bluuebunny/crossref_metadata_2025_split huggingface dataset:
La structure du polyéthyléne consideré comme un mélange de n‐paraffines
Authors: Gubler M. G. , Kovacs A. J. 
Published: April 2003

AbstractOn a mesuré par dilatométrie le volume spécifique de trois poltéthylènes (Haute Pression, Ziegler, Marlex) entre −35 et 175°C après avoir fait subir aux échantillons différents traitements thermiques. Après discussion des paramètres qui déterminent le taux de cristallinité du poltéthylène, on a tenté de relier les variations de × en fonction de la température T, à la structure moléculaire. En admettant que chaque valeur de T correspond à la température de fusion d'une paraffine linéaire comprenant N atomes de carbone, on peut exprimer X en fonction de N et déterminer ainsi la fonction de distribution et la moyenne des longuers des chaǐnons de la fraction cristalline. En supposant que la chaǐne du polyéthylène est formée par la succession alternée des chaǐnons cristallins et des régions amorphes, on peut déterminer la période moyenne de cette alternance qui se révèle indépendante du traitement thermique particulier de l'échantil lon. En associant au moins un groupe méthyle à cette période, on peut déterminer le rapport des groupes CH3/CH2 présents dans chacun des trois poltéthylènes. La comparaison de ces résultats à ceux de la spectrographie I.R. montre un accord d'autant plus satisfaisant que le polymère est moins ramifié.
Polymethylene and the structure of polyethylene: Study of short‐chain branching, its nature and effects
Authors: Willbourn A. H. 
Published: April 2003

AbstractModel compounds in the form of polymethylenes, linear and branched, have been prepared and used to develop methods of measuring the numbers and lengths of branches in polymethylene. The polymethylenes used for calibration work contain deuterated butyl branches; the numbers of branches present in the polymers hava been established by two independent methods: direct assay for deuterium and mass spectrometric analysis of the irradiation products. Using this series a new infrared tecnique has been calibrated absolutely to measure total number of methyl group and also butyl branches specifically. The infrared technique is a compensation method, using solid specimens in a double‐beam spectrometer, in which the compensating material (linear polymethylene) is devoid of the structural features, namely branches, to be measured. Using the same technique and reference samples of ethyl‐branched polymers (Hydropol), a method of estimating ethyl branch concentration has been developed. A study of the gaseous products of irradiation of the butyl‐branched polymethylenes, using mass spectrometric anlysis, has shown the extent to which this technique might provide a quantitative means of identifying and estimating branches in such polymers; it has also greatly strengthened the evidence of earlier workers that low density polymethylenes contain primarily ethyl and butyl branches. The same conclusion, in more quantitative terms, is drawn from an infrared study of various polymethylene‐specimens: practically all the branches observed can be accounted can for as ethyls and butyls present in the ratio of approximately 2:1. Some high density polyethylenes contain a few branches, which appear to be ethyl groups. The effects of the numbers and lengths of branches on degree of crystallinity, crystalline melting point, density, rate of oxidation, and dynamic mechanical properties are illustrated and discussed. The status of theories concerning the mechanism of formation of short side chanis in polymethylene is considered.
A diffusion theory of the visco‐elasticity of rubbery polymers in finite elastic strain
Authors: Mooney M. 
Published: April 2003

AbstractThe molecular mechanism of stress relaxation in a linear polymeric material is conceived of as a process of diffusion in phase space of molecular configuration. The analysis is an extension of the Rouse theory of linear visco‐elasticity to finite, three‐dimensional deformations. A molecule, either open end or crosslinked, is treated as a chain of submolecules, each just long enough that its net length follows approximately the Gaussian distribution law. Variables are separated by transformation to normal coordinates, and diffusion equations are obtained of the form

where ρn is the density in configuration space of the n‐mode of molecular configuration, and Dn is the diffusion constant characteristic of the mode. An exact solution exists in the form

Here βn − 1 is the measure of the recoverable strain in the un direction of the n‐mode, the instantaneous value of the corresponding partial stress being proportional to βn2 − 1. Any partial stress obeys the Boltzmann superposition law, but the total stress does not. The transform equations connecting such pairs of functions as creep and relaxation in the linear theory are here not valid; but, as in the linear theory, in a given case of a single imposed strain the stresses are expressed in terms of a distribution function of relaxation times. Expressions are obtained for the tangential and normal stressed in continuous simple shear at a finite rate. To explain non‐Newtonian viscosity it is necessary to postulate either that the intertangling of the molecules is reduced or that rheological flow units develop in the material which are larger than the individual molecules.
Ultraviolet induced crosslinking and grafting of solid high polymers
Authors: Oster Gerald , Oster Gisela K. , Moroson Harold 
Published: April 2003

AbstractThe production of crosslinks and of sites for grafting in solid high polymers can be achieved by hydrogen abstraction. This hydrogen abstraction reaction can be carried out by means of far ultraviolet light (200–300 mμ). The rate of the reaction is tremendously increased if certain sensitizers are incorporated into the plastic. A comparative study of various aromatic carbonyl compounds has been made to determine which are effective sensitizers. Crosslinking is accompanied by a photolysis of the sensitizer. Sensitizers which are effective for crosslinking are also effective for grafting. For the same degree of crosslinking the high density polyethylenes have greater strength at 150°C. than have the low density polyethylenes. The ultraviolet method differs from the ionizing radiation method in that the dosages required for crosslinking by the former method are the same regardless of the degree of crystallinity of the polyethylene. A further difference is that whereas with the ionizing radiation method extensive Degradation occurs with certain polymers, in the ultraviolet method crosslinking is the predominant reaction.
Mastication of rubber. VIII. Preparation of block polymers by mechanical shear of polymer–monomer systems
Authors: Angier D. J. , Ceresa R. J. , Watson W. F. 
Published: April 2003

AbstractThe mastication of polymers brought into a rubbery state by admixture with monomers causes polymerization of the monomer. The reaction shows dependence on rate of shearing, temperature, and monomer concentration expected for a mechanism of mechanical rupture of the polymer to free radicals which initiate polymerization. Fractional precipitation methods for separating block polymers of polymethyl methacrylatepolystyrene from the homopolymers are applied to the products after masticating both initial polymer‐monomer combinations. The products of reaction indicate that the block polymer does not contain many segments of each polymer. When the two polymers are present either as free or block polymers, the polymethyl methacrylate is preferentially ruptured to form initiation sites.
Mechanism of polyvinyl chloride degradation and stabilization
Authors: Winkler D. E. 
Published: April 2003

AbstractMany articles have been written attempting to explain the degradation processes which take place when polyvinyl chloride is aged. Everyone agrees that hydrogen chloride is evolved, color develops, and the polymer eventually becomes stiff and insoluble as a result of crosslinking. Early workers believed that hydrogen chloride catalyzed the decomposition and that the role of stabilizers was to react with it to render it ineffective. More recent work has shown that hydrogen chloride is not a catalyst for the decomposition in the absence of oxygen and that the function of stabilizers may be quite different from that earlier assumed. In this paper an attempt is made to weigh the results of many workers and to explain the observable changes brought about during degradation by a consistent free radical mechanism. Under milling conditions, temperatures are attained at which even saturated hydrocarbons will oxidize; hence it is not unreasonable to assume the presence of free radicals in polyvinyl chloride. Free radicals may also result from the ejection of a chlorine atom from a polymer chain. At room temperatures chlorine atoms may be formed as the result of the absorption of light energy. Once radicals are produced, degradation in the presence of oxygen may take many routes. A few of these are discussed. Many stabilizers are believed to act by disrupting radical chain processes.
Potentiometric behavior of polyampholytes
Authors: Mazur J. , Silberberg A. , Katchalsky A. 
Published: April 2003

AbstractThe influence of nearest‐neighbor interaction on the potentiometric behavior of polyampholyte is discussed. It is shown how this effect superposes itself on the normal random electrostatic interactions between segments of the chain. Only interactions between oppositely charged nearest neighbors are considered. Other specific interactions, such as ion binding and nearest‐neighbor interaction between like charges, are neglected as being of interest only in special cases. A simplified model is treated in which one of the groups is present in large excess while the other exists only in singlemembered sequences in the chain. It is shown that positive‐negative nearest‐neighbor interaction always has the effect of increasing the strength of the group, an acidic group becoming a stronger acid, a basic group, a stronger base. The effect is most pronounced for groups which are already strong, and, in this case, the titration (proton binding) curve of the polyampholyte is considerably changed; on the other hand, if both groups are weak, the titration curve is hardly affected, even when the interaction is strong. In this case, however, the pH dependence of the degree of ionization of the group present in minority shows peculiarities. The isoelectric point of polyampholytes can be considerably affected by (+ −) nearest‐neighbor interaction, that of molecules containing an excess of basic groups being raised by the interaction, and that of polyampholyte containing an excess of acidic groups being lowered. These shifts are again far more pronounced when the groups involved are strong. It is shown how use can be made of these predictions to analyze and understand the behavior in practical cases. The data for two types of synthetic and one naturally occurring polyampholyte are interpreted in this way, and satisfactory results are obtained
A quantitative investigation on the X‐ray small angle scattering of cellulose fibers. Part I. The concept of scattering power and a method for its determination in electron units
Authors: Heikens D. 
Published: April 2003

AbstractFrom intensity measurements on small angele x‐ray diagrams it is possible to derive the so‐called “scattering power” of the object in question. This quantity, introduced by Porod, taken per unit of volume is identical to the mean square of the fluctuations in electron density. Theoretical equations, necessary for the valuation of fiber diagrams, based on work of MacGillavry and Bruins, and of Vineyard, are adapted for application to measurements with a setup provided with a slit diaphragm. the principle of a convenient practical method to convert the experimental results into electron units, uning noble metal sols of easily computable scattering power, is disclosed.
A quantitative investigation on the X‐ray small angle scattering of cellulose fibers. Part II. The scattering power of various cellulose fibers
Authors: Hermans P. H. , Heikens D. , Weidinger A. 
Published: April 2003

AbstractThis paper reports on quantitative measurements of the small angle scattering of various rayons and ramie fibers as functions of moisture content using a three slit vacuum camera and monochromatic radiation. The scattered intensity was normalized on sample thickness and primary intensity through determination of the absorbance of the sample and of the intensity of the transmitted beam measured in arbitrary units. From these data the scattering power as defined by Porod, being the mean square of the fluctuations of the electron density, was calculated. This quantity was then converted into electron units through calibration of the procedure with exposures of noble metal sols of known composition and thus of computable scattering power. The exprimental results were compared with the scattering power calculated for cellulose fibers when regarded as submicro tow‐phase systems consisting of crystalline cellulose imbedded in a homogeneous mixture of noncrystalline cellulose and water. In the air‐dry state a few of the rayon speciman examined exhibited a scattering power of magnitude consistent with theory. The majority yielded much higher values, up to six times larger (so does dry ramie). This is interpreted by the occurrence of submicro voids to a volume fracton of less than 0.75%, variable from fiber to fiber. This explanation is corroborated by the existenc of a distinct correlation between scattering power and gravimetric density of the fiber. In conclusion, microvoids are the principal scattering “particles” in dry fibers. The values of the scattering power of water swollen rayons and ramie can be interpretated on the basis of a three‐pahse model, with the phases consisting of crystalline cellulose, a homogeneous mixture of amorphous cellulose with water, and water, respectively.
Enzymatic polymerization. I. Molecular weight and branching during the formation of dextran
Authors: Bovey F. A. 
Published: April 2003

AbstractIn order to establish the nature of the reaction by which the dextran molecule is formed we have examined the intensity of scattered light at eleven angles during the polymerization of sucrose in the presence of purified dextransucrase from B‐512‐F Leuconostoc mesenteroides. The molecular weight increases from about 50 × 106 to 100–175 × 106 at complete sucrose conversion, and then continues to increase to over 500 × 106. It is shown that the molecules are highly branched early in the reaction and become even more so as the reaction proceeds. These results are believed to be due to the formation of random, long‐chain branches by rearrangement of linear chains under the influence of a branching enzyme which is more heat‐stable than the polymerizing enzyme.
Kinetics of anionic polymerization of styrene
Authors: O'Driscoll K. F. , Tobolsky A. V. 
Published: April 2003

AbstractThe kinetics of the polymerization of styrene initiated by n‐butyl lithium (BuLi) in benzene and in benzene plus small amounts of tetrahydrofuran (THF) have been investigated. It was found that the rate of polymerization is independent of BuLi concentration over a 100‐fold range in pure benzene. In benzene with added THF, the rate is inversely proportional to the BuLi concentration. A reaction scheme is suggested to expalin these unusual kinetics.
Graft copolymers from poly(styrene co dimethyl maleate) and poly(styrene co allyl acetate)
Authors: Weiss P. , Gerecht J. F. , Krems I. J. 
Published: April 2003

AbstractGraft copolymers, were synthesized from hydrophobic backbone copolymers by introducing hydrophilic grafts at appropriate juncture points. Poly(styrene co dimethyl maleate) of varying composition was prepared by the copolymerization of styrene with dimethyl maleate in the presence of benzoyl peroxide as the initiator. Data on conversion rates of initial monomers to copolymer, infrared measurements, limiting viscosity numbers, and copolymer compositions are presented. The poly(styrene co dimethyl maleate) was resistant to saponification but, when reacted with sodium catalyzed monoethanolamine at its boiling point, yielded the desired poly(styrene co maleic ethanolamide). Addition of ethylene oxide to the available hydroxyl groups yielded, in some instances, water‐dispersible graft copolymers. Poly(styrene co allyl acetate) was prepared by copolymerizing styrene with allyl acetate with use of benzoyl peroxide as the initiator. Water‐dispersible copolymers from this backbone copolymer were prepared by saponification of the acetate groups and the grafting of ethylene oxide to the available hydroxyl groups in the backbone copolymer. Results of analyses, molecular weight determination, and infrared measurements are presented.
High‐energy radiation effects on polyacrylates and polymethacrylates
Authors: Shultz Allan R. 
Published: April 2003

AbstractChemical and physical changes produced in polymethacrylates and polyacrylates by ionizing radiations are examined in the light of data revealing molecular structural changes and ultimate fragmentation products. A 1,4‐diradical or concerted mechanism is postulated for polymethacrylate main‐chain scission.
Vapor pressures of polymer solutions. I. Apparatus for measurement and some results on poly(vinyl acetate) solutions
Authors: Nakajima Akio , Yamakawa Hiromi , Sakurada Ichiro 
Published: April 2003

AbstractAn apparatus is described for the measurement of the vapor pressures and concentrations of high polymer solutions. Results are given for the poly(vinyl acetate)‐benzene and poly(vinyl acetate)‐vinyl acetate systems. For both, the interaction constant, χ12, decreases linearly as the volume fraction of polymer increases from 0.4 to 0.9.
Vapor pressures of polymer solutions. II. Vapor pressure of the poly(vinyl alcohol)‐water system
Authors: Sakurada Ichiro , Nakajima Akio , Fujiwara Hiroyuki 
Published: April 2003

AbstractVapor pressures were measured for the system, poly(vinyl alcohol)‐water at 30°C. with the apparatus reported in the preceding paper. Fractionated samples were used in the form of thin films, carefully dried under high vacuum at room temperature. The degree of crystallinity of these samples was about 0.2, and the degrees of polymerization were 1530 and 335. The relation between the activity of the water and the composition of the gel phase is discussed. The interaction parameter χ12 is evaluated assuming that the crystalline regions are not affected by the water and correspond to the crosslinks in an amorphous network polymer; also that the chain length between two crosslinks is not changed with the composition of the system. χ12 increases with increasing polymer concentration. This behavior is discussed with the aid of heat of dilution data from the literature. The anomalous concentration dependence of the entropy and energy contributions to χ12 may be explained as resulting from the mutual orientation of water molecules and the hydroxyl groups along the polymer chain.
Moisture permeability of polymers. I. Role of crystallinity and orientation
Authors: Lasoski S. W. , Cobbs W. H. 
Published: April 2003

AbstractWith three polymers widely different in polarity—polyethylene terephthalate, polyethylene, and nylon 610—the water vapor permeability P of unoriented films has been shown to increase as the amorphous fraction Xa is increased, following the relation P = PaXa2. For polyethylenes, adherence to this relation is exhibited only with structures having densities above 0.94, a range in which the number of short chain branches is low. Films with densities lower than 0.94 exhibit higher film permeabilities than those calculated on the basis of the permeability of the amorphous areas Pa of “linear” polyethylene; this results from the increase in the number of short chain branches and hence, an increase in Pa of the lower density polyethylenes. The above variation of water vapor permeability with the square of the amorphous fraction may be theoretically accounted for by a linear variation of the diffusion and solubility coefficients with the amorphous fraction. With polyethylene terephthalate and nylon 610, the solubility coefficients do exhibit this linear relation. The square permeability relation appears to be a limiting case for structures in which crystallization does not impose restraints on the segmental motions important in permeability. Where restraints do occur, as in oriented films, a higher order dependency on the amorphous fraction exists. This was exemplified with biaxially and uniaxially oriented polyethylene terephthalate films, with which it was shown that orientation in oriented crystalline films effects a decrease in permeability in addition to that ascribable to crystallinity. This is not true for such films as polystyrene or stretched rubber which has not crystallized. Only those oriented structures in which the orientation is “locked‐in,” as by crystallization, exhibit a decrease in water vapor permeability. The relations of permeability and solubility coefficients to crystallinity have an important utility in that the extent of crystallinity or crystal density may be estimated with the proper data. On the basis of literature water vapor permeability data of Szwarc et al. for two high density polyethylenes at three different vapor pressure differentials, the crystal density of polyethylene was estimated to be 0.995, 1.008, and 0.998 or an average of 1.00, in agreement with Bunn's value calculated on the basis of x‐ray diffraction studies.
Copolymerization of methacrylic acid esters with methacrylonitrile
Authors: Cameron G. G. , Grant D. H. , Grassie N. , Lamb J. E. , McNeill I. C. 
Published: April 2003

AbstractThe reactivity ratios in the copolymerization of methacrylonitrile with styrene, methacrylic acid, and eleven alkyl methacrylates have been determined and the Alfrey‐Price Q and e values calculated. Monomer reactivity in these systems is principally a function of resonance stabilization (Q), polar factors (e) playing a relatively minor role. With the exception of the stearyl ester, the changes in the Q and e values which occur on ascending the homologous series can be accounted for qualitatively in terms of the expected relative electronic displacements and of the steric effects caused by the various alkyl groups. Some correlation between monomer reactivity and the depolymerizability of the corresponding polymer has been noted.
Polymerization of dichlorophosphinic nitrides
Authors: Konecny Jan O. , Douglas Catherine M. 
Published: April 2003

AbstractThe polymerization of the trimer and tetramer of dichlorophosphinic nitride was found to be catalyzed by a variety of organic compounds: ethers, carboxylic acids and ketones, and also by metals. The effect of these substances on the polymerization rate at 211° was explored quantitatively. The tetramer was invariably found to react slower than the trimer, and the same order of reactivities was observed in the copolymerization of the two materials. The catalysts all displayed a comparable activity.
Crystallization kinetics and mechanical properties of polyethylene
Authors: Buchdahl R. , Miller R. L. , Newman S. 
Published: April 2003

AbstractThe kinetics of crystallization of a branched polyethylene have been studied dilatometrically, spectroscopically, and microscopically at small degrees of supercooling (ca. 0–10°C.). In order to assess the extent to which results of different methods are in agreement with each other, apparent induction times and maximuin crystallization rates are compared. On the basis of these data, the results of different experimental techniques using different types of sample are in general agreement. However, there do exist small, but significant, differences which appear to be outside experimental error. The results are shown to be in essential agreement with present theories of nucleation and of crystallization. The observations are interpreted in terms of the processes occurring during crystallization. The relationship of dynamic mechanical properties to previous thermal histories is considered and a qualitative interpretation is presented.