bluuebunny/crossref_metadata_2025_split huggingface dataset:
Diffusion of allyl chloride in polyvinyl acetate. Part II. The transient state of permeation
Authors: Meares P. 
Published: April 2003

AbstractThe permeation rate of allyl chloride through polyvinyl acetate films has been studied as a function of time during the transient period preceding the establishment of steady states of permeation. It was found that two distinct processes could be distinguished. When the ingoing pressure of allyl chloride was changed from a value at which a steady state had been established to a new value, there was a gradual change in the permeation rate to a new steady value. Depending upon the initial and final pressures this change required from several hours to several weeks. When the initial ingoing pressure was small or zero there was a large and immediate increase in the permeation rate when the ingoing pressure was increased. This rapid rate decreased over periods which ranged from about three hours at low ingoing pressures to a few minutes for higher ones, and died away before the more gradual increase in rate had begun to take effect. Using the equations of Frisch, the time lags for transition between pairs of steady states have been calculated, from previously determined sorption and diffusion data, and compared with the observed values. The calculated values were usually smaller than the observed ones. The discrepancy was most serious at low vapor concentrations and decreased with increasing concentration. For concentrations greater than 1 × 10−3 mole cm.−3 there was a close agreement. For comparable concentrations, the discrepancy was less marked for decreasing than for increasing ingoing pressure and was also less for thin membranes than for thicker ones. These observations are consistent with the theory that the swelling of the membrane which accompanies the sorption of vapor gives rise to elastic stresses which slowly decay by viscous movements within the polymer. The initial jump in permeation rate proved more difficult to study. As far as could be determined it occurred instantaneously. When plotted against logarithmic time, S‐shaped curves were obtained very similar in appearance to elastic stress decay curves observed for polymers and predicted theoretically for a series of Maxwell units with a wide distribution of relaxation times. This suggests that the high permeability may arise from lateral strains set up when an instantaneous swelling takes place at the ingoing face of the membrane on the admission of more vapor. The instantaneous stress then decays by elastic motions of segments of polymer molecules, over a period determined by the temperature and initial sweller concentration, and so reduces the high permeation rate. For initially unswollen polyvinyl acetate at 40° the time for half‐decay of the permeation rate was agout 25 minutes for a membrane 32 μ thick. It was found that the peak permeation rate increased as successive experiments were performed with the same membrane. This suggested that permeation through a membrane clamped in a diffusion cell produced orientation parallel to the membrane surface. It has not yet been possible to confirm this.
Monolayer studies of some hydroxylated polyolefin rubbers
Authors: Dean W. R. , Perera V. , Glazer J. 
Published: April 2003

AbstractWhen thin films of natural rubber, gutta‐percha, polybutadiene, and polybutadiene‐styrene copolymers are deposited at the surface of aqueous acidified potassium permanganate, they undergo a surface reaction and spread spontaneously. A study of the products of this reaction has been made, and their surface characteristics are described. The reaction products are polyhydroxy derivatives of the polyolefins and are shown to form stable monomolecular layers at an air‐water interface. The areas of the hydroxylated olefin residues have been determined, and their magnitude and orientation at the interface is discussed. The agreement between experimentally determined areas and theoretical areas (from established interatomic distances) is good. Results suggest that butadiene‐styrene copolymers contain an appreciable number of blocks of contiguous styrene units.
Influence of rate of shear on the apparent viscosity of dilute polymer solutions
Authors: Takemura Tetuo 
Published: April 2003

AbstractThe measured viscosity of polymer solutions varies with the magnitude of the applied shearing stress. In this paper a modified Rouse model of a polymer molecule (which has some stiffness) is used, and the diffusion equation is solved with respect to the co‐ordinates system moving with the polymer molecule. Results indicate: (1) The above phenomena is a natural consequence of the fact that the molecules are caused to rotate by the shearing action. (2) This is the same mechanism with the dynamic viscosity caused by the applied periodic shearing stress.
The hydrolysis of n‐amyltriethoxysilane and phenyltriethoxysilane
Authors: Sprung M. M. , Guenther F. O. 
Published: April 2003

Abstractn‐Amyltriethoxysilane and phenyltriethoxysilane were hydrolyzed in organic solvents in the presence of acidic or basic catalysts. The bulky substituents allow relatively large amounts of low‐molecular‐weight partial hydrolysis products to be isolated and stabilize the silanol functions present against further condensation. Cyclic ethoxypolysiloxanols in the molecular weight range 500–1000 are principal products of acid catalyzed hydrolysis. More extensive condensation occurs under alkaline conditions. Relatively high yields of low‐polymeric silsesquioxanes (octamers and possibly hexamers) are then obtained. The major product obtained from phenyltriethoxysilane, when hydrolyzed in a ketone solvent with a quaternary base as catalyst, is an amorphous high polymer virtually free of functional groups. In inert solvents in the presence of traces of catalyst a very facile rearrangement occurs, giving the octamer (and possibly the hexamer) in very high yield.
Sorption kinetics of water vapor in wool fibers
Authors: Downes J. G. , Mackay B. H. 
Published: April 2003

AbstractUsing a modification of the vibroscope technique, studies have been made of the sorption kinetics of water vapor in single wool fibers. Small changes in water content, described as interval sorption and desorption, occur in two stages, the first occupying a few minutes and the second many hours (at room temperature). This behavior is similar to that recently reported for interval sorption of organic vapors in “glassy” polymers (e.g., acetone in cellulose acetate). The first stage of sorption is considered to be due to diffusion in accordance with Fick's law; the slow increase in concentration during the second stage is thought to result from partial relaxation of the swelling stress. Large changes in water content are described as integral sorption and desorption. In integral sorption the slow second stage of sorption is not observed; the explanation is thought to be that relaxation of swelling stress, and hence the second stage, are greatly accelerated by the transient stress associated with the steep concentration gradient present during integral sorption. The slow second stage is present in integral desorption, the probable reason being that in this case there is no steep concentration gradient. Integral sorption to a given value of relative humidity (R.H.) results in a higher equilibrium water content than if the same R.H. is reached in a series of interval steps. This effect is thought to be related to the hysteresis which is observed in the isotherm in a sorption‐desorption cycle; the transient stress present in integral sorption leaves the material in the same condition as if it had been brought down the desorption curve of the isotherm. The sorption hysteresis is thought to result from metastability of the interchain bonds which undergo relaxation in the second stage of interval sorption and desorption. All the effects observed are likely to be qualitatively characteristic of vapor sorption in any polymer at temperatures below the second‐order transition.
The determination of the stiffness of the chain of a rubber‐like polymer
Authors: Stein Richard S. 
Published: April 2003

AbstractA theory for the infrared dichroism of a crosslinked, rubber‐like amorphous polymer is described. The dichroism of a typical rubber is estimated to be measurable. The dichroism‐stress ratio is independent of strain and degree of crosslinking and serves as a measure of the number of monomer units per statistical segment, an index of chain stiffness.
Effect of pile irradiation on the dynamic mechanical properties of polyethylene
Authors: Deeley C. W. , Kline D. E. , Sauer J. A. , Woodward A. E. 
Published: April 2003

AbstractThe effects of pile irradiation on the damping and resonant frequency of a “high pressure” polyethylene has been investigated over a temperature range from 80 to 550°K. in the audiofrequency region using an apparatus which drives rod‐like specimens in their transverse modes. Using irradiation dosages which result in approximately 4% crosslinking or greater, the mechanical loss peaks found at about 165, 265, and 355°K. in polyethylene are altered. Definite changes in the resonant frequency or modulus‐temperature plots also occur. The 355°K. peak, attributed to the melting of the crystalline portions of the sample, decreases in height and shifts to lower temperatures with increasing irradiation dose. A decrease in the height of the 265°K. peak accompained by a shift to higher temperatures takes place. The 165°K. peak initially increases in height and peak temperature but at higher dosages a marked decrease in the damping maximum occurs. The damping behavior in the 165 and 265°K. regions is discussed in terms of diffusional motion of chain segments in the amorphous polymer portions.
Melting points and heats of fusion of some polyamides and polyesters
Authors: Flory Paul J. , Bedon Helen D. , Keefer Edward H. 
Published: April 2003

AbstractMelting points of three polyamides, four polyesters, and their mixtures with diluents have been determined by application of dilatometry to observe the latent volume change during gradual melting extending over many days in each case. Heats of fusion were calculated from the depressions of the melting point by varying volume fractions of diluents. The results, given in °C. and in cal./g., respectively, are as follows: decamethylene sebacamide, 216°, 24.5; decamethylene azelamide, 214°, 27; the sebacamide of 1,10‐dipiperazyldecane, 129.5°, 34.5; decamethylene azelate, 69°, 31; nonamethylene azelate, 65°, 33; decamethylene terephthalate, 138°, 36; hexamethylene terephthalate 160.5°, 34. The results are compared with those previously reported for related polymers. A possible explanation is suggested for the fact that the heats of fusion of polyesters exceed those for the corresponding polyamides. High melting points appear to be associated with low entropies of fusion rather than with high heats of fusion.
Properties of polyesters of bisphenols and dicarboxylic acids
Authors: Levine Max , Temin Samuel C. 
Published: April 2003

AbstractA series of linear polyesters have been made by polymerization of dibasic acids with acetyl derivatives of p,p′‐diphenolic compounds. The diphenolic compounds were of either the dihydroxydiphenyl or the methylenebisphenol type with varying degrees of alkyl substitution. The crystallinity and first‐ and second‐order transition temperatures of the polymers are considered in terms of their chemical structures. The effects of symmetry and aromaticity are discussed.
α,β‐Unsaturated ketones. II. Copolymerization reactions of trans‐cinnamoylferrocene
Authors: Coleman L. E. , Rausch M. D. 
Published: April 2003

AbstractThe polymerization reactions of trans‐cinnamoylferrocene have been described and a number of copolymers have been characterized. trans‐Cinnamoylferrocene does not homopolymerize using conventional free radical techniques but forms copolymers with styrene, acrylonitrile, methyl methacrylate, ethyl acrylate, butadiene, isoprene, and 1,1‐dihydroperfluorobutyl acrylate.
Graft interpolymers formed by γ‐irradiation of methyl methacrylate‐natural rubber mixtures
Authors: Angier D. J. , Turner D. T. 
Published: April 2003

AbstractOn exposure to Co‐60 γ‐radiation, mixtures of natural rubber and methyl methacrylate yield almost exclusively rubber‐polymethyl methacrylate graft polymers. An appreciable amount of free polymethyl methacrylate is formed only in the presence of a transfer agent or following radiation‐induced degradation of the interpolymer. Structural characterization of the products has been made. The findings are not consistent with random grafting of the synthetic polymer on linear rubber molecules of random molecular size distribution—the rubber component appears to comprise several crosslinked molecules. The influence of the purity of the rubber, monomer concentration, field intensity, the presence of transfer agent, and the gel effect on the rate of formation, yield, and structure of the interpolymer are reported.
Sorption and diffusion in ethyl cellulose. Part IV. Water in ethyl cellulose
Authors: Barrer R. M. , Barrie J. A. 
Published: April 2003

AbstractAn account has been given of sorption and diffusion of water by ethyl cellulose. In contrast with diffusion coefficients of some other penetrants, those of water decrease with increase of water sorption in the manner previously observed by Rouse for water–polythene systems. The sorption isotherms have the opposite curvature to Langmuir or Freundlich isotherms, and hence also to the isotherms of benzene, C4 and C5 paraffins, or acetone sorbed at low penetrant concentration by the same polymer. The results have been interpreted in terms of cluster formation of water molecules either in preexisting cavities in the polymer or, less probably, in the polymer matrix itself. Visual evidence of cluster formation is provided by the onset of light scattering by the membrane as the relative humidity reaches a critical range. The opacity disappears again as the humidity is decreased.
Studies on the low pressure polymerization of ethylene using catalysts containing lithium alkyls
Authors: Frankel Max , Rabani Joseph , Zilkha Albert 
Published: April 2003

AbstractThe low and atmospheric pressure polymerizations of ethylene using catalysts prepared from n‐butyl lithium or isoamyl lithium and titanium tetrachloride were studied. The efficiency of the catalyst depended on the molecular ratio of the alkyl lithium to titanium tetrachloride. Optimum molecular ratio for the n‐butyl lithium–titanium tetrachloride was found to be between 2.15–2.47 with a sharp drop between 2.15–1.49; for the isoamyl lithium the optimum was between 2.5–4.3. Within the examined interval (of atmospheric pressure to a pressure of 60–70 lb./sq. in.) higher pressure caused an increase in the yield of polyethylene. No pronounced effect in polymerization was found in the temperature interval of −10–55°. The catalyst is stable for a few days if kept refrigerated. Petroleum ether, b.p. 40–80°, was the best solvent both for the preparation of the catalyst and for the polymerization. Ligroin, toluene, and especially ether interfered with the polymerization. The polyethylenes obtained melted between 125–135°.
A study of chain transfer in homologous vinyl esters
Authors: Buselli Alio J. , Lindemann Martin K. , Blades Charles E. 
Published: April 2003

AbstractThe principal complication arising out of free radical‐initiated polymerizations involving vinyl acetate has been the chain transfer to monomer and polymer which results in a highly branched polymer chain. Some evidence has also been presented to show that the degree of branching in polyvinyl esters increases with an increasing number of carbon atoms in the vinyl ester. It was of interest, therefore, to obtain a relative measure of the chain transfer constants for successive members of the homologous series of vinyl esters and to relate the constants to the actual structure of the respective polyvinyl ester. Accordingly, the study of the chain transfer in the benzoyl peroxideinitiated polymerizations of vinyl acetate in the presence of a homologous series of ethyl esters of fatty acids was made. Chain transfer constants versus number of carbon atoms in the carboxylate portion of the fatty acid ester resulted in a linear relationship which can be expressed as

where n is the number of non‐α‐methylene groups in the side chain. A concurrent study of the influence of monomer chain lengths of selected vinyl esters on molecular weight of the derived homopolymer was also carried out. The results obtained provide a basis for predicting the trends for changes in branching and degree of polymerization within the homologous series of vinyl esters.
Degradation of addition polymers by ultrasonic waves. IV. The effect of ultrasonic intensity
Authors: Mostafa M. A. K. 
Published: April 2003

AbstractThe effect of ultrasonic intensity on degradation parameters K and y for a polystyrene in benzene sample was investigated. The results are discussed in relation to a theory previously developed for the degradation of addition polymers by ultrasonic waves. It is shown that for a constant ultrasonic frequency the experimental results can be explained by theories which assume that degradation is caused by frictional or impact forces.
Diffusion‐controlled stress relaxation in polymers. III. Stress relaxation in a swelling polymer
Authors: Kishimoto Akira , Fujita Hiroshi 
Published: April 2003

AbstractAn approximate theory of the relaxation of stress in amorphous linear polymers accompanying sorption of a low molecular weight penetrant is worked out on the assumption that the relaxation time of each Maxwellian relaxation mechanism involved is changed in the presence of penetrant by a factor dependent on penetrant concentration. A method is derived from the theory which permits approximate evaluation of the integral diffusion coefficient D̄ of the penetrant in the polymer from stress‐relaxation data on swelling systems. The theory is checked on experimental data for the systems polymethyl acrylate‐water and polymethyl acrylate‐methanol at 40°C., and it is found that, for both systems studied, the values of D̄ computed from mechanical data agree reasonably with those evaluated directly from usual sorption experiments. The theory described presents only a first attempt to the quantitative interpretation of the phenomenon discussed. Further improvement and modification of it is apparently desirable, in view of some drastic approximations incorporated in its mathematical development.
Statistics of flexible macromolecules at interfaces
Authors: Simha Robert 
Published: April 2003

AbstractThe subject is of importance in a variety of colloidal and biological problems. It includes (a) adsorption on solid surfaces, (b) the equation of state of mono or multilayers on liquid interfaces, (c) surface tension of solutions. There are two aspects, namely the molecular configurations at the interface and the resulting contributions to the free energy. Assume the surface to be a regular array of adsorbing sites, each accommodating one chain segment. Unless the segment‐site interaction is extremely large in comparison with kT and of long range, flexible chains will not deposit completely. H. L. Frisch and the author have previously shown for random coils that the average number v of segments adsorbed out of a total of t per chain is proportional to t1/2 and increases with chain flexibility and thus temperature in a good solvent. They also established the consequences of this for (a) and (b). The present discussion, based on work in collaboration with Frisch, includes surface tension and differs from our earlier results at low surface concentration θ. As previously, the treatment neglects fluctuations in v, which are small for large t. The isotherm in dilute solutions is essentially θ/[v(1 − θ)v] = Kc, where K is a function of v, T, depending on the properties of the bulk polymer and solvent and increasing with molecular weight. Deviations from a Langmuir isotherm are less pronounced than for rigid molecules. The second virial coefficient of the pressurearea curve depends on the ratio v/t and hence on molecular weight and flexibility differently from a completely deposited molecule, flexible or rigid. The limiting change in surface tension depends on two‐opposing terms. When adsorption is sufficiently strong, a decrease proportional to K, and hence increasing with molecular weight, results. This competes with an increase proportional to v/t ∝ t−1/2, arising from the activity of the solvent.
Anomalies de la biréfringence d'écoulement de certaines solutions très diluées d'acide desoxyribonucléique
Authors: Joly M. 
Published: April 2003

AbstractL'influence de la concentration sur la biréfringence d'écoulement des solutions de desoxyribonucléate de sodium est étudiée pour divers échantillons d'ADN. Lors du gonflement dans NaCl molaire du gel d'ADN obtenu par précipitation alcoolique, l'ADN se dissout progressivement. Des prélèvements successifs permettent de séparer des fractions qui diffèrent par leurs propriétés en solution diluée. Certaines fractions, principalement celles d'extraction précoce, présentent, aux très faibles concentrations, des anomalies de biréfringence d'écoulement. C'est ainsi qu'à gradient de vitesse constant l'angle d'extinction χ et le facteur optique ψ augmcntent de façon anormalement rapide avec la dilution dès que la concentration devient inférieure à 2 × 10−5 g/ml. Dans les conditions de l'expérience, les particules d'ADN sont pratiquement indéformables; les variations de χ et de ψ. semblent donc indiquer, aux grandes dilutions, une importante diminution de la taille des particiilrs et une augmentation de leur anisotropie. Au contraire, avec les fractions d'extraction tardive, l'augmentation d'anisotropie est souvent accompagnée d'un accroissement apparent de taille. Par contre, avec les mêmes échantillons d'ADN et dnns le même domaine de concentration, la visrosimétric et l'ultracentrifugation ne mettent pas d'anomalir en évidence, d'où une apparente contradiction. La question est discutée tie savoir si les effets observés en biréfringence d'écoulement peuvent être ou non imputés à des intcractions entre les molécules dissoutes. On recherche aussi quel modèle de particule peut être simultanénent compatible avec les résultats de la biréfringence d'écodement, de la viscosité et de la sédimentation, compte tenu des données récentes sur la structure de l'ADN. Certaincs contradictions semblant difficilement réductibles, on est conduit à suggerer l'éventuelle nécessité de reconsiderér la signification physique des grandeurs mesurées et des divers paramètres utilisés pour caractériser les particules de polyelectrolytes macromoléculaires en solutions très diluées.
The second virial coefficients of polymethyl methacrylate mixed fractions in acetone
Authors: Jen‐Yuan Chien , Liang‐Ho Shih , Shih‐Chen Yu 
Published: April 2003

AbstractThe second virial coefficients of two polymethylmethacrylate fractions of M̄w = 1.18 × 106 and 9.2 × 104 and a series of mixed fractions from them have been measured by osmotic pressure and by light scattering in acetone at 25°C. The results show that A is practically insensitive to an admixed lower molecular weight component but very sensitive to any higher molecular weight component contained in the sample. On the contrary, A2 is sensitive to the lower molecular weight component as well as to the higher molecular weight component present. The values of A2 and A for the mixed fractions, estimated according to the theory of Flory and Krigbaum, show agreement in the general character of the A2‐ and A‐composition curves. A broad maximum occurs on the A2‐composition curve around 20% of the higher molecular weight fraction, while a rather sharp maximum occurs on the A‐composition curve around 6% of the higher molecular weight fraction.