摘要:

AbstractWe studied the elution of dextrans in gel permeation chromatography (GPC) using a low‐angle laser light‐scattering (LALLS) system to monitor the molecular weight and the standard refractive index (RI) detector to measure the concentration. In pure water the dextrans show bimodal chromatograms of the RI response as well as of the LALLS response. The first eluted peak reflects the macroion exclusion due to the repulsion between negatively charged macromolecules and equally charged gel. In spite of the resulting distortion of the chromatograms, correct values of the weight‐average molecular weights (M̄w) are obtained from them. If instead of pure water a salt solution (0.1MKNO3) is used as eluant, the charge effect is completely suppressed and single‐peak chromatograms are found. Again correct values of M̄ware obtained, but number‐average molecular weights turn out to be too large owing to axial column dispersion in the coupling arrangement. By introducing a spreading factor, values of M̄ncould be corrected. Investigations of the charge effect were also carried out by monitoring the electric conductivity of the eluted dextran zone. In this way, the phenomenon of ion inclusion, evidently provoked by charged dextran molecules,

ISSN:0887-6266    

DOI:10.1002/polb.1987.090250111

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractLattice constants of the monoclinic form of polyethylene under pressures up to 1.8 GPa at 298 K are investigated by x‐ray diffraction. The thermal expansion from 100 K to 300 K at atmospheric pressure is also studied. The equation of state is calculated by Pastine's method, taking into account the zero‐point vibration, and is compared with experimental results. The calculated results depend largely on the interatomic potential used and the limit of the interatomic distance for summation of the potentials. A change in the angle γ between theaandbaxes results in an anisotropic change in the unit cell dimension with both pressure and temperature; theaandbaxes change at nearly the same rate. The monoclinic form may have a higher density than the orthorhombic form at pressures above 1.0

ISSN:0887-6266    

DOI:10.1002/polb.1987.090250112

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractSolidified cholesteric films of α‐helical poly(γ‐methylL‐glutamate) and poly(γ‐benzylL‐glutamate) were prepared by casting from solutions of the lyotropic cholesteric mesophase. Colored films can be prepared in this manner, so the cholesteric structure is retained with a pitch corresponding to a visible wavelength. Their iridescent colors can cover the full range of the visible spectrum, and the colors remain unchanged for years. Although the films are similar in optical properties to those of fluid cholesteric phases, the temperature dependence of the color is quite different. On stretching, the film undergoes a permanent deformation, and the iridescent color is shifted toward the blue. Ift0is the initial film thickness and Δtis the change in thickness after stretching the film, the relative change in pitch, −ΔP/P0, of the cholesteric structure increases linearly with −Δt/t0in the range −Δt/t0>0.10. This reduction of the pitch is attributed to a decrease in the number of pseudonematic layers in the span of one pitch, which may be interpreted in terms of delamination using an angle‐ply model of t

ISSN:0887-6266    

DOI:10.1002/polb.1987.090250113

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractThin layers of (25–1000 Å) tin were evaporated onto a highly oriented polypropylene sheet. Two rates of deposition were used: 5 and 20 Å/s. For the more rapid deposition rate, a preferred orientation of tin was found in all cases. Here, the Snaaxis lay parallel to the polymer chain (polymercaxis). The same orientation relationship was found for the slower deposition rate, but only at lower Sn film thicknesses; at the higher film thicknesses, a random orientation of crystallites is found. Scanning electron micrographs show an equiaxed tin grain structure for the case of no preferred orientation and a platelet morphology for the case of preferred orientation, the thin dimension of the platelets lying perpendicular to the polymer chain axis. Although no clearcut evidence either for or against crystallographic epitaxy has been found, a plausible case for geometrical epitaxy is presen

ISSN:0887-6266    

DOI:10.1002/polb.1987.090250114

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractThe equilibrium stress‐strain properties and the swelling behavior of moderately cross‐linked model networks of poly(oxypropylene) were studied. Results were in general agreement with the theory of rubber elasticity due to Flory. However, data on the highly cross‐linked networks (M̄c≈ 725) could not be satisfactorily described by the recent theories of elasticity or swelling. This is believed to be primarily due to the marked non‐Gaussian character of the very short network chains and the substantial chemical modification of the polymer by the cross‐linking moiety which inevitably occurs at high cross‐

ISSN:0887-6266    

DOI:10.1002/polb.1987.090250115

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractProcess‐structure‐property relationships in the formation of an elastic fiber from a melt of segmented polyester‐polyether copolymers are described. The “soft” segment, polyethylene oxide, is modified to prevent its crystallization at use temperatures. Features of the polymer related to phase separation of the soft segments and the crystallizable “hard” segments are discussed. An “ideal” morphology of such a thermoplastic elastomeric fiber that would maximize its recoverable extension is defined, and a path toward its realization in a melt spinning pro

ISSN:0887-6266    

DOI:10.1002/polb.1987.090250116

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractCrystalline texture in polymer spherulites appears to be determined in part by interplay during solidification between interface morphology and the diffusion of species segregated at crystal growth fronts; these species are molecules of lower molecular weight (fractionation) or molecules of stereoirregular structure. Early discussions of this behavior were based upon assumption of asinglediffusion coefficient in each case. However, it is now known that, because of reptation, each molecule in a polymer melt diffuses with a diffusion coefficient dependent on its individual molecular weight. In this paper, the influence of reptation upon concentration profiles and diffusion ranges is examined. It is shown that such influence is slight when segregated species have relatively narrow distributions of molecular weight, such as are typical when segregation involves fractionation or is mostly confined to fractionated stereoirregular species blended with crystallizable host polymer. With broad distributions, however, concentration profiles are significantly altered and long segregated molecules dominate morphologically important behavior. Meaningful average diffusion ranges can often be derived and related to appropriately averaged molecular weights of participating molecules. Morphological implications of the various results are outlined.

ISSN:0887-6266    

DOI:10.1002/polb.1987.090250117

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY