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• Physics  (2,547)
• 1970 - 1974  (2,547)
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• 1
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 100-MHz proton NMR spectra of commercial and laboratory-prepared poly(vinyl chloride) (PVC) have been measured in various solvents at high temperature (80-150°C). Tacticity in PVC was determined by the analysis of the β-proton spectrum. The spectrum was calculated assuming that the PVC chain consists of tetrad sequences of monomer units and that their distribution in the chain is described by a simple Bernoulli-sequence statistics with a Pm (the probability of isotactic placement) of 0.45 for commercial PVC polymerized at 50°C. Tacticity calibration curves based on measurements made for the polymer in pentachloroethane and β-dichlorobenzene were established, and they provide a simple method for the measurement of tacticity in PVC directly from the observed spectra. Excluding samples prepared in butyraldehyde solution, the formation of syndiotactic structures in PVC (prepared by free-radical polymerization) was found to be favored by lowering the polymerization temperature. This preference is due to an increase in the activation enthalpy of 510 cal/mole which is required for forming an isotactic placement in the chain during the propagation step.
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• 2
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: An amorphous polypropylene sample was examined by using 13C NMR at 25.2 MHz and all ten possible methyl resonances from monomer pentads were observed. Assignments were made through a consideration of an additivity relationship among the methyl resonances. Confirmation for the assignments was obtained through observed conformity of the methyl resonance intensity distribution with second-order Markov statistics. The relative intensity distribution of the methyl resonances can be used to characterize the structure of polypropylenes with confidence, since experimentally it is shown that an equal nuclear Overhauser effect exists for each of the methyl resonances.
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• 3
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 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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• 4
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: Polystyrene radically polymerized in atmosphere of air is composed of bisegment (C-A) or trisegment (C-A-C) block copolymers consisting of styrene segment (A) and styrene peroxide segment (C). Dielectric measurements of a system of copolymers of styrene and oxygen were obtained above the glass temperature. Three primary relaxations, a, b, and c, in order of descending temperature, were found corresponding to three microphases: styrene phase (phase a), styrene peroxide phase (phase c), and an intermediate phase (phase b) which contains a low concentration of peroxide bonds. An alternating copolymer of styrene and oxygen exhibits the relaxation c alone. With heat treatment above the glass temperature, relaxation c and subsequently relaxation b vanish with thermal degradation of peroxide bonds. The sum of relaxation strengths is linearly related to the content of peroxide bonds which was evaluated by the elementary analysis and DTA. Below the glass temperature, the temperature dependence of dielectric loss of carefully purified polystyrene without peroxide bonds shows very weak peaks which correspond to γ (200°K at 10 kHz) and δ (50°K at 10 kHz) peaks, respectively, in the activation plot. When low molecular degradation products of peroxide bonds are occluded or impurities such as benzaldehyde are added into the specimen, the height of the γ peak is appreciably enhanced, indicating that the reorientation of small polar molecules in polystyrene accompanies the vibration of the phenyl group about the C—C6H5 bond which gives rise to the γ relaxation.
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• 5
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: Band assignments of phase-I PVF2 have been Revised by using additional data obtained by laser Raman spectra of oriented samples. A set of least-squares refined force constants was obtained which reproduce the experimental data to an average error in frequencies of 1.3 cm-1. In order to determine the effect of electrical polarization on the spectra, a Gaussian distribution of the dipole axis was assumed. The calculation shows that polarizations of less than 60% will not significantly affect the Raman spectra.
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• 6
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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• 7
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: A theory is developed by use of the correlation function approach for calculating both the Hv and Vv intensity of scattered light for a concentrated assembly of spherulities. The scattering becomes a function of the radial and tangential polarizabilities of the spherulite αr and αt, the polarizability αm of the medium, surrounding the spherulites, and the volume fraction φs of spherulites. The “effective polarizability of the surroundings” αs, which appeared in previous theories, becomes function of these variables. The theory can explain, for example, why the Vv scattered intensity passes through a maximum during the course of crystallization.
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• 8
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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• 9
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: A lattice theory of orientational disorder in two-dimensional spherulites is developed in which the orientation direction of the optic axis in lattice cells is allowed statistically to deviate from its mean value in a manner correlated with the orientation in neighboring cells. The Hv light scattering patterns arising from such disordered spherulites deviate from the patterns for perfect spherulites in that there is excess intensity at both small and large scattering angles and the intensity at the maximum is lower. A comparison of the calculated scattering angular dependence with that which is experimentally measured permits assignment of values of correlation parameters. A consequence of this disorder is that the spherulite birefringence is reduced below that calculated on the basis of perfect crystalline orientation in agreement with experiment.
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• 10
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 dynamic viscosity η′ of a dilute solution of poly(L-glutamic acid) (DP = 1370) in a mixed solvent made up of aqueous 0.2M NaCl and dioxane (2:1 by volume) is measured over the pH range 4.2-10 and in the frequency range 2-500 kHz. The frequency dependence of η′ in the helix region (low pH) is interpreted in terms of a model molecule consisting of n rigid helical segments connected by universal joints. The steady-flow viscosity, relaxation time, and high-frequency limiting viscosity at pH 4.75 (helical content 80%) are well explained by this model with n = 5. This value of n is consistent with that estimated from the nucleation parameter σ = 1.4 × 10-3 obtained from the relation between reduced steady-flow viscosity and helical content. The high-frequency values of η′ in the coil region (high pH) are fitted by Peterlin's theory. The internal viscosity seems to arise in part from the polyelectrolytic character of the molecule. An additional relaxation at low frequencies in the coil region is ascribed to rotation of molecules elongated by the electrostatic interaction. The lower value of reduced steady-flow viscosity in the coil region in the mixed solvent compared with that in water is interpreted in terms of the lower degree of effective ionization and the selective solvation of water by the polypeptide. No anomaly is observed in the helix-coil transition region, indicating that the relaxation time for helix-coil equilibrium is less than 10-6sec.
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• 11
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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• 12
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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• 13
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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• 14
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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• 15
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: 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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• 16
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 molecular weight distribution on mechanical properties of concentrated polymer solutions was studied by measuring creep compliance and complex modulus for solutions of binary blends of narrow distribution polystyrenes in chlorinated biphenyl. Two-step plateaus in the rubbery plateau region, as reported for undiluted polymer blends, were observed for concentrated solutions provided the molecular weights of component polymers differed greatly. The nth order blending law (n = 1, 2, 3) of Bogue et al. was simplified in form to compare with experimental results. As far as the present version of simplification was concerned, the cubic blending law was better than the quadratic one in describing viscoelastic properties of polymer blends. The cubic blending law reproduced closely the magnitudes of viscoelastic functions such as loss modulus and relaxation modulus but it was not able to predict the two-step plateaus, even when the ratio of molecular weights of components was as large as 10. It also provided a good approximation to reported results on the steady-state compliance Jebo for undiluted binary polymer blends and present results for solution blends. Since the cubic blending law in the simplified version was consistent with previous results on concentration dependence of the steady-state compliance for concentrated solutions of narrow distribution polymers, it gave a unified expression for the steady-state compliance of binary polymer blends and concentrated solutions of narrow distribution polymers.
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• 17
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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 series of polystyrenes with weight-average molecular weight M̄w up to 1.3 × 107 was prepared by anionic polymerization in tetrahydrofuran (THF). Each sample was characterized by gel-permeation chromatography, light scattering, and viscometry. It was found that each sample had an almost symmetrical and very narrow molecular weight distribution (M̄w/M̄n < 1.07). The mean-square unperturbed radius of gyration 〈S2〉0 was determined in trans-decalin at 20.4°C as 〈S2〉0 = 7.86 × 10-18M̄w (cm2). The particle scattering factor was well represented by the Debye equation irrespective of solvent in the range of M̄w < 4 × 106, and only a small deviation was observed in benzene at higher molecular weights. The penetration function Ψ ≡ A2M2/4π3/2NA〈S〉23/2 was found to approach a relatively low asymptotic value of 0.21-0.23 at molecular weights above 2 × 106 in benzene at 30°C, where A2 is the second virial coefficient and NA is Avogrado's number. It was also found that the theta temperature in trans-decalin was affected by the nature of polymer samples. A difference of about 3°C in the theta temperature was observed between two series of anionic polystyrenes, one prepared in THF and the other in benzene, but there was practically no difference in unperturbed chain dimension.
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• 18
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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 polymeric hydrogen form of phthalocyanine is found to be more conductive than the metallic derivatives, in contrast to the behavior of the monomers. In addition, the polymers were found to be much more conductive than the corresponding monomers with the resistivity of the polymers ranging from 7 ohm-cm to about 3 × 106 ohm-cm. The polymers were found to have moderately high dielectric constants ranging from 16 to 1300 at room temperature, depending upon the applied pressure. Based on the dependences of the conductivity and permittivity upon the electric field strength, the average molecular length of the conductive paths within the polymer molecule has been estimated to be 100-1000 Å. In view of these estimated lengths, together with the exponential dependence of the permittivity and conductivity upon the pressure and temperature, the dispersion of the dielectric constants in the range of 10-100 KHz, and the chemical architecture of these ribbonlike polymers, the electronic behavior of these polymers is concluded to be consonant with the model of essentially one-dimensional conduction within and along the chains by freed charges. Much as in a number of previously studied highly conjugated polymers, the present polyphthalocyanines are semiconducting and exhibit nomadic polarization, with dielectric constants ranging from 70 to 1300.
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• 19
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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: 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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• 20
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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 diffraction contrast study with the aid of an image intensifier was undertaken to obtain direct evidence for the existence of a mosaic block structure in polyethylene single crystals grown by self seeding under isothermal conditions. Dark-field microscopy indicates that the crystals do not contain a mosaic block structure. High-resolution electron diffraction confirms that the crystal is coherent (i.e., mosaic block-free) over regions of several thousands of Angstroms. It is concluded that a mosaic structure on the scale of ∼300 Å does not exist in polyethylene single crystals grown under carefully controlled conditions from dilute solutions. Possible reasons for previous results that indicate the presence of a ∼300 Å mosaic block structure are discussed.
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• 21
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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: We feel that the lengthy comments given here come down to a few simple points. For uniform, homogeneous swollen membranes the internal driving force for transport in hydraulic permeation experiments is a concentration gradient not a pressure gradient. Equation (1) is in error because it neglects the frame of reference term 1/(1 - ν1). Equation (19) shows properly the connection between K0 and the various diffusion coefficients. In the particular case discussed here and previously we see no evidence to say that a viscous flow mechanism is operative since we can explain all of the K0 data in terms of reasonable diffusion coefficients if proper consideration is given to the frame of reference correction. This is not to say that in many other cases a viscous flow mechanism will not be present or even predominate.
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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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• 23
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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• 24
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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 root-mean-square end-to-end distances of isotactic poly(tert-butylethylene oxide) fractions were determined in xylene at 80°C from intrinsic viscosity measurements and in o-dichlorobenzene at 80 and 100°C by light scattering. The characteristic dimension (〈L2〉0/M)1/2 was 1.04 × 10-8 cm in xylene and 0.9 and 0.7 × 10-8 cm in o-dichlorobenzene at 80 and 100°C, respectively. The value in xylene corresponds to a C∞ of 15.9. This observation and the large negative temperature coefficient of (〈L2〉0/M)1/2 suggest that poly(tert-butylethylene oxide) exists in a helical block conformation under these experimental conditions. This conclusion is in agreement with earlier reported NMR measurements.
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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 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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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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• 27
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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: Small-angle polarized light scattering from a deformed three-dimensional spherulite is formulated on the basis of the deformation model proposed in Part II of this series. The intensity distribution of scattered light is discussed chiefly for the cross-polarization condition, the so-called Hv polarization, as a function of elongation of the spherulite. In the undeformed state, the scattered intensity distribution forms the typical fourleaf clover pattern, and the intensity decreases with increasing fraction of crystals oriented randomly (type R crystals) within the crystal lamellae of the spherulites. In a system composed of type R crystals and folded-chain crystals (type B crystals) within the lamellae, the four-leaf pattern moves to the horizontal zone near the equator with increasing elongation of the spherulite, and, simultaneously, extends to some extent to the vertical zone near the meridional direction as a parameter measuring the ease of lamellar untwisting increases. In a system composed, in addition to type R and type B crystals, of crystals transformed from type B to type Ca and type Cr due to tilting and unfolding of polymer chains, respectively, within the crystal lamellae an eight-leaf pattern appears, even at small elongation up to about 30%. Each lobe of the eight-leaf pattern undergoes a characteristic change with increasing elongation. In both systems, the scattered intensity increases with sharpening of orientation distribution of crystals within the crystal lamellae.
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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 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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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 diffusion of three monoanionic dyes [Orange II (C.I. Acid Red 7) and two chromium complex dyes] in nylon 6 is discussed on the basis of dye distribution obtained by the film-roll method. Variations of the diffusion coefficients with dye concentration depend characteristically on the dye species and in one case show a maximum near the dye concentration stoichiometric to the amino endgroup concentration in the nylon. These concentration dependences are interpreted on the assumption of two thermodynamically distinct dye populations in equilibrium.
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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 effect of drawing on the glass-transition temperature of amorphous poly(ethylene terephthalate) has been studied. The Tg decreases to a minimum at a draw ratio of 1.5, then increases to a maximum at a draw ratio of about 2.0, and again decreases with increasing draw ratio. The relationship between the change of structure and Tg is discussed in terms of the configurational entropy and the rate of molecular motion in local-mode relaxation. On the basis of configurational entropy, the decrease of Tg at the beginning of drawing depends on the increase of configurational entropy, while at draw ratios above 2.0 it depends on the increase of entropy associated with intermolecular interaction. From the point of view of molecular motion, it is concluded that the change of Tg is determined by local oscillations in the amorphous region.
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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: 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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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, 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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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: Criteria for the solid state synthesis of large, nearly defect-free, polymer crystals are derived and related to experimental observations. Polydiacetylene single crystals are of principal concern, although the concepts presented can be easily generalized. In particular, a least-motion criterion is developed whereby the solid-state reactivity of different diacetylene phases and the most likely polymerization mode of a particular phase can be predicted from a two-parameter description of the relationship between neighboring monomer molecules. Phase stability criteria are considered for four characteristic free energy diagrams which explain the phase behaviors that have been observed for various polymerizing diacetylenes. Reaction uniqueness criteria are discussed as they relate to monomer site point group symmetry, symmetry relations between mutually reacting monomer molecules, and dimensional changes during polymerization.
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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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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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Source: Wiley InterScience Backfile Collection 1832-2000
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Notes: Composite specimens were prepared using soda glass beads and a purified epoxy resin cured with 1,3-propylene diamine. Some beads were treated with a silane coupling agent. The dynamic mechanical properties of these specimens were measured in the temperature range -190 to +180°C using a free-oscillation torsion pendulum. The dynamic mechanical relaxation spectrum showed no feature that could be attributed to the formation of a new interfacial phase and the torsional moduli were unaffected by the use of the coupling agent. Increasing the glass content of the specimens decreased the damping and increased the modulus. An attempt was made to predict the composite modulus using the Kerner equation. When the specimens were immersed in boiling water, two effects were noted. First, water was absorbed in the epoxy resin matrix and changes in the dynamic spectrum were observed. Second, in samples filled with untreated glass debonding occurred and the presence of free water at the interface was indicated by the appearance of a new peak near 0°C.
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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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Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology , Physics
Notes: A new technique was developed to study the molecular mechanics of highly oriented polypropylene during stress relaxation and creep. The polarized infrared spectrum was recorded while the polymer was under load. Stress relaxation effects were investigated during the two-stage process of fast decay followed by a slower “dynamic equilibrium” decay by examining the stress-sensitive 975-cm-1 band and the orientation-sensitive 899-cm-1 band. In the fast decay region, the aligned chains became more highly overstressed and the nonaligned chains quickly relieved themselves of their initial overstress. These findings suggest an exchange of stress from nonaligned to aligned chain segments, without much orientation change. Also, a rupture of very highly overstressed aligned chains is though to occur. In the slow decay region, the aligned overstressed chains showed a relief of stress accompanied by some disorientation or helix distortion. Creep, however, appeared to occur via a process which involved all chains regardless of alignment. It was found that the number of highly stressed bonds increased with time at the expense of the intermediately stressed bonds. Very little change in overall orientation was noted, which probably explains the observed crazing and void formation.
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• 39
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Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology , Physics
Notes: The change of long spacing in polyethylene and nylon-6 during heating at 18°C/min. was measured with an apparatus devised for rapid measurement of the small-angle x-ray diffraction. The apparatus made it possible to obtain a diffraction profile in 1.8 sec. Long spacings increased notably at high temperatures near the melting point, as has been observed during low-rate heating. However, the increase in long spacing during heating was very small in a methoxymethylated nylon-6 sample. This suggests that the increase in the long spacing at high temperature is due to the thickening of crystals. The long spacing in polyethylene samples in the vicinity of the melting point is apparently independent of thermal history.
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• 40
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Notes: The change in standard chemical potential of a number of alkanes on PDMS going from dilute solution to the perfect vapor ΔḠov was measured by gas chromatography over a large range of temperatures. The change in standard chemical potential of the alkane going from the pure liquid to the perfect vapor ΔḠov was calculated from fugacity data. These data were fitted separately to three Taylor's series expansions wherein the (partial) heat capacity of vaporization is zero, constant, and linearly dependent on temperature, respectively. On the basis of statistical and physical arguments it was concluded that the partial excess functions determined by gas chromatography should be described with a temperature-independent partial excess heat capacity.
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• 41
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Notes: The Daniels-type distribution functions of the end-to-end distance of three-dimensional and two-dimensional wormlike chains are obtained to terms of order t-10, by an operational method with use of a digital computer, where t is the ratio of the total chain contour length to the Kuhn segment length in three-dimensional cases and of the contour length to the persistence length in two-dimensional cases. The convergence of the ring-closure probability and the mean reciprocal distance is examined on the basis of these distribution functions. A similar study of the moment-based distribution functions is also made.
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Notes: The rheological behavior of dilute solutions of flexible macromolecules is studied by means of a freely jointed multiple bead-rod model. The solution of the equations describing the mechanics of the system is obtained by means of a numerical procedure, which applies to arbitrary flow conditions. The case of the transient stress in uniaxial elongational flow is developed in some detail. A comparison with bead-spring models shows both quantitative and qualitative differences which are briefly discussed.
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Notes: It is shown that in the general theory of incompressible simple fluids with fading memory there are, for several types of nonsteady shearing motions, simple universal asymptotic relations between the shear stress S12 and the first normal stress difference N1 = S22 - S11. The kinematical situations considered include initiation of steady shearing, rest after steady shearing, and sinusoidal oscillation. In, for example, relaxation following cessation of a steady shearing flow with rate of shear κ, there holds, to within an error O(κ4): \documentclass{article}\pagestyle{empty}\begin{document}$dN_1 (t)/dt = - 2_\kappa S_{12} (t).$\end{document} This and the other derived universal relations between N1 and S12 are either consequences of, or are closely related to a general asymptotic formula [B. D. Coleman and W. Noll, Revs. Mod. Phys., 33, 239 (1961), eq. (6.15)] expressing N1 as an integral of the product of the shear relaxation modulus and the square of the history of the relative shear strain.
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Notes: The thermal expansion contribution due to temperature-dependent π-electron delocalization is evaluated from spectral measurements on a single crystal polydiacetylene (poly-2,4-hexadiyne-1,6-diol bisphenylurethane). The observed temperature independence of backbone associated vibrations (less than ±1 cm-1 change in νC=C and νC≡C between 25 and 90°C) implies that thermal conformational fluctuations and equilibrium defect formation (which produce a negative thermal expansion coefficient) do not measurably affect π-electron delocalization. The separation of equilibrium defects is either much longer than that of nonequilibrium defects or much longer than required to appreciably limit π-electron delocalization in an effectively defect-free polymer. Arguments presented indicate that, in the experimental temperature interval, the observed thermal expansion coefficient in the chain direction is over an order of magnitude larger than the delocalization-associated contribution.
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Notes: Stress crazing is studied in three forms of crystalline, isotactic polypropylene (PP): (1) smectic/nonspherulitic, (2) monoclinic/nonspherulitic, and (3) monoclinic/spherulitic PP. Optical and scanning electron microscopy as well as stress - strain measurements are used to characterize crazing behavior in these three forms as a function of temperature (-210 to 60°C) and of the gaseous environment (vacuum, He, N2, Ar, O2, and CO2). Forms 1 and 2 are found to craze much like an amorphous, glassy polymer in the temperature range between -210 and -20°C, irrespective of environment. The plastic crazing strain is large close to the glass-transition range (ca. -20°C) of amorphous PP and in the neighborhood of the condensation temperature of the environmental gas. Near condensation, the gas acts as a crazing agent inasmuch as the stress necessary to promote crazing is lower in its presence than in vacuum. A gas is the more efficient as a crazing agent, the greater is its thermodynamic activity.Spherulitic PP (form 3) crazes in an entirely different manner from an amorphous, glassy polymer, showing that the presence of spherulites influences crazing behavior much more profoundly than the mere presence of a smectic or monoclinic crystal lattice. Below room temperature, crazes are generally restricted in length to a single spherulite, emanating from the center and going along radii perpendicular, within about 15°, to the direction of stress. They never go along spherulite boundaries. Gases near their condensation temperature act as crazing agents much as in nonspherulitic PP. Above room temperature the crazes are no longer related to the spherulite structure, being extremely long and perfectly perpendicular to the stress direction. Apparently the crystals are softened enough by thermally activated segmental motion to permit easy propagation of the craze. The morphology of the fracture surfaces and its dependence on temperature and environment is described and discussed. Concerning the action of gases as crazing agents it is argued that the gas is strongly absorbed at the craze tip, where stress concentration increases both the equilibrium gas solubility and the diffusion constant. Hence, a plasticized zone is formed having a decreased yield stress for plastic flow. This is considered to be the main mechanism by which the gas acts as a crazing agent. In addition, reduction of the surface energy of the polymer by the adsorbed gas eases the hole formation involved in crazing.
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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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Notes: Processes that impart strength and toughness are discussed along with reinforcement by colloidal plastics to indicate that high strength, except under restricted test conditions, necessitates a dispersed phase. Thereafter the dependence of the nominal and true tensile strengths on the type, size, and concentration of polar segments in polyurethane elastomers is considered. Data are first examined on formulations devoid of plastic domains and then on those containing domain-forming segments that result from the reaction of toluene-2,4-diisocyanate (TDI) with either toluene-2,4-diamine or 4,4′-methylene-bis-(2-chloroaniline) and from the reaction of 4,4′-diphenyl methane diisocyanate (MDI) with 1,4-butanediol (BD). Segments from TDI and either diamine give plastic domains that are especially effective for augmenting strength over an extended temperature range. Segments from MDI and BD are comparatively ineffective, although the formulation studied exhibits high strength at and below room temperature owing to strain-induced crystallization. From data on various segmented and triblock elastomers, general conclusions are drawn regarding the dependence of strength on the characteristics of the domains and the matrix. For some six segmented and triblock elastomers, it is found that the true tensile strength is essentially independent of the weight fraction of domains provided it exceeds 0.20 or thereabouts.
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Notes: The scattering from an assembly of anisotropic rods having correlated orientation is calculated in terms of a correlation function expressing the probability of parallelism of orientation of their optic axes as a function of their separation. The scattering is dependent upon the product of a form factor for the scattering from an individual rod and an interference factor dependent upon this correlation function.
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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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Notes: Four polymers, viz. polystyrene, polycarbonate, poly(methyl methacrylate), and poly-(vinyl chloride), were cooled from the melt to room temperature under hydrostatic pressures of 30 and 1000 atm. Cooling under high pressure increased the density by 0.4-0.6%, and the effect of this has been examined for the torsional creep properties, the dynamic properties at 1 Hz, the Charpy impact strength, the thermal expansivity, and the torsional yield stress. It turned out that, in general, densification affects the thermomechanical properties only slightly.
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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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Notes: Dielectric properties of poly(vinylidene fluoride) have been studied in the frequency range 20 Hz to 1 MHz and between 100 and 220°C, during heating and cooling. The dielectric constant and loss change abruptly at the temperature Tm corresponding to the melting point. At lower frequencies, two types of ionic conductin are observed. One appears below Tm and is attributed to interfacial polarization. The other occurs above Tm and is related to electrode polarization. These results suggest that a crystalline polymer is a heterogeneous medium for ionic transport, while the melt is a homogeneous medium. From these results, the nature of ac ionic conduction in crystalline polymers is discussed. At high frequency, the α relaxation is observed below Tm. It is due to the molecular motion in the crystalline region and disappears at Tm.
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Notes: The molecular motion of unsintered polytetrafluoroethylene (PTFE) was studied by dynamic viscoelastic measurements. From results for variously heat treated suspension polymerized (molding powder) PTFE, the following conclusions are drawn. Molding powder, as received, has a high degree of crystallinity according to calorimetric results and lower magnitude of the γ relaxation, but the behavior of the β relaxation suggests that the crystals are disordered more than those of the sintered PTFE. The β relaxation peak for an emulsion polymerized PTFE (fine powder) occurs at a higher temperature and is sharper than that for the molding powder, so that the crystals of the fine powder are better ordered than that for the molding powder. The behavior of the β relaxation for the radiation induced-polymerized PTFE is affected by polymerization conditions, particularly concentration of emulsifier. It is concluded from the results for the unsintered PTFE polymerized by various methods that the nature of crystalline state is decided during the course of simultaneous polymerization and crystallization. Molding powder as received has a relatively high magnitude of relaxation between 30°C to 180°C, but with little temperature dependence in this temperature range. This relaxation is diminished by gamma-ray irradiation. Since the molding powder has a complicated morphology, the relaxation in this temperature range is attributed to inter-particle friction rather than a relaxation associated with motion on the molecular level.
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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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Notes: The glass-transition region of crosslinked polymers prepared from poly(1,2-propylene phthalate fumarate) and styrene was studied using a torsion pendulum. The glass-transition temperature and the modulus in the rubbery region of these polymers were analyzed in terms of the crosslink density. The styrene concentration at which the maximum crosslink density occurs, as estimated from the viscoelastic data, is found to be in agreement with estimates made by other workers using chemical methods.
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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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Notes: Solution properties of poly[1(2-hydroxyethyl)pyridiniumbenzene sulfonate methacrylate] and poly[1(2-hydroxyethyl)trimethylammoniumbenzene sulfonate methacrylate] were studied. Within a certain concentration range of some added low molecular weight electrolytes, phase separation occurs. The dependence of intrinsic viscosity on molecular weight was determined and the steric factor estimated for both polymers. For nonaqueous solvents, an extrapolation of the dependence of the refractive index increment of the polymer on the refractive index of the solvent leads to an apparent refractive index of the polymer, different from the refractive index determined directly by the immersion method. Some peculiarities of light scattering in solutions with no electrolyte added are mentioned.
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Notes: Gel permeation chromatographic (GPC) separations have been performed with several commercially available column packing materials. The results have been analyzed in the conventional manner to obtain the ratio of weight average to number-average molecular weight, Mw/Mn, for solutes with narrow molecular weight distribution. Various other parameters proposed to measure the efficiency of GPC columns have been evaluated and compared. It is proposed that the experimentally determined value of Mw/Mn for a series of different molecular weight samples with similar, narrow distribution for a given set of columns is a convenient parameter for comparing column efficiency in GPC. This parameter may be calculated from a single chromatogram unlike resolution, R, resolution index, RI, or specific resolution, RS, which require a pair of chromatograms. Results from the Mw/Mn method are usually in agreement with those from the R, RI, and RS calculations but one exception has been found. The number of theoretical plates calculated from the elution of a small molecule or from the polymer peak bears little relation to efficiencies predicted from the proposed Mw/Mn method or from R, RI, or RS.
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Notes: Craze and crack growth have been studied in polycarbonate. The results are correlated by a stress intensity factor derived from fracture mechanics. A new model taking creep into account is proposed to explain the experimental results. Theoretical predictions derived from the model are compared with experimental results. Fair agreement is obtained.
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Notes: Radical formation during tensile deformation of highly oriented poly[p-(2-hydroxyethoxy)benzoic acid] fibers was investigated by electron spin resonance. Stretching of fibers in vacuo and in a stream of nitrogen gas at room temperature generated a large number of radicals which increased rapidly with macroscopic strain, while stretching in air generated only a small number of radicals. The radicals formed in vacuo or in nitrogen decayed rather rapidly after introduction of air. The observed spectrum was apparently a triplet with a line separation of about 7.5 gauss and a small asymmetry. The inspection of the hyperfine structure, line separation, and total width of the spectrum and the comparison between the observed and the calculated spectrum based on a model substance proved that the observed species is a phenoxy type radical generated by rupture of main chains. A small asymmetry of observed spectrum was explained by anisotropy of the g-tensor. The alkyl end-radical generated together with one of the phenoxy type could not be detected, perhaps owing to its high reactivity.
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Notes: The energy level dispersion, along the chain wave vector, of infrared-active methylene rocking modes has been measured as a function of pressure to 40 kbar for a number of polymethylenes. They are crystalline polyethylene and n-paraffins C23H48, C24H50, C28H58, and C29H60. The crystalline factor-group splitting of each chain mode is observed at various pressures, for those polymethylenes which have orthorhombic or monoclinic structures. The effects of crystal structure, intermolecular force field and intramolecular force field on the observed energy levels as well as on the crystalline factor-group splittings are discussed A hydrogen-hydrogen nonbonded repulsion potential has been calculated as a function of interatomic distance rH••H for 2.3 Å < rH••H < 3.0 Å from the observed volume dependence of the factor-group splittings of methylene rocking modes. It is shown that the dynamic potential wells along the normal coordinates of the rocking modes are harmonic up to room temperature.
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Notes: In order to determine the conformation of poly(ethylene oxide) (PEO), 13C satellite spectra of PEO, 1,2-dimethoxyethane (DME), and dioxane were measured at various temperatures in various solvents, and analyzed. Relations between the coupling constants were derived from the linearity between the parameters N = JAB + JA′B and L = JA′B in AA′BB′ spectra of PEO and DME. The vicinal coupling constants for the individual rotational isomers were obtained from the above relations and the temperature dependences of N and L and the enthalpy differences were calculated in each solvent. The gauche rotamer is more stable than the trans isomer by 250-500 cal/mole in all cases examined.
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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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• 65
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 marked effects of chemical structure on the morphology of single crystals in linear aliphatic polyesters have been investigated. Drawn fibers and solution-grown crystals of poly(ethylene sebacate), poly(hexamethylene sebacate), and poly(decamethylene 1,16-hexadecanedicarboxylate) have been studied by small-angle and wide-angle x-ray diffraction. Electron microscopy, and broadline NMR provided supplementary information.The crystal disorder due to irregularity in the cross section of the molecule due to ester groups along the chain direction increases with increase of the methylene sequence length in the chemical repeat unit. On the basis of the x-ray data and electron microscopy, it is proposed that the nature of the fold surface of single crystals of a given polymer, especially a choice of (001) or (hkl) fold surface (flat lamellae or hollow pyramidal crystals), is determined by energetic competition effects between fold geometry and unit cell symmetry. A smooth increase of the long period with increasing crystallization and annealing temperature seems to be general behavior even when a pronounced stepwise increase might be anticipated.
Type of Medium: Electronic Resource
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• 66
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: 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.