bluuebunny/crossref_metadata_2025 huggingface dataset:
Tensile strength of polyurethane and other elastomeric block copolymers
Authors: Smith Thor L.
Published: April 2003

Processes that impart strength and toughness are discussed along with reinforcement by colloidal plastics to indicate that high strength, except under restricted test conditions, necessitates a dispersed phase. Thereafter the dependence of the nominal and true tensile strengths on the type, size, and concentration of polar segments in polyurethane elastomers is considered. Data are first examined on formulations devoid of plastic domains and then on those containing domain‐forming segments that result from the reaction of toluene‐2,4‐diisocyanate (TDI) with either toluene‐2,4‐diamine or 4,4′‐methylene‐bis‐(2‐chloroaniline) and from the reaction of 4,4′‐diphenyl methane diisocyanate (MDI) with 1,4‐butanediol (BD). Segments from TDI and either diamine give plastic domains that are especially effective for augmenting strength over an extended temperature range. Segments from MDI and BD are comparatively ineffective, although the formulation studied exhibits high strength at and below room temperature owing to strain‐induced crystallization. From data on various segmented and triblock elastomers, general conclusions are drawn regarding the dependence of strength on the characteristics of the domains and the matrix. For some six segmented and triblock elastomers, it is found that the true tensile strength is essentially independent of the weight fraction of domains provided it exceeds 0.20 or thereabouts.
The effect of densification on the mechanical properties of amorphous glassy polymers
Authors: Bree H. W. , Heijboer J. , Struik L. C. E. , Tak A. G. M.
Published: April 2003

Four polymers, viz. polystyrene, polycarbonate, poly(methyl methacrylate), and poly‐(vinyl chloride), were cooled from the melt to room temperature under hydrostatic pressures of 30 and 1000 atm. Cooling under high pressure increased the density by 0.4–0.6%, and the effect of this has been examined for the torsional creep properties, the dynamic properties at 1 Hz, the Charpy impact strength, the thermal expansivity, and the torsional yield stress. It turned out that, in general, densification affects the thermomechanical properties only slightly.
Alternating‐current ionic conduction and dielectric relaxation of poly(vinylidene fluoride) at high temperatures
Authors: Yano Shinichi , Tadano Kenji , Aoki Koichiro , Koizumi Naokazu
Published: April 2003

Dielectric properties of poly(vinylidene fluoride) have been studied in the frequency range 20 Hz to 1 MHz and between 100 and 220°C, during heating and cooling. The dielectric constant and loss change abruptly at the temperature Tm corresponding to the melting point. At lower frequencies, two types of ionic conductin are observed. One appears below Tm and is attributed to interfacial polarization. The other occurs above Tm and is related to electrode polarization. These results suggest that a crystalline polymer is a heterogeneous medium for ionic transport, while the melt is a homogeneous medium. From these results, the nature of ac ionic conduction in crystalline polymers is discussed. At high frequency, the α relaxation is observed below Tm. It is due to the molecular motion in the crystalline region and disappears at Tm.
Optical studies of the deformation of model filled rubbers
Authors: Ong C. S. M. , Stein R. S.
Published: April 2003

The strain pattern about a spherical glass bead imbedded in a stretched rubber has been calculated and used to predict the birefringence and light scattering. This is compared with experimental measurements of the retardation pattern observed using a polarization microscope and deduced from the low‐angle laser Hv light scattering pattern. The agreement with theory is favorable. The light scattering is suggestive of similar origins of light scattering from crystallizing rubbers and from inhomogeneously crosslinked rubbers.
Relaxations in the transition region of crosslinked polyesters. II. The glass transition
Authors: Cook W. D. , Delatycki O.
Published: April 2003

The glass‐transition region of crosslinked polymers prepared from poly(1,2‐propylene phthalate fumarate) and styrene was studied using a torsion pendulum. The glass‐transition temperature and the modulus in the rubbery region of these polymers were analyzed in terms of the crosslink density. The styrene concentration at which the maximum crosslink density occurs, as estimated from the viscoelastic data, is found to be in agreement with estimates made by other workers using chemical methods.
Scattering of light from thin polymer films. I. Multiple scattering
Authors: Prud'homme Robert E. , Bourland Larry , Natarajan Raj T. , Stein Richard S.
Published: April 2003

A general method is described to take into account the multiple scattering effect in a small‐angle light scattering from thin polymer films. It is seen that multiple scattering tends to make the scattering envelope more diffuse, reducing the intensity in the high intensity regions and increasing it in the low intensity regions. The method is applied here to a spherulitic system, but it is valid for any other system where the principal scattering is in the forward direction.
Crystallization during polymerization of diazomethane. I. The boron trifluoride catalyzed reaction
Authors: Mucha Maria , Wunderlich Bernhard
Published: April 2003

The polymerization and crystallization of diazomethane was analyzed starting with various monomer and catalyst concentrations by following the monomer concentration and analysis of the solid polymethylene produced. Electron microscopy, thermal analysis, x‐ray diffraction, and viscometry and density determinations were used to characterize the crystals as produced and after etching with nitric acid. The crystals have a fibrillar and a lamellar component and show no regular chain folding of the molecules. The overall process follows only very approximately the path expected for an ideal living‐polymer system capable of reaction in solution and in the solid state. For more detailed correspondence, it was necessary to assume two reaction paths and two crystallization paths.
ESR study of radicals formed during tensile deformation of poly[p‐(2‐hydroxyethoxy) benzoic acid] fibers
Authors: Nagamura Toshihiko , Takayanagi Motowo
Published: April 2003

Radical formation during tensile deformation of highly oriented poly[p‐(2‐hydroxyethoxy)benzoic acid] fibers was investigated by electron spin resonance. Stretching of fibers in vacuo and in a stream of nitrogen gas at room temperature generated a large number of radicals which increased rapidly with macroscopic strain, while stretching in air generated only a small number of radicals. The radicals formed in vacuo or in nitrogen decayed rather rapidly after introduction of air. The observed spectrum was apparently a triplet with a line separation of about 7.5 gauss and a small asymmetry. The inspection of the hyperfine structure, line separation, and total width of the spectrum and the comparison between the observed and the calculated spectrum based on a model substance proved that the observed species is a phenoxy type radical generated by rupture of main chains. A small asymmetry of observed spectrum was explained by anisotropy of the g‐tensor. The alkyl end‐radical generated together with one of the phenoxy type could not be detected, perhaps owing to its high reactivity.
Small‐angle x‐ray study of deformed bulk polyethylene
Authors: Gerasimov V. I. , Genin Ya V. , Tsvankin D. Ya.
Published: April 2003

Scattering by extruded polyethylene films has been used to analyze in detail the small‐angle scattering of x‐rays by strained spherulitic samples. It is shown that the basic small‐angle patterns in spherulitic specimens can be obtained by summing small‐angle reflections from films drawn both parallel and normal to the direction of extrusion. The representation of a complex pattern by superposition of simpler reflection makes it possible to calculate local strains in various regions of spherulites in bulk specimens.
Determination of the Flory–Huggins χ parameter, the heat of dilution, and the excess heat capacity of some alkanes in polydimethylsiloxane by gas chromatography
Authors: Hammers W. E. , De Ligny C. L.
Published: April 2003

The change in standard chemical potential of a number of alkanes on PDMS going from dilute solution to the perfect vapor ΔḠ was measured by gas chromatography over a large range of temperatures. The change in standard chemical potential of the alkane going from the pure liquid to the perfect vapor ΔḠ was calculated from fugacity data. These data were fitted separately to three Taylor's series expansions wherein the (partial) heat capacity of vaporization is zero, constant, and linearly dependent on temperature, respectively. On the basis of statistical and physical arguments it was concluded that the partial excess functions determined by gas chromatography should be described with a temperature‐independent partial excess heat capacity.
Convergence of the distribution functions for wormlike chains
Authors: Shimada Jiro , Fujii Motoharu , Yamakawa Hiromi
Published: April 2003

The Daniels‐type distribution functions of the end‐to‐end distance of three‐dimensional and two‐dimensional wormlike chains are obtained to terms of order t−10, by an operational method with use of a digital computer, where t is the ratio of the total chain contour length to the Kuhn segment length in three‐dimensional cases and of the contour length to the persistence length in two‐dimensional cases. The convergence of the ring‐closure probability and the mean reciprocal distance is examined on the basis of these distribution functions. A similar study of the moment‐based distribution functions is also made.
Time‐dependent photocurrents in polyethylene
Authors: Wintle H. J.
Published: April 2003

A detailed study of the photocurrents in low‐density polyethylene at wavelengths of 350 nm, 300 nm, and 240 nm has confirmed that the current is a linear function of intensity and has established that the observed decrease of current depends on the integrated flux of quanta at the metal–polymer interface, and is independent of intensity and pulse repetition rate. Comparison with electron excitation experiments shows that in the present case, optical ionization occurs within a few angstroms of the interface.

Connections between the present results and known photodegradation data are explored, but no firm correlation can be obtained either for the initial “fast transient” or for the “slow transient” which occurs only in the shorter wavelength region. Possible models for hole injection are presented.
Crazing and fracture in crystalline, isotactic polypropylene and the effect of morphology, gaseous environments, and temperature
Authors: Olf H. G. , Peterlin A.
Published: April 2003

Stress crazing is studied in three forms of crystalline, isotactic polypropylene (PP): (1) smectic/nonspherulitic, (2) monoclinic/nonspherulitic, and (3) monoclinic/spherulitic PP. Optical and scanning electron microscopy as well as stress—strain measurements are used to characterize crazing behavior in these three forms as a function of temperature (−210 to 60°C) and of the gaseous environment (vacuum, He, N2, Ar, O2, and CO2). Forms 1 and 2 are found to craze much like an amorphous, glassy polymer in the temperature range between −210 and −20°C, irrespective of environment. The plastic crazing strain is large close to the glass‐transition range (ca. −20°C) of amorphous PP and in the neighborhood of the condensation temperature of the environmental gas. Near condensation, the gas acts as a crazing agent inasmuch as the stress necessary to promote crazing is lower in its presence than in vacuum. A gas is the more efficient as a crazing agent, the greater is its thermodynamic activity.

Spherulitic PP (form 3) crazes in an entirely different manner from an amorphous, glassy polymer, showing that the presence of spherulites influences crazing behavior much more profoundly than the mere presence of a smectic or monoclinic crystal lattice. Below room temperature, crazes are generally restricted in length to a single spherulite, emanating from the center and going along radii perpendicular, within about 15°, to the direction of stress. They never go along spherulite boundaries. Gases near their condensation temperature act as crazing agents much as in nonspherulitic PP. Above room temperature the crazes are no longer related to the spherulite structure, being extremely long and perfectly perpendicular to the stress direction. Apparently the crystals are softened enough by thermally activated segmental motion to permit easy propagation of the craze. The morphology of the fracture surfaces and its dependence on temperature and environment is described and discussed. Concerning the action of gases as crazing agents it is argued that the gas is strongly absorbed at the craze tip, where stress concentration increases both the equilibrium gas solubility and the diffusion constant. Hence, a plasticized zone is formed having a decreased yield stress for plastic flow. This is considered to be the main mechanism by which the gas acts as a crazing agent. In addition, reduction of the surface energy of the polymer by the adsorbed gas eases the hole formation involved in crazing.
Solvent effects in flow birefringence of polymer solutions. General theory and discussion of form effects
Authors: Fortelný I.
Published: April 2003

A new, more realistic optical model of a dilute polymer solution is used to calculate the intrinsic birefringence. A general formula is derived valid for an arbitrary equilibrium distribution function of particles in the system. Besides the contributions due to the polymer and solvent, the resulting relation for intrinsic birefringence also contains terms reflecting the effect of orientation of solvent surrounding the polymer chain and the contribution of optical interactions between polymer segments and molecules of solvent. A detailed discussion of the optical interactions in an isotropic solvent reveals that the problem may be transformed in the first approximation into that of interactions between excess dipoles; however, any separation of the macroform and microform effects has no theoretical justification. It is shown that the microform effect depends on a detailed optical model of the statistical segment, and this effect is calculated for two simple models. The expression suggested by Tsvetkov cannot be applied to a segment consisting of anisotropic monomers.
Mechanism of dc electrical conductivity in poly(vinyl chloride)
Authors: Lupu A. , Giurgea M. , Baltog I. , Gluck P.
Published: April 2003

Dc conductivity measurements were performed as a function of temperature on unplasticized poly(vinyl chloride) and on PVC plasticized with various amounts of dioctylphthalate. The conductivity curves consist of two or three straight‐line segments denoted I, II, and III with increasing of temperature. The intersection of segments I and II occurs at the glass‐transition temperature Tg. The slope in region I is independent of the DOP concentration, while the slope in region II decreases slowly with an increase in the amount of DOP. No dependence of the conductivity on the molecular weight was found. From the conductivity curves, activation energies were evaluated below and above Tg. These satisfactorily coincide with those determined by dielectric loss or by electrical transient phenomena. A dc conduction mechanism is proposed based on electronic hopping favored by the micro‐Brownian motions responsible for dielectric losses. These motions involve smaller chain lengths below than above Tg. The experimental results are discussed and interpreted in terms of the proposed mechanism.
Viscoelastic study of the conformational transition of poly(methacrylic acid) in dilute aqueous solution
Authors: Okamoto Hideho , Wada Yasaku
Published: April 2003

The dynamic viscosity of dilute aqueous solution of poly(methacrylic acid) (PMA) was measured over the frequency range 2–500 kHz for various degrees of ionization. The relaxation spectrum calculated from the viscosity exhibits a conformational relaxation spectrum in the short‐time region and a rotational one in the long‐time region. The former is fitted by the Zimm theory over the entire range of ionization, including the transition from a compact structure to an open one. The conformational relaxation time begins to increase at the midpoint of the transition region, but the rotational relaxation time increases very markedly in the initial stage of the transition.

The present and previously reported experimental findings are interpreted in terms of the assumption that the compact structure is stabilized by short‐range methyl–methyl bonding as well as “long‐range” methyl–methyl bonding (bonding between methyl groups spatially close but remotely connected along the chain contour). In the initial stage of the transition, the latter primarily break up, resulting in expansion of overall chain dimensions, and subsequently the former are destroyed, resulting in the change in local chain conformation.
The alpha–beta transformation in polypivalolactone. II. A simple mechanical model
Authors: Prud'Homme Robert E.
Published: April 2003

A simple mechanical model based on the equilibrium rate theory of Burte and Halsey is presented in order to explain the stress–strain curve of polypivalolactone (PPL) fibers. A semiquantitative application of this model indicates that the PPL alpha–beta transformation implies the cooperative deformation of at least thrity chain units and that the free energy difference between the alpha and beta states is of the order of 2 kcal/mole of monomer.
Thermal analysis and dilatometry of glasses formed under elevated pressure
Authors: Weitz Alexander , Wunderlich Bernhard
Published: April 2003

Densified glasses, formed from the liquid state by cooling at 5°C/hr under elevated pressures of up to 517 MN/m2, were studied by thermal analysis and dilatometry at ambient pressure. The materials studied were polystyrene, poly(methyl methacrylate), phenolphthalein, sucrose, and a 1 : 1 mixture by weight of potassium and calcium nitrate. Enthalpies of the densified glasses were found to be up to 2–6 J/g greater than the enthalpies of the glasses formed at atmospheric pressure. The major enthalpy and volume relaxation on heating the densified glasses was found to be not correlated The upper temperature limit of the glass‐transition region remained constant for all glasses cooled at various pressures, while the lower temperature limit of the polymeric glasses decreased up to 55°C with increasing pressure. The interpretation of the data suggests that an additional, significant volume relaxation occurred on depressurization at room temperature for all glasses analyzed.
Synthesis and solution properties of linear, four‐branched, and six‐branched star polyisoprenes
Authors: Hadjichristidis N. , Roovers J. E. L.
Published: April 2003

A number of linear, four‐ and six‐branched regular star polyisoprenes were synthesized by anionic polymerization techniques in benzene using lithium as the counterion and polyfunctional silicon chloride compounds as the coupling agents. Light‐scattering measurements in dioxane were performed in order to establish Θ solvent conditions. Determinations of the radius of gyration of the polymers of different structure indicate that g = 〈S2〉0,br/〈S2〉0,lin agree closely with random flight calculations for the ratios. Intrinsic viscosities determined in a Θ solvent establish g′ = [η]br/[η]lin to be 0.773 and 0.625 for the four‐ and six‐branched polyisoprenes, respectively. In a good solvent g′ values are slightly lower. These values are compared with theoretical estimates. Viscosities of 19.29% (w/w) solutions of the polyisoprenes in n‐decane at 25°C are correlated with the intrinsic viscosities of the polymers under Θ conditions.
Crystallization and melting of polyethylene under high pressure. I. Crystallization by slow cooling from the melt
Authors: Maeda Yoji , Kanetsuna Hisaaki
Published: April 2003

Crystallization and melting behavior of linear polyethylene under high pressures up to 6000 kg/cm2 has been investigated with a high‐pressure dilatometer. Crystallization was carried out at a cooling rate of 1°C/min from the melt at each pressure. The samples were characterized by differential scanning calorimetry, density, and electron microscopy. Folded‐chain crystals are formed in the low‐pressure region below 2000 kg/cm2. Crystallization in the intermediate‐pressure region between 2000 and 3500 kg/cm2 gives a mixture of folded‐chain and extended‐chain crystals. The extendedchain crystals are the more stable and predominate at increasing pressure. At high pressures above 4700 kg/cm2, two stages of crystallization and of melting can be observed. The phenomenon suggests that the two kinds of extended‐chain crystals with different thermal stability, i.e., the ordinary extended‐chain crystals and “highly extended‐chain” crystals form through individual crystallization processes from the melt at high pressure.
The statistics of chain sectioning experiments on cellulose fibers
Authors: Holt C. , Sellen D. B.
Published: April 2003

It has been suggested that transverse sectioning of natural cellulose fibers can be used to test ideas about microfibril structure. This proposal has been examined theoretically and numerical calculations of the weight‐distribution curve of sectioned chains are given for several different models. These calculations illustrate the effects that different types of chain folding have on the sectioned size distribution. The difficulties involved in the practical execution of this type of experiment are discussed and it is concluded that fiber‐sectioning experiments described in the literature do not disprove the folded‐chain hypothesis.
Shear‐induced crystallization of polymers. I. The four‐roller apparatus
Authors: Torza S.
Published: April 2003

We describe a new technique for producing fibrous crystals from shear‐induced crystallization of polymer solutions and polymer melts. Our technique makes use of a modified version of the 4‐Roller apparatus originally developed by G. I. Taylor to study the formation of emulsions. This apparatus generates a planar extensional flow field in which macromolecules are extended more easily than in flow fields with transverse velocity gradients.
Characterization of macromolecules in liquid solutions by thermal diffusion. I. Dependence of the soret coefficient on the nature of the dispersing medium
Authors: Gaeta F. S. , Scala G. , Brescia G. , Di Chiara A.
Published: April 2003

Experiments have been carried out on thermal diffusion of macromolecular particles dispersed in various liquids, with the object of checking some predictions of the radiation‐pressure theory of Soret effect in liquids and of establishing a method of physical characterization of macromolecules in liquid solutions. The experimental results confirm the importance of the ratio G between thermal conductivity K and (phase) velocity v of high‐frequency elastic waves of the materials composing the mixture in determining the thermodiffusive behavior of a liquid solution. We have shown that the migration of the macromolecular component takes place in the same direction in which thermal energy is flowing or opposite to it, depending on whether G of the dispersed particles is smaller or larger relative to the G of the liquid.

Another aspect of the same phenomenon may be observed when macroscopic pieces of nonmetallic materials are suspended in a liquid, and heat is made to flow through this solid plunger and the surrounding liquid. The experiments performed with molecular solutions and with macroscopic plungers mutually complement and confirm each other.

Anomalous results obtained in the case of solutions of polyvinylpyrrolidone in methanol are also discussed, and the possibility that this might be the consequence of the existence of a marked velocity dispersion in the high‐frequency region of the spectrum of thermal waves in both water and methyl alcohol is indicated.

Finally the possibility is hinted that thermal diffusion might have been responsible for the phenomena of molecular selection and evolution which ultimately led to the origin of life on our planet.
Pressure dependence of the thermal conductivity, thermal diffusivity, and specific heat of some polymers
Authors: Andersson Per , Sundqvist Bertil
Published: April 2003

The pressure dependence of the specific heat of poly(methyl methacrylate), polystyrene, and atactic and isotactic polypropylene was determined from simultaneous measurements of thermal conductivity and diffusivity in a cylindrical geometry at 300°K and in the pressure range 0–37 kbar. The thermal conductivity and the diffusivity both increase strongly with pressure, while the specific heat decreases. The pressure dependencies are most pronounced at low pressures. The results are compared with other experimental results and with theoretical calculations.
Crystallinity and the effect of ionizing radiation in polyethylene. I. Crosslinking and the crystal core
Authors: Patel  , Keller
Published: April 2003

An extensive study has been carried out on the effect of ionizing radiation on polyethylene in the form of solution‐grown single crystals to follow up preceding investigations which had indicated that the radiation‐induced effects along the fold surfaces could be significantly different from those within the crystal interior. In this first part of the series, radiation‐induced crosslinking was investigated in the case of “crystal core” material. This material, obtained by removal of the fold surface by oxidative degradation with ozone, consists of isolated foldfree crystal layers of dicarboxylic acids of uniform length, the length itself depending on the fold length of the starting crystal. This “core material” was irradiated by γ rays and the effect of crosslinking was followed by GPC analysis by recording the development of dimer, trimer, etc., peaks in the chromatograms. For a given dose, the fractional amount of crosslinked material is independent of the chain length. This, together with other effects described, provides unambiguous evidence that crosslinking occurs at the chain ends or, in other words, that there is no crosslinking within the interior of the paraffinoid lattice. Further, no permanent scission was observed to occur within the lattice, at least in amounts detectable by the present molecular weight measurements. The obvious significance of these effects for radiation studies on paraffinoid substances in general, beyond those of the present long‐chain dicarboxylic acids, is discussed prior to utilizing them in the study of chain‐folded polyethylene crystals in the following parts of the series.
Crystallinity and the effect of ionizing radiation in polyethylene. II. Crosslinking in chain‐folded single crystals
Authors: Patel G. N. , Keller A.
Published: April 2003

In order to ascertain whether the crystal core of irradiated polyethylene single crystals is free from crosslinks—as would follow from the results of Part I—the fold surface of irradiated single crystals was shaved off with ozone and the resulting product examined by GPC for molecular weight. It was found that on ozone degradation the entire material, which had been insolubilized by radiation‐induced crosslinking, has become soluble hence became available for the GPC analysis. The chromatograms displayed the same peaked development with degradation as the unirradiated crystals leading eventually to single traverse dicarboxylic acids. This proves the absence of crosslinks within the crystal interior of the material as examined by GPC. The appearance of some additional low molecular weight material, is attributed to scission at the radiation‐induced double bonds due to ozone which eliminates the possibility of the existence of crosslinks within the lattice such as might provide scission sites for ozone. The conclusion could therefore be reached that, to the extent assessable by our GPC test, there are no radiation‐induced crosslinks within the crystal lattice, hence the crosslinks produced must be entirely confined to the fold surface region of the crystals.
Crystallinity and the effect of ionizing radiation in polyethylene. V. Distribution of trans‐vinylene and trans,trans conjugated double bonds in linear polyethylene
Authors: Patel G. N.
Published: April 2003

Freeze‐dried chain folded single crystals and the single crystals without amorphous surface layers (crystalline cores) of different thicknesses of linear polyethylene were irradiated with 60Co γ‐rays up to 600 Mrad. Concentration of trans‐vinylene double bonds and conjugated diene produced during irradiation of the crystals was measured by infrared. Concentrations of trans‐vinylene and of the conjugated diene were independent of thickness of crystalline core which suggest that the double bonds wer randomly distributed in the crystalline parts of the crystals. Concentrations of trans‐vinylene and of conjugated double bonds were lower in chain‐folded crystals than in the crystalline cores and this suggests that the folds (amorphous surface layers) are less preferential sites for formation of the double bonds. The zero‐order growth and first‐order decay kinetics of trans‐vinylene double bonds was studied by the equation derived by Dole et al1. The equation is strictly obeyed up to 300 Mrad and the results then deviate. Since there is the decay of trans‐vinylene double bonds and though there are no crosslinks in the crystalline cores, it has been suggested that the decay of the double bond does not result in the crosslinks.
Dielectric and depolarization thermocurrent study of the γ relaxation in polyethylene isophthalamide
Authors: Lacabanne C. , Chatain D. , Guillet J. , Seytre G. , May J. F.
Published: April 2003

The depolarization thermocurrents (DTC) from polyethylene isophthalamide are studied below the glass‐transition temperature. The “entire” DTC spectrum is analyzed in terms of a continuous distribution of relaxation times; the corresponding distribution function is very close to that which fits data deduced from bridge measurements.

The complex DTC spectrum can be experimentally resolved into single relaxation time processes. The analysis of each “elementary” DTC peak yields dielectric dispersion and relaxation time which allow one to calculate the frequency variation of the complex dielectric constant. The corresponding Cole–Cole plot is in good agreement with that deduced from studies of the “unresolved” γ relaxation.
Superstructure in segmented polyether–urethanes
Authors: Chang Yeong‐Jen Peter , Wilkes Garth L.
Published: April 2003

The morphology of several series of segmented polyether–urethanes was studied. The “hard” segments contained urethane and urea linkages formed by 4,4′‐dicyclohexylmethane diisocyanate (Hylene W) and selected aliphatic and aromatic monomeric diamines (DA). The “soft” segments were composed of oligomeric poly(ethylene oxide) (PEO), poly(propylene oxide) (PPO), or both PEO and PPO. For studying the composition–morphology relationships, the molecular weight and relative content of PEO, and the relative content of PPO were varied systematically. Different diamines were used as chain extenders. The methods of wide‐angle x‐ray diffraction (WAXD), small‐angle x‐ray scattering (SAXS), polarizing microscopy, scanning electron microscopy (SEM), and differential scanning calorimetry (DSC) were employed in the investigation. The effects of PEO content on domain formation were very significant. Calculations based on a highly simplified model indicated that, for two adjacent molecules, if two hard segments are associated with each other, the probability for the association of the next two hard segments varies inversely with the third power of soft segment length. Copolymers composed of both POE and PPO displayed enhanced domain and anisotropic superstructure. The phenomenon was interpreted in terms of polymer incompatibility. The effects on morphology of different DA's as chain extenders were tentatively accounted for by the symmetry, hydrogen bonding, and rigidity of the hard segments as well as their incompatibility with the soft segments. The formation and deformation of superstructure were of particular interest. A model was proposed to account for the formation of the resultant anisotropic structure and mechanical properties.
Dynamics of macromolecular chains. II. Orientation relaxation generated by elementary three‐bond motions and notion of an independent kinetic segment
Authors: Valeur Bernard , Monnerie Lucien , Jarry Jean‐Pierre
Published: April 2003

In the preceding paper, general equations were established for the motions of chains confined to a tetrahedral lattice. In the present paper, bond orientation correlation and autocorrelation functions are explicitly calculated for the case where only three‐bond elementary motions are considered. Effects due to the chain end are analyzed and the relaxation time distribution function is established. The expressions obtained reflect the influence of the chain structure. Finally, to characterize the dynamic behavior of chains in orientation relaxation experiments, the notion of an independent kinetic segment is proposed.
The role of dislocations in the solid‐state polymerization of monomers having conjugated triple bonds: A study of 2,4‐hexadiyne‐1,6‐diol bis(p‐toluene sulfonate)
Authors: Schermann Walter , Wegner Gerhard , Williams John O. , Thomas John M.
Published: April 2003

The crystal structure of the monomer bis(p‐toluene sulfonate) ester of 2,4‐hexadiyne‐1,6‐diol (pT) is conducive from the viewpoint of both the separation distances and molecular configuration, to polymerization, irrespective of whether initiation is thermal, photochemical, or mechanical. The dislocations present in the monomer and polymer structures have been characterized by employing optical microscopic techniques. The slip system (102)[010] is found to be present in both monomer and polymer crystals but the (010)[001] system is found only in the monomer. On this basis a crystal structure for the monomer is proposed based on existing crystallographic information relating to the structure of the polymer. Dislocations are thought, on energetic grounds, to facilitate nucleation of product in the thermal polymerization but have no observable influence on the photoinduced reaction which proceeds homogeneously through the bulk.
Characterization of selectively degraded poly(ethylene terephthalate)
Authors: Duong D. T. , Bell J. P.
Published: April 2003

To investigate the morphology of unoriented poly(ethylene terephthalate) (PET) films and the selective character of the aminolysis of PET, 67% crystalline polymer samples were degraded with 40% aqueous methylamine at room temperature. The aminolyzed PET samples were subjected to gel permeation chromatography (GPC), viscometry, electron microscopy, and small‐angle x‐ray diffraction (SAXD). Weight loss and density crystallinity measurements were also made.

After 24 hr of aminolysis, the amorphous regions and chain folds were completely removed. The long molecular chains in the semi‐crystalline polymer were reduced to monodisperse rods having a molecular weight of 1,800. The corresponding lamellar thickness was calculated to be 101 Å, consistent with the x‐ray diffraction and electron microscope (EM) measurements. The EM photographs of “stripped” crystals show the lamellar structure previously found for other selectively degraded polymeric materials. The weight of crystalline debris remaining was consistent with the initial crystallinity. After degradation the crystallinity as determined by density was 96%.
Crystal deformation in aromatic polyesters
Authors: Jakeways R. , Ward I. M. , Wilding M. A. , Hall I. H. , Desborough I. J. , Pass M. G.
Published: April 2003

A study has been carried out of the changes in the x‐ray diffraction patterns which occur when oriented fibers or tapes of poly(trimethylene terephthalate) (3GT) and poly‐(tetramethylene terephthalate) (4GT) are subjected to mechanical tensile stress. Although the polymers show very different behavior in detail, in both cases comparatively large reversible lattice strains are observed (∼ several %). The diffraction pattern of 3GT changes monotonically with increasing macroscopic strain, suggesting that the lattice responds immediately to the applied stress, and deforms as though it were a coiled spring. In 4GT, on the other hand, there is no detectable change in the x‐ray diffraction pattern at low macroscopic strains, i.e., low values of the applied stress. At higher stresses, changes in the pattern occur which suggest a definite change in the crystal structure. Finally at the highest values of applied stress, the lattice deformations cease to increase. A preliminary discussion is presented of the relationship of these x‐ray diffraction results to the mechanical stress–strain behavior.
On the refractive indexes and birefringence of nylon 6 yarns as a function of draw ratio and strain
Authors: Gaur H. Angad , De Vries H.
Published: April 2003

A systematic study of the dispersion curves of the refractive indexes of nylon 6 yarns was made. The parameters were the draw ratio and strain. The measurements show that the dispersions of the refractive indexes n∥ and n⊥, parallel and perpendicular to the fiber axis, are equal, independently of draw ratio and strain. The average dispersion equals nF − nC = 109 × 10−4. Consequently, the birefringence is, within experimental accuracy, independent of the wavelength. The refractive indexes and the birefringence show a change in trend at 10–12% strain. This point corresponds to the yield strain in the stress–strain diagrams. The inference is that beyond the yield point the overall molecular orientation must increase less strongly with strain than before. An analysis shows that the Lorentz–Lorenz relation holds for the average refractive index n̄ = ⅓ (n∥ + 2n⊥). So the change in n̄ versus draw ratio is mainly due to the change in density. By applying the Lorentz–Lorenz relation to the change of n̄ on straining, a value of Poisson's ratio (μ) could be derived. The average value found for nylon 6 yarns was μ = 0.48, which means that the density hardly changes with strain.
Laser light scattering studies of poly(L‐lysine HBr) in aqueous solutions
Authors: Lee W. I. , Schurr J. M.
Published: April 2003

A simple theory for the relaxation of concentration fluctuations in polyelectrolyte solutions is presented, and particular results for the high‐salt and no‐salt limiting cases are discussed.

Autocorrelation functions for the fluctuating intensity of scattered light from dilute aqueous solutions of poly(L‐lysine HBr) (PLL‐HBr) with and without added salt have been observed over a wide range of pH. The observed autocorrelation functions are in general very satisfactorily represented by single exponentials except at high pH (>10.5), where considerable aggregation is manifested. Solutions of PLL HBr without added salt exhibit extraordinary behavior, evident at low pH, involving a species with a very slowly decaying autocorrelation function. Though this species is readily annealed to a more ordinary individual free‐molecule form by cycling the pH to 9.5 or higher and back, the resulting molecules are found to require unusually long times to reach internal configuration equilibrium under low pH conditions. Solutions of PLL‐HBr in 0.2M NaBr and 0.1M NaCl are apparently free of similar extraordinary effects and show the normal isothermal helix–coil transition accompanied by a 15–30% rise in the diffusion coefficient to a maximum at pH 10.5, which is interpreted in terms of a change in molecular dimension of an interrupted helix.

The predicted K2 dependence of the reciprocal relaxation time and enhancement of the apparent diffusion coefficient of the polyelectrolyte in the absence of salt is confirmed.
Mechanochemical reaction of polymers by ultrasonic irradiation. I. Mechanochemical reaction in mixtures of polystyrene, styrene, and cyclohexanone
Authors: Fujiwara Hideki , Okazaki Kazufumi , Goto Kunio
Published: April 2003

Mechanical degradation and mechanochemical polymerization in polystyrene–styrene–cyclohexanone mixtures have been studied by ultrasonic irradiation at 60°C. The number of fresh polymer chains after the degradation is 2 × 10−5 mole l−1 hr−1. The rate equations for mechanical scission and mechanochemical polymerization have been deduced. The rate equation for mechanical scission was found to be in agreement with the expression of a previous paper. In addition, the rate equation for mechanochemical polymerization is not essentially different from that for the general radical polymerization in the presence of solvents. The kinetic chain length for polymeric free radicals in the polymerization process has been calculated. The mechanochemical polymerization of styrene was initiated by only one of the two kinds of end radicals after mechanical scission of polystyrene. The molecular weight distributions of the samples after the degradation and the polymerization have been compared and discussed.
Transitions in poly(diethyl siloxane)
Authors: Beatty C. L. , Karasz F. E.
Published: April 2003

An adiabatic heat capacity study of poly(diethylsiloxane) confirms that it has a single glass transition occurring at 130°K, the lowest glass transition reported to date for a high molecular weight polymer. The two previously reported glass transitions are first‐order thermodynamic peaks whose location is dependent upon prior thermal history. Combination of these data with low‐temperature x‐ray diffraction indicates that the transitions in this temperature range are related to a crystal–crystal transformation. A crystal melting transition is observed near 270°K. In addition an anomalous rise in heat capacity near 60°K suggests a sub‐glass transition of unknown origin.
Application of holographic interferometric microscopy to the study of diffusion in the polyvinylpyrrolidone–iodine system
Authors: Cournoyer R. F. , Rhodes M. B. , Siggia S.
Published: April 2003

Interferometric studies of the diffusion of molecular iodine into polyvinylpyrrolidone (PVP) are described. The diffusion process is observed by means of a holographic microscope which, with a camera, permits holograms to be recorded during the polymer–iodine interaction. The holograms are subsequently used to produce interferograms that monitor the diffusion process as a function of time. Measurements taken from the interferograms indicate that the diffusion mechanism is not purely Fickian and that the diffusing boundary of iodine is characteristic of case II diffusion. The interferograms yield values for average diffusion coefficients as a function of sample thicknesses that range from 2.32 to 9.53 × 10−10 cm2/sec.
Persistent polarization in poly(vinylidene fluoride). II. Piezoelectricity of poly(vinylidene fluoride) thermoelectrets
Authors: Murayama Naohiro , Oikawa Takao , Katto Takayuki , Nakamura Ken'ichi
Published: April 2003

The piezoelectricity of PVDF thermoelect rets formed with vacuum‐coated aluminum electrodes has been investigated in detail. The piezoelectricity depends on the β‐form crystal structure of PVDF homopolymer and copolymers. However, the piezoelectricity is not attributed to the stress dependence of the spontaneous polarization of β‐form crystals, but rather to the persistent polarization arising from trapped charges. The trapping mechanism is discussed.
Low‐temperature relaxations in styrene–crosslinked polyester networks
Authors: Cook W. D. , Delatycki O.
Published: April 2003

Two low‐temperature dynamic mechanical relaxations have been observed in networks formed by copolymerization of poly(1,2‐propylene fumarate) and poly(1,2‐propylene phthalate fumarate) with styrene. The γ relaxation which occurs around −100°C (1 Hz) is induced by small amounts of water, while the broad γ′ relaxation is reduced in height by the presence of water. Neither xylene nor 1,2‐propylene glycol induced a γ relaxation. The γ relaxation was ascribed to motions involving a fumarate ester group–water complex.
The effect of prior crystallinity on the flow‐induced crystallization of poly(ethylene oxide)
Authors: Theil Michael H.
Published: April 2003

After flowing in a dilatometer bulb for a small fraction of the duration of the transformation, a relaxed melt of poly(ethylene oxide) (M̄n = (5.9 ± 0.1) × 103) showed marked increases in isothermal crystallization rate. The extent of increase was greater when flow was imposed at modestly later stages rather than at the earliest stage of a crystallization. Kinetic parameters for the flow‐induced crystallizations were obtained via modification of the conventional mathematical treatment of the kinetics of phase change, thereby allowing the analytical resolution of the overall process into flowinduced and quiescent components. Determination of the flow‐induced crystallization parameters required independent determination of the kinetic parameters for quiescent crystallizations at that temperature. The Avrami exponents nf which characterized the flow‐induced portions of the crystallizations were larger for those instances in which flow was imposed at the more advanced stages of the crystallizations, thus indicating a transition in crystallization mechanism. It is suggested that prior crystallinity present at the time of flow contributed to the crystallization by serving as a source of nucleation sites. However, in light of the experimental procedure employed, values of nf approximating 4 that were obtained are not susceptible to mechanistic interpretations now extant.
Infrared spectroscopic evidence of structural defects in the crystalline regions of trans‐1,4‐polychloroprene
Authors: Tabb D. L. , Koenig J. L. , Coleman M. M.
Published: April 2003

Infrared spectra have been obtained for the crystalline regions of samples of predominantly trans‐1,4‐polychloroprenes polymerized at −20, 0, and 40°C. Spectral differences among the polychloroprenes are interpreted in terms of the increase in structural irregularities that occur as the polymerization temperature is increased. Results of this study indicate that crystallization occurs with random inclusion of these structural irregularities into the crystalline domains. The conclusion is supported by the spectra of the crystalline regions of a chloroprene copolymer containing known impurities in the form of 2,3‐dichloro‐2‐butenylene units in addition to the normal 2‐chloro‐2‐butenylene units.
Folded chain crystallization of poly(N‐vinylcarbazole)
Authors: Griffiths C. H.
Published: April 2003

A study of the morphology of thermally induced crystallization in poly(N‐vinylcarbazole) has shown the formation of folded chain lamellae. Diffraction analysis of multiple and single lamellae indicates a paracrystalline structure with hexagonal symmetry about the chain axis and an interchain spacing of 12.00 Å. No sharp reflections due to chain axis periodicity were observed and the chain axis period was calculated from the crystalline density extrapolated to 100% crystallinity. This gave a chain axis period/monomer unit of 2.16 Å consistent with an isotactic 3/1 screw axis and a basic trigonal structure with a = 12.00 Å and c = 6.47 Å.
ESR evidence for main‐chain scission produced by mechanical fracture of polymers at low temperature
Authors: Sakaguchi Masato , Sohma Junkichi
Published: April 2003

ESR spectra have been observed from several polymers (polyethylene, polypropylene, polymethylmethacrylate, polytetrafluoroethylene, and polybutadiene) which were mechanically fractured in vacuum at 77°K. The spectra permit identification of the free radicals produced in chain scission. It has been demonstrated for the polymers of the typemagnified imagesuch as polypropylene and poly(methyl methacrylate), that the mechanical fracture produces two different scission radicals in pairs, namely,magnified imageThe results indicate convincingly that microscopic scission of polymer chains is caused by macroscopic destruction of polymeric material. The critical molecular size for mechanical rupture of polyethylene chains was experimentally determined to be a degree of polymerization between 70 and 100. This size agrees fairly well with the value predicted from a theoretical model.