bluuebunny/crossref_metadata_2025 huggingface dataset:
The quantitative approach to the composition heterogeneity of the products of reactions of polymers
Authors: Noah O. V. , Litmanovich A. D. , Platé N. A.
Published: April 2003

The problem of describing the composition heterogeneity of the products of reactions of substituent groups on a polymer chain when there are interactions between neighboring groups is considered. A Monte Carlo simulation method and a modified first‐order Markovian approximation are proposed for obtaining composition distributions. The conditions of the mathematical experiment (the optimum length of the model chain and the size of the sample population) are found from a comparison of calculated parameters of the distribution of units with the exact values obtained by accurate analytical solution. These conditions depend upon the ratios k0:k1:k2 of rate constants for reaction of groups with neither, one, or both neighboring groups already reacted. The modified first‐order Markovian approximation gives results close to those of the Monte Carlo simulation for fairly long chains (100 units or more). Results are summarized graphically for calculations of the composition heterogeneity for various k0:k1:k2 ratios. As an example of the application of the suggested theoretical approaches the quaternization of poly‐4‐vinylpyridine with benzyl chloride is considered. The individual rate constants were found from experimental kinetic data. The functions of composition distribution calculated with these constants (k0 = 5.8 × 10−4 l mole−1 sec−1, k1 = k2 = 1.7 × 10−4 l mole−1 sec−1) were compared with experimental data obtained by gel permeation chromatography. Fairly good coincidence was found between experimental and calculated data. The satisfactory description of both reaction kinetics and composition heterogeneity by the same constants enables us to conclude that the neighboring group effect is dominant in this reaction.
In situ characterization of solution–grown polymer single crystals by light scattering and kerr effect
Authors: Picot C. , Weill G.
Published: April 2003

Simultaneous measurements of light scattering and electric birefringence on a crystallizing solution of poly(ethylene oxide) (PEO) are shown to lead to the determination of the radius, thickness, and number of crystals at the early stages of the crystallization process.
Solution properties of polymers of pyridinium and ammonium methacrylates.
Authors: Stejskal Jaroslav , Beneš Milan J. , Kratochvíl Pavel , Peška Jan
Published: April 2003

Solution properties of poly[1(2‐hydroxyethyl)pyridiniumbenzene sulfonate methacrylate] and poly[1(2‐hydroxyethyl)trimethylammoniumbenzene sulfonate methacrylate] were studied. Within a certain concentration range of some added low molecular weight electrolytes, phase separation occurs. The dependence of intrinsic viscosity on molecular weight was determined and the steric factor estimated for both polymers. For nonaqueous solvents, an extrapolation of the dependence of the refractive index increment of the polymer on the refractive index of the solvent leads to an apparent refractive index of the polymer, different from the refractive index determined directly by the immersion method. Some peculiarities of light scattering in solutions with no electrolyte added are mentioned.
Craze and crack growths in polycarbonate
Authors: Kitagawa M. , Motomura K.
Published: April 2003

Craze and crack growth have been studied in polycarbonate. The results are correlated by a stress intensity factor derived from fracture mechanics. A new model taking creep into account is proposed to explain the experimental results. Theoretical predictions derived from the model are compared with experimental results. Fair agreement is obtained.
Flow properties of branched polydisperse polymers
Authors: Graessley W. W. , Shinbach E. S.
Published: April 2003

Viscosity and normal‐stress difference as functions of shear rate were examined for poly(vinyl acetate) samples with various degrees of random branching in diethyl phthalate solution. At moderate concentration (c = 0.17 g/ml) the viscosities were depressed by branching, in fair accord with the Bueche theory. However, at higher concentrations (c = 0.35 g/ml) the data showed a progressive trend in the direction of viscosity enhancement by branching, a characteristic which has been observed by other workers in undiluted branched polymers. Accompanying viscosity enhancement was an increase in the temperature coefficient of viscosity, an increase in recoverable compliance (estimated from steady‐state normal‐stress data) and an early onset in the shear rate dependence of viscosity.
Relaxations in the transition region of crosslinked polyesters. I. The β relaxation
Authors: Cook W. D. , Delatycki O.
Published: April 2003

The glass transition region of styrene‐crosslinked poly(1,2‐propylene phthalate fumarate) was studied using a torsion pendulum. The region was composed of two separate relaxations. The major relaxation was the glass transition of the whole network, while the minor relaxation, at a lower temperature, was ascribed to the polyester segments between the crosslinks. A comparison was made between these relaxations and these observed in related polyester networks.
Theory of the local mode relaxation in the glassy state of polymers
Authors: Hayakawa Reinosuke , Wada Yasaku
Published: April 2003

The local modes refer to vibrational motions of the main chain in the glassy state which are thermally excited with a relatively large amplitude and are consequently strongly damped into relaxational motions by the intermolecular viscous force. This paper describes a theory of strengths of the dynamic mechanical and dielectric local mode relaxations, in the latter of which the correlation of dipole arrangement along the main chain is considered. The results are compared with the observed strength and its dependence on temperature and pressure, in particular for the dielectric β relaxation of poly(vinyl chloride). Satisfactory agreement is obtained between theory and experiment.
Dilute solution rheology of flexible macromolecules (bead–rod model)
Authors: Acierno D. , Titomanlio G. , Marrucci G.
Published: April 2003

The rheological behavior of dilute solutions of flexible macromolecules is studied by means of a freely jointed multiple bead–rod model. The solution of the equations describing the mechanics of the system is obtained by means of a numerical procedure, which applies to arbitrary flow conditions. The case of the transient stress in uniaxial elongational flow is developed in some detail. A comparison with bead–spring models shows both quantitative and qualitative differences which are briefly discussed.
Cryoscopy on sulfuric acid solutions of a heterocyclic polymer (BBB) and related compounds
Authors: Berry Guy C. , Eisaman Paul R.
Published: April 2003

Cryoscopic measurements have been carried out on solutions in sulfuric acid of a heterocyclic polymer, its monomers, and certain of its oligomers. The polymer, BBB, is prepared by the polycondensation of 1,4,5,8‐naphthalenetetracarboxylic acid (NTC) with 3,3′‐diaminobenzidine (DAB). The results show that the polymer, its oligomers and one of its monomers, DAB, are all extensively protonated in sulfuric acid, whereas its other monomer is not. The degree of protonation appears to be greater for the polymer than for its low molecular weight oligomers.
Plasticization of poly(dimethyl siloxane) by high‐pressure gases as studied by NMR relaxation
Authors: Assink Roger A.
Published: April 2003

The molecular relaxation behavior of poly(dimethyl siloxane) (PDMS) exposed to various gases pressurized to 207 megapascals (MPa) was investigated by pulsed nuclear magnetic resonance spectroscopy. For a gas of low solubility, such as helium, the gas acts only as a pressurizing medium allowing the effect of pressure on the glass transition to be determined. For gases of high solubility the gas acts not only as a pressurizing medium but also as a plasticizing agent, expanding the polymer lattice and increasing the frequency of molecular motions. The plasticizing effect of argon was found to increase the temperature dependence of the molecular correlation frequency.
Mechanism of formation of shish kebab structures
Authors: Nagasawa Toshio , Shimomura Yasushi
Published: April 2003

To describe the characteristic crystalline structure of polyolefins, Pennings first proposed a model consisting of a combination of an extended chain crystal (a “shish”) and folded chain crystals (“kebabs”). In Pennings' model the “shish” forms first during a crystallization process under stress and then later the “kebabs” overgrow this “shish” structure epitaxially. Because we had some doubts about such a mechanism, we undertook a series of experimental studies on linear polyethylene, particularly in regard to the crystallization process from a solution under shear. Our conclusion is that the crystals grow first by a screw dislocation mechanism, like whiskers, and then later these are deformed by the shear stress to form the shish kebab structures.
Crystallization kinetics of polyethylene under high pressure
Authors: Kyotani Mutsumasa , Kanetsuna Hisaaki
Published: April 2003

The kinetics of isothermal crystallization of polyethylene under high pressures ranging from 840 to 5300 kg/cm2 has been studied dilatometrically. The crystallization rate estimated from the half‐time of the overall transformation increases markedly with pressure. The Avrami exponent n becomes smaller with increasing pressure. Values of n ≈ 2 for the crystallization at 840 and 1950 kg/cm2, and n ≈ 1 at 5100 and 5300 kg/cm2 were obtained. Differential scanning calorimetry and electron microscopy data are presented. It is concluded that extended‐chain crystals grow rapidly, predominantly in one dimension, at high pressure. Relations between log k and Tm/T(ΔT) and Tm2/T(ΔT)2 are nearly linear. Here, k is the crystallization rate constant from an Avrami equation, ΔT = Tm – T, Tm is the melting point, and T is the temperature of crystallization. From the dependence of the slope of the straight line on the crystallization pressure it is concluded that the surface energy of crystal nuclei decreases with increasing pressure.
A systematic experimental study of moiré patterns in the electron image of solution‐grown polyethylene crystals
Authors: White J. R.
Published: April 2003

A systematic study of solution‐grown polyethylene crystals in the electron microscope using dark‐field imaging in several diffracted beams has warranted a detailed analysis of the moiré patterns recorded. Direct proof for the existence of tilt moiré patterns has been obtained for the first time, while parallel and tilt patterns have been positively distinguished. Consideration of the formation conditions and properties of moiré patterns in dark field has been extended to include interference between an electron beam diffracted in both participating crystals with one diffracted in only one of them. Examples of moiré patterns depending thus on double diffraction have been identified.
Pressure and temperature effects on the vibrational frequencies of crystalline polymethylenes. I. Infrared‐active rocking modes
Authors: Wu Che‐Kuang
Published: April 2003

The energy level dispersion, along the chain wave vector, of infrared‐active methylene rocking modes has been measured as a function of pressure to 40 kbar for a number of polymethylenes. They are crystalline polyethylene and n‐paraffins C23H48, C24H50, C28H58, and C29H60. The crystalline factor‐group splitting of each chain mode is observed at various pressures, for those polymethylenes which have orthorhombic or monoclinic structures. The effects of crystal structure, intermolecular force field and intramolecular force field on the observed energy levels as well as on the crystalline factor‐group splittings are discussed A hydrogen–hydrogen nonbonded repulsion potential has been calculated as a function of interatomic distance rH••H for 2.3 Å < rH••H < 3.0 Å from the observed volume dependence of the factor‐group splittings of methylene rocking modes. It is shown that the dynamic potential wells along the normal coordinates of the rocking modes are harmonic up to room temperature.
Morphology and fold length of single crystals in linear aliphatic polyesters
Authors: Kanamoto T.
Published: April 2003

The marked effects of chemical structure on the morphology of single crystals in linear aliphatic polyesters have been investigated. Drawn fibers and solution‐grown crystals of poly(ethylene sebacate), poly(hexamethylene sebacate), and poly(decamethylene 1,16‐hexadecanedicarboxylate) have been studied by small‐angle and wide‐angle x‐ray diffraction. Electron microscopy, and broadline NMR provided supplementary information.

The crystal disorder due to irregularity in the cross section of the molecule due to ester groups along the chain direction increases with increase of the methylene sequence length in the chemical repeat unit. On the basis of the x‐ray data and electron microscopy, it is proposed that the nature of the fold surface of single crystals of a given polymer, especially a choice of (001) or (hkl) fold surface (flat lamellae or hollow pyramidal crystals), is determined by energetic competition effects between fold geometry and unit cell symmetry. A smooth increase of the long period with increasing crystallization and annealing temperature seems to be general behavior even when a pronounced stepwise increase might be anticipated.
Morphology of polytetrafluoroethylene prepared by radiation‐induced emulsion polymerization
Authors: Seguchi Tadao , Suwa Takeshi , Tamura Naoyuki , Takehisa Masaaki
Published: April 2003

The original morphology of polytetrafluoroethylene prepared by radiation‐induced emulsion polymerization was studied by electron microscopy. The morphology depends on molecular weight, which in turn depends on polymerization conditions, especially the emulsifier concentration. The molecular weight decreases with increasing emulsifier concentration. The morphology changes with molecular weight roughly as follows: fibrils below 105, rods between 105 and 5 × 105, and granular particle above 106. The crystallinity is high for all morphologies.
Thermal activation parameters for large strain deformation of polyethylene and polycarbonate
Authors: Wu W. , Turner A. P. L.
Published: April 2003

Experiments were performed to determine the effects of strain rate, temperature, and pressure on the flow stress of polyethylene and Lexan polycarbonate deformed in shear. The results were analyzed to determine the activation enthalpy and the shear and dilatation activation volumes of the rate‐limiting mechanism of the deformation process. Results show that the activation event involves a volume containing several monomer units and that this volume must dilate by as much as 7% during the activation event. The activation enthalpy was approximately 2.5 × 10−12erg for polyethylene and 1.1 × 10−12erg for polycarbonate. The rate‐limiting mechanism for polyethylene seemed to be unchanged by plastic strains of up to 250%.
Non‐Newtonian behavior in steady flow over the range from the lower to the upper Newtonian region for polystyrene solution
Authors: Ito Yoshio , Shishido Shunsuke
Published: April 2003

Graessley's entanglement theory of viscosity modified by a frictional viscosity parameter ηfric is applied to data on solutions of polystyrene in diethyl phthalate at various concentrations and different temperatures. All the data modified give a single master curve over the entire rates of shear, as obtained previously with polydimethyl‐siloxanes of various molecular weights and their solutions of various concentrations. The zero‐shear viscosity η0, the upper Newtonian viscosity η∞, and ηfric are compared. Three activation energies for flow are estimated from η0, η∞ and ηfric, and are compared. The result suggests that the flow behavior in the upper Newtonian region is much more dependent on ηfric than on the entanglement viscosity term ηent. The ratio of zero‐shear entanglement viscosity ηent,0 to ηfric can be used as a measure of the non‐Newtonian behavior of the present solutions. Non‐Newtonian behavior of the investigated polymer solution becomes appreciable at about ηent,0/ηfric = 2.5. These results are in agreement with previous conclusions based on comparison between η0, η∞ and ηfric for polydimethyl‐siloxanes and their solutions.
Formation of kink bands by compression of the extrudate of solid linear polyethylene
Authors: Shigematsu Kazuyo , Imada Kiyohisa , Takayanagi Motowo
Published: April 2003

Extrudates of solid linear polyethylene prepared under proper pressure and temperature conditions have a high c axis orientation along the extrusion direction, with lamellar crystals and amorphous layers stacked alternately along the extrusion direction. Kink bands were formed by compressing the oriented extrudate at room temperature along the extrusion direction. Inspection of the kink bands by wide‐angle and small‐angle x‐ray diffraction and electron microscopy revealed that the fiber axis was rotated from the original axis direction by 70–75° and that the lamellar crystals were inclined to the fiber axis in the kink band by 55–60° and stacked nearly parallel to the kink boundary. The superstructural change during the formation of the kink band could not be interpreted in terms of uniform c axis shear alone. In addition to such a mechanism, it was necessary to take into account intermicrofibril and/or intercrystallite slip.
Deformational, swelling, and potentiometric behavior of ionized poly(methacrylic acid) gels. I. Theory
Authors: Hasa J. , Ilavský M. , Dušek K.
Published: April 2003

By using the model of a randomly coiled chain, a relation is derived describing the equilibrium stress–strain behavior of variously ionized polyelectrolyte gels swollen in solutions of a uni–univalent salt. The effect of the concentration of bound counterions calculated on the basis of the cylindrical model and the effect of the change of length of the statistical chain segment with the change in ionization of the gel on stress–strain, swelling, and potentiometric equilibria is discussed.
Pressure and temperature effects on the vibrational frequencies of crystalline polymethylenes. II. Lattice anharmonicity and the equation of state
Authors: Wu Che‐Kuange
Published: April 2003

The lattice anharmonicity of crystalline polymethylene is interpreted from the observed pressure and temperature dependence of Raman active interchain lattice frequencies of the n‐paraffins C23H48 and C44H90. The temperature dependence of the Lc′ interchain lattice frequency is separated into quasiharmonic and self‐energy shifts. The former is due to the volume dependence of the force constant of the oscillator. The latter is due to the anharmonicity of the dynamic potential, and is obtained as a function of volume and phonon population. The setting angle of the carbon skeleton is predicted to be temperature‐sensitive. While the potential surface of the crystal is asymmetric along the Lc′ normal coordinate, it is essentially symmetrical along the Tb′ coordinate.

The well‐known Mie–Gruneisen equation of state is generalized to include anharmonicities of oscillators through the temperature dependence of their vibrational frequencies.
Partial molar excess free enthalpies of n‐alkenes in apiezon M and alkanes in squalane and polydimethylsiloxane, and the solution theories of prigogine and flory: An investigation by gas chromatography
Authors: Hammers W. E. , Bos B. C. , Vaas L. H. , Loomans Y. J. W. A. , De Ligny C. L.
Published: April 2003

Partial molar excess free enthalpies (or excess chemical potentials) at infinite dilution were obtained over a large temperature range by gas chromatography. Data on n‐alkenes in Apiezon M are interpreted by the Prigogine–Patterson theory; data on normal and branched alkanes in squalane and polydimethylsiloxane (PDMS) are discussed in terms of the Prigogine–Patterson theory and the solution theory of Flory, Orwoll, and Vrij. For the alkane–PDMS systems heats of dilution and partial excess heat capacity data are given.

The aim of this work is to get some insight in the applicability of these solution theories to mixtures of fluids, the properties of which may slightly violate the basic assumptions of these theories. It is shown that orientational order in and a large cross‐sectional chain diameter of the polymer solvent do not affect their applicability to the partical molar excess free enthalpies of apolar mixtures, whereas large dissimilarities between the force fields around the segments of the mixture components and/or dissimilar chain flexibilities detract from the applicability of these theories (alkanes in PDMS).

Special attention has been paid to the effects of dissimilar size and shape of the segments of the mixture compounds on the magnitude of the interchange interaction parameter. It is shown that the multiple‐connected segment model after Lichtenthaler et al. does not warrant a reliable combinatorial contribution. Comparison of the interaction parameters obtained for n‐alkanes in n‐alkanes, Apiezon, squalane, and polyisobutylene and for branched alkanes in squalane reveals that the magnitude of this parameter is affected by small end‐effects due to the relative weakness of methyl‐methylene interactions.
A relationship between network chain concentration and time dependence of rupture for SBR vulcanizates
Authors: Fedors R. F. , Landel R. F.
Published: April 2003

The failure properties of crosslinked elastomers are influenced by variables such as the test rate, test temperature, chemical nature of the elastomers, degree of crosslinking, etc. For an elastomer with a fixed degree of crosslinkingthe time dependence of both the stress‐ and strain‐at‐break, when determined as a function of the test rate and test speed, can be correlated using a time–temperature shift such as the WLF aT shift factor. When a similar study is carried out with a sample having a different degree of crosslinking, the time dependence of both the stress‐ and strain‐at‐break is shifted along the time scale. It is demonstrated here that the time dependence of failure obtained as a function of the degree of crosslinking can be superposed on a master curve by the use of a time shift factor whose value depends directly on the degree of crosslinking.
Unperturbed dimensions of poly(9‐vinyladenine)
Authors: Kaye H. , Chou H. J.
Published: April 2003

The effect of base stacking interactions on the conformation of poly(9‐vinyladenine) (PVAd) was investigated by osmometry, intrinsic viscosity, and light‐scattering measurements. At neutral pH, ideal solution behavior (θ conditions) for this polymer was observed at 26 and 40°C. Intrinsic viscosity measurements revealed a conformational transition on heating from 26 to 40°C, while the ultraviolet absorbance of the solution was insensitive to the change. The transition was accompanied by an inversion in sign of the entropy parameter from negative to positive and an increase in the partial specific volume. At 40°, the variation of intrinsic viscosity with molecular weight corresponded to a random coil conformation, but the characteristic ratio, r̄02/nl2 = 8.6 ± 0.2 indicated that the unperturbed dimensions were smaller than usually observed for comparable vinyl polymers. At 26°, a rare macromolecular phenomenon was found, the intrinsic viscosity–molecular weight relation and the estimated r̄02/nl2 of 6.0–6.8 suggested that the PVAd was in a very highly compacted coil conformation, approaching a semirigid sphere. It is proposed that this effect be named the introversion phenomenon. Unlike polyadenylic acid, whose unperturbed dimensions increase with decreasing temperature due to nearest‐neighbor base stacking, the results reported here suggest that both nearest‐neighbor and long‐range intramolecular base stacking occur in PVAd. The different stereochemical arrangements of bases in PVAd and Poly A are probably responsible for the opposite behavior observed.
Transient and steady‐state water vapor permeation through polymer films
Authors: Hubbell W. H. , Brandt H. , Munir Z. A.
Published: April 2003

Water vapor transport properties for the polymers Kapton H

Reference to a company or product name does not imply approval or recommendation of the product by the University of California or the U.S. Atomic Energy Commission to the exclusion of others that may be suitable.

and Parylene C were determined over a temperature range of 20 to 55°C. Activation energies and entropies for permeation as well as partial molar free energies, heats, and entropies of dilution were calculated for water vapor concentrations ranging from 3 × 10−6 to 1 × 10−3 mole H2O per cm3 of polymer. Mylar A was tested to extend the available data for partial molar heats and entropies of dilution and to compare permeation and diffusion results with the corresponding values in the literature. Diffusion coefficients were measured using the time‐lag technique of Barrer but employing a modified test apparatus. Equilibrium sorption isotherms at 30°C were obtained for Mylar A and Kapton H with a Cahn microbalance. The ratios of the permeability to diffusion coefficients as measured from time‐lag experiments agreed with solubility coefficients within 3% for Mylar A and within 12% for Kapton H. Both polymers obeyed Henry's law. The results were interpreted in light of polymer polarity and morphology.
The growth of shear bands in polystyrene
Authors: Kramer Edward J.
Published: April 2003

Shear‐band growth velocities have been determined as a function of stress and temperature in polystyrene. The results demonstrate that shear bands can propagate under isothermal conditions; an adiabatic temperature rise at the shear band tip is not necessary for continued localization and growth of the band. The velocity is stress activated with a shear activation volume of 4600 Å3 and thermally activated with an activation enthalpy of 2.8 eV. Comparison of these values of the activation parameters with those for bulk shear flow in polystyrene indicates that the shear band propagation is controlled by the plastic strain rate of the glassy polymer immediately ahead of the tip of the band. Argon's molecular kink model of the elemental deformation process is consistent with measured values of the activation parameters whereas Bowden and Raha's dislocation model is not. The shear bands grow at an angle of ca. 38° to the axis of compression, and if the direction of compression is altered, the shear bands will change direction so as to maintain the 38° angle. Current explanations can not quantitatively account for the large deviation of the shear bands from the 45° plane of maximum shear stress.
ESR study of primary radical formation during mechanical degradation of poly(2,6‐dimethyl‐p‐phenylene oxide) solid
Authors: Nagamura Toshihiko , Takayanagi Motowo
Published: April 2003

Radical formation during mechanical degradation of solid poly(2,6‐dimethyl‐p‐phenylene oxide) (PPO) was investigated by electron spin resonance (ESR). The ESR spectrum of PPO fractured at room temperature in air consisted of eight lines with a separation of about 5.5 gauss with g = 2.0043, indicating a small asymmetry. For PPO fractured in liquid nitrogen, a similar spectrum was observed at −196°C in air or in vacuo. These spectra have been identified as belonging to a 2,6‐dimethyl‐substituted phenoxy radical and thus indicate the occurrence of main‐chain rupture. The phenyl radical which was expected to be formed together with a 2,6‐dimethyl‐substituted phenoxy radical could not be detected, but at temperatures below −46°C a small hump was observed at g = 2.034. By subtracting the spectrum observed after decay of this hump from the original one, the resulting curve was the characteristic asymmetric spectrum of a peroxy radical, which was presumably formed by the reaction between a phenyl radical and oxygen. The radical decay curve showed two stepwise‐decaying regions; one located in the temperature region between about −120°C and −80°C where only a small number of radicals decayed, another located in the temperature region from about −30°C to 100°C where almost all mechanically formed radicals decayed. The latter radical decay, which occurred considerably below the glass‐transition temperature of PPO, was attributed to the molecular motions associated with the mechanical β* relaxation on the basis of the activation energy and the temperature region.
Mechanical behavior of SBR–glass bead composites
Authors: Fedors R. F. , Landel R. F.
Published: April 2003

The mechanical properties of crosslinked SBR containing varying amounts of a glass bead filler have been studied. It is shown that the stress–strain response at a given test rate and temperature can be rationalized provided dewetting around the glass bead filler is taken into account. Direct measurements of the volume dilatation as a function of both strain and filler content have been obtained. This information in conjunction with the model proposed herein has been used to satisfactorily reproduce the stress–strain curves to strains up to about 200%. It is also shown that at the break point complete dewetting has occurred so that the rupture properties of the filled are the same as that of the unfilled gum. This was found to be true for all temperatures and rates studied.
Crystallization of polystyrene–poly(ethylene oxide) multiblock copolymers
Authors: Shimura Yukio , Hatakeyama Tatsuko
Published: April 2003

The heat of fusion of poly(ethylene oxide) blocks has been measured by DSC on twelve polystyrene–poly(ethylene oxide) multiblock (AB)n copolymers and two ABA triblock copolymers after conditioning at various times and temperatures. Regardless of the length of polystyrene blocks, copolymers with poly(ethylene oxide) blocks with M̄n = 404 showed no heat of fusion, those with M̄n = 900 almost no peaks, those with M̄n = 1960 small broad peaks, and those with M̄n = 5650 clearly observable peaks. the greatest heat of fusion measured for block copolymers was 60–70% of the value for hompolymer. Small‐angle x‐ray patterns are given. The relation between crystal growth and block length is discussed.
Dynamics of macromolecular chains. I. Theory of motions on a tetrahedral lattice
Authors: Valeur Bernard , Jarry Jean‐Pierre , Geny François , Monnerie Lucien
Published: April 2003

The bond correlation function for a macromolecular model chain on a tetrahedral lattice is derived by considering elementary three‐bond and four‐bond motions. The method of calculation allows the conformational structure of the chain to be involved in the final equations. Moreover, when the three‐bond motions are considered alone, no linearization assumption is required; hence, the theory is valid at short times.
The elastic free energy and the elastic equation of state: Elongation and swelling of polydimethylsiloxane networks
Authors: Flory Paul J. , Tatara Yoh‐Ichi
Published: April 2003

The elastic free energy for a tetrafunctional network is here expressed as

where λ1, etc., are the principal extension ratios relative to the state of reference (wherein 〈r2〉 = 〈r2〉0), and C1, C2, and m are arbitrary parameters. The free energy of a swollen system is taken to be the sum G = Gmix + Gel of Gel and the free energy of mixing \documentclass{article}\pagestyle{empty}\begin{document}$ G_{{\rm mix}} = RT\left[ {n_1 \ln v_1 + n_2 \ln v_2 + \bar \chi n_1 v_2 } \right] $\end{document}. Stress‐strain relations and the chemical potential μ1 are derived from G as functions of the elasticity parameters C1, C2, and m, and of the thermodynamic interaction parameter χ or of \documentclass{article}\pagestyle{empty}\begin{document}$\chi = \bar \chi + n_1 v_2^{ - 1} \partial \bar \chi /\partial n_1 $\end{document}. The dilation of the semi‐open system subject to deformation when exposed to diluent at fixed activity is derived as the sum of the dilation at fixed composition and the dilation due to absorption of diluent. Experiments are reported on the dependence of the equilibrium retractive force on elongation for cross‐linked polydimethylsiloxanes (PDMS) exposed to benzene or hexamethyldisiloxane vapor at regulated activities. Volume fractions of samples covered the range v2 = 1.00 to v2 ≈ 0.30. With the choice of m = ½ the elastic behavior of a given polymer is well represented by one combination of values for C1 and C2 at all dilutions by either diluent. The dependence of the Mooney‐Rivlin (C2) term on volume is thus established, at least for PDMS, and the scope of the semi‐empirical free energy expression and its consequents is greatly enlarged. Values of χ deduced from the equilibrium swelling of the unstrained networks exposed to benzene at various activities are in excellent agreement with those obtained previously from vapor pressures and osmotic pressures on linear PDMS. The results of Allen, Kirkham, Padget, and Price on the elastic behavior of natural rubber are discussed, with particular reference to the coefficients of dilation with elongation which they determined at fixed composition. The present results lend strong support to the principle of additivity of the free energies attributable to the network and to the bulk liquid system, respectively. This principle is fundamental to the analysis of rubber elasticity.
Viscoelastic behavior of glass‐bead filled crosslinked polymers in the dry and swollen states
Authors: Acierno D. , Nicolais L. , Vojta V. , Janáček J.
Published: April 2003

Stress relaxation and moduli of elasticity of the composite system crosslinked poly(2‐hydroxyethyl methacrylate) (PHEMA)–glass beads were studied dry and swollen in water to equilibrium state over the temperature range 5–170°C. The moduli of the composites in the dry state increased with increasing filler concentration, while those of the composites measured in the swollen state up to the volume concentration of the filler v ≅ 0.15 decreased. In this respect the composites behaved as porous systems, i.e., as polymers with macroscopic defects. This effect was explained as a consequence of weak filler–matrix interaction. The results were compared with the existing theories of moduli of the composite materials.
Determination of the coefficients of selective sorption in the system polymer–ternary solvent by the density and refractive index increments method
Authors: Stejskal Jaroslav , Kratochvíl Pavel
Published: April 2003

The method of density and refractive index increments was used for the determination of the coefficients of selective sorption of acetophenone and bromoform on polymer in the system poly(methyl methacrylate)–isopropanol–acetophenone–bromoform as a function of the composition of the ternary solvent. In systems containing more than 80% by volume of bromoform the precipitant—isopropanol—is selectively sorbed. The conditions under which the method gives satisfactory results and some methodological problems of densitometry have been discussed.
Relaxation spectra of concentrated polystyrene solutions
Authors: Osaki Kunihiro , Fukuda Mitsutoshi , Kurata Michio
Published: April 2003

The relaxation modulus G(t) and the stress decay after cessation of steady shear flow were measured on concentrated solutions of polystyrenes in diethyl phthalate. Ranges of concentration c and molecular weight M of the polymer were from 0.112 to 0.329 g/ml and from 1.23 × 106 to 7.62 × 106, respectively. The relaxation spectrum H(τ) as calculated from G(t) for the solution of very high M was found to be composed of two parts. One, at relatively short times, was a broad distribution (plateau zone) with height proportional to c2. The second, at the long‐time end, was very sensitive to concentration and gave rise to a maximum in H(τ) for very high concentrations. The behavior of H(τ) at long times was examined quantitatively by evaluating the longest relaxation time τ10 and the corresponding relaxation strength G10 from G(t) and from the stress decay function, on the assumption of a discrete distribution of relaxation times at long times. The longest relaxation time was approximately proportional to M3.5, even at relatively low concentrations where the zero‐shear viscosity was not proportional to M3.5. The strengths of relaxation modes with the longest few relaxation times are proportional to the third power of concentration.
Fourier transform infrared study of the effects of irradiation on polyethylene
Authors: Tabb D. L. , Sevcik J. J. , Koenig J. L.
Published: April 2003

Fourier transform infrared spectra have been obtained for polyethylene irradiated in oxygen and nitrogen atmospheres. The spectra before and after irradiation have been compared by digital subtraction. The difference spectra are indicative of changes caused by irradiation. Crosslinking and chain scission reactions produce the observed changes.
Persistent polarization in poly(vinylidene fluoride). I. Surface charges and piezoelectricity of poly(vinylidene fluoride) thermoelectrets
Authors: Murayama Naohiro
Published: April 2003

Persistent polarization in poly(vinylidene fluoride) (PVDF) thermoelectrets prepared under high electric field strengths has been studied by measurements of surface charge and piezoelectricity. An anomalous heterocharge appears after the normal homocharge disappears. A model is proposed to explain the surface charge phenomena; the anomalous heterocharge is expressed as a sum of a hidden homocharge and a hidden heterocharge. It is concluded that the anomalous heterocharge as well as the apparent homocharge are not responsible for the piezoelectricity of PVDF electrets. The piezoelectricity is shown to depend on the structure of the original PVDF films or the amount of β‐form crystals. However, the piezoelectricity is not attributed to stress dependence of the spontaneous polarization in the β‐form crystal of PVDF, but to the hidden polarization which bring about the anomalous heterocharge. The hidden polarizations are attributed to trapped charges.
Degrees of order from X‐ray diffraction in highly crystalline poly(vinyl chloride)
Authors: Gouinlock E. V.
Published: April 2003

Convenient x‐ray diffraction instrumentation for assessing PVC order is described. A reflectance diffractometer, copper radiation, a monochromator, and a proportional detector are used to make measurements on low molecular weight, highly crystalline PVC prepared using chain‐transfer agents. Interpretation includes a correction for air scattering, employment of a trimodal noncrystalline pattern, and the calculation of crystallinity from the ratio of the crystalline to the total integrated intensity. The results are reasonably insensitive to the assumptions made. The noncrystalline pattern used is taken to indicate a single, partially ordered mesomorphous phase. A whole polymer prepared in the presence of butyraldehyde, a fraction therefrom prepared by precipitation, and a similar fraction terminated by butyl mercaptan have similar molecular weights (M̄n ca. 1600) and crystallinities of 30, 44, and 44%, respectively. Fractionation apparently effects a separation with respect to syndiotactic content, and the resultant crystallinity appears to be the highest valid x‐ray value reported to date for a PVC polymer, irrespective of polymerization variables, fractionation procedure, or molecular weight. The order in these polymers is due in part to their greater syndiotacticity (about 64% for the fractions by 13C NMR spectroscopy), although a more favorable tactic placement distribution may be involved in addition to a possible effect of molecular weight itself.
Dielectric study of relaxations and polymorphism in poly(diethyl siloxane)
Authors: Pochan J. M. , Beatty C. L. , Hinman D. D. , Karasz F. E.
Published: April 2003

The dielectric behavior of poly(diethyl siloxane) supports the adiabatic calorimetric findings of Beatty and Karasz. In particular, a sub‐Tg transition is observed near −180°C at 100 Hz, the glass transition near −135°C at 100 Hz, and a first‐order transition near −70°C (crystal–crystal transformation). This glass‐transition temperature is the lowest reported polymeric glass transition for polymers.
Polymerization mechanisms and molecular weight distribution. I. Mathematical treatment
Authors: Braks Jorma G. , Huang Robert Y. M.
Published: April 2003

A novel method for determining the polymerization mechanism and the kinetic rate constants from the molecular weight distribution is proposed. The particular criterion function used as basis for parameter adjustment is

where θ is the vector of dependent variables, y(r, θ) is the theoretical molecular weight distribution for the assumed polymerization mechanism, and yE(r) is the experimental molecular weight distribution which is a function of the chain length r. A form of the gradient method of optimization was used to solve the criterion function. The proposed method is particularly powerful since the whole molecular weight distribution is utilized.
Effects of annealing and isothermal crystallization upon crystalline forms of poly(vinylidene fluoride)
Authors: Osaki Shigeyoshi , Ishida Yoichi
Published: April 2003

Poly(vinylidene fluoride) exists in three crystalline forms. Optimum conditions for preparing form III were established by infrared spectroscopy, differential scanning calorimetry, and x‐ray diffraction measurements. Form III is easily obtained by annealing mats of solution‐grown crystals of form II at 175–185°C and is also preferentially formed by isothermal crystallization from the melt between 165 and 175°C. Below 165° crystallization of form II is favored. The melting point of form III is higher than that of form II.
Rheology of dispersions of swollen gel particles
Authors: Taylor N. W. , Bagley E. B.
Published: April 2003

A centrifugal technique was used to determine the swelling, Q (g swollen gel/g dry polymer), of crosslinked polyacrylate gel particles in water. Both centrifugal force and time of centrifugation affected the magnitude of Q but under constant centrifuge conditions it was found that Q−1 was proportional to μ1/2, μ being the ionic strength. The viscoelastic properties of water dispersions of these gel particles were measured as functions of concentration and ionic strength. Viscosity data were reducible to a normalized master curve by plotting (ηsp/cr) versus cr, where cr is a reduced concentration defined as cQ. Values of shear modulus, G, computed from the first normal stress difference measured at various concentrations and ionic strengths also fell on a single curve when plotted against the reduced concentration, cQ. Comparison of these results with those obtained earlier on a similar polyacrylate dispersion, but one in which as much as 20% of the polyacrylate is in a soluble, uncrosslinked form, shows that the soluble fraction has little effect on the magnitude of the viscosity and, moreover, that the presence or absence of the soluble fraction does not affect the transient stress overshoot phenomenon. As in the earlier work, high absolute values of viscosity occur when cQ ≧ 1, that is when the dispersion consists of close‐packed deformable gel particles in intimate contact with little or no interstitial solvent present.
A normal coordinate analysis of trans‐1,4‐polychloroprene
Authors: Tabb D. L. , Koenig J. L.
Published: April 2003

The fundamental vibrational frequencies of an isolated chain of trans‐1,4‐polychloroprene have been calculated. The agreement between the calculated and experimentally observed crystalline frequencies supports the molecular model for the structure of trans‐1,4‐polychloroprene and the force field employed in the calculations. The results of the normal coordinate analysis indicate that there is essentially no coupling between adjacent translational repeat units of trans‐1,4‐polychloroprene.
Photoconduction in polyolefins and in poly(ethylene–carbon monoxide)
Authors: Chan G. Y. C. , Wintle H. J.
Published: April 2003

The ultraviolet photoconductivity of high‐density polyethylene, polypropylene, and poly(ethylene–carbon monoxide) has been studied in the range 360–180 nm. The response of the polyolefins is similar to that found in low‐density polyethylene both in spectral distribution and in time behavior, with hole injection setting in at 3.7 eV. There is evidence also of electron injection in polypropylene at 4.5 eV and higher energies. A copolymer containing 0.5% CO is similar except that the hole threshold is at 4.2 eV, but a 1% CO copolymer shows marked differences, with electron injection being dominant. It is suggested that the change is due to a shift in the Fermi level rather than direct excitation of electrons from carbonyl groups, but some inconsistencies remain in this model.
Driving force for hydraulic and pervaporative transport in homogeneous membranes
Authors: Paul D. R. , Paciotti J. D.
Published: April 2003

Experiments were designed to demonstrate that the chemical potential gradient required for liquid transport through swollen network polymer membranes manifests itself as a concentration gradient and that the rate of transport is independent of how this gradient is established. The fluxes of various liquids through a crosslinked rubber membrane were measured in hydraulic and pervaporation modes of permeation. The pressure applied downstream in the latter act simply to fix the activity of the liquid in the downstream membrane surface. The experiments show the flux is a unique function of this activity, and it does not matter how it is established. Sorption data were used to convert these results into a plot of flux versus concentration differential across the membrane which was analyzed by Fick's law using a model for the concentration dependence of the diffusion coefficient. Measured ceiling fluxes for pervaporation for a number of liquids were found to be the same as those estimated from hydraulic permeation data. A simple mathematical representation for an ideal system is used as a pedagogical device to demonstrate the conclusions.
Nucleation and growth of crazes in amorphous polychlorotrifluoroethylene in liquid nitrogen
Authors: Brown Norman , Fischer S.
Published: April 2003

The density of mature crazes initially increases linearly with stress and then more rapidly at higher stresses. Once the crazes become observable then density was independent of time. The lowest stress at which an appreciable density of crazes was produced corresponds to the proportional limit. The average velocity of mature crazes was constant for a given stress and varied exponentially with the stress. The velocity depended on stress in the same way that the post‐yield point stress depended on strain rate, whereas the yield point varied differently being a nonlinear function of the logarithm of the strain rate.

The density of crazes was quantitatively related to the concentration of surface defects at which the crazes nucleate. The craze velocity was directly related to the diffusion coefficient of N2into the polymer. The analysis indicates that bulk diffusion of the N2governs the craze velocity and that plasticization of the tip of the craze is most important for the nucleation and growth of a craze in PCTFE.
Effect of internal field on the birefringence of polyethylene crystals and on the anisotropy of polymer chains. I. Birefringence effects
Authors: Hong S. D. , Chang C. , Stein R. S.
Published: April 2003

Values of the anisotropy of polarizability of methylene groups deduced from the refractive indexes of n‐paraffin crystals differ appreciably from those obtained from gas‐ or liquid‐phase measurements. The differences is attributed to the erroneous application of the Lorenz—Lorentz internal field to the anisotropic n‐paraffin crystal. A more detailed calculation of the internal field is carried out by detailed summation of the dipolar field over an idealized n‐paraffin crystal in which the molecular chains are replaced by anisotropic rods. With reasonable values of parameters and assumed crystal shape, the discrepancy in polarizability anisotropy is resolved.