bluuebunny/crossref_metadata_2025_split huggingface dataset:
Network polymers. II. Experimental study of swelling
Authors: Lloyd W. G. , Alfrey T. 
Published: April 2003

AbstractThe swelling behavior of vinyl‐divinyl network polymers has been studied. Various monovinyl monomers (styrene, vinyltoluene, p‐tert‐butylstyrene, a series of n‐alkyl methacrylates), divinyl monomers (divinylbenzene, ethylene dimethacrylate), and contacting solvents (ranging from n‐alkanes to water) have been used. Attention is directed to the effects of introducing an initial good‐solvent diluent at the time of polymerization. Results are interpreted in terms of changes of the free energies of solvent‐Polymer mixing and network deformation. The relaxed volume of the network is shown to be closely related to the volume at which it is formed. The network modulus increases with increasing divinyl content and decreases sharply with increasing initial dilution. With high crosslinking and moderate initial dilution, an interesting special case arises: the volume of formation of the network, its relaxed volume, and its equilibrium swollen volume are all almost identical, and the swollen volume is essentially independent of polymer–solvent interaction. Networks prepared from monomers with large pendant groups exhibit a built‐in dilution effect.
Polythiosemicarbazides. I. Preparation and properties of the polymers and some simple metallic chelates
Authors: Campbell Tod W. , Tomic Ernst A. 
Published: April 2003

AbstractThe condensation of N,N′‐diaminopiperazine with methylenebis(4‐phenyl isothiocyanate) proceeded easily in dimethyl sulfoxide solution to give a high molecular weight, soluble, polythiosemicarbazide (I).
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In agreement with the known behavior of monomeric thiosemicarbazides, the polymer reacted readily with various metal ions to give metallic chelates. These chelates did not have the expected thermal stability, however.
“Directional” membrane permeability in polymer–vapor systems
Authors: Petropoulos J. H. 
Published: April 2003

AbstractA theoretical study is presented of the dependence of the vapor permeability of suitable nonhomogeneous polymer membranes on the sense of flow This is based on a simple model of a binary membrane in which the component phases A, B are either intimately mixed, with the composition of the mixture varying continuously across the membrane, or formed into a laminate AB. The influence of various parameters (which represent either properties of the component phases or the experimental conditions) on the magnitude of these flow reversal effects has been investigated. The results have proved useful as an indication of the capability of such membrane valves and of the conditions for optimum performance, as well as for the understanding of the behavior of experimental systems.
Sliding in polytetrafluoroethylene crystals
Authors: Flack H. D. 
Published: April 2003

AbstractStress–strain relationships are calculated for three models of the deformation of monocrystalline polytetrafluoroethylene, \documentclass{article}\pagestyle{empty}\begin{document}$ \rlap{--} ({\rm CF}_{\rm 2} \rlap{--} )_n $\end{document}. The physical models comprise either sliding one molecule or one plane of molecules parallel to the molecular chain axis past its stationary neighbors. The potential energy is calculated for each stage of deformation by semiempirical methods by use of 6‐exp and dipole–dipole interactions. Application of Eyring's activated complex theory leads to stress–strain relationships. These are compared with results of friction measurements on PTFE.
Evidence for ionic clusters in butadiene–methacrylic acid copolymers neutralized with various salts
Authors: Pineri M. , Meyer C. , Levelut A. M. , Lambert M. 
Published: April 2003

AbstractEffects of neutralization on butadiene–methacrylic acid copolymers have been studied. In Hycar CTB with 2% acid groups, small‐angle x‐ray scattering gives evidence of some cation clustering and leads to a value of the mean radius of 5.6 Å for the clusters and a value of the distance between them of 70 Å. When the concentration of salt is increased there is no appreciable change in the distance between clusters or in their size, but their number increases. The structure of clusters has been studied by electron paramagnetic resonance in copolymers neutralized with copper salts. The appearance of a line as in the monohydrated acetate salt permits one to define the structure of clusters consisting of two Cu2+ and four RCOO− ions with two H2O or RCOOH molecules. When the temperature is increased, the signal corresponding to Cu2+–Cu2+ pairs disappears. In high molecular weight butadiene methacrylic acid copolymers with 9% acid groups, we have found the ion pair clusters gathered into larger clusters. In dynamic mechanical properties, a relaxation peak appears at 340°K. We interpret this as due to breaking and possible re‐forming of dipolar associations.
Assessment of nonrandom crosslinking in polymer networks by small‐angle light scattering
Authors: Wun K. L. , Prins W. 
Published: April 2003

AbstractThe angle‐dependent, isotropic light scattering exhibited by a diluent‐swollen, ideal network is theoretically derived and compared with the light scattering exhibited experimentally by swollen real networks. In good diluents the difference is a measure of the spatial nonrandomness of the degree of crosslinking. A nonrandomness index (NRI) is introduced in terms of the Rayleigh ratios at zero scattering angle. A procedure is given for reliably obtaining the zero‐angle Rayleigh ratio from experimental data at finite angles (2–30°). Measurements are reported for a series of poly(2‐hydroxyethyl methacrylate) (PHEMA) networks, prepared at varying stages of dilution (in ethylene glycol, EG) and varying amounts of crosslinker (ethylene glycol dimethyacrylate, EGDMA). The theoretical Rayleigh ratios are calculated by employing the equilibrium degrees of swelling, refractive indices, and Young's moduli of the gels, measured in EG. The NRI is found to decrease upon decreasing the dilution during network formation and upon increasing the average crosslinking density. The NRI provides a probe of the network structure on a (sub)microscopic level. It is suggested that the NRI is closely correlated with the performance of elastomers under mechanical loading conditions.
Crystalline texture of injection‐molded nylon 6
Authors: Mencik Zdenek , Chompff Alfred J. 
Published: April 2003

AbstractInjection‐molded specimens of nylon 6 were examined by x‐ray diffraction as a function of depth in three characteristic directions. A skin and a core were always found to be present which differed in the degree of crystalline perfection and crystal modification. While the core of pure nylon 6 was found to be not oriented, the core of specimens containing nucleating agents was found to contain a typical texture of the monoclinic modification of nylon 6 in which the distribution probability of the a* and c* axes resembles ellipsoids with three unequal axes. A model explaining this texture as due to degenerated (deformed) spherulites is proposed. With a transcrystalline nylon 6 specimen the direction of the fastest growth in the unit cell (which forms the radius of spherulites) is found to be close to the a axis.
Relation of elastic modulus to crosslink and entanglement concentrations in rubber networks
Authors: Langley Neal R. , Polmanteer Keith E. 
Published: April 2003

AbstractThe theory of rubber elasticity relates the elastic modulus of unfilled amorphous rubber to the concentration of elastically effective strands. A theoretical relation between this concentration and the concentrations of potential entanglements, random tetrafunctional crosslinks, and chain ends was proposed recently. In the present work, the new relation was combined with the theory of rubber elasticity and verified experimentally. Polydimethylsiloxane samples were cured by 60Co irradiation and were extensively extracted to determine gel fraction, which was used to calculate concentrations of crosslinking and scission due to irradiation. Equilibrium modulus values determined from creep tests were in excellent agreement with those calculated using the new relation if the average spacing between potential entanglements is 116 (CH3)2SiO units. Thus, in typical commercial silicone rubbers, the contribution to the modulus from trapped entanglements is greater than the direct contribution from crosslinks. The new relation allows the calculation of crosslink concentrations from modulus measurements on other unfilled rubbers once the potential entanglement spacing of the polymer is determined.
Cellulose triacetate single crystals grown from solution at high temperature without inclusion of solvent
Authors: Chanzy H. D. , Roche E. J. 
Published: April 2003

AbstractSingle crystals of cellulose triacetate II (CTA II) free of crystallization solvent can be grown from dilute solution in mixtures of dibenzyl ether and n‐tetradecane. Good results are obtained by using a polymer fraction with a degree of polymerization of 60 and a mixture of 70% n‐tetradecane and 30% dibenzyl ether at 245°C. The lamellar crystals produced are lozenge‐shaped with the longer diagonal parallel to the a axis of the lattice and with {110} as the growth faces. Twin growth occurs frequently with {110} as a twinning plane and less frequently with {210}.
Isotope effect in gas transport. II. Effect of the glass transition on the size of the free volume element
Authors: Ziegel K. D. , Eirich F. R. 
Published: April 2003

AbstractA diffusive gas‐transport isotope effect is used to estimate the size of the free volume element above and below the glass transition for poly(ethyl methacrylate) and poly(vinyl fluoride). The cavity size, as measured by the hydrogen probe molecule, is apparently larger in the glassy region for both polymers than it is above Tg. It is postulated that the number of free volume elements essentially decreases below Tg, so that the total free volume, which is the sum of all such elements, is smaller below the glass transition, in accord with density measurements on bulk polymers.
Gel‐permeation chromatographic studies of cellulose degradation. III. Methanolysis of cellulose
Authors: Manley R. St. John 
Published: April 2003

AbstractThe molecular weight distribution in various celluloses degraded by methanolysis has been studied by gel‐permeation chromatography. It is shown that the accessible portion of the sample apparently degrades preferentially into molecular fragments with a size distribution centered on species with a degree of approximately 8. This result is interpreted as indicating the presence of weak links in the cellulose chains.
Unperturbed dimensions of isotactic poly(tert‐butylethylene oxide)
Authors: Doddi Namassivaya , Forsman W. C. , Price C. C. 
Published: April 2003

AbstractThe root‐mean‐square end‐to‐end distances of isotactic poly(tert‐butylethylene oxide) fractions were determined in xylene at 80°C from intrinsic viscosity measurements and in o‐dichlorobenzene at 80 and 100°C by light scattering. The characteristic dimension (〈L2〉0/M)1/2 was 1.04 × 10−8 cm in xylene and 0.9 and 0.7 × 10−8 cm in o‐dichlorobenzene at 80 and 100°C, respectively. The value in xylene corresponds to a C∞ of 15.9. This observation and the large negative temperature coefficient of (〈L2〉0/M)1/2 suggest that poly(tert‐butylethylene oxide) exists in a helical block conformation under these experimental conditions. This conclusion is in agreement with earlier reported NMR measurements.
Polymer characterization by refractometry
Authors: Beevers R. B. 
Published: April 2003

AbstractIn the use of refractometry for polymer characterization, it is shown that interpretation of data through use of a molar refractivity as defined by the Lorenz‐Lorentz equation is more accurate than by use of the parachor. The disagreement between experimental and calculated values of the unit molar refractivity may be attributed to the arbitrary definition of the residue unit and the method of summation of group refractivities. In general, refractive index should depend on molecular weight and the conditions of polymerization, but this may depend on the dielectric properties and volume fraction of the domains comprising chain ends, initiator fragments, and free volume. The effect of polymer conformation on the molar refractivity of polyisoprene is found to be slight. For copolymer systems, there is a linear dependence of refractive index on weight fractional composition only where there is little order. The refractive index of a copolymer is not independent of the nature of the distribution of the residues along the chain.
Elastic modulus of poly(isobutylene oxide) crystals parallel to the chain axis
Authors: Kaji Keisuke , Shintaku Tadashi , Nakamae Katsuhiko , Sakurada Ichiro 
Published: April 2003

AbstractThe elastic tensile modulus of the crystalline regions parallel to the chain axis E1 for poly(isobutylene oxide) (PIBO) was determined by an x‐ray diffraction method. The stress‐strain (σ—ε) curve calculated from the meridional reflection of (002) shows an inflection point at about 75 MN/m2 or an extension of 0.25%. The observed moduli below and above this point are 29 and 47 GN/m2, respectively, at room temperature. The initial lower modulus agrees well with the value, 29.7 GN/m2, calculated on the basis of the double zigzag structure of PIBO chain determined by Kaji and Sakurada. The higher modulus may be due to an intrachain steric hindrance between the hydrogen atoms of the methylenic group in the main chain and those of the two side methyl groups.
Thickening of crystals during rapid heating. I. Linear polyethylene and nylon‐6
Authors: Sakurai Kensuke , Miyasaka Keizo , Ishikawa Kinzo 
Published: April 2003

AbstractThe change of long spacing in polyethylene and nylon‐6 during heating at 18°C/min. was measured with an apparatus devised for rapid measurement of the small‐angle x‐ray diffraction. The apparatus made it possible to obtain a diffraction profile in 1.8 sec. Long spacings increased notably at high temperatures near the melting point, as has been observed during low‐rate heating. However, the increase in long spacing during heating was very small in a methoxymethylated nylon‐6 sample. This suggests that the increase in the long spacing at high temperature is due to the thickening of crystals. The long spacing in polyethylene samples in the vicinity of the melting point is apparently independent of thermal history.
The viscoelasticity of polymer solutions: Comparison of theory and experiment
Authors: Wang Francis W. , Zimm Bruno H. 
Published: April 2003

AbstractThe theory of the preceding paper is compared with previously unpublished experimental results on the viscoelastic properties of two polystyrene fractions of molecular weight 1.9 × 106 and 1.2 × 106 in nitropropane, which is very nearly a theta solvent, and in toluene, a good solvent. At the concentrations used, around 1%, the theory predicts extensive departures from non‐draining toward free‐draining behavior; these effects are observed. The theory similarly fits experimental data of Johnson on a sample of polystyrene of molecular weight 860,000 in decalin and dioctyl phthalate in the same concentration range.
The effect of inertia on the intrinsic viscosity of polymers
Authors: Szu Shousun C. , Hermans J. J. 
Published: April 2003

AbstractFor the model of an elastic dumbbell, i.e., two beads connected by a Hookean spring, the Langevin equations for the beads are formulated. It is taken into account that the friction force contains terms resulting from the inertia of the liquid. The contribution of the dumbbell to the viscosity is calculated from the rate of energy dissipation. When the inertia of the liquid is neglected, the viscosity contribution reduces to Kramers' result and is independent of the mass of the beads. When the inertia terms are added, the result is nearly independent of this mass, but shows a dependence on the density of the liquid. In liquids of low viscosity, the extra term resulting from the inertia may be as large as 25% of the total viscosity contribution.
Random chain scission of polystyrene in electron irradiated solution
Authors: Herrick Carlyle S. 
Published: April 2003

AbstractMain‐chain scission was the predominant effect when dilute solutions of three linear polystyrenes in 1‐methylnaphthalene and polybenzyl oligomer received up to 2000 megaroentgen of 1.5‐MeV electrons. Values of energy per scission were independent of dose and of the same magnitude as literature values in dioxane and benzene solutions when compared at the same dose rate. In all cases as irradiation progressed, Mw/Mn approached a value of 2 and Mz/Mw approached a value of 1.5 characteristic of a random distribution. Starting from one initial distribution, random numbers were used to simulate random chain scission. A 500 MR (megaroentgen) distribution calculated in this manner matched the experimental distribution after a 500 MR irradiation.
Gel permeation chromatography: Examination of column efficiency
Authors: Cooper Anthony R. 
Published: April 2003

AbstractGel permeation chromatographic (GPC) separations have been performed with several commercially available column packing materials. The results have been analyzed in the conventional manner to obtain the ratio of weight average to number‐average molecular weight, Mw/Mn, for solutes with narrow molecular weight distribution. Various other parameters proposed to measure the efficiency of GPC columns have been evaluated and compared. It is proposed that the experimentally determined value of Mw/Mn for a series of different molecular weight samples with similar, narrow distribution for a given set of columns is a convenient parameter for comparing column efficiency in GPC. This parameter may be calculated from a single chromatogram unlike resolution, R, resolution index, RI, or specific resolution, RS, which require a pair of chromatograms. Results from the Mw/Mn method are usually in agreement with those from the R, RI, and RS calculations but one exception has been found. The number of theoretical plates calculated from the elution of a small molecule or from the polymer peak bears little relation to efficiencies predicted from the proposed Mw/Mn method or from R, RI, or RS.
Electron delocalization contribution to single crystal thermal expansion of a polydiacetylene
Authors: Baughman R. H. , Exarhos G. J. , Risen W. M. 
Published: April 2003

AbstractThe thermal expansion contribution due to temperature‐dependent π‐electron delocalization is evaluated from spectral measurements on a single crystal polydiacetylene (poly‐2,4‐hexadiyne‐1,6‐diol bisphenylurethane). The observed temperature independence of backbone associated vibrations (less than ±1 cm−1 change in νCC and νCC between 25 and 90°C) implies that thermal conformational fluctuations and equilibrium defect formation (which produce a negative thermal expansion coefficient) do not measurably affect π‐electron delocalization. The separation of equilibrium defects is either much longer than that of nonequilibrium defects or much longer than required to appreciably limit π‐electron delocalization in an effectively defect‐free polymer. Arguments presented indicate that, in the experimental temperature interval, the observed thermal expansion coefficient in the chain direction is over an order of magnitude larger than the delocalization‐associated contribution.
Asymptotic relations between shear stresses and normal stresses in general incompressible fluids
Authors: Coleman Bernard D. , Markovitz Hershel 
Published: April 2003

AbstractIt is shown that in the general theory of incompressible simple fluids with fading memory there are, for several types of nonsteady shearing motions, simple universal asymptotic relations between the shear stress S12 and the first normal stress difference N1 = S22 – S11. The kinematical situations considered include initiation of steady shearing, rest after steady shearing, and sinusoidal oscillation. In, for example, relaxation following cessation of a steady shearing flow with rate of shear κ, there holds, to within an error O(κ4):

This and the other derived universal relations between N1 and S12 are either consequences of, or are closely related to a general asymptotic formula [B. D. Coleman and W. Noll, Revs. Mod. Phys., 33, 239 (1961), eq. (6.15)] expressing N1 as an integral of the product of the shear relaxation modulus and the square of the history of the relative shear strain.
Effects of swelling and annealing on the viscoelastic behavior of the melt‐crystallized and solution‐crystallized polypropylene
Authors: Inamura Isamu , Ochiai Hiroshi , Yamamura Hitoshi 
Published: April 2003

AbstractThe effects of swelling and annealing treatments on viscoelastic behavior were studied in melt‐crystallized and solution‐crystallized samples of isotactic polypropylene (iso‐PP) over the temperature range −150 to 150°C. The log E″ versus T curves exhibited α, β, and γ peaks in order of decreasing temperature. The β peak of the melt‐crystallized sample shifted to higher temperatures after annealing, but was not affected by swelling. The α peak of melt‐crystallized polymer was affected by swelling treatments. It increased in height and shifted to lower temperatures almost linearly with the volume fraction of absorbed solvent. The magnitude of the shift was independent of the solvent species—toluene, p‐xylene, tetralin, carbon tetrachloride—however, it depended significantly on the temperature at which the sample had been heat treated. For solution‐crystallized polymer, no peaks in log E″ were observed in the temperature range of the β peak of melt‐crystallized material, but the α peak appeared larger and broader, and at higher temperature than the corresponding peak in the melt‐crystallized polymer. After swelling or annealing, the low‐temperature component of the α peak of the solution‐crystallized sample decreased in height and at the same time a new loss peak appeared at −55 and 0°C, respectively, is swollen and annealed samples. In particular, in the case of annealing treatments, the high‐temperature component of the α peak shifted to still higher temperatures. From these results on the solution‐crystallized sample it can be deduced that the segmental motions in the amorphous phase are very strongly constrained by surrounding crystalline phases as compared with those in the amorphous phase of the melt‐crystallized sample, and the constraints imposed on the segmental motions are released to a great extent by both treatments. Finally, swelling effects on the γ peak were examined. The γ peak of the melt‐crystallized sample decreased in height after swelling. On the other hand, the γ peak of the solution‐crystallized sample separated into two peaks, which might be attributed to the mechanical relaxations in the crystalline and amorphous phases.
Flow properties of poly(methyl methacrylate) solutions
Authors: Graessley William W. , Pennline Henry W. 
Published: April 2003

AbstractViscosity and normal stress behavior were measured for poly(methyl methacrylate) samples of various average molecular weights in diethyl phthalate solution at 30 and 60°C. All samples conformed approximately to the most probable distriution (M̄w/M̄n = 2). Concentrations ranged from 0.113 to 0.38 g/ml, and M̄w from 53,800 to 1,620,000. Despite considerable evidence in the literature of unusual linear viscoelastic behavior for this polymer, its nonlinear properties appear to be rather conventional. The viscosity–shear rate master curve was similar to that found earlier for concentrated solutions of polystyrene and poly(vinyl acetate) of comparable molecular‐weight distribution. The viscosity time constant τo parallels τR, the characteristic time of the Rouse model, although the residual dependence of τo/τR on concentration and molecular weight appears to be slightly different from that for polystyrene and poly(vinyl acetate). Similar conclusions apply to the recoverable compliance Je,o estimated from the normal stress behavior of each solution, and its relationship to the Rouse model compliance JR.