bluuebunny/crossref_metadata_2025 huggingface dataset:
A study of the high field conductance of three polyelectrolytes
Authors: Wissbrun Kurt F. , Patterson Andrew
Published: April 2003

Results of high field conductance measurements on solutions of polyacrylic acid, polystyrenesulfonic acid, and poly‐4‐vinyl‐N‐n‐butylpyridinium bromide have been presented. All the samples studied required appreciable time to reach a steady conductance value after the application of field, this effect diminished with increasing field, was the largest for PSA samples, intermediate for PVPBuBr samples, and smallest for the PAA samples. The extrapolated relaxation times ranged from 2 to 20 microseconds. In the one case where the results for solutions with appreciably different molecular weight polymers could be extrapolated, it appeared that the time lag increased with increase in molecular weight. The high field conductance quotients increased linearly with increasing field in a manner characteristic of weak electrolytes such as acetic acid, but the observed conductance increases were from 6 to 55‐fold larger than for acetic acid at the same field strength. The slopes of the conductance‐versus‐field curves varied as the degree of neutralization or quaternization was varied, indicative of differing degrees of association. In the one case, PAA, where there was appreciable change in the concentration of the samples studied, the high field conductance quotient decreased with increasing concentration, corresponding to an increase of association with increased concentration. Also with PAA, the Wien effect increased with increased molecular weight.
Tensile strength of filled GR‐S vulcanizates
Authors: Bueche F.
Published: April 2003

The tensile strengths of high and low temperature GR‐S rubber vulcanizates containing various fillers have been measured. The fillers used were HAF black, calcium carbonate, and a high styrene‐butadiene copolymer (Pliolite S‐6). Measurements were made as a function of filler concentration, temperature, and degree of crosslinking. These measurements are compared with the predictions of a molecular theory for tensile strength previously published. The following major conclusions are drawn. (1) The theory previously presented for the tensile strength of rubbers is correct in general concept. (2) The increase in strength of GR‐S with added filler is a result of the fact that the filler particles distribute more widely the additional load imposed when a chain breaks. (3) In order for the filler to be effective, the polymer chains must adhere well to its surface. (4) The decrease in effectiveness of fillers at high temperatures is a direct result of the poorer adhesion at higher temperatures.
The strain dependence of stress relaxation in cellulose monofilaments
Authors: Passaglia Elio , Koppehele H. P.
Published: April 2003

The stress relaxation behavior of isotropic and oriented cellulose filaments has been studied at 25° and 50°C. and 50% relative humidity at strains between 0.5 and 5%. Log modulus–log time plots were found to be different at different strains, but superposable one upon the other by simple translation along the log time axis. In this manner a master curve for the relaxation modulus may be obtained. This behavior is hypothesized to result from a strain dependence of the relaxation times in which all the relaxation times have the same dependence on strain. The master curves are used to obtain generalized relaxation distribution functions, which are considerably broader for the isotropic filaments than for the oriented filaments.
Huggins' constant in mixed solvents
Authors: Strauss Ulrich P.
Published: April 2003

When the reduced viscosity of a polymer is determined in a mixed solvent, selective absorption may depress the observed value of Huggins' constant so that comparison with results obtained in single solvents or different mixed solvents becomes meaningless. This undesirable effect would be eliminated if the polymer solutions were first brought to equilibrium with the desired solvent mixture through a semi‐permeable membrane. A method is derived whereby Huggins' constant determined in the conventional manner may be corrected, provided appropriate thermodynamic data are available. The method is demonstrated for a polyelectrolyte‐in simple electrolyte solutions.
Degradation of addition polymers by ultrasonic waves. V. Effect of initial average chain length
Authors: Mostafa M. A. K.
Published: April 2003

The effect of initial weight average chain length of addition polymers (polystyrene in benzene) on the degradation parameters is studied in the light of previously developed theories. Results obtained are compared with those of Jellinek and White. An alternative mechanism of ultrasonic degradation of high polymers is suggested. Its mathematical analysis shows that resonant vibration of polymer molecules is possible. Factors affecting mechanism are discussed to account for the discrepancy between theoretical and experimental results.
Initiation of polymerization by cyclic peroxides
Authors: Baysal B.
Published: April 2003

Bulk and photo initiated polymerization of styrene at 60° have been investigated in the presence of diradical‐producing initiators. Cyclic peroxides such as cyclohexanone peroxide, ascaridole, ergosterol peroxide, dimeric benzaldehyde peroxide, and cyclohexene were used as polymerization initiators. It is concluded that the propagation reactions proceed via monoradicals for these photoinitiated reactions.
The formation of negatively birefringent spherulites in polyhexamethylene adipamide (nylon 66)
Authors: Khoury F.
Published: April 2003

Crystallization of nylon 66 at and above the optical melting point of the polymer has been studied. When heated at constant temperature in the ∼250–265°C. range, the polymer, originally crystallized in the form of positively birefringent spherulites, melts and subsequently crystallizes in the form of negatively birefringent spherulites. The number of spherulites formed and their birefringence decrease as the temperature at which the polymer is heated in the ∼250–265°C. range is increased. In the limit at 265–266°C., non‐birefringent spherulites are formed in the polymer. No crystallization has been detected in polymer heated at constant temperature above 266°C. Negative spherulites are found to grow from predetermined nuclei which persist in the melt above the optical melting point of the polymer. The decrease in the number of spherulites, and hence of effective nucleation centers, with increasing temperature is taken to indicate that nucleation is from polymer aggregates or crystallites and not from foreign particles. Additional evidence is provided to support this view. The optical melting point of the negative spherulites is 268–270°C. Spherulites formed at 260°C. have a degree of crystallite perfection comparable to that of undrawn annealed nylon yarn. Etching experiments indicate that the crystallinity of the spherulites varies inversely with the temperature at which they are formed.
α,β‐unsaturated ketones. III. Copolymers of perfluoroalkyl propenyl ketones with dienes
Authors: Jones F. B. , Coleman L. E. , Stickney P. B.
Published: April 2003

The preparation and properties of copolymers of three perfluoroalkyl propenyl ketones with different 1,3‐dienes are described. Emulsion copolymerization at 50°C. and at 5°C. of perfluoromethyl, perfluoropropyl, and perfluoroheptyl propenyl ketones with 1,3‐dienes, such as butadiene, 1, 1,2‐trifluoro‐3‐chlorobutadiene, 1,1,2‐trifluorobutadiene, and isoprene, has been accomplished and many of the products have exhibited elastomeric properties. Attempted copolymerization of perfluoropropyl propenyl ketone with 1,1,2‐trifluoro‐3,4,4‐trichlorobutadiene or 1,1,2‐trifluoro‐3,4‐dichlorobutadiene did not yield any polymeric products at either 50°C. or at 5°C. Qualitative determinations of thermal stability and solvent resistance have been made for some of the ketone/diene copolymers for comparison with commercial cold GR‐S rubber.
The nitrosation of nylon
Authors: Porter M. R.
Published: April 2003

The nitrosation of nylon 66, with the use of four different nitrosating agents, has been investigated. By the more vigorous nitrosating reactions, heterogeneous nitrosation of nylon yarn occurs rapidly and proceeds to completion in a few hours. In this reaction the amide hydrogen is substituted by a nitroso group to give the structure

By heating the nitrosated polyamides, nitrogen is evolved, and polyesters are formed. The kinetics of this change have been fully investigated. Caustic alkali reacts rapidly with nitrosated nylon. Free radicals are produced on exposure of the nitrosated nylon to visible radiation. Partial nitrosation of nylon yarns has been carried out with the use of a running threadline system; the physical properties of the resulting yarns have been examined.
Purification and viscosity experiments on gum arabic
Authors: van Beek L. K. H.
Published: April 2003

A purification procedure for gum arabic is reported. The impurities can be entirely removed by treating the aqueous solutions with cation exchange resin. The samples are precipitated by acetone. The ionic impurities are found to consist of Mg, and traces of Fe have been confirmed. The effect of these ions on the viscosity contribution is investigated. The presence of these impurities causes a decrease in the limiting viscosity number which can be explained by electrovalent crosslinking. A similar effect is ob served for a sample that has been dried over concentrated sulfuric acid and can in this case be explained by covalent crosslinking.
Kinetic studies on a Ziegler catalyst system
Authors: Gilchrist A.
Published: April 2003

Measurements have been made on the kinetics of the polymerization of ethylene using Ziegler‐type catalysts made from zine di‐n‐butyl and titanium tetrchloride in hydrocarbon solvents. The rate of polymerization was proportional to the square of the ethylene pressure. At catalyst ratios (the molar ratio of zine butyl to titanium tetrachoride in the reaction mixture) less than 0.5, an initial, fast polymerzation was followed by a slower but more persistent polymerization. Both processes increased in velocity with increasing ratio up to 0.5; above this ratio the fast process was not observed while the rate of the slower one decreased with increasing ratio and was very small at unit ratio. At higher ratios the rate increased again as though to reach a limiting value when a very large excess of zine butyl was used. It has not been possible to devise more than speculative interpretations of these results. They suggest that at ratios greater than unity the reaction

may be completed and that the chain initiation step takes place between zine butyl and ethylene, both adsorbed equilibrium‐wise onto the solid, reduced titanium choloride. It is not yet known whether propagation of polymerization occurs along the catalyst surface or at single sites on the surface. If the former is the case and the mobile propagation center is an ion‐pair, the hydrocarbon end being negative and the positive charge lying in the surface, the mobility of this latter charge may limit the rate of propagation. It is possible to explain some of the results obtained most easily from these ideas.
The mechanism of the polymerization of diazoalkanes catalyzed by boron compounds
Authors: Bawn C. E. H. , Ledwith A. , Matthies P.
Published: April 2003

A mechanism is proposed for the polymerization of aliphatic diazo compounds catalyzed by boren trifluoride and similar boron derivatives which satisfactorily accounts for the observed kinetic and molecular weight results. The final polymer molecule is shown to be a baron alkyl of the type . Such molecules are catalysts for the polymerization of fresh diazo compounds and in this manner it has been possible to prepare block copolymers of the type
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The mechanism of polymerization is shown to be similar to the polymerization of ethylene catalyed by aluminum alkyls and possibly to the Ziegler‐type polymerization of α‐olefins.
Polymerization of ethylene by soluble Ziegler catalysts
Authors: Bawn C. E. H. , Symcox R.
Published: April 2003

Kinetic measurements have been made on the polymerization of ethylene to low molecular weight products using a soluble catalyst formed by the interaction of sec‐butyl titanate and aluminum triethyl. A maximum in catalyst activity occured at ratio Al:Ti = 2.5:1 and a scheme is proposed to explain this observation. An interesting feature of the polymerization is the existence of a well‐defined cut‐off pressure of ethylene below which no polymerization occurred.
Polyethers. VI. Aluminum alkyls as catalysts for polymerization of propylene oxide
Authors: Ebert Philip E. , Price Charles C.
Published: April 2003

Solutions of triethyl aluminum, diethyl aluminum chloride, and triisobutyl aluminum are effective catalysts for polymerization of propylene oxide. Very small, but reproducible yields of isotactic polymer were obtained.
The polymerization of epoxides by metal halide catalysts
Authors: Colclough R. O. , Gee Geoffrey , Higginson W. C. E. , Jackson J. B. , Litt Morton
Published: April 2003

Ethylene, propylene, and styrene oxides have been polymerized by a range of metal halide catalysts, high molecular weight products being obtained from the two firstnamed. The limited quantitative evidence presented is consistent with the view that these polymerizations proceed by a coordinate propagation mechanism. The effective catalyst for this stage is essentially a metal alkoxide, formed in an initial cationic polymerization in which a small number of monomer units are attached to the metal atom. The propylene oxide polymers generally contain a fraction of crystalline material, but the proportion of this can be reduced practically to zero (with FeCl3 catalysis) by careful exclusion of water.
Synthesis of graft copolymers
Authors: Smets G. , Poot A. , Mullier M. , Bex J. P.
Published: April 2003

The two‐step synthesis of graft copolymers was carried out by several methods. In the first method, the initial peroxidized polymer was prepared from a copolymer of methyl acrylate and acroyl chloride by recation with tert‐butyl hydroperoxide; the content of perester could be varied. The rate of decomposition of these perester groups and the degradation velocity of this first‐step polymer were determined in benzene solution at various temperatures. The activation energies were 30.1 kcal./mole, respectively, which values correspond to the scission of the OO linkage. Grafting experiments were carried out in dilute solutions (1%) in order to avoid any grafting by transfer to the polymer. The second‐step polymerization followed the square‐root law dependence with respect to the peroxide polymer concentration. This rate was also of the first order with respect to the monomer, i.e., styrene, concentration. The rate of grafting was also evaluated by quantitative fractionation of the reaction products (precipitation method), taking into account the weight per cent of styrene in these isolated graft copolymers. The rate of grafting was also of the first order with respect to the monomer concentration. A comparison of the total rate, Rp, and the rate of grafting, Rg, indicates that, at low perester‐content, Rg is about one‐half of Rp, while at high perester content, Rg is much lower than Rp as a result of the recombination of redicals. These kinetic result are discussed on the basis of a general reaction scheme. In the second method, first‐step polyners carrying tert‐butyl peroxide endgroups, were prepared on the basis of the decomposition of tert‐butyl hydroperoxide in the presence of cupric octoate. The influence of the concentration of this copper salt on the rate of polymerization has been considered. The first‐step polymers so produced can initiate the polymerization of a second monomer, so that block copolymers are obtained by chain extension, probably on both sides. In a third method, the initial peroxidic polymer was obtained by electrolysis of an aqueous solution of polymethacrylic acid. The experimental conditions are discussed. The hydroperoxide‐containing polymers, prepared and isolated at below 10°C., can be used for a second‐step polymerization with another monomer, e.g., acrylamide. Graft copolymers were thus obtained; these hydroperoxidic polymers are, however, relatively unstable, particularly because of the presence of neighboring acid groups.
Grafting of polycaprolactam on a polymethacrylate‐type backbone
Authors: Wichterle O. , Gregor V.
Published: April 2003

Recently it has been found in our laboratories that ϵ‐caprolactam can be very readily polymerized by alkaline catalysts even at room temperature provided diacylamines, such as N‐acetylcaprolactam, are present. As part of the investigation of the mechanism of this reaction, we have prepared polymers of N‐methacryloylcaprolactam containing the active secondary imide groupings attached to a polymethacrylate‐type chain. Methacryloylcaprolactam itself will not, for obvious steric reasons, undergo polymerization, but its copolymers may readily, be obtained; thus it will form a copolymer with styrene with the parameters r1 = 1, r2 = 0. When this copolymer is allowed to react with caprolactam in the presence of alkaline catalysts, the monomer will enter at the sites of imide groupings. Simultaneously with the addition of the lactam to the copolymer, crosslinking of the polymer takes place which causes the formation of insoluble gels at the very beginning of the grafting. It is assumed that crosslinking is due to a reaction of the Claisen condensation type between two diacyl imide groups. This is supported by the fact that the relationship of the reciprocal specific viscosity and time is approximately linear in solution polymerization. The grafting of lactam which is not controlled by diffusion continues at an undiminished rate even after the gel formation. The rates of grafting and crosslinking are proportional to the concentration of sodium caprolactam added.
Influence of bond angle restrictions on polymer elasticity
Authors: Flory P. J. , Hoeve C. A. J. , Ciferri A.
Published: April 2003

The statistical distribution of end‐to‐end distances in polymer chains is re‐examined with particular attention to deviations from Gaussian behaviour. The nature of the error involved in the conventional inversion of the Langevin function is specified. The theory of the rubber elastic equation of state is generalized for the case where the chains display changes in internal energy with change in conformation. The temperature coefficient of the ratio f/T of the retractive force to the absolute temperature is shown to be directly related to the change with temperature of the mean‐square distance r between the ends of the free polymer chain. thus,

where fe = (∂E/∂L)V,T. represents the contribution of the internal energy to the retractive force, and [η]Θ is the intrinsic viscosity at the theta point. Preliminary experiments are reported on stress‐temperature coefficients for (I) crosslinked poly‐(dimethylsiloxane) and (II) polyethylene. For I, it is found that fe = 0, within experimental error, but for II, fe ≅ −f/2. Results for II are explicable on the basis of a potential energy difference of ca. 500 cal./mole between the gauche and trans forms, in agreement with spectropic results for lower hydrocarbons.
An internal friction study of polytetrafluoroethylene
Authors: McCrum N. G.
Published: April 2003

A torsion pendulum has been used to measure the internal friction of polytetrafluoroethylene. The crystallinity of the specimens varied form 48 to 92%, and the measurements were made over a wide temperature range. The site of each relaxation was assigned by observing the variation of relaxation strength and peak height with crystallinity. In this way amorphous relaxations were found to occur at 176.5°K. (0.60 cycle/sec.) and 399°K. (0.62 cycle/sec.). The crystallite relaxations occur at 291°K. (0.28 cycle/sec.) and the crystallite melting point, 600°K. It is concluded that the amorphous regions of polytetrafluoroethylene exist in three phases between 4.2°K. and the crystallite melting point. The supercooled liquid which exists below 600°K. is transformed into an amorphous solid at a temperature in the region of 400°K. This solid undergoes another transformation at approximately 176°K. to form a third phase which is stable down to 4.2°K. The crystallite realaxation centered at 291°K. consists of a series of disordering transitions including the well‐known first‐order transition. There is evidence that hindered rotation occurs within the crystallites at temperatures as low as 220°K.
Graft copolymer formation during the polymerization of vinyl acetate in the presence of polyvinyl alcohol
Authors: Hartley F. D.
Published: April 2003

When aqueous dispersions of polyvinyl acetate are prepared by polymerizing vinyl acetate monomer, emulsified in water in the presence of polyvinyl alcohol and an alkali, with a water‐soluble persulfate catalyst, polyvinyl acetate‐polyvinyl alcohol graft copolymers are formed. The presence of graft copolymers in the dispersions was first established by the techinques of turbidimetric titration and adsorption and partition chromatography on paper. Subsequently the graft copolymers were separated according to species and at the same time the polyvinyl acetate was fractionated on a molecular weight basis, by using a continuous gradient elution chromatographic fractionation technique. The results obtained show that in the fractionation of polymers by chromatographic methods, solubility in the developing solvent is a more important differentiating property than adsorption on the supporting medium. Three dispersions prepared using identical quantities of vinyl acetate monomer and catalyst, but with varying quantities of polyvinyl alcohol, have been fractionated. Two different species of graft copolymer, one water‐soluble and of high polyvinyl alcohol content, and the other water‐insoluble and of low polyvinyl alcohol content, have been isolated from each of the dispersions. The relative amounts of the two species of graft copolymer and the moleculare weight distributions of the polyvinyl acetate were found to differ in the three dispersions. Mechanisms for the reactions giving rise to graft coplymer formation have been postulated which explain these differences. It is suggested that the watersoluble species of graft copolymer are formed in the initial stages of the reaction by the radicals from the decomposing catalyst which first abstract hydrogen atoms from the polyvinyl alcohol molecules to form polymer radicals which then initiate polymerization of vinyl acetate monomer. The water‐insoluble species of graft copolymer are formed at later stages in the reaction by transfer from growing polyvinyl acetate chains on to polyvinyl alcohol molecules, forming polymer radicals which can again initiate polymerizaion of vinyl acetate. In the infrared spectra of both species of graft copolymer an absorption maximum occurs at a wavelength of 8.8μ. An absorption maximum occurring at this wavelength is characteristic of a tertiary alcohol group, and suggests that the grafted polyvinyl acetate chains are attached to the chain carbon atoms of the polyvinyl alcohol molecules to which the hydroxyl groups are also attached.
Graft copolymerization by pre‐irradiation technique
Authors: Ballantine D. , Glines A. , Adler G. , Metz D. J.
Published: April 2003

Trapped free radicals are formed when polyethylene is irradiated with cobalt‐60 gamma rays in the absence of any reactive species‐oxygen, monomer, etc. The net free radical population formed increases with increasing total dose, decreasing temperature of irradiation, and increasing crystallinity of the polymer. Upon addition of a monomer to these vacuum‐irradiated films, the monomer will graft copolymerize. Graft coplymers produced by this technique are the most homogeneous, compared to those formed using other radiation‐induced techniques. If oxygen is present during the irradiation many of the free radicals formed are consumed in reaction with the oxygen to produce peroxides, hydroperoxides, and other oxygen‐containing groups. The ratio of trapped free radicals to those reacted with oxygen increases with increasing crystallinity of the polyethylene. When films irradiated in air are subsequently contacted with monomer, grafting occurs, even at room temperature, and increases in rate at higher tamperatures. It is believed that the initiation of grafting in these films is accomplished by trapped radicals and peroxide decomposition. The graft copolymers formed by this technique are not as homogeneous as those formed in the vacuum irradiation technique, but are far more homogeneous than those formed in either of the simultaneous irradiation‐grafting techniques.
Synthèse des copolymères greffés à partir des polymères ayant subi l'action des radiations ionisantes. II. Influence des conditions de préirradiation sur la cinétique du greffage sur le polyéthylène
Authors: Chapiro Adolphe
Published: April 2003

On a étudié l'influence de la dose at de l'intensité de la préirradiation sur la réaction de greffage des monomères vinyliques sur des films de polyméthylène ayant été préallablement irradiés en présence d'air. Plusieurs types de rayonnements out été utiliés pour l'irradiation des films: rayons gamma du cobalt‐60, rayons‐X de 37 kV et électrons accélérés de 2 MeV. Les films irradiés étaient ensuite chauffés sous vide, en présence de monomère, à 80 et à 135°C. Au cours de la réaction de greffage, les films grossissaient régulièrement dans lels trois dimensions sans que la forme de leur contour extérieur soit modifiée měme pour des taux de greffage très élevés. On a trouvé que la vitesse de greffage à une température donnée était une fonction linéaire du temps de préirradiation jusqu' à des doses de l'ordre de 10 mégarads; pour des doses plus élevées, la vitesse de greffage tend vers une valeur limite. D'autre part les films préirradiés en présence d'air et irradiés ensuite sous vide, perdent leur activité pour le greffage. Pour une dose d'irradiation donnée, la vitesse de greffage est d'autant plus élevée que l'intensité à laquelle a été effectuée la préirradiation est plus petite. L'ensemble de ces résultats confirme l'hypothèse déjà exprimée antèrieurement, selon laquelle l'irradiation en présence d'air produirait dans le polymère des groupements peroxydiques. Ces peroxydes macromoléculaires sont eux‐měmes sensibles à la radiolyse et se décomposent pour des doses élevées. La cinétique de la réaction de greffage est conforme à ne réaction de polymérisation amorcée par les macroperoxydes. Cette polymérisation s'effectue dans un milieu polymère très visqueux, ce qui ralentit la réaction de terminaison et produit des perturbations analogues à celles que l'on observe lors de l'apparition de l'“effet de gel.” De plus la nécessité pour le monomère de pénétrer à l'intérieur du film de polymère, introduit une complication supplémentaire, la concentration instantanée du monomère sur les lieux de la réaction étant contrǒlée par diffusoin. L'influence des branches latérales existant dans le polyéthylène “haute pression” sur la peroxydation radiochimique a été mise en évidence par une étude comparative entre le greffage sur le polyéthlène “basse pression” et sur du polyproylène. Les résultats obtenus montrent que la présence d'hydrogènes tertiaires dans le polypropylène favorise la formation d'hydroperoxydes, tandis que des structures biperoxydiques dominent dans le polyéthylène à chaǐne linéaire. On discute l'ensemble de ces résultats.
Préparation des copolymères greffés du polytetrafluoroéthylène (Teflon) par voie radiochimique
Authors: Chapiro Adolphe
Published: April 2003

Il a été trouvé antérieurement que l'on pouvait greffer différents polymères sur le polytétrafluoroéthylène, en soumettant à l'action des radiations ionisantes ce polymère en présence de monomères vinyliques. Cependant, comme le Téflon est une substance chimiquement très inerte, aucun monomère ne peut pénétrer à l'intérieur de ce polymère dans les conditions usuelles et le greffage est généralement limité à une zone superficielle de celui‐ci. Or on a trouvé que si l'on greffe sur le Téflon dans des conditions expérimentales bien définies un monomère capable de gonfler le produit greffé obtenu, le greffage se poursuit de proche en proche et on obtient finalement un copolymère greffé dont la structure est homogène dans toute la masse. Cette réaction a été étudiée en greffant sur des films de Téflon du styrolène et du méthacrylate de méthyle. Au cours du greffage les films de polymère grossissent régulièrement dans les trois dimensions sans que la forme de leur contour extérieur soit modifiée. Cependant, si la teneur en polystyrolène dans les films dépasse 90% en poids, ceux‐ci tendent à se déchirer à la suite des tensions provoquées par le gonflement du film greffé dans le styrolène. La cinétique de cette réaction est contrǒlée par la diffusion du monomère dans les films partiellement greffés. Les courbes de conversion font apparaǐtre une accélération de la réaction au cours du temps. Elles peuvent ětre représentées par une équation empirique de la forme C% = Atα + B où t représente le temps et où l'exposant α a une valeur généralement comprise entre 2 et 3. Si la vitesse de diffusion du monomère est inférieure à sa vitesse de polymérisation, le greffage est limité à une zone superficielle des films; si par contre on réduit la vitesse de polymérisation en maintenant constante la diffusion, le greffage dans toute la masse du film devient possible. On a étudié l'influence de différentes paramètres sur la cinétique de la réaction. C'est ainsi que l'intensité du rayonnement, la concentration du monomère et la température jouent un rǒle fondamental dans la réaction. Des films de Téflon de différentes épaisseurs ont été greffés dans ces conditions. Une irradiation intermittente favorise également le greffage dans la masse. Quelques propriétés des films de Téflon greffés de polystyrolène dans toute leur masse ont été étudiées. Ces films ne gonflent que faiblement dans le benzène, měme pour des teneurs en polystyrolène de l'ordre de 70%; ils se ramollissent vers 150° sans fondre et conservent une grande inertie chimique. On discute l'ensemble de ces résultats.
Molekulargewichte und molekulargewichtsverteilungen unverzweigter und verzweigter polystyrole
Authors: Meyerhoff G. , Cantow M.
Published: April 2003

Zur Bestimmung von Molekulargewichtsverteilungen muss man die genaue Beziehung zwischen Molekulargewicht und Viskositätszahl kennen. Für Polystyrole erhielten wirdiese Beziehung aus Sedimentation‐und Diffusionsmessungen. Im niedrigeren Molekulargewichtsbereich fanden wir, dass anionische Polystyrole nach Szwarc eine etwas kieinere Viskositätszahl aufweisen wie gewöhnliche Polystyrole. Das normale Polystyrol zeight in diesem Bereich keinen merklichen Verzweigungseinfluss. Jedoch vermindert die Verzweigung [η] für Molekulargewichte > 500 000 beträchtlich. Hier unterscheidet sich das isotaktische Polystyrol vom gewöhnlichen ataktischen, das immer etwas verzweigt ist. Es zeigt sich, dass gelöstes isotaktisches Polystyrol sich wie ideales unverzweightes Polystyrol verhält. Die Beziehung [η] = f(M) als Funktion der Verzweigung kann man durch Kombination der Viskositätstheorie von Debye‐Bueche mit der Konfigurationsstatistik von Zimm‐Stockmayer erhalten. Wir führen dies für das nicht‐ideale Lösungsmittel Toluol durch. Danach ergibt sich, dass bei gewöhnlichen Polystyrolen zwischen M = 105 bis M = 106 etwa nach jeweils 4 × 103 monomeren Einheiten ein Verzweigungspunkt auftritt. Im Gebiet von Mw = 105 bis 1,5 × 106 führten wir verschiedene Fraktionierungen aus. Es wurde dabei die Dreiecksfraktionierung benutzt, die uns als die zur Zeit wirksamste Methode erscheint. Dabei zeigte sich, dass es fast unmöglich ist, für niedrige Molekulargewichte eine genaue Verteilungskurve zu erhalten. Nur durch Zusammenfassung osmotischer, ebullioskopischer und viskosimetrischer Messungen konnten wir verlässliche Resultate rezielen. Das höchste von uns fraktionierte Präparat zeigte einigen Verzweigungseinfluss, der für die höheren Fraktionen stärker wird. Dann ist die Grösse [η] kein Mass mehr für das Molekulargewicht der einzelnen Fraktionen. Daher bestimmten wir Mw für jede Fraktion mit Hilfe der Lichtstreuung. Die sich derart ergebenden Molekulargewichtsverteilungen werden diskutiert.
Properties of isotactic, atactic, and stereoblock homopolymers, random and block copolymers of α‐olefins
Authors: Natta G.
Published: April 2003

The study of several methods of controlling the molecular weight in the stereospecific polymerization of α‐olefins leads us to a better understanding of the neture of coordinated ionic catalysis. Some physical and chemical factors that influence the steric composition of polymers have been examined and a kinetic interpretation of stereoblock Polymers is proposed. A continuous variation of physical properties, particularly of crystallinity, melting point, and densities, and mechanical properties is observed as functions of the length of the steically homogeneous section in stereoblock polymer. This length is related to the number of steric irregularities of the chain. A new method to prepare block copolymers of different monomers is described; these copolymer show evidence of crystallinity due to long sequences of the same monomeric units, but properties different from those of physical mixtures of homopolymer and from those of random copolymer. The production of random copolymer has been examined, particularly of amorphous ethylene‐propylene copolymer having interesting elastomeric properties.
La structure du polyéthyléne consideré comme un mélange de n‐paraffines
Authors: Gubler M. G. , Kovacs A. J.
Published: April 2003

On 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

Model 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

The 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

The 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

The 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

Many 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

The 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

From 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

This 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

In 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.