bluuebunny/crossref_metadata_2025 huggingface dataset:
Stress relaxation of polybutadiene at large deformation. Measurements of stress and birefringence in shear and elongation
Authors: Kimura Shinichi , Osaki Kunihiro , Kurata Michio
Published: April 2003

The rheological behavior of an uncrosslinked polybutadiene on sudden application of finite strain was examined. The shear stress σ, two components of birefringence, and the extinction angle were measured in shear (magnitude of shear γ ≤ 3.5) and tensile stress and the birefringence were measured in uniaxial elongation (elongation ratio λ ≤ 3.8). Measurements were performed at 30°C with a tensile tester equipped with appropriate sample holders. The stress‐optical coefficient was 3.01 × 10−9Pa−1. The first and second normal‐stress differences v1 and v2 were separately evaluated with the use of stress‐optical law. The Lodge—Meissner relation v1 = γσ held good. The ratio v2/v1 was independent of time and varied from about −0.3 to −0.2 with increasing γ in the range of measurements. Each of the stress components was factored into a function of strain and one of time, and the latter was common to all the stress components. Simple formulas were proposed to represent stress components in step deformations.
Microwave properties of low‐density polyacetylene
Authors: Feldblum A. , Park Y. W. , Heeger A. J. , MacDiarmid A. G. , Wnek G. , Karasz F. , Chien J. C. W.
Published: April 2003

The results of an initial study of the microwave properties of low‐density foamlike (CH)x are reported for intermediate dopant levels. The electrical conductivity and dielectric constant are obtained at microwave frequencies, and the results are analyzed in terms of effective medium theory. The possibility of utilizing the doped foamlike (CH)x as an efficient microwave absorber is discussed.
Conformation of linear polyethylene in 1‐chloronaphthalene: Light scattering characterization of polymers. IV
Authors: Suzuki Hidematsu , Muraoka Yoichiro , Inagaki Hiroshi
Published: April 2003

Light scattering measurements were carried out on a linear polyethylene sample NBS 1475 in 1‐chloronaphthalene at 135 and 115°C to determine the weight‐average molecular weight, the second virial coefficient A2, and the z‐average mean‐square radius of gyration. By use of these results, the system is analyzed in terms of the interpenetration function Ψ for A2. Observed values of A2 are rather large but the excluded volume is nevertheless relatively small. Such behavior seem to be similar to that of semiflexible polymers. The characteristic ratio Cn,LS as determined by light scattering is found to be almost twice the literature value of 6.7, which was obtained from viscosity measurements. This discrepancy is explained by comparing the theoretical value of the Flory viscosity parameter Φ at the nondraining limit with values calculated from the light scattering results.
Irreversible effects of moisture on the epoxy matrix in glass‐reinforced composites
Authors: Antoon M. K. , Koenig J. L.
Published: April 2003

The irreversible effects of moisture exposure on anhydride‐crosslinked epoxy resin films are investigated by means of Fourier‐transform infrared spectra. Hydrolytic attack of water at the ester linkages is accelerated in alkaline media and is a mechanically activated process. Matrix hydrolysis is also enhanced in the presence of inorganic fillers.
Dielectric relaxation time of polymers
Authors: Mashimo Satoru
Published: April 2003

The temperature dependence of the dielectric relaxation time of amorphous polymers can be described quite satisfactorily by an expression derived from the theory of the relaxation time for local conformational transitions in a polymer chain. This theory was recently developed using the Kramers theory of the rate constant together with the free‐volume theory.
Conformational properties of polar polymers. I. Poly(vinyl chloride)
Authors: Boyd Richard H. , Kesner Laya
Published: April 2003

A recently developed method for including polar bonds in conformational energy calculations is applied to poly(vinyl chloride). Inductive effects on dipole moments and the effects of intervening atoms on electrostatic interaction energies are represented by polarizability centers in conjunction with bond centered dipoles. Solvation energies are estimated by means of a continuum dipole–quadrupole electrostatic model. Calculated energies of a number of conformations of meso and racemic 2,4‐dichloropentane and the iso, syndio, and hetero forms of 2,4,6‐trichloroheptane give satisfactory representations of isomer and conformer populations. Electrostatic effects are found to be quite important. However they appear to be effectively of sufficiently short range that the calculated conformer energies are found to be fit well by a linear combination of interaction parameters (consisting of gauche, skew chlorine, four‐bond CH2…CH2, CH2…Cl, and Cl…Cl interactions) conventional to vinyl polymers and a special four‐bond interaction that arises when the bond sequence ClCHCH2CHCl is (nearly) coplanar. These interaction parameters when assembled into statistical weight matrices lead to calculated values of both the characteristic ratio and the dipole moment ratio in satisfactory agreement with experiment. Least energy paths for transitions between the most stable conformations are also calculated.
Mixed‐crystal infrared studies of chain‐folding in polyethylene single crystals: Low‐temperature and molecular weight studies
Authors: Cheam T. C. , Krimm S.
Published: April 2003

Infrared spectra of 40 PEH/1 PED mixed crystals have been obtained at low temperature as a function of the molecular weight of the PED. The band contour in the CD2 bending region was resolved into crystalline and noncrystalline components by a least‐squares fitting of Gaussian‐plus‐Lorentzian bands. The splittings of the crystalline component were analyzed in terms of the theory for finite chains of coupled oscillators, with the help of normal coordinate calculations for certain structures. Together with some results on n‐paraffin mixed crystals, our studies show that (i) the spectroscopic observations are associated with interactions of crystalline stems of a single molecule; (ii) the observed crystalline splittings are incompatible with an essentially “switchboard” model of chain folding; (iii) adjacent reentry folding predominates, with folding along single (110) and (200) planes occurring; and (iv) for high molecular weights of PED double (110) fold planes prevail. These results are seen to be consistent with the morphologies known to be associated with the conditions of crystallization.
Crystalline transitions in powders of nylon 66 crystallized from solution
Authors: Starkweather Howard W. , Jones Glover A.
Published: April 2003

Powders of nylon 66 were crystallized from solution in methanol and in other solvents. These powders exhibit a latent heat of about 4.5 cal/g at the Brill transition near 200°C where the unit cell changes from a triclinic to a pseudohexagonal form. The dimensions of the hydrogen‐bonded sheets are almost unchanged up to 240°C, but the separation between the sheets increases with increasing temperature. Above 245°C, the interchain separation increases rapidly, and permits the powder to be extruded in an essentially plastic manner to form coherent extrudates. As the temperature of treatment is increased above 245°C, the latent heat of the Brill transition is reduced toward zero, the heat of fusion is reduced from about 30 cal/g to about 20 cal/g, and an endotherm at 261°C is replaced by one at 267°C.
Flow birefringence of concentrated polymer solutions in two‐dimensional flows
Authors: Fuller G. G. , Leal L. G.
Published: April 2003

The results of flow birefringence measurements are reported for polymer solutions of moderate concentration subjected to a wide range of two‐dimensional flows. These flows were generated in a four‐roll mill which enables one to systematically vary the ratio of the vorticity to the rate of strain in the flow while holding the velocity gradient constant. It is shown that steady‐state birefringence data collected over a wide range of flow types can be correlated against the eigenvalue of the velocity gradient tensor, in agreement with criterion for strong and weak flows from model calculations. Transient birefringence measurements in which purely extensional flows were started from rest are also reported. It was observed that the birefringence went through a pronounced overshoot in time for two different polymer/solvent systems. Flow induced increases in the solution turbidity were also observed and the increased turbidity remained constant over a period of many hours after extensional flows were arrested. The birefringence, on the other hand, decayed to zero almost immediately after the flows were stopped. These changes in the turbidity suggest that crystallization of the polymer was occurring. The qualitative results of experiments are compared to recent network model calculations using the theory of Yamamoto for concentrated polymer systems. It is found that this model can predict qualitatively many of the experimental observations if the function describing the breakage of polymer chain entanglements is allowed to depend on the conformation of the polymer segments bridging the entanglements. In particular, this dependency of the entanglement breakage on the conformation of the network segments leads to a predicted overshoot of birefringence when purely extensional flows are started from rest. It is also demonstrated through this model that birefringence data taken over a wide range of flow types can be used to estimate the degree to which the network deforms affinely with the flow field.
Annealing of polypropylene films crystallized from a highly extended melt
Authors: Schultz J. M. , Lin J. S. , Hendricks R. W. , Petermann J. , Gohil R. M.
Published: April 2003

Thin films of isotactic polypropylene were drawn from the melt at a very high rate of extension. Transmission electron micrographs of this material reveal fibrous crystals lying along the draw direction. The chain axis and fiber axis are identical. Dark field micrographs show a dark/light modulation along the fiber axis. Annealing at temperatures below 110°C produces no qualitative change in the electron microscope observations. Annealing between 110 and 150°C produces gradual dominance of lamellar crystals, oriented normal to the draw direction. Small‐angle x‐ray scattering (SAXS) data exhibit a strong streaking normal to the fiber axis, in broad agreement with the observed fibrosity. A Bragg peak along the draw directions shows that the modulation observed microscopically is a density modulation. The absence of second‐order maxima and the dependence of the SAXS peak on treatment temperature strongly suggest that the axial modulation is a spinodal decomposition of the material into crystalline and amorphous regions.
NMR spin–spin relaxation in solid and molten polyethylene structures
Authors: Kamel I. , Charlesby A.
Published: April 2003

The NMR spin‐spin relaxation (T2) spectra of high‐density polyethylene (PE) has been investigated over a wide range of temperatures, both in the solid and molten states. Previous work in these laboratories has shown that the T2 relaxation spectrum of molten polyethylene differs from that of other polymers studied in that (a) it cannot be decomposed into two relaxation spectra (T2S and T2L) and (b) there is some evidence of a memory effect. This paper attempts to elucidate these observations, and compare them with the spin‐spin relaxation of polyethylene at lower temperatures. In the solid state, the T2 decay comprises both a Gaussian distribution for the crystalline region, and an exponential decay for the amorphous component. The effects of crystallization conditions and of temperature were determined. In the molten state the T2 decay is more complex, but can be resolved into three exponentials. The longest (T2L) component arises as expected from the most mobile, low molecular weight fraction. The T2S component is due to an entangled but mobile network, as in other polymers. In addition, a short relaxation component T2X is observed, which is influenced by previous crystallinity and the processing history of the material, and is ascribed to some vestigial degree of structure in the molten phase.
High‐resolution polymer separations in a four‐pass hairpin thermal field‐flow fractionation column
Authors: Giddings J. Calvin , Martin Michel , Myers Marcus N.
Published: April 2003

A thin‐channel four‐pass hairpin thermal field‐flow fractionation (FFF) column is described, and the advantages of its unique dimensional characteristics are explained. The problem of isolating the performance of this and other separations columns from the ubiquitous polydispersity effects are discussed and treated theoretically. The discussion is extended to size exclusion chromatography, and it is shown that the 2 to 6 times lower selectivity of the latter compared to FFF leads to the requirement for 4 to 36 times more theoretical plates to encounter polydispersity effects and thereby obtain information on polymer molecular weight distribution. A fractogram of six narrow polystyrene samples obtained from the hairpin system is shown to imitate closely the fractograms obtained from two totally different thermal FFF columns, showing that polydispersity dominates and that molecular weight information is revealed for these samples with only a few hundred theoretical plates. Various experimental and theoretical attempts are made to isolate the polydispersity and column contributions to plate height, including cut‐and‐recycle experiments, the observation of plate height versus velocity curves, and the direct calculation of the contributing effects. The various methods are subject to moderate errors, but are in rough agreement. The plate height plots show that the polydispersity effect contributed 53% and 68% to the measured plate height for 51,000 and 160,000 molecular weight samples, respectively. The latter polymer is shown to emerge with ca. 1300 true column plates. It is suggested that much higher column efficiency will be observed in the future if higher retention levels can be experimentally realized.
Polymerization of p‐acryloyloxybenzoic acid
Authors: Menczel Jozsef , Walsh J. P. , Wunderlich Bernhard
Published: April 2003

Polymerization of p‐acryloyloxybenzoic acid by heating on a hot stage was previously reported to lead to a lyotropic mesophase. Using optical microscopy, thermal analysis, and infrared analysis, it was shown that this mesophase involves oligomers of poly(p‐oxybenzoate) formed from the monomer by ester interchange through internal acidolysis.
Generalized Rouse–Zimm theory for polymer solutions
Authors: Hess W. , Jilge W. , Klein R.
Published: April 2003

Generalized Rouse–Zimm equations are derived using a local equilibrium ansatz for the segment distribution function. The relaxation frequencies depend on excluded‐volume effects and other interactions such as entanglement in semidilute solutions through exact static correlation functions. For the case of ring polymers general expressions are given for diffusion coefficients and mean‐square displacements. By use of the “blob” model, explicit results are presented for a dilute good‐solvent system.
Free‐volume estimates in heterogeneous polymer systems. I. Diffusion in crystalline ethylene–propylene copolymers
Authors: Kreituss A. , Frisch H. L.
Published: April 2003

Apparent thermodynamic diffusion coefficients were obtained from carbon tetrachloride, benzene, and n‐hexane sorption‐desorption kinetics in crystalline and amorphous ethylene‐propylene copolymers (with propylene content from 1 to 70 wt. %, and crystallinity from 0% to 77%), in high‐density and low‐density polyethylene, and in polypropylene. The dependence of the diffusion coefficient vs. concentration curves on crystallinity and propylene content in the copolymers is reported. The diffusion coefficient at zero penetrant concentration increases with decrease in crystallinity. The apparent diffusion activation energies in the temperature interval investigated (25 to 75°C) are independent of temperature and are constant for crystalline copolymers. A modified Fujita‐like free‐volume theory for diffusion in crystalline polymer systems is introduced, and the theoretical estimates of diffusion coefficients show satisfactory agreement with experiment.
Electrostatic fiber spinning from polymer melts. II. Examination of the flow field in an electrically driven jet
Authors: Larrondo L. , St. John Manley R.
Published: April 2003

The flow field in an electrically driven jet has been examined and quantitatively analyzed. Using a model fluid, the nature of the streamlines and magnitude of the stream velocities were investigated with the aid of tracer particle photography. It was found that the velocity field is not purely extensional, but contains rotational components as well. Furthermore, the only portion of the jet completely free of any rotational component is the region about the symmetry axis. The extensional strain rate along the symmetry axis increases rapidly with the applied electric field intensity and can attain values in excess of 50 sec−1. This suggests that it might be possible to draw continuous oriented fibers from polymer melts by this technique if the jet can be operated at sufficiently high electric field intensity.
Mesogenic polymers. III. Thermal properties and synthesis of three homologous series of thermotropic liquid crystalline “backbone” polyesters
Authors: Griffin Anselm C. , Havens Stephen J.
Published: April 2003

Details of the thermal behavior, including transition temperatures, transition heats and transition entropies, are reported for three series of nematic liquid‐crystalline “backbone” polyesters having the general structure
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All polysters described above were examined by differential scanning calorimetry and were found to have reproducible thermal behavior once the polymer had been annealed by heating to the isotropic phase and then subsequently cooled. Enantiotropic nematic phases were found for all 30 polysters studied. Many polymers showed multiple endotherms on melting to the nematic phase. Plots of solid–nematic and nematic–isotropic transition temperatures versus number of carbon atoms in the diacid segment (x) for each (y) reveal an even–odd alternation reminiscent of trends in homologous series of small‐molecule liquid crystals. Enthalpies for the solid → nematic and nematic → isotropic transitions do not show such a precise alternation.
Polystyrene–polyisoprene block copolymers in dilute solutions: Characterization of the conformation by small‐angle neutron scattering
Authors: Ionescu L. , Picot C. , Duplessix R. , Duval M. , Benoît H. , Lingelser J. P. , Gallot Y.
Published: April 2003

The variable‐contrast method in small‐angle neutron scattering has been applied to a study of the conformation of polystyrene–polyisoprene block copolymers in dilute solution. The experimental results reveal no intramolecular segregation effect in dilute solutions in toluene and cyclohexane.
Nonlinear stress relaxation of a styrene–butadiene random copolymer
Authors: Merriman H. G. , Caruthers J. M.
Published: April 2003

The isothermal uniaxial stress relaxation response in the vicinity of the glass‐to‐rubber transition has been measured for a lightly crosslinked poly(styrene–butadiene) random copolymer, 85% styrene by weight. The volume change during stress relaxation was determined by measuring the time‐dependent lateral contraction of the specimen with a Hall‐effect proximity detector. The specimen exhibited an instantaneous dilation upon application of the strain and a subsequent time‐dependent volume decrease. The stress relaxation behavior and the associated volume relaxation were determined for a variety of strains and temperatures in both the linear and nonlinear viscoelastic regime. As the applied strain was increased the isothermal tensile modulus decreased and the shape of the log(modulus) vs. log(time) curve was altered. At equal levels of strain the tensile modulus exhibited increasing deviations from the linear viscoelastic response as the temperature was decreased. The maximum difference between the nonlinear tensile modulus and the linear viscoelastic response was observed at short times. Subsequently, the nonlinear tensile modulus began to approach the linear viscoelastic modulus with increasing time. Both the instantaneous dilation and the magnitude of the time‐dependent part of the volume change increased as the level of applied strain was increased and/or as the temperature was decreased. The observed nonlinearity in the tensile stress relaxation response has been quantitively related to the experimentally measured volume relaxation with a free‐volume model.
An apparatus for kinetic‐mechanistic studies of polymer burning and regression rates: Poly(methyl methacrylate)
Authors: Kachi H. , Jellinek H. H. G. , Hall M.
Published: April 2003

An apparatus for determination of regression (weight‐loss) rates before, at, and after ignition as a function of oxidant gas flow rates has been constructed and successfully operated with poly(methyl methacrylate). In addition, flame temperatures, gas evolution kinetics and composition can be ascertained. The apparatus allows a proper evaluation of diffusion processes and chemically controlled processes. The regression rate for PMMA is directly proportional to the air flow rate. At low air flow rates the process is diffusion controlled and the energy of activation is identical with the heat of vaporization of the monomer. There is a liquid monomer layer and on top of it a stagnant vapor layer having the equilibrium vapor pressure of the monomer. At higher flow rates the energy of activation increases steeply. The layers become thin and defective and eventually thermal depolymerization becomes rate determining. This depolymerization has an energy of activation between 30 to 40 kcal mol−1. Experiments have also been carried out in closed quartz tubes. Explosion limits, ignition lags and energies of activation have been determined. The latter were evaluated by the method of Semenoff.
Phase separation of polymer blends in thin films
Authors: Reich S. , Cohen Y.
Published: April 2003

Films of polystyrene‐poly(vinylmethyl ether) blends of various compositions are formed by a dip‐coating procedure, the thickness of the film being controlled by the concentration of the solution. The substrates used are glass and gold. The phase separation process is followed by a laser light scattering experiment in which the total forward scattering intensity is monitored as a function of temperature. Morphological examination shows that phase separation occurs by a spinodal decomposition mechanism. A thickness effect on the phase separation temperature is noticeable when film thickness is smaller than 1 μm. This effect is substrate dependent. In all films formed on gold the spinodal temperature increases as film thickness decreases. Films formed on glass exhibit a destabilizing effect on decreasing film thickness. This effect is slight in films of composition poorer in polystyrene than the critical composition, and is enhanced in films richer in polystyrene. The stabilizing effect of decreasing the thickness of films formed on the gold substrate is considered to reflect mainly a purely geometrical effect. The decreasing dimensionality is shown by simple theoretical considerations to increase the phase‐separation temperature. However, the phase separation behavior of thin films on glass appears to be the result of two kinds of substrate‐polymer interactions in addition to the geometrical effect: (a) electrostatic interaction of the charged glass surface (a destabilizing effect at all film compositions) and (b) selective adsorption of polystyrene on glass.
Effect of orientation and mobility of polymer molecules at surfaces on contact angle and its hysteresis
Authors: Yasuda H. , Sharma Ashok K. , Yasuda Takeshi
Published: April 2003

The contact angle of a water droplet on the surface of a solid polymer or hydrogel (water‐swollen three‐dimensional network) depends on whether a hydrophilic moiety of the polymer molecule is oriented towards the air interface or towards the bulk of the solid, but not on the hydrophilicity of the molecule. Therefore, the short‐range rotational mobility of a polymer molecule has a major influence on the apparent hydrophilicity of a polymer surface as measured by the contact angle of water. By the came principle, the abnormally large hysteresis effect observed in advancing and receding contact angles of water on some polymer surfaces can be attributed to the reorientation of hydrophilic moieties of polymer molecules at the surface. These factors are demonstrated by selected polymer surfaces with different degrees of mobility at the polymer‐air interface.
Determination of the persistence length of an aromatic polyamide‐hydrazide by small‐angle x‐ray diffraction
Authors: Krigbaum W. R. , Sasaki S.
Published: April 2003

Small‐angle x‐ray diffraction measurements were performed upon dimethyl acetamide (DMAc) solutions of four samples of X‐500, an aromatic polyamide‐hydrazide. The solubility improved as the polymer molecular weight increased, the most soluble sample being in the form of a highly oriented, crystalline fiber. Molecular weights determined from the scattering curves indicate that aggregation was present in all solutions. Its extent varied with the solubility of the sample, increased with polymer concentration and, for the lowest concentrations studied, could be reduced by the addition of acetic acid. Radius of gyration values were smaller than those obtained by light scattering, probably because of insufficient resolution of the camera. The mass per unit length along the chain was found to be 18–20 Å, while the radius of gyration of the cross section was 3.5–4.8 Å. Three of the samples gave nearly the same angular intersection for the coil‐and rodlike regions of the scattering curve. Two of these were whole polymers and the other a narrow fraction. The fact that essentially the same intercept was found in all three cases indicates the persistence length as measured for linear chain polymers by small‐angle x‐ray diffraction is independent of the heterogeneity of the sample. The intercepts, after a small correction for excluded volume effects, correspond to persistence lengths in the range 71–88 Å for DMAc solutions, which approximate those determined for dimethyl sulfoxide (DMSO) solutions by light scattering the intrinsic viscosity without correction for excluded volume, but are substantially larger than the DMSO values, corrected for excluded volume of 30–49 Å. We can offer no explanation for this difference.
Piezoelectricity of uniaxially stretched poly(vinylidene fluoride) corona poled at elevated temperature
Authors: Bamji S. S. , Perlman M. M.
Published: April 2003

X‐ray diffraction, thermally stimulated depolarization, and piezoelectric current measurements have been carried out on uniaxially stretched poly(vinylidene fluoride) film, corona poled both negatively and positively at room temperature and at 90°C. Corona poling at elevated temperature considerably enhances the piezoelectric constant and is a more efficient way of charging the film than conventional thermal poling. Advantages over the latter are discussed.
The effect of annealing and mechanical constraint on the morphology structure and stiffness of ultrahigh‐modulus polyethylene
Authors: Capaccio G. , Clements J. , Hine P. J. , Ward I. M.
Published: April 2003

A study has been made of the effects of annealing at high temperature (130°C) on the dynamic mechanical properties and melting behavior of a series of ultrahigh‐modulus polyethylenes. Although annealing always resulted in a substantial decrease in modulus, there were marked differences between samples of moderate draw ratio, depending on whether they are annealed at constant length or unconstrained. On the other hand, the differences were small for high‐draw‐ratio samples, indicating their greater thermal stability. In all cases the −50°C plateau modulus correlated well with the degree of crystal continuity estimated from wide‐angle x‐ray diffraction measurements of crystal length combined with small‐angle measurements of the long period. The corresponding changes in melting behavior were entirely consistent with the changes observed in the mechanical stiffness. Both types of measurement together with the x‐ray results have been used to gain an understanding of the morphological changes occurring on annealing.
Mesomorphic solutions of cellulose triacetate in halogenated organic acids and mixtures of trifluoroacetic acid and dichloromethane
Authors: Patel D. L. , Gilbert R. D.
Published: April 2003

Cellulose triacetate (CTA) forms liquid‐crystalline solutions in trifluoroacetic acid, dichloroacetic acid, and mixtures of trifluoroacetic acid and dichloromethane. Brilliant iridescent coloration, high optical rotations, and birefringent regions with swirl‐like fingerprint patterns suggested the formation of cholesteric liquid crystals. Trifluoroacetic acid–dichloromethane is a particularly excellent solvent mixture to form liquid‐crystal solutions of cellulose acetate. Crude bulk viscosity measurements confirm the formation of an anisotropic phase, and the temperature dependence of the critical concentration for formation of the anisotropic phase, obtained by bulk viscosity measurements at various temperatures, provides confirming evidence. Viscosity decreases with aging, suggesting that CTA is slowly degraded in the solvents studied. This is also confirmed by optical rotatory measurements and by polarizing microscope observations. The miscibility gap is observed as a function of molecular weight, and the differences between the experimental data and Flory's prediction are discussed.
Polarization studies by the TSC technique on a blend of cellulose acetate and polyvinyl acetate
Authors: Pillai P. K. C. , Gupta Brijesh K. , Goel Malti
Published: April 2003

The thermally stimulated current (TSC) technique has been used to study solvent‐cast blends of a cellulose derivative with a vinyl polymer. TSC peaks are observed at 56, 80, and 120°C. Their origin is investigated because the TSC spectra of the blends differ from the spectra of the individual components. Data on blends with components in the weight ratios 25:75, 50:50, and 75:25 indicate that the 50:50 blend shows the greatest polarization. The enhancement of depolarization currents observed on blending is explained on the basis of a Maxwell–Wagner–Sillars polarization due to increased heterogeneity in the structure. Effects of forming conditions (time, temperature, field) on polarization have been investigated. Activation energies and relaxation times are calculated; there is good agreement between the values obtained from the initial‐rise and the full‐curve methods.
Influence of polymerization initiation rate on permeability of aqueous polyacrylamide gels
Authors: Weiss N. , van Vliet T. , Silberberg A.
Published: April 2003

It was shown by Weiss and Silberberg in 1975 that polyacrylamide gels prepared by copolymerization of acrylamide and N,N′‐methylene bis‐acrylamide in water are heterogeneous. A two‐phase model developed in 1979 satisfactorily accounted for the permeability of the gels. These gels had been prepared under standard conditions of initiator and activator concentrations and involved precooling of the reaction mixture to 0°C with completion of the reaction at room temperature, a thermal history not very suitable for kinetic analysis. A procedure was, therefore, devised where gels are prepared at room temperature throughout. Much better correlations are then obtained, and it can be shown that the initiation is controlled by the initiator (ammonium persulfate) concentration times the activator (N,N,N′,N′‐tetramethylethylene diamine) concentration raised to the 1.5 power. These data, discussed in terms of the two‐phase model, show that the initiator concentration directly determines the number of crosslinks in the more dilute, permeability‐determining, gel phase. The faster the initiation, the less permeable a gel results. An increase of permeability with overall degree of crosslinking at constant monomer concentration is a feature only of gels prepared at sufficiently low polymerization initiation rates.
A model for permeation of mixed gases and vapors in glassy polymers
Authors: Koros W. J. , Chern R. T. , Stannett V. , Hopfenberg H. B.
Published: April 2003

A model is discussed which explains reported complex effects of feed composition and pressure on component permeabilities in high‐pressure gas separators based on glassy polymer membranes. A special form of Fick's law which accounts for the fact that penetrants in glassy polymers sorb into and diffuse through two different molecular environments provides the basis for the analysis of gas mixture permeation. Potential deviations from the theory are discussed in terms of separable solubility‐and mobility‐related effects.
A light‐scattering study of deformation of liquid‐crystalline spherulites of poly(γ‐benzyl‐L‐glutamate) in an electric field
Authors: Matsuo Masaru , Ozaki Fumihiko , Konno Yasuyuki , Ogita Tetsuya
Published: April 2003

The deformation of liquid‐crystalline spherulites of poly(γ‐benzyl‐L‐glutamate) (PBLG) in an electric field was investigated by light scattering, polarized‐light microscopy, and birefringence measurements. Under the polarizing microscope, the deformation was found to be dependent upon the field strength. The spherulites deformed perpendicular to the field. Above 75 V/cm in N,N‐dimethylformamide or 120 V/cm in 1,1,2‐trichloroethane, the deformed spherulites were transformed to rodlike textures. With increasing voltage, the rods gradually oriented parallel to the electric field. On the basis of the experimental results, models for affine deformation are proposed. With these models, light‐scattering patterns are calculated. The calculated and experimental patterns agree semiquantitatively.
Small‐angle x‐ray scattering studies of isothermally crystallized bulk polyethylene
Authors: Varnell W. D. , Harrison I. R. , Wang J. I.
Published: April 2003

A set of isothermally melt‐crystallized polyethylene samples was examined using small‐angle x‐ray scattering (SAXS). Time and temperature of crystallization were the variable parameters used to create the set of samples. Following background subtraction, desmearing, and application of the Lorentz factor to the raw SAXS data it is possible to see many orders of reflection. This suggests that much higher degrees of order are present in isothermally melt‐crystallized samples than had previously been thought possible. A combination of SAXS and DSC data indicates that there is no evidence for isothermal thickening in these samples. This study, coupled with data obtained from PE single crystals, produced information concerning the extrapolation of single‐crystal data to fit bulk systems. In addition, the equilibrium melting point T determined is somewhat lower than previously claimed. This study also suggests that the surface energy of the mature crystals is always lower than that of the nucleated state and/or the nucleation factor Kσen increases with decreasing supercooling.
Viscoelastic properties of sulfonated styrene ionomers
Authors: Rigdahl M. , Eisenberg A.
Published: April 2003

The solid‐state viscoelastic properties of polystyrene containing randomly distributed groups of styrene‐p‐sodium sulfonate are studied and compared with the corresponding properties of copolymers of styrene and sodium methacrylate (S‐NaMA). The viscoelastic behavior in the primary transition region of these two ionomers is very similar. As for the S‐NaMA copolymers, it is proposed that sulfonated polystyrene is composed of ion‐rich regions (clusters) immersed in a matrix of low ion concentration. Two peaks are observed in the plot of mechanical loss tangent versus temperature for the sulfonated material. The lower peak is assigned to the glass transition of the ion‐poor matrix and the upper to the glass transition of the clustered regions. As for some other ionomers, the presence of ions is found to slow down the stress relaxation rate, giving a broad distribution of relaxation times. Above a certain ion concentration, the sulfonated polystyrenes are thermorheologically complex owing to the onset of a secondary relaxation mechanism associated with the ion‐rich regions.
The morphology in nafion perfluorinated membrane products, as determined by wide‐ and small‐angle x‐ray studies
Authors: Gierke T. D. , Munn G. E. , Wilson F. C.
Published: April 2003

The morphology of the ionomer resin from which Nafion perfluorinated membrane products are made was studied with wide‐angle and small‐angle x‐ray diffraction. A reflection observed in the small‐angle x‐ray scan from hydrolyzed polymer is attributed to ionic clustering. The effects of equiv wt, cation form, temperature, water content, and tensile drawing on this reflection were studied and are discussed.
Finite‐element analysis of craze deformation
Authors: Bevan I.
Published: April 2003

The finite‐element method is applied to a craze model in order to estimate surface displacements and stresses of an isolated craze in a thin rectangular plate. The limitation of assuming linear‐elastic behavior of the craze fibrils is demonstrated by comparing computed profiles with published experimental ones. Accurate finite‐element estimates of craze surface stresses are obtained from the experimental displacement profile. The analysis is extended to the three‐dimensional case but the difference between the craze displacements at the surface of the plate and those at midthickness is too small to justify the considerable increase in computer time in comparison with that required for two‐dimensional analysis.
A quantitative electron‐microscopic study of a linear polyethylene fraction crystallized at different temperatures
Authors: Voigt‐Martin I. G. , Mandelkern L.
Published: April 2003

Replica and thin‐section electron microscopy was performed on a linear polyethylene fraction (Mw = 1.89 × 105, Mn = 1.79 × 10 5) which was either isothermally crystallized or quenched at difference temperatures. The results are numerically analyzed in such a manner so as to give the distribution of the total long spacing and of the crystallite and amorphous thicknesses. The quantitative information about the maximum and minimum values for these parameters at each crystallization temperature yields important clues as to possible molecular processes involved. Qualitative information regarding general morphology, molecular tilt with respect to the lamellar surface, and possible crystallographic faults are also discussed.
Epitaxial crystallization of polyethylene on organic substrates: A reappraisal of the mode of action of selected nucleating agents
Authors: Wittmann J. C. , Lotz B.
Published: April 2003

Electron microscopy and electron diffraction studies show that polyethylene crystallizes epitaxially onto crystals of homologous series of (i) condensed aromatic hydrocarbons and (ii) linear polyphenyls. The contact planes of the PE chain‐folded lamellae with the (001) faces of the substrate crystals are found to differ for the two series, being (100) and (110), respectively. The underlying epitaxial relationships are best explained by a two‐dimensional lattice matching of polymer and substrate networks. In view of the structural similarities of the present substrates and some well‐known nucleating agents for polyethylene, epitaxy is suggested as a possible mechanism which could explain the nucleating ability of the latter. This is experimentally demonstrated with the potassium salt of phthalic acid.
Crystal stability and mechanical properties of drawn polymers: A statistical‐mechanical approach
Authors: Itoyama Kuniyoshi
Published: April 2003

The partition function is formulated by the generating function method for a stacked lamellar model of alternating crystalline and amorphous layers. The random‐walk problem of enumerating statistical weights for conformations of amorphous chains confined by two parallel walls is solved for the body‐centered cubic lattice as a generalization of the one‐wall model treated by Roe. The mean lengths of loop, tie, and cilia chains and the free energy of the system are calculated for the random‐reentry and‐bridge model as a function of the distance h of separation between crystal layers and as a function of the number N of loop chains in a crystal block as the basic structural element of the system. The mean length of amorphous chains decreases at a given thickness l of the crystal layers with decreasing h or with increasing N. The free energy of the system exhibits no minimum with respect to N, showing that the folded‐chain crystal is thermodynamically stable, especially for relatively small l. Additionally, it is shown that another requirement for stabilizing relatively small crystals (small l) is the formation of an aggregate structure of crystals, whereas a large single‐crystal (large l) is relatively stable, irrespective of h and N. Furthermore, a theoretical model is developed to calculate the force and elastic modulus of a highly deformed stacked system, assuming that the only change in the configurations of amorphous chains within the interlamellar regions is due to deformation, except for scission of tie chains having fewer segments than are needed to span the interlamellar distance of the deformed system. It becomes evident that taut tie chains are effective in increasing the modulus of the stacked system.
Brillouin scattering studies of the effect of orientation on mechanically deformed poly(ethylene terephthalate)
Authors: Cavanaugh David B. , Wang C. H.
Published: April 2003

Brillouin scattering is used to study the internal structure of oriented films of poly(ethylene terephthalate). Splitting in the longitudinal spectrum is observed as the film is stretched, indicating that the crystalline region is developed gradually from the amorphous region. The hypersonic velocity data obtained from these two regions are used to draw directional maps of sound velocity propagation in different directions of the film. The results are discussed and correlated with a recently proposed model. The orientational parameter in the amorphous phase is calculated from the hypersonic velocity data as a function of stretch ratio. The results are found to be in good agreement with published values obtained by a different technique.
Gas sorption and transport in a copolyester and its blend with polycarbonate
Authors: Masi P. , Paul D. R. , Barlow J. W.
Published: April 2003

Sorption and transport measurements for various gases were made with a copolyester formed from 1,4‐cyclohexanedimethanol and a mixture of terephthalic and isophthalic acids. Similar observations for the miscible blends of this copolyester with polycarbonate were made using carbon dioxide. All of these results are described well by dual sorption‐dual mobility models which have been used effectively for other gas‐glassy polymer systems. The sorption and transport parameters deduced experimentally from these systems have been correlated and interpreted in terms of applicable theories. For the blends, the Henry's‐law sorption parameter has been used to deduce a reasonable value of the interaction parameter for the polycarbonate‐copolyester blend system from the Flory‐Huggins theory of mixtures. The Langmuir capacity term from the dual‐sorption model is accurately related to the unrelaxed volume of the glass. Negative deviations of permeability and diffusion coefficients from simple additivity relations were observed and qualitatively interpreted to result from the decrease in volume on mixing for the blends.
The effect of aging on the thermal behavior of sulfonated polystyrene
Authors: Weiss R. A.
Published: April 2003

The thermal properties of an ionomer glass, lightly sulfonated polystyrene, was studied as a function of aging at room temperature after being cooled from the melt. An anomalous endothermic event below Tg was observed by differential scanning calorimetry; the intensity of this excess enthalpy was a function of time and sulfonate concentration. It is suggested that the origin of this relaxation may be due in part to morphological changes that occur as a consequence of electrostatic interactions of the sulfonate groups.
Behavior of concentrated polystyrene solutions in large‐amplitude oscillating shear fields
Authors: Pearson Dale S. , Rochefort Willie E.
Published: April 2003

The limits of linear viscoelastic behavior of polystyrene solutions have been investigated by subjecting them to large‐amplitude oscillatory strains, γ0. At strains less than one we find that the dynamic storage modulus G′(ω,γ0) and the dynamic loss modulus G″(ω,γ0) decrease quadratically with increasing strain. As a measure of the size of the linear viscoelastic region, we have determined the strain at which the moduli have fallen 5% below their zero‐strain values. This strain, γNL, is found to be independent of frequency ω at high frequencies but to increase with decreasing frequency at low frequencies. Behavior of this type is in qualitative agreement with the recent constitutive equation developed by Doi and Edwards. More specifically, we find that the rate of decrease of the storage modulus with increasing strain is quite similar to that predicted by their theory, but that the rate of decrease of the loss modulus is much slower. Some possible approaches for improving the agreement with experimental results are suggested. In the course of our work an interesting hydrodynamic instability was observed. The nature of this instability and methods to avoid it are discussed.
Phase separation in perfluorosulfonate ionomer membranes
Authors: Roche E. J. , Pineri M. , Duplessix R.
Published: April 2003

The extent of phase separation in Nafion® perfluorosulfonate ionomer membranes has been studied by small‐angle neutron scattering (SANS). These polymers, which consist of a perfluorocarbon main chain and a sulfonate‐containing side group, can absorb up to 30% by weight of water. Previous studies have shown that clustering of water occurs, forming particles in the size range observable by SANS. The current study is concerned with the fraction of water molecules which participate in the clustering and the chemical composition of the phases present. Experiments have been made on melt‐quenched samples which have no fluorocarbon crystallinity. The analysis is based on isotopic replacement experiments in which SANS measurements are made on samples hydrated with mixtures of H2O and D2O. Values of the small‐angle x‐ray scattering (SAXS), mean‐square electron density fluctuation, and mass density are used as additional criteria. It is shown that at high water content (more than 15% absorption by weight), a two‐phase model can explain the data with a majority (>60%) of the water molecules in one phase and most (>90%) of the perfluorocarbon in the other phase; a sample hydrated to a lower extent (8% by weight) shows deviations from the two‐phase model. These results are consistent with the scattering behavior at large angles observed by SAXS.
Poly(P‐phenylene sulfide) hexafluoroarsenate: A novel conducting polymer
Authors: Clarke T. C. , Kanazawa K. K. , Lee V. Y. , Rabolt J. F. , Reynolds J. R. , Street G. B.
Published: April 2003

Poly(p‐phenylene sulfide) (PPS) is a melt‐ and solution‐processible polymer which on treatment with AsF5 forms a blue‐black material with a conductivity of 1–10 Ω−1 cm−1. Thermopower measurements indicate that the resulting polymer is p type, consistent with partial oxidation of the PPS by the AsF5. The rate and extent of this doping process prove to be particularly sensitive to the degree of crystallinity of the starting polymer. There is also evidence of crosslinking of the polymer chains during the reaction with AsF5. The details of both the chemistry and physics of the doping of PPS and several of its derivatives are presented.