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  • Articles  (5,088)
  • Physics  (5,088)
  • 1975-1979  (2,541)
  • 1970-1974  (2,547)
  • 1
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The theory developed in Part I of this series is applied to a number of nonvinyl “smooth” chained homopolymers. The agreement between predicted and observed activation energies of diffusion for simple penetrants is generally good, particularly for polyethylene. Discrepancies observed for the smallest penetrants, He and H2, in some polymers may be rationalized in terms of atomic scale irregularities on the polymer chain surface. It is shown that in favorable cases the theory may permit diffusion data to be used as an additional check on the accuracy of conformational energy maps for polymers.
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  • 2
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
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  • 3
    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 model of a tight-fold adjacent reentry fold surface for polyethylene single crystals has been questioned, because it has been speculated that a tight-fold surface should have a density approximating that of the unit cell (∼1.00 g/cm3). This would lead to an overall lamella density of close to unity. In contrast, the majority of measured values are in the range 0.96 to 0.97+ g/cm3. These lower values have been taken as evidence to disprove a tight-fold-surface model. The present calculations made on space filling models of tight folds indicates a fold surface density on the order of 0.75 g/cm3. This produces no inconsistency between a tight-fold model and accepted lamella density values. Further, calculated values of the weight fraction crystallinity of lamella, as a function of the number of carbons in the fold, limits this number to approximately 9 to 11 carbons per fold.
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  • 4
    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
    Additional Material: 7 Ill.
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  • 5
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The relaxation following a change in temperature of amorphous polymers near the glass transition has been calculated. The calculation uses a chain model consisting of cis and trans backbone rotational states. The relaxation is assumed to proceed by localized conformational changes whose rates are controlled by the fractional free volume in small enough regions of the polymer that thermal fluctuations need to be considered. The relaxation is treated as a stochastic process, and an approximate solution is obtained for a finite set of relaxation environments. Using what is believed to be the most plausible set of parameters for polystyrene, relaxation curves are computed for the internal energy that are very similar to the curves obtained by Kovacs and others for the volumetric relaxation of poly(vinyl acetate) and polystyrene.
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  • 6
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The solution behavior of hydrophobic-hydrophilic water-soluble graft copolymers consisting of poly[(ethylene-co-vinyl alcohol)-g-ethylene oxide] was investigated by high-resolution NMR spectroscopy and measurements of solution viscosity in tetrahydrofuran, water, and mixtures thereof at various temperatures. A graft copolymer with a backbone containing 2.7 mole% vinyl alcohol exists in an intramolecular phase-separated conformation in aqueous solution, independent of the temperature. Graft copolymers with backbones containing 20.3 mol% vinyl alcohol exhibit an intramolecular mixed-phase conformation in which the mobility of chains in the hydrophobic region depends on temperature. The temperature dependence of the intrinsic viscosity in water shows a maximum near 50°C.
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  • 7
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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: Concentrated solutions of poly(n-octyl isocyanide) exhibit a mesomorphic structure, most probably nematic in nature. Poly(n-butyl isocyanide) and poly(benzyl isocyanide), of the molecular weights at our disposal, failed to show similar behavior. Upon acidification poly(n-butyl isocyanide) does not change, but the other two polymers turn essentially black. Infrared and proton NMR clearly demonstrate that upon acidification, poly(n-butyl isocyanide) and poly(benzyl isocyanide) are protonated on the nitrogen atom. This process is reversible. Carbon-13 NMR and x-ray patterns indicate that no chemical rearrangement or conformational changes take place upon acidification. This conclusion is supported by infrared studies and by inference from the poor electrical conductivity of the solid acidified polymers.
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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: A new calculation of the vibrational frequencies of poly(ethy1 ethylene) based on the actual molecular geometry was performed. The calculation takes into account new experimental data such far-infrared spectra and Raman spectra of the stretched polymer, infrared spectra of poly(ethyl ethylene)-(2,2;d2) (P-4-1-d2) and poly(ethyl ethylene)-(3,3,4,4;d4) (P-4-1-d4), and Raman spectra of poly(ethyl ethylene)-(1,3,3;d3) and poly(ethyl ethylene)-(3,3,4,4;d4). Refinement produced a set of force constants; it is also applicable to poly(propyl ethylene).
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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: The far-infrared spectra of polystyrene methacrylic acid/(PSMA) ionomers have been investigated as a function of cation and ion-site concentration to obtain spectroscopic evidence of domain formation. A far-infrared band, due to the vibration of a higher-order cluster, is found at 170 cm-1in Na+-form PSMA. This band, which is observed in addition to the known cation-motion bands, is assigned to the vibrations of aggregates involving many cations and anionic sites close together, and the results are discussed in light of ion aggregation models.
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  • 10
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Heat capacities of poly(vinylidene fluoride) (PVF2) and polytetrafluoroethylene (PTFE) have been measured between 5 and 100°K with an accuracy of (1-5)% by adiabatic calorimetry. Calculations based on contributions from known optical lines and the Tarasov continuum model are in good agreement with experimental results down to 30°K for PVF2 and 10°K for PTFE, and yield characteristic temperatures θ1 and θ3 which are consistent with previous values determined from high-temperature (100 - 350°K) data. At lower temperature the measured heat capacity is significantly higher [(30-100)%] than the model prediction, and can be satisfactorily accounted for by the introduction of localized vibrators at a concentration of about 1% as compared to acoustical oscillators and at a characteristic temperature of about 20°K. Using established data on polyethylene for comparison, the principle of additivity for heat capacities is found to be valid down to at least 20°K, convering the region (〈60°K) where interchain vibrations contribute significantly to the heat capacity. Possible reasons for this unexpected behavior are discussed.
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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
    Additional Material: 4 Ill.
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  • 12
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A simulation of the Brownian motion of polyethers and polyethylene is reported. The chains under consideration are confined to a tetrahedral lattice and subjected to conformational energy conditions. The dynamic behavior of the whole chain is studied. The diffusion of individual chain atoms reflects the chemical nature of the chain, and the diffusion of the center of mass, in connection with experimental results, affords a time scale for the simulation. The relaxation of bond orientation, which is connected with fluorescence depolarization, is found to be consistent with the theory of Valeur and co-workers. The relaxation of the total dipole is interpreted in terms of conformational features of the motions and correlations between neighboring dipoles. Finally, relations between chemical structure and dynamic behavior are established. Three classes of polyether chains are to be distinguished: the rigid chain poly(methylene oxide), the highly flexible poly(ethylene oxide) and an intermediate class typified by polyethylene.
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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
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  • 14
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
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  • 15
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The reversible stress-induced crystal-crystal phase transition of poly(tetramethylene terephthalate) (PTMT) has been studied using infrared spectroscopy. Two spectral regions were used to study this transition: the 900-1000 cm-1 methylene rocking region and the 1300-1550 cm-1 methylene bending region. The bands at 917 and 1456 cm-1 are assigned to the ∝ phase. The bands at 935 and 1388 cm-1 have components from the α phase and the β phase. Dynamic stretching experiments performed above and below the glass-transition temperature indicated different mechanisms of the phase transition.
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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: Extra meridional reflections (00l: l = 3, 5, 13, 15, 21) were observed in drawn polyoxymethylene (POM). The 003, 0015, and 0021 x-ray diffraction intensities increase on annealing, while the 005 and 0013 intensities decrease. It is concluded that crystalline regions are of two kinds: in the first, which generates the 003, 0015, and 0021 reflections, the molecular conformation is slightly distorted from the uniform helix by intermolecular steric hindrance between the CH2 groups; and in the second, which generates 005 and 0013 reflections, the molecular conformation is distorted in another way. The second form is converted into the first by annealing. The displacements in the c direction of the CH2 groups and the oxygen atoms from the uniform helix in the first form are about 1.0% and 0.75% of the interval between a CH2 group and an oxygen atom along helix axis of the POM crystal; thus the correct conformation in the stable state is known. The nature of distortion in the second region is not clarified but several characteristics are offered.
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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: Measurements of the spherulitic growth rates of bisphenol-A Polycarbonate plasticized with pentaerythritol tetranonanoate (PETN), trimellitic acid tri(n-octyl-n-decyl)ester (TMDO), and tritolyl phosphate (TTP) are reported. The incorporation of a plasticizer enlarges the crystallization range, decreases the temperature of maximum growth rate and accelerates the kinetics to a considerable extent. The growth-rate parameters are calculated from a least-squares analysis of the experimental data according to the kinetic theory of Hoffman and Lauritzen. From the growth-rate data given here and the overall crystallization kinetics reported previously, concentrations of seeds inducing the crystallization were determined.
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  • 18
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Coisotactic shift contributions caused by sterically crowded isotactic side-chain alkyl groups are proposed for peak assignments of isotactic propylene/butene-1 copolymers. Previously disputed analyses of methine triads and PB tetrads of backbone methylene carbons (α,α′-CH2) have been verified using first-order Markovian distribution theory. Coisotactic shift contributions also account for the reverse order of the propylene-centered triads from that predicted by the Grant-Paul equation.
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  • 19
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Tightly cross-linked poly(styrene-co-divinylbenzene) microgels with molecular weights in the range 107 to 108 g mole-1 were studied in solution in dimethylformamide containing 7 g dm-3 LiBr. Laser light scattering photon correlation spectroscopy (PCS) was used to measure z-average translational diffusion coefficients D̄z and dilute solution viscometry to measure intrinsic viscosities [η]; values of the equivalent hydrodynamic radii 〈Rη3〉η⅓ and 〈RD-1〉z-1 were derived. Weight-average molecular weights M̄w and z-average mean-square radii of gyration 〈S2〉z were determined by conventional light scattering. The microgels were investigated by gel permeation chromatography, and molecular weight data obtained using the [η]M calibration procedure were in satisfactory agreement with results obtained by electron microsocopy and conventional light scattering.
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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
    Notes: Polystyrene networks containing controlled amounts of pendent chains and swollen to equilibrium in benzene have been investigated by inelastic light scattering and stress-strain experiments. Both the cooperative diffusion constant and compression modulus have been shown to decrease drastically when the proportion of pendent chains increased, while the equilibrium segment concentration exhibits only a small variation. The experimental results are discussed in terms of a change of structure and dimensions of the macromolecular strands of the network.
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  • 21
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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 effect of the 1,3-cyclohexane rings in the chain backbone on thermal properties of polyamides, especially the glass-transition temperature, has been studied using polyamides based on 1,3-cyclohexanebis(methylamine). The increase in glass-transition temperature was far greater than that obtained with the analogous polymers containing m-benzene rings. However, the effects of 1,4-cyclohexane and p-benzene rings are nearly equal. Several possible causes for this difference are examined. It is concluded that restricted chain mobility due to steric hindrance of the cis-1,3-cyclohexane ring, the predominant isomer, is the most likely cause of the difference.
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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: X-ray photoelectron spectroscopy (ESCA) has been used for quantitative surface analysis of surface grafts prepared by mutual irradiation of polyethylene (PE) in methyl acrylate (MA) vapor with γ rays and high-energy electrons. The binding-energy shift between the C1s electrons in the ester group of poly(methyl acrylate) (PMA) and in PE is large enough (ca. 3.6 eV) to distinguish the PMA and PE components. The C1s peak-area ratio of ester carbon to other carbons is related quantitatively to graft composition by constructing a calibration curve for a given instrument and excitation source, with a series of homogeneous grafts of known composition used as the calibration standards. Using the calibration curve and the measured peak ratio, the surface composition of the surface grafts is determined. The relations between surface compositions according to ESCA and attenuated total reflection (ATR) infrared spectroscopy and between adhesive bond strength and ESCA composition are discussed. In the electron-induced grafts, the grafted surface reaches maximum adhesive bondability with attainment of 100 mole % MA in the surface detected by ESCA; i.e., with formation of a homopolymer layer. The ESCA composition can be used as an indicator of the presence of the homopolymer layer or as a criterion for predicting adhesive bond strength.
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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: Rheological and rheo-optical data are reported for the poly(terephthalamide of p-aminobenzhydrazide), X-500, in dimethyl sulfoxide solutions in the concentration range 0.2 to 6.0 g/100 ml. The objective of these measurements is to seek evidence of shear-induced isotropic → nematic phase transition. Three types of measurement, Couette, cone and plate, and capillary rheometer, all indicate that this system exhibits flow instabilities at high shear rates and concentrations. In this region both the viscosity and the primary normal stress difference decrease with time under shear. In the capillary rheometer the apparent viscosity is smaller for shorter capillaries and, for short capillaries, there is a range of shear rates in which plug flow and a coiled extrudate are observed. These instabilities may arise from the existence of a mixture of isotropic and nematic phases. At lower shear rates, where the flow behavior appears normal, the concentration dependence of the flow birefringence increases at a critical polymer concentration Cp* This value is in reasonable accord with the concentration corresponding to the change of slope of logη (measured at low shear rate) vs. logCp. Both the latter measurements appear to be sensitive to the onset of the phenomenon, which may be due to a shear-induced transition or the rheological effect of chain entanglements.
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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: A medium B contains a substance C which can diffuse. This mixture of B and C is brought into contact with a medium A which itself can diffuse into B. Now C diffuses through a swollen layer of A and B into A. The present study examines mathematically this process which, among other things, could serve as a model for migration in a system consisting of plastic packaging (polymer plus an additive) and the contents of the package. It is assumed that medium A (contents) with a constant diffusion coefficient diffuses into medium B (plastics) and that the diffusion of substance C (additive) in the pure B and into A can also be described by constant diffusion coefficients. The diffusion coefficient of substance C in the zone of mixed A and B is taken to be dependent on the concentration of A in B. Partition coefficients are assumed to exist at all interfaces between the media. The general equations of this coupled diffusion process are solved explicitly. The solutions are discussed and illustrated by several special cases. Furthermore, the total amount of C in A is calculated as a function of the diffusion coefficients of the partition coefficients of time, and of the concentration of A in B.
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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 structure of the silane coupling agent interphase of fiber-glass reinforced plastics has been studied by Fourier transform infrared and laser Raman spectroscopy. It is found that there is a degree of order in the molecular organization of the coupling agent interphase for the vinyl and cyclohexyl functional silane coupling agents. When a cyclohexyl functional silane is used, crystalline layers of silanetriol on the glass fibers are observed. The extent of order is determined by the structure of the adsorbed species, which is influenced by the structure of the silane in the treating solution. Two factors introducing disorder in the interphase are the magnitude of aggregation of the silanes in solution and irregularities in the topology of the glass surface.
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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: Data on the viscosity of poly(vinyl acetate) (PVOAc) and its concentrated solutions in diethyl phthalate (DEP) and cetyl alcohol (CeOH) are examined over the molecular weight range 8 × 103 〈 M 〈 1.3 × 106, the range 0.15 〈 ϕ 〈 1.0 of the volume fraction ϕ of polymer, the temperature range 308 to 430°K for PVOAc and its solutions in DEP, and at 396°K in CeOH. The latter is the θ temperature for dilute solutions of PVOAc in CeOH. The data are analyzed with the relation η = KXc(αϕ2ϕM/Mc)a exp[1/β(T - T0)], where a is 1 or 3.4 for αϕ2ϕM less than or greater than a constant Mc, respectively, and XC, is a constant. The expansion factor αϕ of the chain dimension is found to be essentially unity for ϕ 〉 ca. 0.25, increasing with decreasing ϕ for smaller ϕ. Both β and T0 depend on ϕ, and T0 also depends on M at low M.
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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
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  • 28
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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 influence of polymer-polymer interactions and ultrasonic parameters on the ultrasonic degradation of polycaproamide in aqueous 40% H2SO4 was investigated. It was found that the rate data for the concentrations studied could be represented well by Ovenall's rate equation. However values of the rate constant chosen to fit Ovenall's equation tend to decrease with increasing concentration of polycaproamide from 0.5 to 2.0 g/100 cm3. With increasing ultrasonic power, the degradation rate increases, but it decreases as frequency is increased. This suggests that cavitation has a dominant role.
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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 shear-dependent complex viscosity η*12, which governs the linear time-dependent stresses in a viscoelastic fluid undergoing infinitesimal shearing oscillations in-line with a viscometric motion, has been investigated. Formulas relating η*12 to measured quantities have been derived for the cone-and-plate and parallel-plate geometries. In the former case, the formula has the same form as that found when there is no steady shearing present. For the parallel-plate geometry, the formula is different because of the radial variation in the viscometric shear rate. In order to determine the empirical significance of this formula, η*12 data were obtained for two fluids, NBS nonlinear sample No. 1 and a 4.3 g/dl aqueous polyethylene oxide (molecular weight, 5 X 106) solution using a Weissenberg rheogoniometer Model R-18. Data were acquired and analyzed using a minicomputer on-line with the rheogoniometer. The obtained data indicate that good agreement between the η*12 measured using the two geometries is obtained only if the derived formulas are used. Also, it is shown that theoretical results of simple-fluid theory are valid for these data.
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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: Poly(tetramethylene terephthalate) (PTMT) undergoes a reversible stress-induced crystal-crystal phase transition. X-ray fiber-diffraction photographs were obtained from the oriented, unstressed (α) phase. Relative intensities were measured from these photographs. These were used to help check the reported structures of the α phase. Structures and observed intensity data from other authors were also utilized. Results show the α phase contains a non-trans, non-gauche bond rotation in the tetramethylene chain and a nonplanar terephthalic acid residue. A tilt of 3.5° between the fiber axis and the c axis was determined in a direction 210° counterclockwise from the b* axis.
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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: The melting behavior of continuous fibrillar crystals of high-molecular-weight polyethylene has been investigated. The macrofibers were grown from dilute solutions in xylene subjected to Couette flow in the temperature range between 103 and 118.5°C. The thermograms, as determined by differential scanning calorimetry, exhibit three melting endotherms with peak temperatures at 141, 150.5, and 159.5°C after extrapolation to zero scan speed. All peaks were found to be strongly superheatable. Reduction of fiber length, in particular by etching with fuming nitric acid, led to the disappearance of the melting peaks at 150.5 and 159.5°C. The remaining peak at 136°C appeared not to be superheatable. The heat of fusion of the fragmented fibers was 69.8 cal/g. Wide-angle x-ray diffractograms taken on a macrofiber while gradually heated at a rate of 0.35°C/min at constant length showed that the triclinic phase present in the fiber disappeared at 130°C and that the orthorhombic cell transformed into the hexagonal modification at 150°C. This hexagonal phase was still observable at 180°C. The retractive force developed on heating at constant length displays first a slight decrease followed by a maximum at 150°C. Beyond the latter temperature the stress decays abruptly corresponding to the temperature at which fracture of the fiber could be observed visually. From all these observations it is inferred that the first melting endotherm in the differential scanning calorimeter (DSC) thermograms arises from the melting of unconstrained fibrillar crystal regions which are able to shrink during fusion. Moreover, the melting of lamellar overgrowths on the elementary fibrils on shish-kebab type may contribute to this endotherm. The second melting endotherm at about 150°C is associated with the transformation of the orthorhombic into the hexagonal lattice in constrained parts of the sample. This latter “rotator” phase allows slippage of the polymer chains past each other, giving rise to stress relaxation. The third endotherm arises from melting of this hexagonal phase and the heat take-up connected with the formation of higher energy gauche states upon randomization of the chains in the melt. Almost smooth, fully constrained fibrillar crystals grown at high temperature absorb more than 15.5 cal/g during this process, indicating that the polymer chains in such fibers must be highly extended.
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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: Odd-numbered polyamides have dipoles with components that point in the same direction in the planar zigzag conformation (rather than alternating as in the even-numbered polyamides). An investigation of the dielectric properties of two odd nylons was undertaken here to see if dipole correlation resulting from this effect could be detected. It was found that the dielectric constant and relaxation strength associated with the α loss process (amorphous phase glass-rubber relaxation) when normalized for dipole concentration was indeed markedly higher in the odd nylons. The effect of uniaxial orientation induced by solid-state extrusion on the isotropy of the dielectric properties was also studied. A previous study on nylon 6-10 found a reduction in relaxation strength of the α process in both the parallel and perpendicular directions but with the perpendicular direction being much stronger than the parallel. A similar result was found here for the odd polyamides. Thus the reduction in intensity appears to be due to effective reduction in the amount of amorphous material and not due to any change in dipole correlation induced by orientation. The anisotropy in relaxation strength can be explained by a composite material effect resulting from parallel stacking of crystal lamellas and interlamellar amorphous material and without invoking any anisotropy in the amorphous-phase dielectric strength. Thus there is no reason to conclude that the amorphous phase undergoes orientation as a result of the crystal-phase orientation.
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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: Effects of tacticity and steric hindrance on excimer formation were investigated in isotactic and atactic polystyrene, poly(o-methylstyrene), poly(m-methylstyrene), and poly(p-methylstyrene) in the presence and absence of a quencher (CCl4). The calculated rate constants for excimer formation in the isotactic polymers except for poly(o-methylstyrene) were almost the same and larger than those in the corresponding atactic polymers. These results indicate that excimer formation was due to not only rotational sampling but also energy migration to trapping sites. It was found that steric hindrance on excimer formation was intimately related to the excition diffusion length in the polymer chain.
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  • 34
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Dielectric studies were performed on crystallized and amorphous polydimethylsiloxane which had been characterized by differential thermal analysis and polarized light microscopy. The crystallized specimen displayed one relaxation near 160 K at 1 kHz while the amorphous specimen showed absorption peaks at 155 and 165 K. For the latter material the high-temperature peak was not due to a true relaxation but resulted from crystal nucleation at 160 K and the subsequent growth of spherulites. The low-temperature peak at 155 K resulted from the relaxation associated with the glass transition. A sharp decrease of dielectric constant was observed for both specimens at the melting point (235 K). For the dielectric relaxation associated with the glass transition in crystallized specimens, the values of the dispersion amplitude, the apparent activation energy at 160 K, and the half-width of the absorption curve are 0.43 and 29 kcal/mole, and 5.6 decades, respectively, which are in marked contrast to the corresponding values of 0.82, 18, and 2.2 for amorphous specimens.
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  • 35
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    New York : Wiley-Blackwell
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
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  • 36
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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 nematic fluid is characterized by five friction coefficients. When dilute polymer coils are added to the fluid, all these coefficients are modified. Three Miesowicz viscosities (measured under an aligning magnetic field) and two coupling coefficients between orientation and flow are discussed. In our calculation, elastic dumbbells are used to model the flexible polymer chains. The results are written in terms of two size parameters R∥ and R⊥ and two chain friction coefficients λ∥ and λ⊥ (the label ∥ refers to a direction parallel to the nematic axis). This could be compared to other experiments (such as translational diffusion) which measure λ∥ and ⊥ directly. They may give useful estimates of coil conformation in nematic solvents.
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  • 37
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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: Consideration of crystallization kinetics in high-molecular-weight polymers shows that adjacent reentry is unlikely in melt crystallization and that sections of individual chains will crystallize concurrently at several sites. Hence the characteristic crystallization process will be that of a loop of chain with both ends attached to different sites on the crystal surface. Analysis of this process leads to predictions of crystallinity values for various conditions of chain mobility in the crystal and of entanglements in the amorphous regions. Observations on polymers crystallized at high undercoolings where a crystallinity of about 30% is usually observed suggest that the common case is that of a highly entangled amorphous layer and rapid, local annealing of the chains but with no long-range motion in the crystal. This model of loop crystallization is shown to agree with available small-angle neutron scattering data. The overall crystallization kinetics are in accord with surface nucleation controlled growth which also arises out of the Lauritzen-Hoffman adjacent reentry model and has been shown to fit experimental results on growth rates.
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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: Some results are reported on the linear viscoelastic properties of polybutadienes with narrow-molecular-weight distributions. The zero shear viscosity η0 varies as M3.4 in the linear samples, and viscosity enhancement is found in star-branched samples with long arms, in good agreement with results reported earlier by Kraus and Gruver. The temperature coefficient of viscosity appears to be slightly larger in stars when the arms become long. The steady state recoverable compliance J0e is 2.1 × 10 -7 cm2/dyn in linear samples of high molecular weight, but it increases to values as much as 10 times larger in the stars. The plateau modulus G0N, obtained from a composite curve for the linear samples, is 1.32 × 107 dyn/cm2. The terminal relaxation spectrum of the stars is too broad to allow an evaluation of plateau modulus.
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  • 39
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: In a previous investigation of a co[poly(ethylene terephthalate)-p-oxybenzoate] containing 30 mole % oxybenzoate units (referred to as T2/30), Krigbaum and Salaris identified the endotherm at tIII = 244°C as a nematic → isotropic transition. Subsequent investigation revealed that the tIII endotherm disappeared if the polymer is heated to the isotropic melt or dissolved and reprecipitated. The loss of the tIII transition might be due to molecular weight reduction, sequence randomization, or erroneous identification of the transition. Viscosity and high-field NMR data eliminate the first two explanations. Annealing studies at temperatures higher than those of the earlier work demonstrate that the tIII transition, in fact, represents the melting of crystallites formed during a high-temperature annealing operation. Moreover, we cannot determine the thermodynamic melting temperature of the copolymer from solid-state annealing studies. Hence, the principal objective of the study of Krigbaum and Salaris, to compare the enthalpies and entropies of the nematic → isotropic and crystal → isotropic transitions, must be fulfilled in future work.
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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: Presently existing theories of small-angle light scattering by polymeric materials are extended by consideration of the total integrated scattering intensity. It is shown how this quantity, known as the total integral or Porod invariant in small-angle x-ray scattering, may be used to calculate the average square of the fluctuations in refractive index and orientation. Calculations are presented using both statistical and model approaches.
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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
    Notes: Two series of vinyl alcohol-vinyl acetate copolymers were prepared by homogeneous and heterogeneous acetylation of the same precursor poly(vinyl alcohol). Their intramolecular monomer distributions were analyzed by IR spectrometry, calorimetry, and differential thermal analysis. The results show a more blocky distribution for the heterogeneously prepared copolymers. The properties of these (co)polymers in dilute aqueous solution were determined by means of viscometry. Whereas the copolymer-solvent interaction parameter of the homogeneously acetylated, random copolymers hardly varied with acetate content, a definite minimum was found for the blocky copolymers at about 7 mole% vinyl acetate. These findings were attributed to the incompatibility of dissimilar sequences, which sharply decreases with decreasing vinyl acetate sequence length. Up to about 17 mole% vinyl acetate content, the solvent quality for the copolymers is at least as good as for poly(vinyl alcohol). In addition, the dilute solution properties of the samples were established in water saturated with 1-butanol. For copolymers with up to about 17 mole% vinyl acetate, at 25°C this mixture is a better solvent than water. The highest increase in solvent quality was found for the homopolymer, whereas the increase diminished with acetate content, irrespective of the intramolecular vinyl acetate distribution. These findings are explained in terms of preferential adsorption of 1-butanol onto the (co)polymer backbone due to hydrophobic interactions and prevention of this process by the bulky acetate groups.
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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: Recent gravimetric studies of the sorption of organic vapors by poly(vinyl chloride) and polystyrene powders have demonstrated several features which promise to be generally useful in studying the structure and properties of the glassy state. The uptake of vapor can be significantly altered by prior thermal or vapor treatment of the polymer, apparently reflecting changes in the microvoid content or free volume of the polymer. Fickian sorption in sufficiently fine powders proceeds to equilibrium in a few minutes. Upon exposure of a polymer powder to an appreciable pressure of vapor, both a rapid Fickian sorption and a slower, relaxation-controlled sorption are observed. Superposition of these processes leads to widely varied sorption kinetics; a model comprising Fickian diffusion and first-order relaxation terms accurately describes the data and allows estimation of equilibrium and rate constants for both processes. After prolonged exposure, removal of a swelling vapor induces a slow reconsolidation of the polymer structure; this deswelling relaxation can be monitored by the decreasing amounts of vapor sorbed in repeated brief exposures to low vapor pressures, and can also be described by a first-order relaxation model. In this regard, the penetrant vapor serves as a molecular probe, monitoring glassy-state relaxation occurring in the absence of penetrant. The same, presumably true equilibrium is ultimately reached both by swelling from a low free-volume state and by consolidation from a preswollen state of high free volume. The rates of both swelling and consolidation relaxations appear to be retarded by the presence of low concentrations of vapor in the polymer, suggesting that vapor molecules may preempt some of the free volume required for relaxation.
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  • 43
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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 kinetics of the photoinitiated polymerization of lauryl acrylate (LA), 1,6-hexanedioldiacrylate (HDDA) and pentaerythritol tetraacrylate (PET4A) have been investigated using differential scanning calorimetry (DSC). An autoacceleration phenomenon is observed with the multifunctional acrylates, but not with lauryl acrylate. The empirical dependences of reaction rate on such parameters as incident light intensity, initiator concentration, and temperature have been established and are in general found to vary with monomer conversion. Apparent activation energies for the photopolymerizations have been determined from rate versus temperature data. The multifunctional acrylates show an increasing activation energy with monomer conversion, whereas the apparent activation energy for lauryl acrylate not only decreases with conversion, but becomes negative at conversions greater than about 30%. The ratio kp/kt1/2 is calculated from rate versus conversion data under constant illumination and the (independently determined) initiation rate. Analysis of rate versus time data under nonsteady-state conditions (light turned off) yields the ratio kt/kp. With these two ratios the rate constants for propagation (kp) and termination (kt) may be separated and their respective values calculated. Both kp and kt are found to decrease substantially with monomer conversion, indicating a significant change in the rates of both the propagation and termination steps as the polymerization advances. These observations are explained in terms of a radical isolation phenomenon and diffusion control of the propagation step.
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  • 44
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Dielectric constant measurements were carried out on a sample of poly(1,3-dioxepane) [CH2—O—(CH2)4—O—], in benzene over the range 25 - 60°C. This chain molecule was found to be very similar to poly(1,3-dioxolane) [CH2—O—(CH2)2—O—] in having a relatively small dipole moment, which increases markedly with increasing temperature. Rotational isomeric-state calculations show that these two characteristics are due to very strong preferences for gauche states in the two central bonds in the sequence CH2—O—CH2—O—CH2. Such pairs of gauche states, necessarily of the same sign, place neighboring-group dipoles in essentially antiparallel orientations. The resulting attenuation of dipole vectors is the origin of the small dipole moment, and the disruption of these preferred conformations with increasing temperature gives rise to the large positive temperature coefficient of the dipole moment.
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  • 45
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The aromatic Polyamide-hydrazide, Monsanto X-500, has been studied by light scattering in dimethyl sulfoxide, a thermodynamically good solvent. The unperturbed dimensions, (〈r02〉av/M)1/2 = 1.93 × 10-8 at 25°C., indicate a rather highly extended chain. The persistence length falls in the range 35-63 Å, which corresponds to a length of between two and four formula units. This is considerably smaller than the values which have been reported for the aromatic polyamides, poly(p-benzamide) and poly(p-phenylene terephthalamide). X-500 appears to approximate coil-like behavior at a molecular weight of 45,000. Theoretical predictions, based upon the 〈r02〉av/bL ratio, are compared with the observation that no evidence for an anisotropic phase has been found in X-500 solutions in dimethyl sulfoxide at polymer volume ranging from 0.12 to 0.19 (depending upon the concentration of added LiCl).
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  • 46
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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: Friction was measured and analyzed for rubber belts sliding against paper and polymer film surfaces of different roughness. As expected, increased paper smoothness created an increase in the friction coefficient. However, it was found that continuous rubber usage during testing also created an increase in friction coefficient for constant surface roughness of both paper and film. This was analyzed as due to an increase in N and C values for the load-dependent friction coefficient, μ = CW-N where W is normal load and Nmax ≈ 0.33 (papers) or Nmax ≈ 0.6 (polymer films). Using adhesion friction theory, it was shown that friction data can be fitted with a unified equation: C = μ0c-N, where μ0 = μ N = 0 and c is a constant for the rubber and belt configuration tested.
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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: The mechanical performances of fiberglass reinforced plastics (FRP) are quite different when the glass fibers are treated with vinyl (VS) and methacryl (γ-MPS) functional silane coupling agents. We have studied the structural basis for this difference on the molecular level using Fourier transform infrared spectroscopy (FT-IR). A high-surface-area silica powder is used to study the coupling agent/matrix interface. Both VS and γ-MPS can react with styrene at the interface. However, when E-glass fiber is used as a substrate, only γ-MPS polymerizes in the coupling agent interphase which consists of many layers of coupling agent molecules while the major portion of the VS does not polymerize in the interphase. The effect of glass surfaces, with and without a coupling agent, on the curing of the polyester resin has also been studied. Silane coupling agents participate in the curing of the polyester resin while untreated E-glass fiber surfaces inhibit the polymerization resulting in different structures from the bulk matrix.
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  • 48
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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
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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: Quiescent and strain-induced crystallization of poly(p-phenylene terephthalamide) (PPTA) from sulfuric acid solution has been studied. Negative spherulites (SA-PPTA spherulites) are formed from hot concentrated solutions by cooling. The spherulite consists of radiating fibrous lamellae several hundred angstroms wide. The electron diffraction pattern indicates that PPTA molecules are oriented perpendicular to the long axes of the fibrous lamellae and that the [010] or [110] direction of the modification I crystal and [010] direction of the modification II crystal are parallel to the long axes of the fibrous lamellae. The width of the lamellae is much smaller than the chain length of the starting PPTA. It appears that hydrolysis of PPTA during melting crystallization determines the chain length, i.e., the width of the fibrous lamella. Stacked, lamellar structures like “row structures” are formed under shear. The longer axes of the fibrous lamellae are oriented perpendicular to the shear direction. It is confirmed by electron diffraction studies that the PPTA molecules are oriented parallel to the shear direction. Well-developed fibrils with the PPTA molecules oriented to the fibril axis, are formed by adding the SA-PPTA spherulites to water with vigorous stirring.
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  • 50
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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: A number of theoretical approaches to the problem of free volume in polymers are discussed. Because some questions in the Bueche approach remain unresolved, the lattice-gas model was studied. Inconsistencies in the independent-vacancy approximation led to consideration of a mean-field model and then a precise Padé-approximant solution, neither of which gave satisfactory agreement with experiment. Introduction of an internal pressure parameter to model the effects of the chainlike structure of polymers restores agreement with experiment.
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  • 51
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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: Molecular motions in poly(L-histidine) (PLH) and its hydrochloride in the solid state have been studied by NMR and dielectric measurements. Four relaxation processes, β,γ,δ, and ε, are observed for PLH. The δ relaxation is assigned to rotation of an imidazole ring about the Cβ—Cγ bond, since the observed activation energy of 2.7 kcal/mole agrees with the calculated energy barrier for rotation of the central imidazole ring about Cβ—Cγ in an imidazole trimer model and the experimentally determined dielectric relaxation strength is consistent with the theoretically estimated value based on the two-state transition theory. The γ relaxation was attributed to the restricted rotational motion about Cα—Cβ. The β relaxation is related to motion of water molecules bound by PLH. The ε relaxation is assigned to the wagging mode of imidazole groups in the defect region as observed for polymers containing pendent aromatic rings. No relaxation is observed in the hydrochloride of PLH due to the increased interaction between imidazolium cations as side groups. This is confirmed by the comparison of dipole moments of protonated and deprotonated imidazoles estimated by molecular-orbital calculations.
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  • 52
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: We propose a theory for the appearance of two-phase structures during the formation of polymer membranes from a casting solution immersed in a coagulant bath. Our model is based on diffusion induced phase separation at the spinodal in the ternary nonsolvent-solvent-polymer system. A simplified treatment of the interdiffusion process by the diffusion layer method permits the formulation of criteria for the formation of two-phase structures in the course of the solvent-coagulant exchange. Our criteria are expressed in terms of the composition dependence of the chemical potentials in the stable and metastable region of the ternary phase diagram. Comparison with experimental results shows qualitative similarities with theoretical predictions.
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  • 53
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Experiments on inflated sheets of crosslinked poly(dimethylsiloxane) covering a sixfold range of compression are combined with measurements in elongation conducted on specimens from the same sample to obtain the relationship of stress to strain over a 24-fold range in the extension ratio λ1. With increase in λ1-1 the reduced force [f] ≡ f(λ1 - λ1-2)-1 rises to a maximum near λ1-1 = 1.2-1.4, then decreases very slowly with further increase in λ1-1. The form of the relationship of [f] to λ1-1 confirms recent theory.
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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: Resonance Raman spectroscopy has been used to measure the strain dependence of four high-frequency vibrational modes in a single crystal of toluene sulfonate diacetylene polymer. The 0.62-μm thick crystal was stretched elastically to 4% strain before fracture occurred. This was equivalent to an ultimate tensile strength of 2.0 × 109 N m-2. The strain dependence of the vibrational modes has been interpreted using a simple point mass and anharmonic spring constant model. A Fermi resonance was observed for two vibrational modes which are degenerate at 2.1% strain and a 1464 cm-1 frequency.
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  • 55
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    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A permanganic etchant has been developed which reveals lamellar and other fine detail in surfaces of at least three crystalline polyolefines, viz., polyethylene (of both high and low density), isotactic polypropylene, and isotactic poly(4-methylpentene-1). In typical treatments of high-density polyethylene ca. 2 μm of material is removed with defective regions suffering preferential attack. The etchant also discriminates between lamellar orientations, eating deeper where side surfaces of laminae are exposed than on fold surfaces, and between different polymers, attacking isotactic polypropylene more strongly than polyethylene. Comparison with other techniques authenticates the detail exposed and samples appear to be otherwise unaltered by their treatment. Besides normal imaging, it is also possible to use etched samples for transmission diffraction studies in the electron microscope. The method has very considerable application for revealing lamellar details in crystalline polyolefines (which can be chosen to be representative or selective according to the nature of the surface used). Examples are given of a wide variety of melt-crystallized morphologies for the three polymers cited and also of lamellae in a drawn polyethylene sample. It is pointed out that permanganic etching is complementary to the technique of chlorosulfonation used to stain polyethylene in a similar way as bright field microscopy is to dark field.
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  • 56
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Gel permeation chromatography (GPC) of polyelectrolytes in dimethylformamide (DMF) is studied. Three methods of monitoring elution (conductimetry, viscosimetry, refractometry) are used to investigate the molecular-weight distribution and, independently, the chemical composition expressed in terms of the ionic charge density as a function of the chain length in two copolymers of acrylonitrile and sodium methallylsulfonate. The distribution on the gel of the neutral salt NaNO3 added to the DMF and used for elution is discussed in terms of Donnan exclusion; in addition, it is concluded that to obtain the correct molecular-weight distribution, GPC measurements must be performed with an eluent containing a neutral salt at a concentration at least 5 × 10-2M to prevent electrostatic exclusion. The main difficulty in reaching rigorous conclusions comes from the dependence of the calibration curve on the salt composition of the eluent owing to interactions - dependent on the quality of the solvent - between the polystyrenes used as standards and the porous silica gel. Nevertheless, this perturbation is small and the agreement between the average molecular weights obtained by GPC and by direct determination is good and indicates that the universal calibration proposed for neutral polymers is also valid for polyelectrolytes.
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  • 57
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
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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: Potential-energy calculations seem to be capable of providing information about the structural characteristics of the folds in crystalline polymers. This paper deals with the conformational analysis of syndiotactic poly(vinyl chloride) (PVC) chains in order to reproduce satisfactory models of folding in the (010), (400), and (M̄10) crystallographic planes. The results imply that tight (010) and (400) folds and, hence, adjacent reentry may occur. The folds are probably stabilized by a weak hydrogen-bond type of interaction. Moreover —CHCl—CH2—CH2—CHCl— segments in the folds have been taken into account, thus obtaining more energetically favored models. The crystal lattice energy has been computed as a function of the PVC unit-cell parameters a and b, releasing the fold's constraint of the stems. The energy minimum corresponds to a noticeable decrease of a in comparison with the experimental value, although the potentials used in the calculations are hard and have van der Waals radii greater than those usually accepted. As a consequence it seems reasonable to suppose that the folds strongly influence the PVC crystal packing and do not allow better interatomic contacts between stems to form.
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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: Infrared measurements of the dichroic ratio of atactic polystyrene absorption bands provide a valuable method of determination of the overall orientation of chains as well as the particular orientation of the trans conformational segments. The orientation process produces the alignment of the chains as well as an increase in the amount of trans conformational segments. A linear relationship is observed between birefringence and dichroic ratio for the absorption bands characteristic of overall orientation. A value of 35° ± 3° is obtained for the angle between the normal to the plane of the benzene ring and the chain axis from both infrared and birefringence determinations.
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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: Ultra-oriented high-density polyethylene fibers (HDPE) have been prepared by solid-state extrusion over 60-140°C range using capillary draw ratios up to 52 and extrusion pressures of 0.12 to 0.49 GPa. The properties of the fibers have been assessed by birefringence, thermal expansivity, differential scanning calorimetry, x-ray analysis, and mechanical testing. A maximum birefringence of 0.0637 ± 0.0015 was obtained, greater than the calculated value of 0.059 for the intrinsic birefringence of the orthorhombic crystal phase. The maximum modulus obtained was 70 GPa. The melting point, density, crystallinity, and negative thermal expansion coefficient parallel to the fiber axis all increase rapidly with draw ratio and at draw ratios of 20-30 attain limiting values comparable with those of a polyethylene single crystal. The properties of the fibers have been analyzed using the simple rule of mixtures, assuming a two-phase model of crystalline and noncrystalline microstructure. The orientation of the noncrystalline phase with draw ratio was determined by birefringence and x-ray measurements. Solid-state extrusion of HDPE near the ambient melting point produced a c-axis orientation of 0.996 and a noncrystalline orientation function of 0.36. Extrusion 50°C below the ambient melting point produced a decrease in crystallinity, c-axis orientation, melting point, and birefringence, but the noncrystalline orientation increased at low draw ratios and was responsible for the increased thermal shrinkage of the fibers.
    Additional Material: 20 Ill.
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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: Interaction of nonidentical polymer molecules in a dilute solution of a mixture of two polymers is quantitatively characterized by A24, the second virial coefficient for interaction of unlike species. This parameter is related to the compatibility of the two polymers in solution and is obtainable experimentally, e.g., by light scattering. With chemically markedly different polymers, A24 depends neither on the molecular weight of the polymers nor on the solvent and becomes characteristic of the polymer pair. For a mixture of two copolymers or of a homopolymer and a copolymer with similar compositions, A24 depends both on the solvent and on the molecular weight of polymers. Under such circumstances A24 ceases to be a quantity given only by the chemical structure of the two polymers; however, under suitable conditions it remains a sensitive function of the difference between the chemical nature of polymer components.
    Additional Material: 2 Ill.
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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 crystallization characteristics of the binary system polyoxyethylene (PEO)-glutaric acid were determined. From the extrapolated melting point depression data the heat of fusion for PEO is 2506 ± 200 cal/mole of repeat unit while the heat of solution for the glutaric acid amounts to 6.7 ± 1.2 cal/cm3. A melting point of 348 K is found for the high-molecular-weight PEO. A calorimetric glass-transition temperature for mixtures of the two components is relatively independent of the melt composition and appears at 217 K. A eutectic is observed whose composition and melting temperature depend on the nature of the PEO crystal phase.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 63
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The influence of macroparticle and solvent inertia on diffusion of interacting spherical Brownian particles is studied. Results are applied to the determination of the spectrum of light and neutrons scattered quasielastically from solutions of macroparticles.
    Type of Medium: Electronic Resource
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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: Raman spectra of stearyl alcohol (n-C18H37OH) indicate that vibrational bands in both the skeletal optical (1000-1200 cm-1) and longitudinal acoustical (0-500 cm-1) regions are considerably perturbed by intermolecular hydrogen bonding. The zone interior skeletal stretching mode reflecting phonon dispersion in the v4 branch of the infinite polyethylene chain is found at 1105 cm-1, approximately 20 cm-1 higher than in the corresponding n-alkane. Similarly the single nodal longitudinal acoustical mode (LAM-1) is found shifted by 12 cm-1 to higher frequency when the expected “mass effect” produced by the —OH group is considered. This shift is further increased to 16 cm-1 at -100°C indicating a further perturbation on this accordion mode due to the increased strength of the hydrogen bond at the low temperatures. The positions of the higher multinodal vibrations, LAM-3 and LAM-5, are also perturbed by the hydrogen bond but by differing amounts. The observation of a low-frequency Raman-active LAM in polytetrahydrofuran [(—CH2CH2CH2CH2O—)n] is discussed in conjunction with the expected effects of hydrogen bonding at the lamellar surface.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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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
    Notes: Laser Raman spectra of atactic poly(vinyl alcohol) (PVA) after heat treatment and/or swelling in water have been obtained. An amorphous Raman band is observed at 1124 cm-1, while a crystalline Raman band is found at 1147 cm-1. A new method for crystallinity determination is proposed, in which the amorphous band is used instead of the crystalline band. The method is superior to others for water-swollen PVA samples. Laser Raman spectra of swollen PVA revealed that swelling causes destruction of a major fraction of the crystalline regions and the remaining intact crystalline part increases with increasing temperature of heat treatment.
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