摘要:

AbstractElectron spin resonance (ESR) spectra of poly(acrylic acid) (PAA) γ‐irradiated in air at room temperature and recorded at room temperature and at liquid‐nitrogen temperature have been studied to identify the radiation products. The ESR spectra are composed of eight lines with hyperfine splittings of 23 ± 1 G and 11 ± 1 G. The method of least‐squares total curve fitting, employing the Lorentzian line shape function, to the observed spectra enabled the assignment of the spectra. Computed spectra obtained by the superposition of a singlet and the spectra due to chain radicals are considered to give the best fits to the observed ESR spectra. The singlet is assigned to the radicals COOH, and the component 10‐line spectra are assigned to the chain radicals CH3CHCH2∼ and/or ∼ CH2CHCH2∼. The observed change in line shape with temperature of the ESR spectra is attributed to the hindered oscillations of the methyl groups about the CαCβbond axis of the chain radicals. The existence of the methyl groups is confirmed by the measur

ISSN:0887-6266    

DOI:10.1002/polb.1989.090270601

出版商:John Wiley&Sons, Inc.    

年代:1989

数据来源: WILEY

摘要:

AbstractThermal measurements were carried out to investigate the macrostructure of as‐cast poly(vinylidene fluoride) (PVDF)/poly(vinyl pyrrolidone) (PVP) blends. At high PVP content, above about 70 wt.%, the two components form a homogeneously mixed amorphous phase whoseTgvaries with composition. Crystals are formed upon casting mixtures richer in PVDF; these systems exhibit complex thermal behavior that cannot be justified by a simple two‐phase model. DSC measurements above room temperature on semicrystalline blends show, in addition to the melting of PVDF crystals at temperatures that decrease on increasing PVP content, a glass transition at about 80°C, independent of composition. Experimental results strongly support the hypothesis that an interphase, composed of essentially undiluted noncrystalline PVDF, is always associated with the lamellar crys

ISSN:0887-6266    

DOI:10.1002/polb.1989.090270602

出版商:John Wiley&Sons, Inc.    

年代:1989

数据来源: WILEY

摘要:

AbstractThe transport of gases in many glassy polymers can be described satisfactorily by means of a “dual‐mode sorption” model. The transport behavior observed with a given gas/polymer system can be characterized by the model parameters, which are obtained from solubility measurements in conjunction with absorption/desorption or permeability measurements. The present study discusses the inverse problem, namely, the prediction of the absorption/desorption behavior of a gas in a glassy polymer from a specified set of dual‐mode sorption parameters. Satisfactory agreement is obtained between reported absorption rates of sulfur dioxide in glassy polycarbonate and of water vapor in Kapton®††Trademark of E. I. du Pont de Nemours&Co.and the rates predicted by the dual‐mode sorption model. This study also confirms the consistenc

ISSN:0887-6266    

DOI:10.1002/polb.1989.090270603

出版商:John Wiley&Sons, Inc.    

年代:1989

数据来源: WILEY

摘要:

AbstractSorption and transport of CO2have been investigated for polyimide films prepared from 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (BPDA) and 4,4′‐oxydianilline (ODA) as well as for a chemically identical commercial polyimide film, Upilex‐R. The BPDA‐ODA polyimide films annealed above the glass transition temperature (270°C) are found to have some degree of ordering owing to molecular aggregation of polymer chains, whereas the films as‐cast are amorphous. The solubility, permeability, and diffusion coefficients decrease significantly with increasing density or increasing average degree of molecular aggregation. The influence of morphology on the parameters in the dual‐mode sorption and transport model has also been investigated. With an increase in density, the Langmuir capacity constant and the diffusion coefficients for Henry's law and Langmuir populations decrease by a larger factor than the Henry's law solubility constant. These results can be tentatively interpreted by assuming either a one‐phase or two‐phase structure for

ISSN:0887-6266    

DOI:10.1002/polb.1989.090270604

出版商:John Wiley&Sons, Inc.    

年代:1989

数据来源: WILEY

摘要:

AbstractA new description of the quasistatic deformation of polymeric glasses is presented. The stress‐strain energy of a glass is defined to comprise two components: a “solid term,” which controls the low‐strain range of deformation, and a “conformational term” proportional to the first strain invariant. By introducing internal variables in terms of classical irreversible thermodynamics, the stress‐strain behavior and the thermoelastic properties of polycarbonate are fairly well described over the whole range of accessible strains. The necking phenomenon is interpreted as a “constrained strain‐induced phase transition” (“one‐way phase transition”). A new version of a Clapeyron‐Clausius equation is derived. Its application yields a new understanding of the temperature dependence of yielding of cold‐drawn polycarbonate. The typical phenomena of a first‐order transition, discussed in the special form of a “one‐way phase transition,” have been fully identified experimentally (by microscopy, stretching‐microcalorimetry, simple extension, and birefringence). Sharp phase boundaries appear just when the new phase is nucleated. The transition then proceeds under a constant force as demanded by thermodynamics. The stress‐strain behavior is shown to be uniquely dependent on temperature at temperatures below the glass‐transition range. General consequences of t

ISSN:0887-6266    

DOI:10.1002/polb.1989.090270605

出版商:John Wiley&Sons, Inc.    

年代:1989

数据来源: WILEY

摘要:

AbstractThe permeation of oxygen dissolved in water through substituted polyacetylene membranes was studied by using an oxygen electrode at 25°C. Many of the membranes (thickness about 200 μm) showed high apparent permeability coefficientsPin the range 10−9−10−8cm3(STP) cm cm−2s−1cmHg−1. The resistancerof the boundary layer and the permeabilityP∞, at infinite membrane thickness were determined from the dependence ofPon membrane thickness. Thervalues of Si‐containing and aliphatic polyacetylenes were usually larger than those of aromatic polyacetylenes. TheP∞, values of Si‐containing and aliphatic polyacetylenes agreed closely with the permeability coefficientsPgfor gaseous oxygen. In contrast,P∞values for aromatic polyacetylenes w

ISSN:0887-6266    

DOI:10.1002/polb.1989.090270606

出版商:John Wiley&Sons, Inc.    

年代:1989

数据来源: WILEY

摘要:

AbstractA model of environmental craze growth has been developed based on the customary meniscus (or Rayleigh‐Taylor) instability model of craze propagation but allowing for the possibility that environmental plasticization may cause the active layer of material adjacent to the craze to be of significant thickness with respect to the fibril spacing. Initially, as the active layer thickness increases, the fibril growth rate increases at constant fibril spacing, but eventually the fibril spacing comes to be controlled only by the active layer thickness and not by the surface tension and stress. This model of craze growth has been coupled to a model of stress‐enhanced case II diffusion that is itself based on the Thomas‐Windle model. Two main regimes of craze thickness growth are distinguished. In one the craze growth rate is controlled by the velocity of the diffusion front, the meniscus instability growth rate is assumed to be relatively slow, so that a significant plasticized active layer exists whose thickness assures that the meniscus instability front travels at the same speed as the diffusion front. In the other regime the propagation of the craze front is sufficiently fast that it also forms the diffusion front, so the growth rate is controlled by a combination of the two processes: diffusion and meniscus instab

ISSN:0887-6266    

DOI:10.1002/polb.1989.090270607

出版商:John Wiley&Sons, Inc.    

年代:1989

数据来源: WILEY

摘要:

AbstractMechanical measurements can be made on Langmuir‐Blodgett (LB) films that have been peeled from their substrates, and are floating on the surface of water, by compressing them between the moving barrier and the Langmuir balance float in a standard monolayer trough. We have used this technique, which utilizes apparatus commonly available where LB films are made, to study multilayers of lead 10,12‐tricosadiynoate (a diacetylene carboxylic acid) that were first polymerized and then peeled from the substrate. For comparison we have performed the same measurements on pieces of mylar, on unpolymerized films, and on films of calcium octadecanoate (a saturated chain fatty acid). We found Young's modulus for films of the saturated chain material, the unpolymerized diynoate, and the polymerized films, to be 6 GPa (900 kpsi), 0.5 GPa, and 6 GPa, respectiv

ISSN:0887-6266    

DOI:10.1002/polb.1989.090270608

出版商:John Wiley&Sons, Inc.    

年代:1989

数据来源: WILEY

摘要:

AbstractA numerical iterative procedure is presented to predict the polymer‐subphase volume that is formed when anionic polysaccharides such as alginic acid (polyuronic acid from kelp) are suspended in an aqueous solution. (The aqueous region surrounding the polymer chain where a strong electrostatic attractive force for counterions exists is defined as the separate polymer subphase within the colloidal phase enclosed by the polymer coil.) Based on the phase‐partition model of Marinsky et al.5and Donnan equilibrium theory, this iterative procedure utilizes the base titration data of the acidic polysaccharide at different ionic strengths as well as the osmotic properties of the sodium form of the polysaccharide. No detailed structural information of alginic acid is required. The resulting calculations show that the polymer subphase, which accounts for a small fraction of the total solution volume, should be regarded as the reaction zone for acid dissociation and metal binding reactions. The volume of polymer subphase thus calculated may also serve as an excellent index for the morphology of the polymer molecule at different ionic strengths, degrees of ionization, polymer concentrations, and extent of polymer‐metal bi

ISSN:0887-6266    

DOI:10.1002/polb.1989.090270609

出版商:John Wiley&Sons, Inc.    

年代:1989

数据来源: WILEY

摘要:

AbstractThe thermal diffusion coefficientDThas been obtained for 17 polymer‐solvent combinations, each of them spanning a range of polymer molecular weights, using thermal field‐flow fractionation. The polymers examined include polystyrene, poly(alpha‐methyl)styrene, polymethylmethacrylate, and polysioprene. The solvents include benzene, toluene, ethylbenzene, tetrahydrofuran, methylethylketone, ethylacetate, and cyclohexane. AlthoughDTwas confirmed as essentially independent of polymer molecular weight, it was found to vary substantially with the chemical composition of polymer and solvent. The results were used to evaluate several thermal diffusion theories; the agreement with theory was generally found to be unsatisfactory. Attempts were then made to correlate the measured thermal diffusion coefficients with various physicochemical parameters of the polymers and solvent. A good correlation was found in whichDTincreases with the thermal conductivity difference of the polymer and solvent and varies inversely with the activation energy of viscous flow of the so

ISSN:0887-6266    

DOI:10.1002/polb.1989.090270610

出版商:John Wiley&Sons, Inc.    

年代:1989

数据来源: WILEY