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  • Physics  (4,402)
  • 1990-1994  (5)
  • 1970-1974  (2,547)
  • 1965-1969  (1,850)
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Pharmacy world & science 15 (1993), S. 105-115 
    ISSN: 1573-739X
    Keywords: Calcium phosphates ; Drug compounding ; Excipients ; Particle size ; Physics ; Powders ; Tablets
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Ten commercially available calcium phosphates used for direct tableting were evaluated. The particle size distributions, powder properties, Sorption isotherms and pH values of aqueous slurries were compared. All samples showed good or at least sufficient flowability. Scanning electron micrographs illustrated the different kinds of manufacturing and gave hints on their expectable behaviour under compaction pressure. The sorption isotherms of identical chemical substances, which had been manufactured by different methods, differed strongly. This can be related to their specific surface areas. Most of the hydroxylapatites have large surface areas and can absorb up to more than 15% water at 93% relative humidity. Dibasic calcium phosphate dihydrate was non-hygroscopic and absorbed less than 1% water. With the exception of monobasic calcium phosphate monohydrate all calcium phosphates behaved quite neutral in water. Monobasic calcium phosphate monohydrate can be regarded as a solid acid. Although the calcium phosphates are usually stable substances, the role of crystal water in the case of dibasic calcium phosphate dihydrate and monobasic calcium phosphate monohydrate is problematic due to possible interactions with active ingredients.
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  • 2
    Call number: 08-STTH WEB
    Keywords: Radiotherapy ; Radiosurgery ; Medical physics ; Radiotherapy ; Radiosurgery ; Physics
    Pages: xiv, 373 p. : ill.
    ISBN: 075030247X
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  • 3
    facet.materialart.
    Leiptig : Fachbuchverl.
    Call number: 08-Phys Lin
    Keywords: Physics
    Pages: 576 p. : ill.
    Edition: 14. Aufl.
    ISBN: 3-446-00772-5
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  • 4
    facet.materialart.
    München : Hanser
    Call number: H0200:68
    Keywords: Philosophy ; Logic ; Physics ; Religion
    Pages: 1184 p.
    ISBN: 3446163670
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  • 5
    facet.materialart.
    New York : Plenum Press
    Call number: 09-NW:149
    Keywords: Physics
    Pages: xii, 247 p. : ill.
    ISBN: 0306437724
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  • 6
    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: Data from the literature are analyzed to show that decay of the chain-end radical of PMMA in the regime of 80-130°C and 1-13000 atm occurs by two mechanisms operating in parallel. These processes are characterized by activation volumes of ca. 70 Å3 (I) and ca. ∼7.5 Å3 (II), suggesting that decay by process I occurs by chain-end diffusion and decay by process II occurs by unzipping of the polymer radical to the monomer.
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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: Poly(ethylene 2,6-naphthalene dicarboxylate) exhibits thermally stimulated chemiluminescence after exposure to ultraviolet radiation and oxygen. The chemiluminescence spectrum is essentially the same as the fluorescence spectrum of the polymer with a maximum intensity at 430 nm. Upon heating, the decay of the luminescence follows a first-order law with an activation energy of 26.3 ± 0.3 kcal/mole. A comparison of the ultraviolet absorption spectra of the polymer before and after exposure to ultraviolet light and oxygen indicates that the naphthalene ring is oxidized. Heating the polymer above 80°C causes decomposition of the initial photo-oxide to produce luminescence.
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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: Use of reduced variables to account for the effect of crosslinking density νe in a styrene-butadiene rubber (SBR) system is demonstrated for general biaxial stress states. Recently published results from stress relaxation tests on five SBR vulcanizates crosslinked to different degrees by tetramethylthiuram disulfide were superposed by using νe as a reduction variable. The equilibrium shear modulus Ge calculated from the master relaxation curve at long reduced times was in satisfactory agreement with other results for SBR. The time-axis shifts were related in a linear logarithmic manner to the crosslinking density but had a slope slightly less than values previously reported for elastomer systems.
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  • 9
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Rotational isomeric-state theory has been applied to investigate chain configurations of a polyester prepared from 4′,5-(1,1,3-trimethyl-3-phenylindan) dicarboxylic acid and 2,2-bis(4′-hydroxyphenyl) propane (POLA polyester). Independent conformations for each repeat monomer unit of the chain have been assumed in the calculations of the unperturbed dimensions. Rotations about the oxygen-phenylene-carbon (O—φ—C) bonds are considered to be free with twofold symmetric potentials. The trans and cis conformations of the carbonyl-phenylene-carbon (O=C—φ—C) and the indan-carbonyl residues are assumed to have equal probability. Two rotational states, trans and cis, are assigned to the ester C—O bonds. Calculation of the reduced unperturbed dimensions (〈r02〉/M)∞ with conformations thus assigned for the bonds in the repeat unit, and comparison with experiment (0.72 ± 0.02 Å2/g) indicate that the conformation in the ester C—O bonds is predominantly trans. An equation for the conformational potential as a function of rotational angle about the ester C—O bond has been formulated using data on potential barriers for low molecular weight compounds. This equation, yielding a potential difference between the cis the trans isomers of 2.5-3.0 kcal/mole, is in good agreement with the prediction made from the calculation of the unperturbed dimensions where a cis/trans ratio of 0.01 for the ester C—O bonds was obtained.
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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
    Additional Material: 1 Ill.
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  • 11
    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 the solvent-nonsolvent gradient and the temperature gradient on the efficiency of the precipitation chromatography is investigated with radically and anionically prepared polystyrene samples. Only a combination of both gradients gives optimal effectiveness of the column. The separating power of the column was determined by using mixtures of well defined samples. From the elution curves of the mixtures the nonuniformity Ufr of fractions can be estimated. For fractions of anionically prepared polystyrenes Ufr is on the average 0.001; this value is of the same order of magnitude as the statistical error. These results show that with this chromatographic method it is possible to determine the narrow molecular weight distributions of anionically prepared polystyrenes (or other polymers) with an accuracy sufficient for kinetic studies.
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  • 12
    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: Much recent work has been carried out on the tear behavior of elastomers, both filled and unfilled, especially by workers at the Natural Rubber Producer's Research Association. By use of a criterion for tearing involving the concept of the tearing energy, the effects of variables such as test temperature, test rate, specimen geometry, and chemical nature of the elastomer have been investigated. The one variable which has not yet been studied is the specific effect of changes in the degree of crosslinking on tear behavior. By use of data published in the literature on the smooth tear behavior of unfilled SBR vulcanizates, it is shown that these data can all be superposed onto a common response curve when the proper normalizations are applied.
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  • 13
    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 rules formulated by Koningsveld for the determination of the critical concentration are shown to be in accord with the Flory-Huggins theory. Sometimes, however, they may not refer to stable conditions, and their application in such cases will result in misleading conclusions.
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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
    Notes: The dynamic mechanical properties of semicrystalline poly(tetramethyl-p-silphenylene siloxane) in three morphological preparations were measured over the wide frequency range of about 0.002 Hz to 500 Hz and the temperature range of about - 190°C to 100°C. The three samples were all isothermally crystallized at 125°C. Two samples had a spherulite size of 25 μ diameter but differed in the time allowed for secondary crystallization. The other sample had a smaller spherulite size. By assuming compliance additivity, the viscoelastic behavior could be separated into five relaxation processes with an indication that a sixth existed at low temperature. Two processes called γ1 and γ2 could be resolved at low temperatures. The γ1 process was associated with the amorphous region since the peak strength was affected by the rate of cooling through the glass transition region; the γ2 peak, unaffected by cooling rate, is attributed to the crystalline part. In the high-temperature region, the β peak is associated with the glass transition and has a shape and location that is essentially independent of the morphology. The highest temperature α2 process, whose maximum was not observed in the experimental range covered, is attributed to the crystalline region and is sensitive to changes in crystallization history. The strength of the α1 process unlike that of the other processes was found to be a function of temperature; it was associated with the noncrystalline region.
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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
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  • 16
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The NMR spectra of water adsorbed at various relative humidities on various cellulose ester membranes have been studied. Membranes of cellulose acetate (CA), cellulose triacetate (CTA), and cellulose acetate butyrate (CAB) were investigated. It was found that the resonance peak of a liquid imbibed in or adsorbed on membranes from high relative humidity is very sensitive to the angle between the membrane plane and the direction of the magnetic field, shifting 5-7 ppm to higher fields as the membrane plane is rotated from a perpendicular to a parallel position with respect to the direction of the external magnetic field. This phenomenon was found to be independent of the nature of the polymeric material (namely CA, CTA, or CAB), porosity of the membrane (varying from an “all bulk” dense sheet to an 80% porosity and 0.2 μm average pore size membrane), nature of the magnetic nuclei (H2O or D2O), intensity of the external magnetic field (60 Mcps or 100 Mcps), and nature of the liquid in the membrane (water, methanol, or n-hexane). It is therefore concluded that the dependence of the position of the resonance peak on the position of the membrane plane with respect to the external magnetic field, is a geometrical phenomenon due to the magnetic “bulk susceptibility” of the medium. Quantitative estimations of the magnitude of the diamagnetic susceptibility effect in a cylindrically rolled sheet are given. These estimates agree well with the experimentally observed “splittings.”
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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: The spin-spin relaxation time T2 and the fraction of short T2 component for composites of natural rubber with carbon black prepared under various conditions have been measured by pulsed NMR. Effect of swelling with a solvent (CCl4), carbon black species (SAF, HAF, SRF) with different surface areas, and different initial carbon black loadings (35, 50, 70 phr) have been determined. Molecular motion in the rubber phase not in the immediate vicinity of the carbon black surface increases rapidly with increasing solvent concentration, yet it is still slightly restricted compared to rubber with solvent alone. On the other hand, molecular motion in the immobilized layer around carbon black and the fraction rubber in that layer are not affected by the solvent. This indicates strong restriction of molecular motion of polymers at the surface. For estimation of the thickness of the immobilized layer, the necessity of using an appropriate measure of surface area accessible to polymer molecules is pointed out. The degree of immobilization in the layer and the thickness of the layer do not vary appreciably with the nature of carbon black or the initial loading of carbon black.
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  • 18
    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: Brillouin scattering of laser light has been used to study the temperature dependence of phonon velocity in a variety of amorphous polymeric systems, particularly internally and externally plasticized methacrylates. Discontinuities in the temperature coefficient of the hypersound velocities are observed at the glass transition temperatures (Tg). This phenomenon is related to changes in the temperature behavior of the specific volume accompanied by corresponding discontinuities in certain second-order thermodynamic quantities. This method was also used to examine the temperature dependence of the Landau-Placzek ratio.This ratio is relatively large in polymer systems and appears to be independent of temperature in the region of the glass transition, provided that there are no internal strains in the sample at the temperature of measurement. Evidence is presented which suggests that the abrupt changes in this ratio at Tg reported by earlier workers were due to kinetic effects related to the relaxation of internal strains above Tg, and the results of recent studies by other investigators, both corroborating and supplementing the present work, are reviewed.
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  • 19
    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: Analysis of the solution fractionation of ethylene-propylene copolymers was carried out by assuming a bivariate normal distribution function for the distribution of molecular weight and chemical composition. It was found that the variation of the molecular weight and composition distributions in fractions was complicated, because two distribution characteristics of the original copolymer affect fractionation to differing extents. The hypothetical cumulative weight distribution curves thus obtained agreed essentially with those obtained experimentally.
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  • 20
    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: Internal viscosity models (IVM) for dilute-solution polymer dynamics differ in how they define the deformational force Fd which includes ϕ, the IV coefficient, and in how they treat polymer rotational velocity Ω. Here, the handling of angular momentum is shown to be crucial. A torque balance in simple shear flow at shear rate G leads to stress symmetry and specification of Ω(G) which differs greatly from the conventional Ω = G/2. This determines the G dependence of viscosity η and normal stress coefficient ζ. There are also implications of a transition in rotational behavior as ϕ approaches a critical value. Predictions of η(G), ζ(G), and η*(ω) are presented for two versions of Fd: one derived recently by the authors and one being most commonly used at present. Limiting cases for high and low ϕ, and for high and low G and ω, are discussed. Some differences exist between predictions of the two Fd models, but these are surprisingly minor.
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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: If the counterion of a polyelectrolyte is not identical with any of the ions of a low molecular weight electrolyte added to the solution, the system may be regarded as a four-component system. Relations for the refractive index increments have been derived which allow the determination of the coefficient of selective sorption of the added electrolyte from the refractive index increments of the components independent of the original counterion of the polyelectrolyte. Equilibrium dialysis and differential refractometry were used to study the interaction of KCl, KBr and NaI with poly[-1(2-hydroxyethyl)pyridiniumbenzenesulfonate methacrylate] or with an analogous polymer containing a toluenesulfonate counterion in aqueous solutions. The coefficient of selective sorption increases in the series Cl- 〈 Br- 〈 I- from strongly negative to strongly positive values; the specific interaction of these counterions with the macroion increases in the same order.
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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 chemical and physical crosslink densities of irradiated polybutadiene were determined using a precise and consistent method. This method included the use of a statistical theory of crosslinking modified to include chain reactions and the use of Langley's theory for calculating the number of trapped chain entanglements. The number of crosslinks formed per unit radiation dose, G(X), was measured for a series of polybutadienes containing various isomeric forms of unsaturation. The physical crosslink density and the molecular weight between entanglements were determined from measurements of the compression modulus of swollen samples.
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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: Thermoelectrets of poly(methyl methacrylate) were exposed to various atmospheres of known relative humidity between 0 and 100% and the thermal current spectra analyzed. The study of the decrease of the heterocharges as a function of the exposure time reveals important differences in stability between the three peaks of the spectrum; the two peaks appearing at low temperatures can be attributed to a uniform volume polarization, and the third peak observed at high temperature to a space charge polarization. The shift of the peaks indicates plasticization of the polymer by water vapor. This effect is reversible when the samples are exposed for a sufficiently long time to a drying atmosphere. The complex variations of the initial rise of the spectrum as a function of the exposure time show that the activation energy of the peaks probably depends upon the degree of hydration of the polymer.
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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
    Notes: The theory of rubber elasticity relates the elastic modulus of unfilled amorphous rubber to the concentration of elastically effective strands. A theoretical relation between this concentration and the concentrations of potential entanglements, random tetrafunctional crosslinks, and chain ends was proposed recently. In the present work, the new relation was combined with the theory of rubber elasticity and verified experimentally. Polydimethylsiloxane samples were cured by 60Co irradiation and were extensively extracted to determine gel fraction, which was used to calculate concentrations of crosslinking and scission due to irradiation. Equilibrium modulus values determined from creep tests were in excellent agreement with those calculated using the new relation if the average spacing between potential entanglements is 116 (CH3)2SiO units. Thus, in typical commercial silicone rubbers, the contribution to the modulus from trapped entanglements is greater than the direct contribution from crosslinks. The new relation allows the calculation of crosslink concentrations from modulus measurements on other unfilled rubbers once the potential entanglement spacing of the polymer is determined.
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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
    Notes: The fracture and craze surfaces of four PVC fractions (M̄w = 51000 to 228000) and two bimodal blends were examined with a scanning electron microscope. The fraction with the lowest molecular weight gave brittle fractures when fatigued in nitrogen and ethanol vapor. Walls of crazed ductile matter formed at the surface of higher molecular weight samples. Thickness of this ductile material increased with molecular weight. There appeared to be a balance between craze propagation into the sample and brittle fracture due to dilitational and tensile stresses in the interior regions of the test films.
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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: Single crystals of cellulose triacetate II (CTA II) free of crystallization solvent can be grown from dilute solution in mixtures of dibenzyl ether and n-tetradecane. Good results are obtained by using a polymer fraction with a degree of polymerization of 60 and a mixture of 70% n-tetradecane and 30% dibenzyl ether at 245°C. The lamellar crystals produced are lozenge-shaped with the longer diagonal parallel to the a axis of the lattice and with {110} as the growth faces. Twin growth occurs frequently with {110} as a twinning plane and less frequently with {210}.
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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: Electron microscope studies are reported for crystals of linear polyethylene formed in dilute solution from very sharp low molecular weight fractions. Emphasis is placed on molecular weights in the range of 1.1 × 103 to 15.1 × 103. The dependence of the crystal habit on the crystallization temperature is very similar to that which has been found for the higher molecular weight species. However, the demarcation temperature for the crystallization of the different morphological forms is very molecular weight-dependent. The conditions under which interfacial dislocation networks form can be clearly defined. The molecular weight must be less than 3000, so that these structures are restricted to very small chain lengths. However, not all crystallization conditions within this allowable molecular weight range yield such dislocations. The formation of interfacial dislocation networks are shown to occur only under very special circumstances. Their occurrence clearly cannot be offered as evidence, as has been done in the past, for a regular, chain-folded interfacial structure.
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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 predictions of a model presented previously are tested with data on five styrenebutadiene-styrene copolymers. Differential scanning calorimetry and laser light transmission are the primary tools, spanning 180-630°K, with some evidence supplied also by electron microscopy and mechanical properties. The existence of a first-order phase transition, characterized by a separation temperature Ts, is verified and found to be predictable by the model. Details of morphology, including transitions in microstructure in certain temperature ranges, are also reported and shown to be consistent with the theory.
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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 kinetics of isothermal crystallization from the glassy state at low temperatures and the morphology of poly(ethylene terephthalate) (PET) filled with additives are reported. Talc, kaolin, silicon oxide, and titanium oxide have been used as fillers; they act as effective nucleating agents for PET. The overall rate of crystallization depends on the volume concentration, the size distribution, and the nucleating ability of the additives. An electron microscopic study reveals a transcrystalline morphology at the surface of the filler particles. The occurrence of transcrystallinity is attributed to extensive heterogeneous nucleation induced at the filler surface. From the shape of the crystallization isotherms, it can be concluded that the crystallization mechanism depends on the type of filler.
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  • 31
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A Raman band of low frequency, arising from an accordionlike vibration of all-trans \documentclass{article}\pagestyle{empty}\begin{document}$ \rlap{--} ({\rm CH}_2 \rlap{--})_n $\end{document} segments and previously observed in normal paraffins and in polyethylene single crystals, has now also been found in bulk and in cold-drawn polyethylene, both linear and branched. The accordionlike vibration, or longitudinal acoustic mode (LAM), in polyethylene is compared with the LAM in normal paraffins. Whereas the Raman bands corresponding to the third (LAM-3) and higher modes are quite intense in a long-chain paraffin such as n-C94H190, they are so weak in polyethylene as to be unobservable with the apparatus used. This is attributed to the presence of the chain fold in polyethylene. Of the two extreme structural models of the fold here discussed, namely the models of “tight folds” and of “loose loops,” only the latter seems capable of accounting for the weakness of LAM-3 and higher modes in polyethylene. A quantity called “nominal Raman length” is defined as the length of that all-trans n-paraffin that would have the same LAM-1 frequency as the polyethylene sample under consideration. The nominal Raman length is always greater than the average long spacing, deduced from discrete x-ray scattering at small angles after applying a Lorentz correction, and, after allowing for chain tilt, is found equal to the segment length between folds. This can be accounted for by both of the models mentioned. As a test of the theory of surface melting the frequency of the accordion vibration of annealed polyethylene single crystals was measured as a function of temperature up to the melting point; no frequency change with temperature was observable. On the basis of the naive idea that there is complete decoupling of the vibrations in the all-trans chain segment from the disordered (molten) surface layer, one would predict that upon surface melting and the concomitant shortening of the all-trans segment, the LAM-1 frequency should increase. A more careful analysis, taking into account the existence of coupling of the LAM to the surface layer, shows that the outcome of this experiment does not necessarily invalidate the idea of surface melting. Bulk polyethylene samples exposed to 60Co γ-radiation for doses up to 100 Mrad show a slight shift of the Raman band to lower frequencies, whereas no such shift was observed upon absorption of a swelling agent. A search, without success, was made for a longitudinal acoustic mode in polypropylene, poly(vinylidene fluoride), nylon 66, and polyoxymethylene.
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  • 32
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A study of the effect of excluded volume on the mean-square optical anisotropy 〈γ2〉 and the mean-square end-to-end distance 〈R2〉 has been carried out for polymer chains of up to 2000 bonds. The calculations have been made for models assuming (a) equiprobability of internal rotations and (b) interdependence of short-range intramolecular interactions. All the results indicate that 〈γ2〉 is practically insensitive to the excluded-volume effect. Concomitantly the behavior of 〈R2〉 has been analyzed.
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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: The fundamental vibrational frequencies of an isolated chain of cis-1,4-polybutadiene have been calculated. Infrared and polarized Raman data are used in the force constant refinement routine. The assignments of the vibrational frequencies are discussed in terms of the potential energy distribution.
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  • 34
    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 theory of Franklin et al. is employed for the calculation of the maximum form birefringence of a polymer having lamellar morphology. The results confirm the experimental conclusion that for low-density polyethylene, the form birefringence approaches 3% of the total birefringence. The theory also predicts the parabolic dependence of the form birefringence on the refractive index of the amorphous phase. It may be applied to estimate the dynamic form birefringence and leads to a value of the dynamic strain-optical coefficient which is of the order of 2-15% of the total.
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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: Small-angle light scattering experiments were conducted on thin films of linear polyethylene fractions over a very wide range of molecular weights. Spherulitic structures were found in all samples with molecular weight 9 × 105 or less. A rodlike morphology predominates for molecular weights between 1 × 106 and 2 × 106. Still higher fractions yield a very disordered superstructure. These results can be correlated with previous studies of the overall crystallization rates and the resulting properties.
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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: Viscosity, light scattering, and precipitation temperature measurements on dilute solutions of high-density and low-density polyethylene fractions have been carried out and a theory by Flory for phase equilibrium of linear polymers has been extended to branched polymer. From the results, it is shown that the entropy parameter ψ, depends on branching; a method for the determination of long-chain branching in polymer fractions is proposed combining precipitation temperature and molecular weight measurements. The method has been applied to the evaluation of long-chain branching in low-density polyethylene.
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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: The dielectric properties of a series of semiconducting polyazophenylenes were studied as a function of temperature and molecular weight in the temperature range 293-600°K and for molecular weights between 5,100 and 62,800 at a constant frequency of 1 kHz. The compounds studied included poly-2,4-diaminotoluene, poly-2,4-diaminoanisole, and poly-2,5-diaminotoluene. The dielectric properties are presented in the usual way in terms of a complex dielectric constant ε* = ε′ - jε″. Activation energies of relaxation processes were evaluated from the areas and widths of the dielectric loss factor, ε″, against reciprocal temperature at constant frequency. The dielectric activation energies were found to be roughly equal to the activation energies from the DC conductivity. This indicates that the conduction mechanism is based on rotational movements of molecules or parts of molecules.
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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: A deviation from Graessley's theory of entanglement viscosity appears at very high shear rates when the flow of polydimethylsiloxanes of various molecular weights and their solutions with various concentrations is measured by the capillary method. In order to explain this deviation, a modified Graessley theory is proposed according to the previously reported suggestion that frictional viscosity appears not to be negligible at high shear rates. A reducing procedure taking a frictional viscosity parameter into account was performed. All of the reduced data are combined to give a master curve in spite of a wide range of molecular weight, concentration, and shear rate (from the lower Newtonian to very highest non-Newtonian flow region). The findings from the reducing procedure completely explain the mechanism of non-Newtonian flow for the bulk polymers with various molecular weights, including those below the critical molecular weight for entanglement, and for polymer solutions at any concentration. The viscosity of the linear polymer system consists of the shear-dependent entanglement term ηent proposed by Graessley and the shear-independent frictional term ηfric. The non-Newtonian behavior depends on the ratio of ηent/ηfric at the shear rate of measurement. The ratio of zero-shear entanglement viscosity ηent,0 to ηfric and the critical shear rate for onset of the non-Newtonian flow may be used as a measure of the non-Newtonian behavior of the system and a measure of capability for its rising, respectively. The Graessley theory is to be included in the present modified theory and is applicable to the case of ηentηfric ≫ 1.
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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
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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: The morphology of solution-grown single crystals of syndiotactic polypropylene with different degree of stereoregularity is compared. A sector formation phenomenon, found in some monolayer single crystals, is discussed in terms of possible crystallographic fold planes, growth planes, and gemination planes. A correlation between thermodynamic and morphological properties such as apparent enthalpy of fusion, critical long spacing, critical annealing temperature, and the number of configurational chain defects along the macromolecule has been found. Two endothermic peaks are observed in the DSC thermograms of single-crystal aggregates of syndiotactic polypropylene. The low-temperature peak is attributed to melting of crystals or parts of crystals with incorporated chain defects. The high-temperature peak corresponds to the melting endotherm of more regular crystalline zones. The peak-area ratio seems to depend on the degree of stereoregularity.
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  • 41
    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: Simultaneous measurements of light scattering and electric birefringence on a crystallizing solution of poly(ethylene oxide) (PEO) are shown to lead to the determination of the radius, thickness, and number of crystals at the early stages 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: The time - temperature superposition principle is well-established for linear viscoelastic properties of polymer systems. It is generally supposed that the same principle carries over into nonlinear phenomena, such as the relationship between viscosity η and shear rate \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \gamma $\end{document}. Guided by this principle and the forms of various molecular theories, one would expect that η - \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \gamma $\end{document} data on the same polymer at different temperatures would superimpose when plotted as η/η0 versus \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \gamma $\end{document}η0/ρT, η0 being the limiting viscosity at low shear rates, ρ the polymer density, and T the absolute temperature. Data on polystyrene melts, obtained in a plate-cone viscometer, appear systematically to violate this principle in the range 140-190°. Such anomalies are absent in concentrated solutions of polystyrene. The trends are similar to those reported by Plazek in the steady-state compliance of polystyrene melts near Tg, but they appear to persist to higher temperatures than the compliance anomaly.
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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: Main-chain scission was the predominant effect when dilute solutions of three linear polystyrenes in 1-methylnaphthalene and polybenzyl oligomer received up to 2000 megaroentgen of 1.5-MeV electrons. Values of energy per scission were independent of dose and of the same magnitude as literature values in dioxane and benzene solutions when compared at the same dose rate. In all cases as irradiation progressed, Mw/Mn approached a value of 2 and Mz/Mw approached a value of 1.5 characteristic of a random distribution. Starting from one initial distribution, random numbers were used to simulate random chain scission. A 500 MR (megaroentgen) distribution calculated in this manner matched the experimental distribution after a 500 MR irradiation.
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  • 45
    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 relationship between the critical point and the precipitation threshold is examined in the Flory - Huggins approximation with concentration-independent interaction parameter χ. Approximate explicit expressions for the difference between the critical point and the threshold can be derived by series expansion of threshold conditions. In the first-order approximation, the concentration difference depends only on the chainlength averages xw, xz, and xz+1, in the second-order approximation it depends on xw, xz, xz+1, and xz+2, etc. For polymers of low polydispersity, the second-order approximation gives a good estimate of the concentration difference; for instance, for polymers with exponential distribution and xw/xn 〈 1.25, the error is lower than ca. 1%. The approximation is not suitable for polymers with xz+1 ≫ xz (including polymers whose cloud-point curve exhibits a triple point). Irrespective of the polydispersity of the polymer, the threshold as well as the whole cloud-point curve depend only on the weight-average and higher averages, xw, xz, xz+1, …, xz+k, where k → ∞; they are, however, independent of the number average xn.
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  • 46
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    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 strain pattern about a spherical glass bead imbedded in a stretched rubber has been calculated and used to predict the birefringence and light scattering. This is compared with experimental measurements of the retardation pattern observed using a polarization microscope and deduced from the low-angle laser Hv light scattering pattern. The agreement with theory is favorable. The light scattering is suggestive of similar origins of light scattering from crystallizing rubbers and from inhomogeneously crosslinked rubbers.
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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: A general method is described to take into account the multiple scattering effect in a small-angle light scattering from thin polymer films. It is seen that multiple scattering tends to make the scattering envelope more diffuse, reducing the intensity in the high intensity regions and increasing it in the low intensity regions. The method is applied here to a spherulitic system, but it is valid for any other system where the principal scattering is in the forward direction.
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  • 48
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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: The tensile stress relaxation of carbon-black-filled SBR was studied in the linear viscoelasticity region as a function of temperature and volume fraction of fillers. Time - temperature superposition was valid, and master relaxation curves were obtained. Carbon black increases the modulus of the compound, especially in the rubbery region, and the time range over which the glass-rubber transition occurred. The shift factor is divided into three regions; an Arrhenius dependence in rubbery and glassy states, and Williams-Landel-Ferry (WLF) dependence in the transition region. The apparent activation energy in the rubbery state increases with the volume fraction of carbon black (or silica) and is unaffected by the structure of the filler. The increase in activation energy is caused by the attachment of rubber chains to the carbon surface. At 30% elongation, the activation energy for carbon-black-filled rubber has a value of 32 kcal/mole, independent of structure and concentration of the filler.
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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: Information, not previously measurable, about the internal crystallization processes occurring within spherulitic films can now be obtained by combining refractive index, birefringence, and small-angle light-scattering measurements. The surroundings of a spherulite in a solid film are composed of both the adjacent spherulites and their interstices (boundaries), and it is shown that different crystallization processes can occur in each of these regions. Upon annealing a quenched isotactic polypropylene film, the rate of crystallization within the interstices of the space-filling spherulites is observed to be greater than the rate of crystallization within the spherulites themselves.
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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: The elastic tensile modulus of the crystalline regions parallel to the chain axis E1 for poly(isobutylene oxide) (PIBO) was determined by an x-ray diffraction method. The stress-strain (σ - ε) curve calculated from the meridional reflection of (002) shows an inflection point at about 75 MN/m2 or an extension of 0.25%. The observed moduli below and above this point are 29 and 47 GN/m2, respectively, at room temperature. The initial lower modulus agrees well with the value, 29.7 GN/m2, calculated on the basis of the double zigzag structure of PIBO chain determined by Kaji and Sakurada. The higher modulus may be due to an intrachain steric hindrance between the hydrogen atoms of the methylenic group in the main chain and those of the two side methyl groups.
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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: The crystallite sizes of α and β forms of nylon 6 along the chain axis were determined by Wallner's method. First the shifts of the maximum positions of meridional reflections from their ideal reciprocal-lattice positions were calculated for the various crystallite sizes. Second, using these relationships, crystallite sizes were estimated from the observed maximum positions of reflections. The estimated values agree well with those from the integral widths of reflections by the method of Hosemann and Wilke.
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  • 52
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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: Free electrophoresis, differential spectral UV analysis, and the determination of the coefficients of selective sorption were used to investigate, in aqueous solutions of halides, the behavior of two polycations, poly[1(2-hydroxyethyl)pyridinium methacrylate] and poly[1(2-hydroxyethyl)trimethylammonium methacrylate]: i.e., one species with and the other without a pyridine ring in the side chain. Electrophoretic data were used to estimate the length of the electrophoretic segment and the approximate charge of the polyion in solutions of the individual salts. A comparison of the data showed that the interaction is not due to the presence of the pyridine ring in the side chain and that the order of activity of the halide anions is the same for both types of polymers.
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  • 53
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    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: When isotactic polystyrene (i-PS) is crystallized from the melt or from the glassy state at rather large supercooling an additional melting peak appears on the curve during scanning in a differential calorimeter. The overall rate of crystallization deduced from the total peak areas as a function of crystallization time did not fit the Avrami equation well. When we omit the area of the additional melting peak in the kinetic analysis a much better fit is obtained. We also observed that no lamellar thickening occurs during isothermal crystallization. In view of the low degree of crystallinity of i-PS these results lead to the idea that a secondary crystallization process takes place within the amorphous parts of the spherulites resulting in this additional melting peak on the DSC curve. The large supercooling needed and the increase in peak area with increasing molecular weight make us suppose that intercrystalline links are probably responsible for the additional melting peak of bulk-crystallized i-PS. Electron microscopic studies of surface replicas of i-PS support this view.
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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: Stress-strain-birefringence relations are measured for a series of unswollen and swollen networks of cis-1,4-polybutadienes which differ both in the degree of crosslinking and in the volume fraction of rubber present during crosslinking. The stress optical coefficient (SOC), the Mooney-Rivlin constants C1, C2 and B1, B2 are calculated. Results show that the unswollen, solution-vulcanized polymers have very low values of C2 and B2, but high SOC. Upon swelling with CCl4, the stress optical coefficients decrease considerably and agree well with the values obtained by Fukuda, Wilkes, and Stein, and by Ishikawa and Nagai. The networks prepared in solution exhibit different behavior from those crosslinked in dry state, suggesting that in order to understand the origin of deviations from kinetic rubber elasticity theory and the Kuhn-Grün birefringence theory, more consideration must be given to the effect of overall network topology on stress-strain-birefringence behavior.
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  • 55
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Molecular relaxation processes in the 77-260°K interval and the structure of polyethylene melt-crystallized under normal and high pressures have been studied. The positions of relaxation transitions and activation energy for molecular relaxation were determined by radiothermoluminescence. The most intense maximum in the glow curve of the sample crystallized under normal pressure is observed in the 200-240°K interval, i.e., in the range of the β transition. In this temperature interval the β relaxation activation energy changes from 15 to 25 kcal/mole. An increase of the pressure under which crystallization takes place results in a substantial decrease of the intensity of the β maximum. This indicates that the β transition of polyethylene is most probably due to the mobility of segments on the chain-folded lamellar surface. For samples melt-crystallized under pressure between 5000 and 7000 atm, relaxation transitions were found at 150 and 190°K. Various processes of molecular relaxation appear to be associated with the maxima observed on the polyethylene glow curve.
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  • 56
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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: Viscosity and normal stress behavior were measured for poly(methyl methacrylate) samples of various average molecular weights in diethyl phthalate solution at 30 and 60°C. All samples conformed approximately to the most probable distriution (M̄w/M̄n = 2). Concentrations ranged from 0.113 to 0.38 g/ml, and M̄w from 53,800 to 1,620,000. Despite considerable evidence in the literature of unusual linear viscoelastic behavior for this polymer, its nonlinear properties appear to be rather conventional. The viscosity-shear rate master curve was similar to that found earlier for concentrated solutions of polystyrene and poly(vinyl acetate) of comparable molecular-weight distribution. The viscosity time constant τo parallels τR, the characteristic time of the Rouse model, although the residual dependence of τo/τR on concentration and molecular weight appears to be slightly different from that for polystyrene and poly(vinyl acetate). Similar conclusions apply to the recoverable compliance Je,o estimated from the normal stress behavior of each solution, and its relationship to the Rouse model compliance JR.
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  • 57
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    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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  • 58
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Transient currents in poly(vinyl chloride) (PVC) are recorded after the application of a step-function electric field for various temperatures. By assuming the Fröhlich rectangular distribution function g(τ) of molecular relaxation times, the limits of relaxation times τ are evaluated. Values of the glass-transition temperature and activation energies of molecular motion determined from a plot of ln τ against 1/T are in satisfactory agreement with those obtained by other methods. By extrapolation to T = ∞, relaxation times are calculated which are in good agreement with those from dielectric loss measurements.
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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 construction and principle of operation of small-angle light scattering apparatus for studies of supermolecular structure in thin polymer films is described. The apparatus can be used to study changes in spherulite structure during crystallization and changes in films subjected to steady or sinusoidal strain. Typical results with polyethylene films are given.
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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: Densified glasses, formed from the liquid state by cooling at 5°C/hr under elevated pressures of up to 517 MN/m2, were studied by thermal analysis and dilatometry at ambient pressure. The materials studied were polystyrene, poly(methyl methacrylate), phenolphthalein, sucrose, and a 1 : 1 mixture by weight of potassium and calcium nitrate. Enthalpies of the densified glasses were found to be up to 2-6 J/g greater than the enthalpies of the glasses formed at atmospheric pressure. The major enthalpy and volume relaxation on heating the densified glasses was found to be not correlated The upper temperature limit of the glass-transition region remained constant for all glasses cooled at various pressures, while the lower temperature limit of the polymeric glasses decreased up to 55°C with increasing pressure. The interpretation of the data suggests that an additional, significant volume relaxation occurred on depressurization at room temperature for all glasses analyzed.
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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 number of linear, four- and six-branched regular star polyisoprenes were synthesized by anionic polymerization techniques in benzene using lithium as the counterion and polyfunctional silicon chloride compounds as the coupling agents. Light-scattering measurements in dioxane were performed in order to establish Θ solvent conditions. Determinations of the radius of gyration of the polymers of different structure indicate that g = 〈S2〉0,br/〈S2〉0,lin agree closely with random flight calculations for the ratios. Intrinsic viscosities determined in a Θ solvent establish g′ = [η]br/[η]lin to be 0.773 and 0.625 for the four- and six-branched polyisoprenes, respectively. In a good solvent g′ values are slightly lower. These values are compared with theoretical estimates. Viscosities of 19.29% (w/w) solutions of the polyisoprenes in n-decane at 25°C are correlated with the intrinsic viscosities of the polymers under Θ conditions.
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  • 62
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The original morphology of polytetrafluoroethylene prepared by radiation-induced emulsion polymerization was studied by electron microscopy. The morphology depends on molecular weight, which in turn depends on polymerization conditions, especially the emulsifier concentration. The molecular weight decreases with increasing emulsifier concentration. The morphology changes with molecular weight roughly as follows: fibrils below 105, rods between 105 and 5 × 105, and granular particle above 106. The crystallinity is high for all morphologies.
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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
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  • 64
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Crystallization and melting behavior of linear polyethylene under high pressures up to 6000 kg/cm2 has been investigated with a high-pressure dilatometer. Crystallization was carried out at a cooling rate of 1°C/min from the melt at each pressure. The samples were characterized by differential scanning calorimetry, density, and electron microscopy. Folded-chain crystals are formed in the low-pressure region below 2000 kg/cm2. Crystallization in the intermediate-pressure region between 2000 and 3500 kg/cm2 gives a mixture of folded-chain and extended-chain crystals. The extendedchain crystals are the more stable and predominate at increasing pressure. At high pressures above 4700 kg/cm2, two stages of crystallization and of melting can be observed. The phenomenon suggests that the two kinds of extended-chain crystals with different thermal stability, i.e., the ordinary extended-chain crystals and “highly extended-chain” crystals form through individual crystallization processes from the melt at high pressure.
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  • 65
    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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