摘要:

AbstractA method for quantitative characterization of the noncrystalline region in poly(ethylene terephthalate) (PET) fibers based on x‐ray wide‐angle diffraction data is elaborated. The procedure consists in a computational resolution of the diffracted intensity into individual peaks for 010, 110, and 100 planes and into isotropic and anisotropic components of diffuse scattering. The results show that the content of mesomorphic regions in the noncrystalline part of PET fibers with draw ratio of λ = 3.0 varies from 12% to 32% depending on the temperature of heat treat

ISSN:0098-1273    

DOI:10.1002/pol.1980.180180501

出版商:John Wiley&Sons, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractSmall‐angle x‐ray scattering has been used to characterize a variety of polyethylene fibers of the so‐called shish‐kebab type. These fibers are aggregates of elementary fibrils each consisting of a backbone with a lamellar overgrowth. Intense scattering is due to voids between the lamellae giving rise to a “Bragg maximum” reflecting the ordering of lamellae along the backbones. It can be described by rather broad distributions for both the interlamellar spacings and the lamellar thicknesses. This is shown by comparing experimental scattering curves with SAXS patterns calculated on the basis of the theory for one‐dimensional scattering of linearly ordered lamellar systems, using the general paracrystalline model. A negative exponential distribution for the center‐to‐center distance of the lamellae, characteristic of a random nucleation process, apparently cannot be employed for the description of these shish‐kebab morphologies. From a discussion on the discrepancies between experimental and theoretical scattering curves it is concluded that the fibers may be inhomogeneous with respect to the statistics of lamellar ordering. This may be due to the nonisothermal character of the crys

ISSN:0098-1273    

DOI:10.1002/pol.1980.180180502

出版商:John Wiley&Sons, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractThe adsorption of well‐characterized comb‐branched polystyrene onto a chrome plate from cyclohexane solution at the θ temperature has been studied by ellipsometry. Both the adsorbance of the polymer and the extension of the adsorbed layer are compared with values for the linear polystyrene of the same molecular mass. The adsorbance is higher than that of the linear polystyrene, whereas the extension of the adsorbed layer is smaller, reflecting the higher segment density of the branched polymer. The extensiontbof the branched polymer is given approximatelytb=tlg s1/2, wheretlis the extension of linear polystyrene of the same molecular mass andg s1/2is the ratio of the radii of gyration of the branched and linear polymers. The ratio of the adsorbancesAb/Alof branched and linear polymer is approximately equal tog s−1. These results indicate that the comb‐branched polymer is adsorbed as a slightly distorted randam coil with extension and adsorbance governed primarily by the experi

ISSN:0098-1273    

DOI:10.1002/pol.1980.180180503

出版商:John Wiley&Sons, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractIn order to explore the correlation between rheo‐optical and mechanical dispersions, orientation and lattice‐deformation retardation spectra are introduced in the phenomenological treatment of the stress‐orientation coefficient and crystal lattice compliance functions in dynamic x‐ray diffraction. A similar complementary treatment of the stress‐optical retardation spectrum is also carried out for the dynamic birefringence. To determine the mechanical and rheo‐optical retardation spectra, a deconvolution method based on the Fourier transform is developed. By this method, the mechanical and rheo‐optical retardation spectra of a low‐density polyethylene are computed from the imaginary components of the corresponding experimental functions; and subsequently, the real and imaginary components of the original functions are recalculated numerically from their respective retardation spectra and compared with the observed ones. The similarity of the normalized mechanical and rheo‐optical retardation spectra demonstrates that the α mechanical dispersion is related to orientation retardation of the crystal grains at their boundaries. Furthermore, separation of crystalline and amorphous contributions to the stress‐optical retardation spectrum is made on the basis of the two‐phase hypothesis for polyethylene. The amorphous contribution to the stress‐optical retardation spectrum is further resolved into two components corresponding to the α and β mechanical dispersions under the assumption that the resolved component for the α dispe

ISSN:0098-1273    

DOI:10.1002/pol.1980.180180504

出版商:John Wiley&Sons, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractThe fine structure of polyethylene film has been investigated by using a high‐resolution scanning electron microscope equipped with a field emission source. The original film surface ofa‐axis‐oriented blown polyethylene film and the surface of a necked region formed by drawing the film in the machine direction were observed. High magnification electron micrographs indicate that the basic unit of internal texture of this film consists of piled‐lamellae units, each pile containing three to ten lamellar crystal sheets. The piled‐lamellae unit acts as one body and does not separate into single lamellae during deformation. Many tie fibrils are formed between adjacent piled‐lamellae units, when the film is drawn in the machine direction. Although little attention has been given to this mechanism, it is important in deformation. This fact seems to be reflected in different shapes of the stress‐strain curves of films drawn the machine direction and perpen

ISSN:0098-1273    

DOI:10.1002/pol.1980.180180505

出版商:John Wiley&Sons, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractA model is presented for analysis of the sorption of mixed gases in glassy polymers at concentrations below which significant plasticization occurs. The well‐known dual‐mode sorption model comprised of a Henry's law term and a Langmuir isotherm term, which has been used extensively for interpretation of single‐component gas sorption data, forms the basis for the analysis of binary mixtures discussed here. Measurements using pure gases provide dual mode parameters which can then be used to predict the resultant sorption isotherms for binary mixtures of any of the pure gases. The proposed analysis is based upon recognition that the Langmuir component of the overall sorption concentration should be governed by competition between the two penetrants for the fixed unrelaxed volume in the polymer, which is believed to be the locus of the Langmuir capacity. This effect may result in a significant depression of the measured sorption of similar penetrants competing for the limited Langmuir capacity. A numerical example is considered which illustrates the range of behavior expected for CO2and CH4in polycarbonate. Deviations from the theoretical predictions of the simple dual‐mode model for binary systems are discussed in terms of plasticizing effects on the Henry's law constant and the Langmuir affinity constant. The analyses proposed here are of direct and critical interest to the applied problems of migration of trace contaminants in glassy polymers and analysis of barrier packaging for foods since all of these applied problems involve mixed‐penetrant sorption. Specifically, it is predicted that the presence of residual monomers or solvents in glassy polymers can produce both anomolously low Langmuir sorption affinity constants and sorption enthalpies compared with the residual

ISSN:0098-1273    

DOI:10.1002/pol.1980.180180506

出版商:John Wiley&Sons, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractA molecular theory of the piezoelectric constant of the α‐helical backbone of polypeptide is developed on the basis of fluctuation formalism. The piezoelectric constant, electric susceptibility, and elastic compliance of the α‐helix are calculated through the method of molecular lattice dynamics by use of normal‐coordinate analysis. Displacements of each atom due to the external stress exerted upon the backbone are also calculated. The piezoelectricity of the α‐helix is concluded to arise mainly from rotation of the CONH bond. The value of the piezoelectric constant of poly(γ‐benzyl‐L‐glutamate) film calculated from the above theoretical constants along with a composite theory is found to agree reasona

ISSN:0098-1273    

DOI:10.1002/pol.1980.180180507

出版商:John Wiley&Sons, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractThe primitive chain model of Doi and Edwards is generalized to include the short‐time relaxation process. Stress relaxation after a sudden imposition of strain is studied in detail. It is shown that in the linear region (small strain) stress relaxation occurs in two steps, the relaxation of chain segments between the fixed entanglement points, and the relaxation of the entanglement points, in accordance with the conventional picture, whereas in the nonlinear region (large strain) there appears a new relaxation process between the above two. The characteristic time of this process is the Rouse relaxation time which the entire chain would have if there were no entanglements, and increases with the square of the molecular weight. This result is consistent with experimental observation

ISSN:0098-1273    

DOI:10.1002/pol.1980.180180508

出版商:John Wiley&Sons, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractPhosphorescence depolarization measurements, under steady state polarized excitation, have been used to examine the relaxation behavior of bulk poly(methyl methacrylate) (PMMA). Poly(methyl methacrylate) bearing phosphorescent labels has been synthesized by copolymerization of small quantities of acenaphthylene (I), 1‐vinylnaphthalene (II), 2‐vinylnaphthalene (III), 1‐naphthyl methacrylate (IV), and 2‐naphthyl methacrylate (V), respectively, with methyl methacrylate. In no case was depolarization of emission due to probe rotation apparent below the onset of the β‐relaxation of the polymer. Rotation of label V was characterized by an activation energy of 94 kJ mole−1in excellent agreement with that of the β relaxation measured by conventional relaxation techniques. This result clearly implicates ester motion in the β relaxation. No motion of label I, which cannot move independently of the polymer backbone, was evident in the vicinity of the β relaxation. Above 378 K the activation energy for rotational relaxation of label I of 460 kJ mole−1is in excellent agreement with published data for the α transition in PMMA. This result is in accord with the general assumption that backbone segmental motion is involved in the α relaxation. However, backbone motion of lesser temperature dependence (Ea= 115 kJ mole−1) is apparent from depolarization behavior of probe I between 343 and 378 K. Label II shows three regions of relaxation behavior. In the temperature range above the β transition motion of the label independent of the polymer is evident (Ea= 44 kJ mole−1). At temperatures in excess of 343 K this motion becomes cooperative with that of the backbone yielding activation energies comparable to those obtained in system I. Label III, while exhibiting depolarization characteristics similar to those of label II in the vicinity of the β relaxation, emitted insufficient intensity to permit estimation of an energy of activation for the motion. The phosphorescence of label IV was completely depolarized over the entire temperature range studied. While phosphorescence intensity and lifetime data may be used to detect the existence of polymeric transitions, the photophysical behavior of the naphthalene species studied is independent of the attachment to the polymer and does not primarily yield information regardin

ISSN:0098-1273    

DOI:10.1002/pol.1980.180180509

出版商:John Wiley&Sons, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractPreliminary small‐angle neutron scattering (SANS) studies have been made of different ionomers in the dry state and after saturation with water. Scattering from the dry samples arises from differences in the neutron scattering cross sections of the ionic and nonionic units in the polymer. The SANS technique is complementary to previous small‐angle x‐ray scattering (SAXS) studies since the SANS contrast differences are generally quite different than those for SAXS. A quantitative comparison is made of SANS and SAXS intensities for a dry cesium salt of an ethylene‐methacrylic acid (E‐MAA) copolymer. For water‐saturated samples the technique of isotopic replacement can be used in conjunction with SANS since saturation can be effected with either H2O or D2O. In this case information about the chemical composition of the phases is obtained from an analysis of the intensity ratioI D 2O/I H 2O. Results are consistent with the presence of a separate phase containing water molecules and ions in a matrix of the nonionic units. A Guinier analysis gives a radius of gyration of 17 Å for a water‐saturated cesium salt

ISSN:0098-1273    

DOI:10.1002/pol.1980.180180510

出版商:John Wiley&Sons, Inc.    

年代:1980

数据来源: WILEY