bluuebunny/crossref_metadata_2025 huggingface dataset:
Solvent crazing of “dry” polystyrene and “dry” crazing of plasticized polystyrene
Authors: Kambour R. P. , Gruner C. L. , Romagosa E. E.
Published: April 2003

The critical strain εc for crazing of polystyrene in each of a variety of organic liquids has been measured along with the degree of swelling of the polymer by the liquid and the attendant reduction in the glass transition temperature Tg of the polymer. The critical strain for the crazing in air and the Tg of each of a set of specimens molded from mixtures of o‐dichlorobenzene and polystyrene have also been determined. Correlations of εc with Tg in the two cases are identical within experimental error for the first 40°C of Tg reduction; these results imply (1) that organic liquids do not exercise a significant surface energy role in solvent crazing and (2) that their only roles are associated with flow processes. Correlation of solvent crazing εc with solubility parameter of the crazing fluid is very poor for several reasons that are discussed.
Hydrodynamic interaction for time‐dependent motions: Steady rotation of a rigid dumbbell
Authors: Szu Shousun C. , Hermans J. J.
Published: April 2003

An expression for the flow field resulting from a time‐dependent force with time‐dependent point of action is derived from the linearized Navier‐Stokes equations. The result is written as a sum of terms, the first of which is the “slow‐change limit” corresponding to a stationary force acting at a stationary position. The application to the steady rotation of a dumbbell shows that this sum corresponds to a series expansion in powers of (L2|Ω|/v)1/2 where 2L is the length of the dumbbell, Ω is its angular velocity, and v is the kinematic viscosity of the liquid. It is pointed out that the results obtained are relevant to the problem of rotatory Brownian motion and to that of non‐Newtonian viscosity.
Steady‐flow viscous and elastic properties of polyisobutylene solutions in low molecular weight polybutene
Authors: Ueda Shigeyuki , Kataoka Tadao
Published: April 2003

Shear stress and first normal‐stress difference of polyisobutylene dissolved in low molecular weight polybutene (concentrations 0.7 to 19 wt‐%) were measured as a function of the shear rate. The dependence of viscosity η on shear rate \documentclass{article}\pagestyle{empty}\begin{document}$\dot \gamma $\end{document} was represented by the equation η = η∞ + (η0 − η∞)/(1 + α\documentclass{article}\pagestyle{empty}\begin{document}$\dot \gamma $\end{document}n) proposed by Cross, where the subscripts (0 and ∞) denote values at infinitesimal and infinite rate of shear, α is a constant associated with rupture of entanglement linkages, and n is a constant. The empirical value of n is 10/13 for 19% solution and 2/3 for the other solutions. The concentration dependence of α was roughly expressed as α = 104 c2.7, where c is the concentration in grams polymer per milliliter solution. The first normal‐stress coefficient ψ12 can be represented by ψ12 = ψ12∞ + (ψ12∞ − ψ12∞)/(1 + β\documentclass{article}\pagestyle{empty}\begin{document}$\dot \gamma $\end{document}m). The analysis of data based on the equations shows that m = 2n and β ≈ α2. The steady‐state compliance Je was calculated from the relation Je = ψ120/2(η0 − ηs)2, where ηs is the solvent viscosity. Je shows a maximum at about c = 0.03 and is directly proportional to c−2 in the higher region of c.
Structural studies on polyformals. III. Poly‐1,3‐dioxocane and poly‐1,3‐dioxonane
Authors: Sasaki Shintaro , Tadokoro Hiroyuki
Published: April 2003

Molecular and crystal structures of poly‐1,3‐dioxocane and poly‐1,3‐dioxonane, the polyformals [OCH2O(CH2)m]m with m = 5 and m = 6, respectively, are analyzed. Poly‐l13‐dioxocane is triclinic, space group with m = 5 and m = 6, respectively, are analyzed. Poly‐1,3‐dioxocane is triclinic, space group (fiber axis) and N (number of chains per unit cell) = 2. Poly‐1,3‐dioxonane is orthorhombic, (fiber axis) = 18.8 Å, and N = 2. The molecular conformations are roughly magnified image
where T, G, and G are the trans, and the two gauche forms, respectively.
Preferential uniplanar orientation mechanism of the (101) crystal plane of regenerated cellulose
Authors: Matsuo Masaru , Nomura Shunji , Kawai Hiromichi
Published: April 2003

The molecular orientation behavior of regenerated cellulose, in both crystalline and noncrystalline phases, was investigated quantitatively under various conditions during coagulation‐regeneration from viscose solution and during drying of the resulting gel film. It was concluded that the stronger the tensions which arise parallel to the film surface during coagulation‐regeneration and drying of the gel film, the more prominent become the uniplanar orientation of the (101) crystal plane and planar orientations of the crystal b axis and noncrystalline chain segments, all parallel to the film surface and associated with considerable distortion and disintegration of the regenerated crystal. This conclusion suggests an orientation mechanism of the cellulose II crystal, namely, rotation of the crystal around the U(101) axis associated with slippage of the (101) crystal plane, the most highly hydrated and most readily dislocated plane, in the direction of the tension, which is also parallel to the surface of the film. The behavior of this type of uniplanar orientation of the (101) crystal plane is characterized semiquantitatively by comparing observed distributions of the orientation of crystallographic axes with those calculated on the basis of a relatively simple model for crystal orientation.
Thermodynamic properties of some concentrated polymer solutions
Authors: Bonner D. C. , Prausnitz J. M.
Published: April 2003

Solubilities of several solvents were measured in four molten polymers by using an isobaric vapor‐pressure apparatus. Solvent concentration ranged from 0.5 to 15 wt‐%. The systems polyisoprene–benzene and polyisobutylene–benzene were studied at 80.0°C; polyisobutylene–cyclohexane was studied at 100.0°C; ethylene–vinyl acetate copolymer (EVA)–cyclohexane, EVA–isooctane, and poly(vinyl acetate)–isooctane were studied at 110.0°C. Of six polymer–solvent systems studied, all except poly(vinyl acetate)–isooctane appear to exhibit hysteresis in a single sorption–desorption cycle starting with dry polymer. The desorption curves of solvent activity plotted versus solvent weight fraction show an inflection point, suggesting localized adsorption of solvent molecules. Experimental data were analyzed with a theory which takes into account adsorption of solvent by polymer in addition to differences in free volumes and intermolecular forces. The theory gives a semiquantitative representation of the experimental data.
Rotational isomeric‐state approximation for the unperturbed dimensions of a POLA polyester
Authors: Tan J. S.
Published: April 2003

Rotational isomeric‐state theory has been applied to investigate chain configurations of a polyester prepared from 4′,5‐(1,1,3‐trimethyl‐3‐phenylindan) dicarboxylic acid and 2,2‐bis(4′‐hydroxyphenyl) propane (POLA polyester). Independent conformations for each repeat monomer unit of the chain have been assumed in the calculations of the unperturbed dimensions. Rotations about the oxygen‐phenylene‐carbon (OϕC) bonds are considered to be free with twofold symmetric potentials. The trans and cis conformations of the carbonyl‐phenylene‐carbon (OCϕC) and the indan‐carbonyl residues are assumed to have equal probability. Two rotational states, trans and cis, are assigned to the ester CO bonds. Calculation of the reduced unperturbed dimensions (〈r02〉/M)∞ with conformations thus assigned for the bonds in the repeat unit, and comparison with experiment (0.72 ± 0.02 Å2/g) indicate that the conformation in the ester CO bonds is predominantly trans. An equation for the conformational potential as a function of rotational angle about the ester CO bond has been formulated using data on potential barriers for low molecular weight compounds. This equation, yielding a potential difference between the cis the trans isomers of 2.5–3.0 kcal/mole, is in good agreement with the prediction made from the calculation of the unperturbed dimensions where a cis/trans ratio of 0.01 for the ester CO bonds was obtained.
Effect of temperature and physical state on the inhibition by additives of radiation‐induced degradation of poly(methyl methacrylate)
Authors: Wündrich Konrad
Published: April 2003

It has been reported in earlier papers that aromatic additives can reduce the rate of radiation‐induced degradation of poly(methyl methacrylate) (PMMA), depending on the concentration, the distribution, and the resonance of the aromatic system. In the present work, the temperature dependence is studied, together with the influence of molecular mobility, which is determined by the physical state of the system. For this purpose, PMMA containing benzene, biphenyl, naphthalene, anthracene, phenanthrene, pyrene, or benz[a]anthracene, was γ‐irradiated at room temperature and also, except with naphthalene and biphenyl, in the temperature range −80 to 160°C. The changes in degradation rate were related to the first excited singlet state and to the resonance energy of the additives. The results suggest that at low temperatures both electron scavenging and transfer of excitation energy occur. At temperatures between the γ transition and the glass transition, the significance of energy transfer compared with electron scavenging increases, whereas the inhibitory effect decreases. Above the glass transition temperature the inhibition decreases more rapidly. This is related to scavenging of radical chain fragments, due to increasing molecular mobility, which causes a decrease in recombination rate. This sensitization of degradation competes with the inhibition by energy transfer and electron scavening, and may prevail at temperatures above 185°C. The opposing effects of these mechanisms can be clearly shown with the system PMMA–benzene. In viscous mixtures, sensitization prevails even at room temperature.
Precipitation chromatography. III. Optimization of the experimental conditions and determination of the polydispersity of fractions
Authors: Böhm L. L. , Casper R. H. , Schulz G. V.
Published: April 2003

The influence of the solvent–nonsolvent gradient and the temperature gradient on the efficiency of the precipitation chromatography is investigated with radically and anionically prepared polystyrene samples. Only a combination of both gradients gives optimal effectiveness of the column. The separating power of the column was determined by using mixtures of well defined samples. From the elution curves of the mixtures the nonuniformity Ufr of fractions can be estimated. For fractions of anionically prepared polystyrenes Ufr is on the average 0.001; this value is of the same order of magnitude as the statistical error. These results show that with this chromatographic method it is possible to determine the narrow molecular weight distributions of anionically prepared polystyrenes (or other polymers) with an accuracy sufficient for kinetic studies.
Statistical thermodynamics of ABA block copolymers. III. Microstructural transitions and model verification
Authors: Leary David F. , Williams Michael C.
Published: April 2003

The predictions of a model presented previously are tested with data on five styrenebutadiene–styrene copolymers. Differential scanning calorimetry and laser light transmission are the primary tools, spanning 180–630°K, with some evidence supplied also by electron microscopy and mechanical properties. The existence of a first‐order phase transition, characterized by a separation temperatureTs, is verified and found to be predictable by the model. Details of morphology, including transitions in microstructure in certain temperature ranges, are also reported and shown to be consistent with the theory.
Effect of relaxation properties on the adhesion of rubber
Authors: Kendall K.
Published: April 2003

The adhesion to glass of rubbers with different relaxation properties but similar surface condition has been compared using the thin film peel test. At higher peeling stresses, the rubber–glass interface fractured at constant velocity and all rubbers gave the same adhesive energy values. However, at lower peel stresses, the lossy rubber appeared to adhere more strongly due to a crack‐slowing phenomenon at the rubber–glass interface.
Morphology of siloxane block copolymers: Tetramethyl‐p‐silphenylene siloxane–dimethylsiloxane
Authors: Kojima M. , Magill J. H. , Merker R. L.
Published: April 2003

The morphological features of random block copolymers of tetramethyl‐p‐silphenylene (TMPS) and dimethylsiloxane (DMS) have been studied as a function of copolymer composition. Wide‐angle and small‐angle x‐ray diffraction coupled with several electron diffraction and microscopy studies were used to investigate these materials. The results of this work clearly indicate that the amorphous segments do not enter into the crystalline lattice of the crystallizable component which is varied in content from 90% to 30%. Over the entire range of compositions the block copolymers are crystallizable. Spherulites can be grown from the melt, and single crystals and/or spherulites may be obtained from solution. Single crystals can be obtained over the entire range of compositions provided ample time is allowed for crystallization. The crystalline TMPS component exhibits tetragonal symmetry at all compositions. The amorphous phase manifests itself as a diffuse halo in patterns obtained by electron and x‐ray diffraction.
Relationship between structure and dielectric behavior of stereoregular poly(methyl methacrylate) in the glassy state
Authors: Tanaka Akira , Ishida Yoichi
Published: April 2003

In order to elucidate the relationship between dielectric behavior and structure in solid polymers, we studied the dielectric relaxation of stereoregular poly(methyl methacrylate) (PMMA) in the glassy state. Assuming that the extremes of molecular structure are attained in the crystal and in solution, the most probable conformation of the main chain in the glassy state is estimated for isotactic and syndiotactic PMMA in terms of conformational analysis, the unperturbed mean‐square end‐to‐end distance in solution, and the NMR second moment in the glassy state. Under the assumption that the molecular structure varies in a limited range near the most probable conformation and that the α‐methyl group rotates freely, the energy barrier for the rotation of the side group is calculated. With the calculated energy barrier, the dielectric relaxation due to the side group is interpreted fairly satisfactorily by the barrier theory of Hoffman and Lauritzen, although the width of the relaxation curve is not. The experimental result that the loss peak of syndiotactic PMMA is located at higher temperature than that of isotactic PMMA is interpreted qualitatively in terms of different conformations for the syndiotactic and isotactic chains.
Theory of phase transition kinetics with growth site impingement. I. Homogeneous nucleation
Authors: Tobin Marvin C.
Published: April 2003

The nonlinear integral equations governing phase transition kinetics with homogeneous nucleation and growth site impingement are developed and solved to the first order for the two‐dimensional case. It is shown that the fractional transformed area at time t is given approximately by a(t) = Kt3/(1 + Kt3). The iteration method used to get the solution is applicable to certain other nonlinear differential and integral equations. It is shown that the theory predicts the total number of growth sites formed, and that the nucleation rate and growth constants can be deduced from this and the gross kinetic data. The extension of the method of three‐dimensional growth is indicated.
Effect of temperature and molecular weight on the rate of spreading of polystyrene melts on plane soda lime glass surfaces
Authors: Lau Wayne W. Y. , Burns Charles M.
Published: April 2003

The effect of temperature T and weight‐average molecular weight M̄w on the rate of spreading of polystyrene melts on plane solid surfaces has been examined. The activation energy E of spreading was estimated to be 25.2 ± 3 kcal/mole, which is of the same magnitude as the activation energy for flow of polystyrene melts. The rate of spreading was found to be inversely proportional to M̄w raised to the 1.5 power. This rate of spreading, measured as the time rate of increase in the liquid–solid contact area, dA/dt, could be expressed as

where γ1v is the melt surface tension and θd and θs are the dynamic and static contact angles, respectively. The numerical value of K has been calculated to be (6.025 ± 3.693) × 10−14 in the temperature range of 110–260°C and for the values of M̄w from 2000 to 37000.
Normal coordinate analysis of cis‐1,4‐polybutadiene
Authors: Coleman M. M. , Tabb D. L. , Farmer B. L. , Koenig J. L.
Published: April 2003

The fundamental vibrational frequencies of an isolated chain of cis‐1,4‐polybutadiene have been calculated. Infrared and polarized Raman data are used in the force constant refinement routine. The assignments of the vibrational frequencies are discussed in terms of the potential energy distribution.
Small‐angle light scattering from hedrites, ovoids, and spiral ovoids. II. Experimental
Authors: Gałȩski A. , Kryszewski M.
Published: April 2003

Procedures for obtaining hedrites, ovoids, and spiral ovoids in polyoxymethylene are described. Results of morphological studies on these structures by optical and electron microscopy are presented. Small‐angle light scattering studies on single isolated supermolecular structures are described. The Vv and Hv diffraction patterns obtained experimentally are discussed in the light of theoretical results of Part I of this study.
On critical concentration determination
Authors: S̆olc K.
Published: April 2003

The rules formulated by Koningsveld for the determination of the critical concentration are shown to be in accord with the Flory‐Huggins theory. Sometimes, however, they may not refer to stable conditions, and their application in such cases will result in misleading conclusions.
Edge yielding in poly(vinyl chloride) films
Authors: Martin John R. , Johnson Julian F.
Published: April 2003

Samples of thin, unplasticized PVC films were fatigued to rupture in nitrogen and ethanol vapor. Examination of the fracture surface edges showed unusual yielding due to the proximity of an unconstrained surface. The scanning electron microscope (SEM) photomicrographs show several indications of supermolecular order in these highly oriented edges and possibly in the relatively unoriented bulk material.
Effect of morphology on the dynamic mechanical properties of a semicrystalline polysiloxane
Authors: Murray A. D. , Markovitz Hershel
Published: April 2003

The dynamic mechanical properties of semicrystalline poly(tetramethyl‐p‐silphenylene siloxane) in three morphological preparations were measured over the wide frequency range of about 0.002 Hz to 500 Hz and the temperature range of about − 190°C to 100°C. The three samples were all isothermally crystallized at 125°C. Two samples had a spherulite size of 25 μ diameter but differed in the time allowed for secondary crystallization. The other sample had a smaller spherulite size. By assuming compliance additivity, the viscoelastic behavior could be separated into five relaxation processes with an indication that a sixth existed at low temperature. Two processes called γ1 and γ2 could be resolved at low temperatures. The γ1 process was associated with the amorphous region since the peak strength was affected by the rate of cooling through the glass transition region; the γ2 peak, unaffected by cooling rate, is attributed to the crystalline part. In the high‐temperature region, the β peak is associated with the glass transition and has a shape and location that is essentially independent of the morphology. The highest temperature α2 process, whose maximum was not observed in the experimental range covered, is attributed to the crystalline region and is sensitive to changes in crystallization history. The strength of the α1 process unlike that of the other processes was found to be a function of temperature; it was associated with the noncrystalline region.
Modified graessley theory for non‐newtonian viscosities of polydimethylsiloxanes and their solutions
Authors: Ito Yoshio , Shishido Shunsuke
Published: April 2003

A deviation from Graessley's theory of entanglement viscosity appears at very high shear rates when the flow of polydimethylsiloxanes of various molecular weights and their solutions with various concentrations is measured by the capillary method. In order to explain this deviation, a modified Graessley theory is proposed according to the previously reported suggestion that frictional viscosity appears not to be negligible at high shear rates. A reducing procedure taking a frictional viscosity parameter into account was performed. All of the reduced data are combined to give a master curve in spite of a wide range of molecular weight, concentration, and shear rate (from the lower Newtonian to very highest non‐Newtonian flow region). The findings from the reducing procedure completely explain the mechanism of non‐Newtonian flow for the bulk polymers with various molecular weights, including those below the critical molecular weight for entanglement, and for polymer solutions at any concentration. The viscosity of the linear polymer system consists of the shear‐dependent entanglement term ηent proposed by Graessley and the shear‐independent frictional term ηfric. The non‐Newtonian behavior depends on the ratio of ηent/ηfric at the shear rate of measurement. The ratio of zero‐shear entanglement viscosity ηent,0 to ηfric and the critical shear rate for onset of the non‐Newtonian flow may be used as a measure of the non‐Newtonian behavior of the system and a measure of capability for its rising, respectively. The Graessley theory is to be included in the present modified theory and is applicable to the case of ηentηfric ≫ 1.
Effects of peroxide bonds and their degradation products on the dielectric relaxations of polystyrene
Authors: Yano Okimichi , Wada Yasaku
Published: April 2003

Polystyrene radically polymerized in atmosphere of air is composed of bisegment (C‐A) or trisegment (C‐A‐C) block copolymers consisting of styrene segment (A) and styrene peroxide segment (C). Dielectric measurements of a system of copolymers of styrene and oxygen were obtained above the glass temperature. Three primary relaxations, a, b, and c, in order of descending temperature, were found corresponding to three microphases: styrene phase (phase a), styrene peroxide phase (phase c), and an intermediate phase (phase b) which contains a low concentration of peroxide bonds. An alternating copolymer of styrene and oxygen exhibits the relaxation c alone. With heat treatment above the glass temperature, relaxation c and subsequently relaxation b vanish with thermal degradation of peroxide bonds. The sum of relaxation strengths is linearly related to the content of peroxide bonds which was evaluated by the elementary analysis and DTA. Below the glass temperature, the temperature dependence of dielectric loss of carefully purified polystyrene without peroxide bonds shows very weak peaks which correspond to γ (200°K at 10 kHz) and δ (50°K at 10 kHz) peaks, respectively, in the activation plot. When low molecular degradation products of peroxide bonds are occluded or impurities such as benzaldehyde are added into the specimen, the height of the γ peak is appreciably enhanced, indicating that the reorientation of small polar molecules in polystyrene accompanies the vibration of the phenyl group about the CC6H5 bond which gives rise to the γ relaxation.
Distribution of monomer configurations in polypropylene as determined with 13C NMR
Authors: Randall J. C.
Published: April 2003

An amorphous polypropylene sample was examined by using 13C NMR at 25.2 MHz and all ten possible methyl resonances from monomer pentads were observed. Assignments were made through a consideration of an additivity relationship among the methyl resonances. Confirmation for the assignments was obtained through observed conformity of the methyl resonance intensity distribution with second‐order Markov statistics. The relative intensity distribution of the methyl resonances can be used to characterize the structure of polypropylenes with confidence, since experimentally it is shown that an equal nuclear Overhauser effect exists for each of the methyl resonances.
Brillouin scattering in amorphous polymeric solids
Authors: Mitchell R. S. , Guillet J. E.
Published: April 2003

Brillouin scattering of laser light has been used to study the temperature dependence of phonon velocity in a variety of amorphous polymeric systems, particularly internally and externally plasticized methacrylates. Discontinuities in the temperature coefficient of the hypersound velocities are observed at the glass transition temperatures (Tg). This phenomenon is related to changes in the temperature behavior of the specific volume accompanied by corresponding discontinuities in certain second‐order thermodynamic quantities. This method was also used to examine the temperature dependence of the Landau‐Placzek ratio.

This ratio is relatively large in polymer systems and appears to be independent of temperature in the region of the glass transition, provided that there are no internal strains in the sample at the temperature of measurement. Evidence is presented which suggests that the abrupt changes in this ratio at Tg reported by earlier workers were due to kinetic effects related to the relaxation of internal strains above Tg, and the results of recent studies by other investigators, both corroborating and supplementing the present work, are reviewed.
Dynamic viscosity of dilute solutions of poly(L‐glutamic acid)
Authors: Nakajima Haruhiko , Wada Yasaku
Published: April 2003

The dynamic viscosity η′ of a dilute solution of poly(L‐glutamic acid) (DP = 1370) in a mixed solvent made up of aqueous 0.2M NaCl and dioxane (2:1 by volume) is measured over the pH range 4.2–10 and in the frequency range 2–500 kHz. The frequency dependence of η′ in the helix region (low pH) is interpreted in terms of a model molecule consisting of n rigid helical segments connected by universal joints. The steady‐flow viscosity, relaxation time, and high‐frequency limiting viscosity at pH 4.75 (helical content 80%) are well explained by this model with n = 5. This value of n is consistent with that estimated from the nucleation parameter σ = 1.4 × 10−3 obtained from the relation between reduced steady‐flow viscosity and helical content. The high‐frequency values of η′ in the coil region (high pH) are fitted by Peterlin's theory. The internal viscosity seems to arise in part from the polyelectrolytic character of the molecule. An additional relaxation at low frequencies in the coil region is ascribed to rotation of molecules elongated by the electrostatic interaction. The lower value of reduced steady‐flow viscosity in the coil region in the mixed solvent compared with that in water is interpreted in terms of the lower degree of effective ionization and the selective solvation of water by the polypeptide. No anomaly is observed in the helix–coil transition region, indicating that the relaxation time for helix–coil equilibrium is less than 10−6sec.
Effect of molecular weight distribution on viscoelastic properties of polymers
Authors: Kurata Michio , Osaki Kunihiro , Einaga Yoshiyuki , Sugie Tsutomu
Published: April 2003

The effect of molecular weight distribution on mechanical properties of concentrated polymer solutions was studied by measuring creep compliance and complex modulus for solutions of binary blends of narrow distribution polystyrenes in chlorinated biphenyl. Two‐step plateaus in the rubbery plateau region, as reported for undiluted polymer blends, were observed for concentrated solutions provided the molecular weights of component polymers differed greatly. The nth order blending law (n = 1, 2, 3) of Bogue et al. was simplified in form to compare with experimental results. As far as the present version of simplification was concerned, the cubic blending law was better than the quadratic one in describing viscoelastic properties of polymer blends. The cubic blending law reproduced closely the magnitudes of viscoelastic functions such as loss modulus and relaxation modulus but it was not able to predict the two‐step plateaus, even when the ratio of molecular weights of components was as large as 10. It also provided a good approximation to reported results on the steady‐state compliance J for undiluted binary polymer blends and present results for solution blends. Since the cubic blending law in the simplified version was consistent with previous results on concentration dependence of the steady‐state compliance for concentrated solutions of narrow distribution polymers, it gave a unified expression for the steady‐state compliance of binary polymer blends and concentrated solutions of narrow distribution polymers.
Radiation crosslinking of elastomers. I. Polybutadienes
Authors: Pearson Dale S. , Skutnik Bolesh J. , Böhm Georg G. A.
Published: April 2003

The chemical and physical crosslink densities of irradiated polybutadiene were determined using a precise and consistent method. This method included the use of a statistical theory of crosslinking modified to include chain reactions and the use of Langley's theory for calculating the number of trapped chain entanglements. The number of crosslinks formed per unit radiation dose, G(X), was measured for a series of polybutadienes containing various isomeric forms of unsaturation. The physical crosslink density and the molecular weight between entanglements were determined from measurements of the compression modulus of swollen samples.
Stability of heterocharges in poly(methyl methacrylate) thermoelectrets. I. Effect of humidity on thermal current spectra
Authors: Vanderschueren J.
Published: April 2003

Thermoelectrets of poly(methyl methacrylate) were exposed to various atmospheres of known relative humidity between 0 and 100% and the thermal current spectra analyzed. The study of the decrease of the heterocharges as a function of the exposure time reveals important differences in stability between the three peaks of the spectrum; the two peaks appearing at low temperatures can be attributed to a uniform volume polarization, and the third peak observed at high temperature to a space charge polarization. The shift of the peaks indicates plasticization of the polymer by water vapor. This effect is reversible when the samples are exposed for a sufficiently long time to a drying atmosphere. The complex variations of the initial rise of the spectrum as a function of the exposure time show that the activation energy of the peaks probably depends upon the degree of hydration of the polymer.
A search for the mosaic block structure in polyethylene single crystals
Authors: Thomas E. L. , Sass S. L. , Kramer E. J.
Published: April 2003

A diffraction contrast study with the aid of an image intensifier was undertaken to obtain direct evidence for the existence of a mosaic block structure in polyethylene single crystals grown by self seeding under isothermal conditions. Dark‐field microscopy indicates that the crystals do not contain a mosaic block structure. High‐resolution electron diffraction confirms that the crystal is coherent (i.e., mosaic block‐free) over regions of several thousands of Angstroms. It is concluded that a mosaic structure on the scale of ∼300 Å does not exist in polyethylene single crystals grown under carefully controlled conditions from dilute solutions. Possible reasons for previous results that indicate the presence of a ∼300 Å mosaic block structure are discussed.
Dynamic viscosity of dilute aqueous solutions of poly(acrylic acid) at frequencies of 2–500 kHz
Authors: Okamoto Hideho , Nakajima Haruhiko , Wada Yasaku
Published: April 2003

The dynamic viscosity of aqueous solutions of poly(acrylic acid) at a polymer concentration of ca. 0.15 g/100 ml has been measured at frequencies from 2 to 500 kHz as a function of degree of polymerization P, degree of neutralization α, and salt (NaCl) concentration Cs. Relaxation spectra have been obtained from the dynamic viscosity. The spectra in the short relaxation time region can be approximated by the Zimm theory for the conformational relaxation of nonionic polymers. The maximum relaxation time τ1 of the Zimm spectra is proportional to P2 and depends rather moderately on α and Cs. Increased deviation is found, however, in the long relaxation time region, in particular for high values of P and α and low values of Cs. The major part of the deviation is interpreted in terms of rotational relaxation of a molecule as a whole. The rotational relaxation time τR is proportional to P3 and increases with increasing α and decreasing Cs. The remaining part of the excess spectra located between τ1 and τR is ascribed to the deviation of the conformational relaxation from the Zimm theory arising from ionization of the polymer.
Quasichemical approach to crosslinked polymer solutions and the swelling equation for polycondensation networks
Authors: Dušek K.
Published: April 2003

The change of free enthalpy and the chemical potential of solvent for mixing of solvent with crosslinked structures formed by stepwise reactions of the polycondensation type has been derived by an adaptation of the quasichemical equilibrium method. Each monomer unit is supposed to bear a different number of crosslinkable contact points, the coupling of which gives rise to chemical bonds, and of uncrosslinkable contact points, involved in interactions with the solvent, which may be of different type. The results are used to analyze the effect of network topology on the parameters of the swelling equation, particularly on a parameter characterizing the network composition. This parameter may be obtained from analytical data or by using the crosslinking statistics; and model calculations show how it varies with monomer conversion.
Low‐frequency dielectric behavior of poly(vinylidene fluoride)
Authors: Uemura Shinsaku
Published: April 2003

An explicit mechanism is described for the anomalous increase in dielectric constant and dielectric loss at low frequencies and high temperatures for poly(vinylidene fluoride) containing ionic impurities. Relations are proposed for the ionic contributions, εi″ and εi″, to the dielectric constant and dielectric loss:

where v0 and D0 are the concentration and the diffusion coefficient of the mobile ions at infinite temperature, q is the charge of an ion (in cgs electrostatic units), l is the distance between electrodes, k is the Boltzmann constant, T is the absolute temperature, Ed is the apparent activation energy for diffusion of the ions, and W is the dissociation energy of the ionic impurities. From the slopes of curves of log εT′ versus 1/T and log ε″T versus 1/T for poly(vinylidene fluoride), energies Ed = 34 kcal/mole and W = 342 kcal/mole were obtained.
Surface tension of polymer mixtures and copolymers
Authors: Schwarcz Andor
Published: April 2003

Contact angles θ of liquids of different polarity were measured on a series of mixtures of solid high polymers and a series of copolymers. The mixtures were composed of an alternating poly(ethylene‐co‐maleic anhydride) (EMA), and its addition product with n‐octadecylamine, poly(ethylene‐co‐N‐n‐octadecylmaleamic acid) (EOM). The co‐polymers were composed of the same monomeric units as the mixtures. The surface tension γs of EOM, calculated from θ by the Good‐Fowkes‐Owens‐Wendt treatment, decreased slightly with increasing molecular weights and then reached a limiting value. Plots of γs against EOM concentration indicated large negative excess surface tension of the units with lower surface tension, EOM, in both series studied. For the mixture series, γa first sharply decreased with the EOM concentration; then it reached a limiting value, the γs of pure EOM, at a very low EOM concentration. This indicates phase separation of the two polymers, and the thickness of a monomolecular surface layer was calculated from these data. For the copolymers, γs varied logarithmically with the EOM concentration. Throughout the whole concentration range, the data fitted the equation developed by Belton and Evans for ideal mixtures.
Relationship between dielectric behavior and molecular conformation of polyisobutylene in the rubbery state
Authors: Tanaka Akira , Ishida Yoichi
Published: April 2003

In order to elucidate the relationship between the dielectric main‐chain relaxation and molecular structure in rubbery polymers, we studied polyisobutylene, which is free from complicating factors such as stereoregularity, branching, isomerism, and crystallinity. On the basis of the known conformation in the crystal and conformations deduced in solution and in the glassy state, we assumed several probable conformations in the rubbery state, and estimated the motional units in terms of the modified Adam—Gibbs theory. A computer simulation based on the above results leads to the conclusion that the local conformation in the rubbery state retains a regularity similar to that in the crystal.
Glass and melting transitions of copolymers of tetrafluoroethylene with propylene and isobutylene
Authors: Brown Daniel W. , Lowry Robert E. , Wall Leo A.
Published: April 2003

Copolymers of tetrafluoroethylene and propylene were prepared that contained 30–65 mole‐% of the former. Reactivity ratios of tetrafluoroethylene‐ and propylene‐ended radicals are 0.008 and 0.06, respectively, resulting in formation of highly alternating copolymers. The glass temperatures, Tg, were determined using a differential scanning calorimeter. Values ranged from 260 to 275°K. A plot of Tg versus composition has a low maximum centered about the equimolar composition. Copolymers of tetrafluoroethylene and isobutylene were prepared that contained 30–56 mole‐% of the former. Reactivity ratios of tetrafluoroethylene‐ and isobutylene‐ended radicals are 0.005 and 0.021, respectively. The glass temperatures of these copolymers range from 257 to 313°K. A higher maximum at the equimolar composition is obtained when Tg is plotted versus composition. Isobutylene‐containing copolymers having 45–54 mole‐% tetrafluoroethylene are crystalline. Melting temperatures range from 416 to 476°K and have their maximum value at the equimolar composition. It is thought that long sequences of alternating units behave as a third entity in these copolymers, the other two being nonalternating units of the two monomers. Unless inhibited, ionic homopolymerization of isobutylene can be appreciable, sometimes resulting in the polymer having two Tg.
Crystal orientation in a semicrystalline polymer in relation to deformation of polymer spherulites. III. Small‐angle light scattering
Authors: Nomura Shunji , Matsuo Masaru , Kawai Hiromichi
Published: April 2003

Small‐angle polarized light scattering from a deformed three‐dimensional spherulite is formulated on the basis of the deformation model proposed in Part II of this series. The intensity distribution of scattered light is discussed chiefly for the cross‐polarization condition, the so‐called Hv polarization, as a function of elongation of the spherulite. In the undeformed state, the scattered intensity distribution forms the typical fourleaf clover pattern, and the intensity decreases with increasing fraction of crystals oriented randomly (type R crystals) within the crystal lamellae of the spherulites. In a system composed of type R crystals and folded‐chain crystals (type B crystals) within the lamellae, the four‐leaf pattern moves to the horizontal zone near the equator with increasing elongation of the spherulite, and, simultaneously, extends to some extent to the vertical zone near the meridional direction as a parameter measuring the ease of lamellar untwisting increases. In a system composed, in addition to type R and type B crystals, of crystals transformed from type B to type Ca and type Cr due to tilting and unfolding of polymer chains, respectively, within the crystal lamellae an eight‐leaf pattern appears, even at small elongation up to about 30%. Each lobe of the eight‐leaf pattern undergoes a characteristic change with increasing elongation. In both systems, the scattered intensity increases with sharpening of orientation distribution of crystals within the crystal lamellae.
Diffusion of monoanionic dyes in nylon
Authors: Komiyama Jiro , Iijima Toshiro
Published: April 2003

The diffusion of three monoanionic dyes [Orange II (C.I. Acid Red 7) and two chromium complex dyes] in nylon 6 is discussed on the basis of dye distribution obtained by the film‐roll method. Variations of the diffusion coefficients with dye concentration depend characteristically on the dye species and in one case show a maximum near the dye concentration stoichiometric to the amino endgroup concentration in the nylon. These concentration dependences are interpreted on the assumption of two thermodynamically distinct dye populations in equilibrium.
Dielectric properties of some semiconducting polyazophenylenes
Authors: Löfgren B. , Sipilä R. , Heleskivi J.
Published: April 2003

The dielectric properties of a series of semiconducting polyazophenylenes were studied as a function of temperature and molecular weight in the temperature range 293–600°K and for molecular weights between 5,100 and 62,800 at a constant frequency of 1 kHz. The compounds studied included poly‐2,4‐diaminotoluene, poly‐2,4‐diaminoanisole, and poly‐2,5‐diaminotoluene. The dielectric properties are presented in the usual way in terms of a complex dielectric constant ε* = ε′—jε″. Activation energies of relaxation processes were evaluated from the areas and widths of the dielectric loss factor, ε″, against reciprocal temperature at constant frequency. The dielectric activation energies were found to be roughly equal to the activation energies from the DC conductivity. This indicates that the conduction mechanism is based on rotational movements of molecules or parts of molecules.
Secondary crystallization of isotactic polystyrene
Authors: Lemstra P. J. , Schouten A. J. , Challa G.
Published: April 2003

When isotactic polystyrene (i‐PS) is crystallized from the melt or from the glassy state at rather large supercooling an additional melting peak appears on the curve during scanning in a differential calorimeter. The overall rate of crystallization deduced from the total peak areas as a function of crystallization time did not fit the Avrami equation well. When we omit the area of the additional melting peak in the kinetic analysis a much better fit is obtained. We also observed that no lamellar thickening occurs during isothermal crystallization. In view of the low degree of crystallinity of i‐PS these results lead to the idea that a secondary crystallization process takes place within the amorphous parts of the spherulites resulting in this additional melting peak on the DSC curve. The large supercooling needed and the increase in peak area with increasing molecular weight make us suppose that intercrystalline links are probably responsible for the additional melting peak of bulk‐crystallized i‐PS. Electron microscopic studies of surface replicas of i‐PS support this view.
Stress, strain, and birefringence relations of swollen cis‐1,4‐polybutadiene crosslinked in solution
Authors: Ong C. S. M. , Stein R. S.
Published: April 2003

Stress–strain–birefringence relations are measured for a series of unswollen and swollen networks of cis‐1,4‐polybutadienes which differ both in the degree of crosslinking and in the volume fraction of rubber present during crosslinking. The stress optical coefficient (SOC), the Mooney–Rivlin constants C1, C2 and B1, B2 are calculated. Results show that the unswollen, solution‐vulcanized polymers have very low values of C2 and B2, but high SOC. Upon swelling with CCl4, the stress optical coefficients decrease considerably and agree well with the values obtained by Fukuda, Wilkes, and Stein, and by Ishikawa and Nagai. The networks prepared in solution exhibit different behavior from those crosslinked in dry state, suggesting that in order to understand the origin of deviations from kinetic rubber elasticity theory and the Kuhn–Grün birefringence theory, more consideration must be given to the effect of overall network topology on stress–strain–birefringence behavior.
Copolymers of ethylene with norbornene derivatives—dynamic mechanical properties
Authors: Wilson T. P. , Von Dohlen W. C. , Koleske J. V.
Published: April 2003

The dynamic mechanical properties have been determined and the β relaxation temperatures Tβ have been located for a series of copolymers of ethylene with norbornene, methylnorbornene, dicyclopentadiene, and octahydrodimethanonaphthalene. The Tβ values show discontinuous changes with changing comonomer content. The several levels of Tβ observed apparently can be associated with the sequence of close multiplets of norbornane moieties ranging from isolated units through pairs to triads and higher. For isolated norbornane units Tβ is around 10°C, while for pairs of these units, probably separated by a C2H4 unit, it is 55°C. The size of the norbornene‐type comonomer has a small but measurable effect on these values of Tβ. The bearing of these results on the problem of defining a value of Tg for polyethylene is discussed.
Temperature dependence of viscosity–shear rate behavior in undiluted polystyrene
Authors: Penwell Richard C. , Graessley William W. , Kovacs André
Published: April 2003

The time—temperature superposition principle is well‐established for linear viscoelastic properties of polymer systems. It is generally supposed that the same principle carries over into nonlinear phenomena, such as the relationship between viscosity η and shear rate \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \gamma $\end{document}. Guided by this principle and the forms of various molecular theories, one would expect that η—\documentclass{article}\pagestyle{empty}\begin{document}$ \dot \gamma $\end{document} data on the same polymer at different temperatures would superimpose when plotted as η/η0 versus \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \gamma $\end{document}η0/ρT, η0 being the limiting viscosity at low shear rates, ρ the polymer density, and T the absolute temperature. Data on polystyrene melts, obtained in a plate‐cone viscometer, appear systematically to violate this principle in the range 140–190°. Such anomalies are absent in concentrated solutions of polystyrene. The trends are similar to those reported by Plazek in the steady‐state compliance of polystyrene melts near Tg, but they appear to persist to higher temperatures than the compliance anomaly.
The scattering of light by correlated assemblies of anisotropic rods in two dimensions
Authors: Prud'Homme Robert E. , Stein Richard S.
Published: April 2003

The scattering from an assembly of anisotropic rods having correlated orientation is calculated in terms of a correlation function expressing the probability of parallelism of orientation of their optic axes as a function of their separation. The scattering is dependent upon the product of a form factor for the scattering from an individual rod and an interference factor dependent upon this correlation function.