bluuebunny/crossref_metadata_2025 huggingface dataset:
Structural relationships in the solid‐state synthesis of poly(bis‐phenyl glutarate diacetylene)
Authors: Day David , Lando Jerome B.
Published: April 2003

This study was undertaken to determine the crystal structure of poly(bis‐phenyl glutarate diacetylene) (poly(BPG)). It was found that this material crystallizes in a C2/c (centrosymmetric) space group. The x‐ray refinement revealed a solid solution of the monomer and polymer. It was determined that the only movement that occurs during polymerization is in the diacetylene rod (a rotation of 33°) and in adjacent phenyl groups (a rotation of 19° and a swing of 6°), while all other atomic positions in the side group remain essentially the same. An infrared investigation and the final refined atomic coordinates with their standard deviations indicates that the BPG crystal was polymerized to an extent of 35%.
Exploratory analysis of the influence of substitutional impurities on the electronic properties of poly(sulfur nitride)
Authors: Parry David E. , Thomas John M.
Published: April 2003

The results of extended Huckel calculations are reported for an isolated (SN)x chain in which some of the S2N2 units of the extended one‐dimensional chain are replaced by (SCH2)2 units. It is found that, inter alia, the metallic behavior of the unsubstituted parent is retained but that the conductivity is lowered to an extent governed by the nature and degree of substitution.
Crystallization of poly(tetramethyl‐p‐silphenylene–dimethylsiloxane) (TMPS–DMS) block copolymers: Morphology and kinetics
Authors: Li H. M. , Magill J. H.
Published: April 2003

The crystallization behavior of random block copolymers of (tetramethyl‐p‐silphenylenesiloxane) and dimethylsiloxane has been studied over a wide range of temperature and composition. The copolymer melting temperature, glass transition temperature, rate of crystallization, crystallinity, and density decrease in magnitude as the dimethylsiloxane block content are raised in this two‐component system. The crystal end‐surface (interfacial) energy increases as the dimethylsiloxane mole fraction decreases in accord with other morphological observations. The morphological changes observed in these copolymers are consistent with the conclusions deduced from the crystallization kinetics. Negatively, birefringent spherulites are observed over the entire crystallization range investigated.
Cooperative model for the mechanical deformation of polymers
Authors: Joseph S. H.
Published: April 2003

A model for the mechanical behavior of solid polymers is proposed in the form of a linear elastic network with transitions. A simplified version of the model involving a single column of two‐site activated processes is found to be a mean‐field system. The failings of this system as a description of yield and glass transition relaxation behavior lead to two extensions to the system: that of many available sites in each activated process, and that of a finite number of such processes in the whole system. These extensions reduce the properties of the system to those of a single activated flow process with a temperature‐dependent activation energy. Agreement is found between this result and time‐temperature shift measurements in the α transition region of several polymers, together with an explanation of the dependence of yield stress on temperature for one of these polymers that is physically more reasonable than the usual constant activation energy proposal.
Calorimetric studies of poly(ethylene terephthalate) stretching over a wide temperature range
Authors: Andrianova G. P. , Arutyunov B. A. , Popov Yu. V.
Published: April 2003

Heat effects and structural transformations in amorphous crystallizable poly(ethylene terephthalate) (PET) during uniaxial stretching accompanied by neck formation, have been investigated by calorimetric and x‐ray methods over a wide range of temperatures and deformation rates. At small deformation (not exceeding 1–2%) and at temperatures below the glass transition temperature of the polymer, PET behaves as an elastic body. Upon stretching at a constant rate, constant heat power is absorbed, heat effects during loading and unloading coincide completely, and no hysteresis is observed. At large deformations (of the order of 50%), cold drawing develops in this temperature range. The internal energy change in cold drawing is zero within experimental error. A periodic heat release during the self‐oscillation regime of drawing PET corresponds to periodic changes in stress, in the rate of the neck formation, and in the appearance of the sample. The temperature limits of the region where crystallization resulting from an uniaxial drawing of the polymer is possible, have been determined, and the heat effect of this phase transition has been measured. Orientation crystallization develops only from 70 to 94°C. These limits are insensitive to changes in deformation rate within one decimal order. The structure of PET in this temperature range has been investigated. The heat of phase transition of orientation crystallization of PET has been determined from the relationship between the measured values of the internal energy change during this process and the limiting degree of crystallinity for the stretched samples. This heat proves to be 5.5 ± 0.1 cal/g.
Induced crystallization of poly(ethylene terephthalate) on small metallic nucleating particles
Authors: Gutzow I. , Dochev V. , Pancheva E. , Dimov K.
Published: April 2003

The induction period for the onset of crystallization was determined in poly(ethylene terephthalate) in the presence and absence of small metallic particles. Two kinds of substrates were used: single microcrystals “transplanted” from the water‐soluble inorganic polymer (NaPO3)x and powders of the same metals (Au, Pt, and Ir). The nucleating activity ϕ of the substrates was determined on the basis of classical nucleation theory. Values of ϕ obtained for PET are compared with the corresponding values in the (NaPO3)x melt and with theoretical concepts.
Molecular conformation and craze fracture
Authors: Haward R. N. , Daniels H. E. , Treloar L. R. G.
Published: April 2003

A craze may fracture either by the breaking of covalent bonds or by a process of “viscous rupture” involving the movement of bulk material in the craze. In the latter case it is necessary that the majority of the chain ends of the polymer molecules passing through the craze‐matrix interface terminate within the craze. We have therefore calculated the probability of a polystrene macromolecule spanning a thin craze and shown that for viscous rupture a craze in a normal commercial polystyrene must be something more than 40 nm thick. As the measured craze thicknesses have generally exceeded 100 nm, a viscous fracture process is clearly possible, though, of course, chain rupture is not excluded by the argument. More difficulties arise when fracture occurs within a specified region of the craze and the possibility of a bond fracture under these circumstances is briefly discussed.
Electron density calculation for polyoxymethylene in cylindrical coordinates by a new fourier method
Authors: Takahashi Yasuhiro , Tadokoro Hiroyuki
Published: April 2003

The electron density of the polyoxymethylene molecule was calculated in cylindrical coordinates by a newly derived Fourier method. The density due to hydrogen could be obtained in addition to that from carbon and oxygen. This method is generally applicable to a helical polymer whose unit cell contains only one molecule composed of a number of chemical repeat units in the fiber identity period.
Effect of polymorphism on the CH stretching region of the infrared spectrum of polyethylene
Authors: Painter P. C. , Runt J. , Coleman M. M. , Harrison I. R.
Published: April 2003

A complex fine structure in the CH stretching region of the infrared spectrum of deformed polyethylene single crystals is reported. The deformed crystals are shown to be transformed from the orthorhombic crystal form to a monoclinic structure. The previously deduced C2/m monoclinic structure does not account for the appearance of the new bands. An alternative but similar monoclinic structure is proposed. The symmetry of this structure is consistent with the Fermi resonance interactions required for the observation of these bands.
A theory for the drawing of oriented crystalline polymers
Authors: Arridge R. G. C. , Barham P. J.
Published: April 2003

The load‐elongation behavior during the postneck drawing stage in the deformation of crystalline polymers is shown to be modeled quantitatively by an aligned short‐fiber composite in which crystalline fibrils form the reinforcing phase in a matrix of less well‐ordered material. Three modes of deformation are distinguished in the model and are shown to correspond to the observed loadelongation relations in polyethylene and polypropylene. The regions are (I) elastic–plastic crystals in an elastic matrix, (II) elastic–plastic crystals in an elastic–plastic matrix, (III) elastic crystals in an elastic–plastic matrix. A requirement of the theory is that the flow stress in the crystals is little affected by temperature whereas that in the matrix falls as the temperature rises. Expressions are given for stress in terms of the applied strain and the relevant parameters of the system: concentration of fibrils, length and diameter of fibrils, and elastic and yield properties of fibrils and matrix.
Thermal properties of some hydrogenated poly(α‐methyl styrenes)
Authors: Gipstein Edward , Barrall E. M. , Yoon Do Y. , Lyerla James
Published: April 2003

The Synthesis of poly(isopropenyl cyclohexane) via the hydrogenation of poly(α‐methyl styrene) is described. Depending on the reaction time and catalyst system a homopolymer or a copolymer is obtained. Under the conditions of synthesis both materials are highly syndiotactic. For the pure hydrogenated homopolymer (>99.9%) the glass transition temperature was found to be 185.4°C, about 20°C above Tg of poly(α‐ethyl styrene). Contrary to expectations, the glass transitions of the 92/8, 33/67 poly(isopropenyl cyclohexane‐co‐methyl styrene) and poly(α‐methyl styrene) are almost identical, as are the decomposition temperature ranges. Thermal data indicate that the decomposition mechanism of the copolymers and hydrogenated homopolymer is random scission. The thermogravimetric curves also indicate that the copolymers are random. Thus, chain stiffness appears not to increase rapidly with hydrogenation of this highly syndiotactic polymer.
NMR study of diffusion of butane in linear polyethylene
Authors: Zupančič I. , Lahajnar G. , Blinc R. , Reneker D. H. , Peterlin A.
Published: April 2003

The diffusion coefficient of butane in linear polyethylene at room temperature as a function of the vapor pressure of butane was measured by the spin‐echo method with a pulsed magnetic field gradient. For the Special morphology of randomly oriented stacks of parallel lamellas the detour factor is 1/3. As long as the blocking factor and migration through the lamellas can be neglected, the local diffusion coefficient Da of the small molecules through the amorphous layers in the direction parallel to the lamellas is three times the apparent diffusion coefficient D derived from the decay of the amplitude of the spin echo under the assumption of an infinitely extended homogeneous medium. The diffusion coefficient and the spin–spin relaxation time both increase exponentially with increasing pressure, i.e., butane concentration in the polymer, while the spin‐lattice relaxation time is pressure independent and seems to be determined by interaction with the amorphous polyethylene matrix.
Delayed yielding of polycarbonate under constant load
Authors: Narisawa Ikuo , Ishikawa Masaru , Ogawa Hiroyuki
Published: April 2003

The time‐dependent yielding of glassy polycarbonate subjected to constant tensile loads has been studied. Application of a constant stress of a magnitude between the yield stress and the stress required for propagation of a neck in constant strain tests results in inhomogeneous yielding after a well‐defined time lag. This delay time increases with decreasing stress and temperature. The critical stress for slowly cooled material is greater than that for quenched material in which the delay time is divided in two regions. The delay time is regarded as the time required for the initiation of inhomogeneous yielding at either edge of the specimen and growth over a certain distance across the specimen. Geometrical observations revealed that the inhomogeneous yielding is shear yielding which is initiated due to stress inhomogeneities caused by mechanical imperfections at the edge of the specimen. The Eyring treatment of delayed yielding can describe fairly well the stress and temperature dependence of the delay time.
Analysis of the equations of state of polyolefin melts in terms of the simha‐somcynsky hole theory
Authors: Zoller Paul
Published: April 2003

Pressure–volume–temperature data on melts of low‐density polyethylene, polypropylene (PP), poly(butene‐1) (PBT), and poly(4‐methylpentene‐1) (PMP) previously reported by us have been evaluated in terms of the Simha–Somcynsky hole theory of polymeric liquids by a determination of the reducing parameters P*, V*, and T* for each system. Literature data on the reducing parameters of linear polyethylene and of a branched polyethylene of intermediate density are also considered. Agreement with theory is best for the polyethylenes and deteriorates markedly in the series PBT:PP:PMP. These higher polyolefins have very low values of P*, thus suggesting a deficiency of the Simha–Somcynsky theory at high reduced pressures P̃ = P/P*. In these polyolefins, systematic variations of the reducing parameters (and molecular parameters derived therefrom) are noted and discussed. Correlations found previously between T* and the moleculer weight M0 of the effective segment of the theory or its hard‐core volume M0V* are obeyed by the polyethylenes only. The higher polyolefins show serious deviations from these correlations.
Diffusion studies of poly(ethylene terephthalate) crystallized by nonreactive liquids and vapors
Authors: Makarewicz P. J. , Wilkes G. L.
Published: April 2003

The diffusion of vapors and liquids which induce crystallization in initially amorphous, unoriented poly(ethylene terephthalate) (PET) films was studied. It was determined that these vapors and liquids penetrate the polymer as distinct fronts, and the kinetics of this penetration and the weight uptake kinetics both follow apparent Fickian behavior. Distinct cavitation advanced into the polymer at the penetrant front–dry polymer interface in certain PET–liquid systems, and phenomenological explanations of its existence and of the general diffusion process observed are offered. Finally, the diffusion of the highly interactive liquids dioxane and methylene chloride into cold‐drawn PET was studied and shown to occur considerably more slowly than does the diffusion of these liquids into unoriented films.
Mechanical property studies of poly(ethylene terephthalate) crystallized by nonreactive liquids
Authors: Makarewicz P. J. , Wilkes G. L. , Budnitsky Y.
Published: April 2003

The mechanical properties of initially amorphous, unoriented poly(ethylene terephthalate) (PET) films crystallized in acetone and dioxane at room temperature were studied under tensile testing conditions. It was found that the nature of the liquid, the morphology it induced, and its significant residual level trapped within the PET following this type of crystallization all influenced the observed mechanical behavior. Further, thermally treating PET at 70, 90, and 174°C prior to the liquid treatments appeared to inhibit the effects of the liquids on the resultant mechanical behavior. Finally, because these liquids penetrated the polymer as distinct fronts, laminate‐type structures were generated in the films. It then was shown that an ideal parallel element laminate could adequately model the mechanical behavior of the films.
Gelation and precipitation of copolymers from solution
Authors: Benson R. , Maxfield J. , Axelson D. E. , Mandelkern L.
Published: April 2003

There are several reports in the literature to the effect that when isotactic polystyrene crystallizes from moderately dilute solution, lamellas (precipitate) form at high crystallization temperatures and gels at low temperatures. We report here the occurrence of a very similar phenomenon during the crystallization of ethylene‐butene‐1 copolymers. The observations for the latter system can be given a straightforward explanation based on the demonstrated compositional fractionation that occurs on crystallization. Low co‐unit content copolymers are associated with lamellas. Gels invariably contain much higher co‐unit content. A generalization of these findings is invoked to explain the previous polystyrene results. A new resonance detected by 13C NMR experiments in this polymer can be ascribed to head–head sequences.
Determination of the distribution of straight‐chain segment lengths in crystalline polyethylene from the Raman LAM‐1 band
Authors: Snyder Robert G. , Krause Steve J. , Scherer James R.
Published: April 2003

It is shown how the shape of the longitudinal acoustic vibration observed in the low‐frequency region of the Raman spectra of crystalline polymers can be used to obtain a quantitative distribution of lengths of straight‐chain segments associated with polymer lamellas. The procedure is demonstrated for a “solid‐state” extrudate of polyethylene and for a bulk‐crystallized specimen of the same polymer. Equations relating the shape of the LAM‐1 band to the shape of the distribution curve are given. The low intensity observed for the LAM‐3 mode relative to LAM‐1 is explained quantitatively without recourse to end effects. LAM‐5 has been observed for bulk‐crystallized polyethylene. For the extrudate we find the distribution of lengths of straight‐chain segments to have a tail on the long‐length side which is not present for the bulk‐crystallized sample. The Raman technique is shown to provide new morphological data unattainable at present by other methods.
The microstructure of poly(vinyl chloride) as revealed by x‐ray and light scattering
Authors: Wenig W.
Published: April 2003

Small‐angle x‐ray scattering (SAXS) and wide‐angle x‐ray scattering (WAXS) as well as small‐angle light‐scattering (SALS) techniques have been applied to investigate the microstructure of a number of commercial poly(vinyl chloride) (PVC) samples. From the wide‐angle x‐ray scattering, crystallinity and crystal size parameters have been determined. The crystallinity of the samples investigated range from 5% to 10%. Superstructure parameters such as crystallite thickness, distribution functions of crystallite and amorphous thicknesses, and size of ordered regions have been obtained by an analysis of the SAXS curves using the cluster model. The crystallinity agrees well with the WAXS crystallinities indicating that most of the crystals are lamellar shaped, though some rodlike entities are present in the sample as is shown by the small‐angle light scattering. From the SAXS analysis, the microstructure is described as clusters of lamella stacks which are identical with the subprimary particles. Their size is determined to be 220–240 Å. Emulsion type PVC also contains lamellar‐shaped crystals. The superstructure, however, of this type of PVC is different from that of mass or suspension‐polymerized material. The SAXS curve does not reveal any correlation between the crystals.
Simultaneous nonlinear diffusion of a solvent and organic penetrant in a polymer
Authors: Frisch H. L.
Published: April 2003

We obtain the exact solution of a fairly large class of somewhat simplified problems involving the simultaneous nonlinear Fickian diffusion of a poor solvent and a dilute organic penetrant, such as a plasticizer, in a semi‐infinite polymer slab immersed in the solvent bath. Such problems can also provide useful estimates during certain time regimes of release of drugs from implants, and pesticides and pheromones from certain slow or controlled‐release polymeric devices, insofar as these are affected by an environmental solvent bath. We assess the effect of various simplifications made (e.g., neglect of the penetrant concentration dependence in the diffusion coefficient, cross diffusion of solvent and penetrant, and a variety of boundary conditions) by solving exactly some additional specialized cases.
Interpretation of spin relaxation in polyisobutylene in terms of specific motions
Authors: Jones Alan Anthony , Lubianez Ronald P. , Hanson Mark A. , Shostak Shelley L.
Published: April 2003

Porton and carbon spin‐lattice relaxation times T1 and nuclear Overhauser enhancements are interpreted in terms of motions likely in linear polyisobutylene. Most of the interpretation is based on relaxation data in the literature, but some additional 1H and 13C pulse Fourier transform experiments were conducted to resolve a disagreement in the literature concerning cross relaxation between the two types of protons present in polyisobutylene. Spin relaxation in solution and the bulk is accounted for by three specific motions considered as independent sources of motional modulation of the dipole–dipole interaction. The first motion is overall isotropic rotatory diffusion which has a known dependence on molecular weight, intrinsic viscosity, and solvent viscosity for polymers in solution, and a known dependence on molecular weight and viscosity for bulk polymers. The effects of overall tumbling account for a decrease of T1 for the methylene and methyl carbons with increasing molecular weight in solution and increase of T1 of methylene carbons with molecular weight in bulk. The second motion considered is backbone rearrangements caused by the three‐bond jump. This motion dominates relaxation of the methylene carbons either in solution or in the bulk allowing for the determination of the associated correlation time. The correlation time characterizing the occurrence of the three‐bond jump in a 5% (wt/vol) solution in CCI4 at 45°C is 58 psec, and in the bulk at 45°C it is 11 nsec. The last motion included in the model is methyl‐group rotation about the threefold symmetry axis. The methyl‐group rotational correlation time is 0.20 nsec in a 5% (wt/vol) solution in CCI4 at 45°C and 0.33 nsec in the bulk at 45°C. The concentration dependence of the backbone motion contrasts strongly with the corresponding dependence of methyl‐group rotation.
Dielectric study of side‐group rotation of methyl methacrylate in copolymers
Authors: Mashimo Satoru , Yagihara Shin , Iwasa Yasuo
Published: April 2003

The dielectric absorption due to the side‐group rotation of the methyl methacrylate (MMA) unit in MMA‐styrene and MMA‐p‐chlorostyrene (pCS) copolymers was measured. The relaxation time for MMA‐pCS copolymers with low MMA contents could be interpreted quantitatively in terms of the Kramers rate‐constant theory at the low‐friction limit. On the other hand, the frictional effect on the relaxation time could not be ignored for any copolymers except for the MMA‐pCS copolymers with low MMA contents. The relaxation time for pure poly(methyl methacrylate) could be interpreted by the Kramers theory at the high‐friction limit.
High‐speed aqueous gel‐permeation chromatography
Authors: Hashimoto Tsutomu , Sasaki Hiroo , Aiura Makoto , Kato Yoshio
Published: April 2003

High‐speed gel‐permeation chromatography (GPC) of water‐soluble polymers has been investigated by using TSK‐GEL, type‐PW columns packed with small porous particles. Being semirigid, the column packing could be operated under high pressure and, therefore, it was possible to achieve high‐speed GPC. A resolution higher than that of ordinary GPC in organic solvent system was attained when the measurement of one sample was completed within 40 min with a 6‐ft column set. Samples with a wide range of molecular weights, from oligomers to polymers having a molecular weight greater than 106, could be fractionated. Dextran, polyethylene glycol, polyacrylamide, poly(vinyl alcohol), and poly(vinyl pyrrolidone) were separated according to molecular size with no evidence of adsorption. Investigation of other water soluble polymers is now in progress.
Kinetics of epoxidation of poly(trans‐1,4‐butadiene) crystals in suspension
Authors: Wichacheewa P. , Woodward A. E.
Published: April 2003

The kinetics of the epoxidation reaction between metachloroperbenzoic acid (MCPBA) and poly‐(trans‐1,4‐butadiene), (PTBD), crystals in toluene suspension was investigated in the 6–21°C range using infrared spectroscopy. Crystals of PTBD with M̄n = 36,000 grown from heptane and from toluene solutions and crystals of PTBD with M̄n = 5500 grown from heptane were studied. For toluene‐grown crystals the total number of double bonds available for reaction increases with reaction temperature. For all preparations studied the epoxidation reaction is initially second‐order—first‐order with respect to [MCPBA] and first‐order with respect to the concentration of the available double bonds. The second‐order rate constant is found to be dependent on temperature, on molecular weight, and also on the crystal preparation conditions. The bromination of PTBD crystals was studied in CCl4 suspension at 0°C; this reaction was found to be complete within 1 hr with the fraction of double bonds brominated consistent with the epoxidation results. The IR spectra for dried mats of brominated and of epoxidized PTBD crystals were obtained: Changes in the amorphous band at 1335 cm−1 due to reaction of double bonds at crystal surfaces were observed. The results of this investigation are discussed in terms of the amorphous content of the PTBD lamellas.
Epitaxial crystallization of polyoxymethylene during cationic polymerization of trioxane
Authors: Takahashi Toshisada , Okazaki Hideo
Published: April 2003

Epitaxial crystallization of polyoxymethylene (POM) during cationic polymerization of trioxane in ethane dichloride was studied. Nascent POM crystals grew epitaxially on the surface of drawn, high‐molecular‐weight POM and on the (001) surface of KCl single crystals. Half‐hexagonal crystals several thousand angstroms in thickness were formed on these substrates. No discrete diffraction maximum could be observed in small‐angle x‐ray scattering patterns, but diffuse streaks were present on both the equator and the meridian of the pattern. These diffuse streaks are due to inhomogeneities in the nascent crystals. It is proposed that the crystals contain voids due to occlusion of reactive chain ends in the crystal. The optical diffraction pattern from a model made up of rectangles agreed qualitatively with the actual x‐ray pattern.
Longitudinal acoustic mode in polymers. IV. LAM‐3 of the general perturbed rod and applications to paraffins and polymers
Authors: Krimm S. , Hsu S. L.
Published: April 2003

The dependence of the LAM‐3 frequency on the various parameters of a perturbed composite elastic rod has been calculated. Together with the previously calculated nonlinear variation of LAM‐1 with these parameters, it can be expected that experimental measurements of both of these bands will permit a more detailed analysis of properties of long‐chain molecules. The predictions of the theory are in complete agreement with experimental results on n‐paraffins. For data on polyethylene and poly(ethylene oxide) reasonable solutions can be found, although the experimental information on polymers is not yet accurate enough or sufficiently devoid of assumptions to permit definitive conclusions to be reached.
Molecular orientation in poly(vinyl chloride) studied by Raman spectroscopy and birefringence measurements
Authors: Robinson M. E. R. , Bower D. I. , Maddams W. F.
Published: April 2003

The ratios of the intensities of Raman scattering in the CCI stretching region for eight combinations of sample orientation and directions of polarization of incident and scattered light have been measured for 15 samples of poly(vinyl chloride) (PVC) containing 0, 5, 10, 15 or 20 pph dioctyl sebacate (DOS) plasticizer which had been drawn uniaxially at 22, 70, 75, 80, or 90°C to draw ratios in the range 1–4.5. The birefringences of the samples were also measured. The Raman data were analyzed to give 〈P2(cosθ)〉cryst and 〈P4(cosθ)〉cryst, the values of the second‐ and fourth‐order Legendre polynomials in cosθ averaged over the distribution of orientations of the crystallites, where θ is the angle between the c axis of a typical crystallite and the draw direction. Comparison of 〈P2(cosθ)〉cryst with the birefrigence showed that the crystallites are more highly oriented than the noncrystalline material in samples containing the higher amounts of plasticizer drawn at the higher temperatures. A value of 13.0 × 10−3 was deduced for the birefringence of fully oriented PVC. The values of 〈P4(cosθ)〉cryst for a given 〈P2(cosθ)〉cryst were found to be higher than predicted by calculations based on two simple models, the pseudoaffine rigid‐rod rotation model and the affine rubber elasticity model.
Ultrahigh draw ratios in polyethylene: Molecular weight effects
Authors: Warner S. B.
Published: April 2003

Removal of the ultrahigh molecular weight fraction in high‐density polyethylene by hydrodynamic crystallization and analysis of the subsequent drawing behavior leads to the conclusion that the small portion of extremely long chains present in polymers with a log‐normal molecular weight distribution is not necessary for the achievement of high draw ratios, that is, in excess of 30×. Furthermore, a certain minimum weight, and therefore chain length, is required for the attainment of high draw ratios. For example, paraffins with a molecular weight of 23,000 draw only up to about 5×. A logical extension of these concepts to other polymer systems is presented.
Transient and steady‐state permeation in poly(ethylene terephthlate) above and below the glass transition
Authors: Koros W. J. , Paul D. R.
Published: April 2003

Transient and steady‐state permeation data are reported for CO2 in semicrystalline poly(ethylene terephthalate) for temperatures ranging from 25 to 115°C over the pressure range from 1 to 20 atm. The pressure dependency of the time lag and permeability disappears completely above the glass transition of the polymer, and Fick's law with a concentration‐independent diffusion coefficient applies. In the glassy state, a concentration‐dependent diffusion coefficient is necessary to describe the data. The form of this concentration dependence is described well by the partial immobilization transport model that attributes a different mobility to each of the two populations of sorbed gas which exist in local equilibrium with each other in glassy polymers. The importance of reporting the pressure used in transport experiments involving glassy polymers is emphasized by comparing the difference in the activation energy of the apparent diffusivity calculated from the measured time lag at 1 and 20 atm. Also, the magnitude of the observed slope discontinuity at Tg in Arrhenius plots of these apparent diffusities is shown to be a function of the upstream pressure used in the experiment. The independently measured time lags are compared with the predicated values calculated from various transport models and found to be described best by the partial immobilization model.
Vibrational spectra and normal coordinate analysis of isotactic poly(alkyl ethylene)s II. Modification I of poly(propyl ethylene) and its deuterated derivatives
Authors: Holland‐Moritz K. , Sausen E. , Djudovic P. , Coleman M. M. , Painter P. C.
Published: April 2003

The vibrational analysis of modification I of poly(propyl ethylene), poly(propyl ethylene)‐(2,2;d2), and poly(propyl ethylene)‐(1,2,2;d3) has been performed using the valence force field derived for poly(ethyl ethylene) and the actual molecular geometry. The band assignments are based on infrared polarization and Raman data.
Heat capacity of poly(vinylidene fluoride) and polytetrafluoroethylene between 5 and 200°K
Authors: Choy C. L. , Leung W. Y. , Chen F. C.
Published: April 2003

Heat capacities of poly(vinylidene fluoride) (PVF2) and polytetrafluoroethylene (PTFE) have been measured between 5 and 100°K with an accuracy of (1–5)% by adiabatic calorimetry. Calculations based on contributions from known optical lines and the Tarasov continuum model are in good agreement with experimental results down to 30°K for PVF2 and 10°K for PTFE, and yield characteristic temperatures θ1 and θ3 which are consistent with previous values determined from high‐temperature (100—350°K) data. At lower temperature the measured heat capacity is significantly higher [(30–100)%] than the model prediction, and can be satisfactorily accounted for by the introduction of localized vibrators at a concentration of about 1% as compared to acoustical oscillators and at a characteristic temperature of about 20°K. Using established data on polyethylene for comparison, the principle of additivity for heat capacities is found to be valid down to at least 20°K, convering the region (<60°K) where interchain vibrations contribute significantly to the heat capacity. Possible reasons for this unexpected behavior are discussed.
Vapor‐induced depolarization currents in electrets
Authors: Cantaloube B. , Dreyfus G. , Lewiner J.
Published: April 2003

The charge decay of polymer electrets in the presence of solvent vapor is analyzed. In order to account for this phenomenon, several hypotheses are considered and tested experimentally. It is shown that the penetration of the solvent is responsible for the observed charge decay, and that it is the rate limiting factor. Moreover, the phenomenon is not due to the screening of the injected charges, but to the motion of these charges, which are liberated by the penetration of the solvent. Finally, the possible applications of this phenomenon in investigations on both the microscopic and macroscopic scale are outlined.
Least‐squares refinement of molecular structure of polyoxymethylene
Authors: Takahashi Yasuhiro , Tadokoro Hiroyuki
Published: April 2003

Least‐squares refinement of the molecular structure of polyoxymethylene was carried out by using intensity data measured with an automatic four‐circle diffractometer. The discrepancy factor was improved to 4.1% by using the anisotropic temperature factor. Physically significant values were obtained for the bond length, bond angles, and internal rotation angle: CO = 1.429 ± 0.008 Å, ∠COC = 112.9 ± 0.6°, ∠OCO = 110.4 ± 0.8°, and τ(CO) = 77.0 ± 0.3°. Samples for x‐ray diffraction measurements were prepared by solid state polymerization of a tetroxocane single crystal.
Simulation of the brownian motion of macromolecular chains. II. Chain dynamics
Authors: Gény F. , Monnerie L.
Published: April 2003

A simulation of the Brownian motion of polyethers and polyethylene is reported. The chains under consideration are confined to a tetrahedral lattice and subjected to conformational energy conditions. The dynamic behavior of the whole chain is studied. The diffusion of individual chain atoms reflects the chemical nature of the chain, and the diffusion of the center of mass, in connection with experimental results, affords a time scale for the simulation. The relaxation of bond orientation, which is connected with fluorescence depolarization, is found to be consistent with the theory of Valeur and co‐workers. The relaxation of the total dipole is interpreted in terms of conformational features of the motions and correlations between neighboring dipoles. Finally, relations between chemical structure and dynamic behavior are established. Three classes of polyether chains are to be distinguished: the rigid chain poly(methylene oxide), the highly flexible poly(ethylene oxide) and an intermediate class typified by polyethylene.
Evidence of distinct water species in cellulosic environments from broad‐line NMR
Authors: Fleming William W. , Fornes R. E. , Memory J. D.
Published: April 2003

Broad‐line NMR measurements were made on water in cellulosic samples. The spectra for oriented rayon at 65% relative humidity and room temperature consisted of a visually apparent doublet (SD) and a narrow singlet (SN) which was shifted upfield about 7 ppm from the center of the doublet. The doublet separation varied as A(3 cos2θ—1), where θ is the angle between the fiber axis and the magnetic field; the maximum doublet separation was 350 mG at both 15.1 and 56.4 MHz, indicating the doublet is dipolar in origin. The peak‐to‐peak linewidth of the narrow singlet was orientation and field dependent. The upfield shift of the narrow singlet from the doublet center was field dependent. Spectra for vacuum‐treated rayon consisted of only the narrow singlet, which was orientation dependent. The doublet separation decreases with increasing moisture content and is essentially zero for oriented rayon samples at 100% relative humidity; the resulting spectra due to the collapsed doublet and SN singlet was an asymmetric line. Temperature‐dependent measurements were made on oriented rayon at 65% relative humidity with the fiber axis parallel to the magnetic field; when the temperature was increased from about 0° the peak‐to‐peak linewidth of the doublet halves and the doublet separation decreased. As the temperature was increased from about 30 to about 65°C, a previously unobserved singlet (SE) became visible. The relative amplitudes of the three lines varied with temperature as follows: The SE singlet increased, the SD doublet decreased, and the amplitude of the SN singlet remained constant. Measurements using oriented cotton samples and randomly packed rayon samples indicated that the NMR line shape of the water spectra depends upon the physical properties of the macromolecular substrate. The doublet component of the spectra is attributed to a water species (SD) which is highly bonded to the macromolecular substrate. The SE singlet is attributed to an energetic water species (SE) which is rapidly tumbling in the macromolecular environment. The SN singlet is not due to free water.
Stress‐induced crystallization of poly(ethylene terephthalate)
Authors: Misra A. , Stein R. S.
Published: April 2003

Quenched amorphous films of poly(ethylene terephthalate) (PET) are stretched at temperatures less thanTg; changes in density, wide‐angle x‐ray diffraction, and small‐angle light scattering are observed. The density increase upon stretching is attributed to an increase in crystallinity accompanied by an increase in the intensity of somewhat diffuse wide‐angle x‐ray diffraction and of bothVVandHVsmall‐angle light scattering patterns. The formation of oriented rodlike superstructure may be discerned from small‐angle light scattering. Annealing of these samples increases the crystallinity as measured from density and leads to an increase in the perfection of crystalline and supercrystalline structure as measured by wide‐angle x‐ray diffraction and small‐angle light scattering. The rodlike morphology changes to form spherulitelike aggregates as observed by small‐angle light scattering and light micrographs. A model is proposed to explain the observations. Studies are extended to stretching films of PET above theirTgand observing changes in birefringence, density, wide‐angle x‐ray diffraction and small‐angle light scattering as a function of elongation and stretching temperature. The formation of defomed spherulitelike superstructure may be discèrned from light micrographs. Results are compared with those obtained upon stretching films belowTg.
Reactivity and gelation. I. Intrinsic reactivity
Authors: Durand Dominique , Bruneau Claude‐Marcel
Published: April 2003

The method of Case is used with the Flory‐Stockmayer gelation criterion to derive a critical transition equation for polycondensation of multifunctional reactants bearing coreactive functional groups of two species A and B, where the B groups may be of unequal intrinsic reactivity. Systems of the types R(A)2/R′(B)4 and R(A)2/R′(B)4/R′′(B)2 are considered with the B groups divided into two classes characterized by a reactivity ratio in the range 0.1 to 10. If the reactivities are sufficiently different the polymerization can be regarded as a multistage process. Intramolecular reactions are not considered.
Reactivity and gelation. II. Substitution effect
Authors: Durand Dominique , Bruneau Claude‐M.
Published: April 2003

The development in Paper I is extended to multifunctional condensations where the functional groups exhibit unequal reactivities induced by substitution effects in the course of the polymerization. A system R(A)2/R′(B)3 is examined to determine how the gel point varies with the strength and positive or negative sense of the substitution effect. As in Paper I, intramolecular interactions are not considered.
Orientation of the remaining amorphous chains during crystallization: Isotactic polystyrene
Authors: Krigbaum W. R. , Taga Tooru
Published: April 2003

The orientation of statistical chain segments in the amorphous regions of a semicrystalline polymer can be characterized quantitatively by x‐ray diffraction. A calculated background (which is orientation independent) must be subtracted, which requires that the intensity profile of the amorphous halo be measured on an absolute scale. Application is illustrated to samples of isotactic polystyrene which were isothermally crystallized at fixed elongation. These samples differ from those of the previous study due to the unintentional introduction of a small amount of crystallinity (0.25% to 1%) which serves as tie points in the drawing operation, giving a stronger amorphous orientation. Preferred orientation of the amorphous chain segments is rapidly depleted during the first few percent of crystallization. The crystallite orientation distribution is quite sharp, and broadens only slowly with crystallization. These results imply that, for the crystallization conditions employed, the crystallite orientation must be determined by nuclei which are formed at the earliest stages of the crystallization process.
Statistical mechanical model for diffusion of simple penetrants in polymers. II. Applications—nonvinyl polymers
Authors: Pace R. J. , Datyner A.
Published: April 2003

The theory developed in Part I of this series is applied to a number of nonvinyl “smooth” chained homopolymers. The agreement between predicted and observed activation energies of diffusion for simple penetrants is generally good, particularly for polyethylene. Discrepancies observed for the smallest penetrants, He and H2, in some polymers may be rationalized in terms of atomic scale irregularities on the polymer chain surface. It is shown that in favorable cases the theory may permit diffusion data to be used as an additional check on the accuracy of conformational energy maps for polymers.
Characterization of the ladder polymerization of a crystalline cyclotetradiyne monomer
Authors: Banerjie A. , Lando J. B. , Yee K. C. , Baughman R. H.
Published: April 2003

The polymerization of the cyclic tetradiyne monomer, [(CH2) 2CCCC(CH2)2]4, containing interstitial chloroform has been investigated using Raman and Fourier‐transform infrared spectroscopy and x‐ray diffraction techniques. A loss of crystallographic register between chains occurs during the polymerization reaction, although crystalline order in the chain‐axis projection is retained. These studies indicate that 50 Mrad of 60Co γ‐ray irradiation produces 1,4‐addition polymerization at most of the diacetylene functionalities. Unreacted diacetylene groups are present primarily, although not completely, in soluble oligomeric material. Infrared spectroscopy indicates that this low molecular weight material has a butatriene (cumulene) backbone structure rather than the acetylenic structure of the insoluble polymer.
Environmental stress cracking of polyethylene: Criteria for liquid efficiency
Authors: Shanahan M. E. R. , Schultz J.
Published: April 2003

The environmental stress cracking (ESC) of polyethylene in nonreacting, nonswelling liquids has been studied using uniaxial creep tests. For active liquids, three types of behavior have been recognized. At low stresses, “pure” ESC occurs; at intermediate stresses, time to failure is largely controlled by the ability of the liquid to flow into a growing crack; and at high stresses, ESC is in competition with failure by necking, and the latter prevails. The liquid does not therefore play a significant role in this last case. Nonactive liquids produce results similar to those observed in air. It is believed that this is because these liquids are unable to flow into growing cracks sufficiently quickly even at low stresses and thus the liquid does not influence failure behavior. This criterion for activity of the liquid is largely determined by the viscosity of the liquid and by the spreading coefficient of the liquid on the solid—a parameter defining the ability of the liquid to wet the solid.
Effect of crystallization time on the properties of melt‐crystallized linear polyethylene
Authors: McCready M. J. , Schultz J. M. , Lin J. S. , Hendricks R. W.
Published: April 2003

Linear polyethylene was crystallized isothermally from the melt. Specimens were removed at different crystallization times and quenched to room temperature. The density, static mechanical properties, and small‐angle x‐ray scattering (SAXS) behavior of these specimens were measured at room temperature. The density and Young's modulus increased with crystallization time, whereas the upper yield point decreased with crystallization time. SAXS data showed that a zero‐angle peak gradually disappeared as crystallization time increased. Concurrently, the breadth of the SAXS peaks, the Bragg angle, and the integrated intensity decreased. Changes in the ratio of second‐ and first‐order peak intensities were also noted. On the basis of the SAXS and density data, it was concluded that a competition exists between the thickening of existing crystals and the creation of new crystallites between the older ones. At relatively low crystallization times, numerous new crystals can form during quenching to room temperature, whereas quenching after prolonged crystallization primarily results in the additional thickening of existing crystals. No change in the density of the amorphous material is found. A model is given whereby the upper yield stress is coupled to these morphological changes through a stress concentration effect caused by a decreased population of chains connecting adjacent crystallites. The tie‐chain population change occurs by their elimination as crystallites disappear.
Kinetics of craze initiation in polystyrene in N‐alcohols
Authors: Iisaka K. , Nishimoto Y. , Shibayama K.
Published: April 2003

The kinetics of craze initiation has been investigated for unmodified and rubber‐modified polystyrenes in n‐alcohols. The dependence on time and temperature of the critical strain at which crazes could be detected visually was determined with a Bergen elliptical strain device. Sorption studies were also conducted at room temperature on films exposed to the saturated vapor of n‐alcohol. The analysis of crazing data in terms of the Eyring model gave activation energies from 9.4 to 17.4 kcal/mole, increasing with increasing chain length of n‐alcohol and increasing rubber content. The activation volume multiplied by a stress concentration factor decreased with increasing rubber content and was nearly independent of the chain length of the n‐alcohol. The larger the diffusion coefficient, which we measured by sorption experiments, the smaller was the activation energy for craze initiation. The values of diffusion coefficients, estimated from the experimental data on craze initiation, were found to be comparable with those from the sorption experiments. It was concluded that the rate of craze initiation on exposure to liquids is controlled by the diffusion of the molecules of liquid into polymer.