bluuebunny/crossref_metadata_2025 huggingface dataset:
The relationship between chemical structure and viscoelastic properties of linear aliphatic polyesters
Authors: Ito M. , Kubo M. , Tsuruta A. , Tanaka K.
Published: April 2003

The effects of Chemical structure on the molecular motions in linear aliphatic polyesters have been investigated with a free‐oscillation torsion pendulum. Broad‐line NMR provided supplementary information. In the γ relaxation which corresponds to the local‐mode motions of main chains in the noncrystalline region, the polyesters which are composed of two methylene units in the diol part of the chemical repeat unit showed an extremely asymmetric loss curve with a relatively high‐loss peak temperature compared with that of the other polyesters. In addition to the two relaxations (β,γ) which have been observed in earlier dielectric measurements, a new relaxation (α) was found on the high‐temperature side of the glass transition of the polyesters. The α relaxation was assigned to molecular motions of methylene segments in the crystalline region. The α and β relaxations of the two‐dimensional series are situated close to the temperatures found for other polyesters with rather long methylene sequence in the chemical repeat unit. The results were explained in terms of a difference on the chain mobility in the noncrystalline regions which may be related to the difference of chemical structure of the polyesters.
Statistical thermodynamics of polymer crystal and melt
Authors: Simha Robert , Jain R. K.
Published: April 2003

A crystalline‐state theory recently developed by Midha and Nanda is commented on and applied to the isobars of polyethylene, poly(vinylidene fluoride), and poly(chlorotrifluoroethylene) at atmospheric pressure, and to an isotherm of polyethylene. Satisfactory agreement with experiment results. This includes the volume change at the melting point Tm and the volume difference ΔV between crystal and melt below Tm, when crystal and the earlier liquid‐state theory are combined. A similar agreement is noted with respect to the results at high pressure. The scaling parameters obtained indicate the approximate role of melt temperature and volume as reducing quantities. An inverse proportionality between Tm and αl, the expansivity of the melt at Tm, derived much earlier for low‐molecular‐weight solids, is recovered with an identical numerical coefficient. The thermodynamic functions of polyethylene are investigated in both phases. For this purpose contributions of internal harmonic modes are considered within the framework of the equivalent s‐mer model. One or, at most, two average frequencies are adequate to represent the temperature dependence of the excess free energy and entropy over the value at absolute zero, when the external contributions are included for the crystal. A similar representation of the hard modes can be adopted for the melt. However, the free energy of segmental disorientation computed either from a constant entropy for the s‐mer or a rotational isomeric state model for the isolated chain does not appear to be an adequate representation over a sufficient temperature range. An additional temperature‐dependent term in the entropy and free energy is introduced and tentatively attributed to a volume‐ and temperature‐dependent short‐range ordering. Good agreement with experiment, including the entropy and temperature of fusion, ensues.
A new technique for studying gelation in polyesters
Authors: Martinelli F. J.
Published: April 2003

A new method for studying polymer network formation has been devised. Crosslinking reactions are carried out in a recording viscometer, which provides accurate determination of incipient gel points and also serves as a high‐speed stirrer. The molten, nonstoichiometric mixtures are reacted to completion to eliminate the inaccuracies inherent in the determination of reaction extent and this, together with the use of esterification reactions with minimal side reactions, reduces many of the problems of previous methods. The experimental results for the reactions of simple model compounds are in very close agreement with Flory's network theory. A system containing crosslinking reagents with unequally reactive groups has also been considered and the accuracy of the method enables the reactivity ratios of the different groups to be calculated.
Steady‐state and dynamic rheology of poly(1‐olefin) melts
Authors: Wang Jeou‐Shyong , Knox Jack R. , Porter Roger S.
Published: April 2003

The steady‐state and dynamic melt rheology for a series of poly(1‐olefins) has been investigated. The series includes poly(1‐butene), poly(1‐hexene), poly(1‐heptene), poly(1‐octene), Poly(1‐undecene), poly(1‐tridecene), poly(1‐hexadecene), and poly(1‐octadecene). The flow behavior was investigated by use of a Weissenberg rheogoniometer. Measurements on poly(1‐butene) were also made using an Instron capillary rheometer. The empirical relationship developed by Cox and Merz was obeyed for the entire series of poly(1‐olefins) at all temperatures investigated. Graessley's theory was used to calculate the flow curves for the poly(1‐olefins) from the measured molecular weight distributions. The purpose was to investigate the effect of polymer composition on the shear rate dependence of viscosity. It was found that all experimental flow curves except those for poly(1‐hexene) can be fitted with the calculated curves from the individual molecular weight distributions. The conclusion is made that flow curves of poly(1‐olefins) depend predominately on molecular weight distribution and are essentially independent of side‐chain length even for poly(1‐olefins) with pendant groups as long as 16 carbon atoms. The low‐shear limiting Newtonian viscosity η0 for all poly(1‐olefins) was expressed by, η0 = KM̄ or by η0 = K′P̄ where M̄w is the weight‐average molecular weight and P̄w is the weight‐average degree of polymerization. The K and K′ values obtained decrease systematically as the side chain is increased.
Influence of extrusion ratio on the thermal properties and morphology of ultradrawn high‐density polyethylene
Authors: Kojima Shunji , Desper C. Richard , Porter Roger S.
Published: April 2003

Solid‐state extrusion of high‐density polyethylene (HDPE) has received considerable attention. It has been shown that extrudate may have high values of optical clarity, tensile modulus (∼70 GPa = 7 × 1011 dyn/cm2), and c‐axis orientation. The effects of extrusion conditions on the properties of the resultant fibers have, however, not yet been clarified. A systematic study has thus been made here to evaluate extrusion pressure, temperature, and extrusion (draw) ratio, and the molecular weight of extruded HDPE. The effects of extrusion ratio on the degree of crystallinity, melting behavior, crystal orientation, and dimensional change along the extrusion direction are reported.
Influence of extrusion ratio on the tensile properties of ultradrawn polyethylene
Authors: Kojima Shunji , Porter Roger S.
Published: April 2003

The tensile properties have been evaluated for high‐density solid‐state polyethylene extruded to different extrusion (draw) ratios. The results are compared with measured and theoretical values on this and other polymers. An extrusion (draw) ratio and a deformation gradient are defined and discussed. The content of extended tie molecules in extruded high‐density polyethylene was calculated from a model and modulus data.
Low‐temperature dielectric spectrum of thermally oxidized polyethylene
Authors: Gilchrist John Le G.
Published: April 2003

Three loss peaks in the dielectric spectra of thermally oxidized polyethylene at temperatures below 50°K are each apparently associated with specific species of nonvolatile oxidation products involving hydrogen atoms. We report how each is influenced by room‐temperature rolling, heat treatment, isotopic substitution, and chemical attack. One, the Vincett‐Phillips peak, is susceptible to attack by Cu2+, Fe3+, and HI, and is attributed to a hydroperoxide species. Its rapid and easy determination has promise in the study of polyethylene oxidation. Carson's (higher‐frequency) peak is tentatively attributed to an alcohol species and a new (lower‐frequency higher‐temperature) peak is described but not yet attributed. A few additional observations are made on the loss peaks associated with antioxidants of the substituted phenol type, as reported by Thomas and King.
Fracture surface morphology and phase relationships of polystyrene/poly(methyl methacrylate) systems. I. Low‐molecular‐weight polystyrene in poly(methyl methacrylate)
Authors: Parent Raymond R. , Thompson Edward V.
Published: April 2003

Samples of low‐molecular‐weight polystyrene (PS) in poly(methyl methacrylate) (PMMA) were prepared by first dissolving PS in methyl methacrylate monomer and then polymerizing the monomer. Forty‐three specimens of varying number‐average molecular weight (2100–49,000) and composition (5–40 wt %) of PS were prepared, and the surface morphology and phase relationships studied by scanning electron microscopy. Four distinct types of phase relationships were observed: (i) a single phase consisting of PS dissolved in PMMA; (ii) PS dispersed in PMMA; (iii) PMMA dispersed in PS; and (iv) regions of PS dispersed in PMMA coexisting with regions of PMMA dispersed in PS. Values of the size and population density of the dispersed particles are reported. Finally, the size and distribution of the dispersed particles and the various types of phase relationships are discussed in terms of the ternary polystyrene/poly(methyl methacrylate)/methyl methacrylate phase diagram.
Selective chemical etching of poly(ethylene terephthalate) using primary amines
Authors: Sweet G. E. , Bell J. P.
Published: April 2003

Several primary amines have been examined as selective degradative etchants for the investigation of poly(ethylene terephthalate) (PET) morphology. The objective is to remove less ordered regions, leaving crystals intact. The amines include 40% and 20% aqueous methylamine, 70%–40% aqueous ethylamine and pure and 40% aqueous n‐propylamine. Weight‐loss and x‐ray diffraction data show that certain concentration of aqueous amine solution simultaneously degrade and crystallize PET. This observation indicates the hazard of using some of these amine reagents to characterize PET morphology since the crystalline structure found after etching is likely to be a result of solvent‐induced crystallization during degradation. Data for 40% aqueous methylamine used at room temperature shows that crystallization does not occur during etching, and in light of earlier research indicates the favorable nature of this reagent as a selective degradative medium for PET. Application of this reagent disclosed that in oriented PET fibers chemical stress cracking occurs, causing the degradative reagent to lose its selectivity.
An ESR study of PMMA mechanoradicals and of their interaction with oxygen
Authors: Pilař J. , Ulbert K.
Published: April 2003

Analysis of ESR spectra of mechanoradicals from poly(methyl methacrylate) reveals that after mechanical degradation in vacuo at 77°K, the sample contains two types of primary radicalsCH2C(CH3)(COOCH3) (I) and CH2C(CH3)(COOCH3)CH2 (II) produced by the breaking of the polymer chain, and secondary radicals CH2C(CH3)(COOCH3)CHC(CH3)(COOCH3)CH2 (III). With increasing temperature, radical I remains stable while II reacts with methylene hydrogen of the polymer chain giving rise to the secondary radical III, which decays and finally disappears as the temperature rises. After admission of oxygen at 113°K, the polymer radicals react with oxygen with formation of polymer peroxy radicals ROO. and diamagnetic dimers. With increasing temperature the latter dissociate again to the original polymer peroxy radicals which gradually decay, if the temperature is increased further. The present results are compared with earlier ones obtained on poly(ethylene glycol methacrylate) (PGMA).
Hydrostatic extrusion of linear polyethylene: Effects of molecular weight and product diameter
Authors: Gibson A. G. , Ward I. M.
Published: April 2003

Oriented rods of linear polyethylene have been prepared by hydrostatic extrusion at 100°C. Materials having a range of different molecular weights were investigated and their behavior was found to correlate well with the melt flow index. The differences in extrusion process characteristics for large‐ and small‐diameter products are discussed. In this context the effect of deformational heating is important and criteria are suggested for determining its significance and also for determining the stability of the process in terms of a critical extrusion pressure.
Chemical degradative stress cracking of poly(ethylene terephthalate) fibers
Authors: Sweet G. E. , Bell J. P.
Published: April 2003

Poly(ethylene terephthalate) (PET), after certain thermal and mechanical histories, exhibits stress cracking when exposed to 40% aqueous methylamine. This reagent has also been used for selective degradation of PET films. Stress cracking is shown to occur during degradation only when a specimen supports an internal or externally applied stress, above a critical level. The cracking density in a filament is shown by the present work to increase as the draw ratio is increased or when the fiber is highly annealed. This increased cracking is associated with an increase in the magnitude of the internal residual stress resulting from molecular orientation developed during these processes. Because of this, crack density and fiber birefringence were found to correlate well. In addition, the geometry of the stress‐cracking pattern along a filament is affected by internal residual stress since the propagation of spiral and helical cracks results from the effect of a biaxial stress field remaining at the filament surface after processing.
Separation of dextrans by gel permeation chromatography
Authors: Soeteman A. A. , Roels J. P. M. , Van Dijk J. A. P. P. , Smit J. A. M.
Published: April 2003

The role of the intrinsic viscosity [η] as separation parameter in gel permeation chromatography (GPC) was studied for dextrans (from Leuconostoc mesenteroids B512) dissolved in water with deactivated silicagel (Porasil) as the column‐filling material. For that purpose specific viscosities of dextran fractions eluted by GPC were measured as a function of the elution volume v. Provided that the elution volumes are corrected for zonal spreading, they are related to the intrinsic viscosities in an unambiguous way, probably reflecting a unique relationship between degree of branching and molecular weights. This was further investigated by developing an iteration method to prepare two calibration curves γ(v) and g(v), respectively, relating ln[\documentclass{article}\pagestyle{empty}\begin{document}$\left[ {\bar \eta } \right]$\end {document}] and InM (M is the molecular weight) to v. It required that the weight‐average molecular weight Mw, the number‐average molecular weight Mn, and the average intrinsic viscosity [\documentclass{article}\pagestyle{empty}\begin{document}$\left[ {\bar \eta } \right]$\end {document}] for a number of dextran samples (broad distributions) be previously known. The calibration curves found lead to consistent values of the above‐mentioned averages. Moreover, they allow‐establishment of the [\documentclass{article}\pagestyle{empty}\begin{document}$\left[ {\bar \eta } \right]$\end {document}]‐M relationship over the range 5000 < M < 500,000.
A simple model illustrative of some features of polymer dynamics
Authors: Jones D. A. , De Haro M. Lopez , Pugh D.
Published: April 2003

A quasi‐one‐dimensional model for the dynamics of a polymer in dilute solution is described. The diffusion equation in the presence of energy barriers to conformational change is solved approximately for the case of high barriers, by a method closely analogous to the method of configuration interaction in molecular quantum mechanics. The dynamic shear viscosity is calculated in terms of the model and the ultrasonic absorption is discussed.
The crystalline core of the row structures in isotactic polystyrene. I. Nucleation and growth
Authors: Petermann J. , Miles M. , Gleiter H.
Published: April 2003

The nucleation and growth of the crystalline core in the row structures of isotactic polystyrene were investigated by transmission electron microscopy. The number of core crystals, nucleated at a specific temperature, depends on the external strain. Their length was found to increase with time if the sample is kept at the straining temperature. If a strained sample is cooled to room temperature and subsequently reheated, no further growth of the core crystals is observed. Obstacles in the path of growth were circumvented by local changes of the growing direction. Melt‐soluble noncrystallizable molecules are rejected by the growing core into the surrounding melt. The observations suggest a growth mechanism of the cores based on the successive self‐induced alignment of molecules at the tip of the growing cores.
A comparison of the rheological properties of polytetrafluoroethylene below its melting point with certain low‐molecular smectic states
Authors: Starkweather Howard W.
Published: April 2003

Polytetrafluoroethylene (PTFE) was extruded from a capillary rheometer at temperatures between the first‐order transition at 30°C and the melting point. Both PTFE at 50–300°C and various smectic states of certain low‐molecular benzylidene anilines obey the following relationship between the shear stress τ and the apparent shear rate $ \dot \gamma :{\rm }\tau = K\dot \gamma ^{{1 \mathord{\left/ {\vphantom {1 4}} \right. \kern-\nulldelimiterspace} 4}} $. The apparent viscosities for the two classes of substances are similar even though their molecular weights differ by a factor of about 104. Both have characteristic shear planes which are parallel to the polymer chains in PTFE and normal to the long axes of the benzylidene aniline molecules. The melting process in virgin PTFE begins near 300°C. Above this temperature, the shear stress at constant shear rate increases and the rheological exponent rises from 0.25 toward 0.5 at the final melting point.
Solution crystallization of nylon 6
Authors: Kyotani Mutsumasa
Published: April 2003

Electron microscopy and x‐ray diffraction data have been obtained on nylon 6 which has been crystallized from solutions in 1,6‐hexanediol and 1,2,6‐hexanetriol. Lamellar single crystals and spherulites of the γ form are obtained by crystallization from 1,2,6‐hexanetriol. The morphology of the single crystals is different from that obtained from glycerine solutions. The spherulites of the γ form are composed of larger lamellae. Sheaflike crystals of the α form are obtained from both solvents. α‐form and γ‐form crystals both grow from 1,2,6‐hexanetriol at appropriate crystallization temperatures. α‐form crystals alone are obtained from 1,6‐hexanediol solution at every crystallization temperature. The long periods measured by small‐angle x‐ray diffraction for the solution‐grown crystals are in the range 56 to 66 Å. The melting behavior of the solution‐grown crystals is examined and discussed. Effects of solvent on growth of the two crystalline forms from solution are investigated.
Quiescent and strain‐induced crystallization of poly(p‐phenylene terephthalamide) from sulfuric acid solution
Authors: Takahashi Toshisada , Iwamoto Hiroaki , Inoue Kazuyuki , Tsujimoto Ishio
Published: April 2003

Quiescent and strain‐induced crystallization of poly(p‐phenylene terephthalamide) (PPTA) from sulfuric acid solution has been studied. Negative spherulites (SA‐PPTA spherulites) are formed from hot concentrated solutions by cooling. The spherulite consists of radiating fibrous lamellae several hundred angstroms wide. The electron diffraction pattern indicates that PPTA molecules are oriented perpendicular to the long axes of the fibrous lamellae and that the [010] or [110] direction of the modification I crystal and [010] direction of the modification II crystal are parallel to the long axes of the fibrous lamellae. The width of the lamellae is much smaller than the chain length of the starting PPTA. It appears that hydrolysis of PPTA during melting crystallization determines the chain length, i.e., the width of the fibrous lamella. Stacked, lamellar structures like “row structures” are formed under shear. The longer axes of the fibrous lamellae are oriented perpendicular to the shear direction. It is confirmed by electron diffraction studies that the PPTA molecules are oriented parallel to the shear direction. Well‐developed fibrils with the PPTA molecules oriented to the fibril axis, are formed by adding the SA‐PPTA spherulites to water with vigorous stirring.
Simulation of the brownian motion of macromolecular chains. I. Local motions and chain conformations
Authors: Gény F. , Monnerie L.
Published: April 2003

Chains confined to a tetrahedral lattice can be considered as models for aliphatic polyethers and polyethylene. The deformations of such chains are analyzed by computer simulation using the Monte Carlo method. The elementary motions that are taken into consideration are three‐bond and four‐bond motions. The local mobility is analyzed in terms of conformational characteristics and compared with some NMR relaxation data.
Hydrodynamic interaction effects on intrinsic viscosity of perturbed chains: Experimental results for polystyrene
Authors: Cuniberti C. , Perico A. , Musi L.
Published: April 2003

Experimental measurements of intrinsic viscosity and radii of gyration of monodisperse samples of polystyrene of molecular weights 2.33 X 105, 4.11 X 105, 6.70 X 105, and 2.3 X 106 dissolved in the homologous series of 1‐chloroparaffins from butane to undecane are reported. The dependence of the viscosity expansion coefficient αη on the expansion factor αs for the radius of gyration is discussed in the light of the results obtained by an expansion of the Fixman theory for perturbed chains to include partial draining. These results give support to the finite chain effect on the hydrodynamics of expanded coils in the usual range of molecular weight. The exponent a in the relation α3η = αas depends on molecular weight and agrees with recent nondraining theoretical calculation for exceedingly high polymers.
Comparison of polarized fluorescence with polarized raman and infrared dichroism measures of orientation in uniaxially drawn poly(ethylene terephthalate)
Authors: Nobbs J. H. , Bower D. I. , Ward I. M.
Published: April 2003

In a number of previous papers the results of studies of molecular orientation in poly(ethylene terephthalate) (PET) by means of refractive index measurements and infrared, Raman and fluorescence spectroscopy have been presented. The present paper attempts to correlate the results of these studies and, in particular, to explain the observation that the fluorescent molecules appear to be more highly oriented than the polymer chains. Of the two explanations considered, that which assumes that the fluorescent molecules align themselves preferentially parallel to those segments of polymer chain in which the glycol residues are in the trans conformation is the more successful. It is also shown that the development of orientation in PET can be described well in terms of a simple modification of the rubber‐network model even for large deformations.
Application of the padé approximant method to excluded volume effects in polymer chains
Authors: Tanaka G.
Published: April 2003

Closed formulas for the expansion factor α and the h function appearing in the second virial coefficient are derived by the Padé approximant method, using the first two or three series coefficients. The equations for α agree well with experimental results for small z, the excluded volume parameter. The equation for h agrees well with data over the entire accessible range of z.
Dynamic mechanical and crystal‐strain measurements on ultrahigh modulus oriented polyoxymethylene: A revised value for the true crystal modulus
Authors: Brew B. , Clements J. , Davies G. R. , Jakeways R. , Ward I. M.
Published: April 2003

Dynamic mechanical measurements on ultrahigh modulus polyoxymethylene have been undertaken over the temperature range −150 to 20°C. Measurements of the longitudinal crystal modulus have also been made by studying changes in the (009) reflection with load, over a similar range of temperatures. The dynamic Young's modulus at 5 Hz reaches a value at low temperatures of 64.5 GPa for the most highly oriented sample. The crystal modulus at low temperatures is 105 GPa, which is almost twice the previously reported room‐temperature value.
The relation between dilatometric and dielectric glass‐transition temperatures
Authors: Phillips P. J.
Published: April 2003

A simple method has been developed for extracting the “static” glass‐transition temperature of a polymer from dielectric relaxation data. Only the temperature of the loss maximum and the activation energy at 1 kHz are required for the procedure.
Characteristics of solid‐state extruded polyethylene
Authors: Kolbeck A. G. , Uhlmann D. R.
Published: April 2003

This paper describes the properties of solid‐state extruded polyethylene as a function of two primary processing variables, extrusion temperature, and area reduction. The polymer was extruded in sheet form, giving a material having an orthotropic mode of orientation. Property data are presented for melting temperature and heat of fusion; sonic modulus, yield stress, and elongation at fracture; small‐angle x‐ray scattering; optical absorption coefficient; and morphology for material etched by ion bombardment at liquid nitrogen temperature. Combining the present results with data previously reported in the literature, it is found that over the temperature range of about 90–120°C, where polyethylene can be successfully extruded to large area reductions, many properties of the extrudates show a surprisingly small dependence on extrusion temperature. A notable exception to this behavior is the elastic modulus, which increases significantly with increasing extrusion temperatures. In contrast to extrusion temperature, area reduction is found to have a major effect on nearly all properties of solid‐state extruded polyethylene. In most cases, the form of this dependence is such that the properties change rapidly at small area reductions and much more slowly at large reductions.
Statistical mechanical model for diffusion of simple penetrants in polymers. I. Theory
Authors: Pace R. J. , Datyner A.
Published: April 2003

Following Di Benedetto it is proposed that noncrystalline polymer regions possess an approximate semicrystalline order with chain bundles that are locally parallel along distances of several nanometers. Packing with on‐average four nearest neighbors is assumed. A spherical molecule may move through such a substrate in two distinct ways: (a) along the axis of a “tube” formed by locally parallel chains or (b) perpendicular to this axis by two polymer chains separating sufficiently to permit passage of the molecule. The first process is relatively fast, generally requires little activation energy, and determines the effective jump length in diffusion. The second is responsible for the activation energy of diffusion, which is taken as the minimum energy necessary to produce a symmetrical chain separation which allows transfer of a molecule. This is calculated as a function of the penetrant diameter d and parameters Γ and β which characterize the interchain cohesion and chain stiffness, respectively. Γ is estimated from the polymer density and cohesive energy density by suitably linearizing a relation given by Di Benedetto for the potential between two polymer chains approximated as infinite strings of Lennard‐Jones force centers. β is shown to be approximately obtainable from the polymer chain backbone geometry and bond rotation potentials. An expression for the diffusion coefficient D is developed which contains only one disposable parameter, the effective jump length.
Statistical mechanical model for diffusion of simple penetrants in polymers. III. Applications—vinyl and related polymers
Authors: Pace R. J. , Datyner A.
Published: April 2003

The theory developed in Part I of this series is modified to accommodate polymers that possess closely spaced, bulky side groups on the chains. The side groups give rise to free space between the chain “cores,” which reduces the chain separation required for penetrant motion transverse to the local chain axis. The theory is then identical to that of Part I, except that penetrant diameters minus a constant factor are employed in place of the normal diameters. In most of the cases studied the reduction factor for a given polymer may be estimated with reasonable precision from chain geometry data. This diameter‐reduction effect is the likely explanation of the apparent proportionality between the activation energy of diffusion and the square of the penetrant diameter reported earlier for vinyl polymers. The data quoted here and in Part II are analyzed to give a semitheoretical correlation between the effective jump length L̄ and ΔE, the activation energy of diffusion. This correlation appears to be equally valid for glassy and rubbery noncrystalline polymers.
High strength elastic polypropylene
Authors: Samuels Robert Joel
Published: April 2003

The transformation of a spun isotactic polypropylene fiber into a high strength elastic fiber has been followed structurally. By examining each stage of the transformation separately, it has been possible to identify the different structural mechanisms that occur as the process proceeds. The recognition of the important role the noncrystalline polymer plays in the process is a particularly significant result of the study.
Strain dependence of the vibrational modes of a diacetylene crystal
Authors: Batchelder D. N. , Bloor D.
Published: April 2003

Resonance Raman spectroscopy has been used to measure the strain dependence of four high‐frequency vibrational modes in a single crystal of toluene sulfonate diacetylene polymer. The 0.62‐μm thick crystal was stretched elastically to 4% strain before fracture occurred. This was equivalent to an ultimate tensile strength of 2.0 × 109 N m−2. The strain dependence of the vibrational modes has been interpreted using a simple point mass and anharmonic spring constant model. A Fermi resonance was observed for two vibrational modes which are degenerate at 2.1% strain and a 1464 cm−1 frequency.
An investigation of the coupling agent/matrix interface of fiberglass reinforced plastics by fourier transform infrared spectroscopy
Authors: Ishida Hatsuo , Koenig Jack L.
Published: April 2003

The mechanical performances of fiberglass reinforced plastics (FRP) are quite different when the glass fibers are treated with vinyl (VS) and methacryl (γ‐MPS) functional silane coupling agents. We have studied the structural basis for this difference on the molecular level using Fourier transform infrared spectroscopy (FT‐IR). A high‐surface‐area silica powder is used to study the coupling agent/matrix interface. Both VS and γ‐MPS can react with styrene at the interface. However, when E‐glass fiber is used as a substrate, only γ‐MPS polymerizes in the coupling agent interphase which consists of many layers of coupling agent molecules while the major portion of the VS does not polymerize in the interphase. The effect of glass surfaces, with and without a coupling agent, on the curing of the polyester resin has also been studied. Silane coupling agents participate in the curing of the polyester resin while untreated E‐glass fiber surfaces inhibit the polymerization resulting in different structures from the bulk matrix.
A permanganic etchant for polyolefines
Authors: Olley R. H. , Hodge A. M. , Bassett D. C.
Published: April 2003

A permanganic etchant has been developed which reveals lamellar and other fine detail in surfaces of at least three crystalline polyolefines, viz., polyethylene (of both high and low density), isotactic polypropylene, and isotactic poly(4‐methylpentene‐1). In typical treatments of high‐density polyethylene ca. 2 μm of material is removed with defective regions suffering preferential attack. The etchant also discriminates between lamellar orientations, eating deeper where side surfaces of laminae are exposed than on fold surfaces, and between different polymers, attacking isotactic polypropylene more strongly than polyethylene. Comparison with other techniques authenticates the detail exposed and samples appear to be otherwise unaltered by their treatment. Besides normal imaging, it is also possible to use etched samples for transmission diffraction studies in the electron microscope. The method has very considerable application for revealing lamellar details in crystalline polyolefines (which can be chosen to be representative or selective according to the nature of the surface used). Examples are given of a wide variety of melt‐crystallized morphologies for the three polymers cited and also of lamellae in a drawn polyethylene sample. It is pointed out that permanganic etching is complementary to the technique of chlorosulfonation used to stain polyethylene in a similar way as bright field microscopy is to dark field.
Solution behavior of [(ethylene‐co‐vinyl alcohol)‐g‐ethylene oxide] graft copolymers
Authors: Endo Ryuichi , Goto Akihiko , Okano Hiroshi , Arai Hidehiko
Published: April 2003

The solution behavior of hydrophobic‐hydrophilic water‐soluble graft copolymers consisting of poly[(ethylene‐co‐vinyl alcohol)‐g‐ethylene oxide] was investigated by high‐resolution NMR spectroscopy and measurements of solution viscosity in tetrahydrofuran, water, and mixtures thereof at various temperatures. A graft copolymer with a backbone containing 2.7 mole% vinyl alcohol exists in an intramolecular phase‐separated conformation in aqueous solution, independent of the temperature. Graft copolymers with backbones containing 20.3 mol% vinyl alcohol exhibit an intramolecular mixed‐phase conformation in which the mobility of chains in the hydrophobic region depends on temperature. The temperature dependence of the intrinsic viscosity in water shows a maximum near 50°C.
Application of gel permeation chromatography to polyelectrolytes: Salt rejection mechanism and molecular‐weight distribution
Authors: Domard A. , Rinaudo M. , Rochas C.
Published: April 2003

Gel permeation chromatography (GPC) of polyelectrolytes in dimethylformamide (DMF) is studied. Three methods of monitoring elution (conductimetry, viscosimetry, refractometry) are used to investigate the molecular‐weight distribution and, independently, the chemical composition expressed in terms of the ionic charge density as a function of the chain length in two copolymers of acrylonitrile and sodium methallylsulfonate. The distribution on the gel of the neutral salt NaNO3 added to the DMF and used for elution is discussed in terms of Donnan exclusion; in addition, it is concluded that to obtain the correct molecular‐weight distribution, GPC measurements must be performed with an eluent containing a neutral salt at a concentration at least 5 × 10−2M to prevent electrostatic exclusion. The main difficulty in reaching rigorous conclusions comes from the dependence of the calibration curve on the salt composition of the eluent owing to interactions—dependent on the quality of the solvent—between the polystyrenes used as standards and the porous silica gel. Nevertheless, this perturbation is small and the agreement between the average molecular weights obtained by GPC and by direct determination is good and indicates that the universal calibration proposed for neutral polymers is also valid for polyelectrolytes.
Rigid backbone polymers. I. Polyisocyanides
Authors: Aharoni Shaul M.
Published: April 2003

Concentrated solutions of poly(n‐octyl isocyanide) exhibit a mesomorphic structure, most probably nematic in nature. Poly(n‐butyl isocyanide) and poly(benzyl isocyanide), of the molecular weights at our disposal, failed to show similar behavior. Upon acidification poly(n‐butyl isocyanide) does not change, but the other two polymers turn essentially black. Infrared and proton NMR clearly demonstrate that upon acidification, poly(n‐butyl isocyanide) and poly(benzyl isocyanide) are protonated on the nitrogen atom. This process is reversible. Carbon‐13 NMR and x‐ray patterns indicate that no chemical rearrangement or conformational changes take place upon acidification. This conclusion is supported by infrared studies and by inference from the poor electrical conductivity of the solid acidified polymers.
Melting behavior of ultrahigh modulus linear polyethylene
Authors: Clements J. , Capaccio G. , Ward I. M.
Published: April 2003

The differential‐scanning calorimetry (DSC) behavior of drawn linear polyethylene (LPE) has been investigated as a function of draw ratio and molecular weight. All the samples examined showed a dependence of the melting temperature on heating rate, an effect generally known as superheating. The magnitude of this effect, as well as the maximum melting temperatures, increased markedly at high draw ratio and high molecular weight. The highest melting temperature recorded was 145°C for a tape of draw ratio 25 and weight‐average molecular weight of 312,000. The results were first considered in terms of the information which might be provided regarding crystal thickness. It was concluded that the DSC data are consistent with previous wide‐angle x‐ray diffraction results in confirming that an extended chain morphology similar to that observed in pressure crystallized LPE is not present in these samples. Secondly, the superheating effects were examined in the light of the possible configurational constraints on the amorphous regions of drawn polymers, along the lines proposed by Zachmann. It is possible to understand the effects of draw ratio and molecular weight very well on this basis, in a manner consistent with previous structural results on these materials.
Rheo‐optical studies on the deformation mechanism of semicrystalline polymers. IV. On the nature of alpha mechanical dispersion of low density polyethylene in relation to the mechanism of spherulite deformation
Authors: Suehiro Shoji , Yamada Takeshi , Inagaki Hajime , Kyu Thein , Nomura Shunji , Kawai Hiromichi
Published: April 2003

The dynamic mechanical and birefringence behavior of three kinds of test specimens, prepared from a low‐density polyethylene by different heat treatments, was investigated over the frequency range 0.008 to 4.3 Hz at various temperatures from 20 to 80°C. Reduction of both kinds of data to the common reference temperature of 50°C revealed rather broad frequency dispersions, corresponding to the α dispersion, with activation energies for the mechanical and optical relaxation processes of around 25 kcal/mole for all specimens. An annealed specimen was further investigated by dynamic x‐ray diffraction to determine the dispersions of crystal orientation and of lattice deformation. The mechanical and birefringence dispersions are associated with the dispersion of crystal orientation and with the relatively elastic nature of the lattice deformation. Thus, the mechanical dispersion could be assigned to an α1 mechanism arising from rotation of crystallites within the spherulites, i.e., a type of grain‐boundary phenomena, but not to an α2 mechanism resulting from a crystal disordering transition or premelting. Combining dynamic birefringence with dynamic crystal orientation, the mechanical α dispersion is further discussed in terms of dynamic orientation behavior of noncrystalline chain segments in order to elucidate the nature of the grain‐boundary phenomena in detail in relation to the dynamic deformation mechanism of the spherulitic crystalline texture, i.e., reorientation of “crystal grains” within orienting lamellae due to intralamellar shearing resulting from the paracrystalline nature of the lamellae. A mechanical model characterizing the grain‐boundary relaxation in association with the reorientation of the crystal grain is also proposed.
Fourier transform infrared study of uniaxially oriented atactic polystyrene
Authors: Jasse Bruno , Koenig Jack L.
Published: April 2003

Infrared measurements of the dichroic ratio of atactic polystyrene absorption bands provide a valuable method of determination of the overall orientation of chains as well as the particular orientation of the trans conformational segments. The orientation process produces the alignment of the chains as well as an increase in the amount of trans conformational segments. A linear relationship is observed between birefringence and dichroic ratio for the absorption bands characteristic of overall orientation. A value of 35° ± 3° is obtained for the angle between the normal to the plane of the benzene ring and the chain axis from both infrared and birefringence determinations.
Fourier‐transform infrared studies of polymer blends. II. Poly(ϵ‐caprolactone)–poly(vinyl chloride) system
Authors: Coleman M. M. , Zarian J.
Published: April 2003

Fourier‐transform infrared (FTIR) studies of the poly(ϵ‐caprolactone) (PCL)–poly(vinyl chloride) (PVC) blend system are presented. The results indicate that there are specific interactions between the PCL and PVC in both the molten and solid states which could be responsible for the apparent compatibility of the amorphous component of these blends. Additionally, FTIR difference spectra are presented to illustrate the potential of this technique for following the kinetics of crystallinity in polymer blend systems.
Dielectric relaxation of polydimethylsiloxane
Authors: Adachi Hiroshi , Adachi Keiichiro , Ishida Yoichi , Kotaka Tadao
Published: April 2003

Dielectric studies were performed on crystallized and amorphous polydimethylsiloxane which had been characterized by differential thermal analysis and polarized light microscopy. The crystallized specimen displayed one relaxation near 160 K at 1 kHz while the amorphous specimen showed absorption peaks at 155 and 165 K. For the latter material the high‐temperature peak was not due to a true relaxation but resulted from crystal nucleation at 160 K and the subsequent growth of spherulites. The low‐temperature peak at 155 K resulted from the relaxation associated with the glass transition. A sharp decrease of dielectric constant was observed for both specimens at the melting point (235 K). For the dielectric relaxation associated with the glass transition in crystallized specimens, the values of the dispersion amplitude, the apparent activation energy at 160 K, and the half‐width of the absorption curve are 0.43 and 29 kcal/mole, and 5.6 decades, respectively, which are in marked contrast to the corresponding values of 0.82, 18, and 2.2 for amorphous specimens.
Geometrical effects in the measurements of mechanical properties in parallel superposed flows
Authors: Powell R. L. , Schwarz W. H.
Published: April 2003

The shear‐dependent complex viscosity η*12, which governs the linear time‐dependent stresses in a viscoelastic fluid undergoing infinitesimal shearing oscillations in‐line with a viscometric motion, has been investigated. Formulas relating η*12 to measured quantities have been derived for the cone‐and‐plate and parallel‐plate geometries. In the former case, the formula has the same form as that found when there is no steady shearing present. For the parallel‐plate geometry, the formula is different because of the radial variation in the viscometric shear rate. In order to determine the empirical significance of this formula, η*12 data were obtained for two fluids, NBS nonlinear sample No. 1 and a 4.3 g/dl aqueous polyethylene oxide (molecular weight, 5 X 106) solution using a Weissenberg rheogoniometer Model R‐18. Data were acquired and analyzed using a minicomputer on‐line with the rheogoniometer. The obtained data indicate that good agreement between the η*12 measured using the two geometries is obtained only if the derived formulas are used. Also, it is shown that theoretical results of simple‐fluid theory are valid for these data.
An examination of the crystal structures present in nylon‐6 fibers
Authors: Stepaniak R. F. , Garton A. , Carlsson D. J. , Wiles D. M.
Published: April 2003

The variety of wide‐angle x‐ray scattering (WAXS) patterns exhibited by nylon‐6 fibers with different fabrication histories is rationalized using a model comprising three limiting structures, viz., an α, a γ, and a pleated α structure. The γ and pleated α structures both have a single broad reflection in the range 2θ = 19° −25°, but differ in their annealing behavior. At 205° (in vacuo), the pleated α structure converts to the normal α structure by removal of the pleats, without breaking any hydrogen bonds. The γ structure, however, remains unchanged under this annealing condition since it is necessary to break all the hydrogen bonding in the structure to convert it to the α form. Different fabrication routes produce fibers which resemble the three ideal structures to varying extents. Fibers extruded at low speeds (and hence low spinline tension) resemble a mixed conventional α/pleated α structure with only a small γ component. Increasing the take‐up speed (and hence the spinline tension) of the as‐spun fiber, or in‐line drawing of the low orientation fiber (without prior storage), increases the γ content. If drawing of the low orientation fiber takes place after several hours storage (off‐line drawing), a largely α structure is produced. The intensity of the 020 reflection in the γ structure is shown to be very dependent on the degree of crystalline orientation in the sample.
Electron microscopic investigation of the molecular mechanism of plastic deformation of polyethylene and isotactic polystyrene crystals
Authors: Petermann J. , Kluge W. , Gleiter H.
Published: April 2003

The molecular process involved in the plastic deformation of crystals of linear polyethylene and isotactic polystyrene by necking was investigated by transmission electron microscopy (TEM). The results for the draw ratio, the height, and the shape of the neck and the molecular structure of the deformed material suggest that plastic deformation occurs basically by the unfolding and bending of the molecules in a deformation region only a few nm wide. The observations are at variance with deformation models involving complete unfolding of the molecules or the breaking off of folded‐chain blocks and the incorporation of these blocks into the deformed material.
Properties of amorphous and crystallizable hydrocarbon polymers. I. Melt rheology of fractions of linear polyethylene
Authors: Raju V. R. , Smith G. G. , Marin G. , Knox J. R. , Graessley W. W.
Published: April 2003

The dynamic moduli G′(ω) and G″(ω) for two groups of linear polyethylene fractions (reported Mw/Mn < 1.2) were measured in the melt state using the eccentric rotating disk method. Values of zero shear viscosity η0 were obtained and compared with published results on similar fractions. Molecular weight data were converted to a common basis through intrinsic viscosities in trichlorobenzene (TCB) at 135°C. With recent data on Mw (light scattering) vs. [η]TCB, for linear polyethylene, the relationship at 190°C, η0 = 3.40 × 10−14(Mw)3.60, was obtained. The flow activation energy Ea was 6.4 kcal (T = 140–195°C). The plateau modulus G at 190°C was determined from the area under the loss modulus peak in one high‐molecular‐weight sample. The value obtained, G = 1.58 × 107 dyn/cm2, corresponds to an apparent molecular weight between entanglements of 1850. The storage compliance J′(ω) becomes anomalously large at low frequencies. The recoverable compliance J could not be determined for any of the fractions.