bluuebunny/crossref_metadata_2025 huggingface dataset:
High‐resolution electron microscopy of polyethylene and paraffin crystals: Stability in the electron beam
Authors: Giorgio S. , Kern R.
Published: April 2003

Uncollapsed polyethylene pyramids (200–1500 Å) in length are irradiated with the electron beam of a 100‐kV transmission electron microscope. Their high stability is remarkable compared to the stability of 1–10 μm crystals collapsed on the substrate, usually taken as a reference. Therefore, the maximum magnifications (300,000–750,000 X) of the microscope can be used and high‐resolution images can be obtained. No lattice defects can be detected in the images of PE pyramids. Irradiation with Dc > 800 C/m2 induces the orthorhombic → hexagonal transition, and slight lattice distortions appear in the high‐resolution image of the hexagonal phase. For an irradiation dose Dc ≈ 2400 C/M2, the diffraction pattern disappears. Normal C36 orthorhombic and monoclinic paraffins have the same stability as orthorhombic PE and high‐resolution patterns are obtained. These exceptional stabilities are discussed in detail. From the diffraction pattern of these uncollapsed pyramids, the fold surfaces of PE pyramids have been indexed as the {111} and paracrystalline distortions in the orthorhombic PE have been measured at low irradiation dose. Along the a and b axes g is ca. 5% and along the chain axis c it is ca. 17%; these values agree with the previous x‐ray determinations of PE crystallized from the melt. The large difference between these two distortion factors may be interpreted in terms of packing.
The dynamics of mechanical relaxation in polyisobutylene
Authors: Hill R. M. , Dissado L. A.
Published: April 2003

The published data on the mechanical response of a set of samples prepared from a single batch of polyisobutylene have been examined and three relaxation/retardation processes have been characterized in the temperature region above the glass transition temperature. It is shown that the time/frequency dependences can be explained in terms of the cooperative theory of relaxation/retardation. It is also shown that the values of the fractional power‐law indices of relaxation/retardation, which are a characteristic feature of the cooperative approach, are independent of the technique used in their observation.
X‐ray scattering from amorphous acrylate and methacrylate polymers: Evidence of local order
Authors: Miller Robert L. , Boyer Raymond F. , Heijboer J.
Published: April 2003

X‐ray scattering patterns from amorphous polymers frequently contain halos corresponding to distances significantly greater than that of van der Waals packing of carbon atoms. Regularities in the positions of such halos as a function of pendant group size have been reported, primarily for the “crystallizable” comb polymers. This work concerns n‐alkyl acrylate, n‐alkyl methacrylate, and cycloalkyl methacrylate polymers with small alkyl groups: regularities in halo position with alkyl group size are seen, but the behavior with size is quantitatively different from that of the comb polymers. A case is made for the existence of a moderate amount of intersegmental order as the normal condition in the condensed amorphous state. The behavior of poly(methyl methacrylate) is anomalous and studies on it may not be used to generalize about the structure of the amorphous state.
Interactions of a sulfonated ionomer with surfactant in nonaqueous media
Authors: Peiffer D. G. , Lundberg R. D.
Published: April 2003

The viscometric behavior of dilute solutions of the sodium salt of sulfonated polystyrene (0–6 mol % sulfonation level), with and without surfactant, is investigated to determine the extent of interaction as the structure of the solvent surfactant, and polymer concentration is varied. Reduced viscosity measurements confirm that formation of a polymer–surfactant complex in a relatively polar solvent is controlled to a large extent by charge–charge and hydrophobic forces. The magnitude of these specific interactions is dependent upon the relative polarity of the solvent medium. In a polar solvent, such as dimethylsulfoxide, the hydrophobic forces are strong enough to prevent expansion of the polymer chain at all surfactant concentrations studied. However, in a less polar medium (as in dimethylformamide) the hydrophobic forces are weaker and cannot prevent some chain expansion. It is interesting to note that in this solvent the polystyrene–cationic surfactant complex exhibits a polyelectrolyte effect. Finally, in a lower‐polarity medium (cyclohexanone) where the hydrophobic forces are weak, solution behavior is dominated by the interaction of the surfactant with the intramolecular sulfonate ion‐pair aggregates.
EXAFS analysis of the structure of ionomer microdomains
Authors: Yarusso D. J. , Ding Y. S. , Pan H. K. , Cooper S. L.
Published: April 2003

Extended x‐ray absorption fine‐structure (EXAFS) measurements were used to determine the near‐neighbor environment of the neutralizing cation in several ionomer system. The observed structure is compared to that existing in analogous low‐molecular‐weight crystalline salts. A wide variety in the degree of local order was observed between different systems even though all exhibit similar small‐angle x‐ray scattering curves indicating the existence of ionic microdomains.
Analysis of the hysteresis curve of ferroelectric polymers by a phenomenological relaxation theory
Authors: Jimbo Masashi , Kobayashi Shin'ichi , Horino Kaoru , Ikeda Susumu , Wada Yasaku
Published: April 2003

A simple relaxation theory for the displacement versus electric field hysteresis of ferroelectric polymers is developed in which the relaxation time is assumed to be a function of electric field, as has been experimentally evidenced by polarization‐reversal switching. The theory gives an analytical expression for the hysteresis curve. The coercive field Ec predicted by the theory agrees well with data on Ec as a function of temperature for poly(vinylidene fluoride) from −60 to 20°C and with data on Ec as a function of frequency for vinylidene fluoride/trifluoroethylene copolymer (73/27 molar ratio) at 20°C over the range 0.01–0.7 Hz.
High‐temperature aging of Halar film. II. Analysis of melting behavior
Authors: Khanna Y. P. , Turi E. A. , Sibilia J. P.
Published: April 2003

Melting behavior of an experimental Halar film, a predominantly alternating 1:1 copolymer of ethylene (E) and chlorotrifluoroethylene (CTFE), has been studied. Differential scanning calorimetry (DSC) reveals single or double melting peaks, depending upon the thermal history. The lower‐temperature melting peak Tm1 is produced only by the thermal treatment and shows a strong dependence on annealing time and temperature. On the basis of the DSC and x‐ray data it can be suggested that Tm1 represents the melting of relatively small crystallites formed upon annealing. The higher‐temperature melting peak Tm2 is always shown at 238°C. (Note: the specification for commercial Halar product is 240°C. The slightly lower melting temperature reported in this study is probably due to the fact that we are dealing with an experimental melt‐processed material.) On the basis of the heating rate study we propose that Halar crystallizes with stable crystals (Tm2 = 238°C) regardless of the crystallization conditions, i.e., quenching, slow cooling, or even annealing. Crystals of Halar have a heat of fusion of approximately 35 cal/g or 146 kJ/kg. Detailed analysis of the melting behavior of Halar is presented.
Comparison of two models for local chain motion
Authors: Lin Y.‐Y. , Jones A. A. , Stockmayer W. H.
Published: April 2003

A connection is presented between the Jones–Stockmayer solution to the three‐bond‐jump equation for local motion and the new correlation function developed by Hall and Helfand. Both correlation functions are based on a diffusional picture for cooperative local motions which allows for the development of a relationship between them. Numerical fits of the Hall–Helfand function to the Jones–Stockmayer function are also given for both the time and frequency domain; these numerical fits are consistent with the analyses of NMR data by both models. The fits and the analyses set a likely range for converting the correlation time of the three‐bond jump to the correlation time for the cooperative transitions in the Hall–Helfand model.
Thermally induced cholesteric‐isotropic transition in lyotropic polypeptide liquid crystals
Authors: Subramanian R. , DuPré D. B.
Published: April 2003

The thermally induced cholesteric to isotropic transition of lyotropic polybenzylglutamate liquid crystals in six solvent combinations was examined optically. The solvents chosen for study support both low and high pitch values, positive and negative pitch temperature coefficients, and polypeptide denaturation. The biphasic zone below the clearing temperature is broad and solvent dependent. Unusual large‐scale phase separations and solution morphologies occur in some solvents. No evidence was found for pretransitional chiral orientational ordering near the clearing point in the high‐temperature isotropic phase.
Evidence for clustering inN‐butyl methacrylate ionomers as shown by thermally stimulated currents
Authors: Vanderschueren J. , Aras L. , Boonen C. , Niezette J. , Corapci M.
Published: April 2003

The relaxation behavior ofn‐butyl methacrylate/methacrylic acid (MAA) copolymers (12 mol % MAA) and their alkaline salts (K, Li) with various degrees of neutralization was investigated from 77 to 400 K by means of thermally stimulated depolarization and polarization methods. For degrees of neutralization higher than 50%, the experimental results were found to be consistent with the existence of complex heterophase structures involving significant widening of the distribution function of relaxation times in the glass transition region, splitting of the side‐chain transition in several discrete relaxation components, and formation of ionic cluster giving rise to their own relaxation process. By systematically studying the influence of polarization conditions, it was also shown that the appearance and stability of such clusters are markedly dependent on the thermal and electrical history of the samples and that the clustering relaxation is closely related to the ionic conductivity via space‐change formation.
Comments on “some evidence against the existence of the liquid–liquid transition. III. The evaluation of the TLL event by differential scanning calorimetry”
Authors: Boyer Raymond F.
Published: April 2003

The volatile‐component evaporation mechanism proposed by Chen et al. to explain molecular‐weight‐dependent endothermic peaks found at temperatures above Tg in anionically prepared polystyrenes (PSs) on first heating in open DSC pans is inconsistent with several bodies of literature data which were overlooked, including similar data with closed DSC pans. Moreover, this mechanism appears deficient in explaining details of the dependence of the endothermic peak temperature on M̄n both below and above the entanglement molecular weight Mc, with a sharp increase in slope at Mc. The original fusion–flow mechanism of Stadnicki et al. is compatible with all other known literature data including results on thermal PS and PMMA fractions. Hot‐stage microscope examination of powdered anionic PSs supports the Stadnicki mechanism from M̄n = 1900 to at least M̄n = 350,000. Addition of small amounts (ca. 1 wt %) of benzene or ethylbenzene to PS results in open‐pan DSC traces without endothermic peaks but with an endothermic slope change indicating gradual loss of diluent at decreasing rate as the temperature is increased from below Tg up through the TLL region.
Rebuttal to “comments on ‘some evidence against the existence of the liquid–liquid transition. III. The evaluation of the TLL event by differential scanning calorimetry’ ”
Authors: Chen J. , Kow C. , Fetters L. J. , Plazek D. J.
Published: April 2003

It is proposed here that readily observable viscous deformation is the common underlying phenomenon which is reflected in several kinds of evidence advanced for the existence of a liquid–liquid transition TLL. These include flow temperature Tf measurements, microscope hotstage coalescence, and differential scanning calorimetry (DSC) measurements. A DSC peak observed at Tg in high‐molecular‐weight bulk‐polymerized poly(methyl methacrylate) is discussed in terms of the presence of conformations of low entropy.
A pulsed NMR study of the effects of initial morphology on the structure of extrusion‐drawn poly(ethylene terephthalate)
Authors: Ito Masayoshi , Kanamoto Tetsuo , Tanaka Koji , Porter Roger S.
Published: April 2003

Proton spin–spin relaxation times and the Weibull coefficient have been measured as functions of temperature for poly(ethylene terephthalate) (PET) drawn at 50°C in both the amorphous and the semicrystalline (50%) states. Two relaxation times T2a (long) and T2c (short) are observed for all samples. They are ascribed, respectively, to the relaxation of the amorphous and of the crystalline components including highly strained noncrystalline segments. Effects of initial morphology are found for chain mobility in the noncrystalline regions and for the crystal perfection, evaluated from T2a and the Weibull coefficient μc of the T2c‐component, respectively. For all draw ratios, T2a for extrudates prepared from the semicrystalline polymer (C‐50) is short compared to that for preparations from the amorphous (A‐50) polymer. In the A‐50 samples, the perfection of stress‐induced crystals increase with increasing draw ratio. In the C‐50 samples, the crystal orientation increases, whereas the perfection decreases with increasing draw ratio. To improve the crystal perfection, annealing at higher temperature or longer time is required for C‐50 as compared with A‐50. The value of μc correlates well with the change in crystal perfection during deformation and annealing.
Electrical and differential scanning calorimetry studies of poly(ethylene oxide) complexed with alkaline‐earth thiocyanates
Authors: Fontanella John J. , Wintersgill Mary C. , Calame J. P. , Andeen Carl G.
Published: April 2003

Audio‐frequency dielectric relaxation measurements and differential scanning calorimetry studies have been performed on poly(ethylene oxide) (PEO) complexed with calcium and barium thiocyanate. The measurements were performed over the temperature range 5.5‐300 K. The relaxation spectrum for the complexed material consists of two peaks. The activation enthalpy for the peak corresponding to the γ relaxation of pure PEO depends upon the size of the dopant cation. The activation enthalpy for the second peak is independent of the nature of the dopant cation and is very similar to that observed for the αc relaxation observed in pure PEO. Furthermore, the room‐temperature electrical conductivity of the complexed materials is much smaller than that for pure PEO and hence very much less than for PEO‐complexed with alkali‐metal salts. However, above Tg the conductivity rises rapidly and is larger for the barium‐thiocyanate‐complexed PEO than for the calcium‐complexed material. Finally, the DSC studies show that one effect of the ions is to shift the glass transition to higher temperatures.
The effect of transcrystallinity on the behavior of fibers in polymer matrices
Authors: Huson M. G. , McGill W. J.
Published: April 2003

Single copper fibers embedded in a polypropylene matrix along part of their length will, on application of a tensile load, break in the absence of transcrystallinity adjacent to the fiber, or pull out of the polymer matrix in the presence of a transcrystalline zone. It is shown that the transcrystalline zone allows thinning of the fiber in the matrix up to the point at which compressive forces created by the shrinkage of the polymer around the fiber on cooling are removed and fiber pullout occurs.
Molecular weight dependence of healing and brittle fracture in amorphous polymers above the entanglement molecular weight
Authors: Adolf Douglas , Tirrell Matthew , Prager Stephen
Published: April 2003

A model based on chain entanglements is developed to predict the molecular weight dependence of the fracture stress for brittle, amorphous polymers. It is then used in conjunction with the reptation model of polymer diffusion to predict the time and molecular weight dependence of the fracture stress in the closely related healing problem. Theoretical predictions are found to be in close agreement with experimental data.
Investigation of ion binding in ionic polysaccharide solutions using Tb(III) as a luminescent probe
Authors: Crescenzi V. , Brittainc H. G. , Yoshinoc N. , Okamoto Y.
Published: April 2003

The luminescence properties of a series of lanthanide‐substituted ionic polysaccharides have been examined in an attempt to learn about the nature of interactions between the metalions and the polymers. Emission and excitation spectra were obtained for Tb(III) complexes with carboxymethyl cellulose, Sclerox S‐1.0, alginate, polygalacturonic acid, amylose sulfate, dextran sulfate, and i‐carrageenan. Studies of the chirality associated with the metal‐ion binding sites were performed through the use of circularly polarized luminescence spectroscopy. It was learned that the lanthanide ions could form complexes with polysaccharides in the electrostatic manner of polyelectrolytes, and that specific ligating groups could further influence the metal‐ion binding characteristics.
The thermal diffusivity of natural rubber
Authors: Brown R. A. , Yahya Razak Abd. Samad Bin
Published: April 2003

Measurements of thermal diffusivities of peroxide‐cured and sulfur‐cured rubbers, over the range 0–100°C and 0–75 phr of carbon, are described. They are based on the asymptotic time dependences of heating and cooling curves, recorded following quenching of the samples into baths at various temperatures. The diffusivities are shown to depend linearly on both temperature and carbon content, to reasonable accuracies over the ranges studied. Some theory bearing on measurement techniques is presented.
Model copolymers of ethylene with butene‐1 made by hydrogenation of polybutadiene: Chemical composition and selected physical properties
Authors: Krigas T. M. , Carella J. M. , Struglinski M. J. , Crist B. , Graessley W. W. , Schilling F. C.
Published: April 2003

Hydrogenation of polybutadienes with from 8 to nearly 100% vinyl content was used to prepare a series of model copolymers of ethylene and butene‐1 with uniform microstructures and narrow molecular weight distributions. They range from readily crystallizable to completely amorphous, depending on the frequency of ethyl side branches (2–50 per 100 skeletal carbons). Melting temperature, secondary transition temperature, density, plateau modulus for the melt, and elastic modulus for the solid were obtained as functions of branch content. The effect of crystallinity on the secondary transition and modulus of the solid is discussed.
Phase transitions in mesophase macromolecules. V. Transitions in poly(oxy‐1,4‐phenylene carbonyl‐co‐oxy‐2,6‐naphthaloyl)
Authors: Cao Miao‐Yong , Wunderlich Bernhard
Published: April 2003

The copolymer system HBA (4‐hydroxybenzoic acid) and HNA (2,6‐hydroxyhaphthoic acid) has been studied mainly by means of differential scanning calorimetry. Heat capacities for the two homopolymers and three copolymers are reported from 175 to 650 K. The heat capacities are additive with composition. The whole copolymer system represents an example of a mesophase intermediate between the liquid‐crystalline and the condis‐crystalline state with a small amount of crystallinity. The disordering transitions (520–620 K) have a eutecticlike phase diagram. The transitions to the isotropic states occur above the decomposition temperatures (600–700 K). The glass transitions (377–434 K) show normal changes in heat capacity (31–34 J/K mol), but are broadened to as much as 200 K.
The effect of pressure on the mechanical properties of polymers. IV. Measurements in torsion
Authors: Moonan W. K. , Tschoegl N. W.
Published: April 2003

Stress relaxation was studied in torsion under superposed hydrostatic pressure using a newly constructed device. Two materials, a styrene–butadiene rubber and a butadiene rubber, were studied in the range from −60 to 30°C at pressures up to 500 MPa. The time–temperature–pressure superposition of the data can be described by the FMT form of the free‐volume theory which uses input from relaxation experiments at high pressure. The applicability of the Havlíček–Ilavský–Hrouz form of the Adam–Gibbs theory was also examined. This theory, which does not require information from high‐pressure relaxation experiments, offers less flexibility than the FMT theory and is less successful in predicting superposition. The data are also examined in light of an adaptation of the Simha–Somcynsky equation of state to the free‐volume theory. Prediction of the effect of pressure by the theory requires a single adjustable parameter. It was possible to calculate the free‐volume parameters of several polymers without use of information from high‐pressure experiments.
Crystallization in oriented poly(ethylene terephthalate) fibers. I. Fundamental aspects
Authors: Desai P. , Abhiraman A. S.
Published: April 2003

The nature of crystallization‐ and mobility‐induced changes during annealing of melt‐spun poly(ethylene terephthalate) precursor fibers of a range of orientations has been examined. The kinetics of crystallization and the accompanying orientational changes have been studied under conditions of constant, low tensile stress, with the accompanying dimensional changes and under a constraint against shrinkage in length, with the stress developed being monitored. The effects of precursor orientation and externally imposed constraints on the course of the fundamental crystallization and orientational relaxation processes are revealed. Oriented crystallization has been shown to have a significant effect on the stress developed and on the dimensions of oriented precursor fibers, with a strong tendency to spontaneously extend as a consequence of the reorientation of crystallizing segments predominantly along the preferred fiber direction. The sequence in which crystallization and major orientational relaxation, if any, occur is found to have a profound effect on the structure and thus the deformability of oriented fibers after annealing above the glass transition temperature.
Relaxation of chemical potential and a generalized diffusion equation
Authors: Jäckle Josef , Frisch Harry L.
Published: April 2003

The effect of slow structural relaxation in a solvent of high viscosity on the chemical potential driving the diffusion of penetrant molecules is described by a generalized diffusion equation with a memory term. The linearized version of this equation is solved for some special cases, and the correlation function of concentration fluctuations in thermodynamic equilibrium is calculated. As a result of the memory term, for very slow relaxation two different stages of the diffusion process can be distinguished.
Energy absorption in polymer crazing
Authors: Pang S. S. , Zhang Z. D. , Chern S. S. , Hsiao C. C.
Published: April 2003

The total energy absorbed by a craze during its development in creep is analyzed and calculated on the basis of a time‐dependent theory of crazing. Experimental measurements of the craze length have been utilized in the energy calculations. For polystyrene the initial energy absorption in the craze region is found to be several hundred times that in the uncrazed medium. This ratio decreases sharply in a short period of time to about 50 to 1 and less and remains low afterward. For polycarbonate, somewhat similar behavior has been found. The initial strain energy absorption by crazing is about 200 times that in the uncrazed region. The energy ratio reduces rapidly to about 55 to 1 and tends to level off thereafter. However, in general, the amount of strain energy absorbed does increase as a function of time, as it should.
A study of the gas barrier properties of highly oriented polyethylene
Authors: Holden P. S. , Orchard G. A. J. , Ward I. M.
Published: April 2003

Measurements of permeability and diffusivity have been undertaken for the gases helium and oxygen in a range of highly oriented polyethylene films. The solubilities deduced for both gases are proportional to the amorphous volume fraction, showing that the noncrystalline regions are the transport medium in all instances. The changes in diffusion coefficient are more complex. A large reduction in diffusion coefficient is observed with increasing draw ratio, and this is particularly marked in the case of the larger oxygen molecule, where significant differences are also observed for different grades of polymer and different drawing conditions. These changes in diffusion coefficient are discussed in the light of previous studies of diffusion in polymers and present knowledge of the changes in structure produced by drawing.
Crystallization of poly(m‐xylylene adipamide) induced by sorption of water
Authors: Inoue Kazuo
Published: April 2003

Sorption of water in quenched amorphous poly(m‐xylylene adipamide) has been studied at 50°C. The sorption process is nearly Fickian at low humidity. At relative humidities higher than about 58%, however, extremely abnormal behavior, such as a decrease in moisture uptake and a change in appearance from transparent to opaque, is found. From x‐ray diffraction analysis, these changes can be attributed to crystallization. Thermal analysis of moistened samples confirmed that the crystallization is due to a drop in crystallization temperature caused by sorption of water. From the relation between the reduction in moisture uptake and the increase in volumetric crystallinity, it is proposed that the change in moisture uptake is caused by the exclusion of water from the crystalline phase.
Crystallization of bisphenol‐A polycarbonate induced by organic salts; physical aspects. I. Crystallization rate, melting behavior, and morphology
Authors: Bailly Ch. , Daumerie M. , Legras R. , Mercier J. P.
Published: April 2003

The presence of organic acid salts in bisphenol‐A polycarbonate (PC) completely modifies the crystallization mechanism, the melting behavior, and the morphology of the polymer. Organic salts are not ordinary nucleating agents for PC since they react with the polymer, producing metal phenoxide chain ends. On reaction, abundant instaneous nucleation is induced. The seeds are likely to be polymer crystalline fragments preexisting in the melt. The phenoxide chain ends significantly increase the growth rate of the crystalline phase. Melting points and enthalpies of fusion are unusually high, suggesting a high degree of crystalline perfection. Thick multilamellar crystals, which are likely to contain chains in extended configuration, are observed by electron microscopy. No trace of spherulitic morphology is found. The chemical instability of PC containing ionic chain ends is also shown to seriously affect the crystallization rate, the maximum degree of crystallinity, and the melting point.
Spectroscopic characterization of acetylene‐terminated sulfone resin
Authors: Koenig Jack L. , Shields Carl M.
Published: April 2003

Fourier‐transform infrared spectroscopy was used to characterize the thermal polymerization of the acetylene‐terminated (AT) resin, bis[4‐(3‐ethynylphenoxy)phenyl]sulfone. Spectral processing techniques (including the method of factor analysis) were utilized in the analysis of the infrared data. The degree of cure was quantitatively monitored as the resin was thermally polymerized. Factor analysis indicated that only one reaction product is spectroscopically distinguishable. Further band analysis indicated the formation of predominantly trans conjugated polyene structures. No evidence for cyclotrimerization was found.
Percolation and effective‐medium theories for perfluorinated ionomers and polymer composites
Authors: Hsu William Y. , Berzins Talivaldis
Published: April 2003

Percolation and effective‐medium theories are applied to model the transport and elastic properties of perfluorinated ionomers. The composite nature of these polymers is emphasized. The effective‐medium theory is generalized to track continuously the evolution from lamellar to fibrillar morphology. The predicted dramatic difference in ion selectivity between lamellar and spherical morphology is verified quantitatively in perfluorinated ionomer blends. The limitations and potential improvements of the effective‐medium theory and its relationship to percolation theory are discussed. Applications of these theories to other multiphase polymer systems are also discussed.
Polymer migration in newtonian fluids
Authors: Jhon Myung S. , Freed Karl F.
Published: April 2003

The theory of Freed and Edwards is used to investigate polymer migration in nonhomogeneous flow fields with confined geometry. Polymer migration from the main flow originates in three effects: (i) nonhomogeneous flow‐field effect, (ii) the confined‐geometry effect, and (iii) the concentration effect. General correlation function formulas for these three effects are explicitly derived. Some specific examples are illustrated and solved by using the harmonic dumbbell and Rouse–Zimm models.
Sorption and diffusion of toluene in isotropic and oriented linear polyethylene
Authors: Ng H. C. , Leung W. P. , Choy C. L.
Published: April 2003

Sorption and diffusion of toluene vapor in linear polyethylene with mass‐fraction crystallinity between 0.48 and 0.82 and draw ratios λ up to 10 have been studied at 30°C. The sorbed concentration in the amorphous phase Ca is little affected by crystallinity, indicating that the free‐volume fraction is roughly the same for all isotropic samples. However, the diffusion path becomes more tortuous with increasing crystalline content, thereby leading to a sixfold drop in the zero‐concentration diffusion coefficient D0. Drawing has more drastic effects, reducing Ca and D0 by factors of 4 and 60, respectively, as λ increases to 10. These large changes result from the transformation of the initially spherulitic material into a fibrous structure, which is composed of aligned microfibrils with taut tie molecules lying on the outer boundaries. The effects of crystallinity and orientation on the concentration dependence of the diffusion coefficient are also discussed.
Conformational behavior of styrene–dymethylsiloxane block copolymers in dilute solution
Authors: Benchabane Mahmed , Van Leemput R.
Published: April 2003

To determine the behavior of a copolymer is dilute solution, a viscosity study has been performed on a polystyrene–polydimethylsiloxane block copolymer in three solvents presenting different thermodynamic conditions. The results are discussed in relation to a mixture of homopolymers and a segregated model. The unperturbed dimensions, obtained by the Stock–mayer–Fixman method, are intermediate between those of the parent homopolymers. The intrinsic viscosity measured in a good solvent, toluene, was close to the weighted averages of those of the corresponding homopolymers of equal molecular weight, but higher in decalin and in butanone, θ solvents for PS and PDMS, respectively. According to the low value obtained for the interaction parameter, the chain is slightly expanded as a result of the interactions between the unlike monomer units. Both segregation and random conformation would probably occur, depending on the quality of the solvent.
Morphological studies of liquid‐crystalline cellulose derivatives. II. Hydroxypropyl cellulose films prepared from liquid‐crystalline aqueous solutions
Authors: Nishio Y. , Yamane T. , Takahashi T.
Published: April 2003

A morphological study of hydroxypropyl cellulose (HPC) was performed on solid films prepared by casting from a liquid‐crystalline aqueous solution at rest or under shear. Electron microscopic observations reveal that many round particles composed of stacked disks are densely packed in the interior of a quiescently cast HPC film, while on the film surface formation of fibrous textures is also noted. Shear‐deformed HPC films exhibit some interesting morphological features according to the shearing conditions. It is found by electron microscopy that the originally round particles become more and more elongated as shear stress increases. The resulting rodlike fibrillar entities are considerably aligned in the shear direction (SD), but form a banded structure with periodic discontinuities of molecular orientation distribution along the SD. A new mechanism of structural transformation is proposed in order to interpret these results.
An investigation of the effect of sample preparation on the thermal behavior and the small‐angle x‐ray scattering of a polyurethane block copolymer
Authors: Miller John A. , Cooper Stuart L.
Published: April 2003

The effect of varying sample preparation parameters on the thermal behavior and on the small‐angle x‐ray scattering (SAXS) properties of a polyether polyurethane were investigated. The polyurethane studied was a methylene bis(p‐phenyl isocyanate) (MDI)/butanediol/poly(tetramethylene oxide) (PTMO) system synthesized in a 6/5/1 mole ratio by a two‐step solution polymerization. The PTMO had a nominal molecular weight of 2000. The samples were compression molded under different conditions for the SAXS experiments. The preparation parameters studied included molding time and temperature, sample thickness, and quenching rate from the molding temperature. The molding temperature has the greatest effect on the SAXS data. In this case the domain size was observed to increase as the molding temperature increased from 130 to 200°C. The thermal properties were also found to be strongly dependent on the molding temperature, as measured by differential scanning calorimetry (DSC). An endotherm related to the annealing that occurs during the molding process appears in each sample near the molding temperature. The other preparation parameters have little or no effect on the SAXS and thermal properties of this sample.
Mechanochemical reactions in an epoxy resin system
Authors: Grayson Michael A. , Wolf Clarence J.
Published: April 2003

Mechanical degradation of the MY720/Eporal (CIBA GEIGY) epoxy resin system was investigated by stress mass spectrometry. Resin coupons were strained to fracture in a unique mass spectrometer system in which the clamping jaws of an Instron tensile tester are located inside the ion‐source housing of a time‐of‐flight mass spectrometer. Several compounds are released at the instant of fracture. However, only one compound, SO2, is not an impurity in either the starting material or the cured resin. A sensitive gas‐chromatographic technique was used to search for SO2 indigenous to the starting material and the unstressed cured resin. The data indicate that SO2 is a mechanochemical reaction product generated during main‐chain bond cleavage of the glassy epoxy resin network.
Copolymers of tetrafluoroethene with chlorotrifluoroethene and with bromotrifluoroethene
Authors: Moggi Giovanni , Bonardelli Piergiorgio , Monti Claudio , Bart Jan C. J.
Published: April 2003

Tetrafluoroethene (TFE)–chlorotrifluoroethene (CTFE) and TFE–bromotrifluoroethene (BTFE) copolymers have been synthesized by solution copolymerization over the entire range of comonomer composition. Crystallinity data are reported and first‐ and second‐order transitions have been investigated by DSC. Glass transition temperatures of TFE‐CTFE copolymers vary in a nonlinear fashion in the range defined by the homopolymers conforming best to the Johnston equation; the behavior in the TFE‐BTFE system is more linear. Whereas TFE‐BTFE copolymers show a steep decrease of melting temperature at higher BTFE content, due to the amorphous character of the polymers, more regular behavior was found for TFE‐CTFE copolymers. Enthalpies of fusion are also reported. The results are discussed in relation to copolymer composition and structure and are compared with data on tetrafluoroethene–hexafluoropropene (FEP) fluorocarbon resins.
Molecular interactions in the poly(vinyl chloride)‐di‐n‐butylphthalate system determined by infrared spectroscopy
Authors: Benedetti Enzo , Posar Francesco , D'Alessio Aldo , Vergamini Piergiorgio , Pezzin Giovanni , Pizzoli Maria
Published: April 2003

Infrared studies of the poly(vinyl chloride) (PVC)/di‐n‐butylphthalate (DBP) system are reported. Spectra of DBP in different solvents seem to be indicative of the ability of DBP to interact with PVC chains in the same way as with polyesters and of competitive interactions between DBP molecules and DBP with PVC. Plots of the width at half‐height of the carbonyl stretching vibration, measured at 25 and at −180°C, as a function of composition, show a sudden change of slope at about 60% PVC concentration by weight, indicating that above this polymer composition interaction between DBP and PVC dominates that between DBP molecules. This change corresponds to a “singularity” observed in the dependence of the glass transition temperature on composition.
Time dependence of mechanical and transport properties of drawn and annealed linear polyethylene
Authors: Decandia F. , Vittoria V. , Peterlin A.
Published: April 2003

Linear polyethylene both as drawn, or drawn and subsequently annealed with free ends, changes its length, density, crystallinity, elastic modulus, sorption, and diffusivity as the sample stands completely unrestrained at room temperature. Most of these changes occur during the first few hours. But they are important on a molecular scale since they suggest strongly that drawn, and drawn and annealed samples are far from equilibrium. As a consequence of the tendency of each mobile tie molecule in the amorphous conformation to retract and to crystallize, the specimen approaches but does not reach complete equilibrium. The transient seems to be caused by slow crystallization of tie molecules which creates crystalline bridges across the amorphous layers.
Random‐coil configurations of aromatic polyesters: Birefringence of poly(triethylene glycol terephthalate) networks in elongation
Authors: Riande E. , Guzman J.
Published: April 2003

Hydroxyl‐terminatd poly(triethylene glycol terephthalate) was crosslinked with an aromatic triisocyanate. Birefringence–stress–strain experiments, performed on the networks at 70°C, showed an anomalous increase in the modulus and a downturn in the birefringence–strain isotherms at high elongations. These results suggest that crystallinity is not responsible for the non‐Gaussian behavior of the chains at high extension. The same kind of experiments were performed over the range 20–70°C. Values of the optical configuration parameter Δa of the order of 13.3 × 10−24 cm3 with negligible temperature coefficient were found for these networks. The quantities Δa and d In Δa/dT were calculated by means of the rotational isomeric state model. Better agreement between the theoretical and experimental values of these parameters was found for poly(triethylene glycol terephthalate) than for poly(diethylene glycol terephthalate). Since the polarities of the two chains are similar, intermolecular interactions involving terephthaloyl residues may be responsible for the discrepancies observed between theory and experiment for Δa in aromatic polyesters.
The β dielectric relaxation in some methacrylate polymers
Authors: Ribelles J. L. Gomez , Calleja R. Diaz
Published: April 2003

Dielectric results at frequencies between 6 × 10−4 and 105 Hz are given for the β relaxation region of poly(methyl methacrylate) (PMMA), poly(ethyl methacrylate) (PEMA), poly(butyl methacrylate) (PBMA), and poly(isobutyl methacrylate) (PisoBMA). Apparent activation energies and relaxation strengths are calculated, as well as the relaxation time distribution and the form factor of the Fuoss‐Kirkwood equation. It is found that in PMMA, PEMA, and PBMA, the activation energy of the β relaxation is the same, the maxima occurring at the same frequency for the same temperatures, in accordance with the dynamic mechanical results of Heijboer, the dielectric results of Mikhailov, and at variance with data of Tetsutani et al. It is also found that the form factor follows the same temperature dependence. Data on the β relaxation of poly(hydroxyethyl methacrylate) (PHEMA), not previously reported, are also presented, and the displacement toward high temperatures of the β relaxation of PisoBMA and PHEMA is justified.
A comparative study of approaches applied to the permeability of binary composite polymeric materials
Authors: Petropoulos J. H.
Published: April 2003

A study has been made of various approaches to the problem of evaluating the permeability of a binary composite polymeric material on the basis of certain fundamental theoretical assumptions. In particular, it is assumed that the component phases form well‐defined microscopic domains and do not interact with each other or with the penetrant. The main characteristics and relative merits of these treatments are considered in detail, and it is shown that considerable information can be obtained about the range of validity and physical significance of certain well‐known formulas, which were previously applied in a largely empirical way. These results indicate specific fields of application (which include filled or semicrystalline polymers, foams, block and graft copolymers, and nonhomogeneous polymer blends) for each of the formulas in question and lead to a deeper understanding of the relation between permeability or analogous properties (such as thermal or electrical conductivity, electrical permittivity, elastic modulus, etc.) and the structural characteristics of composite polymeric (and other) materials.
Linear thermoviscoelasticity and characterization of slightly crystalline EPDM networks
Authors: Scholtens Boudewijn J. R.
Published: April 2003

Three EPDM network families with various degrees of chemical crosslinking and slightly crystalline below about 350 K have been characterized by thermoviscoelastic and equilibrium swelling measurements. Between 300 and 450 K the thermoviscoelasticity of these elastomers, whether cured or not, is complex. Important differences from previous results on noncrystalline EPDM networks are their dependence on waiting time and temperature history below 350 K, and an equilibrium modulus for the uncured elastomers. These effects increase with rising ethylene content of the EPDM and are related to the crystallinity in the networks. A previously proposed modified time‐temperature (t‐T) superposition scheme is also applicable to these data, and the resulting frequency shift functions aT are of the usual WLF type. The vertical shift functions for the relaxational components bT are different from those for the equilibrium moduli. Experimental data demonstrate that the absolute values of the relaxational components, i.e., G″ (ω) and H(τ), are not changed by small variations in crystallinity. In addition, larger variations in crystallinity do not affect their frequency dependence, only their absolute values. On the contrary, the equilibrium modulus, and therefore all characteristics containing this as a component, is extremely sensitive to small variations in crystallinity, and hence in temperature. The linear viscoelastic characteristics of these slightly crystalline networks and their deviations from thermoviscoelastically simple behavior are discussed as functions of the ethylene content, temperature, and degree of crosslinking of the elastomer. The data provide evidence for three contributing factors, namely chemical crosslinks, crystallinity, and a more disordered type of crystallinity termed microparacrystallinity.
Temperature‐dependent melt crystallization kinetics of poly(butene‐1): A new approach to the characterization of the crystallization kinetics of semicrystalline polymers
Authors: Icenogle R. D.
Published: April 2003

The experimental measurements necessary to characterize the crystallization kinetics of a semicrystalline polymer are established by adopting a model for the crystallization of the polymer and specifying the range in which thermodynamic variables and other field interactions with the polymer will be varied during processes of interest. The theory for a model of instantaneous heterogeneous nucleation followed by spherulitic growth is developed. To the extent to which this model accurately describes the crystallization, determination of the spherulitic growth rate and nucleation density as a function of temperature then characterizes the temperature‐dependent crystallization kinetics of a polymer. These have been measured for poly(butene‐1), and, with the adoption of a cooling of the polymer at a constant rate as a processing model, a useful description of the melt crystallization kinetics of poly(butene‐1) is given. Literature data for the crystallization rates of linear polyethylene and isotactic polypropylene, poly(butene‐1), and polystyrene and compared.
Interpretation of photon correlation spectroscopy data: A comparison of analysis methods
Authors: Stock R. S. , Ray W. H.
Published: April 2003

Properties of solutions and colloidal suspensions such as molecular and particle dynamics, diffusivities, and size distributions may be determined through dynamic light‐scattering experiments. Here a number of methods for predicting the details of the linewidth distribution from photon correlation spectroscopy data are reviewed. Their performance on simulated data (with and without noise added) and experimental data from polystyrene latex standards (including a mixture of two standards) is compared. Methods which do not assume a specific form for the distribution are considered. These include cumulants, histograms, exponential sampling, subdistributions, a non‐negatively constrained histogram, and Provencher's constrained regularization. Constrained regularization was found to be most robust to noise present in the autocorrelation function and therefore most reliable for analyzing experimental data; however, the method sometimes oversmoothed the distribution. For bimodal distributions the histogram method performed well in our testing, especially when the approximate peak locations were known a priori. Two linear least‐squares fitting methods, exponential sampling and the non‐negatively constrained histogram, yield accurate values for the overall mean and standard deviation and can be implemented easily on a microcomputer. The linear subdistribution method, although computationally fast, sometimes was not as accurate as other methods.
Application of the method of brather for the determination of complex dielectric permittivity from measurements of isothermal polarization current
Authors: Ribelles J. L. Gomez , Calleja R. Diaz
Published: April 2003

Some years ago, Brather proposed a method for calculation of the real and imaginary parts of the complex dielectric permittivity starting from measurements of isothermal polarization current. This method shows some advantages over the Hamon method, which is normally used. Both methods are applied in this work to the β relaxation of poly(butyl methacrylate). It is concluded that, with the usual accuracy of measurement, a combination of the two methods is advisable; Hamon's method is taken to be a first approximation to that of Brather. Results following the two procedures are compared, and their respective advantages and disadvantages are discussed.
Irradiation of ultrahigh‐molecular‐weight polyethylene
Authors: Shinde A. , Salovey R.
Published: April 2003

An ultrahigh‐molecular‐weight polyethylene material covering a range of crystallinity from 42 to 79% increased in calorimetric crystallinity as a result of chain scission following ionizing irradiation. Carbonyl was formed by a diffusion‐limited reaction of oxygen with long‐lived free radicals. Trans‐vinylene production was linear with radiation dose and was highest for the sample of highest crystallinity but was not sensitive to environment.