permit determination of the stoichiometric ratios.
Diffusion of acetone into cellulose nitrate films and study of the accompanying orientation
Authors: Drechsel Paul , Hoard J. L. , Long F. A. 
Published: April 2003

AbstractStudies have been made of sorption and desorption of acetone by films of cellulose nitrate (11 and 12% N) at 30°C. by following the weight of vapor takeup or loss as a function of time. The takeup‐time curves show marked inflections and plots of takeup versus \documentclass{article}\pagestyle{empty}\begin{document}$\sqrt t$\end{document} are initially nonlinear for both sorption and desorption, indicating that Fick's law with the usual boundary conditions is not obeyed. The rate of vapor takeup is also considerably more rapid and different in character for films cast on glass than for films cast on mercury. A striking result is that for successive sorption‐desorption cycles the rate of sorption decreases markedly, e.g., by a factor of 16 for five cycles. Studies of the optical anisotropy of the films show that the orientation of the polymer molecules normal to the plane of the film is increased by the diffusion process and it is concluded that this accounts for the decreased rate for successive sorption‐desorption cycles and provides an explanation for the diffusion anomalies. A possible cause of this orientation is the observed anisotropic swelling combined with slow movement of the polymer segments.
Crystallization of polyethylene terephthalate
Authors: Cobbs W. H. , Burton R. L. 
Published: April 2003

AbstractA method for following rapid crystallization in polymers using infrared absorption has been devised. The infrared absorption was correlated quantitatively with the density of polyethylene terephthalate for varying degrees of crystallinity and qualitatively with the change in x‐ray diffraction pattern on crystallization of this polymer. This technique has been applied to measure the crystallization–time curves of thin films of polyethylene terephthalate at intervals of 10°C. for temperatures between 120 and 240°C. Half‐times from these curves show a minimum near 190°C. The temperature dependence of the data is discussed in terms of the Volmer‐Becker‐Turnbull theory of nucleation in condensed systems. An activation energy of 20 kcal./mole for short‐range diffusion of chain segments is obtained from the temperature coefficient of the observed induction time. The data on the kinetics of the crystallization are compared with the results of an analysis of Avrami. A constant, A, was introduced into Avrami's equation to give:

A is the limiting volume fraction of crystalline material after a long time and was determined from density measurements. The crystallization was found to follow this equation from 2 through 90% transformation for temperatures from 120 to 180°C. Deviation appeared in the region below 10% transformation at higher temperatures. The value of k was interpreted as indicating plate‐like growth at crystallites from 120 to 180°C.
Rupture of rubber. I. Characteristic energy for tearing
Authors: Rivlin R. S. , Thomas A. G. 
Published: April 2003

AbstractA criterion for tearing of test‐pieces cut from thin sheets of a natural rubber vulcanizate, similar in form to the Griffith criterion for spreading of a crack, is formulated. This criterion involves a characteristic energy for tearing which is independent of the shape of the test‐piece and of the disposition of the cut. It is shown how this characteristic energy can be found experimentally for a particular vulcanizate and used to predict the force required to tear test‐pieces of the vulcanizate.
Properties of dilute solutions of polymethylmethacrylate. II
Authors: Bischoff J. , Desreux V. 
Published: April 2003

AbstractA discrepancy between the previously reported viscosity‐weight‐average molecular weight relationship obtained for fractionated polymethylmethacrylate in acetone and that given by Meyerhoff and Schulz is attributed to the great influence of small chemical inhomogeneities on the molecular dimensions in the poor solvent acetone. Light‐scattering results for the root‐mean‐square end‐to‐end distance R have been recalculated, taking into account a correction pointed out by Oth. It is shown that the results are in excellent agreement with the relation R3 = M[η] 2.1 × 1021 proposed by Flory and Fox, rather than the M1/2 dependence predicted for R by Kuhn.
Benzoyl peroxide initiated polymerization kinetics of vinyl monomers in various solvents
Authors: Conix André , Smets G. 
Published: April 2003

AbstractInitial rates of polymerization in the presence of benzoyl peroxide as initiator have been determined for methyl methacrylate, vinyl acetate, and vinyl chloride in order to determine the order of reaction with respect to the monomer concentration. In the case of methyl methacrylate, the order of reaction is 1 if benzene is used as solvent; with tert‐butylbenzene, the order of reaction is more complex, and can be interpreted by a “complex” formation mechanism (Mark‐Josefowitz) or by cage effect (Matheson). In the case of vinyl chloride and vinyl acetate in the presence, respectively, of ethyl chloride and ethyl acetate as solvent, the order of reaction has been evaluated to 3/2 vs. monomer concentration. On the contrary, addition of benzene, even in small quantities, produces a strong decrease in rate of polymerization in the case of vinyl acetate, and makes it illusory to determine the order of reaction at high monomer concentrations. Preliminary results using azo‐bis‐isobutyronitrile as initiator for vinyl acetate with benzene as solvent have shown that the considerable influence exerted by benzene in the previous case cannot be attributed to a difference of rate of decomposition of the peroxide only. The results are interpretd by the mechanism of chain‐transfer reactions on the solvent, with formation of radicals from which the relative stability is different from that of the growing chains.
Calibrage de la diffusion lumineuse
Authors: Oth A. , Oth J. , Desreux V. 
Published: April 2003

AbstractNous utilisons la méthode de transmission pour calibrer la diffusion lumineuse. Nous vérifions en utilisant des solutions d'indices de réfraction différents que la correction de réfraction est pratiquement n2 pour l'intensité diffusée, l'intensité incidente à travers la cellule devant être corrigée empiriquement pour une réfraction due à la légère divergence du faisceau primaire. A partir de ce calibrage, nous obtenons pour le rapport de Rayleigh du benzène à 20°C. et pour λ 4358 A. R = (48,4 ± 1,5)10−6 cm.−1. Pour les mesures de dissymétrie dans la cellule commerciale semioctogonale “Pyrocell,” nous montrons la présence de réflexions totales pour les solutions d'indice de réfraction ≥ 1,41, réflexions qui peuvent être éliminées aisément en plaçant un verre absorbant dansle fond de la cellule. D'autre part, nous calculons la correction à apporter à la dissymétrie du fait des réflexions de Fresnel quand le faisceau lumineux émerge normalement à la paroi de la cellule.
Copolymerization of isobutylene and styrene at low temperatures in the presence of friedel‐crafts catalysts
Authors: Rehner John , Zapp R. L. , Sparks W. J. 
Published: April 2003

AbstractIsobutylene and styrene were copolymerized at low temperatures, in methyl chloride solution, in the presence of aluminum chloride. The temperature was varied from −30 to −94°C., and the monomer/solvent ratio, the ratio of monomers, and the catalyst concentration were varied over a considerable range. The copolymerization equation was found to be applicable to the data, and the reactivity ratios were determined for various experimental conditions. For an “open” system in which the volume steadily increases during the course of polymerization, it is shown that the copolymerization equation is formally identical to that of Mayo and Lewis, except that concentrations are replaced by amounts of the reacting species. The temperature coefficients of the reactivity ratios in the present system are compared with those for free‐radical systems; some important differences are noted. The reactivity ratios of isobutylene and styrene in the present system are greatly increased under conditions of turbulent agitation. A procedure for the compositional fractionation of the copolymers is described. The results are interpreted in terms of the copolymer chain structure; they appear to admit the postulate that the reactivity ratios and corresponding propagation rate constants are functions of chain length.
Molecular weight dependence of the intrinsic viscosity of polymer solutions. II
Authors: Krigbaum W. R. , Flory P. J. 
Published: April 2003

AbstractIntrinsic viscosities of polystyrene and polyisobutylene fractions in good and in “ideal” solvents have been examined from the point of view of their dependence on molecular weight. A compilation of results is presented which covers exceptionally wide ranges, from several thousand to several to million, in molecular weight. The intrinsic viscosity in an “ideal” solvent (i.e., cyclohexane at 34°C. for polystyrene, or benzene at 24° for polyisobutylene) is remarkably well fitted over the molecular weight range cited above by the relation:

where K is a constant, independent of molecular weight, for a particular polymer at a given temperature. The molecular expansion factor α3 which applies in good solvents (e.g., toluene for polystyrene and cyclohexane and diisobutylene for polyisobutylene) as calculated from:

increases with molecular weight approximately in accordance with the relationship:

However, the quantity (α5 − α3)/M1/2 changes appreciably with M in some cases. This is particularly true for molecular weights below 50,000. Results of an examination of the effect of rate of shear on the viscosity of polystyrene in benzene at 25° and in cyclohexane at 34°, and of the intrinsic viscosity‐molecular weight relation for polystyrene in benzene at 25°, are reported.
A method for studying crosslinking in addition polymerization
Authors: Alfrey Turner , Berdick Murray 
Published: April 2003

AbstractVinyl acetate has been copolymerized with small amounts of the diallyl ester of dithiodiglycolic acid (DADT). A method has been devised for the reduction of the disulfide crosslinks to sulfhydryl groups by means of thioglycolic acid under mild conditions, thereby enabling the recovery of the primary molecules of the original polymers. The method has been applied both to soluble copolymers (made with the lowest concentrations of DADT) and to insoluble space‐network copolymers (made with slightly higher concentrations of DADT). The polymers have been characterized before and after reduction by viscosity determinations. The reduction process had only a negligible effect on the viscosity of poly(vinyl acetate). The rate of reduction was diffusion controlled not only in the case of the gels, but apparently also in cases where soluble polymers were made with amounts of DADT less than necessary for gelation at high conversion. The DADT acted not only as a crosslinking agent, but also as a chain transfer agent. The method is suggested as potentially useful in developing the theory of three dimensional polymerization, and in studying the properties of space‐network polymers.
Studies on heat deterioration of specially prepared natural rubber vulcanizates
Authors: Metz Donald J. , Mesrobian Robert B. 
Published: April 2003

AbstractNatural rubber has been vulcanized to varying degrees of crosslinkage through the use of decamethylene dismethyl azodicarboxylate. The effect of degree of crosslinkage on extent of heat deterioration is demonstrated. Studies are also presented on the beneficial or deleterious action on heat deterioration of various chemical agents incorporated in the free state into natural rubber vulcanizate.
Influence of temperature of polymerization on the structural composition of emulsion polymers of butadiene
Authors: Condon F. E. 
Published: April 2003

AbstractThis report assembles and correlates published data relating to the effect of temperature of polymerization on the structural composition of butadiene polymers, that is, on the relative percentages of polymer double bonds, derived from butadiene, in the 1,2 (vinyl), trans‐1,4, and cis‐1,4 configurations. The data support, and are not in conflict with, the following conclusions: (1) The percentages of vinyl, trans, and cis double bonds in emulsion polymers of butadiene are determined primarily by the temperature of polymerization in the fundamental way that is characteristic of systems of simultaneous competing reactions. (2) Other environmental features, such as type of recipe, and including the presence of a comonomer, e.g. up to 29% of styrene, have comparatively little effect on the relative amounts of vinyl, trans, and cis double bonds. (3) Differences in the physical properties of emulsion polymers of butadiene prepared at the same temperature probably must be attributed to differences in structure other than differences in the relative proportions of vinyl, trans, and cis double bonds, such as the average molecular weight, the molecular weight distribution, and the presence of a comonomer. It is shown that a maximum in the percentage of vinyl double bonds, previously indicated by experiment but attributed to gelation, is inherent to this system of three simultaneous competing modes of polymerization.
Second approximation calculations of mechanical and electrical relaxation and retardation distributions
Authors: Williams Malcolm L. , Ferry John D. 
Published: April 2003

AbstractSecond approximation methods for calculating distribution functions of mechanical relaxation times from complex dynamic data have been improved so that calculations of adequate accuracy can be made over a wider range of variables than was previously possible. Analogous methods for calculating distribution functions of mechanical retardation times and electrical relaxation times are given. The numerical values of the required second approximation correction factors are tabulated.
Gutta. I. Single crystals of alpha‐gutta
Authors: Schlesinger Walter , Leeper H. M. 
Published: April 2003

AbstractGutta, the polyisoprene hydrocarbon obtained from gutta percha or balata, is usually considered to differ from rubber in that gutta is a trans‐isomer and rubber a cis‐isomer of polyisoprene. Most of the data on the basis of which these structures have been assigned come from x‐ray diffraction pictures of polycrystalline polymer. Single crystal data have not been published, although such data would provide more detailed information. Chicle gutta has been shown to be a lower molecular weight modification of gutta from gutta percha. As a consequence of its lower molecular weight chicle gutta is a granular, free‐flowing powder, whereas gutta percha gutta is horny and tends to clump together. Because of its physical characteristics and lower molecular weight, chicle gutta was used first in an attempt to grow single crystals of gutta. By working with dilute solutions, well‐shaped single crystals of chicle gutta as large as 0.35 mm. in the long direction were obtained. From gutta percha Pahang, crystals 0.10 mm. long were isolated. Crystals could be grown either by slow diffusion of solvent or by cooling a supersaturated solution. Crystals were found to be optically anis tropic and to exhibit parallel extinction when examined under crossed Nicols with the polarizing microscope. Crystals obtained were of the alpha modification of gutta.
Texture of some crystalline synthetic polymers by electron microscopy
Authors: Cooper A. C. , Keller A. , Waring J. R. S. 
Published: April 2003

AbstractThe importance of sample preparation is demonstrated with examples of techniques based on (1) evaporation in vacuo, (2) casting from solvent or solvent mixtures, (3) ultrasonic disintegration. Attention is drawn to the “sheaf‐like” arrangement of the microfibrils and to other aspects of the texture. There is evidence of periodicities, but these are considered to vary with the preparation, and may be a consequence of the helical arrangement and “rope‐like” character of the bundles of microfibrils or of a tendency to form a woven texture.
Uncertainties in measurement of osmotic pressure of polymer solutions
Authors: Cleverdon D. , Laker Mrs. D. , Smith P. G. 
Published: April 2003

AbstractFor a particular sample of polystyrene, different osmometric estimates of Mn have been reported. The possibility that the difference is due, in the one case, to permeation of the membrane by low molecular weight polymer has been carefully considered. It is shown that this can not be the explanation. The difference is in some way associated with chemical differences in the membranes used. Apart from these considerations of error, the significance of the number‐average molecular weights of the unfractionated polymers of commerce is shown to be more acutely dependent upon the detail of the low molecular weight end of the distribution than may be realized. The present calculations are based upon a realistic estimate of the low molecular weight polymer content of commercial polymers.
Gutta. II. Interconversion of alpha and beta forms
Authors: Leeper H. M. , Schlesinger Walter 
Published: April 2003

AbstractThe gutta isolated from chicle has been demonstrated to be structurally identical with trans‐polyisoprene from gutta percha and balata but has a molecular weight of 16,000–18,000, about one‐half that of the latter two polymers. Its ease of purification and marked crystalline behaviour suggested its use in a study of gutta polymorphism.The α‐and β‐forms of chicle gutta were prepared and their identities were established by means of x‐ray diffraction measurements and melting properties. The degree of crystallinity and internal molecular strain were shown to affect the melting points of the two forms of gutta through wide ranges. Interconversions of α‐and β‐guttas were effected by means of heat conditioning, solution and reprecipitation, melting and resolidification, and treatment of the gutta with nonsolvents. Dilatometric data were used to describe the change of specific volume when β‐gutta was converted to α‐gutta in a conditioning bath as the temperature was increased stepwise from 30°C. to 80°C. at the rate of 1°C. per hour. The discontinuous, saw‐toothed nature of the specific volume vs. time curve was rationalized on a basis of reactions involving changes in degree of molecular order and relief of strain within the gutta. The curve suggested the following gross reactions: 30–36°C., thermal expansion of β‐gutta of low crystallinity; 36–52°C., increase in degree of crystallinity of β‐gutta; 52–60°C., melting of β‐gutta; 60–64°C., transition of β‐ to α‐gutta; 64–72°C., melting of α‐gutta; 72–80°C., thermal expansion of molten gutta. α‐Gutta, in the melted condition, was shown to undergo a transition, above 72°C., to a form whose stereo identity has not yet been established. The rate of transition from β‐to α‐gutta at temperatures at which α‐is the stable form, appeared to be hastened in the presence of certain liquids.