bluuebunny/crossref_metadata_2025_split huggingface dataset:
Etude cristallographique de la structure de films de polytétrafluoroéthylene greffés de styrègne. Destruction du copolymère greffé par un traitement thermique
Authors: Sella Claude , Chapiro Adolphe , Matsumoto Akira 
Published: April 2003

AbstractOn a étudié les variations de la cristallinité et des paramètres cristallographiques du polytétrafluoroéthylène (PTFE) qui se produisent lors du greffage du styrène dans la masse de ce polymère. On a constaté que les paramètres de la maille cristalline du PTFE restent pratiquement inchangés lorsqu'on greffe du styrène dans la masse du polymère et ceci měme pour des taux de greffage élevés. Au cours d'un tel greffage le taux de cristallinité du PTFE diminue progressivement et tend vers zéro pour les taux de greffage élevés. Ce comportement est différent de celui observé antérieurement dans le cas du polyéthylène (C. Sella, J. Polymer Sci., 48, 207 (1960)). Il démontre qu'au cours du greffage sur le PTFE le styrène ne pénètre pas dans les zones cristallines du polymère mais que l'importance de celles‐ci est progressivement réduite au cours de la réaction. Des clichés de la surface des films greffés, pris au microscope électronique ont mis en évidence une structure hétérogène de celle‐ci. Des échantillons de PTFE fortement greffés ont été soumis à un traitement thermique dans le but d'essayer de recristalliser le polymère. Dans ces conditions, on a observé à 300° une destruction rapide du copolymère greffé, celui‐ci étant scindé en deux phases constituées respectivement par le PTFE initial et par du polystyrène pur. La cinétique de ce processus a été brièvement examinée en mesurant les pertes de poids des films greffés en fonction du temps de chauffage.
Morphology and crystal growth rate of polyethylene crystalline complexes
Authors: Holland V. F. , Lindenmeyer P. H. 
Published: April 2003

AbstractAn investigation of the morphology of crystallization of fractionated linear polyethylene has shown that single crystal platelets may be obtained from dilute xylene solutions only in a limited region of temperature. The variation of this temperature region with molecular weight is greater than would be expected from the theoretical variation in equilibrium melting temperature. Uniformity of the crystallization conditions was sufficient to permit the measurement of size and thickness of the crystals as a function of both time and temperature. It was shown that the change in platelet thickness with temperature cannot be accounted from by the kinetics of nucleation with the assumption that the thickness is essentially equal to the critical nucleus dimension. The crystal growth rate data show that growth occurs by a nucleation process but the data are not compatible with the assumption that nucleation occurs through the formation of a homogeneous monomolecular layer on the growth surface. Evidence is presented to show that crystallization habit is dependent not only on the degree of supercooling but is also a function of some other factor that acts as a resistance or impedance to crystallization.
The effect of phenols on the polymerization of styrene
Authors: Godsay M. P. , Harpell G. A. , Russell K. E. 
Published: April 2003

AbstractThe effect of a variety of phenols on the rate and degree of polymerization of styrene has been studied. With 1‐naphthol it is found that polystyryl radicals abstract the phenolic hydrogen atom, since 1‐naphthol has a far greater effect on the rate and degree of polymerization than 1‐deuteroxynaphthalene. Many phenols do not significantly retard the polymerization of styrene and transfer constants ranging up to 7.7 × 10−3 have been estimated for them. Other phenols, such as 1‐naphthol, 4‐methoxyphenol and 2,6‐diisopropylphenol, significantly decrease the rate and degree of polymerization. Transfer constants for these retarders have been calculated, both from the rate data alone by means of the treatment of Jenkins and from molecular weight data. The estimated values depend on the assumptions made concerning the mode of disappearance of the retarder radicals produced in the transfer reaction. Most of the retarders investigated give transfer constants in the range 10−2 to 10−1 but catechol, tert‐butylcatechol, and pyrogallol give larger values. An increased rate of polymerization observed in mixtures of styrene and some phenols is probably due to a higher rate of production of radicals by the initiator, azobisisobutyronitrile.
Monomer reactivities in radiation‐induced graft copolymerization. Part II. Graft copolymerization to Teflon
Authors: Odian George , Acker Terese , Rossi Albert , Ratchik Elliot 
Published: April 2003

AbstractThe gamma radiation‐induced surface graft copolymerizations of styrene—acrylonitrile and styrene—methyl acrylate to Teflon were studied. It was observed that the compositions of the various grafted copolymers are richer in the more polar monomer than one would predict from the Lewis‐Mayo copolymer composition equation. These results were interpreted in terms of a preferential solvation of the relatively immobile growing graft polymer free radicals by the polar monomers.
Emulsion copolymerization of butadiene and styrene in the presence of carbon black
Authors: Medalia A. I. , Hagopian E. , Hall J. P. 
Published: April 2003

AbstractCarbon blacks inhibit and retard free radical polymerization in bulk and solution. The mechanism of this is discussed in terms of the chemical groups present on the carbon surface. It is shown that the number of free radicals which react during the induction period (polymerization of styrene with AIBN) is much less than the number of quinone groups but of the same order of magnitude as the number of easily oxidizable groups. Inhibition by carbon black was also found in an emulsion polymerization system with cumene hydroperoxide as initiator (no reducing components). By use of highly active redox recipes, reasonable rates of polymerization were obtained at both 50°C. (sugar‐iron‐hydroperoxide recipe) and 5°C. (peroxide‐polyamine recipe), with as much as 40 parts of black per 100 parts of monomers. In these systems, the carbon black was charged as an aqueous dispersion stabilized with Daxad 11; the latices were stable and showed evidence of association between some of the carbon black and some of the latex particles. The coagulated rubber stocks, when compounded and cured, gave properties closely similar to those of dry mixed stocks.
Inhibition and retardation of the polymerization of ethyl methacrylate
Authors: Funt B. Lionel , Williams Fredrick D. 
Published: April 2003

AbstractCombination of C14‐tagged or inactive benzoquinone with tagged or inactive azobisisobutyronitrile was used to study the kinetics of polymerization of ethyl methacrylate. The course of the reaction was followed by dilatometry, and the resultant polymers were assayed for C14 content by liquid scintillation techniques. Molecular weights were obtained by osmometry in order to determine the number of tagged fragments per polymer molecule. A transition from a retarded polymerization to one showing an inhibition period was found at a critical concentration of p‐benzoquinone. This transition was accompanied by a marked change in the C14 content of the polymers. The magnitude of chain transfer or copolymerization was directly estimated from the number of tagged fragments incorporated per polymer molecule. These indicated that no more than two molecules of p‐benzoquinone could copolymerize or that a limit could be set of one chain transfer step per kinetic chain. Hence, neither of these processes can be considered as highly significant in the mechanism. The formation of a transient adduct between primary radicals of initiation and benzoquinone is postulated, and the transition from retarded to inhibited polymerization in this system is discussed on this basis. These ideas were extended to a consideration of the role of primary radical capture and radical reactivity for other monomers, such as styrene and vinyl acetate.
Anionic copolymerization
Authors: O'driscoll Kenneth F. 
Published: April 2003

AbstractPrevious work with anionic copolymerizations held that the terminal carbanion played no role in determining which monomer was next added. Recent work by Graham et al. has demonstrated that this is untrue for monomers of extremely dissimilar polarities. In this paper the kinetics of copolymerization of dissimilar monomers has been developed. As a result it is shown that the ratio of monomers in the initial copolymer d[M1]/d[M2] is directly proportional to the square of the initial monomer ratio ([M1]/[M2])2 when the monomers are dissimilar. The earlier theory resulted in a first‐power proportionality for all cases. Log—log plots of the equation d[M1]/d[M2] = K([M1]/[M2])a show that a has a value of 2.0 for styrene—methyl methacrylate, 1.0 for styrene—isoprene and 1.3 for methyl methacrylate—methacrylonitrile. The conclusion is drawn that values of a of 1.0 and 2.0 represent extremes of behavior for monomers of very similar and very dissimilar polarites. As a corollary of this it is concluded that reactivity ratios for these systems where a is not 1.0 are of questionable theoretical significance.
Stereoregularity and optical anisotropy of polymers
Authors: Tsvetkov V. N. 
Published: April 2003

AbstractThe flow birefringence and the photoelastic effect in films have been used to study the molecular optical anisotropy of stereoisomers of polystyrene (PS), poly(p‐methyl styrene) (PMS), poly(methyl methacrylate) (PMMA), and poly‐(n‐butyl methacrylate) (PBMA). Considerable differences in the optical anisotropy are observed between the atactic and isotactic structures of the molecular chain. These differences change in value and sign for various polymers and in some cases cause a change of the sign of the birefringence. The observed effect is due to the difference between the character of the rotation of the side radicals of the macromolecule in the isotactic and atactic isomers. The molecular optical anisotropy is shown to be especially sensitive to side group rotation in those cases where the positive anisotropy of the principal molecular chain is to a considerable degree compensated by a negative anisotropy of similar absolute value in the side groups. In these cases the study of the molecular optical anisotropy may serve as a sensitive method for studying the stereoregularity. The strain birefringence observed in films of crystallizable polymers is a sum of the two effects: the orientation of chains in the amorphous phase and the orientation of the stereoblocks forming crystallites. These two processes can be differentiated owing to differences in their time dependences, and experimental study of these may serve as a sensitive method for revealing traces of a crystalline phase in a polymer.
Cyclopolymerization. II. Kinetics of polymerization of acrylic anhydride
Authors: Mercier J. , Smets G. 
Published: April 2003

AbstractThe kinetics of polymerization of acrylic anhydride has been studied at 34.6°C. in bulk and in solution in cyclohexanone and in dimethylformamide. The order of reaction with respect to the initiator concentration (azobisisobutyronitrile) varies from 0.67 to 1. The rate of reaction is high; it remains practically constant over a range of monomer concentration from 0.76 to 4.29 mole l.−1; at higher concentrations, it increases linearly with the molar concentration. The results have been interpreted on the basis of a progressive insolubilization of the polymer molecules on account of residual double bonds, and on the basis of the occlusion of growing chain radicals. The presence of trapped radicals was demonstrated by EPR measurements. Their concentration was evaluated by comparison with the spectrum of DPPH; it increases with the time, and with the polymerization temperature. After 8 hr. polymerization at 60°C. it is equal to 5 × 10−4 mole l.−1.
Copolymerization studies. II. Effect of high pressures on monomer reactivity ratios
Authors: Burkhart R. D. , Zutty N. L. 
Published: April 2003

AbstractStudies of the effect of pressure on comonomer reactivity ratios in the styrene—acrylonitrile and methyl methacrylate—acrylonitrile systems show that the values of r1 and r2 increase in both cases and that the relative activation volumes (ΔV11‡ − ΔV12‡) are −9.8 and −9.5 cc./mole respectively, where acrylonitrile is monomer 2. The product r1r2 increases toward unity in both systems. A study of the effect of temperature on these reactivity ratios shows that (ΔH11‡ — ΔH12‡) is essentially zero for methyl methacrylate—acrylonitrile, but 500 cal./mole for styrene—acrylonitrile. Within the pressure range studied, it has been found that the e values for the two monomer pairs are dependent upon pressure, tending to become equal, the higher the pressure, while the Q values are relatively unaffected by pressures up to 1000 atm.
Permeation, solution, and diffusion of water in some high polymers
Authors: Yasuda H. , Stannett V. 
Published: April 2003

AbstractThe equilibrium sorption isotherms of water in polyethylene terephthalate, ethyl cellulose, and rubber hydrochloride have been measured at 25°C. by means of the quartz helix technique. The permeability constants and the diffusion constants have been measured on the same polymers and on polyethylene and polypropylene by the time‐lag technique of Barrer but with a modified apparatus. The solubility coefficients from the sorption measurements (values for polyethylene and polypropylene have been previously reported) are compared with those obtained as the quotient of the permeability and diffusion constants. In the case of polyethylene, polypropylene, and polyethylene terephthalate, excellent agreement between the two sets of values were obtained, but with rubber hydrochloride and ethyl cellulose the sorption values are much higher. These differences are interpreted in terms of clustering of water vapor in the film at higher relative humidities. The modified time‐lag technique showed concentration‐independent diffusion constant for all five polymers.
Modification of spectral and semiconducting properties of polyvinylidene chloride by ultraviolet light of specific wavelengths
Authors: Oster Gerald , Oster Gisela K. , Kryszewski Marian 
Published: April 2003

AbstractPolyvinylidene chloride—polyvinyl chloride copolymer (saran) when irradiated with 254 mμ light produces a species which absorbs maximally at 285 mμ and has a tail in the spectrum which extends into the visible region. Irradiated samples show a further increase in absorption when heated at 100°C., while unirradiated samples are unaffected by such heating. Irradiation at 254 mμ results in crosslinking which is further increased on heating. On the other hand, heating destroys the Carr‐Price reaction exhibited by irradiated material. Heating also destroys the electron spin resonance signal of the irradiated material. Irradiated films are photoconducting, but this property is destroyed by heating. The compound produced irradiation at 254 mμ is destroyed by irradiation at 310 and 365 mμ, but the products are different in the two cases and depend on the presence of oxygen.
Stress relaxation phenomena: Multiple box distribution treatment of relaxation times
Authors: Chang Franklin S. C. 
Published: April 2003

AbstractThe box distribution of relaxation times was generalized for the interpretation of stress relaxation of viscoelastic material under small constant strain. The generalization consists of the use of a number of box distribution functions, each of which is characterized by three parameters; namely, modulus constant, Cj; largest relaxation time, τmj; and width of spectrum. The logarithms of Cj and τmj obtained by applying the multiple box distribution function to published stress relaxation data for polyisobutylene, polystyrene, and GR‐S vulcanizate are linear functions of the reciprocal of absolute temperature, 1/T. The log Cj versus 1/T curves divide into two groups. The group showing relatively small change with temperature is likely due to interchain forces, while the other group, increasing rapidly with decreasing temperature, can be attributed to intrachain forces. Each curve of the latter group consists of three distinct segments of straight line with the middle segment bracketing the glass transition temperature. Thus, the transition from rubbery to glassy state covers a temperature range which can be determined by stress relaxation. Other viscoelastic properties, such as viscosity, activation energy, and tensile stress—strain at various strain rates are discussed on the basis of multiple box distribution.
On the characterization of stereoregular polymers. IV. Application to polypropylene
Authors: Miller Robert L. 
Published: April 2003

AbstractBy viewing a stereoregular polymer as if it were a copolymer, one may obtain relationships between its physical properties and its molecular structure. In particular, melting points and maximum crystallinities were related to sequence propagation probabilities. Thus, in principle, the kinetic parameters for any semicrystalline polymer may be obtained. This information is generally unobtainable by other means. By use of the parameters thus evaluated for a series of polypropylene samples, melting curves were calculated. These represented experimentally determined ones as well as, or better than, existing theories of crystallization.
Time–humidity superposition in some crystalline polymers
Authors: Onogi Shigeharu , Sasaguri Kiichiro , Adachi Tomio , Ogihara Sadahide 
Published: April 2003

AbstractIn order to verify precisely the applicability and reasonableness of the time–humidity superposition method to hydrophilic crystalline polymers, stress relaxation measurements were carried out with films of polyvinyl alcohol and nylon 6 by means of a table model Instron Tensile Tester equipped with a special glass cell to control temperature and humidity. In the case of PVA, only the time–humidity superposition is applicable at humidities higher than that at which the transition begins. For nylon 6, on the other hand, time–temperature and time–humidity superposition apply very well in the transition region and fairly well at higher temperatures and humidities. The results obtained by both the superpositions coincide very well, showing the time–humidity superposition is as reasonable as the time–temperature one. The superposed results were also compared with other existing data, and the reasonableness of the time–humidity superposition was confirmed.
Dynamic mechanical studies of irradiated polypropylene
Authors: Sauer J. A. , Merrill L. J. , Woodward A. E. 
Published: April 2003

AbstractThe internal friction and the dynamic modulus of isotactic polypropylene samples subject to varying degrees of pile irradiation have been studied at low audio frequencies and over the temperature range from 100°K. to over 400°K. The radiation dosages used varied from 5.4 × 1017 to 14 × 1018 nvt. For irradiation doses up to about 3 × 1018 nvt, one observed change is a decrease in the temperature at which the final upswing in damping and drop in modulus occurs, presumably as a result of defects produced in the crystallites by the irradiation. As the irradiation dose increases above 3 × 1018 nvt, all evidence of crystallinity is lost, and the internal friction peak which occurs in the neighborhood of 300°K. and which is associated with the glass transition of the amorphous regions moves to higher temperatures as a result of the increasing chainstiffening effect due to crosslinking. The secondary loss peak at 250°K. attributed to the motion of a small number of segments in the amorphous regions is found to increase in magnitude with increasing dose. The results of density determinations made before and after irradiation and also after subsequent exposure of the irradiated samples to melting temperatures and of solvent extraction studies of the irradiated samples confirm the simultaneous occurrence of crosslinking and of crystalline degradation upon pile irradiation of polypropylene samples.
Microvoids in fibers as studied by small‐angle scattering of x‐rays
Authors: Statton W. O. 
Published: April 2003

AbstractCommercial and experimental fibers show diffuse small‐angle x‐ray scattering which varies in amount and shape, depending upon how the fibers were produced and also upon what aftertreatments they have received. Evidence is given showing that the amount of scattering should be interpreted in terms of the void content or microporosity in the fiber. These voids are too small to be seen by the light microscope, but are found to be measurable in the 15–200 A. range by present techniques. The spinning method greatly affects a fiber's void content. Wet‐spinning and dry‐spinning of a polymer solution produces fibers with a high void content. Melt‐spinning produces yarns with relatively low void content. The cause of this difference is discussed. Voids are shaped by the spinning process in almost all cases. The fiber can be visualized as having longitudinal cracks, crevices, or ellipsoidal. voids in the as‐spun condition, even though no molecular alignment is observed. This shaping was found to arise from a combination of (1) a shearing action of the spinneret and (2) tension on the windup. The voids are further elongated as the fiber is drawn.
The polyelectrolytic nature of cellulose gels in alkali solutions
Authors: Pennings A. J. , Prins W. 
Published: April 2003

AbstractThe swelling of cellulose in alkali solutions has been the subject of numerous investigations in the past. However, there still exists a controversy as to whether the reaction with alkali yields a true alcoholate or an addition compound without ionization of the cellulose. This study presents experimental data on swelling pressures that develop when water‐swollen cellulose is exposed to alkali solutions while its volume is kept constant. The measurements are carried out on extensively extracted and conditioned regenerated cellulose gels with the use of a previously described gel osmometer. It is shown that these pressures can be quite well described using the simple Donnan equilibrium theory put forward originally by Neale in 1929. In this theory, the cellulose is considered as a weak polyacid. From the wet weights and the Na+ ion concentrations inside and outside the cellulose gel, we find the acidic ionization constant to be Ka = 0.52 × 10−14. From free swelling measurements and the corresponding alkali contents, the same value is found. It is shown that the value 1.84 × 10−14 given by Neale is in error, largely due to a nonpermissible approximation in his computations. In the polyelectrolyte model used, the maximum in the free swelling as well as the maximum in the swelling pressure derive directly from the ionization equilibrium. On the basis of ideal behavior, these maxima will occur at a degree of ionization of approximately 0.6, which in the case of our cellulose gels corresponds to a 13.5% NaOH solution outside the gel. Although at higher concentrations the ionization will proceed further, the effect on the unequal Na+ ion distribution becomes less pronounced, thus leading to a decrease in swelling and swelling pressure. In a critical appraisal of earlier work, it is pointed out that the concept of bound alkali and excess alkali in the cellulose gel is unnecessary. On thermodynamic ground, it is also shown that the determination of the bound alkali by pressing excess alkali out of the gel is unreliable. Although admittedly based upon an oversimplified model, the Donnan equilibrium theory provides an explanation for the most salient points in the swelling behavior of cellulose and has in the past been unjustifiably discarded by several authors.