bluuebunny/crossref_metadata_2025 huggingface dataset:
On the structure of glassy polymers. I. Small‐angle X‐ray scattering from polycarbonate
Authors: Renninger A. L. , Wicks G. G. , Uhlmann D. R.
Published: April 2003

The small‐angle x‐ray scattering (SAXS) from glassy bisphenol‐A polycarbonate has been measured using a Bonse–Hart system. The data cover the angular range (2θ) between 20 sec and 2 deg. After correcting for absorption, background, and vertical beam divergence, they have been placed on an absolute basis by comparison with the scattering from a standard silica suspension. The corrected absolute intensity decreases strongly with increasing angle over the range between 20 sec and 30 min, and is nearly constant between 30 min and 2 deg. The magnitude of the scattering in the constant range, 0.44 (electrons)2 Å−3, is well represented by the thermodynamic theory for fluids applied at the glass‐transition temperature. The increase in intensity at smaller angles cannot be described by structures on the scale of the nodules reported in this material (50–200 Å), but can be well represented by a small concentration of heterogeneities (0.04% by volume or less), several thousand angstrom units in size, superimposed on the thermal density fluctuations frozen in at the glass transition.

It is suggested that the nodular features reported for this material are not representative of bulk material but should be associated with surface effects. The bulk structure can—as far as the SAXS is concerned—be well described as a random amorphous solid, containing simple thermal fluctuations and a small concentration of relatively large heterogeneities.
Photoinduced charge transfer at the poly(N‐vinylcarbazole)—tin oxide interface
Authors: Reucroft P. J. , Ghosh S. K. , Takahashi K.
Published: April 2003

An investigation of steady state and transient photoconductivity in films of poly‐(N‐vinylcarbazole) equipped with SnO2 and metal electrodes is described. The studies have shown that photoinduced charge transfer, leading to hole injection into the polymer film, takes place with photons of energy greater than 1.8–1.9 eV. Dark conductivity studies on samples equipped with grounded guard rings have shown that carriers originating in the bulk of the polymer film dominate the dark current when the metal electrode is at negative bias. Thermionic hole emission from the SnO2 electrode is not observed.
Effect of interfacial bonding on the strength of adhesion
Authors: Ahagon A. , Gent A. N.
Published: April 2003

The strength of adhesion has been determined experimentally for an elastomer layer coupled to a rigid substrate by interfacial chemical bonds of varying surface density. Sites for interfacial bonding were obtained by treating glass plates with mixtures of vinyl‐and ethylsilanes in varying proportions. A layer of polybutadiene was then applied and cross‐linked in situ by a free‐radical process. Formation of interfacial bonds to vinyl groups (when present) on the glass substrate is inferred from the proportional increase in strength of adhesion under near‐equilibrium conditions, i.e., at low rates of detachment and at high temperatures. A 35‐fold increase in strength was found for vinylsilane, relative to ethylsilane, in rough agreement with the relative magnitudes of the strengths of covalent and dispersion bonds. However, the absolute magnitudes were much greater than predicted, by a factor of about 25 in both cases. This is attributed to the polymeric character of the elastomer: many molecular bonds must be stressed in order to detach or rupture one.4 In agreement with this hypothesis, the strength of adhesion decreased with increasing crosslinking. Anomalously high adhesion was found with clean glass. It presumably reflects a specific bonding mechanism of unknown type.
NMR measurements on cis‐1,4‐polybutadiene as a function of pressure
Authors: Geissler E.
Published: April 2003

Measurements are reported of the nuclear spin—lattice relaxation time T1 in cis‐1,4‐polybutadiene at room temperature up to a pressure of 3,500 bar. Up to 2,000 bar the relaxation curves are described by a single T1, the pressure variation of which indicates, in the Arrhenius model, an activation volume of 14.5 cm3 mole−1. Above 2,000 bar the effects of strain due to partial crystallization become evident, and multiple relaxation is observed. By measuring the compressibility of this material up to 10 kbar an estimate of the free volume is made, giving

with P in kbar. This measurement is applied in turn to two models of the glassy state, that of Cohen and Turnbull1 which yields an activation volume of 84 cm3 mole−1, and that of Adam and Gibbs,2 which leads to a critical configurational entropy of 7.7 kB.

In the liquid state the transverse nuclear relaxation, measured by the spin‐echo technique, appears to be governed by the same process as T1.
Electrical properties of dry and wet polyglycine
Authors: Michel R. , Seytre G. , Maitrot M.
Published: April 2003

Real and imaginary parts of the dielectric constant of wet and dry polyglycine have been measured for several temperatures over a wide range of frequencies. A simple, rather crude model, proposed earlier for nylon 66, fits the experimental data rather well, but the blocking coefficient p is larger and adsorption effects are more important.
Physical properties and structure of silk. II. Dynamic mechanical and dielectric properties of silk fibroin
Authors: Magoshi Jun , Magoshi Yoshiko
Published: April 2003

Dynamic mechanical and dielectric properties of amorphous regenerated films of silk fibroin were studied as a function of temperature. A mechanical loss tangent peak at about 175°C may be due to the segmental motion of the main chains in the amorphous silk fibroin film. The dynamic modulus of the amorphous silk fibroin increased at 185°C due to the crystallization of the silk fibroin. Dielectric loss tangent peaks were observed at about −40°C and 175°C at 1 kHz. The former is ascribed to the local motion of the amorphous silk fibroin with absorbed water, while the latter seems to originate from the segmental motion of the main chains and the crystallization of silk fibroin.
Dielectric relaxation in concentrated solutions of poly(methyl methacrylate)
Authors: Phillips P. J. , Singh G.
Published: April 2003

Measurements of dielectric relaxation have been made for a series of solutions of poly(methyl methacrylate) in toluene. A range of concentrations between 2% and 20% was used for a number of polymers of differing molecular weights. The dispersion was studied over the frequency range 103‐106 Hz for temperatures between −90°C and +20°C. It has been found that both the distribution of relaxation times and the activation energy increase with increasing concentration. The magnitudes of the effects vary with molecular weight. A significant observation is that the increase in dielectric constant with concentration is not linear.
The nature of multiple melting transitions in cis‐polyisoprene
Authors: Edwards B. C.
Published: April 2003

The multiple melting transitions previously reported for cis‐polyisoprene have been related to different morphological species observed in thin films using transmission electron microscopy. Two distinct types of spherulitic lamellar crystal have been identified which have characteristic growth rates, lamellar thicknesses, and fold planes.

In addition to the α‐lamellar crystals, which grow in prestrained films with the a axis perpendicular to the stretch direction, a second type of lamellar crystal was identified with the b axis perpendicular to the stretch direction: β‐lamellae. From an analysis of the kinetics of growth and the variation of lamellar thicknesses with crystallization temperature, values of the side and surface free energies of the two types of lamellar crystal have been calculated.
A method for experimental determination of the temperature dependence of relaxation times in dielectrics
Authors: Ponevski Ch. , Solunov Ch.
Published: April 2003

A new method is suggested for the experimental determination of the dependence of the relaxation times on the temperature in dielectrics for which the time–temperature superposition principle is valid. The method makes possible the determination of this dependence for a separate relaxation process (for instance, for the β‐relaxation process) over a wide temperature range by means of comparatively simple mathematical operations which are only slightly sensitive to experimental errors. Two or more discharge‐current curves, measured with temperatures increasing in an arbitrary way with time, are used for this purpose.
On the structure of glassy polymers. II. Small‐angle x‐ray scattering from poly(methyl methacrylate)
Authors: Renninger A. L. , Uhlmann D. R.
Published: April 2003

The small‐angle x‐ray scattering (SAXS) from glassy poly(methyl methacrylate) has been measured using a Bonse–Hart system. The data cover the angular range (2θ) between 20 sec and 2 deg. After correcting for absorption, background, and beam divergence, the data have been placed on an absolute basis by comparison with the scattering from a standard silica suspension. The corrected absolute intensity decreases strongly with increasing angle over the range between 20 sec and 30 min, and is nearly constant between 30 min and 2 deg. The magnitude of the scattering in the constant range, 0.6 (electrons)2 Å−3, is within a factor of 1.5 of the value predicted by the thermodynamic fluctuation theory for fluids applied at the glass transition temperature. The increase in intensity at smaller angles cannot be described by structures on the scale of the nodules reported in highly isotactic PMMA (150–200 Å), but can be well represented by small concentrations of heterogeneities, several thousand angstrom units in size, superimposed on the thermal density fluctuations frozen‐in at the glass transition. The bulk structure of this material is well described as a random amorphous solid, containing simple thermal fluctuations and a small concentration of relatively large heterogeneities.
Phase transition in dilute solution of poly(γ‐benzyl‐L‐glutamate) in dichloromethane at a low temperature
Authors: Adachi Keiichiro , Hirose Yumiko , Ishida Yoichi
Published: April 2003

The dielectric constant of solutions of poly(γ‐benzyl‐L‐glutamate) (PBLG) in dichloromethane shows a jump near 195°K, irrespective of frequency. Therefore, the discontinuity is not a dispersion phenomenon but a phase transition in the thermodynamic sense. The transition temperature is independent of the concentration in the range from 0.01 to 10% by weight, but it increases linearly with the logarithm of the molecular weight of PBLG. The height of the jump depends strongly on frequency, concentration, and molecular weight. The viscosity also changes abruptly at 195°K. These results suggest that the PBLG molecule forms a cluster like a liquid crystal or is in a random coil state below the transition point.
The fusion of highly crystalline poly(vinyl chloride)
Authors: Gouinlock E. V.
Published: April 2003

Low molecular weight PVC polymers of known degree of crystallinity (44% by x‐ray diffraction), prepared in the presence of the chain‐transfer agents n‐butyraldehyde and n‐butyl mercaptan, are examined by differential scanning calorimetry in order to ascertain temperatures and heats of fusion. Initial thermal scans are accompanied by large endotherms and appreciable weight losses due to the lability of the terminal groups originating from the chain‐transfer agents. However, further successive scans result in approximately invariant endotherms attributable to crystalline fusion. The maximum melting point, about 265°C, exceeds the value for commercial PVC, about 210°C, but is lower than a value deduced for a hypothetical completely syndiotactic polymer, about 400°C. The average heat of fusion ΔHu is 1180 ± 90 cal/mole, and the resultant entropy of fusion is 1.1 cal/deg/bond. The present ΔHu value differs significantly from previously reported values of 660–785 and 2700 cal/mole, based on melting point depression theory, but appears to be concordant with known heats for a series of vinyl polymers.
Nonlinear viscoelasticity of polystyrene solutions. II. Non‐Newtonian viscosity
Authors: Osaki Kunihiro , Fukuda Mitsutoshi , Ohta Shin‐Ichi , Kim Bong Shik , Kurata Michio
Published: April 2003

The steady shear viscosity η(k) and the stress decay function \documentclass{article}\pagestyle{empty}\begin{document}$ \tilde \eta \left({t,k} \right)$\end{document} (the shear stress divided by the rate of shear k after cessation of steady shear flow) were measured for concentrated solutions of polystyrene in diethyl phthalate. Ranges of molecular weight M and concentration c were 7.10 × 105 to 7.62 × 106 and 0.112–0.329 g/cm3, respectively. Measurements were performed with a rheometer of the cone‐and‐plate type in the range 10−4 < k < 1 sec−1. The Cox–Merz relation η(k) = |η*(ω)|ω=k was tested with the experimental result (|*(ω)| is the magnitude of the complex viscosity). It was found to be applicable to solutions of relatively low M or c but not to those of high M and c. For the latter η(k) began to decrease at a lower rate of shear than |η*(ω)|ω=k did; the Cox–Merz law underestimated the effect of rate of shear. The stress decay function was assumed to have a functional form \documentclass{article}\pagestyle{empty}\begin{document}$\tilde \eta \left( {t,k} \right) = \sum {\eta _p \left( k \right)e^{ - t/\tau p\left( k \right)} } $\end{document} where τ1 > τ2 > …, and the values of τ1, τ2 η1 and η2 were determined for some solutions. The relaxation times τ1 and τ2 were found to be independent of k and equal to the relaxation times of linear viscoelasticity. At the limit of k → 0, η1 and η2 were approximately 60 and 20–30%, respectively, of η and the non‐Newtonian behavior was due to large decreases of η1 and η2 with increasing k. It was shown that η1(k) may be evaluated from the relaxation strength G1(s) for the longest relaxation time of the strain‐dependent relaxation modulus with a constitutive model for relatively high c–M systems as well as for low c–M systems.
Mechanical properties of composite heterogeneous gels
Authors: Janáček J. , Raab M. , Boček B.
Published: April 2003

Composites with a matrix of poly(2‐hydroxyethyl methacrylate) (PHEMA) and 10% by volume of various crosslinked PHEMA polymer fillers (prepared by copolymerization with 0.1, 0.4, 1.0, and 20.0% by weight of ethylenedimethacrylate) of particle size about 1 μm were prepared. Some polymer matrixes were prepared from soluble branched PHEMA (Hydron S), and others by copolymerization, in the presence of the filler with 0.4 and 1.0% of ethylenedimethacrylate as a crosslinking agent. In the case of the uncrosslinked matrix, a linear polymer–crosslinked polymer system, resulted; in the case of the crosslinked matrix, a composite heterogeneous network was formed (in the latter case, the particles of the filler were swollen with monomer during the crosslinking polymerization).

Stress–strain, equilibrium, and ultimate characteristics were measured at 3, 10, 25, 40, 60, and 80°C on samples swollen to equilibrium in water (Tg ≈ −50°C) and at 80, 110, and 140°C on dry samples (Tg ≈ 100°C). Depending on experimental conditions, above all on the distance from the main transition region and on whether the polymer is dry or swollen, it was found that the measured hydrophilic composite systems behaves as a filled system (with the polymer filler acting mostly as solid particles, irrespective of the crosslink density) or as a system with crosslink density fluctuations (where both networks, the matrix and the filler, contribute roughly additively to the properties of the system), or finally as defect heterogeneous systems (where the properties depend primarily on the character of the polymer–filler interface).
Light scattering from polymer films having optically anisotropic rodlike texture. A quantitative test of theories
Authors: Hashimoto Takeji , Murakami Yukinobu , Kawai Hiromichi
Published: April 2003

The light scattering intensity distribution from rodlike crystalline superstructures is quantitatively investigated theoretically and experimentally. The arithmetic average of theoretical Hv scattered intensities at azimuthal angle μ = 0° and μ = 45° is shown to decrease with increasing scattering angle θ in proportion to W−1 at high scattering angles for a system composed of a random assembly of rodlike superstructure having very small lateral dimensions relative to the length. The quantity W is defined as 2π(L/λ) sin θ where L is the length of the rod, and λ is the wavelength of light in the medium. A method is proposed to estimate the length L by using the W−1 dependence. Effects of internal heterogenity, polydispersity in rod length, and finite lateral dimensions of the rodlike superstructure are considered to account for experimental deviation of the scattered intensity distributions from the W−1 dependence. The effect of finite lateral dimensions turns out to be the most important.
Investigation of the dual mode sorption of ammonia in polystyrene by NMR
Authors: Assink R. A.
Published: April 2003

The sorption of ammonia by polystyrene was investigated by pulsed nuclear magnetic resonance (NMR) relaxation techniques. The concentration of sorbed gas was determined from the intensity of the gas signal and analyzed by the dual mode sorption model. The relaxation data were used to examine the validity of assuming that the molecules exchange rapidly between sites and that the adsorbed species is relatively immobile. Both assumptions were found to be substantially correct although the possibility that the adsorbed species may have some small mobility (no more than 5% that of the faster moving molecules) could not be eliminated.
Rubber networks containing unattached macromolecules. II. Viscoelastic properties in small strains of the system ethylene–propylene terpolymer with ethylene–propylene copolymer
Authors: Kramer Ole , Greco Roberto , Ferry John D. , McDonel E. T.
Published: April 2003

Mixtures of crosslinkable ethylene–propylene terpolymer with saturated ethylene–propylene copolymer (molecular weights 3.6, 16.7, and 45 × 104) containing up to 50% by weight of copolymer were crosslinked by sulfur, leaving the saturated copolymer unattached and free to reptate in the terpolymer network. Stress relaxation in small simple elongations (stretch ratio about 1.15) and dynamic Young's modulus at frequencies from 3.5 to 110 Hz were measured at temperatures from 10 to 50°C. Comparison with the properties of the terpolymer crosslinked without added copolymer showed contributions to stress relaxation and mechanical loss attributable to the unattached species. The time required in stress relaxation for the portion of the modulus attributable to the unattached species to decay to half its plateau value, t1/2, is approximately proportional to the 3.5 power of the molecular weight; t1/2 appears to be slightly smaller for networks containing 50% than for those containing 25% unattached component.
Rubber networks containing unattached macromolecules. III. Nonlinear stress relaxation in the system ethylene–propylene terpolymer with ethylene–propylene copolymer and behavior of extracted networks
Authors: Greco Roberto , Taylor Carl R. , Kramer Ole , Ferry John D.
Published: April 2003

Further stress relaxation experiments, mostly at 50°C, are reported on mixtures of crosslinkable ethylene–propylene terpolymer with saturated ethylene–propylene copolymer (molecular weights 3.6 and 45 × 104) containing up to 50% by weight of copolymer, crosslinked by sulfur to leave the saturated copolymer unattached and free to reptate in the copolymer network. Stress relaxation was measured in small simple elongations (stretch ratio about 1.15) on samples which had been extracted to remove a large part of the unattached copolymer and dried. The relative increase in modulus at long times (104 sec) increased with the proportion extracted; at short times (1 sec), extraction of the lower molecular weight copolymer increased the modulus to about the same extent but extraction of the higher molecular weight copolymer affected it very little. The relaxation modulus of the copolymer extracted from sample 50H (50% copolymer of high molecular weight), obtained by difference, agreed with that for the total copolymer except for a small difference probably attributable to molecular weight selectivity in the extraction. Stress relaxation was measured on sample 50H at six higher elongations up to a stretch ratio of 3. The dependence of stress on time and strain was consistent with an analysis based on the following assumptions: (a) linear additivity of the network and unattached copolymer contributions, (b) strain–time factorization of the stress contributions from the individual components, (c) a strain dependence for the unattached component corresponding to the presence of a Mooney–Rivlin C2 term only, (d) a strain dependence for the network component which does not follow the Mooney–Rivlin equation but is dominated by a simple neo‐Hookean term.
Flow, high‐elastic (recoverable) deformation, and rupture of uncured high molecular weight linear polymers in uniaxial extension
Authors: Vinogradov G. V. , Ya. Malkin A. , Volosevitch V. V. , Shatalov V. P. , Yudin V. P.
Published: April 2003

The behavior of narrow molecular weight distribution polymers has been investigated under uniaxial extension at constant deformation rate and at constant stress. It has been established that up to rupture these polymers behave as linear viscoelastic bodies. A detailed investigation of the rupture phenomenon has shown that the rupture of fluid polymers is due to their transition to the rubbery state at critical deformation rates, with the result that they disintegrate like quasi‐cured rubbers. The effect of the temperature and the molecular weight on the critical conditions of rupture has been described in terms of viscoelastic relaxation.
Pressure dependence of dielectric properties of chlorinated polyethylene vulcanizate. I. α relaxation and shift factors
Authors: Naoki Motosuke , Motomura Masatoshi , Nose Takuhei , Hata Toshio
Published: April 2003

The complex dielectric constant was measured under elevated pressure for the α relaxation of vulcanized chlorinated polyethylene. Both temperature and pressure effects on the static dielectric constants, the activation enthalpy, and volume, and the pressure dependence of the glass‐transition temperature were obtained. The dependence of shift factors on temperature was expressed by the Vogel–Fulcher–Tamman–Hesse (VFTH) equation: −log aT = A − B/(T − T0). The parameters A, B, and T0 for each pressure applied were calculated by minimizing the standard deviation between log aT and experiments. The values of the parameters in the Williams–Landel–Ferry (WLF) equation: −log aT = C1(T − Tg)/[C2 + (T − Tg)], were also estimated from the resulting values of the VFTH parameters. All these parameters depended on pressure. The activation volume plotted against T − Tg decreased with increasing pressure.
Thermal analyses of polymers. XIII. Crystalline character of the 70°c transition of poly(ethylene terephthalate)
Authors: Miller Gerald W.
Published: April 2003

The abrupt changes in the linear expansion and dilatometric measurements of poly‐(ethylene terephthalate) near 70°C indicate that the transition may be first order. DTA and DSC data show the normal heat capacity change at 70°C, while annealing for for 30 min. at 110°C induces further molecular order. Rapid quenching of PET after heating to 120°C yields an amorphous sample and measurement by depolarized light transmission as the sample is reheated shows rapid crystallization occurring near 80°C. With the occurrence of shrinkage near 68°C and apparent recrystallization at slow heating rates by depolarized light analyses, further support is added to the first‐order character of this phase transition. Isothermal annealing for short times at temperatures between 50°C and 80°C produces further increases in molecular order. Cyclic and linear PET oligomers do not contribute to the occurrence of the 70°C transition.
A method of calculating the activation energy spectra of polymers
Authors: Ikeda Susumu , Matsuda Kazuo
Published: April 2003

Contraction experiments were performed on hot‐stretched polystyrene during isothermal annealing and tempering. Activation energy spectra were obtained from the experimental data using the Primak theory. In the case of isothermal annealing the theory of Kimmel et al. with shift factors was used. There is an appreciable difference between this spectrum and that obtained from the tempering experiment by the original theory without shift factors. These two spectra should be the same according to the theory. In order to resolve the conflict, we have included a correlation between activation processes in the fundamental equation of the Primak theory. A new formula for calculating the activation energy spectra was obtained. For isothermal annealing, it can be written the same as that of Kimmel et al. The shift factor is also included in the formula for tempering. The activation energy spectra obtained by the new formula gives good agreement between the two methods.
Carbon‐13 nuclear magnetic resonance quantitative measurements of monomer sequence distributions in hydrogenated polybutadienes
Authors: Randall James C.
Published: April 2003

The 1,4–1,2 additions in three hydrogenated polybutadienes are described in terms of triads of monomer units, average sequence lengths, and branches per 1000 carbon atoms. A test for conformity with Markov statistical behavior shows that the measured triad distributions can be closely reproduced assuming a first‐order model. Transition probabilities from the statistical analysis can be used to calculate the relative concentration of any desired sequence. Steric factors during polymerization may lead to the first‐order bias in the monomer distribution.
The morphology of ultradrawn polyethylene. I. Nitric acid etching plus gel permeation chromatography
Authors: Weeks Norman E. , Mori Sadao , Porter Roger S.
Published: April 2003

Transparent strands of high‐density polyethylene of unusually high c‐axis orientation have been produced by a solid‐state extrusion, involving pressure, temperature, and deformation, in an Instron capillary rheometer. Measured values for tensile modulus are higher than previously reported for any polyolefin. Previous modulus and electron microscopic data are consistent with a strand morphology comprised (≤20%) of of extended chain crystals. The remainder resembles an oriented fibrillar morphology such as found in highly drawn polyethylene. In the present study, fuming nitric acid etching of the ultraoriented strands, in combination with gel permeation chromatography (GPC), has provided incisive structural information. The strands exhibit ≥3X the resistance to acid degradation shown by conventionally drawn polyethylene. GPC molecular weight distributions (MWD) of etched samples show a single broad peak with a prominent high molecular weight tail. The crystal size, represented by the MWD, is in agreement with the crystal long period determined by small‐angle x‐ray scattering. The absence of multiple peaks in the etched MWD's is evidence of limited chain folding. The extended chain content, determined from the etched MWD's, is a strong function of strand formation temperature and is in agreement with the fraction of extended chains calculated from modulus measurements.
Elastic behavior of simple model networks
Authors: Smith K. J. , Gaylord R. J.
Published: April 2003

The elastic behaviors of simple networks consisting of but a few chains have been calculated on the basis of the James and Guth theory of elasticity. The calculations show that the number of elastically effective chains in a network is less than the actual number of network chains, and that the total number of chain backbone links distribute themselves equally (approximately) among the effective chains. It is also demonstrated that a chain molecular weight distribution could be of consequence in non‐Gaussian elasticity. Extrapolation of the findings to a macroscopic network suggests that the number of effective chains is one half the number of network chains, and that each effective chain behaves as if it contained twice as many of backbone links as a network chain.
The crystallization of polymer–diluent mixtures
Authors: Fatou J. G. , Riande E. , Valdecasas R. Garcia
Published: April 2003

A theory pertinent to the nucleation of polymer‐diluent systems for molecules of finite molecular weight has been developed. These results have been applied to the crystallization from polyethylene‐α‐chloronaphthalene mixtures using molecular weight fractions of polyethylene ranging from 4,000 to 250,000. This analysis is carried out over the composition range extending from pure polymer to a polymer fraction of 0.30. According to this theory, the interfacial basal free energy decreases as either the molecular weight or diluent concentration decreases.
High‐pressure phases in polymers. II. Spherulitic growth morphology in cis‐polyisoprene
Authors: Edwards B. C. , Phillips P. J.
Published: April 2003

The morphological details of the nucleation and growth of spherulites in cis‐polyisoprene at elevated pressures are discussed on the basis of transmission electron microscopy of films stained in situ by osmium tetroxide and cold‐stage electron diffraction of unstained films. The crystalline structure is unchanged but growth habits are modified. Spherulites begin, as in crystallization at atmospheric pressure, with a single lamella. The formation of a spherulite proceeds primarily through “spawning” and is unaffected by the imposition of pressure. Lamellae tend to propagate as plates or hedrites at supercoolings in excess of 50–60°C (e.g., 1 kbar at 0°C) unlike at atmospheric pressure where only ribbonlike lamellae are observed. Propagation is invariably as sheafs since nucleation of lamellae which grow perpendicular to the primary lamella is suppressed. The nucleation density varies considerably with pressure, a maximum being observed in the pressure plane at constant temperature (e.g., 0.70 kbar at 0°C). It is difficult to resolve clearly the morphological details in the diffusion controlled region because of fine texture. Although much more difficult to achieve experimentally, the effects of pre‐orienting the melt are similar to those occurring at atmospheric pressure.
Diluent effects on molecular motions and glass transition in polymers. I. Polystyrene–toluene
Authors: Adachi Keiichiro , Fujihara Ichiro , Ishida Yoichi
Published: April 2003

The effects of diluent on molecular motions and glass transition in the polystyrene–toluene system was studied by means of dielectric, thermal, and NMR measurements. Three dielectric relaxations were observed between 80 and 400°K. On the basis of NMR measurements on solutions in toluene and in deuterated toluene, relaxation processes were assigned to segmental motions of polystyrene, rotations of toluene, and the local motions of polystyrene and toluene in order of appearance from the high‐temperature side. The concentration dependence of the relaxation strength and of the activation energy for the primary relaxation (that at the highest temperature) show a step increment at about 50% by weight. The activation plots for the primary process were expressed by the Vogel–Tamman equation. With this equation, the temperatures at which the mean dielectric relaxation time becomes 100 sec is determined. This agrees well with the glass‐transition temperature Tg and hence Tg in concentrated solution is expressed by

in terms of the parameters A, B, and T0 of the Vogel–Tamman equation. The values of A and B are, respectively, about 12 and 0.65 and independent of the concentration. The physical meaning of these parameters is discussed.
Optical studies of the crystallization of trans 1,4‐polybutadiene in stretched networks
Authors: Akana Y. , Stein R. S.
Published: April 2003

The stress‐induced crystallization of trans 1,4‐polybutadiene was studied by observing changes in birefringence, stress, x‐ray diffraction, and low angle light scattering during the course of crystallization. From these data, the degree of crystallinity was determined as a function of time, temperature, and elongation. Data were fitted to the Avrami equation, leading to an exponent of the order of unity. Light‐scattering patterns suggested the simultaneous existence of two stretched forms: a rod‐like structure oriented preferentially parallel to the stretching direction and a deformed spherulitelike growth with its greatest extension perpendicular to the stretching direction.
Association of the reaction products in the ozone degradation of polyethylene and its relevance to the study of the fold surface structure
Authors: Patel G. N. , Keller A.
Published: April 2003

An association of reaction products was observed in the course of GPC analysis of ozone treated chain‐folded single crystals of polyethylene which, however, could be eliminated by washing with water. This recognition proved to be important for quantitative studies of the fold surface relying on oxidative fold cutting and should be of interest for studies of oxidative degradation phenomena for their own sake. With the association products appropriately removed, the random fold cutting mechanism could be more closely verified than was possible before. Anhydride linkages are suspected as the source of the association.
Low‐frequency dynamic mechanical behavior of lightly crosslinked 1,5‐trans‐polypentenamer in the rubberlike region
Authors: Hrouz J. , Janáček J.
Published: April 2003

The low‐frequency (10−3 to 5 × 10−1 Hz) dynamic mechanical properties were obtained over the temperature range of 25 to 96°C for 1,5‐trans‐polypentenamer networks prepared in the presence of 0,0.01, 0.02, 0.04, 0.1, 0.2, and 0.4% dicumyl peroxide. For comparison, similar properties of 1,4‐polybutadiene crosslinked with 0.02% dicumyl peroxide were also measured. Superimposed curves for the components of the dynamic compliance, Jp′ and Jp″, reduced to 25°C were obtained and the retardation spectra L were calculated over a range of four logarithmic decades deep in the rubberlike region. It was found that networks containing 0.04 and 0.1% DCP have a small loss maximum Jp″ in the reduced frequency region log ωaT between −2 and 0 which can be assigned to relaxations of untrapped entanglements. The values of (Jp′ − 1/ωη) for very lightly crosslinked polypentenamer networks approached equilibrium very slowly compared to 1,4‐polybutadiene crosslinked to the same degree, which suggests the participation of very long retardation times of this polymer which is also probably reflected in the comparatively high values of C2 of the Mooney–Rivlin equation.
Light scattering investigation of interaction between polymers in dilute solution
Authors: Kratochvíl Pavel , Vorlíček Jiří , Straková Dagmar , Tuzar Zdeněk
Published: April 2003

Parameters characterizing the interaction of nonidentical polymer molecules in dilute solutions of mixtures of two polymers have been defined on the basis of Stockmayer's theory of light scattering in multicomponent systems. Various procedures for evaluation of the interaction parameters from experimental data have been compared. Specific features of the investigation of such interactions are demonstrated with the scattering behavior of the system polystyrene‐poly‐(methyl methacrylate)‐dioxane.
The energetics of kinks in polyethylene
Authors: Boyd Richard H.
Published: April 2003

The energetics of kinks in polyethylene have been investigated by means of conformational energy calculations on crystalline arrays of C14H30, C18H38, and C22H46. All of the parameters required for assessment of relaxation effects by site theory were calculated including the static defect energies, barriers to defect reorientation, and site strains. Up to two deformable coordination shells in the surrounding lattice were included. In the energy minimization calculations, all molecular internal degrees of freedom were allowed to participate. The effects of chain mismatch along the C axis at large distances from the defect were calculated from a continuum theory. The static defect energy is calculated to be 6.6 kcal/mole for C14H30, and the barrier for reorientation of right‐handed to left‐handed kinks is 10 kcal/mole. The barrier to “unkinking” to the nondefect state is 2 kcal/mole. The strain induced by the defect is largely a shear in the {0 0 1} plane in the 〈1 1 0〉 direction. It is concluded that although the barrier to reorientation is consistent with kink reorientation contributing to the γ process the predicted intensity rules out any but a very weak contribution to the total process.
Heterogeneous nucleation of crystallization of high polymers from the melt. III. Nucleation kinetics and interfacial energies
Authors: Chatterjee A. M. , Price F. P. , Newman S.
Published: April 2003

In the melt crystallization of isotactic polypropylene, poly(ethylene oxide) and poly(butene‐1) in contact with substrates, the existence of a fixed number of nucleating sites on the substrate surfaces has been established. When these sites become active successively (the transient in the number of nuclei is long) during crystallization, pseudohomogeneous nucleation on the substrate occurs. Nucleation rates for poly(butene‐1) and poly(ethylene oxide) on substrates and in bulk have been measured. These data can be used for comparing the nucleating ability of substrates. Estimates of the variation of bulk nucleation rates from one volume element to another as well as for repeated crystallization within a given volume element have been included. Finally, the temperature coefficients of heterogeneous nucleation rates have been combined with the temperature coefficient of spherulitic growth rate of poly(butene‐1), to yield values of the interfacial energy parameters appearing in the theory of heterogeneous nucleation. The quantitative characterization of the nucleating ability of substrates by this method is an improvement over the mere use of nucleation densities or nucleation rates.
The optical interference pattern in a polystyrene craze layer
Authors: Doyle M. J.
Published: April 2003

In the interference pattern seen in monochromatic light reflected from a craze layer in polystyrene, the bright fringes are of alternating intensity. The phenomenon is explained in terms of a four‐beam interference. Apart from the two reflections from the outer surfaces of the craze layer others arise from a thin layer of approximately constant thickness within the craze layer at its median plane. The phenomenon provides independent evidence to support the electron microscopic observations of the microstructure of crazes in polystyrene.
Dynamics of macromolecular chains. III. Time‐dependent fluorescence polarization studies of local motions of polystyrene in solution
Authors: Valeur Bernard , Monnerie Lucien
Published: April 2003

Fluorescence anisotropy decay experiments are described for polystyrene in various ethylacetate‐tripropionin mixtures. Decay curve trends agree with the proposed theoretical autocorrelation function. Study of the effects of viscosity shows that the mean relaxation time varies according to a nonlinear law for low viscosities and that the relaxation time θ, reflecting the effects of the possible departures from the motions permitted by an ideal tetrahedral lattice, obeys a law of the type: θ = α + bη. Furthermore, the effects of the direction of the fluorophore transition moment are examined.
Dynamics of macromolecular chains. IV. Quenching and fluorescence polarization studies of polystyrene in solution
Authors: Valeur Bernard , Monnerie Lucien
Published: April 2003

Combined measurements of quenching and fluorescence polarization corroborate the results previously obtained by the polarized fluorescence anisotropy decay technique and, more especially, confirm the form of the proposed orientation autocorrelation function. The use of this method to determine the mean relaxation time of the relaxation time distribution is also explained.
Structural studies of polyesters. VIII. Molecular and crystal structure of polydiketene
Authors: Yokouchi Mitsuru , Chatani Yozo , Tadokoro Hiroyuki
Published: April 2003

The molecular and crystal structures of polydiketene were studied by infrared spectroscopy and x‐ray diffraction. It was confirmed from the infrared spectra that diketene molecules in the crystal polymerize by ring opening upon γ‐ray irradiation. The unit cell of the product as polymerized is orthorhombic,P22121‐D23, witha= 5.43 Å,b= 8.94 Å, andc(fiber axis) = 7.75 Å. Two molecules pass through the unit cellmagnified imageThe molecule has a conformation shown by the Fischer projection for a lefthanded (2/1) helix; The internal rotation angle around the O—C bond is nearlygauche(−84°), unlike other polyesters. On the basis of x‐ray analysis, several molecular conformation models were selected by utilizing calculations of intramolecular interaction energies.
Stress distribution along a craze: Some consequences of knight's analysis
Authors: Verheulpen‐Heymans Nicole
Published: April 2003

It is shown that the distribution of normal stress around a craze, found by Knight using a Fourier transform method may not be uniquely determined, and that in fact the stress field cannot be computed unless the rheological properties of the craze tip material are known.
Effect of fungal degradation on mechanical properties of cellophane
Authors: Bradley S. A. , Carr S. H.
Published: April 2003

Changes in dynamic mechanical properties of cellophane films due either to fungal attack or to hydrochloric acid hydrolysis have been measured. It appears that damage caused by cellulase enzymes that are released from a fungal overgrowth is localized in noncrystalline regions. These effects include a substantial reduction in elastic modulus, a reduction in temperature at which relaxation processes involving chain segmental mobility occur, and a broadening of loss tangent peaks due to segmental mobility and to rotations of methylol groups. Comparing results obtained from cellulase hydrolysis with those obtained from acid hydrolysis, it is clear that enryme attack proceeds by a characteristic and selective process. Implications regarding the embrittlement often seen to accompany biodegradation are discussed.
Brillouin scattering from polymer films
Authors: Patterson G. D.
Published: April 2003

Many polymers cannot be prepared as clear amorphous blocks suitable for classical light scattering studies. However, most linear polymers can be prepared as films which are somewhat transparent. With the advent of high contrast multipass interferometers, these films can now be studied by Brillouin scattering. This work demonstrates the wide range of polymeric materials that can now be studied by Brillouin spectroscopy.
Preparation and characterization of copolymers of chloroprene and methyl methacrylate
Authors: Khan A. A. , Brame E. G.
Published: April 2003

The preparation of chloroprene–methyl methacrylate copolymers in the presence of Lewis acids (Et1.5AlCl1.5) in hydrocarbon solvent and the effect of Lewis acids concentration on copolymer composition are described. 13C NMR spectra were obtained on these copolymers. In samples of high MMA content, tactic placements of MMA were observed as well as several different kinds of sequences for chloroprene and MMA. In samples of low MMA content, no tactic placements of MMA were found but several different kinds of chloroprene sequences were observed. From the analysis of the 13C NMR spectra of the different copolymers examined, it is apparent that all the various kinds of chloroprene sequences in these copolymers can be determined.
Polyethylene networks crosslinked in solution: Preparation, elastic behavior, and oriented crystallization. I. Crosslinking in solution
Authors: De Boer A. Posthuma , Pennings A. J.
Published: April 2003

A study has been made of the crosslinking of linear polyethylene in solution. Networks containing a low number of trapped entanglements and elastically ineffective chain ends were prepared by crosslinking high molecular weight linear polyethylene in 1,2,4‐trichlorobenzene solutions with dicumyl peroxide at 120°C. No syneresis was observed during crosslinking except at high peroxide concentrations. The networks were characterized by swelling measurements, infrared spectroscopy, and differential scanning calorimetry. The crosslinking efficiency, calculated from swelling, was found to be proportional to the square of the polymer volume fraction. The proportionality constant was 0.8, indicating close to unit efficiency for undiluted polymer.

Chemical modification of the polyethylene chains by attachment of peroxide and solvent fragments was of the order of one foreign unit per elastically active network chain, depending on peroxide and polymer concentration. Sol–gel analysis indicated that no chain scission occurred. These results are shown to be consistent with a “cage” mechanism for crosslinking. The possible topological consequence of this mechanism, preferential crosslinking of entanglements, is discussed. The concentration of trapped entanglements was also found to be proportional to the square of the polymer volume fraction. The proportionality constant corresponds to a molecular weight between entanglements of 4000 for the undiluted polymer, which is close to the value of 4200 found for networks prepared from the undiluted polymer. Since the results obtained are based mainly on the use of the swelling equation, different aspects of the applicability of this equation for the evaluation of the crosslinking process are discussed. As regards the reference dimensions, which should be known for a quantitative application of the elastic theory, the results strongly support the use of the dimensions of the network chains after completion of crosslinking.
Generalized correlations for molecular weight and concentration dependence of zero‐shear viscosity of high polymer solutions
Authors: Zakin J. L. , Wu R. , Luh H. , Mayhan K. G.
Published: April 2003

Data are presented to show that two correlations of viscosity–concentration data are useful representations for data over wide ranges of molecular weight and up to at least moderately high concentrations for both good and fair solvents. Low molecular weight polymer solutions (below the critical entanglement molecular weight Mc) generally have higher viscosities than predicted by the correlations.

One correlation is ηsp/c[η] versus k′[η], where ηsp is specific viscosity, c is polymer concentration, [η] is intrinsic viscosity, and k′ is the Huggins constant. A standard curve for good solvent systems has been defined up to k′[η]c ≈︁ 3. It can also be used for fair solvents up to k′[η]c ≈︁ 1.25· low estimates are obtained at higher values.

A simpler and more useful correlation is ηR versus c[η], where ηR is relative viscosity. Fair solvent viscosities can be predicted from the good solvent curve up to c[η] ≈︁ 3, above which estimates are low. Poor solvent data can also be correlated as ηR versus c[η] for molecular weights below 1 to 2 × 105.
Morphology and thermodynamic properties of solution‐grown single crystals of trans‐1,4‐polybutadiene
Authors: Marchetti A. , Martuscelli E.
Published: April 2003

The morphology and thermal behavior of trans‐1,4‐polybutadiene single crystals prepared from dilute solutions in n‐heptane have been investigated by electron microscopy, wide‐angle and low‐angle x‐ray diffraction, and differential scanning calorimetry. The thickness of the single crystals of trans‐1,4‐PBD is much greater, for the same undercooling, than that of other linear polymers. From the calorimetric study, convincing evidence of the presence, in the single crystals, of crystalline blocks of form 1 with two different thermodynamic stabilities is obtained and the relative amounts are calculated. From thermodynamic considerations we find a value of 75°C for the equilibrium transition temperature between forms 1 and 2, 139°C for the equilibrium melting temperature of form 2, and 31.2 erg/cm2 for the fold‐surface free energy of modification 2.