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  • Polymer and Materials Science  (443)
  • 42.75  (6)
  • 1950-1954  (449)
  • 1953  (449)
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Publisher
Years
  • 1950-1954  (449)
Year
  • 1
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    Journal of Polymer Science 10 (1953), S. 1-18 
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: As an alternative method to fractionating the polymer into portions of different molecular weight, in order to obtain the distribution of molecular weights, the method of fitting by statistical moments is proposed. It is shown how from a knowledge of differen order, utilising the inequalities between such averages and their relation to the dispersion of molecular weight, estimates of the distribution function can be obtained: (A) under the assumption of a standard form for the distribution function; (B) without such an assumption, but building up the approximation from a standard form as the norm function and its derivatives; (C) without using any standard form of distribution at all. Numerical examples of the fitting procedures accompany the exposition.
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  • 2
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    Hoboken, NJ : Wiley-Blackwell
    Journal of Polymer Science 10 (1953), S. 19-28 
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The various stages employed in the production of a phenolformaldehyde cast resin are discussed. It is assumed that the chains formed during the condensation stage undergo a rearrangement upon acidification to yield roughly spherical, stabilized micelles. These micelles are concentrated by dehydration until coalescence begins. At this point the chains again rearrange and the resin becomes the continuous phase. Pronounced changes in the properties of the system are observed at this critical point. The effects produced by undercondensation, overcondensation, overdehydration, etc. are mentioned briefly. The ionizable components, by determining the interfacial pH during the curing stage, are shown to be directly related to the rate of cure, stability, color, light transmissibility, etc. of the cured casting. Transparent castings are expected only when an ionizable component of the proper refractive powers is oriented at the interface. An examination of the immediately available data provides a lead to the future changes that can be expected as aging progresses.
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  • 3
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Light-scattering investigations (angular and wavelength dependence) are made on a series of fractionated polymethacrylates; the diffusion constant, sedimentation constant, and intrinsic viscosity [η] are also determined. Molecular weights and diameters of the random coils are in agreement with these methods. Dependence of the diameters of the random coil dst on molecular weight is somewhat stronger than required by Kuhn's root law (dst∼M0,6). The influence of this finding on Debye's scattering function and on the Kirkwood-Riseman viscosity equation is studied.
    Notes: Sur une serie de palyméthacrylates de méthyl fractionnés des mesures de la diffusion lumineuse (en fonction de I'angle et de la longeur d'onde) on été faites, puis la constante de diffusion, la constante de sédimentation dans I'ultrazentrifugeuse et la viscosité intrinshque [η] ont été déterminés. Les poids moléculaires et les diamètres des chaînes souples sont en concordance d'après ces méthodes. La dépendance des diametres des chaines sonples d,l du poids molkculaire est un peu plus forte que d'aprh la loi de Kuhn (dst ≃ M0.6). L'influence de cette decouverte sur la fonction de la diffusion lumineuse de mihe que sur l'equation de la viscosite de Kirkwood et Riseman est étudiée.
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  • 4
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    Hoboken, NJ : Wiley-Blackwell
    Journal of Polymer Science 10 (1953), S. 128-128 
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
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  • 5
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
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  • 6
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    Hoboken, NJ : Wiley-Blackwell
    Journal of Polymer Science 10 (1953), S. 149-155 
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: In this paper an apparatus is described for polymerizing monomers in bulk up to a pressure of 10000 atmospheres and in which the polymerizing substance can be heated and the temperature of the substance measured. Styrene shows an explosive reaction at 10000 atmospheres and at about 70°C. Indene polymerizes slowly when heating at 10000 atmospheres and shows an explosive reaction at 175°C. Both compounds give a solid polymer. Crotonaldehyde heated at 10000 atmospheres gives a brittle, high-melting polymer. Coumarone and some chlorinated ethylenes carbonize when heated at 10000 atmospheres. Butyraldehyde polymerizes to a solid product which rapidly reverts to butyraldehyde.
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  • 7
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Four polystyrene samples were investigated in numerous laboratories by means of viscosimetry, osmometry, light scattering, and ultracentrifuge. The various results are compared and critically discussed. Possible explanations and suggestions for improvement are offered in those cases where considerable discrepancies occur. The results of viscosimetry and osmometry in general do not give satisfactory agreement whereas the light-scattering data, particularly in the high-molecular-weight range, and the few available ultracentrifugal results agree quite satisfactorily.
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  • 8
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Molecular weights of lactoglobuline and trypsin, as determined at pH 6.8, agree with the data generally admitted. However the molecular weight of trypsin in 1/100 M hydrochloric acid solution in the absence of salts, is two to three times lower than the value received in buffered solution at pH 6.8. With the purpose of detecting any combination or polymerization reaction, the study of mixtures showed that no conclusion may be obtained from the values of diffused light intensity at 90° when the diffusion diagram is not rigorously symmetrical.
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  • 9
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
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  • 10
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Samples 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.
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  • 11
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    Hoboken, NJ : Wiley-Blackwell
    Journal of Polymer Science 11 (1953), S. 150-150 
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
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  • 12
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    Hoboken, NJ : Wiley-Blackwell
    Journal of Polymer Science 11 (1953), S. 139-149 
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: This 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.
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  • 13
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Second 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.
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  • 14
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
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  • 15
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    Hoboken, NJ : Wiley-Blackwell
    Journal of Polymer Science 11 (1953), S. 187-189 
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
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  • 16
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    Journal of Polymer Science 11 (1953), S. 177-186 
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The dielectric properties of polyvinyl isobutyral, hexanal, and 2-ethylhexanal have been investigated. Dielectric constants and loss factors were measured at eight frequencies between 50 and 100,000 cycles in the temperature range of 25 to 130°C. Free energies, entropies, and enthalpies of activation were calculated, using the absolute reaction rate theory. The results illustrate the effects of “internal plasticization.” With increasing complexity of the interchain substituent, the electrical relaxation time is lowered, and the free energy, entropy, and enthalpy of dielectric relaxation are also decreased. These changes offer a quantitative measure of the decrease in interchain forces. It was also noted that the normal aldehyde substituents exhibited greater plasticizing action than the branched chain secondary groups. The electrical transition temperatures were compared with independently determined softening and inflection temperatures. The electrical and mechanical determinations were in good agreement for identical samples of the polymers.
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  • 17
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    Hoboken, NJ : Wiley-Blackwell
    Journal of Polymer Science 11 (1953), S. 189-192 
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
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  • 18
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    Journal of Polymer Science 11 (1953), S. 151-168 
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Recent experiments have indicated that the diffusion properties of a penetrant-polymer system may change with time as diffusion proceeds. It is thought that two possible explanations of these time effects are slow changes of polymer structure accompanying diffusion and internal stresses exerted by one part of the polymer sheet on another as it swells. Two theoretical models are set up in order to express these effects quantitatively. The first model is essentially that in terms of which mechanical and other properties of polymers are commonly discussed, involving the concept of an instantaneous change of diffusion coefficient when the concentration changes, followed by a slow drift toward an equilibrium value. The second model expresses the effect of stresses set up between the outer swollen layers and the unattacked center of a polymer sheet during sorption. These stresses are slowly relieved as the diffusion proceeds, leading to a time-dependent diffusion coefficient. The main features of diffusion behavior are established by calculation and the models are shown to account for the various types of sorption and desorption curves observed experimentally under different conditions, e.g., for sheets of different thicknesses and for different ranges of penetrant concentration. As examples, sorption and desorption curves calculated from the first model are shown to agree reasonably well with experimental curves for the methylene chloride-polystyrene system. The rate of sorption and of the associated change in area of the sheet are accounted for by the second model. The presence of internal stresses also provides an explanation for the observation that there may be an appreciable interval of time during which a thin sheet takes up more penetrant than a thicker one under corresponding conditions. On the other hand, it is the slow structural changes which cause the rate of sorption to be not always inversely proportional to the square of the thickness of the sheet. It is concluded that both polymer relaxation and internal stresses play a part in determining diffusion behavior. The particular experimental results examined can be accounted for if the half-life of the slow structural changes is comparable with that of the sorption experiment itself, and if the internal stresses change the diffusion coefficient by a factor of two or three.
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  • 19
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    Journal of Polymer Science 11 (1953), S. 215-220 
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The 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.
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  • 20
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The transition temperatures (TG) of unfractionated vinyl acetate polymers increase from 17° to 26° as the molecular weight increases from 14,000 to 104,000 and from 26° to 28° as the molecular weight increases from 104,000 to 1,120,000. The minimum molecular weight above which increase in molecular weight does not appreciably change TG is about 100,000. TG increases linearly with the reciprocal of the square root of the molecular weight.
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  • 21
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    Journal of Polymer Science 11 (1953), S. 203-213 
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Gutta, 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.
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  • 22
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Hydroxyethylated polyvinyl alcohols (HEPVA's) containing 12, 19, and 35% combined ethylene oxide were prepared by a heterogeneous reaction between dry polyvinyl alcohol (PVA) and liquid ethylene oxide. Another sample containing 18% was prepared by a more nearly homogeneous reaction in the presence of water. These derivatives may be analyzed satisfactorily by the modified zeisel method of Morgan. The properties of the HEPVA's are briefly described. Reaction of HEPVA with p-toluenesulfonyl chloride showed that secondary hydroxyls were tosylated along with the primary and that the two reactions cannot be separated kinetically. This method, useful in estimating the primary hydroxyl content of hydroxyethylcellulose, cannot be applied to HEPVA. The stability of the tosylates indicated, however, that in derivatives containing up to 35% combined C2H4O2 ca. 1/2 ethylene oxide per vinyl alcohol unit, no polyethylene glycol chains were present and all combined ethylene oxide existed as individual hydroxyethyl groups distributed along the PVA backbone. Introduction of ethylene oxide into PVA increased the reactivity of residual secondary hydroxyls toward chemical reagents by destroying the normal high degree of hydrogen bonding and making adjacent domains more accessible for reaction. Very noticeable differences in properties were observed between HEPVA's prepared under differing conditions of heterogeneity. Two such polymers of similar ethylene oxide content showed quite different extents of reactions, susceptibility toward swelling agents, and x-ray diffraction diagrams. These differences are attributed to a more random distribution of hydroxyethyl groups along the PVA backbone in the product of the more homogeneous reaction which leads to a more disordered system.
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  • 23
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    Journal of Polymer Science 11 (1953), S. 225-231 
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: For 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.
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  • 24
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: When a dilute pyridine solution of vinyl chloride polymers or copolymers is heated and a few drops of alcoholic hydroxide are added to the hot solution, a dark brown color develops. The response of vinyl chloride polymers in this reaction is much more intense than that of most other organic compounds, probably due to the conjugated double bonds produced in the main chain through the loss of hydrogen chloride. In addition to straight degradation of the polymer, the formation of an isocyanine dye is suggested by a mechanism which, besides pyridine and the polymer, involves the alkali alkoxide as a reactant.
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  • 25
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A study is made of the behavior under constant shear stress of several carefully characterized samples of polyisobutylene. The materials used are whole polymers and fractions obtained from these by dractional precipitation. As a first step in the characterization, the intrinsic viscosity of each is determined. It is shown that the samples cover a molecular weight range from 1 × 105 to 1 × 106. To provide a more detailed characterization, sedimentation equilibrium experiments are performed with several of the polyisobutylenes. These experiments yield values of several average molecular weights for each polymer, from which data an approximation to the molecular weight distribution can be made. It is pointed out that the whole polymers of isobutylene are very polydisperse. The viscosity-average molecular weights calculated from these experiments are in good agreement with the results of the intrinsic viscosity measurements. The viscoelastic behavior of some of these polymers is then studied by means of creep and recovery experiments. The melt viscosity is determined in two ways, from flow during creep and from the amount of nonrecoverable deformation after elastic recovery. The elastic recovery of the polyisobutylene samples is analyzed in some detail. A method for the reduction of data taken at several temperatures to a standard temperature, previously used for dynamic-mechanical properties and stress relaxation data, is shown to be applicable to elastic recovery data. Furthermore, the results of creep and recovery experiments can be superimposed in favorable cases. The steady-state elastic compliance is evaluated, and errors in its determination discussed. The results would seem to indicate that this quantity depends, at least in part, upon the degree of polydispersity of the polymer. This dependence appears to mask any direct variation with average molecular weight. Finally, it is shown that an average retardation time is directly proportional to the melt viscosity of the polymer.
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  • 26
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    Journal of Polymer Science 11 (1953), S. 269-276 
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Butadiene popcorn polymer reacted readily with oxygen to produce a yellow to orange colored product. The apparent over-all activation energy for the reaction averaged 16.7 kcal. Using the reaction with oxygen as a measure of the degree of unsaturation, the glassy type butadiene popcorn polymer was found to be more saturated that the earlier generation popcorn from which it was grown. The induction period which precedes the logarithmic growth of the polymer when placed in the presence of monomer increased as the oxygen content of the seeds increased. No increase in growth activity was ever attained by exposing the seeds to oxygen. Short exposures of the seeds to oxygen up to three hours at room temperature had no effect on the growth activity of the seeds. No correlation could be found between the seed growth activity and the degree of unsaturation as determined by the oxidation reaction.
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  • 27
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    Journal of Polymer Science 11 (1953), S. 277-280 
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
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  • 28
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    Journal of Polymer Science 11 (1953), S. 280-281 
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
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  • 29
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    Journal of Polymer Science 11 (1953), S. 281-285 
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
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  • 30
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
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  • 31
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    Journal of Polymer Science 11 (1953), S. 299-305 
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Addition of its polymer causes methyl methacrylate to polymerize. The extent of polymerization is linear with time of reaction to at last 5% conversion at 60-90°C. The rate of polymerization is proportional to the first power of the concentration of added polymer and independent of its molecular weight. The molecular weight of the polymer formed increases with increase in reaction temperature. No polymerization caused by polymer occurred with the other polymer/monomer systems tested. The rate and nature of the initiating reaction are discussed.
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  • 32
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    Journal of Polymer Science 11 (1953), S. 289-298 
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The formation of quinonedimethide monomers by pyrolysis of the corresponding dimethyl hydrocarbons has been described by Szwarc in a number of publications. Under certain conditions, the monomers so produced may polymerize to high molecular weight products which are of considerable interest. Some dimethylated hydrocarbons do not, however, appear to from monomers under these conditions, and the products of pyrolysis vary considerably with hydrocarbons of different structure. In this communication, the energetics of the various reactions leading to formation of radicals, quinonedimethide monomers, and products of their dimerization or disproportionation are briefly discussed theoretically. The kinetics of the most probable reaction sequences are discussed in the light of the energetic data, and it is shown that a number of features of results so far obtained can be understood in terms of this preliminary treatment. It is hoped that this approach will prove useful as a guide to the types of reactions to be expected for aromatic hydrocarbons of differing π-electron structure.
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  • 33
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    Journal of Polymer Science 11 (1953), S. 307-323 
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The 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.
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    Journal of Polymer Science 11 (1953), S. 325-352 
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The steady state method is applied to the benzoyl peroxide initiated polymerization of styrene in toluene at 80°C. The reaction mixture is kept homogeneous by stirring. A theoretical discussion shows that the time needed to reach the steady state concentrations with an accuracy of 1% or better is about seven times the average time which the mixture spends in the reaction vessel; this is confirmed by experiment. The experimental results show that the rate of polymerization can be represented by the formula: \documentclass{article}\pagestyle{empty}\begin{document}$$ - dm/dt = kmE^{1/2} ;E = \beta m(1 + \beta m)^{- 1} $$\end{document} where m is the monomer concentration, while k and β are constants. It is found that β = 1.19 liter/mole. The apparent order of the reaction, with respect to monomer, increases from 1.18 when m = 1.8 mole/liter to 1.36 when m = 0.4 mole/liter. An analysis of the limits of experimental error indicates that in the conventional method this change in apparent reaction order would have been of the same order of magnitude as the experimental error. The accuracy of the steady state method, however, is sufficient to establish this change unambiguously. Numerous data from the literature concerning the polymerization of styrene and other monomers are discussed, and are found to be in good agreement with the conclusions reached in the present work. Explanations are offered for a number of discrepancies found in the literature.
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    Journal of Polymer Science 11 (1953), S. 379-380 
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
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    Journal of Polymer Science 11 (1953), S. 381-382 
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    Keywords: Chemistry ; Polymer and Materials Science
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    Journal of Polymer Science 11 (1953), S. 382-384 
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    Keywords: Chemistry ; Polymer and Materials Science
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    Topics: Chemistry and Pharmacology , Physics
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    Journal of Polymer Science 11 (1953), S. 424-424 
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
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  • 39
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
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    Topics: Chemistry and Pharmacology , Physics
    Notes: Studies 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.
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    Journal of Polymer Science 10 (1953), S. 257-273 
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: It has long been known that a single point determination can not describe the rheological properties of a fluid. A new method applicable to nonconducting fluids with viscosities ranging from a few hundred to more than 15,000 poises is described. The method consists of a cup and ball in which the ball is forced into rather than pulled out of the cup. Viscosity is measured electronically as a function of the time required for the ball to move a predetermined distance under a given load. Shear rates are variable over very large ranges. Rheological studies were made of a blown castor oil, three polyisobutylenes, and a high viscosity polystyrene. In addition certain physical properties of polyisobutylenes are presented.
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    Journal of Polymer Science 10 (1953), S. 291-318 
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A 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.
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    Journal of Polymer Science 10 (1953), S. 275-290 
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A 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: \documentclass{article}\pagestyle{empty}\begin{document}$$ V = A(1 - \rm \exp \{ - Bt^k \} )\quad 1\bar 〈 k\bar 〈 4 $$\end{document} 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.
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    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: A survey of the determinations of Rayleigh's constant for liquids shows that a number of different investigators using photographic methods arrive at self-consistent results which are considerably lower than those of Carr and Zimm and that expected from some theoretical views. The former set of results agree with modified theoretical views but neither this nor the determination of molecular weights allows a confirmation of the absolute value of the Rayleigh's constant. The authors recommend the adoption of the values determined photographically.
    Notes: Une revue des déterrninations des constantes de Rayleigh pour les liquides montre qu'un nombre appréciable de chercheurs différents arrivent è des réultats concordants en utilisant des m6thodes photographiques; ces rèultats sont considCablement plus bas que ceux de Carr et Zimm et que ceux prévus par la thérie. Le premier groupe de rbultats confirme des considérations thériques modifiées, mais ni ces réultats ni la dbtermination des poi& moléculahes n'apportent de confirmation de la valeur absolue de la constante de Rayleigh. Les auteurs recommandent l'adoption des valeurs déterminks photographiquement.
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    Journal of Polymer Science 10 (1953), S. 345-350 
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
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    Topics: Chemistry and Pharmacology , Physics
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    Journal of Polymer Science 10 (1953), S. 351-352 
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    Keywords: Chemistry ; Polymer and Materials Science
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  • 46
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    Topics: Chemistry and Pharmacology , Physics
    Notes: Ribonuclease and carboxypeptidase are inactivated by ultraviolet light (2537 A.) with quantum yields of 0.03 and 0.001-0.005 respectively. The quantum yields for low molecular weight proteins are of the order of 0.03 and are higher than those for splitting peptide bonds in typical peptides (0.004-0.0004 or less). It is postulated that the primary process of inactivation involves modification of aromatic residues in proteins. A possible reason for the inverse relationship between quantum yields and molecular weights of enzymes and proteins is discussed.
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    Keywords: Chemistry ; Polymer and Materials Science
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    Topics: Chemistry and Pharmacology , Physics
    Notes: The infrared spectra of synthetic polyisoprenes have been used to obtain quantitative analyses for the various types of addition occurring in the polymers. It is found that the composition of polymers prepared in bulk and emulsion systems is, within experimental error, independent of specific catalyst and per cent conversion of monomer to polymer. The structure of these materials is affected by preparation temperature, increasing temperature leading to a slight increase in 3,4 addition and a large increase in cis 1,4 addition. Polymers prepared in solution with alfin and sodium catalysts show increased amounts of 3,4 addition at the expense of 1,4 addition. Polymers prepared with a cationic catalyst (BF3) are apparently not exclusively linear polyisoprenes.
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    Topics: Chemistry and Pharmacology , Physics
    Notes: Intrinsic 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: \documentclass{article}\pagestyle{empty}\begin{document}$$ [\eta]\Theta = KM^{1/2} $$\end{document} 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: \documentclass{article}\pagestyle{empty}\begin{document}$$ [\eta] = KM^{1/2} \alpha^3 $$\end{document} increases with molecular weight approximately in accordance with the relationship: \documentclass{article}\pagestyle{empty}\begin{document}$$ \alpha^5 - \alpha^3 = 2C_{M\psi 1} (1 - \Theta /T)M^{1/2} $$\end{document} 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.
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    Journal of Polymer Science 11 (1953), S. 53-60 
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: 1A viscometer to which variable pressures may be applied is shown to be convenient for measuring viscosities of sodium thymonucleate (NaTN).2The viscosities of solutions of NaTN investigated vary with velocity gradient. All of the solutions obey the empirical equation: \documentclass{article}\pagestyle{empty}\begin{document}$$ 1/pt = A + Bp $$\end{document} where p is the average pressure on the solutions during the outflow time, t. A is used to calculate what are believed to be characteristic relative viscosities.3The viscosity of solutions of alcohol precipitable NaTN is found to depend on the concentration according to the equation: \documentclass{article}\pagestyle{empty}\begin{document}$$ \eta _{{\rm sp}} /c = [\eta] + k″[\eta]\eta _{{\rm sp}} $$\end{document} Our preparation of NaTN gives values of 11.1 dl./g. and 0.24 for [η] and k″, respectively.4The viscosity of NaTN solutions not easily precipitable depends on the concentration according to the equation: \documentclass{article}\pagestyle{empty}\begin{document}$$ \eta_{{\rm sp}} /c = [\eta] + k′[\eta]^3 c $$\end{document} Our values for [η] and k′ are 21.8 dl./g. and 0.26, respectively.5The viscous behavior of NaTN is discussed in the light of modernP polymer theory.
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    Journal of Polymer Science 10 (1953), S. 587-591 
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
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    Journal of Polymer Science 10 (1953), S. 559-576 
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The configurations of flexible macromolecules are discussed with particular emphasis on some problems arising in the theory of the volume effect. The main points considered are: (1) the relationship between the Kuhn statistical chain element and the carbon bond length; (2) the assumption that a polymer chain is equivalent to a collection of independent beads normally distributed with respect to the center of gravity (“Gaussian gas” model); (3) the distribution of segments of a polymer chain with respect to the center of gravity; (4) the theory of the execluded volume for plane models of a polymer molecule; (5) the relationship between the excluded volume and the local density of polymer segments; (6) the influence of the solvent on the excluded volume; (7) polymer configurations and viscosity.
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    Journal of Polymer Science 10 (1953), S. 591-593 
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
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    Journal of Polymer Science 10 (1953), S. 594-594 
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    Journal of Polymer Science 10 (1953), S. 595-595 
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    Journal of Polymer Science 10 (1953), S. 596-596 
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    Journal of Polymer Science 11 (1953), S. 1-20 
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A series of polyethylene resins made by making progressive changes in temperature, pressure, and catalyst content has been studied by infrared absorption spectroscopy. From the methyl content and the number-averages molecular weight of each resin, it was found that as molecular weight increases degree of branching decreases. Also revealed was the fact that each of the three types of double bond groups present, i. e., RHC=CH2, RHC=CHR, and RRC=CH2, decreases in concentration with increasing molecular weight. Using polarized radiation, high resolution grating spectra were obtained on polyethylene films which had been highly oriented by cold drawing 500%. The results show that the —CH3 terminated branches are not predominantly oriented either parallel or perpendicular to the direction of stretch. It is the authors' view that the chain branches vary in length with a considerable fraction short enough to be essentially at right angles to the long chain axis while others are sufficiently long to be parallel to the long chain axis in stretched polyethylene. When a stretched polyethylene film is heat relaxed (110-115°C.), its spectra using polarized radiation reveal the presence of crystallites in which the long carbon-to-carbon chain axes are predominantly oriented at right angles to the direction of stretch.
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  • 60
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    Notes: Isobutylene 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.
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    Notes: The thermal degradation of polystyrene has been studied in naphthalene solutions in high vacuum. The rates of loss of weight have been determined over a range of temperatures from 350 to 380°C., and the energy of activation has been derived. Also the decrease in intrinsic viscosity with time and the loss of weight as function of polymer concentration have been investigated. The mechanism of degradation in naphthalene solution is similar to that of the thermal bulk degradation; it consists of an initial random chain scission process due to weak links, followed by a reverse polymerization process with chain end initiation.
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    Notes: Rates of adsorption from solution on to charcoal and adsorption isotherms have been determined for unfractionated and fractionated polystyrene samples. The rates and extent of adsorption increase with decreasing solvent power and decreasing molecular weight. The rate curves of the fractionated samples show two distinct steps. Langmuir's adsorption equation is obeyed. Mechanisms of adsorption are discussed.
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    Journal of Polymer Science 11 (1953), S. 399-408 
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    Keywords: Chemistry ; Polymer and Materials Science
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    Topics: Chemistry and Pharmacology , Physics
    Notes: The chain transfer constants of twelve solvents have been determined for the peroxide catalyzed polymerization of styrene and are compared, where possible, with those for methyl methacrylate. The values found are discussed in relation to structure and activity.
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    Journal of Polymer Science 11 (1953), S. 425-431 
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    Keywords: Chemistry ; Polymer and Materials Science
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    Topics: Chemistry and Pharmacology , Physics
    Notes: By means of a mathematical treatment the distributions of the tensile strength of natural rubber and GR-S were studied. As a result of this study it is shown that the distributions are of the so-called doubly exponential type.
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    Journal of Polymer Science 11 (1953), S. 385-398 
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: In this article a conception of the mechanism of crystallization is given, on the basis of which, it is suggested the origin of spherulites might be explained. A tentative explanation of several related phenomena is based on the new concept. Crystallites are conceived to be small collections of strongly oriented polymer which, on fusing, exhibit marked shrinking in the direction of orientation. Particles of amorphous material therefore stretch out in a certain direction during crystallization, as the result of which there is substantial contraction in the other directions. This is termed “auto-orientation.” As the growing crystallite has to be fed from surrounding material, an orienation is initiated in the latter at right angles to the first crystallite. As a result of this orientation, crystallites are formed there which are oriented Perpendicular to the first crystallite. In their turn, these crystallites induce orientation in the surroundings and in this way crystallization becomes autocatalytic in character. Spherulites owe their origin to the fact that the various sectors in a symmetrical spherical order mutually cancel out their stretching and shrinking tendencies. In highly crystalline polymers with rapid nuclear formation there first comes into existence numerous radomly oriented nuclei which proliferate to small crystallites. Wherever these small crystallites come to be arranged in a suitable position, their relative tensions will be cancelled out and they will grow into a spherulite. Simultaneously small crystallites which are in an unfavorable position will be consumed by the growing spherulite, or else oriented in the correct direction and incorporated. As spherulites commonly measure from 10 to 50 microns, compensation between the tensions of the various sectors has to take place at long distance. At higher temperatures, compensation is as a rule found at short distances, i.e., crystallites which are at right angles to each other are in close proximity. Therefore “spherulites” varying individually come into existence as the crystallites are subject to other influences in addition to auto-orientation. At very low temperatures the primary small crystallites are too stable to develop into spherulites. The mechanism of crystallization as thus conceived implies that the melting point of a polymer depends not only upon the dimensions and perfection of the crystallites, but also upon the specific arrangement of the crystallites, i. e., the degree in which they stabilize each other by a mutual compensation of tensions. It also helps to explain the following facts which have been noted in experiments performed with natural rubber: (1) The typical S-shape of the crystallization curve and the constancy of the product of induction period and maximum rate of crystallization. (2) The fact that natural rubber always crystallizes under nonequilibrium conditions. (3) The failure of rubber in latex to crystallize and the fact that the rate of crystallization in films produced from latex is poorly reproducible.
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    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: 1The chemical stabilization of wool by treating reduced wool with dihalogeno compounds (Harris-process) has been studied by preparative organic methods.2The bis-thioethers of cysteine, as postulated by Harris, have been prepared from l-cysteine and aliphatic α,ω-dihalogen compounds X—(CH2)n—X (n = 1-6) and are characterized by elementary analysis and paper hcromatography.3S,S′-Polymethylen-bis-cysteine derivatives have been isolated in good yields from reduced wool which has been previously treated with the cited dihalogen compounds. These were identical with the synthetic bisthioethers.4The course of reactions for the chemical modification of wool has now been verified by preparative chemical means as suggested by Harris in 1941.
    Notes: 1Die chemische Stabilisierung von Wolle durch Einwirkung bifunktioneller Halogen-derivate auf reduzierte Wolle (Harrisverfahren) wurde präparativ-chemisch studiert.2Die von Harris angenommenen Bisthioäther des Cysteins wurden aus l-Cystein und aliphatischen α,ω-Dihalogenverbindungen X—(CH2)n—X mit n = 1-6 dargestellt und durch Elementaranalyse und Papierchromatographie charaketerisiert.3Bei der präparativen Aufarbeitung von reduzierter und mit den genannten α,ω-Dihalogenverbindungen umgesetzter Wolle wurden S,S′-Polymethylenbiscysteine in guten Ausbeuten isoliert, welche mit den synthetischen Verbindungen identisch sind.4Der von Harris 1941 angegebene Reaktionsmechanismus für die chemische Modifizierung von Wolle konnte somit präparativ-chemisch bestätigt werden.
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    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 10 (1953), S. 93-106 
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Obwohl bisher noch keine vollkommen befriedigende Erklärung für die Entstehung eines begrenzt quellbaren Polymeren (Popcorn Polymer) besteht, so kann man jedoch mit Sicherheit sagen, daß dieser heterogenen Polymerisation ein Radikal-Mechanismus zugrunde liegen muß.Für die Bildung des Popcorn-Keims oder -Zentrums wurden verschiedene Erklärungen vorgeschlagen: Kharasch meint, daß jede organische Substanz, die den folgenden zwei Erfordernissen entspricht, als Keim wirken kann: (a) sie muß im Monomeren unlöslich, jedoch quellbar sein und (b) sie muß eine genügende Anzahl von Gruppen enthalten, welche unter passender Aktivierung Radikale bilden Können.Breitenbach behaupter, daß Popcorn-Bildung möglich ist, sobald die Kettenlänge der Moleküle sehr groß wird, da die langen Ketten sich dann ineinander verschlingen und so ein „Gel-Gerüst“ hilden, welches als Popcorn-Keim wirken kann.Fox ist jedoch der Meinung, daß einige chemische Vernetzungsstellen (crosslinks) notwending sind, um einen Popcorn-Nucleus zu bilden, und schlägt z. B. für Methyl-Acrylat einen Mechanismus für die Entstehung dieser Vernetzungsstellen vor. Dieser beruht darauf, daß die Kettenmoleküle Doppelbindungen und angrenzende Methylen-(CH2) Gruppen besitzen, von denen ein Wasserstoff-Atom leicht durch ein Radikal abstrahiert werden kann. Dadurch entstehen Popcorn-Keime mit sowohl an der Oberfläche wie auch im Innern befindlichen Radikalen, die dann mit Monomerem reagieren und wachsende Ketten bilden, sich aber nicht gegenseitig absättigen können, da sie ja nicht frei beweglich sind.Sobald sich der Keim gebildet hat, wird die Wachstumsgeschwindigkeit sehr Groß, da am und im Gel-Gerüst eine Überkonzentration von Radikalen besteht. Diese Geschwindigkeit wächst während der Polymerisation dauernd an und ist am besten mit einer logarithmischen Beziehung zu beschreiben.Die abnormalen physikalischen Eigenschaften des Popcorns sind wahrscheinlich auf die Heterogenen Umstände des Wachstums zurückzuführen. Die überaus schnelle Polymerisation, welche in verschiedenen Teilen des Systems, also wo immer sich ein Keim befindet, stattfindet, verursacht lokale Spannungen, welchen sich das Gel-Gerüst nicht mehr anpassen kann und von denen es daber deformiert wird. Dabei wird dann den am Keim verankerten wachsenden Kettenmolekülen irgendwie eine neue Form aufgeprägt.
    Notes: Popcorn polymerizations occur by a free radical mechanism.No entirely satisfactory explanation for the initial formation of the popcorn nucleus or seed has yet been proposed. Kharasch proposes that any organic substance can act as a nucleus provided it can be made insoluble but still swellable in the monomer and contains a relatively large number of groups which can give rise to free radicals on suitable activation. Breitenbach is of the opinion that popcorn formation can occur whenever very high moleculare weight polymers are formed since some of these long chains will become entangled, thereby forming a gel structure which can act as a popcorn nucleus. If there are methylene groups adjacent to double bonds in the chains, attack by oxygen gives hydroperoxide groups which easily decompose to give free radicals capable of adding monomer and causing chain growth, but incapable of terminating each other as they are immobilized by being attached to the gel structure.Once the nucleus is formed, the growth rate is extremely rapid due to the overconcentration of free radicals on and in the necleus. The rate is found to increase constantly as the polymerization proceeds, and can best be described by a logarithmic relation.The abnormal physical characteristics of popcorn polymers are probably due the heterogeneous nature of their growth. The rapid polymerization in isolated parts of the system causes localized stresses to which the gel structure cannot respond and is twisted out of shape, somehow imparting the new configuration on to the growing chains.
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  • 68
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Il est possible de faire réagir la cellulose d'un tissu de cellulose régénerée, qui a inclus du benzène, avec l'hexamethylenediisocyanate en formant des ponts diurethanes. La cellulose régénerée ainsi obtenue a après le traitement une teneur en azote qui va jusqu' à environ 3,5% ce qui correspond à une proportion de 4 mol C6H10O5 pour 1 mol diisocyanate. Le gonflement de cette cellulose régénerée a diminué de 50% environ. Elle n'est pas soluble dans du Cu(NH3)4(OH)2. Les ponts diurethanes sort resistants au lavage. En traitant les tissus, qui sont preparés avec du diisocyanate, avec l'acide formique à 85% et en faisant réagir de la soude à 10% sur les echantillons dégradés par le bisulfat de potassium, on a pu montrer que le diisocyanate avait réagit avec la cellulose en formant des ponts diurethanes.
    Notes: Cellulose eines Zellwollgewebes kann nach Verdrängung des Wassers durch Inclusion mit Benzol mit Hexamethylendiisocyanat umgesetzt werden. Die Zellwolle hatte nach der Behandlung einen Stickstoffgehalt von bis zu 3,5%, was einem Verhältnis von 4 Molen C6H10O5 zu 1 Mol Diisocyanat entspricht. Der Quellwert dieser Zellwolle ist auf ca. 50% erniedrigt und die Cellulose in Kupferhydroxyd-Ammoniak unlöslich. Die Diisocyanat-vernetzung ist waschfest. Durch Behandlung der mit Diisocyanat vernetzten Gewebe mit 85%iger Ameisensäure und der mit Kaliumbisulfat abgebauten Proben mit 10%iger Natronlauge wird gezeigt, daß das Diisocyanat unter Bildung von Diurethanbrücken mit der Cellulose reagiert.
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    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: The Cellulose of the Kapok seed hair (Eriodendron infractuosum) was isolated carefully and its moleculare distribution determined by the fractionated precipitation of the polymeranalogous nitrates. The composition of the Kapok fiber is similar to that of wood, even than of cotton. The high Km values of diluted solutions of polymer-analogous nitrates may be attributed substantially to the molecular nonuniformity.
    Notes: Die Cellulose des Kapoksamenhaares (Eriodendron infractuosum) wurde schonend isoliert und durch fraktionierte Fällung der polymeranalogen Nitrate deren molekulare Verteilung ermittelt. Die Zusammensetzung der Kapokfaser ist ähnilich der von Holz; auch die molekulare Verteilung ihrer Cellulose gleicht mehr der von Holz als der von Baumwolle. Die hohen Km-Werte von verdüngen der polymeranalogen Nitrate sind im wesentlichen auf die molekulare Uneinheitlichkeit zurückzuführen.
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