摘要:

AbstractPositron lifetimes were measured for four kinds of polyethylene samples and were resolved into four components. The temperature dependence of the two longlived components was examined in detail. In agreement with other results, the longest lived component could be reasonably assigned toortho‐positronium located in amorphous regions. This component was shown to be sensitive to the defects in high‐density polyethylene introducted in the course of its production. Both the intensity and the lifetime of the second longest lived component were structure insensitive, i.e., they did not change even on passing through the melting point. This component has been tentatively assigned to a positronium compound state. The effect of gamma‐ray irradiation was also examined. Although the intensity (I4) of the longest lived component was reduced by the irradiation, correlation betweenI4and the free radical concentration was poor, and the reduction inI4caused by the irradiation is considered to be due to structure change and not to chemical re

ISSN:0887-6266    

DOI:10.1002/polb.1992.090300601

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractThe miscibility of two‐component polymer blends has been investigated using xenon‐129 (129Xe) nuclear magnetic resonance (NMR) to probe the phase morphology. The chemical shift of129Xe dissolved in a given polymer is unique, thus heterogeneous blends with large domain sizes exhibit two129Xe NMR lines. When a single resonance is obtained, the data are consistent with miscibility, yielding an upper bound on the domain size. The temperature dependence of the relative solubilities and chemical shifts of129Xe dissolved in the pure components may allow a determination of the phase morphology in blends exhibiting a single resonance. The method is used to demonstrate that polychloroprene and 25% epoxidized 1,4‐polyisoprene form a miscible

ISSN:0887-6266    

DOI:10.1002/polb.1992.090300602

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractA complete expression for the enthalpy of mixing of inhomogeneous polymer–polymer–solvent systems applicable for small as well as large concentration fluctuations has been developed. This is used to express the free energy of inhomogeneous polymer–polymer–solvent systems in an extended form of the Landau‐Ginzburg functional. The gradient energy parameters obtained here are consistent with the published results. The free energy functional has been applied to develop a generalized continuity equation for spinodal decomposition in polymer–polymer systems. A linearized version of this continuity equation has been used to study the effect of the gradient terms on the dominant wavelength during spinodal de

ISSN:0887-6266    

DOI:10.1002/polb.1992.090300603

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractPermeation of eight gases (He, Ne, Ar, Kr, O2, N2, CO2, and CH4) in three isomeric poly(vinyl methylbenzoates) was measured by the time‐lag method, and the effects of the shape of side groups on gas transport in the polymers were investigated. Thep‐methylphenyl side group of poly(vinylp‐methylbenzoate), which increases both interchain and intrachain distances, caused an increase in gas diffusivity. The diffusivity and density data were consistent with free volume theory. Two other isomeric polymers, poly(vinylo‐methylbenzoate) and poly(vinylm‐methylbenzoate), had lower gas diffusivities than poly(vinylp‐methylbenzoate) and poly(vinyl benzoate). Theo‐methyl andm‐methyl groups on the phenyl ring were found to hinder gas diffusion, i.e., decrease the free volume. In contrast, the solubility of the gases in all these polymers was similar because of their similar chemical structures. The effects of hydroxyl groups also were investigated by the use of poly(vinylm‐methylbenzoate) containing a small number of vinyl alcohol units. The decrease in gas diffusivity was attributed to the decrease of free volume due to hydrogen bonding, but the change of gas solubility was

ISSN:0887-6266    

DOI:10.1002/polb.1992.090300604

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractSorption and diffusion of gases (CO2, N2, and He) in a polyimide (PI2080) film were measured by using an apparatus which gives the sorption rate curves from the initial state to the equilibrium state. Nonlinear isotherms observed for CO2sorption were interpreted successfully in terms of the dual‐mode model for sorption in glassy polymers. Linear isotherms observed for N2and He seemed to obey Henry's law. Two diffusion coefficients (DIandDE) were obtained using the short‐time method and the long‐time method for a Fickian diffusion model, together with the equilibrium solubility (Ce) from each experiment. The initial sorption rate curves agreed with the calculated curves usingDI, however near sorption equilibrium the curves are in accord with the calculated curves usingDE. These observations suggest that some relaxation process is superimposed on the diffusion process. The non‐Fickian transport data were correlated successfully with a model that combines time‐dependent diffusion and the Fick

ISSN:0887-6266    

DOI:10.1002/polb.1992.090300605

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractNozzle profiles capable of generating constant extensional strain rates are termed hyperbolic dies. When used in polymer extrusion, they exhibit greater potential in inducing and retaining polymer molecular orientation than conventional capillary dies. Most mathematical expressions found in the literature involve several processing variables in describing and designing such nozzle profiles. This report reveals that a hyperbolic die profile, although rather complicated, can be expressed with equations in terms of two ordinary geometrical parameters—the exit diameter and the hyperbolic length. This finding greatly simplifies the design procedure of hyperbolic dies. The extensional strain rate of a hyperbolic die can be related to the length‐to‐diameter ratio for any given exit diameter. Examples of various types of die profiles are presented and their constant extensional strain‐rate characteristics are di

ISSN:0887-6266    

DOI:10.1002/polb.1992.090300606

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractSorption isotherms of 2,4‐dinitroaniline and three 4‐amino‐azobenzene derivatives (nonionic dyes with adequate solubility in water) on Nylon 6 (film and fiber) from water were determined at various temperatures. The observed isotherms were curved, not linear. They were very well described in terms of the dual‐mode sorption model, Nernst‐type partitioning, plus Langmuir sorption. The contribution of the Langmuir sorption to the total dye sorption decreased with increasing temperature. The saturation value for the Langmuir sorption increased with the crystallinity of Nylon 6 film, suggesting that the Langmuir sorption is associated with the crystall

ISSN:0887-6266    

DOI:10.1002/polb.1992.090300607

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractZinc‐neutralized sulfonated polystyrene ionomers (ZnSPS) and poly(2,6‐dimethyl 1,4‐phenylene oxide) homopolymer (PXE) form miscible blends up to at least 7.8 mol % sulfonation, as measured by thermal and mechanical criteria. The addition of an equal weight of PXE raises the glass transition temperature of ZnSPS by 40–50°C. However, this miscibility is not achieved by eradicating the microdomain structure present in ZnSPS, even though the PXE coils are considerably larger than the spacings between ionic aggregates. Small‐angle x‐ray scattering indicates that while the average interaggregate spacing is roughly the same in ZnSPS and its 50/50 blend with PXE at a given sulfonation level, the extent of phase separation is reduced upon PXE addition, indicating that more ionic groups are dispersed in the matrix. Factors influencing miscibility in the ZnSPS/PXE materials and related blends a

ISSN:0887-6266    

DOI:10.1002/polb.1992.090300608

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractThe miscibility of copolymersAxB1−xandAyB1−y, derived from the same monomer pair (A, B) but differing in composition, was studied. The systems (A, B) were (S, MMA), (BMA, MMA), (S, BMA), and (CIS, BMA) (S: styrene, CIS:p‐chlorostyrene, MMA: methylmethacrylate, BMA: n‐butylmethacrylate). Miscibility diagrams were recorded, at low and high temperatures, using cast films and dry films. All blend systems feature hightemperature miscibility gaps. Unusual effects of the compositions x and y on miscibility in blendsAxB1−x/AyB1−ywere observed. The classical prediction that miscibility should depend only on the composition difference |x–y| usually is too simple. It appears necessary to consider dyad

ISSN:0887-6266    

DOI:10.1002/polb.1992.090300609

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractChloride ion activity coefficients in aqueous solutions of poly(allylamine) hydrochloride (PAA · HCl) have been determined both in the absence and the presence of simple salts. Without added salt, the activity coefficient depends on the polymer concentration. With added salt, the binding of added counterions by PAAH+is evaluated from the release of chloride ion. The extent of interaction between counterions and PAAH+at a given polymer concentration decreases in the order SO 42−≫ ClO 4−>NO 3−>Cl−>Br−>I−. This order of counterion selectivity agrees with the previous estimation of potentiometric titrations. The result shows that the hydration of the counterion, as well as its charge, plays an important part in counterion bi

ISSN:0887-6266    

DOI:10.1002/polb.1992.090300610

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY