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  • 1
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The initial stage of the suspension polymerization of poly(vinyl chloride) (PVC) is characterized by the formation of colloidally stable micron-sized grains of PVC inside the polymerizing ca. 150 μm vinyl chloride droplets. The fate of these micron-sized PVC grains depends upon the agitation conditions. If no agitation is employed, they serve as growth centers for further polymerization to give a final particle possessing a uniform internal bead morphology. In agitated systems, these grains coagulate early in the conversion to give a more irregular structure in the interior of the PVC particle. The formation of these stable growth centers appears to be unique to PVC. The polymerization of acrylonitrile, also insoluble in its monomer, is characterized by rapid agglomeration of the precipitated polymer throughout the polymerization. In PVC, the colloidal stability of the polymerizing grains is demonstrated to be electrical in nature. A pericellular membrane or skin formed by polymerization in both the water and vinyl phase completely surrounds the polymerizing droplet after about (1-2)% conversion. This skin is responsible for the charge retention of the PVC grains inside the polymerizing monomer droplets.
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  • 2
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Crystallization kinetics has been studied for a polydioxolan (PDOL) sample, over a wide temperature range, by dilatometry and microscopy. The dilatometry results can be analyzed using the Avrami equation. At temperatures higher than 22°C, the crystallization data must be analyzed in two steps: the first part of the curve corresponds to PDOL with a very disordered morphology (Phase I) while the second part of the crystallization curve is related to a spherulitic morphology (Phase II). The passage from the low to the high crystallization temperature region is associated with a change in the Avrami exponent from 3 to 4. The crystal surface free-energy product σσe was found to be 18 × 102 erg2/cm4, very close to that of polyoxymethylene. The crystallization kinetics was studied by microscopy over the temperature range-18 to 35°C. Growth and nucleation rates were recorded. Two phases are found only at temperatures higher than 22°C. The appearance of Phase II is related to a decrease in the growth rate of the sample. From the growth rates, the crystal surface free-energy product σσe was found equal to 17 × 102 erg2/cm4. The detailed analysis of the crystallization of the two phases reveals a complicated process which can be divided into four different steps: (a) growth of a disordered phase, Phase I; (b) nucleation of a higher birefringence structure; (c) propagation of a high birefringence phase; and (d) spherulitic growth, Phase II. The analysis of PDOL crystallization strongly suggests the presence of a hedrite → oval → spherulite transition: the hedrite formation corresponds to step (a), the oval formation to steps (b) and (c), and the spherulite formation to step (d).
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  • 3
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Polyalkane imides based on 3,3′,4,4′-diphenyloxidetetracarboxylic, pyromellitic and 1,4,5,8-naphthalenetetracaboxylic acids, and aliphatic diamines containing 4, 6, 8, 10, or 12 methylene groups have been studied. Relations governing the effect of structure on solubility, heat resistance, density, and crystallizability have been established. Conformation analysis has been carried out and models of the macromolecules have been constructed. The morphology of the crystalline polymers has been studied. For the polymers of the given class, crystallization capability is shown to be associated with the conformational flexibility of the macromolecular unit determining a given acid moiety by the number of methylene groups in the diamine unit.
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  • 4
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Polymorphism in nylon-12 film, which appears on casting from a phenol-ethanol solution, has been investigated by x-ray diffraction and infrared absorption. The casting temperature was varied from 30 to 130°C and the ambient atmospheric pressure from 50 to 760 Torr. Casting at 30°C gives only the α form, while casting above 90°C yields only the γ form. At intermediate temperatures, both α and γ forms are obtained, with the γ content increasing as the casting temperature and/or the rate of evaporation of solvent are increased. The ethanol component of the casting solvent appears to act only as a melting-point depressant for phenol. In contrast, nylon-6 film cast from the same solvent system between 30 and 160°C gives only the α form. It is proposed that the difference in polymorphism of nylons-12 and -6 is caused by differences in molecular flexibility due to the length of the methylene chain.
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  • 5
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
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  • 6
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
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  • 7
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The influence of temperature, frequency, and straight-chain-length distribution on the low-frequency Raman-active longitudinal-acoustical-mode (LAM) bands of polymers is discussed. Specifically, the effect of these factors on the intensity of LAM-1, on the ratio of intensities of LAM-1 to LAM-k, and on peak position is computed or estimated. Band halfwidth and chain-length-distribution halfwidth are found not to be simply related. It is shown that the integrated intensity of LAM-1 is very nearly proportional to the total length of straight chains.
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  • 8
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Excimer formation has been studied in a series of ancenaphthylene - methyl methacrylate copolymers of content varying over the total composition range. In accord with a previous model [Reid and Soutar, J. Polym. Sci. Polym. Lett. Ed., 15, 153 (1977)], the excimer formation has been described by a composite function representative of energy migration and excimer site concentration. In tramolecular energy migration in glassy solutions of the polymers was characterized by use of fluorescence depolarization measurements. The extent of energy migration in the acenaphthylene copolymers is determined by the mole fraction of aromatic chromophore fa. A function Σ descriptive of the excimer site concentration has been generated on the assumption that excimer formation results predominantly from next- to nearest-neighbor interactions. Σ is based upon the pentad distribution of aromatic chromophores in the chain and contains pentad fractions appropriately weighted according to the frequency and relative importance of their potential excimer sites. Reactivity ratios of acenaphthylene and methyl methacrylate in copolymerization at 70°C were ra = 0.80 and rm = 0.57.
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  • 9
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Photocurrents induced by pulsed ultraviolet light in polyhexamethylene adipamide (nylon-66) have been studied. Two transient photocurrents are observed for light wavelenghts shorter than 3000 Å;. The first one is weakly field and temperature dependent and has been ascribed to electron photoinjection. On the whole, the time dependence of the two photoresponses suggests the possible formation of a space charge in the material.
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  • 10
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Stress relaxation has been studied in networks of dihydroxy-terminated polybutadiene (mostly cis:trans:vinyl = 34:40:26) crosslinked by triphenyl methane-4,4′,4″-triisocyanate and containing about 9.5% by weight of unattached linear random styrene-butadiene copolymer with various molecular weights (from 1.4 to 3.3 × 105) and with styrene content and butadiene microstructure chosen to match the average solubility parameter of the end-linked network. Stress relaxation measurements were made also on networks containing no unattached species and containing 9.3% hydrocarbon oil, and on the various uncrosslinked linear polymers. The stretch ratio was 1.25 and the Young's relaxation modulus was calculated from the neo-Hookean stress-strain relation. For the uncrosslinked linear polymers, the relaxation modulus E11(t) corresponds to a rather narrow distribution of relaxation times whose magnitudes were approximately proportional to the 3.4 power of viscosity-average or weight-average molecular weight; for one polymer, the time dependence agreed closely with the prediction of the Doi-Edwards theory modified for a small degree of molecular weight distribution. The disengagement times calculated from the Doi-Edwards theory as modified by Graessley appeared to be of the correct order of magnitude. The contribution of the unattached species in the networks E1(t) was calculated by difference; after multiplication by (1-v22)-1, where v2 is the volume fraction of network, and correction for the difference in monomeric friction coefficient associated with the difference in fractional free volume in the two environments, E1(t) was compared with E11(t) for each linear polymer. The relaxation was slower in the network than in the uncrosslinked polymer by about an order of magnitude, but the form of the relaxation modulus was similar in both environments except for two linear polymers for which the relaxation in the network became very much slower at long times. This behavior appeared to be correlated with a broader molecular weight distribution.
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  • 11
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The effect of 1,3-cyclohexane rings in the chain backbone on the crystal structure of polyamides has been studied using polyamides (denoted 1,3-CBMA-n) obtained from 1,3-cyclohexane-bis(methylamine) (1,3-CBMA) and n-carbon dicarboxylic acids. The crystallinity of the 1,3-CBMA-n polymers changes greatly with variation in the value of n. This is attributed to hydrogen-bond changes associated with the relative length of the diacid moiety to the diamine moiety in the monomeric unit of each polymer. In 1,3-CBMA-6, the cis-1,3-cyclohexane rings are readily accommodated in the molecular chains to form crystals in a manner similar to the m-benzene rings in poly(m-xylylene adipamide) (MXD-6). The crystal lattice, however, is more expanded than in MXD-6 since the 1,3-cyclohexane rings is bulkier than the m-benzene ring. The crystal structure of the 1,3-CBMA-n polymers is essentially the same as that of MXD-6.
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  • 12
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Normal coordinate calculations have been performed for poly(vinylidene chloride) employing a TXTX′ conformational model (X and X′ denote torsional angles of equal value but opposite sign). A valence force field previously determined from the model compounds 2,2-dichloropropane and 2,2-dichlorobutane was directly transferred to the chain conformation of the polymer. The results are in excellent agreement with the observed vibrational spectra and we have been able to satisfactorily assign all the major normal modes.
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  • 13
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
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  • 14
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
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  • 15
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Temperature dependences of diffusion and permeation coefficients of hydrogen and deuterium in glassy and rubbery polymer films have been measured. The size of the free volume element in rubbery polymers has been calculated according to the theory of Frisch and Rogers for the quantum isotope effect, but the free volume is too large for precise calculation below the glass-transition temperature. The cooperative movement of segments is also discussed using the ratio of preexponential factors for diffusion mechanisms above and below the glass-transition temperature.
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  • 16
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Quantitative comparison of previously published NMR spin-relaxation data for polydiethylsiloxane with theoretical predictions for a variety of motional processes allowed both the nature and time scale of molecular motions to be identified. At the lowest temperatures, methyl reorientation produced a T1 minimum and was found to proceed with an activation energy of 2.4 kcal/mole in both amorphous and crystalline phases. Reorientation of the ethyl groups in the amorphous phase was observed at a higher temperature with an activation energy of 9.3 kcal/mole. Relaxation in the melting region was influenced by flexing and stretching of the helical polymer chain. The maximum angular displacement of the chain was estimated to be 24°, with an activation energy for this process of 2.6 kcal/mole.
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  • 17
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Double-exposure speckle patterns created by scattered light were used to study tensile deformation of isotactic polypropylene film. The method makes possible a quantitative investigation of the deformation process (relative magnitude and orientation of the displacement vector, Poisson's ratio μ) by means of a simple optical analysis of stepwise deformations covering the desired range. The displacement vector and Poisson's ratio have been determined with an accuuracy of ± 5% in the range of small deformations (up to 18% relative deformation); and the role of stress relaxation has been examined. Limitations of the method, such as the range of measurable displacements, effect of prestressing, and stability of the system, etc., are discussed. Among advantages of the method are comparative simplicity and accuracy, and the possibility of its application to other systems studied by the small-angle light scattering method.
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  • 18
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The drawing behavior of linear polyethylene homopolymers with weight-average molecular weights (M̄w) from 101,450 to ca. 3,500,000 has been studied over the temperature range 75°C to the melting point. In all cases 1-cm gauge length samples were drawn in an Instron tensile testing machine at a constant cross-head speed of 10 cm/min. With the exception of the lowest molecular weight polymer, it was found that increasing the draw temperature led to substantial increases in the maximum draw ratio which could be achieved, and that this increased monotonically with increasing draw temperature. Measurements of the Young's modulus of the drawn materials showed, however, that the unique relationship between modulus and draw ratio previously established for drawing at 75°C was not maintained to the highest draw temperatures. The highest draw temperature at which this relation held was found to be strongly molecular weight dependent, increasing from ca. 80 to ca. 125°C when M̄w increased from 101,450 to 800,000. In all cases conditions could be found for drawing samples to draw ratios of 20 or more with correspondingly large values of the Young's modulus.
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  • 19
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The effects of pressure on the compressibility and crystallization of poly(ethylene terephthalate) (PET) have been investigated. The Instron capillary rheometer was adapted as a high-pressure dilatometer to perform experiments up to 40,000 psi. Compressibilities of solid and molten PET were measured. The increases in compressibility with increase in temperature for the solid state are discussed in terms of free-volume theory. Results obtained for the melt are explained by invoking the second law of thermodynamics and the effect of pressure on the Gibbs free energy. The effects of temperature and compression rate on the pressure of crystallization (Pc) were also studied. As the crystallization temperature was increased from 240 to 286°C, Pc increased by about 16,000 psi. As the compression rate was raised from 1%/min to 8%/min, Pc increased 10,000 psi. At some undetermined compression rate above 8%/min it seemed impossible to induce crystallization in the melt, even with pressures up to 40,000 psi. Analysis of data on the kinetics of crystallization of PET melt under high pressures revealed low Avrami exponents, for which no unequivocal explanation is offered. It is possible, however, that crystallization at high pressure promotes the formation of a morphology made up of a certain percentage of “extended chains.” The alteration in the attendant spatial geometry involved in the crystallization might explain the lower Avrami exponents found. In another set of experiments, crystallization temperatures (Tc) were measured by slowly cooling PET melt under high pressures. As the pressure was raised from 3000 to 15,000 psi, Tc increased from about 246 to 282.5°C. These results are consistent with thermodynamic theory.
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  • 20
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
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  • 21
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The environmental stress cracking (ESC) of polyethylene has been studied under conditions of dynamic equilibrium with the liquid for low-swelling liquids. Even among active ESC agents, there is a clear relative order of efficiency. It has been shown that the liquid becomes less efficient with increasing equilibrium swelling. This fact has been attributed to local plasticization of the crack front leading, in turn, to a reduction in the high-stress concentrations associated with a wedge-shaped crack. Some semiquantitative ideas are proposed in an attempt to explain the relation between ESC efficiency and volume/volume sorption.
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  • 22
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Doi and Edwards have recently proposed a molecular theory for the dynamics of entangled polymer liquids based on a tube model to represent the mutual constraints on configurational rearrangement of the chains. Expressions for diffusion coefficient, plateau modulus, zero-shear viscosity, steady-state recoverable compliance, and terminal relaxation time can be devloped, and relations among these properties that depend only upon observable quantities can be obtained. Several such relations are derived and are compared with experimental observations.
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  • 23
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The isothermal crystallization of isotactic polypropylene at different temperatures in the presence of fibrous substrates has been investigated. It is shown that preferential transcrystalline growth occurs at the fiber surface and that changes in nucleation density in the bulk material adjacent to the fibers also occur, the extent of which is dependent on temperature and fiber volume fraction. The effects are discussed in terms of the diffusion of heterogeneities in the bulk due to interaction and the adsorption on the fibers.
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  • 24
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: It is shown that the partial molal volumes (pmv) of the repeat units of nonionic polymers in aqueous solutions calculated from pmv group contributions, obtained from pmv data for small molecules and salts in aqueous solutions, agree in most instances to within ± 1 cm3/mole with the experimental values. The pmv of ionic polymers calculated from pmv group contributions have been found to be always larger than the experimental values. The difference gives a lower bound of the cooperative electrostrictive effect of neighboring charged sites of the polymer chain on surrounding water molecules.
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  • 25
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
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  • 26
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
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  • 27
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The morphology of linear polyethylene of Mw/Mn 1.19 crystallized isothermally from the melt has been investigated. Electron microscopy (EM) of stained thin sections gave exceptionally well-defined images. There were no qualitative differences between Regime I and Regime II crystallization, but the lamellae grown at lower supercooling were thicker, larger, and had fewer spiral growths per unit area of fold surface. Small-angle x-ray scattering indicated a much sharper distribution of lamellar thicknesses than EM and Raman LAM did. This is evidence of the complementary nature of the techniques and not a contradiction. EM also revealed nonrepresentative features in detail. There were extremely thin lamellae formed on cooling, indicating molecular weight segregation even in this fractionated material, and there were extremely thick lamellae, attributed to isothermal thickening. As the representative lamellae are also supposed to have thickened isothermally, this raises the issue of when and how the lamellae which are the primary products of crystallization can be identified.
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  • 28
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The course of melting of melt-crystallized polyethylene fractions and of a poly(ethylene oxide)-polystyrene-poly(ethylene oxide) triblock copolymer has been followed by small-angle x-ray scattering (SAXS). Changes in the intensity and shape of the SAXS curves indicated that both surface melting and melting over the full crystallite thickness (full-strand melting) take place. Full strand melting is the final, irreversible process. Comparison with an analytical model indicates that in the earlier stages of the irreversible, full-strand process the crystallites melt out randomly throughout the bulk. Later stages may occur by the simultaneous melting of a larger stack of crystallites.
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  • 29
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The thermally stimulated current (TSC) technique has been used to investigate three anionic polystyrenes of M̄n 17,000, 71,700, and 1.55 × 106, i.e., M 〈 Mc, M 〉 Mc, and M ≫ Mc, where Mc is the entanglement molecular weight. A current maximum near Tg designated TMg, has relaxation times which follow an Arrhenius equation. A second current maximum at T 〉 Tg appears to be the Tll process and is designated TMll. Relaxation times for it follow a Vogel equation. TMg and TMll vary with molecular weight, increasing below Mc and leveling off above Mc at a temperature of about 170°C. Values of TMg and TMll are compared with values of Tg and Tll obtained from torsional braid analysis, which involves melt flow; and with differential-scanning-calorimetric values on fused films, where there is no transport of polymer. It is concluded from such cross-comparisons that TSC, at least for polystyrene, is a quasistatic test which may involve microscopic viscosity. Macroscopic viscosity does not play a role. The ratio TMll/TMg is in the range 1.10-1.16, similar to Tll/Tg values by other methods. A few comments about Tll in atactic poly(methyl methacrylate) by the TSC method are given.
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  • 30
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The morphology of poly(butylene terephthalate) (PBT) crystallized from the melt at various temperatures was studied by small-angle light scattering, polarizing microscopy, and wide-angle x-ray diffraction. Spherulites with a maltese cross at 45° to the polars formed at lower temperatures while spherulites having an apparently higher melting point with a maltese cross along the polars (0°-90°) formed at higher temperatures. The spherulite size and crystallinity increased with increasing crystallization temperature. The Hv scattering patterns arising from the spherulites formed at lower temperature showed intensity maxima at azimuthal angles of 0° and 90°, while those obtained at higher temperatures showed the more common 45° intensity maxima. Microtomed samples from molded PBT bars showed spherulites with a 45° maltese cross which changed to a 0°-90° maltese cross upon heating just prior to melting. The skin-core effect due to varying thermal histories in these molded bars was clearly observed. Solvent crystallized films contained positive 0°-90° spherulites. Some changes occurring upon uniaxial stretching of PBT films are also discussed.
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  • 31
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Rheological studies were carried out on concentrated m-cresol solutions of two helical synthetic polypeptides; poly-γ-benzyl-L-glutamate (PBLG; molecular weight, 150,000) and poly-∊-carbobenzyloxy-L-lysine (PCBZL; molecular weight, 200,000). Steady shear measurements were made over a range of 0.01-16,000 sec-1 to obtain steady shear viscosity and first normal stress difference. Dynamic viscosity and dynamic storage modulus were measured both by oscillatory shear between cone and plate and also by an eccentric rotating disk device over frequency ranges of 0.1-400 and 0.1-63 rad/sec, respectively. The concentration ranges were such that both liquid crystalline and isotropic solutions were investigated. The previously reported observations of an apparent negative first normal stress difference within a defined range of shear rate for liquid crystalline solutions were confirmed for the PBLG and PCBZL solutions. At high shear rates the peaks in plots of steady shear viscosity against concentration were profoundly suppressed but peaks in first normal stress difference versus concentration were not. The observation of liquid crystalline order in PCBZL/m-cresol solutions at room temperature constitutes evidence that the inverse coil-helix transition temperature is lower in concentrated solutions than in dilute solutions. The critical concentration for formation of the liquid crystalline phase was higher for PCBZL than for PBLG, despite a higher axial ratio, due to helix flexibility.
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  • 32
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The finite deformation elasticity of gels of stiff rodlike polymer chains is discussed theoretically. Unlike a rubber composed of flexible polymer chains, the elasticity of this system is energetic, and arises from the elastic deformation of the stiff chains which are forced to bend under macroscopic strain. The stress-strain curve of this system is shown to be nonlinear even if the bending of the rods is small, and has a characteristic S-shaped form which is unlike that of a rubber. The effect of orientational order is also discussed.
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  • 33
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Heat capacities of liquid selenium have been measured by computer interfaced differential scanning calorimetry in the metastable region with an accuracy of ± 1% from 330 to 520°K. To avoid crystallization, the measurements were done on cooling. A semiquantitative fitting of the heat capacity to vibrational energy contributions, free volume (hole) effects, and heats of reaction from the changes in the ring-chain and depolymerization equilibria was possible to within ±5% of the newly measured and literature data between the glass transition temperature (ca. 303°K) and 1000°K. It could be established that the shift in the ring-chain equilibrium is not the major reason for the overall decrease in heat capacity above the glass transition temperature. The floor temperature, which was earlier placed at about 356°K, is possibly below the glass transition temperature. The increase in heat capacity beyond 800°K has been linked with the depolymerization reaction.
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  • 34
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The influence of molecular weight and temperature on the tensile drawing behavior of polypropylene has been studied, with particular reference to the production of ultra-high-modulus oriented materials. It has been shown that the optimum draw temperature is molecular weight independent to a good approximation, and that high-modulus products can be obtained for M̄w in the range 180,000-400,000, the highest modulus being achieved for polymer with M̄w = 181,000. As in the case of linear polyethylene, under optimum drawing conditions the Young's modulus relates only to the draw ratio. Low-temperature moduli as high as 25-27 GPa were recorded, which compare favorably with a previously reported value of 42 GPa for the crystal-lattice modulus. Although the drawing behaviour of the samples studied appeared comparatively insensitive to molecular weight, some of the properties of the draw materials, notably melting point and shrinkage at high temperature, showed a wide range of behavior.
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  • 35
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Thermoelasticity studies of poly(vinyl alcohol) networks swollen in aqueous glycol indicate that the effects of specific polymer-diluent interactions diminish at high swelling, much as in the situation of poly(vinyl alcohol) in pure water reported earlier. In 20% glycol, the ratio of the energy component fe of the force to the total force f was found to be -0.59 at high swelling. Swelling was controlled by the degree of network crosslinking. Evidence that fe/f could be determined under the condition of a null thermal expansion coefficient was not obtained; in fact, the contrary was indicated.
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  • 36
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Fourier transform infrared spectroscopy has been used in conjunction with differential scanning calorimetric measurements to investigate the nature of molecular degradation and its effect on the phase transition temperatures in irradiated polytetrafluoroethylene (PTFE). Both the 19 and 30°C transitions are observed to exhibit similar shifts to low temperatures upon irradiation. Infrared absorbance subtraction data from irradiated PTFE indicate a continual decrease in sample crystallinity accompanied by an increase in the number of free and bonded —COOH groups with increasing dose consistent with molecular degradation by chain scission. By comparing infrared band intensities on a number of irradiated PTFE samples with those from short chain perfluoro n-alkanes, it was determined that the overall reduction in chain length caused by irradiation was primarily responsible for the observed reduction in both phase transition temperatures.
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  • 37
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Solution-grown crystals of fractions of isotactic polypropylene (IPP) with different degrees of stereoregularity have been obtained by isothermal crystallization from α-chloronaphthalene, using a self-seeding technique. Electron micrographs of samples, crystallized under the same undercooling, show that, with decreasing fraction of isotactic pentads, the perfect rectangular shape of the single crystal is lost and the presence of more complex morphologies is increasingly observed. The equilibrium dissolution temperature Td of IPP fractions, from polymers prepared with a titanium based catalyst, decreases linearly with decreasing percentage of isotactic pentads. An extrapolated value of 171°C is obtained for the equilibrium dissolution temperature of a crystal of IPP with 100% isotactic pentads, i.e., an IPP crystal free of configurational defects. The melting temperature T′m and the apparent enthalpy of fusion ΔH*f of crystallized and annealed crystal aggregates have been determined by differential calorimetry. The equilibrium melting temperature Tm also depends greatly upon the isotactic pentad concentration. For 100% concentration the extrapolated value of Tm is 181°C. Tm decreases about 1°C per 1% decrease in the isotactic pentad population. The observed equilibrium melting and dissolution temperature depression does not follow the predictions of the Flory equation for copolymer crystallization. In fact, the effect of decreasing probability of isotactic sequence propagation is to depress Td and Tm much more rapidly. The apparent enthalpy of fusion of both solution-grown crystals and melt-recrystallized samples decreases with an increase in the number of configurational impurities along the chain. For the most stereoregular fraction the average length of isotactic stereoblocks has been compared with the lamellar thickness of solution-grown lath-shaped single crystals.
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  • 38
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The glass-transition temperature (Tg) and the elastic modulus of nylon-6 and its mixtures with 4% w/w LiCl and with 2% LiCl+3% LiBr were investigated. In one set of experiments care was taken to avoid absorption of moisture during the measurements. In another set of experiments, samples were exposed to atmospheric humidity for different lengths of time. Both unoriented and oriented specimens were investigated. The presence of 4% LiCl almost doubles the amount of moisture absorbed at equilibrium by nylon-6. The Tg was found to be greatly affected by the moisture content and by salt type. When strict precautions to exclude moisture are taken, the addition of 4% LiCl raises the Tg of nylon-6 by about 25°C. The elastic modulus of oriented samples is increased by the addition of salts provided moisture is completely absent. This beneficial effect is, however, completely eliminated when samples are allowed to equilibrate with atmospheric moisture.
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  • 39
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A series of poly(aryloxyphosphazene)s was prepared with phenoxy and p-ethylphenoxy substituents in various ratios. The thermal, morphological, and rheological properties of this series of polymers were studied by differential thermal analysis, x-ray analysis, and rheometrics mechanical spectroscopy. Thermal analysis showed that the resulting polymers follow melting-point-depression- and glass-transition-temperature-composition relationships expected of random copolymers. The lower first-order transition temperature [T(1)] disappears near equimolar substitution while the higher first-order transition temperature (Tm) persists over the whole range of compositions. X-ray analysis revealed that crystalline order in the polymer chain direction is destroyed by nearly equimolar substitution but lateral order remains. The rheological characterization of a copolymer with nearly equimolar substitution showed that the polymer is in a pseudocrosslinked state indicating the existence of chain-to-chain interactions. When a small amount of an antioxidant (6-dodecyl-1,2-dihydro-2,2,4-trimethylquinoline) is added, the lateral order of the copolymer is destroyed, and its rubbery plateau modulus decreases by several fold.
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  • 40
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Examination of the highly oriented aramid fiber, Kevlar, at high magnification in an optical microscope in the extinction position between crossed polars gives an image with regions of regular fine bands. The diffraction pattern shows first order but no zero order. This is interpreted as being due to the passage of depolarized scattered light from a material with regularly spaced discontinuities. This is identified with the pleated structure proposed by Dobb et al.
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  • 41
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    New York : Wiley-Blackwell
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
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  • 42
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Small-angle x-ray scattering has been used to characterize a variety of polyethylene fibers of the so-called shish-kebab type. These fibers are aggregates of elementary fibrils each consisting of a backbone with a lamellar overgrowth. Intense scattering is due to voids between the lamellae giving rise to a “Bragg maximum” reflecting the ordering of lamellae along the backbones. It can be described by rather broad distributions for both the interlamellar spacings and the lamellar thicknesses. This is shown by comparing experimental scattering curves with SAXS patterns calculated on the basis of the theory for one-dimensional scattering of linearly ordered lamellar systems, using the general paracrystalline model. A negative exponential distribution for the center-to-center distance of the lamellae, characteristic of a random nucleation process, apparently cannot be employed for the description of these shish-kebab morphologies. From a discussion on the discrepancies between experimental and theoretical scattering curves it is concluded that the fibers may be inhomogeneous with respect to the statistics of lamellar ordering. This may be due to the nonisothermal character of the crystallization process.
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  • 43
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A molecular theory of the piezoelectric constant of the α-helical backbone of polypeptide is developed on the basis of fluctuation formalism. The piezoelectric constant, electric susceptibility, and elastic compliance of the α-helix are calculated through the method of molecular lattice dynamics by use of normal-coordinate analysis. Displacements of each atom due to the external stress exerted upon the backbone are also calculated. The piezoelectricity of the α-helix is concluded to arise mainly from rotation of the CO—NH bond. The value of the piezoelectric constant of poly(γ-benzyl-L-glutamate) film calculated from the above theoretical constants along with a composite theory is found to agree reasonably with experiment.
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  • 44
    Electronic Resource
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    New York : Wiley-Blackwell
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A model is presented for analysis of the sorption of mixed gases in glassy polymers at concentrations below which significant plasticization occurs. The well-known dual-mode sorption model comprised of a Henry's law term and a Langmuir isotherm term, which has been used extensively for interpretation of single-component gas sorption data, forms the basis for the analysis of binary mixtures discussed here. Measurements using pure gases provide dual mode parameters which can then be used to predict the resultant sorption isotherms for binary mixtures of any of the pure gases. The proposed analysis is based upon recognition that the Langmuir component of the overall sorption concentration should be governed by competition between the two penetrants for the fixed unrelaxed volume in the polymer, which is believed to be the locus of the Langmuir capacity. This effect may result in a significant depression of the measured sorption of similar penetrants competing for the limited Langmuir capacity. A numerical example is considered which illustrates the range of behavior expected for CO2 and CH4 in polycarbonate. Deviations from the theoretical predictions of the simple dual-mode model for binary systems are discussed in terms of plasticizing effects on the Henry's law constant and the Langmuir affinity constant. The analyses proposed here are of direct and critical interest to the applied problems of migration of trace contaminants in glassy polymers and analysis of barrier packaging for foods since all of these applied problems involve mixed-penetrant sorption. Specifically, it is predicted that the presence of residual monomers or solvents in glassy polymers can produce both anomolously low Langmuir sorption affinity constants and sorption enthalpies compared with the residual-free case.
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  • 45
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Wide-angle and small-angle x-ray diffraction patterns of 11 poly(N-(10-n-alkyloxycarbonyl-n-decyl)maleimides) (PEMI) (including only even members of the series) have been obtained on unoriented samples. They show major maxima at two diffraction angles. The one at the larger angles is due to the interaction of neighboring n-alkyl side-chains. The smaller one (which shows second and third orders of diffraction in higher members of the series, n = 14 to n = 22, where n is the number of methylene groups in the external n-alkyl sequence in the side chain) is related to the distance between lamellar planes formed by the main chains. In all cases, the measured layer separation di is higher than the structural unit length L of the side-chain in the most extended conformation, and lower than the length corresponding to two side-chains. On the basis of the experimental results reported here, a model is proposed for the packing of these comblike polymers in the solid state. The mode of packing is also supported by infrared spectra in the 720 cm-1 region for the —CH2— rocking mode of vibration of the n-alkyl side-chain.
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  • 46
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The relation between the thermal behavior of extended-chain crystals (ECCs) of polyethylene and the phase transitions, i.e., orthorhombic ↔ hexagonal ↔ melt, of polyethylene at high pressures above about 400 MPa has been studied by high-pressure differential thermal analysis (DTA), and with a high-pressure and high-temperature x-ray diffraction apparatus equipped with a position-sensitive proportional counter measuring system. The original sample used in this study consists mainly of two kinds of ECC, which we designate as “ordinary extended-chain” crystals (OECCs) and “highly-extended-chain” crystals (HECCs). Experimental results at pressures below 300 MPa substantiate the results previously reported: i.e., the phase diagram indicating the relation between the melting temperatures and pressure for the OECCs and HECCs can be determined for pressures up to 500 MPa.In heating at pressures above about 500 MPa, the peak intensity of the (100) reflection of the hexagonal structure decreases in two stages with increasing temperature. The phenomenon corresponds to the thermal behavior determined by high-pressure DTA in which two small endothermic peaks can be observed at temperatures above that of the crystal transition evidenced by the strong peak. This phenomenon suggests melting in two stages of hexagonal structures with different thermal stabilities, and that the change at higher temperature may be due to fusion of the hexagonal phase annealed either below or above the transition temperature.
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  • 47
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Dielectric relaxation measurements were made on methyl methacrylate - styrene and methyl methacrylate-p-chlorostyrene copolymers at temperatures higher than the glass transition temperature Tg. It was found that the temperature dependence of the relaxation time can be described satisfactorily by an expression derived recently for chain motion in amorphous polymers. The temperature Tg obtained from the expression agrees well with that determined by differential thermal analysis.
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  • 48
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Small-angle x-ray diffraction measurements were performed upon dimethyl acetamide (DMAc) solutions of four samples of X-500, an aromatic polyamide-hydrazide. The solubility improved as the polymer molecular weight increased, the most soluble sample being in the form of a highly oriented, crystalline fiber. Molecular weights determined from the scattering curves indicate that aggregation was present in all solutions. Its extent varied with the solubility of the sample, increased with polymer concentration and, for the lowest concentrations studied, could be reduced by the addition of acetic acid. Radius of gyration values were smaller than those obtained by light scattering, probably because of insufficient resolution of the camera. The mass per unit length along the chain was found to be 18-20 Å, while the radius of gyration of the cross section was 3.5-4.8 Å. Three of the samples gave nearly the same angular intersection for the coil-and rodlike regions of the scattering curve. Two of these were whole polymers and the other a narrow fraction. The fact that essentially the same intercept was found in all three cases indicates the persistence length as measured for linear chain polymers by small-angle x-ray diffraction is independent of the heterogeneity of the sample. The intercepts, after a small correction for excluded volume effects, correspond to persistence lengths in the range 71-88 Å for DMAc solutions, which approximate those determined for dimethyl sulfoxide (DMSO) solutions by light scattering the intrinsic viscosity without correction for excluded volume, but are substantially larger than the DMSO values, corrected for excluded volume of 30-49 Å. We can offer no explanation for this difference.
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  • 49
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Mixtures of two “monodisperse” samples of polystyrene (M1 = 4.53 × 104, M2 = 10.3 × 104; Mw/Mn 〈 1.01) in cyclohexane were allowed to separate into two phases at different polymer concentrations and temperatures. The compositions in the two phases were measured by gel permeation chromatography, and used to determine isothermal binodals. From the binodal data the critical temperature and concentration were estimated as functions of the composition of the polymer mixture, and the separation factor σ for each polymer component was calculated. In contrast with typical results in the literature, σ was almost independent of molecular weight of the polymer. It is shown by deriving a general expression for σ that theoretical prediction of σ requires accurate knowledge about the Flory-Huggins interaction parameter as a function of the concentrations of individual polymer components.
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  • 50
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Cellulose triacetate (CTA) forms liquid-crystalline solutions in trifluoroacetic acid, dichloroacetic acid, and mixtures of trifluoroacetic acid and dichloromethane. Brilliant iridescent coloration, high optical rotations, and birefringent regions with swirl-like fingerprint patterns suggested the formation of cholesteric liquid crystals. Trifluoroacetic acid-dichloromethane is a particularly excellent solvent mixture to form liquid-crystal solutions of cellulose acetate. Crude bulk viscosity measurements confirm the formation of an anisotropic phase, and the temperature dependence of the critical concentration for formation of the anisotropic phase, obtained by bulk viscosity measurements at various temperatures, provides confirming evidence. Viscosity decreases with aging, suggesting that CTA is slowly degraded in the solvents studied. This is also confirmed by optical rotatory measurements and by polarizing microscope observations. The miscibility gap is observed as a function of molecular weight, and the differences between the experimental data and Flory's prediction are discussed.
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  • 51
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: It was shown by Weiss and Silberberg in 1975 that polyacrylamide gels prepared by copolymerization of acrylamide and N,N′-methylene bis-acrylamide in water are heterogeneous. A two-phase model developed in 1979 satisfactorily accounted for the permeability of the gels. These gels had been prepared under standard conditions of initiator and activator concentrations and involved precooling of the reaction mixture to 0°C with completion of the reaction at room temperature, a thermal history not very suitable for kinetic analysis. A procedure was, therefore, devised where gels are prepared at room temperature throughout. Much better correlations are then obtained, and it can be shown that the initiation is controlled by the initiator (ammonium persulfate) concentration times the activator (N,N,N′,N′-tetramethylethylene diamine) concentration raised to the 1.5 power. These data, discussed in terms of the two-phase model, show that the initiator concentration directly determines the number of crosslinks in the more dilute, permeability-determining, gel phase. The faster the initiation, the less permeable a gel results. An increase of permeability with overall degree of crosslinking at constant monomer concentration is a feature only of gels prepared at sufficiently low polymerization initiation rates.
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  • 52
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A set of isothermally melt-crystallized polyethylene samples was examined using small-angle x-ray scattering (SAXS). Time and temperature of crystallization were the variable parameters used to create the set of samples. Following background subtraction, desmearing, and application of the Lorentz factor to the raw SAXS data it is possible to see many orders of reflection. This suggests that much higher degrees of order are present in isothermally melt-crystallized samples than had previously been thought possible. A combination of SAXS and DSC data indicates that there is no evidence for isothermal thickening in these samples. This study, coupled with data obtained from PE single crystals, produced information concerning the extrapolation of single-crystal data to fit bulk systems. In addition, the equilibrium melting point T0m determined is somewhat lower than previously claimed. This study also suggests that the surface energy of the mature crystals is always lower than that of the nucleated state and/or the nucleation factor Kσen increases with decreasing supercooling.
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  • 53
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
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  • 54
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The morphology of the ionomer resin from which Nafion perfluorinated membrane products are made was studied with wide-angle and small-angle x-ray diffraction. A reflection observed in the small-angle x-ray scan from hydrolyzed polymer is attributed to ionic clustering. The effects of equiv wt, cation form, temperature, water content, and tensile drawing on this reflection were studied and are discussed.
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  • 55
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    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The finite-element method is applied to a craze model in order to estimate surface displacements and stresses of an isolated craze in a thin rectangular plate. The limitation of assuming linear-elastic behavior of the craze fibrils is demonstrated by comparing computed profiles with published experimental ones. Accurate finite-element estimates of craze surface stresses are obtained from the experimental displacement profile. The analysis is extended to the three-dimensional case but the difference between the craze displacements at the surface of the plate and those at midthickness is too small to justify the considerable increase in computer time in comparison with that required for two-dimensional analysis.
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  • 56
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
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  • 57
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Two types of films showing different characteristic x-ray equatorial patterns were prepared from chloroform and N,N-dimethylformamide solutions of poly(γ-methyl L-glutamate-co-γ-benzyl L-glutamate). In the film cast from chloroform solution, the x-ray pattern on the equator consisted of a remarkable mixture of sharp and diffuse reflections, with the sharp reflections corresponding to integral values of 1/3k. On the other hand, in the film cast from N,N-dimethylformamide solution, a well-defined x-ray pattern was observed. An explanation for this characteristic pattern of chloroform-cast film was made on the basis of a structural model wherein stacking faults or dislocations are incorporated into the ordered structure characteristic of N,N-dimethylformamide-cast film. Two domains divided by a stacking fault are mutually displaced along the (100) crystal planes, but the shape and size of the unit cell is everywhere the same. The intensity distribution of x-ray diffraction was calculated as a function of the probability of a stacking fault occurring in a regular sequence of (100) planes. The best correspondence with observation was obtained with a stacking fault in every three layers, on the average.
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  • 58
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The partition function is formulated by the generating function method for a stacked lamellar model of alternating crystalline and amorphous layers. The random-walk problem of enumerating statistical weights for conformations of amorphous chains confined by two parallel walls is solved for the body-centered cubic lattice as a generalization of the one-wall model treated by Roe. The mean lengths of loop, tie, and cilia chains and the free energy of the system are calculated for the random-reentry and-bridge model as a function of the distance h of separation between crystal layers and as a function of the number N of loop chains in a crystal block as the basic structural element of the system. The mean length of amorphous chains decreases at a given thickness l of the crystal layers with decreasing h or with increasing N. The free energy of the system exhibits no minimum with respect to N, showing that the folded-chain crystal is thermodynamically stable, especially for relatively small l. Additionally, it is shown that another requirement for stabilizing relatively small crystals (small l) is the formation of an aggregate structure of crystals, whereas a large single-crystal (large l) is relatively stable, irrespective of h and N. Furthermore, a theoretical model is developed to calculate the force and elastic modulus of a highly deformed stacked system, assuming that the only change in the configurations of amorphous chains within the interlamellar regions is due to deformation, except for scission of tie chains having fewer segments than are needed to span the interlamellar distance of the deformed system. It becomes evident that taut tie chains are effective in increasing the modulus of the stacked system.
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  • 59
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The kinetics and equilibria of SO2 sorption in Kapton polyimide film have been studied at temperatures from 25 to 55°C and equilibrium sorption pressures up to 0.76 atm. The data are described well by the dual-mode model of sorption and transport in glassy polymers. The assumption of “partial immobilization” is required to correlate the transport data: the mobility of the Langmuir component of the sorbed population relative to the Henry's-law component is close to zero at 25°C, and increases to roughly 5% of the Henry's-law component mobility at 55°C. The heat of sorption is anomalously low, suggesting the presence of residual solvent in the film, a suggestion confirmed by annealing studies. However, the study also shows that partial removal of the residual has a relatively minor effect on the measured SO2 sorption level and transport rates at 55°C.
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  • 60
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Light scattering patterns are calculated for imperfect three-dimensional spherulites with fluctuations in the twist angle. The fluctuations are described in terms of a parameter characterizing the distance correlation function. Cases are considered in which (i) the principal axis of the scattering element makes a constant angle with the radius but there is disorder in the twist angle about the axis, and (ii) there is combined twist disorder and orientation disorder of the scattering elements. Calculations suggest that the disorder in the twist angle may lead to a decrease in the higher-order variation of scattered intensity with scattering angle and deviation from the four-leaf-clover-type scattering characteristic of a perfect spherulite at lower scattering angles. On the other hand, disorder in orientation has little effect on the scattering pattern.
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  • 61
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A high resolution carbon-13 NMR study of an ethylene-butene copolymer has yielded a spectrum whose resonances could be assigned to isolated ethyl branches, 1,3-diethyl branching as well as 1,2-diethyl branches resulting from head-to-head butene polymerization. All these structures are present in the same sample. An examination of all the published spectra of low-density (branched) polyethylenes has revealed many examples of heretofore unassigned resonances which can be associated with this latter type of diethyl branching in these polymers. Spin-lattice relaxation times have been determined, when feasible, for the carbon atoms in each of the three branched structures.
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    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The effect of heterogeneous chlorination of high-density polyethylene on its crystalline regions was investigated by NMR, x-ray diffraction, differential scanning calorimetry, and infrared spectroscopy. Crystallites remained inaccessible to attack by chlorine, even after extensive chlorination, however, their perfection was affected by extensive chlorination of the adjacent amorphous regions.
    Additional Material: 3 Ill.
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  • 63
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Partitioning of macromolecules between pore and bulk solutions directly affects both equilibrium and transport processes such as exclusion chromatography and movement of solutes through porous media. Because of interactions between macromolecules and the pore wall, the variation of the macromolecule activity with concentration is different inside the pore than in bulk solution. This difference causes a concentration dependence of the distribution coefficient, as reported in experiments involving exclusion chromatography. In order to explain this effect, we develop a model for a concentration-dependent distribution which explicitly accounts for a coupling between pore-macromolecule and macromolecule-macromolecule interactions. Predictions using this model are reported for the case of rigid spherical macromolecules in both cylindrical and slit pores, including both steric (hard sphere-hard wall) and long-range (screened electrostatic) interactions. An important result is the existence of a general correlation between the first order concentration effect and measurable properties of the macromolecule and porous medium.
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    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Cellulose-hydrazine complexes have been prepared by soaking cellulose fibers in anhydrous hydrazine, and their structures have been investigated by x-ray diffraction. The unit cells for the complexes formed by native ramie (cellulose I) and by Mercerized ramie and Fortisan (both cellulose II) have different dimensions, but all contain sections of four chains; and the x-ray patterns suggest significant changes in the chain stagger, as compared with the uncomplexed structures. The differences between the Mercerized ramie and Fortisan complexes may reflect the differences in morphology and crystallinity of these materials. Reconversion to cellulose is effected by soaking in water. For the cellulose II complexes a hydrate intermediate is observed in this process. The hydrate is a two-chain unit cell and contains approximately one water molecule per glucose residue.
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  • 65
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The space-time step-step correlations of a polymer chain, described by a self-avoiding random walk on a cubic lattice, are studied by simulating its behavior on a computer. Chains of N = 16 and N = 32 beads are studied. The short-time behavior of the correlations is characterized by peaks, which become depressed and broadened with increasing interstep distance. The long-time behavior is characterized by extremely slow decay, which goes to zero in about the same time for all interstep distances. The short-time behavior is a consequence of the rotation of parts of the chain smaller than or equal to the static coherence length ζ. These short-time processes also seem to be responsible for the relaxation of the square of the end-to-end distance, since in both cases the relaxation is of the order of 6N2. The long-time behavior of the correlations is a consequence of the rotations of parts of the chain greater than the coherence length. The correlations vanish when the entire chain has had time to rotate in space. Our results suggest that this corresponds to the relaxation of the end-to-end vector.
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  • 66
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The results of flow birefringence measurements are reported for polymer solutions of moderate concentration subjected to a wide range of two-dimensional flows. These flows were generated in a four-roll mill which enables one to systematically vary the ratio of the vorticity to the rate of strain in the flow while holding the velocity gradient constant. It is shown that steady-state birefringence data collected over a wide range of flow types can be correlated against the eigenvalue of the velocity gradient tensor, in agreement with criterion for strong and weak flows from model calculations. Transient birefringence measurements in which purely extensional flows were started from rest are also reported. It was observed that the birefringence went through a pronounced overshoot in time for two different polymer/solvent systems. Flow induced increases in the solution turbidity were also observed and the increased turbidity remained constant over a period of many hours after extensional flows were arrested. The birefringence, on the other hand, decayed to zero almost immediately after the flows were stopped. These changes in the turbidity suggest that crystallization of the polymer was occurring. The qualitative results of experiments are compared to recent network model calculations using the theory of Yamamoto for concentrated polymer systems. It is found that this model can predict qualitatively many of the experimental observations if the function describing the breakage of polymer chain entanglements is allowed to depend on the conformation of the polymer segments bridging the entanglements. In particular, this dependency of the entanglement breakage on the conformation of the network segments leads to a predicted overshoot of birefringence when purely extensional flows are started from rest. It is also demonstrated through this model that birefringence data taken over a wide range of flow types can be used to estimate the degree to which the network deforms affinely with the flow field.
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  • 67
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The existence of local order in two epoxy resins of the diglycidyl ether of bisphenol-A (DGEBA) type has been investigated using Rayleigh scattering and Brillouin spectroscopy. The resins differ in their molecular weight distributions and their relative concentrations of epoxide and hydroxyl groups. The complementary use of both techniques in elucidating the thermal behavior of local order is illustrated, and the use of the latter technique to study thermal acoustic phonons and hypersonic relaxation is discussed. Both techniques independently show that molecular aggregates exist in each resin system. The scattering-envelope dissymmetry shows that the resin with the high epoxide/hydroxyl group ratio contains aggregates up to 20 nm in size, and the low-ratio resin exhibits sizes up to 70 nm. These aggregates are thermally unstable in the temperature range studied (293-443 K). Dissolution in chloroform shows that these aggregates are reduced in size and that further structural changes occur which are dependent on solvent concentration. Aggregate volume fractions were determined for a range of aggregate size. Brillouin spectroscopy indicated that both resins exhibit hypersonic relaxation in the temperature range studied. The complex longitudinal moduli of the resins were superimposable under a WLF temperature transformation comparable to the difference in their static glass transition temperatures. Molecular aggregate size, number, and stability are related to the epoxide/hydroxyl ratio of the resins and the degree of intermolecular hydrogen bonding.
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